the INDUSTRIAL ENVIRONMENT ~—its EVALUATION & CONTROL | ayG 1d 1oed i A ¥ ALEQRNIA 3 3 aa EA S55 U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES Public Health Service Center for Disease Control National Institute for Occupational Safety and Health 1973 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 #2 7/552 T 59 #7 N3F/ 1173 PUBL FOREWORD In 1958 the Public Health Service’s Occupa- tional Health Program introduced the Syllabus, a compilation of training aids, in conjunction with courses presented by the Service to industrial hy- giene personnel. Training people in the profession of indus- trial hygiene was not a new concept in 1958. The Occupational Health Activity of the Public Health Service was established in 1914 to protect and preserve the health of the American worker. From the very beginning, one of the tenets of our or- ganization was the promotion and improvement of industrial hygiene and industrial medicine. In 1970 Congress passed the Occupational Safety and Health Act. This Act specifically instructed the National Institute for Occupational Safety and Health (NIOSH) to “. . . 1) develop and establish recommended occupational safety and health standards, and 2) perform all func- tions of the Secretary of Health, Education and Welfare under Sections 20 (Research and Re- lated Activities) and 21 (Training and Employee Education) of this Act.” This third edition, which has become an indus- trial hygiene textbook rather than a syllabus, is the most comprehensive to date. The subject mat- ter is extremely broad, covering topics from math- ematics to medicine. The first few chapters, in addition to providing historical information, cover such areas as mathematics, chemistry, biochemis- try, physiology and toxicology. Other chapters deal iii with specific areas of interest to those concerned with evaluating the potentially harmful effects of physical and chemical air contaminants. New chapters have been added on safety, solid waste, and control of water pollution. It is not possible to provide sufficient information in any of the chapters to make the reader an authority; rather, the book is to be used in conjunction with other training aids. References are included at the end of each chapter for further study. Authors of chapters in this edition were se- lected for their expertise in the particular subject covered. In reviewing the affiliations of the auth- ors, it is interesting to note that there are 15 representatives from universities, 19 from indus- try, and 12 {rom the consulting field, as well as several representatives from State agencies and technical societies. The appreciation of the National Institute for Occupational Safety and Health is extended to the contractor, George D. Clayton & Associates, Southfield, Michigan, and the contributing authors. They have shared their expertise at a time when overwhelming demands are being made upon them. This work was performed under Contract No. HSM-99-71-45 by George D. Clayton & Associ- ates, Southfield, Michigan; Mr. William D. Kelley, Acting Director of the Division of Training (NIOSH, Cincinnati, Ohio) had direct responsi- bility for the coordination of this manuscript. ET AUTHORS (Numbers in parentheses indicate the pages on which the authors’ contributions begin.) MARY O. AMDUR, Ph.D., Associate Professor of Toxicology, Department of Physiology, Harvard School of Public Health, Boston, Massachusetts (67) JOSEPH R. ANTICAGLIA, M.D., Department of Otolaryngology, Thomas Jeffer- son University Hospital, Philadelphia, Pennsylvania (309) EDGAR C. BARNES (retired), formerly Director, Radiation Protection, Westing- house Electric Corporation, Pittsburgh, Pennsylvania (377) HARWOOD S. BELDING, Ph.D., Professor of Environmental Physiology, Depart- ment of Occupational Health, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania (563) FRANK E. BIRD, Jr., Director, International Safety Academy, Macon, Georgia (681) DONALD J. BIRMINGHAM, M.D., Professor, Department of Dermatology and Syphilology; Professor and Acting Chairman, Department of Occupational and Environmental Health, Wayne State University, School of Medicine, Detroit, Michigan (503) JAMES H. BOTSFORD, Senior Noise Control Engineer, Bethlehem Steel Cor- poration, Bethlehem, Pennsylvania (321) LIAL W. BREWER, Industrial Hygiene Chemist, Environmental Health Depart- ment, Sandia Laboratories, Albuquerque, New Mexico (257) HOWARD E. BUMSTED, Senior Research Engineer, Applied Research Labora- tory, United Steel Corporation, Monroeville, Pennsylvania (223) GEORGE D. CLAYTON, President, George D. Clayton & Associates, Southfield, Michigan (1) LEWIS J. CRALLEY, Ph.D. (retired), formerly Director, Division of Field Studies, U.S. Public Health Service, National Institute for Occupational Safety and Health, Cincinnati, Ohio (85) BERTRAM D. DINMAN, M.D., Sc.D., Director, Institute of Environmental and Industrial Health, University of Michigan School of Public Health, Ann Arbor, Michigan (75 and 7197) DAVID A. FRASER, Sc.D., Professor of Industrial Health, School of Public Health, Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, North Carolina (155) HENRY FREISER, Ph.D., Professor, Department of Chemistry, University of Arizona, Tucson, Arizona (207) RICHARD D. FULWILER, Sc.D., Head, Industrial Hygiene, Procter & Gamble Company, Cincinnati, Ohio (583) CLARENCE G. GOLUEKE, Ph.D., Director, Sanitary Engineering Research Laboratory, University of California (Berkeley), Richmond Field Station, Rich- mond, California (657) LEWIS S. GOODFRIEND, President, Lewis S. Goodfriend & Associates, Morris- town, New Jersey (667) C. L. GRANT, Ph.D., Professor of Chemistry, Kingsbury Hall, University of New Hampshire, Durham, New Hampshire (247) FRED I. GRUNDER, Assistant Director, Laboratory Services, George D. Clayton & Associates, Southfield, Michigan (19) BRUCE A. HERTIG, Sc.D., Director, Laboratory for Ergonomics Research, Department of Mechanical and Industrial Engineering, University of Illinois, Urbana, Illinois (413) VAUGHN H. HILL, Consultant, Engineering Services Division, E. I. du Pont de Nemours & Company, Inc., Wilmington, Delaware (533) ANDREW D. HOSEY (retired), formerly Director, Division of Criteria and Stan- dards Development, NIOSH, DHEW, Cincinnati, Ohio (95) DON D. IRISH, Ph.D. (retired), formerly Director of Biochemical Research Lab- oratory, Dow Chemical Company, Midland, Michigan (7) Vv AUTHORS — continued JOHN E. KAUFMAN, Technical Director, Illuminating Engineering Society, New York, New York (349) ROBERT G. KEENAN, Director, Laboratory Services, George D. Clayton & Associates, Southfield, Michigan (/67 and 181) WALTER H. KONN, Supervisor of Field Operations, Industrial Hygiene Depart- ment, General Motors Technical Center, Warren, Michigan (85) JON L. KONZEN, M.D., Corporate Medical Director, Owens Corning Fiberglas Corp., Fiberglas Tower, Toledo, Ohio (693) ADRIAN L. LINCH, Supervisor, Medical Laboratory, E. I. du Pont de Nemours & Company, Chambers Works, Deepwater, New Jersey (277) MORTON LIPPMAN, Ph.D., Associate Professor, Institute of Environmental Medicine, New York University Medical Center, New York, New York (101) P. H. McGAUHEY, Sc.D., Director Emeritus, Sanitary Engineering, University of California, Richmond, California (657) PAUL L. MICHAEL, Ph.D., Professor, Occupational Health, Pennsylvania State University, Environmental Acoustics Laboratory, University Park, Pennsyl- vania (299) DAVID MINARD, Ph.D., M.D., Chairman, Department of Occupational Health, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Penn- sylvania (399) JOHN T. MOUNTAIN (retired), formerly Supervisory Research Biochemist, U.S. Public Health Service, National Institute for Occupational Safety and Health, Cincinnati, Ohio (31) JOHN E. MUTCHLER, Chief, Engineering Services, George D. Clayton & Asso- ciates, Southfield, Michigan (573 and 597) LEONARD D. PAGNOTTO, Chief of Laboratory, Massachusetts Department of Labor and Industries, Division of Occupational Hygiene, Boston, Massa- chusetts (167) JANET L. PATTEEUW, Mathematician, George D. Clayton & Associates, South- field, Michigan (17) JACK E. PETERSON, Ph.D., Chief, Environmental Health Engineer, Medical College of Wisconsin, Marquette University, Milwaukee, Wisconsin (517) THOMAS J. POWERS, President, Operation Service and Supply Corp., Sarasota, Florida (647) STANLEY A. ROACH, Ph.D., Consultant, Welwyn, Hertfordshire, England (739) MARTIN RUBIN, Ph.D., Professor of Biochemistry, Georgetown University Hos- pital, Washington, D.C. (37) BERNARD E. SALTZMAN, Ph.D., Professor of Environmental Health, Depart- ment of Environmental Health, University of Cincinnati, Cincinnati, Ohio (7/23) HARRY F. SCHULTE, Group Leader, Industrial Hygiene Group, Los Alamos Scientific Laboratory, University of California, Los Alamos, New Mexico (579) ROBERT D. SOULE, P.E., Chief, Industrial Hygiene Services, George D. Clayton & Associates, Southfield, Michigan (333 and 711) ERWIN R. TICHAUER, Sc.D., Professor of Biomechanics, The Center for Safety, and Director, Division of Biomechanics, Institute of Rehabilitation Medicine, New York University, New York, New York (437) VICTORIA M. TRASKO (retired), formerly Public Health Advisor, Bureau of Occupational Safety and Health, Public Health Service, Department of Health, Education and Welfare, Cincinnati, Ohio (703) : JAMES L. WHITTENBERGER, M.D., Professor of Physiology, Harvard Univer- sity, School of Public Health, Boston, Massachusetts (51) GEORGE M. WILKENING, Head, Environmental Health & Safety Department, Bell Telephone Laboratories, Inc., Murray Hill, New Jersey (357) GEORGE W. WRIGHT, M.D., Head, Medical Research Division, St. Luke’s Hospital; Professor, Department of Medicine, Case Western Reserve University, Cleveland, Ohio (493) vi CONTENTS CHAPTER 1 PAGE Introduction : J 1 George D. Clayton CHAPTER 2 The Significance of the Occupational Environment As Part of the Total Ecological System 7 Don D. Irish, Ph.D. CHAPTER 3 Review of Mathematics — i 11 Janet L. Patteeuw CHAPTER 4 Review of Chemistry I I 19 Fred I. Grunder CHAPTER 5 Review of Biochemistry 31 Martin Rubin, Ph.D. and John T. Mountain CHAPTER 6 Review of Physiology 51 James L. Whittenberger, M.D. CHAPTER 7 Industrial Toxicology 61 Mary O. Amdur, Ph.D. CHAPTER 8 Principles and Use of Standards of Quality for the Work Environment 75 Bertram D. Dinman, M.D., Sc.D. CHAPTER 9 The Significance and Uses of Guides, Codes, Regulations, and Standards for Chemical and Physical Agents 85 Lewis J. Cralley, Ph.D. and Walter H. Konn CHAPTER 10 General Principles in Evaluating the Occupational Environment 95 Andrew D. Hosey CHAPTER 11 Instruments and Techniques Used in Calibrating Sampling Equipment 101 Morton Lippman, Ph.D. CHAPTER 12 Preparation of Known Concentrations of Air Contaminants 123 Bernard E. Saltzman, Ph.D. CHAPTER 13 Sampling Air for Particulates 139 Stanley A. Roach, Ph.D. CHAPTER 14 Sizing Methodology 155 David A. Fraser, Sc.D. vii CONTENTS — continued CHAPTER 15 PAGE Sampling and Analysis of Gases and Vapors 167 Leonard D. Pagnotto and Robert G. Keenan CHAPTER 16 Direct Reading Instruments for Determining Concentrations of Aerosols, Gases and Vapors 181 Robert G. Keenan CHAPTER 17 Medical Aspects of the Occupational Environment 197 Bertram D. Dinman, M.D., Sc.D. CHAPTER 18 Separations Processes in Analytical Chemistry 207 Henry Freiser, Ph.D. CHAPTER 19 Spectrophotometry 223 Howard E. Bumsted CHAPTER 20 Emission Spectroscopy 247 C. L. Grant, Ph.D. CHAPTER 21 Gas Chromatography 257 Lial W. Brewer CHAPTER 22 Quality Control for Sampling and Laboratory Analysis 277 Adrian L. Linch CHAPTER 23 Physics of Sound 299 Paul L. Michael, Ph.D. CHAPTER 24 Physiology of Hearing 309 Joseph R. Anticaglia, M.D. CHAPTER 25 Noise Measurement and Acceptability Criteria 321 James H. Botsford CHAPTER 26 Vibration 333 Robert D. Soule, P.E. CHAPTER 27 Illumination : 349 John E. Kaufman CHAPTER 28 Non-Ionizing Radiation 357 George M. Wilkening CHAPTER 29 Ionizing Radiation 377 Edgar C. Barnes viii CONTENTS — continued CHAPTER 30 PAGE Physiology of Heat Stress [SE 399 David Minard, Ph.D., M.D. CHAPTER 31 Thermal Standards and Measurement Techniques [— JE 413 Bruce A. Hertig, Sc.D. CHAPTER 32 Ergonomic Aspects of Biomechanics 431 Erwin R. Tichauer, Sc.D. CHAPTER 33 The Influence of Industrial Contaminants on the Respiratory System EE — 493 George W. Wright, M.D. CHAPTER 34 Occupational Dermatoses: Their Recognition, Control and Prevention 503 Donald J. Birmingham, M.D. CHAPTER 35 Principles of Controlling the Occupational Environment __.. 511 Jack E. Peterson, Ph.D. CHAPTER 36 Personal Protective Devices 519 Harry F. Schulte CHAPTER 37 Control of Noise Exposure .... 533 Vaughn H. Hill CHAPTER 38 Control of Exposures to Heat and Cold trim mt pm mre pt imei rs 563 Harwood S. Belding, Ph.D. CHAPTER 39 Principles of Ventilation — 573 John E. Mutchler, P.E. CHAPTER 40 Instruments and Techniques Used in Evaluating the Performance of Air Flow Systems 583 Richard D. Fulwiler, Sc.D. CHAPTER 41 Local Exhaust Systems _..._____ ~ 597 John E. Mutchler, P.E. CHAPTER 42 Design of Ventilation Systems } 609 Engineering Staff of George D. Clayton & Associates CHAPTER 43 Control of Industrial Stack Emissions _____ 629 Engineering Staff of George D. Clayton & Associates CHAPTER 44 Control of Industrial Water Emissions 647 Thomas J. Powers ix CONTENTS — continued CHAPTER 45 Control of Industrial Solid Waste ___. P. H. McGauhey, Sc.D. and Clarence G. Golueke, Ph.D. CHAPTER 46 Control of Community Noise from Industrial Sources en Lewis S. Goodfriend CHAPTER 47 Frank E. Bird, Jr. CHAPTER 48 Design and Operation of an Occupational Health Program Jon L. Konzen, M.D. CHAPTER 49 The Design and Operation of Occupational Health Programs in Governmental Agencies Victoria M. Trasko CHAPTER 50 An Industrial Hygiene Survey Checklist Robert D. Soule, P.E. 657 711 CHAPTER 1 INTRODUCTION George D. Clayton HISTORY OF INDUSTRIAL HYGIENE Industrial hygiene is the science of protecting man’s health through the control of the work en- vironment. Man and his environment are indi- visible. They react upon each other in the form of a “give-and-take” relationship. Frequently it is assumed that man moves through his environment and molds it to his desires; however, it may be more productive to think of the environment and man as moving through and changing each other simultaneously, Historically, there was very little concern for protecting the health of the worker prior to 1900. Man's life, at the dawn of civilization, was a strug- gle for existence, and the mere job of survival was an occupational disease. As stratification of social classes progressed, slaves performed the common labor; and this continued until relatively recent times. The propensity of man towards war pro- vided a fluid and steady slave supply. So disdainful was the idea of manual labor, that at one period in their culture Egyptians were prohibited by law from performing it. With this attitude of society in regard to the working man, it is no wonder there were no efforts made to control the working environment and to provide a healthful, comfort- able place in which to work. As early as the fourth century, B. C., lead tox- icity in the mining industry was recognized and recorded by Hippocrates, although no concern was demonstrated for the subsequent protection of the worker. Approximately 500 years later, Pliny the Elder, a Roman scholar, made reference to the dangers inherent in dealing with zinc and sulfur, and described a bladder-derived protective mask to be used by laborers subjected to large amounts of dust or lead fumes. For the most part, however, the Romans were much more concerned with en- gineering and military achievements than with any type of occupational medicine. In the second century, Galen, a Greek phy- sician who resided in Rome, wrote voluminous theories on anatomy and pathology. Dogmatic in his writing, Galen recognized the dangers of acid mists to copper miners, but he gave no impetus to the solution of the problem. The advent of feudalism in the Middle Ages did little to improve work standards; possibly the sole advancement of the age was the provision of assistance to ill members and their families by the feudal “guilds.” Observation and experimentation flourished in the great universities of the 12th and 13th centuries, but the study of occupational di- seases was virtually ignored. Further achievements in the field of industrial hygiene were sadly lacking until the publication, in 1473, of Ulrich Ellenbog’s pamphlet on occu- pational diseases and his notable hygiene instruc- tion. Hazards associated with the mining industry were effectively described in 1556 by Georgius Agricola, a German scholar. His “De Re Metal- lica” was translated into English in 1912 by Her- bert and Lou Henry Hoover. Agricola’s 12-sec- tioned treatment included suggestions for mine ventilation and protective masks for miners, a dis- cussion of mining accidents and descriptions of what we refer to today as “trench foot” (effects on the extremities due to lengthy exposure to the cold water of damp mines) and silicosis (a disease of the lungs caused by inhalation of silica or quartz dust). As late as the 16th century industrial hygiene was fraught with mysticism. For example, it was believed that demons inhabited the mines and could be controlled by fasting and prayer. Typical of the Renaissance was the alchemist, Paracelsus. For five years this Swiss doctor’s son worked in a smelting plant and subsequently published his observations on the hazards of that industry. The book was laden with erroneous conclusions, such as the attribution of miners’ “lung sickness” to a vapor comprised of mercury, sulfur and salt; nevertheless, his warnings about the toxicity of certain metals and outline of mercury poisoning were quite advanced. Generally accepted as the first inclusive treatise on occupational diseases was “De Morbis Arti- ficum” by Bernardo Ramazzini, an Italian phy- sician. Published in 1700, this book described silicosis in pathological terms, unrefined as they were, as observed by autopsies on miners’ bodies. Ramazzini outlined “cautions” which he felt would alleviate many industrial hazards, but these were for the most part ignored for centuries. “De Morbis,” however, had a gargantuan effect on the future of public hygiene. The question asked by Ramazzini, which was later to be included in al- most every physicians case history of a patient, was “Of what trade are you?” The 18th century saw many notable physicians scratching the surface of the industrial hygiene problem. Sir George Baker correctly attributed “Devonshire Colic” to lead in the cider industry and was instrumental in its removal. Percival Pott, in recognizing soot as one of the causes of scrotal cancer, was a major force in the passage of the “Chimney-Sweepers Act of 1788.” Both a political and medical influence, Charles Thackrah wrote a 200-page treatise dealing with occupa- tional medicine. A farsighted scientist, Thackrah asserted that “Each master . . . has in great meas- ure the health and happiness of his workpeople in his power . . . let benevolence be directed to the prevention, rather than to the relief of the evils.” Thomas Beddoes and Sir Humphry Davy collab- orated in describing occupations which were prone to cause “phthisis” (tuberculosis). Davy also aided in the development of the miner's safety lamp. In spite of these numerous advances, the 18th century developed few true safeguards for work- ers. It was not until the English Factory Acts of 1833 were passed that government first showed its interest in the health of the working man. These are considered the first effective legislative acts in the field of industry and required that some concern be given to the working population. How- ever, this concern was in practice directed more toward providing compensation for accidents than controlling the causes of these accidents. Various European nations followed England’s lead and de- veloped Workmen’s Compensation Acts. These laws stimulated the adoption of increased factory safety precautions and inauguration of medical service in industrial plants. A sense of “community re- sponsibility” was evolving, epitomized by the in- terest of newspapers and magazines in the control of the environment. For example, the London Hlustrated News, one of the most popular publi- cations of the 19th century, affixed the blame in a mine explosion to negligence in proper gas- testing methods. The same article made a point of the fact that no safety lamps had been pro- vided. In 1878, the last of the English “factory acts” centralized the inspection of factories by creating a post for this purpose in London. The United States had an early 20th century champion of the cause of social responsibility for workers’ health and welfare in the person of Alice Hamilton, a physician. She presented substan- tiated evidence of a relationship between illness and exposure to toxins; she went further by pro- posing concrete solutions to the problems. This was the start of an “Occupational Medicine Ren- aissance.” Public awareness was becoming acute and legislation was being passed. In 1908 the federal government passed a compensation act for certain civil employees, and in 1911 the first state compensation laws were passed; by 1948 all the states had passed such legislation. These Workmen's Compensation Laws were important factors in the development of industrial hygiene in the United States, as it became more profitable to control the environment than to pay for the compensation. The U. S. Public Health Service has been a world leader in evaluating diseases of the working man and development of controls, as well as fos- tering an interest in occupational diseases by var- ious state agencies, universities, management and unions. The U. S. Public Health Service and the U. S. Bureau of Mines were the first federal agen- cies to conduct exploratory studies in the mining and steel industries, and these were undertaken as early as 1910. The first state industrial hygiene programs were established in 1913 in the New York Department of Labor and by the Ohio De- partment of Health (see Chapter 49). One of the earliest attempts made to link the industrial environment with a specific disease was the exploration of the high incidence of tubercu- losis among garment workers. Given needed au- thority in 1912 by Presidential action, the Public Health Service embarked upon investigations in many industries and backed up their findings with concrete, workable solutions. By 1933 federal employee health service was offered by the Tennessee Valley Authority, followed by the Army, Navy, Air Force and Atomic Energy Commission less than ten years later. The great depression of the 1930’s had gone far to convince the federal government of a real need for intervention in the economy and welfare of American life. On an even larger scale, the creation of international bodies, such as the International Labor Organization and the World Health Organization, has given the world common goals for which to strive. Through studies and consulting services these organizations share the magnitude of the problem. They realize that technical advances necessarily have disadvantages as well as advantages, particularly in the field of industrial hygiene. For example, as the develop- ment of atomic energy progresses, a radiation hazard exists which was heretofore unknown. RECENT DEVELOPMENTS Today we view occupational medicine in-an entirely new light. A tenet of our modern society is that every worker has the right to the fulfillment of his spiritual and material needs, while at the same time enjoying freedom from fear of trauma’ and disease. Our emphasis has shifted from cor- rectional to preventive industrial hygiene, and occupational medicine has now become an integral part of medical education. The rapid advance- ment in automation provides a tremendous chal- lenge in the field of environmental control. Although the United States has moved more rapidly than any other nation in the world in ferreting out diseases of the work force and de- veloping control measures, the ever increasing de- sirc of our society for an acceleration in elim- ination of diseases caused by the environment, and specifically the work environment, has demanded a far greater effort than what has been shown in the past. Congress has reacted to these social de- mands by passing three major pieces of legislation: I. The Metal and Nonmetallic Mine Safety Act of 1966. Health and safety standards for metal and nonmetallic mines are spelled out in this Act. A Review Board (The Federal Metal and Nonmetallic Mine . Safety Board of Review) is created, con- sisting of five members, appointed by the President, with the advice and consent of the Senate. Groundwork is laid for the cre- ation of advisory committees to assist the Secretary of the Interior; these committees are expected to include an equal number of persons qualified by experience and affiliation to present the viewpoint of op- erators of such mines, and of persons sim- ilarly qualified to present the viewpoint of workers in these mines, as well as one or more representatives of mine inspection or safety agencies of the state. The Act also provides for mandatory reporting (at least annually) of all accidents, injuries and oc- cupational diseases of the mines; and ex- panded programs are developed for the education of personnel in the recognition, avoidance and prevention of accidents or unsafe or unhealthful working conditions. Finally, this Act promotes sound and effective coordination between federal and state governments in mine inspection pro- cedures. Major deficiencies of this Act in- cluded the fact that no health represent- atives were provided on Advisory Com- mittees, nor was there a provision for re- search in mine safety or miner health. The Federal Coal Mine Health and Safety Act of 1969. This Act attempts to attain the highest degree of health protection for the miner. It delineates mandatory health standards and provides for the creation of an Advisory Committee to study mine problems. Additional authority is given, through this Act, to the federal govern- ment to withdraw miners from any mine which is found to be in danger, and pro- hibits re-entry into any such mine. The Act itself reads, to “provide, to the great- est extent possible, that the working con- ditions in each underground coal mine are sufficiently free of respirable dust con- centrations in the mine atmosphere to per- mit each miner the opportunity to work underground during the period of his en- tire adult working life without incurring any disability from pneumoconiosis or any other occupation-related disease during or at the end of such period.” This is ac- complished by the control of dust stand- ards and respiratory equipment; the de- velopment of rules for roof support, proper ventilation, grounding of trailing cables, distribution of underground high- voltage and a provision for mandatory medical examinations for the miners at fixed intervals, Occupational Safety and Health Act of 1970. The declared Congressional purpose of the Occupational Safety and Health Act of 1970 is to “assure so far as possible every working man and woman in the na- tion safe and healthful working conditions and to preserve our human resources.” Under its terms, the federal government is authorized to develop and set mandatory occupational safety and health standards applicable to any business affecting inter- state commerce. The responsibility for promulgating and enforcing occupational safety and health standards rests with the Department of Labor; the Department of Health, Education and Welfare is respon- sible for conducting research on which new standards can be based and for imple- menting education and training programs for producing an adequate supply of man- power to carry out the purposes of the Act. The latter’s responsibilities are carried out by the National Institute for Occupational Safety and Health. Among the functions which may be carried out by the Institute is the one which calls for prescribing of regulations requiring employers to meas- ure, record and make reports on the ex- posure of employees to potentially toxic substances or harmful physical agents which might endanger their safety and health. Employers required to do so may receive full financial or other assistance for the purpose of defraying any additional expense to be incurred. Also authorized are programs for medical examinations and tests as may be necessary to determine, for the purposes of research, the incidence of occupational illness and the suscepti- bility of employees to such illnesses. These examinations may also be at government expense. Another HEW function is an- nual publication of a list of all known toxic substances and the concentration at which toxicity is known to occur. There will also be published industrywide studies on chronic or low-level exposure to a broad variety of industrial materials, proc- esses and stresses on the potential for ill- ness, disease or loss of functional capacity in aging adults; also authorized at the written request of any employer or author- ized representatives of employees, is de- termination by HEW as to whether any substance normally found in the place of employment has potentially toxic effects. Such determinations shail be submitted to both the employer and the affected em- ployee as soon as possible. Information obtained by the Department of Health, Education and Welfare and the Depart- ment of Labor under the research pro- visions of the Act is to be disseminated to employers, employees and organizations thereof. Space does not permit a detailed discussion of each of these pieces of legislation, but they are required reading for any student interested in in- dustrial hygiene. SCOPE & FUNCTION OF INDUSTRIAL HYGIENE Definition of the Profession Industrial hygiene is both a science and an art. It encompasses the total realm of control, including recognition and evaluation of those fac- tors of environment emanating from the place of work which may cause illness, lack of well being or discomfort either among workers or among the community as a whole. Definition of the Professional The industrial hygienist is a competent, quali- fied individual educated in engineering, chemistry, physics, medicine or a related biological science. His abilities may encompass three major areas: (1) recognition of the interrelation of environ- ment and industry; (2) evaluation of the impair- ment of health and well-being by work and the work operations; and (3) the formulation of rec- ommendations for alleviation of such problems. Scope The scope of industrial hygiene is threefold. It begins with the recognition of health problems created within the industrial atmosphere. Some of the more frequently encountered causes of these problems are: chemical causes (liquid, dust, fume, mist, vapor or gas); physical energy (electromag- netic and ionizing radiations); noise, vibration and exceedingly great temperature and pressure ex- tremes; biological (in the form of insects, mites, molds, yeasts, fungi, bacteria and viruses) and ergonomic (monotony, repetitive motion, anxiety and fatigue, etc.). These stresses must all be evaluated in terms of their danger to life and health as well as their influence on the natural bodily functions. The second heading encompassed within the scope of industrial hygiene is that of evaluation. The “work atmosphere” must be evaluated in terms of long-range as well as short-range effects on health. This can be accomplished by a com- pilation of knowledge, experience and quantitative data. Finally, industrial hygiene includes the devel- opment of corrective measures in order to elim- inate existing problems. Many times these control procedures will include: a reduction of the number of persons exposed to a problem; the replacement of harmful or toxic materials with less dangerous ones; changing of work processes to eliminate or minimize worker exposure; adoption of new ven- tilation procedures; increasing distance and time between exposures to radiation; introduction of water in order to reduce dust emissions in such fields as mining; “good housekeeping,” including clean toilet facilities and adequate methods of dis- posing of wastes; and the provision of proper pro- tective working attire. Function A unique field, industrial hygiene employs the chemist, physicist, engineer, mathematician and physician in order to adequately fulfill the re- sponsibilities inherent in the profession, which include: 1. Examination of the industrial environment; 2. Interpretation of the gathered data from studies made in the industrial environment; 3. Preparation of control measures and proper implementation of these control measures; 4. Creation of regulatory standards for work conditions; 5. Presentation of competent, meaningful testimony, when called upon to do so by boards, commissions, agencies, courts or investigative bodies; 6. Preparation of adequate warnings and precautions where dangers exist; 7. Education of the working community in the field of industrial hygiene; and 8. Conduct of epidemiologic studies to un- cover the presence of occupation-related illness. WHERE ARE THE NEEDS? There are approximately 4,000 industrial hy- gienists in the United States. These dedicated scientists often undergo periods of deep frustra- tion as they attempt to coordinate facts and arrive at workable solutions. The realization that time is of the essence in dealing with potential health hazards makes the industrial hygienist keenly aware of his great responsibilities. An alert re- sponse by an astute industrial hygienist could save the lives and health of many workers. A true statesman, the good industrial hygienist learns to temper his findings and conclusions with patience; for he knows that oftentimes employers will not be receptive to the tremendous cash outlays nec- essary to implement a good industrial hygiene program. Currently, industrial hygienists are employed by industry, federal, state and local governments, universities, insurance companies and unions. Many large industries have staffs of ten or more people. Other industries, depending upon their organization, will have only one industrial hygien- ist at the corporate office and trained technicians in each of the company’s plants. Small industries (less than 5000 employees) unless they have highly specialized problems, have not found the need to employ a full-time industrial hygienist. These companies either use the services available to them from government agencies or retain in- dustrial hygiene consultants. A number of excellent universities offer a Master’s degree in industrial hygiene. Harvard, the first university to confer this degree, started their program in /918. Since they pioneered such a program 55 years ago, there are at least eight more universities offering graduate programs in industrial hygiene leading to a Master’s or Doc- torate degree. Their names, as well as informa- tion on grants and scholarships can be obtained from the National Institute of Occupational Safety and Health, Rockville, Maryland. With the advent of new federal laws protecting the health of the worker, the need for professional industrial hy- gienists and technicians will increase dramatically in the 1970’s. Those companies which currently do not have need for an industrial hygienist will hire at least one as a result of the recently enacted legislation. Companies which had a small staff will find it to their advantage to increase their capabilities and provide more comprehensive ser- vice than they did in the past. There are only two or three cities in the United States which currently have comprehensive indus- trial hygiene programs. Other cities will find that protecting the health of the worker is a solid in- vestment and consequently will develop programs. There are not more than ten states in the United States providing comprehensive industrial hygiene programs. Just as with industries, the states will need a large number of industrial hygienists in the 1970s to fulfill the requirements of the Occu- pational Safety and Health Act. Additional fund- ing by the federal government will spur the de- velopment of such programs. Unions have begun to realize the benefits of employing a full-time professional industrial hygienist on their staffs. Presently at least three industrial hygienists are employed by unions. This trend will continue with increased awareness of the union officials of the benefits accruing to the workers through sound industrial hygiene programs. CONTENTS AND OBJECTIVES OF THE SYLLABUS The chapters which follow are written by per- sons of outstanding reputation in the particular field covered by his (her) chapter. A group of distinguished professionals has been selected from various types of industries, from universities, con- sulting groups and government, from the east to the west coast, all having the desire of providing a manuscript sufficiently comprehensive that it will encompass the entire environmental field, includ- ing subjects not commonly considered part of in- dustrial hygiene; i.e., water pollution, safety and solid waste. Our objectives have been: 1. To compile into one source the diversity of expertise needed to attain competency in the recognition, evaluation and pre- scription of methods of control of environ- mental problems. 2. For the use of persons having a basic sci- ence degree who are entering the field of industrial hygiene and environmental con- trol, provide a manual which will furnish them with the broad scope of knowledge required for an intelligent approach to the diversity of problems encountered in this field. 3. To make available a tool which may be used as a text in training courses or in uni- versities to introduce graduate students to the field of industrial hygiene and environ- mental health. 4. To introduce persons having a specialty in one of the facets of industrial hygiene or environmental health to all other facets of this profession. It is our aim to reach the beginners in the pro- fession, whether in government, industry, research or universities; the graduate students entering the profession from cognate fields and persons having a specialty who need a “refresher” in the related fields. The world in which we live is so complex, we believe that any individual truly interested in one facet of the environment should be, at the least, somewhat knowledgeable in the various categories of environmental control methods. CHAPTER 2 THE SIGNIFICANCE OF THE OCCUPATIONAL ENVIRONMENT AS A PART OF THE TOTAL ECOLOGICAL SYSTEM Don D. Irish, Ph.D. OCCUPATIONAL AREA IS PART OF THE WHOLE The occupational ecological system is a signif- icant part of the total ecological system. Since it can be measured, we can exert some control over it and make contributions to the health and well- being of the people in the occupational ecological system. These contributions can favorably affect the impact of the total system on our population since a worker may spend one-fourth of his time in the occupational area, and workers are a significant part of the total population. The purpose of this chapter is to examine the relation of the occupational environment to the total ecological system, to observe the significance of this relationship to the work of the industrial hygienist, and to recognize the favorable effect that his work in the occupational environment could have on the total system. Nonoccupational exposure is an exceedingly complex and variable factor. Recognition of such exposure is necessary to an understanding of the overall environmental impact on man. The man who drove to work in heavy traflic or walked down a busy street received much greater exposure to carbon monoxide from automobile exhaust than he would have in an acceptable work area. Sim- ilarly, a worker who smokes one pack or more of cigarettes per day will be exposed to many times the amount of carbon monoxide that he would be exposed to in an acceptable work en- vironment. This smoker would also be exposed to many times the amount of particulate matter from his smoking than he would contact in an acceptable work area. There are many other nonoccupational ex- posures but these examples serve to illustrate two obvious areas of excessive exposure in the non- occupational area. Such exposures cannot be ig- nored by those responsible for the health and well- being of people even if their responsibility is pri- marily in the occupational area. OCCUPATIONAL INTERACTION WITH NONOCCUPATIONAL In considering the occupational area one must recognize the interaction with the nonoccupational area and the significance of this interaction to the health and well-being of the individual. We learned a long time ago that a man who drinks a lot of alcoholic beverages is much more susceptible to injury from exposure to carbon tetrachloride; also, that a man with excessive exposure to silica dust is more susceptible to tuberculosis. kept in mind. The following illustration demonstrates a dif- ferent kind of interaction. We were studying the blood bromide concentration of men exposed to low concentrations of methyl bromide in their work. The environmental exposure in their op- erating area was carefully measured. The ex- posure was well within acceptable limits. Clinical studies verified this fact. It was valuable to es- tablish a relationship between exposure and blood bromide at exposures within acceptable limits, as this would be useful in the future as a clinical check on the workmen. One day a workman from this group was found to have a blood bromide concentration sufficiently high to be of concern if it had come from exposure to methyl bromide. Investigation revealed that he had been taking inorganic bro- mide medication which accounted for the high blood bromide. Workmen may be brought to the clinic for regular preventive checkups. Biochemical meas- urements on these workmen may be exceedingly valuable to verify acceptable exposure, also to catch any indication of fluctuations in operating conditions and allow correction before significant exposure can occur. This is a very useful system, but we must be sure we have all the facts before we conclude what caused any observable bio- chemical changes. THE INDIVIDUAL AS PART OF THE ECOLOGICAL SYSTEM Ecology is defined in Webster's dictionary (1971) as “The science of the totality or pattern of relations between organisms and their environ- ment.” I prefer to call ecology the science of the interaction of everything with everything else. The ecological system is the system within which these interactions take place. The ecological system is not exactly synon- ymous with the environment. My environment in- cludes everything around me. The ecological sys- tem includes me. The individual person is a highly significant factor in the control of the environment in the interest of the health and well-being of the person. A freight elevator was installed with all the usual safety devices. It was approved by state in- spectors. A switch on the door made it necessary to close the door before the hand switch would operate the elevator. A tall lanky lad found that he could get his toe to operate the switch closed by the elevator door, and with contortion he could Such possible interactions should be still reach the operaung switch. It would have been easier to close the front door, but it was a challenge. He was that rarity, a man with the reach to do it. No one knows how many times he operated the elevator this way, but one day he left his other foot over the edge of the elevator and seriously injured that foot when the elevator passed the next floor. Yes, fools can be very in- genious in overcoming “foolproof” engineering. Misoperational problems are not limited to mechanical injury. There was the individual who liked a window wide open. Under certain wind conditions the air from the window blew across the face of a hood so as to allow volatile chemicals to escape from the face of the hood into the work area around the hood. There was also the man who liked to “sniff” perchloroethylene. He arranged his work so that he could be “high” on perchlorocthylene a large part of his work day. The individual is a significant part of the oc- cupational ecological system. His understanding and cooperation are essential to attaining a health- ful work environment. We hope this understand- ing will carry over to some degree to the non- occupational ecological system. PEOPLE IN THE ENVIRONMENT An important factor in the environment of an individual is “people.” People in both the occu- pational and the nonoccupational environments are of significance to the health and well-being of that individual, One day the psychologist in our personnel de- partment asked me if we were having any com- plaints of noise from a certain operation. I told him we were, but we could find no justification for the complaints based on noise measurements made in the area. He commented, “You won't; the workers just don’t like the foreman.” In another instance we found it desirable to coordinate a careful study of the environment with a concurrent clinical study of the workmen in the area. One group of older, experienced workmen refused to cooperate. They liked the foreman and their work and were afraid we might make some changes. With friendly understanding, the purpose was explained and they were reassured. You are always dealing with people in the occu- pational environment, Another illustration introduces a different problem. Joe came into the clinic with a mashed thumb. The physician tried to get an understand- ing of the reason for the accident. He asked, “What happened, Joe?” “Oh, I got my thumb in between a couple of drums.” “You have a good record, Joe, why did this occur?” “I was thinkin’,” “What were you thinking about, Joe?” “Oh, I was thinkin’ about my wife’s sister.” Knowing that health or financial problems in the family may worry people, the physician asked, “What's wrong with your wife's sister?” Joe answered with ecstatic fervor, “Doc, there just ain’t nothin’ wrong with my wife's sister.” We should recognize that people in the non- occupational environment may have an effect which may result in misoperation. Such misopera- tion can lead to exposure to chemical substances, physical energies, or mechanical injury. This can occur either on or off the job. The problem of people in the environment is not measured by any analytical instrument, though the instrument may measure a misoperation caused by people. The problem of people is not controlled by preventive engineering alone, though it can help. Effective operation requires a good understanding of people and the ability to get their understanding and cooperation. This is an obligation of the industrial hygienist, the physician and other persons responsible for control of the environment in the interest of the health and well- being of the workmen. CHEMICALS, ENERGIES AND ORGANISMS The usual considerations in the occupational environment are more measurable than people. Chemical substances arc a concern of the indus- trial hygienist. Physical energies include: ionizing radiation, a concern of the health physicist; heat, light and noise, a concern of the industrial hy- gienist; and mechanical injury, a concern of the safety engineer. Then there are biological organ- isms (other than man) which are a concern of the sanitary engineer. These are part of the environment both on and off the job. These can be controlled in the occu- pational environment by good engineering and good operating procedures attained with the understanding and cooperation of the employees. Yes, people are also very important here. We observed that men from a specific opera- tion were reporting to the clinic with mild com- plaints which seemed similar to complaints that would be expected from an over-exposure to a solvent used in the operation. Careful analysis by the industrial hygienist, in many locations and at many different times, did not show enough solvent in the air to cause the trouble. A continuous re- cording analytical instrument was devised in the research laboratory and installed in the operating area. Through its use we found that when either the supervisor or the industrial hygienist was not around, the operator was inclined to leave a leak or spill to be cleaned up by the next shift operator. The men named this instrument the “Squealer” as it was telling us of their misoperation. They began to work with an eye on the recorder. They realized that when the “Squealer” did not squeal they felt better. They changed the name of the instrument to the “Stink clock.” The supervisor told us he saved the price of the instrument by reduced sol- vent loss, and that the overall operation by the men greatly improved. We had their understand- ing and their cooperation. They realized that we were interested in their health and well-being. During regular preventive observation of the men in the clinic, lack of adverse effects may show that exposures to chemical substances in thes en- vironment have not been excessive. It should not be taken to mean that excessive exposures are impossible or unlikely under other circumstances of use. For example, a supplier assured his customer that there was no hazard from skin contact asso- ciated with a particular material because there had been frequent skin contacts with the material in their own operations with no adverse effects. They neglected to indicate how they handled the material, or that contacts were always followed by immediate decontamination of the skin. In use by the customer, the material was spilled on a man’s skin. He was several miles out in the “bush” in northern Canada in the winter with the temper- ature below zero Fahrenheit, and with no water available for decontamination. The man died from poisoning due to skin absorption of the material. Simple experiments on animals in the toxicological laboratory showed that the material was very toxic when absorbed through the skin. When a supplier indicates that no problems have cen encountered in handling a particular material, ask how they handle it. Ask them what toxicological informa- tion they have on the material. In controlling the occupational environment in the interest of health and well-being, established acceptable exposure limits for a healthful environ- ment are very useful. These acceptable exposures are expressed as “acceptable concentrations” by the American National Standards Institute and as “threshold limit values” by the American Confer- ence of Governmental Hygienists (such standards are discussed in detail in Chapter 8). These limits are not exacting scientific thresholds of response. They are the judgments of people with knowledge and experience. The intelligent use of these limits depends on the understanding and judgment of the man who must control the occupational en- vironment. We must recognize that the industrial hygienist usually deals with a variable exposure. Enough analyses are needed to clearly define the probable fluctuations and to establish a significant time weighted average. Maximum concentrations must be determined as well as duration and frequency of peaks of exposure. The summation of this in- formation to define the exposure situation requires the good judgment of a knowledgeable industrial hygienist. The application of the established ac- ceptable limits for a healthful environment also requires the good judgment of a knowledgeable industrial hygienist. Acceptable limits cannot be used effectively as just a routine check point. Those people responsible for suggesting ac- ceptable limits or for using acceptable limits are part of the ecological system — the industrial hy- gienist, the physician, the toxicologist and all the other environmental control people. The effective- ness of their operation can have a very significant effect on the occupational ecological system. When an injury does occur, clinical observa- tion of the victim can provide very valuable in- formation and should be reported in the literature. As was discussed in the previous section, the ex- posure can be variable. Most important, be sure vou know all of the chemical substances or phys- ical energies to which the victim was exposed and, hopefully, quantitation of exposure. During the carly development of 2,4 dichloro- phenoxy acetic acid (2,4 D), careful toxicological studies were made on animals in the toxicological laboratory. It was concluded that the material at the high dilution used in the field as a weedkiller was not a significant hazard. After years of use there was a report of a death in Canada from 2,4 D. The man drank a glass full of the diluted solution from the spray tank with suicidal intent. The physician who observed the man in the clinic and the manager of the contract spray company where the solution had been mixed, both con- firmed that it was, in fact, 2,4 D. Calculating from the toxicological information, I did not think this was possible. An agricultural scientist was going to visit the area where this death occurred so I asked him to investigate. He asked the foreman of the spray crew, “What did you use as a weed- killer before you used 2,4 D?’ “Oh, we used sodium arsenite.” “Then you stopped using so- dium arsenite?” “No, we just added 2,4 D to the sodium arsenite.” The man who died had drunk enough sodium arsenite to have killed ten people. When you draw a conclusion from that first clinical case, be sure you know all of the materials to which the victim was exposed. This serves as a reminder that peo- ple are involved, people between you and the actual circumstances of the incident. As previously stated valuable information on the nature and amount of exposure can be ob- tained by biochemical measurements on a person suspected of exposure. This depends on the ab- sorption, transport, metabolism and excretion of the material. Blood, urine or exhaled air analysis can give valuable clues to the nature of certain of the materials to which the person was exposed. The analysis used depends on the way the body handles the material in question. Many volatile organic materials are exhaled in the breath. In- frared analysis can give an indication of the nature of the material and some indication of the amount of exposure. To illustrate, a man came into the clinic and reported that he had been exposed to a certain volatile solvent. Infrared analysis of his exhaled air showed that he had not been exposed to the solvent he indicated but to a very different solvent. Had the clinic proceeded on the basis of his report of exposure, the handling of the case would have been in error. Some biochemical measurements can be very useful when wisely used. COMPLEXITY OF THE WHOLE The ecological picture as a whole is too com- plex to understand or to control when considered in its entirety (both occupational and nonoccu- pational). Yet, those who are responsible for the health and well-being of people in the system must keep the total picture in mind. That total picture includes the chemical sub- stances, physical energies and biological organisms in the occupational area which we can measure and over which we can have some control. As pre- viously discussed, the exposures can be variable. Levels of concentration alone are not enough. One must know the frequency and duration of ex- posures. There is no simple mathematical pro- cedure which will give a specific numerical answer. One can determjirie the time weighted average and the maximum concentration, duration and fre- quency of peak concentrations. These are mean- ingful if one has sufficient analytical data which represent the actual exposure conditions. These exposure conditions can then be related to the acceptable limits proposed by various organiza- tions. This comparison gives some understanding of the significance of possible exposures in the area studied. In addition, however, one must keep in mind the complexity of the whole. The final de- cision requires judgment of the whole based on available knowledge and experience. Comparable factors are in the nonoccupational area where we have little control. Hopefully, we may have some effect by carry-over of experience from the occupational area. In both the occupa- tional and nonoccupational area the individual is an important factor. The people in the environ- ment of the individual both on and off the job have a significant effect. OBTAINING UNDERSTANDING AND COOPERATION Obtaining the understanding and cooperation of people in the environment of concern is critical to effective control of that environment. This state- ment has been made several times in this chapter. It was a significant factor in many of the illustra- tions used. This is such an important part of effective control that it justifies summation here for emphasis. Without understanding and coop- eration all the most careful measurements and careful engineering of an operation may be in- effective. We repeat fools are most ingenious in overcoming “foolproof” engineering. It is simple to state “Get their understanding and cooperation.” Getting it is not always that simple. How does one get it? The method will vary with the industrial hygienist and with the people in the operation of concern. The following methods are suggested as having been successful under many circumstances. What you will do de- pends on your judgment of the particular circum- stances with which you are concerned at a partic- ular time and the people with whom you are concerned. Previous mention was made of the value of a careful environmental survey and concurrent clin- ical study of the men involved as a preventive control. Before such a study is made, it is valuable to get all the men in the operation together. A regular safety meeting can be used; it should in- clude all the people — supervisors as well as laborers. Explain what is intended and why. In- vite questions from the group. Answers and ex- planations should be in simple, direct language which they can understand. During the survey of the environment, the workers’ interest and understanding may be help- ful. You can obtain a lot of information on the operation from the individual workmen. When the survey is complete, it should be reported to the whole group. Tell them basically what was found, in language they can understand. Indicate what should be done, if anything, to assure a good work 10 environment. When they understand that you have a sincere interest in the workers’ health and well- being, it increases their cooperation in effectively controlling the operation. When you are checking the environment of an operation, talk with the individual workmen. Ask them for information and suggestions. Including them in control efforts will result in more effective cooperation. Take every opportunity to inform all the people who may be concerned with your area of operation. Discussion at safety meetings is use- ful in getting information to a group. Also look for a chance for discussion with individuals, — all individuals — executives, supervisors, engineers, operators, janitors. You should also be concerned with the design of a new production unit. Your cooperation with the engineers in design and construction can aid in giving consideration to control of the eviron- ment. Inclusion of good environmental control principles in the design and in the construction of a new production unit is essential, It can save a lot of reconstruction later. It also can make the control of the environment in the interest of health and well-being a much more effective operation. When talking with groups at a safety meeting or with individual workmen, take every oppor- tunity to discuss also the application of their understanding of healthful working conditions to their off-the-job activities. Through the under- standing and cooperation of the employees, we may also have a significantly favorable effect on the nonoccupational ecological system as well as the occupational; hopefully, some of the “under- standing” will be carried over by the workmen to their off-the-job activities. PRACTICAL CONTROL Yes, the total picture is complex, yet there are a lot of practical things that can be done. We can measure the chemical substances, physical ener- gies and biological organisms in the occupational environment. We can control them through good engineering and good operation. We can and must obtain the understanding and cooperation of the employee in order that our environmental con- trol may be effective. We can compare our find- ings with the acceptable limits suggested by various groups. With an understanding of the basis of these limits and the significance of our findings, we can judge the effectiveness of our control. We must recognize the possible impact of both occu- pational and nonoccupational factors. The most effective use of our present knowl- edge should be made. We nced to make an effort to increase that knowledge through toxicological, environmental and clinical research. We should recognize the complexity of the whole ecological system. This complexity should not discourage us from the effective application of the good practical knowledge which is available. With the practical application of all the factors discussed and the understanding and cooperation of the workers, our efforts can have a very favorable effect on health and well-being. CHAPTER 3 REVIEW OF MATHEMATICS Janet L. Patteeuw INTRODUCTION The mathematics required in the practice of industrial hygiene is that usually included in mathematics courses which precede the calculus and includes an introduction to statistics. It as- sumes, as a minimum, a previous acquaintance with elementary algebra and plane geometry at the high school level. COMPUTATION Laws of Exponents Exponents provide a shorthand method of writing the product of several like factors. If b Is any number and n is a positive integer, the product of n of the quantities b is denoted by br". Symbolically, bb: -b=b", where n is the exponent, b is the base, and b" is read “b to the nth power.” This definition can be extended to include exponents other than positive integers. If n and m are positive integers, the fol- lowing properties hold: b=] if b#0 bom The theorems on exponents follow easily from the preceding definitions: ( 1 ) bm . bn=pm+ n bm 2 — hymn (2) },=b (3) (bm) =pm-n (4) (ab)"=a"-b" ay" a" (5) (%) = po Scientific Notation Very large and very small numbers can be ex- pressed and calculated efficiently by means of scientific notation, a method which depends pri- marily on the use of exponents. A number is said to be expressed in scientific notation when it is written as the product of an integral power of 10 and a rational number be- tween | and 10. For example, 253=2.53 X10? B I 1 _ B 0.0253=2.53X | (~=2.53X =253X10" The procedure illustrated by these examples may be stated as follows: (1) Place the decimal point to the right of the 11 first non-zero digit, thus obtaining a number be- tween 1 and 10. (2) Multiply this number by a power of 10 whose exponent is equal to the number of places the decimal point was moved. The exponent is positive if the decimal point was moved to the left and negative if it was moved to the right. By use of the laws of exponents and scientific notation, computations involving very large or very small numbers are simplified. For example, 378,000,000,000 xX 0.000004 - } 2000 _3.78X 10" X4X107° To 2xi1or =3.78X2X 10" =7.56 X10? =756. Significant Digits Measurements, in contrast to discrete counts, often result in what are called approximate num- bers. For example, the dimensions of a table are reported as 29.6” by 50.2”. This implies that the measurement is accurate to the nearest tenth of an inch and that the table is less than 50.25” and more than 50.15” in length. Similarly, using sym- bolic notation, 29.55” < width < 29.65”. Thus the areca of the table is not 29.6 X50.2= 1485.92 square inches. Instead the exact arca is between 29.55 X 50.15 =1481.9325 square inches and 29.65.X50.25=1489.9125 square inches; it is clearly nonsense to report the area as 1485.92 with six non-zero digits when even the fourth digit is in doubt. It thus becomes important to indicate the digits which are “significant.” In making measurements the number of sig- nificant digits that can be recorded is determined by the precision of the instruments used. It is possible to indicate the accuracy of a measurement by actually giving the tolerance or possible error. For example, the length of the table could have been recorded as 50.21 == 0.02 inches, indicating that the actual length lies between 50.19 and 50.23 inches. Another method of indicating accuracy is to express all measurements in scientific notation. The digits in the rational number are then called significant digits. For example, 124.6 can be written as 1.246 X 10* where 1, 2, 4 and 6 are the significant digits. This method clarifies measure- ments such as 24,000 by indicating whether they are accurate to the nearest thousand, hundred or ten units, Summarizing the preceding, the significant “digits in a number are: (1) Non-zero digits (2) All zeros which are not used to place the decimal, i.e. zeros only if they are: (a) between non-zero digits (b) at the right of non-zero digits and are, in some way, indicated as significant at the right of non-zero digits which occur after a decimal point. (¢) For example, Number Significant Digits 24,000=2.4X 10’ 2,4 24,000 = 2.400 X 10’ 2,4,0,0 1087 = 1.087 X 10° 1,0,8,7 0.0015=1.5x 10" 1,5 0.0003 =13 x 10 3 Computational Accuracy In any computation involving sums and differ- ences, the number with the least number of digits following the decimal point determines the number of decimal places to be used in the answer, For example, 2883 43.46 : 0.1376 2926.5976 should be 2927. Since 2883 has no digits following the decimal place the answer must be expressed as 2927. With products or quotients the accuracy of the result depends on the number of significant digits in the component measurements. Thus the number of significant digits to be retained in the result is ‘the least number of significant digits in any of the “factors. For example, 8.216 X 3.71 =30.48136 should be 30.5. Since 3.71 has only three significant digits, only three should be retained in the result. Note that in the use of a formula involving ab- solute constants, these constants may be assumed to have as many significant digits as desired; in other words, they may be ignored in any determination Rounding In performing computations, it is recom- mended that rounding be accomplished after the calculation has been performed in order to incur the least possible error. The rules of rounding state that in rounding off a digit: (1) Add 1 if the succeeding digit is more than 5 (2) Leave it unchanged if the succeeding digit is less than 5 (3) If the succeeding digit is exactly 5 round off the number so that the final digit is even. In each of the following examples the number is rounded to three digits: (1) 45273 is rounded to 45300 (2) 45243 is rounded to 45200 (3) 45250 is rounded to 45200 (4) 45350 is rounded to 45400 (5) 45250.03 is rounded to 45300. Logarithms Lengthy computations can often be greatly simplified by the use of logarithms. The formal definition states that if b is any positive number different from 1, and b¥=x, then the exponent y is called the logarithm of x to the base b. In symbols, y=log,x. For example, log, 9=2 since 32=9. It is important to note that a logarithm is an exponent. Since this is true the same properties that hold for exponents also hold for logarithms. They can be restated in the following manner: (1) log, (x+y) =log,x +iog.y (2) log, (3) = log,x — logy (3) log, (x*) Common Logarithms. Logarithms which use 10 as a base are called common or Briggsian logarithms. Usually these are written simply as log x, without any base indicated, meaning log, x. In order to find the common logarithm of a number note first that log 1=0 and log 10=1 since 10°=1 and 10'=10. Thus the logarithm of any number between 1 and 10 will be a value between 0 and 1. The values have been calculated n log, x. of the number of significant digits to be retained in and are available in tabular form. A portion of the result of the computation. such a table is shown below. ) Table 3-1 N 0 1 2 3 4 5 6 7 8 9 50 6990 6998 7007 7016 7024 7033 7042 7050 7059 7067 517076 7084 7093 7101 7110 70118 7126 7135 7143 7152 52 7160 7168 7177 7185 7193 7202 7210 7218 7226 7235 53 7243 7251 7259 7267 7275 7284 7292 7300 7308 7316 54 7324 7332 7340 7348 7356 7364 7372 7380 7388 7396 . Note that the decimal points are omitted in such a called the characteristic, and a positive decimal table. Hence fraction between O and 1, called the mantissa log 5.34=0.7275. In order to find common logarithms of num- bers larger than 10 or less than 1, the method of scientific notation is used. The logarithm of such “a number can be written as the sum of an integer, 12 ’ For example, 534=534X10*= 10" "7X 10? = 1077 Thus log 534=2.7275. More simply, in finding the logarithm of a number written in scientific notation, the characteristic is the exponent of the power of 10 and the mantissa is the entry in the table corresponding to the first part. For example, log 52=1.7160. This same rule applies to numbers less than 1, although the result can be written in many different ways. For example, 0.00534 =5.34 xX 107 fog 0.00534 = —=3+0.7275 10—-3+0.7275-10 7.7275 -10 3.7275 = —2.2725. The final form, — 2.2725, is the most inconvenient since it does not contain a characteristic and man- tissa. When the logarithm of a number is known, it is a simple process of using the tables and working backwards in order to find the original value, called the antilogarithm. Natural Logarithms. The natural or Napierian system of logarithms employs as its base the irra- tional number e whose decimal expansion is 2.71828 . . . . Natural logarithms are usually denoted by In x or log.x. Tables also exist for the natural logarithms of numbers between 1 and 10. To obtain the natural logarithms of other numbers the number must again be written in scientific notation. Then the properties of logarithms are applied. For example, 642 = 6.42 X 10* In 642 =in 6.4242 In 10 = 1.85942 +2(2.30259) = 6.46460. Note that the number to the left of the decimal point in a natural logarithm does not indicate the location of the decimal point in the antilogarithm. Logarithmic Conversions. Tn order to change log- arithms with a base b into logarithms with any other base a it is only necessary to multiply by the constant factor log,b. That is, log,x =log,x + log,b. Specifically, for conversions between natural and common logarithms, log x =0.4343 + In x In x=2.3026 - log x. Computation with Logarithms. Simplification in computation is obtained by the use of the three basic properties of logarithms stated above. Con- sider, for example, the heat stress equation Ena = (10.3) (V)"* (42=VP,). This computation can be greatly simplified by writing it in the form log E,..=log 10.3+0.4 log V +log (42— VP,). GRAPHING A graph is a pictorial representation of the relationship between two or more quantities. By this means a union is formed between the two ele- mentary streams of mathematical knowledge — algebra and geometry. Cartesian (Rectangular) Coordinate System The most common two-dimensional graph makes use of linear scales for each of the quantities in 13 being considered. Two perpendicular lines and a unit of length are chosen. Customarily the hori- zontal line is called the x-axis and the vertical line the y-axis. By this means a one-to-one correspon- dence can be established between the points in a plane and all ordered pairs of real numbers. This is demonstrated in Figure 3-1. T no = nN F-—————e WN + i I i I I I I (=1,-2) +3 Figure 3-1 Linear Functions An equation in which none of the variables is raised to a power is called a linear or first-degree equation. The graph of such a function is always a straight line. A linear equation often appears in what is known as slope-intercept form: y=mx +b, where x is the independent variable; y is the dependent variable; b is the y-intercept, the value for y when x=0; and m is the slope, the change in y divided by the change in x. As an example consider the graph of the equation y="3x + 2 shown in Figure 3-2. Since the y-intercept is 2, the line passes through the point (0, 2). Since the slope is —3/2, the line falls three units vertically for every two units that it runs horizontally. Second and Higher Degree Equations There are many forms of second and higher degree equations, but few will be encountered in industrial hygiene. One exception may be the parabola which has the general form y=Ax*+ Bx+C. As an example, consider the equation o y=dx="-. The simplest method of graphing such a function is to form a table of values that satisfy the equation. Table 3-2 yl 1 0 1 2 3 4 5 6 7 8 ‘x| —45 0356 758 156 0 5 - Figure 3-2 The graph of this function is illustrated in Figure 1 5 3- de T t 3 4 nN + Figure 3-3 Exponential Functions An exponential function is any function in which a constant is raised to a variable power and has the general form y=a(c’*). A number of ventilation, dilution and noise level equations are of this type. Should such a function be graphed on rectangular coordinate paper when, for example, c¢ > 1 and b is positive, the result is a curve of the type shown in Figure 3-4. —t—+—+ 6 7 8 9 10 14 (0,a) Figure 3-4 If the logarithm of both sides of the equation y=a(c") is taken the result is log y =log a+ bx log c. If x and log y are taken as the variables, this equation has the slope-intercept form of the equation of a straight line, y=mx +b. This equa- tion may then be plotted as a straight line on semi- logarithmic paper, which has a linear scale on the horizontal axis and a logarithmic scale on the ver- tical one. As shown in Figure 3-5, the y-intercept becomes log a while the slope is b log c. l 1 I I T \ 4 — —t 4 5 | 2 3 Figure 3-5 Power Functions A power function has the general form y= ax. Graphing such a function on rectangular coordinate paper often requires the finding of a great number of points. However, if the logarithm of both sides of the equation is taken the result is log y=log a+b log x. If log x and log y are the independent and dependent variables respec- tively, the form of this equation is again the slope- intercept form of a straight line, y=mx+b. This equation may then be plotted on logarithmic paper, which has a logarithmic scale on both axes. The plot will be a straight line with slope b and y-inter- cept log a as shown in Figure 3-6. a » on —-+ on + ~ + ® + © + Figure 3-6 STATISTICS Frequency Distributions In any study of statistics the main concern, either in fact or in theory, is with sets of numerical data. The entire set is usually called the popula- tion while some subset of it which is being con- sidered is called a sample. One of the first steps in analyzing a population is to arrange the mem- bers of the sample in an array, thus exhibiting the frequency distribution of the population. The frequency distribution that occurs most often in both industry and nature is the normal FREQUENCY X Figure 3-7 15 distribution. This distribution can be represented by a bell-shaped curve; that is, a symmetrical curve with most of the values falling somewhere near the middle of the range of values, as shown in Figure 3-7. Many other distributions have also been char- acterized. In fact, studies of the distribution of measurements of particulate air pollutants and particle sizes indicate that a suitable frequency function is that of the log-normal distribution. In this distribution, the logarithms of the actual meas- urements are approximately normally distributed. A special type of logarithmic paper, called log- probability paper, is used to plot this distribution. Measures of Central Tendency In addition to the general information provided by a frequency distribution, there are quantitative characterizations of a population called param- eters. The first of these is a measure of central tendency, a number about which the data tend to concentrate. If the distribution of a set of numbers is ap- proximately normal, three measures of central tendency are frequently used. The most important of these is the arithmetic mean, the sum of all the values divided by the number of values. Symboli- cally, n x Xi X, txt +x, _ i=l n "on If one or more of the values appears more than once, the calculation may be simplified by multi- plying each of the values by the number of times it appears. Then X = n I (xf) -_ i=l X N , where f; is the frequency with which x; appears and N is the total number of values being consid- ered. This is the method used to calculate a time- weighted average, such as that used in referring to threshold limit values. The second common measure is the median, the middle observation when the numbers are arranged in order of magnitude. If there are an odd number of values, the median is uniquely de- fined; if there are an even number, the average of the two middle values is used. For example, the median of the numbers 7.11, 21, 24, 31, 92 is 21124 2 Another measure of central tendency is the mode, the number in a collection which occurs most frequently, if such a number exists. This value is often not uniquely defined, or, if it is, may not be representative of the sample. If the frequency distribution is approximately log-normal rather than normal, the most appro- priate measure of central tendency is the geometric mean. This is defined as the nth root of the product . of the n values. Symbolically, or 22.5. Xe =\} X1* X2 °° Xp. This calculation can be greatly simplified by the use of logarithms. 1 Since Xe = (X1 * Xz * * * Xa)? log X,= : (log x; + log x, + * *+log x,) =) ( log x ) = 1 nN i=] 1 n and x; =antilog |— log x, )| n\ i=l Again, if some of the values should appear more than once, as in a particle size distribution, the formula becomes n X, = antilog E Y fi-log s)] i i=l This computation may be carried out by the use of either common or natural logarithms. Measures of Dispersion A second numerical characterization of a pop- ulation is provided by a measure of dispersion, a number describing how the values of the collection deviate from some central value. If the distribution is approximately normal, the appropriate measure of dispersion is the stan- dard deviation. The difference between any value in a set of data and the mean is called the deviation from the mean. If these deviations are squared, summed, and divided by n—1, the resulting num- ber is the variance of the distribution. The positive square root of the variance is the standard devia- tion. Symbolically, n I To simplify calculations, this may also be written as, n 2 , ¥ ( zx) i=1 n (n—1) Again, if some of the values should appear more than once, this frequency of appearance, f;, is introduced into the equation. In that case nY i= Ss= As a computational aid the standard deviation may also be written as n 2 ( . x fi x; ) i=1 N (N-1) The significance of the standard deviation lies in the fact that if a distribution is approximately normal, 68.3% of the observations will lie within one standard deviation of the mean, 95.4% will lie within two standard deviations of the mean, and n N x f; Xi? — = S= 16 99.7% will lie within three standard deviations of the mean. A graphic presentation of this is shown in Figure 3-8. -30c -20 -lo X loo 20° 30 2% 16% 50% 84% 98% Figure 3-8 When the distribution is approximately log- normal, the standard geometric deviation is the appropriate measure of dispersion. The equation log x; — ( i=l for this measure is log Xi ) n (n—1) I Again, when some of the values appear more than once the frequency, f;, is introduced. Then, n n 2 N Xf, log x y flog x ) i i=1 } 1= N (N-1) The significance of the standard geometric deviation is analogous to that of the standard devi- ation if we recall that in a log-normal distribution the logarithms of the values are approximately normally distributed. Thus, 68.3% of the values lie between X,/s, and X, * s;, 95.4% lie between Xg/ 28, and X, * 2s,, and 99.7% lie between x,/3sg and x, + 3s,. It should be noted that these are the principles which govern the use of log-probability graph paper. Testing Hypotheses Frequently an investigator has in mind a par- ticular hypothesis or assumption about the popu- lation being sampled. This usually consists of as- signing a specific value to one or more of the parameters of the population, such an assignment depending on past experience. Then a test must be devised whereby the hypothesis is either ac- cepted or rejected once the sample has been taken. The determination of this test depends on certain characteristics of the population which will not be discussed here. A good statistical reference such as those cited at the end of this chapter will pro- vide a detailed method for selection of a test sta- tistic. It should be understood, though, that the failure to reject a hypothesis does not imply that it is true; it simply means that the information is such that we are not in a position to reject the hypothesis. n I n sg = antilog sg = antilog Curve Fitting In addition to characterizing a population, the methods of statistics are often used in making pre- dictions. This involves the consideration of rela- tionships between two or more variables. Such a study usually begins with the plotting of the points on a rectangular coordinate system, giving a visual image of the relationship between the variables. In the case where the values of y are fairly well approximated by a linear function of x, linear correlation is said to exist. A measure of the closeness of this correlation is given by the linear correlation coefficient n L i=I r= ‘ n i n YI xi—x)2°Y (yi—y)? i=1 i=1 If this value is close to 0, there is little linear rela- tionship between the variables; while if it is near +1 or — 1, the linear relationship may be greater. However, the extent of such a relationship depends strongly on the sample size. Also, there may be a high degree of correlation that is not of the linear type and thus not indicated by the linear correla- tion coefficient. When a relationship is seen to exist between two variables, it is often desirable to approximate the function in order to predict the value of one variable from the other. This is often accom- plished simply by joining the data points by a curve that appears to best approximate the rela- tionship, as shown in Figure 3-9. (xi—x) * (yi—y) 50 + 40 + Figure 3-9 An equation of this curve can then be found by substituting points on the curve into the general equation of the curve and solving the resulting 17 equations simultaneously. A more precise method of determining the equation is given by the method of least squares, a procedure which minimizes the error committed in fitting a curve of a definite type to a set of data. A detailed description of this method can be found in most of the references cited at the end of this chapter. Dimensional Analysis ‘Expressions of concentrations of atmospheric contaminants in industrial hygiene are usually cor- rected to 25°C and 760 mm Hg pressure, but the actual conditions are frequently not sufficiently re- moved from this standard to require temperature and pressure corrections, When calculating con- centrations, recall that one gram-mole is the amount of material in grams equal to the molec- ular weight of the material. Also, at standard tem- perature and pressure (0°C and 760 mm Hg), one gram-mole of any compound in the gaseous state occupies 22.4 liters. Terms Peculiar to Industrial Hygiene The concentration of gases and vapors is usu- ally expressed as parts per million parts of air, ppm, on a volumetric basis. parts 10° parts (air) micro-liter liter (air) cubic meters 108 cubic meters (air) cubic feet 10% cubic feet (air) This is similar to the concept of percent, OL % 100 parts The concentration of fumes, mists, dusts, and of gases and vapors on occasion, is expressed as milligrams of material per cubic meter of air, mg/ M3. Examples (1) Given the concentration of a contaminant in ppm, convert to mg/M?. ppm = Since 1 ppm, 10° liters ._f 1 liter 1 gram-mole Concentration = ( 10° i) * ( 22.4 liters ) x ( MW Grams ) % ( 10° sy gram-mole Ms? __ grams =10° MF —mg = At 25°C and 760 mm Hg, one gram-mole of a perfect gas or vapor occupies 24.45 liters. There- fore, under these conditions, Molecular Weight 24.45 (2) Derive an equation for the preparation of me _ M3 ppm X a known concentration of a volatile liquid P =Pressure in mm Hg given the following: p =Density in grams per milliliter Vr =Chamber volume in liters v ~~ =Volume of material to be used in MW = Molecular weight of a substance milliliters T = Absolute temperature C =Concentration in ppm (vml) p em 22.4 liters gm-mole T 760 C (ppm) = ml gm-mole MW gms 273 x 10° parts Vr Liters 10° parts 224 T 1760 _ wv) (p) MW 273 P = Xx 10°. Vi Recommended Reading 1. ANDRES, P. G., H. J. MISER and H. REINGOLD. Basic Mathematics for Science and Engineering. John Wiley and Sons, Inc., New York, 1958. BASHAW, W. L. Mathematics for Statistics. John Wiley and Sons, Inc., New York, 1969. BOWKER, ALBERT H. and GERALD J. LIEBER- MAN. Engineering Statistics. Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 1960. COCHRAN, WILLIAM G. and GERTRUDE M. COX. Experimental Designs. John Wiley and Sons, Inc., London, 1957. COOLEY, HOLLIS R. and HOWARD E. WAH- LERT. Introduction to Mathematics. Houghton Mifflin Company, Boston, 1968. HICKS, CHARLES R. Fundamental Concepts in the Design of Experiments. Holt, Rinehart and Winston, New York, 1964. KUSNETZ, HOWARD L. and DAVID QUONG. 18 12. 13. “Review of Mathematics.” The Industrial Environ- ment — Its Evaluation and Control. United States Government Printing Office, Washington, D.C., 1965. MOORE, JOHN T. Fundamental Principles of Mathematics. Rinehart and Company, Inc., New York, 1960. MORONEY, M. J. Facts from Figures. Books, Baltimore, 1971. NATRELLA, MARY G. Experimental Statistics, Handbook #91. United States Government Printing Office, Washington, D.C., 1963. RICHARDSON, MOSES. Fundamentals of Mathe- matics. The Macmillan Company, New York, 1966. SNEDECOR, GEORGE W. and WILLIAM G. COCHRAN. Statistical Methods. The Iowa State University Press, Ames, Iowa, 1968. WINE, R. LOWELL. Statistics for Scientists and Engineers. Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 1964. Penguin CHAPTER 4 REVIEW OF CHEMISTRY Fred I. Grunder INTRODUCTION Chemistry is that branch of the physical sci- ences which plays an extremely important role in the characterization and quantitative measurement of the toxic substances of interest in the field of occupational health. A proper understanding of the several phases of chemistry permits the oc- cupational health specialist to use this tool effec- tively in solving the environmental problems in this field. A proper understanding of inorganic chemistry is required for the appreciation of the properties of the mineral and inorganic chemical substances which are of concern to the health and well-being of the worker exposed to these mater- ials as airborne particulates, fumes, or mists in the workplace. A basic grasp of organic chemistry is important because of the great variety of toxic organic solvent vapors and particulate compounds encountered in industrial operations. Analytical chemistry is a major tool used in occupational studies in the evaluation of chemical hazards, in- cluding the levels of airborne contaminants in the working environment and the concentrations of toxic substances, intermediates, and metabolites in the human or animal body tissues and fluids. GENERAL INORGANIC CHEMISTRY It can be observed readily that the world is composed of a tremendous variety of material substances. Superficial inspection reveals many of these to be composed of two or more identifiable components. Often more deliberate study will show the components to be made up of still other distinguishable substances. If the examination process is continued with ever-increasing sophisti- cation, there will come a point where further sub- division will no longer be possible. The materials which cannot be divided into simpler chemical entities are called elements. The smallest unit which can be recognized as a particular element is known as an atom. Each atom of an element is chemically identical to every other atom of the same element, while uniquely different from those of other elements. There are presently 105 known elements, from which the material of the universe is made. Atoms are composed principally of positively- charged protons, negatively-charged electrons and uncharged neutrons. The protons are situated at the center of the atom along with uncharged neu- trons in the nucleus. The electrons are oriented at some distance from the nucleus and impart size and electrical balance to the atom. Each atom has the same number of protons as electrons to maintain electrical neutrality. The number of pro- tons in the nucleus is the atomic number which 19 uniquely defines the elemental identity of the atom. The number of protons combined with the num- ber of neutrons approximates the atomic weight. The atomic weight of an atom is proportional to its true, physical mass. Hence, 12.0 grams of carbon (atomic weight=12) contain 6.023 X 10** carbon atoms. The mass in grams of any element which is equal to that element’s atomic weight is called one gram-molecular weight, or one mole, which always contains 6.023 x 10** (Avogadro’s Number) atoms of that element. Each of the ele- ments has a name and a symbol assigned to it. For example, the eleventh element (atomic num- ber 11) is called sodium which has the chemical symbol Na. Elements combine with one or more other ele- ments in definite ratios to form compounds. The smallest unit of a compound is called a molecule. Molecules are held together by the sharing of pairs of electrons between the atoms to form chemical bonds. Bonds are classified according to the ex- tent of the sharing involved. A covalent bond is one in which the pair of electrons is shared equally by two atoms. An example of a covalent bond is the hydrogen molecule in which the two identical atoms share the lone electron pair. If the atoms involved are not from the same chem- ical element, the chances of equal sharing are diminished. In extreme cases, the bond is known as ionic. Sodium chloride (NaCl) is a good ex- ample of an ionic bond, the sodium existing essen- tially as the positively-charged ion and the chlorine as the negative chloride ion. Sharing of more than one electron pair leads to double and triple bond- ing. The nitrogen molecule is an example of a higher-order bond. In this case, the two atoms share three pairs of electrons to form a triple bond. The chemical symbol for a compound is merely a composite of its constituent atoms along with numerical indications of the ratios of the combin- ing elements to one another. For instance, the symbol for water, H,O, represents a molecule which contains two atoms of hydrogen and one of oxygen. The molecular weight of a compound is equal to the sum of the atomic weights of all the atoms making up the molecule of that compound. Similarly to the case for individual atoms, the mass in grams of any compound which is equal to that compound’s molecular weight is called one mole which contains 6.023 x 10** molecules of that compound. Often it is convenient and useful to express a molecular symbol or formula as more than just an accounting of the atoms present. It is known, for example, that certain groupings of atoms appear regularly in chemistry. They are called “groups” or “functional groups” or “radicals” and they are treated as separate elemental forms when writing the formula. In organic chemistry the methyl (CH,-) and ethyl (C,H,-) groups are common functional substituents in class com- pounds. Confusion is avoided in organic chem- istry by using constitutional or structural formulas. For example, the formula for ethyl alcohol, is written as CH,CH,OH or C,H,OH rather than C,H,O (a molecular formula) to emphasize the constitutional arrangement of the atoms within the molecule and to distinguish it from methyl ether (CH,OCH,) which has the same molecular formula. Chemistry uses the element symbols to abbre- viate complex descriptions of chemical reactions. For instance, if a reaction is initiated between hydrogen and oxygen in a mixture, water will be produced. The whole reaction can be written as the symbolic expression: 2H,+ 0, —> 2H,0. The exact way in which a chemical reaction is written expresses certain essential aspects of the reaction. This equation identifies the reactants as hydrogen and oxygen and shows that they com- bine in a ratio of two molecules of H, to one of O, to yield two molecules of H,O. A complete de- scription of the above reaction would include a description of the pertinent reaction conditions. It is significant that the equation is balanced with respect to both the numbers and the kinds of atoms in the reactants and the products. In cor- rect chemical equations, atoms cannot be created, destroyed, or transmuted. In organic chemistry (see discussion of bonds in section on Organic Chemistry) where the structure of molecule is especially important reactants and products are written structurally: H H H H \ / |] C=C +HBr —> H-C-C-H / \ |] H H H Br Chemical reactions occur because the final prod- ucts are energetically more stable than the initial reactants under the conditions of the reaction. The difference in energy between reactants and prod- ucts can commonly be observed as heat liberated, as in the burning of wood. Consideration of the amounts of liberated heat of reaction is important in thermodynamics where this is shown quan- titatively as part of the chemical equation: CaO + CO, —> CaCO, + 42.5 kcal/mole. The value of 42.5 kcal/mole is the amount of energy released as heat in the reaction. It is given the symbol AH and is defined as the heat of re- action. In tabular form, positive values for heats of reaction represent endothermic reactions which absorb heat from the surroundings. The reaction of CaO and CO, releases heat energy, indicating that it is exothermic and that the heat of reaction is negative (AH=-42.5 kcal/mole). It appears positive in the preceding equation because it is a positive product of the reaction. Another expres- sion for the same reaction is: 20 CaO + CO,—>»CaCaO,, AHjeqe =-42.5 kcal/mole. Basically, chemists are concerned with four types of chemical reactions, i.e. combination, decom- position, displacement, and double decomposition. Examples of these are as follows: Combination: Mg + Cl, —>MgCl, Decomposition: heated in 2HgO—>»2Hg + O,1 (gas) test tube Displacement: Fe (spatula) + CuSO, (solution) > FeSO, (in solution) + Cu (coating on spatula) Double Decomposition: AgNO, (solution) + NaCl (solution) AgCl7 (precipitate) + NaNO, (solution) Chemical reactions go to completion when one of these four conditions is met: 1) Increasing the concentration of one of the reactants: Ag™ ion (in solution) +Cl~ ion (added in excess as metallic chloride solution) —>AgCl| (precipitate) Silver chloride has a very low solubility product which means that the product (Agt) X (CI) cannot exceed its value of 1.56 X 107° moles per liter*; *One gram mole is the number of grams equal to the molecular weight of a sub- stance. Removing one of the products as a gas: A CaCO, = CaO + CO. 1 The escape of the gaseous product, car- bon dioxide, allows quicklime to be formed from limestone in a kiln. Removing one of the products as a pre- cipitate: Pb (C,H,0,)., + H.S (gas) —> PbS | +2CH, COOH When hydrogen sulfide is passed into a weakly acid solution of a soluble lead salt, the lead is converted completely to highly insoluble lead sulfide. Removing one of the products as a slightly ionized substance: NoOH + NH,CI=NaCl +NH,OH and NH,OH=NH, + H,O The addition of sodium hydroxide to ammonium chloride produces slightly ionized ammonium hydroxide which dis- sociates into ammonia and water. As a re- sult the reaction shifts almost entirely to the right. In the examples of chemical reactions given above there are two additional basic classifica- tions: first, reactions involving an electron transfer and a resulting change in the oxidation state of a substance and, secondly, reactions where there is no oxidation-reduction process. Thus, in the burn- ing of magnesium in chlorine gas, magnesium is oxidized from the elemental to the divalent (+2) 2) 3) 4) state while chlorine is reduced from the elemental to the negative (— 1) state whereas in the double decomposition reactions there is no oxidation-re- duction process occurring, but only an exchange of elements whose reactions go to completion for the reasons state® previously. The following dis- cussion treats further the matter of oxidation- reduction, an extremely important aspect of an- alytical chemistry processes. In the water molecule, H,O, the hydrogen atoms are essentially ionized by the oxygen’s strong affinity for electrons. The resulting charge and oxidation state for hydrogen is then +1 and that for oxygen is —2. In the elemental form (H, & O,) hydrogen and oxygen display no net charge and they have an oxidation state of 0. The reaction of hydrogen and oxygen to form water however, involves a transfer of electrons. The hydrogen atoms’ loss of their electrons to the oxygen atom is called oxidation; the gain of these electrons by the oxygen is called reduction. Re- actions of this type are called oxidation-reduction reactions or redox reactions. In any redox reac- tion, the total number of electrons lost by an oxi- dized species must exactly equal the number of electrons gained by the reduced species. This re- lationship enables redox reactions to be used in quantitative analysis. The amount of a substance in a redox reaction which will give up or receive one mole of electrons (6.023 X 10%* electrons) is called an equivalent. Naturally occurring materials, irrespective of their elemental make-up, assume three different descriptions or states: solids, gases and liquids. Solids have a definite shape and volume and are held together by strong inter-molecular and inter- atomic forces. For many substances, the forces are strong enough to maintain the atoms in def- inite, ordered arrays called crystals. Solids hav- ing little or no crystalline character are called amorphous. Gases, on the other hand, have weaker at- tractive forces between individual molecules. As a result, gases diffuse rapidly and assume the shape of their container; their volumes are easily affected by changes in temperature and pressure. Because true gases (the fixed gases) are relatively free of interactions between individual molecules, the behavior of a gas is dependent on only a few general laws based upon the properties of volume, pressure, and temperature. Under normal con- ditions, for instance, the pressure exerted by a gas multiplied by its volume is a constant at a fixed temperature and a given number of molecules: PV = constant. A temperature rise will produce a correspond- ing increase in pressure at constant volume and fixed number of molecules. A temperature rise will also produce a corresponding increase in volume at constant pressure and number of molecules: T,/T,=P,/P, or T,/T,=V,/V, where T, =absolute temperature (degrees Kelvin or Rankin) of a gas whose volume is V, and T,=absolute temperature of a gas whose volume is V,. At constant temperature and pressure, equal 21 volumes of gases contain equal numbers of mole- cules regardless of the nature of the gas. A volume of 22.4 liters will contain one mole or 6.02 X 10% molecules (or atoms of a monatomic gas) at sea- level pressure and 0°C or 32°F. An equation for relating the four properties of gases (P, V, num- ber of moles, T) which is applicable over a fairly wide range of conditions is called the ideal gas law; PV =nRT, where P = pressure V =volume n =number of moles T =temperature in degrees absolute R = gas constant (deter- mined by the units used for the other four). When dealing with gases, it is customary to express volumes in terms of standard conditions of temperature and pressure. Thus, if data are obtained at conditions other than standard it is necessary to correct the volumes. For this pur- pose, an adaptation of the ideal gas law is used: V,—(P/P,) (T/T) V where V,= volume at standard temperature and pressure P, =standard pressure T, =standard temperature in degrees absolute V =volume observed P =pressure observed T =temperature observed in degrees absolute The molecules of the liquid state of matter are separated by relatively small distances such that the attractive forces between molecules tend to hold the molecules within a definite volume at a fixed temperature. The repulsive forces between molecules also exert a sufficiently strong influence, however, that volume changes caused by increases in pressure may be neglected. One of the most useful properties of liquids is their ability to dissolve gases, other liquids, and solids. Solvents are covalent compounds in which the molecules are much closer together than a gas; therefore, the intermolecular forces are rela- tively strong. When the molecules of a certain covalent solute are physically and chemically sim- ilar to those of a liquid solvent, the intermolecular forces of each are of the same magnitude and the solute and solvent will usually mix readily with each other. The amounts of dissolved solutes are com- monly expressed in terms of concentrations in sol- vents. The molarity of a solution is the number of moles of solute per liter of solution, designated by “M”. The molality is the number of moles of solute per 1000 grams of solvent, designated by “m”. The normality, “N”, of a solute is the num- ber of gram-equivalent weights of solute per liter of solution. The expression “parts per million” represents one part by weight of solute per one million parts by weight of solvent in liquid sys- tems. One “ppm” is equivalent to one microgram per milliliter or to one milligram per liter of solution. In aqueous solutions the concepts of acidity and basicity are important. For most purposes an acid can be described as a hydrogen ion (proton) donor. Hydrochloric acid is an excellent example of a strong acid. Similarly, a base is described as a hydrogen ion acceptor. Sodium hydroxide is an example of a strong base. For aprotic compounds which have no ionizable hydrogen, an acid can be defined as a substance (such as aluminum chlor- ide) which accepts an electron pair from a base, and any substance, (such as NH,) that can behave as an electron pair donor is a base. In aqueous systems, the acidity or basicity of a solution is measured by pH which is defined as the negative logarithm of the hydrogen ion con- centration (expressed in moles per liter). It ranges from 1 to 14, pH 14 being extremely basic (the hydroxide ion, OH", greatly predominating), pH 1 being extremely acidic (the hydrogen ion, H+, greatly predominating), and pH 7 being neutral (the hydrogen ion and hydroxide ion concentra- tions equal). The basic concepts of general chemistry pre- sented in this section are designed to provide the non-chemist members of the industrial hygiene profession with a general understanding of the principles of chemistry as they relate to the appli- cation of analytical chemistry to occupational health. The reference texts cited at the end of this chapter should be consulted periodically, as the needs of work situations require, to obtain the more detailed information on the aspects of in- dividual problem areas. ORGANIC CHEMISTRY Organic chemistry is the study of carbon com- pounds, excluding the limited number of those inorganic substances which contain carbon such as carbon monoxide, carbon dioxide, carbonates and metal carbonyls. The common elements found in the thousands of organic compounds in- clude carbon, hydrogen, oxygen, nitrogen, phos- phorus, sulfur, chlorine, bromine, and iodine, in the order of their relative occurrence. Organic chemistry is involved in most activities of modern life. The basic principles of organic chemistry are applied to the study of drugs, rubber, clothing, plastics, explosives, fuels, paints, solvents and numerous other essential commodities. The carbon atom forms four covalent bonds. These bonds may be to other carbon atoms, to hydrogen, oxygen, one of the halogens (chlorine, bromine, iodine, fluorine), nitrogen, sulfur or to other atoms. The bonds may involve single elec- tron-pairs which form single bonds, two electron- pairs giving double bonds (—=C=C<), or three electron-pairs forming triple bonds (—=C=C—). More than one million organic compounds are known. Their existence is due to the unique ca- pacity of carbon atoms to join together forming chains or rings. Compounds formed from hydro- gen and carbon only are called hydrocarbons. The aliphatic series of saturated hydrocarbons provides the simplest example of this property. H—C—H methane i H H A ethane HoH H H H Hblilns propane HoH oH 3 us hexacontane Homologous series of compounds are named ac- cording to the number of carbon atoms in the longest chain. The standard (International Union of Pure and Applied Chemistry) rules for naming carbon compounds are summarized below: 1) The longest continuous chain of carbon atoms is named as the parent compound. 2) The carbon atoms in this chain are given numbers starting at one end, and substi- tute groups are given numbers correspond- ing co their position on the chain. The direction of the numbering is chosen to give the smallest sum for the numbers of the side chain constituents: ® ® © ® Oo CH,-CH,-CH-CH.CH, | CH. CH; is named 2-methyl- 3-ethyl pentane CH, 3) If the same group appears more than once, the prefix di-, tri-, or tetra- is used to in- dicate how many groups there are: CH, CH, CH, CH, or 2,4-dimethyl- | | | 3-ethyl pentane CH, - CH, - CH, - C - CH, ® @ 6 © Oo 4) With two identical side chain groups at one position, numbers are given for each: CH, or 2,2-dimethyl | pentane CH, -CH,-CH, -C-CH, ®@| ® @ ® CH,® 5) If several different substituent groups are present, they are assigned according to the alphabetical arrangement of substituents or in order of increasing size of the side chain. Branched chains often have names of their own. CHa CH- is an isopropyl group. For ex- cH 3 ample, CH, cH,” Thus, CHOH is called isopropanol CH, N cH,” The field of organic chemistry is generally divided into two broad classes of organic compounds, aliphatic compounds and aromatic compounds. Aliphatic Hydrocarbons The saturated hydrocarbons, which contain only single bonds, are also known as alkanes or paraffinic hydrocarbons. The general formula for these compounds is C,H,,+. where n is an integer. They are less reactive than the unsaturated hydro- carbons and are insoluble in water, sodium hy- droxide and sulfuric acid. They do, however, undergo reaction under certain vigorous condi- tions, When treated with either chlorine or bromine and light or a catalyst, a halogen atom can substitute for a hydrogen atom: light —C-H+Cl, — -C-Cl+ HCl | | They can be heated from 400° to 600°C to pro- mote thermal decomposition, a process called cracking, and yield simpler alkanes, alkenes and hydrogen. Alkenes are unsaturated, olefinic hydrocarbons. They contain at least one carbon-carbon double bond. The suffix -ene is substituted for -ane in naming them. The parent hydrocarbon chain is chosen as the longest chain containing the double bond. The position of the double bond is desig- nated by the number of the first carbon atom in- volved in the double bond. Thus, CH,CH= CHCH, is 2-butene, and CH,=CHCH,CH, is 1-butene. The double bond is given the lowest number, so the compound CH,-CH-CH = CH-CH, | CH, is 4-methyl-2-pentene rather than 2-methyl-3- pentene. Characteristic reactions of this group occur at the carbon-carbon double bond. The most char- acteristic reaction of the alkenes is the addition reaction. Generalized, this reaction can be rep- resented: \ / CHCH,CH, is called isopentane. J | | {Hyz— —CC YZ Many substitution groups can be represented by Y and Z (examples are H,, HX, X,, H,SO,, H,0O and others where — X is used to indicate a halo- gen such as chlorine or bromine). The paraffin-base oils contain mainly saturated open-chain hydrocarbons, whereas asphalt-base C=C 23 oils contain appreciable amounts of naphthenes such as cyclopentane, cyclohexane and their alkyl derivatives. The major fractions separated from crude petroleum are shown in the following table: TABLE 4-1 Major Fractions in Crude Petroleum Boiling Point Composition Fraction Range, °C (Approximate) Gas <20 C,-C, Petroleum Ether 20-60 C.-C, Ligroin (Light Naphtha) 60-100 C,-C, Natural Gasoline 40-205 C,-C, + Cycloalkanes Kerosene 175-325 C,-C, t Aromatics Fuel Oil 300-375 C.-C, Lubricating Oil >300 C,,-C.;s Asphalt or Petro- leum Coke >300 >C,; Aromatic Hydrocarbons Benzene is the simplest of the aromatic com- pounds; it has the formula C,H, and its structure is: H H Cc-C HC 2 cn, ~c=c— H H although experimental evidence indicates that all the carbon-carbon bonds are equivalent, The correct structure is often shown as: Q Where the circle indicates that the multiple bonding is shared equally among 2ll six carbon atoms. Benzene readily undergoes substitution reac- tions, such as halogenation: (Fe catalyst) CH, +X, —>»C,H,X+HX (X=Cl, Br) Benzene is very stable and resists addition re- actions which would destroy the ring system. In naming monosubstituted derivatives of benzene, the substituent’s name is prefixed to “benzene.” Thus: yz Cl / NO, _ is chlorobenzene _ is nitrobenzene Some aromatic compounds are better known by such common names as: CH, pz OH | O O toluene phenol | Pz NH, pz COOH aniline benzoic acid For aromatic derivatives containing two ring sub- stituents, the position on the ring is designated by the use of the terms ortho (0), meta (m), and para (p) as exemplified by: Br Br | oO © Br o-dibromobenzene m-dibromobenzene |Br O p-dibromo- Br benzene When the substitution groups are different, they are named successively and the compound name is terminated with “benzene.” If one of the sub- stitution groups provides a compound which has a commonly accepted name (e.g., toluene or phenol) any further derivative is named after the last-named compound: Br CH. O) p-bromoiodo- O) p-nitro- benzene toluene 1 NO, Br HO o-bromo- phenol If more than two substitution groups are attached to the ring, numbers (starting with the parent group) are assigned to each carbon atom to indi- cate the position of each substituent: CH, ® “ _NO, ® ® ® ® @ NO! 2, 4, 6-trinitrotoluene (TNT) 24 Halogen Derivatives of the Hydrocarbons Halogenated hydrocarbons are obtained from the substitution ~reaction of hydrocarbons with HX or X, under varied conditions. Generalized, the reaction with halogens is represented: R-H+X,—>»R-X+HX where R is an alkyl group and X is a halogen, such as chlorine or bromine. One or more halogen atoms may be attached to a chain or ring structure; each additional atom changes the physical and chemical properties of the preceding compound in a series. For example, the successive derivatives of methane are: HC1 CH, + Cl, — CH,CI used as a local an- + Cl, esthetic for minor (HCl) surgical operations — a gas CH,CIl, commercially used +Cl, asa solvent and in (HCI) quick-drying paints and varnishes CHCl, (chloroform) — a +Cl, commercial solvent (HCl) and anesthetic CCl, (carbon tetrachlor- ide) — very toxic; an important solvent. Typical aromatic halogen derivatives, such as the chlorobenzenes, are obtained by the substi- tution reaction of the halogens with the aromatic hydrocarbon. The halogen derivatives of benzene are called aryl halides which are generally less re- active than the alkyl halides. Halogenation may proceed with the complete substitution of hydro- gens attached to the ring carbons. Oxygen Derivatives of the Hydrocarbons An oxygenated carbon compound is one con- taining oxygen in a functional group attached to a chain or ring carbon. The alcohols have the gen- eral formula ROH, where R is an alkyl group. If the hydroxyl group (-OH) is attached directly to an aromatic ring, it is referred to as phenol, cresol, xylenol, or naphthol. Alcohols are often prepared by conversion of an alkene by adding sulfuric acid to the double bond and hydrolysis of the resulting alkylsulfuric acid: H,SO, H,0 CH,=CH, —> CH,CH,0S0,0H —> CH,CH,OH ethyl alcohol. The characteristic reactions of alcohols involve either the replacement of the OH hydrogen or of the entire hydroxyl group. ROH+HX—>»RH+H,0 X=CI Br, I ROH+M—>RO M++1/2H, M =metal such as Na, Mg, Al Some of the common alcohols are: methyl alcohol (methanol) CH,OH ethyl alcohol (ethanol) CH,CH,OH CH isopropyl alcohol (isopropanol) ">CHOH 3 Ethers have the general formula R-O-R’. Their names are derived from those of “R” groups fol- lowed by the word “ether.” Thus, CH,OC,H; is methyl ethyl ether and Diethyl ether is the most common member of this is diphenyl ether. class of compounds. It is used as a solvent and an anesthetic. Ethers are often prepared by dehydra- tion of alcohols: H,SO, 2 ROH —> R-O-R’+H,0 heat Ethers, as compared with alcohols are fairly inert. Aldehydes and ketones are carbonyl com- pounds having one and two alkyl groups respec- tively joined to the carbonyl function: Oo oO rc rR-c” H NR’ aldehyde ketone (R and R’ may be either aromatic or aliphatic) These compounds can be prepared by oxida- tion of alcohols: Cu, heat or H RCH,OH —K,Cr,O.—> R-C Oo Cu, heat or Oo RCHOHR’—K,Cr,O,/—> R-C R’ oO I The carbonyl group (-C-) is primarily responsible for the characteristic reactions of these compounds which can be oxidized to carboxylic acids or re- duced to alcohols. They also undergo addition re- actions involving the carbon-oxygen bond such as the analytically important one with sodium bi- sulfite: R H i C + NatHSO,~ —> R-G-SO, Nar I OH Some common aldehydes are: HCHO Formaldehyde CH,CHO Acetaldehyde 25 CH,=CHCHO Acrolein HC=0 Benzaldehyde A few common ketones are: CH, > C=0 Acetone H.C H.C Oo “C7 Methyl Ethyl Ketone CH,CH, oO I —_— CC — Benzophenone Carboxylic acids contain a carboxyl group 2° : (-C ) and are acidic in nature. The general “NOH formula for monocarboxyl acids is RCOOH where R may be aromatic or aliphatic. These acids can be obtained by the oxidation of primary alcohols, aldehydes or alkyl benzenes. KMnO, RCH,0OH —> RCOOH oO In the reactions that occur, the hydroxyl is usually the reacted group. A typical reaction is one of the type: COOH KMnO, 4 > or K.Cr,O, 0 0 Rc? +z—>RC? NOH NZ where Z may be Cl, OR’, NH,, etc. Some of the common acids are: HCOOH CH,COOH Acetic acid Formic acid COOH / Benzoic acid Isomers are defined as compounds having the same molecular formula but a different structure. There are essentially two major types of isomer- ism: structural isomerism and optical isomerism. Examples of structural isomers include the pen- tanes, all of which have the empirical formula C,H,, but different physical and chemical prop- erties: CH,-CH,-CH,-CH,-CH, n-pentane CH, CH, | “SCHCH,CH, CH,-C-CH, / | CH, | CH, iso-pentane neopentane A more striking example of structural isomerism is the compound C,H,O. This can be the molec- ular formula for methyl ether CH,OCH, or ethyl alcohol CH,CH,OH, two compounds showing marked differences in physical and chemical properties. Optical isomers involve a central atom to which a number of different groups are attached. Two optical isomers are molecules which are identical except for the spatial orientation of the groups attached to the central, asymmetric atom. They are mirror-images of one another. The most readily observed difference between the two is the difference in the rotation of the plane of polariza- tion if a beam of plane-polarized light is allowed to pass through a solution of the compound. This type of isomerism is useful in identifying certain biochemical reaction products. ANALYTICAL CHEMISTRY The analytical methods used in industrial hygiene may be divided into classical chemical methods and instrumental methods. Such a dis- tinction is based more on the historical develop- ment of analytical chemistry than on any clear differences between the two methods, as both the strictly chemical and the instrumental methods usually are completed with a physical measure- ment, such as spectrophotometry. It is possible to further separate the classical chemical methods as volumetric or gravimetric. Classical Chemical Methods of Analysis A volumetric analysis is one which is com- pleted by measuring the volume of a liquid re- agent of known concentration required to react completely with a substance whose concentration is being determined. The chemical reaction must be such that the amount of the known reactant can be related exactly to the amount of the anal- ysis substance present. A reaction, to be useful for volumetric analysis, must be rapid, complete and have a sharp endpoint. Two basic types of reactions may be considered as representative of volumetric analyses. Acidimetry and alkalinity reactions involve the neutralization of acids and bases. A titrimetric procedure is used to determine the amount of a standard solution of a reagent (i.e., one of pre- cisely-known concentration) required to react 26 completely with a specific chemical substance in a prepared solution of a sample. Titrations dependent upon neutralization re- actions must be complete at a definite endpoint based on an abrupt change in pH which occurs at the equivalence point. An example of a neu- tralization reaction in an aqueous system is the following: NaOH + HCI—>NaCl + H,0 When the hydrogen ion (H+) and hydroxide ion (OH™) concentrations are equal, the solution is said to be neutral (pH 7.0 aqueous solution). However, the actual pH at the equivalence point of an acid-base titration is not necessarily equal to 7.0, since it depends on the degree of ionization and hydrolysis of the products of the reaction. The majority of titrimetric procedures use an indicator to determine the endpoint accurately. An indicator is generally a complex organic com- pound having a weakly acidic or basic character capable of a sharp transformation in color over a definite, but narrow, pH range. Several factors play a role in determining the pH interval over which a given indicator exhibits a color change: 1) Temperature, 2) Electrolyte concentration (total ionic strength), 3) Effect or organic solvent systems. Two sources of error that may occur when de- termining the end-point of a titration using visual indicators are: 1) The indicator does not change color at or near the hydrogen ion concentration that prevails at the equivalence point; 2) Very weak acids (or bases) cannot be titrated with satisfactory results. The first of these sources of error can easily be corrected by using a blank. The second, however, cannot be remedied because of the difficulty in deciding exactly where the color change occurs. The other type of chemical reaction suitable for titrimetry is called oxidation-reduction or “redox.” The ions of a large number of elements can exist in different oxidation states. Suitable oxidizing or reducing agents can cause a redox reaction with such ions. Many of these reactions satisfy the requirements of volumetric analysis. One of the most widely used oxidizing agents is potassium permanganate (KMnO,). It has an intense purple color which can serve as its own indicator for the endpoint. The reagent will oxi- dize metallic ions from low to high oxidation states and negative ions such as chloride to chlorine at the zero or ground state. Its use in some reactions is restricted due to the multiplicity of possible reactions that may occur in the presence of more than one oxidizable substance, Potassium dichromate (K,Cr,0,) is another important oxidant. It is not as powerful as po- tassium permanganate and some of its reactions proceed slowly. However, the solid reagent can be obtained in high purity and stable, reliable solutions may be prepared conveniently. Dichro- mate solutions are most useful for titrations car- ried out in 1 to 2 normal acid or alkaline solutions. A substance which is useful both as an oxidiz- ing and as a reducing agent is iodine, generally used in the form of the triodide ion, I,”, which is formed by the reaction of iodine, I,, with the iodide ion I". The indirect or iodometric methods involve the treatment of a solution with an ex- cess of iodine and then measuring the amount of iodine used. Starch is an indicator for iodimetry and iodometry. Iodometry is used regularly for the determination of aldehydes and hydrogen sulfide collected in sampling reagents of sodium bisulfite or ammoniacal cadmium sulfate, respectively. Gravimetric analyses constitute another im- portant group of analytical methods for determin- ing substances quantitatively. A gravimetric method is one in which the analysis is completed by making a weight determination. A gravimetric procedure requires that the analytical substance must be separated quantitatively from other chem- ical entities in the sample. Numerous techniques are available for this separation. These include precipitation, solvent extraction, volatilization, complexation and electrochemical separations. Precipitation methods are the most common gravimetric procedures. However, all precipitates are not suitable for gravimetric analysis. The precipitate must have a sufficiently low solubility to insure that the solubility losses do not affect the results of the analysis seriously. Further, it must be possible to isolate the precipitate quan- titatively from the liquid by simple, rapid filtra- tion and to free it readily of contaminants by a simple treatment. The exact chemical composi- tion of the precipitate must be definite to allow calculation of the component of interest. Ideally, the precipitate should not be hygroscopic and should have a large molecular weight relative to the analytical constituent contained therein. Solid-liquid solvent extractions involve both simple removal of impurities by dissolving them from the desired precipitate and the reaction of the solvent with a component to make it either soluble or insoluble. Soxhlet extractions are good examples of the latter technique. Organic solvents find considerable application to this type of ex- traction. Liquid-liquid extractions make use of two mutually immiscible liquids to redistribute the de- sired solute on the basis of differences in solubility. The extraction of a metallic salt from an acid solution into an organic solvent is one example. Solid-gas extractions are used to remove a desired gas from a mixture of gases. Adsorption of volatile organic compounds from the air by activated carbon is an example of solid-gas ex- traction. Another useful technique in gravimetric anal- ysis involves the use of volatilization methods. Simple examples include the determination of water by loss on ignition and the decomposition, evolution and subsequent weighing of carbon di- oxide. Volatilization methods can be classified either as evaporation and/or sublimation or as distillation and aeration procedures. The drying of a sample to remove water and the separation of aluminum chloride are accomplished by evap- oration and sublimation techniques, respectively. 27 In the case of liquid mixtures of organic sub- stances, the individual components may be sep- arated effectively by distillation at atmospheric pressure or under vacuum. The determination of carbonate by the generation and removal of car- bon dioxide followed by subsequent weighing is an example of a gravimetric aeration technique. Elemental substances may be separated from other substances and metallic constituents depos- ited quantitatively by electro-chemical separations. In electrolytic methods, a pure deposit that ad- heres firmly to the electrode is required. Temper- ature, the presence of complexes and the evolu- tion of hydrogen affect the quality of a deposit. Deposits obtained from complex ions in solution tend to be dense and adherent. Heating and stir- ring the solution during electrolysis speeds up deposition as a result of higher current densities. When the material has been completely deposited, it may be dried and weighed. Instrumental Methods of Analysis The final measurement in an analytical de- termination has been greatly facilitated in recent years by the use of highly sophisticated instru- mentation. The industrial hygienist should never lose sight, however, of the preparatory work nec- essary before the final measurement can be made. Instrumentation is available for the qualitative and quantitative analysis of both inorganic and organic compounds. The basic feature of ultraviolet and visible spectrophotometry is the selective absorption by aqueous and other solutions of definite wave- lengths of light in the ultraviolet and visible re- gions of the electromagnetic spectrum. The funda- mental law governing ultraviolet-visible absorption photometry is Beer's Law which relates the ab- sorption of light linearly to concentration: A=kC “A” is the absorbance of the solution, “C” is the concentration and “k” is a constant whose value depends upon the wavelength of the radi- ation, the nature of the absorbing system, and the optical path length or cell thickness. Absorption data for spectra are usually recorded in terms of absorption versus wavelength. Wavelengths used for analysis are those at which the substance ab- sorbs strongly. Ultraviolet and visible spectro- photometry is used in occupational health lab- oratories for the determination of inorganic sub- stances and numerous organic contaminants of air, urinary metabolites and such blood compo- nents as carboxyhemoglobin and circulating heavy metals. Infrared spectrophotometry makes analytical use of the molecular vibrations and rotations in chemical substances exposed to radiation from the infrared region of the spectrum. The atoms within a molecule vibrate and rotate at definite frequen- cies which are characteristic of that molecule. A sample placed in a beam of radiation in a dis- persive infrared spectrophotometer absorbs energy at certain definite frequencies characteristic of the molecular components in the sample cell and will transmit the other frequencies. The absorption (or transmittance) within a specific frequency range may be correlated with the specific motions of the functional chemical groups of a molecule to identify their presence or absence. No two compounds with different molecular structures can have identical infrared spectra. Hence, the infrared absorption spectrum is a char- acteristic physical property (it is often termed a “fingerprint”’) of a compound, and it is a powerful tool in both qualitative and quantitative analyses, particularly for organic compounds as well as for certain inorganic structures, notably CO, SiO, and NO bonds. Quantitative analysis may be per- formed on a sample by selection of a specific absorption band whose response varies directly with the concentration of a given chemical species. X-ray diffraction and fluorescent methods are based upon physical properties related to the atomic numbers of the constituent atoms in chem- ical compounds and not on any chemical prop- erties of these substances. When monochromatic x radiation strikes a crystalline material, the planes of the atoms in the material diffract the x ray beam at angles which depend upon the interplanar spacings in the crystal lattice. An appropriate x-ray spectrometer is used to scan and measure the wavelength and intensity of the diffracted rays. The resulting x-ray diffrac- tion pattern is characteristic of the components of a sample, and crystalline materials, such as quartz (a form of free silica) or asbestos can be identified readily in mixtures of compounds. The sample patterns are compared with those of “standards to identify and measure quantitatively the crystalline components of a sample. X ray fluorescence is produced by an element which is irradiated by an intense beam of x rays. This fluorescence is observed as secondary x rays whose wavelengths are characteristic of that ele- ment. An x-ray spectrometer can be used to dis- perse the emitted secondary x rays and elements identified in the resulting spectrogram. Analytical curves are prepared from standard series of the pure compounds and the elemental constituents determined quantitatively. Errors of less than five percent are common with this method. The sensi- tivity (limit of detection) will vary from a few parts per million by weight to one percent depend- ing on the element and the matrix material. Emission spectroscopy and atomic absorption spectrophotometry are complementary techniques for the determination of atoms, ions, and a few molecular substances. The region of the electro- magnetic spectrum involved includes the near in- frared, the visible and the ultraviolet. The methods for analysis make practical use of this radiation for both qualitative and quantitative determinations. Flame emission and emission spectrographic techniques are based upon the excitation of atomic and ionic species to higher energy levels from which states they emit characteristic wavelengths of light as they return to their individual ground states. In flame emission, the sample solution is aspirated into a flame and certain wavelengths are monitored to detect characteristic emissions. An emission spectrograph uses electrical energy to excite the atomic (or molecular) species in a solid or liquid sample. The complete emission spectrum 28 is dispersed with a diffraction grating or a prism. The spectra are detected by phototubes or are recorded on a photographic emulsion supported on a plate or film. The recorded spectrograms are examined in a comparator-densitometer using qualitative and quantitative standards of reference. Flame emission spectroscopy is also used for quan- titative analysis since the amount of light emitted at a characteristic wavelength is proportional to the concentration of element. Atomic absorption spectrophotometry makes use of the property that the atomic vapors of an element will absorb that element's characteristic radiation in proportion to its concentration in a flame. The sample is aspirated in solution form into a flame as in flame emission spectroscopy. The operating principle is based upon the decrease in the intensity of a monochromatic beam of light from a hollow cathode lamp or other source con- sisting of the same elemental substance. Atomic absorption is used mostly for quantitative analyses and, as with flame emission and arc and spark emission spectroscopy, it is valuable for the de- termination of metallic and metal-like elements in any type of sample which can be solubilized. The term gas or vapor phase chromatography includes all chromatographic separation techniques using a gas as the mobile phase. Gas-liquid chromatography (GLC) makes use of a liquid distributed over the surface of a solid support as the stationary phase in the form of a column and a gas’ (helium, argon, nitrogen or hydrogen) as the mobile phase. The injected sample is vaporized and transported onto the column with one of the common carrier gases. The stationary phase adsorbs the sample components but not the carrier gas. Different compounds in the sample are retained to varied degrees by the stationary phase; hence, they pass through the column at different rates. The mobile carrier gas phase, which flows continually through the column, car- ries the different sample components through the column to appear in turn at a detecting device used in establishing the retention times of the individual compounds and in providing a signal for amplification to a recorder or integrator for a quantitative analysis. The output is recorded as a series of peaks on a strip chart recorder or fed to an electronic integrator for direct readout. The elution time is a function of the component, the particular stationary phase and the column tem- perature. When the separate sample components have been identified, standardization of the GLC method is performed with a series of gas or vapor standards under identical chromatographic condi- tions. Measurement of peak areas, preferably by electronic integrators, provides the basis of quan- titative analysis. This instrumental technique is extremely useful for the determination of organic contaminants in ambient and industrial atmos- pheres. A wide variety of electrochemical methods de- pend on the phenomena that occur within an electrochemical cell. One electrochemical method that is used for specific analyses is polarography or voltametry in which the current passing through a solution is measured as a function of the applied voltage. Essentially every element and many or- ganic functional groups may be responsive to polarographic analysis. The polarographic be- havior of any substance is unique for a given set of experimental conditions. If an unknown sub- stance can undergo either cathodic’ reduction or anodic oxidation, qualitative and’ quantitative analysis is possible. Polarographic recordings, called polarograms, are obtained by measuring the current and the applied voltage between a special type of polarized microelectrode and a non-polar- ized reference cell. Typical applications of polaro- graphy include the analysis of samples for lead, cadmium, zinc or mercaptans. A second electrochemical technique useful in many applications is based upon the use of ion- selective electrodes. These electrodes are used for the measurement of several cations (positive ions) and anions (negative ions) in solution in- cluding K+, Nat, Ag+, H,O+, CI, F~ and NO," Three types of electrodes in common use are glass, liquid and solid state membrane electrodes. Glass membrane electrodes depend on the pres- ence of certain compounds in glass to render them useful for the determination of certain ions. One of the properties of the glass electrode is its highly selective response to hydrogen ions when used as a pH electrode. Other glass membrane electrodes are available for the determination of ions such as sodium, potassium and calcium. Liquid mem- brane electrodes respond to a potential established across the interface between the solution to be analyzed and an immiscible liquid that bonds selectively with the specific ion. This type of elec- trode has been developed for the perchlorate and nitrate ions. Solid state membrane electrodes have the opposite property of glass (i.e., useful for measuring anions); have been developed re- cently and their operation depends upon the prin- ciple of selective precipitation. Thus, the fluoride ion electrode consists of a single crystal membrane of lanthanum fluoride supported between a refer- ence solution and the sample solution. Specific ion electrodes are so closely related to pH electrodes that they tend to be affected by acidity or basicity changes; however, these effects can be overcome by buffering an unknown sample to a pH near the neutral point. The sensitivity of these electrodes depends upon each particular type. 29 Only a few of the analytical methods available to occupational health have been discussed. Sub- sequent chapters will elaborate on analytical prin- ciples and techniques in greater detail, particularly with regard to applications in occupational health. In addition, the list of recommended texts for ad- ditional reading should be consulted regularly. Suggested Further Reading 1. ANDREWS, DONALD H. and RICHARD J. KOKES. Fundamental Chemistry, Second edition, John Wiley and Sons, Inc., New York, 1965. BRODE, W. R. Chemical Spectroscopy, Second edi- tion, John Wiley and Sons, Inc., New York, 1943. 3. DAL NOGARE, S. and R. S. JUVET, Jr. Gas- Liquid Chromatography, Interscience Publishers, New York, 1958. DANIELS, FARRINGTON and ROBERT A. AL- BERTY. Physical Chemistry, Second edition, John Wiley and Sons, Inc., 1961. DAY, R. A, Jr. and A. L. UNDERWOOD. Quanti- tative Analysis, Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 1967. FIESER, LOUIS F. and MARY FIESER. Introduc- tion to Organic Chemistry, D. C. Heath and Com- pany, Boston, 1957. JACOBS, MORRIS B. The Analytical Toxicology of Industrial Inorganic Poisons, Interscience Pub- lishers, 1967. 8. KLUG, HAROLD P. and LEROY E. ALEX- ANDER. X-ray Diffraction Procedures. John Wiley and Sons, Inc., New York, 1954. LAITINEN, HERBERT A. Chemical Analysis, McGraw-Hill Book Company, Inc., New York, 1960. LINGANE, J. J. Electroanalytical Chemistry, Sec- ond edition, Interscience Publishers, New York, 1958. MELLON, M. G. (Ed.) Analytical Absorption Spec- troscopy, John Wiley and Sons, Inc., New York, 1950. POTTS, W. 1., Jr. Chemical Infrared Spectroscopy, Volume I, Techniques, John Wiley and Sons, Inc., New York, 1963. . SILVERSTEIN, R. M. and G. C. BASSLER. Spec- trometric Identification of Organic Compounds, John Wiley and Sons, Inc., New York, 1967. SKOOG, DOUGLAS A. and DONALD M. WEST. Fundamentals of Analytical Chemistry, Second edi- tion, Holt, Rinehart and Winston, Inc., New York, 1969. . WILLARD, HOBART H., N. HOWELL FURMAN and CLARK E. BRICKER. Elements of Quantita- tive Analysis, Fourth edition, D. Van Nostrand Com- pany, Inc., Princeton, New Jersey, 1956. . WILLARD, HOBART H., LYNNE L. MERRITT, Jr.. and JOHN A. DEAN. Instrumental Methods of Analysis, Fourth edition, D. Van Nostrand Com- pany, Inc., Princeton, New Jersey, 1965. ro CHAPTER 5 REVIEW OF BIOCHEMISTRY Martin Rubin, Ph.D. and John T. Mountain INTRODUCTION In some respects the life process resembles a gyroscope. It is in metastable equilibrium requir- ing a continuous energy input to function in a structure carefully designed and built to accommo- date the system. Yet, despite the intrinsic delicacy of its operation, it is remarkably able to cope with and recover from stresses that would cause altera- tions in its equilibrium. Living systems are in- credibly complex and require an exquisite inte- gration of processes to fulfill the requirements of energy production, structural formation and main- tenance and homeostasis — the maintenance of the status quo. Biochemistry provides the scientific discipline to accommodate much of our present knowledge of life. It is convenient to review the subject from the viewpoint of the divisions that have been enumerated. To show how normal bio- chemical processes may be affected by chemical agents, examples of biochemical pathology will be cited, as well as clinical applications of biochem- istry in the detection of occupational disease. Energy Production The fundamental reaction by which energy is produced in the body may be written: 30, + 2(-CH.-) =2CO, + 2H,O + energy (Equation 1) This is an oxidative process by which oxygen has been added to the fuel source, (-CH,-) to produce the waste materials carbon dioxide, water and energy. As in other energy transformations, the total amount of energy available is independent of the path by which the change occurs. It de- pends only upon the difference between the free energy of formation of the reactants on the left and the products on the right. Although the chemical change in the energy- producing system can be written as depicted, the actual source of the available energy originates in the relative positions of electrons in the orbital structures of the atoms involved in the reactions. At one end of the spectrum of electron movement we recognize that an atom may release an electron altogether. The change Fet+ = Fet++ 4 electron represents such an oxidation of Fet + to Fet++ with release of an electron. Since such a process can occur only with the simultaneous acceptance of the electron by another moiety, an oxidation is coupled by a reduction. In biological systems, for example, the oxidative loss of the electron from the Fe++ structure is frequently coupled with ac- ceptance by oxygen according to the reaction electron + 1,2 O, + H+ # OH~ 31 in this case the oxygen atom has been reduced by acceptance of the electron. The total process Fet+ + 1/20, + H+ = Fet++ + OH™ + energy represents a transformation from reactants on the lett to products on the right at a lower energy level. The statement of the reaction involved in the major biological source of energy (equation 1) represents a less extreme movement of electrons than that described for the iron atom. In essence the formulation suggests that the movement of an electron pair from its essentially equidistant point between the carbon and hydrogen atoms in the structure H —C— H closer to the oxygen atoms in the product structures 10: C 0: and 0: H H involves a decrease in the energy levels of the reactants and products. The available liberated energy can be usefully trapped by the organism. The energy-trapping mechanism must be one which provides the potential for the conversion of the chemical-bond energy of oxidation to heat, electrical, mechanical or new formulations of chemical bond energy by means of specialized transducers. To fulfill its function in living systems the overall reaction of energy production implies the availability of oxygen, the fuel substrate (-CH,-), the removal of waste products (CO,, H,O, and other materials) and a system for control of energy made available by oxidation. These conditions may not prevail due to injuries related to the in- dustrial environment. Silicosis may impair oxygen transport from lung to blood; carbon monoxide may combine with hemoglobin to prevent it from carrying oxygen. The cells may not have access to substrate when the cell membrane is poisoned: thus glucose cannot move into the cell due to in- activation of the phosphorylating enzymes. Waste products cannot be removed when kidney func- tion is damaged by toxic agents such as mercury, uranium, and phenolic substances. Oxygen Metabolism Life ceases within minutes when the contin- uous supply of oxygen is interrupted. A responsive integrated physical, mechanical, hydraulic and chemical system provides this essential element. The diffusion of oxygen from the air inspired in the lungs to the tissues, where it is utilized, is facilitated by a sequential decrease in its partial pressure. The pO, of approximately 158 mm in the inspired air decreases to about 103 mm in the alveolar spaces of the lung, 100 mm in the arterial blood, and 37 mm in the peripheral venous blood subsequent to tissue utilization. The mechanical system of the muscle-controlled collapsible lung provides for the volume flow of oxygen containing air. The hydraulic arrangement of the heart pump and blood vessels allows for the fluid movement of the blood which serves as the oxygen transport medium. In the blood the biconcave doughnut- shaped erythrocyte (red cell) serves as a package for the oxygen transporting protein hemoglobin. This cellular bundle has manifest advantages in protecting and controlling the delivery system. Hemoglobin From the viewpoint of the biochemist, the protein hemoglobin provides an intriguing example of the evolution of a molecular structure adapted to a specific function, The total molecule, with a molecular weight of approximately 64,000 is made up of four sub- units of about 16,000. Each subunit has two essential components. One is a polypeptide chain of somewhat more than 140 linearly condensed amino acids. Associated with each polypeptide chain is a planar iron-porphyrin complex, heme, which serves as the oxygen binding moiety. The heme structure fits into a cavity of the poly- peptide. In simplified diagramatic outline, the hemoglobin structure can be visualized as illus- trated in Figure 5-1. In order to most effectively fulfill its biological oxygen transport function with- in the red cell package, the molecule of hemo- Perutz MF: The hemoglobin molecule, Scientific Amer- ican, Nov. 1964. Figure 5-1. Hemoglobin Structure globin has been carefully designed. It is globular in shape so that it provides maximum volume in the least space. High solubility of the protein is maintained by a large number of charged groups on the surface of the molecule. These tend to attract and hold polar water molecules close to the protein. The hydrophilic shell helps to keep hemo- globin in the aqueous phase. During a normal lifetime, a human will pro- duce five different types of polypeptides which will pair to form four different kinds of hemoglobin. Alpha and epsilon polypeptides appear first in ambryonic life followed by alpha and gamma chains in the foetus. With birth, the gamma chain production ceases, to be replaced by the combina- tion of alpha and beta chains of hemoglobin A, the major component of adult hemoglobin. Start- ing with birth, small quantities of a second hemo- globin, A,, made up of alpha and delta chains are to be found in the erythrocyte. The ultimate ar- rangement in space of the polypeptide chains is dependent upon the sequence of the polymeriza- tion of the alpha amino acids of which they are composed. In the typical amino acid structure: R +H,N-C-COO~ H the R group can represent a variety of possible substituent groups. When it is a hydrogen atom, the total structure would be H +H,N-C-COO", the amino acid glycine. H An uncharged hydrophobic lipid group such as: h. CH, — CH gives the total structure: CH; | H.C —CH | + H,N—CH COO, the amino acid valine. When the substituent groups are ionizable, as in glutamic acid: +OOC-CH,CH,CH-COO~ NH, +H,NC lysine. tH,N(CH,) ,-CH-COO~ NH, ! The polymer resulting from linkage of the amino acids through alpha amino and carboxyl ends will have points of charge extending from the chain of this primary backbone structure: R R | - - - NH-CH-CONH-CH-CO- - - The subsequent arrangement in space of the pep- tide chain depends upon interactions between groupings. The bonding of a hydrogen atom of the peptide linkage between nitrogen and a reactive peptide oxygene atom, (a “hydrogen bond”): R \ N-H----0 — H—C H | c C— _ | °R // Te — 0 ~NH can lead to coiling of the chain in the shape of an alpha helix. This has the overall appearance of a straight cylinder with the peptide backbone wound in a spiral. In addition to the hydrogen bonds, the availability of appropriately placed oppositely charged, “R”, side chain groupings can assist in the maintenance of a specific three-dimensional conformation of the structure. -COO™---NH,* Sharp bends in the chain are made possible by the linkage of the cyclic amino acid proline CH,-CH, O | I C CH—C-—-- \ / NH More definite intrachain linkage is achieved, for example, by covalent bonding of sulfur atoms from reactive cysteine amino acids: aA In the case of the hemoglobin polypeptides made up of approximately 140 amino acid resi- dues, a significant contribution to the structure arises from the interaction of the uncharged hydro- phobic R side groupings. These interact by Van der Waals surface forces to provide an essentially uncharged internal cavity from which water mole- cules are excluded and into which a ‘“heme” oxygen binding structure carefully fits. Hemoglobin is packaged in the erythrocyte with a variety of enzymes and other substances which play a supporting role in its function and survival. The red blood cell, in humans, has lost its original nucleus; has no mitochondria — those “powerhouses” of the tissue cells—yet uses energy. It has a limited capacity for synthesis, and wear and tear will limit its life span. The term “the rancid red cell,” applied to aging cells, seems appropriate; although it functions in oxygen transport, too much oxygen can injure the cell. The anti-oxidant, Vitamin E, is one of its safe- guards. Normally, alpha tocopherol, the principal E Vitamin is adequate as supplied in the usual 33 diet, but special conditions such as high oxygen pressure warrant supplementation. Hence the astronauts’ diet includes a proprietary orange drink with a high content of this vitamin. Oxides of nitrogen as well as more complicated nitrogen compounds — amines, nitro compounds, the sulfa drugs — either directly or through their metabolites can oxidize the iron of hemoglobin to the ferric state. In most people, fortunately, the enzymes of the cell can regenerate hemoglobin by reducing the ferric iron. However, there exists a substantial population in which this process func- tions poorly. Infants do not have fully developed methemoglobin reducing systems. Drinking water standards for nitrate nitrogen take cognizance of this. There are persons who by reason of genetic defects are inordinately susceptible to methemo- globinemia from contact with a variety of common drugs and chemicals such as naphthalene, sulfas, anti-malarials, nitro and amino compounds. The frequency of such individuals is relatively high (ca. 10% ) among American Negroes). Its signif- icance in industrial hygiene and its relation to glucose-6-phosphate dehydrogenase deficiency has been noted in the literature. A smaller frequency of the population are known to exhibit hemoglobin variants — sickle cell, type M, Portland, etc. These variants arise from substitution of different amino acids in the molecule. The variant hemo- globins lack durability. Chemical stress may cause irreparable damage, with anemia resulting. Lists of substances known to induce methemoglobinemia and hemolytic anemia appear in the references. Other Proteins As in the case of hemoglobin, the three-dimen- sional structure of the vast array of proteins found in the body is determined by the sequence of the amino acids of their primary structure. The extent of their helical structure, charge interaction, cross- linking and other secondary and tertiary structural characteristics flow from this factor. In general, the proteins dissolved in the body fluids are glo- bular in shape. A notable exception is the plasma protein fibrinogen which is long and narrow. As in the case of hemoglobin, its structure is in keep- ing with its function in blood clotting. The straw- shaped fibrinogen molecule readily forms a mat to trap the formed elements of the blood to form a clot at the bleeding point. Other proteins of the blood plasma include albumin, the major constituent of the plasma pro- teins. Albumin provides a regulatory influence on the fluid balance of the blood through its osmotic effect. The globulin proteins of the plasma in gen- eral provide the potential for immunologic de- fenses. Upon exposure of the organism to anti- genic foreign proteins or small molecules linked to protein (haptens) the immune defenses of the body produce a protective protein antibody able to react and neutralize the antigen. The globulin fraction of plasma proteins, especially the gamma globulins, provide this defensive capability. Struc- tural proteins, such as collagen in connective tissue, are generally long and linear. Collagen is a triple-stranded counter-twisted triple helix. Ker- atin of skin, hair and nails is constructed of single peptide chains of alpha helices counter-twisted into bundles of triple chains. This structure pro- vides both strength and flexibility. A deficiency of the serum protein, «-1 anti- trypsin, has been found in some persons with chronic respiratory disease. The deficiency has been correlated with emphysema and a genetic de- pendence established. Experimental evidence indi- cates proteolytic enzymes released from injured cells may exacerbate the damage unless suppressed by antitrypsin. Studies of coal miners have yielded controversial conclusions. The frequency of anti- trypsin deficiency, which is highest among persons of North European ancestry, makes it a factor to consider in investigations of emphysema and res- piratory diseases. The measurement of serum anti- trypsin is routinely carried out in many clinical laboratories, although usually in relation to other diseases. Enzymes Enzymes, the catalysts of the body, are also proteins. As for other proteins their three dimen- sional structure or conformation is the conse- quence of the sequence of the amino acids in their primary structure. The ordered geometry of the enzymes in space provides specific sites at which the substrate molecules upon which they act may become fixed. As a consequence of the localiza- tion of the substrate at the active site of the enzyme the energy required to initiate a subse- quent reaction is decreased. This decrease in activation energy means that a larger fraction of the molecules will have sufficient energy for reaction even at body temperature, as compared to relatively extreme conditions of pH and temper- ature required for similar reactions in vitro. The reaction rate will consequently increase. Enzymes thus increase the speed of the reaction. Nearly any influence which changes the shape of the enzyme molecule will influence its ability to function as a catalyst. Modifications in the hydrogen ion con- centration (pH) of the environment will influence the charge distribution of the enzyme surface and may thus alter the shape of the enzyme or modify the ability of charged substrates to approach and be affixed to the active site. Characteristically enzymes are found to be most cffective at an op- timal pH. Other influences such as the concen- tration of charged particles in the medium may also influence the enzyme surfaces. Thus the ionic strength of the solution is significant. The ambient temperature is important because with in- creasing temperature the substrate molecules have increasing energy. More of the molecules are capable of reacting and the rate of the reaction in- creases. On the other hand the enzyme protein also is susceptible to the influence of an increase in temperature and may be inactivated (denatured) with loss of catalytic capacity. The positive and negative effects balance at a point of optimal temperature. For many enzymes this is body temperature. The catalytic role of enzymes is critical in the performance of metabolism. Factors which in- fluence their rate of reactivity markedly alter body function. The availability of substrate molecules is clearly a limiting consideration. When substrate molecules are present in such high concentration 34 that they continuously occupy all the active cata- lytic sites of the enzyme the reactions may proceed at maximal velocity (Vua..). On the other hand, the removal of substrate by alternative com- petitive pathways of reaction, or the presence of molecules in the medium which compete for the active catalytic site may slow a given enzymatic reaction in a sequence of reactions to the point at which it becomes the rate limiting step in an overall metabolic process. Other forms of inhibi- tion are known. When, for example, a component of the medium other than the substrate can attach to the enzyme surface in such a way as to alter the configuration of the active site, it may simul- taneously decrease the catalytic activity of the enzyme. This “allosteric inhibition” provides a mechanism for the control of enzyme activity and with it a method of process control in the cell. An additional control mechanism involves the accumulation of the products of a given reaction or sequence of enzymatic reactions. Since many systems operate at initial and final energy levels which are not widely separated, the pileup of product may be sufficient to slow or halt the - progress of the reaction. This feedback inhibition can be exerted at a single enzymatic step or in a chain of reactions. The structure of an enzyme and hence its catalytic activity may be modified by other in- fluences. In the body these proteins are subjected to a continuous process of breakdown. This may occur by oxidation and hydrolytic scission (pro- teolysis) of the peptide chains. External influences such as the presence of toxic metals in the body can interact with active catalytic enzyme sites or react elsewhere with the molecule to render it ineffective. Interruption of the function of a critical enzyme can have over- whelming toxic effects for the organism. A classic example of this, and of so-called “lethal synthesis,” occurs when fluoracetate is metabolized in the citric acid cycle (Figure 5-2): fluocitrate is formed, which bonds irreversibly to the enzyme aconitase, rendering the system in- operable. While many enzymes function as a single pro- tein entity, a number require the presence of other co-factors and activators. The vitamins, especially those of the B-vitamin group, are in this category. Thiamine, biotin and lipoic acid are. co-enzymes frequently associated with enzymes required for the addition and removal of carbon dioxide from substrates. Nicotinamide, riboflavin, and ascorbic acid have roles in energy transfer associated with oxidation /reduction reactions. Pantothenic acid is an essential component of the enzyme complex, coenzyme A, involved in the metabolism of acetyl groups. Vitamin B-12, cyancobalamin, has the trace metal cobalt as an integral portion of its structure and is a component of the enzyme system which is concerned with the metabolic handling of a one-carbon unit. Folic acid, another member of the B-vitamin family, has a related function. In the absence of an adequate nutritional sup- ply of the vitamins, the function of the enzymes of which they are components is severely com- promised. The resulting metabolic malfunction CH3CO~CoA CoA Acetyl-CoA CH, COOH H,0 [HC COOH CH, COOH HOC COOH -— ¢ COOH 0=C-COOH ~~ H,0 CH, COOH CH,, COOH Oxaloacetate Citrate c/s -Aconitate NAD (H+H® NAD ~~ H,0 H CHa COOH HOG COOH HOC COOH HC COOH H CH,COOH Malate Isocitrate H,O NADP (HH? ooo ger HOOC CH Fumarate CH, COOH iT alosuecinate Fe—flavin (H,) N22 CO; Fe- flavin NAD (H+H™) NAD ~~ 0=C COOH CH, COOH = Se CH, CH, COOH Lipoate CH, COOH Succinate COz Movs a-Ketoglutarate CoA Figure 5-2. Steps in the Tricarboxylic Acid Cycle 35 finds expression many ways. Tiredness, lack of energy, anemia, loss of weight, loss of appetite and a host of subclinical and, in the acute stages, overt clinical manifestations can occur, Cobalt has been mentioned as a component of the total enzyme systems involved in the meta- bolism of single carbon units. Other metals fulfill related functions as enzyme co-factors. Calcium and magnesium have prominent roles in hydrolytic reactions. Copper, iron and molybdenum serve for the purposes of oxidation/reduction systems. Zinc occurs in hydrogen transport enzyme systems, in the hydration of carbon dioxide to form carbonic acid and, as does manganese, in enzymes involved in the cleavage of peptide bonds. With the excep- tion of calcium and iron, nutritional deficiencies are rare for these trace elements. It is generally the fact that the intestine provides a barrier to the excess accumulation of the metals, On the other hand the nutritional intake of iron and cal- cium may be marginal for some portions of the population. Women during the childbearing years are subjected to continuous iron loss in menstrual bleeding. Their nutritional replacement of this loss is frequently insufficient to maintain homeostasis. At times of rapid skeletal growth in children, during periods of lactation and in older age for both women and men the usual intake of calcium may also be marginal or insufficient. Types of Enzymes. In the course of the previous discussion some examples have been cited of the types of reactions catalyzed by enzymes. A syste- matic grouping on this basis would include the 1) oxidoreductases, enzymes concerned in oxida- tion/reduction reactions 2) the transferases, en- zymes which bring about the movement of a mo- lecular grouping from a substrate to a recipient 3) the hydrolases, which are involved in cleavage of bonds by the addition of the elements of water 4) the lyases, a group of enzymes whose function is the cleavage of a segment of a molecule 5) the isomerases, which catalyze the rearrangement of the molecular framework and 6) the ligases, which bring about the combination of molecular struc- tures by covalent linkage. The isolation of enzymes of distinctive struc- ture but which perform the same catalytic function is a subject of considerable interest. These iso- enzymes by virtue of their variable cellular distri- bution and modified responsiveness to controlling mechanisms, are able to provide enhanced modu- lation of the complex integration of the reactions which occur in metabolism. The fact that organs of the body and consequently the tissues and cells of which they are composed may have specialized functions is a matter of considerable import for the diagnosis of disease. When liver tissue is de- stroyed as in acute hepatitis, the breakdown of the liver cells releases cellular enzymes to the plasma. By measuring the plasma enzyme activity of the liver transferases such as glutamic-pyruvic trans- aminase and the liver dehydrogenases such as lactic dehydrogenase, it becomes possible for the physician to obtain a biochemical index of the cellular destruction. Muscle tissue damage, as in acute myocardial infarction or in the wasting diseases of muscular dystrophy can be monitored 36 by the activity level of the phosphate group trans- fer enzyme, creatine phosphokinase, Differentia- tion between damage to the liver or the heart can be made by the identification in plasma of the respective lactic dehydrogenase isoenzyme. Because of their essential functions the en- zymes are vulnerable points of attack by external influences. Toxic agents from the environment as well as drugs used for diagnosis and therapy can induce marked changes in the entire organism by alteration of the rates of enzyme reactivity. Measurement of the activity of the enzyme cholinesterase has been very useful in surveillance of exposure to anti-cholinesterase insecticides. The enzymes in the blood, like that in the nervous tissue, split acetyl choline into acetic acid and the base, choline, but other substrates may be used in following the reaction. Depression of enzyme ac- tivity below normal is an indicator of response to the agent. In other cases serum enzymes may be in- creased, rather than depressed, as a result of toxic injury to cells or organs. There are five isoen- zymes of lactic dehydrogenase occurring in serum. These may be separated by electrophoresis, using standard clinical laboratory equipment. They are designated by number according to their rate of migration, and their proportions reflect, in large degree, their tissue of origin. The heart con- tributes much of LDH isoenzyme No. 1, the liver mostly LDH isoenzyme No. 5. Recent work on animals, and a few cases of mercury exposure of workmen suggests that an increase of LDH iso- enzyme No. 5 over normal proportions may serve as an indicator of liver injury from exposure to inorganic mercury. Protein Synthesis Under normal conditions the continuous break- down of protein is matched by protein biosyn- thesis. The individual stays in nitrogen balance in that nitrogen constituents provided in the diet are matched by nitrogen excretion in feces and urine. During periods of growth the increase in cell mass requires that protein synthesis be accelerated. More nitrogen is retained than is excreted. The individual is in a state of positive nitrogen balance. Whether for replacement or for growth the continuous need for protein synthesis is met by an exquisitely coordinated mechanism in the cell. The problems to be solved are formidable. The flow of requisite structural components, the amino acids, must be maintained and controlled in the cell environment. The transfer of the amino acids from the plasma across the cell wall requires a specific transport mechanism and a supply of energy. Once within the cell the amino acids need to be selected and arranged in the proper sequence so that when final linkage takes place between their adjacent amino and carboxyl groups, the re- sulting polypeptide chain will have the exact se- quence requisite for its biologic and biochemical function. To provide an inkling as to the dimen- sions of the problem, consider that thousands of proteins of specific structure may be required, that variation in sequence of amino acids may result in uncountable structural modification, and that the initiation and termination of the synthetic events must be completely controlled if the cell is to avoid death by atrophy or by the uncon- trolled overgrowth of cancer. The somewhat more than two dozen individual amino acids required for protein synthesis have their original source in the dietary intake. When in- gested in the form of food proteins, they are cleaved in the intestine by the proteolytic enzymes of the pancreas, (trypsin, chymotrypsin and an array of peptidases) to the constituent amino acids which are then actively absorbed across the intestinal wall into the plasma. While the processes of meta- bolic transformation can convert most of the amino acids from one structural form to another, a number can be provided only from food sources. These “essential amino acids” include valine, methionine, threonine, leucine, isoleucine, phen- ylalanine, tryptophan and lysine. For adequate nutrition a protein intake of between 1 to 2.5 g/kg/day from a variety of foods including meat, eggs, milk and plant sources is considered req- uisite. The lower value provides for normal tissue replacement in the adult while the higher value is needed for the rapidly growing infant. Following absorption from the intestine, the amino acids circulate in the plasma for utilization directly in cellular protein synthesis or metabolic conversion. The uptake of amino acids by the cell involves their specific “active transport,” an energy requiring process, across the cell membrane. While the detailed mechanism of membrane transport is not clarified, it is established that in some instances the process is controlled by an initial attachment of hormones to specific receptor sites on the cell membrane. This triggers the subsequent events which bring about the cellular synthesis of proteins. Blueprints for Proteins Protein synthesis starts with the stimulation of the cell nucleus to read an appropriate portion of its stored genetic information in its macromolec- ular double-stranded desoxyribonucleic acid (DNA) and produce from this template a mes- senger ribonucleic acid (mRNA) which will serve as the information source for protein synthesis in the cell cytoplasm. The mRNA moves from the nucleus to the cytoplasm and affixes to the ribo- somes located in the fine structure of the cell sap. At this point the amino acids of the cytoplasm are selectively activated using available energy from the “high energy” chemical bond of adenosine triphosphate (ATP) to attach to a carrier transfer ribonucleic acid (tRNA). The activated amino acid is then delivered to the ribosome where it is attached to the template of the messenger RNA. Depending upon the nature of the code of the RNA the various activated amino acids are tied to the ends of the growing peptide chain to form the linear peptide. The tRNA, having delivered its specific amino acid, returns to the cytoplasm for reloading of an amino acid. The processes which signal the start of protein synthesis and its completion at the end of the peptide chain are not clearly understood as yet for mammalian cell systems. It appears though that a regulatory code provides for the start and stop signal of protein biosynthesis. 37 The remarkable capability of living things to transmit hereditary information resides in the unique structure of the nucleic acids. Their build- ing blocks are the nucleotides composed of the sequence: base-sugar-phosphate. The bases are derived from the purine and pyrimidine classes of compound by minor functional group modifi- cations (Figure 5-3). The sugars in the nucleo- tides are either of the ribose or 2-desoxyribose structure with the nucleotide assembly linked by way of a phosphate ester. Not only does the nucleotide serve as a common structural unit in the nucleic acid but also in an isolated unit as a co-factor of many enzyme systems to be later dis- cussed. The linkage of nucleotides to form a strand of nucleic acid is through the combination of a phosphate of one nucleotide to the sugar of a second. In this way the nucleotide bases extend horizontally from the linear chain in the same way that the rungs of a ladder are tied to the frame. In actuality two chains of nucleotides associate with the bases in apposition and are linked through hydrogen bonds. The total system would be ap- proximated by visualizing the rungs of the ladder to be cut in the center of each but held together so that they still had a ladder appearance. A further complication is that the ladder instead of being in one plane is twisted in a right-handed helix. In order for this structure to serve as an information mechanism it unfolds so that a single strand of nucleotides is exposed to the environ- ment. Synthesis of a new strand now takes place by the linear alignment of complementary bases to those of the original strand. The lineup of bases in the newly formed nucleic acid (mRNA and tRNA) provides for the specific ability of the new structure to selectively pick a given amino acid from the environment for protein synthesis on the ribosomal surface. Protein synthesis can be influenced by environmental factors. Inhalation of vanadium pentoxide alters the content of the amino acid cystine in the hair of rats and the fingernails of workmen. The lungs of coal miners with emphysema contain more of the fibrous tissue protein, collagen, than do normal lungs or ab- normal, but not emphysematous, lungs. Protein synthesis can be altered or stopped by exposure of man to environmental factors and this can re- sult in enzyme induction or repression, misdirected or uncontrolled protein synthesis. These changes then manifest themselves as clinical changes, lesions or death. Hormones Hormones are defined as a class of endogenous compound effective in low concentration in con- trolling or modifying metabolic processes at a dis- tant receptor. Their activity may be exerted on a target cell to induce metabolic change directly, or they may serve to cause the production of a second hormone which in turn controls cellular function, or a given hormone may have both types of end result. The hormones originating in the pituitary gland in response to “releasing factors” have gen- erally been divided into two groups depending upon their anatomical source. Hormones of the anterior lobe include the gonadal active follicle stimulating hormone (F.S.H.), the luteinizing hor- NH, H CH N “Ng : 275 SN Je : =, Ls 4 0 \ H NORE OH H Thymine Adenine PYRIMIDINES PURINES NH , | 0 NZ H J No H Cytosine Guanine 0.©.0 of Re NH, Gt 0 N NN F 0=:P—0—CH, N N" TH ol: H H 0 0) _ H H HO OH Adenosine Triphosphate Figure 5-3. Typical Pyrimidine, Purine and Nucleotide Fragment 38 mone (L.H.), and prolactin whose major effects act directly upon their specific target cells. In addition, the anterior pituitary also produces other protein hormones which may also have more gen- eral metabolic effects. Thyroid stimulating hor- mone acts directly upon the thyroid gland to induce the capture of plasma iodide by the gland, its incorporation into a protein thyroglobulin, scission of the protein to yield a second amino acid hormone thyoxine which circulates in the plasma partly bound to a carrier protein, thyroid binding hormone. Thyroxine acts as a potent regu- lator of cellular metabolism inducing a marked increase in the rate of oxygen utilization simul- taneously with a sharp increase in cellular me- tabolism. The growth hormone of the anterior pituitary is especially effective in inducing protein synthesis in early development. Increase in cell mass, development of the long bones and accel- erated utilization of carbohydrate are among its noteworthy effects. The primary effect of the adrenocorticotropic stimulating hormone (ACTH) is to induce the synthesis of the steroid hormones of the adrenal cortex. Two hormones of the pos- terior pituitary have regulatory functions. Oxytocin and vasopressin are peptides of eight amino acids each. The major effect of the former is to cause contraction of smooth muscles. Vasopressin has a significant action on the kidney inducing salt and water retention. Although several dozen intermediates and ster- oid metabolites have been isolated from the adrenal cortex, two compounds represent the major hormonal products of the gland, Cortisol (hydrocortisone) is elaborated upon the stimulus of ACTH by a biosynthetic pathway which starts with the two-carbon acetate unit. Successive com- binations of three such units lead to a six-carbon intermediate which is then degraded to the five- carbon isoprenoid structure. Condensation of three five-carbon units leads to the C-15 farnesol moiety which in turn doubles to form the 30- carbon linear squalene structure. It is of interest that these intermediates in the pathway of mamma- lian biosynthesis also occur in the plant world and lead to the familiar essential oils. Cyclization of squalene produces the condensed four-ring struc- ture of the steroid nucleus and degradation of the side chain produces the C-27 sterol, cholesterol. When the nutritional circumstances of the indi- vidual provide a greater supply of C-2 acetate units than can be utilized for energy or biosyn- thetic turnover the excess is converted into fats, including cholesterol. The combination of exces- sive lipid intake, especially saturated fats, and a sedentary and stressful life style is associated with high concentrations of cholesterol in the plasma and with atherosclerotic plaque deposition in the vascular system. Individuals in this category are high risk possibilities for coronary disease. Although not universally accepted, some evi- dence suggests that carbon monoxide and carbon disulfide may elevate cholesterol and promote plaque formation. Vanadium compounds have been found to inhibit cholesterol synthesis in ani- mals and man; however, after some time the orig- 39 inal effectiveness disappears. The additional meta- bolic degradation of cholesterol in the adrenal gland produces cortisol. This steroid hormone provides the stimulus for a biochemical response to stress. It induces conversion of amino acids to glucose and stimulates the adipose storage areas of lipids to release fatty acid for transport to the liver for utilization as an energy source. The second major steroid hormone of the adrenal cortex is aldosterone. The role of this hormone is to assist in the control of the excretion of salt and water. When the adrenal is destroyed as in Addison’s disease, the accelerated loss of salt and water can have rapidly fatal consequences. Other steroid hormones include progesterone produced by the corpus luteum and the placenta in preg- nancy to maintain the uterine cellular structure, estradiol formed in the ovary and responsible for the development of secondary female sexual char- acteristics and testosterone, the sex hormone in the testes responsible for analogous processes in the male. Mention should be made of the important hormone epinephrine of the adrenal medulla. It is another means for biologic response to stress in that its production and distribution in response to a neural signal causes constriction of the blood vessels with increase in blood flow, release of glucose from the liver to the plasma and fatty acid from the lipid stores. All these responses provide an added capability to meet emergency contin- gencies. Several other glands provide significant factors for metabolic control. The pancreas is the source of the protein hormones, insulin and glucagon, which exert a direct control over the glucose level of the blood. Insulin is released from the pancreas upon elevation of blood sugar after a meal or for other reasons. By incompletely understood mechanisms the hormone accelerates the transfer of the sugar from the circulation to the cells where it may be stored as the polymer glycogen until required. Glucagon on the other hand, is elaborated when blood sugar levels fall below the normal range. Its major biochemical effect is to cause breakdown of glycogen and re- lease of glucose to the circulation. Parathyroid hormone formed in the parathyroid gland and thyrocalcitonin a product of the thyroid gland are involved in the maintenance of calcium homeo- stasis. In response to a decrease in the normal cir- culating level of calcium, the released parathyroid hormone produces a sequence of biochemical re- sponses whose net result is to elevate the con- centration of plasma calcium. Hormone induced breakdown of bone cells provides colcium and simultaneously phosphate which is cleared by the kidney by hormone induced phosphaturia. Sec- ondary conservation of calcium occurs at the kidney simultaneously with increased absorption at the intestine. An elevation of plasma calcium is followed by increased secretion of thyrocalci- tonin producing enhanced deposition of the ele- ment on the skeletal surface and fall in circulating calcium levels. The biochemical balancing of the two hormones provides a fine adjustment for homeostasis of plasma calcium which is basically maintained by interaction of plasma calcium with the mineral reserves of the bone. For these hor- mones and most others described above recent investigations have established a common se- quence of events leading to their biochemical consequences. At the target cell hormone specific receptor sites on the cell membrane are stimulated to activate the membrane enzyme adenyl cyclase. In turn the enzyme converts adenosine triphos- phate (ATP) to cyclic adenosine monophosphate (cAMP) which in the intercellular milieu initiates the cellular events characteristic of the hormonal response. The formulation of this “second mes- senger” concept has provided a framework for further study of the intriguing question of the mechanism of the profound effects of trace amounts of hormonal substances. In essence the overall picture is one of an amplification system in which a trigger mechanism provokes a signif- icantly enhanced response. An interesting correl- ative change that occurs with the membrane fixa- tion of most hormones is the release and cellular uptake of calcium ion. This event has been in- voked to explain the electrical changes observed in the membrane upon hormonal stimulus. Hormone production or function is known to be altered by some metals and organic compounds. Lead interferes with thyroid hormone production; the synthesis of epinephrines depends on adequacy o: copper for an amine oxidase. It has been re- ported that a deficiency of norepinephrine was associated with treatment for alcoholism with antabuse; this compound is known to bind to copper. Chromium has been found to be an essential element, notably for its role in glucose metabolism. It is apparently an adjunct to insulin. Some elderly diabetics have been benefited by ad- ministration of chromium. The Heme Porphyrin Structure While the globin protein serves as the struc- tural framework, it is the iron-porphyrin combina- tion which is responsible for the molecular trans- port of oxygen. At the time of synthesis of hemo- globin in the young red cell all components, the globin protein, the porphyrin structure and the iron atom must be at the right place at the right time. The biosynthesis of the porphyrin molecule starts with the amino acid glycine which couples with activated succinic acid in the presence of an enzyme catalyst to yield, after elimination of CO,, delta aminolevulinic acid: activated COO~ COO | succinic acid CH, (CH.)., + coenzyme | | A+CO, succinyl- CH, - C—0 (coenzyme | | A) O-—C- CH, See] | CH, —COO~ NH, + | glycine NH, Two molecules of delta aminolevulinic acid join asymetrically to form porphobilinogen in the presence of an enzyme catalyst: COO~ COO~ COO~ CH, COO~ CH, | CH, CH, CH, CH, | | CH, (---->0=C Cc — C | | I | +NH, —CH,—C CH, NH, + —CH,— C C \ / 0 N Ny | NH, + H and four molecules of porphobilinogen link in linear fashion and then ring close to form the im- portant intermediate structure uroporphyrinogen. By selective loss of carbon dioxide and hydrogen atoms, this is converted to the essential structure protoporphyrin IX (Figure 5-4). Insertion of the iron atom completes the as- sembly of the heme structure for junction with the globin to form hemoglobin. Porphyrin Chemistry Certain aspects of the heme structure are of special significance to its oxygen transport func- tion. The planar structure of the molecule permits it to slip readily into the cavity of the globin pro- tein. It is held there by several forces. The anionic charges of the porphyrin carboxyl side chains are linked to points of positive charge in the globin protein. The conjugated double bonds of the por- phyrin confer aromatic character upon the struc- ture with consequent availability of pi electrons. These interact with analogous aromatic structures strategically located in the cavity wall. The iron atom, linked by coordinate bonding to four nitro- gen atoms of the porphyrin has two coordinating bonds available for additional linkage. One is 40 (Ha H4C _ =n LA N CH, - H H- = ©00C-H,C-H A =CH > Sg CH, HC pa x ©00C Figure 5-4. Structure of Protoporphyrin IX utilized for linkage to a histidine amino acid of the globin structure and the sixth linkage is avail- able for the reversible binding of oxygen. In addition to the heme structure of hemo- globin, porphyrins are essential in the processes of energy production. In the cytochrome mole- cules, they perform the task of electron transport from one energy level to another. Subtle changes in the structure, as by conversion of the -CH=CH, H | side chains to —C— CH, and alterations in the OH structure of the combining protein serve to con- vert the molecule from its role of oxygen to elec- tron transport. Breakdown of the porphyrin structure involves cleavage of the ring to form a linear tetrapyrrole followed by scission of the tetrapyrrole to a di- pyrrole structure. The accompanying color changes of the molecules provide the green pigment of bile and then the cla’ brown pigment of feces. When liver damage o- obstruction inhibits the catabolism or excretion of the bile pigments, they appear in the blood ana skin as the yellow color of jaundice. Abnormalities of porphyrin metabolism are common to a number of industrial health prob- lems. Delta aminolevulinic acid accumulates in @ and the reduced flavin nucleotide. The latter com- pound feeds into the mitochondrial electron trans- port system for capture of the available energy in the form of the ATP high energy bond. an 41 urine in lead poisoning and special chromatog- raphy columns are commercially available for assaying its urine content. Lead also increases the urinary coproporphyrin; this substance was once regarded as criterion for lead poisoning. As noted, accumulation of porphyrin waste products may cause porphyria or bilirubinemia unless the liver functions to convert them into less toxic, excretable compounds. The induction of liver enzymes, by DDT, to enhance bilirubin detoxica- tion, has been noted. Metabolism of Lipids While carbohydrate and lipid can largely re- place each other in the human diet some lipid ap- pears essential to supply not only dietary palat- ability but also the highly unsaturated fatty acids that can not be produced by metabolic intercon- versions. The high caloric value of lipids also makes this class of nutrient a valuable energy storage reservoir. Upon ingestion the lipids along with other dietary nutrients are emulsified in the stomach and pass to the upper intestine where the bile acids, originating in the liver by catabolism of cholesterol, assist in the stabilization of the dispersed nutrients. The dietary lipids are then cleaved by the pancreatic lipases to yield fatty acids as well as mono and diglyceride scission products of the nutrient triglycerides. In the mucosal cells of the intestine a separation and re- shuffling of the lipid constituents takes place. Short chain fatty acids proceed by way of the portal circulation to the liver while the longer chain fatty acids are resynthesized into triglyc- erides. Dietary cholesterol is esterified to a great extent with unsaturated fatty acids during intes- tinal cellular transport. The lipids which move into the lymphatic circulation after absorption do so in the form of small droplets called chylomicrons. These are stabilized by a coating of protein which inhibits their tendency toward agglomeration. The lymphatic drainage is discharged into the circula- tion at the thoracic duct. Lipids are then picked up by adipose tissues or are metabolized by the liver. The course of lipid metabolism in the liver or peripheral tissues involves a process of sequen- tial degradation by which the fatty acid chains are reduced two carbons at a time to yield acetyl coenzyme A. This common catabolic end point serves as the primary fuel source of the cell. The mechanism by which the catabolic sequence occurs is of some interest. In the first step the fatty acids are activated by the use of ATP bond energy to form their acyl thiol coenzyme A esters. In this form they are dehydrogenated to yield the alpha- beta unsaturated compounds (Reaction I). R-CH,—CH, CO~CoA — R— CH=CH —CO~CoA In a second step a hydrolase enzyme adds a molecule of water across the double bond to pro- duce a beta hydroxyl acyl derivative (Reaction R-CH =CH-CO~CoA + HOH — R—CH— CH, —CO—CoA. OH In the third step the hydroxyl group is oxidized by a dehydrogenase enzyme with a nicotinamide H (III) | OH The reduced nicotinamide co-factor proceeds to surrender the hydrogen to mitochondrial oxidation for additional energy capture as the ATP bond. R—C—CH,—CO— CoA — R- O The acetyl coenzyme A produced in this reaction feeds into the tricarboxylic acid (TCA) cycle. The residual fatty acid derivative is ready for further degradation by another two carbon units. The reverse process of fatty acid synthesis av) CH, CO CoA+CO, This in turn adds a second acetyl coenzyme A unit, loses carbon dioxide and ends as a C-4 keto acid, CH,-CO-CH,-CO CoA. By reversal of pre- vious reactions, essentially, the body produces a C-4 fatty acid, butyric acid, CH,-CH, — CH, — CO CoA. Repetition of the procedure results in chain elongation to form the longer chain acids. It is interesting to note that the process of fatty acid anabolism is not identical with the catabolic route. This difference provides the organism with the advantage of multiple points of metabolic con- trol. The final step in the synthesis of triglyceride is the addition of the activated fatty acid to phos- phorylated glyceride to form the final product. In addition to the storage of lipids in adipose tissue the materials of this category have an essential structural role in cell membranes. The generalized structure of these compounds consist of a digly- ceride coupled through a phosphoric ester to a nitrogenous constituent. In the formula R — PO, CH, CH, NH, * as for cephalin for example, the structure has a highly hydrophobic fatty diglyc- eride, R, head with a charged ionic polar nitro- genous tail. The net result is that the molecule orients itself in an aqueous medium with the polar group in the water phase and the lipid structure oriented in the opposite direction. -When com- bined with cholesterol and proteins these phos- pholipids provide the structure of the cell mem- brane which allows for remarkable specificity and selectivity for the passage of small molecules. Modification in structure by substitution on the nitrogen atom provides for the multiplicity of the class of phosphatides. Attachment of the carbo- hydrate inositol yields the inositides. Substitution of the glyceride fatty acid by aldehydes yields the family of plasmalogens. The prostaglandins are an interesting family of lipid substances. Although fatty acids, chem- ically, they are tissue and cell hormones func- tionally. 42 co-factor to produce the corresponding keto acid (Reaction III). R—C—CH,— CO CoA—R—C—CH,— CO CoA. I O In a final step of the process the fatty acid is cleaved to yield a molecule with two less carbon atoms with the simultaneous formation of an acetyl coenzyme A compound. C — CoA + CH,-CO — CoA. | Oo accounts for the fact that nutritional excesses can convert dietary constituents to fat. Acetyl co- enzyme A by mediation of a biotin cofactor enzyme temporarily adds a molecule of carbon dioxide to form malonyl coenzyme A. (Reaction IV). HOOC — CH, — CO — CoA. The analgesic effects of aspirin are ascribed to its inhibition of prostaglandin synthesis. Metabolism of Carbohydrates Dietary sugars and starches provide most of the carbohydrate in human nutrition. The starch macromolecule is hydrolyzed in the intestine by the pancreatic enzyme amylase. After cleavage to glucose this monosacchoride and others present in the food are absorbed across the mucosal surface of the intestine. For the most part the hexose sugars such as galactose and fructose are con- verted to glucose either during absorption or sub- sequently in the liver. After transport through the portal blood from intestine to liver the glucose is cither utilized in the liver as an energy source, polymerized for storage as glycogen or proceeds through the peripheral circulation as part of the glucose supply to the tissues. Two major pathways characterize the catabolism of glucose. The first is the process of glycolysis by which glucose is converted anaerobically to pyruvic acid or further to lactic acid. The second alternative sequence, the pentose phosphate shunt, is an aerobic degradation of glucose which subserves certain specialized needs of the organism. Glycolysis starts with the energy requiring phosphorylation of glucose to yield its 6-phos- phate. Rearrangement of the molecule by en- zymatic isomerization yields fructose 6-phosphate which is further phosphorylated to produce fruc- tose-1, 6-diphosphate. This latter reaction is also endogenous in its requirement for an energy source. After phosphorylation at the ends of the molecule, scission takes place in the center to pro- duce two phosphorylated C-3 units, phosphogly- ceric aldehyde and phosphodihydroxyacetone. En- zymatic isomerization converts the latter to the former compound. In essence, then, one six- carbon sugar is converted to two three-carbon sugars. In the next stage of glycolysis the aldehyde group is converted to an acid with some of the released energy trapped in the form of the reduced nicotinamide co-factor. In turn, the reduced co- factor feeds into mitochondrial oxidation to pro- vide usable energy in the form of the high energy ATP bond. The glycolytic process continues with shift of the phosphate from its position at the end to the center of the molecule. The 2-phosphogly- ceric acid loses a molecule of water to produce the enol phosphate which in turn relinquishes the phosphate to produce pyruvic acid. Under the usual conditions of oxygenation the pyruvic acid is oxidatively decarboxylated to yield carbon di- oxide and acetyl coenzyme A. During vigorous muscular exercise the pyruvic acid is reduced to lactic acid which is released to the plasma for re- turn to the liver. The glycolytic sequence thus starts with a six-carbon sugar, glucose, traps some of the decrease in free energy in the form of meta- bolically useful reduced co-factor or in the bond energy of ATP and provides four of its six carbons as acetyl coenzyme A for further metabolism. The second major pathway for metabolism of glucose is oxidative, requiring oxygen for the first step. An enzyme, glucose-6-phosphate dehydro- genase, utilizing nicotinamide-adenine dinucleotide phosphate, (NADP), as a co-factor converts the glucose-6-phosphate substrate to the correspond- ing acid. The resulting decrease in free energy from the starting material to the reaction products is partly held in the form of the reduced nucleotide to be utilized elsewhere in the body for anabolic purposes, for example, the reductive steps involved in lipid biosynthesis depend on the availability of NADPH. Decarboxylation of the gluconic acid produces a five carbon pentose sugar. In an intri- cate series of recombinations and scissions the five-carbon pentose is eventually degraded to car- bon dioxide. In contrast to muscle tissue which metabolizes glucose almost entirely by the Embden- Myerhof glycolytic path, the oxidative sequence of the pentose shunt occurs in other cells, espec- ially liver and erythrocytes, as an alternative al- though less significant mode of carbohydrate breakdown. The significance of this pathway is that it offers a means for the body to provide the pentoses needed for nucleic acids, yields NADPH needed for a number of anabolic tasks, and offers an alternate means for interconversion of carbo- hydrates as well as the breakdown of glucose. The reversal of carbohydrate breakdown can occur from any metabolite which is convertible to py- ruvic acid. Such possible sources include the lipids and the proteins. Thus most foodstuffs can ultimately yield storage carbohydrate in the form of liver and muscle glycogen. At some points in the glycolytic and glycogen synthesizing pathways the reaction energetics is highly unfavorable for anabolism. At such points alternative steps cir- cumvent this problem. For reversal of glycolysis one such step is the conversion of pyruvic acid to phosphoenolpyruvate. The problem has been solved by addition of carbon dioxide to pyruvate, to form oxalacetate followed by conversion of the ketoacid to phosphoenolpyruvate in a coupled re- action. While the breakdown of glycogen to glu- cose-l-phosphate is catalyzed by the complex group of phosphorylase enzymes the synthesis of the storage polymer follows an alternative path- way. Glucose-6-phosphate is coupled to the nu- cleotide uridine which serves as a carrier of the saccharide in the form of uridine diphosphate glucose (UDPG). In this form the glucose is avail- able as well for interconversion to other sugars such as galactose and the amino sugars. The latter form a significant component of the mucopoly- saccharides, a complex structural polymer espec- ially of connective tissues. Protein Metabolism Amino acids derived from proteins can enter into the mainstream of energy production by elim- ination of the nitrogen of the amino group and oxidative conversion of the product to a fatty acid derivative. These reactions, which occur primarily in the liver, may be depicted in the following stages: R-CH-COOH — R-C-COOH — R-C-COOH + NH, — R-COOH +} CO, | | NH, NH The ammonia produced in the sequence is com- bined with carbon dioxide to yield the excreted waste product urea, NH,CONH, (Cf. Figure 5-5). For the adult on a usual mixed diet approximately 20-30 g/day of urea will be formed and excreted through the kidney into the urine. Uric acid is the end product of purine metabolism in man. Metabolism of Acetyl Coenzyme A The conversion of proteins, carbohydrates and lipids to the two-carbon acetyl unit in the form of its coenzyme A combination makes this a focal point of energy metabolism. By means of the tri- carboxylic acid (TCA) cycle, the two carbons of the acetyl group are converted to carbon di- oxide. The difference in the free energy levels of the acetyl group and its product carbon dioxide is held temporarily by the conversion of the oxi- dized form of the nicotinamide co-factor (NAD) to the reduced state, NADH. The steps involved ] 0 43 in the TCA cycle consist of a series of enzymatic condensations, redox reactions, and decarboxyl- ations summarized in Figure 5-2. The net result of the total process is the elimination of the acetyl group in the form of CO, and the formation of reduced co-factors for energy trapping in mito- chondrial oxidation. Mitochondrial Oxidative Phosphorylation Part of the energy released by catabolism is made available to the body in the form of heat. For all other purposes, however, it must be har- nessed in a way which will permit its utilization in subsequent coupled energy requiring reac- tions. This is achieved in the process of mito- chondrial oxidative phosphorylation. The oxida- tion process is controlled by subdivision of energy release into incremental steps. At appropriate points in the reaction chain, energy available from oxidative change is used to couple inorganic phos- Citrulline aspartate +CO +N : TE Hq \ v \ ny Arginine \ Ornithine succinate | ‘ ' (minor process) 7 Arginine Fumarate UREA Dawkins MSR, Rees KR: A Biochemical Approach to Pathology. London, Arnold, 1959. Figure 5-5. Urea Cycle phate to adenosine diphosphate (ADP) to form the important energy storage form adenosine tri- phosphate (ATP). The reaction: ADP+Pi— ATP requires approximately 8000 Cal/mol to form the phosphate anhydride bond. Conversely when the ATP molecule is coupled in an appro- priate enzyme system with an energy requiring reaction it is able to make available the 8000 Cal/ mol of its “high energy” phosphate bond. In an appropriate system this energy can be utilized for new chemical bonding, electrical, or mechanical energy. Steps in Mitochondrial Oxidative Phosphorylation The free energy change (-AF”) represented by the change from reactants to products, can be measured in calories or recalculated in terms of the change in electrode potentials, (E,”), expressed in volts since the two terms are related by the expression: AF’ =7"AE’ nF where n represents the number of electrons (or hydrogen atoms) in- volved and F is the Faraday (96,487 coulombs). From this relation it can be calculated that a difference of 1 volt between the E’, values when n=2 represents a change of 46,166 gram-calor- ies. For mitochondrial oxidative phosphorylation the initial redox step at a value of E’;=-0.32 for the system NAD*+/NADH+H* ends with the reaction 1/2 O,/H,O at a value for E’, of + 0.82. The difference between these E’; values provides a measure of the total potential energy available to the system. In order to capture and utilize this energy, mitochondrial oxidative phos- phorylation takes place in discrete steps with a cascading change in the energetic levels of the system. Step 1: NAD+/NADH + H+ In the previously described reactions of the TCA cycle the abstraction of a hydrogen atom to- 44 gether with its electron has been illustrated (Fig- ure 5-2). The acceptance of the hydrogen atom and electron by NAD™ represents the reduction of the co-factor coupled with the oxidation of the substrate. This change may be viewed in simplistic terms as a transfer of the potential energy of the donor to the recipient, NADH. The electrode po- tential of the NAD+t/NADH -+ HT system is about -0.32 volts as it operates in the cell. Step 2: In the second step of mitochondrial oxidation the coupled reaction occurs by which the reduced nicotinamide co-factor, NADH, transfers its hy- drogen and associated electron to a riboflavin co- factor, flavin adenine dinucleotide (FAD). The overall paired reactions may be written as follows: a) NADH+H+ — NAD+ 2H b) FAD +2H-— FADH, Since the flavoprotein oxidized/reduced couple has an E’, value of -0.06 volts the reaction rep- resents a difference of -0.26 volts. This change is more than sufficient to provide enough energy to convert adenosine diphosphate and inorganic phosphate to adenosine triphosphate, ADP + P, ATP since the energy requirement is about 8000 Cal, equivalent to 0.15 volts. Thus at this step of oxidative phosphorylation the respiratory chain is able to capture some of the released energy in the form of the reusable high energy bond of ATP. Step 3: In the next step of electron transport the re- duced flavin nucleotide transfers the hydrogens and associated electrons to the quinoid structure, coenzyme Q. The energy change implicit in the process is only 0.06 volts, insufficient for the for- mation of a high energy phosphate bond. Flavoprotein H, — Flavoprotein + 2H Coenzyme Q + 2H+ — Coenzyme OH, Step 4: From reduced coenzyme Q the electrons are transferred to the iron porphyrin system cyto- chrome b while the released protons appear in the medium. QH, — Q + 2 electrons + 2H+ 2 cytochrome b (valence + 3) = 2 cytochrome b (valence + 2) The change in E’, of approximately 0.26 volts is sufficient to allow for the formation of an addi- tional high energy ATP bond. Step 5: Movement of the electrons from cytochrome b to the iron porphyrin cytochrome C, involves a change in energy level of only 0.03 volts, insuffi- cient for the formation of an ATP molecule. Step 6: The final sequence of mitochondrial oxidation involving the electron transport from cytochrome ¢ to cytochrome a, cytochrome a, and finally to oxygen with simultaneous uptake of protons from the medium to form water, is accompanied by a modification in E’, of a total of 0.73 volts. While this overall change would accommodate the for- mation of three ATP bonds in fact only one is formed. The overall process of mitochondrial oxidative phosphorylation, starting with the substrate MH, energy source and ending in the transfer of the hy- drogen with its electron to form water, provides three ATP high energy bonds of a total seven that are theoretically possible. This is nonethe- less a rather efficient mechanism for an energy transducer. One would compare this efficiency of about 43% with conventional systems such as the internal combustion engine or steam turbine and decide that it was rather good. In summary, the process of energy formation starts with potential substrates from any of the major classes of nutrient proteins, carbohydrates, and lipids. By use of enzyme catalysts, a series of vitamin co-factors, and mineral elements in a syn- chronized interlocking organized chain, the poten- tial energy implicit in the enzyme substrates is efficiently captured in the form of the chemical bond energy of the ATP molecule for use in energy requiring coupled reactions. Uncoupling of Oxidative Phosphorylation Some drugs and toxic agents have the capacity to interfere with the linkage of the energy captur- ing step of ATP bond formation and the process of electron transport in the mitochondrial electron transport system. As a result the engine con- tinues to run, generates heat, but makes no prog- ress. The transmission has been “uncoupled” from the wheels. As one may anticipate, substrates such as fats are consumed, but ATP bond energy for anabolic purposes is lacking. “Uncouplers” such as dinitrophenol were consequently used for weight reduction many years ago, but have been discarded because of their associated toxicity. Sweating may occur when the uncoupled energy is released, as observed in pentachlorphenol poisoning. Removal of Wastes The direct waste products of metabolism are water, carbon dioxide, nitrogen in the form of ammonia and a variety of minor specialized or- ganic catabolites. The excretion of salts is par- tially regulatory and partially a waste disposal process. The continued processing of all these materials is essential for the functioning of the organism. Water, the major constituent of the body, requires continued input for replacement of the insensible loss of perspiration, in the moisture of the outgoing breath and as a solvent to remove solid wastes by solution in the urine. Control of fluid adjustment by the kidney is achieved by a feedback mechanism triggered by the osmotic pressure of the blood as it flows over the osmor- ceptors of the kidney and by the sodium content of the blood as it flows through the adrenal cortex. The multiple controlling systems, especially the hormones (particularly aldosterone) of the adrenal cortex and the posterior pituitary hormone vaso- pressin, integrate the water balance at the kidney level. The combustion of foods to yield carbon di- oxide throws a continuous acid load upon the body. Carbon dioxide, a gas under ambient con- ditions, is in equilibrium with water to form car- bonic acid by the reaction: 45 CO, + H,0 = H.CO, This reaction proceeds slowly under usual condi- tions but is tremendously speeded in the body by the zinc enzyme of the red cell, carbonic anhy- drase. Since the acidity of the blood is carefully maintained at approximately a pH of 7.4, the carbonic acid generated by metabolism is rapidly neutralized to yield the bicarbonate anion, HCO,™, which returns to the plasma from the erythrocyte. The hydrogen ion from this reaction is neutralized by the buffers of the blood, notably oxyhemo- globin HbO,™, which simultaneously loses oxygen at the tissues and provides for the neutralization of the proton. The reaction HbO, + H+ — HHb + O, thus simultaneously unloads oxygen at the tissues and provides for the neutralization of hydrogen ion arising from the carbonic acid of metabolism. The process is reversed at the lungs. The oxygenation of hemoglobin forms the stronger acid oxyhemo- globin which in turn liberates a proton for re- combination with bicarbonate to form carbonic acid which in turn is converted to CO, by eryth- rocyte carbonic anhydrase to produce the CO, exhaled in the expired air. This mechanism for the elimination of carbon dioxide is one of rapid adjustment. The partial pressure (pCO,) of the blood is constantly monitored by neural receptors which bring about changes in respiration to ac- commodate to the need for release of metabolic carbon dioxide. One is aware of the slowed breathing of sleep when metabolism is decreased. At such a time the demand for oxygen intake and carbon dioxide elimination is minimal compared to the accelerated breathing during vigorous exercise. The rapid adjustment of the lungs to acid load is supported by the slower fine modulation at the kidney. One of the major excretory components of the urine is its phosphates. It will be recalled that phosphoric acid has three ionizable groups which function at various points in the acidity scale. The anion pair H,PO, ~/HPO,= is one which is operative in the maximal acidity range of urine which is roughly from about pH 4.6 to pH close to 8.0. Variations in acid load in the body can be compensated by a mechanism which results in the shift in the phosphate buffer pair by neutralization of the hydrogen ion of the acid. The reaction HPO,= + H+ = H,PO, proceeds to the right and provides a means for the excretion of the acid load in the urine. The elimination of the nitrogen load of meta- bolism is essentially by means of its conversion in the liver to urea and excretion of this product in the urine as has been previously discussed. It is clear that damage to the liver will inhibit the de- toxification of ammonia through its conversion to urea. Not only does this detoxification mechanism fail with liver damage but so also are other meta- bolic detoxifications inhibited. Failure of kidney function by damage or disease is equally serious. The accumulation of nitrogenous waste products, azotemia, is usually monitored by measurement of the urea content of the blood. Continued eleva- tion of blood urea offers a poor prognosis of recovery. BIOCHEMICAL MONITORING To this point, the authors have presented a body of factual information on the subject of bio- chemistry. Hopefully, the reader seeks to find how this may be applied to the problems for which he requires solutions. The first fact that may be obvious from the material presented is that all men are created equal — but different! While genetic categories may be separated, within groups each individual has his own biochemical pattern. This suggests it might be desirable to have a biochemical profile of a worker available for comparison with his subsequent work and medical history. The de- velopment of automated procedures in clinical chemistry makes this feasible. An application of biochemical profiling to an industrial health prob- lem is cited in the reading list. Researchers inter- ested in finding sensitive indicators of injury to toxic agents may be intrigued by the pattern de- picted in Figure 5-6. This combines data from serum, tissue from lung and adrenals, and leu- cocyte assays into one picture. Adrenal stress is evident from the elevation of adrenal succinic - dehydrogenase: the leucocyte enzymes appear to respond opposite, and to a greater degree, than serum enzymes. One might be led to suspect that leucocyte enzymes may provide a better index of response to injurious exposure than do serum enzymes. Only adequate research will either cor- roborate or discredit such suspicions. The tech- niques of leucocyte separation and assays are de- scribed in the literature cited. General monitoring by profiling such as these cases may be useful, but always requires interpre- tation; a worker may have an alcoholic week- end, or a current infection, and confuse the inter- pretation. Monitoring of workers for exposure to metals has been facilitated by the development of the convenient and sensitive methods of atomic ab- sorption spectroscopy. Assay of cholinesterase activity of blood has been mentioned as useful in monitoring exposure to anti-cholinesterase insecticides. Another type of monitoring involves analysis of urine for the metabolite of the agent to be controlled: for ex- ample, measurement of urinary phenol content to evaluate degree of exposure to benzene. With the prospect that regulatory agencies are aiming at setting biological standards for many or- ganic, as well as inorganic substances, the subject of the next section becomes especially relevant. DETOXIFICATION PROCESSES The ability of the body to neutralize potentially damaging materials is remarkable. Heavy metals such as lead are shunted into the skeletal system where they are effectively buried in the bone. This protective process fails when the breakdown of bone, as in fever, may cause a release of the metal in quantity greater than can be handled by the normal slow and low level elimination in the urine and feces. In these circumstances, or when the in- coming load is greater than can be effectively han- 46 dled, the toxic symptoms of lead poisoning result. In his modification of the environment man has also introduced new factors in the problem. The radio- isotopic elements uranium, strontium and pluton- ium also are buried in the bone for purposes of detoxication. These elements, however, retain their intrinsic toxicity associated with their continuing radiation. The net long term result is the radiation damage of the surrounding cells and the develop- ment of cancer. Organic compounds are converted, if possible, to forms which can be excreted by the body or are non-toxic. The liver oxidases have a remarkable capability to add an -OH group to otherwise poorly reactive compounds. Aromatic materials such as benzene are converted to phenols. Ali- phatic and heterocyclic compounds are hydroxy- lated to form alcohol derivatives. This mechanism provides a handle by which the organism is further able to convert the compounds to a water soluble product which can be excreted in the urine. Phenols, for example, can then be conjugated with sulfuric acid to form an ethereal sulfate, ROSO,H, derivative. Sulfate derivatives of this kind are readily excreted in the urine. An alternative con- jugation is by way of the sugar acids resulting in the formation of a soluble derivative of the form RO(CHOH), COOH. Conjugation with amino acids, especially glycine or cysteine, also results in the formation of soluble products that can be cleared through the kidney and eliminated in the urine. Where the toxic agent is susceptible to hydrolytic cleavage, the appropriate enzymes may break them down to their non-toxic component structures. A variety of esterases and proteolytic enzymes are available for the cleavage of amide, peptide and ester bonds. One of the more serious groups of environmental and industrial toxicants is the family of amines, R-NH,. The oxidation of these compounds to aldehydes and acids and their conjugation to more hydrophilic derivatives are frequent modes of their detoxication (Table 5-1). The converse process of reduction, especially of industrial nitro derivatives, R-NO,, provides a mechanism for conversion to more tractable prod- ucts for elimination. Despite these ingenious metabolic mechanisms for detoxication, it is clear that the continued pollution of our environment is proceeding with materials in quality and quantity beyond our capac- ity to handle. Some evidence is available of some increased body burdens of lead and of an accum- ulation of organic insecticides in our tissues until the last several years. The remarkable biochem- ical homeostatic mechanisms need help from the technical, political and social efforts which are essential for solution of our critical environment problems. Selected Reading: Textbooks 1. McGILVERY, R. W., Biochemistry, W. B. Saunders Co., Philadelphia (1970). WEST, E. S., W. R. TODD, H. S. MASON, J. T. VAN BRUGGER, Textbook of Biochemistry, The MacMillan Co., New York (1966). 3. WHITE, A., P. HANDLER, E. L. SMITH, Princi- ples of Biochemistry, 4th Edition McGraw-Hill Book Company, New York (1968). 2. (Ona) 1dvV Biochemical Profile of Rats (Germ Free) Exposed to Coal Dust. Control Values as Reference. Abbreviations: LDH — Lactic Dehydrogenase HBDH — Hydroxy Butyrate Dehydrogenase G-6 PD — Glucose-6-Phosphate Dehydrogenase APT — Alkaline Phosphatase SDH — Succinic Dehydrogenase AT — Serum Anti-trypsin TIBC — Total Iron Binding Capacity of Serum / — Slant Line Indicates Ratio Value Courtesy Dr. Larry K. Lowry, Toxicology Section, NIOSH. Figure 5-6. Profile, Germ Free, Coal Exposed, Control 47 TABLE 5-1 Major Types of Detoxication Foreign Detoxication Type substance product examples Methylation Incrg. Compounds of As, Te (CH), Se -CH; N-CH, Ring N compounds @ QH Certain complex aromatic OCHg4 phenols CHOH-CH,NHCH4 Acetylation Aromatic Amines NHCOCH 4 Amino Acids (Known exceptions: aromatic amine carcinogens, also aliphatic amines). RGHCOOH NHCOCH e.g., Benzidené - hydroxvlated aliphatic amines - aldehvdes. Ethereal sulfate Phenols OSO 3H -OSO3H (Cyclohexanol glucuronide) Acetyl Aromatic Hydrocarbons S-CH,CHCOOH Mercapturic acid lalogenated Aromatic HC's © - - 3 1 SCH,CHCOOH Polycvclic HC's NHCOCH, NHCOCH, Br— Sulfonated esters CoH SO,-CH,4 CoH. acetyl cysteyl- Nitroparaffins (C,HANO,) C4 lg-acetyl cysteyl- Thiocyanate Cyanide, inorganic Organic Cyanides RCNS (Nitriles) Clycine Aromatic Acids Aromatic-aliphatic acids CONHCH,COOH -NHCH,COOH Furane carboxylic acids Thiophene ! Polycyclic " (Bile acids) Glucuronate Aliphatic (1°, 2°, 39) OCgligOg and Aromatic Hydroxyl O (Ether) C=0 Aromatic Carboxyl T OCH Of (Ester) Glucose Hydrazone Hydrazine " derivatives ? NH,N = CHC HgO4 Courtesy Dr. H. E. Stokinger, Toxicology Section, NIOSH. 48 Other Books: 1. DAWKINS, M. S. R. and K. R. REES, 4 Biochem- ical Approach to Pathology, Arnold, London (1959). T. G. F. HUDSON, Vanadium, Toxicology and Biological Significance, Elsevier, New York (1964). SEVEN, M. J. (Ed.) Metal Binding in Medicine, J. B. Lippincott Co., Philadelphia (1960). . STANBURY, JOHN B,. JAMES B. WYNGAAR- DEN and DONALD S. FREDERICKSON, The Metabolic Basis of Inherited Disease, 3rd edition, Blakiston Div., McGraw-Hill, New York (1972). UNDERWOOD, E. J., Trace Elements in Human and Animal Nutrition, 3rd edition, Academic Press, New York and London (1971). WILLIAMS, R. T., Detoxification Mechanisms, Chapman and Hall, London (1959). Articles: 1. ALLISON, A. C., “Lysosomes and the Toxicity of Particulate Pollutants,” Arch. Intern. Med., 535 No. Dearborn, Chicago, Illinois 60610, 7/28:131 (1971). DJURIC, D., et al, “Urinary lodine — Azide Test —(A Measure of Daily Exposure and a Predictive Test of Hypersusceptibility to CS.),” Brit. J. Ind. Med., Tauistock Square, London WC1 (U.K.), 22:321 (1965). FRAJOLA, W. T., “(Biochemical Profiles) Serum Enzyme Patterns,” Fed. Proc., 9650 Wisconsin Ave- nue, Washington, D.C., 19, No. 1, Pt. 1 (March 1960). 49 11. GUENTER, C. A., M. H. WELCH and J. F. HAM- MARSTEN, “Alpha-1 Antitrypsin Deficiency and Pulmonary Emphysema,” Ann. Rev. Medicine 23:283 (1971). LEISE, ESTHER M., IRVING GRAY and MAR- THA K. WARD, “Leucocyte Lactate Dehydroge-- nase Changes as an Indicator of Infection Prior to Overt Symptoms,” J. Bact. 96:154 (1968). MENGEL, C. E., “Rancidity of the Red Cell: Peroxidation of Red Cell Lipid,” Am J. Med. Sci., 600 So. Washington Square, Philadelphia 6, Penn., 255:341 (1968). MOUNTAIN, J. T., “Detecting Hypersusceptibility to Toxic Substances,” Arch. Environ. Health, 535 No. Dearborn, Chicago, Illinois 60610, 6:537 (1963). SCHEEL, L. D., R. KILLENS and A. JOSEPH- SON, “Immunochemical Aspects of Toluene Diiso- cynate (TDI) Toxicity,” Amer. Industr. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 25:179 (1964). SCHROEDER, H. A., “The Role of Chromium in Mammalian Nutrition,” Am J. Clin. Nutr., 21:230 (1968). STOKINGER, H. E., J. T. MOUNTAIN and L. D. SCHEEL, “Pharmacogenetics in the Detection of the Hypersusceptible Worker,” Ann N. Y. Acad. Sci., 12 E. 63rd St.,, New York 10021, 757:968 (1968). THOMPSON, R. P. H., et al, Treatment of Un- conjugated Jaundice with Dicophane (DDT), Lan- cet, Vol. II, p. 4 (1969). CHAPTER 6 REVIEW OF PHYSIOLOGY James L. Whittenberger, M.D. INTRODUCTION Physiology is the basic biomedical science which deals with function in living organisms. Since form and function cannot be studied apart from each other, anatomy and physiology were undoubtedly two of the earliest biomedical sciences to be developed. As rapid expansion of natural sciences occurred, particularly in the first half of the twentieth century, specialization and fragmen- tation has led to splitting off of several fields from the parent discipline of physiology — including biochemistry, biophysics, and more recently, mo- lecular and cell biology. For the purposes of this Syllabus, we shall assume that physiology is con- cerned with the full range of function, from the activities of a living cell to the performance of the whole organism. A major concern of physiology is the role of environmental factors in influencing function. A fundamental principle of mammalian physiology is that basic intracellular processes can proceed only if the fluid environment surrounding each cell is maintained in a nearly constant state with re- spect to temperature, oxygen supply, acidity and nutrients. A major role of most systems of the body — respiratory, circulatory, alimentary and excretory for example — is to maintain near- constancy of the so-called internal environment of the body. By contrast, the external environment is variable over wide limits — in temperature, humidity, ionizing and nonionizing radiation en- ergy, barometric pressure, and presence of noxious gases and particles. Interaction between the or- ganism and the external environment is continuous and calls upon various protective and adaptive responses of the organism. In ordinary life and in the usual working environment these adjustments are automatic and unconscious; they put no par- ticular strain on the organism and are a part of healthy existence. A primary objective of industrial hygiene engi- neering is to control the occupational environment so that workers will not be exposed to extremes of heat and noise, or to unsafe levels of noxious gases, dusts and fumes. The degree of control needed depends on the type and extent of biologic response that might be induced. Since it is not economical to control the environment completely, it is important to know the nature and extent of biologic response in order to make rational deci- sions about the extent of control needed in relation to other measures that can be used to protect the health of the workers. For example, it may not be feasible (too costly) to control the heat in the particular environment; however, a biological re- 51 sponse to heat (that is, a heat stress study curve) can be used to determine a safe level (using tem- perature and time) of exposure to heat and when the worker should be given a rest period. The kinds of biologic response to occupational environmental stresses range from harmless physi- ologic responses (such as respiratory and circula- tory adjustments to physical exercise) through a variety of toxicologic manifestations which may include acute diseases such as chemical pneu- monias and chronic diseases such as silicosis, or cancer of various organ systems. Thus the re- sponses to environment involve toxicology, pathol- ogy and other medical specialties besides physiol- ogy; but these sciences cannot be understood with- out a basic knowledge of physiology and bio- chemistry. BASIC CELL FUNCTIONS The basic unit of all living organisms is an individual cell. Certain principles are common to almost all cells and represent minimal require- ments for maintaining the integrity of the cell. Thus a human liver cell and a free-living ameba do not differ much in their means of exchanging materials with the immediate environment, obtain- ing energy from nutrients, synthesizing proteins, and reproducing themselves. The difference among cells in the different tissues of the body usually represents a specializa- tion of some one function of the functions common to all cells. Thus the excitability of nerve cells represents a specialization of electrical phenomena common to the membranes of almost all cells; the transport of food molecules across intestinal cells is a specialization of transport mechanisms that are very similar in all cells. Types of Molecules Water forms the medium in which all living processes occur, and life as we know it is incon- ceivable in the absence of water. Sixty percent of the body weight is water, and 80% of the weight of a cell is water. Because so many different mole- cules can dissolve in water, it is an ideal medium for chemical reactions. Water participates in prac- tically every process in the organism and without this medium we could not have a circulatory system. Despite the importance of water, the chem- istry of living systems is centered about the chem- istry of carbon which makes up 45 percent of the dry weight of the body. Carbon atoms can form four separate bonds with other atoms, in particular with other carbon atoms, making possible the formation of large molecules with a variety of structures. In combination with hydrogen, oxy- gen, nitrogen, and occasionally sulfur and phos- phorus, carbon compounds make up the major classes of organic molecules in the body — pro- teins, lipids, carbohydrates and nucleic acids. Pro- teins constitute about 17% of the body weight — they make up much of the structure of the body as connective tissues and muscle. They catalyze most of the chemical reactions in cells and serve many specific functions, for example, as hor- mones, carriers of oxygen and carbon dioxide (hemoglobin), and as the principal mechanism of immunity (antibody formation). Lipids make up about 15% of body weight and because of their relative insolubility in water perform a very important role in the permeability of cell membranes. One class of lipids includes the steroid hormones. Carbohydrates constitute only about 1% of body weight, but supply most of the energy needs of the body. Nucleic acids are even smaller in amount, but include the largest and most specialized molecules in the body — the deoxyribonucleic acid (DNA) molecules which are the blueprints of genetic information in the cell nucleus, and the ribonucleic acid (RNA) molecules which transcribe and carry the infor- mation in forms that can be used to synthesize proteins in the cytoplasm. Energy and Cellular Metabolism Metabolism refers to the sum of chemical re- actions taking place in a living cell or organism; it includes both the process of fragmentation of large molecules into smaller ones and the synthesis of large molecules from raw materials in the cell. Both processes go on simultaneously in different parts of the cell, with hundreds of chemical reac- tions taking place in an orderly fashion. That such reactions can take place at normal body temperature is due to the presence of special protein molecules which act as catalysts. Although enzymes are not destroyed by the reactions they catalyze, like all biologic molecules they are in a state of dynamic equilibrium between the rate of breakdown and the rate of synthesis. The cell’s ability to control these rates is one mechanism for control of the rates of metabolism within cells. Some enzymes are highly specific, acting on only one type of substrate molecule; others interact with a range of substrate molecules which have a particular type of chemical bond or grouping which is specific for the enzyme. Over 900 differ- ent enzymes have been identified and there are undoubtedly many more to be discovered. THE INTERNAL ENVIRONMENT Like a free-living single-celled organism in the sea, every cell in the body is bathed in an aqueous medium — the extra-cellular fluid — which in salt composition is not dissimilar to that of the sea (at the salt concentrations which probably obtained when terrestrial life evolved from the sea). The extracellular fluid provides ready access to nutrients and oxygen, serves the needs for waste disposal and stabilizes conditions outside the cell membrane. The extracellular fluid — the internal envir- onment of the body — consists of two compart- 52 ments. Eighty percent of it surrounds the cells within tissues in all parts of the body; the re- mainder is within the vascular system — the liquid part of the blood — the plasma. Since the blood is pumped to all parts of the body, where cells are close to capillaries, there is rapid exchange be- tween plasma and extracellular fluid. Conse- quently, the composition of the two fluid com- partments is very similar, except for the presence of proteins in the plasma. The proteins do not normally pass through the capillary wall and they serve a very useful role in controlling fluid ex- change in the capillaries. Homeostasis This important concept, first enunciated by Claude Bernard, refers to the relative fixity of the internal environment and the role of many organs and systems in stabilizing the internal en- vironment. The temperature, the concentrations of oxygen, carbon dioxide, nutrients, and inor- ganic ions — all must remain relatively unchanged in the extracellular fluid. Virtually every system of the body contributes to this stability — the liver adds or subtracts molecules as needed, the lungs delicately adjust the oxygen and carbon di- oxide in the blood, the kidneys excrete or absorb the right amount of water and salts, and so on. The activities of tissues and organs are regulated and integrated with each other so that any change in the internal environment automatically initiates a reaction to minimize the change. Thus stability is achieved in the presence of wide fluctuations in activity of the total organism and wide ranges of external environmental conditions. NEURAL CONTROL MECHANISMS The development of the human nervous sys- tem is one of the most remarkable of evolutionary achievements. The nervous system is a major interface between the organism and the environ- ment; it serves in many of the mechanisms that maintain homeostasis; it controls posture and body movements; it is the seat of subjective experience, memory, language, and the thought processes that characterize human activity, The fundamental unit of the nervous system is the neuron, which consists of cell body, den- drites, and the axone, which may be several feet in length. Only about 10% of the cells in the nervous system are neurons, the remainder serv- ing mainly as supporting elements. The connections between nerve cells, called synapses, play a key role in the transmission of impulses in the nervous system; one cell may be directly connected with as many as 15,000 other cells by means of synapses. The basic mechanism of impulse transmission is the action current which results from depolarization of the cell membrane under the influence of chemical or mechanical events. The threshold for depolarization differs in different parts of the neurons and is influenced by the local environment of the cell; this is also true of the synapse. Nerve stit:ulation or alteration of local ions may be excitatory (lowering threshold for depolarization and action potential genera- tion), or inhibitory (raising the threshold). Presumably the mechanism whereby impulses are transmitted through synapses involves the re- lease of a chemical at a cell terminal, with rapid diffusion to a reactive site on the second cell. With few exceptions (acetyl choline in the para- sympathetic system and norepinephrine in the sympathetic system), the identity of these trans- mitters is unknown. There are three functional classes of neurons: 1) afferent neurons which frequently are con- nected to sensory receptors (touch, taste, smell, sight, etc.) and which transmit information in the form of coded action potentials from the peripheral to the central nervous system; 2) efferent neurons, which transmit action potentials from centers in the spinal cord and brain to skeletal muscle, smooth muscle, or secretory cells in the periphery; and 3) interneurons, which make up 97% of the total and which provide the vast number of inter- connections in the central nervous system. The sensory receptors are of special interest in environmental health for their responsiveness or lack of responsiveness to different kinds of energy in the environment. For example, ex- tremely sensitive receptors in the eye respond to electromagnetic energy in the narrow visible spec- trum, but the eye has no receptors which respond to long wave frequencies or to ionizing radiation. The auditory system is highly developed to trans- late sound energy into nerve action potentials, and smell receptors respond to as little as 4 to 8 mole- cules of a substance. Other receptors respond selectively to mechanical stresses and to changes in chemical energy. Although receptors in general are adapted to respond to a particular kind of energy, they usually can be activated by other forms applied in sufficient strength. For example, the visual receptors normally respond to light but they can be activated by intense mechanical stim- uli, such as a blow on the eyeball. The Reflex Arc The reflex arc illustrates many of the com- ponents of nervous control. The five components are a receptor, an afferent nervous pathway to carry action potentials to the central nervqQus system, an integrating cemter in the spinal cord or brain, an efferent pathway to carry action potentials from the central nervous system, and the effector which is activated. The receptor detects an environmental change (temperature, pressure, etc.), perhaps by a change of permeability, and alters its signals to the affer- ent nerve. The integrating center receives input from many receptors and from other parts of the nervous system. The net result of these inputs is an “order” which is transmitted by the efferent pathway to a muscle or gland. If the initial stim- ulus is cold exposure, the integrating center would be in the brain, and the effector response would be an increase in skeletal muscle tone and constric- tion of skin blood vessels which would conserve heat by diminishing blood flow. Such responses are automatic and usually not consciously per- ceived. Divisions of the Nervous System Overall the nervous system is divided into 53 central and peripheral portions, the central includ- ing both the brain in its several parts within the cranium, and the spinal cord within the vertebral column. Another way of dividing the system is into afferent and efferent components; the afferent includes the pathways from the specialized re- ceptors and from other sensory nerve endings in tissue; the efferent system leaves the brain and spinal cord to transmit impulses to skeletal mus- cle, cardiac muscle, smooth muscle, and glands. Autonomic Nervous System The efferent system to skeletal muscle is the somatic nervous system; the other part of the efferent system is known as the autonomic nervous system. It deserves special attention because of its role in maintaining homeostasis. It provides dual innervation to the heart, the smooth muscle of lungs, blood vessels, intestinal tract, and other organs, and to secretory glands. The dual systems differ physiologically and anatomically and are called the sympathetic and parasympathetic sys- tems. Whatever one division does to an effector organ, the other usually does the opposite; thus action potentials over the sympathetic nerves to the heart increase the heart rate, while action potentials over the parasympathetic fibers decrease it. Dual innervation with nerves inducing op- posite effects provides a fine degree of control over an effector organ. In general the sympathetic system helps the body cope with challenges from the outside en- vironment (increasing flow to exercising muscles, constricting other vessels to sustain blood pres- sure, increasing metabolism, etc.) whereas the parasympathetic system is more active in diges- tion and other resting activities. Activation of the sympathetic system is likely to have widespread effects in the body, partly because the adrenal medulla is concurrently stimulated to secrete epin- ephrine (adrenalin) into the blood. HORMONAL CONTROL MECHANISMS A second communications and control system is provided by the glands of internal secretion, which secrete specific chemicals into the blood- stream which then circulates them throughout the body, where they may affect a small number of target cells or in some instances a large number of cells. An example of the former is the effect of thyrotropic hormone from the anterior pituitary, affecting only the cells of the thyroid gland. An example of widespread effect is that of insulin, which increases the entry of glucose into most cells of the body, except in the brain. Except for maintenance of reproductive ac- tivities, the body is capable of functioning without the endocrine glands, including even the anterior pituitary — the so-called master gland. However, the level of function in the absence of hormones is very deficient. Metabolic activities are depressed and resistance to infection and other stresses is much below normal; in addition there are other abnormalities that relate to specific hormones. A general principle pertaining to hormones is that they are always present in the blood, at con- centrations that depend on 1) the rate of produc- tion in specific cells, 2) the amount of storage in those cells, 3) the rate of release into the blood and 4) the rate of removal from the blood by absorption in a target organ, inactivation, or excre- tion. The control systems may act on one or more of these factors. Until recent years, the endocrine systems were studied independent of the central nervous sys- tem, although it was recognized that the anterior pituitary was anatomically closely related to the base of the brain (the hypothalamus), and that emotional states could influence the function of the thyroid, the adrenal, and the reproductive glands of internal secretion. Now close functional, as well as anatomic, relationships between the two great communication systems of the body are well established. In a sense the central nervous system “leads” the major components of the endocrine system by the secretion of “releasing factors” in the hy- pothalamus. These control the production and secretion of six separate hormones of the anterior pituitary: 1. The thyrotropic hormone regulates the production of thyroid hormone in the cells of the thyroid; The adrenocorticotropic hormone (ACTH) regulates the production of cortisol in the adrenal cortex; The luteotropic hormone controls the pro- duction of progesterone; The follicle-stimulating hormone controls the maturation and release of ova from the ovary; The lactogenic hormone (prolactin) con- trols the production of milk by cells in the breast; and The so-called growth hormone, which has multiple metabolic effects. In addition to these effects mediated by the anterior pituitary, the hypothalamus secretes two other hormones formerly thought to be produced by the posterior pituitary — the anti-diuretic hor- mone which regulates the reabsorption of water in the kidney, and the hormone oxytocin, which stimulates contraction of the gravid uterus. In addition to its central role in regulating the above hormones, the hypothalamus controls the autonomic nervous system, which in turn controls the secretion of epinephrine. There are a few hormones, such as insulin and aldosterone which are not regulated by the hypothalamus or pituitary. Part of the control of hormone production is the negative feedback effect of the hormone produced by the target organ. Thus thyrotropic hormone from the pituitary stimulates the thyroid cells to produce thyroid hormone, but thyroid hormone, either produced by the organism or ad- ministered as a drug, depresses the output of “re- leasing factor” from the hypothalamus and in turn the output of thyrotropic hormone by the anterior pituitary. Some of the mechanisms by which hormones act are known; others are not known. They do not create new functions of cells, but are usually found to alter rates at which existing processes proceed by increasing the activity of a critical en- zyme (by increasing its production or by activating 6. 54 a stored form) or by altering the rate of mem- brane transport. For example, one of the actions of insulin is to increase the rate of entry of glucose into cells. Actions of hormones on cells often involve interactions with other hormones; for ex- ample, epinephrine causes release of fatty acids from adipose cells only when thyroid hormone is present. The role of hormones, especially those pro- duced by the adrenal cortex, is important in the recognition of the responses of the body to any kind of stress, be it exposure to toxic chemicals, extremes of heat and cold, heavy exercise, and other stresses. Some effects of a toxic chemical may be direct effects on specific cells while the remaining effects are secondary to increased pro- duction of cortisol. Since adrenal cortical hor- mones play important roles in the inflammatory process, in immune responses, and in diverse me- tabolic processes, it is clear that a knowledge of hormones is essential to understanding the mecha- nisms of response to stress. RESPIRATORY SYSTEM In common understanding, the respiratory sys- tem includes only the lungs and conducting air- ways. Logically, the term should include the cir- culatory system as well, since the two systems are jointly responsible for meeting the respiratory needs of the body, providing as they do the mech- anism whereby the countless billions of cells are kept in minute to minute contact with the external environment for access to oxygen and for elimina- tion of carbon dioxide. The basic role of the lungs and related com- ponents of the system is to provide the essential conditions under which rapid exchange of oxygen and carbon dioxide can take place between the atmosphere and the blood coming to the pul- monary capillaries. A large surface is needed and this is provided by the estimated area of 70 square meters for an adult male’s alveolar surface, where pulmonary capillary blood is in close jux- taposition to the alveolar gas. The rate at which oxygen must be taken into the body (and propor- tional amounts of carbon dioxide released) varies from about 200 ml/min at rest to 30 times that amount during exhausting exercise. If this wide range of need is to be met without significant change in the internal environment, there must be corresponding changes in the rates at which pul- monary capillary blood is replaced and alveolar gas is exchanged with ambient air; these changes are accomplished by integrated responses of the cardiovascular system so that ventilation and per- fusion of the alveolar surface is always closely matched in healthy individuals. Airways The conducting portion of the respiratory sys- tem appears well-designed as a low resistance pathway for uniform distribution of gases to the alveolar surface, with numerous characteristics which “condition” the air and protect the lungs from at least the largest of infectious or noxious particles in the atmosphere. Some of the protec- tive aspects are as follows: The convoluted, moist, and richly vascular mucosa of the nose protects nose-breathers from inhaling particles larger than S or 10 microns in diameter; soluble gases are largely removed by absorption, and the inspired air is warmed and moistened (or cooled under hot, dry conditions). In addition, the sense of smell receptors in the upper reaches of the nose may serve a protective role. The tracheobronchial system is lined with cilia which constantly force toward the larynx a “car- pet” of mucus which is secreted by mucosal glands. The mucus carries with it the microorgan- isms and particles which have impinged upon it, as well as macrophages which move out of the alve- oli, often with a burden of material scavenged from the alveolar surface. When the mucus reaches the pharynx it is usually swallowed, but may be ex- pectorated. These “pulmonary clearance” mech- anisms play an important role in preventing pul- monary effects from inhalation of dusts, fumes, and other materials of concern in occupational exposure. The cough mechanism is a coordinated pattern of mechanical events that tends to expel foreign materials from the tracheobronchial tree. Other pulmonary responses occur in response to environmental exposures, but are less clearly protective. Most important of these is the bronch- ospasm which characterizes the response to many irritant gases. The partial or complete closure of bronchioles certainly impedes access to the alveoli, but it does so at the cost of greatly increased breathing effort and impeded gas exchange in se- vere cases. An asthma-like response is a normal reaction to many inhaled irritants; it also may represent hypersensitivity of such severity that further occupational exposure must be prevented. Pulmonary Ventilation Under precise nervous and chemical control, the respiratory muscles intermittently expand the thorax in such manner that the lungs are con- tinually changing volume. The elastic properties of the lung tend always to empty the lung, but the thorax exerts an opposite effect, except when lung and thorax volumes are large. Consequently, the lung retains a substantial amount of gas even when all respiratory muscles are at rest. In quiet breathing inspiratory muscles contract to enlarge the thorax and lungs; expiration is largely passive. Both frequency of cycling and the volume cycled (tidal ventilation) are variable; respiratory move- ments can thereby alter the minute volume (tidal volume times frequency per minute) from about 6 liters at rest to over 100 liters during heavy ex- ercise. The ventilation rate is adjusted to main- tain the alveolar partial pressure of oxygen and carbon dioxide approximately constant. The in- creases of ventilation with increasing levels of physical activity are very important in maintaining the homeostasis of the body; such increases may be critical in determining the amount of exposure to noxious or potentially noxious gases or particles in the atmosphere. Of each breath, at rest, approximately one- third does not exchange significantly with alveolar gas because about that amount of space is ac- counted for by the conducting airways and the volume of alveoli not perfused by blood. This 55 “dead-space” is normally about 180 ml in adult males and can be substantially increased in certain types of breathing appliances such as gas masks. Small increases in dead-space can be compensated by increased depth of breathing, but excessive dead-space can interfere with the adequacy of respiration. Work of Breathing Normally the work of respiratory muscles in ventilating the lungs accounts for a very small part of the total oxygen demand of the body — normally less than 3%. This is not the case when resistance to gas flow in the air passage is increased by bronchospasm or excess of secretions, or when the lung is diseased, as in pneumoconiosis, pul- monary fibrosis, and other occupational or non- occupational lung disease. In such conditions the increase of respiratory work may put a real bur- den on the whole cardiorespiratory system. Other conditions can also greatly increase the work of breathing, for example, the resistance of breath- ing through a gas mask, or having to breathe through a tracheostomy tube that is too small. Ordinarily the respiratory muscles themselves are capable of performing the extra work required in the conditions mentioned above. This would not be the case when respiratory muscles are weak- ened by diseases such as myasthenia gravis or po- liomyelitis, or by exposure to chemicals such as organophosphate pesticides. Flow of Respiratory Gases The ventilatory and gas exchange functions of the lungs are linked to the gas exchange needs of the body not only by the mass transport role of the circulatory system but by the peculiar respira- tory functions of the blood. If oxygen could be transported only by physical solution in the blood, the kinds of organisms we know could not have evolved. The secret to efficient transport of oxy- gen (and to a large extent carbon dioxide also) is the red pigment hemoglobin, which combines loosely with oxygen, picking up a full load at the partial pressure of oxygen in the lungs and re- leasing a large part of the load at the partial pres- sures pertaining around the capillaries of tissues. Normal blood, by means of its hemoglobin-packed red cells, contains about 20 ml of oxygen per 100 ml blood at the alveolar oxygen pressure of ap- proximately 100 mm Hg, compared to only 0.3 ml per 100 ml blood in physical solution. Under these conditions the hemoglobin is nearly satu- rated with oxygen. Since the hemoglobin is half- saturated at approximately 25 mm Hg, the blood can give up half its load of oxygen without low- ering the pericapillary oxygen pressure to levels that would fail to provide adequate diffusion from interstitial tissue into cells. Control of Respiration The precise regulation of breathing to main- tain alveolar oxygen and carbon dioxide levels essentially constant in the face of wide changes in body metabolism has always fascinated respi- ratory physiologists. Several factors are known, some closely interrelated (oxygen, carbon dioxide, and hydrogen ion concentration), but no theory fully explains the most remarkable adaptation of respiration — the hyperventilation which occurs in proportion to the level of exercise. Some of the control factors have special im- portance in certain occupational situations. Excess of carbon dioxide (as in contaminated atmos- pheres or rebreathing of expired air) is a powerful stimulant, causing 5-to 10-fold increase of ventila- tion at 5-7% CO, breathing. The mechanism may be a direct CO, effect on respiratory nerve cells or an indirect effect of increased hydrogen ion concentration in the cerebro-spinal fluid bath- ing the nerve cells. In oxygen-deficient atmospheres the respira- tory stimulation due to hypoxia is evident, the mechanism involving activation of specific recep- tor cells in the vicinity of the carotid arteries and the aortic arch. The strength of this stimulus was misjudged for a long time because of the inter- relationships of O, and CO, effects. Just as high CO, is a powerful stimulant, the loss of CO, is a potent depressant. Thus the increase of ventila- tion due to hypoxia eliminates CO, out of propor- tion to metabolic production; the level of CO, pressure falls; blood becomes relatively alkaline; and the respiratory drive is inhibited. If there is time for acid-base adjustments to low CO,, as in acclimatization to high altitude, the depressing ef- fect of low CO, disappears and the stimulating effect of hypoxia becomes more evident, with ben- eficial consequences to the organism in terms of higher partial pressures of oxygen throughout the body. THE CIRCULATORY SYSTEM The heart and blood vessels, with the blood contained therein, are the efficient internal trans- portation system of the body. The system is dual, the right side of the heart pumping blood only to the lungs while the left side pumps the freshly aerated blood to the rest of the body. The nor- mal adult has about five and a half liters of blood; each side of the heart pumps at a rate of about five liters per minute at rest and can increase the output about five-fold during heavy exercise. Changes of cardiac output involve both fre- quency of contraction and volume expelled with each stroke. The automatic rhythmicity of the electrical generator of the heart is subject to both nervous and chemical influences. Efferent auto- nomic nerves from the cardiac control centers in the brainstem can strongly slow or speed up the cardiac beat; epinephrine and drugs can also af- fect the rate of firing or the speed of transmission through the conducting system. The stroke output is affected by both intrinsic and extrinsic factors. A fundamental property of heart muscle is that the greater the stretch during relaxation, the greater the energy of the subse- quent contraction; thus a speeding up of return of blood for the veins will tend to increase the dias- tolic filling (increasing the stretch of heart muscle fibers) and automatically increase the force pro- pelling the increased quantity of blood into the arterial system. In addition, the “tone” and force of heart muscle contraction can be influenced by chemicals such as epinephrine and norepinephrine. 56 The Systemic Arterial System The arterial system which connects the left cardiac ventricle with capillary beds throughout the body has two basic characteristics: 1) the thick elastic walls of the aorta and other large arteries which enable the system to accept pulses of blood from the contracting ventricles and hold the blood in a high pressure reservoir while it flows off more or less steadily through the peripheral arterioles, and 2) the arterioles themselves, which because of their overall high resistance to flow tend to keep arterial pressure up during cardiac diastole and which, equally importantly, are sub- ject to local control, so that tissues and organs have perfusion rates adjusted to their metabolic needs. The arterial system contains about 15% of the total blood volume, at pressures which range in a young adult from about 110 mm Hg at the end of cardiac systole to about 70 mm at the end of diastole. This pressure is normally adequate to serve the blood flow needs of all tissues, including the brain when the body is upright. This is not true when there are sudden losses of blood volume (hemorrhage), failures of cardiac output (func- tional or organic in nature), or when arteriolar tone is sufficiently diminished (as after prolonged bed rest, immobility from other causes, heat ex- haustion, and fainting due to various causes). The local control of arteriolar tone (determin- ing resistance to flow) seems designed largely to protect the brain and heart. During muscular ex- ercise the smooth muscle in arterioles supplying active muscles relaxes allowing greater flow to the muscles; simultaneously there is contraction of smooth muscle in arterioles of other tissues, vir- tually shutting off flow to organs whose function can be temporarily suspended, such as the diges- tive organs. Vasoconstriction of this sort never affects flow to the brain or the heart. In addition to nervous control of local blood flow, other factors can markedly affect arteriolar resistance and hence flow; these include local metabolites such as CO,, heat, and chemicals like histamine and epinephrine. Capillary-Tissue Exchange When blood passes through the arterioles of the systemic circulation, the relatively high re- sistance is associated with a fall in pressure to about 35 mm Hg at the arterial end of the capil- lary. The number of capillaries is vast, the aggre- gate cross-sectional area of capillaries being esti- mated at 600 times the cross-sectional area of the aorta. This “widening of the stream” into a so- called capillary lake is associated with a greatly decreased flowrate, down to about 0.07 cm/sec. The large capillary area, slow flow, and pressure gradient from capillary to tissue provide ideal conditions for movement of nutrients and oxygen into the extracellular space. The system also evolved in a way to facilitate return of substances to the capillary lumen. One mechanism relates to net fluid movement at oppo- site ends of the capillary. Where pressure is abuot 35 mm Hg the hydrostatic pressure forces fluid and its contained electrolytes and nutrients out into the tissue space. The capillary wall is essentially impermeable to protein molecules, so the proteins continue to exert an osmotic force tending to at- tract fluid into the vessel. At the venous end of the capillary the filtration pressure has fallen to 15 mm Hg, considerably smaller than the osmotic pressure exerted by the proteins. Therefore net fluid movement is out of the capillary at one end and into the capillary at the other end, the rates tending nearly to balance each other. A second mechanism, which facilitates gas transfer, is the role of hemoglobin in transporting carbon dioxide. When hemoglobin enters the cap- illary and gives up part of its load of oxygen it becomes less acid, because oxyhemoglobin is more acid than reduced hemoglobin. This permits hem- oglobin to act as a buffer, to absorb some of the carbon dioxide which is higher in the tissue than in the blood. The Veins The venous system is the larger caliber, low resistance collecting system that connects the sys- temic capillary beds to the right side of the heart. About 50% of the total blood is at any time in the veins. Although veins are much thinner than arteries, they are elastic and they do contain smooth muscle. Consequently they are not just a passive collecting system; under nervous influence the overall tone of the system can increase, reduc- ing volume and temporarily increasing venous re- turn to the heart. This serves as a sort of “instant transfusion” to counter the effects of sudden loss of blood. The Lymphatics The lymphatics are a semi-independent sys- tem of thin-walled vessels that converge into trunks that empty into the large veins in the ab- domen or thorax. Lymphatic capillaries start in tissue spaces, where they pick up protein and excess fluid filtered from regular capillaries. They serve a specific transport function for fat drop- lets absorbed by cells of the intestinal mucosa. The lymphatic systems also plays a role in defense against infectious or noxious materials, since most lymphatic vessels have lymph nodes interposed between tissue spaces and the venous system. The Pulmonary Circulation The pulmonary circulation carries the same flow of blood as the systemic circulation but is otherwise quite different. The pulmonary vascu- lar pressures are in general much lower than sys- temic vascular pressures. Vasoconstriction and consequent local shunting are present in the pul- monary circulation, but much less developed than in the systemic circulation. Diseases of the pul- monary circulation are usually secondary to ex- tensive disease of pulmonary tissue, as in emphy- sema, fibrosis, and occupational lung diseases. Integration of Cardiovascular Function As with other biologic systems, the heart and blood vessels are under nervous and chemical control which tends to stabilize the internal envir- onment. One of the requirements for maintenance of adequate blood flow throughout the body is a sufficient head of arterial pressure. It is, therefore, not surprising to find that any stress tending to 57 lower arterial pressure (such as hemorrhage, loss of fluids from the body due to severe vomiting or diarrhea, traumatic shock, heat exhaustion) will trigger mechanisms designed to restore blood pres- sure. These include general arteriolar constriction (except cerebral and coronary arteries), increase in heart rate, and movement of fluid from extra- cellular space into the blood vessels. The inte- grated nature of cardiovascular responses to stress often makes it possible to use a simple measure- ment such as pulse rate to assess the degree of stress (more accurately the degree of response to stress). Thus pulse rate can be used to measure fairly reliably the intensity of exercise or heat stress (assuming given levels of physical fitness or acclimatization to heat). REGULATION OF WATER AND ELECTROLYTES As emphasized earlier, the proper functioning of cells in the mammalian body requires near- constancy of the internal environment — the tem- perature, oxygen supply, nutrient supply, hydrogen ion concentration, and appropriate concentrations of water, sodium, potassium, calcium, magnesium, and other substances. To some extent this con- stancy can be maintained by internal shifts of elements — from storage reservoirs, or by move- ment from one compartment to another, as might occur with movement from blood plasma to ex- tracellular fluid to intracellular fluid and the re- verse. The real problem is to maintain constancy under the usual conditions of variations of intake and output of a substance. This involves the con- cept of balance — how is output of water (or sodium, or calcium) controlled so that the “right” amount is retained when intake is varied? The balance for water, as an example, in- volves a daily intake of about 2.5 liters in a normal adult under average conditions: 1 liter from food, 0.3 L from metabolic conversions, and 1.2 L from drinking water or beverages. An equal amount is lost each day — by urination 1.5 L, by evaporation from lungs and skin 0.9 L, and the remainder by sweating or in feces. The major role in regulating body water, elec- trolytes and other substances is performed by the kidneys. These small organs, weighing less than 1% of total body weight,” receive nearly one- quarter of the output of the heart in serving this regulatory role. The kidney serves its unique function by a combination of three processes. Each microscopic unit of the kidney (or nephron) includes a capil- lary tuft (glomerulus) which filters plasma into a surrounding space (Bowman’s capsule), which is the beginning of a tubule. The tubule processes the glomerular filtrate in complex ways before joining other tubules which ultimately constitute the system for carrying urine to the exterior of the body. The glomerular filtrate contains all the com- ponents of plasma except proteins, which are gen- erally too large to pass through capillary walls and capsule membranes. The amount of filtrate is large — about 180 liters per day for both kid- neys — and if most of it were not reabsorbed the body would be in a precarious position in a matter of minutes. A simple calculation will show that the entire plasma volume passes through the glo- meruli some 60 times a day. Fortunately the “wanted” substances are reabsorbed to a high de- gree, if not totally. Ninety-nine percent of the water is reabsorbed by the tubules, together with 99.5% of the sodium and 100% of the glucose, compared to about 50% for urea, a waste prod- uct. The reabsorption involves both active and passive transport. Sodium is reabsorbed by an energy-consuming process which requires the presence of aldosterone, an adrenal cortical hor- mone. Water reabsorption to some extent follows sodium reabsorption, but is also very much in- fluenced by the anti-diuretic hormone produced in the hypothalamus. Glucose is actively reab- sorbed by a process which normally returns all the filtered glucose to peritubular capillaries, but the process can be overloaded if blood glucose is ele- vated above a certain limit. The excess of sugar filtered into the glomeruli then escapes into the urine, as is frequently the case in diabetes. The third renal mechanism is of particular im- portance in toxicology, because many foreign substances are eliminated in the urine by secre- tion from tubular cells. Like tubular reabsorption, tubular secretion involves both active and passive transport. Of the many substances secreted, only a few, such as hydrogen ion and potassium, are normally found in the body. How mechanisms evolved for transporting the large numbers of foreign substances is a mystery. Analysis of the balance of water and many ions, combined with study of the ways these sub- stances are handled by the kidney, shows that the concentrations of most of the ions which de- termine the properties of the extracellular fluid are regulated primarily by the kidneys. Thus the kid- neys are not “glorified garbage disposal” units for elimination of nitrogenous wastes so much as they are guardians of the minute to minute composition of all the body fluids and electrolytes. THE DIGESTIVE SYSTEM The function of this system is to accept raw materials in the form of food stuffs, minerals, vitamins and liquids in the external environment, to prepare such materials for absorption, and to absorb them into capillaries or lymphatics for distribution to the body. The system also has a limited role in excreting materials from the body. Since the digestive tract is largely a tube open at both ends, in a real sense the contents of the gastro-intestinal tract remain exterior to the body. In order to gain access to the body, ingested ma- terials must run a gamut of extreme acidity in the stomach and a series of enzymatic attacks starting in the mouth and extending to the large intestine. Some large molecules such as cellulose remain unaltered and are excreted in the feces. Other large molecules which could not otherwise pass through membranes are broken down into constit- uent amino acids or monosaccharides which are readily absorbed. Almost all digestion and absorption of food and water takes place in the small intestine. The 58 volume of fluid absorbed is far greater than that taken in as food and beverages. The latter aver- age about 800 gm of food and 1200 ml of water/ day in adults. To this is added 1.5 L of saliva in the mouth, about 2 L of acidic gastric secretions, 2 L of pancreatic and biliary secretions and 1.5 L of intestinal secretions; this adds up to about 8.5 L absorbed per day, with only 0.5 L passing into the large intestine. Most of the carbohydrate ingested is in the form of starch. The starch is split to disaccharides by the amylases from saliva and from the pan- creas. Further splitting into monosaccharides is brought about by enzymes in the small intestinal mucosa, after which the sugar molecules are ac- tively transported into the blood. Proteins are broken down first into peptides, then into free amino acids which are actively trans- ported across intestinal cells. In adults very little protein is absorbed as such, but in the newborn child proteolytic enzymes are absent; thus a new- born child can absorb protective antibodies from its mother’s milk. Most digestion of fat occurs in the small in- testine from the combined actions of pancreatic lipase and bile salts secreted by the liver. The lat- ter act primarily as emulsifying agents. Fatty acids are resynthesized to triglycerides in the intestinal cells, whence they are secreted into the lymphatics as small lipid droplets. The large intestine has relatively little capacity to absorb or secrete. Water and sodium continue to be absorbed from contents of the large intes- tine. The remaining contents are largely desqua- mated epithelial cells from the small intestine, bac- teria, and the indigestible residue of food. Con- trary to popular opinion, there is no absorption of toxic materials from unexpelled contents of the large intestine. REGULATION OF ENERGY BALANCE The energy released in the breakdown of or- ganic molecules in the body performs biologic work (muscle contraction, synthesis of new mole- cules, or active transport) or appears as heat in the cells. The biologic work done by skeletal muscles in moving external objects (or raising the body to a height by walking uphill) is considered external work. The internal work done by skeletal muscles, by heart muscle and by other tissues ap- pears ultimately as heat. Thus all energy utilized in the body is converted to heat, except during growth and during periods of net fat synthesis, when energy is being stored. The metabolic rate is the total energy ex- penditure, measured in kilocalories, per unit time. During fasting conditions, when there can be no net energy storage, the rate of metabolism can be measured either directly or indirectly. The direct method is simple in theory but difficult in practice — it consists of measurement of total heat produced per unit time when the individual is enclosed in a whole-body calorimeter. The easier method is to measure the rate of oxygen utilization, assuming that fats, carbohydrates, and proteins are being utilized in a constant ratio, and that the oxygen-heat equivalents are the same for the three classes of compounds. These assumptions are suf- ficiently accurate for most purposes, one liter of oxygen being required for the combustion of ap- proximately 4.8 kilocal. of fat, protein, or carbo- hydrates. The oxygen utilization of a healthy adult under standard conditions of rest, 12 hours fasting and a relaxing environment corresponds to a heat pro- duction of 40 kilocal. per hour per square meter of surface area — about equal to the heat pro- duction of a 100 watt light bulb. Metabolic rate is higher in the young than in adults and is lower in females than in males of equal weight. In late adulthood the resting metabolic rate declines, for reasons which are not clear. The ingestion of food increases metabolic rate by 10 to 20%, due to a specific action of protein and not due to in- creased activity of the digestive processes. The above factors influence the standard me- tabolic rate by amounts which are trivial compared to the effects of physical activity. Since hard physi- cal work can increase metabolic rate by about fifteen-fold it is most important that the average level of physical activity be considered in estimat- ing the energy requirements of the body. Two hormones also have a very significant effect on metabolic rate: epinephrine release, as occurs during emotional or physical stress, may cause a rapid increase of oxygen utilization by as much as 30% ; thyroxin administration, or release of the hormone from the thyroid, causes a slower but very prolonged increase of oxygen utilization which affects all cells of the body except those of the brain. Control of Food Intake Normal adults live for long periods with an essentially constant body weight. This must mean that food intake exactly balances the internal heat produced and the external work done. There is no net storage or loss of energy from fat sources. A number of theories have been developed to ex- plain this adjustment — the levels of blood sugar or fat storage affecting appetite centers in the hypothalamus, and other possibilities. The role of specific afferent inputs to the hypothalamic centers has not been well-defined. Clearly there are in- fluences from higher brain centers as well. One of the most intriguing relationships is that be- tween levels of physical activity and food intake. It is generally known that high levels of physical activity are accompanied by increased appetite and increased food intake to keep body weight constant. A few studies have suggested that this relationship does not hold below certain levels of activity that in a sense are “optimal”; below these levels an inverse relation holds — the more sed- entary an individual becomes the more likely he is to overeat. Obesity When the mechanisms which govern the bal- ance between energy intake and energy expendi- ture are malfunctioning, the most likely result is “overeating” and obesity. This is often called America’s No. 1 health problem because obesity is so prevalent and mortality rates are about 50% higher in the overweight than in those of standard 59 weight. If obesity, because of the obvious im- portance of social and economic factors in its etiology, is considered an environmental health problem, it must share with cigarette smoking a ranking as two of the most important environ- mental health problems in this country. As in many other diseases and conditions pre- disposing to disease, there are undoubtedly multi- ple factors in the etiology of obesity. Experimental obesity has been produced in rats by injuries to the hypothalamus. Obesity is associated with cer- tain endocrine disorders. There are undoubtedly many “constitutional” factors which influence the metabolism and storage of foodstuffs and which presumably make one person more “susceptible” to obesity than another. Ultimately, however, the defect is failure of food-intake control mechanisms to adjust to energy expenditure over a long enough period of time for obesity to develop. Often the predominant cause seems to be psychological or psycho-social. Regulation of Body Temperature With the evolution of mechanisms for main- tenance of a constant body temperature, the mam- mals and birds achieved freedom from the marked extremes of temperature that characterize the at- mosphere near the surface of the earth. The nearly constant temperature, around 90-103° F in mam- mals and around 108° in birds, greatly facilitates the action of enzymes in the chemical processes which go on continuously in cells. The body temperature is in fact variable over a substantial range — from about 96° F in early morning after sleep to as much as 104° (rectally) during heavy exercise. Such excesses of temper- ature quickly return to about 98° when exercise is over. In fever the temperature may be equally high or higher, but in this case the heat control mechanism (“thermostat”) is set at a higher level. Under extreme heat stress, the control mechanisms may fail and the temperature reach 107° or higher. At such temperature the brain is severely affected and death may ensue (heat stroke). The usually quoted body temperature of 97.6- 98.6° F is about the diurnal range of normal oral temperature. Deep body temperatures are a de- gree or so higher and skin temperatures are sev- eral degrees lower. The body temperature is a measure of the balance between heat gain (metabolism, incident radiation from warm bodies) and heat loss. With changes in heat gain or heat loss, adaptive changes take place to keep body temperature essentially constant. In cold exposure, heat gain could the- oretically be increased by secretion of epinephrine and thyroid hormone; this rarely if ever occurs. Heat gain is in fact increased by increases in skeletal muscle tone, involuntary shivering, and voluntary muscular activity. Heat loss is curtailed by vasoconstriction of blood vessels supplying the skin and by various behavioral adjustments such as changing body contours to reduce surface area, increasing insulation by use of clothing, and seek- ing shelter. More important environmental exposures in industry are heat stresses from excessive tempera- ture and humidity and from radiant heat load. These exposures, and the physiologic and behav- ioral responses thereto, will be considered in a separate chapter. DEFENSE MECHANISMS AGAINST INFECTION At least as important as physical and chemical factors in the environment are the hosts of micro- biologic agents in the environment. Two classes of microorganisms are of particular concern to man — the bacteria and viruses. Most bacteria are complete cells, capable of reproducing them- selves. The viruses, essentially nucleic acid cores in a protein coat, lack the enzyme machinery for energy production and the ribosomes necessary for protein synthesis. They can survive only in- side other cells, whose metabolic mechanisms they utilize. The first line of defense against microorganisms is the complex of anatomic and microchemical barriers provided by external and internal body surfaces. The skin, with its thick layers of cells and secretions, is almost impervious to microor- ganisms. The mucous membranes contain secre- tions which inhibit bacterial growth and they us- ually flow toward the exterior, as in the case of tracheobronchial mucus. When microorganisms gain access to the body, they may multiply and produce toxins, producing the signs and symptoms of an infection. The mechanisms for controlling growth or killing mi- croorganisms and for neutralizing toxins involve the formation of antibodies, the action of comple- ment, and the activities of phagocytic cells. These phenomena are interrelated. Most of the phagocytic cells are either in the blood stream (white blood cells) or are closely associated with the vascular and lymphatic sys- tems, including lining cells of bone marrow, liver, spleen and other lymphoid tissue. Despite the great importance of these cells, there is little knowledge of the mechanisms controlling their production. Most bacterial infections result in prompt increases of circulating granulocytic cells; viral infections tend to increase lymphocytes, but decrease other white blood cells. Antibodies are specialized plasma proteins capable of combining chemically with the specific antigens which induced their formation. Most antigens have molecular weights greater than 10,000; however, smaller molecules may act as antigens after attaching themselves to proteins of the host cells. The antigens involved in infection are usually bacterial toxins or proteins of the 60 microorganism’s surface. Components of almost any foreign cell can act as antigens. The plasma proteins known as complement are normally present in plasma and are not in- duced by antigens. The complement assists in killing bacteria, after an antibody has combined with its specific antigen in the wall of a bacterium. The complement apparently kills the bacterium after damaging the wall at the site of the antigen- antibody complex. Complement and antibodies also predispose bacteria to phagocytosis by phago- cytes in the vicinity. In addition to antibody formation and phago- cytosis, a third defense mechanism plays a signi- ficant role in resistance to viral infections. This is the formation of the protein interferon in re- sponse to a viral infection of a particular cell. Unlike antibodies, interferon is not specific; all viruses stimulate production of the same inter- feron, and interferon inhibits the growth and mul- tiplication of many different viruses. At present there is no way of using this information to im- prove treatment of virus infection. Allergy Allergy is an acquired hypersensitivity to a particular substance — an antigen-antibody re- action that results in cell damage. The term is usually reserved for the response to nonmicrobial antigens. The addition of complement to the anti- gen-antibody complex probably triggers cell dam- age and inflammatory response. The puzzling fea- ture is why the response is so inappropriate to the antigen stimulus. Symptoms are often localized to the surface exposed, for example the respiratory response to aero-allergens such as ragweed pollen. Generalized allergic responses may also occur with widespread liberation of histamine to produce hives, extensive skin eruption, bronchospasm, rapid heart rate and hypotension. In extreme ex- amples, death can occur, as for example, from the sting of a single bee. Preferred Reading 1. C. H. BEST AND N. B. TAYLOR, The Physiolog- ical Basis of Medical Practice, The Williams and Wilkins Co., 1966. GUYTON, A. C., Texthook of Medical Physiology, W. B. Saunders Co., 1971. 3. ARTHUR J. VANDER, JAMES H. SHERMAN, DOROTHY S. LUCIANO, Human Physiology: The Mechanism of Body Function, McGraw-Hill Book Company, 1970. ABRAHAM WHITE, P. HANDLER, and E. SMITH, Principles of Biochemistry, McGraw-Hill Book Co., 1968. 5. WRIGHT, SAMSON, Applied Physiology, Oxford University Press, 1965. CHAPTER 7 INDUSTRIAL TOXICOLOGY Mary O. Amdur, Ph.D. INTRODUCTION Toxicology is the study of the nature and action of poisons. The term is derived from a Greek word referring to the poison in which ar- rows were dipped. Mythology, legend and history indicate the growth of toxicological knowledge. The early emphasis was on ways to poison people. The 19th century saw the development of tests for identification of various poisons, such as the Marsh test for arsenic. These found use in legal medicine and criminology, the area known as forensic toxi- cology. Since about 1900, there has been increas- ing social concern for the health of workers ex- posed to a diversity of chemicals. “This has led to intensive investigations of the toxicity of these materials in order that proper precautions may be taken in their use. This is the area of industrial toxicology which concerns us here. Some industrial hazards have been known for centuries. For example, clinical symptoms of lead poisoning were accurately described in the 1st century A.D. The Romans used only slave labor in the great Spanish mercury mines at Almaden, and a sentence to work there was. considered equivalent to a sentence of death. French hatters of the 17th century discovered that mercuric ni- trate aided greatly in the felting of fur. Such use led to chronic mercury poisoning so widespread among members of that trade that the expression “mad as a hatter” entered our folk language. Ex- posure to other hazardous substances is an out- growth of modern technology. In addition to newly developed chemicals, many materials first synthe- sized in the late 19th century have found wide- spread industrial use. The hydrides of boron, for example, have been known since 1879, but the first report on their toxicity appeared in 1951 as a series of case histories of people, mostly young chemical engineers, who had been exposed to boron hydrides in the course of their work. Toxicological research now has its place in assessing the safety of new chemicals prior to the extension of their use beyond exploratory stages. Information on the qualitative and quantitative actions of a chemical in the body can be used to predict tentative safe levels of exposure as well as to predict the signs and symptoms to be watched for as indicative of excessive exposure. An eluci- dation of the mechanism of action of the chemical can hopefully lead to rational rather than sympto- matic therapy in the event of damage from exces- sive exposure. Both in the application of newer refined research techniques of toxicology and in his communication of knowledge vital to the public health, the toxicologist considers old as well as new 61 hazardous substances. This point was well made by Henry Smyth! who said “Most people are care- ful in handling a new chemical whether or not they have been warned specifically of its possible toxicity. Despite the potential hazards of hun- dreds of new chemicals each year, most injuries from chemicals are due to those which have been familiar for a generation or more. It is important for the perspective of the toxicologist that he keep this fact well to the forefront of his mind. He must not neglect talking about the hazards of the old standbys, lead, benzene and chlorinated hydro- carbons just because this week he discovered the horrifying action of something brand new. Part of his responsibility is a continuing program of com- munication aimed at informing everyone of the means required to handle safely any chemical whatsoever.” DISCIPLINES INVOLVED IN INDUSTRIAL TOXICOLOGY In order to assess the potential hazard of a substance to the health of workers industrial toxi- cology draws perforce on the expertise of many disciplines. Chemistry: The chemical properties of a com- pound can often be one of the main factors in its toxicity. The vapor pressure indicates whether or not a given substance has the potential to pose a hazard from inhalation. The solubility of a sub- stance in aqueous and lipid media is a guiding factor in determining the rate of uptake and ex- cretion of inhaled substances. The toxicologist needs to determine the concentration of toxic agents in air and in body organs and fluids. It is important to know if a substance is, for example, taken up by the liver, stored in the bones, or rap- idly excreted. For this, analytical methods are needed which are both sensitive and specific. Biochemistry: The toxicologist needs knowledge of the pathways of metabolism of foreign com- pounds in the body. Such information can serve as the basis for monitoring the exposure of work- men, as for example the assessment of benzene exposure by the analysis of phenol in the urine. Differences in metabolic pathways among animal species form one basis for selective toxicity. Such knowledge is useful, for example, in developing compounds that will be maximally toxic to insects and minimally so to other species. Such knowl- edge can also serve as a guide in the choice of a species of experimental animal with a metabolic pathway similar to that of man for studies which will be extrapolated to predict safe levels for human exposure. Rational therapy for injury from toxic chemicals has as its basis an understanding of the biochemical lesion they produce. One out- standing example is the development of B.A.L. (British Anti-Lewisite, 1,2-dimercaptopropanol) which arose from studies of the inhibition of sulf- hydryl enzymes and the manner of binding of arsenic to these enzymes. This led to the use of B.A.L. in therapy for industrial poisons (such as mercury) which interfere with sulfhydryl enzymes. Studies of the nature of the reaction of organic phosphorus esters with the enzyme acetylcholine esterase led to the development of 2-PAM (2- pyridine aldoxime methiodide) which reverses the inhibition of the enzyme. In conjunction with atropine, 2-PAM provides rational therapy for treatment of poisoning by these compounds. In the important area of joint toxic action, under- standing comes from elucidation of biochemical action. If, for example, Compound A induces enzymes which serve to detoxify Compound B, the response to the combination may be less than additive. On the other hand, if Compound A should act to inhibit the enzyme that serves to detoxify Compound B then the response may be more than additive. Physiology: The toxicologist obviously needs to know something of the normal functioning of organ systems. Modern toxicology is moving more and more towards the search for means to detect reversible physiological changes produced by concentrations of toxic substances too low to produce irreversible histological damage or death in experimental animals. Measurement of in- creases in pulmonary flow-resistance has proved a sensitive tool for assessing the response to irri- tant gases and aerosols. Tests of pulmonary func- tion can be used to assess response of workmen to industrial environments. Renal clearance and other kidney function tests can serve to detect renal damage. The effects of exercise or non- specific stress on the degree of response to toxic chemicals is another important research area in modern toxicology. Pathology: The toxicologist is concerned with gross and histological damage caused by toxic substances. Most toxicological studies include a thorough pathological examination which may in- clude examination of subcellular structure by electron microscopy. Immunology and Immunochemistry: It is recog- nized that immunology and immunochemistry con- stitute an important area for investigation in in- dustrial toxicology. The response to many chem- icals, especially inhaled products of biologic origin, has as its basis the immune reaction. Physics and Engineering: The toxicologist who is concerned with inhalation as the route of exposure needs some knowledge of physics and engineering in order to establish controlled concentrations of the substances he studies. If the toxic materials are to be administered as airborne particles, knowl- edge is needed of methods of generation of aero- sols and methods of sampling and sizing appro- priate to the material studied. Without careful attention to these factors, toxicological studies are of limited value. An understanding of the factors 62 governing penetration, deposition, retention and clearance of particulate material from the respira- tory tract requires knowledge of both the physical laws governing aerosol behavior and the anatomy and physiology of the respiratory tract. The grow- ing interest in prolonged exposure to closed at- mospheres encountered in manned space travel or deep sea exploration has led to experimental studies involving round-the-clock exposures of experimental animals for long periods. Such stud- ies raise additional engineering problems above and beyond those of maintaining the more con- ventional exposure chambers, Statistics: Statistics are used in the analysis of data and in the establishing of an experimental design that will yield the maximum of desired information with the minimum of wasted effort. The toxicologist relies heavily on statistics, as the calculation of the LD,, (Lethal Dose — 50% probable) is a statistical calculation. Experi- mental studies of joint toxicity are planned in accord with established statistical designs. Communication: The ultimate aim of the toxi- cologist is (or should be) the prevention of dam- age to man and the environment by toxic agents. One important function is the distribution of in- formation in such terms that the people in need of the information will understand it. The toxicologist’s responsibility does not end with the publication of his research results in a scientific journal for the erudition of his peers. He is called upon to make value judgments in extrapolation of his findings in order to advise governmental agen- cies and others faced with the problem of setting safe levels, be they air pollution standards or Threshold Limit Values for industrial exposure or tolerance levels of pesticide residues in food. In addition to this, when he makes such value judg- ments, he should above all be honest with himself and with those he advises, that they are value judgments and as such should be subject to fre- quent review as new knowledge and experience accumulate. DOSE-RESPONSE RELATIONSHIPS Experimental toxicology is in essence biolog- ical assay with the concept of a dose-response relationship as its unifying theme. The potential toxicity (harmful action) inherent in a substance is manifest only when that substance comes in contact with a living biological system. A chem- ical normally thought of as “harmless” will evoke a toxic response if added to a biological system in sufficient amount. For example, the inadvertent inclusion of large amounts of sodium chloride in feeding formulae in a hospital nursery led to infant mortality. Conversely, for a chemical normally thought of as “toxic” there is a minimal concen- tration which will produce no toxic effect if added to a biological system. The toxic potency of a chemical is thus ultimately defined by the relation- ship between the dose (the amount) of the chem- ical and the response that is produced in a bio- logical system. In preliminary toxicity testing, death of the animals is the response most commonly chosen. Given a compound with no known toxicity data, the initial step is one of range finding. A dose is administered and, depending on the outcome, is increased or decreased until a critical range is found over which, at the upper end, all animals die and, at the lower end, all animals survive. Between these extremes is the range in which the toxicologist accumulates data which enable him to prepare a dose-response curve relating percent mortality to dose administered. From the dose-response curve, the dose that will produce death in 50 percent of the animals may be calculated. This value is commonly ab- breviated as LD,,. It is a statistically obtained value representing the best estimation that can be made from the experimental data at hand. The LD,, value should always be accompanied by a statement of the error of the estimated value, such as the probability range or confidence limits. The dose is expressed as amount per unit of body weight. The value should be accompanied by an indication of the species of experimental animal used, the route of administration of the compound, the vehicle used to dissolve or suspend the ma- terial if applicable, and the time period over which the animals were observed. For example, a publication might state “For rats, the 24 hr. ip LD,, for “X” in corn oil was 66 mg/kg (95% confidence limits 59-74).” This would indicate to the reader that the material was given to rats as an intraperitoneal injection of compound X dis- solved or suspended in corn oil and that the in- vestigator had limited his mortality count to 24 hours after administering the compound. If the experiment has involved inhalation as the route of exposure, the dose to the animals is expressed as parts per million, mg/m? or some other ap- propriate expression of concentration of the ma- terial in the air of the exposure chamber, and the length of exposure time is specified. In this case the term LC,, is used to designate the concentra- tion in air that may be expected to kill 50 percent of the animals exposed for the specified length of time. Various procedures have been recommended for the estimation of the LD,, or LC,,. For in- formation on the more commonly used techniques, papers such as those of Bliss,> Miller and Tainter,? Litchfield and Wilcoxon* or Weil® may be con- sulted. The simple determination of the LD, for an unknown compound provides an initial compara- tive index for the location of the compound in the overall spectrum of toxic potency. Table 7-1 shows an attempt at utilizing LD,, and LC,, val- ues to set up an approximate classification of toxic substances which was suggested by Hodge and Sterner.® Over and above the specific LD,, value, the slope of the dose-response curve provides useful information. It suggests an index of the margin of safety, that is the magnitude of the range of doses involved in going from a non-effective dose to a lethal dose. It is obvious that if the dose- response curve is very steep, this margin of safety is slight. Another situation may arise in which one compound would be rated as “more toxic” than a second compound if the LD,, values alone were compared but the reverse assessment of rel- 63 ative toxicity would be reached if the comparison was made of the LD, values for the two com- pounds because the dose-response curve for the second compound had a more gradual slope. It should thus be apparent that the slope of the dose- response curves may be of considerable signifi- cance with respect to establishing relative tox- icities of compounds. For an excellent non-math- ematical discussion of the underlying concepts of dose-response relationships, Chapter 2 of Loomis’ is well worth reading. TABLE 7-1 Toxicity Classes LD:-Wt/kg 4 hr Inhalation Toxicity Descriptive Single oral dose LCs — PPM Rating Term Rats Rats 1 Extremely toxic I mgorless <10 2 Highly toxic 1-50 mg 10-100 3 Moderately toxic 50-500 mg 100-1,000 4 Slightly toxic 0.5-5 g 1,000-10,000 5 Practically non-toxic 5-15 ¢g 10,000-100,000 6 Relatively harmless 15 g or more >100,000 By similar experiments dose-response curves may be obtained using a criterion other than mor- tality as the response and an ED,, value is ob- tained. This is the dose which produced the chosen response in 50 percent of the treated ani- mals. When the study of a toxic substance pro- gresses to the point at which its action on the organism may be studied as graded response in groups of animals, dose-response curves of a slightly different sort are generally used. One might see for example, a dose-response curve relating the degree of depression of brain choline esterase to the dose of an organic phosphorus ester or a dose-response curve relating the in- crease in pulmonary flow-resistance to the con- centration of sulfur dioxide inhaled. ROUTES OF EXPOSURE Toxic chemicals can enter the body by vari- ous routes. The most important route of exposure in industry is inhalation. Next in importance is contact with skin and eyes. The response to a given dose of toxic agent may vary markedly de- pending on the route of entry. A cardinal princi- ple to remember is that the intensity of toxic ac- tion is a function of the concentration of the toxic agent which reaches the site of action. The route of exposure can obviously have an influence upon the concentration reaching the site of action. Parenteral: Aside from the obvious use in admin- istration of drugs, injection is considered mainly as a route of exposure of experimental animals. In the case of injection, the dose administered is known with accuracy. Intravenous (iv) injection introduces the material directly into the circula- tion, hence comparison of the degree of response to iv injection with the response to the dose ad- ministered by another route can provide informa- tion on the rate of uptake of the material by the alternate route. When a material is administered by injection, the highest concentration of the toxic material in the body occurs at the time of en- trance. The organism receives the initial impact at the maximal concentration without opportunity for a gradual reaction, whereas if the concentra- tion is built up more gradually by some other route of exposure, the organism may have time to develop some resistance or physiological ad- justment which could produce a modified re- sponse. In experimental studies intraperitoneal (ip) injection of the material into the abdominal fluid is a frequently used technique. The major venous blood circulation from the abdominal con- tents proceeds via the portal circulation to the liver. A material administered by ip injection is subject to the special metabolic transformation mechanisms of the liver, as well as the possi- bility of excretion via the bile before it reaches the general circulation. If the LD,, of a com- pound given by ip injection was much higher (i.e., the toxicity is lower) than the LD,, by iv injec- tion, this fact would suggest that the material was being detoxified by the liver or that the bile was a major route of excretion of the material. If the values for LD,, were very similar for ip and iv injection, it would suggest that neither of these factors played a major role in the handling of that particular compound by that particular spe- cies of animal. Oral: Ingestion occurs as a route of exposure of workmen through eating or smoking with con- taminated hands or in contaminated work areas. Ingestion of inhaled material also occurs. One mechanism for the clearance of particles from the respiratory tract is the carrying up of the particles by the action of the ciliated lining of the respira- tory tract. These particles are then swallowed and absorption of the material may occur from the gastro-intestinal tract. This situation is most likely to occur with larger size particles (2. and up )although smaller particles deposited in the alveoli may be carried by phagocytes to the up- ward moving mucous carpet and eventually be swallowed. In experimental work, compounds may be ad- ministered orally as either a single or multiple dose given by stomach tube or the material may be incorporated in the diet or drinking water for periods varying from several weeks or months up to several years or the lifetime of the animals. In either case, the dose the animals actually receive may be ascertained with considerable accuracy. Except in the case of a substance which has a corrosive action or in some way damages the lin- ing of the gastro-intestinal tract, the response to a substance administered orally will depend upon how readily it is absorbed from the gut. Uranium, for example, is capable of producing kidney dam- age, but is poorly absorbed from the gut and so oral administration produces only low concentra- tions at the site of action. On the other hand, ethyl alcohol, which has as a target organ the central nervous system, is very rapidly absorbed and within an hour 90 percent of an ingested dose has been absorbed. The epithelium of the gastro-intestinal tract is poorly permeable to the ionized form of or- 64 ganic compounds. Absorption of such materials generally occurs by diffusion of the lipid-soluble non-ionized form. Weak acids which are pre- dominately nonionized in the high acidity (pH 1.4) of gastric juice are absorbed from the stom- ach. The surface of the intestinal mucosa has a pH of 5.3. At this higher pH weak bases are less ionized and more readily absorbed. The pK of a compound (see Chapter 5) thus becomes an im- portant factor in predicting absorption from the gastro-intestinal tract. Inhalation: Inhalation exposures are of prime im- portance to the industrial toxicologist. The dose actually received and retained by the animals is not known with the same accuracy as when a com- pound is given by the routes previously discussed. This depends upon the ventilation rate of the indi- vidual. In the case of a gas, it is influenced by solubility and in the case of an aerosol by par- ticle size. The factors that influence the dose of a substance retained in an inhalation exposure will be discussed later. For the moment, suffice it to say that the concentration and time of ex- posure can be measured accurately and this gives a working estimate of the exposure. Two tech- niques are sometimes utilized in an attempt to determine the dose with precision and still admin- ister the compound via the lung. One is intra- tracheal injection which may be used in some ex- periments in which it is desirable to deliver a known amount of particulate material into the lung. The other is so called “precision gassing.” In this technique the animal or experimental sub- ject breathes through a valve system and the vol- ume of exhaled air and the concentration of toxic material in it are determined. A comparison of these data with the concentration in the atmos- phere of the exposure chamber gives an indica- tion of the dose retained. Cutaneous: Cutaneous exposure ranks first in the production of occupational disease, but not neces- sarily first in severity. The skin and its associated film of lipids and sweat may act as an effective barrier. The chemical may react with the skin surface and cause primary irritation. The agent may penetrate the skin and cause sensitization to repeated exposure. The material may penetrate the skin in an amount sufficient to cause systemic poisoning. In assessing the toxicity of a compound by skin application, a known amount of the ma- terial to be studied is placed on the clipped skin of the animal and held in place with a rubber cuff. Some materials such as acids, alkalis and many organic solvents are primary skin irritants and pro- duce skin damage on initial contact. Other ma- terials are sensitizing agents. The initial contact produces no irritant response, but may render the individual sensitive and dermatitis results from future contact. Ethyleneamines and the catechols in the well known members of the Rhus family (poison ivy and poison oak) are examples of such agents. Chapter 34 is devoted to the damaging effects of industrial chemicals on the skin. The physiochemical properties of a material are the main determinant of whether or not a material will be absorbed through the skin. Among the important factors are pH, extent of ionization, water and lipid solubility and molecular size. Some compounds such as phenol and phenolic deriva- tives can readily penetrate the skin in amounts sufficient to produce systemic intoxication. If the skin is damaged, the normal protective barrier to absorption of chemicals is lessened and penetra- tion may occur. An example of this is a descrip- tion of cases of mild lead intoxication that oc- curred in an operation which involved an inor- ganic lead salt and also a cutting oil. Inorganic lead salts would not be absorbed through intact skin, but the dermatitis produced by the cutting oil permitted increased absorption. Ocular: The assessment of possible damage result- ing from the exposure of the eyes to toxic chemi- cals should also be considered. The effects of acci- dental contamination of the eye can vary from minor irritation to complete loss of vision. In ad- dition to the accidental splashing of substances into the eyes, some mists, vapors and gases pro- duce varying degrees of eye irritation, either acute or chronic. In some instances a chemical which does no damage to the eye can be absorbed in sufficient amount to cause systemic poisoning. The extreme toxicity of fluoroacetate was discovered accidentally in this manner by a group of Polish chemists who tested it for lachrymatory action in a rabbit. They had hoped that fluoroacetate would be as irritating to the eyes as iodoacetic acid. The latter had proved unsuitable for warfare purposes because of the purple cloud of iodine vapor that betrayed its presence when it was exploded in a bomb. Their rabbit showed no signs of eye irrita- tion, but alerted their interest when it had con- vulsions and died. An excellent reference on ocu- lar effects of toxic chemicals is “Toxicology of the Eye” by Grant.® CRITERIA OF RESPONSE After the toxic material has been administered by one of the routes of exposure discussed above, there are various criteria the toxicologist uses to evaluate the response. In modern toxicological research, these criteria are oriented whenever pos- sible towards elucidating the mechanisms of ac- tion of the material. Mortality: As has been indicated, the LD,, of a substance serves as an initial test to place the compound appropriately in the spectrum of toxic agents. Mortality is also a criterion of response in long term chronic studies. In such studies, the investigator must be certain that the mortality ob- served was due to the chronic low level of the ma- terial he is studying; hence an adequate control group of untreated animals subject to otherwise identical conditions is maintained for the duration of the experiment. Pathology: By examination of both gross and microscopic pathology of the organs of animals exposed, it is possible to get an idea of the site of action of the toxic agent, the mode of action and the cause of death. Pathological changes are usually observed at dose levels which are below those needed to produce the death of animals. The liver and the kidney are organs particularly sensi- tive to the action of a variety of toxic agents. In some instances the pathological lesion is typical 65 of the specific toxic agents, for example, the sili- cotic nodules in the lungs produced by inhalation of free silica or the pattern of liver damage re- sulting from exposure to carbon tetrachloride and some other hepatotoxins. In other cases the dam- age may be more diffuse and less specific in nature. Growth: In chronic studies the effect of the toxic agent on the growth rate of the animals is another criterion of response. Levels of the compound which do not produce death or overt pathology may result in a diminished rate of growth. A record is also made of the food intake. This will indicate whether diminished growth results from lessened food intake or from less efficient use of food ingested. It sometimes happens that when an agent is administered by incorporation into the diet, especially at high levels, the food is unpalat- able to the animals and they simply refuse to eat it. Organ Weight. The weight of various organs, or more specifically the ratio of organ weight to body weight may be used as a criterion of re- sponse. In some instances such alterations are specific and explicable, as for example the increase of lung weight to body weight ratio as a measure of the edema produced by irritants such as ozone or oxides of nitrogen. In other instances the in- crease is a less specific general hypertrophy of the organ, especially of the liver and kidney. In a summary of data from two major industrial tox- icology laboratories where a wide variety of com- pounds had been screened for toxicity,’ it was pointed out that in using body growth, liver weight and kidney weight as criteria of response, a change in one or more of these was observed at the lowest dose at which any effect was seen in 80 percent of 364 studies. If liver and kidney pathology were included in the list, then a change in one or more criteria was observed at the lowest dose at which any effect was seen in 96 percent of these studies. The other 4 percent included materials with very specific action such as the organophosphorus in- secticides which will produce alterations in acetyl- choline esterase at very low levels. Such non- specific increases in organ weight are difficult to interpret and may not of necessity represent a harmful] change, but they lower the threshold at which a dose may be termed “no effect.” Physiological Function Tests: Physiological func- tion tests are useful criteria of response both in experimental studies and in assessing the response of exposed workmen. They can be especially use- ful in chronic studies in that they do not necessi- tate the killing of the animal and can, if desired, be done at regular intervals throughout the period of study. Tests in common clinical use such as bromsulphalein retention, thymol turbidity, or serum alkaline phosphatase may be used to assess the effect of an agent on liver function. The ex- amination of the renal clearance of various sub- stances helps give an indication of localization of kidney damage. The ability of the kidney (especi- ally in the rat) to produce a concentrated urine may be measured by the osmolality of the urine produced. This has been suggested for the evalua- tion of alterations in kidney function.® Alterations may be detected following inhalation of materials such as chlorotrifluoroethylene at levels of reversi- ble response. In some instances measurement of blood pressure has proved a sensitive means of evaluating response.’ Various tests of pulmonary function have been used to evaluate the response of both experimental animals and exposed work- men. These tests include relatively simple tests which are suitable for use in field surveys as well as more complex methods possible only under laboratory conditions. Simple tests include such measurements as peak expiratory flowrate (PEFR), forced vital capacity (FVC), and 1- second forced expiratory volume (FEV, ,). More complex procedures include the measurement of pulmonary mechanics (flow-resistance and com- pliance) and their application in epidemiologic surveys. Information on the effects of various agents on the lungs is discussed in Chapter 33. Biochemical Studies: The study of biochemical response to toxic agents leads in many instances to an understanding of the mechanism of action. Tests of toxicity developed in animals should be oriented to determination of early response from exposures that are applicable to the industrial scene. Many toxic agents act by inhibiting the action of specific enzymes. This action may be studied in vitro and in vivo. In the first case, the toxic agent is added to tissue slices or tissue homo- genate from normal animals and the degree of in- hibition of enzymatic activity is measured by an appropriate technique. In the second case, the toxic agent is administered to the animals; after the desired interval the animals are killed and the degree of enzyme inhibition is measured in the appropriate tissues. A judicious combination of in vivo and in vitro studies is especially useful when biotransformation to a toxic compound is involved. The classic example of this is the work of Peters '* on the toxicity of fluoroacetate. This material, which was extremely toxic when admin- istered to animals of various species, did not in- hibit any known enzymes in vitro. Peters’ work demonstrated that fluoroacetate entered the car- boxylic acid cycle of metabolism as if it were acetic acid. The product formed was fluorocitrate which was a potent inhibitor of the enzyme aconi- tase. Biological conversion in the living animal had resulted in the formation of a highly toxic compound. He coined the term “lethal synthesis” to describe such a transformation. An elegant paper by Cremer'® on the ethyl lead compounds is worth discussing as an example of research tech- niques in this area. She injected rats with tetra-, tri-, and di-ethyl lead and with lead acetate. Symp- toms of excitability, tremors and convulsions were observed in the animals injected with the tetra- ethyl and triethyl lead but not in the animals in- jected with diethyl lead or the inorganic lead. The triethyl lead was more potent than the tetraethyl lead, which suggested that perhaps the toxic re- sponse resulted from biologically formed triethyl lead. By analytic methods, she was able to dem- onstrate the presence of triethyl lead in the tissues of animals poisoned with tetraethyl lead. She found in vitro that liver preparations were capable of converting tetraethyl lead to triethyl lead. She measured the metabolism of brain slices from ani- mals treated in vivo and found that the oxygen 66 consumption was lowered in animals receiving tetraethyl or triethyl lead but not in animals treated with diethyl lead or lead acetate. Turning again to in vitro experiments, she measured the oxygen consumption of brain cortex slices from normal animals to which the ethyl lead compounds were added. These experiments showed that tetraethyl lead is without effect and that triethyl lead is the active component. The fundamentals of the metabolism of toxic compounds are discussed in Chapter 5. The clas- sic reference in the field is Detoxification Mecha- nisms by Williams.** The term “biotransformation” is in many ways preferable to “detoxication” for in many instances the toxic moiety may be the metabolic product rather than the compound ad- ministered. There are some instances, of course, such as the conversion of cyanide to thiocyanate, which are truly “detoxication” in the strict sense. Tests for the level of metabolites of toxic agents in the urine have found wide use in indus- trial toxicology as a means of evaluating exposure of workmen. These are commonly referred to as biologic threshold limits which serve as biologic counterparts to the TLV’s. The presence of the metabolic product does not of necessity imply poisoning; indeed the opposite is more commonly the case. Normal values have been established and an increase above these levels indicates that exposure has occurred and thus provides a val- uable screening mechanism for the prevention of injury from continued or excessive exposure. Ta- ble 7-2 lists some of these metabolic products which have been used to evaluate exposure as well as the agents for which they may be used. TABLE 7-2 Metabolic Products Useful As Indices Of Exposure Product in Toxic Urine Agents Organic Sulfate Benzene Phenol Aniline Hippuric Acid Toluene Ethyl benzene Thiocyanate Cyanate Nitriles Glucuronates Phenol Benzene Terpenes Formic Acid Methyl alcohol 2, 6, dinitro-4- TNT amino toluene p-nitrophenol Parathion p-aminophenol Aniline There are other instances in which a biochem- ical alteration produced by the toxic agent is useful as a criterion of evaluating exposure. Lead, for ex- ample, interferes in porphyrin metabolism and in- creased levels of delta-aminolevulinic acid may be detected in the urine following lead exposure. Levels of plasma choline esterase may be used to evaluate exposure to organic phosphorus insec- ticides. Levels of carboxyhemoglobin provide a means of assessing exposure to carbon monoxide. Levels of methemoglobin can be used to evaluate exposure to nitrobenzene or aniline. Hemolysis of red cells is observed in exposure to arsine. Analysis of blood, urine, hair, or nails for various metals is also used to evaluate exposure, though whether these would be termed “biochemical tests” depends somewhat on whether you are speaking with an engineer or a biochemist. The use of biologic threshold limit values pro- vides a valuable adjunct to the TLV’s which are based on air analysis. The analysis of blood, urine, hair, or exhaled air for a toxic material per se (e.g., Pb, As) or for a metabolite of the toxic agent (e.g., thiocyanate, phenol) gives an indication of the exposure of an individual worker. These tests represent a very practical application of data from experimental toxicology. Research in industrial toxicology is often oriented towards the search for a test suitable for use as a biologic threshold which will indicate exposure at a level below which damage occurs. Behavioral Studies: When any toxic agent is ad- ministered to experimental animals, the experi- enced investigator is alert for any signs of abnor- mal behavior. Such things as altered gait, bizarre positions, aggressive behavior, increased or de- creased activity, tremors or convulsions can sug- gest possible sites of action or mechanisms of action. The ability of an animal to maintain its balance on a rolling bar is a frequently used test of coordination. The loss of learned conditioned reflexes has also been used and by judicious com- bination of these tests it is possible to determine, for example, that the neurological response to methyl cellosolve differs from the response to ethyl alcohol.’ Ability to solve problems or make perceptual distinctions has been used on human subjects, especially in an effort to determine the possible effects of low levels of carbon monoxide and other agents which might be expected to in- terfere with efficient performance of necessary tasks, thus creating a subtle hazard. Effects on neurological variables such as dark adaptation of the eye are much used by Russian investigators in determining threshold limit values. Reproductive Effects: It is possible that a level of a toxic material can have an effect on either male or female animals which will result in decreased fertility. In fertility studies the chemical is given to males and females in daily doses for the full cycle of oogenesis and spermatogenesis prior to mating. If gestation is established, the fetuses are removed by caesarean section one day prior to delivery. The litter size and viability are com- pared with untreated groups. The young are then studied to determine possible effects on survival, growth rate and maturation. The tests may be repeated through a second and third litter of the treated animals. If it is considered necessary the test may be extended through the second and third generation. Teratogenic Effects: Chemicals administered to the pregnant animal may, under certain conditions, produce malformations of the fetus without induc- ing damage to the mother or killing the fetus. The experience with the birth of many infants with limb anomalies resulting from the use of thalido- mide by the mothers during pregnancy alerted the toxicologists to the need for more rigid testing in 67 this difficult area. Another example of human ex- perience in recent times was the teratogenic effect of methyl mercury as demonstrated in the inci- dents of poisoning in Minamata Bay, Japan. The study of the teratogenic potential poses a very complex toxicological problem. The susceptibility of various species of animal varies greatly in the area of teratogenic effects. The timing of the dose is very critical as a chemical may produce severe malformations of one sort if it reaches the embryo at one period of development and either no mal- formations or malformations of a completely dif- ferent character if it is administered at a later or earlier period of embryogenesis. For a discussion of a recommended method of teratogenic testing and a summary of the literature in this area, the paper by Cahen'® may be consulted. Carcinogenicity: The study of the carcinogenic effects of a toxic chemical is a complex experi- mental problem. Such testing involves the use of sizeable groups of animals observed over a period of two years in rats or four to five years in dogs because of the long latent period required for the development of cancer. Efforts to shorten the time lag have led to the use of aging animals. This may reduce the lag period one third to one fourth. Various strains of inbred mice or hamsters are frequently used in such experiments. Quite frequently materials are screened by painting on the skin of experimental animals, especially mice. Industrial experience down through the years has made plain the hazard of cancer from exposure to various chemicals. Among these are many of the polynuclear hydrocarbons, beta-naphylamine which produces bladder cancer, chromates and nickel carbonyl which produce lung cancer. An excellent summary of recent experimental work in the area of the production of lung cancer in experi- mental animals is given by Kuschner.! The FDA Advisory Committee on Protocols for Safety Evaluation Panel on Carcinogenesis has recently published in the literature their Report on Cancer Testing in the Safety Evaluation of Food Additives and Pesticides.’* The particular emphasis is on testing materials which would come into contact with man principally through the diet, either as food additives or as contaminating resi- dues on food products as in the case of pesticides; however, many fundamental points pertinent to the overall area of experimental testing for carcin- ogenesis by the toxicologist are raised and thoughtfully discussed. This reference is highly recommended reading. For ubiquitous substances air quality standards must consider contributions from all sources, food and beverages, water, am- bient air, and smoking, as well as those from the industrial environment, e.g., asbestos and lead. FACTORS INFLUENCING INTENSITY OF TOXIC ACTION Rate of Entry and Route of Exposure: The de- gree to which a biological system responds to the action of a toxic agent is in many cases markedly influenced by the rate and route of exposure. It has already been indicated that when a substance is administered as an iv injection, the material has maximum opportunity to be carried by the blood stream throughout the body, whereas other routes of exposure interpose a barrier to distribution of the material. The effectiveness of this barrier will govern the intensity of toxic action of a given amount of toxic agent administered by various routes. Lead, for example, is toxic both by in- gestion and by inh-lation. An equivalent dose, however, is more readily absorbed from the res- piratory tract than from the gastro-intestinal tract and hence produces a greater response. There is frequently a difference in intensity of response and sometimes a difference even in the nature of the response between the acute and chronic toxicity of a material. If a material is taken into the body at a rate sufficiently slow that the rate of excretion and/or detoxification keeps pace with the intake, it is possible that no toxic response will result even though the same total amount of material taken in at a faster rate would result in a concentration of the agent at the site of action sufficient to produce a toxic response. Information of this sort enters into the concept of a threshold limit for safe exposure. Hydrogen sulfide is a good example of a substance which is rapidly lethal at high concentrations as evidenced by the many accidental deaths it has caused. It has an acute action on the nervous system with rapid production of respiratory paralysis unless the vic- tim is promptly removed to fresh air and re- vived with appropriate artificial respiration. On the other hand, hydrogen sulfide is rapidly oxi- dized in the plasma to non-toxic substances and many times the lethal dose produces relatively lit- tle effect if administered slowly. Benzene is a good example of a material which differs in the nature of response depending on whether the ex- posure is an acute one to a high concentration or a chronic exposure to a lower level. If one used as criteria the 4 hr LC;, for rats of 16,000 ppm which has been reported for benzene, one would conclude (from Table 7-1) that this material would be “practically non-toxic” which, of course, is contrary to fact. The mechanism of acute death is narcosis. Chronic exposure to low levels of benzene on the other hand produces damage to the blood-forming tissue of the bone marrow and chronic benzene intoxication may appear even many years after the actual exposure to benzene has ceased. Age: It is well known that, in general, infants and the newborn are more sensitive to many toxic agents than are adults of the same species, but this has relatively little bearing on a discussion of industrial toxicology. Older persons or older ani- mals are also often more sensitive to toxic action than are younger adults. With aging comes a di- minished reserve capacity in the face of toxic stress. This reserve capacity may be either func- tional or anatomical. The excess mortality in the older age groups during and immediately following the well known acute air pollution incidents is a case in point. There is experimental evidence from electron microscope studies that younger animals exposed to pollutants have a capacity to repair lung damage which was lost in older animals.*? State of Health: Pre-existing disease can result in greater sensitivity to toxic agents. In the case of 68 specific diseases which would contraindicate ex- posure to specific toxic agents, pre-placement med- ical examination can prevent possible hazardous exposure. For example, an individual with some degree of pre-existing methemoglobinemia would not be placed in a work situation involving expos- ure to nitrobenzene. Since it is known that the uptake of manganese parallels the uptake of iron, it would be unwise to employ a person with known iron deficiency anemia as a manganese miner. It has been shown that viral agents will increase the sensitivity of animals to exposure to oxidizing type air pollutants. Nutritional status also affects re- sponse to toxic agents, Previous Exposure: Previous exposure to a toxic agent can lead to either tolerance, increased sensi- tivity or make no difference in the degree of re- sponse. Some toxic agents function by sensitiza- tion and the initial exposures produce no observ- able response, but subsequent exposures will do so. In these cases the individuals who are thus sensitized must be removed from exposure. In other instances if an individual is re-exposed to a substance before complete reversal of the change produced by a previous exposure, the effect may be more dangerous. A case in point would be an exposure to an organophosphorus insecticide which would lower the level of acetylcholine ester- ase. Given time, the level will be restored to nor- mal. If another exposure occurs prior to this, the enzyme activity may be further reduced to dangerous levels. Previous exposure to low levels of a substance may in some cases protect against subsequent exposure to levels of a toxic agent which would be damaging if given initially. This may come about through the induction of en- zymes which detoxify the compound or by other mechanisms often not completely understood. It has been shown, for example, that exposure of mice to low levels of ozone will prevent death from pulmonary edema in subsequent high ex- posures.>® There is also a considerable “cross tolerance” among the oxidizing irritants such as ozone and hydrogen peroxide, an exposure to low levels of the one protecting against high levels of the other. Environmental Factors: Physical factors can also affect the response to toxic agents. In industries such as smelting or steel making, high tempera- tures are encountered. Pressures different than normal ambient atmospheric pressure can be en- countered in caissons or tunnel construction. Host Factors: For many toxic agents the response varies with the species of animal. There are often differences in the response of males and females to the same agent. Hereditary factors also can be of importance. Genetic defects in metabolism may render certain individuals more sensitive to a given toxic agent. CLASSIFICATION OF TOXIC MATERIALS Within the scope of this chapter it is not possi- ble to discuss the specific toxic action of a variety of materials, although where possible specific in- formation has been used to illustrate the principles discussed. It might, however, be useful to con- sider several ways in which toxic agents may be classified. No one of these is of itself completely satisfactory. A toxic agent may have its action on the organ with which it comes into first contact. Let us assume for the moment that the agent is inhaled. Materials such as irritant gases or acid mists produce a more or less rapid response from the respiratory tract when present in sufficient concentration. Other agents, such as silica or asbestos, also damage the lungs but the response is seen only after lengthy exposure. Other toxic agents may have no effect upon the organ through which they enter the body, but exert what is called systemic toxic action when they have been ab- sorbed and translocated to the site of biological action. Examples of such agents would be mer- cury vapor, manganese, lead, chlorinated hydro- carbons and many others which are readily ab- sorbed through the lungs, but produce typical toxic symptoms only in other organ systems. Physical Classifications: This type of classification is an attempt to base the discussion of toxic agents on the form in which they are present in the air. These are discussed as gases and vapors or as aerosols. Gases and Vapors: In common industrial hygiene usage the term “gas” is usually applied to a sub- stance which is in the gaseous state at room tem- perature and pressure and the term “vapor” is applied to the gaseous phase of a material which is ordinarily a solid or a liquid at room tempera- ture and pressure. In considering the toxicity of a gas or vapor, the solubility of the material is of the utmost importance. If the material is an irri- tant gas, solubility in aqueous media will deter- mine the amount of material that reaches the lung and hence its site of action. A highly soluble gas, such as ammonia, is taken up readily by the mu- cous membranes of the nose and upper respira- tory tract. Sensory response to irritation in these areas provides the individual with warning of the presence of an irritant gas. On the other hand, a relatively insoluble gas such as nitrogen dioxide is not scrubbed out by the upper respiratory tract, but penetrates readily to the lung. Amounts suf- ficient to lead to pulmonary edema and death may be inhaled by an individual who is not at the time aware of the hazard. The solubility coefficient of a gas or vapor in blood is one of the factors de- termining rate of uptake and saturation of the body. With a very soluble gas, saturation of the body is slow, is largely dependent upon ventilation of the lungs and is only slightly influenced by changes in circulation. In the case of a slightly soluble gas, saturation is rapid, depends chiefly on the rate of circulation and is little influenced by the rate of breathing. If the vapor has a high fat solubility, it tends to accumulate in the fatty tissues which it reaches carried in the blood. Since fatty tissue often has a meager blood supply, com- plete saturation of the fatty tissue may take a longer period. It is also of importance whether the vapor or gas is one which is readily metabo- lized. Conversion to a metabolite would tend to lower the concentration in the blood and shift the equilibrium towards increased uptake. It is also of importance whether such metabolic prod- ucts are toxic. For a discussion of the interplay 69 of factors relating to the uptake of gases and va- pors, Chapter 5 of Henderson and Haggard** or Chapter 6 of Patty*? should be consulted. Aerosols: An aerosol is composed of solid or li- quid particles of microscopic size dispersed in a gaseous medium (for our purposes, air). Special terms are used for indicating certain types of par- ticles. Some of these are: “dust”, a dispersion of solid particles usually resulting from the fracture of larger masses of material such as in drilling, crushing or grinding operations; “mist”, a disper- sion of liquid particles, many of which are vis- ible; “fog”, visible aerosols of a liquid formed by condensation; “fume”, an aerosol of solid particles formed by condensation of vaporized materials; “smoke”, aerosols resulting from incomplete com- bustion which consist mainly of carbon and other combustible materials. The toxic response to an aerosol depends obviously on the nature of the material, which may have as a target organ the respiratory system or may be a systemic toxic agent acting elsewhere in the body. In either case, the toxic potential of a given material dispersed as an aerosol is only partially described by a state- ment of the concentration of the material in terms of weight per unit volume or number of particles per unit volume. For a proper assessment of the toxic hazard, it is necessary to have information also on the particle size distribution of the ma- terial. Understanding of this fact has led to the development of instruments which sample only particles in the respirable size range. Chapters 13 and 14 discuss analytical methods for obtaining the needed data. The particle size of an aerosol is the key factor in determining its site of deposi- tion in the respiratory tract and, as a sequel to this, the clearance mechanisms which will be avail- able for its subsequent removal. The deposition of an aerosol in the respiratory tract depends upon the physical forces of impaction, settling, and diffusion or Brownian movement which apply to the removal of any aerosol from the atmosphere, as well as upon anatomical and physiological fac- tors such as the geometry of the lungs and the air-flow rates and patterns occurring during the respiratory cycle. The interrelationship of these factors has been examined both theoretically and experimentally. The monograph by Hatch and Gross, “Pulmonary Deposition and Retention of Inhaled Aerosols™** gives an excellent discussion of the subject and should be required reading for anyone entering the field of environmental toxi- cology. The most recent theoretical treatment is that of the Task Force on Lung Dynamics** which also gives an excellent summary of past work. In the limited space available only one point will be emphasized here, namely, the toxicological importance of particles below 1 pm in size. Aero- sols in the range of 0.2-0.4 um tend to be fairly stable in the atmosphere. This comes about be- cause they are too small to be effectively removed by forces of settling or impaction and too big to be effectively removed by diffusion. Since these are the forces that lead to deposition in the respiratory tract, it has been predicted theoretically and con- firmed experimentally that a lesser percentage of these particles is deposited in the respiratory tract. On the other hand, since they are stable in the atmosphere, there are large numbers of them present to be inhaled, and to dismiss this size range as of minimal importance is an error in toxicological thinking which should be corrected whenever it is encountered. Aerosols in the size range below 0.1um are also of major toxicological importance. The percentage deposition of these extremely small particles is as great as for 1um particles and this deposition is alveolar. This fact was predicted theoretically by Findeisen as far back as 1935*° and has been confirmed experi- mentally.?® Particles in the sub-micron range also appear to have greater potential for interaction with irritant gases, a fact which is of importance in air pollution toxicology. Chemical Classification: Toxic compounds may be classified according to their chemical nature. Vol- ume II of Patty*? is so structured and is an excel- lent practical reference. Industrial Toxicology by Hamilton and Hardy?’ is also arranged more or less according to the chemical classification. Since both of the authors were distinguished as indus- trial physicians (the late Dr. Alice Hamilton being one of the pioneers in that area), the book is more oriented to medical signs and symptoms than to- wards experimental toxicology. Several more spe- cialized works deal with certain types of chem- ical compounds. Among these may be included Browning’s Toxicity of Industrial Metals*® and Toxicity and Metabolism of Industrial Solvents*® and Gerarde’s Toxicology and Biochemistry of Aromatic Hydrocarbons .*° Physiological Classification: Such classification at- tempts to frame the discussion of toxic materials according to their biological action. Most such systems (including the present one) have as their basis the now classic scheme proposed by Hender- son and Haggard.* Irritants: The basis of classifying these materials is their ability to cause inflammation of mucous membranes with which they come in contact. While many irritants are strong acids or alkalis familiar as corrosive to non-living things such as lab coats or bench tops, bear in mind that inflam- mation is the reaction of a living tissue and is dis- tinct from chemical corrosion. The inflammation of tissue results from concentrations far below those needed to produce corrosion. As was indi- cated earlier in discussing gases and vapors, solu- bility is an important factor in determining the site of irritant action in the respiratory tract. Highly soluble materials such as ammonia, alka- line dusts and mists, hydrogen chloride and hydro- gen fluoride affect mainly the upper respiratory tract. Other materials of intermediate solubility such as the halogens, ozone, diethyl or dimethyl sulfate and phosphorus chlorides affect both the upper respiratory tract and the pulmonary tissue. Insoluble materials such as nitrogen dioxide, ar- senic trichloride, or phosgene affect primarily the lung. There are exceptions to the statement that solubility serves to indicate site of action. One such is ethyl ether and other insoluble compounds that are readily absorbed unaltered from the alve- oli and hence do not accumulate in that area. In the upper respiratory passages and bronchi where 70 the material is not readily absorbed, it can accum- ulate in concentrations sufficient to produce irrita- tion. Another exception is in materials such as bromobenzyl cyanide which is a vapor from a liquid boiling well above room temperature. It is taken up by the eyes and skin as a mist. In initial action, then, it is a powerful lachrymator and up- per respiratory irritant, rather than producing a primarily alveolar reaction as would be predicted from its low solubility. Irritants can also cause changes in the me- chanics of respiration such as increased pulmon- ary flow-resistance or decreased compliance (a measure of elastic behavior of the lungs). One group of irritants among which are sulfur dioxide, acetic acid, formaldehyde, formic acid, sulfuric acid, acrolein and iodine produce a pattern in which the flow-resistance is increased, the compli- ance is decreased only slightly and at higher con- centrations the frequency of breathing is de- creased. Another group among which are ozone and oxides of nitrogen have little effect on resis- tance, produce a decrease in compliance and an increase in respiratory rate. There is evidence that in the case of irritant aerosol, the irritant po- tency of a given material tends to increase with decreasing particle size®’ as assessed by the in- crease in flow-resistance. Following respiratory mechanics measurements in cats exposed to irri- tant aerosols, the histologic sections prepared after rapid freezing of the lungs showed the anatomical sites of constriction.?> Long term chronic lung impairment may be caused by irritants either as sequelae to a single very severe exposure or as the result of chronic exposure to low concentra- tions of the irritant. There is evidence in experi- mental animals that long term exposure to respir- atory irritants can lead to increased mucous secre- tion and a condition resembling the pathology of human chronic bronchitis without the intermediary of infection.** *¢ The epidemiological assessment of this factor in the health of residents of polluted urban atmospheres is currently a vital area of research. Irritants are usually further subdivided into primary and secondary irritants. A primary irri- tant is a material which for all practical purposes exerts no systemic toxic action either because the products formed on the tissues of the respiratory tract are nontoxic or because the irritant action is far in excess of any systemic toxic action. Ex- amples of the first type would be hydrochloric acid or sulfuric acid. Examples of the second type would be materials such as Lewisite or mustard gas, which would be quite toxic on absorption but death from the irritation would result before sufficient amounts to produce systemic poisoning would be absorbed. Secondary irritants are ma- terials which do produce irritant action on mucous membranes, but this effect is overshadowed by systemic effects resulting from absorption. Exam- ples of materials in this category are hydrogen sulfide and many of the aromatic hydrocarbons and other organic compounds. The direct con- tact of liquid aromatic hydrocarbons with the lung can cause chemical pneumonitis with pulmonary edema, hemorrhage and tissue necrosis. It is for this reason that in the case of accidental inges- tion of these materials the induction of vomiting is contraindicated because of possible aspiration of the hydrocarbon into the lungs. Asphyxiants: The basis of classifying these ma- terials is their ability to deprive the tissue of oxy- gen. In the case of severe pulmonary edema caused by an irritant such as nitrogen dioxide or laryngeal spasm caused by a sudden severe exposure to sulfuric acid mist, the death is from asphyxia, but this results from the primary irritant action. The materials we classify here as asphyxiants do not damage the lung. Simple asphyxiants are physiologically inert gases which act when they are present in the atmosphere in sufficient quan- tity to exclude an adequate oxygen supply. Among these are such substances as nitrogen, nitrous oxide, carbon dioxide, hydrogen, helium and the aliphatic hydrocarbons such as methane and ethane. All of these gases are not chemically unreactive and among them are many materials which pose a major hazard of fire and explosion. Chemical asphyxiants are materials which have as their specific toxic action rendering the body in- capable of utilizing an adequate oxygen supply. They are thus active in concentrations far below the level needed for damage from the simple as- phyxiants. The two classic examples of chemical asphyxiants are carbon monoxide and cyanides. Carbon monoxide interferes with the transport of oxygen to the tissues by its affinity for hemoglobin. The carboxy-hemoglobin thus formed is unavail- able for the transport of oxygen. All aspects of current research on carbon monoxide were the subject of a recent conference of the New York Academy of Sciences and the monograph result- ing from this meeting is an excellent reference." Over and above the familiar lethal effects, there is concern about how low level exposures will affect performance of such tasks as automobile driving, etc. In the case of cyanide, there is no interference with the transport of oxygen to the tissues. Cyanide transported to the tissues forms a stable complex with the ferric iron of ferric cytochrome oxidase resulting in inhibition of en- zyme action. Since aerobic metabolism is de- pendent upon this enzyme system, the tissues are unable to utilize the supply of oxygen, and tissue “hypoxia” results. Therapy is directed towards the formation of an inactive complex before the cyanide has a chance to react with the cytochrome. Cyanide will complex with methemoglobin so ni- trite is injected to promote the formation of meth- emoglobin. Thiosulfate is also given as this pro- vides the sulfate needed to promote the enzymatic conversion of cyanide to the less toxic thiocyanate. Primary Anesthetics: The main toxic action of these materials is their depressant effect upon the central nervous system, particularly the brain. The degree of anesthetic effect depends upon the ef- fective concentration in the brain as well as upon the specific pharmacologic action. Thus, the ef- fectiveness is a balance between solubility (which decreases) and pharmacological potency (which increases) as one moves up a homologous series of compounds of increasing chain length. The anesthetic potency of the simple alcohols also rises 71 with increasing number of carbon atoms through amyl alcohol which is the most powerful of the series. The presence of multiple hydroxyl groups diminishes potency. The presence of carboxyl groups tends to prevent anesthetic activity which is slightly restored in the case of an ester. Thus acetic acid is not anesthetic, ethyl acetate is mildly so. The substitution of a halogen for a hydrogen of the fatty hydrocarbons greatly in- creases the anesthetic action, but confers toxicity to other organ systems which outweighs the anes- thetic action. Hepatotoxic Agents: These are materials which have as their main toxic action the production of liver damage. Carbon tetrachloride produces se- vere diffuse central necrosis of the liver. Tetra- chloroethane is probably the most toxic of the chlorinated hydrocarbons and produces acute yel- low atrophy of the liver. Nitrosamines are cap- able of producing severe liver damage. There are many compounds of plant origin such as some of the toxic components of the mushroom Amanita phalloides, alkaloids from Senecio, and aflatoxins which are capable of producing severe liver dam- age and in some instances are powerful hepato- carcinogens. Nephrotoxic Agents: These are materials which have as their main toxic action the production of kidney damage. Some of the halogenated hydro- carbons produce damage to the kidney as well as to the liver. Uranium produces kidney damage, mostly limited to the distal third of the proximal convoluted tubule. Neurotoxic Agents: These are materials which in one way or another produce their main toxic symptoms on the nervous system. Among them are metals such as manganese, mercury and thal- lium. The central nervous system seems partic- ularly sensitive to organometallic compounds, and neurological damage results from such materials as methylmercury and tetraethyl lead. Trialkyl tin compounds may cause edema of the central nervous system. Carbon disulfide acts mainly on the nervous system. The organic phosphorus in- secticides lead to an accumulation of acetyl cho- line because of the inhibition of the enzyme which would normally remove it and hence cause their main symptoms in the nervous system. Agents which act on the blood or hematopoietic system: Some toxic agents such as nitrites, aniline and toluidine convert hemoglobin to methemoglo- bin. Nitrobenzene forms methemoglobin and also lowers the blood pressure. Arsine produces hemo- lysis of the red blood cells. Benzene damages the hematopoietic cells of the bone marrow. Agents which damage the lung: In this category are materials which produce damage of the pul- monary tissue but not by immediate irritant ac- tion. Fibrotic changes are produced by materials such as free silica which produces the typical sili- cotic nodule. Asbestos also produces a typical damage to lung tissue and there is newly aroused interest in this subject from the point of view of possible effects of low level exposure of individuals who are not asbestos workers. Asbestosis was the subject of a recent conference of the New York Academy of Sciences and the papers in the re- sulting monograph present the various aspects of current research in the area.** Other dusts, such as coal dust, can produce pneumoconiosis which, with or without tuberculosis super-imposed, has been of long concern in mining. Drinker and Hatch?” is a classic reference in this area and Hunter*® discusses at length occupational expo- sures to dusts. Many dusts of organic origin such as those arising in the processing of cotton or wood can cause pathology of the lungs and/or alterations in lung function. The proteolytic en- zymes added to laundry products are an occupa- tional hazard of current interest. Toluenediisocya- nate (TDI) is another material which can cause impaired lung function at very low concentra- tions and there is evidence of chronic as well as acute effects.’ Chapter 33 discusses materials in this category. References 1. SMYTH, H. F., JR.: “The Communication Lines and Problems of a Toxicology Laboratory Working for Industry.” Arch. Indust. Health, 15: 269 (1957). BLISS, C. L.: “The Determination of the Dosage- Mortality Curve from Small Numbers.” Quart. J. Pharm. and Pharmacol. 11: 192 (1938). MILLER, L. C. and M. L. TAINTER: “Estimation of the EDw and Its Error by Means of Logarithmic- Probit Graph Paper.” Proc. Soc. Exptl. Biol. and Med. 57: 261 (1944). LITCHFIELD, J. T., JR. and F. WILCOXON: “Simplified Method of Evaluating Dose-Effect Ex- periments.” J. Pharmacol. 96: 99 (1949). WEIL, C. S.: “Tables for Convenient Calculation of Median-Effective Dose (LC» or ED#) and In- struction in Their Use.” Biometrics 8: 249 (1952). HODGE, H. C. and J. H. STERNER: “Tabulation of Toxicity Classes.” Am. Indust. Hyg. Quart. 10: 93 (1949). LOOMIS, T. A.: Essentials of Toxicology, Chapt. 2, “Numbers in Toxicology,” Lea and Febiger, Phila- delphia (1968). GRANT, W. M.: Toxicology of the Eye, Charles C. Thomas, Springfield, Illinois (1962). ROWE, V. K.,, M. A. WOLF, C. S. WEIL and H. F. SMYTH, JR.: “The Toxicological Basis of Threshold Limit Values. 2. Pathological and Bio- chemical Criteria.” Am. Indust. Hyg. Assoc. J. 20: 346 (1959). ZAPP, J. A.: The Toxicological Basis of Threshold Limit Values. 3. Physiological Criteria. Am. Indust. Hyg. Assoc. J. 20: 350 (1959). FERRIS, B. G., JR.: “Use of Pulmonary Function Tests in Epidemiologic Surveys.” Bull. Physio-Path. Resp. 6: 579 (1970). PETERS, R. A.: Lethal Synthesis. Prac. Royal Soc. B. 139: 143 (1952). CREMER, J.: “Biochemical Studies on the Toxicity of Tetraethyl Lead and Other Organo-lead Com- pounds.” Brit. J. Indust. Med. 16: 191 (1959). WILLIAMS, R. T.: Detoxication Mechanisms. John Wiley and Sons, New York, (1959). GOLDBERG, M. E., C. HAHN and H. F. SMYTH, JR.: “Implication of Altered Behavior Induced by an Industrial Vapor.” Tox. Appl. Pharm. 4: 148 (1962). CAHEN, R. L.: “Evaluation of the Teratogenicity of Drugs.” Clin. Pharmacol. Therap. 5: 480 (1964). KUSCHNER, M.: The J. Burns Amberson Lecture: “The Causes of Lung Cancer.” Am. Rev. Resp. Dis. 98: 573 (1968). FOOD AND DRUG ADMINISTRATION ADVIS- ORY COMMITTEE ON PROTOCOLS FOR SAFE- TY EVALUATION. Panel on Carcinogenesis. 10. 11. 12. 13. 14. 15. 16. 17. 18. 72 “Report on Cancer Testing in the Safety Evaluation of Food Additives and Pesticides.” Tox. Appl. Pharm. 20: 419 (1971). WAYNE, L. G. and L. A. CHAMBERS: “Biological Effects of Urban Pollution.” Arch. Environ. Health 16: 871 (1968). STOKINGER, H. E. and L. D. SCHEEL: “Ozone Toxicity. Immunochemical and Tolerance Produc- ing Aspects.” Arch. Env. Health 4: 327 (1962). HENDERSON, Y. and H. W. HAGGARD: Noxious Gases, Chapter 5, Reinhold, N.Y. (1943). PATTY, F. A.: Industrial Hygiene and Toxicology, 2nd Ed. Interscience, N.Y. (1958). HATCH, T. F. and P. GROSS: Pulmonary Depo- sition and Retention of Inhaled Aerosols. Academic Press, N.Y. (1964). TASK GROUP ON LUNG DYNAMICS “Deposi- tion and Retention Models for Internal Dosimetry of the Human Respiratory Tract.” Hith. Physics 12: 173 (1966). FINDEISEN, W.: “Uber das Absetzen Kleiner in der Luft suspendierten Teilchen in der menoshlichen Lunge bei der Atmung.” Arch. Ges. Physiol. 236: 367 (1935). MORROW, P. E. and F. R. GIBB: “The Deposition of a Submicronic Aerosol in the Respiratory Tract of Dogs.” Am. Indust. Hyg. Assoc. J. 19: 196 (1958). HAMILTON, A. and H. E. HARDY: [Industrial Toxicology, 2nd Ed. Hoeber, N.Y. (1949). BROWNING, E.: Toxicity of Industrial Metals, Butterworths, London (1961). BROWNING, E.: Toxicity and Metabolism of In- dustrial Solvents, Elsevier, N.Y. (1965). GERARDE, H. W. Toxicology and Biochemistry of Aromatic Hydrocarbons, Elsevier, N.Y. (1960). AMDUR, M. O. and M. CORN: “The Irritant Potency of Zinc Ammonium Sulfate of Different Particle Sizes.” Am. Indust. Hyg. Assoc. J. 24: 326 (1963). NADEL, J. A., M. CORN, S. ZW], J. FLESCH and P. GRAF: “Location and Mechanism of Airway Constriction After Inhalation of Histamine Aerosol and Inorganic Sulfate Aerosol.” Inhaled Particles and Vapors 11 Ed. C. N. Davies Pergamon Press p. 55, Oxford (1967). RIED, L.: “An Experimental Study of Hypersecre- tion of Mucus in the Bronchial Tree.” Brit. J. Exp. Pathol. 44: 437 (1963). DAHLHAMN, T.: “Mucous Flow and Ciliary Activ- ity in Trachea of Healthy Rats and Rats Exposed to Respiratory Irritant Gases.” Acta. Physiol. Scand. 36: Supp. No. 123 (1952). COBURN, R. F. (Editor): “Biological Effects of Carbon Monoxide.” Ann. N.Y. Acad. Sci. 174: Art. 1, 430 pp. (1970). WHIPPLE, H. E. (Editor): “Biological Effects of Asbestos.” Ann. N.Y. Acad. Sci. 132: Art. 1, 766 pp. (1965). DRINKER, P. and T. HATCH: Industrial Dust, 2nd Ed. McGraw-Hill, N.Y. (1954). HUNTER. D.: The Diseases of Occupations, 4th Ed. Little, Brown & Co., Boston (1969). PETERS, J. M.: “Cumulative Pulmonary Effects in Workers Exposed to Toluene Diisocyanate.” Proc. Royal Soc. Med. 63: 372 (1970). 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. Preferred Reading: Books 1. BOYLAND, E., R. GOULDING, Modern Trends in i Appleton - Century - Crofts, N.Y.C. 1968). BROWNING, E., Toxicity of Industrial Metals, Butterworths, London (1961) and Toxicity and Metabolism of Industrial Solvents, Elsevier, N.Y. (1960). Extremely comprehensive and well refer- enced in their specific areas. 10. 11. 12. Elsevier Monographs on Toxic Agents. This series was edited by the late Ethel Browning. They are available in paper back editions. They deal with specific materials i.e., Beryllium, Arsenic, Aromatic Hydrocarbons, Vanadium, Aromatic Amines, etc. A list of the ones in print should be obtainable from Elsevier Publishing Co., 52 Vanderbilt Ave., New York, N.Y. HAMILTON, A. and H. E. HARDY, Industrial Toxicology, 2nd Ed., Hoeber, N.Y. (1949). HATCH, T. F. and P. GROSS. Pulmonary Deposi- tion and Retention of Inhaled Aerosols, Academic Press, N.Y. (1964). Available in paper back. An excellent reference. LOOMIS, T. A., Essentials of Toxicology, Lea & Febiger, Phila. (1968). NIOSH, Toxic Substance List, (1971). PATTY, F. A., Industrial Hygiene and Toxicology Vol. I and II 2nd Ed. Interscience, N.Y. (1958). Probably the best practical reference for industrial toxicology. SUNSHINE, 1., Handbook of Analytic Toxicology, Ed., Chem. Rubber Co., Cleveland, Ohio (1971). STOKINGER, H., ED., Beryllius: Its Industrial Hy giene Aspects, Acad. Press, N.C.Y. (1966). GERARDE, H. W., Toxicology and Biochemistry of Aromatic Hydrocarbons, Elsevier, New York (1960). HENDERSON and HAGGARD, Noxious Gases, Reinhold, N.Y. (1943). Cincinnati, Ohio 73 Journals: (English) A.M.A. Archives of Environmental Health; Amer- ican Industrial Hygiene Association Journal and The British Journal of Industrial Medicine have many articles on industrial toxicology. Journals: (Foreign) Medicina del Lavoro — Italian Archives des Maladies Professionelles — French Gigiena i Sanitariya — Russian (Translation Avail- able) Pracovni lekarstvi (Czechoslovakian) Japanese Journal of Labor Science Abstracts: Chemical Abstracts Exerpta Medica Abstracts in Occupational Health and Industrial Medicine Bulletin of Hygiene (British) Scientific Reports on Industrial Hygiene and Occu- pational Diseases in Czechoslovakia (Published An- nually by Inst. of Indust. Hyg. & Occ. Diseases in Prague. In English) Hygienic Guides: A series of useful pamphlets published by Am. Industrial Hygiene Association, 210 Haddon Ave., Westmont, N.J. 08108. CHAPTER 8 PRINCIPLES AND USE OF STANDARDS OF QUALITY FOR ) THE WORK ENVIRONMENT B. D. Dinman, M.D., Sc.D. INTRODUCTION Rationale Total removal of all potentially harmful agents from the work place is the only absolute method of assuring worker safety and health. Since this optimum is not always possible, exposure to po- tentially toxic substances is unavoidable. Accord- ingly, it has become necessary to define quantita- tively which exposure levels are not attended by a risk to the worker’s health or well-being. Basic Underlying Principles An understanding of the dose-response rela- tionship (see Chapter 7) is a basic determinant of the feasibility of such standards. In brief, all chemical agents cause biological response as a function of the quantity absorbed and the period of time over which such absorption occurs. Thus, there should be a dose (concentration and time dependent) which does not exceed the capability of the organism to metabolize, detoxify or excrete such compounds. This dose is usually referred to as a “no effect” level. The “no effect” level — is a puristic concept because there is always some biological or chem- ical alteration when the organism encounters some exogenous material.” > Whereas in the United States it is clearly understood that such responses are not deleterious per se, in the Soviet Union this is not explicitly recognized. Nevertheless, in the United States a “no effect” level is implied to be one which does not produce any deleterious or undesirable effect upon human health and well- being or overload the normal protective mecha- nisms of the body.” Thus a biological accommodation, e.g., a non- specific alteration in brain waves, a decreased serum catalase (an enzyme normally present in the body far beyond stress demands), is seen as probably not having immediate or long-term cffect on health. Such changes are not deleterious in and of themselves. By contrast, although exposure to H,S at concentrations of 30-50 ppm produces no changes other than self-limited eye irritation, such concentrations are, in normal circumstances, unacceptable. This is in keeping with the WHO* definition of health which considers any encroach- ment upon human well-being as being ill health and, therefore, undesirable. Problems in Definition of “No Effect Level” It can be seen that there may be profound dif- ferences of opinion as to what constitutes a “no effect” level. The preponderant opinion in the *World Health Organization 75 United States holds that slight deviations within homeostatic limits of biological change are not deleterious... All necessary life processes required by living organisms are associated with perturba- tions of a steady state. Thus the basic processes of digestion and absorption are associated with considerable fluxes of, e.g., electrolytes, lipids, proteins, etc., at concentrations which deviate from those found between meals. With each eye- lid flicker there are attendant electrical discharges along multiple nerve pathways that previously were essentially quiescent. Therefore, it should be apparent that for all bodily functions there are constant deviations from a “steady state”; such represent necessary accommodative change to en- vironmental alteration in its broadest sense. While such generalizations are useful, the problem becomes more difficult when one attempts to define the actual limits beyond which change becomes deleterious. Though practically any change is considered as being potentially detri- mental by the U.S.S.R., it becomes difficult to reconcile this position with the concept of a normal range associated with homeostasis. On the other hand, the question might well be asked whether the accumulated energy expenditures re- quired by accommodation over a lifetime do not contribute to the long-term depletion of life forces which might accelerate the process of aging. In the strictest sense a “no effect” level does not exist; however, for operational purposes the range of biological response which exceeds homeo- static limits must be ascertained. The problems of defining the effect such stresses (within homeo- static limits) may have over a long-term should be appreciated. Other Variables Influencing the Use of Workroom Air Quality Standards Work-rest cycle. All quality standards make cer- tain assumptions regarding the work-rest cycle. Basically, most standards currently utilized in the United States imply an 8-hour day within a 40- hour week.* Thus, each work period is followed usually by a 16-hour non-exposed period, during which restituting processes (e.g., detoxification, excretion) occur. Where more prolonged work exposure periods occur, the possibility of a greater total dose being absorbed as well as less time being available for restitution make application of the usual quality standards inappropriate. With deviations from the usual work-rest cycles (e.g., as with continuous exposure in submarines or space capsules), other environmental quality status standards must be applied. Worker Health Status. The standards utilized de- pend upon an essentially healthy work force. This stems from the fact that persons with a compro- mised function or pathological condition may not be capable of dealing with absorbed chemicals in the expected manner. Accordingly, such individ- uals may not be able to completely excrete each day’s burden of an absorbed agent; this can lead to a progressive accumulation of such materials. Adverse Climate Conditions. Since adverse cli- mate conditions place an accommodative burden upon an individual, the additional work involved in accommodating to occupational stressors may be excessive. Accordingly, in such circumstances quality standards may require modifications re- flecting such additional physiologic loadings. Special Genetic and Biological Susceptibility. Be- cause of genetic and biological factors (e.g., glu- cose-6-phosphate dehydrogenase or serum anti- trypsin deficiencies) specific to some few (i.e., 5-10%) individual workers, these workers may possess an undue susceptibility to agents found in the work environment. It is necessary to detect the presence of such unusual persons at special risk prior to work exposure, since quality stan- dards are designed for the normal person and do not apply to special risk workers.* Implications of the Premises Underlying Quality Standards It becomes immediately apparent that quality standards cannot be utilized without a full under- standing of the foregoing premises concerning 1) the work-rest cycle, 2) worker health status, 3) climatic conditions and 4) special susceptibil- ities. In addition, their use requires concomitant use of adequate environmental monitoring and medical surveillance. The former stems from the need to document the fact that these limits are not being exceeded; the latter requirement, to deter- mine that persons with pathologic or biologic de- viations are not exposed (see Chapter 17). PRINCIPLES FOR DEVELOPING WORKROOM AIR QUALITY STANDARDS Extrapolation by Chemical Analogy A. Principle. When dealing with a new chemical, animal or human toxicity data are usually un- available. Therefore, the prevailing principle is that the quality of response of a chemical may be assumed to be analogous to that produced by similar substances. Chemicals that are struc- turally similar should produce a similar biological response. Thus, as a first approximation, some estimate of toxic potential can be obtained. Obvi- ously, the use of such assessments, since they are not absolute predictors of qualitative effects, may be dubious for prediction of quantitative response. Nevertheless, as of 1968, 24% of all Threshold Limit Values published by the American Confer- ence of Governmental Industrial Hygienists were based upon analogy.® B. Limitations. (1) Inconsistency of qualitative effect: Not infrequently one compound in a chemical family of compounds will respond in a totally atypical manner when compared with others of that family. Accordingly, some risk may be attached to predictions of safety or toxicity based upon chemical analogy. Inconsistency of quantitative effect: as fraught with risk as is prediction of qual- itative risk on the basis of chemical an- alogy, estimating quantitative effect is even more hazardous. Animal Experimentation Principles and Purposes. Before workers are ex- posed to any chemical agents in the workplace, it is advisable to know the toxic effect such materials possess. On this basis one can design the protec- tive measures to protect workers and deal with medical problems caused by such materials. How- ever, in the case of new chemicals, there is often little or no information upon which to act. Ac- cordingly, an important method of developing such new information utilizes animal experimentation. In some cases clinical experience does exist, but it is often fragmentary, and rarely provides the detailed information needed concerning the metabolites produced following chemical absorp- tion. Data on metabolites is useful in estimating the degree of absorption of substances. Experi- mentation with an animal host which responds to substances in a manner similar to man can pro- vide such information. The design of animal experiments should re- flect the conditions of industrial usage of the sub- stance in question. Since agents encountered in the workplace may act systemically or locally following skin or mucous membrane exposure, skin testing for possible absorption and systemic tox- icity, primary irritation or sensitization is indi- cated. Exposure of animals to vapors, mists, aero- sols or gases for determination of pulmonary ef- fects and uptake or systemic toxicity is extremely relevant to the industrial milieu. By contrast, ex- periments utilizing gastro-intestinal or subcutane- ous absorption are less frequently used except for range-finding toxicity purposes. Difficult questions revolve about the problems of extrapolation of animal information to man. As a rule, it is desirable to seek toxicological in- formation derived from more than one animal species wherever possible. Quite frequently vari- ous species respond in differing fashions qualita- tively and quantitatively. Since no one species consistently reacts as does man, one can never predict which species is most like man. Accord- (2) . ingly, it is an operating principle, until otherwise 76 demonstrated, that man should be considered as responding as does the most sensitive animal spe- cies; design of control programs should be devel- oped from that point of departure. Another important factor concerns the num- ber of animals of any one species which are put to test. Here again, because even within any one group of animals, biological individuality will op- erate, enough animals must be tested. Thus, one attempts to ensure, within a reasonable degree of probability, that even the most sensitive of the group will be tested. In this regard, statistical techniques can be utilized with a view toward de- termining which confidence limits attend upon animal population size choice. One last consideration relates to dose ranges used in such experiments. Obviously, a wide range of doses is useful for different purposes. The large doses help force the question, “toxic or non-toxic?” while also providing clearcut answers as to the specific organs susceptible to damage. Likewise, a lower range of doses must be used to give a clearer estimate of thresholds of response. Criteria of Response — Organ Change. While gross changes in structure clearly delineate the bodily organ at risk of damage, such data are of limited usefulness. This follows since all control measures must be designed so as to prevent any serious, irreversible damage. Thus, while such bodily changes delineate serious responses, satis- factory control is achieved only when exposure prevents even a minimal alteration beyond the homeostatic range. Accordingly, more important data derive from functional changes rather than pathological organ alteration. Functional Response — Biochemical Changes. Detection of altered organ function occurring prior to structural change provides the organism with greater probability of avoiding permanent damage. Such functional changes are frequently expressed when organs of detoxification produce some meta- bolic alteration of the absorbed chemical agent. Insofar as such organ of detoxification is not pre- sented with an amount of chemical which does not exceed its detoxification rate, it can continue to cope with such chemical exposures. Experimen- tation should be designed to define such rate limits in terms of what represents both excess load- ings as well as those burdens with which the or- ganism can successfully deal. Especially impor- tant is definition of the “break point” in detoxi- fication rates. Such experiments help define the safe “dose”; in addition, quantitative biochemical indicators of over-exposure may also be delineated. As an example of this, one can assay how much absorption of an organo phosphorous pesticide is safe in terms of depression of red cell acetylcholine esterase, or how much lead exposure has occurred by estimation of urinary coproporphyrin or delta aminolevulinic acid. Likewise, measurement of the metabolites of trichloroethylene, e.g., trichlor- acetic acid, provides useful indicators of the exis- tence and degree of absorption of that solvent. Neurophysiologic Response. Recently, changes in nervous system function have been studied ex- tensively as a parameter of toxic or subtoxic ex- posure. Largely as a result of Russian studies, investigation of neurofunctional response has been considered as possibly indicating early change. Where changes in neurologic function impair higher functions, e.g., alertness, cognition, such alterations have obvious industrial implications as regards safety and performance adequacy. How- ever, the relation of certain measurements, e.g., nerve chronaxie, to occupational exposure is prob- lematic. Nevertheless, such studies of higher ner- vous function increasingly have been undertaken to delineate man’s response to his occupational environment. Other types of response: (1) Carcinogenesis: Obviously, given the serious implications of occupationally 77 induced cancer, studies designed to de- tect such a change are of the utmost importance. Here, the problems of dose-response re- lationships become extremely com- plex, since definition of a threshold of response is problematic. Accordingly, testing here is directed largely toward de- fining whether such a hazard exists; the use of animal experiments for establish- ing operational control is directed mainly toward defining the necessity for total isolation or substitution. In the present absence of truly effective therapy, once the malignant alteration has been in- duced, the value of such preclinical in- dicators is limited. Mutagenesis and teratogenesis: Mutagen- esis is the process wherein normal cells are converted into genetically abnormal cells. The result of such alteration, par- ticularly since it involves the genetic proc- esses which determine normal cell growth and division, are changes in structure and function. This process may result in malignant or other aberrations. Teratogenesis refers to the process whereby abnormalities of the off-spring are generated. Such usually results from damage to embryonal structures in the first trimester of pregnancy, or because of alteration of germinal elements, i.c., ovarian cells or spermatozoan. While these responses are extremely im- portant — especially where women may be at a risk, the danger of mutagenesis could theoretically also affect male gen- erative tissue. While little such testing has been undertaken with a view toward protection of working populations, seri- ous consideration should be given to such studies in the future. Application of Animal Data Principles of Application: (1) Use of the most sensitive species: because the detoxification represents in essence a genetically controlled metabolic degra- dation process, it follows that various ani- mal species will respond differently to toxic chemical exposure. Unfortunately, just how any species — including man — will respond is not predictable. Accord- ingly, when the human quantitative re- sponse to a chemical agent is unknown, prudence would dictate that the design of environmental quality standards assume that man responds as does the most sen- sitive species. Application of the dose-response curve to setting standards: primarily, environ- mental quality standards are intended to quantitatively indicate the amount of contaminant which may be present in the workplace without causing harm to man. Obviously, experiments should be di- rected toward determining the concentra- (2) (2) tion at which “no effect” is produced, i.e., one which is safe. Experiments which permit the develop- ment of a dose-response curve indicate the several ranges of response. In this manner, the doses producing “no re- sponse,” a minimal response and the more severe response are defined. In most circumstances, a linear relationship be- tween these doses emerges with the use of logarithmic plots. While a dose-re- sponse curve can be estimated without data points being available in the “no response” or safe range, downward ex- trapolation to this area holds some risk. Problems will occur when a break occurs in such a linear response curve; this is seen particularly in the low dose range. Safety margins and their bases: because of problems inherent in interpretation of toxicological data (see above), it is desirable to have a margin of safety be- tween the lowest effective dose and a proposed TLV. Expressed mathemati- cally, TLV =lowest effective dose/safety factor. The safety factor depends upon the nature of the response* produced by such lowest effective dose. Where such responses consist of reversible irritation of skin or mucous membranes, safety fac- tors between the dose producing these phenomena and the recommended TLV tend to be low. By contrast, minimal dose-related responses characterized by toxicity usually possess a greater safety margin or factor. The range of safety fac- tors associated with A.C.G.LH. TLV’s has been estimated to extend between 0.2 and 10. A safety factor of 0.2 denotes that the Threshold Limit Value is 0.2 fold (or 20%) higher than the dose which pro- duces a response; a factor of 10 states that the TLV is 10 fold (or 1000% ) higher than the dose producing a thres- hold response. While the use of safety margins as an extrapolation process for estimation of the “no response” area is useful, their limitations should be recognized. For one thing, departures from the linearity of the dose-response curve are apt to occur in such estimates of lower ranges. Further- more, given a steep dose-response line, in the biologically reactive range, the “no effect” level tends to be estimated with a high degree of error. Finally, when deal- ing with agents that appear to be active at extremely low levels, i.e., 5-10 ppm, departures from linearity appear quite 3) *What constitutes evidence of a “response” varies. In the United States biochemical, physiologic or even re- versible changes in organ morphology may constitute the “minimal” response. In the U.S.S.R. more credence is placed upon subtle neurophysiologic change as evi- dence of a deleterious alteration (see section on Func- tional Response). 78 common; this introduces even more chance of an unrealistic standard being set if a 5- or 10-fold safety margin is applied.” It is for such reasons that data in the “no effect” range are preferred by those set- ting work environmental quality stan- dards. Problems in the Use of Animal Data for the Establishment of Environmental Quality Standards In the absence of data based upon human ex- perience, extrapolation from animal experiments must be used in establishing environmental qual- ity standards. But because our concerns are di- rected toward prevention of human harm, the limi- tations inherent in animal-derived data should be recognized. Whether man will respond as the most reactive or least reactive species tested fre- quently cannot be predicted. Further, the ques- tion as to whether the most sensitive species has been tested is frequently unanswered. Finally, whether the animal response has any parallel to human responsiveness cannot be answered. (This has occurred in the case of induction of bladder tumors by aromatic amines; unless the dog is tested — a relatively uncommon test animal — such chemicals do not ordinarily produce bladder tumors in the animals usually used in the labora- tory.) For these reasons, human exposure data assume considerable importance in quality stan- dard development, though animal-derived infor- mation may be commonly the only type in exis- tence. Sensitization. This type of response, sensitization, is produced with difficulty in animals. Accord- ingly, if animal testing is relied upon, the poten- tial for such responses may be undetected. Genetic Defects Peculiar to Man. A number of genetic defects found in various human “strains” have no parallel in animals. Such defects occur commonly in human populations and can deleteri- ously affect the mode of response to certain envi- ronmental chemicals (e.g., glucose-6-phosphate dehydrogenase defects will impede the detoxifica- tion process among persons having this aberration who are exposed to various aromatic amines). Accordingly, animal testing alone will not predict whether a chemical might cause untoward reac- tions in such susceptible populations. HUMAN DATA AND INDUSTRIAL EXPERIENCE AS A BASIS FOR STANDARD DEVELOPMENT The Necessity for Human Data It should be readily apparent from the fore- going that animal data form a problematic basis for the development of occupational environment quality standards. While such data are highly use- ful in developing a broader understanding of bio- logical response (e.g., metabolism, full range of effects), such information in itself has obvious shortcomings in setting quality standards. It is for this reason that experience based upon human exposure to the substance in question is of ulti- mate importance in determining standards of safety. Such data can result from inadvertent or in- tentional experimental exposure. Concerning the latter, the availability of animal experiments be- comes critical; only after thorough exposition of toxicity by this method is human experimentation justified. Specific Needs Fulfilled by Human Toxicity Data 1. Irritation and nausea: since the less severe degree of irritation can only be detected by subjective means, it is obvious that animal experimentation may not provide such information in this response range. Allergic response: since animals rarely demonstrate this type of response, human experience is necessary if such effect is to be detected. Odor evaluation: since no quantitative measures of odor are presently practicable, this response can only be evaluated by questioning the experimental subject. Ob- viously, animal experiments are useless in this regard. Higher nervous function effects: an im- portant consideration in occupational safety and health revolves about environ- mental effects upon human performance. While animal experimentation increasingly involves measurement of neurophysiologic response, extrapolation of such test pro- cedures for the assessment of, e.g., visual performance, manipulation of various de- vices leads to obvious inadequacies. Thus human testing, particularly where relevant work tasks are performed, meets a unique need in occupational safety evaluation. Human metabolic pathways: while much of such information can be derived from animal experiments, ultimately application of such data for hazard assessment and control design represents an extrapolatory exercise. Thus human exposures will pro- vide the ultimate quantitative and qualita- tive information regarding human metab- olism of the substance in question. The Use of Data Derived from Occupational Experience Validity requirements: 1. Environmental sampling adequacy: in order to relate human safety or damage to environmental agents, it is necessary to have some quantitative measurement of its presence. Usually this means extensive sampling of the work environment over time and space, but especially as related to worker absorption opportunities. That is, good industrial hygiene sampling practice (see Chapter 10) is necessary to ade- quately assess quantitative exposure. In brief, in the cases of gases, vapors or dusts, samples should be taken at breath- ing zones. In addition, in the case of dusts, quantitative characterization of the particulates of respirable size are especially pertinent. Obviously, care should be exer- cised that sufficient numbers of samples are taken to represent adequately the full 79 range as well as average of concentrations. Human surveillance adequacy: for data based on human experience to be valid, the human portion of the agent-host inter- action also must be characterized. Indeed, if no untoward effect is claimed, detailed medical evaluation of those exposed is re- quired. In addition, it is possible to evalu- ate environmental concentrations by meas- urement of metabolites or of the agents themselves in biological media. Although such correlations between concentrations in biological material and the work envi- ronment may be constructed from occupa- tional exposure situations, usually insuffi- cient data or range of exposures mitigate against development of such a regression line. However, such measurements taken under experimental exposure conditions have been extremely useful (see below, Human Experimentation). Problems Encountered in the Use of Occupational Exposure Data Irregularity of exposure: most occupa- tional exposures are of a fluctuating char- acter, both in terms of duration and con- centrations. Thus the need for having suf- ficient samples representative of the “peaks,” “valleys” and mean concentra- tions encountered becomes essential. Mixed exposures: occupational exposures to a single agent are rather uncommon. Thus, while the material in question might be specifically measured in the environ- ment, it becomes problematic whether the human response results from exposure to that particular agent per se. Furthermore, the biological response can rarely be ra- tionally apportioned as a function of the relative concentration of multiple agents. Whether such agents are acting additively, synergistically or antagonistically can mark- edly alter responses. Hence, since occu- pational exposures are mixed, this limita- tion on their use for occupational environ- mental quality standard development must be recognized. For a more detailed dis- cussion of evaluation of mixtures, see ref- erence (3). As regards the agents in such a mixed exposure, the question of the specificity of the measurement technique for the mate- rial of interest becomes significant. This is especially pertinent where mixtures of chemically similar substances are encoun- tered; interferences may also make such measurements of the components of such mixtures non-specific. Absence of long-term data: while meas- urements of human response over the short-term experience are readily observed, the long-term effects of such exposures are infrequently available. While drastic ef- fects of long-term exposure may be de- tected — and then with difficulty, e.g., bladder tumors, subtle effects are infre- quently reported or investigated. 4. Special susceptibility: unless sufficiently large populations of exposed workers are studied, the few persons who may be at special risk because of genetically deter- mined special susceptibility will not be en- countered. Such persons may be at special risk either for reasons that are well-defined, e.g., defects in metabolism, or because of poorly understood reasons (allergic sensi- tivity). Indeed, while such persons may constitute a small proportion of a potential population at risk, this does not constitute a reason for such effects being ignored if they could potentially be prevented. Human Experimentation Ethical Considerations. While it has long been recognized that each man has a moral duty to act charitably toward others, e.g., make blood or skin graft donations, some subtle and gross abuses of human experimentation have made reassessment of that practice necessary. Accordingly, a number of moral codes have been drawn up to protect the person of such subjects (Nuremberg Tribunal Code, the World Medical Association’s 1964 Dec- laration of Helsinki, American Medical Associa- tion, etc.). Minimally, at least four requirements should be met before experiments are considered: 1. Safety should have been extensively estab- lished in animal species; Volunteers must be free of any coercion whatsoever and be fully and completely informed of all possible effects in a clearly understood fashion; There must be no possibility of permanent damage, and the subject must be com- pletely free to terminate the experiment at any time; A written agreement of the volunteer to participate in the experiment which is fully described should be obtained. Practically, it is mandatory that there be suf- ficient insurance coverage for each subject to compensate him voluntarily in the event of injury. Design Requirements 1. In testing with airborne narcosis producing materials, assuming sufficiently large cham- bers and modalities for testing behavioral and other functional parameters, exposures are made in 3 ranges, i.e., “no effect,” at borderline levels and at levels producing measureable, though minimal, narcosis in most subjects. In this manner, 3- to 4- hour exposures can aid in estimating the safety factor for human exposure, the safe limit and the rates of uptake and elimina- tion of the agent. The latter two are determined by plotting blood concentra- tions against atmospheric concentrations as a function of time; such data are ex- tremely valuable in estimating the extent of previously unknown exposure given a blood concentration at any given time after exposure.® In testing with airborne irritants, utilizing the aid of an otolaryngologist, examina- tions are performed both before and after 2. 80 exposure in a dynamic chamber. Because of the possibility of the development of accommodation, exposures should last at least 15 minutes; such exposures should be repeated 10 times in order to establish whether — and to what degree — accom- modation occurs. A repetition of these exposures after 10 to 14 days will help establish whether sensitization occurs. Further, repetition has another urgency, since experience has shown that single ex- posure tests usually lead to unnecessarily low limits.® Testing cutaneous irritation and sensitiza- tion (see Chapter 34). Measurement of Response. Since a major reason for permitting the use of human volunteers is the eliciting of data indicative of minor functional change, the criteria of response should accordingly reflect this need. Thus, functional measurement of biochemical (e.g., enzymatic, immunochemical), neurophysiologic (e.g., EEG, conditioned and un- conditioned reflexes) organ activity (EKG, liver or kidney function tests) and other parameters (comfort, esthetic) should be measured at the most sensitive and systematically higher levels. While functional change may represent normal and reasonable homeostatic adaptation mecha- nisms rather than being deleterious, each such change must be carefully elucidated and individ- ually evaluated for its broadest implication as regards potential human harm. STANDARDS OF QUALITY FOR THE WORKPLACE IN COMMON USE Quality Standards Used in the United States United States Historical Development. In 1941 the American Conference of Governmental Indus- trial Hygienists (A.C.G.I.LH.) established a com- mittee of industrial hygienists for the purpose of establishing the maximal allowable concentrations (MAC) for atmospheric contaminants in the workplace. Five years later such a list of recom- mended MAC values was suggested for use in industry. However, certain difficulties attended this designation, MAC. For one, these values were based upon time-weighted averages (see below) and did not represent a maximal ceiling value inherent in the name. For another, inherent in the title was an implication that such concen- trations were “allowable,” and thus a certain ap- probation was attached to concentrations below and up to such concentrations. At other times and places, this latter problem was associated with the use of the designation, Maximal Permissible Concentrations, or MPC. In order to obviate these problems, in the 1960’s the term Threshold Limit Value (TLV) was substituted for MAC. This new term, TLV, did not suffer these problems; without the impli- cations associated with “allowable,” more empha- sis could be given to the practice of attempting to keep ambient concentrations below any designated value to the most practicable extent. The A.C.G.I.H. Threshold Limit Values (TLV) Nature of the TLV of air for occupational environments — TLV values refer to airborne 3. concentrations of substances and represent condi- tions under which it is believed that nearly all workers may be exposed eight hours a day for a forty-hour week over a working lifetime without adverse effect. Because of wide variation in indi- vidual susceptibility, exposure of an occasional individual at, or even below, the Threshold Limit may not prevent discomfort, aggravation of a pre- existing condition or occupational illness. The TLV’s represent eight-hour, time-weighted averages, i.e., airborne concentrations averaged with regard to their duration, occurring over an eight-hour period. Certain chemical agents are associated with a “c” or ceiling designation; exposure to concentra- tions in excess of this value should not be per- mitted regardless of duration. Such designations stem from the fact that such agents may provide irritation, sensitization or acute poisoning immedi- ately, or after a short latent period, upon even short exposures. Examples of such compounds among the respiratory irritants are chlorine, for- maldehyde, vinyl chloride; narcotic agents such as methyl chloride; sensitizers such as toluene-2,4- diisocyanate; or those compounds which rapidly accumulate, such as benzene. For those substances not given a “c” designa- tion, excursions above the TLV are permitted. These agents produce their principal effects by cumulative, repeated exposure; thus, short excur- sions will not necessarily produce deleterious ef- fects. The TLV’s for such substances should be considered as average values integrated in relation to time. In general, the permissible range of fluc- tuations depends upon: the nature of the poison in general, the intensity of concentration required to produce acute effects, the frequency with which the average maximum tolerable concentration is exceeded, the duration of such excesses, and the cumulative effects of the exposure. For such a complex of reasons, it should be apparent that expert opinion should shape the use and interpre- tation of the TLV’s. However, the A.C.G.I.H. gives some guidance for determining how great an excess above the TLV is permissible. For sub- stances not having a “c” designation, the following guides apply: TLV Range Excursion TLV ppm* or mg/M?#* Factor Otol 3 >1 to 10 2 >10 to 100 1.5 >100 to 1000 1.25 *Whichever unit is applicable Thus, a substance having a TLV of 5 ppm may fluctuate above the TLV, reaching a value of 10 ppm for periods of up to 15 minutes. However, the time-weighted average for an eight-hour day should not exceed 5 ppm. It is noted that the “Excursion TLV Factor” decreases as the mag- nitude of the TLV increases. Not to decrease this factor and increasing TLV magnitude would per- 81 mit exposure to large absolute quantities, a condi- tion that is minimized at low TLV’s. Moreover, larger factors at the lower TLV’s are consistent with the difficulties in analyzing and controlling trace quantities.” Where the TLV’s previously were given in terms of a volume per volume basis, i.e., parts per million, the trend appears to be for statement of TLV’s on the basis of mass per volume, e.g., milligrams per cubic meter (mg/M*) in addition to “ppm.” Most toxic dusts are listed in terms of million particles per cubic foot and in mg/M* of respirable dust. Procedure for Establishment of Values. Experts in industrial hygiene and toxicology annually re- view a list of over 400 substances. On the basis of literature data and personal information known to committee members, TLV’s are recommended. Opportunities are afforded for comment by inter- ested persons or organizations. In the case of a new substance being added or a change in the TLV of a material on the list, such new value is listed for two years as a “tentative” value, so that such parties may submit any additional informa- tion for the committee’s consideration. In addi- tion, periodically the committee publishes a “Doc- umentation of TLVs;” this provides a detailed review for each substance and the bases utilized in assigning the TLV’s.” American National Standards Institute (formerly, American Standards Association) Z-37 Committee Standards (ANSI) Nature of ANSI, Z-37 workplace quality stan- dards, maximal acceptable concentrations: Time-weighted average: This Standard is essen- tially the same as the time-weighted eight-hour average of the A.C.G.I.H. Threshold Limit Value (TLV). Acceptable Ceiling Concentration. The Standard establishes the maximum level allowable concen- tration during the period of exposure, assuming that the time-weighted eight-hour average concen- tration is not exceeded. However, excursions above this ceiling may be permitted under certain conditions, as in: Maximum Acceptable Peak Concentrations. These constitute the exceptions to the ceiling level noted above. The peak concentrations noted are speci- fied as to their concentration, the duration of such excursion(s), and the number of time(s) such peaks may occur in one eight-hour day. Formulation Procedure. The Z-37 committee of ANSI is composed of governmental, industrial, professional society and university-based experts in industrial toxicology, hygiene and medicine. Assignments for standard development are given to committee members or others having experi- ence with the material in question. The committee votes upon the standard which is then sent for- ward for other Institute approval and ultimate publication as a Standard. Maximal acceptable concentrations are published for a number of ma- terials as individual documents which give the basis for such judgments. In addition, analytical and sampling methods are recommended; the Standard publication also describes the toxicity of the material as well as its physical and chemical properties. Federal Standards Under the Occupational Safety and Health Act of 1970, the National Institute for Occupational Safety and Health (NIOSH) has the responsibility for developing criteria and recommended stan- dards and the Department of Labor has the re- sponsibility for promulgating standards. The initial compilation of health and safety standards promulgated by the Department of Labor’s OSHA was derived from national con- sensus standards and recognized Federal Stan- dards. In addition to these sources there have been, and are being developed, documents by NIOSH from formulations which are reviewed by NIOSH and its consultants. Inputs from selected professional societies, other Federal agencies and such interested parties as organized labor and trade associations are also obtained. Finally, the criteria document with the recommended standard is forwarded to the Secretary of Labor. His con- siderations benefit from any additional review he deems appropriate. The Secretary of Labor has the responsibility for promulgating standards. In some cases he may refer for study and review a recommended stan- dard to an advisory committee in accordance with provisions of the Act. However, regardless of whether this step is taken, if this is a 6 b regula- tion, he must publish it as a proposed regulation and standard so that objections and comments can be heard before such a standard is effective. Note: Standards promulgated under author- ity of Section 6 a of the Act and emergency stan- dards under Section 6 c of the Act can be promul- gated without going through the “proposed” stage.) In addition, under the Federal Coal Mine Health and Safety Act of 1969 (P.L. 91-173) NIOSH has the responsibility for transmitting to the Secretary of Interior recommended health standards. After a similar review and hearing process such standards are promulgated by the Department of the Interior. State Regulations and Standards While most states have lists of in-plant Air Quality Standards, the majority have essentially adopted those of the ACGIH TLV’s. Accordingly, these are all eight-hour time-weighted averages, although Pennsylvania has also developed a series of short-term limits. These latter differ from the ACGIH values in that specific exposure durations for such excursions are stated in the Pennsylvania regulations. WORKPLACE QUALITY FORMULATIONS IN USE OUTSIDE THE UNITED STATES U.S.S.R. Philosophy. Standards are absolute limits that may not be exceeded during any part of the work- ing day, regardless of lower concentration that may have existed during that day. These Stan- dards are legally binding. The major scientific bases utilized in setting MAC's in the U.S.S.R. derive from reactions of the higher nervous system and physiological al- teration. Feasibility does not seem to be consid- 82 ered in the standard setting process, although there is some question as to whether such standards represent goals or working realities. Thus, because such minimal physiological or neurofunctional changes (= adaptive re- sponses?) are considered as designating the bor- derline between harm and safety, and since a safety margin is then applied, the Soviet Standards tend to be lower than those found in the United States. However, close examination of these dif- ferences reveals that in actuality only relatively few cases of gross differences (more than 4-fold) exist!” Formulation Procedures. Much of the work in- volved in establishing standards is performed by the Academy of Medical Sciences, and The Insti- tute of Industrial Hygiene and Occupational Dis- eases in Moscow, as well as other institutes. The data are then evaluated by the Permanent Com- mittee for the setting of MAC’s. Ultimately, standards are promulgated as Soviet Standard 245-63 by the U.S.S.R. Ministry of Health. West Germany Maximum allowable concentrations (MAK- Werte) are developed by an expert commission of the German Research Association (Deutschen Forschungsgemeinschaft) and are adopted in total by the Ministry of Labor & Welfare. In essence, they reflect the values adopted by the A.C.G.I.H. with some variations. The values adopted repre- sent legal standards. A documentation is presently in preparation. United Kingdom The Factory Inspection Service of the Depart- ment of Employment utilizes a list of standards which act as benchmarks for the inspectorate. The values used are essentially those of the A.C.G.1.H. France Although French legal codes are extremely detailed regarding precautionary measures (e.g., medical, technical) for the protection of workers exposed to toxic substances, only a very few, spe- cific materials are given numerical values in French codes. This stems from recognition of the reality that such values do not represent inflexible, abso- lute dividing lines between safety and hazard. Others Eastern Bloc Nations. Legal standards specifically stated in terms of numerical values are the rule. These are then promulgated by the Ministries of Health or those relating to production and are legally binding. It is of interest to note that most frequently (except for Bulgaria) the values cited are not identical with those adopted in the U.S.S.R. Asiatic. Several of these recommend tests of stan- dards of air quality in workplaces. The most not- able of these is Japan; the numbers recommended by the Japanese Association of Occupational Health largely reflect those published by the A.C.G.L.H. UTILIZATION OF STANDARDS OF QUALITY FOR THE OCCUPATIONAL ENVIRONMENT The Philosophic Basis of Their Use Consideration of the foregoing should clearly indicate that the formulation of quality standards has no absolute informational basis. The variabil- ity of biological response, the judgmental elements which enter into evaluation of environmental and biological data, the imprecise nature of the biolog- ical response — all of these imply that after such evidence is weighed, a less than absolute decision must be reached. While a numerical value is ulti- mately decided upon, the non-absolute nature of the data upon which it is based should suggest that such value must not be taken to represent an absolute boundary between the positively safe and the positively unsafe. Thus, for example, if the “safe” value is 50, this cannot be taken to mean that 49 is always safe or that 51 represents an unsafe area. At best, such values represent bench- marks, or guides for protective action. Within this context, if a time-weighted average of 49 is at- tained, this should not be understood to mean that a lower value should not be pursued. Conversely, a value of 51 does not mean that damage to the individual so exposed will necessarily ensue. Within the context of legal codes such values do in- dicate the boundary between ‘“‘safe” and “unsafe.” Application of TLV’s must take into account the multiple biological considerations discussed in this chapter and elsewhere and the elements of pro- fessional judgment inherent in the formulation of such standards (see section on Principles for De- veloping Workroom Air Quality Standards). Obviously, repeated excursions above an air quality standard should not be tolerated. Where “c” or ceiling values are listed (see above), such excursions may lead to health or functional im- pairment, e.g., for liposoluble volatile solvents with narcotic properties as trichloroethylene or carbon disulfide. With substances not having such ceiling designations, excursions above such TLV’s may only be permitted consistent with the recommended level (see above discussion of A.C.G.I.H. values). In the event that a survey indicates excursions above TLV’s, the competent authority is respon- sible for more definitive evaluation of such situa- tions. Thus, repeated samples of the work envi- ronment representative of temporal and spatial variations in worker exposure should be obtained, consistent with good sampling procedures (see Chapter 10). In addition, medical biological evaluation of the workers at possible risk is indicated. The ap- propriate medical examinations should delineate whether health damage, actual or potential, is occurring. Samples of biological media (blood, urine, expired air, tissues such as hair) should be analyzed to determine whether undue body burdens are being taken up. If such more definitive evaluations indicate the presence of an occupational risk to worker health and safety, appropriate control action is necessi- tated. That such values represent indicators for further evaluation and control action must be clearly understood. Such values can only be prop- erly utilized by those possessing knowledge regard- ing these facts as well as an understanding of health implications of the specific environmental agent concerned. Thus a considerable element of judgmental evaluation is required; there should be 83 no automatic, unthinking application of such val- ues for the protection of worker safety and health. Appropriate Application of Standards Health and Medical Control. Possibly the most important use of quality standards relates to their use for medical control. Since medical and clinical laboratory testing imply certain costs, judicious planning for their deployment requires some guide- lines to determine the frequency and extent of medical surveillance consistent with worker safety and health. Thus, if threshold limit values are repeatedly exceeded, more frequent and extensive medical surveillance is indicated while and after control measures are being accomplished. Cer- tainly, as such quality standards are exceeded, the nature of medical testing becomes quite different than if these standards are never approached. It should be clearly indicated that even if such qual- ity standards are not exceeded, medical surveil- lance cannot be neglected or omitted. However, their stringency should reflect the degree to which standards are approached or exceeded. It should be emphasized that medical action becomes useless as regards prevention unless coordinated with ap- propriate engineering action for amelioration of workplace contamination. Design of Engineering Controls and Practices. Given such numerical values, it becomes possible for the design engineer to ascertain that engineer- ing control of the process is required. With a knowledge of the physical properties of the mate- rial in question, the amounts used and the possible loss from the process, one can then formulate the ventilation or enclosure requirements necessary which will capture the contaminant in question and prevent its escape to the work environment. Good engineering practice should never permit the workplace concentration to reach the quanti- tative level prescribed by the standard. It should be recognized that the economic cost of controls may mount geometrically as lower levels of work- place contamination are sought. Consequently, there is decreasingly less merit in attempting to attain absolute levels of capture, nevertheless, while the lowest level feasible should be sought, it can be seen that quality standards do provide benchmarks against which performance can be measured, consistent with economic considera- tions. Surveillance of Adequacy of Control and Mainte- nance Practices. Once such control equipment is installed, its performance should be monitored. Given accumulation of material in ducts or fans, wear and aging of equipment, the performance of such equipment will tend to deteriorate. The point at which maintenance or replacement is required — with its attendant economic cost — can be determined by monitoring the work area. Since such decisions and the attendant depreciation costs may be considerable, the benchmarks for environmental quality become useful in rational planning of maintenance and replacement. Use for Development of Analytical Techniques. In the realm of environmental monitoring, the de- sign of analytical methodologies requires that some specific range of sensitivity should be sought if the method is to have practical use. Thus, the analyst can use such quality standards in ascertaining how such analysis need be carried out. For example, while wet chemical methods may be quite ade- quate for the measurement at the 100 ppm level, at one-thousandth of this level other techniques may be called for, e.g., gas chromatography. Thus, knowing what concentration range must be meas- ured is of obvious value; quality standards clearly indicate such ranges. Basis for Communication and Interaction Among the Various Specialty Disciplines in the Occupa- tional Health Team Misuse of Standards — Comparison of Standards with Single Environmental Determinations. Gen- erally speaking, to properly evaluate environ- mental quality in the workplace, the obtaining of a short-period single determination has little or no value. Likewise, to compare such short-period sample with an 8-hour environmental quality standard represents a misuse of such standards. Since most standards represent time-weighted av- erages (see above), one sample probably cannot provide such an evaluation, unless it is an eight- hour sample or can be reliably related to the full- shift exposure. Even where ceiling values (see above) are exceeded, a single sample may be invalid unless it is clearly related to the worker, e.g., in relation to his breathing zone. Obviously, quality standards have meaning only when ade- quate industrial hygiene sampling techniques are utilized (see Chapter 10). 84 References 1. 10. DINMAN, B. D. “The ‘Non-Concept’ of ‘No Threshold’: Chemicals in the Environment.” Science 175: 495-97, 1515 Massachusetts Ave., NW, Washington, D.C. (1972). HATCH, T. F. “Permissible Levels of Exposure to Hazardous Agents in Industry.” J. Occup. Med. 14: 134-37, 49 East 33rd St., New York, N.Y. (1972). Threshold Limit Values of Airborne Contaminants and Intended Changes, Adopted by the A.C.G.I.H. for 1971. American Conference of Governmental Industrial Hygienists, Cincinnati, Ohio (1971). STOKINGER, H. E. and J. T. MOUNTAIN. “Prog- ress in Detecting the Worker Hypersusceptible to Industrial Chemicals.” J. Occup. Med. 9: 537-41, 49 East 33rd St., New York, N.Y. (1967). STOKINGER, H. E. “Criteria and Procedures for Assessing the Toxic Responses to Industrial Chem- icals in Permissible Levels of Toxic Substances in the Working Environment.” ILO Occupational Safety and Health Series, No. 20 Geneva, Switzer- land (1970). SMYTH, H. F., JR. “The Toxicologic Bases of TLV:1; Experience with TLV’s Based Upon Animal Data.” A.[l.H.A. J. 20: 341-345, 210 Haddon Ave., Westmont, N.J. (1959). Ibid, Reference 5, pg. 174. STEWART, R. D., H. H. GAY, D. S. ERLEY, C. L. HAKE and J. E. PETERSON, “Observations on the Concentrations of Trichloroethylene in Blood and Expired Air Following Human Exposure.” ALH.A. J. 23: 167-170, 210 Haddon Ave., West- mont, New Jersey (1962). AMERICAN CONFERENCE OF GOVERNMEN- TAL INDUSTRIAL HYGIENISTS. Documentation of the Threshold Limit Values for Substances in Workroom Air. Third edition, P.O. Box 1937, Cin- cinnati, Ohio (1971). TRUHAUT, R. Reference 5, pg. 53. CHAPTER 9 THE SIGNIFICANCE AND USES OF GUIDES, CODES, REGULATIONS, AND STANDARDS FOR CHEMICAL AND PHYSICAL AGENTS Lewis J. Cralley, Ph.D., and Walter H. Konn INTRODUCTION The passage of the Social Security Act (1935), assured the eventual acceptance in the United States of the philosophy that the worker had the right to earn a living without endangering his health. During the period since 1935 a number of states’ *** adopted codes and regulations gov- erning conditions of work to prevent injury to health and in many instances established threshold limit values which limited levels of exposures in the working environment. The adoption of state codes and regulations governing the control of the working environment led to greatly accelerated research to obtain data both for the establishment of rational threshold limit values and for their extension to cover as many agents as possible. This research, in turn, led to new procedures for studying the effects of environmental agents on worker health.’ Signifi- cantly, this research revealed that many agents which gave rise to acute responses from high ex- posure levels over a relatively short period of time elicited a different response to lower levels of ex- posure to the same agents over a prolonged period of time. Through data obtained both from epidemio- logic and animal research, a body of knowledge has been acquired which permits establishing the rationale for threshold limit values. This rationale is succinctly stated by Hatch:® “1) There exists a systemic dose-response relationship between the magnitude of exposure to the hazardous agent and the degree of response in the exposed individual, and 2) there is a graded decrease in the risk of injury as the level of the exposure goes down, which risk becomes negligible when exposure falls below a certain tolerable level. Thus, in the face of recognized potential dangers associated with certain physical and chemical agents, these prin- ciples say that such agents can be dealt with safely at some acceptable level of contact above zero and, therefore, that they do not have to be elim- inated altogether from industry in order to protect the workers’ health.” PROMULGATION OF GUIDES, CODES, REGULATIONS AND STANDARDS Two general procedures are used in the estab- lishment of occupational safety and health laws. The first is through statutes promulgated by legis- lative action. The second procedure is through 85 codes, regulations and standards promulgated by agencies with rule-making authority. The latter procedure is, by far, the most common one and is more readily responsive to need for changes. Promulgations through either course of action have the same force and effect of law. A code is a body of law established either by legislative or by administrative agencies with rule- making authority. It is designed to regulate com- pletely, so far as a statute may, the subject to which it relates. “New York State Industrial Code Rule No. 12 Relating to Control of Air Con- taminants in Factories” is an example of such a code.” A regulation is an authoritative rule dealing with details of procedure; or, a rule or order hav- ing the force of law, issued by an executive author- ity of government. The State of Michigan “Regu- lation Governing the Use of Radioisotopes, X Ra- diation and All Other Forms of Ionizing Radia- tion” is an example.® A standard is any rule, principle or measure established by authority. The term “occupational safety and health standard” under the Occupa- tional Safety and Health Act of 1970 means “a standard which requires conditions, or the adop- tion or use of one or more practices, means, methods, operations, or processes, reasonably nec- essary or appropriate to provide safe or healthful employment and places of employment.” A guide is an instrument that. provides direc- tive or guiding information. Examples of guides are the “American Industrial Hygiene Association Guides”! and the “Threshold Limit Values of Airborne Contaminants and Physical Agents” adopted by the American Conference of Govern- mental Industrial Hygienists."* Although such guides, per se, do not have the force of law, their values may be incorporated into codes, regulations and standards that do have the force of law. SOURCES OF DATA FOR EXPOSURE LIMIT VALUES Exposure limit values are based on data aris- ing out of experimental animal and human studies and from data on industrial experience obtained through clinical and epidemiologic studies of workers. Interrelated data from the three sources give the most rational data upon which to base exposure limits. Animal and human experimental data are most suitable for deriving biologic re- sponse data on single substances or specific com- binations of substances. Workers, however, are seldom exposed to such limited combinations of substances in their work environment. Also, the personal habits of workers, such as cigarette smok- ing, consumption of alcoholic beverages, and use of drugs may alone have a profound influence on the health profile of workers, or they may have an additive or synergistic action on exposures in the work environment. The health of the worker rep- resents the influence of his twenty-four hour a day environment over a lifetime. Thus procedures and data are needed which will distinguish between health patterns from on and off-the-job stresses. Well designed epidemiologic studies can delineate the influence of multiple on and off-the-job stresses in the environment and have the advantage of being able to study workers over a lifetime. Research to obtain biologic response data upon which to base exposure limit values is very costly and time consuming. The resources for such studies come mainly from government, industry and foundations. The research may be carried out at facilities operated by the government, edu- cational institutions, foundations, consultants and industry. The Occupational Safety and Health Act of 1970 will stimulate research at all these levels for obtaining data upon which to base ex- posure limit values. NATURE AND SOURCES OF EXPOSURE LIMIT VALUES As stated previously, occupational health codes, regulations and standards may be both general and specific in their coverage depending on their objectives and the procedures intended for their implementation. Any one act may cover a single or several elements to accomplish the stipulated requirements including such areas as threshold limit values, methods and procedures for monitoring the environment, methods of con- trol, use of respiratory protective equipment and protective clothing, and handling of waste. The establishment and use of exposure limit values are so fundamentally a part of occupational health, codes, regulations and standards that special attention is devoted to their development, significance and use. The American Conference of Governmental Industrial Hygienists publishes annually a list of “Threshold Limit Values of Airborne Contami- nants and Physical Agents.”'" The lists are re- viewed annually and values are updated as relative data becomes available. Intended changes are published as a part of the annual list and com- ments supported with data are requested. The threshold limit values of the American Conference of Governmental Industrial Hygienists are airborne concentrations of substances and levels of physical agents below which values it is believed that nearly all workers may be exposed repeatedly eight hours per day, forty hours per week, without adverse effect. In the use of these values, medical surveillance is recommended to detect workers who are hypersusceptible to specific chemicals or physical agents, so that they can be removed from the exposure or given special protection. Ceiling 86 values in connection with threshold limit values represent exposure values which should not be exceeded and relate to substances which are fast acting and whose threshold limits are more appro- priately based on a particular biologic response. In instances where the cutaneous route is an im- portant source of absorption, substances are marked with the notation “skin” to stress this property since the threshold limit value refers only to inhalation as the source of entry of the agents into the body. The American National Standards Institute, Inc., publishes consensus standards of acceptable concentrations for chemical and physical agents.'* The standards are useful in establishing engineer- ing procedures for the prevention of objectionable levels of chemical and physical agents in the work environment. Acceptable concentration values are presented in terms of a time-weighted eight-hour workday, acceptable ceiling concentrations within an eight-hour workday, and acceptable maximum peak concentrations for short specified durations. American National Standard acceptable concen- trations are values below which ill effects are un- likely. The values are not to be used as the basis for establishing the presence of occupational disease. The Commonwealth of Pennsylvania Depart- ment of Health has established a list of short-term limits as a part of the “Regulations Establishing Threshold Limit Values in Places of Employ- ment.”"* The short-term limit is the upper limit of exposure for which a workman may be exposed to a contaminant for a specified short period. Short-term episodes are included in the daily aver- age concentrations for compliance with the estab- lished threshold limit values for contaminants to which workers may be exposed for an eight-hour workday. The Committee on Toxicology of the National Research Council (operating arm of the National Academy of Sciences and National Academy of Engineering) publishes a list of recommended emergency exposure limits.”* These recommended emergency exposure limits are not intended to be used as guides in the maintenance of healthful working environments but rather as guidance in advance planning for the management of emer- gencies. The American Industrial Hygiene Association publishes a Hygienic Guide Series'® covering an extensive list of chemicals. A hygienic guide for a given material contains the following information: Significant Physical Properties: Hygienic Stan- dards (limits) for eight-hour, time-weighted ex- posures, short exposure tolerance, and atmospheric concentrations immediately hazardous to life; Toxic Properties, including exposure via inhala- tion, ingestion, skin contact and eye contact; In- dustrial Hygiene Practice, including industrial uses, evaluation of exposures, hazards and their recom- mended controls; and Medical Information, in- cluding emergency treatment and special medical procedures. The National Institute for Occupational Safety and Health, Public Health Service, Department of Health, Education, and Welfare has a responsi- bility for developing and publishing criteria deal- ing with toxic materials and harmful physical agents which will describe safe levels of exposure for various periods of employment.” The Institute also is responsible for conducting and publishing research, including industry-wide studies, which will lead to the development of criteria documents. A number of official agencies and organiza- tions publish recommended exposure limits for specific agents. Examples include: National Bu- reau of Standards Handbook No. 59 “Permissible Dose for Ionizing Radiation”® and Handbook No. 93 “Safety Standards for Non-medical X Ray and Sealed Gamma Ray Sources;”'® “Intersociety Guidelines for Noise Exposure Control”'” devel- oped by an Inter-society Committee representing the American Industrial Hygiene Association, American Conference of Governmental Industrial Hygienists, Industrial Medical Association, and the American Academy of Ophthalmology and Otolaryngology. A number of organizations have programs for developing threshold limits for biologic materials, i.e., urine and blood. The National Institute for Occupational Safety and Health, Office of Re- search and Standards Development,'® has devel- oped a procedure whereby consultants are ap- pointed to a committee for the purpose of estab- lishing biologic threshold limits for specific substances. The Permanent Commission and In- ternational Association on Occupational Health? has established a committee for developing inter- national standards for levels of contaminants and their metabolites in biologic materials. The Amer- ican Industrial Hygiene Association established a Committee on Biochemical Assays to study and recommend procedures for determining levels of specific contaminants and their metabolites in biologic materials, and recommend levels indica- tive of excessive exposure. The International Labour Office,” Geneva, Switzerland, publishes model codes, codes of prac- tice, guides and manuals in the areas of occupa- tional safety and health. The publications cover both chemical and physical exposures and treat the subject in depth. SIGNIFICANCE AND USE OF EXPOSURE LIMIT VALUES Exposure limit values are the crux of most occupational health codes, regulations and stan- dards. If there is no exposure to a harmful agent it follows that the presence of this agent does not create a health problem. Also the toxicity of a material per se, though extremely important, is not the sole criterion of whether or not a health problem is present where the material is encoun- tered. The terms “toxicity” and “hazard” are not synonymous. Many factors, in addition to the toxic nature of a material, are important in eval- uating a hazard potential. These include the chem- ical and physical properties of the toxic substances, the ability of the toxic substances to interact with surrounding materials, and the influence of sur- rounding conditions such as temperature and hu- midity on the toxic substances, as well as the concentration, stability, and conditions of use of 87 the toxic substances and the conditions under which they are encountered. The toxicity of a substance expressed in terms of a threshold limit value, however, is an impor- tant criterion and concept in evaluating the pres- ence of a health hazard. As stated in the introduc- tion, threshold limit values are based on the concept of a dose-response relation between the agent and its health effects on the worker, that this is of a graded nature, and that consequently there is a lower level of exposure at which level the substance will exert no deleterious effect on the worker. The application of this knowledge to assure that workers are not exposed to concentra- tions above these threshold values is an important concept in the prevention of occupational diseases. Due to individual variations in susceptibility and the many unknown factors in the working environ- ment and their effects on a given toxic material, the threshold limit value of a material is not a fine distinction between a safe and dangerous condi- tion. Though levels of exposure may be kept within a designated threshold limit value, this is no assurance that an individual worker may not show some deleterious effects if he has unusual susceptibility. The importance of ceiling levels, skin absorption, etc. must also be considered es- pecially if they are contained as an integral part of the threshold limit value. Biologic standards, i.e., the concentration of a specific agent in the urine or blood, represents the body burden of that agent and may be used as a monitor of the exposure of a worker to a specific substance. Thus biologic levels of a mate- rial represent the integrated relation of a combina- tion of the complex chemical and physical char- acteristics of an exposure on the worker and can be used to indicate where excessive exposures have occurred, when removal from further ex- posure is indicated, etc. As with threshold limit values, biologic standards do not represent a fine line of distinction between safe and dangerous conditions and alone are not definitive of a state of disease. It must also be stressed that the body burden of an agent represents all sources and routes of exposure and is not limited to industrial exposures. Habits, hobbies, etc. that may involve factors which influence the absorption and reten- tion of a substance may be important. The application of exposure limit values in the evaluation of the work environment requires a knowledge of the limit values, of their application and meaning, and of acceptable methods and pro- cedures for measuring exposure levels. The latter is discussed separately under the heading ‘“Selec- tion of Methods and Procedures for Measuring Exposure Levels.” Threshold limit values are expressed as time- weighted averages for an eight-hour workday and forty-hour workweek. The time-weighted averages for specific substances, unless designated by special categories or ceiling limits, permit limited excur- sions above the threshold limit value provided they are compensated by offsetting excursions below the value. In the application of threshold limit values to mixtures of toxic substances, in the absence of other information, their effects are considered ad- ditive. Thus their additive factor should not exceed unity in terms of their individual exposure concen- trations over the threshold limit values. Threshold limit values are becoming increas- ingly significant since they are used in most occu- pational health codes, regulations, and standards as the yardstick for measuring compliance. Ex- ceeding the values can bring on severe penalties. It is extremely important that the employer have worker exposure monitoring data assuring com- pliance with relevant standards. These monitor- ing data should include time-weighted averages, extent of excursions above time-weighted averages, ceiling levels, and short-term exposure levels as relevant, In addition to data monitoring exposure levels, data on levels of exposure in the general room area and at contaminant disseminating sites are useful in assuring the ability of the control system to adequately contain the contaminant and of its continuing satisfactory performance. SELECTION OF METHODS AND PROCEDURES FOR MEASURING EXPOSURE CONCENTRATIONS The measurement of exposure concentrations in the working environment assume utmost impor- tance since compliance to standards are based upon comparison of existing levels of exposure with values stipulated in the standards. In the adoption of exposure limit values into standards, it must be assumed that there are valid, tested and reproducible procedures for the collection and analysis of the agent involved. Seemingly small errors or departures from accepted practices may have a considerable impact, on the one hand on the health protection afforded the workers through application of the standard should inadvertently low values be obtained, and on the other hand on the economic loss involved for compliance should inadvertently high values be obtained in measuring exposure levels. In some standards acceptable methods and procedures are listed for measuring exposure levels for compliance. Where this is not done, reliance must be placed upon the experience and competence of the persons involved. The decisions include not only methods and procedures to be used but also the assurance of representative sam- ples, the proper calibration of equipment, the use of internal controls, and a sampling regimen that will satisfy compliance requirements. For these reasons, laboratories engaged in measuring worker exposure levels, either through the collection of airborne samples or biologic fluids, should be ac- credited for this purpose. ENACTMENT OF OCCUPATIONAL HEALTH GUIDES, CODES, REGULATIONS, AND STANDARDS A number of official agencies have rule-mak- ing authority for the enactment of occupational health legislation for the protection of the worker. The most recent and comprehensive legislation of this nature, Public Law 91-596 enacted by the 91st Congress,” “establishes authority in the Secre- 88 tary of Labor for the adoption and enforcement of standards for safe and healthful working condi- tions of working men and women employed in any business affecting commerce.” The safety and health standards promulgated under the Walsh- Healey Act, as well as other established federal standards relating to construction work, ship re- pairing, shipbuilding, shipbreaking and longshor- ing operations were adopted as safety and health standards under the Federal Occupational Safety and Health Act, and are subject to revision under that Act. Exceptions to this primarily relate to the Atomic Energy Act of 1954, and the Federal Coal Mine Health and Safety Act of 1969 since the Occupational Safety and Health Act of 1970 does not apply where other federal agencies regu- late under applicable federal law. The Occupational Safety and Health Act established a National Institute for Occupational Safety and Health within the Department of Health, Education, and Welfare to conduct re- search and training, develop criteria, publish a list of toxic substances, and make inspections relative to these responsibilities. The Act also provides for the participation of state official agencies in carrying out the provisions of the Act. The Federal Metal and Nonmetallic Mine Safety Act? vests authority in the Secretary of the Interior for promulgating and carrying out health and safety standards “for the purpose of the pro- tection of life, the promotion of health and safety, and the prevention of accidents in Metal and Non- metallic Mines.” The Federal Coal Mine Health and Safety Act of 19692 vests authority in the Secretary of the Interior to promulgate and enforce standards for the protection of life and the prevention of injuries in a coal mine. The Act directs the Secretary of Interior to develop and promulgate, as may be appropriate, improved mandatory safety standards and to promulgate mandatory health standards transmitted to him by the Secretary of Health, Education, and Welfare. The Act also provides cooperation and assistance to states in the develop- ment and enforcement of effective state coal mine health and safety programs. The Bureau of Mines, Department of Interior, also has responsibility for the approval of respira- tory devices for protection against the inhalation of gaseous and particulate substances.** The Atomic Energy Commission has author- ity for establishing radiation standards in a number of areas. Examples include “Standards for Pro- tection Against Radiation”®® and “Licenses for Radiography and Radiation Safety Requirements for Radiographic Operators.”*® The former sets forth a very detailed set of standards which have the effect of law. The latter specialized standard was published because of the large number of isotope sources used for radiography and the fact that many overexposures had occurred during radiographic procedures. Several state agencies have responsibilities for establishing and enforcing standards for protecting the health of workers coming within their juris- dictions. The enactment of the Occupational Safety and Health Act of 1970, however, had a . profound influence on the Federal-State relation- ship in this area since the latter covers all workers engaged in activities related to commerce. Desig- nated state agencies with standards and programs approved by the Department of Labor can by agreement undertake the enforcement of the Fed- eral Act within their boundaries. SIGNIFICANCE AND IMPACT OF OCCUPATIONAL SAFETY AND HEALTH ACT OF 1970 The Occupational Safety and Health Act of 1970 has brought important, new dimensions in safeguarding the health of workers and in the practice of industrial hygiene. Although the im- pact of many of these newer dimensions is imme- diate, new interpretations and applications of the Act are made by the courts as the need arises. Thus it will be many years before the full impact of the Act is fully realized. The coverage of the Act is comprehensive and has brought into its jurisdiction numerous workers heretofore excluded from such benefits. Generally, the Act applies to all workers employed in places of work, engaged in a business affecting commerce, except for government employees. To appreciate the impact of the Occupational Safety and Health Act it is necessary to review briefly the coverage by regulations and the prac- tices prior to its enactment. Prior to 1936 the only regulations and guides relating to occupational health were administered , by state and local governmental agencies. In most instances the guides and regulations were very general, difficult of enforcement, and relied on professional judgment with respect to compliance. Most of the states had no programs relating to occupational health, and those that existed were far tpo minimal in staffs and funds to carry out effective programs. The Walsh-Healey Act of 1936 (41 U.S.C. 35; 49 Stat. 2036) which enabled the Federal Government to establish standards for safety and health in work places engaged in activities relating to Federal contracts, was the forerunner in estab- lishing today’s concepts of occupational health reg- ulations. The 1936 Act stimulated research into the cause, recognition, and control of occupational disease and led to the development of occupa- tional health programs by official organizations, insurance companies, foundations, managements and unions. Subsequently other Federal legisla- tion had further impact on the promulgation of Federal safety and health standards. These in- clude the Service Contract Act of 1965 (41 U.S.C. 351; 79 Stat. 1034), Public Law 85-742, Act of 1958 (33 U.S.C. 941; 72 Stat. 835), Public Law 91-54, Act of 1969 (40 U.S.C. 333; 83 Stat. 96), and the National Foundation of Arts and Human- ities Acts (79 Stat. 845). The interim period be- tween 1936-1970 also saw a number of states issuing occupational safety and health regulations to cover workers in their jurisdictions. None of the occupational health programs in official agencies during this period, however, were adequate in —scope, staff, or funds to carry out their responsi- bilities. 89 The lack of uniformity within the various reg- ulations established by Federal, state and local official agencies led to great confusion in indus- tries that operated interstate. Programs by industry for compliance with regulations had to vary from state to state and could not be established on a uniform corporate-wide basis. The Occupational Safety and Health Act of 1970 has brought a restructuring of programs and activities relating to safeguarding the health of the worker. Uniform occupational health regulations now apply to all businesses engaged in commerce, regardless of their locations within the jurisdic- tion. Threshold limit values have been incorpo- rated into the regulations and now have the effect of law. In the earlier years, the establishment of threshold limit values, whether with the effect of law or used as guides, was done more on the basis of professional opinion and judgment than on the basis of facts. Data were minimal on the health effects of exposures to most materials encountered in industry. Uniformity of procedures and meth- ods for the collection and analysis of airborne con- taminants was generally lacking. The interpreta- tion of compliance with a regulation or threshold limit value was often that of professional judgment. Information on investigations and inspections rela- tive to violations and compliance of standards was usually restricted to the official agency and man- agement concerned. Likewise, medical data ob- tained through the examination of workers in many instances were not available to the medical de- partment of the industry. The Occupational Safety and Health Act of 1970 has more clearly defined procedures for es- tablishing regulations, the conduct of investiga- tions for compliance, and the handling and avail- ability of exposure data on workers, the keeping of records, etc. The Act provides for a greatly accelerated program by the National Institute for Occupa- tional Safety and Health (NIOSH) to conduct research on the health effects of exposures in the work environment, to develop criteria for dealing with toxic materials and harmful agents, including safe levels of exposure, to train professional per- sonnel for carrying out various responsibilities prescribed by the Act, and in general, to conduct research and assistance programs for protecting and maintaining worker health. The first standard promulgated on the basis of a criteria document developed by NIOSH was “Standard for Exposure to Asbestos Dust” (Fed- eral Register Vol. 37, No. 110 — Wednesday, June 7, 1972). This standard is especially sig- nificant ‘because as the first of such permanent standards for a number of target hazardous mate- rials, it is anticipated that it will serve as the basic model for other standards to come. The asbestos standard includes sections on definitions; permissible exposures; methods of compliance; work practices; personal protective equipment; method of measurement; monitoring, both personal and environmental; caution signs and labels; housekeeping; recordkeeping, including employee notification; medical examinations; and medical records. This standard differs from prior standards in OSHA regulations, which specified only the per- missible concentrations of airborne contaminants or permissible levels at physical exposures (Occu- pational Safety and Health Standards, Paragraphs 1910.93, 1910.95, 1910.96 and 1910.97 of the Federal Register, Vol. 36; No. 105, May 29, 1971). The far reaching provisions of the new standard include the specification of methods of compliance, which include engineering controls such as ventilation and wet methods; personal protec- tive equipment such as respirators, and including shift rotation of employees to reduce exposure; caution signs and labels, not only for the work place in which asbestos is handled but also for products containing asbestos fibers; recordkeeping, including a requirement that employees exposed to airborne concentrations of asbestos fibers in excess of the limits shall be notified in writing of the ex- posure as soon as practicable but not later than five days of the finding; and medical examinations, including preplacement, annual and termination of employment examinations and specifying the minimum requisite examination procedures and tests which shall be included. The interpretation of the general duty clause requirements for providing a safe and healthful working environment and the publication of the permanent asbestos standards add new dimensions to the protection of employee health. Both em- phasize that final responsibility for compliance with the provisions of the Occupational Safety and Health Act remains with the employer. The Act prescribes procedures for use by the Secretary of Labor in promulgating regulations. It is of special interest that threshold limit values for exposures to toxic materials and harmful agents are contained in the regulations, and have the effect of law. Since procedures are given for measuring exposure levels to specific materials and agents in the standards promulgated by the De- partment of Labor, the use of professional judg- ment as required in the past for such activities is largely obviated, as is also the interpretation of the values obtained. The employee or his repre- sentative now has the right to observe monitoring procedures and have access to data on exposure levels. Disagreements on the validity of monitor- ing data and its meaning are now relegated to the courts for settlement. Professional skills and judg- ments are still required, however, in applying the intent of the many aspects of the Act in safe- guarding workers’ health. The Act has had a similar impact on the medical and nursing programs in industry.>” Many medical programs in industry had already seen the transformation from the earlier emphasis on the treatment of traumatic injuries to the modern concept of the prevention of occupational diseases and injuries. This trend, however, has not been universal and the fact remains that a vast number of workers still do not have immediate access to medical and nursing services. Among the changes in industrial medical pro- grams brought on by the Act is the maintenance 90 of medical records on employees and the access to data contained in them. All practicing physi- cians representing employers are now required to keep records of the occupational injuries and ill- nesses of their employees. Standards for specific materials and agents prescribe the nature of med- ical examinations to be given the employees, the length of time the employer must maintain the records, and who may have access to these rec- ords data. Specifically, both the Assistant Secre- tary of Labor for Occupational Safety and Health and the Director, National Institute for Occupa- tional Safety and Health, and authorized physi- cians and medical consultants may have access to these data. Also, medical data from examinations required by the regulation shall be given the em- ployer, and upon request by the employee, must be given to the employee’s physician. The industrial physician, with the knowledge that the employee has information on both his ex- posure levels to toxic materials and harmful agents and on his health status, must now maintain a pre- ventive program for follow-up of situations where excessive exposures have occurred or where bio- chemical or medical tests indicate early or impend- ing changes in employee health patterns. Since the health profile of a worker represents the effect of his twenty-four hours a day environment, the industrial physician is finding it prudent to obtain information on workers’ off-the-job activities and habits, such as hobbies, smoking, use of drugs, that either may directly affect their health or may have an additive influence to on-the-job stresses.. There has been a similar change in the prac- tices of industrial nursing over the past dec- ades.?®2* 3 The Occupational Safety and Health Act of 1970 will provide a major impetus not only in increasing the number of industrial nurses avail- able for medical services to workers, but also in using their fullest capability both in carrying out preventive medical programs and in maintaining and promoting the optimal health of the worker. In the early practice of industrial nursing, activities were largely centered around the emergency treat- ing of traumatic injuries and were prescribed in written orders of a physician. Advancing indus- trial technology along with modern concepts of preventive medical services soon assured that the industrial nurse could no longer accept such a lim- ited role. The industrial nurse, in addition to giving specific medical services, is now called upon to give broad health counseling to the worker in his overall environment. The Act will increasingly propel the industrial nurse to give a more compre- hensive service in promoting worker health. This will necessitate a close working relationship with both the industrial hygienist and the safety offi- cer, and will require a knowledge of the toxic materials and harmful agents in the in-plant en- vironment. A number of sources are available for keeping informed on enforcement aspects relating to the Act as well as citations and their review by the Occupational Safety and Health Review Commis- sion where appeal has been made by the em- ployer.®"" > 33 The following citations issued by the Occupational Safety and Health Administration and their review, where appealed, by the Review Commission, show the impact which the Act will have on occupational health and the practice of industrial hygiene and of the importance of keep- ing informed on these decisions. A landmark ruling defining the employer’s re- sponsibilities with respect to providing a safe and healthful working environment is contained in Case 10 before a Hearing Examiner of the Occu- pational Safety and Health Review Commission, U.S. Department of Labor. The case involves the Omaha, Nebraska plant of the American Smelt- ing and Refining Company (ASARCO) and a citation dated July 7, 1971. The citation alleged that ASARCO, at a plant in Omaha, Nebraska, was in violation of Section 5 (a) (1) of the Act, which provides that “Each employer shall fur- nish to each of his employees employment and a place of employment which are free from recog- nized hazards that are causing or likely to cause death or serious physical harm to his employees.” The following description of the alleged vio- lation is set forth in this citation: “Airborne concentrations of lead significantly exceeding levels generally accepted to be safe working levels, have been allowed to exist in the breathing zones of employees working in the lead- melting area, the retort area, and other work places. Employees have been, and are being ex- posed to such concentrations. This condition constitutes a recognized hazard that is causing or likely to cause death or serious physical harm to employees.” ASARCO contended that the levels of air- borne lead found in its Omaha plant during an OSHA inspection, in excess of the threshold limit value (TLV) of 0.2 milligram per cubic meter of air (0.2 mg Pb/M?) did not constitute a recog- nized hazard causing or likely to cause death or serious physical harm to its employees in view of the protective safety measures in effect. These included the use of respirators, transferring em- ployees from high exposure jobs and its biological sampling program. The Act, however, places the responsibility upon employers to provide safe and healthful working conditions for its employees, as far as possible. It does not allow employers to provide unsafe, unhealthful or hazardous working condi- tions for its employees even though the adverse effects of such working conditions are attempted to be minimized. ASARCO’s first responsibility, as set forth by the Hearing Examiner, was to pro- vide safe and healthful working conditions, by reducing the levels of airborne concentrations of lead to the generally recognized safe level of 0.2 mg Pb/M?, or as close to that figure as possible. ASARCO argued that no hazard likely to cause death or serious physical harm to employees existed at its Omaha plant because no evidence was presented that any of its employees suffered from lead intoxication or had been in any way injured by the airborne concentrations of lead found to exist at its plant. It should be stated here that ASARCO also collected air samples and the results of analyses generally confirmed the findings of the OSHA representative. The Hear- 91 ing Examiner, however, found that proof of a violation of Section 5 (a) (1) of the Act does not depend upon proof that a hazard has pro- duced injury. All that is required is a showing that the hazard is likely to cause serious physical harm or death. During the hearing, it was found that ASARCO’s preventive program, consisting of blood lead determinations, transferring of em- ployees from job to job and the availability of approved respirators in work places having high concentrations of lead “simply has not worked.” The Hearing Examiner, after review of all evidence, found that the levels of airborne concen- trations of lead significantly in excess of the thres- hold limit value (TLV) of 0.2 mg Pb/M? consti- tuted a violation of Section 5 (a) (1) of the Act, upheld the original citation and affirmed the proposed penalty of $600.00. This finding, that concentrations of an airborne material above the threshold limit value alone constitutes a violation of the Act, is a profound interpretation of the employer’s responsibilities with respect to provid- ing a safe and healthful working environment. On May 28, 1971, the Occupational Safety and Health Administration issued a citation for serious violation for exposure to mercury.** Ex- cessive concentrations of mercury vapor in the work environment were found by investigators from the National Institute for Ocupational Safety and Health. Visible pools of mercury were found in many areas. In response to the citation, the management claimed that the pools of mercury resulted from pipeline leakage when the mercury cell operation was shut down for scheduled main- tenance and equipment installation. The man- agement stated that the condition had been cor- rected and that steps had been taken to tighten up maintenance and housekeeping procedures. A citation for serious violation of section 5 (a) (1) of the Act was issued by the Occupa- tional Safety and Health Administration following an accident in which three employees were killed and two seriously injured from exposure to hy- drogen sulfide gas.?* The quantity of hydrogen sulfide gas evolved at an operation from the slurry, when partially decomposed fish were treated with a mild solution of sulfuric acid, could not have been sufficient to cause serious injury or death. A further investigation revealed that deadly quan- tities of hydrogen sulfide gas could have been evolved through another operation. Another worker cut a hole for ventilation through a metal floor-ceiling resulting in the reaction of the iron with the sulfur in phenothiozene thus forming iron sulfide, which reacted with the sulfuric acid. Judge William J. Bronz, Occupational Safety and Review Commission (Docket No. 31), dismissed the citation and proposed penalty. He ruled that past experience did not indicate the need for pro- tection when working with the slurry. The em- ployer could not have reasonably foreseen the probability of serious injury or death to employees arising out of such an episode. A citation was issued relative to workers being subjected to noise levels in excess of those per- mitted under 2 9 C F R 1910.95 (b) (1).* The employer contended that he had complied with the regulation by providing employees with pro- tective equipment. Judge James A. Cronin, Jr., Occupational Safety and Health Review Commis- sion (Docket No. 158), ruled that the citation and penalty were appropriate. He stated that the employer was aware that the employees were not wearing the ear muffs provided for protection from noise, and had taken no affirmative action, even though an inspector from the Occupational Safety and Health Administration had indicated the violation. He further brought out that the Senate Report on the Act did not intend for 5 (b) relating to the employees’ duty under the Act to diminish the employer’s responsibility. A citation was issued for the failure of a com- pany to provide protective gloves to employees working with a solvent in violation of 2 9 C F R 1910.132(a).’" Three employees were working with “Stoddard Solvent” five days a week, 8 hours a day. The “Stoddard Solvent” was a petroleum distillate containing paraffins, napthenes, and aro- matics. Evidence indicated that the solvent could cause irritation upon prolonged exposure. The citation was affirmed by Judge Harold A. Ken- nedy, Ocupational Safety and Health Review Commission (Docket No. 79). It was brought out that although the solvent was not classified hazardous under the context of the consideration by any known agency, this did not mean that it was not a hazard within the meaning of the standard. The fact that employees who had used the solvent intermittently for years had received no injuries did not reduce the inherent risk or the duty to provide protective equipment. A citation was issued for alleged violation of 29 CF R 1910.252 (f) (2) (i) relative to lack of adequate ventilation at a welding and cutting site.®® The employer asserted that there was no violation of the regulation and that the compli- ance officer had incorrectly calculated the volume of the welding bays and had failed to establish substantial evidence of lack of mechanical venti- lation. Judge Joseph L. Chalk, Occupational Safety and Health Review Commission (Docket No. 262), ruled in favor of the employer. It was noted that the volumes of the welding bays, di- vided by fiberized glass curtains, could not be calculated to imaginary lines at the ends of the bays and should include all space reasonably open to the welding area. A citation was issued for serious violation of 29 CFR 1918.93 (a) (1) (i) and (ii).*® Fifty- four employees were working in a ship’s hold in concentrations of carbon monoxide between 100 and 200 ppm. The citation was affirmed and the penalty deemed appropriate by Judge John J. Larkin, Occupational Safety and Health Review Commission (Docket 296). The Captain’s claim of lack of knowledge of the fact was not mitigating since the current standard under the longshoring law had been in effect for a number of years. The Captain had not examined the testing equipment, nor required that records of measurements be kept as specified by the standard. Following meas- urements for carbon monoxide by the compliance officer, employees were removed from the hold 92 of the ship. The employees were returned to the hold before a second measurement for carbon monoxide was made by the compliance officer, which showed no decrease in the carbon monoxide concentration. SUMMARY The significance of and guidance from guides, codes, and regulations has changed with advances in the art and science of industrial hygiene and in the enactment of recent laws. The implications, interpretations of, and application of the Occu- pational Safety and Health Act of 1970 will con- tinue to be developed as standards are promul- gated by the Secretary of Labor and as they are interpreted by the administrative and judicial processes specified by the Act. References 1. TRASKO, V. M. Occupational Health and Safety Legislation: A Compilation of State Laws and Reg- ulations. Supt. of Documents, U.S. Government Printing Office, Washington, D.C. 20402. Public Health Service Bulletin No. 357, 1954. RANK, R. M. and T. H. SEYMOUR. Directory and Index of Safety and Health Laws and Codes. Supt. of Documents, U.S. Government Printing Of- fice, Washington, D.C. 20402. U.S. Dept. of Labor, Bureau of Labor Standards, 1969. 3. TRASKO, V. M. Occupational Health and Safety Legislation: A Compilation of State Laws and Reg- ulations. Supt. of Documents, U.S. Government Printing Office, Washington, D.C. 20402. Public Health Service Bulletin No. 357, Revised 1970. EDE, L. and M. T. BARNARD. A Report on State Occupational Health Legislation. U.S. Dept. of Health, Education and Welfare, Public Health Serv- ice, Bureau of Occupational Safety and Health, 1014 Broadway, Cincinnati, Ohio 45202, 1971. CRALLEY, L. V,, L. J. CRALLEY and G. D. CLAYTON. [Industrial Hygiene Highlights: “Epide- miologic Studies of Occupational Diseases,” pp. 7-11. Industrial Hygiene Foundation of America, Inc. Pittsburgh, Pa., 1968. . CRALLEY, L. V,, L. J. CRALLEY and G. D. CLAYTON. Industrial Hygiene Highlights: “Intro- duction,” pp. 1-6. Industrial Hygiene Foundation of America, Inc., Pittsburgh, Pa., 1968. New York State Industrial Code Rule No. 12, Re- lating to Control of Air Contaminants in Factories, effective April, 1961. State of New York, Depart- ment of Labor, Board of Standards and Appeals, 11 N. Pearl St., Albany, N.Y. 12207. State of Michigan Regulation Governing Use of Radioactive Isotopes, X Radiation and all other Forms of Ionizing Radiation. Michigan Department of Public Health, Division of Occupational Health, Lansing, Mich. Public Law 91-596, 91st Congress (84 Stat. 1590) “Occupational Safety and Health Act of 1970.” American Industrial Hygiene Association, Hygienic Guides. American Industrial Hygiene Association, 210 Haddon Avenue, Westmont, New Jersey 08108. Threshold Limit Values of Airborne Contaminants and Physical Agents with Intended Changes adopted by the American Conference of Governmental In- dustrial Hygienists, Secretary-Treasurer, P.O. Box 1937, Cincinnati, Ohio 45201. American National Standards Institute, Inc., 1430 Broadway, New York, New York 10018. Rules and Regulations, Commonwealth of Penn- sylvania, Department of Health, Chapter 4, Article 432, “Regulations Establishing Threshold Limits in Places of Employment.” Commonwealth of Penn- sylvania, Department of Health, P.O. Box 90, Har- risburg, Pa. 17120. Emergency Exposure Limits Recommended by Na- tional Academy of Science. National Research 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. Council Committee on Toxicology (operating arm of National Academy of Engineering and National Academy of Sciences) 2101 Constitution Avenue, Washington, D.C. 20418. National Bureau of Standards Handbook No. 59, “Permissible Dose from External Sources of Ionizing Radiation.” U.S. Department of Commerce, Na- tional Bureau of Standards. For sale by Superin- tendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. National Bureau of Standards Handbook No. 93. “Safety Standards for Non-medical X Ray and Sealed Gamma Ray Sources.” U.S. Department of Commerce, National Bureau of Standards. For sale by Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. WALWORTH, H. T., Chairman. Intersociety Com- mittee on Guidelines for Noise Exposure Control: Guidelines for Noise Exposure Control. American Industrial Hygiene Association Journal, 28: 418, Westmont, N.J. 08108, 1967. National Institute for Occupational Safety and Health, Office of Research and Standards Develop- ment. Parklawn Building, 5600 Fishers Lane, Rock- ville, Maryland 20852. TRUHAUT, R., Chairman, Prof. Centre de Recher- ches Toxicologiques de la Faculte de Pharmacie, Paris, France. Permanent Commission and Inter- national Association of Occupational Health, Sub- Committee on Allowable Limits of Occupational Exposure to Potentially Toxic Substances, Conveyed by Air. International Labour Office, Occupational Safety and Health Series. Occupational Safety and Health Branch, Geneva, Switzerland. CAMPBELL, E. E. American Industrial Hygiene Association Accreditation of Industrial Hygiene Analytical Laboratories. 1.os Alamos Scientific Lab- oratory, University of California, Los Alamos, New Mexico. “Federal Metal and Nonmetallic Mine Safety Act.” Public Law 89-577 (80 Stat. 772) 1966. “Federal Coal Mine Health and Safety Act of 1969.” Public Law 91-173, 91st Congress (83 Stat. 742). Respiratory Protective Devices Manual. Chapters 8 and 9, pp. 79-104. Am. Ind. Hyg. Assoc. & Am. Conf. Gov't. Ind. Hygienists, Box 453, Lansing, Michigan 48902, 1963. 93 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. Atomic Energy Commission: Title 10-Atomic En- ergy, Part 20, “Standards for Protection Against Radiation,” Superintendent of Documents, U.S. Gov- ernment Printing Office, Washington, D.C. 20402. Atomic Energy Commission: Title 10-Atomic En- ergy, Part 34, “Licenses for Radiography and Radi- ation Safety Requirement for Radiographic Opera- tions.” For sale by Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. KEY, M. M.: The Impact of the Occupational Safety and Health Act of 1970 on the Practice of Medicine. Presented at California Medical Associa- tion Meeting, San Francisco, California, February 14, 1972. BROWN, M. L.: Nursing in Occupational Health. Public Health Reports 79: No. 11, November 1964. BROWN, M. L.: “A Profile of Occupational Health Nursing.” Journal Occupational Health Nursing 18: No. 2, February 1970. EDE, L.: “Legal Relations in Nursing.” Journal Occupational Health Nursing 17: pp. 9-15, Decem- ber 1969. Occupational Safety and Health Reporter. Bureau of National Affairs, Inc., Washington, D.C. 20037. Employment Safety and Health Guide. Commerce Clearing House, Inc., 425 13th Street, N.W., Wash- ington, D.C. 20004. Environmental Health Letter. 1097 National Press Building, Washington, D.C. 20004. Occupational Safety and Health Reporter. No. 5, pp. 80, Bureau of National Affairs, Inc., Washing- ton, D.C. 20037, June 3, 1971. Employment Safety and Health Guide, Vol. 2, pp. 20101 (#15050). Commerce Clearing House, Inc., 425 13th Street, N.W., Washington, D.C. 20004. Employment Safety and Health Guide, Vol. 2, pp. 20115 (#15064). Commerce Clearing House, Inc., 425 13th Street, N.W., Washington, D.C. 20004. Employment Safety and Health Guide, Vo. 2, pp. 20125 (#15075). Commerce Clearing House, Inc., 425 13th Street, N.W., Washington, D.C. 20004. Employment Safety and Health Guide, Vol. 2, pp. 20141 (#15084). Commerce Clearing House, Inc., 425 13th Street, N.W., Washington, D.C. 20004. Employment Safety and Health Guide, Vol. 2, pp. 20149 (#15088). Commerce Clearing House, Inc., 425 13th Street, N.W., Washington, D.C. 20004. CHAPTER 10 GENERAL PRINCIPLES IN EVALUATING THE OCCUPATIONAL ENVIRONMENT Andrew D. Hosey INTRODUCTION Evaluating the occupational environment re- quires a multidisciplined approach. A fundamen- tal need exists for the input of the knowledge of engineers, chemists, health physicists, physicians, toxicologists, nurses, production supervisors, and others in the elimination of hazards which threaten workers. The most successful approach coordi- nates these many disciplines and incorporates ef- fective communication between the employer and employee for the recognition, evaluation and con- trol of potential hazards. Obviously it is not always practical to enlist such a group of workers, management, and highly skilled professionals in Industrial Hygiene for most plants. It is essential, however, that each person evaluating the work environment be knowledge- able of the contributions of other professions to the solution of specific problems. For example, an engineer studying ventilation control for ben- zene should know the chemistry of benzene and the influence of benzene upon man. Likewise, the physician studying the work environment should have a knowledge of the engineering requirements for control, as well as the chemical sampling and analytical techniques used. GENERAL PRINCIPLES The general principles in evaluating the occu- pational environment concern recognition of po- tential hazards, preparation for field study, con- ducting the field study, and interpretation of the survey results. The recognition of potential hazards includes becoming familiar with the processes, maintain- ing an inventory of physical and chemical agents encountered, periodically reviewing the different job activities of a work area, and studying the existing control measures. The procedures in the preparation for a field study embrace the selection of proper instruments, calibration of equipment, and the development of the required analytical methods. Factors to consider in conducting a field study are all related to sampling; where, when, how long, and how many samples, as well as the merits of general area versus breathing zone sam- pling should be weighed. Once the survey has been conducted, the industrial hygienist must in- terpret the results. Health standards and previous data are available for comparison. Knowledge of proper corrective measures is an integral part of the industrial hygienist’s responsibilities. This chapter presents the guidelines to be con- sidered by an industrial hygienist in planning a 95 strategy for evaluation of the occupational envi- ronment. RECOGNITION OF POTENTIAL HAZARDS The investigator must become familiar with all processes used in the particular plant or other establishment. He must learn what chemicals or substances are used and produced and the inter- mediate products, if any. This information may be obtained by asking questions during the survey, by visual observation, and by a study of process flow sheets usually contained in technical books that describe the particular operation. It is of ut- most importance that a list of all chemicals and products used be obtained for future reference during the evaluation of the environment. The variety of substances capable of causing occupa- tional diseases increases steadily. New products are constantly being introduced which require the use of new raw materials or new combinations of older substances, and new processes. It has been estimated that new (and some potentially toxic) substances are introduced into industry at the rate of one every 20 minutes and that about 10,- 000 such materials are in use today. New uses for physical agents in industrial processes are increas- ing at a rapid rate. Examples include the use of lasers, microwaves, supersonic welding equipment, and many others. These, too, are potentially haz- ardous unless proper control measures are insti- tuted. Toxicity of Raw Materials and Products It is important for the investigator to recognize that the toxicity of a substance is not the sole cri- terion, or necessarily the most important, of the existence of a health hazard associated with a par- ticular industrial operation. The terms “toxicity” and “hazard” are not synonymous. The nature of the process in which the substance is used or gen- erated, the possibility of reaction with other agents (physical or chemical), the degree of effective ventilation control or the extent of enclosure of the process materials all relate to the potential hazard associated with each use of a given chem- ical agent (see Chapter 9). Such an assessment must be made along with due consideration of the type and degree of toxic responses the agent may elicit in both the average and, possibly, hypersus- ceptible workers. After the list of chemicals used and produced is obtained, it is necessary to determine which of these are toxic and to what degree. Information of this nature can be found in the latest texts and in scientific journals, Hygienic Guides published by ? the American Industrial Hygiene Association (A.LH.A.),* the Z-37 Standards published by the American National Standards Institute (A.N.S.I.),? and by correspondence with toxicologists, techni- cal information centers, and manufacturers. Toxic Substances, a recent publication by the National Institute for Occupational Safety and Health? con- tains over 8000 substances. The list, which is revised annually, gives the concentration at which each substance is known to be toxic and should serve as an excellent reference source in the area of toxicology. Many companies publish a list of toxic materials used in their plants for use by safety personnel, foremen, and others. Similar information should be obtained also on the po- tential hazards of physical agents in use. A num- ber of guides, standards, and texts are available for this purpose. Sources of Air Contaminants Many potentially hazardous operations can be detected by visual observation during the prelim- inary survey. The most dusty operations can be easily spotted, although this does not necessarily mean they are the most hazardous. It must be remembered that the dust particles which cannot be seen by the unaided eye are the most hazard- ous because they are of respirable size. Further- more, dust concentrations must reach extremely high levels before they are readily visible in the air. Thus the absence of a visible dust cloud does not mean necessarily that a dust-free atmosphere exists. However, those operations that generate fumes, such as welding, can be spotted visually. Reference to the list of raw materials, products and byproducts will indicate possible air contami- nants. In any burning operation, a knowledge of the fuels used will indicate the air contaminants generated. Separation processes can produce chemicals or particulates which are potentially hazardous, The presence of many vapors and gases can be detected by the sense of smell. Trained ob- servers are able to estimate rather closely the concentration of a limited number of solvent va- pors and gases in the workroom air by the odor level. For many substances, however, the odor threshold concentration is greater than the per- missible exposure levels. For example, if the odor of carbon tetrachloride vapor is barely perceptible, this indicates the amount is generally too great for a continuous exposure. In fact, concentrations of some vapors and gases may be present in concen- trations considerably in excess of the permissible level, but may not be detectable by their odor. New Stresses — Changes in Processes As indicated above, new chemical products and physical agents are continually being intro- duced and used in industrial processes. The in- vestigator must be aware of these and must ascer- tain the potentially hazardous nature of these be- fore they are used so that any necessary safeguards can be inaugurated. Many companies, especially the larger ones, have such information available and will generally make it accessible to the in- vestigator. Furthermore, the employer should in- form employees of these potential hazards and should establish controls for their protection. 96 Job Activities Review A review of the worker’s routine job require- ments should be made. Changes in his job re- quirements or modifications of techniques to ac- complish his work can have a profound effect upon his exposure to health hazards. Overtime require- ments for particular jobs should be determined so that the contribution of overtime and the re- lated prolonged exposure of workmen to health hazards can be evaluated. Control Measures in Use The preliminary survey would not be com- plete unless the types of control measures in use and their effectiveness are noted. Control measures include local exhaust and general ventilation, pro- tective respiratory devices, protective clothing, and shielding from radiant heat, ultraviolet light, or other forms of radiant energy. General guides to effectiveness include the presence or absence of dust on floors and ledges; holes in ductwork, fans not operating or rotating in the wrong direction (the latter has been found to occur in many plants and it should be noted that, even though a blower is operated backward, it will still exhaust some air, but not the required amount); or the manner in which personal protective devices are treated by workmen. During the preliminary survey it may be desirable to conduct a check on local exhaust ventilation systems in use to determine if sufficient airflow is provided to remove the con- taminants from the workers’ breathing zone. The manual, “Industrial Ventilation,”* will serve as a useful guide for this purpose since it describes test procedures and contains examples of many types of systems with the recommended airflows. Adequate notes must be made during an eval- uation of the environment. The speed and accur- acy of preparing a report of an investigation will depend largely on information recorded in the form of notes. SELECTION OF INSTRUMENTS TO EVALUATE THE WORK ENVIRONMENT Sampling instruments used to evaluate the en- vironment for occupational health hazards are generally classified according to type as follows: (1) direct reading; (2) those which remove the contaminant from a measured quantity of air; and (3) those which collect a known volume of air for subsequent laboratory analysis. Most of the equipment used by industrial hy- gienists is found under the first two types. The third group includes various types of evacuated flasks, plastic bags, or other suitable containers for collecting known volumes of contaminated air to be returned to the laboratory for analysis. The choice of a particular sampling instru- ment depends upon a number of factors. Among these are: (1) portability and ease of use; (2) ef- ficiency of the equipment or device; (3) reliability of the equipment under various conditions of field use; (4) type of analysis or information required; (5) availability; and (6) personal choice based on past experience and other factors. No single, universal sampling instrument is available and it is doubtful if such an instrument will ever be developed. In fact, the present trend is the development of a greater number of spe- cialized instruments such as the direct reading gas and vapor detectors. In evaluating a worker’s exposure or the en- vironment in which he works, an instrument must be used that will provide the necessary sensitivity, accuracy, reproducibility, and, preferably, rapid results. Detailed discussions of instruments used for sampling for particulates are given in Chapter 13, for gases and vapors in Chapter 15, and for direct reading instruments for aerosols, gases and vapors in Chapter 16, as well as in “Air Sampling Instruments for Evaluation of Atmospheric Con- taminants” published by the American Conference of Governmental Industrial Hygienists.” Instru- ments for assessing noise exposure and for other physical agents are discussed in subsequent chap- ters of this manual. One of the older, but still valid, discussions on this subject is “Sampling and Analyzing Air for Contaminants” by Silverman." Those whose responsibilities include the collec- tion and analysis of samples will find this publi- cation a worthwhile reference. The use of continuous monitoring devices to evaluate the working environment has increased tremendously in recent years. While these devices are normally not designed for field use, many are available in sizes that are convenient for this pur- pose. In general, however, many industries install these devices in areas where exposures to certain gases or vapors may vary considerably. Examples include the use of continuous monitors for carbon monoxide in tunnels or plant areas where this gas is produced or used, monitors for chlorinated hydrocarbons such as in the production of carbon tetrachloride or trichloroethylene, and monitors for certain alcohols. Many of these continuous detecting and recording instruments can be equipped to sample at several remote locations in a plant and record the general air concentrations to which workers may be exposed during a shift. Many large plants have added computerized equip- ment to the recorders so that the data may be readily available and summarized for instant re- view. However, as is the case with other instru- ments, continuous monitors must be calibrated periodically and the interferences known. After selecting the instrument, the industrial hygienist, compliance officer, or other person col- lecting samples must become familiar with the de- vice and its limitations. He must know, for ex- ample, whether or not the particular instrument is specific for the contaminant to be determined, what other substances interfere with the test, and the accuracy and sensitivity of the device. He must also be familiar with the response time, which is the time interval from the instant samples are taken to the time the instrument shows a reading or the chemical reaction takes place in a detector tube. Furthermore, in the case of detector tubes, the readings must be made under good lighting conditions, preferably in daylight.” "11! CALIBRATION OF INSTRUMENTS Instruments and techniques used in calibrating sampling equipment are discussed in detail in Chapter 11. This brief discussion is included to stress the necessity for following recommended procedures in order that the data resulting from the analysis of field samples (whether by direct reading devices in the field or by equipment that collects samples for subsequent laboratory analy- sis) will truly represent concentrations in the en- vironment, and particularly concentrations to which the worker is exposed. Since the amount of sample, whether collected by means of a filter, an impinger, or a bubbler or indicated by a direct reading instrument, depends upon the volume of air sampled and its duration, it is essential that the device operate at a known rate of airflow. Thus, the equipment must be cali- brated against a standard airflow measuring de- vice both before and after use in the field. The exact rate of airflow must be recorded so that when it is multiplied by the sampling time, the total volume of air sampled or collected will be known. This volume of air is used in calculating the concentration of contaminant to which the worker was exposed. Furthermore, direct reading instruments and detector tubes must be calibrated against a known concentration of the substance for which they are used. Results obtained during a survey or study are no more accurate than the instruments used to obtain the data. In some sit- uations the investigator must do his own cali- brating, but more frequently this is done by others at a central laboratory. ESTABLISHING PROPER ANALYTICAL METHODS The use of accurate, sensitive, and reproduc- ible analytical methods is equally as important as the proper calibration of the sampling equipment. In evaluating the occupational environment the concentration of contaminant in the ambient air is generally small. In fact, the direct reading instru- “ments and other devices used to collect samples for 97 subsequent analysis are required to detect quan- tities of substances in the microgram or part-per- million range. Thus, a sufficient quantity of sam- ple must be collected to enable the analyst to determine accurately this small amount of sub- stance. When available, standard methods of analysis should always be used. Unfortunately, only a few such methods have been tested under various sit- uations and conditions. In the field of industrial hygiene the A.C.G.I.H. has available a “Manual of Analytical Methods” that contains about 20 methods.’”> Many of the nearly 200 A.LLH.A. Hygienic Guides! contain recommended methods of analysis. This same organization also publishes Analytical Guides, which to date cover 61 methods of analysis. The American Public Health Asso- ciation as prime contractor with the National Air Pollution Control Administration, and through the Intersociety Committee, has been developing methods for air sampling and analysis; the first 60 of these have been published as a manual entitled “Methods of Air Sampling and Analysis,” Amer- ican Public Health Association, 1015 Eighteenth Street, NW Washington, D.C., 1972." While these methods were developed primarily for the field of air pollution, most of them can be used for sampling and analysis of environmental con- ditions in plants. The American Society for Testing and Mate- rials'* initiated Project Threshold in March, 1971 to validate test methods in the field of air pollu- tion. Many of these methods can be used also for sampling and analyzing contaminants in the work- place. Several methods have been developed and tested, the latest of which is a tentative fluorescent method for beryllium. The reason for this lack of tested standard methods is the tremendous amount of time and personnel required to perform the necessary test- ing. There are nearly 500 substances included in the latest TLV list (A.C.G.I.LH.) but there are perhaps less than 100 standardized methods avail- able to determine compliance or non-compliance with the U.S. Department of Labor’s regulations under the Occupational Safety and Health Act of 1970. This does not mean that methods other than the standard methods cannot be used. How- ever, these other methods must also be tested and calibrated against known concentrations of the substance in question. Many analytical methods have been published in the literature and the methods should be evaluated in the laboratory prior to performing an analysis. MAKING THE FIELD SURVEY The nature of the substance or condition to which workers may be potentially exposed will usually have been determined during the prelim- inary survey. The problem, then, is to determine the intensity of exposure and to do this one must collect samples of the air or use direct reading in- struments. Every effort must be made to obtain samples that represent the worker’s exposure. To decide what constitutes a representative sample, the investigator must answer these five basic questions: (1) where to sample; (2) whom to sample; (3) how long to sample (sampling dura- tion); (4) how many samples to take; and (5) when to sample — day or night, what month or season. Where to Sample Where the purposes of the sampling are to evaluate a worker's exposure and to determine his daily, time-weighted average exposure, it is necessary to collect samples at or as near as prac- tical to his breathing zone and also in the area adjacent to his normal work station, or general room air. Sometimes it is necessary to sample at the operation itself because of the difficulties of placing a sampling device at his breathing zone or attaching it to his person. On the other hand, if the purpose of sampling is to define a potential hazard, to check compliance with regulations, or to obtain data for control purposes, samples rep- resentative of the worker's exposure must be col- lected. In some cases it is necessary to sample the general room air also to define certain exposures. Whom to Sample Personnel exposure is best determined by mon- itoring the different job tasks in a suspect area. Personnel monitors properly attached to workers directly exposed should give a representative sam- ple to actual breathing zone exposure. Actual ex- 98 posure sources can be documented with the proper number of personnel samples combined with the results from stationary sampling points. Job de- scriptions for area personnel and the time spent at each task are of primary importance in deter- mining potential exposure, How Long to Sample The volume of air sampled and duration of sampling is based upon the sensitivity of the ana- lytical procedure or direct reading instrument; the estimated air concentration; and the Standard or TLV of the particular contaminant. Thus, the volume of air sampled may vary from a few liters, where the estimated concentration is high, to sev- eral cubic meters where low concentrations are expected. Knowing the sensitivity of the method, the TLV, and the sampling rate of the particular instrument in use, the minimum sampling time can be determined. The above applies to devices that collect a known volume of air for later analysis. The duration of sampling should represent some identifiable period of time — usually a complete cycle of an operation — to determine an operator’s exposure. Another technique is to sample on a regular schedule, for example, so many minutes of each hour. This procedure usually requires more samples than cyclic-type sampling but, when used in conjunction with the cyclic-type sampling, gives more confidence in the results and recom- mendations. Evaluation of worker’s daily time-weighted average exposures is usually best accomplished when analytical methods will permit, by allowing the worker to work his full 7- or 8-hour shift with a personal breathing zone sampler attached to his person. Techniques have been developed in re- cent years that allow full shift sampling for many dusts, fumes, gases and vapors. These techniques, which include the use of filters and miniature cy- clones to sample airborne dusts and activated charcoal to sample many gases and vapors have been developed successfully in recent years for many airborne contaminants. The concept of full shift integrated personal sampling is much pre- ferred to that of short term or general area samp- ling if the results are to be compared to standards based on time-weighted average concentrations. When methods that permit full shift integrated sampling are not applicable, time-weighted average exposures can be calculated from alternative short term or general area sampling methods by applying the general formula explained in Chapter 3. The first step in calculating a worker’s or group of workers’ daily, time-weighted exposure is to again study the job descriptions obtained for the persons under consideration and ascertain how much time out of each day they spend at various tasks. Such information is usually available from the plant personnel office or foreman on the job. In many situations the investigator must make time studies himself to obtain the correct information. Even though this information was obtained from plant personnel, it should be checked by the investigator because in many situations what the investigator observes and the times given by plant personnel do not agree. From this information and the results of the environmental survey, a daily, time-weighted average 8-hour exposure can be calculated. This assumes that a sufficient num- ber of samples have been collected or readings obtained with direct reading instruments under various plant operating conditions to give a true picture of the exposure. Where sampling for the purpose of comparing results with airborne contaminants whose toxico- logical properties warrant short term and ceiling limit values, it is necessary to use short term or grab sampling techniques to define peak concen- trations and estimate peak excursion durations. For purposes of further comparison, the time- weighted average 8-hour exposure can be calcu- lated using the values obtained by short term sampling. How Many Samples to Take There is no set rule to determine the number of replicate samples that are necessary to evalu- ate a worker’s exposure, provided that a minimum number are taken to characterize the exposure in time and space. A single sample will never suffice even if the investigator believes that this concen- tration would be maintained throughout the work shift. If the indicated concentration is near or above the TLV or Standard, repeated sampling should be done. Ordinarily, contaminants are not generated at a constant rate, and the concentra- tion can vary considerably from time to time. Only rarely does an operation release contami- nants into the workroom air at a fairly constant rate. Chapters 13 and 15 describe sampling pro- cedures for particulates, gases, and vapors, includ- ing information on the number of samples needed. The concentration found in single sample may have been too high or too low due to a number of factors and if the sample had been collected at another time, the results could very well be con- siderably different. Several dozen samples may be necessary to define accurately a daily, time- weighted average exposure for a worker who performs a number of tasks during the shift. When to Sample Another area to be considered in sampling is when to sample — a determination of the work shift or seasonal period during which samples should be collected. If, for example, an operator continues working for more than one shift, sam- ples should be collected during each shift that he works. It has been found that in many situations airborne concentrations of toxic substances or exposure to physical agents may be different for each shift. Furthermore, and this applies to plants located in areas where large temperature differ- ences occur during different seasons of the year, samples should be collected during summer and winter months. Normally, there is more general ventilation during the summer months than in winter, a factor which tends to dilute the concen- tration of the contaminant. INTERPRETATION OF FINDINGS Interpretation of the analyses of samples col- lected or from direct reading instruments is the final step in evaluating the environment. A great deal of common sense and judgment must be used in interpreting the results of an environmental 99 study. Before an investigator determines that a worker or group of workers is exposed to a hazard injurious to health, he must have the following facts: (1) nature of substance or physical agent involved; (2) intensity (concentration) of expos- ure; and (3) duration of exposures, which will have been determined from the preliminary survey and the results of air sampling done during the environmental study. In many cases, adverse ef- fects from exposure to toxic materials or physical agents do not appear until the exposure has oc- curred for several years. The purpose of TLVs or Standards is to protect against the future appear- ance of such symptoms. Comparison of Results with Standards Results of the environmental study must be compared with standards before an employer can be cited for a violation or control measures can be recommended. It must be emphasized again that the samples collected during the study must be representative of the worker's daily, time- weighted average exposure, if there is a standard for such exposure, before a comparison can be made. In connection with the enforcement of the Occupational Safety and Health Act, the standards for exposure to gases, vapors, dust, ionizing and non-ionizing radiation are contained in the Code of Federal Regulations (CFR), Title 29, Part 1910, Occupational and Environmental Health Standards. These were first published in the Fed- eral Register, Vol. 26, No. 105, May 29, 1971 and are subject to revision. At this writing, most of these standards are the same as the A.C.G.I.H. 1970 TLVs, but about 20 are the latest A.N.S.I. Z-37 Standards. In 1971, for the first time A.C.G.LH. published a combined list of Thresh- old Limit Values for airborne contaminants and physical agents.’* Included in the latter are guide- lines (TLVs) for noise, lasers, microwaves, ultra- violet radiation, and heat stress. Basic Radiation Protection Criteria'® should be consulted for stan- dards on ionizing radiation. Other guidelines in this area include the A.ILH.A. Hygienic Guides! A.N.S.I. Standards,? and the A.S.H.R.A.E. Guide’" for temperature and humidity. Many states have adopted standards in the above area, some of which are more stringent than those referred to above. Since a state may qualify to administer and enforce a State Occupational Safety and Health Program under provisions of the Federal Act, the standards in effect in a par- ticular state must be consulted by the investigator. Federal standards adopted to date (1972) are minimum legal requirements and they will no doubt be modified from time to time as new data become available. State standards must be “at least as effective” as Federal standards. When state standards are applicable to products distrib- uted or used in interstate commerce, they must be such as are required by compelling local condi- tions and do not unduly burden interstate com- merce. Comparison of Results with Previous Data As indicated earlier in this discussion, many of the larger industrial establishments utilize con- tinuous monitors to maintain a record of concen- trations of various gases and vapors in certain areas of their plants. These data must be related to worker exposure. Other companies that em- ploy industrial hygienists ordinarily have data on exposures of workmen to various toxic substances as well as certain physical agents. If at all possi- ble, the investigator should make every effort to study these data and compare them with the re- sults of his study. In many cases the data may not be the same and there may be good reasons for the discrepancy. In many instances the data on exposures will be more complete and detailed when taken from company records than when ob- tained by an investigator from a one- or two-day investigation of certain hazardous operations in that plant. Thus, considerable embarrassment can be avoided if the above suggestion to check other recorded data is followed. In addition to data available from company records, other sources of such information include the results of previous studies conducted by Fed- eral, state and local agencies, some insurance com- panies, and consultants. Here again, results of these studies may be different than those obtained by the investigator so great care must be exercised in making comparisons. SUMMARY The conduct of environmental surveys and studies is only one phase in the over-all effort in determining occupational health hazards. Such surveys are valuable only if all environmental factors relating to the workers’ potential exposures are included. In evaluating workers’ exposures to toxic dusts, fumes, gases, vapors, mists, and physi- cal agents, a sufficient number of samples must be collected, or readings made with direct reading instruments, for the proper duration to permit the assessment of daily, time-weighted average expos- ures and evaluate peak exposure concentrations when needed. It is essential that the proper instrument be selected for the particular hazard under study and that it be calibrated periodically to insure that it is sampling at the correct rate of airflow and, in the case of direct reading instruments, that they have been calibrated against known concentrations of the contaminant in question. For those samples to be analyzed in the laboratory, a method must be used that is accurate, sensitive, specific, and reproducible for that particular contaminant. Adequate notes taken during environmental studies are a necessity. An investigator or inspec- tor cannot rely upon his memory after a study is completed to provide the detailed information nec- essary for the preparation of a report. Finally, sound judgment should be exercised both during the actual survey and while preparing the report. References 1. AMERICAN INDUSTRIAL HYGIENE ASSOCIA- TION. A.I.H.A. Hygiene Guide Series, 66 South Miller Rd., Akron, Ohio 44313. AMERICAN NATIONAL STANDARDS INSTI- TUTE. Minimum Requirements for Sanitation in Places of Employment, ANS.I. Z-4.1, New York, N.Y. (1968). CHRISTENSEN, HERBERT E. (Ed.). Toxic Sub- stances — Annual List 1971, U.S. Dept. Health, Education & Welfare, HSMHA, NIOSH, Rockville, 100 Md. (1971). AMERICAN CONFERENCE OF GOVERNMEN- TAL INDUSTRIAL HYGIENISTS COMMITTEE ON INDUSTRIAL VENTILATION. Industrial Ventilation — A Manual of Recommended Prac- tice, P.O. Box 453, Lansing, Michigan, 48902, 12th ed. (1972). AMERICAN CONFERENCE OF GOVERNMEN- TAL INDUSTRIAL HYGIENISTS. Air Sampling Instruments for Evaluation of Atmospheric Con- taminants, 1014 Broadway, Cincinnati, Ohio 45202. SILVERMAN, L. Air Conditioning, Heating & Ven- tilating, “Sampling and Analyzing Air for Contami- nants;” (Aug. 1955). MORGENSTERN, A. S., R. N. ASH and J. R. LYNCH. American Industrial Hygiene Association Journal 31: 630 “The Evaluation of Gas Detector Tube Systems: I. Carbon Monoxide (1970). £ ASH, R. N. Trans. 32nd Annual Meeting of Amer- ican Conference of Governmental Industrial Hy- gienists, “The PHS Detector Tube Study: A Prog- ress Report,” Detroit, Michigan (May 10-12, 1970). ASH, R. N. and J. R. LYNCH. American Industrial Hygiene Association Journal 32: 410, “The Evalua- Yon of Gas Detector Tube Systems: II. Benzene,” 1971). ASH, R. N. and J. R. LYNCH. American Industrial Hygiene Association Journal 32: 490, “The Evalua- tion of Gas Detector Tube Systems: III. Sulfur Dioxide,” (1971). AMERICAN CONFERENCE OF GOVERNMEN- TAL INDUSTRIAL HYGIENISTS — AMERICAN INDUSTRIAL HYGIENE ASSOCIATION. Joint Committee, American Industrial Hygiene Associa- tion Journal 32: 488, “Direct Reading Detecting Tube Systems.” (1971). AMERICAN CONFERENCE OF GOVERNMEN- TAL INDUSTRIAL HYGIENISTS. Manual of Analytical Methods, P.O. Box 1937, Cincinnati, Ohio 45201. “Methods of Air Sampling and Analysis,” American Public Health Association, 1015 Eighteenth Street, NW, Washington, D.C. (1972). AMERICAN SOCIETY FOR TESTING AND MATERIALS. Project Threshold, 1916 Race Street, Philadelphia, Pa. 19103. AMERICAN CONFERENCE OF GOVERNMEN- TAL INDUSTRIAL HYGIENISTS. Threshold Limit Values for Airborne Contaminants and Physical Agents with Intended Changes Adopted by A.C.G.I.H. in 1971, P.O. Box 1937, Cincinnati, Ohio 45201 (1971). NATIONAL COMMITTEE ON RADIATION PROTECTION. Basic Radiation Protection Guide, NCRP Report No. 39, P.O. Box 4687, Washington, D.C. 20008. AMERICAN SOCIETY OF HEATING, REFRIG- ERATING AND AIR CONDITIONING ENGI- NEERS. A.S.H.R.A.E. Guide, 345 E. 47th Street, New York, N.Y. 10017 (Published annually). Preferred Reading American Industrial Hygiene Association Journal. Archives of Industrial Health. Environmental Science and Technology. Journal of the Air Pollution Control Association. Journal of Occupational Medicine. British Journal of Industrial Hygiene. Bulletin of Hygiene (London). Heating, Refrigeration and Air Conditioning. Analytical Chemistry. Industrial Hygiene Digest. Journal of Laboratory and Clinical Medicine. Noise Control. . Toxicology and Applied Pharmacology. New England Journal of Medicine. . Air Sampling Instruments Manual (ACGIH). Encyclopedia of Chemical Technology (Interscience Publishers). Handbook of Chemistry and Physics (Chemical Rubber Pub. Co.) LLE.S. Lighting Handbook (Illuminating Engineer- ing Society). Handbook of Dangerous Materials (Sax). CRNA NA I~ CHAPTER 11 INSTRUMENTS AND TECHNIQUES USED IN CALIBRATING SAMPLING EQUIPMENT Morton Lippmann, Ph.D. INTRODUCTION Importance of Accurate Calibrations and Periodic Recalibration Air samples are collected in order to determine the concentrations of one or more airborne con- taminants. To define a concentration, the quantity of the contaminant of interest per unit volume of air must be determined. In some cases, the con- taminant is not extracted from the air; i.e., it may simply alter the response of a defined physical sys- tem. An example is the mercury vapor detector, wherein mercury atoms absorb the characteristic ultra-violet radiation from a mercury lamp, re- ducing the intensity incident on a photocell. In this case, the response is proportional to the mer- cury concentration and not to the mass flowrate through the sensing zone; hence, it measures con- centration directly. In most cases, however, the contaminant is either recovered from the sampled air for subse- quent analysis or is altered by its passage through a sensor within the sampling train, and the sam- pling flowrate must be known in order to ulti- mately determine airborne concentrations. When the contaminant is collected for subsequent analy- sis, the collection efficiency must also be known, and ideally should be constant. The measurements of sample mass, of collection efficiency and of sample volume are usually done independently. Each measurement has its own associated errors, and each contributes to the overall uncertainty in the reported concentration. The sample volume measurement error will often be greater than that of the sample mass measurement. The usual reason is that the volume measurement is made in the field with devices designed more for portability and light weight than for precision and accuracy. Flowrate measure- ment errors can further affect the determination if the collection efficiency is dependent on the flow- rate. Each element of the sampling system should be calibrated accurately prior to initial field use. Protocols should also be established for periodic recalibration, since the performance of many transducers and meters will change with the ac- cumulation of dirt, corrosion, leaks, and misalign- ment due to vibration or shocks in handling, etc. The frequency of such recalibration checks should initially be high, until experience is accumulated to show that it can be reduced safely. Types of Calibrations Flow and Volume. If the contaminant of interest is removed quantitatively by a sample collector at 101 all flowrates, then the sampled volume may be the only air flow parameter that need be recorded. On the other hand, when the detector response is de- pendent on both the flowrate and sample mass, as in many length-of-stain detector tubes, then both quantities must be determined and controlled. Finally, in many direct-reading instruments, the response is dependent on flowrate but not on in- tegrated volume. In most sampling situations the flowrates are, or are assumed to be, constant. When this is so, and the sampling interval is known, it is possible to convert flowrates to integrated volumes, and vice-versa. For this reason flowrate meters, which are usually smaller, more portable and less ex- pensive than integrated volume meters, are gener- ally used on sampling equipment even when the sample volume is the parameter of primary inter- est. Normally, little additional error is introduced in converting a constant flowrate into an integrated volume since the measurement and recording of elapsed time generally can be performed with good accuracy and precision. Flowmeters can be divided into three basic groups on the basis of the type of measurement made; these are integrated-volume meters, flow- rate meters, and velocity meters. The principles of operation and features of specific instrument types in each group will be discussed in succeeding pages. The response of volume meters, such as the spirometer and wet-test meter, and flowrate met- ers, such as the rotameter and orifice meter, are determined by the entire sampler flow. In this respect they differ from velocity meters such as the thermoanemometer and Pitot tube, which measure the velocity at a particular point of the flow cross section. Since the flow profile is rarely uniform across the channel, the measured velocity will invariably differ from the average velocity. Furthermore, since the shape of the flow profile usually changes with changes in flowrate, the ratio of point-to-average velocity will also change. Thus, when a point velocity is used as an index of flow- rate, there is an additional potential source of error, which should be evaluated in laboratory calibrations which simulate the conditions of use. Despite their disadvantages, velocity sensors are sometimes the best indicators available, as for example in some electrostatic precipitators where the flow resistance of other types of meters cannot be tolerated. Calibration of Collection Efficiency. A sample collector need not be 100% efficient in order to be useful, provided that its efficiency is known and constant, and taken into account in the cal- culation of concentration. In practice, acceptance of a low but known collection efficiency is a rea- sonable procedure for most types of gas and vapor sampling, but is seldom, if ever, appropriate for aerosol sampling. All of the molecules of a given chemical contaminant in the vapor phase are es- sentially the same size, and if the temperature, flowrate, and other critical parameters are kept constant, they will have the same probability of capture. Aerosols, on the other hand, are rarely monodisperse. Since most particle-capture mech- anisms are size-dependent, the collection char- acteristics of a given sampler are likely to vary with particle size. Furthermore, the efficiency will tend to change with time due to loading; e.g., a filter’s efficiency increases as dust collects on it, and electrostatic precipitator efficiency may drop if a resistive layer accumulates on the collecting electrode. Thus, aerosol samplers should not be used unless their collection is essentially complete for all particle sizes of interest. Determination of Sample Stability and Recovery. The collection efficiency of a sampler can be de- fined by the fraction removed from the air passing through it. However, the material collected can- not always be completely recovered from the sampling substrate for analysis. In addition, the material can sometimes be degraded or otherwise lost between the time of collection in the field and recovery in the laboratory. Deterioration of the sample is particularly severe for chemically re- active materials. Sample losses may also be due to high vapor pressures in the sampled material, exposure to elevated temperatures, or to reactions between the sample and substrate or between dif- ferent components in the sample. Laboratory calibrations using blank and spiked samples should be performed whenever possible to determine the conditions under which such losses are likely to affect the determinations de- sired. When the losses are likely to be excessive, the sampling equipment or procedures should be modified as much as feasible to minimize the losses and the need for calibration corrections. Calibration of Sensor Response. When calibrating direct-reading instruments, the objective is to de- termine the relationship between the scale read- ings and the actual concentration of contaminant present. In such tests the basic response for the contaminant of interest is obtained by operating the instrument in known concentrations of the pure material over an appropriate range of con- centrations. In many cases it is also necessary to determine the effect of environmental co-factors such as temperature, pressure and humidity on the instrument response. Also, many sensors are non-specific and atmospheric co-contaminants may either elevate or depress the signal produced by the contaminant of interest. If reliable data on the effect of such interferences are not available, they should be obtained in calibration tests. Pro- cedures for establishing known concentrations for such calibration tests are discussed in detail in Chapter 12. Sampling and Calibration Standards and Errors Use and Reliability of Standards and Standard Procedures. Calibration procedures generally in- volve a comparison of instrument response to a standardized atmosphere or to the response of a reference instrument. Hence, the calibration can be no better than the standards used. Reliability and proper use of standards are critical to accurate calibrations. Reference materials and instruments available from, or calibrated by, the National Bureau of Standards (NBS) should be used when- ever possible. Information on calibration aids available from NBS is summarized in Table 11-1. TABLE 11-1 NATIONAL BUREAU OF STANDARDS (NBS) — STANDARD REFERENCE MATERIALS (SRM’s)* INTENDED FOR USE AS PRIMARY INSTRUMENT CALIBRATION STANDARDS BY AIR POLLUTION'LABORATORIES SRM No. Description 1625 SO, Permeation Tube, Individually Calibrated, Effective length = 10 cm, Permeation Rate = 0.28 ug SO,/min. @ 25°C. 1626 Same as above, except that effective length = 5 cm. 1627 Same as above, except that effective length = 2 cm. 1610 Hydrocarbon in Air compressed gas mixture, 68 standard liters @ 500 psi in disposable cylinder. Concentration = 0.103 == 0.001 mole percent, calculated as methane, as de- termined by flame ionization. 1611 Same as above, except that concentration = 0.0107 == 0.0001 mole %. 1612 Same as above, except that concentration = 0.00117 == 0.00001 mole %. 1613 Same as above, except that concentration = 0.000102 == 0.000002 mole %. 1601 Carbon Dioxide in Nitrogen compressed gas mixture, 68 standard liters @ 500 psi in dis- posable cylinder. Concentration = 0.0308 == 0.0003 mole %. 1602 Same as above, except that concentration = 0.0346 == 0.0003 mole %. 1603 Same as above, except that concentration — 0.0384 == 0.0004 mole %. * Available from the Office of Standard Reference Materials, Room B 314, Chemistry Bldg., National Bureau of Standards, Washington, D. C. 20234. 102 Test atmospheres generated for the purpose of calibrating collection efficiency or instrument response should be checked for concentration using reference instruments or sampling and ana- lytical procedures whose reliability and accuracy are well documented. The best procedures to use are those which have been referee or panel tested; i.e., methods which have been shown to yield comparable results on blind samples analyzed by different laboratories. Such procedures are pub- lished by several organizations, which are listed in Table 11-2, Those published by the individual TABLE 11-2 ORGANIZATIONS PUBLISHING RECOMMENDED OR STANDARD METHODS AND/OR TEST PROCEDURES APPLICABLE TO AIR SAMPLING INSTRUMENT CALIBRATION Abbreviation Full Name Mailing Address APCA Air Pollution Control Association 4400 Fifth Avenue Pittsburgh, Pa. 15213 ACGIH American Conference of Governmental P.O. Box 1937 Industrial Hygienists Cincinnati, Ohio 45201 AIHA American Industrial Hygiene Association 66 South Miller Rd. Akron, Ohio 44313 ANSI American National Standards Institute, Inc. 1430 Broadway New York, N.Y. 10018 ASTM American Society for Testing and Materials, 1016 Race Street D-22 Committee on Sampling and Philadelphia, Pa. 19103 Analysis of Atmospheres EPA Environmental Protection Agency Office 5600 Fischer’s Lane of Air Programs Rockville, Md. 20852 ISC Intersociety Committee on Methods for 250 W. 57th Street Air Sampling and Analysis New York, N.Y. 10019 TABLE 11-3 SUMMARY OF RECOMMENDED AND STANDARD METHODS RELATING TO AIR SAMPLING INSTRUMENT CALIBRATION No. of Panel Organization ~~ Methods Types of Methods Tested Reference ACGIH 19 Analytic methods for air contaminants Yes Manual of Analytic Methods®® AIHA 117 Analytic methods for air contaminants No Analytic Guides®® ISC 46 Analytic methods for air contaminants t Health Laboratory Science 6(2) (Apr. 1969) 7(1) (Jan. 1970) 7(2) (July 1970) 7(4) (Oct. 1970) 8(1) (Jan. 1971) ASTM 20 Analytic methods for air contaminants * Part 23, Annual Book of ASTM 5 Recommended practices for sampling NA ASTM Standards®® procedures, nomenclature, etc. APCA 3 Recommended standard methods for NA J. Air Pollut. Cont. Assoc. continuing air monitoring for fine 13:55 (Sept. 1963) particulate matter ANSI 1 Sampling airborne radioactive materials NA ANSI N 13.1-1969 EPA 6 Reference methods for air contaminants No Fed. Register 36 (84) (April 30, 1971) 7 All methods will be panel tested before advancing from tentative to standard. * Seven methods are undergoing panel validation under Phase 1-ASTM Project Threshold. Additional methods will be panel evaluated in subsequent phases. NA Not applicable. organizations have been supplemented in recent years by those approved by the Intersociety Com- mittee on Methods for Air Sampling and Analysis, a cooperative group formed in March, 1963, com- posed of representatives of the Air Pollution Con- trol Association (APCA), the American Confer- ence of Governmental Industrial Hygienists (ACGIH), the American Industrial Hygiene As- sociation (AIHA), the American Public Health Association (APHA), the American Society for Testing and Materials (ASTM), the American Society of Mechanical Engineers (ASME), and the Association of Official Analytical Chemists (AOAC). “Tentative” methods endorsed by the Intersociety Committee have been published at random intervals since April, 1969, in “Health Laboratory Science,” a publication of APHA. These “Tentative” methods become “Standard” methods only after satisfactory completion of a cooperative test program. Lists of published “Ten- tative” and “Standard” methods for air sampling and analysis are summarized in Table 11-3. Sources of Sampling and Analytical Errors. The difference between the air concentration reported for an air contaminant on the basis of a meter reading or laboratory analysis, and true concen- tration at that time and place represents the error of the measurement. The overall error is often due to a number of smaller component errors rather than to a single cause. In order to mini- mize the overall error it is usually necessary to analyze each of its potential components, and con- centrate one’s efforts on reducing the component error which is largest. It would not be productive to reduce the uncertainty in the analytical pro- cedure from 10% to 1.0% when the error asso- ciated with the sample volume measurement is + 15%. Sampling problems are so varied in practice that it is only possible to generalize on the likely sources of error to be encountered in typical samp- ling situations. In analyzing a particular sampling problem, consideration should be given to each of the following: a) Flowrate and sample volume b) Collection efficiency c¢) Sample stability under conditions antici- pated for sampling, storage and transport d) Efficiency of recovery from sampling sub- strate e) Analytical background and interferénces introduced by sampling substrate f) Effect of atmospheric co-contaminants on E.— [15% 4+ 22 4 102 + 102] — [429] V2 — =+ 20.6% It should be remembered that this provides an estimate of the deviation of the measured con- centration from the true concentration at the time and place the sample was collected. As an estimate of the average concentration to which a workman was exposed in performing a given operation, it would have additional uncertainty, dependent upon the variability of concentration with time and space at the work station. CALIBRATION INSTRUMENTS AND TECHNIQUES FOR FLOW AND VOLUME CALIBRATION In this section, the various techniques used for measuring sampling rate or sampled volume in samplers and in laboratory calibrations of sam- plers will be discussed in terms of their principles of operation and their sources of error. Some may be considered primary measurements, while some are secondary or derived. Primary measurements generally involve a direct measurement of volume on the basis of the physical dimensions of an enclosed space. Secondary standards are reference instruments or meters which trace their calibra- tions to primary standards, and which have been shown to be capable of maintaining their accuracy with reasonable handling and care in operation. X SAMPLE COLLECTOR samples during collection, storage and analyses. Cumulative Statistical Error. The most probable value of the cumulative error E. can be calculated from the following equation: E.— [E+E + E+ ... +E? For example, if accuracies of the flowrate measurement, sampling time, recovery, and analy- sis are = 15, 2, 10, and 10% respectively, and there are no other significant sources of error, then the cumulative error would be: a 1) DRAIN TUBE VALVE 104 Powell CH, Hosey AD (eds): The Industrial Environment — Its Evaluation and Control, 2nd Edition. Public Health Service Publication No. 614, 1965. Figure 11-1. Marriotti Bottle % "1 COUNTER WEIGHT | | 1 een AIR I _caviTy wv | ~FLUID LLC NNT TT TT TT 1 1 1.1 fe STAND PIPE =| Powell CH, Hosey AD (eds): The Industrial Environment — Its Evaluation and Control, 2nd Edition. Public Health Service Publication No. 614, 1965. Figure 11-2. Schematic Drawing of a Spiro- meter Instruments which Measure or Are Calibrated in Volume Units Water Displacement. Figure 11-1 shows a sche- WAY VALVE matic drawing of a Mariotti bottle. When the valve at the bottom of the bottle is opened, water drains out of the bottle by gravity, and air is drawn via a sample collector into the bottle to replace it. The volume of air drawn in is equal to the change in water level multiplied by the cross sec- tion at the water surface. The Casella Standard Thermal Precipitation uses a water-filled aspirator with an orifice at the discharge end of the cylinder which limits the flowrate to 7 cm?/min. * Spirometer or Gasometer. The spirometer (Fig- ure 11-2) is a cylindrical bell with its open end under a liquid seal. The weight of the bell is counterbalanced so that the resistance to move- ment as air moves in or out of the bell is negligible. It differs from the Mariotti bottle in that it meas- ures displaced air instead of displaced liquid. The volume change is calculated in a similar manner, i.e., change in height times cross section. Spirom- eters are available in a wide variety of sizes?! and are frequently used as primary volume standards. “Frictionless” Piston Meters. Cylindrical air dis- placement meters with nearly frictionless pistons are frequently used for primary flow calibrations. The simplest version is the soap-bubble meter illustrated in Figure 11-3. It utilizes a volumetric laboratory buret whose interior surfaces are wet- ted with a detergent solution. If a soap-film bub- ble is placed at the left side, and suction is applied at the right, the bubble will be drawn from left to right. The volume displacement per unit time (i.e., flowrate) can be determined by measuring the time required for the bubble to pass between two scale markings which enclose a known volume. Soap-film flowmeters and mercury-sealed pis- ton flowmeters are available commercially from several sources.) In the mercury-sealed piston, most of the cylindrical cross section is blocked off BURET rn SOAP BUBBLE A=Tr(D/2)? TO HAND PUMP OR SQUEEZE BULB Powell CH, Hosey AD (eds): The Industrial Environment — Its Evaluation and Control, 2nd Edition. Public Health Service Publication No. 614, 1965 Figure 11-3. Bubble Meter 105 by a plate which is perpendicular to the axis of retains its toroidal shape due to its strong surface the cylinder. The plate is separated from the tension. This floating seal has a negligible friction cylinder wall by an O-ring of liquid mercury which loss as the plate moves up and down. "| GAS PRESSURE GAUGE | GAS THERMOMETER / WATER FUNNEL | FOR FILLING GAS OUTLET ON BACK OF METER WATER LEVEL SIGHT GLASS WATER LEVEL GAS INLET ON BACK OF METER CALIBRATING POINT PARTITIONED DRUM (ROTOR) Powell CH, Hosey AD (eds): The Industrial Environment — Its Evaluation and Control, 2nd Edition. Public Health Service Publication No. 614, 1965. Figure 11-4. Wet Test Meter Wet-Test Meter. A wet-test meter (See Figure water seal at the inlet or outlet. In spite of these 11-4) consists of a partitioned drum half sub- factors, the accuracy of the meter usually is within merged in a liquid (usually water) with openings one percent when used as directed by the manu- at the center and periphery of each radial cham- facturer. ber. Air or gas enters at the center and flows into ~~ Dry-Gas Meter. The dry-gas meter shown in Fig- an individual compartment causing it to rise, there- ure 11-5 is very similar to the domestic gas meter. by producing rotation. This rotation is indicated It consists of two bags interconnected by mechani- by a dial on the face of the instrument. The vol- cal valves and a cycle-counting device. The air or ume measured will be dependent on the fluid level gas fills one bag while the other bag empties it- in the meter since the liquid is displaced by air. self; when the cycle is completed the valves are A sight gauge for determining fluid height is pro- switched, and the second bag fills while the first vided and the meter may be leveled by screws and ~~ one empties. Any such device has the disadvan- a sight bubble which are provided for this purpose. tage of mechanical drag, pressure drop, and leak- There are several potential errors associated age; however, the advantage of being able to use with the use of a wet-test meter. The drum and the meter under rather high pressures and volumes moving parts are subject to corrosion and damage often outweighs these errors, which can be de- from misuse, there is friction in the bearings and termined for a specific set of conditions. The the mechanical counter, inertia must be overcome alternate filling of two chambers as the basis for at low flows (<1 RPM), while at high flows volume measurement is also used in twin-cylinder (>3 RPM), the liquid might surge and break the piston meters. Such meters can also be classified 106 MECHANICAL VALVE AND COUNTER MECHANISM METER READOUT INDEX BELLOWS OR DIAPHRAGMS Powell CH, Hosey AD (eds): The Industrial Environment — Its Evaluation and Control, 2nd Edition. Public Health Service Publication No. 614, 1965. . Figure 11-5. Dry Gas Meter 107 Figure 11-6. Schematic Diagram Showing Principle of Operation of Twin-Lobed Positive Dis- placemen t Meter 108 as positive displacement meters. Positive Displacement Meters. Positive displace- ment meters consist of a tight-fitting moving ele- ment with individual volume compartments which fill at the inlet and discharge at the outlet parts. A lobed rotor design is illustrated in Figure 11-6. Another multicompartment continuous rotary meter uses interlocking gears. When the rotors of such meters are motor driven, these units become positive displacement air movers. Volumetric Flowrate The volume meters discussed in the preceding paragraphs were all based on the principle of con- servation of mass; specifically the transfer of a fluid volume from one location to another. The flowrate meters in this section all operate on the principle of the conservation of energy; more specifically, they utilize Bernoulli’s theorem for the exchange of potential energy for kinetic energy and/or frictional heat. Each consists of a flow restriction within a closed conduit. The restric- tion causes an increase in the fluid velocity, and therefore an increase in kinetic energy, which requires a corresponding decrease in potential energy, i.e., static pressure. The flowrate can be calculated from a knowledge of the pressure drop, the flow cross section at the constriction, the den- sity of the fluid, and the coefficient of discharge, which is the ratio of actual flow to theoretical flow and makes allowance for stream contraction and frictional effects. Flowmeters which operate on this principle can be divided into two groups. The larger group, which includes orifice meters, venturi meters, and flow nozzles have a fixed restriction and are known as variable-head meters, because the differential pressure head varies with flow. The other group, which includes rotameters, are known as variable- area meters, because a constant pressure differen- tial is maintained by varying the flow cross section. Variable-Area Meters (Rotameters). A rotameter consists of a “float” which is free to move up and down within a vertical tapered tube which is larger at the top than the bottom. The fluid flows upward, causing the float to rise until the pressure drop across the annular area between the float and the tube wall is just sufficient to support the float. The tapered tube is usually made of glass or clear plastic and has a flowrate scale etched directly on it. The height of the float indicates the flowrate. Floats of various configurations are used, as indicated in Figure 11-7. They are convention- ally read at the highest point of maximum diam- eter, unless otherwise indicated. Most rotameters have a range of 10:1 between their maximum and minimum flows. The range of a given tube can be extended by using heavier or lighter floats. Tubes are made in sizes from about 8 to 6 inches in diameter, covering ranges from a few cm?/min. to over 1,000 ft*/min. Some of the shaped floats achieve stability by having slots which make them rotate, but these are less com- monly used than previously. The term “rota- meter” was first used to describe such meters with a READ HERE | | I | [ SPHERICAL PLUMB BOB [ Ni \-READ HERE—t 1 | | | shy i SPOOL CYLINDRICAL (MARKED) Powell CH, Hosey AD (eds): The Industrial Environ- ment — Its Evaluation and Control, 2nd Edition. Public Health Service Publication No. 614, 1965. Figure 11-7. Typical Rotameter Floats spinning floats, but now is generally used for all types of tapered metering tubes. Rotameters are the most commonly used flow- meters on commercial air samplers, especially on portable samplers. For such sampler flowmeters, the most common material of construction is acry- lic plastic, although glass tubes may also be used. Because of space limitations, the scale lengths are generally no more than four inches and most com- monly nearer to two inches. Unless they are in- dividually calibrated, the accuracy is unlikely to be better than = 25%. When individually cali- brated, == 5% accuracy may be achieved. It should be noted, however, that with the large taper of the bore, the relatively large size of the float, and the relatively few scale markers on these rotameters, the precision of the readings may be a major limiting factor. Calibrations of rotameters are performed at an appropriate reference pressure, usually atmos- pheric. However, since good practice dictates that the flowmeter should be downstream of the sample collector or sensor, the flow is actually measured at a reduced pressure, which may also be a vari- able pressure if the flow resistance changes with loading. If this resistance is constant, it should be known; if variable, it should be monitored, so that the flowrate can be adjusted as needed, and appropriate pressure corrections can be made for the flowmeter readings. Variable-Head Meters. When orifice and venturi meters are made to standardized dimensions, their calibration can be predicted with ~ += 10% 109 Radius Taps 4 4 / LT ror TH TN TT=N DT Hoon ip] ;. D2 === Yd lll Ll lL [LL LL LL LLL LL 2 (a) (b) Perry JH, et al: Chemical Engineering Handbook, 4th Edition. New York, McGraw-Hill, 1963. Figure 11-8. Square-Edged or Sharp-Edged Orifices. The plate at the orifice opening must not be thicker than 1/30 of pipe diameter, 1/8 of the orifice diameter, or 1/4 of the distance from the pipe wall to the edge of the opening. (a) Pipe-line orifice. (b) Types of plates. 110 0.95 xX £ O S 5 0.90 Q oO ‘© > cs 0.85 oO > oO £ © 0.80 S £ QL ° 2 0.75 oO 2 oO 5 € 0.70 © ‘» Oo oO 0.65 0.60 0 0.5 | 2 3 4 5 6 Downstream pressure tap location in pipe diameters Perry JH, et al: Chemical Engineering Handbook, 4th Edition. New York, McGraw-Hill, 1963. Figure 11-9. Coefficient of Discharge for Square-Edged Circular Orifices for Ng.,>30,000 with the Upstream Tap Location between One and Two Pipe Diameters from the Orifice Position 111 accuracy using standard equations and published empirical coefficients, The general equation? for this type of meter is: W = qipi = KYA, y2g. (P,—P,)p, (1) where: K=C/ yl —p¢ C = coefficient of discharge, dimensionless A, = cross-sectional area of throat — ft? g. == 32.17 ft/sec® P, = upstream static pressure — lb/ft? P, — downstream static pressure — lb/ft* q, = volumetric flow at upstream press. & temp.-ft®/sec. W = weight-rate of flow — Ib/sec. Y = expansion factor (see Figure 11-10) = ratio of throat diameter to pipe diameter, Orifice Meters. The simplest form of variable- head meter is the square-edged, or sharp-edged orifice illustrated in Figure 11-8. It is also the most widely used because of its ease of installa- tion and low cost. If it is made with properly mounted pressure taps, its calibration can be de- termined from equation (1) and Figures 11-9 and 11-10. However, even a non-standard orifice meter can serve as a secondary standard, provided it is carefully calibrated against a reliable reference instrument. While the square-edged orifice can provide accurate flow measurements at low cost, it is in- efficient with respect to energy loss. The perma- nent pressure loss for an orifice meter with radius taps can be approximated by (1 — p*), and will often exceed 80%. dimensionless Venturi Meters. Venturi meters have optimal con- p, = density at upstream press. & temp. verging and diverging angles of about 25° and 7° — Ib/fte. respectively, and thereby have high pressure re- 1.0 2 2 2 2 R=0 |f=03|F=05|F=07 RS Sen Y po SE +—=1 PFORIFICES 0.9 p =0 pd St . ~J Fool” | 2 oS Eo DZ RNS NOZZLES p=04 >. J [ VENTURIS p05] 0.8 O 002 0.04 006 0.08 0.0 0.2 O0lI4 Ole d-r k Perry JH, et al: Chemical Engineering Handbook, 4th Edition. New York, McGraw-Hill, 1963. Figure 11-10. Values of Expansion Factor Y for Orifices, Nozzles, and Venturis coveries, i.e., the potential energy which is con- verted to kinetic energy at the throat is recon- verted to potential energy at the discharge, with an overall loss of only about 10%. For air at 70°F and 1 atm. and for 4 < f < V2, a standard venturi would have a calibra- tion described by: Q—212p8D* yh (2) where Q = flow — ft*/min. B = ratio of throat to duct diameter, dimensionless D = duct diameter — inches h = differential pressure — inches of water. 112 Other Variable-Head Meters. The characteristics of various other types of variable-head flowmeters, e.g., flow nozzles, Dall Tubes, centrifugal flow elements, etc. are described in various standard engineering references.*® In most respects they have similar properties to the orifice meter, ven- turi meter, or both. One type of variable-head meter which differs significantly from all of the above is the laminar- flow meter. These are seldom discussed in en- gineering handbooks because they are used only for very low flowrates. Since the flow is laminar, INLET "T" CONNECTION the pressure drop is directly proportional to the flowrate. In orifice meters, venturi meters and related devices, the flow is turbulent and flowrate varies with the square root of the pressure dif- ferential, Laminar flow restrictors used in commercial flowmeters consist of egg-crate or tube bundle arrays of parallel channels. Alternatively, a lami- nar flowmeter can be constructed in the laboratory using a tube packed with beads or fibers as the resistance element. Figure 11-11 illustrates this kind of homemade flowmeter. It consists of a “T” ASBESTOS PACKING STOPPER Sa NN sss EEL LST ESL LS. TUBE OPEN TO FLUID LL LLL LL LL LLL Lt Ll lL Ll) ATMOSPHERE PIPET OR GLASS TUBE ~— GRADUATED FLASK LL 22828 LL LL LLL 280882820108) XL LLLLLL 4 Fe / Powell CH, Hosey AD (eds): The Industrial Environment — Its Evaluation and Control, 2nd Edition. Public Health Service Publication No. 614, 1965. Figure 11-11. connection, pipet or glass tubing, cylinder and packing material. The outlet arm of the “T” is packed with material, such as asbestos, and the leg is attached to a tube or pipet projecting down 113 Drawing of a Packed Plug Flow Meter into the cylinder filled with water or oil. A cali- bration curve of the depth of the tube outlet below the water level versus the rate of flow should pro- duce a linear curve. Saltzman* has used tubes filled with asbestos to regulate and measure flow- rates as low as 0.01 cm®/min. Pressure Transducers. All of the variable-head meters require a pressure sensor, sometimes re- ferred to as the secondary element. Any type of pressure sensor can be used, although high cost and fragility usually rule out the use of many Liquid-filled manometer tubes are sometimes used, and if they are properly aligned and the density of the liquid is accurately known, the col- umn differential provides an unequivocal measure- ment. In most cases however, it is not feasible to use liquid-filled manometers in the field, and the pressure differentials are measured with mechani- electrical and electro-mechanical transducers. cal gages with scale ranges in centimeters or inches Dwyer Instruments, Inc.: Bulletin #A-20. Michigan City, Indiana. Figure 11-12. How the Magnetic Linkage Works™* *From I. W. Dwyer Co. Literature 12A—At zero position, pressures on both sides of the diaphragm are equal. The support plates of the diaphragm are connected to the leaf spring which is anchored at one end. The horseshoe magnet attached to the tree end of the spring straddles the axis of a helix but does not touch the helix. The indicating pointer is attached to one end of the helix. The helix, being of high magnetic permeability, aligns itself in the field of the magnet to maintain the minimum air gap between the magnet’s poles and the outer edge of the helix. 12B—When pressure on the “high” side of the diaphragm increases or pressure on the “low” side of the diaphragm decreases, the diaphragm moves toward the back of the case. Through the linkage, the diaphragm moves the spring and the magnet. As the magnet moves parallel to the axis of the helix, the helix turns to maintain the minimum air gap. Movement of the diaphragm is resisted by the flat spring which determines the range of the instrument. Precise calibration is achieved by varying the live length of the spring through adjustment of the spring clamp. 114 of water. For these low pressure differentials the most commonly used gage is the Magnehelic®, whose schematic is illustrated in Figures 11-12A and 11-12B. These gages are accurate to == 2% of full scale and are reliable provided they and their connecting hoses do not leak, and their cali- bration is periodically rechecked. Critical-Flow Orifice. For a given set of upstream conditions, the discharge of a gas from a restricted opening will increase with a decrease in the ratio of absolute pressures P,/P,, where P, is the down- stream pressure, and P, the upstream pressure, until the velocity through the opening reaches the velocity of sound. The value of P,/P, at which the maximum velocity is just attained is known as the critical pressure ratio. The pressure in the throat will not fall below the pressure at the critical point, even if a much lower downstream pressure exists. Therefore, when the pressure ratio is below the critical value, the rate of flow through the restricted opening is dependent only on the up- stream pressure. It can be shown, that for air flowing through rounded orifices, nozzles and venturis, when P, < 0.53 P,, and S,/S, > 25, the mass-flowrate w, is determined by: w — 0.533-05:P1 T 1b/sec (3) where: C, = coefficient of discharge (normally ~ 1) S, = duct or pipe cross section in square inches S, = orifice area in square inches P, — upstream absolute pressure in Ib/sq. in. T, = upstream temperature in °R Critical-flow orifices are widely used in indus- trial hygiene instruments such as the midget im- pinger pump and squeeze bulb indicators. They can also be used to calibrate flowmeters by using a series of critical orifices downstream of the flow- meter under test. The flowmeter readings can be plotted against the critical flows to yield a cali- bration curve. The major limitation in their use is that the orifices are extremely small when they are used for flows of 1 ft°/min or less. They become clogged or eroded in time and, therefore, require frequent examination and/or calibration against other reference meters. By-Pass Flow Indicators. In most high-volume samplers, the flowrate is strongly dependent on the flow resistance, and flowmeters with a suffic- iently low flow resistance are usually too bulky or expensive. A commonly used metering element for such samplers is the by-pass rotameter, which actually meters only a small fraction of the total flow; a fraction, however, which is proportional to the total flow. As shown schematically in Figure 11-13, a by-pass flowmeter contains both a vari- able-head element and a variable-area element. The pressure drop across the fixed orifice or flow restrictor creates a proportionate flow through the VALVE ROTAMETER Figure 11-13. Schematic of By-Pass Flow Indicators parallel path containing the small rotameter. The scale on the rotameter generally reads directly in ft3/min or liters/min of total flow. In the versions used on portable high-volume samplers there is usually an adjustable bleed valve at the top of the rotameter which should be set initially, and peri- odically readjusted in laboratory calibrations so that the scale markings can indicate overall flow. If the rotameter tube accumulates dirt, or the bleed valve adjustment drifts, the scale readings can depart greatly from the true flows. Flow Velocity Meters As discussed previously, point velocity is not the parameter of interest in sampling flow meas- urements. However, it may be the only feasible parameter to measure in some circumstances, and it usually can be related to flowrate provided the sensor is located in an appropriate position and is suitably calibrated against overall flow. Velocity Pressure Meters. The Pitot tube is often used as a reference instrument for measuring the velocity of air. A standard Pitot, carefully made, will need no calibration. It consists of an impact tube whose opening faces axially into the flow, and a concentric static pressure tube with 8 holes spaced equally around it in a plane which is 8 diameters from the impact opening. The differ- ence between the static and impact pressures is the velocity pressure. Bernoulli's theorem applied to a Pitot tube in an air stream simplifies to the dimensionless formula V— y2gP, (4) where: V = linear velocity g. = gravitational constant P, — pressure head of flowing fluid or ve- locity pressure. Expressing V in linear : feet per min., P, in inches of water (hy), (Ib.-mass) (ft.) V = 1097 2 (5) p . where: p = density of air or gas in Ib. /ft.? If the Pitot tube is to be used with air at standard conditions (70°F and 1 atm.), formula (5) reduces to: V — 4005 yh, (6) where: V = velocity in ft./min. h, = velocity pressure in inches of H,O There are several serious limitations to Pitot tube measurements in most sampling flow calibra- tions. One is that it may be difficult to obtain or fabricate a small enough probe. Another is that the velocity pressure may be too low to measure at the velocities encountered. For example, at 1000 ft./min., h, = 0.063 inches of water, a low value, even for an inclined manometer. Heated Element Anemometers. Any instrument used to measure velocity can be referred to as an anemometer. In a heated element anemometer, the flowing air cools the sensor in proportion to the velocity of the air. Instruments are available with various kinds of heated elements, i.e., heated thermometers, thermocouples, films, and wires. x 0 C L A IONS— COLLECTOR SURFACE Z FLOW] 2 | CENTRAL DISC. ION DEFLECTION ON VOLTAGE SUPPLY TEE. SATE d— A— TS S— CC — — — * SN | ANALOG OUT +2 4 + L 2 lon = DEFLECTION | MEASUREMENT CIRCUIT | | | ~~ | | | 1999 — — es a i] ~ | | | | big VOLTAGE SUPPLY AND be RANGE SELECTION, SCALING, AND CONTROLLER | READOUT. _ ae Thermo-Systems, Inc.: leaflet “TSI-54100-671.” St. Paul, Minnesota. } Figure 11-14. lon-Flow Mass Flowmeter 116 They are all essentially nondirectional, i.e., with single element probes, they measure the airspeed but not its direction. They all can accurately meas- ure steady state airspeed, and those with low mass sensors and appropriate circuits can also accu- rately measure velocity fluctuations with frequen- cies above 100,000 Hz. Since the signals pro- duced by the basic sensors are dependent on am- bient temperature as well as air velocity, the probes are usually equipped with a reference ele- ment which provides an output which can be used to compensate or correct errors due to tempera- ture variations. Some heated element anemome- ters can measure velocities as low as 10 ft./min. and as high as 8,000 ft./min. Other Velocity Meters. There are several other ways to utilize the kinetic energy of a flowing fluid to measure velocity beside the Pitot tube. One way is to align a jeweled-bearing turbine wheel axially in the stream and count the number of rotations per unit time. Such devices are gener- ally known as rotating vane anemometers. Some are very small and are used as velocity probes. Others are sized to fit the whole duct and become rr rr Lr i 1 1 1 1 1. 1 7 indicators of total flowrate and sometimes are called turbine flowmeters. The velometer, or swinging vane anemometer described in Chapter 40, is widely used for meas- uring ventilation air flows, but has few applica- tions in sample flow measurement or calibration. It consists of a spring-loaded vane whose displace- ment is indicative of velocity pressure. Mass Flow and Tracer Techniques Thermal Meters. A thermal meter measures mass air or gas flow rate with negligible pressure loss. It consists of a heating element in a duct section between two points at which the temperature of the air or gas stream is measured. The tempera- ture difference between the two points is depend- ent on the mass rate of flow and the heat input. Mixture Metering. The principle of mixture meter- ing is similar to that of thermal metering. Instead of adding heat and measuring temperature dif- ference, a contaminant is added and its increase in concentration is measured; or clean air is added and the reduction in concentration is measured. This method is useful for metering corrosive gas streams. The measuring device may react to some MANOMETER TO SOURCE THREE WAY VALVE SPIROMETER OF VACUUM WET TEST METER Powell CH, Hosey AD (eds): The Industrial Environment — Its Evaluation and Control. 2nd Edition. Public Health Service Publication No. 614, 1965. Figure 11-15. Calibration Setup for Calibrating a Wet Test Meter 117 physical property such as thermal conductivity or vapor pressure. lon-Flow Meters. In the ion-flow meter illustrated in Figure 11-14, ions are generated from the cen- tral disc and flow radially toward the collector surface. Airflow through the cylinder causes an axial displacement of the ion stream in direct pro- portion to the mass flow. The instrument can measure mass flows from 0.1 to 150 standard ft.?/min., and velocities from 1 ft./min. to 12,000 ft./min, Procedures for Calibrating Flow and Volume Meters In the limited space available, it is not possible to provide a complete description of all of the techniques available, or to go into great detail on those which are commonly used. This discussion will be limited to selected procedures which should serve to illustrate recommended approaches to some commonly encountered calibration procedures. Comparison of Primary and Secondary Standards. Figure 11-15 shows the experimental set-up for checking the calibration of a secondary standard (in this case a wet-test meter) against a primary standard (in this case a spirometer). The first step should be to check out all of the system ele- ments for integrity, proper functioning, and in- terconnections. Both the spirometer and wet-test meter require specific internal water levels and leveling. The operating manuals for each should be examined since they will usually outline simple procedures for leakage testing and operational procedures. After all connections have been made, it is a good policy to recheck the level of all instruments and determine that all connections are clear and have minimum resistance. If compressed air is used in a calibration procedure it should be cleaned and dried. Actual calibration of the wet-test meter shown in Figure 11-15 is accomplished by opening the by-pass valve and adjusting the vacuum source to obtain the desired flowrate. The optimum range of operation is between one and three revolutions per minute. Before actual calibration is initiated the wet-test meter should be operated for several hours in this setup to stabilize the meter fluid as to temperature, absorbed gas, and to work in the bearings and mechanical linkage. After all ele- ments of the system have been adjusted, zeroed and stabilized several trial runs should be made. During these runs, should any difference in pres- sure be indicated, the cause should be determined and corrected. The actual procedure would be to instantaneously divert the air to the spirometer for a predetermined volume indicated by the wet- test meter (minimum of one revolution), or to near capacity of the spirometer, then return to the by-pass arrangement. Readings, both quan- tity and pressure of the wet-test meter, must be taken and recorded while it is in motion, unless a more elaborate system is set up. In the case of a rate meter, the interval of time that the air is entering the spirometer must be accurately timed. The bell should then be allowed to come 118 to equilibrium before displacement readings are made. A sufficient number of different flowrates are taken to establish the shape or slope of the calibration curve with the procedure being re- peated three or more times for each point. For an even more accurate calibration the setup should be reversed so that air is withdrawn from the spirometer. In this way any unbalance due to pressure differences would be cancelled. A permanent record should be made of a sketch of the setup, data, conditions, equipment, results, and personnel associated with the calibra- tion. All readings (volume, temperatures, pres- sures, displacements, etc.) should be legibly re- corded, including trial runs or known faulty data, with appropriate comments, The identifications of equipment, connections and conditions should be so complete that the exact setup with the same equipment and connections could be reproduced by another person solely by use of the records. After all of the data have been recorded, the calculations such as correction for variations in temperature, pressure and water vapor are made using the ideal gas laws: P, 273 VeVi X760 XT, where V, = volume at standard conditions (760 mm & 0°C) V, = volume measured at conditions P,and T, T, = temperature of V, in °K P, = pressure of V, in mm Hg In most cases the water vapor portion of the ambient pressure is disregarded. Also, the stand- ard temperature of the gas is often referred to normal room temperature, i.e., 21°C rather than 0°C. The manipulation of -the instruments, data reading and recording, calculations and resulting factors or curves should be done with extreme care. Should a calibration disagree with previous calibrations or the supplier’s calibration, the en- tire procedure should be repeated, and examined carefully to assure its validity. Upon completion of any calibration the instrument should be tagged or marked in a semi-permanent manner to indi- cate the calibration factor, where appropriate, date and who performed the calibration. (7) Reciprocal Calibration by Balanced Flow System. In many commercial instruments it is impractical to remove the flow-indicating device for calibra- tion. This may be because of physical limitations, characteristics of the pump, unknown resistance in the system® or other limiting factors. In such situations it may be necessary to set up a recip- rocal calibration procedure, that is, where a con- trolled flow of air or gas is compared first with the instrument flow, then with a calibration source. Often a further complication is introduced by the static pressure characteristics of the air mover in the instrument. In such instances supplemental pressure or vacuum must be applied to the system to offset the resistance of the calibrating device. An example of such a system is illustrated in Figure 11-16. FLOW INDICATOR 2 @ OOO INSTRUMENT TO BE CALIBRATED SAMPLE LINE CALIBRATED ROTOMETER AIR Powell CH, Hosey AD (eds): The Industrial Environment — Its Evaluation and Control. 2nd Edition. Public Health Service Publication No. 614, 1965. Figure 11-16. Setup for Balanced Flow Calibration The instrument is connected to a calibrated rotameter and source of compressed air. Between the rotameter and the instrument an open-end manometer is installed. The connections, as in any other calibration system, should be as short and resistance-free as possible. In the calibration procedure the flow through the instrument and rotameter is adjusted by means of a valve or restriction at the pump until the manometer indicates “0” pressure difference to the atmosphere. When this condition is achieved the instrument and rotameter are both operating at atmospheric pressure. The indicated and cali- brated rates of flow are then recorded and the procedure repeated for other rates of flow. Dilution Calibration. Normally gas-dilution tech- niques are employed for instrument response cali- brations; however, several procedures®™* have been developed whereby sampling rates of flow could be determined. The principle is essentially the same except that different unknowns are in- volved. In air-flow calibration a known concen- tration of the gas (i.e., carbon dioxide) is con- tained in a vessel. Uncontaminated air is intro- duced and mixed thoroughly in the chamber to replace that removed by the instrument to be cali- brated. The resulting depletion of the agent in the vessel follows the theoretical dilution formula: C; = Ce" (8) where: C, = concentration of agent in vessel at time, t C, = initial concentration att — 0 e — base of natural logarithms b — air changes in the vessel per unit time t = time The concentration of the gas in the vessel is determined periodically by an independent method. A linear plot should result from plotting concen- 119 tration of agent against elapsed time on semi-log- paper. The slope of the line indicates the air changes per minute (b) which can be converted to the rate (Q) of air withdrawn by the instru- ment from the following relationship: Q = bV; where V — volume of the vessel. This technique offers the advantage that vir- tually no resistance or obstruction is offered to the air flow through the instrument; however, it is limited by the accuracy of determining the con- centration of the agents in the air mixture. CALIBRATION OF SAMPLER’S COLLECTION EFFICIENCY Use of Well Characterized Test Atmospheres In order to test the collection efficiency of a sampler for a given contaminant it is necessary either: 1) to conduct the test in the field using a proven reference instrument or technique as a reference standard, or 2) to reproduce the atmos- phere in a laboratory chamber or flow system. Techniques and equipment for producing such test atmospheres are beyond the scope of this chapter. They are discussed in detail in Chapter 12 and in various other sources.” !® 112 In the discussion to follow, it will be assumed that appro- priate test atmospheres are available. Analysis of Sampler’s Collection and Downstream Total Collector The best approach to use, when it is feasible, is to operate the sampler under test in series with a downstream total collector, as illustrated in Fig- ure 11-17. The sampler’s efficiency is then de- termined by the ratio of the sampler’s retention to the retention in the sampler and downstream col- lector combined. When the penetration is esti- mated from downstream samples there may be additional errors if the samples are not repre- sentative. ) TC ( S=Sample Under Test TC= Total Collector AMC= Air Mover, Flowmeter and Flow Control Figure 11-17. Sampler Efficiency Evaluation with Downstream Total Collector: Analysis of Collections in S and TC trated in Figure 11-18. When this approach is Analysis of Sampler’s Collection and used, it may be necessary to collect a series of Downstream Samples In some situations it is not possible or feas- ible to quantitatively collect all of the test mate- rial which penetrates the sampler being evaluated. For example, a total collector might add too much flow resistance to the system, or be too bulky for efficient analysis. In this case, the degree of pene- tration can be estimated from an analysis of a sample of the downstream atmosphere, as illus- 2) samples across the flow profile rather than a single sample, in order to obtain a true average concen- tration of the penetrating atmosphere. Analysis of Up-and Downstream Samples In some cases, it may not be possible to re- cover or otherwise measure the material trapped within elements of the sampling train such as sampling probes. The magnitude of such losses o— TSp reams AMC TS p= Downstream Sampler Total Collector Figure 1- 18. Sampler Efficiency Evaluation with Downstream Concentration Sampler: An- alysis of Collections in S and TSp fT ~ N TSy RE AMC ) 3 AMC) TSp mere AMC TS y= Upstream Sampler Total Collector Figure 11-19. Sampler Efficiency Evaluation with Upstream and Downstream Concentration Samplers: Analysis of Collections in TS, and TSp can be determined by comparing the concentra- tions up-and downstream of the elements in ques- tion as illustrated schematically in Figure 11-19. DETERMINATION OF SAMPLE STABILITY AND/OR RECOVERY For trace contaminants the stability and re- covery from sampling substrates are difficult to predict or control. Thus, these factors are best explored by realistic calibration tests. Analysis of Sample Aliquots at Periodic Intervals after Sample Collection If the sample is divided into a number of ali- quots which are analyzed individually at periodic intervals, it is possible to determine the long term rate of sample degradation or any tendency for reduced recovery efficiencies with time. These analyses would not however provide any informa- tion or losses which may have occurred during or immediately after collection which had different rate constants. Such losses should be investigated using spiked samples. Analysis of Spiked Samples If known amounts of the contaminants of interest are intentionally added to the sample substrate, then subsequent analysis of sample aliquots will permit calculation of sample recovery efficiency and rate of deterioration. These results will be valid only insofar as the added material is equiva- lent in all respects to the material in the ambient air. There are two basic approaches to spiked sample analyses: 1) the addition of known quan- tities to blank samples, and 2) the addition of radioactive isotopes to either blank or actual field collected samples. When the material being analyzed is available in tagged form, the tag can be added to the sample in negligible or at least known low concentrations. If there are losses in sample processing or analysis, 121 the fractional recovery of the tagged molecules will provide a basis for estimating the comparable loss which took place in the untagged molecules of the same species. CALIBRATION OF SENSOR RESPONSE Direct-reading instruments are generally deliv- ered with either a direct-reading panel meter, a set of calibration curves, or both. The tendency of the unwary and inexperienced user is to be- lieve the manufacturer’s calibration, and this often leads to grief and error. Any instrument with cali- bration adjustment screws should of course be suspect, since such adjustments can easily be changed intentionally or accidentally, as in ship- ment. All instruments should be checked against ap- propriate calibration standards and atmospheres immediately upon receipt and periodically there- after. Procedures for establishing test atmospheres are discussed earlier in this chapter and in Chapter 12. Verification of the concentrations of such test atmospheres should be performed whenever pos- sible using analytical techniques which are referee- tested or otherwise known to be reliable. With these techniques, calibration curves for direct reading instruments can be tested or gener- ated. When environmental factors such as tem- perature, ambient pressure, and radiant energy may be expected to influence the results, these effects should be explored with appropriate tests whenever possible. Similarly, the effects of co- contaminants and water vapor on instrument re- sponse should also be explored. SUMMARY AND CONCLUSIONS Because the accuracy of all sampling instru- ments is dependent on the precision of measure- ment of the sample volume, sample mass or sam- ple concentration involved, extreme care should be exercised in performing all calibration pro- cedures. The following comments summarize the philosophy of air sampler calibration: 1. 2. 11. 12. Use standard devices with care and atten- tion to detail. All standard materials and instruments and procedures should be checked periodically to determine their stability and/or operat- ing condition. Perform calibrations whenever a device has been changed, repaired, received from a manufacturer, subjected to use, mis- handled or damaged and at any time when there is a question as to its accuracy. Understand the operation of an instrument before attempting to calibrate it and use a procedure or setup which will not change the characteristics of the instrument or standard within the operating range re- quired. When in doubt about procedures or data, assure their validity before proceeding to the next operation. All sampling and calibration train connec- tions should be as short and free of con- strictions and resistance as possible. Extreme care should be exercised in read- ing scales, timing, adjusting and leveling, and in all other operations involved. Allow sufficient time for equilibrium to be established, inertia to be overcome and conditions to stabilize. Enough points or different rates of flow should be obtained on a calibration curve to give confidence in the plot obtained. Each point should be made up of more than one reading whenever practical. A complete permanent record of all pro- cedures, data and results should be main- tained. This should include trial runs, known faulty data with appropriate com- ments, instrument identification, connec- tion sizes, barometric pressure, tempera- ture, etc. When a calibration differs from previous records, the cause of change should be de- termined before accepting the new data or repeating the procedure. Calibration curves and factors should be properly identified as to conditions of cali- bration, device calibrated and what it was calibrated against, units involved, range 122 and precision of calibration, date and who performed the actual procedure. Often it is convenient to indicate where the orig- inal data is filed and to attach a tag to the instrument indicating the above informa- tion. References 1. CAPLAN, P.: Calibration of Air Sampling Instru- ments. I, in Air Sampling Instruments, 4th Ed. Amer. Conference of Governmental Industrial Hygienists, P.O. Box 1937, Cincinnati, Ohio 45201 (1972). PERRY, J. H., et. al., Eds.: Chemical Engineering Handbook, 4th Ed. McGraw-Hill, New York (1963). AMERICAN SOCIETY OF MECHANICAL EN- GINEERS: Flow Measurement by Means of Stan- dardized Nozzles and Orifice Plates—ASME Power Test Code (PTC 19.5.4-1959), New York (1959). SALTZMAN, B. E.: Preparation and Analysis of Calibrated Low Concentrations of Sixteen Toxic Gases. Anal. Chem., 33: 1100-12 (1961). . TEBBENS, B. D,, and D. M. KEAGY: “Flow Cali- bration of High Volume Samplers.” Amer. Industr. Hyg. Assoc. Quart., 17: 327-329 (December 1953). MORLEY, J., and B. D. TEBBENS: “The Electro- static Precipitator Dilution Method of Flow Meas- urement.” Amer. Industr. Hyg. Assoc., Quart., 14: 303-306 (December 1953). SETTERLIND, A. N.: “Preparation of Known Con- centrations of Gases to Vapors in Air.” Amer. In- dustr. Hyg. Assoc. Quart., 14: 113-120 (June 1953). BRIEF, R. S., and F. W. CHURCH: “Multi-Opera- tional Chamber for Calibration Purposes.” Amer. In- dustr. Hyg. Assoc. J., 21: 239-244 (June 1960). DREW, R. T., and M. LIPPMANN: Calibration of Air Sampling Instruments II; Production of Test Atmospheres for Instrument Calibration, in Air Sampling Instruments, 4th Ed., Amer. Conference of Governmental Industrial Hygienists, P.O. Box 1937, Cincinnati, Ohio 45201 (1972). LODGE, J. P.: Production of Controlled Test At- mospheres, In Air Pollution 2nd Ed., Vol. Il, A. C. Stern, Ed. Academic Press, New York. (1968). . COTABISH, H. N., P. W. McConnaughey and H. C. MESSER: “Making Known Concentrations for In- strument Calibration.” Amer. Industr. Hyg. Assoc. J. 22: 392-402 (1961). : HERSH, P. A.: “Controlled Addition of Experi- mental Pollutants to Air.” J. Air Pollut. Cont. As- soc. 19: 164-1770 (Mar. 1969). COMMITTEE ON RECOMMENDED ANALYTI- CAL METHODS: Manual of Analytical Methods (loose-leaf) ACGIH, P.O. Box 1937, Cincinnati, Ohio 45201 (1957, plus periodic additions). ANALYTICAL CHEMISTRY COMMITTEE: An- analytical Guides (loose-leaf) AIHA, Westmont, New Jersey 08108 (1965, plus periodic additions, which also appear as issued in AIHA Journal). ASTM D-22 COMMITTEE ON SAMPLING AND ANALYSIS OF ATMOSPHERES: 1970 Annual Book of ASTM Standards—~Part 23 Water; Atmos- pheric Analysis. ASTM, Phila., Pa. 19103 (1970, with annual revisions). CHAPTER 12 PREPARATION OF KNOWN CONCENTRATIONS OF AIR CONTAMINANTS Bernard E. Saltzman, Ph.D. INTRODUCTION Known low concentrations of air contaminants are required for many purposes. There has been a technical explosion in recent years in the de- velopment of a great variety of monitoring instru- ments for measuring concentrations of air con- taminants, based upon electronic means. These devices are invaluable; however, they are secon- dary measuring devices and must be calibrated. New chemical analytical procedures for air con- taminants have been developed by extrapolating methods from the high concentrations at which they have been demonstrated to the low concen- trations of interest. It is essential that these pro- cedures be tested to demonstrate their validity. An extensive program of collaborative testing of methods at accurately known low concentrations is now beginning because of 1) the increase in regulatory activities and 2) the legal and economic consequence of measurements required to deter- mine compliance. Another use for known concen- trations is for toxicological and scientific investi- gations of the effects of these concentrations. Such work provides the basis for control standards. Thus known concentrations are essential for cali- brating instruments, for collaborative testing of analytical methods and for scientific studies. When a highly precise system is employed, accurately known concentrations may be attained. With less accurate systems, the values are nominal. These may suffice for many purposes, or may be deter- mined accurately by use of a standard or reference analytical procedure. Two general types of systems are used for generating known concentrations. Preparation of a batch mixture has the advantage of simplicity and convenience in some cases. Alternatively, a flow-dilution system may be employed. This has the advantage of being capable of providing theo- retically unlimited volumes at known low con- centrations, which can be rapidly changed if de- sired, and of compactness. A flow-dilution system requires a metered source of diluent air, and a source for supplying known amounts of gases, vapors or aerosols; these flows are combined in a mixing device. The techniques will be described in detail below. Many articles have been pub- lished on this subject. Broad coverage is given in papers by Saltzman,* Cotabish et al.,> and Hersch.® A comprehensive book by Nelson is cited in the Preferred Reading section. 123 PREPARATION OF BATCH MIXTURES OF GASES AND VAPORS Introduction Known concentrations of gases and vapors were first prepared by introducing accurately measured quantities of the test compound into an appropriate chamber containing clean air. Various modified systems have been developed for certain special purposes. These methods gener- ally require relatively simple equipment and pro- cedures. However, a serious disadvantage is the fact that only limited quantities of the mixture can be supplied. In certain cases erroneously low concentrations result from appreciable adsorption losses of the test substance on the walls of the vessel. Losses in excess of 50% are common.*® When air dilutions of solvents or other combus- tible materials are prepared, it should be borne in mind that there is a serious explosive hazard un- SAMPLE INLET PIPETTE OR BURETTE SAMPLE OUTLET ABSORBING PAPER |_— ALUMINUM — | FoIL STRIPS oD oD Amer. Ind. Hyg. Assoc. J. 22:392, 1966. Figure 12-1. 5 Gallon Mixing Bottle less care is taken to keep the concentration out- side of the explosive limits. These methods are convenient for many substances which are not too reactive. They may be used to prepare nominal concentrations, to be verified by chemical analyses. They should not be used as primary standards without such verification or prior experience. Bottles Figure 12-1 illustrates a simple technique for preparation of vapor mixtures utilizing a S-gallon glass bottle. A quantity of volatile liquid is pi- petted into the bottle onto a piece of paper to assist in its evaporation. The bottle may then be tumbled with aluminum foil inside to facilitate air and vapor mixing. The mixture is withdrawn through a glass tube from the bottom of the bottle rather than from the top to avoid leakage and losses occurring around the stopper. As the mix- ture is withdrawn, air enters the top of the bottle to relieve the vacuum. A sealed chamber may be used in a similar manner, with mixing provided by an electric fan. (Danger! Sparks from brushes may explode some mixtures!) It can be seen that the disadvantage of this technique is that the concentration decreases dur- ing the withdrawal process. Assuming the worst possible case of complete turbulent mixing in the bottle or chamber, the change in concentration is given by equation 1. C/C, =e W/V (1) Where C = final concentration in bottle or chamber C,= initial concentration W = volume withdrawn, liters V = original volume of mixture, liters Some calculated values are shown in Table 12-1. TABLE 12-1 Decrease in Concentration vs. Fractional Volume Withdrawn W/V C/C, 0.05 0.962 0.10 0.905 0.25 0.779 0.50 0.606 This table shows the maximum depletion er- rors produced by withdrawal of the mixture. Smaller errors result if the incoming air does not mix completely with the existing mixture. Up to 5% can be withdrawn without serious loss. These errors are avoided by use of plastic bags or pres- sure cylinders, as described below. Figure 12-2 indicates a simple commercial as- sembly for calibrating explosive-gas meters. A sealed glass ampule containing a hydrocarbon, such as methane, is placed inside a polyethylene bottle and broken by shaking against a steel ball. The mixture is then carefully squeezed into the instrument to be calibrated, taking care not to suck back air. Another similar instrument manu- factured by Mine Safety Appliances Co. is com- prised of a cartridge of isobutane which is used to fill a small syringe. This is injected into a larger syringe which is then filled with air. The latter syringe serves as a gas holder for the mix- 124 POLYETHYLENE BOTTLE a — GAS MIXTURE - | GLASS AMPOULE CONTAINING GAS BROKEN AMPOULE ~ \ Bx 0 _ METAL BREAKER LO Amer. Ind. Hyg. Assoc. J. 22:392, 1966. Figure 12-2. J-W Gas Indicator Test Kit ture. These devices are relatively simple, con- venient and sufficiently accurate for this purpose. Plastic Bags A variety of plastic bags have been found to be very useful for preparing known mixtures in the laboratory. Long term stability is generally good only with relatively inert vapors such as of halogenated solvents and hydrocarbons. Among the materials used have been Mylar, Scotchpak, Saran and polyvinyl chloride. Bags are fabricated from sheets by thermal sealing. Mylar bags are popular because of their strength and inertness. This material requires a special thermal plastic adhesive tape (Schjeldahl). Tedlar, Teflon and Kel-F are considerably more expensive materials, which also require expensive sealing equipment capable of providing regulated pressures and high temperatures. They are preferred for use in pho- tochemical studies involving ultraviolet irradia- tion. Surprisingly, for most applications the less expensive materials give superior performance. Volatile contaminants may be baked out of the sheets by keeping them in an oven for a few days. A valve of the type used for tires, or a rigid plastic tube may be sealed to a corner to serve as the inlet. The inlet tube to the bag may be closed with a rubber stopper or serum cap, a cork or a valve according to the material being handled. Bags are available commercially. The 3’ x 3’ or 2’ x 4’ size contains over 100 liters. The major advantage of using flexible bags is that no dilution occurs as the sample is withdrawn, These bags also are very handy for sampling pur- poses since the empty bags are transportable. Bags should be tested frequently for pinhole leaks. This may be done by filling them with clean air and sealing them. If no detectable flattening occurs within 24 hours, the leakage is negligible. A simple arrangement may be used for pre- paring a known mixture in a plastic bag. The bag is alternately partly filled with clean air and then completely evacuated several times to flush it out. Then clean air is metered into it through a wet or dry test meter. The test substance is added to this stream at a tee just above the entrance to the bag. If it is a volatile liquid, it can be injected with an accurate syringe through a septum. Suf- ficient air must subsequently be passed through the tee to completely transfer the injected mate- rial. When the desired volume has been intro- duced, the bag is disconnected and plugged or capped. Its contents may be mixed by gently kneading the bag with the hands. Adsorption and reaction on the walls is no great problem for relatively high concentrations of inert materials. However, low concentrations of reactive materials such as sulfur dioxide, nitro- gen dioxide and ozone are partly lost, even after prior conditioning of the bags.**™* Larger sizes are preferable to minimize the surface-to-volume ratio. Losses of 5 or 10% frequently occur dur- ing the first hour, after which the losses are a few percent a day. Conditioning of the bags with similar mixtures is essential to reduce these losses. The similar or identical mixture is stored for at least 24 hours in the bag, and then evacuated just before use. A recent compilation by Schuette® lists the commercial sources of these plastic sheets and needed accessories. A tabulation is presented of uses described in 12 papers, listing the plastic material, the gas or vapor stored, their concentra- tions and comments. Another recent study!’ focussed upon industrial hygiene applications. Good stability in Saran bags was found for mix- tures containing benzene, dichloromethane and methyl alcohol; and for Scotchpak bags contain- ing benzene, dichloromethane and methyl isobutyl ketone. Percentage losses were greater for lower concentrations (i.e., 50 ppm). Losses greater than 20% were observed in the first 24 hours for Saran bags containing methyl isobutyl ketone vapors, and for Scotchpak bags containing methyl alcohol vapors; however, concentrations stabilized after 2 to 3 days. These results are typical of those obtained by the other investigators prev- iously cited. It is difficult to draw generalized conclusions from these reports, other than the need for cau- tion in applying plastic bags for low concentra- tions. Losses should be determined for each ma- terial in each type of bag. Even the past history of the bag must be considered. For laboratory applications properly conducted, known mixtures can be prepared very conveniently in plastic bags. Pressure Cylinders Preparation of certain gas mixtures can be done conveniently in steel cylinders.® This is very useful for mixtures such as hydrocarbons in air or carbon monoxide in air, which can be stored for years without losses. With other substances, there are losses due to factors such as polymeriza- tion, adsorption, or reaction with the walls. In some cases, as the pressure decreases in the cyl- inder, material desorbs from the walls and yields a higher final concentration in the cylinder than was initially present. Concentrations should be 125 low enough to avoid condensation of any compo- nent at the high pressure in the cylinder, even at the lowest temperature expected during its use. Care must be taken to use clean regulators, of appropriate materials, which will not adsorb or react with the contents of the cylinder. A serious safety hazard exists in preparation of compressed gas mixtures. As mentioned previously, there is a possibility of explosion of combustible substances. This may occur because of the heat of compres- sion during a too rapid filling process. Excessive heat also may cause errors in the gas composition. Certain substances with a high positive heat of formation, such as acetylene, can detonate even in the absence of oxygen. Also, explosive copper acetylid can be produced if this metal is used in the manifolds and connections. Proper equip- ment, including armor-plate shielding, and ex- perience are required for safe preparation. Be- cause these and accurate pressure gauges are not ordinarily available, it is recommended that the mixtures be purchased from the compressed gas vendors who have professional staff, experience and equipment for such work. These vendors can prepare mixtures either by using accurate pressure gauges to measure the proportions of the com- ponents or by actually weighing the cylinders as each component is added. They also can provide an analysis at a reasonable extra charge; however, these figures are not always reliable. Calculations The calculations for preparation of batch mix- tures are based upon the close adherence to the Perfect Gas Law that is usual at low partial pres- sures. Calculations for dilute gas concentrations are based upon the simple ratio of the volume of test gas to the volume of mixture, as shown in equation 2. PPM. — 10° v/V (2) Where P.P.M. arts per million by volume v — volume of test gas in mixture, liters V — volume of mixture, liters In the case of volatile liquids the calculation is based upon the ratio of moles of liquid to moles of gas mixture, equation 3. The moles of liquid are determined by dividing the weight injected by the molecular weight of the liquid. The moles of gas mixture are calculated by dividing the total volume of mixture by the molecular volume cal- culated from equation 4 for the temperature and pressure of the mixture. 10° w/M.W. PPM. -———— (3) V/V 5 760 \ (t + 734) Vis 20? (2) 298.2 4) where w — weight of volatile liquid introduced, grams M.W. — gram molecular weight of liquid V — gram molecular volume of mixture under ambient conditions, liters P — ambient pressure, Torr t — ambient temperature, °C These calculations are illustrated by the’ fol- lowing: Example 1. A volume of 5 ml of pure carbon monoxide is added to a plastic bag into which 105 liters of air are metered. What is the concentra- tion (ppm by vel.) of the carbon monoxide? Answer: PPM. = 10°x0.005/105 = 47.6 Example 2. A dish containing 12.7 g of car- bon tetrachloride is placed in a sealed cubical chamber with inside dimensions of 2.1 meters for each edge. The final temperature is 22.5° C, and the barometer reading is 755 mm. Hg. What con- centration (ppm by vol.) is achieved? Answer: M.W. of CCl, = 12.01 + 4 x 35.457 — 153.84 760\ (295.7 (722) X (2553) 24.43 ppm _ 16°X127/15384 ©1000 x (2.1)%/24.43 FLOW-DILUTION SYSTEMS Introduction Flow-dilution systems offer the advantage of being very compact. Since it is possible to operate them continuously, there is no theoretical limit to the volumes of gas mixture that can be provided. In a properly designed system, concentrations can be changed very rapidly. Because of the relatively small gas volume of this system, the explosive hazard is less than that of batch systems. Any losses by adsorption on surfaces occur only in the initial minutes of operation. After a brief period, the surfaces are fully saturated and no further losses occur. Because of these advantages, flow- dilution systems are popular for accurate work with most substances. Gas-Metering Devices A variety of devices can be used to monitor the flows in a flow-dilution system. The accuracy of final concentration is, of course, dependent upon the accuracy of the measurements of the component flows. Rotometers are commonly used. Orifice meters and critical orifices are also fre- quently employed. The calibration equations and techniques are given in detail in Chapter 11. Be- cause rotometers are very commonly used, a few points of importance to this application will be discussed. The pulsating flows provided by the diaphragm pumps utilized in many systems may result in serious errors in most meter readings. Rotometer readings may be high by a flow factor of as much as 2, depending upon the wave form of the pul- sating flow. It is therefore essential for accurate measurements to damp out such pulsations by assembling a train comprised of the pump, a surge chamber and a resistance, such as a partially closed valve. The error can be determined by running the pulsating flow through the rotometer and into a wet-test meter, and comparing the two measurements. The latter should be taken as cor- rect. The reason for this error is that although the flowrate passing through the rotometer is pro- V —=2447x 126 portional to the first power of the gas velocity, the lifting force on the ball is proportional to the velocity raised to a power of between 1 and 2. For completely turbulent flows, which are common, the exponent is 2; in this case if the velocity fluc- tuates in a sine wave the ball position will corre- spond to the root mean square value, which is 1.414 times the correct mean value. If the wave form is spiked, even greater deviations occur. There are two types of corrections of flow meter calibrations for ambient pressure and tem- perature. The first is the correction to the actual flow because of the fact that the measured value is dependent upon the density and in some cases the viscosity of the gas flow, both of which are affected by ambient pressure and temperature. Application of the appropriate correction factor to the value from a calibration graph made under standard pressure and temperature conditions then will give the correct actual gas flowrate under ambient conditions. A second correction may be applied to convert the actual gas flowrate to that under standard conditions. This latter correction is made on the basis of the perfect gas equation. It should be kept clearly in mind that the first calibration correction is dependent upon the spe- cific device being employed. The two bases, am- bient or standard conditions, should not be con- fused, and the proper one must be employed for the application. Construction and Performance of Mixing Systems A flow-dilution system is comprised of a met- ered test substance source, a metered clean-air source and a mixer to dilute the test substance to the low concentration required. The total flow of mixture must be equal to or greater than the flow needed. It is highly desirable to use only glass or Teflon parts for constructing the system. Some studies have been made with metal and plastic tubing which have shown that these must be con- ditioned with the dilute mixtures for periods of hours or days before they cease absorbing the test substances. * 11 Two other factors must be kept in mind in the construction of a mixing system. The pressure drops must be very small and the system should preferably be operated at very close to atmos- pheric pressure. Otherwise, any changes in one part of the system will require troublesome read- justment of the flows of other components. The interactions may require several time-consuming reiterative adjustments. The second factor to con- sider is that the dead volume of the system must be minimized to achieve a rapid response time. For example, assume that we are metering a flow of 0.1 ml/min. into a diluent air stream, and that the dead volume of the system to the dilution point is 1 ml. To accomplish one volume change will require 10 minutes. In order to be certain that this dead volume is completely flushed out, five volume changes are needed, corresponding to a time lag of 50 minutes before the full concentra- tion of test gas reaches the dilution point. Figure 12-3 illustrates a convenient all-glass system for making gas dilutions. The test gas is connected at the extreme right through a ball joint Anal. Chem. 33:1100, 1961. Figure 12-3. All Glass System and capillary tube. The dilution air is metered into the side arm. A trap-like mixing device in- sures complete mixing with very little pressure drop. The desired flow can be taken from the side arm, and the excess vented through the waste tube which may be connected to a Tygon tube long enough to prevent entrance of air into the flow system. If desired, this vent tube can be run to a hood or adjacent window. By clamping down on the vent tube any desired pressure can be ob- tained in the delivery system. The dilution air must be purified according to the needs of the work. Air can be passed over a bed of carbon, silica gel, or ascarite, or bubbled through a scrubbing mixture of chromic acid in concentrated sulfuric acid if necessary. Another convenient method of purification is to pass the air flow through a universal gas mask canister. The purification system must be designed accord- ing to the specific needs of the work. SOURCE DEVICES FOR GASES AND VAPORS Introduction A variety of source devices are described be- low for providing high concentrations of gases and vapors which can be diluted with pure air to the level desired. Each possesses specific advantages and disadvantages. Selection of a device depends upon the needs of application and the equipment available to the user. Figure 12-4 shows a self- dilution device that can be generally applied to reduce the concentration provided by the source when necessary for work at very low concentra- tions. The flow of gas or vapor passes through two branches in proportions determined by re- stricters R, and R,. An appropriate absorbent such as carbon, soda lime, etc. in the latter branch completely removes the gas or vapor from the stream. Thus the combined output of the two 127 branches provides the same flow at a fractional concentration of the input depending upon the relative values of the two flow restricters. Fur- thermore, rotation of the three-way stopcock also provides either the full concentration or zero con- centration, or completely cuts off the flow. J. Air Pollution Control Assoc. 19:164, 1969. Figure 12-4. Self-Dilution Device Vapor Pressure Method Figure 12-5 illustrates the vapor pressure method for providing a known concentration of a volatile liquid. A flow of inert gas or purified air is bubbled through a container of the pure liquid. Liquid mixtures are less desirable because the more volatile components evaporate first and the vapor concentrations change as the evaporation proceeds. In the common bubbler only 50 to 90% of the saturation vapor pressure is usually ob- tained. Equilibrium concentrations therefore are obtained by operating the bubbler at ambient or elevated temperature and passing the vapor mix- ture through an accurately controlled constant temperature bath which cools it down. The excess vapor is condensed, and the final concentration is very close to equilibrium vapor pressure at the cooling bath temperature. A filter must be in- cluded to insure that a liquid fog or mist does not escape. It is desirable to operate the constant temperature bath below ambient temperature so that liquid does not condense in the cool portions of system downstream. The application of this method to carbon tetrachloride has been described recently.’? Another version of this arrangement is shown in Figure 12-6. This utilizes a wick feed from a small bottle containing the additive as a source of =e i FILTER INERT GAS ROOM (OR ELEVATED) TEMP. SATURATOR TEMPERATURE CONSTANT BATH Amer. Ind. Hyg. Assoc. J. 22:392, 1966. Figure 12-5. the vapor, and an ice bath for the constant tem- perature. Motor Driven Syringes Figure 12-7 illustrates a system using a 50 or 100-ml glass hypodermic syringe which is driven P, Og Wick Additive J. Air Pollution Control Assoc. 19:164, 1969. Figure 12-6. Vapor Saturator Vapor Saturator by a motor drive at uniform rates that can be con- trolled to empty it in periods varying from a few minutes to an hour. A gas cylinder containing the pure component or mixture is connected at the right side. The bubbler is a safety device to pro- tect the glass apparatus from excessive pressures if the tank needle valve is opened too wide. The tank valve is cautiously opened and a slow stream of gas vented from the bubbler. The syringe is manually filled and emptied several times to flush it with the gas. This is done by turning the three- way stopcock so that on the intake stroke the syringe is connected to the cylinder and on the discharge stroke to the delivery end. After flush- ing, the syringe is filled from the cylinder and the motor drive is set to discharge it over the desired period of time. This motor drive should include a limit switch to shut off the motor before it breaks the syringe, and a revolution counter for measur- ing the displacement. From the known gear ratio, the screw pitch and a measurement of the plunger diameter with a micrometer, the rate of feed can be calculated with an accuracy and reproducibility of parts per thousand. At low delivery rates the back diffusion of air into the syringe from the delivery tip may cause an error. Thus, if the syringe is set to empty over a one-hour period, towards the end as much as half of the gas mixture contents could be air that has diffused in backwards. This error is easily minimized by inserting a loose glass wool plug in the delivery system and using capillary tubing for the delivered flow. Diffusion Systems Figure 12-8 illustrates a diffusion system that can provide constant concentrations of a volatile liquid. The liquid is contained in the bottom of a long thin tube and is kept at a constant known temperature. As the air flow is passed over the top, vapor diffuses up through the length of the 128 or His ry 41 C d J JF = I — — 11= <4 + — 3 41— p p= -1F TE = Fl — 41-4 4155 4 3 -— wf Be h - & A dR] Anal. Chem. 33:1100, 1961. Figure 12-7. Motor Driven Syringe tube at a reproducible rate and mixes with the stream. The rate is determined by the vapor pres- sure of the liquid, the dimensions of the tube and the diffusion constants of the vapor and of air. If substantial amounts of a liquid are evaporated and the liquid level drops, the diffusion path length increases slightly. The quantity of liquid evapo- rated can be determined from volume markings on the tube or by weighing the tube at the begin- ning and end of the period of use. Experimental values have been tabulated and the limitations of this method described.(*®) Porous Plugs Figure 12-9 illustrates a micrometering sys- tem''* that both measures and controls small flows of gas in the range of 0.02 to 10 ml/min, 129 7 | i Figure 12-8. Diffusion System This is based on the principle of diffusion of test gas through an asbestos plug under a controlled pressure difference. The input is connected to a asbestos output _Jdo pressure > tap on diluted flow system Figure 12-9. Micrometering System cylinder containing pure gas or gas mixture. The asbestos plug is contained in one leg of the “T” bore of a 3-way stopcock as shown in the figure. The asbestos fiber is acid-washed, of the type used in the laboratory for Gooch crucibles. The degree of tamping is determined by trial and error to pro- vide the desired flow range. The cylinder needle valve is opened cautiously to provide a few bub- bles per minute from the waste outlet in the lower portion of the figure. The height of water or oil above the waste outlet determines the fixed pres- sure on the lower face of the asbestos plug, which produces a fixed rate of diffusion of the gas through the plug to the capillary delivery tip. The meter is calibrated by connecting the delivery end to a graduated 1-ml pipette with the tip cut off, containing a drop of water. The motion of the drop past the markings is timed with a stop watch. This is repeated for different heights of liquid obtained by adjustment of the levelling bulb. The calibration plot of flowrates in ml/min. against the heights of liquid over the waste outlet in cm. is usually a straight line passing through the origin. The gas cylinder should never be disconnected until the liquid pressures equalize; otherwise the liquid may surge up and wet the asbestos plug. If this occurs, it must be discarded, the bore dried and repacked and the new plug calibrated. This device is a very convenient and precise method for metering low flows in the indicated range. The output flow remains constant for weeks, but should be checked occasionally. The delivery tip is connected to the mixer shown in Figure 12-3. For low delivery rates, the dead volume is minimized by using capillary tubing. The levelling bulb vent is connected to a tap on the diluted gas manifold. This provides a cor- rection for back pressure of the system into which the flow is being delivered. An appreciable back pressure changes the pressure differential across the asbestos plug. The bulb vent connection causes the liquid level to rise in the vent tube. If the vent area is small compared to the area of the liquid surface in the bulb, this compensates al- most exactly for the back pressure by increasing the upstream pressure on the plug enough to main- tain a constant pressure differential. Permeation Tubes Permeation tubes are very useful sources for liquifiable gases. Because of their potential pre- cision, recent collaborative tests of methods have employed them when applicable. The National Bureau of Standards now certifies the sulfur diox- ide type. Because of their importance as pri- mary standards, they are described below in some detail. In these devices the liquid is sealed ufider pres- sure in inert Teflon tubes. The vapor pressure may be as high as 10 atmospheres. The gas per- meates out through the walls of the tube at a constant rate of a few milligrams per day for 130 periods as long as a year. Figure 12-10 illustrates three types of seals: steel or glass balls, a Teflon plug bound with wire and a Teflon plug held by a crimped metal band. Figure 12-11 shows some other types of seals and construction. In order to International Symposium on Identification and Measure- ment of Environmental Pollutants, c/o National Re- search Council of Canada, Ottawa, Ontario, Canada, 1971. Figure 12-10. Three Types of Seals: (1) Steel on Glass Balls, (2) a Teflon Plug Bound with Wire, and (3) a Teflon Plug Held by a Crimped Metal Band extend the lifetime of some tubes, a glass or stain- less steel bottle containing the liquified gas may be attached to the Teflon tubing, as shown in Figure 12-11A or B. At low pressure, such as in permeation tubes containing nitrogen dioxide (b.p. 21.3°C), a sufficiently tight seal may be obtained by pushing the Teflon tube onto the neck of the glass bottle and by pushing a glass plug in at the top. For higher pressures, such as in tubes con- taining propane (vapor pressures 10 atm. at 25°C), a stainless steel bottle is used, as shown in Figure 12-11B. The seals are made by crimp- ing Ya’ Swagelok ferrules on the ends of the Teflon tube. Another type of seal is illustrated in Figure 12-11C in which a FEP Teflon plug is fused to a FEP Teflon tube by means of heat. All tubes, especially if the contents are under pressure, should be handled with caution. If they have been chilled in dry ice during filling, room for expansion of the liquid upon warming to ordi- nary temperatures should be provided. Tubes should be protected from excessive heat. They should not be scratched, bent, or mechanically —_— 20 _L a —/ Env. Sci. Tech. 5:1121, 1971. Figure 12-11. A & B. A Glass or Stainless Steel Bottle Attached to Teflon Tubing Figure 12-11C. An FEP Teflon Plug Fused to an FEP Teflon Tube abused. After a new tube has been prepared, sev- eral days or weeks are required before a steady permeation rate is achieved at a thermostated temperature. Saltzman, Burg, et al.” reported that tubes made of FEP Teflon should be annealed at 30°C for a period in order to equilibrate the Teflon and achieve a steady rate. Otherwise, a pseudo-stable rate is achieved which is not repro- duced after appreciable temperature fluctuations. Gravimetric calibrations may be made by weighing the permeation tubes at intervals and plotting the weight against time. The slope of the line fitted by the method of least squares to the measured points is the desired rate. This process may take as long as several weeks with an ordinary balance because of the necessity of waiting to obtain measurable weight differences. However, if a good micro balance is available, the calibra- tion can be shortened to a day. Static charges which develop on some permeation tubes can cause serious weighing errors unless discharged with a polonium strip static eliminator. For a cor- rosive gas, the balance may be protected from corrosion by inserting the permeation tubes into glass-stoppered weighing tubes. The weight his- tory of a nitrogen dioxide tube over a 37 week period is shown in Figure 12-12. The tubes are used by passing a metered air flow over them in a vessel thermostated to == 0.1°C, as illustrated in ; FE > ill 131 Figure 12-13. Close temperature control is essen- tial because the temperature coefficient is high. A relatively inexpensive apparatus may be used for volumetric calibration purposes!®!’ which makes possible a calibration in less than an hour. A Gilmont Warburg compensated syringe manometer measures the evolved gas from a per- meation tube with a sensitivity of 0.2 microliter. Exposures of some types of permeation tubes must be very carefully controlled. Thus, nitrogen dioxide tubes exposed to high humidity develop blisters and long term changes in permeation rates; even the moisture content of the flowing gas passing over the tube affects the rate. These effects are likely due to the formation of nitric acid within the Teflon walls and/or inside the tube in the liquid nitrogen dioxide. A similar problem occurs with hydrogen sulfide tubes, which precipitate colloidal sulfur within the walls of the tube when exposed to oxygen. It is therefore de- sirable never to remove such tubes from their operating environments. Figure 12-14 illustrates a system which accomplishes this. A slow stream (50 ml/min.) of dry nitrogen from a cylinder is passed over the tube to flush away the permeated gases. This stream can be blended with a metered pure air flow in a flow dilution system to produce known concentrations of the gas. When calibra- tion is desired, the gas flow from the nitrogen cylinder is temporarily shut down and a volu- metric calibration performed within an hour or so. High precision has been obtained in this manner. The quantitative relationships for permeation through a tube of unit length are given'® by equation 5: G —=730P x M.W. x p,/log(d,/d,) (5) where G = mass permeation rate, pg/min. per cm of tube length P — permeation constant for the gas through the plastic, in cc (STP) cm/cm®sec(cm Hg) M.W. — molecular weight of gas d, — outside diameter of tube d, = inside diameter of tube p, = gas pressure inside tube, mm Hg log = logarithm to base 10 The permeation rates have high temperature coefficients. Equation 6 shows the usual relation- ship in the form of the Arrhenius equation. 10e{S2) =e {1 —J 8 G) ~2303 x(t; T, (6) where G,, G, = gravimetric rates at different temperatures T,, T, = corresponding temperatures, °K (= °C+273.16) E — activation energy of permeation process, cal/g mol R — gas constant, 1.9885 cal/g mol °K Table 12-2 lists permeation rates for various tubes, some of which are commercially available, together with some data for activation energies. GRAMS WEIGHT, 100 AGE, THOUSAND MINUTES 200 300 400 [ I I T I I Env. Sci. Tech. 5:1121, 1971. Figure 12-12. Weight History of a Nitrogen Dioxide Tube over a 37-Week Period AGE, WEEKS LOW PRESSURE- DROP INLET FILTER REMOVABLE, INERT-LINED INERT CONNECTING CAPS,FOR EASY ACCESS. TUBING 7 HEAT EXCHANGER SIDE FILLED WITH GLASS BEADS. (for high volume flow use a coil of copper tubing upstream) THERMOMETER / (short as possible) " \ ANALYZER N £ INLET Fri CONSTANT TEMPERATURE WATER BATH x "DYNACAL" PERMEATION \ TUBE ON DOWNSTREAM POROUS SIDE. GLASS PLATE Figure 12-13. Passage of a Metered Air Flow over Tubes 132 1©glololo lol b (© O ,0 Env. Sci. Tech. 5:1121, 1971. Figure 12-14. A System Never Requiring Removal of Tubes From Their Operating Environ- ment Table 12-2 PERMEATION RATES FOR SOME TEFLON PERMEATION TUBES' Rates are in ug/min. cm Activation Energies, E, are in Kcal/g. mol Dynacel Tubes” A.I.D. Tubes? FEP Teflon® TFE Teflon® Substance Rate E Rate Rate E Rate E SO, 0.422 13.8 0.279 NO, 1.714 14.7 1.230 2.09 14.6 HF 0.185 H,S 0.457 16.0 0.229 Cl, 2.418 14.0 1.430 NH, 0.280 0.165 CH,SH 0.036 10.0 0.030 Propane 0.080 15.0 0.035 0.132 16.2 1.86 13.0 Propene 0.240 5.13 15.4 n Butane 0.012 0.024 15.8 0.258 12.7 Butene-1 0.0316 14.8 0.368 12.4 @ Available from Metronics Associates, Inc., Palo Alto, Calif. 94304. Tubes are 3/16” O.D., 18” 1.D. Rates are at 30°C. ® Available from Analytical Instrument Development, Inc., West Chester, Pa. 19380. Tubes are FEP Teflon, 0.250” O.D. and 0.062” wall thickness except for methyl mercaptan, which is 0.030” wall thickness. Rates are at 30°C. ©0.250” O.D. and 0.030” wall thickness, as reported by Saltzman et al.'” Rates are at 25°C. 133 rhs; Anal. Chem. 33, 1100, 1961. Figure 12-15. Electrolytic Generator Miscellaneous Generation Systems Figure 12-15 illustrates an electrolytic gen- erator that was developed' as a suitable source of arsine and stibine. The solution is electrolyzed by passing a DC current through the platinum wire electrodes (0.41 mm diameter x 3 cm long) shown in the figure. The lower electrode is the cathode at which hydrogen and small quantities of arsine or stibine are liberated. The stream of purified air bubbles through the fritted tube end near the cathode and flushes the gas mixture into the outlet. At low current densities there was an appreciable time lag before arsine or stibine ap- peared. The generation rate of arsine or stibine was not proportional to the current but was accel- erated at higher currents. To achieve high cur- rent densities wire electrodes rather than plates were used. Another system used successfully was an aerated chemical solution mixture.! Thus, a 30% w/v solution of potassium cyanide served as a source of hydrogen cyanide. A relatively constant concentration could be obtained for as long as 10 hours. The strength and pH of the solution affected the concentration of hydrogen cyanide 134 produced. The air bubbled through the solution should be free from carbon dioxide, since carbonic acid can displace hydrogen cyanide. Because the dissolved salt tended to crystallize at the air inlet and plug it, the aeration was stopped every hour for a few moments to allow the solution to re-enter the inlet and redissolve the accumulated salt. In another application, hydrogen chloride was ob- tained by aeration of a 1 : 1 concentrated hydro- chloric acid-water mixture. Bromine was ob- tained by aerating saturated bromine water in contact with a small amount of liquid bromine. In all of these procedures it is, of course, desirable to thermostat the bubbler to provide constant concentrations. An interesting technique for preparing highly reactive or unstable mixtures is to utilize chemical conversion reactions. A stable mixture of a suit- able compound is passed over a solid catalyst or reactant to produce the desired substance in the air stream. A table of reactions presented by Hersch? indicated some of these possibilities. Others may be determined from the literature. Multistep conversions also may be utilized. SOURCE DEVICES FOR AEROSOLS Introduction Preparation of aerosol mixtures is much more complex and difficult than that of gas and vapor mixtures. A major consideration is the size dis- tribution of the particles. Commonly a log normal distribution describes the values; this is character- ized by a geometric mean and a standard geo- metric deviation. The usual aerosol source device supplies a range of sizes. However, certain spe- cial types supply uniform-sized particles. If the standard geometric deviation is less than 1.1, the particles are considered homogeneous, or mono- disperse. There is also a great variety of particu- lar shapes, including spherical, crystalline, irregu- lar, plate-like, spiked, and rod-shaped or fibrous. If the material is a mixture of compounds, the composition may vary with size. Certain sub- stances may be present on the surfaces, which also can be electrostatically charged. All of these prop- erties are affected by the source devices and the methods of treatment. In the generation of known concentrations of aerosols, the choices of the operating parameters are determined by the ob- jectives of the study, which may be to duplicate and study a complex aerosol existing naturally or in industry, or to prepare a simple pure aerosol for theoretical examination. A good general treat- ment of this subject with 257 references was pub- lished by Raabe.'® Dry Dust Feeders A comprehensive description of methods of producing solid aerosols was given by Silverman and Billings.'* One of the most convenient and widely used methods is to redisperse a dry powder. Standard test dusts are available, such as road dust, fly ash, silicates, silica, mineral dust and many pigment powders and chemicals. Because these may tend to agglomerate, the degree of pack- ing of the powder must be controlled and repro- ducible. A simple method consists of shaking the powder on a screen into the air stream. Mechan- ical systems attempt to provide a constant feed rate by use of moving belts or troughs, or by rotating turn tables, screws or gears. Because of the erratic behavior of loosely packed dust, the popular Wright dust feed mechanism achieves closer control by compressing the dust in a tube into a uniform cake. A rotating scraper advanced by a screw slices off a thin layer of the cake continuously. In all of these devices the dust is dispersed by an air jet, which also serves to break up some aggregates. The dusty cloud is passed into a relatively large chamber, which serves to smooth out any rapid fluctuations. Concentra- tions may fluctuate + 20% over a period of a half hour, due to variations in the packing of the dust or laminations in the cake. Settling cham- bers, baffles, or cyclones may be added to the system to remove coarse particles, and ion sources to remove electrostatic charges. Nebulizers The compressed air nebulizer, Figure 12-16, is a convenient and useful device to produce aero- sols from liquids. The liquid stream is drawn through a capillary tube and shattered into fine droplets by the air jet. The DéVilbiss nebulizer wing Wily Vln COMPRESSED AIR IN Amer. Ind. Hyg. Assoc. J. 29.66, 1968. Figure 12-16. Compressed Air Nebulizer (Ou DIAM.) 135 } AEROSOL UNIFORM DROPLETS ORIFICE =-—LIQUID FEED LIQUID] (30 psig) ——COUPLING ROD $=—1—PIEZOELECTRIC 3 CRYSTAL tL _100-kHz. SIGNAL Inhalation Carcinogenesis, April 1970 (CONF0691001, AEC Symposium Series 18). Figure 12-17. Ultrasonic Droplet Generator is simple, but holds only about 10 ml of liquid. Modifications can be added,’ such as utilizing a recirculating reservoir system for the liquid (Lauterbach), providing baffles to intercept and return coarse droplets (Dautrebande), droplet shattering baffles (Lovelace) and nozzle controls. The characteristics of these devices have been described in detail.*° Rather coarse sprays are obtained by pumping the liquid mechanically through tangential nozzles, as is done in fuel oil burners. The air flow merely carries off the droplets. Somewhat different is the ultrasonic droplet generator, Figure 12-17, which utilizes an intense acoustic field to produce fine droplets. In the version illustrated the pres- surized liquid is ejected from the orifice as a fine stream, which is disrupted by the vibrations of the coupling rod into remarkably uniform-sized drop- lets (coefficient of variation < 1%). Commercial aerosol cans utilize a mixture of liquid to be atomized and a volatile propellant (usually a Freon compound such as dichlorodi- fluoromethane). The rapid evaporation of the propellant from the liquid emerging from the noz- zle orifice shatters the stream into droplets hav- ing a broad size range. Electrostatic dispersion also has been utilized to break up a liquid stream by electrically charging the orifice. The droplets should be discharged by passage near an ion source soon afterwards, These liquid sources can be readily applied to supply solid aerosols by dispersing a solution or colloidal suspension. The solvent evaporates from the droplets naturally or upon warming, leaving a smaller particle of crystalline solute, or a clump of one or more colloidal particles according to their theoretical probabilities of occurrence in the volume of the droplet. The nature of the materials and of the drying process often affects the nature of the particles, which may exhibit shells or crusts. Passing the particles through a high temperature zone may be employed to chemically decompose them (e.g., production of metal oxides from their salts) or to fuse them into spherical particles. Vaporization and Condensation of Liquids The principle of vaporization and condensa- tion was utilized in the Sinclair-LaMer generator for materials such as oleic acid, stearic acid, lub- ricating oils, menthol, dibutyl phthalate, dioctyl phthalate and tri-o-cresyl phosphate, as well as for sublimable solids. The system is illustrated in Figure 12-18 (from Fuchs and Sutugin — see AEROSOL g OUTLET AR — SF TF—7= ~~ — Davies CN (ed): Aerosol Science. New York, Academic Press, 1966. Figure 12-18. Sinclair LaMer Generator ~ AIR Preferred Reading). Filtered air or nitrogen is bubbled through the hot liquid in the flask on the left. Another portion of the entering air is passed over a heated filament coated with sodium chlor- ide, to provide fine condensation nuclei. The vapor passes into the empty superheater flask on the right, in which any droplets are evaporated, and then up the chimney in which it is slowly cooled. The supersaturated vapor condenses on the sodium chloride particles to produce a mono- disperse aerosol. Although the condensation nu- clei vary in size they have only a slight effect on 136 the final aerosol droplet size, which is much larger. This system has been widely utilized as a con- venient monodisperse source in the 0.02 to 30 micron size range. Spinning Disc Aerosol Generators A very useful generator for monodisperse aerosols is based upon feeding the liquid con- tinuously onto the center of a rapidly spinning disc (60,000 rpm). When the droplet on the edge of the disc grows to a sufficient size, the centri- fugal force exceeds that of surface tension and the droplet is thrown off. A commercial system, illustrated in Figure 12-19, produces liquid drop- lets in the 1 to 10 micron size range. Smaller satellite drops are diverted down by an air stream into a compartment around the disc. The larger particles escape to the outer compartment, and are passed around a sealed radioactive ion source to remove the electrostatic charges, then to the outlet. Solid particles also can be generated from solutions and suspensions. The sizes are con- trolled by varying the concentrations. Miscellaneous Generation Systems Many dusts can be produced by means dup- licating their natural formation. Thus, hammer or impact mills, ball mills, scraping, brushing and grinding of materials have been employed. Com- bustion (e.g., tobacco smoke), high voltage arcing, and gas welding or flame cutting torches can be used. Organic metallic compounds (e.g., lead tetracthyl) may be burned in a gas flame. Metal powders can be fed into a flame, or burned spon- taneously (thermit and magnesium). Molten metals may be sprayed from metallizing guns. Metal wires can be vaporized by electrical dis- charges from a bank of condensers. A fluidized bed may be utilized as a reproducible source of particulate material. Gaseous reactions also may be employed to produce aerosols, such as reaction of sulfur trioxide with water vapor, or of am- monia and hydrogen chloride. Finally, photo- chemical reactions can be utilized. The natural process for producing oxidative smog has thus been duplicated by irradiating automobile exhaust. References I. SALTZMAN, B. E.: Preparation and Analysis of Calibrated Low Concentrations of Sixteen Toxic Gases. Anal. Chem. 33:1100 (1961). COTABISH, H. N., P. W. McCONNAUGHEY, and H. C. MESSER: Making Known Concentrations for Instrument Calibration. Amer. Ind. Hyg. Assoc. J., 22:392 (1961). HERSCH, P. A.: Controlled Addition of Experi- mental Pollutants to Air. J. Air Pollution Control Assoc., 19:164 (1969). BAKER, R. A., and R. C. DOERR: Methods of Sampling and Storage of Air Containing Vapors and Gases. Int. J. Air Poll., 2:142 (1959). WILSON, K. W. and H. BUCHBERG: Evaluation of Materials for Controlled Air Reaction Chambers. Ind. Eng. Chem. 50:1705 (1958). CLEMONS, C. A., and A. P. ALTSHULLER: Plas- tic Containers for Sampling and Storage of Atmos- pheric Hydrocarbons Prior to Gas Chromatographic Analysis. J. Air Pollution Contral Assoc. 14:407 (1964). ALTSHULLER, A. P.,, A. F. WARTBURG, 1. R. COHEN, and S. F. SLEVA: Storage of Vapors and LIQUID SUPPLY TURBULENCE MIXING CHAMBER — DAMPING Fem —————— - FLOW LIQUID FEED SCREEN FILTER | HEATER | METER SPINNING DISK MOTOR SATELLITE ‘REMOVAL HEAD PRIMARY DROPLETS SATELLITE DROPLETS MAIN AIR BLOWER SATELLITE AIR BLOWER PARTICLE CHARGE NEUTRALIZER |—= TEST AEROSOL OUTLET Environmental Research Corp.: 1970-1971 Catalog, Instrument Div. St. Paul, Minnesota. Figure 12-19 Spinning Disc Aerosol Generator 10. 11. 12. 13. 14. 15. 16. Gases in Plastit Bags. Int. J. Air Wat. Poll. 6:75 (1962). CONNER, W. D,, and J. S. NADER: Air Sampling with Plastic Bags. Amer. Ind. Hyg. Assoc. J. 25:291 (1964). SCHUETTE, F. J.: Plastic Bags for Collection of Gas Samples. Atmospheric Environment 1:515 (1967). SMITH, B. S,, and J. O. PIERCE: The Use of Plas- tic Bags for Industrial Air Sampling. Amer. Ind. Hyg. Assoc. J. 31:343 (1970). ALTSHULLER, A. P., and A. F. WARTBURG: Interaction of Ozone with Plastic and Metallic Ma- terials in a Dynamic Flow System. Int. J. Air and Water Poll. 4:70 (1961). ASH, R. M,, and J. R. LYNCH: The Evaluation of Gas Detector Tube Systems: Carbon Tetrachloride. Amer. Ind. Hyg. Assoc. J. 32:552 (1971). ALTSHULLER, A. P., and I. R. COHEN: Applica- .tion of Diffusion Cells to the Production of Known Concentrations of Gaseous Hydrocarbons. Anal. Chem. 32:802 (1960). AVERA, C. B.,, JR.: Simple Flow Regulator for Extremely Low Gas Flows. Rev. Scientific Instru- ments 32:985 (1961). O’KEEFE, A. E., and G. C. ORTMAN: Primary Standards for Trace Gas Analysis. Anal. Chem. 38:760 (1966). SALTZMAN, B. E.: “Permeation Tubes as Primary Gaseous Standards.” International Symposium on Identification and Measurement of Environmental Pollutants, Ottawa, Ontario, Canada, June 14, 1971. 137 17. 18. 19. 20. SALTZMAN, B. E., W. R. BURG, and G. RAMAS- WAMI: Performance of Permeation Tubes as Stand- ard Gas Sources. Env. Sci. Tech. 5:1121 (1971). RAABE, O. G.: Generation and Characterization of Aerosols, p. 123, Conference on Inhalation Car- cinogenesis, Oak Ridge National Laboratory, Gat- linburg, Tenn., Oct. 8-11, 1969. (CONF-691001). SILVERMAN, LESLIE, and C. E. BILLINGS: Methods of Generating Solid Aerosols. J. Air Pol- lution Control Assoc. 6:76 (1956). . MERCER, T. T., M. I. TILLERY, and H. Y. CHOW: Operating Characteristics of Some Com- pressed Air Nebulizers. Amer. Ind. Hyg. Assoc. J. 29:66 (1968). Preferred Reading FUCHS, N. A, and A. G. SUTUGIN: Generation and Use of Monodisperse Aerosols. Chapter 1 in Aero- sol Science, Edited by C. N. Davies, Academic Press, New York, N. Y., 1966. GREEN, H. L., and W. R. LANE: Chapter 2 in Par- ticulate Clouds: Dusts, Smoke and Mists. E. & F. N. Spon., Ltd.,, London, 1964, NELSON, G. O.: Controlled Test Atmospheres, Ann Ar- bor Science Publishers, Inc., Ann Arbor, Mich. 1971. SILVERMAN, LESLIE: Experimental Test Methods. pp. 12-1 to 12-14, Air Pollution Handbook, Edited by Magill, P. L, F. R. Holden, C. Ackley, F. G. Sawyer, McGraw-Hill Book Co., New York, N. Y., 1956. CHAPTER 13 SAMPLING AIR FOR PARTICULATES S. A. Roach, Ph.D. INTRODUCTION The particulates of significance to industrial hygienists include all particles, solid or liquid, which are suspended in air and may be inhaled. The particles may be of all sizes from molecular dimensions up to about 100 microns in diameter. The three main types of particulates are dust, mist and fume. Primary Airborne Dust Primary airborne dust consists of solid par- ticles rendered airborne during the crushing, grind- ing or attrition of hard, rock-like materials. Dust particles generally have irregular shapes. Secondary Airborne Dust Secondary airborne dust is produced by disper- sion into the air of fine powder from a bulk source or from previously settled primary airborne dust. Airborne particles, on close examination, are often found to consist of clumps or aggregates of smaller particles adhering together. Mist A mist is formed from a material which is liquid at room temperature. Mist particles are the airborne droplets rendered airborne by bubbling, boiling, spraying, splashing or otherwise agitating a liquid and also by condensation from air super- saturated with the vapor of the substance. Mist particles are generally spherical in shape. Primary Fume A fume is formed from a material which is solid at room temperature. Fume, like certain mist formations, is produced by condensation from air super-saturated with the vapor of the material. More commonly, fume is the airborne solid par- ticulate formed in the air above molten metal, by vaporization of the metal, oxidation of the vapor and condensation of the oxide. Fume particles generally have irregular shapes. Secondary Fume Secondary airborne fume is produced by dis- persion into the air of fume from a bulk source or by redispersion of settled primary fume. The air- borne particles of secondary fume are almost al- ways much coarser than those of the primary type, consisting of clumps of innumerable, very fine par- ticles. Sampling is performed by drawing a measured volume of air through a filter, impingement de- vice, electrostatic or thermal precipitator, cyclone or other instrument for collecting particulates. The concentration of particulate in air is denoted by the weight or number of particles collected per unit volume of the air sample. The weight of col- lected material is determined by direct weighing or by chemical analysis, as appropriate. 139 The number of particles collected is deter- mined by counting the particles in a known por- tion of the sample. This is accomplished using a microscope with a travelling stage and eyepiece graticule or with an automatic particle counter. The size of the particles is determined by separat- ing them according to size during sampling or by separating out the different sizes of collected par- ticulate in the laboratory, using a microscope (Walton, 1954)" or liquid settling (Drinker and Hatch, 1954).2 When a particle is released from rest and falls in air, it is subject to the downward force of gravity and the opposing aerodynamic drag of the atmos- phere. Balance between these forces is readily attained and the particle falls with a steady ve- locity known as its terminal velocity. Over a wide range of sizes, from approximately 1 to 50 mi- crons, the terminal velocity is proportional to the specific gravity of the particle, p, and the square of its diameter, d. When the diameter is expressed in microns, the terminal velocity of a spherical particle falling freely in air is approximately 0.003 pd? cm/sec or 0.006 pd* ft/min. The terminal velocity of particles is dependent on the aerody- namic properties which also determine the pro- portion of inhaled particulate that deposits in the respiratory tract and the site of deposition (Lipp- mann, 1970).3 The preferred ‘diameter’ or size of a particle is its ‘equivalent’, or ‘aerodynamic’ diameter. This is equal to the diameter of spherical particles of unit density which have the same falling velocity in air as the particle in question. For some types of particles with extreme shape, other parameters are sometimes used. Thus, asbestos fibers, which are very long in relation to their diameter, are characterized by their length. Amongst particles which are inhaled, those with an equivalent diameter greater than 20 mi- crons are deposited by impingement in the nose and upper respiratory tract. Smaller ones down to 0.5 micron in diameter are carried into the smaller airways and alveoli, and are deposited there under gravity. Those between 0.1 and 0.5 micron in diameter are also inhaled, but are mostly exhaled with the air since their terminal velocity is so low that there is not sufficient time for them to be deposited in the time the air is in the respiratory tract. The very smallest, those whose diameter is less than 0.1 micron, have such a small volume and mass that they have significant Brownian motion from the irregular impact of gas molecules, and are deposited readily. However, their weight is so small that particles smaller than 0.1 micron dia- meter seldom make up a hygienically significant proportion of the jinhaled particulate. The above diameters refer to the size of the separate airborne entities, each of which may consist of several par- ticles clumped together. It is the aerodynamic properties of these clumps rather than those of the individual particles which determine where they will be deposited. THE PURPOSE OF SAMPLING The main reason for sampling for atmospheric particulates is to estimate the concentration in the air which is inhaled by the employees. A deter- mination may be made of the concentration of all the particles or just those which have particular sizes or shapes. This is done in order to assess whether there is a risk to the health of workers exposed to the environment. This judgment is made by comparing the results against hygiene standards. The results obtained by atmospheric sampling depend very much on the time and place where the samples are taken and the type of instrument used. Those concerned with setting hygiene stan- dards usually take account of the wide variation in the results that may be obtained, and take great care that there shall be no misinterpretation of the values inserted in the standards. Variations in Time Dust concentrations can vary around the aver- age value from zero up to 2'2 times the average, even in conditions where the work appears to be done at a steady rate. The appropriate hygicne standard may place an upper limit on the average concentration over a work shift, or on the maxi- mum concentration during this period, or both. Variations in Space It is important to determine the concentration in air which may be inhaled. When planning and executing a survey of the particulates in workroom air, onc should bear in mind that the concentra- tion close to a machine or process is usually quite different from the concentration in the inhaled air. As a general rule, the concentration may vary considerably over a distance of a few feet, or even over a distance of a few inches. This is cspecially true when there are few sources of contaminant and the employees work close to a source. There should be no physical obstruction between the air sampler inlet and the operative’s nose and mouth. Whenever there is any doubt, the sampler inlet should be within a foot of the operative’s nose and mouth, and yet be out of the line of sight. Variations between Instruments Unfortunately, no two different types of air- borne particulate sampler yield the same result. It takes the most painstaking tests to yicld simi- lar results from two identical instruments. There- fore, the instrument used must be the same type and must be used in the same way as that inferred in the hygiene standard. Thus, when using the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Values (TLVs) of airborne contaminants as hygiene stan- dards (Threshold Limits Committee, ACGIH, an- nually) the documentation on particular sub- 140 stances must be consulted to verify the methods to be used. (Threshold Limits Committee, 1971). As a general rule the substances in the main list of values should be collected with total dust sam- pling instruments and the weight concentration should be determined. Those listed under “Min- eral Dusts” should be collected according to type, either with an impinger, total dust sampler, respi- rable dust sampler, or membrane filter. It is in- advisable to rely upon converting the results from one type of sampling instrument or method into those which might be obtained from another sam- pling instrument or method. THE VOLUME OF THE SAMPLE OF AIR People at work inhale about 10 cubic meters of air in 8 hours, depending on their energy ex- penditure. Those who work physically hard may inhale 20 cubic meters and those with sedentary occupations only 5 cubic meters. However, the volume of the sample of air taken for assessment of particulate concentration need not equal, or even be related to the volume of air inhaled. The primary need is to obtain a representative sample of the air of sufficient volume to contain enough particles that can be accurately weighed, counted or chemically analyzed. The volume of the sample of air may be as little as 5 ml or more than 50 cubic meters. The whole sample or a small fraction of it, perhaps 1 percent or less, may be assessed. The concentration of particulates in atmosphere which may be safely inhaled is very low, so a high flowrate is generally desired to collect the required quantity of particulate in a short time. The sampling gear should also be sufficiently portable to enable sampling at the place of work, as near to the operative’s nose and mouth as practicable. Particulate sampling instru- ments which have the highest flowrates tend to be the least portable. Some portability may also be sacrificed so as to collect a large quantity of particulate and thereby to simplify the laboratory assessment. The limit to the sensitivity of a given weighing procedure or analytical technique effectively sets a minimum to the required volume of air which constitutes a sample. The sampling procedure and method of assessment should be sensitive enough to measure the concentration in air of one-tenth the hygiene standard. Therefore, the minimum volume of the sample of air must be 10 > analytical sensitivity hygienc standard concentration When the analytical sensitivity is measured in milligrams and the hygiene standard in milligrams per cubic meter, the volume of the sample of air is given in cubic meters. THE DURATION OF EACH SAMPLE PERIOD The minimum duration of the run for each sample depends upon the volume flowrate of the sampler. Minimum duration per sample 10 > analytical sensitivity Hygiene standard concentration Xx flowrate Units should, of course, be consistent in the above formula. The sensitivity of different weighing or ana- lytical procedures can be very different. There- fore, the analytical sensitivity must be known in order to proceed with the sampling in an orderly and effective manner. For example, a common element in many particulate sampling procedures is a cellulose filter paper which is weighed before and after sampling. The filter paper may weigh anything from 0.05g to 5g according to size. The sensitivity of the weighing procedure is limited by difficulties arising from the equilibrium water con- tent of the cellulose in moist air, which varies with humidity and temperature. When the filter papers are dried to constant weight or compari- son unused filters are used as a ‘tare’, cellulose papers may be weighed to 0.1 percent of the weight of the paper. Thus, Minimum duration of sampling = 0.01 Xx weight of paper Hygiene standard concentration X flowrate Where the duration of the sampling is ex- pressed in minutes, the hygiene standard is in mg/M?, the flowrate is in liters per minute and the weight of the paper is in milligrams: Minimum duration of sampling (mins) = 10 X weight of paper (mg) TLV (mg/M*) X flowrate (1/min) Another useful form of the same equation is given by calculating the volume of air to be sam- pled. Thus, TLV (mg/M¥) wt. of paper (mg) vol. of sample (1) Similar expressions can be found for other weighing or analytical procedures and as such are extremely useful for choosing a satisfactory com- bination of sampling method, duration of sampling and flowrate. INSTRUMENTATION Sampling Trains A sampling train for particulates has the fol- lowing critical elements in this order: air inlet orifice, particulate separator, air flowmeter, flow- rate control valve and suction pump. Equally im- portant are the motor and power supply for the pump and the power supply, if any, for the par- ticulate separator. The Air Inlet. The air entry orifice should be as short as possible to keep wall losses to a minimum. Nevertheless, it is sometimes necessary to have a probe tube connected to the air inlet as in the case when the concentration of particulate is highly localized. Having the entry at a floor- or bench- mounted instrument might result in a false read- ing. Wall losses may be excessive in probe tubes which are longer than three feet or have sharp bends. In such cases the particulate in the tube must be dissolved or washed off and added to the sample. If the particulate separator is small and light, a length of tubing may be inserted between it and the air flowmeter to avoid the problem of wall losses in a probe tube upstream of the separator. 141 The Particulate Separator. The particulate sep- arator is the most important element in the sam- pling train. The efficiency must be high and re- liable. The pressure drop across the separator should be low in order to keep to a minimum the size of the necessary suction pump and motor. It may consist of a single element such as a filter or impinger or there may be two or more elements in series, so as to separate the different sizes of par- ticles, The Air Flowmeter. The air flowmeter is com- monly an air rotameter, but may be a gas-meter or an orifice meter. Where the flowrate is constant or automati- cally controlled, there may be only an on-off indi- cator that the device is functioning. In such cases the flowrate through the sampling train is meas- ured in the laboratory and checked after sampling. The flowrate should be checked with the sample of particulate in place since sometimes the filters affect the flowrate drastically. Similar considerations apply in sampling trains with an integral flowmeter. The value shown by a rotameter, gas-meter or orifice meter is partly dependent upon the air pressure at the entry to the meter, and upon the magnitude and frequency of pulsations in the air flow. Measurement of the air flowrate, or calibration of the flowmeter should be performed before and after sampling, with all the elements of the sampling train in circuit. Flow Control The flowrate control may be manually oper- ated if in the form of a needle valve or a simple pinch valve. When filters are employed the flow- rate control may need repeated adjustment while sampling, since particulates clog the filter. This effect may be mitigated by using a sampling train with a high internal resistance. Automatic flow- rate control may be obtained with a critical orifice. Otherwise, electrical or pneumatic means may be utilized. A critical orifice is a simple and popular means of achieving constant flow. The principle of the method is to draw the air through the orifice under “critical” flow conditions and constant up- stream pressure. The volume flowrate of a gas into an orifice increases as the pressure differential across it in- creases until a point is reached when the air is moving through the orifice at a velocity equal to the velocity of sound through the gas. The volume flowrate then stays the same for any further in- crease in pressure differential. The downstream to upstream pressure ratio below which the volume flowrate becomes constant is known as the criti- cal pressure ratio. This is approximately 0.53 for air through a well-rounded orifice. At atmos- pheric pressure upstream, the flow becomes criti- cal as the downstream pressure is reduced below 400 mm mercury. The orifice is placed in the sampling train at the entry or at a point where the upstream pressure is constant, and the pressure differential is maintained in excess of 400 mm mercury. The critical pressure drop, 400 mm mercury, reflects a resistance to flow. This may be reduced by making a gradual enlargement or evasé on the discharge side of the orifice in the form of a 1-in-5 enlargement for 15 orifice diame- ters. This reduces the necessary overall pressure drop because of the pressure recovery in the ex- pansion piece. In practice, an orifice having an overall pressure drop of 100 mm mercury at crit- ical flow is made fairly easily. A critical orifice should be calibrated from time to time as it may become worn by the par- ticulates passing through it. If a critical orifice is not used the flowrate may be maintained constant with devices down- stream of the particulate separator, such as by having a flow-regulating valve followed by a pres- sure-regulating valve downstream. The pressure drop necessary to maintain control with this lat- ter system is about 250 mm mercury. Even with particulate separators which have a resistance independent of the dust loading, it is advisable to have a pressure-regulator as the per- formance of most pumps tends to vary with time. The Pump The suction pump is commonly a motor driven rotary pump but other kinds are also used, includ- ing diaphragm pumps, centrifugal fans, hand oper- ated crank pumps or piston pumps. The pump must produce sufficient air horse-power and draw the necessary flowrate through the sampling train under the most adverse conditions of air-flow re- sistance. When making up a sampling train, it is helpful to measure the air-flow resistance contrib- uted by each element, as it is often found that a high resistance contributed by a secondary ele- ment such as tubing, elbows, connections or other fittings can be easily reduced. The weight of the necessary pump and motor increases roughly in proportion to the pressure drop and the flowrate through the system. Rotary pumps utilized in this work to produce a fairly high pressure drop of 50-350 mm of mercury are generally the sliding vane type although multi-lobe blowers or gear pumps can be used. Centrifugal fans are suitable where the pressure drop through the sampling train is less than 10 mm of mercury. Somewhat higher pressure drops, up to 100 mm of mercury, can be sustained with small multi-stage centrifugal turbines. If the required sample volume flowrate is less than 5 liters per minute, diaphragm pumps and piston pumps can be used. The very lowest flowrates, less than 100 cc per minute, are accom- modated by water displacement apparatus. Power Supply The power supply is commonly line current, but nickel-cadmium rechargeable batteries may be used on the smaller sampling trains and are es- sential for the greatest portability. Otherwise, manual operation is used. Disposable dry cells are not very suitable but they have been used. Sometimes electricity is not available on site or is banned for reasons of safety, so hand power or approved coal mine dust personal sampler pumps may have to be used, or compressed air or water ejectors may be feasible. Compressed air ejectors can provide flowrates up to 200 liters/ minute against 400 mm of mercury pressure drop, utilizing compressed air at a pressure of 20 Ibs. per square inch. Low sampling flowrates, up to 142 10 liters per minute, may also be obtained with small ejectors working from bottled Freon, carbon dioxide or compressed air. COLLECTION DEVICES Particulate Separators Usually particulate separators are suitable for determining either the mass concentration or the number concentration. Nowadays, the mass con- centration instruments are divided into two broad categories, those with and those without a pre- selector. The pre-selector separates those particles which are larger than about 5 microns. (Task Group on Lung Dynamics, 1966).° Filtration Many instruments used in assessing the mass concentration of airborne particulates incorporate a filter. Common filter paper consists of an irreg- ular mesh of fibers about 20 microns in diameter or less. Air passing through the filter changes direction around the fibers and the particles in suspension impinge there. The largest particles, those greater than about 30 microns, also deposit to a significant extent by direct interception or by sieving action, and the very finest particles, less than 0.5 micron, also deposit through their diffusion caused by Brown- ian motion. With particles greater than 0.5 micron diameter deposition efficiency generally increases with the velocity of the airstream and with the density and diameter of the particles. Deposition by diffusion dominates over deposition by impinge- ment of the very smallest particle sizes and de- creases as the diameter of the particles increases. Consequently, there is a size at which the com- bined efficiency by impingement and diffusion is a minimum. This is always below 0.5 micron diameter and usually below 0.2 micron diameter. The weight of particles below 0.5, and cer- tainly of those below 0.2, micron diameter, is us- ually less than 2% of the airborne dust of hy- gienic significance so that in practice the amount of deposition by diffusion may be ignored. Sam- ples which consist primarily of freshly formed metal fumes would be exceptions. Cellulose fiber filter papers are relatively in- expensive, are obtainable in an almost unlimited range of sizes, have high tensile strength, show little tendency to fray during handling and are low in ash content. Their main disadvantage is their hygroscopicity, which must be allowed for in the weighing procedure. Whatman No. 41 is the most widely used cellulose filter as it combines good efficiency with low flow resistance. Filters made of glass, asbestos, ceramic, car- bon or polystyrene fibers less than 20 microns in diameter have a higher efficiency than cellulose filters and may be favored for this reason. How- ever, their principal advantage over cellulose fil- ters is the ease of determining the blank weight, and this is the reason that glass fiber papers have become very popular in recent years. The resis- tance of a filter increases with thickness and com- pression of the filter mat and with the dust loading. A good filter material for particulate sampling is made of thickly matted fine fibers and is small in mass per unit face area. Membrane Filters Membrane filters may be used to collect sam- ples of particulates for examination under the microscope. They are thus used to determine number concentration as well as mass concentra- tion. A membrane filter is a micro-porous plastic film made by precipitation of a resin under con- trolled conditions. The polymers used are cellu- lose esters, polyvinyl chloride or acrylonitrile. These filters are not very stiff and are therefore supported on a metal gauze or other grid. Spe- cial types have an integral nylon support to give added strength. In manufacture the pore size is controlled within close limits, and membrane fil- ters are obtainable with mean pore sizes of from 0.01 micron to 10 microns in diameter. They are usually 140 microns thick, and have an efficiency close to 100% for particles larger than the mean pore size. On the surface, the particles are filtered out in a sieving action so they may be examined under the microscope as on a glass slide although many particles smaller than the nominal pore size are trapped within the filter. They are ob- tainable with a grid stamped on, which facilitates counting over a known area. They may also be obtained black, which is advantageous for certain white, opaque dusts. Common types are soluble in cyclohexane or other organic solvents, which facilitates separation of the particulates when required. When immersion oil is placed on a membrane filter, it becomes transparent and the particles may be examined under the microscope by transmitted light. Difficulties arise with minerals whose re- fractive index is close to that of the filter material. Membrane filters may be used in the deter- mination of mass concentration where it is feasi- ble to employ a low air sampling flowrate. They have a high air-flow resistance. A common mem- brane filter used for dust sampling has a nominal pore size of 5 microns. Impingement on a flat plate Some particulate separators rely upon im- pingement on a flat plate held close to a jet of the air containing the particles in suspension. These have been used for many years. Their popularity is waning but they still are an important type. These instruments are operated by drawing air at very high velocity, 50-300 meters per second, through a small jet. The jet may be circular or rec- tangular in cross-section, 0.5 mm to 1.0 mm in diameter or width, and 1 mm to 5 mm from the deposition surface. Particles down to about 1 micron diameter are efficiently thrown out by the centrifugal force as the air in the jet turns through 90 degrees or more. The forces involved are not sufficient to re- move particles much smaller than 1 micron in diameter. With high velocity jets the coarser par- ticles are thrown with increasing force against the plate and may bounce off, or break up. The sur- face of the deposition plate is usually wetted or greased to cushion the particles and trap them. 143 The collected particles are counted by eye under a microscope and the result is a useful compara- tive index of the concentration of particulates in the sampled air. The count obtained in a particu- lar concentration is very dependent on the spe- cific type of instrument and the nature of the particulate so that the counts obtained with other types may be different by a factor of up to 10. Therefore, it is imperative to use the same type of impingement instrument when making repeat surveys in a given environment. Electrostatic Precipitation Electrostatic precipitation has been utilized successfully in atmospheric sampling. These sys- tems have the advantages of negligible flow resis- tance, no clogging and precipitation of the dust on a metal cylinder whose weight is unaffected by humidity. A power pack is needed to supply the high voltage and precautions have to be taken to guard against electric shock. The wire and tube or “tulip” system is used. The tube is a light alloy cylinder about 6 in. long and 1% in. dia., held horizontally. The tube is grounded. A stiff wire, supported at one end, is aligned along the center of the tube and serves as the charged electrode. The tip of the wire is shar- pened to a point. A high d.c. voltage, between 10 kv, and 20 kv, is applied to this central elec- trode. The corona discharge from the tip charges the particles in suspension in air drawn into the tube. Under the action of the potential gradient between the wire and the tube the charged par- ticles migrate to the inside surface of the tube. The migration velocity of the charged particles greater than 1 micron in diameter increases in proportion to particle diameter. On the other hand, migration velocity is approximately inde- pendent of particle diameter for particles smaller than 1 micron in diameter. Therefore, very high separation efficiencies are attainable with electro- static precipitators and they are ideal for particles smaller than 1 micron in diameter. Thermal Precipitation A particle in a thermal gradient in air is sub- ject to differential molecular bombardment from the gas molecules, so that it is subject to a force directed away from the hot sources. This is the principal mechanism involved in thermal precipi- tation. The air is drawn past a hot wire or plate and the dust collects on a cold glass or metal sur- face opposite the hot element. A high thermal gradient is needed so the gap between the wire or plate and the deposition surface is kept small (0.5-2 mm). The migration velocity induced by the thermal gradient is small, and very nearly in- dependent of particle diameter. However, the system has severe limitations in the maximum flowrate possible with high deposition efficiency. It is, therefore, used only for collecting sufficient particulate for examination under the microscope. Due to the temperature involved it is not suitable for mists except those of liquids with high boiling oint. P When the particulate is collected on a glass coverslip and viewed dry, the visibility of the particles under the orthodox light microscope is far better than that obtained with a membrane filter. Elutriators Elutriators are an important and sometimes essential feature of sampling trains used for min- eral dusts. They are used as pre-selectors, ahead of other particulate separators to remove the larger particles. There are two classes of elutria- tors employed in sampling air for particulates: horizontal elutriators and vertical elutriators. “7 TT A single element of a horizontal elutriator used in this work is a thin, horizontal, rectangular duct. Commonly the horizontal elutriator package con- sists of several such elements stacked one above the other, connected in parallel to a common exit. (Walton, 1954).¢ The theory is fairly easily un- derstood and performance closely matches theory. Suppose a flowrate, Q, of air is passing uniformly along a horizontal duct of length L, width W and height H. The time, T, it takes for air to pass through the duct is LWH/Q. Among the particles entering the duct those which, in time T, would fall freely under gravity a distance greater than H would all deposit on the floor of the duct. Thus, the minimum terminal velocity (Vc) for 100% capture by the elutriators, is Ve = H/T = Q/LW. Also, among those particles with terminal velocity, V, (V less than Vc) a proportion would be cap- tured by deposition on the floor of the duct. The percentage captured in this way is 100(V/Vc) %. The proportion, P, not captured by the elutriator would be 100(1-V/Vc)% of those with terminal velocity less than Vc. P—=100 (1-V/Vc)% =100 (1-VLW/Q) % (1) Thus, P is independent of the height of the duct, provided the floor area and flowrate are constant. It may also be shown that under streamline flow conditions, errors in the above formulae through assuming uniform flow cancel out. Flow is main- tained streamline by making H small. Since the performance is independent of its height, the duct may be made as thin as practicable. All ducts with the same ratio of floor area to flowrate (LW/Q) have the same performance under streamline flow conditions. A vertical elutriator is a single vertical tube, either parallel sided or in the shape of an inverted, truncated cone. The air with particles in suspen- sion is drawn or blown upwards through the tube. Suppose a flowrate, Q, of air is passing uniformly up a parallel sided, vertical duct, cross-sectional area A. The upward air velocity is Q/A »equal to Vc. None of the particles which have a ter- minal velocity in air exceeding Vc, would be car- ried up the tube by the air. The particles with zero terminal velocity in air would be carried up the tube with velocity Vc. Those with a terminal velocity, V, between zero and Vc, would be car- ried up at a velocity Vc-V and proportionately fewer would pass through the tube. The percent- age, P, passing through the tube, P= 100 (1-V/Vc)% = 100 (1-VA/Q)% .(2) P is independent of the length of the tube, pro- 144 vided the cross-sectional area and flowrate are con- stant. It is important to maintain streamline flow in elutriators so their cross-sectional area must be small. However, since the performance of a verti- cal elutriator is dependent on cross-sectional area, this type is only used in sampling at very low flowrates. The conical form of vertical elutriator, with a small entry at the tip at the bottom, is used to pro- mote smooth flow through the elutriator. A par- allel portion is usually arranged at the top, where the cross-sectional area is largest and the final per- formance therefore determined. Perfect streamline flow is not realized in prac- tice even with horizontal elutriators. The effects of a disturbance to streamline flow on the col- lection characteristics may be understood by con- sidering the collection characteristics of a hori- zontal elutriator under conditions of perfect mix- ing. At a point a distance 1 from the entrance to an elutriator element of width W, length L and height H the average forward velocity of the air- stream, dl Q de WH The horizontal base area of small element length dl is Wdl. The number of particles of terminal velocity V falling on this area in time dt is thus CVW d1 particles per minute, where C is the concentration of particles in the air over the ele- ment. The volume of the air above the element is WH dl, thus the rate of change of concentration with time, dC —CVWwdl dt ~~ WHAI _ —CV TH From which C=C, exp — (Vt/H), where Co is the concentration at t,, when the air enters the elutriator. The time to pass through the elutriator is LWH, so that the concentration at Q the exit is C, exp — (VLW/Q). Thus the per- centage, P, of particles in the air entering the elutriator which pass through it without depositing, P — 100 exp — (VLW/Q) Elutriators are commonly designed on the assump- tion of uniform flow, and so as to capture 50% of particles of 5 microns equivalent diameter. (Orenstein, 1960). The expected performance of such an elutriator under streamline flow (equa- tions 1 and 2) and under perfect mixing condi- tions (equation 3) are shown in Fig. 13-1. Streamline flow is often nearly achieved and the performance comes close to theoretical. (Ham- ilton, 1967).% Such elutriators have an inherent fail-safe feature in that if due to distortion of the plates or poor design streamline flow is seriously disturbed, capture of coarse particles is reduced and the estimated sample concentration errs on the high side. On the other hand, flowrate control is 100 + 75 = x e Oo w - ul 50 + o z & 2 254 a 2 0 0 2 4 6 8 10 EQUIVALENT DIAMETER OF PARTICLES (microns) Figure 13-1. The Performance of Horizontal Elutriators Line A - Streamline flow condi- tions; elutriator designed to allow 50% of particles of 5 microns equivalent diameter to pass through — Line B - Perfect mixing in elutriator designed as for Line A — Points C -° Size selector characteristics recommended by the ACGIH for “respirable” dust sampling — Line D - Perfect mixing conditions; elutriator designed to allow 50% of particles of 3.5 mi- crons equivalent diameter to pass through. particularly important. If the flowrate is low, coarse particles are removed to a greater extent, giving an additional error on the low side. The reverse occurs when the flowrate is high. Cyclones Miniature cyclones of simple construction have been used in recent years as pre-selectors ahead of other particulate separators, and serve the same purpose as elutriators. Cyclones 10 mm to 50 mm diameter are employed, for example, when test- ing compliance with current Threshold Limit Val- ues for “free” silica; that is, quartz, cristobalite, tridymite and fused silica dust (Threshold Limits Committee, 1972).° The air enters a cyclone tangentially at the side of a cylindrical or inverted cone shaped body, swirls around inside and leaves along the axis from a tube at the top. Coarse dust is thrown to the side and collects in the base of the cyclone. The air velocities in a cyclone are very high and the flow is highly turbulent. The centrifugal acceleration of a particle in the rotating airstream turning at an angular ve- locity, , is o’r, where r is the radius of rotation. The diameter of cyclones in common use and the flowrates employed give centrifugal accelerations in excess of one hundred times gravitational ac- celeration. The air in a cyclone rotates several times before leaving and consequently the dust deposits as it would in a horizontal elutriator of floor area several times the cyclone outer surface area, and under a force over one hundred times gravity. Consequently, the volume of a cyclone is 145 much smaller than a horizontal elutriator with the same flowrate and efficiency. The characteristics of a size selector for test- ing compliance with current Threshold Limit Val- ues for free silica are indicated in Fig. 13-1, at points C, and the size-efficiency performance of an elutriator under perfect mixing conditions to sim- ulate this are indicated in Fig. 13-1 at line D. Cyclones have similarly shaped size-efficiency performance curve. However, the detailed pat- tern of air-flow through a cyclone depends so much on the design adopted that the performance of cyclones of particular design must be checked experimentally. The orientation of a cyclone is not as critical as that of an elutriator so a small one may safely be fastened to an operative’s clothing. Further, small errors in flowrate are counter-balanced to some extent by changes in the size-efficiency char- acteristics. Thus, if flowrate is low, coarse parti- cles are removed to a lesser extent, giving an op- posite error, and the reverse occurs when the flow- rate is high. The air-flow resistance of a cyclone is higher than that of an elutriator for the same flowrate. Nevertheless, the resistance is largely independent of dust loading and small in comparison with the resistance of customary filters downstream. CHOICE OF SAMPLING INSTRUMENTS There are at least 50 different types of samp- ling instruments used in particulate sampling, each with its own proponents. Further, there are new ones being developed every month. Amongst those in regular use at the present time for determin- ing concentration as mass of particulate per unit volume of air are the electrostatic precipitator and many filter paper methods. The common instru- ments for determining the concentration as num- ber of particles per unit volume of air are: the im- pinger, the membrane filter method, the thermal precipitator and the light scattering automatic par- ticle counter. All these instruments and many others are described in “Air Sampling Instru- ments.” (American Conference of Governmental Industrial Hygienists, 1972).1° The choice of instrument in particular circum- stances is very often dictated by the limited choice of instruments actually in the hands of the hy- gienist at the time the measurements are needed. The problem may be one of deciding which of two not very suitable instruments is least likely to give rise to erroneous conclusions rather than one of choosing the ideal instrument. For example, when sampling for a mineral dust, a “respirable” dust sampler may be needed. However, the sampling equipment available for total dust measurements is simpler and less expensive than that for respi- rable dust. If the proportion of fine dust in all the airborne dust is known, the concentration of fine dust in the air could then be inferred from a sim- ple measurement of the concentration of all the atmospheric dust (total dust). In particular cases, upper limits can be placed on the proportion of fine dust, recognizing that in effect an additional factor of safety is thereby in- corporated. Again, in the absence of any precise information on the proportion of fine dust, the total dust concentration may be used as a working limit. Obviously, if the total dust concentration is less than a certain value, any fraction of it will also be less than this same value. Thus, lack of elutriators, cyclones or other pre-selectors need not necessarily be a bar to pro- ceeding with mineral dust sampling in an orderly and effective manner. In many cases the simplest of measurements will suffice. In others, the pro- portion of fine dust is so small that a more sensi- tive and precise method incorporating a pre-selec- tor is justified. Similarly, in addition to the particulate being studied, background material and other contami- nants are also collected. It is necessary to consider whether simply to weigh all the particulate, recog- nizing the safety factor that would be incorporated by assuming it was uncontaminated, or to analyze the particulate in the laboratory. The procedure selected influences the choice of sampling instru- ments as each procedure possesses a different sensitivity. Taking an example from number count instruments, when determining an airborne as- bestos dust exposure, it has to be borne in mind that the thermal precipitator, impinger and Royco particle count are progressively simpler tech- niques from the operational standpoint, but less easily related to the membrane filter fiber count needed for asbestos dust. Electrostatic Precipitators Electrostatic precipitators normally do not have a preselector ahead of the collecting tube. They are therefore suitable for all those particu- lates listed in the TLV document of the ACGIH except mineral dusts evaluated by count. They may also be used for nuisance particulates. Be- cause of the high efficiency for separating particles smaller than 1 micron in diameter, they are very often used when sampling for fumes. The two types commercially available are the Mine Safety Appliances Electrostatic Sampler and the Bendix Electrostatic Air Sampling System. The former has a fixed flowrate of 66 1/min from a 50 c/sec frequency supply, and the latter is variable be- tween 90 1/min and 200 1/min. The ionizing voltage should be maintained sufficiently high to collect all the particles but not so high as to pro- duce arcing between the central electrode and the collecting tube. A check that the dust has all been collected is to observe that the downstream end of the collecting tube is clear of dust. There is a practical limit of about 100 mg to the amount of dust that can be collected on each tube, as a thick layer of dust is easily dislodged and may be lost on handling. For very high dust concentrations, a coiled filter paper liner may be used to enable higher dust loads to be carried successfully. The ends of the sampling tube should be capped when the sample has been collected and the outside of the tube wiped clean. The dust may be washed or wiped off the tube. If the tube is washed, it 146 should be allowed to return to room temperature before weighing, or balance errors will occur. The tube can be weighed on a semi-micro balance to 0.25 mg. Filter Methods So-called ‘respirable’ dust sampling instru- ments include a pre-selector to separate the coarser particles before collection. (Aerosol Technology Committee, 1970)."* These instruments normally incorporate filters to collect the fine particulate. Such instruments without a pre-selector are suit- able for other particulates in the ACGIH list of TLVs. The Casella Gravimetric Dust Sampler Type 113A incorporates a horizontal elutriator for a flowrate of 2.5 1/min (Dunmore, Hamilton and Smith, 1964)'2 and the Casella Hexhlet incorpo- rates a horizontal elutriator for a flowrate of 50 1/min (Wright, 1954).* In both instruments the fine dust is collected on a filter. In the Dorr-Oliver and Mine Safety Appli- ances respirable dust samplers the size selection is achieved by using a small cyclone upstream of a filter. Where a 10-mm nylon cyclone is used, the flowrate is 1.7 1/min and for the UNICO V4 -inch HASL cyclone, 9 1/min. With all respirable dust samples, it is partic- ularly important to maintain a constant and non- pulsating sampling flowrate to ensure correct size selection characteristics, A particulate sampler without a pre-selector and incorporating a filter may be made up from parts available in the laboratory. Whatman No. 41 cellulose filter paper or GF/A glass filter paper are used. The principal source of error in weighing cellulose papers arises from the hygroscopic na- ture of the paper. This error can be kept within bounds by strict observance to a drying and weigh- ing routine. The flowrate, sampling interval and size of filter are then chosen to yield a weight of dust amounting to at least one percent of the paper, and preferably more than two percent. Glass fiber filters are available either with or without an organic binder. The binder increases the mechanical strength of the paper. Glass fiber filters without binder are used when the binder would constitute an interference in the analysis for organic matter in the particulate. Even with the binder, glass fiber filters are quite friable and must be handled with care. Analysis of the dust for iron, aluminum, sodium, potassium, magnesium and silica is not possible because of interference from large amounts of these in the glass fibers. Polystyrene fiber filters such as the Micro- sorban filter, have a flow resistance which is rel- atively low, being comparable to Whatman No. 41, while their efficiency of collection is relatively high and is comparable to that of glass filters. Since they have poor mechanical strength, they must be well supported in the filter holder, Membrane filters have a low mass and low ash content. However, they have a high flow re- sistance. Cellulose filter paper such as Whatman No. 41 has an air flow resistance of 10 in. water gauge when the face velocity through the paper is 50 cm per sec, whereas a membrane filter with a pore size of 2 microns or less has an air flow resistance of at least 50 in. water gauge under the same conditions. Particle collection takes place almost exclusively at the surface of the filter, and when more than a single layer of dust particles is collected on the surface, the resistance rapidly increases and there is a tendency for the deposit to slough off the paper. A filter holder should be used which provides a positive seal at the edge, without leakage. It must not abrade or tear the filter. A screen or other mechanical support may be required for the filter, to prevent rupture or displacement in service. A back-up screen is necessary with glass fiber, polystyrene and membrane filters. Filter thimbles are available in cellulose fiber and cloth. They are sometimes filled with loose cotton wool to reduce clogging. The advantage of a filter thimble is that large samples can be col- lected before clogging. A typical procedure for weighing filters is as follows: The weighing vessels used in a typical pro- cedure are light screw-top cans with a pin- hole in the lid. 1. Remove the lid from a weighing ves- sel, place the filter inside and place the weighing vessel in a drying oven at 110°C. (60°C for membrane filters). Dry for 2 hrs exactly. 2. Screw on the lid of the weighing vessel and cool it in a desiccator with silica gel for exactly 20 min. 3. Weigh immediately. 4. Repeat steps 1 to 3. The two weights should check to 0.1 percent. Otherwise repeat procedure, For most chemical analyses, it is necessary either to remove the sample from the filter, or to destroy the filter. Inorganic particles are usually recovered from cellulose paper filters by wet ash- ing (digesting in concentrated acid) or dry ashing (muffling, incinerating) the filter. Samples can be recovered from polystyrene and membrane fil- ters by dissolving the filter in a suitable solvent. The background level on the filter of the ma- terial to be analyzed must be determined. Filters contain various elements as major, minor and trace constituents, and the filter medium of choice for analyzing particular elements must be one with little or no background level for the elements being analyzed. Impinger The impinger is the instrument used in the series of studies by the U.S. Public Health Ser- vice 1925-1940 in dusty trades on which the Threshold Limit Values of the American Confer- ence of Governmental Industrial Hygienists for Mineral Dusts were largely based. It is still a common method for mineral dust sampling in the United States, although it is being superceded by dry filtration. The dust-laden atmosphere is drawn 147 through a glass jet, the end of which is set a fixed distance from the bottom of a flask. The jet is immersed in water or alcohol and the particles strike the bottom of the flask and become sus- pended in the liquid. A sample of the liquid is then placed in a counting cell and the particles are counted using a low-power microscope. The sampling time is usually 10-30 min or more. When long sampling times are used, the suspension can be diluted to the point where concidence errors are insignif- icant. The following method represents standardized methodology for the impinger sampling technique: The sampling instrument is the standard im- pinger, operated at a rate of 1.0 cfm + 5 percent at 3 in. mercury negative pressure, or the midget impinger operated at 0.1 cfm = 5 percent at 12 in. water negative pressure. The sampling instrument and the indicating gauge on the flow-producing apparatus should be calibrated at regular intervals. Counting Cell The counting cell should be no more than 1.0 mm and no less than 0.25 mm in depth with an allowable variation of == 5 percent from the nom- inal depth. Optical System A. The microscope should be equipped with the following: objective 10X (16 mm) 0.25 N.A. ocular (eyepiece) 20X condenser 0.25 N.A. B. The counting area is defined by an ocular grid such as a Whipple disc and should be accurately measured by means of a stage micrometer. C. Kohler illumination is used except that after this has been achieved, the eyepiece is removed and the iris diaphragm of the microscope condenser is closed until the disc of light seen in the back lens of the objective is about one-half of the lens. Further reduction of brightness may be accomplished, if desired, with neutral den- sity filters. Collecting Liquid The collecting liquid usually is 95% ethyl al- cohol although distilled water or mixtures of dis- tilled water and alcohol (ethyl or isopropyl) may be used. Treatment of Collected Samples A. All glass-ware must be clean and the equip- ment protected against dust contaminants in the field. One impinger flask, a “blank” flask, is treated exactly like the others ex- cept that no air is drawn through it. B. The diluting liquid should be 95% ethyl alcohol. C. The impinger nozzle is rinsed down inside and out with diluting liquid as the sample is made up to a known value. Samples having a low concentration of dust are di- luted as little as possible. Dense samples are diluted so that no more than about 2,000 particles/mm? will appear in the counting area of the cell. Not less than 5 ml of original or diluted sample should be taken for further dilution, and dilu- tions should be made in steps not exceed- ing 10 parts of dilution liquid to 1 part of original or diluted sample. The dust suspension must be shaken vigorously by hand for at least 30 sec. before a portion is removed for dilution. Preparation for Counting A. The sample to be counted is shaken to ensure a uniform suspension and a por- tion is transferred immediately to a clean cell by means of a clean pipette, taking care to prevent the inclusion of air bubbles, B. Two cells are filled from each sample and from a “blank” flask. C. Sample counting should start at the end of the settling time and should be completed in 10 min. The settling time should be 30 min/mm of cell depth. Counting A. Before counting, the ocular grid should be cleaned to remove dust particles. The counting plane is the bottom liquid- glass interface of the cell. The microscope is focused up and down slightly with the fine focus adjustment in order to bring in- dividual particles in and out of focus for more positive detection and counting. Fields selected for counting should be uni- formly distributed over the counting plane of the cell. Observation should not be made through the microscope while fields are being selected, . At least five fields of equal area should be counted in each of two cells. For a dust sample, when the first five fields of the first cell counted yield a total count of less than 100 particles, additional fields of known area should be counted; the total area counted is recorded and used in cal- culation of concentration. For each cell from the “blank” flask only five fields need be counted. E. The same total area should be counted in the second cell as is counted in the first. F. Total counts from the two cells of the same sample should be compared; and when the ratio of the greater to the lesser count is larger than 1.2, additional pairs of cells should be counted until a pair yields counts which satisfy this criterion. The count of this pair should be used for calculating the concentration of the sample. . Five fields of the same area as that used for dust sample counting should be counted in each of two cells from a “blank” flask. The average blank count should be used in calculation of net count. If the blank count exceeds 30 particles/mm? of counted area, all the samples should be rejected. B. 148 H. Observers are cautioned that their ability to see particles probably improves during the first few minutes of counting as their eyes become accustomed to the task. A brief period of counting is suggested prior to recording data. Fatigue can cause a deterioration in counting efficacy; conser- vative judgment should be exercised on when to discontinue counting because of fatigue. Membrane Filters The membrane filter method is commonly used for assessing asbestos dust exposure. In order to view the dust under the micro- scope it is necessary to use immersion oil to render the filter transparent. The refractive index of membrane filters is about 1.5, close to that of chrysotile asbestos (Np = 1.55), so that under ordinary illumination the chrysotile may itself be very nearly invisible when using an immersion oil closely matched to the filter. A phase contrast microscope is therefore used to increase the visi- bility of the chrysotile. The method given below is based on the standardized techniques recom- mended by the National Institute for Occupational Safety and Health. Sampling Procedure Samples for evaluation of asbestos exposure are collected on Millipore AA Membrane filters (37 mm diameter, 0.8 pm pore size) by personal samplers operated by battery-powered pumps, worn by the employees. The filters are contained in plastic filter holders and are supported on thick pads which also aid in controlling the distribution of air through the filter. The face cap of the filter holder is removed and filter used open face during sampling. The sampling rate is about 2 liters/min. A minimum sampling period of 15 minutes (for evaluation of excursion limit) and several samples of up to 4 hours for evaluation of 8-hour average are normally required. Samples with a visible deposit may be too heavy to count; compare the appearance of the collected samples with a clean filter. Heavy concentrations of visi- ble dust in the air (100 to 500 fibers/ml) may re- quire short sampling periods of only 5 minutes, or less. The following specifications should be con- sidered minimum for the microscope used for counting of asbestos fibers. 1. Microscope body with a binocular head and a fine focus accuracy of 0.005 mm. Binocular with 10X Huygenian eyepieces Porton reticle Mechanical stage Kohler illumination (preferably built in and having provisions for adjusting light intensity) Abbe condenser with an adjustable iris 7. 40-45X (0.65-0.75 N.A.) Positive (bright field) phase-contrast objective Nh a 8. Annular ring condenser diaphragm (cor- responding to the objective) 9. Phase ring centering telescope 10. Green filter 11. Stage micrometer Counting To prepare samples for microscopic examina- tion, a drop of the mounting medium is placed on a freshly cleaned standard (25 mm x 75 mm) microscope slide, using a dropper or applicator. Mounting the sample The mounting medium used in this method is prepared by dissolving 0.1 g of membrane filter per ml of a 1:1 solution of dimethyl phthalate and diethyl oxalate. The exact proportions of the 3 components are not critical, but the medium must have as high a viscosity as possible without being difficult to handle. The index of refraction of the medium thus prepared is Nj, = 1°47. The volume of the drop is approximately 0.05 ml. A wedgeshaped piece about 1 cm x 2 cm is excised from the filter using a scapel and for- ceps, and placed dust side up on the drop of mounting solution. A #1-12 coverslip carefully cleaned with lens tissue is placed over the filter wedge. Slight pressure on the coverslip achieves contact between it and the mounting medium. Clearing of the filter with this method is slow, re- quiring about 15 min. The sample may be ex- amined as soon as the mount is transparent. A minimum of twenty fields, located at ran- dom on the sample, or a sufficient number of fields to provide a minimum of 100 fibers, are counted and fibers having length greater than 5pm are recorded. Any particle having an aspect-ratio of 3 or greater is considered a fiber, Royco Particle Count Method In the Royco particle counter a thin filament of the particulate laden air is drawn past an in- tense light beam and the light scattered at right angles is sensed by a photo cell. Air is contin- uously drawn through the center of a hollow cube or chamber with windows in the sides. Particles in suspension scatter light from a tungsten fila- ment lamp focused on the center of the chamber. The scattered light is viewed by a lens system and photomultiplier. The pulse train from the photo- multiplier passes to a linear variable-gain amplifier and fixed-level discriminator and then to a decade counter. Time switches automatically switch a sequence of size discrimination channels so that the count may be restricted to successive size ranges or to all particles above a lower size-limit. The standard model counts above 0.3 micron and in 14 stages up to 10 microns at 0.3-, 1-, or 3- or 10-minute intervals. The counts are read off, plotted on a pen recorder, or printed out. An optional filtered dilution system can be incorporated to reduce co- incidence errors in high concentration. Overall calibration is performed against mono- disperse polystyrene latex spheres. The air is fil- tered through a membrane filter after passing the counting chamber so that the sample may be sub- sequently check-counted by eye, under the micro- scope. The instrument is extremely expensive, large, complicated and not very portable. Its great ad- vantage is that it is automatic and suitable for de- 149 termining the size distribution of mists. It must be noted that the accuracy of the Royco particle counter is dependent upon the surface characteris- tics, including shape, of the particles being counted. Thermal Precipitators Two types of thermal precipitators are at pres- ent in use, namely the “standard” thermal precipi- tator, manufactured by Casella, and the “long run- ning thermal precipitator,” designed and developed at the Mining Research Establishment, manufac- tured in clockwork pump form by Ottway and Casella, and in an all electric form by Casella. In the standard thermal precipitator, dust-laden air is drawn vertically into the sampling head and down a narrow vertical channel between two cir- cular glass coverslips, Halfway between these two coverslips is stretched a horizontal wire, heated electrically. Dust is deposited by the thermal ef- fect, opposite the wire, in two strips on the cover- slips. At the sampling site, the instrument is as- sembled in the sampling position so that the air channel through the head is vertical. Current for the heating wire is supplied by a 6 V rechargeable battery. Alternatively, line power may be used with a transformer having a 6 V outlet in series with a rheostat and AC ammeter. Air is drawn through the sampling head at 5-7 ¢cm*/min. In the laboratory the coverslips are mounted, dust side down, on microscope slides, and are viewed under the microscope. The slide should first be examined under the 16-mm objective for any unevenness in density along its length, and any contamination of the cover-glass in areas remote from the deposit. The extent of the deposit should be clearly defined, and if, owing to heavy contamination, the edge of the deposit is not easily seen, the sample should be rejected. The length of the deposit should be measured with a stage vernier under a 16-mm objective. A traverse should be selected either centrally or 2 mm from either end. If the examination of the deposit under the 16-mm objective has shown that there is a defect where a traverse would normally be made, a new position should be chosen which is clear of defect, yet as near as possible to the original position. The total length of the traverse counted should be 2 mm, 1 mm either side of the center of the dust deposit. The projected areas of the particles are com- pared with the areas of the globes or circles on the eyepiece graticule. All particles whose sizes are greater than the 1-micron circle are usually counted. These may be either single particles or aggregates. The criteria for including an indi- vidual particle or aggregate in the count are as follows: 1. 2. At some stage in focusing, a clear margin It falls within the specified size range. of separation is visible between the particle and all its neighbors. The airborne dust is deposited over a very small area on the cover glasses and to avoid over- crowding, it is necessary to restrict the volume of air sampled. An endeavor should be made to ob- tain slides with an optimum of 50,000 particles larger than 1 micron with outside limits of 25,000- 75,000. Slides with densities above and below these limits are liable to give a seriously inaccurate estimate of the dust concentration. The recom- mended method of illumination in the microscope is the Kohler system. A compensating 15 x or 17 x eye-piece is recommended with the achromatic type objective. In the long running thermal precipitator (LRTP) the dust-laden air is drawn down a verti- cal passage, and along a horizontal channel, the floor of which is formed by a glass coverslip. Particles settle out from the air by gravity and the remainder are precipitated thermally beneath a heated wire. A sample of up to 8 hours duration can be obtained with this instrument, compared with 10-30 min for a sample using a standard instrument. The instrument is hung or supported in the sampling position, with the top surface approxi- mately horizontal. To reduce contamination, the sampling head may be sealed during the journey to and from the sampling position. The instru- ment should not be subjected to excessive bump- ing during the journey back to the laboratory and should remain in an upright position until the sample can be removed. The counting procedure to be followed for LRTP samples is generally the same as described for standard thermal precipitator samples, the fol- lowing being the main points of differences: 1. The slides should be set up on the micro- scope with the thermally precipitated zone to the left of the microscope stage. The length of the traverse to be counted should be estimated by marking the posi- tion of the thermally precipitated zone un- der the 16-mm objective and then moving the microscope stage 1 mm to the left of this position and counting 14.5 mm to the right of this point — any particles outside these limits are to be regarded as con- tamination. The traverse to be counted should be 6 mm from the most clearly defined end of the thermally precipitated zone. The width of the deposit, to be used in calculating the result, should be measured at the thermally precipitated zone. The dust deposits on these slides are oc- casionally heavy and the use of the full 60- micron graticule width may entail pro- longed counts, producing fatigue and a fal- ling-off in the counting accuracy. In such cases use may be made of the subdivision of the graticule to count either 40- or 20- micron traverses. 150 STATISTICAL CONSIDERATIONS In order to determine how many samples to take, and where and when to take them, it is necessary to keep in mind the objective of the sur- vey and to understand how to cope with the varia- tions in the results that are obtained. Begin by making a list of the people who are employed in a particular work-place or work- places. The place to sample follows from inquiry about where they are working. Surveys vary from “one time” to “continuous monitoring.” In a one-time survey the objective is to find out as quickly as possible if the concentration exceeds the hygiene standard at the time the samples are being taken. Continuous monitoring refers to regular sampling over a period of weeks, months or even years to check whether the environment is deteriorating (or improving). Representative Sampling When several employees are doing similar jobs, the question arises which employees to investigate. For example, the sampling may be based on the reasoning that if the environment of those whose exposure is the greatest complies with the recom- mendations of the TLV document, then the en- vironment of every employee in the group will comply. The hygienist should judge which em- ployees are representative of those with the highest exposure. They may be those in the location where there is the most dust, or those who do their job in such a way as to produce the highest airborne dust concentration. The alternative is to use a random sampling procedure through the whole group. Individuals from a group may be chosen by selecting names at random. They may be further subdivided into smaller groups exposed to markedly different dust concentrations, and each group sampled sepa- rately. The spacing of samplings over the period un- der study should be planned ahead of time. The atmospheric samples may be taken at regular in- tervals or at times chosen at random beforehand. If taken at regular intervals the interval should not coincide with any other regular cycle of events which might be related to the concentration of atmospheric particulates. Sampling by the Workday Threshold Limit Values refer to the time- weighted average concentration for a 7- or 8-hour workday and 40-hour workweek. Samples of the atmosphere are often taken for periods of 5 to 30 minutes or for a full shift, depending on the ap- parent particulate concentration, the assessment procedure to be used, and the duration of the operation being studied. A 15-minute sample dur- ation is used in many cases. The maximum num- ber of such 15-minute results taken with one samp- ling instrument in an 8-hour workday is 32. Such a set of 32 results, whose average was lower than the TLV, could be taken as showing that the en- vironment complied with the TLV document on that workday with respect to the airborne partic- nlates being determined. Particulate sampling procedures differ from this becanse often, for good practical reasons. only a few results have been obtained, perhaps as few as four or five. When fewer than 32 15-minute re- sults are obtained it is necessary that the accept- able upper limit of their average be made lower than the TLV to compensate for the loss of in- formation. The distribution of averages of two or more results is a normal distribution when the parent distribution is normal. More important, even if the parent distribution is not normal, the distribu- tion of the average tends rapidly to normal form as the number of results increases. In most cases it may be assumed for all practical purposes that with four or more results their average is distrib- uted normally. Consequently, the error of this av- erage can, in practice, be estimated by reference to a table of the normal distribution. (Roach, Baier, Ayer and Harris, 1967).'* The standard deviation of the average of n results is o/ YT, where o is the standard deviation representing the dispersion be- tween the individual results. Suppose, for example, the individual results obtained over the course of a shift varied about their average with a coefficient of variation of 35% . With 32 results, the 90% confidence limits of the average would be == 10% of the average. Thus, since only one side of the distribution is of concern, one would be at least 95% confident, when the observed average equals the TLV, that the true average did not exceed that TLV by more than 10%. If fewer than 32 results are available the same degree of confidence can be obtained only by lowering the acceptable upper limit of their average until the upper confidence limit again equals 1.1 x TLV. In practice, the coefficient of variation may be less than, or vary much greater than, the example 35%. A general formula for the acceptable upper limit to the average, x (max) given in terms of the standard deviation, ¢, and the number of results, n, is: X (max) = TLV — 1.6 (= a. When the standard deviation is not known from previous results, it has to be estimated from the sampling results. A simple and efficient esti- mate from a few samples is obtainable from the range. The possibility of error in this estimate is also taken into account by lowering the accept- able upper limit to the average accordingly. The limit so calculated may be found conveniently from Table 13-1.'* The limit is TLV — (k X range), where k is found in the table, from the number of results obtained. When the limit so calculated is less than the observed average, the environment cannot safely be said to have complied; and when the limit is higher than the observed average, it can be stated with some assurance that the environment did comply. In this way the hygienist can make a simple confidence test for compliance and make proper allowance for the number of sample re- sults actually obtained. Whereas it is possible to state that the con- ditions examined on a particular workday com- plied with the TLV document, it is not possible to infer from the results of sampling on one day 151 TABLE 13-1 k Values for the Range Number of Results k 32 0. 10-31 0.1 6-9 0.2 5 0.3 4 0.4 3 (0.8) 2 (0.9) whether these conditions were representative of any other period. The hygienist may choose the day to be samp- led with the aim of sampling a day representative of the highest concentration. However, it must be borne in mind that, even with careful observation of the processes, cross-questioning of the em- ployees, ventilation measurements, and studies of air contaminant control equipment, the judgment may be little more than intelligent guesswork. The average concentration will vary not only from time to time during a day but also from one day to another, from one week to another, and from one year to another. The results of successive visits to a workplace may be plotted on a control chart for prediction purposes. This is a useful means for predicting ahead when an environment is getting out of con- trol, as might happen, for example, with an in- crease in production or with seasonal fluctuations. The successive averages are plotted by date. The chart is set up by first considering a sample of, say, 20 visits. A warning line is drawn 2 standard deviations above the grand average, and an action line 3 standard deviations above this average. The standard deviation here is that be- tween the average concentrations from the 20 visits. The warning line should, of course, be at or below the TLV at the outset. Subsequent re- sults should all fall below the warning line. A point falling above this line should be followed by a repeat visit. A repeated point falling above this warning line or a single point falling above the ac- tion line indicates that there is good cause for immediate action to be taken to reduce the dust concentration, A supplementary chart may be drawn up for the range. This, in combination with the control chart for averages, will show whether loss of con- trol is due to an increase in average dust concen- tration or to dust “floods” occurring within each shift. The latter condition will show up as points above the action line on both charts. Sampling by the Week Some particulate sampling methods necessitate a minimum sampling duration of 8 hours in order that the sample can be determined with sufficient sensitivity. In order to collect enough samples in a workshop to be representative of average con- ditions, it is necessary to have several instruments being used at the same time and/or to extend each survey over several days. In such situations a workplace may be defined in terms of the area in which people work on one or a group of identical or similar machines. A workplace can then be assigned its dust category, above or below the hygiene standard, according to the time-weighted average concentration of peo- ple working there. This could be determined by sampling continuously or at representative inter- vals during working hours over one week. The sampling should have been carried out at a mini- mum of 5 locations, or at a minimum of 5 loca- tions on successive shifts in the area, each loca- tion being selected to provide a representative sample of air to which one fifth of the employees are exposed or exposed for a fifth of their time. In a workplace where the weekly average ex- posure lies below the TLV, an occasional shift average may exceed the hygiene standard. Ac- cordingly, provided no more than one shift ex- posure exceeds the hygiene standard and the time- weighted average concentration for the workplace does not exceed the hygiene standard, it may be classified favorably. The k — values given in Table 13-1 may be used for deciding whether the grand average allows a favorable report. Sampling by the Quarter Continuous monitoring permits the environ- ment to be assessed at quarterly intervals. Since mineral dust pneumoconiosis are the result of at least some years of exposure, health may be pro- tected provided the quarterly or 6-monthly average mineral dust concentration is below the corres- ponding TLV. Shorter period surveys or sample durations are really only necessary in these circum- stances through the practical inconvenience of the longer period. A workplace may thus be assigned its cate- gory according to the time-weighted average con- centration determined by sampling continuously or at representative intervals during the previous quarter. Time weighted average concentration — Average concentration during working hours X No. of hours worked per quarter 520 Three months is sometimes an inconveniently long time to wait in uncertainty, such as in a new environment, or in a workplace where use of the mineral has just begun, or airborne dust measure- ments have not previously been made. The common situation exists where the mineral is used regularly and is likely to continue in use for some time. In such a situation a procedure is needed which develops into a regular 3-monthly schedule of sampling. However, there are other situations in which the mineral may be used rarely or sporadically or for only a short period, possi- bly for a few days, with no expectation of repeated use. In these cases, there is a need for rules on the acceptable maximum concentration for short periods. At a new workplace, in order to give early warning should the time-weighted concentration be especially high, it should first be assigned a 152 category according to the level of the time- weighted average concentration over a full shift. After one week of sampling it should be reclassi- fied according to the level of the time-weighted average concentration adjusted to 40 hours. Subsequent reclassification might then be made quarterly, based upon results from samples taken during the previous quarter. Provided no more than one week exposure exceeds the hygiene stan- dard and the average for the workplace does not exceed the hygiene standard, it is classified in the favorable category. The spacing of the samples over a 13-week sampling period should be planned in advance. The samples should be taken at regular intervals or at times chosen beforehand, whether the dura- tion of each sample is a few minutes, a shift, a week or even 13 weeks. The longer the duration of each sample and the more samples that are taken, the more accurately will the average con- centration be estimated. Sufficient assurance that the average concentration lies below a given level would be gained by showing that the upper 90% confidence limit of the average lies below that level. In a workplace where the long-term average concentration lies below the threshold limit value, an occasional quarterly average may exceed the threshold limit value. Accordingly, even though the most recent quarterly average exposure ex- ceeds the threshold limit value, an environment could be classified favorably if the time-weighted average concentration during the last four succes- sive quarters lies below the threshold limit value. There are workplaces where the conditions change through applying new methods of work, through replacing machines or through changes in the ventilation systems. A workplace that has un- dergone such changes which may affect its classi- fication should be regarded as a new one. Further, a workplace where the material is used irregularly, or for a few days at a time, or where its regular use cannot be foreseen, should be assigned a cate- gory according to the time-weighted average con- centration over a single workday. References 1. WALTON, W. H. “Factors in the Design of a Mic- roscope Eyepiece Graticule for Routine Dust Counts.” J. of Phys. D: Applied Phys. (formerly: Brit. J. Appl. Phys.), Suppl. No. 3.:29 Instit. of Physics and Physical Soc., 47 Bellgrave Sq., SWI, London, Eng., (1954). DRINKER, P., and T. HATCH, Industrial Dust. McGraw-Hill Book Co. Inc., New York, N. Y., (1954). LIPPMANN, M. “Respirable Dust Sampling.” American Industrial Hygiene Association Journal, 210 Haddon Ave., Westmont, N. J., Vol. 31, p. 138, (1970). THRESHOLD LIMITS COMMITTEE: “Threshold Limit Values of Airborne Contaminants.” American Conference of Governmental Industrial Hygienists, P.O. Box 1937, Cincinnati, Ohio 45201 (published annually). TASK GROUP ON LUNG DYNAMICS: “Deposi- tion and Retention Models for Internal Dosimetry of the Human Respiratory Tract.” Health Physics. P.O. Box 156, East Weymouth, Maryland 02189 Vol. 8, p. 155, (1962). 6. WALTON, W. H. “The Theory of Size-Classifica- tion of Airborne Dust Clouds by Elutriation.” J. of 10. 11. Phys. D: Applied Phys. (formerly Brit. J. Applied Phys.), Instit. of Physics and Physical Soc., 47 Bell- grave Sq., SW1, London, Eng., Suppl. No. 3, 529- 540, (1954). ORENSTEIN, A. J., Ed. “Proceedings of the Pneu- moconiosis Conference held at the University of Witwaterwand, Johannesburg,” Little Brown, Boston, Mass., 9-24 p. 619, February (1959). HAMILTON, R. J. “Inhaled Particles and Vapours II,” Pergamon Press, Oxford, England, (1967). THRESHOLD LIMITS COMMITTEE: “Documen- tation of the Threshold Limit Values for Substances in Workroom Air.” American Conference of Gov- ernmental Industrial Hygienists, P.O. Box 1937, Cin- cinnati, Ohio 45201, (1971). “Air Sampling Instruments.” American Conference of Governmental Industrial Hygienists, 1014 Broad- way, Cincinnati, Ohio, (1971), AEROSOL TECHNOLOGY COMMITTEE, Ameri- 153 12. 13. 14. can Industrial Hygiene Association: “Guide for Res- pirable Mass Sampling.” American Industrial Hy- giene Association Journal, 210 Haddon Ave., West- mont, N. J. 08108, Vol. 31, p. 133, (1970). DUNMORE, J, R. G. HAMILTON and D. S. G. SMITH, “An Instrument for the Sampling of Res- pirable Dust for Subsequent Gravimetric Assess- ment.” J. of Phys. E: Sci. Inst., (formerly J. Sci. Inst), 47 Bellgrave Sq., SW1, London, England, Vol. 41, p. 669, (1964). WRIGHT, B. M. “A Size Selecting Sampler for Air- borne Dust.” Brit. J. Ind. Med., Brit. Med. Assoc. House, Lavistock Sq., London, WC1, England, Vol. 11, p. 284, (1954). ROACH, S. A, E. J. BAIER, H. E. AYER and R. L. HARRIS. “Testing Compliance with Threshold Limit Values for Respirable Dusts.” Amer. Ind. Hyg. Assoc. J., 210 Haddon Ave., Westmont, N. J. 08108, Vol. 28, p. 543, (1967). CHAPTER 14 SIZING METHODOLOGY David A. Fraser, Sc.D. CHARACTERISTICS OF AIRBORNE PARTICLES The most important single parameter useful in predicting or explaining the behavior of airborne particles is a description of their size. This fact can be appreciated more clearly when the wide range of sizes likely to be present is considered. Particle sizes may range from 107° cm. in diame- ter for condensation nuclei to 107 cm., the upper limit for respirable particles, thus covering four orders of magnitude. If the smallest size is vis- ualized as a steel ball 1 mm. in diameter, then at the same scale, the largest size would be 10 meters in diameter. It would be surprising if these parti- cles obeyed the same laws or indeed if they could be measured using the same instrument. If the relative masses of these two particles is considered, the comparison becomes truly astounding (10%). With the same scale a molecule of air would be less than half a millimeter in diameter and the average distance between molecules of air would be approximately 10 cm. Thus, one could vis- ualize particles smaller than 10 cm. on our scale, for example of the order of 0.1 micrometer (0.1 pm), floating about with only occasional contact with molecules of air. When contact did occur, however, the exchange of energy in the collision would be sufficient to alter the course of the par- ticle. On the other hand, a large particle on this scale of perhaps a meter in diameter would be bombarded constantly by air molecules and its motion hindered considerably. In this case how- ever, a collision with a single air molecule would probably go unnoticed. Thus, in attempting to describe the behavior of an airborne particle the most important description has to be its size; many characteristics of dust clouds such as rate of set- tling, agglomeration, Brownian motion, and dif- fusion must be primarily size-dependent. On the other hand, if one wished to compare the behavior of two dust clouds having approxi- mately the same size of particles, other factors could become important. The density of the parti- cles might differ by a factor as high as two or three, and the shape could range from spherical for liquid droplets to needles for fibers or flat platelets in the case of mica or graphite. Certainly these differences would also alter the predicted behavior of the particles, The hazard of airborne particles results from interaction with the tissue of the lung. In order to reach the deep lung, the particles must pass through the nasopharyngeal region, the trachea, and the bronchi. In each of these regions the air- flow is quite turbulent and larger particles tend 155 to be removed by impaction. These particles are transported to the mouth by the mucociliary flow, and therefore enter the gastrointestinal tract. Par- ticles smaller than approximately ten micrometers in diameter, however, can penetrate into the deeper regions of the lung and be deposited where the mechanism for removal involves phagocytosis, a much slower process. Thus the size of particles of concern as a health hazard is generally con- sidered to be below 10 micrometers in diameter. The lower size of the respirable range is less well defined. Particles smaller than a few tenths of a micrometer in diameter are subject to Brownian motion and are deposited in the lung by diffusion with reasonable efficiency. Since it would require millions of these small particles to equal the mass of one 10-micrometer particle the actual dose to the lung may be quite small. There are, of course, certain specific cases as radioactive materials where particles smaller than 0.1m in diameter are most important. Quite apart from physiological considerations there are physical factors which affect the num- bers and sizes of particles found in the air. These particles comprise a dynamic system which is con- stantly changing. Large particles tend to be re- moved rapidly by sedimentation while smaller ones are likely to agglomerate. In the production of small particles from a bulk material the amount of energy required to reduce relatively coarse ma- terial to extremely fine particles may be phenome- nal and therefore many industrial processes such as grinding or crushing may be incapable of pro- ducing particles smaller than 0.1 micrometers in diameter. Welding operations, on the other hand, produce copious quantities of 0.01 micrometer fumes. Any given sample of airborne dust may therefore contain a wide variety of shapes as well as sizes of particulate matter. This, of course, makes a description of par- ticle distribution somewhat difficult. If all the particles were of one size, one would merely have to measure that size to define the distribution. If they were all spherical one could measure a sam- ple of the particles and perhaps report an average size. If the shapes are irregular, however, one must first decide what dimension is to be con- sidered as the particle diameter. Three possi- bilities are shown in Figure 14-1. Martin’s diam- eter is the length of a line which divides the par- ticle into two equal areas. This line could be drawn in any direction for the first particle to be measured, but all other particles should be meas- ured in a direction parallel to the first. If the par- ticles are randomly oriented and a large number 9¢1 MARTIN'S DIAMETER FERET'S DIAMETER PROJECTED AREA DIAMETER Figure 14-1. Geometric Diameters for Irregularly Shaped Particles are measured, the direction of measurement is not important. Feret’s diameter is the distance between the extreme boundaries of the particle. Again all measurements should be made in the same direction. The projected area diameter is the diameter of a circle having the same cross-sec- tional area as the particle. Other possibilities would be to measure the longest or shortest di- mension of the particle. Estimates of the aver- age size obtained by measuring the shortest di- ameter would yield the smallest value. Mar- tin’s diameter would be followed next by the projected area diameter and Feret's diam- eter. Measuring the longest dimensions would yield the greatest average diameter. Which then would be nearest to the correct or most useful estimate? Obviously neither the shortest nor the longest dimensions accurately describe the mass of the particles measured although recent work has indicated the smallest dimension may most nearly predict the aerodynamic behavior of fibrous par- ticles. Martin’s diameter would seem to under- estimate the true size and Feret’s diameter would appear to be an over-estimate. The projected area diameter therefore would seem to offer the best estimate of the true size. It is worth noting that for spherical particles all of these estimates would be the same. This statement may take on more significance when one realizes that as particle-size decreases all particles tend to approach the spheri- cal or at least an isometric shape. 50 + 40 + 30 + NUMBER o 20+ o STATISTICAL CONSIDERATIONS A sample of airborne dust will always yield particles of many different sizes and therefore can be called polydisperse. When we consider the be- havior of airborne particles, the degree of this polydispersity is usually far more important than factors of shape and perhaps even density. There- fore a simple statement of the average diameter is not very useful in describing these particles. It would indeed be desirable to also be able to de- scribe the degree of polydispersity. If we would assume that the sizes of the particles followed the normal or Gaussian distribution (bell shaped) we could use the powerful techniques of statistics to describe and analyze the distribution’. Thus we could say that 67% of all the particles had sizes falling between the limits of plus or minus 1 stan- dard deviation from the mean, 95% between plus or minus 2 standard deviations and 99.7% be- tween plus or minus 3 standard deviations. The average size of the distribution would be given simply by: where d is the average size of the distribution, and N; is the number of particles of size d;; the stan- 5 6 7 8 9 10 SIZE - MICROMETERS Figure 14-2. Log — Normal Size Distribution 30 =} ge + ls lL fe PARTICLE DIAMETER - MICROMETERS —_— | ti frmmeffrm} frre] I 2 5 10 20 30 40 50 60 70 8 90 95 98 99 CUMULATIVE % LESS THAN OR EQUAL TO STATED DIAMETER Figure 14-3. Summated Size-Number, Size-Surface and Size-Mass Distributions Plotted on Log-Probability Paper 158 dard deviation would be a measure of polydis- perity: a g= (Edi — dD Niy1/2 YN-1 Unfortunately, the particle sizes of most aero- sols are not normally distributed due to the loss of larger particles by sedimentation and other fac- tors mentioned above. Instead the curve is us- ually skewed toward the smaller sizes. A typical skewed distribution is shown in Figure 14-2; the data is given in Table 14-1. Hatch* showed, how- TABLE 14-1: Particle-Size Distribution size-um number In Y% 0.5 10 10 5 0.7 22 32 16 1.0 26 58 29 1.4 29 87 43 2.0 37 124 62 2.7 28 152 76 3.8 22 174 87 5.4 14 188 94 7.7 8 196 98 10.9 4 200 100 ever, that if one plotted the logarithm of the par- ticle size instead of the actual size the result closely approximated a normal distribution. Thus, we can say that: d= 1 IN, log d; =o (Sgn and _ go ide Y (log d; — log d)*N;\ 1/2 g IN, —1 ) We are saying that the log-normal distribution pro- vides a reasonably good approximation of the particle-size distribution usually found in airborne dusts. It should be noted, however, that other possibilities do exist and such occurrences as bi- modal distribution or the mixing of dusts from two entirely different sources (smoke and dust for in- stance) happen frequently. If we accept the log-normal distribution as rep- resenting the actual size-distribution of airborne particles, we can simplify our calculations by re- sorting to a graphical solution. If we plot the summated size-distribution on logarithmic-prob- ability paper, the result should be a straight line if the assumption of a log-normal distribution is correct. The lower line of Figure 14-3 is such a plot of the data from Figure 14-2. From this graph we can read directly the median or 50% size. In the illustration 50% of the particles are larger than 1.5 micrometers and 50% are smaller. We can also read any other points on the curve. 80% of the particles measured were smaller than 3.0 micrometers in diameter and 95% were smal- ler than 5.0 micrometers. As a measure of the polydispersity we can also find the standard devia- tion by dividing the 84.13% size by the 50% size, in this case 3.4 micrometers, divided by 1.5 micrometers gives a standard geometric deviation, og, of 2.26, a dimensionless number. The same value for gy could, of course, be obtained from the other end of the curve by dividing the 50% size by the 15.87% size. The standard geometric deviation therefore represents the slope of the line and along with the median size is sufficient to describe the distribution. The log-probability distribution described above is expressed mathematically as follows: _ IN (log d — log dg)? FO = igo VE 2 log? my where F(d) is the frequency of occurrence of the diameter d, LN is the total number of particles, a, is the standard geometric deviation and dg; is the geometric mean diameter. This function pre- dicts the existence of all sizes of particles from zero to infinity. Since the number of particles contributing to the extremes of the distribution is small, the confidence bands around the two ends of the line are wide and become narrowest at the 50% size. It can be shown that in order to esti- mate the median size within 10% of the true mean with 95% confidence, a minimum of 200 particles must be measured. If, on the other hand, we wished our estimate of the median size to be within 5% of the true mean with the same degree of confidence, we would have to measure at least 1000 particles. In the example given above we estimate the median size to be 0.15 microm- eters. For most purposes this is an adequate esti- mate and therefore the measurement of 200 par- ticles is sufficient. The number-size distribution of the particles having been established, other parameters of in- terest can also be determined. If we wished to examine the distribution of mass among these particles, assuming a constant density, we could multiply the frequency of occurrence of particles in each of our size ranges by the cube of the aver- age diameter for that range and summate these weighted frequencies. This is shown in Table 14-2. TABLE 14-2: Size-Mass Distribution Data size n d d? dn Xdn X%dn 0.5 10 0.25 0.02 02 .02 00 0.7 22 0.6 0.22 4.9 5.1 0.0 1.0 26 0.85 0.61 16. 21.1 0.3 1.4 29 1.2 1.7 46. 67.1 0.8 2.0 37 1.7 6.1 230. 297.1 3.0 2.7 28 23 10.2 290. 587.1. 17.0 3.8 22 32 32.0 700. 1287.1 16.0 54 14 46 93.0 1300. 2587.1 33.0 7.7 8 6.5 260. 2100. 4687.1 59.0 109 4 9.3 790. 3200. 7887.1 100.0 Plotting these data as summated percentages on log-probability paper produces a curve which rep- resents the mass distribution of the aerosol. This is plotted as the upper curve of Figure 14-3. From this curve we can obtain the mass-median diam- eter or the size below or above which half of the mass of the particles would occur. It should be noted that had the density of the particles been included in weighting each frequency range in the above calculation, the density factor would have cancelled when dividing through by the grand summation to reduce the data to percentages. It is also apparent that the standard geometric devi- ation of the size-mass distribution (the slope of the line) is identical to that of the number distri- bution. The size-mass distribution is often useful in predicting the actual dose to the lung resulting from the inhalation of a given amount of dust or the weight of material collected by a filter or other collection device which is efficient only for par- ticles larger than a given size, A similar technique can be used to describe the distribution of surface-area for the particles in question, assuming spherical symmetry of the particles. In this case the number-frequency of particles in each range is weighted by multiplying by the square of the average diameter of the range. This has been done in Table 14-3 and plotted as TABLE 14-3: Size-Surface Distribution sizz nd d: dn Yd:n X%dn 0.5 10 0.25 0.06 0.6 0.6 0.04 0.7 22 0.6 0.36 7.9 8.5 0.6 1.0 26 0.85 0.72 19. 27.5 2.0 1.4 29 1.2 1.4 41. 68.5 6.8 2.0 37 1.7 3.6 140. 208.5 14.8 2.7 28 23 5.3 149. 357.5 25.3 3.8 22 3.2 10.0 220. 577.5 40.8 5.4 14 4.6 20.1 180. 757.5 53.5 77 8 6.5 40.2 320. 1077.5 76.0 109 4 9.3 83.0 332. 1409.5 100.0 the middle line of Figure 14-3. The surface-area distribution is sometimes useful in comparing or predicting surface related phenomena such as the scattering of light, adsorption of vapors or the reaction of insoluble particles with biological tis- sues. Hatch* has proposed equations which per- mit the direct calculation of the mass-median (M;) and surface-median (S,;) diameters from the size-median diameter without the weighting pro- cedures described above. The most important of these is given below: log M;=log d; + 6.9078 log*o, Since o, is the same for the mass and number distributions, calculation of M; permits the curve describing the entire mass distribution to be drawn immediately. MEASUREMENT TECHNIQUES The technique of measuring the size of air- borne particles has to begin with the selection of 160 the sampling instrument. The factors which must be considered to prevent bias of the sample in favor of either larger or smaller particles have been described in Chapter 13. Once a representa- tive sample has been obtained a specimen of this must be prepared for observation and measure- ment using a standardized technique. Care must be taken that the preparation of this specimen and the measurement technique itself does not intro- duce bias and destroy the representative nature of the specimen, Optical Microscopy In order to serve as a standard method in the field of Industrial Hygiene, a technique should be suitable for use generally in laboratories across the nation. This may preclude the use of certain exotic instruments that are so expensive or compli- cated that they are found only in a few highly specialized laboratories. For the counting and sizing of airborne dust particles, the optical micro- scope is usually available and can be operated by a trained technician. For particle-size analysis any good quality clinical microscope is adequate. Be- cause the size of the smallest particles to be meas- ured will approach the theoretical limit of resolu- tion of the optical system, the illumination either built into the microscope or provided by the oper- ator should meet the requirements of either Kohler or critical illumination. Thus the operator must have some knowledge of the optical system that he will use. The optical microscope’ is comprised of five basic components: (1) the light source, (2) the condenser lens which focuses the light on the specimen, (3) the specimen stage which holds and makes possible movement of the specimen, (4) the objective lens which produces an intermediate and magnified image of the object and (5) the ocular which further magnifies the intermediate image and presents it as a virtual image to the eye. The heart of the instrument is the objective lens, for the quality of the final image can be no better than that of the intermediate image produced by this lens. The quality of the image is better de- scribed as the resolution or fineness of detail that is preserved by this lens. The limit of resolution is given by the Abbé equation: 0.61) d=— 7 SIN a where d is the shortest distance separating two fine lines at which the two lines can still be dis- tinguished; A is the wave-length of the light used; n is the index of refraction of the medium between the specimen and the lens; and « is the half angle subtended between the axis of the optical system, the periphery of the lens and the specimen. It is, therefore, the maximum angle through which the lens can receive light from the specimen. This angle, of course, can not exceed 90° or the speci- men would have to be inside of the lens. The sine of a can approach 1.0 as a limit and is usually 0.94 for a high magnification lens. The index of re- fraction of the medium is also limited, being 1.0 for air, 1.33 for water and 1.515 for the usual immersion oils. The product of the index of re- fraction and the sine of « is called the numerical aperture (N.A.) of the lens. This will range from 1.25 for a high magnification (97x) oil immersion lens to less than 1.00 for a low power lens. The wavelength of the light used is limited to the visi- ble spectrum. Thus the shortest visible wavelength will be at the violet end of the spectrum and of the order of 400 millimicrons. Substituting these values in the Abbé equation shows that the theo- retical limit of resolution for any optical lens must be approximately 200mu (0.2 yum). In order to attain this, however, the full numerical aperture of the lens must be utilized, and this is possible only with a condenser lens having a high numerical aperture and either Kohler or critical illumination. In addition to this the objective lens must be of high quality and corrected for chromatic abbera- tions for three colors. Such a lens is called an apochromatic objective. - The quality of the ocular is somewhat less im- portant. The limit of resolution of the eye is us- ually taken to be approximately 0.1 mm. If the finest detail in the specimen is magnified to 0.1 mm, it will be discernible to the eye. Therefore, the finest detail resolvable by the objective lens (0.2 um) has to be magnified only 500 times in order to be visible. If the high-dry objective (us- ually 46x) were used, a 10x ocular would accomp- lish this since the overall magnification would be 46x10 or 460. Certain refinements which are available in oculars such as wide field, flat field (for photographic purposes), high eyepoint (for people who wear glasses) and higher magnifica- tions (15-20x) may be desirable and convenient even though they may contribute little to actual improvement of the image. Preparation of Specimens Given a satisfactory optical system, the speci- men must be suitably prepared for observation and measurement. The sample may have been obtained in the same manner as described in Chap- ter 13 for dust counting, with either the midget impinger or a membrane-filter. In either case the sample would be prepared in the same manner in the Dunn cell or the haemocytometer or by using the proper immersion fluid to render the membrane-filter transparent. There is no need to relate the sample used for size analysis to any particular volume of air, and it is often convenient, therefore, to collect separate samples for size an- alysis in order to obtain a greater number of par- ticles. Occasionally, one may be working with a bulk sample of material, and in this case great care must be taken to spread a representative sam- ple uniformly on a microscope slide in such a man- ner that bias is not introduced by selectively re- taining the small particles on the glass surface. It must be remembered that the collection of the sample resulted in the concentration of the par- ticles either on a surface or in a liquid and thus may have resulted in agglomeration or other change from the airborne state. It may, therefore, be necessary to subject the particles to a deag- glomeration procedure such as insonation in an ultrasonic generator prior to the preparation of the final specimen. In general it is felt that collection 161 on the membrane filter causes less change from the airborne state than other methods. Reticles and Calibration When the specimen has been properly pre- pared on the microscope slide it must be focused in the field of the microscope. Actual measurement then consists of superimposing on the field a suit- able scale, reticle or measuring device. The first device that was used intensively for this purpose was the Filar micrometer. It is, in fact, a substi- tute eye piece which superimposes on the field a scale comprised of 100 units. Part of this scale is a movable verticle cross-hair which is controlled by a micrometer screw thread connected to a drum dial. The circumference of the drum dial is divided into 100 units and can be read to 0.1 unit by means of a vernier. One complete rotation of the drum dial (100 units) moves the cross-hair one division of the field scale. In practice the cross-hair must be moved in one direction until it just touches one boundary of the particle to be measured. A reading of the drum dial is taken and the traverse continued until the other side of the particle is reached. The difference between the two drum dial readings gives the Feret’s diameter of the particle in units. A minimum of 200 par- ticles are measured in this manner. The Filar micrometer, however, is a tedious instrument to use. The measurement of Feret’s diameter obtained with this instrument is less representative as the particles depart from isome- tric. For these reasons reticles which are more easily used have come into favor. The most common of these is the Porton ret- icle which is named after the research group in England that was responsible for its design. It consists of a photographically reduced and repro- duced transparent grid which is mounted exactly in the focal plane of either the Hygens or the Ramsden ocular. The grid is thus superimposed on the field of the microscope. A picture of this grid superimposed on a dust specimen is shown in Fig- ure 14-4. It consists of a large rectangle one half of which is divided into six smaller rectangles. Along the top and bottom of the rectangle are a series of circles or dots of increasing size. The diameter of each dot is larger than the previous one by the square-root of two. Thus the diameter of any circle in Porton-units is given by: d= y2» where n is the number of the circle. The height of the large rectangle is 100 units and its length is 200 units. Either the length or height can be cali- brated against a stage micrometer to determine the value of one Porton unit in micrometers. Measure- ments are made by comparing the size of the par- ticles with the circles to find the circle that would completely enclose the particle. This can be done visually and without superimposing the circle on the particle by moving the stage of the micro- scope. Therefore, all particles contained in the area defined by the six smaller rectangles can be sized before moving on to a new field. This tends to minimize the possible bias of sizing only the larger particles. There is, of course, a natural tendency to equate projected areas of the particles Figure 14-4. and circles. In many cases this projected area diameter is more desirable than Feret’s diameter. The entire analysis can be done by one operator and only one reading is required for each meas- urement. The calibration of any reticle placed in the optical system consists of comparing that reticle to a stage micrometer substituted for the actual specimen and using exactly the same optics that are used for measurement. Thus one cannot cali- brate the optical system using the 10x objective and then switch to the 46x or oil immersion objec- tive to size the particles. Nor can a calibration be transferred from one microscope to another even if similar lenses are used. The tube length of the microscope on older models can sometimes be adjusted to make the calibration result in even numbers. It is good practice, therefore, to include the calibration data with each size analysis and also, if possible, a photo-micrograph superimpos- ing the reticle directly on the image of the stage micrometer so that the reader can see for himself that the calibration is at least approximately correct. The Porton Reticle 162 Superimposed on a Dust Field RELATED TECHNIQUES Although the standard method for particle- size analysis with the optical microscope is usually adequate to describe the implication to health of airborne particles, there may be special situations which require the application of more sophisti- cated techniques. Smoke and fume particles may well lie below the limit of resolution of the optical system. Continuous monitoring using automated instrumentation and an immediate readout may be desired. It is appropriate therefore to describe a few of the techniques which may be useful in re- search or specialized field application. The Electron Microscope! Because of the short wavelength associated with a beam of electrons, the theoretical limit of resolution of the electron microscope is extremely small. In practice resolution between 10 and 20 angstrom units is readily attainable. Physically the electron microscope is quite analogous to the op- tical microscope. It consists of a heated filament which is the source of electrons, a condenser lens, a mechanical stage, an objective lens, a projector lens and a fluorescent screen which converts the electron image into visible light. Electrons, hav- ing both mass and charge, have a short path length or penetrating power through any medium, and a high vacuum is necessary if they are to travel the length of the microscope column. Since the speci- men must be placed in the vacuum, only dry non- volatile materials can be examined. These must be extremely thin (0.1u or less) and be supported on a thin film of low density material. Classically, films of collodion or Formvar (R) approximately 100 A° thick are used to support the specimen. These films in turn are supported on 200 mesh grids of copper or stainless steel ¥8 in. in diameter. Preparation of the specimen consists of trans- ferring the airborne particles which may have been collected by a technique described in Chapter 13 to a previously prepared film and grid. Because of the high magnification of the electron microscope and consequently the small field to be observed, the preparation of the specimen without introduc- ing bias is more critical than in the case of optical microscopy. ‘The particular technique will de- pend on the method that was used to collect the sample. If the dust sample was collected in water by impingement, a drop of the particulate suspen- sion may be placed on the grid and allowed to evaporate to dryness. If a bulk sample of insolu- ble dust is to be examined, a dilute suspension of the particles in distilled water may be prepared. Insonation by ultrasonic energy is often useful to deagglomerate the particles. If the sample has been collected on the membrane filter, it may be transferred to a grid by placing a small piece of the filter face down on a Formvar (R) grid and removing the filter media by solution in ethyl ace- tate as described by Fraser.” Airborne dusts or fumes may be deposited directly on the filmed grids by electrostatic or thermal precipitation. In each case, however, the size distribution may be altered.” Shadow-casting, the technique of evap- orating a thin film of metal on the specimen from a low angle, can be used effectively to enhance the detail and increase the contrast of any of the above preparations. Impaction Devices Impingement implies the collection of particles in a liquid medium. Impaction, on the other hand, describes the deposition of particles on a dry (or adhesive coated) surface. If air moving at high velocity is forced to change direction abruptly by an obstacle, particles entrained in the air may be unable to follow the air stream and, due to their momentum, may collide with the barrier. If in a single instrument air is drawn through a series of orifices of decreasing size, the velocities attained will increase as the cross-sectional area of the ori- fice decreases. With increasing velocity, smaller particles will be forced to collide with an obstacle such as a microscope slide placed in the path of the jet. Only large particles will be deposited on the first stage of this device while smaller particles will deposit on subsequent stages. Such a device is called a “cascade impactor” and is used to col- lect particles in various size fractions. It should be noted that the range of sizes collected on each stage depends on the density and shape of the particles as well as the diameter and therefore 163 represents the aerodynamic behavior of the par- ticles. The number or weight of particles col- lected on each stage can be determined by count- ing, using an optical microscope, by weighing or by chemical analysis. If the density of the dust is known and a size-distribution is obtained for each stage, a relationship can be calculated which will permit one to predict what size of particles will be deposited on each stage for dusts of differ- ent densities. For subsequent analyses it is only necessary to determine the mass of material col- lected on each stage in order to describe the par- ticle-size distribution. The volume flow of air through the device must of course, be kept con- stant. Because of the varieties of sizes, shapes and densities of airborne particulates inertial impactors are usually calibrated with reference to a stan- dard material. If this standard consists of spherical particles having a density of 1 gm/cc (polysty- rene latex balls), then in subsequent analyses par- ticles of irregular shapes and varying densities will be classified according to their aerodynamic equivalence to these unit density spherical particles. A recent innovation has been the Anderson sampler which is a multi-orifice cascade impactor. A number of orifices of the same size are arranged in concentric circles on each stage. Orifice diam- eters decrease for each succeeding stage and the diameters of the circles in which they are arranged are staggered on alternating plates; thus the orifice plate serves as the collecting plate for the preced- ing stage. This design has a number of advan- tages over single jet impactors. The multiple jets permit large air flows and the collection of larger samples. The plate construction can be quite thin and light-weight permitting more sensitive weigh- ing. The instrument has fewer parts and each time the plates are cleaned the jets are also cleaned. The orifices are circular and therefore the machin- ing can be more precise and the calculations simp- ler. There is a minimum size of particle which can be collected by inertial impaction. This is the smallest particle that can be collected when the air passing through the jet reaches sonic ve- locity. This maximum velocity limits the collec- tion of particles by this technique to those larger than a few tenths of a micrometer in diameter. It may be desirable to follow the cascade impactor with a membrane filter or an electrostatic precipi- tator to collect smaller particles. Centrifugal Collectors Centrifugal classifiers or cyclone separators have been used commercially for many years to provide aerodynamically sized fractions of bulk materials. In sampling technology they are gen- erally used as pre-filters to eliminate particles larger than the respirable size. In a few instances the technique has been used to provide informa- tion concerning the size of airborne particles. When an air stream containing dust is forced to follow a circular path, the particles experience a centrifugal force which tends to move them across the stream lines toward the outer wall of the vessel or duct. The centrifugal force increases as the radius of curvature decreases. In the cy- clone collector the air stream is introduced tan- gentially into the widest section of a cone and forced to follow a spiral path of decreasing radius of curvature to the apex of the cone. Thus the centrifugal force increases to a maximum at which point all particles larger than a minimum size will intersect the wall of the cone and be collected. The minimum size that will be collected depends on the dimensions of the cone, the inlet velocity of the air and the distance that the particle must travel perpendicular to the direction of the air flow in order to reach the side. The greatest effi- ciency will be provided by a long narrow cone operating at high air velocity.” For any given cyclone the minimum size can be increased or decreased by varying the air velocity. Goetz de- signed an aerosol spectrometer which passed the air in a narrow channel between two concentric rotating cones so that the larger particles were eliminated at the larger end and smaller ones were deposited near the apex. By examining the surface of the outer cone and measuring the dis- tance between the point of inlet and point of deposition, and knowing the speed of rotation and therefore the centrifugal force, he was able to calculate the aerodynamic size of the particle. This instrument was particularly useful in investi- gating the effect of air, temperature and humidity on the size of particles. Light Scattering In the search for automated techniques, instru- ments which can detect light reflected or scattered from the surface of airborne particles have been developed. A major advantage of such a tech- nique is that the particles need not be collected but are examined in their airborne state. These instruments may respond to light scattered by all particles contained in a fixed volume or the light from individual particles. While the former are sensitive to changes in the number of particles. they are of little use in determining the size of the particles since many small particles may scatter the same amount of light as a few larger ones. Since the light from a discrete particle is reflected from its surface, it can be related to its size. This, however, is not a simple relationship since light may also be diffracted by the edge of the particle or adsorbed a specific wavelength by colored particles. This is further complicated when the particle-size approaches the wavelength of the light. Thus the intensity of light scattered depends on the angle of observa- tion relative to the direction of the incident beam, the greatest intensity usually being observed in the forward direction or looking back toward the light source. The original theory of light scattering was described by Rayleigh for large particles and by Mie for small particles approaching the wavelength of light.* Mathematical functions and tables have been constructed to describe the light scattered at various angles by transparent isotropic spheres. This is, of course, most useful, but one has only to consider the effect of particle shape ranging from flat platelets to long fibers to imagine the com- plexity of the practical situation. In spite of this, light-scattering devices can be calibrated empiri- cally for a particular dust with a standard chemical or optical method and can be extremely useful for 164 routine monitoring of clean rooms, animal inhala- tion chambers, certain industrial processes and testing of filter penetration. Measurement of Electrical Charge Airborne particles undergo a continuous bom- bardment of approximately 10° collisions per sec- ond by the molecules which comprise the air. If a portion of these molecules are electrically charged ions, this charge will be transferred to the particles and if the ions are unipolar the particles assume this polarity. Due to the coulom- bic force of repulsion between like charges this charge will be distributed on the surface of the particles. The first ions which approach the neu- tral surface experience no repulsive force but as the total charge on the particle increases additional ions approaching the surface must overcome a force of repulsion if contact is to be made with the surface. It is apparent that there will be a maxi- mum number of charges that a particle can accept for a given concentration and energy of the ions in its environment. This maximum will be a func- tion of the surface area of the particle. A charged particle which finds itself in an electrostatic field between two plates will migrate toward the plate of opposite polarity. The velocity that it attains will depend on the field strength as well as the charge to mass ratio of the particle. Since the ratio of the surface to the mass is great- est for small particles, this will also be true for the charge to mass ratio. Small particles will there- fore have a greater mobility in the electrical field than larger ones. In recent years instruments have been devel- oped to take advantage of the phenomena to clas- sifiy particles according to their size.” The air- borne particles are first subjected to a dense con- centration of unipolar ions. Maximum charging of the particles can usually be attained in a few milliseconds. They are then passed between a series of plates each of which subjects the parti- cles to an electrostatic field of increasing strength. Thus the free ions will be eliminated by the first field while small charged particles will be collected by the next, and larger particles by subsequent plates. A sensitive electrometer connected to each of the plates can measure the electrical current collected at each stage. Thus the fraction of the current flowing in each stage becomes a measure of the number of particles of each size that com- prise the overall particle-size distribution. The major advantage of the charge measuring technique is its ability to cope with the total range of particle sizes from air ions to large dust parti- cles and its great sensitivity for the smallest parti- cles. The equipment, however, is extremely com- plicated and expensive, and it is not now feasible to use it as a field instrument. SUMMARY Information concerning the distribution of air- borne particles can be obtained by means of a variety of methods and techniques which measure any one of several physical properties of the par- ticles. The interpretation of the results from measuring different physical properties may be quite different and not necessarily comparable. It is most important, therefore, that the sampling device, the measurement technique, and the param- eter measured be chosen with careful considera- tion of the application to be made of the data. It is often true that as the sophistication of the instrumentation increases, the actual parameters measured become more obscure. The industrial hygienist should be thoroughly familiar with the basic concepts and the relatively simple techniques that can be used for estimating the size of airborne particles, since these provide a basis for standardi- zation of automated equipment and a solution to problems when such equipment is not available. References 1. HERDAN, G. Small Particle Statistics, Academic Press, Inc., Butterworths, London, 1960. HATCH, T. F. and P. GROSS. Pulmonary Deposi- tion and Retention of Inhaled Aerosols, Academic Press, N. Y., 1965. . NEEDHAM, G. H. The Practical Use of the Micro- scope, Charles C. Thomas, Springfield, Ill., 1958. . WYCOFF, R. W. G. The World of the Electron Microscope, Yale University Press, New Haven, Conn., 1958. FRASER, D. A. “Absolute Method of Sampling and Measurement of Airborne Particulates,” Arch. Ind. Hyg. and Occ. Med. 8, 412 Chicago, Ill. (1953). CARTWRIGHT, J. and J. W. SKIDMORE. “The Size Distribution of Coal and Rock Dusts in the Electron and Optical Microscope Ranges,” Ann Occ. Hyg. 3, 33 (1961). DAVIES, C. N. “The Separation of Airborne Dust and Particles,” Proc. Inst. Mech. Engrs. 1B, 185-198, 1952. GREEN, H. L. and W. R. LANE. Particulate Clouds, Dusts, Smokes and Mists, 2nd Ed., Van Nos- trand, Princeton, New Jersey (1964). WHITBY, K. T. and W. E. CLARK. “Electrical Aerosol Particle Counting and Size-Distribution 2. 165 Measuring System for the 0.015 to 1 ym Size Range,” Tellus 18, 573 (1966). RECOMMENDED READING Books FUCHS, N. A. The Mechanics of Aerosols, Per- gamon Press, London (1964). . DAVIES, C. N. (editor) Aerosol Science, Academic Press, London (1966). . SINCLAIR, D. Handbook on Aerosols, US.A.E.C., Washington, D. C. (1950). DAVIES, C. N. (editor) Inhaled Particles and Vapor, Pergamon Press, Oxford (1961). MERCER, T. T. (editor) Assessment of Airborne Particles, Charles C. Thomas, Publisher, Fort Laud- erdale (1971). GREEN, H. L. and W. R. LANE. Particulate Clouds: Dusts, Smokes and Mists, 2nd Ed., E. & F. N. Spon, Ltd. London (1964). DRINKER, P. and HATCH, T. F. Industrial Dust, 2nd Ed., McGraw Hill, New York (1954). HERDAN, G. Small Particle Statistics, Pub. Co., New York (1953). REIST, P. C. An Introduction to Aerosol Science, Academic Press, New York (in preparation). MERCER, T. T. Aerosol Technology in Hazard Evaluation, Am, Ind. Hyg. Assoc. Westmont, New Jersey (in preparation). Periodic Publications Journal of the American Industrial Hygiene Assoc. Journal of the Air Pollution Control Assoc. Staub British J. Applied Physics Environmental Science and Technology Review of Scientific Instruments Health Physics British Journal of Industrial Medicine Annals of Occupational Hygiene Journal of Colloid Science Elsevier 10. SexNAUr en ~ — CHAPTER 15 SAMPLING AND ANALYSIS OF GASES AND VAPORS Leonard D. Pagnotto and Robert G. Keenan INTRODUCTION This chapter deals principally with manual methods of sampling and analysis of industrial atmospheres for gaseous and vaporous contam- inants (see Chapter 10 for a discussion of the “General Principles in Evaluating the Occupa- tional Environment” and Chapter 16 for the dis- cussion on “Direct Reading Instruments for De- termining Concentrations of Aerosols, Gases and Vapors”). For industrial hygiene purposes, a substance is considered to be a gas if this is its normal physical state at room temperature and atmospheric pres- sure; it is called a vapor if, under the environ- mental conditions, a conversion of its liquid or solid form to the gaseous state results from its vapor pressure affecting its volatilization or sub- limation into the atmosphere of the container, the process equipment, or the workroom. In this chapter the term “gaseous” is used therefore in a general sense in discussing gases or vapors. Basic Sampling Techniques There are two basic methods for the collection of gaseous samples. The first involves the use of a gas collecting device, such as an evacuated flask or bottle, to obtain a definite volume of an air-gas mixture at a known temperature and pressure. This type of sample is called a “grab” or “instan- taneous” sample as it is collected almost instan- taneously, i.e., usually within a few seconds to 1-2 minutes maximum, and is thus representative of the atmospheric conditions at the sampling site at a given point in time. This method is used when the atmospheric analyses are limited to such gross contaminants as mine gases, sewer gases, carbon dioxide and carbon monoxide (above 0.2 percent) and other situations where the concen- trations of contaminants are in the percentage range. However, with the increased sensitivity of modern gas chromatographic, infrared and other analytical techniques, instantaneous sampling of ever lower concentrations of atmospheric contam- inants is becoming more feasible. The collectors are resealed immediately after sampling to prevent any losses of the sample by diffusion. The second method for the collection of gas- eous samples involves the passage of a known volume of air through an absorbing or adsorbing medium to remove the desired contaminants from the sampled atmosphere. This technique provides a sample of the atmosphere over a recorded time period and is termed “integrated sampling.” The contaminant which is removed from the air stream becomes concentrated in/on the collecting me- 167 dium; the sampling period is chosen to permit the collection of a sufficient quantity of the contam- inant for the subsequent analyses. Sampling Criteria Whereas airborne particulate substances are readily scrubbed or filtered from sampled air streams due to their larger physical dimensions and to the operation of agglomerative, gravita- tional or inertial effects, gases and vapors form true solutions in the atmosphere and thus require either sampling of the total atmosphere using a gas collector or the use of a more vigorous scrub- bing technique to separate the gas or vapor from the surrounding air molecules. Selected sampling reagents which react chemically with contam- inants in the air stream can improve the collection efficiencies of the sampling procedures. In devis- ing an integrated sampling scheme, it is essential to consider the following basic requirements: 1. Provide an acceptable efficiency of collec- tion for the contaminant(s) involved; Maintain this efficiency at a rate of air flow which can provide sufficient sample for the intended analytical procedure(s) in a rea- sonable and acceptable period of time; Retain the collected gas or vapor in a chemical form which is stable during trans- port to the laboratory or other analytical site; Provide the sample in a form which is suit- able for the analytical procedure(s); Require minimal manipulation in the field; Avoid the use of corrosive or otherwise hazardous sampling media if possible. Whereas most of these criteria are self-explan- atory, some elaboration on the first and second is desirable. It is extremely important that the col- lection efficiency of a sampling system be known, either from published, well-documented data, as summarized in Table 15-1 for a variety of com- mon contaminants found in industrial atmos- pheres, or as a result of an independent evaluation as an essential part of planning a future survey. In making such an evaluation, known concentra- tions of gases and vapors must be prepared (see Chapter 12) and used in a dynamic or static test system to determine the efficiency of the proposed sampling device. The efficiency must be defined in terms of such variables as the type of scrubber, porosity of frits used in the scrubber, size of scrubber, the height, volume, nature, and temper- ature of the collecting medium, rate of air flow, stability of the sample during collection, losses by adsorption on the walls of the probe, connecting 2. 4. 5. 6. TABLE 15-1 Collection and Analysis of Gases and Vapors Air Minimum Sorption Flow Sample Collection Inter- Gas or Vapor Sampler Medium (L/m) (L) Efficiency Analysis ferences Ref. Ammonia Midget 25 ml O.IN 1-3 10 +95 Nessler en (13) Impinger Sulfuric Reagent Acid Petri 10 ml of 1-3 10 +95 " RU Bubbler above Benzene Glass 5 ml Nitra- 0.25 3-5 +95 Butanone Other Aro- (15) Bead ting Acid Method matic Hy- Column drocarbons Carbon Fritted 10mlO.1 N 1 10-15 60-80 Titra- Other Acids (13) Dioxide Bubbler Barium with 0.05N Hydroxide Oxalic Acid Ethyl Fritted 15 ml Spec- 1 20 +90 Alcohol Other Aro- (26) Benzene Bubbler trograde Extraction, matic Hy- i or Isooctane Ultraviolet drocarbons Midget Analysis Impinger Formalde- Fritted 1% 1-3 25 +95 Liberated Methyl (13) hyde Bubbler 10 ml Sulfite Ti- Ketones Sodium trated, 0.01 Bisulfite N Iodine Hydrochloric Fritted 0.005 N 10 100 +95 Titration Other (13) Acid Bubbler Sodium 0.01 N Chlorides Hydroxide Silver Nitrate Hydrogen Midget 15 ml 5% 1-2 20 +95 Add 0.05 N Mercaptans, (13) Sulfide Impinger Cadmium Iodine, 6N Carbon Sulfate Sulfuric, Disulfide, back titrate Organic 0.01 N Sulfur Sodium Compounds Thiosulfate Lead, Tetra- Dreschel 100ml 0.1M 1.8-2.9 50-75 100 Dithizone Bismuth, (27) ethyl, Tetra- Type lodine Mono- Thallium, methyl Scrubber chloride in Stannous 0.3N Hydro- Tin chloric Acid Mercury, Midget 15 ml of 1.9 50-75 91-95 Same as Same as Diethyl and Impinger above Above Above Dimethyl : sel] Midget 10 ml 0.IM 1-1.5 100 91-100 Dithizone Copper (28) Impinger lodine Mono- chloride in -3N Hydrochloric Acid Nickel Midget 15 ml 3% 2.8 50-90 +90 Complex er (29) Carbonyl Impinger Hydrochloric with alpha- Acid Furil- dioxime 168 TABLE 15-1 (cont'd) Collection and Analysis of Gases and Vapors Air Minimum Sorption Flow Sample Collection Inter- Gas or Vapor Sampler Medium (L/m) (L) Efficiency Analysis ferences Ref. Nitrogen Fritted 20 - 30 ml 0.4 Sample 94-99 Reacts Ozone in (30) Dioxide Bubbler Saltzman until with 5 fold (60-70 Reagent* color Absorbing excess micron appears Solution Peroxyacyl pore Probably Nitrate size) 10 ml of Air Ozone Midget 1% Potas- 1 25 +95 Measure Other (31) Impinger sium Iodide Color of oxidizing in IN Iodine agents Potassium Liberated Hydroxide Phosphine Fritted 15m 0.5% 0.5 5 . 86 Complexes Arsine, (32) Bubbler Silver Diethyl with Stibine, Dithiocar- Absorbing Hydrogen bamate Solution Sulfide in Pyridine Styrene Fritted 15 ml Spec- 1 20 - +90 Ultraviolet Other (26) Midget trograde Analysis Aromatic Impinger Isooctane co Hydro- carbons Sulfur Midget 10 ml Sodium 2-3 2 99 Reaction of Nitrogen (33) Dioxide Impinger, Tetrachloro- Dichloro- Dioxide, Fritted mercurate sulfito- Hydrogen## Rubber mercurate Sulfide : and Formal- dehyde- para- rosaniline Toluene Midget 15 ml Marcali 1 25 95 Diazotiza- Materials (12) Diiso- Impinger Solution tion and containing cyanate . Coupling Reactive Reaction Hydrogen attached to Oxygen (phenol) Certain other Diamines Vinyl Fritted Toluene 1.5 15 +99 Gas Other (34) Acetate Midget (84 with Chroma- Substances Impinger fritted tography with same and bubbler retention simple only) time on Midget Column Impinger in Series * 5 gram sulfanilic # Add sulfamic acid after sampling. 140 ml glacial acetic acid ## Filter or centrifuge any precipitate. 20 ml of 0.1% aqeous N-(1-naphthyl) ethylene diamine 169 tubing or collecting device which may necessitate a rinsing with a special reagent to remove the adsorbate which must then be added to the col- lected portion in the sampling device. The collection of sufficient sample for the in- tended method of analysis is a matter which must be discussed by the field and laboratory personnel jointly when the survey plans are made. The field men must discuss as fully as possible with the chemists the nature of the processes involved in the survey so they may select the best combina- tion of sampling and analytical methods to meet the sensitivity requirements of the analytical method, minimize the effects of potential inter- ferences and complete each sampling within a time period which is consistent with the cyclic nature of processing operations or with the exposure con- ditions (see Chapter 10). INSTANTANEOUS OR GRAB SAMPLING Numerous types of devices are used in instan- taneous or “grab” sampling to obtain a definite volume of air within a gas collector. These in- clude vacuum flasks, vacuum bottles, gas- or liquid-displacement type collectors, metallic col- lectors, glass bottles, syringes and plastic bags. Air samples must be collected with these devices at a known temperature and pressure to permit the reporting of the analyzed components in terms of standard conditions, normally 25°C and 760 mm of mercury for industrial hygiene purposes. - Grab samples are collected usually where gross components of gases in air such as methane, carbon monoxide, oxygen, and carbon dioxide are to be analyzed. The samplers should not be used for collecting reactive gases such as hydrogen sulfide, oxides of nitrogen and sulfur dioxide since there may be a reaction with dust particles, mois- ture, wax sealing compound or glass which would alter the composition of the sample. It is pref- erable when reactive substances are collected in grab samples that the analyses be made directly in the field. Grab samples are not limited to sampling gross amounts of gases or vapor. The introduction of highly sensitive and sophisticated instrumenta- tion, including infrared spectrophotometry and gas chromatography, has extended the applica- tions of grab sampling to low levels of contam- inants." In areas where the atmosphere remains constant the grab sample will be representative of the average as well as the momentary concentra- tion of the components and thus it may truly represent an integrated equivalent. Where the at- mospheric composition varies, peaks and valleys of contamination will be observed, and numerous samples must be taken to determine the average concentration of a specific component. The chief advantage of grab sampling methods is that their collection efficiency is normally considered to be 100 percent; there must, of course, be no losses due to leakage or chemical reaction preceding analysis. Evacuated flasks are heavy-walled glass con- tainers, usually of 250 or 300, but frequently of 500 or 1000, milliliter capacity (Figure 15-1A) from which 99.97 percent or more of the air has 170 been removed by a heavy duty vacuum pump. The internal pressure after the evacuation is prac- tically zero. The neck is sealed by heating and drawing during the final stages of evacuation. These units are simple to use since no metering devices or pressure measurements are required. The pressure of the sample is taken as the baro- metric pressure reading at the site. After the sample has been collected by breaking the heat- sealed end, the flask is resealed with a ball of wax and transported to the laboratory for analysis. A variation of this procedure with evacuated flasks is to add a liquid absorbent to the flask before it is evacuated and sealed to preserve the sample in a desirable form following collection. Partially evacuated containers or vacuum bot- tles are prepared with a suction pump just before sampling is performed although frequently they are evacuated in the laboratory the day before a field visit. No attempt is made to bring the in- ternal pressure to zero, but temperature readings and pressure measurements with a manometer are recorded after the evacuation, and again after the sample has been collected. This type of col- lector may include heavy-walled glass bottles, metal or heavy plastic containers with tubing connectors which are closed with screw clamps or stopcocks. The volume of air or gas taken into the bottle may be computed as described later in this chapter. BREAKING SCRATCH WAX~— FILLED CARTRIDGE Sampling and Analysis of Mine Atmosphere, Miner's Circular 34. U.S. Dept. of Interior, 1948. Figure 15-1. Grab Sample Bottles (A) Evac- uated Flask (B) Gas or Liquid Displacement Type Gas or liquid displacement collectors include 250-300 ml glass bulbs (Figure 15-1B) fitted with end tubes which can be closed with greased stop- cocks or with rubber tubing and screw clamps. They are used widely in collecting samples con- taining O,, CO,, CO, N,, and H, or other com- bustible gases for analysis by an Orsat or similar analyzer. Other devices operating on the liquid displacement principle include aspirator bottles of various sizes which have exit openings at the bottom of the bottles through which the liquid is drained during sampling. In applying the gas displacement technique, the samplers are purged conveniently with a bulb aspirator, hand pump, small vacuum pump or other suitable source of suction. Satisfactory purg- ing is achieved by drawing a minimum of ten air changes of the test atmosphere through the gas collector. The collectors mentioned in the gas displace- ment section can also be filled by liquid displace- ment. The most frequently employed liquid is water. In sampling, liquid in the container is drained or poured out slowly in the test area and replaced by air to be sampled. Application of this method is limited to those gases which are in- soluble in and non-reactive with the displaced liquid. The solubility problem can be minimized by using mercury or water conditioned with the gas to be collected. Mercury, however, must be used with caution since it may create an exposure problem if handled carelessly. Flexible plastic bags" are used to collect air and breath samples containing organic and in- organic vapors and gases in concentrations ranging from parts per billion to more than 10 percent by volume in air and also to prepare known concen- trations of gases and vapors for equipment cali- bration.* The bags are easily inflated without stretching to their full volume using rubber squeeze bulbs or small hand pumps. They are available commercially in a variety of sizes, up to 9 cubic feet, but they may also be made in the laboratory. They are manufactured from several plastic ma- terials including Saran, Scotchpak, Aluminized Scotchpak, Mylar, Aluminized Mylar, Teflon, Kel-F, Polyethylene and Polyester. The bag ma- terials are from 1 to S mils in thickness and may be purchased in 100-foot or longer rolls of large sheets which may be cut to the desired size. Some, such as Mylar, may be sealed with a hot iron using a Mylar tape around the edges. Others, such as FEP Teflon, require high temperature and con- trolled pressure in sealing. Certain plastics, in- cluding Mylar and Scotchpak, may be laminated with aluminum which seals the pores and reduces the permeability of the inner walls to sample gases and the outer walls to moisture. Sampling ports may consist of a sampling tube molded into the fabricated bag and provided with a closing device or a clamp-on air valve. The 6- and 12- liter size are suitable for many industrial hygiene samples to be analyzed by infrared spectrophotom- etry using a 10-meter gas cell. Plastic bags have the advantages of being light, nonbreakable and inexpensive, and they permit the entire sample to be withdrawn without the difficulty associated with dilution by replacement air as is the case with rigid containers. Plastic bags, however, must be used with cau- tion since generalization of recovery character- istics of a given plastic cannot be extended to a broad range of gases and vapors. Important fac- tors to be considered in using these collectors are: absorption and diffusion characteristics of the plastic material, concentration of the gas or vapor, 171 and reactive characteristics of the gas or vapor with moisture and with other constituents in the sample. A valuable summary of information sources on the storage properties of gases and vapors in plastic containers has been provided by Schuette’ and Nelson.!° The bags must be leak tested and precondi- tioned for 24 hours to the chemical vapors to be tested before they are used for sampling. Pre- conditioning consists of flushing the bag three to six times with the test gas, the number of refills depending on the nature of the bag material and the gas. In some cases it is recommended that the final refill remain in the bag overnight prior to the use of the bag for sampling. Such pre- conditioning is usually helpful in minimizing the rate of decay of a collected gas except for nitrogen dioxide. At the sampling site the air to be sampled is allowed to stand in the bag for several minutes, if possible, before removal and subsequent refilling of the bag with a sample. Once collected, the in- terval between sampling and analysis should be minimal. Hypodermic syringes of 10- to S50-milliliter volume have also been used successfully for air sampling. These units are available usually in glass, but the disposable plastic type have also been used successfully. Ten milliliter Plastipak®! syringes have been shown to have excellent re- tention properties for methane, hydrogen and other gases in normal mine air, but some loss of carbon dioxide was observed over a storage period of a week. The advantages of these units are cost, convenience and ease of use. INTEGRATED SAMPLING Integrated (or “‘continuous’) sampling of the workroom atmosphere must be performed when the composition of the air is not uniform, the sensitivity requirements of the method of analysis necessitates sampling over a minimal (10-30 min- utes) finite period, or when compliance or non- compliance with an 8-hour time-weighted average air standard must be established. Thus, the pro- fessional observations and judgment of the indus- trial hygienist are called upon in devising the strategy for the procurement of representative samples to meet the requirements of an environ- mental survey of the workplace. Sampling Pumps An integrated air sampling method requires a relatively constant source of suction as an air moving device. A vacuum line, if available, may be satisfactory. The most practical source, how- ever, is an electrically powered pump or blower for prolonged periods of sampling. These come in various sizes and types and must be chosen for the sampling devices with which they will be used. If electricity is not available or if flammable vapors present a fire hazard, aspirator bulbs, hand pumps, a portable unit operated by means of com- pressed gas (Freon; Unijet Sampler) or battery- operated pumps (activate outside the area to avoid a spark) are suitable for sampling at rates up to 2-3 liters per minute. For higher sampling re- quirements, ejectors using compressed air or a water aspirator may be employed. An air aspirator is usable where the pressure is constant. When compressed air or batteries are to be used as the driving force for a pump, the length of the sampling period is important in re- lation to the supply of compressed air or the life of the rechargeable battery. These units must not be allowed to run unattended and periodic checks on the air flow must be made. Measurement of Air Flow Air volume may be measured directly by means of an aspirator bottle, or by dry or wet test meters, but these units are used primarily in the laboratory for calibration purposes. The common practice in the field is to sample for a measured period of time at a constant, known rate of air flow. Direct measurements are made with rate meters such as rotameters and orifice or capillary flowmeters. These units are small and convenient to use, but at very low rates of flow their accuracy decreases. The sampling period must be timed carefully with a stop watch. Many pumps have inlet vacuum gauges or outlet pressure gauges attached. These gauges, upon proper calibration with a calibrated wet or dry gas meter, can be used to determine the flow- rate through the pump. The gauge may be cali- brated in terms of cubic feet per minute or liters per minute. If the sample absorber does not have enough resistance to produce a pressure drop, a simple procedure is to introduce a capillary tube or other resistance into the train behind the sam- pling unit. Sampling Trains Samplers are always used in assembly with an air moving device (source of suction), and an air metering unit. These are the basic essentials. Frequently, however, the sampling train may con- sist of a filter, probe, absorber (or adsorber), flowmeter, flow regulator and air mover. The filter is included to remove any particulate matter that may interfere in the analysis. It should be ascertained that it does not also remove the gaseous contaminant of interest. The probe or sampling line is extended beyond the sampler to reach a desired location. It also must be checked to determine that it does not collect a portion of the sample. The meter which follows the sampler indicates the flow-rate of air passing through the system. The flow regulator controls the air flow. Finally at the end of the train the air mover pro- vides the driving force. Collection Efficiency of Samplers Several methods of testing the efficiency of an absorbing, or adsorbing, device are available. One or more of these methods should be employed for periodic evaluation of individual units, in par- ticular fritted bubblers whose porosities are sub- ject to change from the effects of sampling corro- sive atmospheric contaminants. A recommended test system is a gas tight chamber or tank in which known concentrations of a given contaminant can be prepared. Ab- sorbers are attached to sampling ports and op- erated under simulated field conditions to de- termine their collection efficiencies. Frequently the relative efficiency of a single 172 absorber can be estimated by placing another in series with it. Any leakage is carried over into the second collector. The absence of any carry- over is not in itself an absolute indication of the efficiency of the test absorber since it may be possible that the contaminant is not stopped effectively by either absorber. Analysis of the two legs of a U-tube containing silica gel used in sam- pling a contaminant is a useful check on the col- lection efficiency of the first leg of the tube. Another valuable technique is the operation of the test absorber in parallel or in series with a different type of collector having a known high col- lection efficiency (an absolute collector if one is available) for the contaminant of interest. By running the test absorber at different rates of flow the maximum permissible rate of flow for the device can be ascertained. Discussion of Variable Factors Influencing Efficiency of Collection A high collection efficiency is achieved when a chemically reactive sampling medium is used at a sufficiently slow rate to collect a contaminant with which it reacts to form a nonvolatile product. Such is the case in neutralization reactions of caustic scrubbing solutions with acid gases such as HF, HCI, SO, and nitrous fumes and the hy- drolysis of toluene diisocyanate in Marcali Solu- tion.'? Other examples are given in Table 15-1 where collection efficiencies of 95 percent are reported generally for this type of sampling sys- tem. Long-term sampling may thus be conducted provided an excess of the collecting reagent is maintained. Gases and vapors can also be collected satis- factorily in liquids that are not reactive if the contaminant is readily soluble in the medium. Thus, methanol and formaldehyde may be ab- sorbed readily in water and esters in alcohol. The vapor pressure of these contaminants is lowered by the solvent effect of the absorbing liquid. A discussion of the theoretical and practical aspects of absorbing vapors in non-reacting liquids is given by Elkins.’® It is emphasized that the variable which determines the efficiency of col- lection in a given system is the ratio of the volume of sampled air to the volume of the collecting liquid. The concentration of vapor in the air actually has no effect on the collection efficiency of non-reacting absorbing media. Other factors to be considered are: the degree of contact be- tween the gas or vapor being sampled and the absorbent, duration of contact of the contaminant with the absorbent, rates of diffusion of gas and liquid phases, degree of solubility of the contam- inant in the absorbent, and volatility of the con- taminant. The collection efficiency (the ratio of the amount of contaminant retained by the absorbing medium to that entering it) need not be 100 per- cent as long as it is known, constant and repro- ducible. The minimal acceptable collection per- formance in a sampling system is usually 90 percent, but higher efficiency is certainly desirable. When the efficiency falls below the acceptable minimum, sampling may be carried out at a lower rate, or at a reduced temperature by immersing
  • * Other factors that affect the collection efficiency include the volatility of vapor, mesh size of silica gel, rate of airflow and temperature. Desorption of organic vapor is usually com- plete after the exposed gel has stood overnight in a correctly chosen solvent although, for many organic substances, the required elution period is much shorter. The lower molecular weight ke- tones are completely removed in an hour with water, benzene is eluted with isopropyl alcohol in about the same period whereas toluene and xylene GLASS INLET TUBE i Z 3 oO © D3 « - ax & FF or E Swit EL = =n ©O i F242 30 Jw a -O eS, 92 °F 3 He J Wao wn 2 2 Qo v3 =x oO oo Ww uw wu Q © oO FT WE ox <2 x NE a O TT, 20 nod on om nn Ld FO ow <0 n Arad 2 0 x od wn Ja J WW x << oO - § << Og J i! 7 ® | © / 4 RNS SS SYST RK k SS SS SNK RR AR TTT 4 EH HE oS 2 Ade et ee ee Ba eee ety EC CS tT TO OI SE SSE SS SSSSSSSSSSSS SSO \ x ] N i'd N N oO N 0 Oo : N 0 Ts SS RE EY $4 a - Cm 2 ed ree RRR REESE Figure 15-3. Silica Gel Adsorber 176 Elkins HB: The Chemistry of Industrial Toxicology, 2nd Edition. New York, John Wiley & Sons, p. 280. are desorbed more slowly. Other desorbing agents mentioned in the liter- ature for silica gel are acetone and dimethyl- sulfoxide. The latter*' has been found particularly useful if the analysis is performed by gas chroma- tography. The retention time of this solvent is considerably greater than that of many common organic compounds. tained with carbon disulfide; the addition of water after an initial contact period of two hours im- proved the desorption of toluene, xylene and certain halogenated hydrocarbons. Non-polar sol- vents are unsuitable for displacing vapors of aro- matic hydrocarbons. Aliphatic hydrocarbons, for example, will not displace benzene. The use of microcolumns of silica gel has been recommended for reducing bulkiness and cost of mailing sampling equipment.** Glass col- umns containing 500 mg of 42/80 mesh silica gel are prepared in three sections, and air is sampled at the low rate of 60 milliliters of air per minute. The presence of water and other polar substances may cause non-polar substances like benzene, cyclohexane, and toluene to migrate to a different section of the column. It was found necessary to analyze each section (by ultraviolet spectropho- tometry) after elution with 5S milliliters of alcohol. Collection efficiency may be determined by the extent of migration of the adsorbate. Most lab- oratories now use gas chromatographic methods to analyze the eluates from solid adsorbents. In condensation methods vapors or gases are separated from sampled air by passing the air through a coil immersed in a cooling medium, dry Poor recoveries were ob-v" ice and acetone, liquid air or liquid nitrogen. The device is not considered to be a portable field technique ordinarily. It may be necessary in cer- tain cases to use this method where the gas or vapor may be altered by collecting in liquid or where it is difficult to collect by other techniques. Nitrogen dioxide and mercury vapor have been collected by this method prior to the development of more modern procedures. A feature of this method is that the contaminating material is ob- tained in a concentrated form. The partial pres- sure of the vapor can be measured when the sys- tem is brought back to room temperature. ANALYSIS OF GASES AND VAPOR A complete listing of methods of gas and vapor analysis is not intended, but a few of the commonly employed procedures are mentioned in Tables 15-1 and 15-4. Details of the analyses are found in the literature cited; additional procedures are found in the recommended publications listed in the reference section. APPENDIX I The direct measurement of the volume of an instantaneous (grab) sample of an atmosphere must be corrected to standard conditions of tem- perature and pressure in order to calculate the absolute quantity of matter which is to be de- termined. An understanding of the fundamental gas laws and their application is essential for this purpose. Examples of their applications are pre- sented in this appendix. TABLE 15-4 Gases and Vapors Collected on Solid Adsorbents and Their Analysis Air ~~ Adequate Sorption Flow Sample Collection Gas or Vapor Sampler Medium (L/m) (L) Efficiency Analysis Ref. Wide range of Straight 0.5 grams 0.1 to 1 2-10 # Desorb with 16-19 organic tube, 5 12 X 20 carbon disulfide, vapors inches mesh Inject into long, Activated chromatograph 6mm di- Charcoal ameter Wide range of U Tube 10 grams 3-5 25 # Extract with 20-25 organic 8-16 alcohol, water, vapors mesh acetone for Silica Gel ultraviolet analysis or with dimethyl- sulfoxide for chromatography Nitrogen U Tube 10 grams 3-5 10-30 +90 Desorb with 13 dioxide 8-16 50 ml sulfuric mesh acid-peroxide Silica Gel solution * # Depends on nature of solvent vapor, amount of adsor- bent, sampling time and size of sample. For many or- ganic vapors a sample of 25 liters will not leak into second arm of U tube. 177 * 1 ml concentrated Sulfuric Acid and 6 drops 30% hy- drogen peroxide to 200 ml of water. . CALCULATIONS Application of Gas Laws At 0° C (273°K) and 760 mm pressure a gram molecular weight of any perfect gas will oc- cupy a volume of 22.414 liters. If we ignore deviations from ideal behavior, oxygen of this volume would weigh 32 grams and nitrogen 28 grams, their molecular weights respectively. If there is a change in temperature and pressure the molar volumes of these gases will be altered. Ac- cording to the laws of Boyle and Charles the change in molar volume will be inversely propor- tional to its pressure and directly proportional to its absolute temperature (°C +273). In order for the actual measured volumes of gases and gas air mixtures to have meaning, they must be corrected to standard conditions of tem- perature and pressure (STP), 0° C (273°K) and 760 mm of mercury pressure. From a consideration of the laws of Charles and Boyle is derived the equation: Poar. ” 273 760 ~ 273+t° C A correction for the presence of water vapor is made by subtracting the partial pressure of the water vapor in the air from the barometric pres- sure: Vsre = Ves, X 273 273+t° C t°® C=temperature at which the sample was taken. If this formula is applied to a grab sample in a 12-liter volume bottle taken at 22°C at a baro- metric pressure of 760 mm, and a partial pressure of water vapor at 22°C of 19.8 mm, Vgpp=10.8 liters. If an analysis of the grab sample showed it contained 5 mg of carbon tetrachloride, then: Py. = P X Vsre = V ens. X 760 g 22.414 0.005 22.414 MW 10°="154 10°=67 PPM = Vere 10.8 MW =molecular weight of carbon tetrachloride 22.414 =molar volume (liters) of carbon tetrachloride at standard conditions of temperature and pressure (STP) If the sample was taken in a partially evac- uated flask, and a manometer reading showed that 365.1 mm of pressure remained in the flask, the formula for the corrected volume is: ” Pyar. — P,P, 273 Viste = Vineas. X 760 X 273+ C VSTP=5.5 PPM =132 Conversion Formulas mg per liter X 1000 = mg per cubic meter mg per liter X 28.32 = mg per cubic foot mg per cubic foot X 35.314 = mg per cubic meter 178 The common practice among industrial hy- gienists is to assume that air samples taken in normal factory air are at 25°C and 760 mm of mercury pressure. One gram molecular weight of a gas occupies 24.45 liters under these conditions. PPM (parts per million of a contaminant) may then be calculated from an air sample with the following simplified version of the expression given earlier: 24,450 X mg per liter PPM = molecular weight (contaminant) mg per liter = mg of contaminant in one liter of air sample collected References 1. VAN HOUTEN, R. and G. LEE. “A Method for the Collection of Air Samples for Analysis by Gas Chromatography.” Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 30:465 (1969). 2. OORD, F. “A Simple Method to Collect Air Sam- ples in a Plastic Bag.” Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 31:532 (1970). 3. CURTIS, E. H. and R. H. HENDRICKS. “Large Self Filling Sampling Bags.” Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 30:93 (1969). 4. CONNER, W. D. and J. S. NADER. “Air Sampling with Plastic Bags.” Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 25:291 (1964). 5. VANDERKOLK, A. L. and D. E. VAN FAROWE, “Use of Plastic Bags for Air Sampling.” Am Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 26:321 (1965). 6. SMITH, B. S. and J. O. PIERCE. “The Use of Plastic Bags for Industrial Air Sampling.” Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 32:343 (1970). 7. STEWART, R. D. and H. C. DODD. “Absorption of Carbon Tetrachloride, Trichloroethylene, Tetra- chloroethylene, Methylene Chloride, and 1,1,1,-Tri- chloroethane through the Human Skin.” Am. Ind. Hyg. Assoc, J., 66 South Miller Rd., Akron Ohio 44313, 25:439 (1964). 8. APOL, A. G.,, W. A. COOK, and E. F. LAW- RENCE. “Plastic Bags for Calibration of Air Sam- pling Devices.” Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 27:149 (1966). 9. SCHUETTE, F. J. “Plastic Bags for Collection of Gas Samples.” © Atmos. Environ., Oxford, England, 1:515 (1967). * 10. NELSON, G. O. “Controlled Test Atmospheres, Principles and Techniques.” Ann Arbor Science Pub- lishers, Inc., P. O. Box 1425, Ann Arbor, Mich., pp. 76-82 (1971). 11. LANG, H. W. and R. W. FREEDMAN. “The Use of Disposable Hypodermic Syringes for Collection of Mine Atmosphere Samples.” Am. Ind. Hyg. Assoc. 2 66 South Miller Rd., Akron, Ohio 44313, 30:523 1969). 12. MARCALI, K. “Microdetermination of Toluene Diisocyanate in Atmosphere.” Analyt. Chem., 1155 16th St., N. W., Wash., D. C. 29-552 (1957). 13. ELKINS, H. B. The Chemistry of Industrial Toxi- cology. John Wiley and Sons, Inc., New York, N.Y. (1959). 14. ELKINS, H. B.,, A. HOBBY and J. E. FULLER. “The Determination of Atmospheric Contaminants: I-Organic Halogen Compounds.” AMA Archives of Ind. Hyg. & Occup. Med. (formerly J. Ind. Hyg. & Toxicol., 535 N. Dearborn St., Chicago, Ill. 60610, 19:474 (1937). 15. SCHRENK, H. H., S. J. PEARCE and W. P. YANT. “A Microcolorimetric Method for the De- 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. termination of Benzene,” U. S. Bureau Mines Report Investigation 3287, Pittsburgh, Pa. (1935). FRAUST, C. L. and E. R. HERMANN. “The Ad- sorption of Aliphatic Acetate Vapors onto Activated Carbon.” Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 30:494 (1969). REID, F. H. and W. R. HALPIN. “Determination of Halogenated and Aromatic Hydrocarbons in Air by Charcoal Tube and Gas Chromatography. Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 29:390 (1968). WHITE, L. D, D. G. TAYLOR, P. A. MAUER, and R. E. KUPEL. “A Convenient Optimized Meth- od for the Analysis of Selected Solvent Vapors in the Industrial Atmosphere.” Amer. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 31:225 (1970). OTTERSON, E. J. and C. U, GUY. “A Method of Atmospheric Solvent Vapor Sampling on Activated Charcoal in Connection with Gas Chromatography.” Transactions of the Twenty-Sixth Annual Meeting of the American Conference of Governmental In- dustrial Hygienists, Phila., Pa., p .37, American Con- ference of Governmental Industrial Hygienists, Cin- cinnati, Ohio (1964). FAHY, J. P. “Determination of Chlorinated Hydro- carbon Vapors in Air.” AMA Archives of Ind. Hyg. & Occup. Med. (formerly J. Ind. Hyg. & Toxicol.) 535 N. Dearborn St., Chicago, Ill. 60610, 30:205 (1948). FELDSTEIN, M., S. BALESTRIERI and D. A. LEVAGGI. “The Use of Silica Gel in Source Test- ing.” Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 28:381 (1967). PETERSON, J. E.,, H. R. HOYLE and E. J. SCHNEIDER. “The Analysis of Air for Halogen- ated Hydrocarbon Contaminants by Means of Ab- sorption on Silica Gel. Am. Ind. Hyg. Assoc. Quart., 66 South Miller Rd., Akron, Ohio 44313, 17:429 (1956). WADE, H. A., H. B. ELKINS and B. P. W. RUO- TOLO. “Composition of Nitrous Fumes from In- dustrial Processes.” Arch. Ind. Hyg. Occup. Med., 535 N. Dearborn St., Chicago, Ill. 60610, 1:81 (1950). WHITMAN, N. E. and A. E. JOHNSTON. “Sam- pling and Analysis of Aromatic Hydrocarbon Vapors in Air: A Gas-Liquid Chromatographic Method.” Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Ak- ron, Ohio 44313, 25:464 (1964). CAMPBELL, E. E. and H. M. IDE. “Air Sampling and Analysis with Microcolumns of Silica Gel.” Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Ak- ron, Ohio 44313, 27:323 (1966). YAMAMOTO, R. K. and W. A. COOK. “Deter- 179 27. 28. 29. 30. 31. 32. 33. 34. mination of Ethyl Benzene and Styrene in Air.” Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 29:238 (1968). ANALYTICAL GUIDE ON LEAD — ORGANIC TETRAMETHYL AND TETRAETHYL LEAD, Analytical Guides Committee, Am. Ind. Hyg., Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 30:193 (1969). ANALYTICAL GUIDE ON MERCURY—MONO- METHYL AND MONOETHYL MERCURY SALTS, DIMETHYL AND DIETHYL MER- CURY, Analytical Guides Committee, Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 30:194 (1969). BRIEF, R. A, F. S. VENABLE and R. S. AJE- MIAN. “Nickel Carbonyl: Its Detection and Po- tential for Formation.” Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 27:72 (1965). ANALYTICAL GUIDE — NITROGEN DIOXIDE, Analytical Guides Committee, Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 31:653 (1970). BYERS, D. H. and B. E. SALTZMAN. “Deter- mination of Ozone in Air by Neuiral and Alkaline Iodide Procedures.” Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 19:251 (1958). DECHANT, R., G. SANDERS and R. GRAUL. ‘Determination of Phosphine in Air. Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 27:75 (1966). ANALYTICAL GUIDE — SULFUR DIOXIDE, Analytical Guides Committee, Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 31:120 (1970). DEESE, D. E. and R. E. JOYNER. “Vinyl Acetate: A Study of Chronic Human Exposure. Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 30:449 (1969). Preferred Reading 1. ELKINS, H. B. The Chemistry of Industrial Toxi- cology. John Wiley and Sons, Inc., New York, N. Y., 2nd ed. (1959). JACOBS, M. B. The Analytical Chemistry of Indus- trial Poisons, Hazards and Solvents. Interscience Publishers, Inc., New York, N. Y., 2nd ed. (1949). JACOBS, M. B. The Analytical Toxicology of In- dustrial Inorganic Poisons. Interscience Publishers, Inc.,, New York, N. Y. (1967). INTERSOCIETY COMMITTEE METHODS OF AIR SAMPLING AND ANALYSIS, American Public Health Association, 1015 Eighteenth Street, N. W., Washington, D. C. (1972). CHAPTER 16 DIRECT READING INSTRUMENTS FOR DETERMINING CONCENTRATIONS OF AEROSOLS, GASES AND VAPORS Robert G. Keenan INTRODUCTION This chapter deals with direct reading instru- ments which may be portable devices or fixed-site monitors; it does not include those instruments which have been designed primarily for use in the laboratory. Direct reading instruments are used for on- site evaluations for a number of reasons, includ- ing: 1. To find the sources of emission of hazard- ous substances on the spot; To ascertain if select OSHA air standards are being exceeded; To check the performance of control equip- ment; As continuous monitors at fixed locations, a. To trigger an alarm system in the event of a breakdown in a process control which could result in the accidental re- lease of copious amounts of harmful substances to the workroom atmos- phere; To obtain permanent recorded docu- mentation of the concentrations of a contaminant in the atmospheric en- vironment for future use in epidemi- ological and other types of occupa- tional studies, in legal actions, to in- form employees as to their exposure, and for information required for im- proved design of control measures. Such on-site evaluations of the atmospheric concentrations of hazardous substances make pos- sible the immediate assessment of undesirable ex- posures and enable the industrial hygienist to make an immediate correction (including a shut- down) of an operation, in accordance with his judgment of the seriousness of a situation, without permitting further risk of injury to the workers. It cannot be over-emphasized that great caution must be employed in the use of direct reading instruments and in the interpretation of their re- sults. Many of these instruments are nonspecific and the industrial hygienist may find it necessary before recommending any action to make certain of his on-site findings by supplemental sampling and laboratory analyses to characterize fully the chemical nature of the contaminants in a work- room area and to develop the supporting quantita- tive data with more specific methods of greater accuracy. Such precautions become the more mandatory if the industrial hygienist has not had extensive experience with the particular process EE 181 area in question or when the possibilities of a change in the process or in the substitution of chemical substances may have occurred. The last possibility must always be foremost in the minds of industrial hygienists. Calibration The calibration of any direct reading instru- ment is an absolute necessity if the data are to have any meaning. Considering this to be axio- matic, we must also recognize that the frequency of calibration is dependent upon the type of in- strument as well as individual instruments within any one class. It is well known that certain classes of instruments, because of their design and complexity, require more frequent calibration than others. It is also recognized that peculiar “quirks” in an individual instrument produce greater variations in its response and general per- formance, thus requiring a greater amount of at- tention and more frequent calibration than other instruments of the same design. Direct personal experience with a given instrument serves as the best guide in this matter. Another unknown factor which can be evalu- ated only by experience is the variability of samp- ling locations. For example, when locating a par- ticular fixed-station monitor at a specific site, consideration must be given to such problems as the presence of interfering chemical substances, the corrosive nature of contaminants, vibration, voltage fluctuations and other disturbing influences which may affect the response of the instrument. Finally, the required accuracy of the measure- ments must be determined initially. Obviously, if an accuracy of * 3 percent is needed, more fre- quent calibration must be made than if += 25 percent accuracy is adequate in the solution of a particular problem. Properties of Aerosols An aerosol is an airborne solid nr liquid sub- stance. Aerosol particles normally present in am- bient air have been dispersed as a result of na- ture’s or man’s activities. The latter source is of greatest concern to environmental control special- ists. Aerosols are generated by fire, erosion, sub- limation, condensation and the abrading action of friction on minerals, metallurgical materials, or- ganic and other inorganic substances in construc- tion, manufacturing, mining, agriculture, trans- portation and other gainful pursuits. Aerosols are classified conveniently as dusts, fumes, smokes, mists and fogs according to their physical nature, their particle size, and their method of generation. Dusts range from 1 to 150 pm in diameter; they are produced mechanically by grinding and other abrasive actions occurring in natural and commercial operations. Fumes are particulate substances whose diam- eters range from 0.2 to 1 um; they are produced by such processes as combustion, distillation, cal- cination, condensation, sublimation, and chemical reactions. They form true colloidal systems in air. Examples are such substances as heated metals or metallic oxides, ammonium chloride, hot asphalt and volatilized polynuclear hydrocarbons from coking operations. Smokes are colloidal systems whose particle sizes range from 0.3 to 0.5 um in diameter. They are produced by the incomplete combustion of carbonaceous materials such as coal, oil, tobacco, and wood. Mists and fogs cover a wide range of particle sizes and are considered to be primarily liquid; they may consist of liquids, such as water vapor, condensed on the surfaces of submicroscopic par- ticles of dust or gaseous ions. Mineral, vegetable and animal fibers constitute a unique situation insofar as exposures are con- cerned. Inhalation of asbestos fibers up to 200 pm in length has been reported.’ Microscopic procedures are used to assist in the identification of, and to determine, the atmospheric concentra- tion of fibrous materials. Properties of Gases and Vapors Gases and vapors are “elastic fluids,” so-called because they take the shape and volume of their containers. A fluid is generally termed a gas if its temperature is very far removed from that re- quired for liquefaction; it is called a vapor if its temperature is close to that of liquefaction. In the field of occupational health, a substance is considered a gas if this is its normal physical state at room temperature and atmospheric pres- sure. It is considered a vapor if, under the exist- ing environmental conditions, conversion of its liquid or solid form to the gaseous state results from its vapor pressure affecting its volatilization or sublimation into the atmosphere of the con- tainer, which may be the process equipment or the workroom. Our chief interest in distinguishing between gases and vapors lies in our need to assess the potential occupational hazards associ- ated with the use of specific chemical agents, an assessment which requires a knowledge of the physical and chemical properties of these sub- stances (see Chapter 15). Characteristics of Direct Reading Instruments Direct reading instruments for atmospheric contaminants are classified as those devices which provide an immediate indication of the concentra- tion of aerosols, gases, or vapors by a dial read- ing, a strip chart recording, a tape printout or a color change on an impregnated paper or in an indicator tube, These devices, when properly cali- brated and when used with full cognizance of their performance characteristics and limitations, can be extremely helpful to industrial hygienists who are engaged in on-site evaluations of potentially hazardous conditions. There are many types of 182 instruments which depend on certain physical or chemical principles for their operation. They are discussed later in this chapter. The advantages of direct reading instruments include: 1. Immediate estimations of the concentra- tion of a contaminant, permitting on-site evaluations; Provision of permanent 24-hour records of contaminant concentrations using con- tinuous monitors; Attachment of alarm system to instrument to warn workers of build-up of hazardous situations; Reduction of number of manual tests; Reduction of number of laboratory analyses; . Provision of more convincing evidence for presentation at hearings and litigation pro- ceedings; 7. Reduced cost of obtaining individual re- sults. The disadvantages of different types of direct reading instruments may include some of the following: High initial cost of instrumentation; Need of frequent calibration; Lack of adequate calibration facilities; Lack of portability; Lack of specificity. DIRECT READING PHYSICAL INSTRUMENTS The physical properties of aerosols, gases, and vapors are used in the design of direct read- ing physical instruments for quantitative estima- tions of these types of contaminants in the atmos- phere. The principles upon which these instru- ments are based are presented in the following discussion, Operating Principles Aerosol Photometry (Light Scattering). The prin- ciple of aerosol photometry is the generation of an electrical pulse by a photocell which detects the light scattered by a particle. A pulse height analy- zer estimates the effective particle diameter. The number of electronic pulses is related to the num- ber of particles counted per unit flowrate of the sampled gaseous medium. Calibrations may be made using a reference standard such as polysty- rene spheres whose diameters and refractive index are known although the aerosol under study is the reference of choice because of the unique effects of shape factor, angle of scatter, and refractive index, as well as particle size. Whereas certain commercial instruments are designed to give a size analysis based upon the above principles, there are others which use a forward light scat- tering principle to provide an integrated measure- ment of total particle concentration in a large illuminated volume. The latter are used in moni- toring particulate concentrations in experimental rooms and exposure chambers. Aerosol photometry can usually provide only an approximate analysis of particulate classified according to particle size in plant surveys because SNELN= of the impracticality of calibrating the instrument with each type of particulate suspension which is to be measured. The great variations in shape, size, degrees of agglomeration and refractive in- dices of the mixture of chemical components in a given dust or fume suspension make such a cali- bration exceedingly difficult. Whereas aerosol photometry can, therefore, provide an indication of the particulate concentration in the different particle size ranges of interest, it is still necessary to perform size distribution analyses by microsiev- ing and microscopic procedures for greatest accu- racy. Chemiluminescence. Chemiluminescence is a phe- nomenon which occurs with certain chemical re- actions. The process provides a distinctly colored glow which accompanies such reactions as the oxi- dation of certain decaying wood, of luciferin in fireflies and of yellow phosphorus. Recently, ana- lytical advantage of this phenomenon is taken in the reaction of ozone with such other gases as ethylene and nitric oxide for the measurement of ozone or nitrogen oxides in ambient atmospheres. The chemiluminescent principle has been in- corporated into continuous ambient air monitors which are selective for ozone or for NO — NO. Measurements of ozone at concentrations extend- ing from 0.001 to 1 ppm in ambient atmospheres are based upon the photometric (photomultiplier tube) detection of the chemiluminescence pro- duced by the flameless gas phase reaction of the ozone in the air sample stream with ethylene gas whose flow from a bottled supply is regulated through a calibrated capillary tubing to the reac- tor chamber. Similarly, NO measurements from 0.01 to 5,000 ppm are based upon the chemiluminescent reaction of NO and ozone to produce NO, and O., + hy. The ozone is produced from bottled oxygen by an in-line ozone generator. Monitoring of NO, is accomplished by means of an NO, to NO catalytic converter which operates in a bypass line on a timed sequence basis. Thus, NO, meas- urements can be obtained by difference. The selectivity of these instruments is en- hanced by the use of narrow-band optical filters to provide negligible interference effects from other atmospheric contaminants. Although designed for ambient air studies, these instruments may be used advantageously as fixed-station monitors of in- plant atmospheres. Colorimetry (see Photometry) Combustion. A combustible gas or vapor mixture is passed over a filament heated above the ignition temperature of the substance of analytical interest. If the filament is part of a bridge circuit, the re- sulting heat of combustion changes the resistance of the filament, and the measurement of the im- balance is related to the concentration of the gas or vapor in the sample mixture. The method is basically nonspecific, but it may be made more selective by choosing appropriate filament temper- atures for individual gases or vapors or by using an oxidation catalyst for a desired reaction such as Hopcalite for carbon monoxide. Combustible gas indicators must be calibrated 183 in the laboratory for their response to the antici- pated individual test gases and vapors, such as benzene, toluene, hexane (for hydrocarbons in general), carbon monoxide, acetone, and styrene. These instruments are definitely portable and they are valuable survey meters in the industrial hy- gienist’s collection of field instruments. Readings are in terms of 0-1000 ppm or 0-1.0 Lower Ex- plosive Limit (LEL). However, it is essential to recognize that industrial atmospheres rarely con- tain one gaseous contaminant and that these indi- cators will respond to all the combustible gases present. Hence, supplementary sampling and an- alytical techniques should be used for a complete definition of hazardous environmental conditions. Conductivity, Electrical. A gas-air mixture is drawn through an aqueous solution. Those gases which form electrolytes produce a change in the electroconductivity as a summation of the effects of all ions thus produced. Hence, the method is nonspecific. If the concentrations of all other ion- izable gases are either constant or insignificant, then the resulting changes in conductivity may be related to the gaseous substance of interest. Tem- perature control is extremely critical in conduct- ance measurements; if thermostated units are not used, then electrical compensation must enter into the measurements to allow for the 2% per degree C conductivity temperature coefficient average for many gases. The electrical conductivity method has found its greatest application in the continuous monitor- ing of sulfur dioxide in ambient atmospheres. However, a lightweight portable analyzer which uses a peroxide absorber to convert SO, to H,SO, is now available; this battery operated instrument can provide within one minute an integrated read- ing of the SO, concentration over the 0-1 ppm range. A larger portable model which may be operated off a 12-volt automobile battery is also available for the higher concentration ranges of SO, encountered in field sampling. Conductivity, Thermal. The specific heat of con- ductance of a gas or vapor is a measure of its concentration in a carrier gas such as air, argon, helium, hydrogen, or nitrogen. However, thermal conductivity measurements are nonspecific and the method finds its greatest usefulness in estimat- ing the concentration of the separately eluted com- ponents from a gas chromatographic column. The method operates by virtue of the loss of heat from a hot filament to a single component of a flowing gas stream, the loss being registered as a decrease in electrical resistance measured by a Wheatstone bridge circuit. The applications of this method are limited mostly to binary gas mixtures and are based upon the electrical unbalance produced in the bridge circuit by the difference in the filament resistances of the sample and reference gases passed through the separate cavities in the thermal conductivity cell. Coulometry. Coulometry is the precise measure- ment of the quantity of electricity passing through a solution during an electrochemical reaction. The substance of analytical interest is oxidized or re- duced at one electrode in a primary coulometric analysis or it may react stoichiometrically (in a secondary coulometric analysis) with one of the electrolytic products. The method is capable of a high degree of precision. It is used in the auto- matic monitoring of part per billion to part per million concentrations of reactive inorganic gases present in ambient atmospheres; air samples are drawn through the electrolytic cell in which the reactant is generated in controlled quantities to meet the concentration requirements. The method is basically nonspecific; it is made more selective for specific atmospheric oxidants by adjusting the concentration, pH and composition of the electrolyte used in the reaction. In certain instances a chemical filter or a selective membrane is used to remove serious interferents from the sampled gas stream. Both portable and fixed mon- itor types of instruments, based upon this princi- ple, are used to monitor ozone, nitrogen dioxide and sulfur dioxide concentrations. Flame Ionization. The hydrogen flame ionization detector (FID) is a stainless steel burner in which hydrogen is mixed with the sample gas stream in the base of the unit; combustion air or oxygen is fed axially and diffused around the jet through which the hydrogen — gas mixture flows to the cathode tip where ignition occurs. A loop of plati- num serves as the collector electrode which is set about 6 mm above the tip of the burner. The cur- rent carried across the electrode gap is propor- tional to the number of ions generated during the burning of the sample; the detector responds to all organic compounds, except formic acid, but its response is greatest with hydrocarbons and di- minishes with increasing substitution of other ele- ments: notably oxygen, sulfur and chlorine. Its low noise level of 1072 amperes provides a high sensitivity of detection and it is capable of the wide linear dynamic range of 107. Its usefulness is enhanced by its insensitivity to water, the per- manent gases and most inorganic compounds thus simplifying the analysis of aqueous solutions and atmospheric samples. It is used to great advan- tage in both laboratory and field models of gas chromatographs as well as in hydrocarbon ana- lyzers which are set up as fixed station monitors of ambient atmospheres in the laboratory or field. Hydrocarbon analyzers, operating with an FID detector, are carbon counters; their response to a given quantity of a typical C, hydrocarbon is six times to that of methane, at a fixed flowrate of the sample stream. Thus, the instrumental character- istics such as sensitivity, are usually given as methane equivalent. In addition to hydrocarbons, these analyzers respond to alcohols, aldehydes, amines and other compounds which will produce an ionized carbon atom in the hydrogen flame. The electronic stability of at least one model is within 1 percent over 24 hours of operation; this instrument is equipped with electronic span cali- bration to improve the accuracy of the data. Gas Chromatography. Gas chromatography is a physical process for separating the components of complex mixtures and is now being used profitably as a portable technique for in-plant studies. A gas chromatograph consists of (1) a carrier gas sup- 184 ply complete with a pressure regulator and flow meter, (2) an injection system for the introduc- tion of a gas or vaporizable sample into a port at the front end of the separation column, (3) a stainless steel, copper or glass separation column containing a stationary phase consisting of an inert material, such as diatomaceous earth, used alone as in gas-solid chromatography (GSC) or as a support for a thin layer of a liquid substrate, such as silicone oils, in gas-liquid chromatography (GLC), (4) a heater and oven assembly to con- trol the temperature of the column(s), injection port and detector unit, (5) a detector and (6) a recorder for the chromatograms produced during the separations. The separations are based upon the varied affinities of the sample components for the packing materials of a particular column, the rate of carrier gas flow and the operating tempera- ture of the column. Improved separations are made possible by the use of temperature program- ming. The sample components, as a consequence of their varied affinities for a given column, are eluted sequentially and thus evoke separate re- sponses by the detection system whose signal is amplified to produce a peak on the strip chart recorder. The height and area of the peak are proportional to the concentration of the eluted sample component. Calibrations are made using known mixtures of the pure substance in a gas- air mixture prepared in a 5- to 100-liter Saran bag or other suitable container. The time of retention on the column and supporting analytical techniques (infrared spectrophotometry, for example) are used in the identification of the individual peaks of a chromatogram. The method is capable of providing extremely clean-cut separations and is one of the most useful techniques in the field of organic analysis. It is sensitive to fractional part per million concentrations of organic substances. The most commonly used detectors include flame ionization, thermal conductivity and electron cap- ture (see Chapter 21 on Gas Chromatography). Rugged, battery operated, portable gas chro- matographs have been refined to the point where they may now be considered practical for many field study applications. These instruments may now be obtained with a choice of thermistor-type thermal conductivity, flame ionization and electron capture detectors and, in some instances, the lat- ter two types are interchangeable. Complete with gas sampling valve, rechargeable batteries, appro- priate columns and self-contained supplies of gases, these chromatographs have much to offer to the industrial hygienist engaged in on-site analyses of trace quantities of organic compounds and the permanent gases. The gas lecture bottles provide 8 to 20 hours of operation dependent on the flow- rates and must be recharged using high pressure gas regulators. The retention times of the com- pounds of analytical interest must be determined in the laboratory for a given type of column, as is true for the laboratory type chromatographs. Photometry (Colorimetry). Photometry is the measurement of the relative radiant power of a beam of radiant energy, in the visible, ultraviolet or infrared region of the electromagnetic spectrum, which has been attenuated as a result of passing through a solution, a gas-air mixture containing a substance such as mercury vapor, ozone or ben- zene vapor, a suspension of solid or liquid par- ticulates in air or other gaseous medium, or a photographic image of a spectral line or an x-ray diffraction pattern on a photographic film or plate. Photometers used for the indicated types of appli- cations contain (1) a lamp or other generating source of energy, (2) an optical filter arrange- ment to limit the bandwidth of the incident beam of radiation, (3) an optical system to collimate the filtered beam, which is then passed through (4) the sample system contained in a cuvette or gas cell to (5) a photocell, bolometer, thermo- couple or pressure sensor type of detector where the signal is amplified and fed to a (6) readout meter or to a strip chart recorder. The more sophisticated technique is termed spectrophotometry which makes use of prisms made of glass (visible region), quartz (ultravio- let), and sodium chloride or potassium bromide (infrared) or of diffraction gratings, instead of optical filters, to provide essentially monochro- matic radiation as a “purer” source of energy. Spectrophotometers are used mostly in labora- tories for highly specific and precise analytical de- terminations. Most field type colorimetric analyzers have been designed to function as fixed-station moni- tors for the active gases such as oxides of nitrogen, sulfur dioxide, “total oxidant,” ammonia, alde- hydes, chlorine, hydrogen fluoride, and hydrogen sulfide. These instruments require frequent cali- bration with zero and span gases at the sampling site to assure the provisions of reliable data. How- ever, built-in automated calibration systems, which standardize regularly zero and span controls against pure air and a calibrated optical filter, are now available from one source of colorimetric an- alyzers for the nitrogen oxides, sulfur dioxide and aldehydes. A further advantage is the 0-10 ppm working range of these instruments with the op- tional capability of extending the upper limit to 10,000 ppm. Another recent advance is the provision of a portable, colorimetric analyzer for NO,-NO, by ‘another manufacturer. This instrument, which uses dual photometric cells, is designed for rugged field use, may be operated from a 12-volt automo- bile battery and operates over the 0-2.0 ppm range, with higher ranges available. It may also be used as a field monitor, if desired. Polarography. Polarographic analysis is based on the electrolysis of a sample solution using an easily polarized microelectrode (the indicator electrode) and a large nonpolarizable reference electrode. In laboratory instruments the indicator electrode is a noble metal, usually a dropping mercury electrode for reduction reactions and a platinum electrode for oxidation reactions. The reference electrode may be a pool of mercury on the bottom of the electrolysis vessel or a saturated calomel electrode. The method provides both qualitative and quantitative information. As the increasing volt- age to the polarographic cell is applied at a steady 185 rate, the decomposition potentials of electroreduci- ble (or electrooxidizable) ions are reached in turn. At the decomposition potential of a given ion, the current increases rapidly and then levels off to a limiting current thus producing an S- shaped curve or “wave.” The value of the half- wave potential is characteristic of the discharged ion in a given electrolyte. The height of the wave, i.e., the rise in the current, is proportional to the concentration of the discharged ion species in the sample, The method has been used largely for the an- alysis of metallic ions and organic species. Manu- facturers of modern field instruments, however, are taking advantage of advanced, compact, long- lived polarographic sensors to provide continuous monitors for oxygen in such diversified environ- ments as furnace atmospheres, flue gases, auto ex- hausts, space vehicles, manholes and physiology test chambers. These portable instruments may be easily cali- brated for gaseous oxygen by exposing the sensor to ambient air and adjusting the calibration pot to provide a meter reading of 20.9 on the 0-25 percent scale. These instruments provide a rapid response to changes in the concentration of oxy- gen and should prove valuable to the industrial hygienist who may encounter oxygen deficient at- mospheres during his surveys. Radioactivity. Radioactive substances emit three principal types of radiation, vis. alpha (a), beta (B), and gamma (y). Radioactive particles and gases may be monitored manually or automatically in gas streams, in ambient atmospheres, in process water or in solid process materials or products by means of ionization chambers, scintillation detec- tors or Geiger-Mueller counters. Choice of detec- tors for alpha, beta-gamma or alpha-beta-gamma monitors is determined by the isotopes of interest. Electronic recorders are available for graphic pres- entation of monitoring data. Portable lightweight air monitors for gamma, beta-gamma, and alpha-beta-gamma radiation are available with interchangeable probes to survey work areas for the different types of radiation en- countered. One such instrument thus provides the capability of measuring alpha and weak beta ra- diation using one probe and gamma radiation up to 10 or 60 mr per hour with the others. Other portable survey meters include the “Cutie Pie” with ranges of 50, 500, and 5000 mr per hour and a fast neutron survey meter designed with tissue equivalent response in making health hazard sur- veys in the range of 0.2 to 14 MEV around reac- tors and neutron generators. A summary of the operating characteristics of the current (1972) commercially available direct reading physical instruments is presented in Table 16-1. The information provided in this table is based upon that given in the manufacturers’ liter- ature; in certain instances, e.g., repeatability, a range of values may represent either the specifica- tions given by more than one source of supply or different applications of an operating principle to the estimation of multiple chemical entities. In other cases, the information has not been provided TABLE 16-1 Direct Reading Physical Instruments Principle Applications Repeat- of Pp Code* Range ability Sensitivity Response Operation Remarks (Precision) Aerosol Measures, records and controls A 107% to 10> Not given 107% ug Not given Photometry particulates continuously in & ug per liter per liter areas requiring sensitive detec- B (for 0.3 tion of aerosol levels; detection wm DOP) of 0.05 to 40 um diameter par- ticles. Computer interface equipment is available. Chemilumin- Measurement of NO in ambi- B 0to 10,000 = 0.5to Varies: ca 0.7 sec escence ent air selectivity and NO, af- ppm += 3% 0.1 ppb NO Mode ter conversion to NO by hot to 0.1 ppm and 1 sec catalyst. Specific measurement NO; mode; of 0,. No atmospheric inter- Longer ferences. period when switching ranges Colorimetry Measurement and separate re- A ppb& ppm = 1 to 0.01 ppm 30 sec. cording of NO,-NO,, SO,, to- & += 5% (NO,, SO,) to 90% tal oxidants, H,S, HF, NH,, B of full C1, and aldehydes in ambient scale air. Combustion Detects and analyzes combus- A ppm to B ppm <30 sec. tible gases in terms of percent 100% LEL on graduated scale. Available with alarm set at 3 LEL. Conduc- Records SO, concentrations in A Oto2ppm <=*1% to 0.01 ppm 1to 15 tivity, ambient air. Some operate off & +=10% sec. (lag) Electrical ~~ a 12-volt car battery. Operate B unattended for periods up to 30 days. Coulometry Continuous monitoring of NO, A Selective: +4% of varies: 4 to <10 min. NO,, 0; and SO, in ambient & Oto 1.0 full scale 100 ppb to 90% air. Provided with strip chart B ppm overall, dependent of full recorders. Some require at- or to 100 on instru- scale. tention only once a month. ppm ment range (optional) setting. Flame Continuous determination & B Selective: +1% of Not given 5 min. Ionization recording of methane, total hy- Oto 1 ppm; full scale (cycle (with gas drocarbons and carbon mon- 0 to 100 time) chromato- oxide in air. Catalytic conver- ppm graph) sion of CO to CH,. Operates up to 3 days unattended. Same Separate model for continuous B 0-20 ppm +4% of 0.005 ppm 5 min. as above monitoring of SO,, H,S and full scale (H.S); (cycle total sulfur in air. Unattended 0.01 ppm time) operation up to 3 days. (SO,) Flame Continuous monitoring of total B Oto 1 ppm =*=1% of 1 ppm to <0.5 sec. Ionization hydrocarbons in ambient air; as CH,; X1, full scale 2% full to 90% (Hydro- potentiometric or optional cur- X10, X100, scale as of full carbon rent outputs compatible with X1000 with CH,; 4 ppm scale Analyzer) any recorder. Electronic sta- continuous to 10% as bility from 32° to 110°F. span adjust- mixed fuel. ment 186 TABLE 16-1 (Continued) Principle Applications Repeat- of & Code* Range ability Sensitivity Restome Operation Remarks (Precision) me Gas On site determination of fixed A Depends on Not given <1 ppb mn Chromato- gases, solvent vapors, nitro and detector (SF,) with graph, halogenated compounds and electron Portable light hydrocarbons. Instru- capture ments available with choice of detector; flame ionization, electron cap- <1 ppm ture or thermal conductivity (HC’s) detectors and appropriate col- umns for desired analyses. Re- chargeable batteries. Infrared Continuous determination of a B From ppm =*+=1% of 0.5% of 0.5 sec. Analyzer given component in a gaseous to 100% full scale full scale to 90% (Photom- or liquid stream by measuring depending of full etry) amount of infrared energy ab- on appli- scale sorbed by component of inter- cation est using pressure sensor tech- nique. Wide variety of appli- cations include CO, CO,, Fre- ons, hydrocarbons, nitrous ox- ide, NH,, SO, and water vapor. Photometry, Direct readout of mercury va- A 0.005 to +10% of 0.005 Not given Ultraviolet por; calibration filter is built 0.1 and meter read- mg/m* (tuned to into the meter. Other gases or 0.03 to ing or == 253.7 mp) vapors which interfere include 1 mg/m? minimum acetone, aniline, benzene, ozone scale and others which absorb radi- division, ation at 253.7 mp. whichever is larger Photometry, Continuous monitoring of SO,, B 11t03,000 +2% 0.01 to <30 sec. Visible SO, H.S, mercaptans and total ppm (with 10 ppm to 90% (Narrow- sulfur compounds in ambient air flow of full centered air. Operates more than 3 days dilution) scale. 394 my. unattended, band pass) Particle Reads and prints directly par- B Preset (by =*0.05% es Not given Counting ticle concentrations at 1 of 3 selector (probability (Near preset time intervals of 100, switch) of coinci- Forward 1000 or 10,000 seconds, corre- Particle Size dence) Scattering) sponding to 0.01, 0.1 and 1 Ranges: : cubic foot of sampled air. 0.3,0.5, 1.0, 2.0, 3.0, 5.0, and 10.0 pm. Counts up to 107 particles per cu. ft. (35 x 10%/ liter) Polar- Monitor gaseous oxygen in flue A 0-5 and *+1% of Not given ~~ 20 sec. ography gases, auto exhausts, hazard- 0-25% reading at to 90% ous environments and in food constant of full storage atmospheres and dis- sample scale solved oxygen in wastewater temperature samples. Battery operated, por- table, sample temperature 32° to 110°F, up to 95% relative humidity. Potentiometric re- corder output. Maximum dis- tance between sensor and am- plifier is 1000 feet. 187 TABLE 16-1 (Continued) Principle of Operation Applications & Remarks Code* Repeat- ability (Precision) Response Range Sensitivity Time Radio- Continuous monitoring of am- activity bient gamma and x-radiation by measurement of ion cham- ber currents, averaging or in- tegrating over a constant re- cycling time interval, sample temperature limits 32°F to 120°F; 0 to 95% relative hu- midity (weatherproof detec- tor); up to 1,000 feet remote sensing capability. Recorder and computer outputs. Com- plete with alert, scram and fail- ure alarm systems. All solid- state circuitry. Radio- activity Continuous monitoring of beta B or gamma emitting radioactive materials within gaseous or liquid effluents; either a thin wall Geiger-Mueller tube or a gamma scintillation crystal de- tector is selected depending on the isotope of interest; gaseous effluent flow — 4 cfm; effluent sample temperature limits 32° F to 120°F using scintillation detector and —65°F to 165°F using G-M detector. Complete with high radiation, alert and failure alarms. Radio- activity Continuous monitoring of ra- B dioactive airborne particulates collected on a filter tape trans- port system; rate of air flow — 10 SCFM; scintillation and G- M detectors, optional but a beta sensitive plastic ‘scintilla- tor is - provided to reduce shielding requirements and of- fer greater sensitivity. Air sam- ple temperature limits 32°F to 120°F; weight 550 pounds. Complete with high and low flow alarm and a filter failure alarm. B 0.1to 107 mR /hr. 10 to 10° cpm 10 to 10° cpm +10% (Decade Accuracy) <1 sec. +2% full scale (rate meter accuracy) <1077 uCi of 1-131 per cc of air and 1077 uCi of Cs-137 per cc of water using a scintillation detector 0.2 sec. at 10° cpm (rate- meter) +2% of full-scale (rate-meter accuracy) 0.2 sec. at 10° cpm (rate- meter) 10724 Ci of Cs-137 per cc of air using a scintillation detector * Code: A-Portable Instruments; B-Fixed Monitor or “Transportable” Instruments. Taken from Draeger Detector Tube Handbook, Draegerwerk. Liibeck, West Germany, 1970, pp. 33-71. in a manufacturer’s list of specifications for an instrument and this has been so noted in Table 16-1. The material presented under “Applications and Remarks” provides information on the indi- vidual substances which may be analyzed directly by the stipulated technique along with specified interferences and other important considerations. This tabulation is not an official certified list; it is intended as a useful guide in selecting direct read- 188 ing physical instruments on the basis of desired operating parameters. DIRECT READING COLORIMETRIC DEVICES Operating Principles Direct-reading colorimetric devices utilize the chemical properties of an atmospheric contami- nant for the reaction of that substance with a color-producing reagent. Reagents used in detec- tor kits may be in either a liquid or a solid phase or provided in the form of chemically treated pa- pers. The liquid and solid reagents are generally supported in sampling devices through which a measured amount of contaminated air is drawn. On the other hand, chemically treated papers are usually exposed to the atmosphere and the reac- tion time noted for a color change to occur. Liquid Reagents. Liquid reagents may be sup- plied in sealed ampoules or in tubes for field use. Such preparations are provided in a concentrated or a solid form for easy dilution or dissolution at the sampling site. Representative of this type of reagent are the ortho-tolidine and the Griess-Ilso- vay kits for chlorine and nitrogen dioxide, respec- tively. Although the glassware needed for these applications may be somewhat inconvenient to transport to the field, methods based on the use of liquid reagents are more accurate than those which use solid reactants. This is due to the in- herently greater reproducibility and accuracy of color measurements made in a liquid system. Chemically Treated Papers. Papers impregnated with chemical reagents have found wide applica- tions for many years for the detection of toxic substances in air. Examples include the use of mercuric bromide papers for the detection of ar- sine, lead acetate for hydrogen sulfide, and a freshly impregnated mixture of o-tolidine and cupric acetate for hydrogen cyanide. When a spe- cific paper is exposed to an atmosphere contain- ing the contaminant in question, the observed time of reaction provides an indication of the concen- tration of that substance. Thus, in the case of hydrogen cyanide a S-second response time by the o-tolidine-cupric acetate paper is indicative of a concentration of 10 ppm of HCN in the tested atmosphere. Similarly, sensitive detector crayons have been devised for the preparation of a reagent smear on a test paper whose response to a specific toxic substance in a suspect atmosphere may then be timed to obtain an estimation of the atmospheric concentration of a contaminant. Crayons for phosgene, hydrogen cyanide, cyanogen chloride, and Lewisite (ethyl dichloroarsine) have been formulated for this purpose.® Colorimetric Indicator Tubes. Colorimetric indi- cating tubes containing solid reagent chemicals provide compact direct-reading devices, which are convenient to use for the detection and semiquan- titative estimation of gases and vapors in atmos- pheric environments. There are tubes for nearly two hundred atmospheric contaminants on the market, and seven U.S. companies manufacture and/or distribute these devices currently in this country. Whereas it is true that the operating procedures for these tubes are simple, rapid and convenient, there are distinct limitations and po- tential errors inherent in this method of assessing atmospheric concentrations of toxic gases and vapors. Therefore, dangerously misleading results may be obtained with these devices unless they are used under the supervision of an adequately trained industrial hygienist who (1) enforces rig- 189 idly (a) the periodic (as required) calibration of individual batches of each specific type of tube for its response to known concentrations of the contaminant and (b) the refrigerated storage of all tubes to minimize their rate of deterioration; (2) informs his staff of the physical and chemical nature and extent of interferences to which a given type of tube is subject and limits the tube’s usage accordingly; and (3) stipulates how and when other independent sampling and analytical pro- cedures will be employed to derive needed quanti- tative data. Colorimetric indicating tubes are filled with a solid granular material, such as silica gel or alumi- num oxide, which has been impregnated with an appropriate chemical reagent. The ends of the glass tubes are sealed during manufacture. When a tube is to be used, its end tips are broken off, the tube is placed in the manufacturer's holder, and the recommended volume of air is drawn through the tube by means of the air moving de- vice provided by the manufacturer. This device may be one of several types such as a positive displacement pump, a simple squeeze bulb, or a small electrically operated pump with an attached flow meter. Each air moving device must be cali- brated after each usage or after sampling 100 tubes as an arbitrary rule or more often if there are reasons to suspect changes due to effects of a corrosive action from contaminants in tested atmospheres. An acceptable pump should be correct to within == 5% by volume; with use, its flow characteristics may change. It should also be checked for leakage and plugging of the inlet after every 10 samples. In most cases, a fixed volume of air is drawn through the detector tube although, with some systems, varied amounts of air may be sampled. The operator compares either an absolute length- of-stain produced in the column of the indicator gel or a ratio of the length-of-stain to the total gel length against a calibration chart to obtain an in- dication of the atmospheric concentration of the contaminant that reacted with the reagent. In another type of tube, a progressive change in color intensity is compared with a chart of color tints in making the estimation. In a third type of detector, the volume of sampled air which is re- quired to produce an immediate color change is noted; it is intended that this air volume should be inversely proportional to the concentration of the atmospheric contaminant. The remainder of this chapter is devoted to the direct-reading, colori- metric indicating detector tube systems because of the widespread use of these devices. Detector Tube Characteristics Reagents and Interferences. Complete informa- tion on the formulations of the chemical reagents used in the manufacture of the commercial de- vices is not available owing to the understand- ably competitive nature of this enterprise. How- ever, there is sufficient knowledge of the chemical nature of certain solid reactants commonly used for this purpose to provide the limited informa- tion on chemical reactants, products, color changes, and stated interferences given in Table TABLE 16-2 Select List of Detecting Reactions in Colorimetric Indicating Tubes* Reagents in Test Gas ~~ Pre- Ampoule or Color Stated or Vapor cleanse Conversion Indicating Product(s) Change Interferences Layer Layer Layer Acetone None None 2, 4-Dinitro- A hydrazone Pale Yellow Other ketones and : phenylhydra- to Yellow aldehydes, alcohols, zine esters Acrylo- None (1) Chromate (2) Mercuric (1) Hydrogen Yellow to HC1, HCN, organic nitrile (VI) Com- chloride cyanide red CN compounds, pound (3) Methyl (2) Hydrogen aromatic solvents red chloride (3) Red form of indicator Alcohol Drying None Chromate Chromic (III) Yellow to Other oxygenated agent (VD) compound green compounds compound Ammonia None None (1) Acid (1) Ammo- Orange to Amines, (2) Bromo- nium salt dark blue Hydrazines phenol blue (2) Blue form of indicator Aniline None (1) Furfural (2) Acid (1) Schiff White to Ammonia base red (2) Dianiline derivative Arsine Copper None Gold Colloidal White to Phosphine, compound compound gold weak violet stibine (to retain grey reduced S com- pounds, H.,Se, NH, and HC1) Benzene Acid and None (1) Formalde- (1) Diphenyl- White to None affect the aldehyde hyde methane brown indication (to retain (2) Sulfuric (2) p-Quinoid other acid compound aromatics) Carbon None None (1) Hydrazine (1) Carbonic White to None affect the Dioxide (2) Crystal Acid Mono- blue indication violet hydrazide (2) Blue form of indicator Carbon Copper None (1) Copper Copper Pale blue None affect the Disulfide compound compound Dialkyldi- to yellowish indication (except (to retain (2) Amine thiocar- green H.,S) H.S) bamate Carbon Chromate None (1) Iodine Iodine White to Acetylene and Monoxide (VI) com- pentoxide (and carbon brownish easily cleaved pound (to (2) Selenium dioxide) green halogenated retain dioxide hydrocarbons H,S,C.H,, (3) Fuming petroleum sulfuric acid com- pounds) 190 TABLE 16-2 (Continued) Select List of Detecting Reactions in Colorimetric Indicating Tubes* Reagents in Test Gas Pre- Ampoule or Color Stated or Vapor cleanse Conversion Indicating Product(s) Change Interferences Layer Layer Layer Carbon None (1) Fuming (2) Dimethyl- (1) Phosgene Yellow to Fluorochloro- Tetra- Sulfuric amino-ben- (2) “Blue blue methane chloride acid zaldehyde reaction compounds (3) Dimethyl- product” aniline Chlorine Drying None o-Tolidine “Yellow White to Bromine, chlorine agent reaction yellow dioxide; discolora- product” tion by nitrogen dioxide Chloro- None None Permanganate “Yellowish Violet to Other organic prene Brown yellowish compounds with Reaction brown carbon-carbon Product” . double bonds Cyanogen None (1) Pyridine (3) Barbituric (1) & (2) White to Cyanogen Chloride (2) Water acid Glutacon- pink bromide aldehyde cyanamide (3) “Pink Reaction Product” Ethyl Drying None Chromosul- ~~ Chromic (III) Orange to Easily oxidized acetate agent furic acid compound brown green organic compounds including other acetates Formalde- None (1) Xylene (2) Sulfuric (1) Dixylyl White to Other aldehydes hyde vapor acid methane pink and styrene (2) “Pink quinoid compound” Hydra- None None (1) Acid (1) Hydra- Yellow to 1,1-Dimethyl zine (2) Bromo- zinium salt blue hydrazine, ammonia, phenol blue (2) Blue form amines of indicator Hydro- Drying None Bromophenol Yellow form Blue to Chlorine; chloric agent blue of indicator yellow R.H.>80% Acid Hydro- Lead com- None (1) Mercuric (1) Hydrogen Yellow to None affect the cyanic pound (to Chloride chloride red indication (except Acid retain (2) Methyl (2) Red form those not retained H,S,HCI1, red of indicator in precleanse layer) SO,,NO, and NH,) Hydrogen None None Zirconium- Alizarin Pale violet High humidity fluoride alizarin to pale lake yellow Hydrogen None None Lead Lead White to None affect the sulfide compound Sulfide light brown indication Mercaptan None (2) Sulfur (1) Copper (1) Copper White to Other mercaptans, solution compound mercaptide yellowish hydrogen sulfide, (2) Yellowish brown ammonia, brown copper amines compound 191 TABLE 16-2 (Continued) Select List of Detecting Reactions in Colorimetric Indicating Tubes* Reagents in Test Gas ~~ Pre- Ampoule or Color Stated or Vapor cleanse = Conversion Indicating Product(s) Change Interferences Layer Layer Layer Methyl None (1) Sulfur (3) o-dianisi- (1) & (2) White to Halogens, halides, bromide trioxide dine Bromine brown halogenated (2) Perman- (3) “Brown hydrocarbons ganate Reaction Product” Mono- Drying None Sulfuric acid “Yellow White to Butadiene and other styrene agent Reaction yellow polymertending Product” organic compounds Nickel None (2) Dioxime (1) Iodine (1) Nickel Pale brown Iron pentacarbonyl, tetracar- iodide to pink hydrogen sulfide, bonyl (2) Nickel sulfur dioxide dioxime complex Nitrogen Drying None N,N’-di- “Bluish grey White to Ozone, chlorine dioxide agent phenylben- Reaction bluish grey (NO,) zidine Product” Nitrous None (1) Chromium (2) N,N’-di- (1) Nitrogen White to Ozone, chlorine fumes (VI) com- phenylben- dioxide bluish grey (NO + pound zidine (2) “Bluish NO,) grey reac- tion product” Ozone None None Indigo Isatine Pale blue Chlorine, to white nitrogen dioxide Perchlor- None (1) Perman- (2) N,N’-di- (1) Chlorine White to Halogens, hydrogen oethylene ganate phenylbenzi- (2) “Greyish greyish halides, easily dine blue Reaction blue cleaved halogenated Product” hydrocarbons, petroleum vapor Phenol None (1) 2,6-di- (2) Activated (1) & (2) White to Other aromatic bromoqui- silica gel Indophenol ~~ blue hydroxy compounds, none chlor- dye quinones; ammonia imide and amines discolor indicating layer Phosgene Drying None (1) Dimethyl- Bluish green Yellow to Carbonyl agent aminobenz- complex bluish bromide aldehyde green (2) Diethyl- aniline Phosphine Copper None Gold Colloidal White to Arsine, compound compound gold weak greyish stibine (to retain violet reduced sulfur com- pounds, NH,,H,S & H,Se) Sulfur Copper None lodine/ Sulfuric Blue to Nitrogen dioxide = compound Starch acid white dioxide (to retain H.S) 192 TABLE 16-2 (Continued) Select List of Detecting Reactions in Colorimetric Indicating Tubes* Reagents in Test Gas Pre- Ampoule or Color Stated or Vapor cleanse Conversion Indicating Product(s) Change Interferences Layer Layer Layer Toluene Drying None (1) Iodine (1) & (2) White to Xylenes, benzene agent pentoxide Iodine brown (2) Dilute sulfuric acid Trichloro- None (1) Sulfuric (3) o-diani- (1) & (2) Pale grey Some other halo- ethane acid sidine Chlorine to brownish ~~ genated hydrocar- (2) Oxidizing (3) “Brownish red bons; petroleum agent red Reaction hydrocarbons & Product” aromatic compounds >1000 ppm Trichloro- None (1) Perman- (2) o-toli- (1) Chlorine White to Halogens, halides, ethylene ganate dine (2) “Orange orange easily cleaved Reaction halogenated Product” hydrocarbons, petroleum distillate vapors Vinyl None None Permanganate Light brown Violet to Organic compounds chloride manganese light with carbon-carbon compound brown double bond * Taken from Draeger Detector Tube Handbook, Draegerwerk. Liibeck, West Germany, 1970, pp. 33-71. 16-2. From this table it is apparent that the lack of specificity encountered with certain detector tubes is due to the use of common reagents for numerous compounds. Thus, the use of a hexa- valent chromium compound for the oxidation of a wide variety of organic substances with the pro- duction of a green chromic reaction product is a completely nonspecific procedure for these sub- stances. This type of detector tube must be used with the realization that all readily oxidizable sub- stances may affect the indication and efforts should therefore be taken to ascertain the chemical nature of the various associated contaminants in each exposure situation. Further, aromatic hydrocar- bons, hydrides, halides, and chlorinated hydrocar- bons provide other examples of class compounds for which single formulations in detector tube re- actants may have been used. Such formulations limit the usefulness of these tubes in mixed expos- ure areas as the estimations are then based on the results of the reaction of a mixture of contami- nants. Furthermore, errors of estimation may be positive or negative depending upon whether a stain is intensified (or lengthened) by the presence of a similarly reacting contaminant or bleached by a differing chemical contaminant present in the sampled air stream. This general situation has evoked a great deal of criticism of detector tube systems by the industrial hygiene profession which recognizes the need for improved devices of this type. Efforts to overcome this cross sensitivity have been attempted by: a. Use of a pre-layer to re- move certain known interferences from the air stream before they reach the indicating layer; and b. Use of a conversion layer to transform the de- sired gaseous substance to a different chemical compound which can then react with the indicat- ing layer. Examples of the incorporation of a pre-layer in the formulation of a tube include the Drager Arsine 0.05/a and the Benzene 0.05 tubes. The former uses a copper compound to retain in the pre-layer such interferences as hydrogen sulfide, hydrogen selenide, mercaptans, ammonia, and hy- drogen chloride, but allows arsine to pass through to the indicating layer containing a gold com- pound with which the arsine reacts to yield a weak violet-gray color. The benzene 0.05 tube has an acid-aldehyde reagent to remove toluene, xylene and naphthalene; benzene passes on into the indi- cating layer where it produces a brown color from its reaction with formaldehyde and sulfuric acid. Another difficulty arising from detector tube reagents is the catalyzed reaction of gaseous con- taminants with one another due to the active con- tact surface provided by the column of chemicals in the detector tube. This phenomenon has been observed with sulfur dioxide and nitrogen dioxide when these gases are brought into closer molecu- lar contact in detector tubes than that prevailing 193 in ambient atmospheres where their reaction rate with each other is generally low. Quality Control. The rigid control of the purity of reagents, grain size of the gel, method of pack- ing the tubes, moisture content of the gel, uni- formity of tube diameter, and proper storage pre- cautions is required for the optimal performance of any detector tube. The lack of such controls will lead to an inferior product whose use may produce disastrous results in the evaluation of health related problems. Thus, an incompletely responsive tube could cause a hazardous situation to remain uncorrected. Conversely, an overly re- active response may cause undue concern, wasted effort and needless expense for unwarranted cor- rections. Failure of certain manufacturers to maintain a rigid control over manufacturing practices has been observed in the past. Although it has been established’ that an elevated moisture content above 20% will cause a rapid deterioration of the silica gel used in the potassium pallado-sulfite formulation for a carbon monoxide tube, one ob- server found during a visit to a detector tube manufacturing facility that there was a lapse of many hours following the packing but preceding the hermetical sealing of the tubes. Indeed, such a practice permits the entry of not only moisture but also other contaminating vaporous substances which might produce a deleterious effect on the reagent’s future response to the analysis sub- stance. Another critical parameter is the tube diam- eter. Manufacturing variations in the internal diameter of the narrower tubes can produce ap- preciably different cross sectional areas. Saltzman has pointed out that this situation leads to cali- bration errors as high as 50 percent due to a varying volume of air sample per unit cross sec- tional area as compared with those provided under standard test conditions.” At least one manu- facturer minimizes the effect of this source of error by loading equal amounts of the indicating gel into each tube; the variations in cross sectional areas are then compensated by corresponding vari- ations in the filled lengths of the tubes.* The manufacturer provides calibration scales which permit the positioning of each tube in accord- ance with its filled length when measuring the length of stain and thus reduce the overall error of measurement of the gas concentration. Variations in the grain size of the gel, in the purity of the reagents and the cleanliness of the air in the tube manufacturing facility can affect the properties of different batches of the indicat- ing gel markedly. If not controlled carefully, these parameters can cause marked and unpredict- able changes in the number of active centers on the solid surface of the gel and thus affect the reaction velocity of the indicating system. The method of storage has a profound effect on the shelf life of an indicator tube. Deteriora- tion of the tubes increases greatly at elevated tem- peratures and storage under refrigeration by both the manufacturer and the user is mandatory to realize a useful shelf life which may approximate 194 two years for some of the tubes. Multiple layer tubes may have a shorter shelf life due to diffusion of chemicals between layers. For these reasons a realistic expiration date for tubes stored under refrigeration should be stamped on each box of tubes by the manufacturer. Calibration. Saltzman has presented an excellent treatment of the theory of indicator tube calibra- tion where he has developed a basic mathematical analysis of the relationships between the variables which affect the length of stain, i.e., the concen- tration of test gas, volume of air sample, sampling flowrate, grain size of gel, tube diameter and other variables. This source should be consulted for a full appreciation of the complex interrelationships between the factors affecting the kinetics of indi- cator tube reactions. It is sufficient to point out in this chapter that the length of stain is propor- tional to the logarithm of the product of gas con- centration and air sample volume as shown in the following equation:’ L/H=In (CV) + In (K/H) where: L = the length of stain in centimeters, C= the gas concentration in parts per million, the air sample volume in cubic centimeters, a constant for a given type of indicator tube and test gas, a mass transfer proportionality factor having the dimensions of centimeters, and known as the height of a mass transfer unit. If this mathematical model is correct for a given indicator tube, a linear plot of L versus the logarithm of the CV product, for a fixed constant flowrate, will yield a straight line with slope =H. The significance of this equation is the implication that it is important to control the flowrate, which may produce a greater effect on the length of stain than does the concentration of the test gas. There- fore, in the optimal design of an indicator tube it is desirable that the reaction rate be sufficiently rapid to permit the establishment of equilibrium between the indicating gel and the test gas and thus produce a stoichiometric relationship between the volume of stained indicating gel and the quan- tity of the absorbed test gas. Such equilibrium conditions may be assumed to exist when stain lengths are directly proportional to the volume of sampled air and are not affected by the sampling flowrate.” With this situation a log-log plot of stain length versus concentration for a fixed sam- ple volume may be prepared in the calibration of a given batch of tubes. From the preceding discussion of the com- plexity of the heterogeneous phase kinetics of in- dicator tube reactions, the quality control prob- lems associated with their manufacture and stor- age, and the difficulties posed by interfering sub- stances, it is obvious that frequent, periodic cali- bration of these devices should be made by the user. Dynamic dilution systems for the reliable preparation of low concentrations of a test gas or vapor are recommended for this purpose (see Chapter 12). Such calibrations should be per- formed before each use if there has been an appreciable period since the last calibration was performed. Evaluation of Performance As of January 1, 1972, the results of the eval- uation of gas detector tubes for five substances had been published by the National Institute for Occupational Safety and Health ® 10-21-1218 The results are as follows: No. of Manufactured Tubes Meeting Approval Criterion Within + 25% + 50% Substance at 95% C.L.* at 95% C.L. Benzene None 3 Carbon Monoxide None 8 Carbon Tetrachloride None None Perchloroethylene 3 es Sulfur Dioxide 4 _— *95% Confidence Level References I. HARRINGTON, D. U. S. Bureau of Mines Infor- mation Circular No. 7072 (1939), Washington, D.C. 2. TIMBRELL, V. “The Inhalation of Fibrous Dusts,” Biological Effects of Asbestos, Annals of the New York Academy of Sciences, 132, 255-273 (Decem- ber 31, 1965), New York, New York. 3. WITTEN, BENJAMIN and ARNOLD PROSTAK. “Sensitive Detector Crayons for Phosgene, Hydrogen Cyanide, Cyanogen Chloride, and Lewisite.” Ana- lytical Chemistry, 29, 885-887, 1155 Sixteenth NW, Washington, D. C. (1957). 4. SALTZMAN, BERNARD E., Ph.D. “Direct Read- ing Colorimetric Indicators” Air Sampling Instru- ments, Section S. American Conference of Govern- 195 10. mental Industrial Hygienists, P. O. Box 1937, Cin- cinnati, Ohio, Fourth Edition, pp. S-1 and S-11 (1972). SILVERMAN, L. and G. R. GARDNER. “Potas- sium Pallado-Sulfite Method for Carbon Monoxide Detection,” American Industrial Hygiene Associa- tion Journal, 26, pg. 2, 210 Haddon Ave., Westmont, New Jersey (March-April, 1965). KUSNETZ, HOWARD L. “Evaluation of Chem- ical Detector Tubes,” Paper presented at Chemical Section, National Safety Congress, Chicago, Illinois (October 27, 1965). SALTZMAN, BERNARD E. “Direct Reading Colorimetric Indicators,” Section S, Air Sampling Instruments, American Conference of Governmental Industrial Hygienists, Cincinnati, Ohio, Fourth Edi- tion (1972). SALTZMAN, BERNARD E. “Basic Theory of Gas Indicator Tube Calibration,” American Industrial Hy- giene Association Journal, 23, pg. 112-126, 210 Had- don Ave., Westmont, New Jersey 08108 (March- April, 1962). MORGANSTERN, ARTHUR S., ROBERT M. ASH, and JEREMIAH R. LYNCH. “The Evalua- tion of Gas Detector Tube Systems: 1. Carbon Monoxide,” American Industrial Hygiene Associa- tion Journal, 31, pg. 630-632, 210 Haddon Ave. Westmont, New Jersey 08108 (September-October, 1970). ASH, ROBERT M. and JEREMIAH R. LYNCH. “The Evaluation of Gas Detector Tube Systems: Benzene,” American Industrial Hygiene Association Journal, 32, pg. 410-411, 210 Haddon Ave., West- mont, New Jersey 08108 (June, 1971). ASH, ROBERT M. and JEREMIAH R. LYNCH. “The Evaluation of Gas Detector Tube Systems: Carbon Tetrachloride,” American Industrial Hygiene Association Journal, 32, pg. 552-553, 210 Haddon Ave., Westmont, New Jersey 08108 (August, 1971). ASH, ROBERT M. and JEREMIAH R. LYNCH. “The Evaluation of Gas Detector Tube Systems: Sulfur Dioxide,” American Industrial Hygiene Asso- ciation Journal, 32, pg. 490-491, 210 Haddon Ave., Westmont, New Jersey 08108 (July, 1971). ROPER, C. PAUL. “An Evaluation of Perchloro- ethylene Detector Tubes,” American Industrial Hy- giene Association Journal, 32, pg. 847-849, 210 Had- don Ave., Westmont, New Jersey 08108 (December, 1971). CHAPTER 17 MEDICAL ASPECTS OF THE OCCUPATIONAL ENVIRONMENT Bertram D. Dinman, M.D. THE PHYSICIAN, NURSE AND INDUSTRIAL HYGIENIST (The Occupational Health Protection Team) The Role of The Physician Elucidation of Human Parameters of Response. The health of man in the working environment is the central theme of occupational health. While measurement of atmospheric concentrations of an environmental pollutant, per se, in the work place is of interest, it has little relevance to occupational health except in terms of what it means to man’s health and well-being. Hence, measurements of environmental contamination must be evaluated in terms of their effects, or lack of them, upon humans. In order to elucidate the effects upon man of potentially deleterious physical or chem- ical agents found in the work place, the physician, as a specialist in human biology, must provide and interpret such “readouts” of human response. Only then can the main component of this “agent- host” interaction be defined. Only within such a frame of reference may the ultimate significance for man be ascertained of such quantifications of occupationally encountered biological, physical or chemical agents. Promotion of Human Health. The physician’s role in occupational health cannot be that of a mere passive interpreter of human response. He has a positive responsibility for utilizing his special expertise in conjunction with his societal status to actively promote health in industry. One as- pect of this responsibility relates to occupationally- related disease and injury; the other to prevention, where feasible, of non-occupational health deter- ioration; e.g., diabetes or glaucoma detection. Regarding the former, the physician must be pre- pared to extend his capacities so as to detect early, even subclinical responses; in addition he must be unhesitating in his readiness to insist upon management’s taking notice and acting upon his recommendations for amelioration and control of the working environment. In the industrial en- vironment, the ex cathedra stance carries only limited impact as compared to the private practice physician-patient relationship. It is because of this reality that the physician requires all the available facts to buttress his opinion. Here the industrial hygienist with his quantitative evaluation of the situation provides the irreplaceable other portion of the equation, “man + agent = effect.” As to the physician’s responsibility for preven- tion of the deleterious effects of non-occupational disease, here his duty parallels usual medical functions elsewhere. However, by virtue of the physician’s place in the industrial setting, he has 197 several advantages over the practitioner in the private sector. This largely stems from his knowl- edge of human interactions in the work place; he is in a unique position to evaluate the social as well as the physical demands made upon the worker in industry. Thus, hypertensive cardiovascular disease is a process which is not purely biological; its course is affected by the transactions between the patient and his socio-economic environment. A not insignificant segment of this environment is constituted by that setting in which the worker spends approximately one-fourth his life span, i.e., the work place. Operationally, this gives the physician the opportunity to manipulate within limits the human environment within the work place so as to favorably influence the course of the employees’ health and well-being. The Role of the Nurse The nurse is the “front line” worker in occu- pational medicine. It is the nurse whom the worker meets 90% of the time when he encounters the medical department. She must be ready to keep a highly “tuned” ear. Information bearing upon the work environment or the individual's health will be imparted to her long before it is transmitted to others. Therefore, as the eyes and ears of the medical department she must guard against “tun- ing out” worker plaints and statements. Given human tendencies for just such response after years of listening, both the physician and nurse must be constantly alert to prevent the develop- ment of a hardened, unsympathetic auditor. While suspending value judgments as regards the merit, — or lack of same, — of employee complaints is difficult, nevertheless all such information inputs contain some value, positive or otherwise. Workers perceive through the nurse the attitude toward them of the medical organization. If they conclude that their statements are consistently ignored, dis- puted or denied, soon this invaluable intelligence concerning the total work environment within the plant will disappear. From these facts stem the reality that the actions and treatment afforded by the industrial nurse will primarily determine the effectiveness of the medical department. However, the nurse is not merely a passive reporter. While not implying that she is practicing psychiatry, nevertheless as a skillful listener she fulfills many of the requirements for promotion of mental hygiene. As a sympathetic auditor, she provides the opportunity for verbal ventilation, a significant part of the therapist-patient transaction. Beyond even this role, the nurse is being given greater responsibilities in worker evaluation. Many more components of the pre-placement and peri- odic medical evaluation process are being relegated by the physician to the nurse. While restrictions imposed by various of the Medical Practice Acts must be observed, nevertheless with the aid of new automated devices many of these exam- inations are being performed by the nurse. Ex- ecution of the amanuensis by use of appropriately designed printed forms can conserve significant portions of physician time. Indeed, it appears that given sympathetic listening, such historical portions of the medical examination can be more effectively performed by the nurse rather than the physician. The Role of The Industrial Hygienist As alluded to previously, the physician in private practice can frequently assume an author- itative relationship with the patient. However, in the world of business and industry decisions are usually made and action taken upon the basis of quantitative objective parameters. While by the use of clinical laboratory modalities the physician can provide many mensurable descriptions of human response, such data may or may not be a reflection of work environment-induced biological change. For example, while anemia may result from chronic benzene absorption, it may also stem from non-occupational medical causes. Thus, in any determination of the reality of possible ben- zene exposure, it is necessary to know whether sufficient benzene was present in the work en- vironment to cause the observed anemia. Only the industrial hygienist can provide this necessary environmental quantification. Without this infor- mation it should be readily apparent that the phy- sician can only guess at causal relationships be- tween the worker’s condition and the work place. Such “guesses” are not considered, and should not be, sufficient basis for action by industrial man- agement. The Need for Coordination of the Work of the Medical Team with the Industrial Hygienist Evaluation of the Host-Agent Interaction. It should be apparent from the foregoing that meas- urement of environmental parameters, while intel- lectually interesting, has little relevance in industry except in terms of its human health implications. It is equally clear that human biological response is usually non-specific in nature. It is only when these two components, environmental and biolog- ical, are interdigitated does reality emerge. Ac- cordingly, both medical personnel and industrial hygienists have their contribution to make in elucidating this reality. Since the host-environment interaction is a dynamic ever-changing relation- ship, an on-going relationship must be developed and maintained between these two disciplines, medicine and industrial hygiene. From the results of such quantitatively validated investigations ap- propriate engineering and medical control pro- grams are developed. Evaluation of the Efficacy of Occupational Hazard Control Programs. In response to validated needs for industrial hazard control, engineering measures (e.g., ventilation, enclosure, etc.) are instituted. Despite the highest quality of engineering design and performance, because such measures are con- trolled, operated and maintained by men, human 198 imperfections impose themselves upon the efficacy of such controls. While physical and chemical measurements of the effectiveness of such approaches to hazard control are useful, once more their relevance to the ends desired are man-oriented. Therefore, the adequacy of control performance must be meas- ured in terms of human protection or its lack. Once more, the inputs of the biological scientist (the physician) and the physical scientist (the industrial hygienist) are required to round out the entire picture. Only by coordinating their inter- relating investigational data can these two con- tributors to industrial health control be effective. Since these interactions may be long-term as well as immediate, adequately coordinated record sys- tems must be developed. Such systems must not only provide records of events, they must be so designed as to provide adequate and early signals of ongoing failures or inadequacies of control sys- tems. Once more, coordination of medical and work environment data must be carefully built into such recording methods. Detection of New or Potential Problems. Among the greatest challenges to occupational health is the delineation of new occupational hazards. Early warning systems for new health conditions arising out of the working environment have only infrequently been achieved before harm has been done. As quantitative environmental and biolog- ical indicators develop greater sensitivities, the potential for detection of a problem before human harm occurs becomes more feasible. With thou- sands of new chemical agents entering the indus- trial scene there is an increasing opportunity for development of new knowledge as well as for pre- venting human damage. Only by coordinating the activities of the medical and industrial hygiene components of the occupational health team will this potentiality be realized. The Special Qualifications of the Physician Specialist in Industry Preventive Medicine in Industry 1. Primary prevention (a) Definition: This has been defined as the pre- vention of the occurrence of disease or disability arising from pathological processes. While its ac- complishment in relationship to the usual chronic or degenerative disease process has been less than spectacular, the potentials for realization of the concept of primary prevention are uniquely feas- ible in the industrial setting. (b) Applicability to environmentally induced dis- ease: While the mechanisms responsible for the common degenerative disease processes (e.g., cancer, heart disease, diabetes) remain obscure, the etiologies of environmentally induced diseases are relatively accessible. Thus, if the etiological agents causing occupational diseases can be pre- vented from contacting the human host, a poten- tially pathologic process can be totally prevented. Within the limits of an adequate perspective, one cannot imply that certain biological variables, e.g., age, sex, nutritional status, do not affect the course of an agent-host interaction. These variables, and other poorly defined, genetically controlled factors, will also affect the human response. But while the importance of these determinants of human re- sponse to environmentally encountered agents can- not be disregarded, the intrinsic potency of occu- pational chemical or physical agents can be pre- vented from being expressed. The knowledge that such agents are capable of inciting human damage upon absorption leads logically to design of meas- ure directed toward prevention of this event. This in turn requires that the physician have the capa- bility of quantitatively determining which level of contaminant presents no health hazard (viz., the “no-effect” portion of the dose-response relation- ship) so that control design criteria can be de- veloped. Another potential method of primary preven- tion depends upon detection of special suscepti- bilities of individual workers to certain occupa- tional hazards. Obvious examples, such as crane operators with inadequacies in their visual fields, come to mind. More subtle potential opportunities for prevention arise out of detection of inborne defects in certain metabolic processes, e.g., a “serum antitrypsin,” activity defect which inter- feres with normal cleansing of the lungs, should preclude such workers’ contact with pulmonary irritants. (¢) Limitations in primary prevention: One con- siderable limitation placed upon the efficacy of primary prevention stems from the fact that at present there are few existant physical or clinical laboratory indicators of special susceptibility to environmental agents. Thus, which worker, upon exposure to benzene, will develop a leukemic re- sponse cannot be adequately predicted; similarly, predictors of special susceptibility to low back injury are not existent. 2. Secondary Prevention (a) Definition: By secondary prevention we refer to the precluding of progression of disease or dis- ability resulting from some pathologic process. (b) Work and disease acceleration: While the causation of the usual degenerative disease process rarely directly results from occupational exposure, there is sufficient reason to believe that certain work demands may unfavorably influence the course of common degenerative disorders. Thus, the requirement of the brittle diabetic for strict and regular dietary control makes rotating shift work difficult for such an individual. The anxiety, physical and mental strain associated with jobs requiring rapid, weighty decisions or excessive travel may aggrevate coronary artery disease. Workers with chronic bronchitis hardly make fit candidates for jobs wherein there exists risks of exposure to pulmonary irritant gases and vapors. Since medical evaluation can detect such individ- uals, even though medical measures have not pre- vented the occurrence of such disease processes, exclusion from such risk can prevent acceleration or aggravation of those pathological processes. (c¢) Limitations upon secondary prevention: As previously discussed, it is our inability to predict response or understand the inhergnt nature of many diseases which limits our ability to prevent disease. Similarly, in many cases which factors associated with work or a pathologic process may 199 accelerate or aggravate such conditions also re- main obscure. Furthermore, peculiar to the prob- lem of prevention at the secondary level is the fact that such activity is usually most productive when directed to an early stage of development. Ac- cordingly, effectiveness here depends upon pre- existence indicators of minimal or subliminal dis- ease; unfortunately our abilities in this regard are at present somewhat limited. Understanding the Patho-physiology of Human Response to Environmental Change 1. Physiological principles (a) Mechanism of human response: While pre- viously discussed (see Chapter 6) extensively, some mention of the interplay of homeostatic mechanisms should be reviewed. Because the human organism lives within a dynamic ever- changing environment and receives a constant stream of external stimuli, the ability to adapt to such continuous change is a necessity of existence. In effect, this means that the body must be able to change the rate at which various activities were previously occurring. While physiologically at the whole organ level of organization this is readily perceived, e.g., as a tachycardia in response to running, at the cellular level similar changes in rates of metabolic activ- ities must occur. Similarly as with the previous example, until an optimal new rate which meets the new demand is achieved, activity may over- shoot and then compensate by slackening in at- tempting ultimately to ascertain what the optimum might be. Thus oscillation about an optimum rate, i.e., the eventual new steady state, has been characterized as a “hunting phenomenon.” This control system also has an information gathering component which reports all activity changes to control centers; the latter, in response to such in- formation directs the activity to hasten or slacken. In turn, it is receptive to new information which assesses the result of the control center’s pre- vious directions. In effect, what we have described is a self-regulating dynamic system. It should be emphasized that this system can meet new conditions within limits. Essentially, the rate at which it may function has finite limits, i.e., “rate limits,” at all levels of biological organ- ization. It is such “rate limits” at the cellular level which determine the response of the body to agents encountered at this level. Among the most prominent at this level of organization are the physical and chemical agents; these rate limits are at the heart of such encounters which constitute the science of toxicology. 2. Toxicologic principles While these are described in more detail in Chapter 7, review of the dose-response relation- ship is especially pertinent to the role of medicine in industry. The physician clearly recognizes that the effectiveness of therapeutic agents are a func- tion of the quantity of a medication given as well as the time period over which such agent is ad- ministered. However, for unknown reasons the same considerations are not usually applied to non-therapeutic elements, e.g., lead. In short, “poisons” are considered to be “poisonous” re- gardless of dose and time consideration. Regard- less of such a viewpoint, the fact remains that the same dynamic principles of dose and time apply to all elements or compounds entering the bodily economy. That is, when the organism encounters a material in its internal milieu, as long as too much is not presented over too short a time period, i.e., the body’s rate limit for handling such a compound is not exceeded, such a foreign mater- ial will have little if any effect. For most practical purposes, this appears true regardless of the ma- terial. That this must be the case is reflected in the fact that sophisticated analysis will find all 92 original elements in the body. It should, therefore, be apparent that the dose-response relationship (Chapter 7) is basic to an understanding of the effect of “foreign” elements or compounds in the body. (a) Measurement of response or body loadings The numerous methods utilized by the body to bind, transport or readily excrete a foreign element have been reviewed in Chapter 7. Thus detoxification mechanisms which depend upon the formation of polar conjugates, e.g., glucuronates, sulfates, also present an opportunity to measure the body’s effectiveness in dealing with a chemical. Measurements of such or similar metabolites in various body excreta provide a readily utilized technique to both detect such responses as well as measuring any effectiveness of metabolic handling. Similarly, certain non-polar solvents, because of their low solubility in blood (essentially an aqueous medium), readily diffuse from the lungs upon cessation of exposure. This too can be measured to gain insights into the amounts which have previously been taken up in the body. Fol- lowing the breath concentration of such solvents as they leave the lungs over a time course permits even more exact estimates of such body loadings. Other possible indirect measurements of body loadings may be elucidated by measurements of altered bodily functions induced by such foreign materials. For example, exposure to SO, will pro- duce bronchial constriction; the increased airway resistance which ensues can be readily measured and the amount of effect determined. While this last measurement can be derived from human experimental exposures, at least at relatively low concentrations, other metabolic in- sights frequently require analysis and extrapolation from animal data. (b) Extrapolation from animal data (1) Values By loading animals with varying concentra- tions of toxic materials, both the threshold for effect as well as related excretory and metabolic handling rates can be ascertained. Data require the study of multiple species, since some of these animal species may not handle certain agents in a similar fashion as man; nevertheless, where suffi- cient data are collected such information may be applicable to setting levels which are not deleter- ious as well as determining the rates at which man might safely handle such material (see Chapter 8). By construction of appropriate curves describing lung excretion over time periods, it is possible to estimate from similar curves in exposed workers the quantity of a chemical they have absorbed; 200 thus the means of estimating risk as well as iden- tifying the absorbed agent, can aid the occupa- tional health team in determining its course of action for both treatment and prevention. That is, this latter end can be achieved since indications of overexposure suggest the failure of established control measures. (2) Limitations Unfortunately, the use of animal testing to predict human response has limitations arising from the fact that man is a higher and different mammal from species used for such test purposes. This problem in extrapolation from animals to man is exemplified by the fact that because of metabolic pathway differences, aromatic amines, e.g., beta naphthyl amine, which clearly produce urinary bladder tumors in man, have not such effect in rats, mice or other rodents. Likewise sensitization processes, e.g., to toluene diiso- cyanates, which occur in man, cannot be repro- duced in animals. Accordingly, in view of such extrapolation problems negative results found after animal exposure to toxic chemicals is no guarantee of safety to man. Though this risk may be min- imized by testing several different species, the results of such investigations must be applied to man with caution. Understanding Manufacturing Processes 1 Periodic plant inspection (a) As with production and management personnel, the physician in industry should be totally aware of everything that occurs in the plant from its roof to sub-basement. In order to place any human aberration in its occupational context he should be familiar with every step of every process in the plant. In order to attain such understanding, it is useful if plant tours be made with technical and production personnel who can explain any rami- fications of any process, work station relationships, job requirements, material used or product pro- duced within the plant. This may require an understanding of chemistry, physics or mechanics which such personnel can impart. The physician must be familiar with every job, its title (official or otherwise) and demands in order to visualize it when such are referred to by workers who come to the medical department. Since every industrial plant is a dynamic, organic entity, what occurs within the plant is subject to constant change. Accordingly, such tours should be frequent and regularly repeated. (b) Plant tours can be of even more value to the physician if carried out with an industrial hy- gienist. Many of the health ramifications of ma- terials and processes which are unknown to pro- duction or other plant technical personnel can be readily recognized and their significance estimated by industrial hygienists. For example, while the safety hazards of Stoddard solvent are self evident, the industrial hygienist should recognize and be prepared to answer the question of how much benzene may be present. Furthermore, by careful use of environmental measurement devices in the plant, he comes to be recognized as having a responsibility for protecting health. Such tours with the industrial hygienist, and especially work- ing tours, serves to demonstrate to employees that there is a serious team effort directed toward making the work place safe and healthy (see below). ? The Position of the Physician in the Management- Labor Relationship 1. The honest broker The physician, as a staff member of the man- agement group, does not have executive respons- ibility (except in the medical department) within the plant hierarchy. As any other staff person, he is essentially an advisor, with management having the executive rights and responsibilities for action. Thus management need not heed the advice of any staff member, although if untoward results ensue it is the executive who is held responsible. While it is obvious to much of management that tech- nical advice, e.g., engineering, marketing, etc., should be heeded, this occasionally may not be so apparent to management as regards medical ques- tions. Since the executive is subject to multiple pressures and demands, frequently they may be inclined to “trade-off” long-term requirements to solve “short-term” needs. Thus, it can be seen that while production requirements make imme- diate demands on management, that on occasions when health or safety requirements might impede production, they might be induced to “short-cut” such inhibitions upon production. While top management most frequently can see the long-term objective, the daily demands imposed upon middle or lower management more frequently leads them to such “short-term” ob- servations. While this is yet another reason why the medical departments should report at the highest levels, this does not relieve them of the responsibility for vigorously presenting the ration- ale behind their judgments. Most assuredly, the position and responsibility of the medical organization is to consistently pro- mote all activities designed to protect employee health and welfare. This reinforces the fact that as a staff individual, given the responsibility for health and welfare, he should take a position based upon only these questions. While such health controls as are required to meet these demands may indeed intrude upon “short-term” production requirements, these latter requirements are clearly not his responsibility, and should not intrude upon professional judgments. Thus the medical department should be the “honest broker,” always acting upon the basis of health need re- quirements. While this may make for some short- term problems for management, if such health and safety positions are soundly based they are more profitable for all concerned in the long-run. If such a consistent position is taken by the medical department, the trust of all — management and labor — will follow. If the medical department thus sincerely follows up all health and safety problems brought to their attention by employees, such a position of integrity is further re-inforced. Both the physician and the industrial hygienist have their responsibilities for equitable, fair and consistent evaluations based upon facts, uncolored by either the desires of management or labor. 2. The medical department and the confidence of labor and management — privileged communica- 201 tions. All information dealing with health and welfare matters should be treated carefully and within the context of a written management policy. Personal medical questions especially should be dealt with as priviledged information. Thus the “need to know” should govern how information is handled, e.g., while personal medical details are not necessary for the ends of management, such information should only be made available in terms of management needs and comprehension. Therefore, detailed information describing the medical status of any individual is neither needed nor useful to management. The functional ability of a worker in terms of his ability to do a specific job is pertinent and necessary. Similarly the rela- tionship of health hazards to production rather than the intimate medical details of the situation, are required by management. MEDICAL APPROACHES TO CONTROL OF THE OCCUPATIONAL ENVIRONMENT Medical Examination Procedure — A Re-Orientation of Medical Practices The historical examination. While medical prac- titioners generally have been trained to reflexly think in terms of the diseased patient, in the indus- trial setting it becomes necessary for him to ap- preciate that he is dealing in the main with essentially healthy individuals. While the histor- ical examination of any person should consider him in terms of deviation from normal, it is also important to evaluate the worker in terms of his functional, total health status. Accordingly, it be- comes appropriate to carry out the medical history by use of self completion questionnaire. Thus, not only is greatest economy of physician time and cost achieved, it is possible for him to readily obtain an ‘entire health inventory. This is in con- trast to the usual situation wherein an individual consults a physician because of some health com- plaint, and the historical examination becomes oriented to elaboration of some specific pathologic process, affecting a specific organ system. The physical examination. The same principle as elaborated above applies here also. Thus, inves- tigations directed toward the whole person rather than toward a single organ system directs the phy- sical examination. It should, therefore, be obvious that in dealing with the relatively HEALTHY person the physical examination should take an- other form. For example, in a cost-yield basis the relative cost of percussion and auscultation of the chests of large numbers of individuals is high in terms of the information obtained. Thus, for large numbers of persons it becomes less costly, for ex- ample, to obtain a chest X ray and a timed vital capacity determination rather than to laboriously perform a chest examination. This is especially true since essentially the same information is ob- tained. Thus any deviations obtained by such a “screening examination” can be followed up by the usual more elaborate examination procedures. Certainly, in view of the relatively few deviations expected in an essentially healthy population, such procedure has its obvious cost-effectiveness sav- ings and yields. Much of the physical as well as historical ex- amination can be performed by paramedical per- sonnel. With the rapid development of medical- electronic investigative techniques, increasingly more of the examination can be achieved by these means. Use of the clinical laboratory for examination of ostensibly normal individuals. Our increasing capability to inexpensively and rapidly carry out clinical laboratory tests makes use of such deter- minations ever more fruitful. As automated lab- oratory procedures develop, the per unit cost decreases. In this fashion, a complete health pro- file can be more adequately and rapidly achieved. Problems arising out of the work environment may cause changes which can be detected by tests, such as multiphasic examination (i.e., medical, laboratory). This profile provides a useful base- line which aids in the detection of any possible subsequent health deviations. Should any physical or chemical agent produce health change, a health profile previously obtained has obvious compar- ison values for use in the control of health hazards. Where small numbers of workers are involved, consideration should be given to the purchase of multiphasic laboratory services. The cost per worker for such services in this case will be far less expensive than the cost of setting up a lab- oratory. Accordingly, medical services for small plants should seriously investigate contract pro- posals and performance of such commercial lab- oratories. The Pre-Placement and Pre-Employment Examination Philosophy and Purposes. The basic purpose of the pre-placement examination is to determine the capability of the job applicant to perform a spe- cific job for which he is to be hired. Thus such an evaluation is directed toward capabilities, not disabilities. While not all employees necessarily require testing of color perception, such evalu- ations become highly pertinent for workers for jobs requiring this adequacy; e.g., in color print- ing, color-coded electrical wiring, etc. While this theory applies in part, in reality many corporations recognize the point that they accept the whole worker with all his immediate health problems and possibly his long-term medical problems. This becomes especially pertinent as more and more of health and medical benefit costs are assumed through employer purchased health insurance. Accordingly, pre-placement examinations increas- ingly have become pre-employment examinations, so that total health evaluation becomes increas- ingly the rule. Nevertheless, there is still required an evalu- ation of physical and psychological capabilities to perform a specific range of jobs. It therefore be- comes necessary for the medical department to determine that a prospective employee does not have a pre-existing health problem that can be aggravated by his expected range of work duties. What has been previously stated regarding the use of electronic medical modalities and paramedical personnel applies equally here. However, it still remains the responsibility of the occupational health team to be fully cognizant of the job re- quirements and work environment so as to design 202 an appropriate examination regimen. This once more underlines the necessity for the occupational health group to be comprehensively knowledge- able concerning any and all jobs, their peculiarities or needs within the plant. Values and limitations. While fitting the right man in the right job is the aim of these examinations, the limitations inherent in this procedure must be recognized. These largely stem from the limita- tions inherent in medical prognostication of spe- cial susceptibility or inherent biological risk. The inability to clearly determine which individual possesses an inherent weakness of the lower back immediately comes to mind. Certainly the present inability to clearly evaluate the state of psycholog- ical fitness of an individual to fit into a specific social and physical environment presents even more serious problems. Recognizing these inherent weaknesses makes even more apparent the need for periodic re-evaluation of workers. Job restrictions and transmission of information to management. Once more, the executive is pri- marily interested in being informed of the job applicant’s ability to do a job. Accordingly, all medical information derived from such examina- tions should remain privileged information, in- accessible to all but medical personnel. Manage- ment should be fully informed of job abilities; why limitations are necessary in terms of specific medical diagnoses is neither necessary to his needs nor pertinent. Management should be kept in- formed through established channels (usually through the personnel departments) largely in terms of fitness to do a certain job. If medical conditions require job limitations or restrictions, such restrictions upon activities should be clearly and simply stated; the medical details as to “why” should not be divulged. The purpose of these job restrictions is to pre- vent deleterious effects upon the employee’s health. Since each person undergoes dynamic changes with time, the medical department has a responsibility for following and re-evaluating the appropriateness of such restrictions as time passes. As regards the need for follow-up of individuals placed under job restrictions, plant tours will also serve to determine whether the persons with re- strictions are performing in appropriate jobs. As for re-evaluation, this too requires periodic re- examination to determine the current appropriate- ness of work restrictions previously applied. The Periodic Health Examination Philosophy and purposes. As related to the work- ing environment, present limitations in our knowl- edge of human response to environmental changes requires that the periodic re-evaluation of exposed workers be performed. Thus, early detection of health changes becomes the primary orientation of this examination. In addition, because of the inexorable course of aging, those responsible for health protection need detect such changes so that work conditions do not accelerate or aggravate the aging process. Method of execution. General health maintenance: Too often the pathology oriented physician seeks only to elucidate the presence of disease. How- ever, equally important is a careful evaluation of the individual’s hygiene of living. Due consider- ation should be directed toward elaboration of life habits, e.g., smoking, diet, social interactions and mental health, sleep patterns, etc. Out of such a matrix of life habits and styles emerges a picture of the whole man, and the effects of his life style upon health and well being. While inquiry into medical status is appropriate and accepted, the physician in industry must carefully direct such evaluation of a personal nature along the same lines of action of the medical practitioner whose appropriate concern is the whole man. Only in- sofar as he is recognized as being primarily con- cerned with the employee’s well being, this ap- proach is proper. Otherwise, this all-encompassing approach may represent an encroachment by the employer upon a realm of employee’s personal life which is wholly inappropriate. Obviously, the methods employed in these examinations should be consistent with the cost-yield considerations noted above. Examination of workers exposed to occupational risk. Such examinations should be oriented toward medical and health evaluation procedures which delineate human responses to special environ- ments. For example, workers handling defatting solvents should be carefully examined to determine that dermatoses do not ensue. Other examples of special occupational risks, e.g., potentially hepa- totoxic solvent, pulmonary irritants, etc., will de- termine which clinical and laboratory examina- tions are required. Again, the health protection team must be completely familiar with the risk potentials of all jobs in the plant so as to intelli- gently design such examinations. Since engineering controls may fail or personal protective devices may be inadequately utilized, such examinations of workers at special risk should be regularly and periodically carried out. Record and scheduling systems should be so de- signed that these examinations are not missed and so that the information gathered can be rapidly and rationally reviewed. This requires both care- ful organizational efforts and design of medical records. Sources of information regarding occupational risks. The clinical literature in occupational med- icine and industrial hygiene is a rich mine of infor- mation. Herein will usually be found, to varying degrees of adequacy, much information regarding human response to environmental agents. In ad- dition, the literature concerning experimental in- vestigation of these special risks also becomes essential (see suggested readings). However, the occupational health team should be aware of the shortcomings inherent in that body of information. Newly encountered occupational chemicals may be associated with little available data concerning clinical effects. However, the ex- perimental literature can contribute to an under- standing of risk potentials. For example, while there is little clinical data concerning N-dimethyl- nitrosoamines, the experimental literature exten- sively documents that agent’s potential for carcino- genesis in animals. Accordingly, that agent should be treated as a potential carcinogen in the work 203 place, despite an absence of such recorded effects on man. The problems of extrapolation of data derived from animal experiments to man are self evident (see Chapter 7). Therefore, the experimental literature while potentially useful for health con- trol requires that it be used with appropriate care. This makes even more important the need for careful periodic clinical evaluation being per- formed with due consideration of such animal data. Other Examinations Separation Examinations. If a worker has been exposed to some occupational hazard and is to be separated from employment, it is the employer’s responsibility to ascertain his health status before such an event. While the legal responsibility of the employer ends only in part with discharge, any subsequent change may represent an aggra- vation or progression of a disease state incurred while at work. If a later status represents disease progression caused by work, the employer should be made aware of his legal and moral respons- ibility. If his future condition is unrelated to a work incurred condition, then equity demands that this ascertainment also be made. It should be apparent that the role of the medical department is to accumulate and evaluate all health information so that the best medical opinion can be clearly and equitably applied to the matter in question. THE ROLE OF THERAPY IN OCCUPATIONAL MEDICINE For Occupational Disease The Occupational Medical Practitioner as a Spe- cialist. In the treatment of occupational disease of a non-surgical nature, the occupational medical practitioner should be prepared to provide def- initive therapy. Certainly, in the area of clinical toxicology, such physicians more frequently en- counter these problems, e.g., as in chemical plants, than do their fellow practitioners. Thus all ramifi- cations (diagnosis, treatment and management) should be clearly within his competence. Should such medical problems arise, the occupational health specialist should be prepared to assume responsibility for all such cases, making use of appropriate medical or surgical consultants as the patient’s complications may require. The Use of Consultants (1) Principles governing choice Since the occupational medical specialist should know more about occupational diseases and the conditions of the work place, it follows that he should assume responsibility for medical management and direction of such occupationally caused problems. However, as noted above, should complications involving special organ sys- tems arise, e.g., cardiovascular, respiratory, etc., it is appropriate that such specialists be consulted. Nevertheless, except for unusual reasons the re- sponsibility should remain in the occupational medical specialist’s hands. A close working rela- tionship with such specialists should be developed in each case, as such physicians are invariably non-cognizant of in-plant conditions or the effects of toxic or physical agents. While it becomes the occupational medical specialist's responsibility to cooperatively aid the outside specialist in be- coming aware of those problems, the latter should not nevertheless abandon his primary responsibility. In one case of surgical problems, it is axio- matic that the best specialist help is the least expensive in the long-term prospect as well as being the most effective. While full responsibility for surgical treatment and management should be in such specialist’s hands, the occupational med- ical specialist still has an important role to play. Again, since he is the most knowledgeable regard- ing work requirements or opportunities for less demanding tasks, he is in the best position to guide the rehabilitation of the injured worker dur- ing the recovery phase. Close cooperation with physicians, utilizing both extra- and intra-mural (i.e., plant) facilities can lead to the most effective programs of rehabilitative therapy. (2) Limitations It should be pointed out that in many, if not most, jurisdictions the worker has the final and definitive choice of who should treat his occupa- tional disease or injury. Thus, the occupational medical specialist must observe this legal right. However, if the work force has confidence in the medical capabilities and the probity of the plant physician, most often the worker will accept his ministrations. However, should he decide other- wise, the plant physician has an ethical respons- ibility for cooperating with and aiding the manage- ment of the outside physician. Therapy of Non-Occupational Disease Stated Positions. It has been the position of or- ganized medicine that plant medical departments should not become involved in the treatment of non-work conditions. The only qualification of this position is related to treatment of minor con- ditions, e.g., headache, indigestion, of a non-re- curring nature for which the patient would not ordinarily seek medical help. Except for making it medically possible for the worker to safely finish his work-shift, he was to refer other medical prob- lems to the private practitioner. Trends in Occupational Medicine Regarding Man- agement of Non-Occupational Conditions. Because of increased medical care utilization, rising health expectations and modes of medical practice, the availability of primary medical care has become somewhat diminished. Accordingly, strict appli- cation of the foregoing principles have been tempered by present realities. Especially in areas where medical care resources are limited, the plant physician is seen as providing a scarce capability. As health care delivery systems become integrated, it would appear that the occupational health spe- cialist will play a more active role within such systems. In addition, since the employer assumes in- creasingly more financial responsibility for general medical care, he demands that medical care utili- zation become optimized. All of these forces can- not but help affect the present and future patterns of occupational health practice. While the form 204 such activity will take is unclear, given the present dynamism of this system, changes in such patterns of care are and will be occurring. OPPORTUNITIES FOR RESEARCH IN THE PRACTICE OF OCCUPATIONAL HEALTH Research in the Natural History of Disease. Use of Medical Records. At present, medical records in industry are largely oriented toward providing a data base for the several immediate respons- ibilities of the medical department. They are pri- marily directed toward providing the medical in- formation necessary to adequate management of medical conditions. Except where they also pro- vide health base lines needed for estimation of alteration due to environmental factors encoun- tered in the work place or because of periodic health evaluation program needs, they are fre- quently ill-suited for long-range assessments. In the past such records consisted of hand entries into medical forms. As such, ready assess- ments of large populations could not be achieved. Until the development of electronic tape and disc data storage systems, existent record systems in- hibited worker-population studies. However, it is becoming increasingly possible to store and readily retrieve discrete data “bits” involving large num- bers of workers. As such capabilities become in- creasingly more available, it should be possible to more readily use the masses of industrial health data presently unavailable. Given these capabil- ities, invaluable opportunities for the development of new medical knowledge will present themselves. Because working populations represent a useful cross-section of the active, non-hospitalized, the opportunity for delineation of the long-term, natural history of disease arises. In addition, study of the long-term effects of environmental stresses upon health should be accessible. As an example of the former type information, industrial populations have been useful in develop- ing new insights upon the effects of diabetes, hy- pertension and cardiovascular disease on long- term health status and productivity. Because such non-hospitalized populations can be studied, the misapprehensions derived from biased populations investigated in hospitals arc avoided. Elucidation of the Effects of Environmental Pollution upon Health The Work Population as an Exposed Population. Because occupational exposures usually are more intensive than that incurred by the general popu- lation, working groups represent ideal study groups for the evaluation of such environmental effects. Relatively higher doses of common environmental pollutants (e.g., CO, SO.) encountered in industry should, theoretically, accelerate the rate of devel- opment of deleterious health effects, if any, as compared to the rate of development possible because of lower doses in the community. Coupled with the advantage of the possibility of long-term observations is the fact that large numbers of ex- posed groups are concentrated in one area. Given adequate record systems the opportunities for epidemiological investigation are unparalleled. The Use and Limitations of the Epidemiologic Method. The epidemiologic method depends upon the systematic collection of information which makes possible the comparison of one population’s behavior with that of another similar group. Thus one assumes that the variables determining, e.g., health status, are completely similar in all regards except for a specific variable acting on only one of these two groups. Obviously, as many of these variables are op- erating upon both groups they must be defined, since assumptions of such comparability in all re- gards (except for the one under scrutiny in the group at risk) are unacceptable. Thus, data col- lection involves large numbers of variables, e.g., age, sex, activity and residence. These must be adjusted for in both groups. The use of industrial populations in this connection given adequate data collection, should be obvious. Especially pertinent is the opportunity for construction of a control group derived from a working population in order to estimate health or mortality experience. Such comparison groups are essentially the only group with which a working population at a special en- vironmental risk can be compared. Nevertheless, the use of industrial populations for delineation of occupational health risks pre- sents some attendant problems. One of these re- lates to assessment of exposure to a risk, since frequent in-plant job turnover may make tracing individual work or exposure experience difficult, especially in certain occupations, e.g., chemical operations. In addition, workers who are no longer on the rolls are a source of loss to a population of some consequence. This follows since they may have left employment because of incurring the health consequence under study. While conclu- 205 sions indicating a positive association between work and some condition might only lead, at worst, to underestimation of risk, the significance of absence of an association becomes severely compromised because of such losses. This points up the obvious need for careful, painstaking fol- low-up of those separated from the groups under study. However, carefully performed multi-cor- poration or industry-wide studies, e.g., of mortal- ity, have succeeded in providing valuable medical knowledge.’ Studies of morbidity have been less satisfactory, yet present a considerable potential source of valuable medical information. References 1. LLOYD, J. W.: J. Occup. Med., 49 East 33rd St., New York 10016, 13:53 (1971). Preferred Reading 1. Council on Occupational Health: “The Role of Med- icine Within a Business Organization.” J. Amer. Med. Assoc. 535 No. Dearborn St., Chicago, Ill. 60610, 210:1446-1450, 1969. 2. IBID: “Guide to the Development of Company Medical Policies.” Arch. Environ. Hlth. 535 No. Dearborn St., Chicago, Ill. 60610, 71:729-733, 1965. 3. IBID: “Guide to Diagnosis of Occupational Illness.” J. Amer. Med. Assoc. 535 No. Dearborn St., Chi- cago, Ill. 60610, 7196:297-298, 1966. 4. MAYERS, M. R.: Occupational Health Hazards of the Work Environment. The Williams and Wilkins Co., Baltimore, Md. 1969. 5. SHEPARD, W. P.: The Physician in Industry. Mc- Graw-Hill Book Co., New York City, 1961. 6. ROSS, W. D.: Practical Psychiatry for Industrial Physicians, Chas. C. Thomas, Springfield, 11l., 1956. 7. JOHNSTONE, R. T. and S. W. MILLER.: Occu- pational Diseases and Industrial Medicine. W. B. Saunders Co., Philadelphia, 1960. CHAPTER 18 SEPARATIONS PROCESSES IN ANALYTICAL CHEMISTRY Henry Freiser, Ph.D. INTRODUCTION Industrial hygiene chemistry is an extremely de- manding branch of analytical chemistry. Whereas many areas of applied chemical analysis are self- limiting, e.g., gas, mineral or metallurgical anal- yses, the field of industrial hygiene chemistry covers the tremendous breadth of the thousands of chemical substances encountered in man’s working environment. This complexity is compounded further by the need to separate, characterize and determine quantitatively trace quantities of these organic and inorganic substances in the presence of overwhelming quantities of bulk materials con- taining chemical interferences. The successful ap- plication of all modern physical and chemical methods of analysis to the detection and deter- mination of these individual chemical entities re- quires in many instances, the preliminary separa- tion and concentration of an analytically desired constituent from the bulk diluents and interfering elements present in biological tissues and fluids, complex mixtures of aerosols or industrial process materials and finished products. The daily solu- tion of these problems requires a full understand- ing of the basic principles of the separation proc- esses which must be applied to these sample systems to obtain the accurate analytical data needed for the valid and complete assessment of environmental conditions and their effects on the health of the worker. This chapter provides a basic theoretical treat- ment of two of the most powerful techniques used in inorganic separations; i.e., solvent extraction and ion exchange chromatography. These methods have provided the foundation of numerous ana- lytical procedures used in the industrial hygiene laboratory. The solvent extraction technique has been used widely for rapid, cleancut separations of trace level quantities of analytically desired elements and compounds (dithizonates, dithio- carbamates and 8-quinolinates of the heavy metals, phenolic compounds and ferric chloride, as ex- amples) from biological and environmental sam- ple materials. Ion exchange chromatography has proved to be extremely valuable in separating fractional part per million concentrations of inter- fering chemical elements from one another to in- crease the specificity, accuracy and sensitivity of their final method of estimation in diverse indus- trial hygiene samples. CLASSIFICATION OF SEPARATION PROCESSES Although great strides have been made in the development of highly selective analytical meth- ods, the analytical chemist is called upon to deal 207 with samples that are increasingly complex. As a result, inclusion of separation steps might be nec- essary even with highly discriminatory instru- mental methods such as neutron activation or atomic absorption analysis. Furthermore, separa- tion of a component of interest from the sample medium may also serve to concentrate it, which would effectively increase the sensitivity of the analytical method ultimately employed. One of the most powerful approaches to sep- arations involves using pairs of phases in which the component of interest transfers from one to the other in a manner that differentiates it from interferences. It is useful to classify phase separa- tion processes according to (a) the state of the phase pair involved (solid, liquid or gas), (b) whether the phase is in bulk or spread thin as on a surface and (c) the means of contacting the phase pair: (i) batch, (ii) multistage (iii) countercurrent. Bulk and “thin” phases can be distinguished in that by the latter is meant a spreading of the phase involved over a relatively large surface area. Thus, both distillation and gas-liquid chromatog- raphy (GLC) are separations involving gas-liquid phase pairs but in the latter, the liquid phase is spread out as a thin layer on a largely inert solid supporting material. Similarly, solvent extraction and liquid partition chromatography (either paper or column) involve a liquid-liquid phase pair but in the latter, one of the liquid phases is present as a supported thin layer. In these two examples cited, the mode of contacting the phases can also be different. In a simple distillation process, a batch of the mixture is placed in the boiler and the distillate contains the more volatile components. In contrast, with GLC, the gas mixture moves countercurrently to the immobilized liquid layer ensuring that the increasingly depleted mobile gas phase encounters a fresh clean portion of the im- mobilized liquid phase. In countercurrent proc- esses, a large number of equilibration (or approx- imate equilibration) steps occur. It is possible to carry out separations involving bulk phase pairs with countercurrent contacting. Thus, fractional distillation, in which a packed distillation column and reflux head are used, involves countercurrent contacting. This chapter is devoted to the description of the principles and practices of two-phase separa- tion processes, solvent extraction and ion ex- change, which are important in dealing with com- plex aqueous mixtures. Elsewhere in this syllabus (Chapter 21) several forms of chromatography are also covered. SOLVENT EXTRACTION General Principles and Terminology Solvent extraction is a process in which a _ solute of interest transfers from one solvent into a second which is essentially immiscible with the first. Because the extent of such transfer for var- ious solutes can be varied individually from neg- ligible to essentially total extraction, through con- trol of the experimental conditions this process provides the basis for many excellent separations. Fundamentally, all solvent extraction proce- dures can be described in terms of three aspects, or steps: First, the distribution of the solute, called the extractable complex or species, between the two immiscible solvents. This step can be described quantitatively by Nernst’s Distribution Law which states: The ratio of the concentrations of a solute distributing between two essentially immiscible solvents at constant temperatures is a constant, provided that the solute is not involved in chem- ical interactions in either solvent phase, or [A], Kp, = [A] (1) where A is a solute distributing between an or- ganic solvent in which the molar concentration of A is expressed as [A], and an aqueous phase as A without subscript. The constant Kj, is called the distribution constant. Second, chemical transformations to produce an extractable species are of primary importance in solvent extraction processes inasmuch as most of the substances of interest, particularly metal ions, are not usually encountered in a form that can be extracted into an organic solvent. This second aspect of extraction concerns the chemical interactions in the aqueous phase or formation of the extractable complex. Third, chemical interactions in the organic phase may be necessary, such as self-association or mixed ligand complex formation. Such chem- ical interactions do not negate the validity of the Nernst distribution law, but obviously the extrac- tion cannot be described quantitatively by such a simple equation. For this purpose it is necessary to know how each of the contributing reactions affects the extent of extraction and this is dis- cussed in the following sections. The extent of extraction may be described in terms of the distribution ratio as follows: D _ Caw AT (2) A where D is the distribution ratio, C4, and C, correspond to the total analytical concentration of component A in whatever form it is present in the organic (,) and aqueous (A) phase, respectively. If the substance does not enter any chemical re- actions in either phase, then D, reduces to Kj,,. (K = distribution constant) Another important way of expressing extent of extraction is by the Fraction Extracted Fi — Cai \ = DRv (3) | Caco) Vo+ CLV DsRy +1 where F = fraction extracted, V, and V are the respective volumes of the organic (,) and aqueous 208 phases, Ry is the phase volume ratio, Vo/V (others as in equation 2). The percentage extrac- tion is simply 100F. Equation (3) demonstrates the possibility of increasing the extent of extraction with a given D value by increasing the phase volume ratio. If instead of a single batch extraction, a second or third extraction is carried out on the same aqueous solution by successive portions of organic solvent such that Ry remains the same, the additional fractions extracted are F(1-F) and F(1-F)2, re- spectively. The fractions remaining in the aque- ous phase following n successive extractions is ( 1-F) n=1 Separation Factor: If two substances A and B are present in a solution in an initial concentration ratio, C,/Cp, then upon extraction their concentration ratio in the organic phase would be C,F,/C Fy, where F, and Fy are the corresponding fractions extracted. The ratio F,/Fg, which is the factor by which the initial concentration ratio is changed by the separation, is a measure of separation. A corollary measure of separation which represents the change in the ratio of concentrations remain- ing in the aqueous phase is (1-F,)/(1-Fy). Two substances whose distribution ratios differ by a constant factor will be separated most effi- ciently if the product, D,Dy, is unity. As an illus- tration of this principle, consider the case of a pair of substances whose distribution ratios are 10° and 10! respectively. If these substances were present in equal quantity, then a single extraction would remove 99.9% of the first and 90% of the second. A much more efficient extraction would be obtain- able if, using the same factor of 100 between the distribution ratios, the two distribution ratios were 10+" and 107'. In this case respective fractions extracted would be 90% and 10%. Classification of Extraction Systems The following classification refers essentially to inorganic systems, particularly those involving metal ions. There are, of course, many organic compounds which are extracted without any sig- nificant chemical reaction such as alcohols, ethers and carboxyl compounds. Systematic changes in the extraction of such compounds by various sol- vents can be related to molecular weight, hydrogen bonding and less specific interactions. Chemical reactions are at the very heart of metal ion extractions. Most metal salts are soluble in water, but not in organic solvents, particularly of the hydrocarbon and chlorinated hydrocarbon types. This results not only from the high dielec- tric constant of water but, more importantly, from its ability to coordinate with the ions, especially the metal ion, so that the hydrated salt more nearly resembles the solvent. To form an extract- able metal complex it is necessary to replace the coordinated water from around the metal ion by groups, or ligands, that will form an uncharged species that will be compatible with a low dielec- tric constant organic solvent. Formation of an extractable metal species can be accomplished in a great variety of ways which makes a classification of extractions based on this very useful, particularly as a guide to the under- standing of the thousands of different extractions systems now in use. The formation of an uncharged species that is extractable by the relatively non-polar organic solvent can involve 1. Simple (monodentate) coordination alone, as with GeCl,, 2. Heteropoly acids, a class of coordination complexes in which the central ion is com- plex rather than monatomic, as with phos- phomolybdic acid, H,PO, * 12Mo0QO,, 3. Chelation (polydentate coordination) alone, as with Al (8-quinolinolate) ,, 4. Jon-association alone, as with Cs, (C,H,),B™ or 5. Combinations of the above, such as: a. Simple coordination and ion-associa- tion — e.g, (“Onium”*t), FeCl, [“Onium” stands for one of the follow- ing cation types, hydrated hydronium ion, (H,0),0+, a rather labile cation requiring stabilization by solvation with an oxygen-containing solvent, a substituted ammonium ion, R, NH+ , where R is an alkyl or aralkyl group and N may vary from 1 to 3, a sub- Table 18-1 stituted phosphonium ion R P+, sti- bonium ion R,Sb+, sulfonium ion and other ions of this sort, including the important category of cationic dyes such as Rhodamine B]. b. Chelation and ion-association with either positively or negatively charged metal chelates — e.g.,, Cu(2, 9-di- methyl-1, 10-phenanthroline) , + .Cl1O,~ or 3 (n-C,HNH,t) Co (Nitroso R Salt) ,~* — and, finally, c. Simple coordination and chelation — e.g., Zn(oxinate), ¢ pyridine. This category is of significance for chelates that are coordinatively unsaturated — i.e., those with a monoprotic bidentate reagent in which the coordination num- ber of the metal is greater than twice its valence. An examination of the foregoing material and of Table 18-1 serves to underline the close rela- tionship between inorganic and analytical chem- istry employed in the principles and practice of metal extraction systems. A thorough understand- ing of analytical solvent extraction of metals re- quires a deep appreciation of many branches of coordination chemistry. Metal Extraction Systems PRIMARY SYSTEMS I. Simple (Monodentate) Coordination Systems 1. Certain halide systems — e.g., HgCl,, GeCl, 2. Certain nitrate systems — e.g., (UO2*) (TBP), (NO;), II. Heteropoly Acid Systems — e.g., H,PO, * 12MoO, III. Chelate Systems A. Bidentate chelating agents a) 4-Membered ring systems Reactive Grouping 1. Disubstituted dithiocarbamates — e.g., Nat, (C,H,), NCSS™ or (C,H,CH,), NCSS™ Xanthates — e.g., Nat, C,H, OCSS~ 2. Dithiophosphoric acids — e.g., diethyldithiophosphoric acid 3. Aursinic and arsonic acids — e.g., benzenarsonic acid b) 5-Membered ring systems 1. N-Acyl hydroxylamines — e.g., N-benzoylphenylhydroxylamine (BPHA) or benzohydroxamic acid 2. N-nitroso-N-arylhydroxylamines — e.g., Cupferron, (N-nitrosophenyl-hydroxy- lamine) or neocupferron, (N-nitrosonaphthylhydroxylamine) 3. a-Dioximes — e.g., Dimethylgloxine, cyclohexane-dionedioxime (Nioxime) 4. Diaryldithiocarbazones — e.g., Dithizone, (diphenyldithiocarbazone) 5. 8-Quinolinols — e.g., Oxine, (8- quinolinol), Methyloxine, (2-methyl-S- quinolinol) Reprinted from Anal. Chem. 36:93R, 1964, Copyright 1964 by permission of copyright owner. 209 S=C-—S§~ S—P—S~ O—As—0O" 0=C-N-0O" O=N—-N—-0O" N=C—-C=N" N—N=C-S§" N=C-C—-0" the American Chemical Society. Reprinted with 6. Quinoline-S-thiols, dithioxamides — e.g., thio-oxine, (quinoline-8-thiol) N, N’didodecyldithiooxamide N=C-C-§" 7. Quinoline-S-selenol N=C—-C-—Se” 8. O-Dihydroxybenzenes — e.g., catechol, phenylfluorone, rhodizonic acid “0-C=C-0" 9. o-Dimercaptobenzenes — e.g., toluene-3, 4-dithiol S$-C=C-§" 10. Thionalid (thioglycolic-B-aminophthalide) O—C—-C-—S~ c) 6-Membered ring systems 1. B-Diketones — e.g., Acetylacetone, TTA (thenoyltrifluoroacctone) dibenzoylethane, Morin, quercetin, quinalizarin O0=C-C=C-0" 2. o-Nitrosophenols — e.g., 1-nitroso-2- naphthol O=N—-C=C-0" 3. o-Hydroxyloximes — e.g., salicyladoxime N=C—-C=C-0~ d) Larger ring systems 1. Mono or dialkyl-phosphoric or -phos- phonic acids O=P—OHO=P—-0O" B. Polydentate chelating systems 1. Pyridylazonaphthol (PAN) and pyridylazoresorcinol (PAR) N=C—N=N-C=C-0" 2. o, o’ Dihydroxyazobenzenes — e.g., 2, 2’ -dihydroxy-5’-isopropy 1-4-methyl- 4-nitroazobenzene O—-C=C—N=N-C=C-0" 3. N, N’-(Disalicylidene) ethylenediimine (also S analog) “O0-C=C—N=C-C=N-C=C—-0" 4. Glyoxal bis(2-hydroxyanil) (also S analog) “O-C=C—N=C—-C=N-C=C—-0" IV. Simple Ion Association Systems A. Metal in cation 1. Inorganic anions — e.g., Cs*, I,” or PF~ Tetraphenylboride anion Dipicrylamine anion Alkylphenolate anion Carboxylate and perfluorocarboxylate anions NRW MIXED SYSTEMS V. Ton Association and Simple Coordination Systems A. Metal in cation I. Oxygen solvents — e.g., alcohols, ketones, esters, ethers — e.g., [(UO,) (ROH), 1+2 2NO,~ 2. Neutral phosphorus compounds, phosphates, phosphonates, phosphinates, phosphine oxides, and sulfides B. Metal in anion (paired with “onium” ion) 1. Halides — e.g., FeCl,” 2. Thiocyanates — e.g., Co(CNS),™ 3. Oxyanions — e.g., MnO,~ VI. lon Association and Chelation Systems A. Cationic chelates 1. Phenanthrolines and polypyridyls — e.g., Cu(I) (2, 9-dimethylphenanthroline),* 2. Tetraalkyl methylenediphosphonates — e.g., (RO),P—CH, —P(OR), 210 B. Anionic chelates 1. Sulfonated chelating agents a. 1-Nitroso-2-naphthol — e.g., Co (III) (nitroso R salt), b. 8-Quinolinol — e.g., Fe(III) (7-iodo 8-quinolinol-5 sulfonate), VII. Chelation and Simple Coordination Systems — e.g., Th(TTA), « TBP, Ca (TTA), * (TOPO), GENERAL EXPERIMENTAL TECHNIQUES Methods of Extraction: (1) Batch Extraction When experimental conditions can be adjusted so that the fraction extracted is 0.99 or higher (DRy>100) then a single or batch extraction suffices to transfer the bulk of the desired sub- Y FRITTED DISC > 1 Morrison GH, Freiser H: Solvent Extraction in Analytic Chemistry. New York, John Wiley & Sons, 1957, p. 23. Figure 18-1. Continuous Extractor for Use with a Solvent Lighter Than Water. 211 stance to the organic phase. Most situations in analytical extraction fall into this category. The usual apparatus for a batch extraction is a separa- tory funnel such as the Squibb pear-shaped type. (For additional special types of funnels see ref- erence (1).) Even when the DRy of the desired substance is as low as 10, carrying out batch extraction twice will transfer 99% of the material to the organic phase. If one chooses as a desirable criterion of sep- aration of a pair of substances that one be at least 99% extracted and the other no more than 1%, then it can be seen that D,Ry>100 and D.,Ry<0.01. (2) Continuous Extraction For substances whose DRy values are rela- tively small, even multiple batch extraction cannot conveniently or economically (too much organic solvent required) be used. Continuous extraction using volatile solvents can be carried out in an apparatus in which the solvent distilled from an extract collection flask is condensed, contacted with the aqueous phase and returned continuously to the extract collection flask. Continuous extrac- tion apparatus for solvents that may be either heavier or lighter than water is shown in Figures 18-1 and 18-2. (3) Countercurrent Distribution (CCD) A special multiple-contact extraction is needed to bring about separation of two substances whose D values are very similar even under optimum conditions. In principle, countercurrent distribu- tion could be carried out in a series of separatory funnels, each containing an identical lower phase. The mixture is introduced into the first portion of upper phase in the first funnel. After equilibration, the upper phase is transferred to the second funnel and a new portion of upper phase (devoid of sam- ple) is introduced into the first funnel. After both funnels are equilibrated the upper phase of each is moved on to the next funnel and a fresh portion of upper phase is again added to the first funnel. This process is repeated as many times as nec- essary collecting the upper phases as “elution fractions.” With automated CCD equipment several hun- dred transfers can be accomplished conveniently which permit the separation of two solutes whose D,/D, is less than two. The relation of the distribution ratio, D, of a solute in a CCD process to the concentration in the various separatory funnels or stages can be shown to be given by the binomial expansion: [F+ (I-F)]"=1 (4) where F, the fraction extracted, is DRy/1 + DRy, as shown in (3), and n is the number of stages in the CCD process. Morrison GH, Freiser H: Solvent Extraction in Analytical Chemistry. New York, John Wiley & Sons, 1957, p. 23. Figure 18-2. Continuous Extractor for Use with a Solvent Heavier Than Water The fraction T, . of the solute present in the rth stage for n transfers can be calculated from _ nl (DRy)* (5) r! (n-r)! (1+DRy)" A modification of CCD useful for laboratory purposes involves the use of a small number of separatory funnels (e.g., three) together with a larger number of transfers of upper phase por- tions (e.g., eight) and collecting the first upper phase portions as the product fraction. This means it would be possible to separate quantitatively a substance with a D of 10 from one whose D is 0.1. Experimental Techniques: (1) Introduction Selection of a particular extraction method from the large number of methods available in- volves consideration of the behavior of inter- ferences that might be present as well as that of the substance of interest. Another factor of im- portance is the means to be employed in the analytical determination of the species in question. 212 Some of the chelate systems, e.g., dithizone, are colored sufficiently to provide the basis of a spec- trophotometric determination. If the extract is to be aspirated into the flame of an atomic absorption apparatus, however, a dithizone solution would not be as desirable as a non-benzenoid reagent be- cause of its behavior in the flame. The problem is simplified greatly by the exis- tence of abundant literature which permits the selection of a method on the basis of similarity or even matching of separation problems. Although even those experienced in extraction methods generally proceed in a new problem by following published precedents, a better understanding of the design of an extraction procedure can benefit from the careful study upon which previous work is based. (2) Choice of Solvent Solvents differ in polarity, density and ability to participate in complex formation. Generally it is more convenient to use a solvent denser than water when the element of interest is being ex- tracted and a less dense solvent when interferences are extracted away from the element of interest. Ion association complexes in which one of the ions is strongly solvated, such as the hydrated hydronium ion, O(H,0),*, as in the extraction of chloride complexes from HCI solutions (e.g., H+, FeCl,~), can be extracted most effectively with oxygen-containing solvents such as alcohols, esters, ketones and ethers. Similarly, with coor- dinatively unsaturated chelates; i.e., in which the coordination number of the metal ion is greater than twice its oxidation state, such as ZnOx, (where Ox refers to the 8-hydroxyquinolinate anion), use of an oxygen-containing solvent will increase extractability significantly over that ob- tainable with hydrocarbon and chlorinated hydro- carbons. On the other hand, ion association complexes involving quaternary ammonium, phosphonium or arsonium ions, and chelates that are saturated coordinatively may be readily extracted in hydro- carbons as well as in oxygenated solvents. In such cases, the principle of “like dissolves like,” as ex- pressed by the Hildebrand “solubility parameter,” 8, (defined as the heat of vaporization of one cc of a liquid) offers a guide to extractability. Simply expressed, in the absence of specific chemical in- teractions, a substance will be more extractable in a solvent whose 8 value most closely matches its own. Thus, 8-hydroxyquinoline (§=10) is more extractable into benzene (8 =9.2) than CCl, (8 =28.6) than heptane (§ =7.4). The absence of 8 values for many extractable species hampers the full applicability of this principle. It must not be assumed that the best solvent to use is always that which gives the highest ex- tractability because a poorer solvent is often more selective. (3) Stripping and Backwashing Occasionally it is of advantage to remove the extracted solute from the organic phase as part of the analytical procedure. This process, called stripping, may be accomplished by shaking the organic phase with a fresh portion of aqueous solution containing acids or other reagents which will decompose the extractable complex. Backwashing is the technique of contacting the organic extract with a fresh aqueous phase. The combined organic phase, containing almost all the desired element and some of the impurities (ex- tracted to a smaller extent), is shaken with small portions of a fresh aqueous phase containing the same reagent concentrations initially present. Under these conditions, most of the desired ele- ment remains in the organic phase whereas the bulk of the impurities are back-extracted (back- washed) into the aqueous phase because of their lower distribution ratios. (4) Treatment of Emulsions Rapid reappearance of a sharp phase bound- ary after shaking two immiscible liquids depends on the avoidance of emulsion formation. Tendency to form emulsions decreases with increasing inter- facial tension. With liquids of relatively high mutual solubility or in the presence of surfactants, the interfacial tension is low and the tendency to form emulsions correspondingly high. Also of importance in avoiding emulsions is the use of solvents of low viscosity and whose densities are significantly different from water. With systems that tend to form emulsions, repeated inversion of the phases rather than vigorous shaking is helpful. In an extreme case, use of a continuous extractor rather than a separatory funnel is often successful. Tendency to emulsion formation can be reduced by addition of neutral salts or an anti-emulsion agent. Important Experimental Variables (1) Chelate Experimental Variables As seen from Table 18-1, many chelating ex- tractants are weak acids and can be represented as HR. For a chelate extraction process Kex Mr+ +nHR (org) = MR, (org) +nH+ the extent of extraction is described by the ex- pression D — Cu = K¢Kp c Ki [HR]", - [HR]", "Sow TK, TE (6) where K; is the formation constant of the metal chelate MR,,, Ka the acid dissociation constant of the chelating agent HR, Kp and Kj the dis- tribution constants of reagent and chelate, respec- tively. The combination of constants in equation (6) is called the overall extraction constant, K,. Representative values of K., are listed in Table 18-2. Equation (6) shows that the value of D in- creases with the concentration of the reagent in the organic phase and decreases with the hydrogen ion concentration in the aqueous phase. From this we see the importance of pH control in chelate extractions. Inasmuch as the extractions of dif- ferent metal ions with a given reagent are char- acterized by different extraction constants, the extraction curves (%E vs pH) will be similar but displaced in pH. Figure 18-3 shows a typical set of extraction curves for various metal dithizonates. It will be noted that, while the curves of all of the 213 divalent metal ions are parallel, those for Ag(I) and TI(I) are less steep, as a result of n in equa- tion (6) being 1. From the curve we can conclude that at pH 2, Hg (II) is 100% extracted; Ag, Cu, Bi are fractionally extracted, and the other ions listed not extracted at all. It would be simple to: separate Hg(II) from Sn(Il), Pb, Zn, TI(I) and Cd in a mixture by extracting with dithizone at pH 2 but difficult to separate it from Ag, Cu and Bi. Since Bi is only 10% extracted at this pH, backwashing several times with fresh aqueous (pH 2) portions would quantitatively remove Bi (90% of remaining amount each time) from the extract without appreciably affecting the extracted Hg. Table 18-2 Extraction Constants, K., and pH, /, Values of Selected Metal Chelate Systems Extractant 8-Quinolinol Dithizone 0.10M CHC], 10—*M CCl, Metal Ion log Kx pH,/, log Kex pH,/, Agt — 6.5 7.18 -32 A+ —-5.22 2.87 Not extracted Ca:+ —17.9 10.4 Not extracted Cd>+ — 4.65 2.14 2.9 Cut 1.77 1.51 10.53 -1.3 Fe*t 4.11 1.00 Not extracted Pb2+ — 8.04 5.04 0.44 3.8 Zn:+ — 3.30 2.3 2.8 One useful way to condense extraction infor- mation from curves such as in Figure 18-3 or from expressions such as equation (6) is to specify the pH,/, (called “pH one half’) value for the metal ion obtained with a particular concentration of the reagent. The pH,/, is the value of the pH at which half the metal is extracted. Thus from Figure 18-3, the pH,/, values for the dithizonates are 0.3 for Hg, 1.0 for Ag, 1.9 for Cu, 2.5 for Bij, 4.7 for Sn, 7.4 for Pb, 8.5 for Zn, 9.7 for Tl and 11.6 for Cd. For a single batch extraction, a minimum of three units difference in pH,/, is re- quired to permit the quantitative separation of two metal ions, although as mentioned above the tech- nique of backwashing can reduce this requirement. The factor ey in equation (6) which represents the fraction of the total metal concentration in the aqueous phase that is in the form of the simple hydrated metal ion, points to the importance of masking agents in improving selectivity of extrac- tion. Masking agents are auxiliary complexing agents which form charged water-soluble com- plexes whose effectiveness in inhibiting other re- actions (e.g., extraction) of metal ions increase with the formation constants of the masking com- plex, the concentration of the masking agent, and, for the many masking agents which are bases, with the pH. A number of representative values are listed in Table 18-3. As an illustration of masking let us consider a mixture of Ag+ and Cu** from which we wish to extract Agt selectively. As can be seen from Figure 18-3, Agt can be extracted quantitatively 100 80 60 % E 40 20 Figure 18-3. Qualitative Extration Curves for Metal Dithizonates at pH 3 but without any masking agent present, Cu*t is also appreciably extracted. In the pres- ence of 0.1M EDTA, the value of log a., = —6.6 (estimated from Table 18-3) which would displace the extraction curve of copper dithizonate to the right increasing pH,/, by 3.3 units [according to equation 6)]. Since the value of log a, under these conditions is about —0.2, EDTA has little effect on the extraction curve of Ag dithizonate. Hence, in the presence of 0.1M EDTA at pH 3, Agt will be selectively extracted from Cu?*+. Similarly the use of cyanide as masking agent will permit the selective extraction of Al*t+, which does not form a CN~ complex, by 8-hydroxyquinoline in the presence of such transition metal ions as Cu, Fe, as well as Ag which form strong cyanide complexes. Other examples of successful masking can be predicted with the help of Table 18-3. We will return to the use of masking in the discussion of ion exchange separations. Kinetic factors may be important in all types of extraction, but since they are observed most frequently with chelate extraction systems, they will be discussed here. Generally, extraction equilibrium can be achieved in one or two minutes of normal shaking because mass transfer rates are reasonably rapid. Occasionally it is observed, particularly with some chelates, that the formation of an extractable complex or the dissociation of a masking complex is slow enough to affect the course of the extraction. For example, most sub- stitution reactions of Cr*+ are very slow, so that although Crit forms stable chelates it is rarely extracted in the usual chelate extraction proce- 214 dure. Less dramatic but of analytical utility is the significant difference in the speed of formation of other metal dithizonates which makes it possible to separate Hg*t+ from Cu?t and Zn*t from Ni*+ by limiting the shaking periods to one minute. (2) Ion Association Extraction Systems As with chelate systems, ion association ex- traction equilibria involve a number of contrib- uting reactions. For example, for the extraction of Fe*t out of HCI solutions into ether: Fe*t+ +4 ClI- = FeCl,~ H(H,0),++FeCl,- = H,0,*, FeCl,~ H,0,*, FeCl,~ = H,0,*, FeCl,~ (ether) From these equations, the importance of chloride and acid can be seen. About 6M HCI is required for optimum iron extraction. Ether, as an oxygen containing solvent, is needed to stabilize the H,O,* ion. If (C,H,),Nt is used, then the iron can be extracted out of a much less acidic solution (provided that the chloride concentration was about 6M) and, more significantly it would be possible to use benzene, CCl, or CHCI, as well as oxygen-containing solvents for the extraction. In many ion association extraction systems, high electrolyte concentrations are found effective in increasing the extent of extraction. The addi- tion of such salts, referred to as salting-out agents, serves two purposes. The first, and more obvious, is to aid in the direct formation of the complex by the mass action effect. That is, the formation of a chloro or nitrato complex, for instance, is promoted by increasing the concentration of CI~ Table 18-3 Values of Masking Factor [-log ay from Equation (6)] For Representative Metal Ions and 0.1M Masking Agents at Various pH Values or NO,~. Second, as the salt concentration in- creases, the concentration of “free”, i.e., uncom- plexed, water decreases because the ions require a certain amount of water for hydration. Because Lit is more strongly hydrated than K+, LiNO, is pH= 2 5 8 10 a much better salting-out agent than KNO, for Ag EDTA 0 05 3.7 5.5 nitrate extraction systems even though equimolar NH 0 0.1 4.6 72 solutions supply the same nitrate concentration. CN’ 47 107 167 19.0 Metal Extraction Systems Al (no masking NH, or CN") In this section the application of a few rep- EDTA = 1.8 82 14.5 18.3 [resentative extractants are described in periodic OH- 0 0.4 93 17.3 array. Elements extractable as diethyldithio- F 10.0 145 145 17.3 carbamates are shown in Figure 18-4. The num- . ayaa’ ’ ’ ber under each element represents the lowest pH Ca (no masking NH, or CN-) at which it will be extracted. Because the reagent EDTA 0 32 7.1 8.9 is non-aromatic, solutions of its chelates can burn Citrate 0 1.8 2.5 2.5 with a smokeless flame so this reagent is widely Cd EDTA 1.8 79 122 14.0 used as a separation or preconcentration step pre- NH, 0 0 2.3 6.7 paratory to atomic absorption spectrometry. CN 0 0.7 10.1 14.5 The application of dithizone is shown in Figure Cu (II) 18-5. Because of the highly conjugated reagent, the chelates are all highly colored in the visible EDTA 46 10.7 15.0 16.8 range which provides the basis of sensitive spec- NH, 0 0 3.6 8.2 trophotometric determinations. Fe (111) Extractions with 8-quinolinol (8-hydroxyquin- EDTA 10.3 17.2 22.0 26.4 oline, oxine) are described in Figure 18-6. These OH- 0 3.7 9.7 13.7 chelates also are used in spectrophotometric and F- 5.7 8.9 9.8 13.7 fluorimetric determinations. : " The extraction of metal ions from hydrochloric Pb (no masking NH, o SN ) 102 144 162 acid into ethyl ether is shown in Figure 18-7. OH- 0 0 05 27 Outline of Illustrative Extraction Procedures Citrate 1.0 4.2 4.2 5.3 In this section several extraction procedures will be outlined as a means of illustrating the ap- Zn EDZA 28 is 124 42 plication of principles discussed above. Naturally CN- 0 0 75 12.3 for a working method, more detailed procedures : : in the references should be consulted. Precautions Sodium Diethyldithiocarbanate S H 7 He (CoH5)pN-C_ - + Li Be Na B C N O F Ne Na Mg Al si P S Cl A Vv C M F C Ni C Z G Ge A S Br Kr K Ca Sc Ti y x a ls 0 ¢ u p 2 s $9 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te 1 Xe ~5 3 3 3 3 5 -0.7 Cs Ba La Hf Ta W Re 0s Ir Pt Au He Tl Pb Bi Po At Rn 1 -1 3 -0.2 1 Fa Ra Ac Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa 6's Np Pu Am Cm Bk Cf E Fm Mv 102 103 Morrison GH, Freiser H: Solvent extractions in radiochemical separations. Ann. Rev. of Nuclear Sci., vol. 9, 1959. Figure 18-4. Elements Extractable with Sodium Diethyithiocarbamate. The number under an element symbol indicates the pH value at which the element can be completely extracted. 215 Li Na Rb Cs Fa Be Mg Ca Sr Sc La Ac Ti Zr HE Ce Th Vv Nb Ta Pr Pa Cr Mn ~11 Mo Tc W Re Nd Pm U Np Dithizone H | N-=-N \ C-SH B / N=N Al Fe Co Ni Cu Zn Ga 6 7 8 1 8 Ru Rh Pd Ag Cd In <0 <0 13 8 Os Ir P Au Hg T1 2 <0 2 <0 Tm Yb Lu Mv 102 103 Morrison GH, Freiser H: Solvent extractions in radiochemical separations. Ann. Rev. of Nuclear Sci., vol. 9, 1959. Figure 18-5. Elements Extractable by Dithizone. See Figure 18-4 for explanation of numbers. peculiar to trace element determinations must be observed carefully. Li Na . Rb Cs Be Mg Ca 13 Sr 11 Ba Ra EB Se =r op (1) Extraction of Cd with Dithizone It is possible to separate Cd from Pb or Zn by using a highly alkaline solution during extraction and from Ag, Hg, Ni, Co and Cu by stripping the 8-Quinolinol CID OH Vv 3 Cr Nb Mo 6 Ta 1.5 Ww 2.5 Nd U 5 Mn 7 Tc Re Pm Np Fe 2 Ru 9 Os Sm Pu 4 stable. Cd at a pH of 2 where these other dithizonates are A solution containing up to 50 ug Cd is treated B Al 5 Co Ni Cu Zn Ga 7 4,5 3 4 3 Rh Pd Ag Cd In 1 5 3 Ir Pt Au Hg T1 Eu Gd Tb Dy Ho Am Cm Bk Cf E Ge Sn 2.5 Pb 85 Er Fm N 0 F P S cl As Se Br Sb Te I Bi Po At 4 Tm Yb Lu My 102 103 with tartrate (to avoid hydroxide precipitation) and made basic with an excess of 25% KOH. This is now shaken with successive 5 ml portions of He Ne Xe Rn Morrison GH, Freiser H: Solvent extractions in radiochemical separations. Ann. Rev. of Nuclear Sci., vol. 9, 1959. Figure 18-6. Elements Extractable by 8-quinolinol 216 H He Li| Be B C N 0 F pe Na Mg Al si P S cl A . — roe K Ca Sc Ti | V| Cr Mn Fe|lCo Nil Cu Zn |Ga Ge As|Se Br Kr [—" fe we wd === —— Rb Sr Y Zr Tc Ru Rh Pd Ag Cd [In Sni|SbfiTej I Xe Cs Ba La Hf Ta W Re Os Ir |Pt Au Hg T1|Pb Bi|Po| At Rn Fa Ra Ac Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th |Pal U Np Pu Am Cm Bk Cf E Fm Mv 102 103 Morrison GH, Freiser H: Solvent extractions in radiochemical separations. Ann. Rev. of Nuclear Sci., vol. 9, 1959. Figure 18-7. Elements Extracted in Chloride System: Solid Blocks—Appreciably Extracted, Broken Blocks—Partially Extracted dithizone in CHCI, until the aqueous layer remains yellowish brown (to indicate excess dithizone). The combined extracts are shaken for two minutes with an aqueous solution buffered at pH 2 which will strip the Cd quantitatively. To remove small amounts of Cu and Hg that may accompany the Cd, reextract with a fresh portion of dithizone at pH 2. The Cd will remain in the aqueous phase. (2) Extraction of Pb with Dithizone A slightly acid solution containing up to 100 ng Pb is treated with aqueous NH, and KCN prior to extraction with dithizone in CHCI,. Under these conditions no metal other than Bi, Tl or Snt* will interfere. (3) Cu with Sodium Diethyldithiocarbamate Adjust the pH of a solution containing up to 50 ug Cu to 4.5 — 5.0 with acetate buffer, add sodium EDTA, followed by Na diethyldithtio- carbamate and shake mixture for one minute. Add butyl acetate and shake again for one minute. Backwash the extract with dilute H,SO,. There is essentially no interference. (4) Fe with 4,7-Diphenylphenanthroline (Bathophenanthroline) Add NH,OH + HCl to a solution containing up to 10 pug Fe to produce Fe(11), adjust the pH to 4 with sodium acetate, add bathophenanthroline dissolved in ethanol. Add n-hexanol and shake to extract. The iron complex absorbs strongly at 533 nm. (5) Germanium with Hydrochloric Acid To the sample, which may be dissolved in H,PO, and HNO,, add concentrated HCI. The GeCl, that forms may then be extracted with por- tions of CCl,. To return Ge to an aqueous phase prior to determination, a solution of ammonium oxalate-oxalic acid may be used for stripping. Suggestions for Further Reading In addition to reference (1) which is a general 217 text covering the principles of solvent extraction and its applications to separation and analysis, the Biennial Reviews (2) published in even-numbered years from<1958 to the present include compre- hensive surveys of newly published extraction re- views; the references listed in (2) are very helpful. (1) G. H. Morrison and H. Freiser, “Solvent Extraction in Analytical Chemistry.” John Wiley & Sons, New York (1957). (2) See Anal. Chem. 30, 632 (1958); ibid 32, 37 (1960); ibid 34, 64R (1962); ibid 36, 93R (1964); ibid 38, 131R (1966); ibid 40, 522R (1968). ION EXCHANGE General Principles and Terminology Ion exchange is a process in which ions of the same sign are exchanged between a (usually aqueous) solution and an immobilized phase, not necessarily a crystalline solid, which consists of macromolecular species having many ionizable functional groups, called exchange sites. The earliest ion exchange materials used, clays and zeolites, are indeed solid, but currently most widely used ion exchangers are synthetic resins that are high molecular weight polymers having a high concentration of ionizable functional groups, (3-6 meq/g dry resin). Both cationic and anionic exchange resins are available in granular bead form in a variety of mesh sizes. A cation exchange resin contains either strong (sulfonic) or weak (carboxylic) acid groups as the fundamental exchange site, with the former being more commonly used. The cation exchange reaction can be written H+, R—+1/nMn+ — I/mMn +] R +H+t+ where Ht, R™ signifies the resin in the acid or H form and M"+, nR~ the resin in the M"t form. The equilibrium constant of the exchange re- action, Kx, called the exchange constant, is [Mn+ yn [H+] - [Mn+] 1/n [H+]g where brackets signify concentrations in the aque- ous and resin (subscript R) phases. It is con- venient to use milliequivalents per gram of resin to describe resin concentrations and milliequiv- alents per milliliter (Normality) for solution con- centrations. It should be noted that Kix is ex- pressed in terms of concentrations rather than the more rigorously correct activities. This is not only more practical but, because the resin phase is equivalent to an extremely concentrated elec- trolyte solution (e.g., about 5-6 molar in NaCl) activity, coefficients are difficult to evaluate ac- curately. Representative values of K;x for cation exchange are listed in Table 18-4. Similarly, the equilibrium of an anion ex- change process =K MI! Kix =K 3 /n R#, CIF Xn = R¥ LX 4+CI can be expressed by [X1y" [CT] XT" [CF Tw The extent of cation exchange may be expressed by a distribution ratio, Dy, which like equation (2) for extraction, is the ratio of total metal con- centration in the resin phase, Cyr), (meq/g), to the total metal concentration in the aqueous phase, Cy (normality) Kix =Kx/» (8) _ Cum Usually the metal ion in the resin phase is uncom- plexed and can be represented as [M"*]r but in the aqueous phase the frequent use of complexing agents suggests the use of the same masking factor Dy that is incorporated in equation (6). Hence, equation (8) becomes Mr + A (10) A major difference between masking in ion ex- change and solvent extraction is the requirement that the masking complex for the metal cation be anionic, because cationic metal complexes (e.g., M(NH,)** or M(phenanthroline) >t) are also strongly absorbed on the resin. If the resin is initially in the H+ form the dis- tribution ratio may be related to the exchange constant by the following equation [note analogy win [HY Ir to (6)] n=l] Hy) _[M+], (M»+] When the exchanged ion is present in small quantities, the resin loading, i.e. the [Ht]g, re- mains substantially constant so that DM is in- versely proportional to [H*]* which signifies the importance of dilution on the extent of exchange, particularly as the charge (n) of the metal ion increases. Another important means of describing the extent of exchange is F, the fraction exchanged, which is given by (note resemblance to equation (3)) n ¢ am Du 218 — Cum ‘Ww _Du(W/V) Cyr) W + Cx Vv Du(W/V) +1 where W is the weight of the resin in grams and V, the volume of the aqueous phase in milliliters. The fraction of metal remaining in solution is 1-F or [Dn(W/V) +1] Properties of Ion Exchange Materials Typical commercial cation exchange resins of the strong acid type are Dowex 50 and Amberlite IR-120, while Amberlite IRC 50 is weakly acidic. The strong acid types can function throughout the pH range but Amberlite IRC 50 must be used at a pH of 7 or higher. Commercial anion exchange resins of the strong base type include Dowex 1, Dowex 2, Amberlite IRA-400 which can be used throughout the pH range but the weakly basic resins such as Dowex 3 or Amberlite IR-4B must be used at pH 7 or below. The exchange capacities for the strong acid and base resins is of the order of 3-5 meq/g dry resin whereas that of the weak acid and base resins is about 10 meq/g. These ion exchange resins are available with different degrees of crosslinking which affects both the hardness of the resin beads and their selectiv- ity. Typically the resin is about 8% crosslinked with divinylbenzene (denoted in the listing of the resin as Dowex 50-X8), but at higher crosslinking a significant drop of exchange of larger ions im- parts a greater ion size selectivity to the resin. This can be seen from Table 18-4 by the insensi- F (12) Table 18-4 Concentration Exchange Constants, K}'/», For Some Metal Ions on Dowex 50 Resins of Different Ex- tents of Crosslinking (Measured in Terms of Percent Divinylbenzene (DVB)). 4% DVB 8% DVB 16% DVB Lit 0.76 0.79 0.68 Nat 1.20 1.56 1.61 NH, + 1.44 2.01 2.27 K+ 1.72 2.28 3.06 Agt 3.58 6.70 15.6 Mg? + 0.99 1.15 1.10 Zn*+ 1.05 1.21 1.18 Cot 1.08 1.31 1.19 Cut 1.10 1.35 1.40 Cdz+ 1.13 1.36 1.55 Pbz+ 2.20 3.46 5.65 Ni + 1.16 1.37 1.27 Cat 1.39 1.80 2.28 Sr2+ 1.57 2.27 3.16 Ba*+ 2.50 4.02 6.52 Crit 1.6 2.0 2.5 Cet 1.9 2.8 4.1 La#t 1.9 2.8 4.1 From O.D. Bonner et al., J. Phys. Chem., 61, 326 (1957) and 62, 250 (1968). Table 18-5 Concentration Exchange Constants, K¥!/» For Some Anions on Dowex 1 and Dowex 2. Ion " Dowex 1 Dowex 2 OH~ 0.09 0.65 F- 0.09 0.13 Br 2.8 2.3 I- 8.7 7.3 CN- 1.6 1.3 NO,~ 3.8 3.3 CNS- em 18.5 ClOo,~ —_— 32 H,PO,~ 0.25 0.34 HCO,” 0.32 0.53 HSO,~ 1.3 1.3 HSO,~ 4.1 6.1 SO,~ 2.55 0.55 HCOO~ 0.22 0.22 CH,COO~ 0.17 0.18 From O.D. Bonner et al., J. Phys. Chem., 61, 326 (1957) and 62, 250 (1968). tivity of a small ion such as Li+ to degree of crosslinking, whereas for a large ion such as K+ or Agt, the KN changes significantly. The effect is not as dramatic with the more highly charged ions but may still be observed with Ba**+ and Pb*+, General Experimental Techniques Two means of employing ion exchange resins are the batch technique, in which a portion of the resin is added to the solution to selectively remove an ion of interest, and column techniques which may involve either “column filtration” or chrom- atography. Both column techniques can serve to separate ions too similar to permit use of the batch technique; chromatography is both more powerful and more inconvenient than column fil- tration. The following typical values of the extent of removal by a batch ion exchange using a Dowex 50 x 8 resin are illustrative. (These values could be derived from equations (11) and (12)). (1) For g of resin in the H form equilibrated with 100 ml 0.1 M HCI which is 0.02M in Ca, Sr, or Ba to be 97%, 98%, and 99.3% removal, respectively. If only trace levels of the metal ions were present, the percent removal would be 98.8%, 99.3%, 99.8% of these metal ions. Hence, when resin loading is kept low the ex- change is more efficient. (2) The effect of ionic charge may be seen from the value of NH, remaining in solution =4% when a gram of resin is equilibrated with 40 ml of 0.01M NH,Cl. The corresponding Mg is 0.01% if 40 ml of 0.005M Mg Cl, is used. (3) The effect of the concentration of the counter ion may be seen from a comparison of the 0.01% Mg remaining in solution mentioned in (b) where the aqueous phase would then be 0.01M in HCI and the value of 4% Mg remaining if the aqueous phase were 0.1M in HCI at equi- librium. 219 With the help of values in Tables 18-4 and 18-5 and equations (11) and (12), one can cal- culate the feasibility of separating various pairs of ions. For example, from equation (12) for re- moval of 99% of a metal ion M,, (assuming a V/W value of 25:1) a value of Dy, of at least 2500 is needed. Under similar experimental con- ditions a Dy, of 0.25 or less for a second metal ion, of which 99% or more will remain in the aqueous solution, For metal ions of the same charge, it is evident from the similarity of values of Ki; as well as the form of equation (11) that, unless great variation in ay for the pair of ions can be achieved, quan- titative separation of the ions using a simple batch process is hopeless. A number of interesting and useful batch separations can be carried out, how- ever, by adjusting conditions to obtain sufficiently different values of the masking factor, ay, of the pair of metal ions. For example, a mixture of Ca**+ and Cu*t at concentrations of 107M or lower can be separated using Dowex 50-X8 in the Na- form by adding 0.1M EDTA and adjusting the pH suitably. In the absence of EDTA the distribution values are DC = 40,000 and DC = 25,000, so that both metal ions would be quantitatively removed from solution. From Table 18-3 we can estimate that at pH 3, ac, is between 1 and 0.1 but a, is 107%. Hence under these conditions Cat (Dg, > 4000) will be quantitatively taken up by the resin while Cu?t (Dg, — 0.008) will remain entirely in solu- tion (as Cu-EDTA complex). When differences in Dy values for a pair of ions cannot be made large enough to permit use of a batch technique, an ion exchange column must be used. Although column chromatographic methods represent the ultimate separation effi- ciency these are rather complicated, requiring either close attention or automatic fraction col- lectors. The technique of column filtration, how- ever, offers both speed and simplicity while pro- viding significantly greater separating efficiency than the batch process. In preparation of an ion exchange column for analytical use several precautions should be ob- served. The resin, usually about 8% crosslinked and about 50-100 mesh, is slurried in water in a beaker. After allowing the mixture to stand for a few minutes to settle the large particles, the turbid supernatant liquid is poured off. This process is repeated a few times in order to remove the fine particles which would otherwise clog the column. The resin is slurried again with water and poured into a tube which is provided with a plug of glass wool or sintered glass disk (coarse porosity) on which the ion exchange bed will rest. Because air bubbles in the column interfere with the flow of liquids through the tube and can lower column efficiency drastically, the miniscus of the liquid must never be allowed to fall below the top of the column. This, as well as the desired flowrate, is controlled by a stopcock or pinchclamp at the bottom of the tube. All columns should be conditioned prior to general use to remove impurities. For both strong cation and anion exchange resins, conditioning is carried out by passing through the column, in suc- cession, about 3-4 bed volumes each of IM NaOH, 1M HCI, water, 95% ethanol and water for two to three cycles. The conditioning ends with either NaOH or HCI depending whether the cation exchange resin is to be used in either the Na- or H-form (for the anion exchange resin this is either the -OH or Cl-form), and then rinsed with water until a qualitative test (with a suitable indicator) verifies completeness of rinsing. Regeneration of the column after some use is necessary in order to avoid leakage of exchanged ions into the effluent. This can be carried out by passing either HCl (from 1-3M) for cation ex- change resins or NaOH (1-3M) until tests of the effluent reveals the completeness of ion removal. If a particularly strongly held metal ion is on the cation exchange column, a complexing agent like ammonium citrate or EDTA can be used effec- tively in the regenerative solution. It is useful to keep in mind that the theory of ion exchange column chromatography behavior is almost identical with that of other chromato- graphic systems. The concentration profile of a particular ion moving down the column under the influence of a solvent (eluent) resembles a Gaussian (bell shaped) curve. When enough eluent has been added, the ionic component will emerge. The elution volume corresponding to the peak (maximum concentration) of the curve is described by the relation Vax = Dy*W ( 1 3 ) where Dy is the distribution ratio of the ion under the conditions of the elution and W is the weight of the resin in the column. The peak concentra- tion, Cx, is given by the equation C= (meq)x fNY\ 1/2 a (14) where (meq) is the number of meq of the ion on the column and N is the number of theoretical plates. Since V,.x and N are both linearly related to W and hence to column length at constant column width, the value of C,.y is inversely pro- portional to the square root of column length. The width in milliliters of an elution band (i.e., the concentration-volume profile of an eluted ion) is proportional to the square root of the column length. Hence, the relative width of a particular elution band decreases with the square root of column length. Column filtration is a process involving separa- tion of two ions on an ion exchange column by passing a given (reasonable) volume of an eluent through the column to quantitatively remove one of the ions but essentially none of the other. Two ions can be successfully separated by column filtration provided that the D value for the ion retained on the column is at least 100 (compared to at least 2500 for batch) while the D for the ion washing through the column may be three or smaller (0.25 for batch). Even such large differences in D are unusual for metal ions of the same charge unless ay values can be modi- fied by suitable masking agents. If the ratio of DM /DM, is below 30, column filtration may not 220 be used and a full-fledged chromatographic pro- cedure must be used, Outline of Illustrative Ion Exchange Procedures As in the corresponding section on extraction, several ion exchange procedures will be outlined to illustrate the principles and indicate the range of applications. (a) Non-Chromatographic Applications The determination of phosphate is simplified and improved by the removal of cations. Passing an acidified solution of the sample through a cation exchanger (H- form) removes all inter- fering cations. Analogously, phosphate interferes with the determination of a number of cations. For example, the atomic absorption determination of Ca*t is preferably carried out after removing phosphate by passing the sample through an anion exchanger (Cl- form). Fluoride can be separated from all interfering cations prior to determination with the F~ selective electrode. Sodium or potassium can be determined in the presence of transition metal ions such as Ni", Cu*t, Co*t, Fe*t+, V*+ by passing the mixture through a column of Dowex 2 in the citrate form which will remove interfering metals as anionic ci- trate complexes. Utilization of column filtration with an anion exchanger in the CyDTA form, permits the separation of Ca and Mg from Al*+, Cu?+, Fe*t, Mn?+, and Zn>+. A series of several concentrations of HCI can be used to wash the metal ions of the NHyOH group successively through an anion exchange column in the chloride form. With 9M HCI, Ni*+ will come through, with 4M HCI, Co*t; with 1M HCI, Fe*t, and finally using water, Zn*t+ will wash through. This order is a consequence of the increasing stability (Ni—Zn) of the chloroanionic complexes of these ions. (b) Chromatographic Applications As differences in D value decrease, separations naturally become more difficult. This implies longer columns, slower flowrates, more carefully controlled conditions and almost continuous mon- itoring of the column effluent or automated frac- tion collectors. One of the most promising new developments in liquid chromatography of all types (adsorption, partition, etc., as well as ion exchange) is that involving exceptionally long and narrow columns through which the eluent is forced under very high pressure. This renders practical the use of columns of very great separating effi- ciency (large number of theoretical plates) in pro- cedures which give sharply defined bands without excessively long run times. High pressure liquid chromatography should make it possible to extend the present scope of application of ion exchange (as well as other types) chromatography to almost any organic or inorganic electrolyte mixture. Suggestions for Further Reading Samuelson (1) is the classic text on ion ex- change and its application to analytical chemistry. Ringbom (3) is responsible for the excellent treatment of the role of complexation in improving ion exchange separations. A wealth of references to current develop- ments is to be found in the biennial ion exchange review in Analytical Chemistry (4). (1) O. Samuelson, “Ion Exchange Separa- tions in Analytical Chemistry,” Ed., John Wiley & Sons, (1963). (2) W. Rieman and H. Walton, “lon Ex- change in Analytical Chemistry,” Per- gamon Press, Oxford (1970). (3) A. Ringbom, “Complexation in Analyt- ical Chemistry,” John Wiley & Sons, New York (1963). (4) H. Walton, Analytical Chemistry, 42, 86R (1970). Other Separation Processes Although it is impossible in this brief chapter to do more than simply mention other methods of separation, it might be of some value to point these out as having useful application and high potential in problems of environmental analysis. New York Liquid-liquid partition chromatography which is based on the selective distribution of solutes between two liquids: an immobilized liquid spread thin on a largely inert solid support in contact with a mobile eluent liquid with which the immo- bilized liquid may or may not be miscible. This process which can be carried out on either a col- umn or paper and can best be understood as a modified multistage countercurrent solvent extrac- tion process. Many of the recently published methods for separating inorganic ions, partic- ularly those of so-called reverse phase partition (the immobilized phase is organic — the eluent is aqueous) are direct adaptations of extraction systems. Thin layer chromatography analogous to paper but makes use of noncellulosic materials, e.g., silica, alumina, which are capable of being heated (for activation of substrate or development re- actions) to much higher temperatures. TLC is more often the two dimensional analog of colum- nar adsorption chromatography (but not exclu- sively so) in which the immobilized phase is a solid of high surface area. Exclusion chromatography is a separation process based on the relative size of adsorbate molecules and adsorbent pores or channels. Mo- lecular sieve materials such as the inorganic zeolites and the organic gels are used successfully as column packing materials for chromatographic fractionation of both relatively small and large molecular weight mixtures. Zeolites are open silicate networks with highly uniform pore sizes that can be available in diameters from 4.2A to about 9.0A. For example, molecular sieve 4A will adsorb molecules whose diameter is under 4A (H,0, CO,, H,S, SO,, and hydrocarbons contain- ing one or two carbon atoms) but will exclude all others. Type 5A sieve will adsorb straight chain hydrocarbons and derivatives up to about fourteen carbon atoms but will exclude all branched chain and cyclic compounds. Because of their silicate 221 Second character, zeolite sieves will exhibit a strong pref- erence for polar over non-polar molecules of equal size. Zeolite sieves are frequently used in gas-solid chromatography. Gel permeation chromatography which may utilize either hydrophilic gels like Bio-Gel (a poly- acrylamide) or Sephadex (a cross-linked dextron) or hydrophobic gels such as Styragel (a sponge- like cross-linked polystyrene), are generally used as a column packing in liquid chromatography. This technique is particularly useful for size sep- aration of high molecular weight mixtures such as protein and polymeric fractions, although a mix- ture of mono-, di- and tri-saccharide can be easily separated (Sephadex). A number of separation processes are based on the differential migration of charged species in solution when subjected to an electric field gra- dient. Of particular interest is electrophoresis carried out on a supporting medium of filter paper, cellulose acetate, or gel layer which is soaked in a buffered electrolyte and subjected to a d.c. voltage with electrodes placed at each end of the paper (or gel). A sample of the material to be separated breaks up into zones because of the differential migration rate influenced by the charge, size and shape of the species. Greater variation in behavior of inorganic ions and, hence, improvement in sep- aration can be brought about by variation of pH, oxidation state, and the ability to form complexes. Interposing a thin perm-selective membrane between two solutions forms the basis of dialysis and, with the addition of an electric field gradient, electrodialysis which have been used for separations used more for recovery and purifica- tion than analysis per se. Nevertheless, as a means of removing interferences, such methods can be of value. . Fractional distillation is a separation process for liquid mixtures based on differences in vola- tility. By the addition of a non-volatile component that can interact with the volatile components in a differential manner, (called extractive distilla- tion) such volatility differences can be increased. Zone refining involves countercurrent frac- tional recrystallization by moving a narrow band heater slowly along a column of the solid material. The small melted zone contains most of the im- purities so that the cooled recrystallized material becomes significantly purer, while the impurities concentrate at one end of the column. The process can be repeated several times. This technique could be useful in concentrating trace level im- purities. Thermal diffusion, which does not involve phase separation, can be used to separate gas or liquid mixtures by virtue of the concentration gradient produced in a homogenous fluid mix- ture to which a temperature gradient is applied. Thermal diffusion is a sufficiently powerful tech- nique to permit separation of the gaseous isotopes of helium, of chlorine, and of C'*H, from C'*H, as well as the components of liquid hydrocarbon mixtures. Preferred Reading 1. CASSIDY, H. G., Fundamentals of Chromatog- raphy, Vol. 10 of Techniques of Organic Chemistry, A. Weissberger, edit. BLACK, R. J, E. L. DURRUM and G. ZWEIG, Manual of Paper Chromatography and Paper Elec- trophoresis, Academic Press, New York (1958). KIRCHNER, J. G., Thin Layer Chromatography, Interscience Publ., New York (1967). T. L. THOMAS and R. L. MAYS, Separations with Molecular Sieves, in Vol. IV, Physical Methods in Chemical Analysis, W. Berl, edit., Academic Press, New York (1961). DETERMANN, H., Gel Chromatography, Springer Verlag, New York (1968). 222 10. WIEME, R. J., Theory of Electrophoresis in Chro- matography, E. Heftmann, edit., Reinhold, New York (1967). MICHL, H., Techniques of Electrophoresis in Chro- matography, E. Heftmann, edit, Reinhold, New York (1967). . CARR, C. W,, Dialysis in Vol. IV Physical Methods in Chemical Analysis, G. Berl, edit., Academic Press, New York (1961). PFANN, W. G., Zone Refining, John Wiley & Sons, New York (1958). DICKEL, G., Separation of Gases and Liquids by Thermal Diffusion in Vol. IV Physical Methods in Chemical Analysis, G. Berl, edit.,, Academic Press, New York (1961). CHAPTER 19 SPECTROPHOTOMETRY H. E. Bumsted INTRODUCTION Table 19-2. The electromagnetic spectrum of energy ex- Principal and Complementary Colors tends from the gamma rays emitted by radioactive - elements with wavelengths of less than 0.1 na- Transmitted ~~ Wavelength Complementary nometer to radio waves with a wavelength greater Color (nm) Colors than 250 millimeters. However, this chapter will . . deal only with a very small section of this spec- Violet 380-435 Yellowish Green trum, namely the ultraviolet (185 to 380 nanom- Blue 435-480 Yellow eters), the visible (380 to 800 nanometers) and Green 500-560 Purple the infrared (0.8 to 50 micrometers). A schematic Yellow 580-595 Blue dingram is shown i» Figure 19-1. Orange 595-650 Greenish Blue e terms used in spectrophotometry are Red 650-780 Bluish Green gradually changing, and unless one is familiar with - the old and new forms, confusion may result. The new and old terms are shown in Table 19-1. trum associated with the generation of heat. Ab- sorption of infrared energy results in molecular Table 19-1. vibrations, such as bending or stretching of the Terms in Common Usage in Spectrophotometry interatomic bonds, and molecular rotation. The type of vibration is dependent on the wavelength New Old Value of the incident radiation. When certain types of molecules absorb ultra- Angstrom, A 107° . : : ws g Meter violet energy, energy in the ultraviolet or visible Nanometer Millimicron 107 meter regions is emitted as the excess energy is released. Micrometer Micron 107° meter This is called fluorescence and is a valuable tool Millimeter Millimeter 107 meter for the chemist in identifying and quantitating Nanogram 10° gram such compounds. Microgram Gamma 107° gram The absorption of energy by solutions follows Milligram 10~¢ gram two basic laws. The Bouguer (1729), or Lambert (1760), law states that when a beam of plane- parallel monochromatic light enters an absorbing medium at right angles to the plane surfaces of the medium, the rate of decrease in intensity with the length of the light path through the absorbing medium is proportional to the intensity of the beam. Mathematically this can be expressed as Visible light can be divided into the six prin- cipal colors as shown in Table 19-2. These are the principal colors seen when white light is dif- fracted into its primary colors by a prism or dif- fraction grating. Various shades and tones of these colors are possible. When visible light is absorbed by a compound, there are resulting I=, e*" energy changes involving the valence electrons. where The ultraviolet portion of the spectrum is that I = Unabsorbed Intensity portion of the sun’s energy which causes sunburn I, = Incident Intensity and similar skin damage. The absorption of ultra- violet energy causes energy changes involving the K= Constant ionization of atoms and molecules. b = Cell Thickness (light path length) Infrared radiation is the portion of the spec- Bernard's (1852), or Beer's (1852), law Gamma Xrays "Soft" Vacuum Near Visible Near IR Far Micro Radio | rays | [reaye uv | uv | IR IR Waves | 0.1 1.0 10 200 400 8p0 Nanometers —_— 0 2.5 25 4p0 8 0 crometer 0]. 40 250 Millimeters Figure 19-1. Schematic Diagram of Electromagnetic Spectrum. Note that the wavelength scale is not linear. 223 states that the intensity of the energy decreases exponentially with the increase in concentration. Mathematically this can be written as 2.303 log * =K’ C Where C is the concentration of the absorbing material. Combination of these two laws forms the basic law of spectrophotometry. It takes the form of: log > =abe where —a— is the absorptivity, a constant de- pendent upon the wavelength of the radiation and the nature of the absorbing material, whose con- centration —c— is expressed in grams per liter. The product of the absorptivity and the molecular weight of the absorbing substance is called the “molar absorptivity” (e). Absorbance A is the product of the absorptiv- ity, the optical pathlength and the concentration; ie. A=abc The absorbance of a 1-cm layer of a solution containing 1 percent by weight of the absorbing 1% The term “transmittance %” is the percent of the incident light passing through the absorbing solution and is related to the concentration exponentially. Thus, when the transmittance is plotted against concentration on semi-logarithmic graph paper a straight line should result if the system follows Beer’s law. Absorbance is directly related to concentration and can be plotted against concentration on linear coordinate graph paper. When such a plot gives a straight line the system follows Beer's law. Most dilute systems will follow Beer's law over a limited range of concentration. Beer’s law requires monochromatic radiation. However, most spectrophotometers and all filter photometers em- ploy a finite group of light frequencies. The wider the band of the radiation, the greater will be the deviations from Beer’s law. Temperature changes, ionization of the solute, stray light and changes in the pH of the solute, may cause deviations from Beer's law. While it is desirable to have the analytical sys- tem follow Beer's law, it is not essential if a good reproducible calibration curve can be prepared. VISIBLE LIGHT SPECTROPHOTOMETRY Introduction Analytical methods utilizing the visible sec- tion of the electromagnetic spectrum are of great importance. Most methods for the determina- tion of metals in trace concentrations involve the production of a colored complex with some or- ganic reagent. To be of value for analytical pur- poses the color-producing reaction should have the following characteristics: I. Reagent and the color complex should be stable. 2. The reaction should be stoichiometric. solute is represented by the term A 224 3. The color development should be rapid and color should resist fading. 4. The reaction should be specific for the element to be determined. 5. The reaction should show no more than minor variation with pH, temperature and other factors. 6. The color complex should be soluble in a solvent which is transparent in the area of spectral absorbance of the complex. 7. The color complex should have a sharp absorbance band. Methods of color development generally fall into the following categories: redox methods complex formation diazo and coupling reactions condensations and addition salt formation chromophoric changes in valence . substitution. Color procedures used may be classed as either single or mixed color. In the single color procedure, the color producing reagent is either colorless or the excess reagent is removed from ° the solution by suitable extractions. An example of this is the color complex formed with hexa- valent chromium by s-diphenylcarbazide. Here the reagents are colorless but react with hexa- valent chromium to produce a red complex. Oxi- dation of manganese to permanganate is another example of a single color method. The absorb- ance spectrum of the permanganate ion is shown in Figure 19-2. This ion shows a strong absorb- ance at 525 nanometers. The determination of lead with dithizone (di- phenylthiocarbazone) is an example of the mixed color technique. Dithizone dissolved in chloro- form has a bright green color with a maximum absorbance at 625 nanometers as shown in Fig- ure 19-3. In this figure Curve 1 is the absorbance spectrum of the dithizone solution which has been used to extract the reagent blank. It shows a zero absorbance or 100 percent transmittance at 610 nanometers and an absorbance at 515 nanom- eters which is due to traces of lead in the re- agents. Curve 2 is the spectrum of the dithizone after extracting a solution containing 10 micro- grams of lead. The increase in absorbance at 515 nanometers is evident. Figure 19-4 illustrates the change in absorbance as the lead dithizonate in- creases from 0.0 to 3.0 micrograms per ml of chloroform. The absorbance is set at 0.0 with the reagent blank. This will correct for any lead in the reagents. Then the absorbance is measured for the three standard solutions. It is evident that the standards follow Beer’s law. As a general rule, the complementary color is used to measure any colored complex. For ex- ample, if the solution to be measured is red, green light should be used. When any colored reaction is used, it is ad- visable to determine the absorbance spectrum of the reaction product with the spectrophotometer to be used for the analysis. From this spectrum the proper wavelength to be used for the pro- NoVA LN ~ Figure 19-2. Visible Absorbance Spectrum of Permanganate lon in Water. 225 0.7 rT / / 0.6 + / / 0.5T 4 / 3 / @ 0.49 T « / 2 / o 0.3 T _“ CURVE | 0.24 0.1 1 i 4 L 4 L I I I I I I 425 450 475 500 525 550 575 600 625 650 675 7 \ CURVE 2 \ REFERENCE CELL — \ CHLOROFORM WAVELENGTH —NANOMETERS Figure 19-3. Absorption Spectra of Dithizone and Lead Dithizonate in Chloroform. cedure will be evident and any instrumental vari- ation or shifts in the wavelength scale of the particular instrument will be corrected. In some instances, it is possible to utilize the bleaching effect of some ion on a colored organo- metallic complex to measure the concentration of the ion of interest. An example of this is the bleaching effect of fluoride ion on thorium or zir- conium alizarin lakes. In this case, the loss of color of the lake is directly proportional to the amount of fluoride present. While many color-producing reactions are available, some ions of interest do not form col- ored complexes that are suitable for analytical procedures. Frequently it is possible to produce a suspension of a finely divided uniformly sized precipitate. When a beam of light is passed through such a suspension, energy is lost due to light scattering. Under proper conditions this loss is proportional to the amount of precipitate. This analytical technique is called nephelometry. Such procedures require very rigid control of all condi- tions such as temperature, pH and concentrations of reagents to produce uniform size precipitates or reproducible results cannot be obtained. Proce- dures for the determination of chloride, as silver chloride, and sulfate, as barium sulfate, are exam- ples of the application of this technique. 226 Instrumentation The first techniques of spectrophotometry in- volved the direct comparisons of colors produced in unknown solutions with those of standards pre- pared under similar conditions. Observations were made with the naked eye using a common light source. Such techniques can still be used to obtain a rough estimate of the concentration. From this beginning, Nessler tubes developed. The color reaction is carried out in both a series of standards and unknowns. The solutions are placed in a series of long flat-bottom tubes and diluted so that the column of solution is either 10 or 20 centimeters in depth. After mixing, the color of the unknowns is matched against the standards. The unknown solutions can be brack- eted between two standards and a rough approxi- mation of the concentration can be made. The Duboscq colorimeter developed from this technique. Light illumination from a common light source is passed up through the bottom of a pair of matched cups, through the solution and through a matched set of glass plungers. A prism system brings the light beams to a common axis. Light from each cup illuminates one-half of the viewed field. The intensities of the two halves of the viewed field are matched visually by raising or lowering the plunger in one cup. The depth is Wayelgngth - Na mefer Figure 19-4. Absorption Spectra of Lead Dithizonate. measured on a scale. From previously prepared calibration curves it is possible to estimate the concentration. The ability of the eye to match intensities varies with wavelength and intensity. The eye is best at about 500 nanometers and under the best conditions can be accurate to within 1 or 2 percent. CONDENSING LENS EE Ee FILTER Another version of this technique is the wedge comparator. The light beam is split into two seg- ments. One passes through the standard solution and one through the unknown. A neutral wedge of glass is moved into the exit beam of the stand- ard solution to attenuate the light intensity until it matches the unknown. 5 PHOTOCELL LIGHT SOURCE SAMPLE CELL GALVANOMETER Figure 19-5. Schematic Diagram of Filter Photometer. 227 The next instrumental development was the single-beam photometer. The basic design of this type of instrument is shown in Figure 19-5. The light from the source passes through a filter, through the solution, and strikes a photocell. With the solvent in the light path and the proper filter in position the light intensity is adjusted to give a reading of 100 on the scale. Next the standards are inserted and the scale readings are recorded. Then the unknown solutions are inserted and read. The intensity of the light source can be adjusted either by a rheostat in series with the light source or a diaphragm in the light path. To eliminate errors due to variations in the light source with time, the double-beam photom- eter was developed. In this instrument the fil- tered light is separated into two beams. One beam is reflected to a reference photocell. The remain- ing beam passes through the solution to be meas- ured and strikes a second photocell. The net out- put of the two photocells, connected in opposition, is balanced by a variable resistor to give a zero reading on a galvanometer for the blank solution. The standards and unknowns are inserted into the beam and the deflections of the galvanometer are read; from the calibration curve the concentrations of the unknown can be determined. Filters avail- able for these instruments were generally wide band-pass filters and lacked the narrow spectral band width required by Beer's Law, MIRROR PRISM OR GRATING — Ce LIGHT A.| SOURCE / VARIABLE SLIT— COLLIMATING MIRROR MIRROR SAMPLE CELL PHOTOMULTIPLIER — Beckman Instruments, Inc.: Bulletin 134-D. Fullerton, California. Figure 19-6. Schematic Diagram of Prism or Grating Spectrophotometer. The next development was the prism or grating single-beam spectrophotometer. The basic instru- mental design is shown in Figure 19-6. In this instrument light from the source is refracted by a prism or diffracted by a grating into its spec- trum. A series of adjustable exit slits limits the wavelengths striking the sample. This spectro- photometer has a narrow band-pass which im- proves the conformity to Beer’s Law. The position of the grating or the prism is set to the proper wavelength and the blank is inserted in the beam. After balancing the instrument with the shutter closed, the shutter is opened and the meter set to 100 percent transmittance or 0 absorbance by adjustment of the slit width and the sensitivity control. The standards are inserted in the beam and the absorbance determined for each concen- tration. The absorbance of the unknowns can be measured and the concentration determined from the calibration curve. The light-measuring devices used in this type of instrument are either photocells or photo-multi- plier tubes. Generally two photocells are available to cover the entire spectral range. These instru- ments are much more expensive than photometers but give greater accuracy and reproducibility as well as monochromatic character of the light used in the analysis. A more recent development has been the ratio- recording spectrophotometer. In this instrument the light beam from the source is refracted by a prism and strikes a rotating segmented disc. One half of the disc is open allowing the beam to pass through a reference cell and eventually strike a detector. The other half of the disc is a mirror that reflects the light through the sample cell to the detector. The detector system produces a read- ing which is the ratio of the two beams. Such in- struments eliminate all variations due to voltage or electronic fluctuations. Any of the newer in- 228 struments can be coupled to a recorder to give a permanent record of the results. Applications Visible spectrophotometry has many uses in the analyses needed in environmental control work. Several examples are discussed. 1. Biological Analysis. Frequently, the measurement of some ion in a biological specimen is the best indicator of an exposure. The analysis of blood or urine for lead is an excellent means of evaluation of the worker’s exposure. The blood or urine is ashed, the ash dissolved and extracted with a chloroform solution of dithizone at pH of 9.5. The lead reacts with the dithizone to form lead dithizonate. The lead dithizonate in the dithizone-chloroform solution is determined at 510 nanometers. By proper con- trol of pH and use of complexing agents it is pos- sible to eliminate interferences from other metallic ions. The determination of manganese in urine is a useful measure of the exposure of workers to manganese. The urine is ashed and the manganese is oxidized to permanganate ion. The color of per- manganate can be measured at 525 nanometers. The determination of mercury in urine has taken on increased importance with the recent emphasis on mercury pollution. The urine is ashed under a reflux condenser, extracted with dithizone in carbon tetrachloride. The dithizone mercury solution is further extracted with 9N ammonium hydroxide twice to remove the unreacted dithizone leaving the single color of the mercury dithizon- ate. This is measured at a wavelength of 475 nanometers. Many other ions of interest in environmental control work may be determined by spectrophoto- metric procedures. 2. Air Sample and Sample Analysis. Lead can be determined in air samples by dithizone after ashing and solution of the sample. Under proper conditions the reaction is specific. Several methods are available for the deter- mination of iron. Under proper conditions, iron as ferric chloride in 28 percent hydrochloric acid can be measured directly at 460 nanometers. This method is not specific, for other colored metals in solution may affect the results. Specific reagents such as dipyridyl and ortho-phenanthroline are available for the determination of iron in trace quantities. As mentioned earlier, manganese can be oxi- dized to permanganate ion whose concentration can be measured at 525 nanometers. While the reaction is specific for manganese, the presence of easily oxidized materials can reduce the per- manganate ion and seriously affect the results. Arsenic can be vaporized as arsine and ab- sorbed in a solution of silver diethyldithiocar- bamate in chloroform solution. The color pro- duced is measured at 560 nanometers and the arsenic content determined from a calibration curve. Chromium, in the hexavalent state, can be complexed with s-diphenylcarbazide and read at 540 nanometers. The reaction under the proper conditions is specific. 229 Aldehydes after absorption in sodium bisulfite solution can be determined using Schiff’s reagent. The reaction is not specific for any one aldehyde in the presence of other aldehydes. The measure- ment is made at 560 nanometers. Sulfates as barium sulfate, or chloride as silver chloride may be measured by nephelometric tech- niques under carefully controlled conditions. All reagents, except the precipitating agent, are added and the solution diluted to volume. The absorb- ance is measured at 500 nanometers. The pre- cipitating agent is then added and the precipitate allowed to form for a specific time period. The absorbance is again measured at the same wave- length. The difference in absorbance is a measure of the sulfate or chloride ion. ULTRAVIOLET SPECTROPHOTOMETRY Many compounds containing specific types of chemical bonds will absorb ultraviolet light strong- ly at very specific wavelengths. The ultraviolet spectrum from 210 to 380 nanometers is of most interest since the ultraviolet spectrophotometers in use are not capable of operation below 210 nan- ometers. Some compounds of environmental in- terest, such as ketones, aldehydes, esters and organic acids absorb below this point. However, many other compounds of great in- terest do absorb ultraviolet light above 210 nan- ometers. In general, all aromatic compounds such as benzene, toluene, and xylene have strong ab- sorbing bands. The absorbance spectra of benzene and toluene vapors are shown in Figure 19-7. The spectra of these two compounds show many rela- tively intense absorption bands with good resolu- tion. While these two compounds are homologs, their spectra are quite different. Figure 19-8 gives the spectra of different concentrations of benzene dissolved in cyclohexane. While the resolution is not as good as that observed in the vapor state, it is still sufficient to identify the compound. Even at a concentration as low as 0.20 milligram per milliliter appreciable absorption occurs at 254.6 nanometers. Phenolic type compounds also exhibit strong absorbance bands in the ultraviolet region. Some inorganic materials show strong absorb- ances in the ultraviolet range. Iodine absorbs strongly at 352 and 440 nanometers. Nitrates and nitrites absorb at 270 and 225 nanometers, re- spectively. One of the prime requirements for analytical work in this section of the spectrum is a solvent that is relatively transparent to ultraviolet light. A solvent must have a cutoff point well below the absorbing band to be measured. The cutoff point in the ultraviolet region is the wavelength at which the absorbance of a 10-mm path length approaches unity with water as the reference. Table 19-3 gives the cutoff wavelengths for many of the more common solvents. Generally the solvents of greatest use are methanol, ethanol, isopropanol, isooctane, cyclo- hexane, sulfuric acid and water. Since absolute ethanol is distilled with benzene, it usually con- tains traces of benzene which make it unsatis- factory as a solvent. Figure 19-7. Ultraviolet Spectra of Benzene and Toulene Vapor. 230 0420 [mg/ml Figure 19-8. Ultraviolet Spectra of Benzene in Cyclohexane. 231 Table 19-3. Ultraviolet Cutoff Wavelength, Nanometers Grade Solvent Reagent Spectrographic * Acetone 327 330 Benzene 279 280 N-butanol 268 210 Carbon tetrachloride 263 265 Chloroform 245 245 Cyclohexane 210 Ethanol 219 Isooctane 220 210 Isopropanol 218 210 Methanol 218 210 Methylethyl ketone 327 Nitric Acid — 6N 334 Sulfuric Acid — 6N 215 Trichloroethylene 287 Tetrachloroethylene 292 290 Toluene 285 285 Water 212 “Ultraviolet spectrophotometric and Fluorescence Data”, J. A. Houghton and George Lee. Am. Ind. Hyg. J. Vol. 22, No. 4, page 296, 301, 1961. When the material of interest does not absorb in the ultraviolet region, it is sometimes possible to couple it with an absorbing compound to give an absorbing complex. The sensitivity of ultraviolet methods is much greater than that found with either visible or infrared methods. Frequently, it is necessary to dilute an absorbing compound to the range of 1 microgram per milliliter to read the absorbance. A solution of styrene in cyclohexane as a concen- tration of 2 micrograms per milliliter gives an absorbance of 0.300 at a wavelength of 247 nanometers. Much information can be obtained from the absorbance spectrum. If the system is essentially transparent in the region from 210 to 800 nanom- eters, it contains no conjugated unsaturated or benzenoid system, no aldehyde or keto groups, no nitro group and no bromine or iodine. When absorbance bands do appear, their wavelength will give some indication as to the identity of the group causing the absorbance. Several tables of chromo- phoric groups and their wavelengths have been published and can be used for identification.’ Instrumentation Many types of ultraviolet spectrophotometers are available. They can be generally classed as single or double beam with either a prism or grat- ing for the refraction or diffraction, respectively, of the spectrum. In the single-beam instruments, the unit is balanced against the solvent to read zero absorbance, then the sample is moved into the beam and the absorbance measured. Several of the visible range spectrophotometers can be 232 converted to ultraviolet spectrophotometers by a suitable attachment. In some double-beam instruments the beam is chopped by a rotating disc containing an open and a mirrored segment. The beam is sent through the sample cell and then through the reference cell. In other instruments the beam is split and sent through both the reference and the sample cells. Initially, with the solvent in both the sample and the reference light paths the instrument is adjusted to give a zero absorbance at the wave- length to be used. When the sample is placed in the sample beam, the absorbance due to the cells and the solvent is cancelled and the instrument measures the absorbance of the solute only. An example of a double beam instrument is shown in Figure 19-9. The single-beam instruments are much lower in price than the double-beam instruments. While it is not necessary to have a recording instrument, it is very convenient to have a recorded spectrum produced by the instrument. If not, the spectrum must be determined by a point-to-point scan and plotting of the points. This is a time-consuming operation. In ultraviolet spectrophotometry the cells used must be transparent to ultraviolet light. This re- quires that the cells usually be constructed of pure silica because the ordinary glass cells used in visible work absorb much of the ultraviolet. Silica cells are expensive and must be handled with care to prevent scratching and etching. Light sources used are generally either hydrogen, deuterium or xenon lamps. These sources all require special power supplies and in many cases auxiliary cooling systems. Many types of detector tubes may be used. All these tubes have their specific properties. In the less expensive instruments the 1P21 photo- tube is used as the detector. More expensive photomultiplier tubes are available which are more sensitive in specific regions. In summary the ultraviolet spectrophotometer is a valuable tool for both the qualitative and quantitative analyses required in environmental work. It offers many possibilities for the analysis of air pollutants. At times it may be the only method available for the analysis of trace amounts of organic pollutants. Applications While it is not possible to discuss all the pos- sible determinations that can be made with ultra- violet light, a few will be briefly discussed to illus- trate possible procedures. If long-path gas cells are available for the spectrophotometer, it is pos- sible to determine benzene, toluene or xylene di- rectly in air samples. A standard curve is first pre- pared in the ppm (parts per million) range using the absorbance measurements obtained with known concentrations of the aromatic hydrocarbon vapor at the wavelength giving the maximum absorbance. The absorbance of the air samples are then de- termined under the same conditions. From the calibration curve prepared earlier it is possible to estimate the concentration of the aromatic hy- drocarbon, directly in the air sample. Where a suitable gas handling system or gas Collimating Mirror Mirror Prism Slit Collimating Mirror Prism Slit Mirror Cary Inst. Div. of Varian: Model 15 Optical Diagram. Monrovia, California. Figure 19-9. Schematic Diagram of cells are not available, it is possible to absorb the aromatic hydrocarbon in a transparent solvent and determine it in this solvent as was shown earlier in Figure 19-8 of this section. Calibration curves must be prepared to compensate for in- complete absorption in the solvent. It is possible to determine phenols and cresols in dilute sodium hydroxide solutions directly in the absorbing solution. The phenolic-type com- pounds are absorbed in a dilute caustic solution and after dilution the absorbance is measured at the wavelength of maximum absorbance. From previously prepared calibration curves the amount of phenolic compounds can be determined. It must be emphasized that it is not possible to identify the specific phenolic compound present. The re- sults will give only total phenolic content. The use of the ultraviolet spectrophotometer for the identification of polynuclear aromatic hy- drocarbons was developed by Sawicki.” Benzene extracts of air samples are dissolved in a chlor- inated solvent and passed through a chroma- tographic column. Specific sections of the column are extracted with a suitable solvent and the ultra- violet spectrum is determined. The polynuclear aromatic hydrocarbons can be identified and quan- titated by the ultraviolet spectra using previously prepared calibration curves. More recent work has utilized the trapping of gas chromatographic peaks and the identification and quantitation of the 233 Hydrogen Lamp Slit Shutter Mirror Lamp Lens Sample Cell Beam Phototube Splitter Reference Cell Phototube Double Beam Spectrophotometer. material present by ultraviolet spectrophotometry. With all the recent emphasis on mercury pollu- tion, the ultraviolet absorbance spectrum of mer- cury vapor has been utilized for the quantitative determination of this element. Mercury strongly absorbs ultraviolet light of wavelength of 253.6 nanometers. Many direct reading instruments are available for the determination of mercury in air. Recent development of the mercury meter for water analysis also utilizes this property. The sample is ashed with potassium permanganate, sulfuric and nitric acids and reduced to elemental mercury with stannous chloride. The mercury is vaporized from the liquid by a stream of filtered air and passed through a cell and the absorbance of 253.6 nanometer ultraviolet light is measured. From previously prepared calibration curves the mercury content of the sample can be determined. It should be emphasized that any organic com- pound that absorbs at this wavelength and can be vaporized along with the mercury vapor into the gas cell will be determined as mercury and will cause high results. Acetone, for example, can cause serious interference in the determination of mercury. While the above examples are only a few of the possibilities for the use of ultraviolet spectrom- etry, experience in the technique will open up many other uses. It is a powerful tool for the solution of many analytical problems. 5000 2 WCMico0 13001200 1100 1000 WAR Munthe cu 700 600 2.0 3.0 4.0 5.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0 Figure 19-10. Infrared Spocra of Chiorinated Hydrocarbons — Wavelength in Micrometers. 234 INFRARED SPECTROPHOTOMETRY Introduction The section of the electromagnetic spectrum extending from 0.8 to 200 micrometers is classed as the infrared region. However, most of the analytical uses of this energy fall in the range of 0.8 to 50 micrometers, which can be explored with commercially available instruments. Absorp- tion of energy in this section of the spectrum results from the vibrational-rotational stretching and bending modes in the molecule. The infrared absorption spectrum of a compound can be char- acterized as a fingerprint of that compound. The absorbance bands are so definite that it is possible to identify stereoisomers from their spectra. It is possible to define the structure of complex mole- cules, such as penicillin, from study of its infrared spectrum. The infrared region is divided into three pri- mary sections, the rock salt (sodium chloride) or fundamental region from 2 to 16 micrometers, the potassium bromide region from 10 to 25 micrometers and the cesium iodide region from 10 to 38 micrometers. These regions are so named because of the material used for the prisms and cell windows. Silica and glass cannot be used in infrared equipment since they absorb any energy with a wavelength above 4 micrometers. Much valuable information can be gained from the absorbance bands found in the fundamental region. This section is usually divided into the “group frequency” region from 2.5 to 8 mi- crometers and the “fingerprint region” 8 to 16 micrometers. In the group frequency region the principal absorption bands are primarily due to vibration of units consisting of only two atoms of the mole- cule, units which are more or less dependent only on the functional group giving the absorption and not on the complete molecule structure. Structural influences may cause small shifts in absorption bands from their normal position. In the region from 2.5 to 4.0 micrometers the absorption is due to hydrogen stretching vibrations with elements of mass of less than 20. The center range from 4 to 6.5 micrometers is termed the unsaturated region. Primarily, triple bonds cause absorption from 4.0 to 5.0 micrometers. Double bonds frequently absorb in the region from 5.0 to 6.5 micrometers. Careful study of the absorption bands can help to identify and distinguish between C=0, C=C, C=N, and N=0 bonds. Absorptions in the region from 8.0 to 16.0 micrometers are single-bond stretching frequencies and bending vibrations of poly-atomic systems in- volving motions of bonds linking a substituent group to the remainder of the molecule. This is the fingerprint region. While too many absorption bands appear in this region to allow for specific identification it is possible to determine much in- formation about the molecule. Ortho, meta and para substitutions are easily identified. Chlorinated molecules absorb strongly in this region. Figure 19-10 shows the infrared spectra of five of the chlorinated hydrocarbons. Carbon tetrachloride and tetrachloroethylene show a com- plete absence of any absorption below 6 microm- 235 eters. As hydrogen is added to the molecule the bands at 3.3, 3.4, and 3.6 micrometers appear in the spectra. The intense absorption bands above 11 micrometers are typical of chlorinated com- pounds. From these spectra it is quite evident that there is little problem identifying the specific compound present. Generally for liquid work the light path is relatively short. These spectra were prepared using a cell with a light path of 0.25 mm, Inorganic molecules also have characteristic absorption bands in the rock salt region. The inorganic material is generally ground to a very small particle size in a clear mineral oil and a mull prepared or it can be dispersed in potassium bromide powder and pressed into a pellet. As will be discussed later, methods are available to de- termine small amounts of alpha quartz in respi- rable dust by the pellet technique. Some of the specific absorption bands of in- terest in environmentab control work are shown in Table 19-4. Many more complete tabulations of absorption bands are available in the literature. One of the most useful is the COLTHUP chart.? From the data in Table 19-4 it is evident that the bands tend to overlap in some areas. For example the esters, acids, ketones and aldehydes all show strong absorption bands in the same region. Bands in the fingerprint region may make it possible to identify the particular type of compound present. Table 19-4. Specific Infrared Absorption Bands Absorption Band Grouping Micrometers Alkanes, CH,-C,-CH, = 3.35 to 3.65 Alkenes CH=CH, 3.25 to 3.45 Alkyne C=C 3.05 to 3.25 Aromatic Hydrocarbons 3.25 to 3.35 Aromatic (Subst, benzenes) 6.15 to 6.35 Alcoholic (OH) 2.80 to 3.10 Acids (COOH) 5.75 to 6.00 Aldehydes (COH) 5.60 to 5.90 Ketones (C=0) 5.60 to 5.90 Esters (COOR) 5.75 to 6.00 Chlorinated (C-Cl) 12.80 to 15.50 It should be pointed out that while infrared is a very valuable analytical tool it does have its deficiencies. The sensitivity of infrared methods is much less than that for the ultraviolet methods. As an example, in the determination of mineral oil using the 3 micrometer bands, the minimum concentration that can be determined with con- ventional cells is 1 milligram per milliliter of solvent. Water and lower molecular weight alcohols cannot be used as solvents as they damage the cell windows. Moisture condensation on cell windows will also cause severe damage to the cell windows. In addition, water absorbs infrared energy strongly. A solvent, to be of value in infrared work, should have as few absorption bands as possible and none in the region of interest. No organic solvent is completely transparent to infrared radi- ation. Carbon disulfide and carbon tetrachloride are the common solvents. Carbon tetrachloride absorbs strongly from 12.5 to 13.5 micrometers while carbon disulfide absorbs strongly at 4.5 and 6.5 micrometers. Tetrachloroethylene is transpar- ent except in the region from 10 to 16 microm- eters. The high-boiling liquid Freons also are useful as solvents. The solvent may influence the spectrum of the solute. Particular care should be exercised in the selection of a solvent for com- pounds which are susceptible to hydrogen bonding effects. All solvents must be free of water. Instrumentation Basically, an infrared spectrophotometer con- sists of a source to produce the radiation, a mono- chromator to disperse the radiation, a sample compartment, a detector and a recorder. The equipment may be classified as either a single- or a double-beam system. In the single-beam system the beam passes through a single sample cell and to the detector. In this system it is necessary to deter- mine the spectrum of the solvent, the combined spectrum of the solvent-solute mixture and then subtract the spectra to determine the net spectrum of the solute. In the double-beam system the incident beam is chopped and sent alternately through the sample cell and then through the reference cell. The beams are then brought to the same detector. The detector balances the signal it receives from both cells by driving a comb in and out of the reference beam to alter the intensity of the reference beam to equal that of the sample beam. The position of the comb is transmitted to the recorder. An ex- ample of a double beam instrument is shown in Figure 19-11. The source in most infrared spectrophotom- eters is either a Nernst glower or a Globar. The Nernst glower consists of a mixture of zirconium and yttrium oxides which is formed into a hollow rod 2 millimeters in diameter and 30 millimeters long. The surface temperature is between 1500° and 2000°C. The glower furnishes a wide range of infrared wavelengths, with maximum emission at 1.4 micrometers. A secondary heating source is necessary to light the glower since it is non- conducting when cold. It must be protected from drafts but still must be ventilated to remove the vaporized oxides and binders from the glower. The Globar source is a solid rod of sintered silicon carbide. It is self-starting and is heated to 1300° to 1700°C. Maximum intensity occurs at 1.9 micrometers. Although it is less intense than the Nernst glower, it is more suitable for work beyond 15 micrometers, since its radiant energy output decreases less rapidly with increasing wave- length. The monochromator is generally a Littrow mount. The beam from the collimating mirror is focused on the entrance slit. Either a grating or a prism may be used to disperse the incident beam. The prisms are made from single crystals of either sodium chloride or potassium bromide, depending upon the required working range of the instrument. The grating provides better dispersion and thus better resolution but is usable over only a limited range. Two gratings are generally used to cover 236 the entire range of the instrument . . wach is used only in the first order. The detectors are of a thermal type. Photo- conductors are not applicable except in the near infrared region. A special type thermocouple is the most widely used. Quartz fibers are used to support a blackened gold foil receiver less than one micron in thickness to which is fastened the hot junction made by welding two different semi- conductors together at one end. The semicon- ductors must have a high thermoelectric efficiency. The cold junction is maintained at a constant temperature and kept darkened. The pair is housed in an evacuated steel casing with a po- tassium bromide or cesium iodide window. A second type of thermal detector is: the bolometer. It produces an electrical signal as the result of a change in resistance of a metallic con- ductor with temperature as the infrared energy is absorbed. Cells for infrared use consist of polished, op- tically flat discs of sodium chloride or potassium bromide separated by an amalgamated lead spacer and held liquid-tight by a holder. Liquid cell path lengths range usually from 0.1 mm down so that only a thin layer of the sample is exposed to the beam. Gas cells with path lengths of 1 meter are available for analysis of air pollutants. Infrared cells are very expensive and must be protected from any contact with moisture either in the sample or by exterior condensation to prevent etching of the crystals. The potassium bromide pellet technique was developed to handle materials that could not be dissolved in a suitable solvent. The material to be examined is reduced to a fine powder, dispersed in high-purity potassium bromide powder and formed into a pellet under high pressure. The pellet is placed in the cell compartment and the spectrum determined. Instruments to be used for pellet analysis should be equipped with a beam condensing system to concentrate the incident beam to a small size. Using the condensing sys- tem the pellet size can be kept small and the dilu- tion of the sample by the potassium bromide is reduced. Applications The use of infrared spectrophotometers in en- vironmental control analysis has been quite limited in the past probably due to the cost of the equip- ment and a limited knowledge of its possibilities. It is extremely valuable for the qualitative and quantitative analysis of solvents. With experience in the technique, simple solvent mixtures can be analyzed qualitatively from one spectrum. An esti- mate of the quantitative analysis can usually be made from the same spectrum. A known syn- thetic can be prepared at the approximate concen- tration and its spectrum determined. By com- paring the spectra of the unknown and known mixtures it is possible to get an estimate of the actual concentration. For complex solvents, it is usually advisable to fractionate the mixture and examine the frac- tions by infrared analysis. The determination of airborne mineral oil on filters used to collect particulate material is pos- . n |, BOLOMETER 45° MIRROR recevme - RECEIVI Rye . EXIT SLIT 8.9 CM. FOCUS ATTN yy FRISH | voumaee - a teers = 2 AMPLIFIER - _ = COLLIMATOR -— MIRROR [ 45° MIRRORS WAVELENGTH 75 CM.FOCUS : } 1, MIRROR CAM 8 RECORDER / Fy ENTRANCE DRIVE MOTOR \ PARTITION MIRROR SAMPLE CELL INTERRUPTER CM. Fi - 20 CM:-FoCus IS SWITCH ON SHAFT DRIVE ~—=| SHAFT SYNCHRONOUS RECORDER DRUM MOTOR err REFERENCE EE : | CELL - —~ (COMPENSATING) |_| Power = AMPLIFIER a) 3 20 CM. FOCUS PEN B PEN & COMB. | |MOTOR DRIVE Baird Associates: Bulletin XXXII. Cambridge, Massachusetts. Figure 19-11. sible using infrared. The oil is first extracted from the filter with ether or hexane. The solvent is allowed to evaporate at room temperature. The oil is then redissolved in a known volume of carbon tetrachloride. The absorbance of the sam- ple is determined over the range of 3 to 4 microm- eters. The mineral oil content is calculated from a previously prepared calibration curve, using a comparable oil. The fixed gases such as carbon monoxide, sulfur dioxide and ammonia can be determined di- rectly in air by use of gas cells with a one meter light path. The gases have definite spectra and can easily be identified. The technique requires relatively large volume air samples. 237 Schematic Diagram of a Double Beam Infrared Spectrophotometer. One recent development is the determination of alpha quartz in respirable air samples as is re- quired by both the Coal Mine Safety and Health Act and the Occupational Safety and Health Act. The dust sample and filter are ashed or the dust removed from the filter by ultrasonic means and ashed. The ashed sample 1s mixed with potassium bromide and formed into a pellet under high pres- sure. The infrared absorbance is measured at 13.1 micrometers. Using a previously prepared cali- bration curve, the alpha quartz content is then determined. Under carefully controlled conditions it is possible to measure 10 micrograms of quartz by this technique. FLUORESCENCE SPECTROPHOTOMETRY Introduction Use of the fluorescence properties of certain compounds as an analytical tool has become im- portant in the environmental control field only in the last few years. The analysis of beryllium in particulate material collected in air samples is based on the flourescence of a beryllium morin complex. Later work on the polynuclear aromatic hydrocarbons has developed additional interest in this technique. Fluorescence spectrometry is a highly sensitive analytical tool which can be used to measure con- centrations as low as 107 to 107'° grams per milliliter. Few colorimetric procedures are of value at concentrations below 107" grams per milliliter. Fluorescence is essentially an electronic phe- nomenon and is primarily concerned with light of wavelengths in the region of 200 to 800 nanom- eters. When light in this region strikes some com- pounds they absorb energy at specific wavelengths which are characteristic of the compound. This is called the absorption spectrum of the com- pound. As a result of this absorption of energy, some of the molecules are raised from the ground state to a higher energy level called a singlet or excited state. Since this excited state is unstable, the molecule tends to return to the ground state by emitting the absorbed energy as fluorescence. As some of the released energy is lost by other means, the energy released as fluorescence is al- ways less than the absorbed energy. Therefore, the wavelength of the fluorescence is longer than that of the absorbed energy. The absorption and release of energy as fluorescence takes place in 107 seconds. In some instances the absorbed energy may be released in two steps. First a small amount of energy is lost, allowing the molecule to reach the triplet or metastable state. It then returns to the ground state by releasing energy slowly. The energy lost from the triplet to the ground state is . called phosphorescence. As in fluorescence, the energy lost by phosphorescence is less than the total absorbed energy and thus, the wavelength of the phosphorescence is longer than that of the absorbed energy. Since the energy release is slower, phosphorescence is more persistent than fluorescence. Not all organic compounds exhibit fluores- ence. In general, the compounds which fluoresce are aromatic or contain conjugated double bonds (i.e., alternating single and double bonds). Those compounds containing electrons which undergo energy transformations readily should fluoresce. Any radical, which when added to the molecule increases the freedom of these electrons, will en- hance the fluorescence. Conversely, any radical which tends to restrict the electrons’ ability to absorb energy will decrease the fluorescence. Two different spectra are generally shown for compounds showing fluorescence. The excitation spectrum is obtained by measuring the variation in intensity of a strong emission wavelength as the wavelength of the excitation energy is changed. Conversely, when the wavelength and intensity are measured over the emission range using a 238 strong excitation wavelength, an emission spec- trum is obtained. The effects of substitution upon fluorescence can be illustrated with benzene, aniline and nitro- benzene. In dilute solutions, aniline is 40 to 50 times ‘more fluorescent than benzene whereas nitrobenzene does not fluoresce. The — NH, group increases the freedom of the electrons while the — NO, group tends to decrease the freedom. Many factors may affect the intensity of fluor- escence. Among the more important are instru- mental parameters, concentration, solvent, pH, temperature and the stability of the compound to light. Instrumental slit widths and light intensity can affect the intensity and all instrumental param- eters must be kept constant during any set of determinations. Concentration plays a very important role in the intensity of emitted light. Generally the fluor- escence is viewed at right angles to the incident light. The fluorescence emitted must pass through the cell and some is reabsorbed by the solution. The higher the concentration of the compound, the greater the energy which is reabsorbed and lost. Consequently, a linear relationship between concentration and fluorescence exists only in a very dilute solution. Solvents used in fluorescence measurements may affect the results radically. Many solvents may contain impurities which will fluoresce and need extensive purification to make them usable. Solvents such as water, simple alcohols, ether or hexane can be used. The fluorescence wavelength may shift rather widely as the solvent is varied. Ionization of the fluorescing compound may change or eliminate fluorescence. Thus, pH may become an important factor in any measurement. Aqueous buffer solutions are frequently used to control pH. Fluorescence intensity tends to increase as the temperature is lowered and decreases as the tem- perature is raised. The fluorescence may change by as much as 5 percent per degree of temperature change. Some compounds tend to decompose under the influence of ultraviolet light. Thus, as the concentration of the solute decreases the intensity of fluorescence decreases, except in those cases where the decomposition products may fluoresce. Quenching is the term applied to the loss of fluorescence. As mentioned earlier, the compound itself may cause concentration quenching. Some compounds can reduce or eliminate fluorescence. Quenching can be caused by inner filter effects, energy degradation, chemical change, absorption and/or intersystem transfer. It should be pointed out that all glassware must be kept very clean. Many detergents fluoresce and should not be used to clean cuvettes (sample cells). Chromic acid absorbs ultraviolet light and should not be used for cleaning glassware for fluorescent procedures. Concentrated nitric acid is frequently used to clean cuvettes. Instrumentation There are several types of instruments avail- able on the market. Many of the UV-visible light spectrophotometers have fluorescence attachments. SSS; oO POWER SUPPLY i A] PHOTOMETER Oo RECORDER MIRROR EMISSION MONOCHROMATOR EXCITATION MONOCHROMATOR —— | ELLIPSOIDAL CONDENSER XENON LAMP PHOTOM IER © ONUBET- REMOVABLE SAMPLE I | OPTICS BASE PLATE SAMPLE F———- REMOVABLE SAMPLE —— ——L_— 1 Base PLATE r — American Instruments Co.: Bulletins 2392H and 2423-1. Silver Springs, Maryland. Figure 19-12. Schematic Diagram of Two Types of Spectrophotofluorometers. 239 In these the excitation is caused by the entire spectrum of the ultraviolet region. The emitted radiation is measured at a right angle to the in- cident beam. The emitted radiation is analyzed by filters, gratings or prisms. With these instru- ments the excitation spectrum cannot be deter- mined. These units are generally suitable for routine analysis. The second general type of instrumentation involves units with two monochromators. With these spectrophotofluorometers a specific wave- length can be used for excitation and the fluores- cence spectrum can be determined. Since both the excitation and emission spectra are valuable for identification purposes, these systems are very valuable for the identification of unknown sam- ples. These instruments can be either direct read- ing or equipped with a recorder. Schematic diagrams of two different spectro- photofluorometers are shown in Figure 19-12. 500 T 200 + P21 R446S 100 1 AMINCO 809 50 20 RELATIVE ANODE RESPONSE o l 1 I 1 200 300 400 500 The light source is an important part of any spectrophotofluorometer. The xenon-arc lamp is commonly used. It produces a continuous spec- trum from 200 to 800 nanometers and has a greater intensity in the ultraviolet region than does the tungsten lamp. The xenon-arc lamp produces large amounts of ozone and should be locally ex- hausted to remove the toxic gas. Mercury lamps give a discontinuous spectrum consisting of high intensity lines at 365, 405, 436 and 546 nanometers. If the compound to be studied is excited in this region, the mercury lamp is very satisfactory. It is not satisfactory for studying compounds excited by other wavelengths, The cells used are of either glass or silica. If the exciting wavelength is above 320 nanometers the cheaper glass cells can be used. Below this wavelength silica cells are required. All cells shoud be checked for fluorescence. The detectors are photomultiplier tubes. Since 7102 AT 1250V 194° KELVIN {ORY ICE) ALL OTHERS AT 700V ROOM TEMP. R446S \ AMPLIFIER Jarrell Ash. Div., Fisher Scientific Co.: Bulletin 160A. Waltham, Massachusetts, p. 5. Figure 19-17. izing the metallic mercury and carrying it to a sample cell mounted in the light-path in place of the burner. The absorption of light of a wave- length of 253.7 nanometers is measured. The mercury content is determined from a calibration curve prepared under identical conditions. The use of atomic absorption for the deter- mination of lead in biological speciments has been studied and many procedures have been published. The analysis of urine directly for lead has been unsuccessful with commercial instruments due to the heavy salt concentrations. The large amount of solids in the urine causes clogging of the nebulizer and variations in the atomization rate and the presence of large amounts of sodium causes interference. The detection limit for lead is approximately the same concentration as that found in normal urines. Extraction of the urine or blood, after ashing, with APDC in methylisobutyl ketone has been re- ported. Co-precipitation of the lead with bismuth and solution of the precipitate has also been suggested. Several modifications of equipment have been suggested for the analysis of urine or blood for lead directly. The tantalum boat has been sug- gested. An acidified solution of the urine or blood is placed in the boat, the boat is advanced to the edge of the flame to dry the sample. Then the boat is placed directly in the flame to ash the sample and vaporize the lead. The Delves cup procedure for blood has been suggested. The blood sample (0.1 ml) is placed in a small nickel cup and dried at the edge of the flame. After drying, the cup is pushed into the flame directly under a nickel tube. The lead is vaporized and passes into the tube where it can be held in the light-path for a longer period of time to enhance the sensitivity. The tantalum strip or carbon rod furnace has been suggested as a technique for the analysis of 245 Schematic Diagram of a Basic Atomic Absorption Spectrophotometer. blood. A few microliters of blood are placed in a depression in the tantalum strip or in a cavity in the carbon rod. An electrical current is passed through the strip or the rod to dry the blood. The current is then increased to vaporize the lead. In its present state of development atomic absorption spectrophotometry is a very valuable tool for an environmental control laboratory. SUMMARY Spectrophotometry is a valuable tool for the solution of many of the analytical problems of an environmental health laboratory. This chapter has presented a discussion of the principles of the techniques of spectrophotometry and their appli- cation to this type of analysis. The methods were presented as illustrations of the principles, and specific details can be found in any of the standard texts on analytical chemistry. The actual choice of the method will depend upon the equipment available in the laboratory, and the type of sample submitted for analysis. References 1. Amer. Ind. Hyg. Association J. 22, 296-301, 66 South Miller Rd., Akron, Ohio 44313, 1961. Int. Air. Poll. J. 2, 273-283, 1960. Opt. Soc. Am. J. 40, 397, American Institute of Physics, 335 E. 45th St., New York, New York 10017, 1950. 2. 3. Preferred Reading 1. WILLARD, H. H, L. L. MERRITT, and J. A. DEAN, Instrumental Methods of Analysis, D. Van Nostrand Company, Inc., 1965. HARRISON, G. R,, R. C. LORD, and J. R. LOOF- BOUROW, Practical Spectroscopy, Prentice-Hall, 1948. . NACHTRIEB, N. H., Spectrochemical Analysis, McGraw-Hill, 1950. SANDELL, E. B., Colorimetric Determination of Traces of Metals, Interscience Publishers, Inc., 1950. JACOBS, M. B., The Analytical Toxicology of In- dustrial Inorganic Poisons, Interscience Publishers, Inc., 1967. . “Atomic Absorption Spectroscopy,” ASTM STP 443, American Society for Testing Materials. . ROBINSON, J. W., Atomic Absorption Spectros- copy, Marcel Derker, 1966. . ELWELL, W. T. and J. A. F. GIDLEY, Atomic Absorption Spectrophotometry, Pergamon Press, 1966. 246 10. 11. WILLIAMS, R. T. and J. W. BRIDGES, “Floures- cence of Solutions: A Review,” J. Clin. Pathology 17, 371, 1964. FRIEDEL, R. A. and M. ORCHIN, Ultraviolet gh 9 Aromatic Compounds, J. Wiley and Sons, nc., 1951. BELLAMY, L. J., The Infrared Spectra of Complex Molecules, John Wiley and Sons, Inc., 1954. CHAPTER 20 EMISSION SPECTROSCOPY C. L. Grant INTRODUCTION Emission spectroscopy is that method of anal- ysis that depends on the fact that energized atoms, ions, and molecules emit electromagnetic radiation when they lose energy. The characteristic line spectra emitted in flames, arcs, sparks, and related sources are highly specific for each element. Fur- ther, spectral line intensities are functionally re- lated to element concentrations in the excitation source. Thus, when samples are introduced to these sources, both qualitative and quantitative analyses can be accomplished. As a survey method, probably no other analyt- ical technique provides so much information for a given amount of effort. A wide variety of sample types and forms can be analyzed, usually with a minimal amount of pretreatment. Up to 70 ele- ments may be detected and estimated simultan- eously, although procedures of this breadth are not generally attempted. The detection capability varies widely with elements, but it is generally best for the lower atomic number elements. Ab- solute detection limits are often below 10 nano- grams which makes the technique quite useful for the analysis of small samples; i.e., one milligram or less. When sample size is not limiting, large spectrographs with high resolution readily provide detection capabilities as low as a few parts per million; and, in ideal cases, the limits may be as low as a few parts per billion. In view of the above, it is not surprising that some of the earliest applications of emission spec- troscopy were in the field of occupational health. Industrial workers are exposed to many substances containing toxic elements. Some elements tend to accumulate in body tissues and, therefore, very low concentrations of these elements in drinking water and/or air can be hazardous. For the safety of workers, it is necessary to monitor concentra- tions of toxic elements in the working environment and in body samples such as blood, urine and feces. The enormity of this analytical problem requires techniques of broad scope, high selectivity and detection capability, and adequate precision and accuracy. Emission spectroscopy is such a technique. PRINCIPLES Atomic line spectra are produced when energy is added to atoms in the ground state in an amount sufficient to cause some electrons to move from their normal energy levels to higher energy levels. In this form, the atom is said to be “excited.” When the electrons return to their normal energy levels, they release energy stepwise in the form of radiation. Each step accounts for a definite 247 amount of energy. The radiation produced has specific frequencies corresponding to the energies associated with the various steps, as indicated by the relationship E=hv. where: E= energy of the radiation (photon) h = Planck’s constant v = frequency of radiation An element is characterized by as many dif- ferent spectra as the atom has electrons. Lines originating from the electron transitions of the neutral atom are called arc lines, whereas those from the singly ionized atom are called the first spark spectra. Although greater degrees of ion- ization do occur to a limited extent in conventional spectroscopic sources, the lines originating from neutral atoms and singly ionized atoms are the ones of major analytical interest. The number of spectral lines produced for any element depends on the atomic structure. Ele- ments with comparatively few valence electrons produce relatively simple spectra (e.g., alkalis and alkaline earth metals). In contrast, an element such as uranium produces thousands of discrete lines, none of which are very intense. The spec- trographic determination of elements with very complex spectra is less attractive than for elements with simple spectra. This is due to possible in- complete resolution of lines of very similar wave- lengths and also because elements with very com- plex, less intense spectra exhibit only fair detection limits. While all the elements can be excited, gaseous elements, bromine and iodine are only infrequently determined this way. These elements can occa- sionally be determined with conventional excita- tion procedures by measuring the band spectrum of a compound such as calcium fluoride. How- ever, this approach is not widely used. Carbon, phosphorus, and sulfur have their most sensitive lines below 2000A and, therefore, require the availability of a vacuum spectrograph to overcome air absorption. Fortunately, most elements that are readily studied by optical emission spec- troscopy produce useful lines between 2000 and 8000A. In this wavelength region, simple optical, photographic and electronic equipment can be used to isolate and record spectral lines. Qualitative analysis by emission spectroscopy is based on the fact that the atomic structure for each element is different. Therefore, a unique set of spectral lines is produced for each element; and these lines serve as a fingerprint. Line identi- fication is usually accomplished by comparison of lines in the unknown spectrum with lines in a series of standard spectra prepared from pure elements. Quantitative analysis is based on the fact that the intensity of a spectral line depends on the amount of parent element present in the excita- tion source. When the spectra are photographically recorded, relative intensities are estimated by measuring the optical density with a densi- tometer. Density values are then converted to relative intensities by means of an emulsion cali- bration curve relating these two variables for the particular emulsion involved, at the wavelength of interest. Alternately, line intensity can be re- corded photoelectrically, thereby eliminating many of the errors inherent in photographic procedures. SYSTEM COMPONENTS Analysis by optical emission spectroscopy in- volves four main steps: 1) vaporization and ex- citation, 2) resolution of emitted radiation into constituent wavelengths, 3) recording spectral lines, and 4) interpretation. Vaporization and Excitation The total radiation output of a spectroscopic source is dependent on the aggregate of the proc- esses of volatilization and excitation. Often, a clear distinction between these two processes is not made, probably because both are occurring simultaneously in most sources. For optimum reproducibility in the production of spectra, it is important to know which process is most im- portant in a particular situation so that it may be properly controlled. The comprehensive treatise by Boumans! is an excellent source of information on this topic. Vaporization can be accomplished by thermal means as exemplified by flames, direct current arcs, ohmic heating and laser evaporation. The commonly used high voltage spark discharge pro- motes vaporization by bombardment with positive ions and high velocity electrons. Of course, the vaporization process is seldom entirely thermal or entirely bombardment; and, therefore, no sharp separation between these sources should be assumed. Flames. When a solution is aspirated into a flame in the form of minute droplets, desolvation occurs leaving small residue particles. Decomposition and vaporization of these particles produce a vapor containing atoms and molecules which are then excited via inelastic collisions with high velocity molecules liberated by chemical reaction between the fuel gases. Since the energy available in a flame is relatively limited, the spectra obtained are quite simple. As a consequence, spectral in- terferences are uncommon, thereby making it pos- sible to employ comparatively inexpensive spec- trometers of low dispersion. Because of the comparatively low temperature of common flames such as air-acetylene, this source was traditionally considered suitable only for the determination of easily vaporized and excited elements such as the alkalis and alkaline earths. However, Fassel et al.>* showed that many elements that tend to form stable oxides in normal stoichiometric flames can be dissociated to produce analytically useful atomic populations in 248 a fuel rich oxygen-acetylene flame. Pickett and Koirtyohann* reported the successful use of the nitrous oxide-acetylene flame for the emission determination of many elements previously con- sidered to be too refractory for analysis by this method. The development of a system for study- ing desolvation and vaporization processes of single droplets by Hieftje and Malmstadt® gives further promise for the development of optimized systems of flame vaporization and excitation. These developments coupled with the comparative simplicity of spectra produced by flame excitation and the inherent reproducibility of flames for quantitative work, suggest a bright future for flames in the field of environmental analysis. Arcs. The direct current arc is usually considered to be the most sensitive source for trace element analysis by emission spectroscopy. One reason for this high detection capability resides in the fact that comparatively large samples (100 milli- grams or more) can be employed. Most of the current in this type of discharge is carried by the electrons which impact on the anode and quickly elevate it to very high temperatures. This pro- motes rapid sample vaporization with an attendant high concentration of atoms in the analytical gap. Typically, nonconducting powders, solution residues, and similar samples are placed in the crater of a supporting graphite or carbon elec- trode. Three typical electrode geometries for di- rect current arc analyses are shown in Figure 20-1 ; © || © Oo E F G Figure 20-1. Some Typical Electrode Geo- metries. (A), (B) and (C). Many other electrode shapes have been employed in direct current arc work." These variations in electrode configuration in- fluence volatilization rates of elements and related aspects of the volatilization-excitation process. The choice of graphite and carbon as materials of construction for electrodes is based on the fact that (1) they are electrically conductive, readily manufactured in high purity, and easily shaped and (2) the carbon vapor produced during use does not depress the excitation characteristics of the arc since the ionization potential of carbon is greater than that of most elements determined by this method. One of the major objections to the use of the direct current arc is its tendency toward poor reproducibility in quantitative analysis. If we re- member that the sample-containing crater is an- alogous to a miniature distillation pot, any fixation of the arc at one or a few spots on the anode results in temperature gradients that will promote selective volatilization of the sample. This type of behavior is generally nonreproducible from one burn to the next. The use of “spectroscopic buffers,” extensively discussed by Boumans,' can greatly improve this situation if the buffer is care- fully selected. Such buffers are usually compounds containing elements having low ionization poten- tials which tend to reduce the effective excitation temperature of the arc plasma and increase the population of neutral atoms. Using various buffers in a free-burning 10-ampere direct current arc in air at atmospheric pressure, Boumans reported a range of temperatures from 5,000 to 6,200°K. Many of the objectionable features of the direct current arc can be reduced by directing an annular stream of gas upwards around the sample as it is arced. This system, first proposed by Stallwood,” reduces arc wander. In addition, it has a tendency to reduce selective volatilization, thus oftentimes improving both precision and accuracy. If an inert gas is employed, the cy- anogen bands are eliminated, thereby opening up a region of the spectrum which contains a num- ber of sensitive lines. Although we frequently go to great lengths to eliminate selective volatilization, sometimes it is possible to take advantage of this phenomena. In this approach, the shutter of the spectrograph is opened only while elements of interest are in the analytical gap. With the overall exposure level reduced, very large samples may be used; and this may produce a significant gain in detection capability. Many examples of this procedure have been described by Ahrens and Taylor.® Occasionally, the addition of certain com- pounds to the sample can be used to induce chem- ical reactions which will either promote or reduce selective volatilization. One of the best known ex- amples of this procedure is the carrier-distillation method first described by Scribner and Mullin.? A comparatively large sample (100 mg.) is mixed with a carrier such as gallium oxide or silver chloride and then packed into a deep-cratered electrode of the type shown in Figure 20-1 (C). Many investigators also like to put a vent hole in the center of the sample to permit a smooth evolu- tion of gases after the arc is struck. The electrode geometry is especially chosen to reduce heat loss from the sample-containing anode. Volatile im- purities are transported into the excitation zone with the carrier while the refractory matrix is left behind. Spark Discharges. Spark discharges are those in which the energy flow between the electrodes varies in a cyclic fashion, usually with a change of polarity each time the energy flow drops to zero. Because the discharge is being constantly 249 reignited, there is improved random sampling of electrode surfaces. Consequently, this discharge is generally considered to provide better precision but less sensitivity than arc discharges. The poorer sensitivity compared to a direct current arc is largely because the electrodes remain relatively cool, and considerably less sample is consumed. Despite this restriction, spark discharges have been employed with increasing frequency for trace analysis due to their excellent reproducibility. A comprehensive review of the characteristics of spark discharges was published by Walters and Malmstadt.® The most extensive application of spark dis- charges is for the analysis of metals as self-elec- trodes. However, powders have been analyzed by blending and compressing with graphite to form conductive briquets. Solutions have been analyzed by a variety of innovative procedures. In the porous cup technique developed by Feldman, a solution slowly percolates through the porous bot- tom of a hollow electrode [Figure 20-1 (D)]. As the liquid sample seeps through the porous bottom of the electrode, the spark discharge vaporizes and excites the residue to produce an emission spectrum. Another very versatile solution method involves the use of a rotating graphite disc that dips into the solution to be analyzed and trans- ports fresh solution on its periphery into the spark excitation zone [Figue 20-1 (E)]. For very small samples, some solution meth- ods are impractical because of the volume of sample required for analysis. In such situations, residues from the evaporation of these solutions can be analyzed. One of the best known solution residue methods is the copper-spark technique of Fred, Nachtrieb, and Tomkins.’? A hydrochloric acid solution containing a very small amount of sample (<0.2 mg) is applied to the end of high purity copper rods and dried. The copper rods are then mounted, and the sample is subjected to spark excitation. Excellent detection capabil- ities are realized with this procedure; but, of course, copper cannot be determined and solvents that react with copper cannot be used. In an at- tempt to circumvent this limitation, Morris and Pink'* employed flat-topped graphite electrodes [Figure 20-1 (F)] which had been treated with Apiezon-N grease to render them impervious to solutions. This procedure, called the graphite- spark technique, has exhibited detection capabil- ities in the nanogram range for several elements. A variation of this approach employs the rotating “platrode” developed by Rozsa and Zeeb' in which a graphite disc is substituted as the bottom electrode so that solution volumes up to 0.5 ml can be evaporated [Figure 20-1 (G)]. Plasmas. The plasma jet, sometimes called the gas-stabilized direct current arc, is an excitation source which has been used advantageously for the analysis of solutions.'®'® In this procedure, the solution is aspirated into a chamber by an inert gas under pressure and then swept through a small orifice into a direct current arc discharge. When the gas flow is increased through the orifice, the electrical conductivity of the jet rises, resulting in a high temperature at the core of the discharge. The special advantages of this system are the ex- cellent detection capability and the high degree of reproducibility. Precision values are generally much improved over conventional direct current arc excitation. Another plasma excitation system of special interest is the induction-coupled plasma. In the system described by Dickinson and Fassel,'” the solution is converted into an aerosol by an ultra- sonic generator. A condenser system is employed to desolvate the aerosol particles which are then introduced to the center of a donut-shaped argon plasma in a clear quartz tube. Power is supplied by a high frequency generator operating at 30 MHz. With this system, solutions were introduced at a rate of 0.3 ml/min. For many elements, detec- tion capabilities were in the nanogram/ml range. Since the temperature of this source is on the order of 10,000°K, even the most refractory spe- cies are dissociated; and chemical interferences from matrix elements should be drastically re- duced. The induction-coupled plasma deserves considerable attention in future methodological development. Another very unique and potentially useful plasma source has been described by Kleinmann and Svoboda.’ In this system, the sample is evap- orated from a graphite disc which is resistively heated. The evolved vapors are excited by a low voltage, high frequency, induction-coupled dis- charge in argon. Moderately good detection capa- bilities were obtained. Since the ideal of sep- arating vaporization and excitation is attained in this source, there is an excellent opportunity to control interferences from elements which make up the bulk of a sample. Laser Excitation. The analysis of very small areas of samples can be accomplished by emission spec- troscopy using a laser to vaporize the sample. This system, first described by Brech and Cross,'" em- ploys a high intensity pulsed laser beam focused on a spot that may be as small as 10 microns in diameter. With biological and geological spec- imens, it provides a means of gaining much greater insight into compositional variations than can be attained by bulk analytical systems. A major problem with the system is the diffi- culty in obtaining precise quantitative results. Reasons for this difficulty relate to problems in controlling the laser output energy, and the fact that it is extremely difficult to prepare standards for the establishment of calibration curves. Re- cently, however, Scott and Strasheim*’ have de- scribed the use of a Q-switched neodymium laser without an auxiliary excitation system. They ob- tained promising results in the analysis of alum- inum alloys with relative standard deviations in the range of 2% to 4%. Clearly, the ultimate potentialities of laser excitation for emission spec- trographic analysis have not been realized. Resolution of Emitted Radiation. Prisms and diffraction gratings are used to resolve the emitted light from a spectroscopic source into its com- ponent wavelengths. A variety of commercial in- struments are available with differing geometric arrangements of the necessary optical components. For additional details, the interested reader can 250 consult the recent text by Slavin.?' Only a few points of special interest in the analysis of indus- trial hygiene samples will be considered here. One of the most important propeities of a spectrograph is dispersion, usually expressed as the reciprocal linear dispersion in A/mm. According to Mitchell,>* “It is in general not the elements to be determined, but the source to be used and the composition of the material to be examined, insofar as its major constituents are concerned, which decide the instrument to be used.” When the number of lines produced by the major com- ponent is large, the reciprocal linear dispersion of the spectrograph must be small so that lines from the matrix material will not interfere with lines of elements to be determined. Fortunately, the major elements in most biological samples yield relatively simple spectra; and so, a spectro- graph of only moderate dispersion is adequate. Of course, the industrial hygienist also encounters samples whose major components yield very com- plex spectra. For example, a plant processing heavy metals could yield dust samples which would produce extremely complex spectra re- quiring a large instrument with small reciprocal linear dispersion. Detection capability can be a very important consideration in the analysis of typical industrial hygiene samples. In those cases where sample size is not limited, dispersion is the most critical factor governing detection limits. In a large spec- trograph with low reciprocal linear dispersion, a given amount of background radiation is spread over a large area while the line remains un- affected. Jarrell** emphasized that this increase in line-to-background ratio occurs only up to the critical dispersion, i.e., the point at which the slit and line widths are equal. When the industrial hygienist is interested in analyzing extremely small samples, the absolute quantity of an element is more important than its relative concentration. Mitteldorf** has empha- sized that the critical consideration here is the speed of the spectrograph (approximately de- fined as light yield). Thus, we would normally use a small spectrograph of high speed (typically f/10) for micro samples. In contrast, a large spectrograph with optical speed on the order of f/30 might be employed where sample size is not limiting. Recording Spectral Lines. Spectral lines are re- corded either photographically on films and plates or photoelectrically. Emulsions of widely varying speed and resolving power are available to photo- graph the various wavelength regions of interest. When the investigator wishes to determine ele- ments over a wide concentration range with mod- erate precision and accuracy, an emulsion of moderate contrast and high speed is selected. For precise quantitative analysis, an emulsion of high contrast is usually preferred. Direct photoelectric recording of spectral line intensities is considerably more precise than photographic recording and is, therefore, often used for quantitative work. However, direct readers are expensive and sometimes lack the flexibility required for survey analyses. There- fore, it is unlikely that photographic recording will become obsolete in the immediate future. Quantitative Measurements. In order to do quan- titative analysis by emission spectroscopy, it is necessary to estimate the intensity of spectral lines. When lines are recorded photographically, their optical densities can be measured by a micro- photometer. In this system, a narrow slit of light is scanned through the spectral line. A photo- electric detector records the decrease in light trans- mission associated with the blackening on the photographic plate. The photoelectric detector output is recorded as optical density of the spec- tral line. Next, optical densities must be translated into relative intensities by means of an emulsion cali- bration curve. To prepare an emulsion calibration curve, a variety of procedures are used including the use of rotating step sectors and filters with known light transmittances. Several accepted cali- bration procedures have been carefully described along with worked examples in ASTM Designation E 116.> For high volume repetitive quantitative deter- minations, direct reading spectrometers are gen- erally employed to reduce the manual effort re- quired. Photoelectric detectors are mounted be- hind exit slits located in the proper positions to record selected spectral lines. Calculation pro- cedures have also been automated by using com- puters to handle data reduction.?®*" Even when spectra are recorded photographically, data reduc- tion can be greatly facilitated via computer hand- ling. Besides speeding up computations, errors are minimized, and precision is frequently improved. SCOPE Sample Types Considering the variety of excitation sources which have been devised, it should be clear that emission spectroscopy provides the capability for detecting traces of most elements in solids, liquids, or gaseous samples. Solid metal specimens can be analyzed directly as self-electrodes, or they may be converted to other forms such as solutions. Inorganic powders can be directly analyzed; or they, too, may be converted to solution form. Solid specimens which contain large amounts of organic matter are usually either wet digested or dry ashed prior to analysis. Otherwise, the rapid combustion of organics may cause vaporization losses and inefficient excitation of the elements to be deter- mined. Despite this fact, some methods have been devised for the direct analysis of organic solids and fluids without ashing. A wide variety of solu- tions such as natural water and acid digests of samples can be analyzed either by direct solution aspiration or by analysis of the solution residues. Gaseous samples can be analyzed by excitation in hollow cathode discharge tubes or in flowing sys- tems. In short, the diversity of sample types that can be analyzed by emission spectroscopy is one of the great strengths of the method. Sensitivity Throughout much of the literature, the terms, sensitivity and detection limit, have been used interchangeably. In this discussion, sensitivity is 251 defined as the ability to discern a small change in concentration of analyte at some specified con- centration. Thus, sensitivity is directly correlated with the slope of the analytical curve relating line intensity to analyte concentration. Sensitivity is also inversely related to the reproducibility of line intensity measurement. For high sensitivity, we require a large slope for the analytical curve and a small value for the standard deviation of line intensity. It should be apparent from the foregoing sec- tions that sensitivity is controlled by a multiplicity of factors in the total analytical procedure. Sample treatments such as selective preconcentration can improve sensitivity. Choice of excitation source, the fundamental properties of the spectrograph and the extent to which its performance is opti- mized, choice of detector, and the method of data manipulation all affect sensitivity. Concentration Ranges Although there is no hard and fast rule which precludes using emission spectroscopy for the de- termination of high concentrations of elements, the most advantageous concentration range lies below 10 percent. In fact, the preponderance of applications deal with determinations between 1 percent and the limit of detection. Limit of detection is defined here as the small- est quantity or concentration of analyte that can be detected “with certainty.” Apparently, then, limit of detection is merely a special case of sensi- tivity which depends on an ability to distinguish a difference in line intensity for a small increment of analyte in comparison to the blank signal. Thus, the limit of detection is inversely correlated with sensitivity. The limit of detection also depends on the definition of “with certainty.” Although it is widely accepted that a statistical definition should be used, there is little agreement on the proper confidence level. To assume that a single value for the confidence level is correct seems naive. It is much more realistic to allow each in- vestigator to choose a probability level that suits the particular requirements of the problem at hand. Some specific procedures necessary to achieve improved detection limits have been discussed by DeKalb et al.?* for both photographic and photo- electric sensors. It must be emphasized, however, that many of these detection limits are reported for ideal situations in which there is no matrix interference or other limiting characteristic. In addition, many different definitions of the detec- tion limit have been employed by various investi- gators, thereby making direct comparisons very difficult. It should also be remembered that limits of detection do not represent concentrations that can be determined with the same quantitative pre- cision and accuracy expected for higher concen- trations. In general, the lower limits for good quantitative precision are approximately 10 times the detection limits. While much can be accomplished through the selection of optimum instrumental conditions, sensitivity and detection limits can also be en- hanced by sample preparation procedures that provide an enrichment of the analyte. Some typical procedures are described in Chapter 18 of this syllabus. Aside from the extra effort re- quired in sample preparation, a major precaution with enrichment procedures is the possible intro- duction of impurities from chemical reagents which obscure the true pattern of variation present in the original samples. Precision and Accuracy Precision is defined here as the extent of agreement of a series of measurements with their average, frequently measured by the standard de- viation. It is essential to express the conditions under which the data have been obtained. Com- monly, precision is expressed as the percent rela- tive standard deviation (sometimes called coeffi- cient of variation). If we accept that a realistic value for the pre- cision of a total analytical method applied to a given material should include components from the sampling step, the sample preparation step, and the measurement step, then the difficulty in making general statements for different methods is obvious. Nonetheless, it is generally conceded that the precision of emission spectroscopic tech- niques is superior to chemical methods at very low concentrations and inferior to chemical meth- ods at concentrations much above 1 percent. Usually, methods that employ solutions for the final intensity measurement give better pre- cision than direct methods with solids. One rea- son for this difference is that larger samples are usually employed for solution methods. Under ideal conditions, percent relative standard devia- tions of = 1% can be obtained with solutions except when impurity concentrations approach their detection limits. Good reproducibility is also attained for the analysis of metals as self-elec- trodes. With the direct excitation of powdered solids, sample heterogeneity becomes more im- portant; and percent relative standard deviations of = 5 to 10% are more typical. For survey procedures which cannot be optimized for each element determined, percent relative standard de- viations of + 25% or larger might be considered acceptable. Accuracy is defined as a quantitative measure of the variability associated with the relating of an analytical result with what is assumed to be the true value. Strictly speaking, accuracy can never be exactly measured because true values are never known. However, when primary standards are available, the accuracy can be specified within acceptable limits. Since quantitative emission spectroscopy re- quires the establishment of an analytical calibra- tion curve based on standard samples, the accuracy is limited by the quality of the available standards. The precision of a method is sometimes thought to be an estimate of accuracy. However, a method can easily yield very precise but highly inaccurate results if systematic error is present. For example, a common misconception is that synthetic solu- tion standards obviate the need for primary stand- ards in the analysis of miscellaneous materials which can be converted to solution form. Un- fortunately, this concept overlooks all of the sys- tematic errors that can occur while converting 252 samples to solutions.?® The recent activity of the National Bureau of Standards in the preparation of standard reference materials certified for trace amounts of different elements in matrices such as orchard leaves, beef liver, and serum will be of tremendous help to the emission spectroscopist concerned with the accuracy of his procedures. STEPS OF A QUANTITATIVE METHOD The first step in any quantitative analysis by emission spectroscopy is to clearly define the problem by designating the elements to be deter- mined and the expected concentration ranges. Any special aspects of the sample such as its major element composition, its quantity, and its physical form should also be noted. Reference standards are required which are similar, both chemically and physically, to the samples to be analyzed. For example, if we wish to determine the concen- tration of several trace metals in water residues in which the matrix is a mixture of calcium, po- tassium, magnesium, and sodium salts, we nor- mally require standards with a matrix of these same salts to match volatilization-excitation be- havior. It may even be necessary to alter the ratios of the salts in the standards to match par- ticular water samples. Lacking standards of similar physical and chemical composition, the samples must be modified to correspond with standards that are available. This may entail con- version to solutions, inorganic powders, or some related operation. Once the physical form of samples and stand- ards has been decided and the analytical require- ments specified, it should be possible to make an optimum choice of the excitation system, assum- ing that several are available. Similarly, we should attempt to insure that the spectrograph will pro- vide sufficient resolving power and adequate speed for the detection and estimation of the elements to be determined. This means that we must be able to locate lines of the analyte elements which are free from interferences by lines of the matrix elements. Further, these lines must be sufficiently sensitive to provide measurable optical densities down to the concentration levels required by the analysis. In prior discussions, we have inferred that quantitative analysis involves only the construc- tion of an analytical calibration curve relating in- tensity of the line of an element to be determined to the known amount of that element in a series of standards. However, because of the multitude of factors that affect the total amount of light emitted by a given weight of an element, this direct approach has usually not provided ade- quate precision and accuracy. To circumvent this difficulty, the principle of internal standardization is employed. In this procedure, concentration of the element to be determined is measured in terms of the ratio of the intensity of the analysis line to the intensity of a “homologous” line of another element present in fixed concentration in all sam- ples and standards. The internal standard element may be a major component of the matrix which is present in invariant concentration. Alternatively, it may be an element which is absent in the sam- ples and which has been added in constant amount from an external source. In this manner, uncon- trollable fluctuations such as variations in excita- tion efficiency that affect both lines to a similar extent will not alter the intensity ratio between the lines. Unfortunately, it is usually impossible to find line pairs whose intensity ratios are com- pletely insensitive to changes in chemical and physical composition of the sample. However, the literature provides references to many line pairs which are sufficiently insensitive to extraneous in- fluences to permit excellent precision in quantita- tive work. After preparation of samples and standards, they are excited in random order and recorded on a photographic plate or photoelectrically. If the lines are recorded photographically, their op- tical densities are measured and converted to rela- tive intensities by means of an emulsion calibration curve. The intensity ratios of analytical lines rela- tive to the selected internal standard lines are calculated and plotted on log-log paper versus the respective concentrations of the elements in the standards. Intensity ratios for the unknown con- centrations in the samples are then read from these calibration curves. Analytical calibration curves must be fre- quently checked. Day-to-day variations in atmos- pheric conditions will exert sufficient influence on excitation processes and photographic emulsions to cause significant curve shifts. The extent to which an investigator must check for curve shifts and recalibrate is partially dependent on the re- quired precision and accuracy of the analyses being performed. For a summary of recommen- dations, the ASTM Designation E305-67 titled “Establishing and Controlling Spectrochemical Analytical Curves” should be consulted.*! APPLICATIONS IN INDUSTRIAL HYGIENE Analysis of Biological Tissues and Fluids The work of Tipton and Stewart?®? is a typical example of a dry ash-direct current arc excitation procedure for surveying trace element contents of biological tissues and fluids. Samples of food, urine, and feces are dried and ashed at 550°C after treatment with double distilled sulfuric acid. This treatment produces a clean ash of mixed sulfates and oxides. The ash is combined with a graphite buffer containing 2,000 parts per million of palladium which serves as the internal stand- ard. Synthetic standards of similar composition are prepared from inorganic materials. The ele- ments Ag, Al, B, Ba, Be, Cr, Co, Cu, Fe, Mn, Mo, Ni, Pb, Sn, Sr, Ti, V, Zn, and Zr are deter- mined at concentrations down to 1 part per million or less in a few cases with typical percent relative standard deviations on the order of += 10%. A typical procedure employing wet ashing of biological fluids prior to spectroscopic analysis is described by Niedermeier et al.** In this procedure, 2 ml of blood serum are digested with high purity nitric and perchloric acid. A battery of samples is treated simultaneously using a number of di- gestion tubes in a constant temperature block which can be maintained at 130°C. After ashing, the excess acid is evaporated; and the residue is 253 dissolved in ammonium chloride solution which serves as a spectroscopic buffer. An aliquot of the solution is transferred to a graphite electrode and evaporated to dryness in a vacuum desiccator. Synthetic standards are prepared in a matrix solu- tion with composition closely approximating that of normal human blood serum. Excitation is ac- complished by a 10-ampere direct current arc. Selected lines of Cu, Fe, Al, Ba, Mn, Ni, Cs, Sn, Sr, Cr, Zn, Pb, Mo and Cd are monitored with a direct reading emission spectrometer. Data anal- ysis is accomplished by an IBM 7040 computer. For rapid survey purposes, the procedure de- scribed by Bedrosian et al.* is especially attractive because ashing of the sample is not required. Ma- terials such as animal tissue, blood serum, stool, bone, and plant leaves are dried. Twenty-five mg of samples are blended with graphite containing lutetium and yttrium as internal standards. The blended mixture is formed into a 3/16 inch diam- eter pellet using a small hand press. The pellet is placed in a graphite electrode, and a 1 mm diam- eter vent hole is placed in the center of the pellet. Electrodes are mounted in a Stallwood jet, and a gas mixture of 20% oxygen and 80% helium is used while the samples are excited by a 25-ampere direct current arc. They detected 26 elements in these various matrices at 1 part per million or less. Quantitation is accomplished using standards containing known concentrations of the trace metals in a matrix of p-nitrobenzene-azo-resorcinol which serves to simulate the organic matrix of samples being analyzed. The authors reported percent relative standard deviations of = 15% or less. Water Samples The determination of trace metals in natural waters is of great interest from a toxicological point of view. An excellent survey procedure for the determination of 19 minor elements in water has been described by Kopp and Kroner.** In this procedure water samples are filtered through a 0.45-micron membrane filter. Total dissolved solids are determined, and a volume of sample is selected to contain 100 mg of solids when con- centrated to 5 ml. A portion of this concentrate is placed in a porcelain combustion boat and analyzed in triplicate using a rotating disc elec- trode and high voltage spark excitation. Standard solutions for construction of the analytical cali- bration curves are prepared using known amounts of the elements to be determined in a matrix of sodium, potassium, calcium and magnesium in proportions approximating the average composi- tion of U. S. waters. Line intensities are recorded photoelectrically, and background is used as an internal standard. The concentration range is from 0.01 to 100 parts per million in the concentrated solution. Thus, the lower limits for the original samples depend on the degree of concentration employed to get 100 mg of dissolved solids. Pre- cision expressed as the percent relative standard deviation was on the order of = 5%. Recoveries from known additions varied from 80% to 113%. Analysis of Air Samples Not all spectrochemical analytical procedures are devised to determine multiple elements simul- taneously. For exampie, O’Neil*® described a pro- cedure for the determination of beryllium in air- borne dust. A high volume air sampler is used, and the sample is collected on Whatman No. 41 filter paper. The filter is ignited in a platinum crucible, and the ash weighed and mixed in def- inite proportions with an internal standard (lute- tium) and graphite. The mixture is excited in an 11-ampere direct current arc and burned to com- pletion. The author reported being able to detect 0.1 nanogram of beryllium in an electrode. Ac- ceptable precision and accuracy was reported. Of course, procedures have also been described for determining a large number of trace elements in air particulates. For example, the procedure by Keenan and Byers?” permits the determination of 20 elements collected on paper filters. SUMMARY Emission spectroscopy provides an effective analytical technique as both a survey method and as a quantitative analysis tool. The appli- cability of this technique is being continually ex- tended in the industrial hygiene field. References 1. BOUMANS, P. W. J. M.: Theory of Spectrochemical Excitation, Plenum Press, New York, 1966. FASSEL, V. A., R. H. CURRY and R. N. KNISE- LEY: “Flame Spectra of the Rare Earth Elements.” Spectrochim, Acta, 18: 1127 (1962). FASSEL, V. A. and V. G. MOSSOTTI: “Atomic Absorption Spectra of Vanadium, Titanium, Nio- bium, Scandium, Yttrium, and Rhenium.” Anal. Chem., 35: 252 (1963). PICKETT, E. E. and S. R. KOIRTYOHANN: “The Nitrous Oxide-Acetylene Flame in Emission Anal- ysis — 1. General Characteristics.” Spectrochim. Acta, 23B: 235 (1968). HIEFTIJE, G. M. and H. V. MALMSTADT: “A Unique System for Studying Flame Spectrometric Processes.” Anal. Chem., 40: 1860 (1968). MITTELDORF, A. J.: “Spectroscopic Electrodes.” The Spex Speaker (Spex Industries Inc.), X, No. 1 (1965). STALLWOOD, B. J.: “Air-Cooled Electrodes for the Spectrochemical Analysis of Powders.” J. Opt. Soc. Amer., 44:171 (1954). AHRENS, L. H. and S. R. TAYLOR: Spectrochem- ical Analysis, Addison-Wesley Publishing Co., Inc., Reading, Mass., 1961. SCRIBNER, B. F. and H. R. MULLIN: “Carrier- Distillation Method for Spectrographic Analysis and Its Application to the Analysis of Uranium-Base Materials.” J. Res. Natl. Bur. Stds., 37: 379 (1946). WALTERS, J. P. and H. V. MALMSTADT: “Emis- sion Characteristics and Sensitivity in a High-Voltage Spark Discharge.” Anal. Chem., 37: 1484 (1965). FELDMAN, C.: “Direct Spectrochemical Analysis of Solutions Using Spark Excitation and the Porous Cup Electrode.” Anal. Chem., 21: 1041 (1949). FRED, M., N. H. NACHTRIEB and F. S. TOM- KINS: “Spectrochemical Analysis by the Copper Spark Method.” J. Opt. Soc. Amer., 37: 279 (1947). MORRIS, J. M. and F. X. PINK: “Trace Analysis by Means of the Graphite Spark.” Symposium on Spectrochemical Analysis for Trace Elements, ASTM Special Tech. Pub. No. 221, p. 39 (1957). ROZSA, J. T. and L. E. ZEEB: “Trace Determina- tion in Lube Oil.” Petrol. Processing, 8: 1708 (1953). MARGOSHES, M. and B. F. SCRIBNER: “The Plasma Jet as a Spectroscopic Source.” Spectro- chim. Acta, 15: 13 (1959). OWEN, L. E.: “Stable Plasma Jet Excitation of 2. 10. 11. 14. 15. 254 17. 18. 19, 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34, 35. 36. Solutions.” Appl. Spec., 15: 150 (1961). DICKINSON, G. W. and V. A. FASSEL: “Emis- sion Spectrometric Detection of the Elements at the Nanogram per Milliliter Level Using Induction- Coupled Plasma Excitation.” Anal. Chem., 41: 1021 (1969). KLEINMANN, I. and V. SVOBODA: “High Fre- quency Excitation of Independently Vaporized Sam- ples in Emission Spectrometry.” Anal. Chem., 41: 1029 (1969). BRECH, F. and L. CROSS: “Optical Microemission Stimulated by a Ruby Laser.” Appl. Spec., 16: 59 (1962). SCOTT, R. H. and A. STRASHEIM: “Time-Re- solved Direct-Reading Spectrochemical Analysis Using a Laser Source With Medium Pulse-Repetition Rate.” Spectrochim. Acta, 26B: 707 (1971). SLAVIN, M.: Emission Spectrochemical Analysis, Wiley-Interscience, New York, 1971. MITCHELL, R. L.: The Spectrographic Analysis of Soils, Plants and Related Materials, Commonwealth Bur. Soil Sci. (Gt. Brit.) Tech. Commun. 44, (1948). JARRELL, R. F.: “Optical Qualities of Spectro- scopic Instruments.” Encyclopedia of Spectroscopy (G. L. Clark, ed.), Reinhold, New York, 1960. p. 243. MITTELDORF, A. J.: “Spectrochemical Analysis for Trace Elements.” ibid., p. 308. AMERICAN SOCIETY FOR TESTING AND MATERIALS, COMMITTEE E-2 ON EMISSION SPECTROSCOPY: Methods for Emission Spectro- chemical Analysis, 6th Ed., Amer. Soc. Testing and Materials, Philadelphia, Pa. 1971. MARGOSHES, M. and S. D. RASBERRY: “Fitting of Analytical Functions with Digital Computers in Spectrochemical Analysis.” Anal. Chem., 41: 1163 (1969). BALDWIN, J. M.: Computer-Assisted Data Reduc- tion and Report Generation for Flame Spectrometry, 1971. Document IN-1460, National Technical In- formation Service, U. S. Dept. of Commerce, Spring- field, Va. 22151. DEKALB, E. L., R. N. KNISELEY and V. A. FASSEL: “Optical Emission Spectroscopy as an Analytical Tool.” Ann. N. Y. Acad. Sci., 135: 235 (1966). GRANT, C. L.: “Sampling and Preparation Errors in Trace Analysis.” Developments in Applied Spec- troscopy, Vol. 8 (E. L. Grove, Ed.), Plenum Press, New York, 1970. MEINKE, W. W.: “Standard Reference Materials for Clinical Measurements.” Anal. Chem., 43 (No. 6): 28A (1971). AMERICAN SOCIETY FOR TESTING AND MATERIALS, COMMITTEE E-2 ON EMISSION SPECTROSCOPY: Methods for Emission Spectro- chemical Analysis, 6th Ed., Amer. Soc. Testing and Materials, Philadelphia, Pa., 1971. TIPTON, I. H. and P. L. STEWART: “Long Term Studies of Elemental Intake and Excretion of Three Adult Male Subjects.” Developments in Applied Spectroscopy, Vol. 8 (E. L. Grove, Ed.), Plenum Press, New York, 1970. NIEDERMEIER, W., J. H. GRIGGS and R. S. JOHNSON: “Emission Spectrometric Determination of Trace Elements in Biological Fluids.” Appl. Spec., 25: 53 (1971). BEDROSIAN, A. J, R. K. SKOGERBOE and G. H. MORRISON: “Direct Emission Spectrographic Method for Trace Elements in Biological Materials.” Anal. Chem., 40: 854 (1968). KOPP, J. F. and R. C. KRONER: “A Direct-Read- ing Spectrochemical Procedure for the Measurement of Nineteen Minor Elements in Natural Water.” Appl. Spec., 19: 155 (1965). O'NEIL, R. L.: “Spectrochemical Determination of Beryllium in Air-Borne Dust at the Microgram and Submicrogram Levels.” Anal. Chem., 34: 781 (1962). 37. KEENAN, R. G. and D. H. BYERS: “Rapid Analyt- ical Method for Air-Pollution Surveys. The Deter- mination of Total Particulates and the Rapid Semi- quantitative Spectrographic Method of Analysis of the Metallic Constituents in High Volume Samples.” Arch. Ind. Hyg. Occupational Med., 6: 226 (1952). Recommended Reading 1. >w 255 HARRISON, G. R,, R. C. LORD and J. P. LOUF- BOUROW: Practical Spectroscopy, Prentice-Hall, New York, 1948, SAWYER, R. A.: Experimental Spectroscopy, 3rd Ed., Dover, New York, 1963. Analytical Chemistry (Journal Article). Applied Spectroscopy (Journal Article). Spectrochimica Acta (Journal Article). CHAPTER 21 GAS CHROMATOGRAPHY Lial W. Brewer INTRODUCTION Chromatography is a collective term for sep- arations of mixtures based on the partition of substances between two immiscible heterogeneous phases, one of which is a stationary or fixed phase with a large surface area, and the other a moving or mobile phase which flows over the first phase. Gas chromatography is the most recent branch of chromatography and includes all the chroma- tographic processes in which the substance to be analyzed occurs in the gaseous or vapor state or can be converted into such a state. Development Although the first records of gas chromatog- raphy go back hundreds of years, its true history began during World War II when a large industrial chemical company instituted a crash program for its development.? The first published work ap- peared in the early 1950’s based on the successful experiments by James and Martin,® following an earlier suggestion made by Martin and Synge in 1941.* In the years between 1952 and 1956 the early apparatus and initial methods of application were developed. In 1956 the first commercial in- struments appeared on the market, and since that time there has been a spectacularly rapid and widespread development in theory, techniques and applications of gas chromatography. Today, it is one of the most widely applied and versatile ana- lytical tools available in basic and applied research and in quality control. Applications The success of gas chromatography is due to its simplicity of operation, high separation power and speed. The technique is capable of separating and measuring nanogram amounts of substances. In general, gas chromatography is suitable for analysis of substances with vapor pressures of at least 10 millimeters of mercury at the temperature of the column. Because the gas chromatograph separates, detects, qualitates and quantitates the individual components of a volatilized sample in a single step, it is an indispensable tool in every branch of chemistry. The wide choice of column packings, detectors and temperature controls al- lows versatile applications not only to the field of chemistry but also biology, medicine, industrial research and control, environmental health and scientific studies of the structure of chemical com- pounds, chemical reactions, partition coefficients, heats of solution and many others. Specific separations and measurements accom- plished by the use of gas chromatography in the medical-biochemical field include saturated and unsaturated fatty acids in low concentration, posi- 257 tional and configurational isomers of unsaturated fatty acids, straight-chain and branched-chain fatty acids, sterols and steroids, alkaloids, amino acids, urinary aromatic acids, bile acids, vitamins, blood gases, and toxic trace components in air, water, food and pesticides. Recent developments in the field of toxicology enable the fractionation and determination of such substances as steroids, lipids, barbiturates, drugs and blood alcohol.” The limited size of samples available and the low concentration of substances present in the field of toxicology make it a valuable tool for the complete characterization and analysis of mixtures of toxic substances. The progressive development of pyrolysis has led to the separation and identification of polymers and non-volatile substances. Advances have also been made in the miniaturization of gas chromatographic equipment. For example, a very small gas chro- matograph-mass spectrometer was sent on one of the moon shots to separate and identify atmos- pheric components automatically. The aerospace” and nuclear submarine fields” have also used gas chromatographs to check air quality in working and sleeping environments for personnel. Gas chromatography has been used recently in the remote sampling and analysis of tunnel atmos- phere after nuclear testing at the Nevada Test Site. In the field of industrial hygiene the chroma- tograph has been used to identify and quantitate solvent exposures by the analysis of breath sam- ples. When toxic organic substances have either no recognized biological metabolite or one whose excretion cannot be correlated with atmospheric concentrations of the initial substance, it is diffi- cult to evaluate the effects of exposures; however, breath analysis by a gas chromatographic pro- cedure may be developed for certain organic solvents found to be expired after exposure at predictable rates. In addition, many industrial hygiene departments operate product identification programs which require the complete analysis of proprietary products. Additives to many com- mercial products can appreciably increase the toxic properties of less hazardous materials. An example is the addition of carbon tetrachloride to typewriter cleaner, which normally contains only trichloroethylene. Another example is the addi- tion of benzene to gasoline for an increased per- formance efficiency. Before the development of gas chromatography tedious procedures involving fractional distillation and determination of ‘phys- ical constants were required for detection of such additives. The analysis of solvents for changes in formu- lations is performed frequently in the industrial hygiene laboratory. The regular product may be analyzed and comparative chromatograms pre- pared for other batches at specific times to check for any alteration of the product. Furthermore, many solvents of unknown composition (trade name given without compositional information or, in other cases, a lost label or marking) can be analyzed for complete identification and deter- mination of components. In-plant air samples con- taining solvent vapors can be chromatographed, avoiding the tedious chemical separation methods. Chlorinated hydrocarbons, for example, can be readily assayed in mixtures and each component identified whereas only total chlorinated hydro- _ carbons can be determined chemically. This is extremely important since each compound has a different Threshold Limit Value and tolerance level. There is almost no type of vaporous compound whose analysis by gas chromatographic methods has not been described in the literature. A partial list of pertinent references is included at the end of this chapter. THEORETICAL ASPECTS OF GAS CHROMATOGRAPHY Principle Gas chromatography can be compared ana- lytically to fractional distillation; however, it is a much more efficient type of separation technique. A good distillation column may have 100-200 theoretical plates, whereas a chromatographic column may separate components with 1000 to 500,000 theoretical plates. Basically, gas chroma- tography consists of the partition of compounds between two phases. One phase is a fixed or stationary phase. This phase may be either a solid, as in adsorption chromatography, or a liquid held by a solid, as in partition chromatography. The second phase is mobile and is generally re- ferred to as the moving phase. This phase may be a gas, liquid, vapor, or volatile solid. There are two principles of separation based on the pre- viously noted difference in the nature of the sta- tionary phase: (1) gas-solid chromatography (GSC) in which the moving phase is a gas and the stationary phase is an active solid such as alumina, charcoal, silica gel, molecular sieves, or the newer plastic granules (e.g., Poropak®); (2) gas-liquid chromatography (GLC) in which the moving phase is a gas and the stationary phase is a liquid distributed on an inert solid support. GLC is used for the separation of a variety of compounds, generally organics, while GSC is used for the sep- aration of gases. The principle of operation involves the intro- duction of small amounts of a gaseous or liquid sample solution containing nanogram amounts of analytically desired gaseous or vaporizable com- ponents which are carried” under controlled tem- perature conditions by an inert carrier gas into a column containing the stationary phase. Phase equilibria occur between the sample components, the mobile phase and the stationary phase; the components are separated, due to differences in absorption, solubility and chemical bonding, into distinct bands (or zones) of molecules. These fractions move through the column at different rates and emerge as separated components, as shown in Figure 21-1. The carrier gas emerging from the column passes through a detector which produces a signal proportional to the quantity (a) -/\ JS (b) N JAVAY (c) V4 COMPONENT A N T/L @ DON COMPONENT B Szepesy L: Gas Chromatography. Chemical Rubber Company Press, 1970, p. 14. Figure 21-1. umn at Different Rates. 258 Separation of Components Into Bands of Molecules Which Move Through Col- of each component. The detector response is amplified and shown on the recorder as a peak. The chromatogram that is obtained is a plot of time versus the intensity of a series of peaks representing the eluted components in the carrier stream. The length of time required for each of the peaks to appear on the chart is the retention time and is characteristic for each of the sub- stances present under a given set of chromat- ographic conditions. The retention time, there- fore, identifies the substance, and the area of the peak is a quantitative measurement which is pro- portional to the amount of each fraction present. A proper selection of injection port, column, and detector temperatures, column materials, and the detector determines the effectiveness of the chromatographic separations of the components of each type of sample. Basic Design There are many commercial models of gas chromatographs available today, with considerable variation in design and arrangement of compo- nents. The latest trend in design is the modular concept, consisting of a simple addition of com- ponent parts with different functions. Starting with the basic unit, the performance of the ap- paratus can be expanded by addition of other units, depending on the type of analysis to be done. Gas chromatography may also be combined with other chromatographic, spectrometric and chemical methods of analysis by collecting the sep- arated components from the gas chromatograph and incorporating other equipment into the sys- tem, either directly or indirectly. The recent coupling of computers with gas chromatographs allows completely automatic operation along with the storage and processing of data for estimation of the concentrations of the sample components. The basic design of the apparatus consists of: (1) carrier gas system, (2) sample injector, (3) column, (4) thermostat, (5) detector and (6) recorder. Figures 21-2 and 21-3 show schematic diagrams, respectively, of single and dual column assemblies, respectively. A general discussion of the components, with a brief explanation of the parameters pertinent to different applications of gas chromatography, is presented for the selection of proper instrumentation. COMPONENTS OF THE GAS CHROMATOGRAPH Carrier Gas System The carrier gas is the mobile phase used to transport the sample through the column at a se- lected steady rate. To ensure constant and repro- ducible conditions, the system is composed of a gas cylinder, pressure and/or flow control, man- ometer, flow meter and pre-heater. In principle, any gas which does not interfere either with the stationary phase or the components of the sample would be a suitable carrier. How- ever, the properties of the carrier gas affect the separations in the column as well as the detection of the emerging components. The gases generally used are: helium, argon, hydrogen and nitrogen. Other gases may also be used. In selecting a carrier gas, detection is the primary factor to be considered since separation can be improved by some means other than changing the carrier gas. Since hydrogen is so reactive and flammable, helium is the ideal carrier for use with thermal conductivity detectors. Nitrogen, though readily available, is not too useful for these detectors since its thermal conductivity does not differ too greatly from that of many sample components. The thermal detector measures the difference be- tween the heat conductivity of the pure carrier gas and that containing the components of the sample. The greater the difference between the two heat conductivities the greater will be the observed signal. The thermal conductivity of gases is inversely proportional to the square root of their molecular weight and consequently hydrogen and helium are the most suitable carrier gases for - PACKED COLUMN = | ee OVEN RECORDER DETECTOR Instruments, Inc.: What Is Gas Chromatography. Tulsa, Oklahoma. Figure 21-2. Si 259 ngle Column. PRESSURE GAUGE SAMPLE INJECT DETECTOR — / CARRIER GAS SUPPLY Prepared by Sandia Laboratories draftsmen. OVEN FLOWMETER PRESSURE REGULATOR Figure 21-3. Dual Column. thermal conductivity detection. The most commonly used types of carrier gases and their use with various detectors are as follows: Air and Oxygen may be used in certain cases as carrier gas with the flame ionization and thermal detectors. However, their use is lim- ited by the possibility of reactions with the stationary phase or the components of the sample. Argon is the most generally used gas with radiation detectors such as Beta ionization, and with flame ionization detectors, with lim- ited use in thermal detectors. Carbon Dioxide is used with flame ionization and gas density balance detectors, with limited use with the thermal detector. Carbon Monoxide is used with the flame ion- ization detector. Helium is used with the thermal conductivity, thermionic emission, flame ionization and cross. section detectors. Hydrogen is used with the gas density and thermal conductivity detectors. It is used as a fuel with the flame ionization detector. To avoid the possibilities of impure hydrogen, the use of hydrogen produced from the elec- trolysis of water is ofen more suitable for the operation of flame ionization detectors. Neon is used with radiation detectors. Nitrogen is used with radiation, flame ioniza- tion and gas density detectors. It has limited use with the thermal conductivity detector. SF, is used when detecting permanent gases using a density balance detector. A constant flowrate is important to eliminate the effect of changes in column resistance. Heat- ing of the gas before it enters the sample injector is necessary in the case of some detectors and ad- visable in other detection methods and is accom- plished by means of a pre-heater. Sample Injection System The sample injector, located ahead of the column, is designed to allow the introduction of a sample rapidly and in a reproducible manner into the column. It is essential that representative samples of the material to be analyzed be intro- duced. Since such samples must be small in quantity, a careful manipulative technique must be employed with the method of injection. It is highly desirable that the sample injection be al- most instantaneous to convert the sample into a composite plug of gas which is pushed through the column by the carrier gas. This is accomplished by the enclosure of the injection port in a metal (My (2) (3 (4) (5) Syringes #1, 3, 4 and 5: Hamilton Syringe Catalog. Syringe #2: Beckman Syringe Instruction Sheet. Figure 21-4. Syringes Used in Gas Chroma- tography (1) Hamilton 10 ul. liquid syringe, (2) Beckman variable volume liquid micro- syringe, (3) purge type gas syringe, (4) stan- dard Hamilton gas syringe and (5) large vol- ume transfer and dilution syringe. 260 =f ~r 5 000 Beckman Instruments, Inc.: Bulletin #756A. Fullerton, California. Figure 21-5. Gas Sampling Valve (Beckman). block which is heated independently to a temper- ature approximately 50 to 100 degrees above the column temperature. The solvent and sample are, therefore, flash evaporated when injected, without changing the gas flow or the thermal conditions of the column. The quantity of liquid sample ranges from 1 to 10 microliters and gas samples vary from 0.05 to 50 milliliters. Most samples are introduced by means of a small, calibrated syringe or a microsyringe, such as the Hamilton syringe. These syringes are made for delivering either liquids or gases. Liquid syringes are available in sizes of 1 microliter to 500 microliters. Gas tight syringes are available in sizes of 50 microliters to 2500 microliters. For calibration with larger volumes of gases, plastic syringes are available in sizes from 0.5 to 1.5 liters. Figure 21-4 shows several types of syringes used in gas chromatography. Samples may also be introduced to the column using a gas sampling valve, illustrated in Figure 21-5. The gas sample may be introduced to the gas sampling loop under pressure or by drawing the sample into the loop using a small vacuum pump or a two-way squeeze bulb. The gas sample can also be delivered to the loop from a pressure container, such as a plastic or rubber bag or a large syringe. The only requirement is that suffi- cient sample be available to thoroughly purge the sample loop, as shown in Figure 21-6. A third method of injection is by the use of a sealed ampoule which is broken inside a chamber, which replaces the gas sampling valve, so that the sample is swept into the column. CARRIER GAS GAS SAMPLE SN “YX VENT | | VALVE "A" \ | | “oO yr | > - I | ~ "an ~% ! | \ Je . VALVE "C \ o | | 90° GAS SAMPLING 90 I VALVE | I [ ; CARRIER ! _ TO SOLUMN | | VALVE "8" // al | la — | | C J I ! OVEN | LS —— J Instruments, Inc.: What Is Gas Chromatography. Tulsa, Oklahoma. Figure 21-6. Gas Sampling. 261 Other types of samplers include pyrolysis sys- tems and solid samplers. The Column The column is the “heart” of the chromat- ograph. Provided that the equipment is good and operating conditions are suitably chosen, the analysis will be as good as the performance of the column selected because it is here that separation of the sample components is effected. Because of the wide variation in packing materials and liquids used as stationary phases, the long life, and the ease of changing columns in the instrument, it is possible for the analyst to select the best packing and column length for each particular sample type. Several columns with different types of packings can be built into the same apparatus and can be operated in series or parallel with each other. PACKED COLUMN Columns are rigid containers made of stainless steel, copper, aluminum or glass. There are two basic types of columns — the packed column and the capillary or open tubular column (Golay). The packed column consists of a length of tubing 1-6 millimeters I.D. and usually 0.5 to 6 meters in length, wihch is normally coiled or looped to be accommodated in the space provided in the in- strument. This tubing is packed with a finely divided inert solid support, which is coated with a thin layer of a nonvaporizable liquid, referred to as the liquid phase. The capillary column is an empty tube, the inner walls of which serve as the support or adsorbent. This type of column has an I.D. of 0.1-1.0 millimeter and usually is 30-100 meters in length. The basic difference between gas-liquid and gas-solid chromatography is in the column pack- CAPILLARY COLUMN TUBING TUBING PACKING SUBSTRATE SOLID SUPPORT Ie J WITH SUBSTRATE (SHOWN 2 TIMES ACTUAL SIZE) COLUMN TYPES OPEN TUBULAR PACKED L(CAPILLARY) PACKED (NORMAL) NON-POROUS PACKING PACKED WITH COATED WITH LIQUID - POROUS LIQUID~- PACKED POROUS POROUS COATED GSC GSC GLC GSC GSC GLC GLC GLC GLC GLC Instruments, Inc.: What Is Gas Chromatography. Tulsa, Oklahoma. Figure 21-7 & 8. Types of Columns and their Operation. Various Size Sample Tubes (us- ually 1 to 10 ml volume). 262 ing. In gas-liquid chromatography the column is packed with a solid material made up of particles on which is deposited a known volume of non- volatile liquid constituting the liquid phase. In gas-solid chromatography the packing is generally an active solid (adsorbent) which separates the sample components by differences in their adsorp- tion characteristics. Figures 21-7 and 21-8 illus- trate the two types of columns and their types of applications. The following factors influence the efficiency of a column: Column Length — the efficiency is directly proportional to the length; however, analysis time is also increased with length due to flow resistance. Therefore, the column length is selected by references to the degree of separa- tion and the analysis time required. Column Diameter — the performance of the column increases with decreasing column di- ameter. Columns with 2-4 millimeter I.D. give optimal separation. Nature of Solid Support — the material should be inert and porous, provide a large surface area, and be heat stable. Granule Size of Support — the column effi- ciency is dependent on the particle size. The solid support phase is graded on the basis of the mesh size through which it will pass. The column diameter generally determines the proper mesh size as follows: 6-millimeter diameter column — 60/80 mesh 3-millimeter diameter column — 80/100 mesh Quantity of Liquid Phase — the concentration is adjusted in accordance with the mesh size. The optimum range is 10-15% by weight. Type of Liquid Phase — the principal char- acteristics to be considered are polarity, vola- tility, low viscosity and thermostability. Temperature Control — it is essential for the temperature to be maintained thermostatically at a point suitable for separating the com- ponents of the sample. The control can either be isothermal or programmed such that the temperature is accurately reproduced for samples and standards. Solid Supports The purpose of the solid support is to provide a large surface area for holding a thin film of liquid phase. The main requirements for adequate sup- port material are: chemical inertness and stability, large surface area, relatively low pressure drop and mechanical strength. Such material may be or- ganic or inorganic but must be of a known and standard size. The most commonly used materials consist of diatomaceous earth processed or modi- fied in various ways. Since diatomaceous earth supports are not completely inert, they are often treated chemically to inactivate them. An example of diatomaceous earth supports are the Chromo- sorbs (Johns-Manville Corp.) Chromosorb P — calcinated diatomaceous earth processed from firebrick (C-22). Chromosorb W — flux-calcinated diatomite prepared from Celite Filter Aids. Chromosorb G — developed especially for gas chromatographic analysis. The various Chromosorbs are available in different 263 qualities, such as non-acid washed, acid washed, silanized with hexamethyldisilane, and acid washed and silanized with dimethyldichlorosilane. Besides the various diatomaceous earth sup- ports, porous polymer beads, Teflon and glass beads are used. The Poropak® resins are examples of porous polymer beads which have partition properties of a highly extended liquid surface with- out the problems of support polarity or liquid phase volatility which hamper gas-liquid chroma- tography. The general properties and applications of some types of Poropak® resins are as follows: Poropak N — an intermediate polarity pack- ing useful in separating formaldehyde from aqueous solution. Stable to 250 degrees C. Poropak P — has the lowest polarity of all types and has the ability to separate systems of intermediate polarity. Usable up to 300 degrees C. Poropak P-S — is similar to type P; however, the labile sites have been deactivated by silan- ization to improve peak shape and the effi- ciency of separation with aldehydes and glycols. Poropak Q — separates hydrocarbons by vapor pressure and is usable up to 300 de- grees C. Poropak Q-S — is similar to type Q; however, labile sites are deactivated by silanization, and as a result highly polar materials such as organic acids may be analyzed in aqueous solution and show no tailing. Poropak R — is suitable for the separation of water from highly reactive inorganics such as chlorine and hydrochloric acid. Poropak S — is suitable for the separation of normal from branched alcohols and is stable up to 250 degrees C. Poropak T — has the highest polarity of all the Poropak® resins and is stable up to 250 degrees C. Poropak® resins may be used for the separa- tion of most gases and compounds in the moderate boiling range (up to 200°C.). High boiling aro- matic and cyclic materials are strongly retained by Poropak® and are very difficult to elute. When strongly polar materials, such as acids or alde- hydes, are to be analyzed silane treated supports should be used. All Poropak® resin columns re- quire a pre-treatment before use. The column should be purged with gas while heating to rid the resin of residual preparation chemicals. Liquid Phase The liquid phase of the column packing is that chemical which actually is responsible for the separation of the various compounds in the mix- ture in gas-liquid chromatography and must be capable of dissolving the components and releas- ing them, preferentially by the difference in their volatility, from the solution. The liquid used will be chosen to effect separation of the compounds to be analyzed. In general, the choice of liquid phase is based on the polarities of the substance to be separated and of the liquid phase. The higher the polarity of the liquid the more it will retain polar components compared to non-polar substances with the same boiling point. The liquid phase should be non-volatile, thermostable, and have low viscosity. Its boiling point should be approximately 250 to 300 degrees C. which will be higher than the optimal temperature at which the analysis is performed. The column coatings which are non-polar liquids are: squalane, silicone oil, esters of high molecular weight alcohols, dibasic acids and Apiezon L. The polar com- pounds are: polyethylene glycol, polyesters, ethers, carbohydrate esters, and derivatives of ethylenedi- amines. Table 21-1 lists some of the common liquid phases with their properties and appli- cations.? Table 21-1 Some Common Liquid Phases Solvents: Acetone =A; Benzene =B; Chloroform =C; Methanol =M; Toluene=T; Water=W. Polarity: non-polar= —; fairly polar= +; strongly polar= + +. S Maximum Liquid phase Ol temperature, Polar- Applications vent °C ity Tri-isobutylene A 30 + Saturated and unsaturated C,-C; hydrocarbons Dimethylsulpholane M 50 + + Saturated and unsaturated C,-C, hydrocarbons n-Hexadecane (n-cetane) B 50 — C,-C, hydrocarbons, halogen derivatives B, B-Oxy-dipropionitrile M 70 + + C,-C, paraffins, olefins, cyclo-paraffins, aro- matics, alcohols, ketones, esters Paraffin oil T 100 — Hydrocarbons, chlorine compounds, sulphides Carbowax 400 (polyethylene M™M 120 + + C,-C,; alcohols, ethers, ketones, amines glycol) Tricresyl phosphate (tritolyl C 125 + + Aromatics, halogen derivatives, oxygen com- phosphate) pounds Carbowax 600 M 140 + + Oxygen compounds, halogen derivatives, ni- trogen compounds Squalane T 150 — Hydrocarbons, halogen derivatives, sulphides (hexamethyltetracosane) Dinonyl phthalate* A 150 + Hydrocarbons, halogen derivatives, oxygen compounds Carbowax 1500* M 150 + + Aromatics, oxygen compounds, halogen deriv- atives, nitrogen compounds, sulphur com- pounds Carbowax 6000 M 200 + + Aromatics, oxygen compounds, halogen deriv- atives, nitrogen compounds, sulphur com- pounds Carbowax 20 M* M 200 + + As above, plus polyfunctional alcohols Ucon LB (polypropylene M 200 + Aromatics, alcohols, ketones, essential oils, glycol) amines Ucon HB (polynikylene M 200 + As above glycol) Silicone oil DC 550* A 200 — Esters, aldehydes, hydrocarbons, boranes Benton 34 T 200 + + Aromatics Polyesters of succinic acid » (e.g. LAC 296) C 200-240 + ) Esters of fatty acids, ethers, essential oils, Polyesters of adipic acid C 200-240 + { and amino-acid esters (e.g. Resoflex) Silicone elastomer, A 250 + Phenols, aromatics, terpenes, steroids XE 6A XE 60 (cyano) Apiezon M T 275 — Higher alcohols, fatty acid esters, essential oils Apiezon L* T 300 — Higher oxygen compounds, fatty acids, nitro- gen compounds, steroids, metal organic compounds Silicone elastomer, SE 30 T 300 — Alkaloids, steroids, nitriles, hydrocarbons, in- (dimethyl) organic and metal organic compounds Silicone elastomer, T 300 + Alkaloids, steroids, carbohydrates SE 52 (methyl-phenyl) Silicone grease (vacuum) T 350 — Fatty acid esters, halogen compounds, inor- ganic compounds Poly-phenyl tar T 400 — Polycyclic aromatics Inorganic salts and salt Ww 400-500 — Inorganic and metal organic compounds, cutectics (e.g. LiCl) metal halides * According to the survey of the Data Sub-Committee of the Gas Chromatography Discussion Group the most widely used liquid phases. Budapest. “Gas Chromatogsaphy,” Butterworth & Co. Ltd.,, London, England; Muszaki Konyvkiado, 264 To some degree the detector used must also be considered when selecting a column. For ex- ample, if a thermal conductivity detector is used, and the sample contains water (which the detector senses), Teflon would be a better support since it suppresses the tailing of the water peak which would otherwise obscure some peaks. On the other hand, the flame ionization detector does not respond to water and therefore the problem of tailing does not occur. When the electron capture detector is used, a liquid phase with low bleeding rate is very important. In such systems, DC-200 silicone oil with high viscosity is recommended. Adsorbents In gas-solid chromatography various adsorb- ents are used as column packings. With the growth of gas-liquid chromatography, the use of adsorb- ents and their applications are: Silica Gel — used in the analysis of inorganic gases and light hydrocarbons. Molecular Sieves — used for the separation of permanent gases such as hydrogen, oxygen, nitrogen, carbon monoxide, methane and ethane. Carbon dioxide and higher hydro- carbons are adsorbed irreversibly on molecular sieves at low temperatures. Activated Charcoal — used for the separation of air, carbon monoxide, methane, carbon di- oxide, acetylene, ethylene, ethane, propylene and propane. «Chromosorb — used for the separation of ni- trogen, hydrocarbons, acid gases and basic gases. Poropak Q — can be used to separate such widely different materials in the gas phase as air, carbon dioxide, sulfur dioxide, nitrous oxide, nitric oxide, hydrogen sulfide, hydrogen cyanide, carbon oxysulfide, hydrogen chloride, chlorine and ammonia. Poropak N — used to separate acetylene from ethylene and ethane. The regeneration time and temperature for adsorbents is as follows: Alumina, silica gel and activated charcoal — 30 minutes at 100°C. Molecular sieves — 30 minutes at 300°C. Poropak N and T — 30 minutes at 180°C. Poropak Q, R, S, Q-S — 30 minutes at 230°C. Chromosorb — 30 minutes at 140°C. Detectors Detectors must sense continually, rapidly and with high sensitivity the components which appear in the carrier gas as it emerges from the column, by means of changes in a physical or chemical property of the effluent gas stream. The corre- sponding electrical response is amplified and fed to a recorder. One of the chief factors in the wide-spread application of gas chromatography is the availability of a great variety of highly effi- cient detectors. The essential quality of a detector is deter- mined by the following factors: (1) sensitivity, (2) signal-to-noise ratio, (3) drift, (4) linearity, (5) independence of extraneous variables, (6) ease of calibration, (7) speed of response, (8) chemical inertness, and (9) range of application. There are basically eight types of detectors: Thermal Conductivity (katharometer) — measures change in heat capacity. Gas Density — measures change in density. “Flame Ionization — measures difference in flame ionization due to combustion of the sample. Beta-Ray Ionization — measures current flow between two electrodes caused by ionization of the gas by a radioactive source. Photo-Ionization — measures current flow between two electrodes caused by ionization of the gas by ultraviolet radiation. Glow-Discharge — measures the voltage change between two electrodes caused by the change in discharge by different gas com- positions. Flame Temperature — measures change in temperature caused by difference in gas com- position in the flame. Dielectric Constant — measures the change in the dielectric constant caused by difference in composition of gas between plates of a capacitor. A summary of the common commercial de- tectors is presented in Table 21-2. A description of several detectors is as follows: Thermal Conductivity Detector — the most widely used detector. Uses either a hot wire or thermistor as the sensing element. The re- sistance changes due to sample components, and the detector measures the thermal con- Table 21-2 Summary of the Common Commercial Detectors Analyzable Maximum Sens. Name Type Materials GMS/Sec. Thermal Conductivity Measures Changes All 1077 (Katharometer) in Heat Capacity Ion Cross Section Beta-Ray Ionization All 1077 Argon Diode Beta-Ray Ionization Most Organics 107 Electron Affinity Beta-Ray Ionization Electron Absorbing 1074 Materials Only Flame Ionization Ionization In Hydrogen Flame All Organics 1072 Thermionic Emission Hot Filament Ionization All 107° 265 ductivity of the sample stream as opposed to the reference stream of the pure carrier gas. The response is approximately proportional to the concentration of sample component in the detector. This type of detector is a non- destructive detection system. Examples of thermal conductivity are shown in Table 21-3. Table 21-3 Examples of Thermal Conductivity Relative Gas Conductivity at 100°C (Air=1) Hydrogen 6.94 Helium 5.54 Methane 1.72 Ethane 1.09 Oxygen 1.032 Air 1.000 Nitrogen 998 Carbon Monoxide .924 Methyl Alcohol 127 Carbon Dioxide .690 Acetone 557 Carbon Tetrachloride .288 Ionization Gage Detector — uses a heated filament to ionize substances having ionization potentials less than that of helium. Only a small fraction of the effluent passes through the gage. The ionization current produced in the cell is a measure of the concentration of the sample component. Flame Ionization Detector — uses hydrogen/ air or hydrogen/oxygen flame. This flame ionizes the organic sample material and the ions are collected by an electrode which is positive in relation to the flame. This elec- trical potential causes a current flow which is an instantaneous measurement of the com- ponent concentration. This detector has a high sensitivity, about 500-2000 times that of the thermal detector. It also has a fast response time, a very small effective cell vol- ume and a high signal-to-noise ratio. Beta Argon Ionization Detector — a radio- active source ionizes the effluent from the column causing an ion current to flow from the collision of metastable argon ions with the sample molecules. This current is a measure of concentration. The sensitivity is much higher than that of the thermal conductivity detector for all components except light gases with ionization potentials above 11.7 electron volts. Minimum detectability of components is in the general range of 107° grams per sec. This gauge is less sensitive than the flame ionization gauge. Electrolytic Conductivity Detector — used for the detection of halogen, sulfur and nitrogen containing organic compounds. Its principal use is for the detection of residues of chlor- inated hydrocarbon type pesticides and nitro- 266 gen containing pesticides such as carbamates and triazines. The Coulson'® electrolytic con- ductivity detector is probably the simplest to operate and easiest to maintain of all the ele- ment selective detectors. Yet it has good selectivity and sensitivity. The system consists of a prolyzer, a gas-liquid contactor, a gas- liquid separator, and a simple pair of platinum electrodes in a d.c. bridge circuit. The pyro- lyzer converts the organically bound halogen, sulfur, or nitrogen to oxidized or reduced sub- stances that form electrolytes when dissolved in water. These electrolytes are detected by the change they produce in the conductivity of water in the detector cell. Conductivity is measured between the two platinum electrodes of the cell by means of a simple d.c. bridge and recorded continuously on a one-millivolt strip-chart recorder. Semiconductor Thin Film Detector — a de- tector for gaseous components, based on the fact that the adsorption and desorption of gases causes changes in electrical conductivity of semiconductors. At high temperatures (near 400°C) the adsorption and successive desorption processes on the surface of semi- conductors take place very rapidly and may indicate a marked change in electrical con- ductivity by the use of thin film semiconduc- tors. This property of thin film is applicable to the detection of gaseous components. An example of this type detector is the P-N junction. P-N Junction Detector — this semiconductor thin film detector has the advantage over the original type of thin film detector in that the sensitive element is readily available and does not have to be specially prepared. The ele- ment is a reversed biased semiconductor diode. These diodes are affected by ambient gases. Glow-Discharge Detector — the composition of the gas chromatographic effluent is meas- ured by the change in voltage across a gaseous discharge. Radio-Frequency Discharge Detector — the collisions between sample components and r-f excited rare gas atoms causes changes in light emission. Low vapor concentrations are measured by changes in this light emission when the solute molecules are ionized. Micro Cross-Section Detector — a concen- tration of ion pairs is produced when the effluent stream is subjected to ionization radi- ation. The number of ion pairs is proportional to the cross-section area available for ioniza- tion in each sample. As solute concentration increases, more ion pairs are formed; thus greater current is passed. Helium Beta Ionization Detector — a simple and ultra sensitive gas chromatographic de- tection device which was developed for the analysis of permanent gases. The detector consists of two electrodes closely spaced (ap- proximately 1 mm) either in a concentric or parallel geometry. The internal detector vol- ume is 150 microliters. A tritium impregnated foil serves as one electrode. A constant po- tential is applied to one electrode while the other electrode lead is connected to an elec- trometer capable of measuring small (10~ amps) changes in current. Helium passing from a chromatographic column is excited to the metastable state (energy level = 19.8 ev). All permanent gases except neon are ionized in turn and produce a positive increase in the detector current. Neon shows a negative peak. Sensitivity as low as 10 ppb is demonstrated with chromatograms for hydrogen, oxygen, argon, nitrogen, carbon monoxide and carbon dioxide. Linear response is shown over a range of 10,000. Electron Capture Ionization Detector — this detector utilizes an ion chamber containing a gas with free electrons at an applied potential just great enough to collect completely the free electrons generated by a radioactive source. Molecules from the sample (which have an affinity for the free electrons) will capture the free electrons and become negative ions. The detector current decreases in the presence of the electron capturing molecules. Other types of detectors include the Gas Density Balance, Alkali Flame Ionization, and Alpha Ionization as well as mass spec- trometers and automatic titrators. Temperature Control For precise and reproducible gas chromat- ographic analysis there must be temperature control of (1) the injection system, (2) the col- umn, (3) detector and (4) fraction collector, if used. The injection system must be heated to a point that will volatilize the sample instantaneously and keep it in the vapor state until it reaches the column, which is also heated to assure that the sample components remain in the gaseous state for the passage through the separation column. The detector likewise must be heated to keep the sample components in the vapor phase. The temperature of each component part of the gas chromatograph must be precisely controlled and reproducible so that constant sample retention times may be attained. If a fraction collector is used, its temperature must also be high enough to keep the components gaseous until collected in a cold trap. Each instrumental component can have a sep- arate control system or the temperature of the assembly may be controlled by a single system. In the single control system the injector, column, detector and fraction collector are all located in a constant temperature oven. When the component parts have separate controls, each can be set at an optimal value. Generally, the single temperature control is for isothermal operating conditions. 267 If the sample components have a very wide boiling range, programmed temperature control is most valuable. In the programmed mode, the injector, detector and collector are set at a con- stant temperature and the column temperature is varied at a known and constant rate. This shortens the analysis time considerably when dealing with the widely separated boiling point components. The programmed temperature control must be very reproducible or the results can be confusing. As the control must be regulated very closely, these systems are costly. A comparison of chromat- ograms prepared using constant and programmed column temperatures is shown in Figure 21-9. Recording Devices The response of the detector is plotted as a chromatogram by the millivolt recorder. The chromatogram is a plot of detector response versus time. With only carrier gas flowing through the detector, the recorder is adjusted to read zero. This zero reading is referred to as the base line. Each separated component evokes a response by the detector which registers a peak on the chromat- ogram. The chromatogram will give two different kinds of information: (1) identification by reten- tion time, the time it takes for the peak to appear after injection of the sample, and (2) quantitative estimation of a component of the sample, which can be obtained by comparing the area of the peak with that produced by a standard sample of the same component substance at a known con- centration. There are two types of strip chart recorders in use — the galvanometric and potentiometric. Galvanometric recorders are inexpensive but re- quire an amplifier. Potentiometric recorders are more expensive but do not always require an amplifier. Figure 21-10 is a diagrammatic example of a typical chromatogram indicating the several meas- urements of interest. Digital readout may be employed by using one of several types of printing integrators, which merely print out numbers corresponding to the area under the chromatographic curve. There are several types of integrators: mechanical, electro- mechanical and electronic. The most generally used is the mechanical or disc integrator, which measures mechanically the height of the curve. The electromechanical integrator converts the voltage change from the detector signal to a dig- ital signal directly. The electronic integrator is similar to the electromechanical unit but uses a voltage totaling circuit instead of a direct signal. A. CONSTANT COLUMN C TEMPERATURE D E F B G A 5 15 25 35 45 = 55 5 TIME (MIN.) 8. PROGRAMMED COLUMN TEMPERATURE v v | 5 v 25 v a5 v a 5 v 55 v 6 5 v TIME (MIN.) Prepared by Sandia Laboratories draftsmen. Figure 21-9. A Comparison of Chromatograms Prepared Using Constant and Programmed Column Temperatures. w wn < Oo & ir PEAK x HEIGHT 2 BASE LINE 5 | u RETENTION | pearl. =~ TIME ~~ 'WIDTH 1 1 1d L L 1 1 I I 1 I I 0 5 10 15 20 25 30 MINUTES Prepared by Sandia Laboratories draftsmen. Figure 21-10. Diagrammatic Example of a Typical Chromatogram. 268 Other readout systems may be used as an- cillary equipment, such as mass spectrometers, attached directly through concentrators to the chromatograph, or flow type infrared or ultraviolet spectrophotometers. Collection Systems The system for collecting chromatographed sample components can be very simple or quite elaborate. The simplest system is that of collecting the vapor on a cold plate at the detector outlet. This technique can be used with salt plates for infrared spectral analysis. The vapor may also be collected in miniature condensers cooled with ice, dry ice-acetone or other cryogenic systems. The vapor may be kept in this stage, passed through heated tubes to gas analysis systems such as in- frared gas analysis cells, or introduced into mass spectrometer sampling systems through a helium separator. The collection system may be as original as the chromatographer can develop to satisfy the requirements of his analytical problems and in- struments. QUALITATIVE ANALYSIS From the foregoing information it is obvious that practically any vaporous mixture can be separated by gas chromatographic techniques. One of the main problems, however, is the qualitative determination of the mixture components. There are four basic methods which have been used for the identification of separated compo- nents: (1) comparison of known compound chromatograms with the unknown, (2) plotting of homologous series, (3) use of dual columns, and (4) identification by auxiliary instrumentation. When members of homologous series are chromat- | START ographed under reproducible conditions, the re- sults can be plotted as the number of carbon atoms versus log of retention volume. The plot can then be used for a determination of the carbon content of the component of interest. An example is shown in Figure 21-11. 60 n-decane 50 ot 40 n-nonane > 30 £€ 2 o > 20 n-octane $ 1S c hd @ n-heptane @® 10 n-hexane 6 1 6 7 8 9 10 Number of carbon atoms —s—— Prepared by Sandia Laboratories draftsmen. Figure 21-11. Example of Plot to Determine Carbon Content of Component. mo Cee DETECTOR NO.I I jo re FR —— ~ nN / \ DETECTOR NO.2 Prepared by Sandia Laboratories draftsmen. Figure 21-12. Dual Detector Response. 269 90 COLUMN: 2 FT. BENZYL ETHER 20 REGULATOR PRESSURE: 23 Ibs. CARRIER GAS: HELIUM FLOWRATE : 40 CC/MIN. 70 CURRENT : 250 MILLIAMPERES CHART SPEED: 0.5 IN/MIN. co TEMPERATURE: 40°C " SENSITIVITY: 20 EXCEPT AS NOTED UNKNOWN 50 CHROMATOGRAM A 2.0 CC SAMPLE 40 30 20 80 PROPYLENE PROPANE |-- 70 — PENTANE |= --ISOPENTANE BUTENE 2 CIS ISOBUTYLENE -| — ETHANE-|-- BUTENE 2 INJECTED 80 CHROMATOGRAM B 3.0 CC SAMPLE KNOWN 50 40 30 20 21201981716 1514131211109 8 76 5432 | 0 TIME IN MINUTES Beckman Instruments, Inc.: Bulletin #756A. Fullerton, California. Figure 21-13. Illustration of Use of a Known Sample to identify the Components of the Un- known Sample. 270 When dual columns are used different reten- tion times of the individual components are ob- tained. The use of dual detectorss results in a different response to the sample components due to the specificity of the detector. Figure 21-12 illustrates the dual detector response. A more specific method for qualitative analysis is the use of auxiliary instrumentation such as infrared, ultraviolet or mass spectrometry. The sample components are trapped at the outlet from the gas chromatograph, transferred to the appro- priate instrument and subjected to a qualitative analysis by the independent technique. The separation achieved depends upon the column, the temperature, the detector and flowrate of the carrier gas. Therefore, it is imperative that all these parameters be kept the same for both the sample and the standard used for the deter- mination of component peak location. It is im- portant to know that the unknown component is eluted in the same time as a known compound. It is also important to know that no other com- pound can appear at this location with the param- eters used. Figure 21-13 illustrates the use of a known sample to identify the components of the unknown sample. QUANTITATIVE ANALYSIS The prime application of gas chromatography is, of course, quantitative analysis. It is well known that the area under a chromatographic peak is proportional to the amount of the respon- sible sample component in the carrier gas stream. This means that the use of gas chromatography for quantitative analysis requires a knowledge, first, of the area of the peak and second, the propor- tionality factor to convert this measurement to a concentration unit. Areas can be determined by any of the follow- ing methods: 1. Automatic integrator Polar planimetry Cutting out the peak and weighing the chart paper on an analytical balance Multiplying the peak height by the peak width at half the peak height Calculating the area of the triangle formed by the two tangents drawn through the inflection point of the peak, using the base line as the base of the triangle. The most commonly used of these methods are 1, 2 and 4. The areas are expressed in any con- venient unit, the most common unit being cm. In the ideal case, where detector response is the same for all components in a mixture, a simple relationship is used to calculate percentage. As an example, assume that we have an ideal four-com- ponent mixture of methane, ethane, propane and butane. The areas are 2.50, 1.25, 5.00 and 0.625 cm?, respectively. The total area = 9.375 cm”. The percentages are then: methane = 26.67%, ethane = 13.33%, propane = 53.33% and bu- tane = 6.67%, making the total 100% . The ideal case, however, does not always apply. The re- sponse factors are different for individual com- pounds, and this must be taken into consideration before calculation of percentage values. 2. 3. 4 wn 271 The sample components may also be collected at the detector outlet and analyzed by means of infrared or ultraviolet spectrophotometry, mass spectrometry or computer coupling. The most popular method of quantitation in the laboratory is by means of standard curves prepared by plotting the detector response versus concentration as shown in Figure 21-14. oP co CHa Area, CM? 10 20 30 40 50 Conc. % 0 Prepared by Sandia Laboratories draftsmen. Figure 21-14. Plot of Detector Response Ver- sus Concentration. OPERATION OF THE GAS CHROMATOGRAPH Selection of Parameters for Operation Carrier Gas — the choice depends on cost, availability, nature of sample, safety and the type of detector. Type of Column — selection is dependent on the polarity and volatility of the packing as compared with the substances to be separated, (see section on “Columns”). Detector — selection is based on sensitivity for type of sample component to be analyzed, (see section on “Detectors”). Temperature Controls — the setting for the temperature of the injection block is deter- mined by the boiling point of the least volatile compound in the sample. In general, it is maintained at a temperature of 50-100 de- grees C above the column temperature, which may be maintained at the limit specified for the packing it contains. The detector must also be maintained at a specified temperature which is dependent on the type of detector used and the analysis performed. All temper- ature controls are set and allowed to stabilize before injection of the sample. Column Preparation Many liquid phases require conditioning be- fore use. This is accomplished by heating the column at a slightly higher temperature than the intended operating temperature for six to twelve hours to “bleed off” any excessive coating in the column. Sample Collection Methods Samples of contaminated air may be collected in many ways, some of which are: (1) Glass or metal double-valved sampling flasks through which the sample is drawn by means of a small carbon vane pump or double-ended squeeze bulb. (2) An evacuated glass or metal single-valved flask or bulb, into which the sample is drawn. (3) Plastic or rubber bags which may be used for nonreactive gases are filled using either a double-ended squeeze bulb, for small volumes up to 1 liter, or by carbon vane pumps, for volumes up to 20 liters. (4) Adsorption on active solids while drawing the contaminated air through the solid contained in a sampling tube. (5) Absorption in a suitable solvent using standard air sampling equipment (i.e., im- pinger or bubbler). (6) Collection in large volume gas tight sy- ringes which are then capped to prevent leakage. There are two methods for the collection of air samples which are to be transported over long distances for analysis. The method of choice is to collect the air contaminant directly onto an active solid contained in a sampling tube. An alternate method is to first collect the air sample in a glass, metal, rubber or plastic container and then the air is passed through a tube containing an active solid adsorption of the contaminant. In either case the tube is sealed and sent to the laboratory for future analysis. Air volumes must always be re- corded so that concentrations can be calculated. Sample Preparation Some substances, such as gases, can be injected directly into the chromatograph, but ordinarily, there may be some preliminary purification needed Operator Column Length Dia. Liquid Phase wt. 7 eee ee eee Support Mesh Carrier Gas Rotometers Inlet Press psig Rate ml/min CHART SPEED SAMPLE Size Superlco, Inc.: Catalog 1971. Figure 21-15. which may be simple or complicated, depending on the compound to be analyzed. Because some substances in a mixture are similar, they cannot be separated from each other unless they are first converted into derivatives such as acetates or esters, thus producing larger molecules which may be separated more easily. Finally, after purification and derivative formation, the sample must be added to a suitable solvent which will volatilize at the temperature of the injection chamber. The solvents most frequently used for this purpose are acetone, alcohol, chloroform and hexane. In most cases, nanogram amounts of a sample are injected by means of a micro-syringe calibrated in microliters. It is apparent that the preparation of the sam- ple for analysis can be a tedious, time-consuming task and this phase is one of the few disadvantages of gas chromatography. Presentation of Chromatographic Data The precise reproduction of one’s analyses or those of other investigators requires all of the pertinent information to be made available. The following data must be included in chromat- ographic reports: type of sample, instrument used, identification of the column and the conditions of operation, date of analysis, results and name of operator. Figure 21-15 illustrates a convenient tabulation report form. CALIBRATION For accurate quantitative analysis the gas chromatographic system must be calibrated using Date Detector Voltage Sensit. Flow Rates, ml/min Hydrogen Air Scavenge Spht Temperature, °C Det Inj Column Initial Final Ratio Solvent Conc. Illustration of a Convenient Tabulation Report Form. known concentrations of the components of in- terest. Several methods are available for preparing known concentrations of gases and vapors for this purpose. PRESSURE GAUGE PRESSURE REGULATOR MIXING VESSEL —= Prepared by Sandia Laboratories draftsmen. A simple system for the preparation of known concentrations of gases by a dynamic method is shown in Figure 21-16 where known amounts of the gas (A) are mixed with a diluting gas (B) to FLOWMETER Figure 21-16. Dynamic Method. yield the required concentration (C). A second method which may be used for the preparation of known concentrations of either gases or vapor in air is the static method where a known volume of gas or volatile liquid is intro- duced (with an accurate volume measuring device) through a septum into a previously evacuated rigid container of known volume. The gas or vapor is then mixed with the diluting gas and stirred by either mechanical or thermal methods and samples are withdrawn from the vessel for use in calibra- 273 tion, This static system is shown in Figure 21-17, which illustrates the known gas (A), the diluting gas (B) and the known gas concentration (C). Samples from either type of calibration system can be introduced directly to the gas sampling valve of the chromatograph or they may be con- tained in a plastic or rubber bag from which the samples may be removed using gas tight syringes to transfer them to the chromatograph. These standard samples are chromatographed and the detector response is plotted versus concentration. MIXING VESSEL Prepared by Sandia Laboratories draftsmen. Figure 21-17. Static System. For an accurate calibration, the concentration of the known mixture must be determined by standard chemical methods. Infrared spectro- photometry is a convenient procedure for deter- mining the concentration of many components. There are several companies which market pressure containers of gases in labeled concentra- tions in nitrogen or other diluents; these may be used in the calibration of gas chromatographic systems. These mixtures are very convenient, but the concentrations must be verified by independent analyses before using for calibration purposes. SPECIAL TECHNIQUES Displacement Chromatography Samples collected on active solids may be analyzed chromatographically by a technique called displacement, where the sample collection tube is inserted just ahead of the chromatographic column. A solvent vapor, for which the active adsorbent has a greater affinity than for the sample components, is passed through the collection tube displacing the sample onto the chromatographic column. This technique, when properly applied, presents essentially a plug of the sample to the column, by concentrating the sample as the dis- placement vapor replaced the components on the active solid. Long Line Sampling It is possible to sample gaseous contaminants in air over relatively great distances by using 0.5- inch I.D. tubing and moving the sample through the line at 1 liter per minute using a large capacity vacuum pump. Line losses are negligible if the sample lines have been pressure checked before samples are taken. Sampling distances up to 6500 feet have been used.'! Portable Chromatographs There are available many very good portable chromatographs which may be taken to the work areas for sample analyses. The difficulty, however, arises in obtaining a large enough sample for analysis of trace contaminants. A sample concen- trating chromatograph has been developed (per- sonal communications) which samples the air through a small tube of activated silica gel. After the sample has been collected valves are changed and the air contaminants are released from the adsorbent by heat and presented directly to the gas chromatographic column for analysis. The versa- tility and applications of the portable chromat- ograph are progressing at an encouraging pace fortunately, as this type of unit is needed greatly throughout the whole environmental health field. Process Chromatography The process unit is capable of performing re- peat analyses of stream effluents, liquid or gaseous, for many components. This type of analysis can be programmed and the data fed to a computer for analysis; the results may be fed to a control system where necessary adjustments are made in processes if the analysis indicates the need. Process control by gas chromatography has wide-spread use in the chemical industry. Pyrolysis Pyrolysis, the thermal decomposition of sam- ples, is an important new branch of the identifi- cation methods. This technique may be used in the identification of polymers, high molecular weight organic and inorganic compounds, and also low boiling compounds, by producing the char- acteristic breakdown products. It has also been used in the characterization of microorganisms.!? Essentially, the technique employed is similar to that used in displacement chromatography but the displacement column is replaced by a combustion oven located just ahead of the partitioning column of the instrument. The output display has been called a pyrogram, which has an extremely com- plex nature. Since pyrolysis reactions are unpre- dictable the pyrolysis conditions must be very closely regulated for reproducible analyses. Miscellaneous ; Some recent applications have been published based on the work of investigators in the fields of air pollution, clinical medicine, toxicology and allied areas. Air Pollution — Using a two section column, Bethea'® was able to determine nitrogen di- oxide with a lower detection limit of 200 ppm. Gas chromatography of gases emanating from the soil has been successful in separating the component mixture using a three column sys- tem equipped with a thermal detector.’ A short silica column has been used to determine nitrogen dioxide at 50-60 degrees with hy- drogen as a carrier gas.'® Nitrogen dioxide has been collected and concentrated on Molecular Sieve 5A and determined by chromatography on a Poropak Q column'®. Lawson!” has de- termined nitrogen oxides in air by gas chromatography. 274 Medicine and Toxicology — Many articles are being published on the determination of al- cohol in breath samples, using various chro- matographic methods. Lowe'® reviewed the determination of volatile organic anesthetics in gases, blood, and tissue by gas chromatog- raphy. The direct determination of organic sol- vents in blood was described by Schlunegger.® References 1. BAYER, E. Gas Chromatographie, Springer-Verlag, Berlin, 1959 (proved the 450 year old work of Brun- schwig, a Strassburg surgeon). 2. TIETZ, N. W. Fundamentals of Clinical Chemistry, W. B. Saunders & Co., Philadelphia, Pa., p. 118, 1970. 3. JAMES, A. T. and A. J. MARTIN. Biochem. J. 50:679 (1952). 4. MARTIN, A. J. and R. L. SYNGE. Biochem. J. 35:1358 (1941). 5. Steroids (a) CREECH, B. G. 2:194 (1964). (b) YANNONE, M. E., D. B. McCOMAS and A. J. GOLDFIEN. J. Gas Chromatography, 2:30 (1964). (c) COX, R. 1. J. Chromatography, 12:245 (1963). (d) LUISI, M.,, G. GAMBASSI, V. MARESCOTTI, C. SAVI and F. POLVANI. J. Chromatog- raphy, 18:278 (1965). (e) CAGNAZZO, G., A. ROSS and G. BIGNARDI. J. Chromatography, 19:185 (1965). Lipids (a) FINLEY, T. N, S. A. PRATT, A. J. LAD- MAN, L. BREWER and M. B. McKAY. “Mor- phology and Lipid Analysis of Alveolar Lining Material in Dog Lung.” J. Lipid Research, 9:357 (1968). Barbiturates (a) PARKER, K. D., C. R. FONTAN and P. L. KIRK. Anal. Chem., 35:356, 1155 W. 16th Street N.W., Washington, D.C. (1963). Drugs (a) MOORE, J. M. and F. E. BENA. “Rapid Gas Chromatographic Assay for Heroin in Illicit Preparations.” Anal. Chem., 44:385 (1972). Blood Alcohol (a) PARKER, K. D,, C. R. FONTAN, Y. L. YEE and P. L. KIRK. “Gas Chromatographic De- termination of Ethyl Alcohol in Blood for Medicolegal Purposes.” Anal. Chem., 34:1234 (1962). 6. Aerospace (a) WEBER, T. B.,, J. R. DICKEY, N. N. JACK- SON, J. W. REGISTER and C. P. CONKLE. “Monitoring of Trace Constituents in Simu- lated Manned Spacecraft.” Aerospace Med., 35:148 (1964). 7. Nuclear Submarines (a) JOHNSON, J. E. Nuclear Submarine Atmos- pheres Analysis and Removal of Organic Con- taminants, NRL Report 588, 1962. 8. BREWER, L. W. and D. R. PARKER. Gas Chro- matographic Analysis of Gases Found in Post-Shot Tunnel Systems, SC-RR-71-0337, June 1971. 9. SZEPESY, L., cSc. Gas Chromatography, CRC Press, Cleveland, Ohio, 1970. 10. COULSON, D. M. Journal of Gas Chromatography, 3:134 (1965). 11. PARKER, D. R. and L. W. BREWER. “Techniques for Remote Sampling of Gases.” American Ind. Hyg. Assoc. J., 32:475, 210 Haddon Ave., West- mont, New Jersey (July 1971). 12. REINER, E. J. Journal of Gas Chromatography, 5:65 (1967). 13. BETHEA, R. M. and M. C. MEADOR. Journal of Chromatog. Sci., 7:655 (1969). J. Gas Chromatography, 14. VAN CLEEMONT, O. Journal of Chromatography, 45:315 (1969). 15. KURADO, D. Kagaku to Koygo, (Tokyo) 43:361 (1969). 16. LaHUE, M. D., J. B. PATE and J. P. LODGE. J. of Geophysical Research, 75:2922 (1970). 17. LAWSON, A. and H. G. McADIE. J. of Chromatog. Sci., 8:723 (1970). 18. LOWE, H. J. Theory of Applications of Gas Chro- matography to Internal Medicine, Hahnemann Sym- posium, 1st, 1966, H. S. Kroman, Editor, 194-209, Grune and Stratton, New York, N. Y., 1968. 19. SCHLUNEGGER, U. P. Minnesota Medicine, 52:175 (1969). Preferred Reading Calibration (a) SPARKS, H. E. “An Improved Injection Tech- nique for Calibration in Quantitative Gas Chroma- tography.” Journal of Gas Chromatography, 6:410 (Aug. 1968). (b) THOMAS, M. D. and R. E. AMTOWER. “Gas Dilution Apparatus for Preparing Reproducible Dy- namic Gas Mixtures in Any Desired Concentration and Complexity.” Journal of Air Pollution Control Association, 16:618 (Nov. 1966). (c) ANGELY, L., E. LEVANT, G. GUIOCHON and G. PESLERBE. “General Method to Prepare Stand- ard Samples for Detector Calibration in Gas Chro- matographic Analysis of Gases.” Anal. Chem., 41:1446 (Sept. 1966). (d) DeGRAZIO, R. P. “A Gas Mixing and Sampling Flask.” Journal of Gas Chromatography, 6:468 (Sept. 1968). Columns (a) OTTENSTEIN, D. M. “Column Support Materials for Use in Gas Chromatography.” Journal of Gas Chromatography, 1:11 (April 1963). (b) DANE, S. D. “A Comparison of the Chromato- graphic Properties of Porous Polymers.” Journal of Chromatography Science, 7:389 (July 1969). (c) CONDON, R. D. “Design Considerations of a Gas Chromatography System Employing High Efficiency Golay Columns.” Anal. Chem., 31:1717 (Oct. 1959). (d) ASTM Special Technical Publication No. 343: Gas Chromatographic Data, American Society for Test- ing and Materials, Philadelphia, Pa. (e) ASTM Special Technical Publication No. DS-25A: Gas Chromatographic Data Compilation, American Society for Testing and Materials, Philadelphia, Pa. Fractional Collection (a) BIERI, B. A.,, M. BEROZA and J. M. RUTH. “Col- lection and Transfer Device for Gas Chromato- graphic Fractions.” Journal of Gas Chromatography, 6:286 (May 1968). (b) BALLINGER, J. T., T. T. BARTELS and J. H. TAYLOR. “Gas Chromatographic Fraction Trap — Infrared Cell.” Journal of Gas Chromatography, 6:295 (May 1968). Injection Systems BACK, R. A, N. J. FRISWELL, J. C. BODEN and J. M. PARSONS. “A Simple Device for Injecting a Sample from a Sealed Glass Tube into a Gas Chromatograph.” J. of Chromatog. Sci., 7:708 (Nov. 1969). Medical Applications PARKER, K. D., C. R. FONTAN, J. L. YEE and P. L. KIRK. “Gas Chromatographic Determination of Ethyl Alcohol in Blood for Medicolegal Pur- poses.” Anal. Chem., 34:1234 (Sept. 1962). Qualitative and Quantitative Analysis (a) KAYE, W. and F. WASHA. “A Rapid-Scan for Ultraviolet Spectrophotometer for Monitoring Gas Chromatograph Effluent.” Anal. Chem., 36:2380 (Nov. 1964). (b) MESSNER, A. E.,, D. M. ROSIE and P. A. ARGA- BRIGHT. “Correlation of Thermal Conductivity Cell Response with Molecular Weight and Structure.” Anal. Chem., 31:230 (Feb. 1959). Pyrolysis (a) SARNER, S. F.,, G. D. PRUDER and E. J. LEVY. “Vapor-Phase Pyrolysis for Effluent Identification and Repdiion Studies,” American Laboratory, 57-65, ct. . ’ (b) TAKEUCHI, T., S. TSUGE and T. OKUMOTO. “Identification and Analysis of Urethane Foams by Pyrolysis Gas Chromatography.” Journal of Gas Chromatography, 6:542 (Nov. 1968). (c) JERMAN, R. I. and L. R. CARPENTER. “Gas Chromatographic Analysis of Gaseous Products from the Pyrolysis of Solid Municipal Waste.” Journal of Gas Chromatography, 6:298 (May 1968). (d) GROTEN, B. “Application of Pyrolysis Gas Chro- matography of Polymer Characterization.” Anal. Chem., 36:1206 (June 1964). Sampling Methods SCHUETTE, F. J. “Plastic Bags for Collection of 0s Jamples Atmospheric Environment, 1:515 ). 276 Miscellaneous (a) MENDRUP, R. F,, Jr. and J. H. TAYLOR. “Gas Chromatographic Analysis of Trace Contaminants in Liquid Ammonia.” Journal of Chromatography Sci- ence, 8:723 (Dec. 1970). (b) POMMIER, C. and G. GUIOCHON. “Gas Chro- matographic Analysis of Mild Carbonyls.” Journal of Chromatography Science, 8:486 (Aug. 1970). (c) CALLEY, I, M. “Septum Performance in Gas Chro- matography.” Journal of Chromatography Science, 8:408 (July 1970). (d) ZLATKIS, A., H. R. KAUFMAN and D. E. DUR- BIN. “Carbon Molecular Sieve Column for Trace Analysis in Gas Chromatography.” Journal of Chro- matography Science, 8:416 (July 1970). (e) KARASEK, F. W. and K. R. GIBBINS. “A Gas Chromatograph Based on the Piezo-electric Detec- tor.” Journal of Chromatography Science, 9:535 (Sept. 1971). (f) BREWER, L. W. and D. R. PARKER. Gas Chro- matographic Analysis of Gases Found in Post-Shot Tunnel Systems, SC-RR-71-0337, June 1971. CHAPTER 22 QUALITY CONTROL FOR SAMPLING AND LABORATORY ANALYSIS Adrian L. Linch INTRODUCTION The measurement of physical entities such as length, volume, weight, electromagnetic radiation and time involves uncertainties which cannot be eliminated entirely, but when recognized can be reduced to tolerable limits by meticulous attention to detail and close control of the significant vari- ables. In addition, errors often unrecognized, are introduced by undesirable physical or chemical effects and by interferences in chemical reaction systems. In many cases, absolute values are not directly attainable; and, therefore, standards from which the desired result can be derived by com- parison must be established. Errors are inherent in the measurement system. Although the uncer- tainties cannot be reduced to zero, methods are available by which reliable estimates of the prob- able true value and the range of measurement error can be made. In this chapter the fundamental procedures for the administration of an effective quality con- trol program are presented with sufficient explana- tion to enable the investigator to both understand the principles and to apply the techniques. First, the detection and control of determinate and in- determinate error will be considered. Based on this foundation, the types of errors and meanings of the common terms used to define an accurate method are discussed as a basis for application of quality control to sampling and analysis. The theory, construction, applications and limitations of control charts are developed in sufficient depth to provide practical solutions to actual quality control problems. Additional statistical approaches are included to support those systems which may require further refinement of precision and accur- acy to evaluate and control sampling and analysis reliability. Finally, a discussion of collaborative testing projects and intralaboratory quality control pro- grams designed to improve and test the integrity of the laboratory’s performance completes the sur- vey of quality control principles and practices. QUALITY CONTROL PRINCIPLES Total Quality Control A quality control program concerned with sampling and laboratory analysis is a systematic attempt to assure the precision and accuracy of future analyses by detecting determinate errors in analysis and preventing their recurrence. Confi- dence in the accuracy of analytical results and 277 improvements in analysis precision are established by identification of the determinate sources of error. The precision will be governed by the in- determinate error inherent in the procedure, and can be estimated by statistical techniques. For a result to be accurate, the procedure must not only be precise, but must also be without bias. Tech- niques have been developed for the elimination of bias. The quality control program should cover instrumental control as well as total analysis con- trol. The use of replicates submitted in support of the quality control program provides assurance that the procedure will remain in statistical control. Quality must be defined in terms of the char- acteristic being measured. Control must be re- lated to the source of variation which may be either systematic or random. Usually the basic variable is continuous (any value within some limit is possible). A numerical value of an analysis for which the range of uncertainty inherent in the method has not been established cannot be reliably considered a reasonable estimate of the true or actual value. The basic quality control program incorporates the concepts of: 1. Calibration to attain accuracy 2. Replication to establish precision limits 3. Correlation of quantitatively related tests to confirm accuracy, where appropriate. Evaluation of the overall effectiveness of the qual- ity control program encompasses a number of parameters: Equipment and instruments The current state of the art Expected ranges of analytical results Precision of the analytical method itself Control charts to determine trends as well as gross errors Data sheets and procedures adopted for control of sample integrity in the labora- tory Quality control results on a short term basis (daily if appropriate) as well as on an accumulated basis. The manipulative operations which are directly influenced by quality control include: 1. Sampling techniques 2. Preservation of sample integrity (identifi- cation, shipping and storage conditions, contamination, desired component losses, etc.) Aliquoting procedures Dilution procedures oO vawN= 5. Chemical or physical concentration, sep- aration and purification 6. Instrument operation. Statistical Quality Control Statistical quality control involves application of the laws of probability to systems where chance causes operate. The technique is employed to detect and separate assignable (determinate) from random (indeterminate) causes of variation. “Sta- tistics” is the science of uncertainty; therefore, any conclusions based on statistical inference contain varying degrees of uncertainty, which is expressed in terms of probability statements. Uncertainty can be quantified in terms of well defined statis- tical probability distributions, which can be ap- plied directly to quality control. The application of statistical quality control can most efficiently indicate when a given procedure is in statistical control, and a continuing program that covers sampling, instrumentation and overall analysis quality will assure the validity of the analytical program. Further development of statistical tech- niques and applications will be found in the fol- lowing sections in this chapter. Quality Control Charts’ The Shewhart Control Chart® is one of the most generally applicable and easily adapted sta- tistical quality control techniques which can be applied to almost any phase of production, re- search or analysis. Control charts originally were developed for control of production lines where large numbers of manufactured articles were in- spected on a continuous basis. Since analyses frequently are produced on an intermittent basis, or on a greatly reduced scale, less data are avail- able to work with. Therefore, certain concessions must be made in order to respond quickly to ob- jectionable changes in the analytical procedure. This control chart may serve several func- tions: 1. To determine empirically and to define ac- ceptable levels of quality 2. To achieve the acceptable level established 3. To maintain performance at the established quality level. Certain assumptions reside in this technique. The first and major assumption is that there will be variation. No process or procedure has been so well perfected, or so unaffected by its environ- ment that exactly the same result will always be produced. Either the device used for measurement is not sufficiently sensitive or the operator per- forming the measurement is not sufficiently skilled. The sources of variation present in analytical work include: 1. Differences among analysts Instrumental differences Variations in reagents and related supplies Effect of time on the differences found in items 1, 2 and 3 Variations in the interrelationship of items 1, 2 and 3 with each other and with time. A “system of chance causes” is inherent in the nature of processes and procedures and will produce a pattern of variation. When this pattern is stable, the process or procedure is considered to be “in statistical control” or just “in control.” 2 3. 4. 5 278 Any result which falls outside of this pattern will have an assignable cause which can be determined and corrected. The control chart technique provides a means for separating the assignable cause variant from the stable pattern. The chart is a graphical presen- tation of the process or procedure test data which compares the variability of all results with the average or expected variability from small arbi- trarily defined groups of the data. The control chart also compares “within group” variability to “between group” variability. The technique in effect is a graphical analysis of variance. The data from such a system can be plotted with vertical scale in test result units and the hori- zontal scale in units of time or sequence of results. The average value or mean, and the limits of the dispersion (spread, or range of results) can be calculated. Details for the construction and inter- pretation of quality control charts can be found in later sections of this chapter. ERRORS Introduction Numbers are employed to either enumerate objects or to delineate quantities. If sixteen air samples are taken simultaneously at different lo- cations in a warehouse where gasoline-powered fork lift trucks are in motion, the number, i.e., the count, would be the same regardless of who counted them, when the count was made or how the count was made. However, if each individual sample is analyzed for carbon monoxide, sixteen different numbers, i.e., the concentration, un- doubtedly would be obtained. Furthermore, when replicate determinations are made on each sam- ple, a range of carbon monoxide concentrations would be found.? Experimental errors are classified as determi- nate or indeterminate. A fifteen count of the ware- house samples would be a determinate error quick- ly disclosed by recount. An indeterminate error would be encountered due to the inherent variabil- ity in repetitive determinations of carbon mon- oxide by gas chromatography, infrared or a color- imetric technique. If the estimation of carbon monoxide concen- tration is made with a length of stain detector tube and a 6.5-mm stain length equivalent to 57 ppm is recorded by the observer, whereas the true stain length is 6.0 mm and equivalent to 50 ppm, the observational error would be (57-50) X 100+ 50 = 14%. All analytical methods are subject to errors. The determinate ones contribute constant error or bias while the indeterminate ones produce ran- dom fluctuations in the data. The concepts of ac- curacy and precision as applied to the detection and control of error have been clearly defined and should be used exactly. A concept of the difference between accuracy and precision can be visualized by the pattern formed by shots aimed at a target as shown in Fgure 22-1. From the scatter of four shots, one can see that a high degree of precision can be at- tained without accuracy and that accuracy with- out precision is possible. The ultimate goal is, X x x IMPRECISE AND INACCURATE x X x PRECISE BUT INACCURATE © ACCURATE BUT IMPRECISE PRECISE AND ACCURATE Powell CH, Hosey AD (eds): The Industrial Environ- ment — Its Evaluation and Control, 2nd Edition. Pub- lic Health Services Publication No. 614, 1965. Figure 22-1. Precision and Accuracy of course, accuracy with precision target number 4, (See also ASTM Designation D-1129-68 for definitions.)® Accuracy. Accuracy relates the amount of an element or compound recovered by the analytical procedure to the amount actually present. For results to be accurate, the analysis must yield val- ues close to the true value. Precision. Precision is a measure of the method’s variability when repeatedly applied to a homo- geneous sample under controlled conditions, with- out regard to the magnitude of displacement from the true value as the result of systematic or con- stant determinate errors which are present dur- ing the entire series of measurements. Stated con- versely, precision is the degree of agreement among results obtained by repeated measurements or “checks” on a single sample under a given set of conditions. * Detection and Elimination of Determinate Error The terms “determinate” error, “assignable” 279 error, and ‘‘systematic” error are synonymous. A determinate error contributes constant error or bias to results which may agree precisely among themselves. Sources of Determinate Error. A method may be capable of reproducing results to a high degree of precision, but only a fraction of the component sought is recovered. A precise analysis may be in error due to inadequate standardization of solu- tions, inaccurate volumetric measurements, inac- curate balance weights, improperly calibrated in- struments or personal bias (color estimation). Method errors that are inherent in the procedure are the most serious and most difficult to detect and correct. The contribution from interferences is discussed later. Personal errors other than inherent physical visual acuity deficiencies (color judgment) include consistent carelessness, lack of knowledge and per- sonal bias which are exemplified by calculation errors, use of contaminated, or improper reagents, nonrepresentative sampling or poorly calibrated standards and instruments. Types of Determinate Error. Additive: An addi- tive error occurs when the mean error has a con- stant value regardless of the amount of the constit- uent sought in the sample. A plot of the analytical value versus the theoretical value (Figure 22-2) will disclose an intercept somewhere other than zero, 4 ~ Ww 3 g - 2 S 7 0 | 1 1 | | 2 3 4 THEORETICAL VALUE Powell CH, Hosey AD (eds): The Industrial Environ- ment — Its Evaluation and Control, 2nd Edition. Pub- lic Health Service Publication No. 614, 1965. Figure 22-2. Additive Error Proportional: A proportional error is a deter- minate error in which magnitude is changed ac- cording to the amount of constituent present in the sample. A plot of the analytical value versus the theoretical value (Figure 22-3) not only fails to pass through zero, but discloses a curvilinear rather than a linear function. 4 ‘o- Ww 3 3 s I 2 Oo = 5 J Z 0 Loc. poo yoy 2 3 4 THEORETICAL VALUE Powell CH, Hosey AD (eds): The Industrial Environ- ment — Its Evaluation and Control, 2nd Edition. Pub- lic Health Service Publication No. 614, 1965. Figure 22-3. Proportional Error Recovery of “Spiked” Sample Procedures. A re- covery procedure in which spiked samples are used provides a technique for the detection of deter- minate errors. Although it does not provide a cor- rection factor to adjust the results of an analysis, the technique does provide a basis for evaluating the applicability of a particular method to any given sample. It allows derivation of analytical quality control from the results, thus providing the basis for an excellent quality control program. The recovery technique applies the analytical method to a reagent blank; to the sample itself, in at least duplicate; and to “spiked” samples, pre- pared by adding known quantities of the substance sought, to separate aliquots of the sample which are equal in size to the unspiked sample taken for analysis. The substance sought should be added in sufficient quantity to exceed in magnitude the limits of analytical error, but the total should not exceed the range of the standards selected. The results are first corrected for reagent in- fluence by subtracting the reagent blank from each standard, sample, and “spiked” sample result. The average unspiked sample result is then sub- tracted from each of the “spiked” determinations, the remainder divided by the known amount orig- inally added, and expressed as percentage recov- ery. Table 22-1 illustrates an application of this technique to the analysis of blood for lead content. Specifications for acceptance of analytical re- sults usually are determined by the state of the art and the final disposition of the results. Recoveries of substances within the range of the method may be very high or very low and approach 100 per- cent as the errors diminish and as the upper limit of the calibration range is approached. Trace an- alysis procedures which inherently have relatively 280 large errors when operated near the limits of sensi- tivity deliver poor recoveries based on classical analytical criteria and yet, from a practical view- point of usefulness may be quite acceptable (Table 22-1 — 2 ug spike). Poor recovery may reflect interferences present in the sample, excessive ma- nipulative losses, or the method’s technical inade- quacy in the range of application. The limit of sensitivity may be considered the point beyond which indeterminate error is a greater quantity than the desired result. Control Charts. Trends and shifts in control chart responses also may indicate determinate error. The standard deviation is calculated from spiked sam- ples and control limits (usually = 3 standard de- viations) for the analysis are established. Calcula- tion of the standard deviation is discussed in Chap- ter 3 and an in-depth discussion of control limits is treated in reference’. In some cases, such as BOD and pesticide samples, spiking to resemble actual conditions is not possible. However, tech- niques for detecting bias under these conditions have been developed.® Control charts may be prepared even for sam- ples which cannot be spiked or for which the re- covery technique is impractical. A reference value is obtained from the average of a series of TABLE 22-1 LEAD IN BLOOD ANALYSIS Basis: 10.0 g blood from blood bank pool, ashed and lead determined by double extraction, mixed color, dithizone procedure. Analyst: DIM ng Pb Optical pg Pb found Recovery, added Density Total Recovered % None-blank 0.0969 — —_— — S-Calibration Point 0.2596 — — _. None 0.1427 1.6 me rn None 0.1337 1.3 _. — None 0.1397 1.4 — — None 0.1397 1.4 ee — Average 0.1389 1.4 en er 2.0 0.1805 2.9 1.5 75 4.0 0.2636 54 40 100 6.0 0.3372 7.8 6.4 107 8.0 0.3925 9.4 8.0 100 10.0 0.4437 11.4 10.0 100 30.0 Total — 36.9 29.9 96 Calculation of mean error® Mean error=36.9 — (30.0+5X 1.4) =0.1 pg for entire set = 29—(2.0+1.4)=0.5 pg for 2 ug spike Calculation of relative error Relative Error= (0.1 X 100) /37.0=0.27 % for entire set =(0.5%X100)/3.4=14.7% for 2 pg spike Q 20 © = OUT OF CONTROL Mh ee iil inane, UPPER - CONTROL LIMIT o wn Z 1.50 ac O 2 oO LOWER Ss —25 CONTROL LIMIT - < 1.0 e 1 1 5 10 IS 20 DAY NUMBER Figure 22-4. Lead in Blood Control Chart replicate determinations performed on a composite or pooled sample which has been stabilized to maintain a constant concentration during the con- trol period (nitric acid in urine). An example has been prepared from a blood lead study (Figure 22-4). Although these data were drawn from the same blood pool used to illustrate the appli- cation of the spiking technique for quality control, the consecutive aliquot analyses plotted as a con- trol chart furnish additional information. The con- trol limits were reduced to = 2 standard devia- tions to further sharpen the trends. There may be preliminary evidence of personal bias as shown by KD’s versus JD’s performance. Change in Methodology. Analysis of a sample for a particular constituent by two or more methods that are entirely unrelated in principle may aid in the resolution of determinate error. In Table 22-2, an interlaboratory evaluation of three different methods for the determination of lead concentration in ashed urine specimens (mixed color dithizone, atomic absorption and polarography) is summarized. If the highly spe- cific polarographic method was selected as the primary standard, then the dithizone procedure is subject to a + 7.4 pg/1 bias as compared with a +3.6 pg/1 bias in the atomic absorption method for lead. Effect of Sample Size. If the determinate error is additive, the magnitude may be estimated by plotting the analytical results versus a range of sample volumes or weights. If the error has a constant value regardless of the amount of the component sought, then a straight line fitted to the plotted points will not pass through the origin. The effect of urine volume on the analysis for lead is shown in Figure 22-5. Elimination. a) Physical. In many cases error can be reduced to tolerable levels by quantitating the magnitude over the operating range and de- veloping either a corrective manipulation directly in the procedure or a mathematical correction in the final calculation. Temperature coefficients (parameter change per degree) are widely applied to both physical and chemical measurements. For example, the stain length produced by carbon monoxide in the detector tubes previously cited for illustration is dependent on the temperature as well as the air sampling rate and CO concentra- tion. Therefore, when these tubes are used out- side the median temperature range, a correction must be applied to the observed stain length (Table 22-3).7 As a general rule, most instruments exhibit maximum reliability over the center 70 % of their range (midpoint = 35%). As the extreme to either side is approached the response and reading errors become increasingly greater. Optical dens- ity measurements, for example, should be confined to the range 0.045 to 0.80 by concentration ad- justment or cell path choice. Extrapolation to limits outside the range of response established for the analytical method or instrumental measure- ment may introduce large errors as many chemical and physical responses are linear only over a rela- tively narrow band in their total response capa- bility. In absorption spectrophotometric measure- ments, Beer’s law relating optical density to con- centration may not be linear outside of rather nar- row limits in some instances (colorimetric deter- mination of formaldehyde at high dilution by the chromatropic acid method). b) Internal Standard. The internal standard technique is used primarily for emission spectro- graph, polarographic, and chromatographic (liquid or vapor phase) procedures. This technique en- ables the analyst to compensate for electronic and “ mechanical fluctuations within the instrument. 281 80 |- Ww Ss 3 60 | Oo > w T Ss 40 | J wn w = E20 | 27 2 1 1 L 0.3 1.0 2.0 3.0 MICROGRAMS OF LEAD 0.008 * 0.005mg/| Figure 22-5. Effect of Sample Size on Determination of Lead in Urine TABLE 22-2 TABLE 22-3 AN INTERLABORATORY STUDY OF THE KITAGAWA CARBON MONOXIDE DETERMINATE ERROR IN THE DETECTOR TUBE NO. 100 DITHIZONE PROCEDURE FOR THE Temperature Correction Table DETERMINATION OF LEAD Chart Correction Concentration (ppm) IN NINE URINE SPECIMENS Readings 0°C 10°C 20°C 30°C 40°C Polaro- Mixed (ppm) (32°F) (50°F) (68°F) (86°F) (104°F) graphic Color Dithizone Atomic Absorption 1,000 800 900 1,000 1,060 1,140 Method Found Difference Found Difference 900 720 810 900 950 1,030 800 640 720 800 840 910 10 25 15 10 0 14 28 14 22 8 700 570 640 700 740 790 12 12 0 16 4 600 490 550 600 630 680 500 410 470 500 520 560 15 20 5 16 1 400 340 380 400 420 440 21 20 ~1 22 1 300 260 290 300 310 320 22 30 8 24 2 200 180 200 200 200 210 27 40 13 36 9 100 100 100 100 100 100 19 22 3 22 3 *Kitagawa, T., “Carbon Monoxide Detector Tube. No. 100,” National Environmental Instruments, Inc., 1971, 12 22 10 16 4 Fall River, Mass. Mean ae +74 pe +3.6 substance to which the instrument will respond in a manner similar to the contaminant in the sys- tem. The ratio of the internal standard response In brief, the internal standard method involves to the contaminant response determines the con- the addition to the sample of known amounts of a centration of contaminant in the sample. Condi- 282 tions during analyses will affect the internal stan- dard and the contaminant identically, and thereby compensate for any changes. The internal stan- dard should be of similar chemical composition to the contaminant, of approximately the same con- centration anticipated for the contaminant, and of the purest attainable quality. A detailed discus- sion of the sources of physical error, magnitude of their effects, and suggestions for minimizing their contribution to determine bias and error will be found in the literature®. c) Chemical Interference. The term “inter- ference” relates to the effects of dissolved or sus- pended materials on analytical procedures. A re- liable analytical procedure must anticipate and minimize interferences. The investigator must be aware of possible in- terferences and be prepared to use an alternate or modified procedure to avoid errors. Analyzing a smaller initial aliquot may suppress or eliminate the effect of the interfering element through dilu- tion. The concentration of the substance sought is likewise reduced; therefore, the aliquot must contain more than the minimum detectable amount. When the results display a consistently increasing or decreasing pattern by dilution, then interference is indicated. An interfering substance may produce one of three effects: 1. React with the reagents in the same man- ner as the component being sought (posi- tive interference). 2. React with the component being sought to prevent complete isolation (negative inter- ference). 3. Combine with the reagents to prevent fur- ther reaction with the component being sought (negative interference). The sampling and analytical technique em- ployed for the surveillance of airborne toluene diisocyanate (TDI) in the manufacturing environ- ment furnishes a good example in which all three factors can be encountered. The TDI vapor is absorbed and quantitatively hydrolyzed in an aqueous acetic acid-hydrogen chloride mixture to toluene diamine (MTD) which then is diazotized by the addition of sodium nitrite. The excess nitrous acid is destroyed with sulfamic acid and the diazotized MTD coupled with N-1-Naph- thylethylenediamine to produce a bluish-red azo dye. In the phosgenation section of the opera- tions, the starting material (MTD) may coexist with TDI in the atmosphere sampled. If so, then a positive interference will occur as the method cannot distinguish between free MTD and MTD from the hydrolyzed TDI. This problem can be resolved by collecting simultaneously a second sample in ethanol. The TDI reacts with ethanol to produce urethane de- rivatives which do not produce color in the coupling stage of the analytical procedure. The MTD is determined by the same diazotization and coupling procedure after boiling off the eth- anol from the acidified scrubber solution. Then the difference represents the TDI fraction in the air sampled. 283 On the other hand, if the relative humidity is high or alcohol vapors are present, negative inter- ference will reduce the TDI recovered by forma- tion of the carbanilide (dimer) or the urethane derivative which will not produce color in the final coupling stage. Alternative methods have not been developed for these conditions. If high concentra- tions of phenol are absorbed, then a negative in- terference will arise from side reactions with the nitrous acid required to diazotize the MTD. This loss can be avoided by testing for excess nitrous acid in the diazotization stage and adding addi- tional sodium nitrite reagent if a deficiency is indi- cated. An estimate of the magnitude of an interfer- ence may be obtained by the recovery procedure. If recoveries of known quantities exceed 100%, a positive interference is present (Condi- tion 1). If the results are below 100%, a nega- tive interference is indicated (Condition 2, or 3: see reference (8) for details). Indeterminate Error and Its Control Nature. Even though all determinate errors are removed from a sampling or analytical procedure, replicate analyses will not produce identical re- sults. This erratic variation arises from random error. Examples of this type of variation would be variation in reagent addition, instrument re- sponse, line voltage transients and physical meas- urement of volume and mass. In environmental analysis the sample itself is subject to a great va- riety of variability. Although indeterminate errors appear to be random in nature, they do conform to the laws of chance; therefore statistical measures of precision can be employed to quantitate their effects. A measure of the degree of agreement (preci- sion) among results can be ascertained by analyz- ing a given sample repeatedly under conditions controlled as closely as conditions permit. The range of these replicate results (difference between highest and lowest value) provides a measure of the indeterminate variations. Quantification. 1) Distribution of Results. Inde- terminate error can be estimated by calculation of the standard deviation (o) after determinate errors have been removed. The calculation of this value is discussed in Chapter 3. When indeterminate or experimental errors occur in a random fashion, the observed results (x) will be distributed at random around the average or arithmetic mean (x). Given an infinite number of observations, a graph of the relative frequency of occurrence plotted against magnitude will describe a bell- shaped curve known as the Gaussian or normal curve (Figure 22-6). However, if the results are not occurring in a random fashion, the curve may be flattened (no peak), skewed (unsymmetrical), narrowed, or exhibit more than one peak (multi- modal). In these cases the arithmetic mean will be misleading, and unreliable conclusions with re- spect to deviation ranges (o) will be drawn from the data. A typical graph illustrating skew, multi- modes, and a narrow peak is shown in Figure 22-7. In any event the investigator should confirm the tts i CU ———— te—95.5% —— F+—68.3%—* TRAIN... SEA “30 "20 "0 X to *20 *30 MAGNITUDE Figure 22-6. Gaussian or Normal Curve of Frequencies normalcy of the data at hand. Various procedures are available to test this assumption. One method is to construct a histogram, if the sample is large enough, and then to plot a normal curve having the same mean and standard devia- tion with the histogram to see how well the normal curve fits. This is an imprecise method at best and, unless there is an extremely good fit of a normal curve laid over the resulting histogram or polygon, the cumulated distribution should be plotted on normal probability paper before pro- ceeding. As an example the following table gives the frequency distribution of the results of a series of 145 similar tests: Grams Frequency Grams Frequency 0.8485 2 0.8275 21 0.8455 1 0.8245 14 0.8425 2 0.8215 5 0.8395 6 0.8185 4 0.8365 7 0.8155 3 0.8335 23 0.8125 2 0.8305 55 These data are plotted in Figure 22-8. Now hav- ing looked at the fit, we decide how good it is. The graph does not really tell whether the depar- 1S - wn A ? ww Sm wlio TS Oo 3 8 9 = at] < | I 40 80 120 LEAD CONCENTRATION: _yg PER 100gms. DATA FROM 61 PARTICIPATING LABORATORIES ( KEPPLER ET AL-7) Figure 22-7. Frequency Distribution of Lead in Blood: Analytical Results 284 .8515 + PR wn E .8395 + S = Sh wn - 2 = w = —“_ w x 3 .8275 + < w Ral = .8155 +--+ tt tt ty I 2 5 10 20 30405060 70 80 90 95 98 99 99.8999 99.99 PERCENT OF CASES Figure 22-8. Plot of a Frequency Distribution ture from fit is significant. The most accurate way of testing for normality is to use the X? test for normality of data. However, the calculations are tedious and time consuming for desk calculator computation. Standard X* computer programs are commonly available, but judgment must be used to weigh the cost of getting an accurate determina- tion against the value of the information. The distribution of results within any given range about the mean is a function of o. The proportion of the total observations which reside withinX = 1¢,X = 2 sand X = 3 ¢ have been thoroughly established and are delineated in Fig- ure 22-6. Although these limits do not define ex- actly any finite sample collected from a normal group, the agreement with the normal limits im- proves as n increases. As an example, suppose an analyst were to analyze a composite urine speci- men 1000 times for lead content. He could reas- onably expect 50 results would exceed X += 2 ¢ and only 3 results would exceed Xx = 3 ¢. How- ever, the corollary condition presents a more use- ful application. In the preceding example, the analyst has found Xx to be 0.045 mg. per liter with o== 0.005 mg/1. Any result which fell outside the range 0.035-0.055 mg/1 (0.045 = 2 o) would be questionable as the normal distribution curve indicates this should occur only 5 times in 100 determinations. This concept provides the basis for tests of significance, a concept which is discussed in detail in any good statistical reference such as those cited in this chapter or Chapter 3. 2) Range of Results. The difference between the maximum and minimum of n results (range) also is related closely to ¢. The range (R) for n results will exceed o multiplied by a factor d, only 285 5% of the time when a normal distribution of errors prevails, Values for d,: n d, 2 2.77 3 3.32 4 3.63 5 3.86 6 4.03 Since the practice of analyzing replicate (usually duplicate) samples is a general practice, application of these estimated limits can provide detection of faulty technique, large sampling er- rors, inaccurate standardization and calibration, personal judgment and other determinate errors. However, resolution of the question whether the error occurred in sampling or in analysis can be answered more confidently when single determina- tions on each of three samples rather than dupli- cate determinations on each of two samples are made. This approach also reduces the amount of analytical work required.® Additional information relative to the evaluation of the precision of ana- lytical methods will be found in ASTM Stan- dards.?® 3) Collaborative Studies or “Round Robins.” After an analytical method has been evaluated fully for precision and accuracy, collaborative test- ing should be initiated, The values for precision and accuracy as determined by the results from a number of laboratories can be expected to be in- ferior when compared with the performance of the originating laboratory. Because technicians in dif- ferent laboratories apply to their procedure their own characteristic determinate and indeterminate errors which may differ significantly from the orig- inal technique, the values for precision and accur- acy will disclose the true reliability (ruggedness, or immunity to minor changes) of the method. Participation in collaborative programs will aid the investigator in evaluating his laboratory’s per- formance in relation to other similar facilities and in locating sources of error. Duplicate analyses are employed for the de- termination and control of precision within the laboratory and between laboratories. Initially, ap- proximately 20% of the routine samples, with a minimum of 20 samples, should be analyzed in duplicate to establish internal reproducibility. A standard or a repeatedly analyzed control, if avail- able, should be included periodically for long-term accuracy control. The control chart technique is directly applicable, and appropriate control limits can be established by arbitrarily subgrouping the accumulated results or by using appropriate esti- mates of precision from an evaluation of the pro- cedure. CONTROL CHARTS Description and Theory The control chart provides a tool for distin- guishing the pattern of indeterminate (stable) variation from the determinate (assignable cause) variation. This technique displays the test data from a process or method in a form which graph- ically compares the variability of all test results with the average or expected variability of small groups of data — in effect, a graphical analysis of variance, and a comparison of the “within groups” variability versus the “between group” variability (see Figure 22-6 for the pattern of variation of data). The data from a series of analytical trials can be plotted with the vertical scale in units of the test result and the horizontal scale in units of time or sequence of analyses. The average or mean value can be calculated and the spread (dispersion or range) can be established (Figure 22-4). The determination of appropriate control lim- its can be based on the capability of the procedure itself or can be arbitrarily established at any de- sirable level. Common practice sets the limits at + 3 ¢ on each side of the mean. If the distribu- tion of the basic data exhibits a normal form, the probability of results falling outside of the control limits can be readily calculated. The control chart is actually a graphical pres- entation of quality control efficiency. If the pro- cedure is “in control,” the results will fall within the established control limits. Further, the chart will disclose trends and cycles from assignable causes which can be corrected promptly. Chances of detecting small changes in the process average are improved when several values for a single con- trol point (an x chart) are used. As the sample statistical size increases, the chance that small changes in the average will not be detected is de- 286 creased. A sample size of n=4 usually is selected. The basic procedure of the control chart is to compare “within group” variability to “between group” variability. For a single analyst running a procedure, the “within group” may well represent one day’s output and the “between group” repre- sents between days or day-to-day variability. When several analysts or several instruments or labora- tories are involved, the selection of the subgroup unit is critical. Assignable causes of variation should show up as “between group” and not “with- in group” variability. Thus, if the differences be- tween analysts should provide assignable causes of variation, their results may not be lumped to- gether in a “within group” subgrouping. Application and Limitations In order for quality control to provide a means for separating the determinate from indeterminate sources of variation, the analytical method must clearly emphasize those details which should be controlled to minimize variability. A check list would include: Sampling procedures Preservation of the sample Aliquoting methods Dilution techniques Chemical or physical separations and puri- fications Instrumental procedures Calculation and reporting results. The next step to be considered is the applica- tion of control charts for evaluations and control of these unit operations. Decisions relative to the basis for construction of a chart are required: 1. Choose method of measurement 2. Select the objective a. Precision (Figure 22-4) or accuracy evaluation (Figure 22-9) NS NE UN- b. Observe test results, or the range of results c. Measurable quality characteristics (Fig- ure 22-4), (Figure 22-9) and (Figure 22-10) 3. Select the variable to be measured (from the check list above) Basis of subgroup, if used: a. Size A minimum subgroup size of n=4 is frequently recommended. The chance that small changes in the process aver- age remain undetected decreases as the statistical sample size increases. Frequency of subgroup sampling Changes are detected more quickly as the sampling frequency is increased. Control Limits Control limits (CL) can be calculated, but judgment must be exercised in deter- mining whether or not the values obtained satisfy criteria established for the method, i.e., does the deviation range fall within limits consistent with the solution or con- trol of the problem. After the mean (X) of the individual results (X), and the mean of the range (R) of the replicate re- 4. 110 \ LO J nimi om we mmm im elo so ie UPPER > CONTROL LIMIT $ o 100 a * n pratt LOWER 95 CONTROL LIMIT 90 - I T I I 5 10 5 20 CONSECUTIVE DAYS Figure 22-9. Recovery of Lead from Blood sult differences (R) have been calculated, Upper Control Limit (UCL) on then CL can be calculated from data estab- Range =D,R lished for this purpose (Table 22-4).° Lower Control Limit (LCL) on Grand Mean (X) =ZX/k Range =D,R CL’s on Mean=X =+ A, Where: k=number of subgroups A,, D, Range (R) =ZR/k, ord, o and D, are obtained from Table 22-4, R o — TECHNICIAN A oo — " B so4 " 340 = Sse : 30 < 2 na £ CONTROL 220 1—H LIMIT 10 ¢~ I 1 J F M 5 2 2 Figure 22-10. Lead in Urine Analysis — % Exceeding Threshold Limit (0.1 mg/Liter) on Weekly Basis 287 may be calculated directly from the data, or from the standard deviation (0) using factor d,. The lower control limit for R is zero when n =6. The calculated CL’s include approximately the en- tire data under “in control” conditions, and there- fore, are equivalent to = 3 o limits which are commonly used in place of the more laborious calculation. Warning limits (WL) set at = 2 o limits (95% ) of the normal distribution serve a very useful function in quality control (see Figure 22-4 and 22-9). The upper warning limit (UWL) can be calculated by: UWL=R+2 oy UWL=R + 2/3 (D,R) Where the subgrouping is n=2, UWL re- duces to UWL =2.51R. CONSTRUCTION OF CONTROL CHARTS Precision Control Charts The use of range (R) in place of standard deviation (o) is justified for limited sets of data n =10 since R is approximately as efficient and is easier to calculate. The average range (R) can be calculated from accumulated results, or from a known or selected o (d, 0). LCLr=0 when n =6. (LCL =lower control limit). The steps employed in the construction of a precision control chart for an automatic analyzer illustrate the technique (Table 22-5): 1. Calculate R for each set of side-by-side duplicate analyses of identical aliquots. 2. Calculate R from the sum of R values divided by the number (n) of sets of duplicates. 3. Calculate the upper control limit (UCLy) for the range: UCL;=D,R Since the analyses are in duplicates, D, = 3.27 (from Table 22-4). 4. Calculate the upper warning limit (UWL): UWL;=R +20 It =R + 2/3(D,R) = TABLE 22-4 FACTORS FOR COMPUTING CONTROL CHART LINES* Observations in Factor Factor Factor Factor Subgroup (n) A, d, D, D, 2.51R UCL = R ] UWL = - =. ; | 2 3 4 5 mesure ORDER OF RESULTS Permission granted, William D. Kelley, Acting Assistant Director, Division of Laboratories and Criteria Develop- ment, National Institute for Occupational Safety and Health. Figure 22-11. Precision Control Chart 288 2 1.88 1.13 327 0 3 1.02 169 258 0 4 0.73 2.06 228 0 5 058 233 212 O 6 048 253 200 O 7 042 270 192 0.08 8 0.37 2.85 1.86 0.14 *ASTM Manual on Quality of Materials, American Society of Testing and Materials, Philadelphia, 1951. TABLE 22-5 PRECISION (DUPLICATES) DATA Date Data Range (R) 9/69 # 825.1249 0.2 #16 25.0 24.5 0.5 #24 109 10.6 0.3 10/69 # 7126 12.4 0.2 #16 26.9 26.2 0.7 #24 4.7 5.1 0.4 2/70 #6 92 89 0.3 #12 13.2 13.1 0.1 #16 16.2 16.3 0.1 #22 88 8.8 0.0 4/70 # 6 149 149 0.0 #12 17.2 18.1 0.9 #18 21.9 22.2 0.3 5/70 # 6 348 32.6 2.2 #12 37.8 37.4 0.4 6/70 # 6 40.8 39.8 1.0 #10 46.0 43.5 2.5 #17 40.8 41.2 0.4 #24 38.1 36.1 2.0 7/70 # 6122 125 0.3 #12 25.4 26.9 1.5 #18 20.4 19.8 0.6 R=14.9/22 =0.68 UCL=3.27X0.68=2.2 UWL =2.51X0.68=1.7 (D, from Table 22-4) which corresponds to the 95% confidence limits. 5. Chart R, UWL; and UCL 0n an appropri- ate scale which will permit addition of new results as obtained as shown in Figure 22- 11 and Table 22-5. 6. Plot results (R) and take action on out-of- control points. ucL —ORDER _,. Permission granted, William D. Kelley, Acting Assistant Director, Division of Laboratories and Criteria Develop- i National Institute for Occupational Safety and ealth. Figure 22-12. Accuracy Control Chart ACCURACY CONTROL CHARTS — MEAN OR NOMINAL VALUE BASIS X charts simplify and render more exact the calculation of CL since the distribution of data which conforms to the normal curve can be com- pletely specified by X and ¢. Stepwise construc- tion of an accuracy control chart for the automatic analyzer based on duplicate sets of results obtained from consecutive analysis of knowns serves as an example (Table 22-6): 1. Calculate X for each duplicate set 2. Group the X values into a consistent ref- erence scale (in groups by orders of mag- nitude for the full range of known con- centrations). | 2 3 4 5 3. Calculate the UCL and lower control limit (LCL) by the equation: CL== A,R (A, from Table 22-4). 4. Calculate the Warning Limit (WL) by the equation: WL== 2/3 A,R 5S. Chart CL’s and WL’s on each side of the standard which is set at zero as shown in Figure 22-12 (“order” related to consecu- tive, or chronological order of the an- alyses) and Table 22-6. 6. Plot the difference between the nominal value and X and take action on points which fall outside of the control limits, CONTROL CHARTS FOR INDIVIDUAL RESULTS In many instances a rational basis for sub- grouping may not be available, or the analysis may be so infrequent as to require action on the basis of individual results. In such cases X charts are employed. However, the CLs must come from some subgrouping to obtain a measure of “within group” variability. This alternative has the advantage of displaying each result with re- spect to tolerance, or specification limits (Figures 22-4, 5, 9 and 13). The disadvantages must be recognized when considering this approach. 1. The chart does not respond to changes in the average. 2. Changes in dispersion are not detected un- less an R chart is included. TABLE 22-6 ACCURACY DATA Date Calibration Range Nominal (N) Values X N-X 9/69 10-400 ppm 100 ppm 22.9,21.5/ 22.2 -0.7 22.7,22.3 22.5 -0.4 1.7-69.7 scale 22.9 10/69 10-400 100 21.6, 21.3/ 21.5 0.0 1.5-67.6 21.5 2/70 10-400 100 23.6,24.1/ 23.9 —-0.6 1.4-62.5 24.5 4/70 10-400 100 25.8,26.5/ 26.2 +0.2 1.6-59.4 26.0 26.0, 26.7 26.4 +04 5/70 10-150 100 72.2,70.2/ 71.2 +1.2 6.3-83.0 70.0 6/70 10-150 100 71.0, 70.8/ 71.1 +0.1 71.0,71.3 71.2 +0.2 6.6-85.0 71.0 7/70 10-150 60 14.9, 14.7/ 14.8 —-0.2 15.1, 14.4 14.8 —-0.2 1.8-33.5 15.0 289 3.00 2.00 AIR ANALYSIS TLVC 1.00 o TML-B oO TEL-C Xx TEL-D + FURNACES 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 J .07 .08 .09 .10 110 120 130 URINE ANALYSIS Mg PB /L Figure 22-13. 3. The distribution of results must approxi- mate normal if the control limits remain valid. Additional refinements, variations and control charts for other variables will be found in standard texts. 11, 12 MOVING AVERAGES AND RANGES The X control chart is more efficient for dis- closing moderate changes in the average as the subgrouping size increases. A logical compro- mise between the X and X approach would be ap- plication of the moving average. For a given series of analyses, the moving average is plotted. Such a set of data is shown in Table 22-7. The moving range serves well as a measure of acceptable vari- ation when no rational basis for subgrouping is available or when results are infrequent or ex- pensive to gather. OTHER CONTROL CHARTS FOR VARIABLES Although the standard X and R control chart for variables is the most common, it does not al- ways do the best job. Several examples follow where other charts are more applicable. Variable Subgroup Size The standard X and R chart is applicable for a constant size subgroup of n=2,34,5. In some cases such a situation does not exist. Control limit 290 Relationship of Previous Monthly TLV Coefficient to Urinary Lead Excretion values must be calculated for each sample size. Plotting is done in the usual manner with the con- trol size limits drawn in for each subgroup de- pending on its size. R or ¢ Charts In some situations the dispersion is equal over a range of assay values. In this case, a control chart for either range or standard deviation is appropriate. When the dispersion is a function of concen- tration, control limits can be expressed in terms of a percentage of the mean. In practice such control limits would be given as in the example below: = 5 units/liter for 0-100 units/liter concentration =* 5% for >100 units/liter concentration An alternative procedure involves transforma- tion of the data.’* For example, logarithms would be the appropriate transformation. X and ¢ Charts If the subgroup size exceeds 10, the Range Chart becomes inefficient. The use of a o chart would then be appropriate. Where the cost of ob- taining the test data is high, the increase in effi- ciency using ¢ rather than R may be worthwhile. OTHER STATISTICAL TOOLS Rejection of Questionable Results The question whether or not to reject results which deviate greatly from X in a series of other- MOVING AVERAGE AND RANGE TABLE TABLE 22-7 (N=2) Sample Assay Sample Nos. Moving Moving No. Value Included Average Range STANDARD DEVIATION 1 17.09 Re — — 2 17.35 1-2 17.22 +0.26 3 17.40 2-3 17.38 +0.05 4 17.23 3-4 17.32 -0.17 5 17.00 4-5 17.12 -=0.23 6 16.94 5-6 16.97 =0.16 7 16.68 6-7 16.81 —0.26 8 17.11 7-8 16.90 +043 9 18.47 8-9 1779 +1.36 10 17.08 9-10 17.78 —1.39 11 17.08 10-11 17.08 0.00 12 16.92 11-12 17.00 -0.16 13 18.03 12-13 17.48 +1.11 14 16.81 13-14 17.42 —1.22 15 17.15 14-15 16.98 +0.34 16 17.34 15-16 17.25 +0.19 17 16.71 16-17 17.03 —0.63 18 17.28 17-18 17.00 +0.57 19 16.54 18-19 1691 —0.74 20 17.30 19-20 16.92 +0.76 26 - 24 - Figure 22-14. 120 1 160 wise normal (closely agreeing) results frequently arises. On a theoretical basis, no result should be rejected, as the one or more errors which render the entire series doubtful may be determinate er- rors that can be resolved. Tests which are known to involve mistakes, however, should not be re- ported exactly as analyzed. Mathematical basis for rejection of “outliers” from experimental data may be found in statistics text books.!* Correlated Variables — Regression Analysis A major objective in scientific investigations is the determination of the effect that one variable exerts on another. For example a quantity of sam- ple (x) is reacted with a reagent to produce a re- sult (y) The quantity x represents the indepen- dent variable over which the investigator can exert control. The dependent variable (y) is the direct re- sponse to changes made in x, and varies in a ran- dom fashion about the true value. If the relation- ship is linear, the equation for a straight line will describe the effect of changes in x on the response y: y=a+b x, in which a is the intercept with the y axis and b is the slope of the line (the change in y per unit change in x). In chemical analysis a is a measure of constant error arising from a color- imetric determination, trace impurity, blank, or other determinate source. The slope b may be controlled by reaction rate, equilibrium shift or the resolution of the method. The term “regression analysis” is applied to this statistical tool. A typical application is exhibited in Figure 22-14 which relates the concentration of lead in blood to the standard deviation of the method.* For this relationship, y=0.0022 + 0.054x. Addi- 1 1 1 1 1 3 1 L 1 1 1 200 240 280 320 360 400 po PD 291 Standard Deviation of Data from 10 Laboratories (Keenan et al) tional useful information can be obtained by cer- tain transformations and shortcuts, ® 1# 15 16 GRAPHIC ANALYSIS FOR CORRELATIONS Useful shortcuts may be elected to determine whether a significant relationship exists between x and y factors in the equation for a straight line (y=a+bX). The data are plotted on linear cross section paper and a straight line drawn by inspec- tion through the points with an equal number on each side or fitted by the least squares method. If the intercept a must be zero (a blank correc- tion may produce such a situation), the fitting is greatly simplified. Then on each side equidistant from this line draw parallel lines corresponding to the established deviation (0) of the analytical procedure, tally up the points falling inside of the band formed by the = o lines and calculate per- cent correlation (conformance= No, within band x 100/total points plotted). This technique is illustrated in Figure 22-13 which was used to relate urinary lead excretion to the airborne lead concentration obtained by personnel monitor sur- veys.’” In this case more than one TLV was in- volved, so the TLV coefficient (TLVC) transfor- mation was used for estimation of total lead ex- posure (TLVC = alkyl Pb found , Inorganic Pb found, TLV TLV : A plot of the monthly coefficients versus corre- sponding average urinary excretion disclosed only a 69% conformance, whereas a plot of the previ- ous month’s TLVC’s versus current month’s aver- age urinary excretion gave a 78% conformance. Furthermore, inspection of the chart indicated most of the “outliers” were contributed by the furnace crew. Deletion of this group raised con- formance to 86% for the balance of the opera- tion.!” Correlations above 80% are considered quite good [see also reference (16)]. Curvilinear functions can be accommodated, especially if a log normal’ function is involved and a plot of the data on semi-log paper yields a straight line.’® Log-Log paper also is available for plotting complex functions. = 44 — % ABNORMAL BLOOD SPECIMENS BARS-NO CYANOSIS II 40 — — 10 36 — — 9 32 — 8 28 — — 7 7 ee 20 — —5 16 — ) — 4 12 — fm 3 8 — — 2 4 — — 0 x irra 0 JJASONDJFMAMJUJASONDJFMAMJJUASONDJFMA I ! 1955 1956 (J. M. Wetherhold, A. L. Linch and R. C. Charsha. Amer. Ind. Hyg. Assoc. J. 20: 396, 1959) Figure 22-15. 292 Relation of Abnormal Blood Specimens to Cyanosis Incidents A combination of curvilinear and bar charts in some cases will reveal correlations not readily detected by mathematical processes. The data de- rived from an industrial cyanosis control program*® illustrate an application which revealed a rather significant relationship between abnormal blood specimens and the frequency of cyanosis cases on a long-term basis (Figure 22-15). In fact one trend line could be fitted to both variables, and the predicted ultimate improvement was attained in 1966 when abnormal blood specimens dropped below 2% and the cyanosis cases below 4% .%° Grouping data on a graph and approximating relationships by the quadrant sum test (rapid corner test for association) can provide useful results with a minimum expenditure of time.'® 2! In those cases where application of mathe- matical tools are tedious or completely impractical, a system of ranking is sometimes applicable to the restoration of order out of chaos. Again with reference to the cyanosis control program, a re- lationship between causative agent structure and biochemical potential for producing cyanosis and anemia was needed. Ten factors (categories) common to some degree for each of the 13 com- pounds under study had been recognized. The 13 compounds were ranked in each category in re- verse order of activity (No. 1 most, No. 13 least active) and the sum of the rankings obtained for each compound. These sums then were divided by the number of categories used in the total rank- ing to obtain the “score.” The scores were then arranged in increasing numerical order in colum- “nar form. The most potent cyanogenic and anemi- agenic compounds then appeared at the top of the table and the least at the bottom.*° CHI SQUARE TEST Control charts are a convenient tool for daily checking with reference standards, but the answers are not always as nearly quantitative as needed. Periodic checking of the accumulated daily refer- ence results to determine more rigorously whether all of the data belong to the same normal distribu- tion may become necessary. One approach to this question and to assign a probability to the answer is provided by the Chi Square (X?) test. The Chi Square distribution describes the probability distribution of the sums of the squares of independent variables that are normally or ap- proximately normally distributed. The general form of the expression provides a comparison of observed versus expected frequencies.” The Chi 9.40 9.20 | X 13 3 I" 2 9.00 | X X 2 10 14 5 _ Y 8.80 A x - g X S 5 a X 8.60 | 7 X X 6 8.40 | x 2 8.20 | a X S00 | 9.00 920 9.40 9.60 9.80 10.00 10.20 1040 1060 10.80 11.00 SAMPLE X (%K) Powell CH, Hosey AD (eds): The Industrial Environment — Its Evaluation and Control, 2nd Edition. Public Health Service Publication No. 614, 1965. Figure 22-16. Youden’s Graphical Technique 293 Square test is applied to variables which fall within the Poisson distribution. THE ANALYSIS OF VARIANCE (ANOVA) The analysis of variance is one of the most useful statistical tools. Variation in a set of re- sults may be analyzed in such a way as to disclose and evaluate the important sources of the varia- tion. For a detailed description of this technique consult standard statistics textbooks. YOUDEN’S GRAPHICAL TECHNIQUE! ® 2 Dr. W. J. Youden has devised an approach to test for determinate errors with a minimum of ef- fort on the part of the analyst. Two different test samples (X and Y) are pre- pared and distributed for analysis to as many in- dividuals or laboratories as possible. Each partici- pant is asked to perform only one determination on each sample (NOTE: It is important that the samples are relatively similar in concentration of the constituent being measured.) Each pair of laboratory results can then be plotted as a point on a graph (Figure 22-16). A vertical line is drawn through the average of all the results obtained on sample X; a hori- zontal line is drawn through the average of all the results obtained on sample Y. If the ratio of the bias to standard deviation is close to zero for the determinations submitted by the participants, then one would expect the distribution of the paired values (or points) to be close to equal among the four quadrants. The fact that the ma- jority of the points fall in the (+,+) and (—,—) quadrants indicates that the results have been influenced by some source of“bias. Furthermore, one can even learn something about a participant’s precision. If all participants had perfect precision (no indeterminate error), then all the paired points would fall on a 45° line passing through the origin. Consequently the distance from such a 45° line to each participant’s point provides an indication of that participant’s precision. INTRA-LABORATORY QUALITY CONTROL PROGRAM Responsibilities The attainment and maintenance of a quality control program in the laboratory is the direct responsibility of the laboratory manager or super- visor. The fundamental quality control techniques are based on: 1. Calibration to ensure accuracy 2. Duplication to ensure precision 3. Correlation of quantitatively related tests to confirm accuracy and continual scrutiny to maintain the integrity of the results re- ported. The individual technician can contribute sig- nificant assistance in this effort by his desire to deliver the best possible answers within the inher- ent limits of the equipment and procedure. Part of supervision’s responsibility is adequate instruction to provide the “man on the bench” with sufficient “know how” to apply the principles on a routine basis. 294 i The guidelines established by the American Industrial Hygiene Association for Accreditation of Industrial Hygiene Analytical Laboratories’? delineate the minimum requirements which must be satisfied in order to qualify for proficiency rec- ognition. Precision Quality Control In addition to the use of internal standards, recovery procedures and statistical evaluation of routine results, the laboratory should subscribe to a reference sample service to confirm precision and accuracy within acceptable limits. Apparatus should be calibrated directly or by comparison with National Bureau of Standards (NBS) certified equipment or its equivalent, reagents should meet or exceed ACS standards, calibration standards should be prepared from AR (analytical reagent) grade chemicals,>® and standardized with NBS standards if available. To illustrate, in a labora- tory engaged in an exposure control program based on biological monitoring by trace analysis of blood and urine for lead content, at least two calibration points, blanks and a recovery should be included in each batch analyzed by the dithi- zone procedure. In addition, the wavelength integ- rity and optical density response of the spectro- photometer should be checked and adjusted — if necessary by calibration with NBS cobalt acetate standard solution. Until the standard deviation for the analytical procedure has been established within acceptable limits, replicate determinations should be made on at least two samples in each batch (either aliquot each sample or take dupli- cate samples), and thereafter with a frequency sufficient to ensure continued operation within these limits. Control charts are probably the most widely recognized application of statistics. They provide “instant” quality control status when plotted daily, or at other intervals sufficiently short to disclose trends without undue oscillations from over-refine- ment of the data. Examples selected from a lead surveillance program illustrate the value of control charts. Figure 22-9 for analytical control is based on recoveries of known quantities of lead added to blood. From this chart and an analysis of the data itself, several conclusions may be drawn: 1. Background (“natural” lead) concentra- tions lay very close to the ultimate sensi- tivity of the method (35 = 5 ug). 2. The variability of the back-ground lead concentration exerts a relatively strong controlling effect on the recovery. 3. Although only a short period is covered, a downward trend is noticeable. 4. A control limit set at 98% = 5% prob- ably is more realistic. The same technique was applied to the evalu- ation of the quality of an exposure control pro- gram. A one year section from the control chart is presented in Figure 22-10. The graph provided several significant conclusions upon which action was initiated: 1. An alleged bias in the technicians per- formance was ruled out as each had about the same number of peaks and valleys dur- ing the period (each technician in turn an- alyzed all of the urine specimens for the entire week plotted). 2. Trend lines which were drawn in by in- spection disclosed a much closer correla- tion with production rate than with an al- leged seasonal (temperature) cycle. 3. The peaks in the short term oscillations were connected with particular rotating shift crews who engaged in “dirty” work habits that were corrected from time to time. 4. No correlation could be established with fixed station air analysis data. These examples are but two applications of a very extensive specialty within the field of statis- tics; therefore, the reader is referred to standard texts for additional information on refinements and procedures for extracting significant informa- tion from control charts.’ 2* On the basis of its raw simplicity, amount of information available for a minimum expenditure of time and effort, graphic presentation and the ease of comprehen- sion, the control chart cannot be over-recom- mended. Accuracy Quality Control A standard or well defined control sample should be analyzed periodically to confirm accur- acy of a procedure. The control chart technique is directly applicable to long-term evaluation of the reliability of the analyst as well as the accuracy of the procedure. To attain and maintain the high level of analytical integrity presented earlier in this chapter the three major sources of ‘“assign- able cause” errors must be reduced to a minimum level which is consistent with cost penalties and the objective of the study for which the analytical service is rendered: 1. Equipment errors can be reduced to toler- able limits by calibration with primary physical standards such as those supplied by the National Bureau of Standards. 2. Method errors can be controlled by precise standardization of reagents, use of cali- brated volumetric glassware and weights, refined manipulative techniques (personal errors), recognition and correction of per- sonal bias (color estimation), elimination of chemical interferences, and corrections for physical influences such as the effect of temperature and actinic light. 3. Personal errors other than inherent phys- ical visual acuity (color judgment) include consistent carelessness, lack of knowledge, calculation errors, use of contaminated or improper reagents, poor sampling tech- nique and use of poorly calibrated stan- dards and instruments. Interlaboratory Reference Systems Participation in interlaboratory studies whether by subscription from a certified labora- tory supplying such a service or from a voluntary program initiated by a group of laboratories in an attempt to improve analytical integrity’! is highly recommended. Evaluation of the analytical method as well as evaluation of the individual 295 laboratory’s performance can be derived by spe- cialized statistical methods applied to the data collected from such a study. However, inasmuch as most investigators will not be called upon to conduct or evaluate interlaboratory surveys, the reader is referred to the literature in the event such specialized information is needed. 2% 27 28 In the absence of such programs, the investigator, or laboratory supervisor, should make every effort to locate colleagues engaged in similar sampling and analytical activity and arrange exchange of standards, techniques, and samples to establish integrity and advance the art. SUMMARY Identification of the determinate sources of error of a procedure provides the information re- quired to reduce assignable error to a minimum level. The remaining (residual) indeterminate er- rors then determine the precision of analyses pro- duced by the procedure. Statistical techniques have been developed to estimate efficiently the precision. For a procedure to be accurate, the re- sults must be not only precise, but bias must be absent. Several approaches are available to elimi- nate bias both within the laboratory and between laboratories by collaborative testing. Quality con- trol programs based on appropriate control charts must be employed on a routine basis to assure ad- herence to established performance standards. The total analysis control program must include instru- mental control, procedural control and elimina- tion of personal errors. The use of replicate de- terminations, “spiked” sample techniques, refer- ence samples, standard samples and quality con- trol charts will provide assurance that the pro- cedure remains in control. The guidelines established by the American Industrial Hygiene Association for Accreditation of Industrial Hygiene Analytical Laboratories!? further summarizes in a succinct fashion the re- quirements for proficiency. Quality Control and Equipment Routine quality control procedures shall be an integral part of the laboratory procedures and functions. These shall include: 1. Routinely introduced samples of known content along with other samples for an- alyses. 2. Routine checking, calibrating, and main- taining in good working order of equip- ment and instruments. 3. Routine checking of procedures and re- agents. 4. Good housekeeping, cleanliness of work areas, and general orderliness. 5. Proficiency Testing — The following cri- teria shall be used in the proficiency test- ing of industrial hygiene analytical labor- atories accredited by the American Indus- trial Association. a) Reference Laboratories Five or more laboratories shall be des- ignated as reference laboratories by the American Industrial Hygiene As- sociation ‘based on the appraisal of competence of the laboratories by the Association. The reference laboratories may be judged competent: (1) in all industrial hygiene analyses or (2) specific industrial hygiene analyses. Proficiency samples shall be sent to desig- nated reference laboratories for analyses. These data will be used for grading analy- tical data received from laboratories seek- ing or maintaining accreditation by the Association. b) Method of Grading Laboratories shall be graded on the basis of their ability to perform an- alyses within specified limits deter- mined by the reference laboratories. Satisfactory performance shall be the reporting of results within two stan- dard deviations of the mean value ob- tained by the reference laboratories. Exception shall be made in cases where too few laboratories are in exis- tence, a new procedure has not been adequately tested, or the range in vari- ation from reference laboratories is too great to apply this method of grading. c¢) Number and Suitability of Samples Samples shall be either environmental materials, biological fluids, or tissues or synthetic mixtures approximating these. They shall be packaged, as nearly possible, in an identical manner and the containers will be chosen so as to avoid exchange of the test ma- terial between the samples and con- tainer. Samples shall be analyzed by each participating laboratory in suffi- cient number and at proper intervals for the results to form an adequate basis for accreditation in the opinion of ATHA. d) Frequency of Samples Samples shall be submitted to each lab- oratory quarterly. e) Satisfactory Performance Satisfactory performance is a consid- ered scientific judgment and is not to be judged exclusively by any inflexible set of criteria. The judgment shall be made, however, on the basis of the re- sults submitted by the laboratories and a statistical estimation of whether the results obtained are probably repre- sentative of analytical competence con- sidering inherent variables in the method. 6. Records The industrial hygiene analytical labora- tory shall maintain records and files proper and adequate for the services given. These shall include: a) The proper identification and num- bering of incoming samples. b) An adequate and systematic number- ing system relating laboratory samples to incoming samples. 296 ¢) An adequate record system on internal logistics of each sample including date of incoming sample, analysis and pro- cedures, and reporting of data. d) A records checking system of the cali- bration and standardization of equip- ment and of internal control samples. The program includes: . Nature, extent of use and results of routine interlaboratory quality control procedures. 2. Procedures for routine calibration and maintenance of reagents,” equipment and instruments. 3. Nature, extent and results of routine checking and evaluation of analytical pro- cedures. Intra- and inter-laboratory eval- uations of precision and accuracy. References 1. 10. 11. 12. KELLEY, W. D. Statistical Method — Evaluation and Quality Control for the Laboratory. Training Course Manual in Computational Analysis. U.S. Dept. of Health, Education and Welfare Public Health Service (1968). SHEWHART, W. A. Economic Control of Quality of Manufactured Products. Bell Telephone Labora- tories (1931). . LINCH, A. L., H. V. PFAFF. “Carbon Monoxide — Evaluation of Exposure by Personnel Monitor Surveys.” Am. Ind. Hyg. Assoc. J. 32 (Nov., 1971). AMERICAN CHEMICAL SOCIETY. “Guide for Measures of Precision and Accuracy.” Anal. Chem. 35: 2262 (1963). . AMERICAN SOCIETY FOR TESTING MATERI- ALS. ASTM Manual on Quality Control of Ma- terials — Special Technical Publication 15-C. Phil- adelphia, Pa. (1951). YOUDEN, W. J. Statistical Methods for Chemists. John Wiley and Sons, New York, N.Y. (1951). KITAGAWA, T. Carbon Monoxide Detector Tube No. 100. National Environmental Instruments, Inc., P.O. Box 590, Fall River, Mass. (1971). KATZ, M. (Editor) Manual of Methods for Air Sampling and Analysis — Part 1. The Intersociety Committee (1972). GRIM, K., A. L. LINCH. “Recent Isocyanate-In- Air Analysis Studies.” Am. Ind. Hyg. Assoc. J. 25: 285 (1964). AMERICAN SOCIETY FOR TESTING AND MA- TERIALS. Proposed Procedure for Determination of Precision of Committee D-19 Methods — Man- ual on Industrial Water and Industrial Wastewater. 2nd edition. 1016 Race Street, Philadelphia, Pa. 19103 (1966 printing). KEPPLER, J. F., M. E. MAXFIELD, W. D. MOSS, G. TIETJEN and A. L. LINCH. “Interlaboratory Evaluation of the Reliability of Blood Lead An- alysis.” Am. Ind. Hyg. Assoc. J. 31:412, 210 Had- don Ave., Westmont, New Jersey 08108 (1970). CRALLEY, L. J.,, C. M. BERRY, E. D. PALMES, C. F. REINHARDT, and T. L. SHIPMAN. “Guide- lines for Accreditation of Industrial Hygiene Ana- lytical Laboratories.” AIHA J. 31:335, 210 Had- don Ave., Westmont, New Jersey (1970). . COWDEN, D. J. Statistical Methods in Quality Con- trol. Prentice Hall, Inc., Englewood Cliffs, New Jersey (1957). BAUER, E. J. A Statistical Manual for Chemists. 2 edition. Academic Press, New York, N.Y. 1971). . TARAS, M. J,, A. E. GREENBERG, R. D. HOAK, and M. C. RAND. Standard Methods for the Ex- amination of Water and Wastewater. 13th edition. American Public Health Assoc., Washington, D. C. (1971). 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. HINCHEN, J. D. Practical Statistics for Chemical Research. Methuen and Co., Ltd.,, London (1969). LINCH, A. L,, E. G. WIEST and M. D. CARTER. “Evaluation of Tetraalkyl Lead Exposure by Person- nel Monitor Surveys.” Am. Ind. Hyg. Assoc. J. qa 210 Haddon Ave., Westmont, New Jersey 1970). LINCH, A. L. and M. CORN. “The Standard Midget Impinger-Design Improvement and Minia- turization.” Am. Ind. Hyg. Assoc. J. 26:601, 210 Haddon Ave., Wesmont, N.J. (1965). WETHERHOLD, J. M., A. L. LINCH and R. C. CHARSHA. “Hemoglobin Analysis for Aromatic Nitro and Amino Compound Exposure Control.” Am. Ind. Hyg. Assoc. J. 20:396, 210 Haddon Ave., Westmont, N. J. (1959). STEERE, N. V. (editor) Handbook of Laboratory Safety. 2nd edition, The Chemical Rubber Co., Cleveland, Ohio (1971). WILCOXON, F. Some Rapid Approximate Statis- tical Procedures. Insecticide and Fungicide Section — American Cyanamid Co., Agricultural Chemicals Division, New York, N.Y. (1949). MAXWELL, A. E. Analyzing Qualitative Data. John wie & Sons, Inc., Chap. 1,.pp. 11-37, New York 1964). DUNCAN, A. J. Quality Control and Industrial Sta- tistics. 3rd edition, R. D. Irwin, Inc.,, Homewood, Illinois (1965). YOUDEN, W. V. “The Sample, the Procedure, and the Laboratory.” Anal. Chem. 32:23A-37A, 1155 16th St. NW, Washington, D. C. (1960). AMERICAN CHEMICAL SOCIETY. Reagent Chemicals. 4th edition, American Chemical Society 297 26. 27. 28. Publications, Washington, D. C. (1968). AMERICAN SOCIETY FOR TESTING AND MATERIALS. ASTM Manual for Conducting an Interlaboratory Study of a Test Method. Technical Publication No. 335. Available from University Microfilms, Ann Arbor, Michigan (1963). WEIL, C. S. “Critique of Laboratory Evaluation of the Reliability of Blood-Lead Analyses.” Am. Ind. Hyg. Assoc. J. 32:304, 210 Haddon Ave. West- mont, N.J. (1971). SNEE, R. D. and P. E. SMITH. Statistical Analysis of Interlaboratory Studies. Paper prepared for pres- entation to the Am. Ind. Hyg. Conference in San Francisco, Calif. (May 15-19, 1971). Preferred Reading In addition to references 6, 8, 9, 10, 14, 15, the fol- lowing periodicals are recommended: American Industrial Hygiene Association Journal Journal of the Air Pollution Control Association Analytical Chemistry (American Chemical Society) Environmental Science & Technology (American Chemical Society) Pollution Engineering (Technical Publishing Co.) Air Pollution Manual — 2nd edition — American Industrial Hygiene Association, 1971. NELSON, G. O. Controlled Atmosphere — Princi- ples and Techniques (recommended for calibration reference) Ann Arbor Science Publishers, Inc., Ann Arbor, Mich. 1971. LEITHE, W. The Analysis of Air Pollutants (Trans- lated from original German by R. Kondor) Ann Ar- bor — Humphrey Science Publishers, Ann Arbor, Mich. 1970. CHAPTER 23 PHYSICS OF SOUND Paul L. Michael, Ph.D. INTRODUCTION The sensation of sound is produced when pres- sure variations having a certain range of charac- teristics reach a responsive ear. These pressure variations may be produced by any object that vibrates in a conducting medium with the proper cycle rate, or frequency, and amplitude. Sound may consist of a single frequency and amplitude; however, common noise spectra have many dif- ferent frequency components with many different amplitudes. This chapter is concerned primarily with those practical aspects of sound that are related to its characteristics in a given space and to its propaga- tion through specified media. Basic terminology, noise measurement, and practical calculation pro- cedures such as combining sound levels are em- phasized. BASIC TERMINOLOGY Amplitude: The amplitude of sound may be described in terms of either the quantity of sound produced at a given location away from the source or the overall ability of the source to emit sound. The amount of sound at a location away from the source is generally described by the sound pres- sure or sound intensity, while the ability of the source to emit sound is described by the sound power of the source. Free Field: A free field exists in a homogeneous, isotropic medium free from boundaries. In a free field, sound radiated from a source can be measured accurately without influence from the test space. True free-field conditions are rarely found except in expensive anechoic (echo-free) test chambers; however, approximate free-field conditions may be found in any homogeneous space where re- flecting surfaces are at great distances from the measuring location as compared to the wave- lengths of the sound being measured. Frequency (f): The frequency of sound describes the rate at which complete cycles of high and low pressure regions are produced by the sound source. The unit of frequency is the cycle per second (cps) which is also called the hertz (Hz). The frequency range of the human ear is highly dependent upon the individual and the sound level, but a normal- hearing young ear will have a range of approxi- mately 20 to 20,000 cps at moderate sound levels. The frequency of a propagated sound wave heard by a listener will be the same as the frequency of the vibrating source if the distance between the 299 source and the listener remains constant; however, the frequency detected by a listener will increase or decrease as the distance from the source is de- creasing or increasing (Doppler effect). Loudness: The loudness of a sound is an observer’s im- pression of its amplitude, an impression also de- pendent on the characteristics of the ear. Noise and Sound: The terms noise and sound are often used interchangeably, but generally, sound is descrip- tive of useful communication or pleasant sounds, such as music, while noise is used to describe dis- cord or unwanted sound. Period (T): The period is the time required for one cycle of pressure change to take place; hence, it is the re- ciprocal of the frequency. The period is measured in seconds. Pitch: Pitch is used as a measure of auditory sensa- tion that depends primarily upon frequency but also upon the pressure and waveform of the sound stimulus. Pure Tone: A pure tone refers to a sound wave with a single simple sinusoidal change of level with time. Random Noise: Random noise is made up of many frequency components whose instantaneous amplitudes occur randomly as a function of time. Resonance: Resonance of a system exists when any change in the frequency of forced oscillation causes a de- crease in the response of the system. Reverberation: Reverberation occurs when sound persists after direct reception of the sound has stopped. The reverberation characteristic of a space is speci- fied by the “reverberation time” which is the time required after the source has stopped radiating sound for the rms sound pressure to decrease 60 dB from its steady-state level. Root-Mean-Square (rms) Sound Pressure: The root-mean-square (rms) value of a changing quantity, such as sound pressure, is the square root of the mean of the squares of the instantaneous values of the quantity. Sound Intensity (I): The sound intensity at a specific location is the average rate at which sound energy is trans- mitted through a unit area normal to the direction of sound propagation. The units used for sound intensity are joules per square meter per second. Sound intensity is also expressed in terms of a level (sound intensity level L;) in decibels refer- enced to 107? watts per square meter. Sound Power (P): The sound power of a source is the total sound energy radiated by the source per unit time. Sound power is normally expressed in terms of watts. Sound power is also expressed in terms of a level (sound power level Lp) in decibels referenced to 10722 watts. Sound Pressure (p): Sound pressure normally refers to the rms value of the pressure changes above and below atmospheric pressure when used to measure steady-state noise. Short term or impulse-type noises are described by peak pressure values. The units used to describe sound pressures are newtons per square meter (N/m?®), dynes per square centi- meter (d/cm*), or microbars. Sound pressure is also described in terms of a level (sound pressure level L,) in decibels referenced to 2 X 10™* new- tons per square meter. Velocity (c): The speed at which the regions of sound- producing pressure changes move away from the sound source is called the velocity of propagation. Sound velocity varies directly with the square root of the density and inversely with the compressi- bility of the transmitting medium as well as with other factors; however, for practical purposes, the velocity of sound is constant in a given medium over the normal range of conditions. For example, the velocity of sound is approximately 1130 ft/sec in air, 4700 ft/sec in water, 13,000 ft/sec in wood, and 16,500 ft/sec in steel. Wavelength (1): The distance required for one complete pres- sure cycle to be completed is called one wave- length. The wavelength (A), a very useful tool in noise control work, may be calculated from known values of frequency (f) and velocity (c): (1) White Noise: A=c/f White noise has an essentially random spec- trum with an equal-energy-per-unit frequency bandwidth over a specified frequency band. NOISE MEASUREMENT Steady-state sounds, ones that have relatively constant levels over time, are usually measured with instruments having root-mean-square (rms) characteristics. The time interval over which sim- ple periodic sound pressure patterns must be measured is equal to an integral number of periods of that sound pattern, or the interval must be long compared to a period. If the sound pressures do not follow a simple periodic pattern, the interval must be long enough to make the measured value essentially independent of small changes in the interval length. In all cases, there must be more than 10 peaks per second for the noise to be con- sidered to be steady-state for measurement pur- poses. Single prominent peak pressures which may occur over a very short period of time, and peak pressures that are repeated no more than 2 per 300 second, cannot be measured by conventional rms- type instruments because the peaks are not re- peated often enough for long-time integrations to be meaningful. These single pressure peaks are normally measured in terms of the maximum in- stantaneous level that occurs during a specified time interval. Just as rms measuring instruments cannot be used to measure single or widely spaced peak pres- sures, peak measuring instruments cannot be used to measure sustained noises unless the waveform is known to be sinusoidal or is otherwise predict- able. In most cases, the relationship of the peak reading to the rms reading of common noises with complex waveforms cannot be established in a practical way. Peak pressure value of a sinusoidal waveform is about 3 dB greater than the rms value of that signal; however, as the waveform becomes more complex the differences may exceed 25 dB for common noises. Noises with peak pressures occurring at rates between 2 and 10 peaks per second are difficult to measure in that they cannot be clearly defined as peak- or sustained-type noises. If the waveforms of the pressure peaks are complex and repeat be- tween 2 and 10 times per second, an oscilloscope should be used to determine the pressure or energy contribution of the noise. The Decibel (dB) The range of sound pressures commonly en- countered is very wide. For example, sound pres- sures well above the pain threshold (about 20 newtons per square meter, N/m?) are found in many work areas, while pressures down to the threshold of hearing (about 0.00002 N/m?) are also of wide interest. This range of more than 10° N/m? cannot be scaled linearly with a practical instrument because such a scale might be many miles in length in order to obtain the desired accuracy at various pressure levels. In order to cover this very wide range of sound pressures with a reasonable number of scale divisions and to pro- vide a means to obtain the required measurement accuracy at extreme pressure levels, the logarith- mic decibel (dB) scale was selected. By defini- tion, the dB is a dimensionless unit related to the logarithm of the ratio of a measured quantity to a reference quantity. The dB is commonly used to describe levels of acoustic intensity, acoustic power, hearing thresholds, electric voltage, elec- tric current, electric power, etc., as well as sound- pressure levels; thus, it has no meaning unless a specific reference quantity is specified. Sound Pressure and Sound-Pressure Level Most sound-measuring instruments are cali- brated to provide a reading of root-mean-square (rms) sound pressures on a logarithmic scale in decibels. The reading taken from an instrument is called a sound-pressure level (L,). The term “level” is used because the pressure measured is at a level above a given pressure reference. For sound measurements in air, 0.00002 N/m?* com- monly serves as the reference sound pressure. This reference is an arbitrary pressure chosen many years ago because it was thought to approximate the ‘normal threshold of young human hearing at 1000 Hz. The mathematical form of the L, is written as: L,=20 log > dB , (2) where p is the measured rms sound pressure, p, SOUND PRESSURE LEVEL IN dB RE 0.00002 N/m? 120 PNEUMATIC CHIPPER (at 5 ft.) Ho TEXTILE LOOM 100 NEWSPAPER PRESS 90 DIESEL TRUCK 40 mph (at 50 ft) 80 70 PASSENGER CAR 50 mph (at SO ft.) CONVERSATION (at 3 ft.) 60 50 QUIET ROOM 40 30 20 10 0 Figure 23-1. Sound Pressure in N/m? Figure 23-1 shows the relationship between sound pressure in N/m? and L, in dB, and illus- trates the advantage of using the dB scale rather than the wide range of direct pressure measure- ments. It is of interest to note that any pressure range over which the pressure is doubled is equiva- lent to six decibels whether at high or low levels. For example, a range of 0.00002 to 0.00004 N/m?, which might be found in hearing measure- is the reference sound pressure, and the logarithm (log) is to the base 10. Thus, L, should be writ- ten in terms of decibels referenced to a specified pressure level. For example, in air, the notation for L, is commonly abbreviated as “dB re 0.00002 N/m2.” SOUND PRESSURE N/m2 20 10 TEENAGE ROCK-N-ROLL BAND 5 2 I POWER LAWN MOWER (at operator's ear) 0.5 MILLING MACHINE (at 4 1) 0.2 GARBAGE DISPOSAL (at 3 ft) 0.1 VACUUM CLEANER 0.05 0.02 AIR CONDITIONING WINDOW UNIT (at 25 ft.) 0.0! 0.005 0.002 0.001 0.0005 0.0002 0.0001 0.00005 0.00002 301 Relationship between A-Weighted Sound-Pressure Level in Decibels (dB) and ments, and a range of 10 to 20 N/m?, which might be found in hearing conservation programs, are both ranges of six decibels. *An equivalent reference 0.0002 dynes per square centimeter is often used in older literature. The microbar is also used in older literature inter- changeably with the dyne per square centimeter. The L, referenced to 0.00002 N/m? may be written in the form: L,=20 log (p/0.00002) =20 lop p—log 0.00002 =20 log p— (log 2 —log 10°) =20logp—(0.3-5) =20 (logp+4.7) =20log p+94 re 0.00002 N/m? . (3) Sound Intensity and Sound-Intensity Level Sound intensity (I) at any specified location may be defined as the average acoustic energy per unit time passing through a unit area that is nor- mal to the direction of propagation. For a spheri- cal or free-progressive sound wave, the intensity may be expressed by =P I=2. 4) where p is the rms sound pressure, p is the density of the medium, and c is the speed of sound in the medium. It is obvious from this definition that sound intensity describes, in part, characteristics of the sound in the medium, but does not directly describe the sound source itself. Sound-intensity units, like sound-pressure units, cover a wide range, and it is often desirable to use dB levels to compress the measuring scale. To be consistent with Equations (2) and (4), intensity level (L;) is defined as Li=10 log 1 dB (5) where 1 is the measured intensity at some given distance from the source and I, is a reference intensity. The reference intensity commonly used is 107% watts/m?. In air, this reference closely corresponds to the reference pressure 0.00002 N/m? used for sound-pressure levels. Sound Power and Sound-Power Level Sound power (P) is used to describe the sound source in terms of the amount of acoustic energy that is produced per unit time. Sound power may be related to the average sound intensity produced in free-field conditions at a distance r from a point source by P= Love 47r? ’ (6) where I,.; is the average intensity at a distance r from a sound source whose acoustic power is P. The quantity 4=r? is the area of a sphere surround- ing the source over which the intensity is averaged. It is obvious from Equation (6) that the intensity will decrease with the square of the distance from the source; hence, the well-known inverse-square law. Power units are often described in terms of decibel levels because of the wide range of powers covered in practical applications. Power level Lp is defined by Le=101log . (7) where P is the power of the source, and P, is the reference power. The arbitrarily chosen reference power commonly used is 10™'? watt. Figure 23-2 shows the relationship between sound power in watts and sound-power level in dB re 1072 watt. SOUND POWER LEVEL, SOUND POWER dB RE 10-12 WATT IN WATTS 170 —— 100,000 160 —— 10,000 150 —— 1000 140 —— 100 130 —+— 10 120 + | Ho —— 107" 100 —— 1072 90 —— 1073 80 —— 1074 70 —— 107% 60 —— 10°¢ 50 —+— 1077 40 —+— 1078 30 —4+— 10°? 20 —+— 107° 10 =— 10°" 0 —— 0712 TURBOJET ENGINE COMPRESSOR CONVERSATION | Figure 23-2. Relationship between Sound Power Level in Decibels (dB) and Sound Power in Watts Relationship of Sound Power, Sound Intensity, and Sound Pressure Many noise-control problems require a prac- tical knowledge of the relationship between pres- sure, intensity, and power. An example would be the prediction of sound-pressure levels that would be produced around a proposed machine location from the sound-power level provided for the ma- chine. Example: Predict the sound-pressure level that would be produced at a distance of 100 feet from a pneumatic chipping hammer. The manufacturer of the chipping hammer states that the hammer has an acoustic power out- put of 1.0 watt. From Equations (4) and (6) in free field for an omnidirectional source: 2 2 P=1I fpr =P AVE AT (8) pC where Ppc pr. ©) If P is given in watts, r in feet, and p in N/m? then, with standard conditions, Equation (9) may be rewritten as 3.5pX 102 Sute® |r and, for this example, =| EE ) Pave = 100): 0.187 N/m The sound-pressure level may be determined from Equation (2) to be: 302 0.187 £ 0.00002 Noise levels in locations that are reverberant can be expected to be somewhat higher than predicted because of the sound reflected back to the point of measurement. COMBINING SOUND LEVELS It may be necessary to combine sound-pres- sure levels (decibels) during hearing conservation or noise-control procedures. For example, it may be necessary to predict the overall levels in an area that will result from existing levels being combined with those of a new machine that is to be installed. The combination of levels in various frequency bands to obtain overall or weighted overall sound- pressure levels is another example, Sound-pressure levels cannot be added arith- metically because addition of these logarithmic quantities constitutes multiplication of pressure ra- tios. To add sound-pressure levels, the corre- sponding sound pressures must be determined and added with respect to existing phase relationships. For the most part, industrial noise is broad- band with nearly random phase relationships. Sound-pressure levels of random noises can be added by converting the levels to pressure, then Octave Band Center Frequency (Hz) Sound-Pressure Level (dB) L,=201lo =79.4 dB re 0.00002 N/m?. A good procedure for adding a series of dB values is to begin with the highest levels so that calculations may be stopped when lower values are reached which do not add significantly to the total. In this example, the levels of 100 and 97 have a difference of 3 that corresponds with L,(3)=1.8 in Table 23-1. Thus, 100 dB+97 dB=100+1.8=101.8 dB. Combining 101.8 and 95, the next higher level, gives 101.8 +0.8 =102.6 dB which is the total of the first three bands. This procedure is continued with one band at a time until the overall sound-pressure level is found to be about 104 dB. Octave Band Center Frequency .........._.......... 31.5 63 (Hz) Sound Pressure Level oe 45.8 61.9 (A-Weighted) (dB) These octave band levels with A-frequency weight- ing can be added by the procedure described above to obtain the resultant A-weighted level which is about 103 dBA. A large majority of industrial noises have ran- dom frequency characteristics and may be com- bined as described in the above paragraphs. How- ever, there are a few cases of noises with pitched or major pure-tone components where these calcu- lations will not hold, and phase relationships must 125 77.8 85.4 91.7 303 to intensity units which may be added arithme- tically, and reconverting. the resultant intensity to pressure and finally to sound-pressure levels in dB. Equations (2) and (4) can be used in free-field conditions for this purpose. A more convenient way to add the sound-pres- sure levels of two separate random noise sources is to use Table 23-1. To add one random noise level L,(1), measured at a point to another, L,(2), measured by itself at the same point, the numerical difference between the levels, L,(2) — L,(1), is used in Table I to find the corresponding value of L,(3) which, in turn, is added arithme- tically to the larger of L,(1) or L,(2) to obtain the resultant of L,(1) +L, (2). If more than two are to be added, the resultant of the first two must be added to the third, the resultant of the three sources to the fourth, etc., until all levels have been added, or until the addition of smaller values do not add significantly to the total. The overall sound-pressure level produced by a random-noise source can be calculated by adding the sound-pressure levels measured in octave bands shown in the follow- ing table: Example: 31.5 63 125 250 500 1000 2000 4000 8000 94 94 95 100 97 90 88 The overall sound-pressure level calculated in the above example corresponds to the value that would be found by reading a sound level meter at this location with the frequency weighting set so that each frequency in the spectrum is weighted equally. Common names given to this frequency weighting are flat, linear, 20 kc, and overall, The corresponding A-weighted sound-pressure level (dBA)* found in many noise regulations may also be calculated from octave band values such as those in the above example if the adjust- ments given in Table 23-2 are first applied. For example the octave band levels with A-weighting corresponding to the above example would be: 250 500 1000 2000 4000 8000 100 98.2 91.0 86.9 be considered. In areas where pitched noises are present, standing waves will often be recognized by rapidly varying sound-pressure levels over short distances. It is not practical to try to predict levels in areas where standing waves are present. *The A-weighted frequency weighting approxi- mates the ear’s response characteristics for low level sound, below about 55 dB re 0.00002 N/m?, TABLE 23-1 Table for Combining Decibel Levels of Noises with Random Frequency Characteristics Sum (Lg) of dB Levels L, and L, Numerical L,: Amount to Difference = be Added to Between Levels the Higher of L,andL, LiorL, 0.0to 0.1 3.0 02to 0.3 2.9 04to 0.5 2.8 0.6to 0.7 2.7 0.8to 0.9 2.6 1.0to 1.2 2.5 . 13to 1.4 2.4 Step 1: Determine 15t0 1.6 23 the difference 17to 1.9 22 between the two 20t0 2.1 2.1 levels to be 22t0 2.4 2.0 added (L, and 2.5t0 2.7 1.9 L.). 28to 3.0 1.8 Step 2: Find the 31to 33 1.7 number (L,) 34to 3.6 1.6 corresponding 37t0 4.0 1.5 to this difference 41to 4.3 1.4 in the Table. 4410 4.7 1.3 Step 3: Add the 48 to 5.1 1.2 number (L,) to S21 36 11 the highest of 57to 6.1 1.0 L, and L, to 6.2to 6.6 0.9 obtain the 6.7t0 7.2 0.8 resultant level 73t0 7.9 0.7 Lr=(L, or L,) 8.0to 8.6 0.6 +L, 8.7to 9.6 0.5 ’ 9.7 to 10.7 0.4 10.8 to 12.2 0.3 12.3 to 14.5 0.2 14.6 to 19.3 0.1 19.4t0 = 0.0 When the sound-pressure levels of two pitched sources are added, it might be assumed that the resultant sound-pressure level L,,(R) will be less, as often as it is greater, than the level of a single source; however, in almost all cases the resultant L,(R) is greater than either single source. The reason for this may be seen if two pure-tone sources are added at several specified phase dif- ferences (see Figure 23-3). At zero phase dif- ference, the resultant of two like pure-tone sources is 6 dB greater than either single level. At a phase difference of 90°, the resultant is 3 dB greater than either level. Between 90° and O°, the re- sultant is somewhere between 3 and 6 dB greater than either level. At a phase difference of 120°, the resultant is equal to the individual levels; and 304 TABLE 23-2 A-Frequency Weighting Adjustments f(Hz) Correction 25 —44.7 3 heresies —-394 40 —346 50 -30.2 B83. iv ei ies —26.2 80 —-22.5 100 -19.1 138 icin —16.1 160 -13.4 200 —109 250 ee, — 8.6 315 - 6.6 400 — 48 500 ... eatin - 32 630 - 19 800 —- 0.8 1000 .......ciinn.... 0.0 1250 + 0.6 1600 + 1.0 2000... + 1.2 2500 + 1.3 3150 + 1.2 4000 ................ + 1.0 5000 + 0.5 6300 - 0.1 8000 ................ - 1.1 10000 - 25 12500 — 43 16000 ................ —- 6.6 20000 —- 93 between 120° and 90°, the resultant is between 0 and 3 dB greater than either level. At 180°, there is complete cancellation of sound. Obviously, the resultant L,(R) is greater than the individual levels for all phase differences from O° to 120°, but less than individual levels for phase differences from 120° and 180° — a factor of 2:1. Also, most pitched tones are not single tones but com- binations thereof: thus, almost all points in the noise fields will have pressure levels exceeding the individual levels. FREQUENCY ANALYSES General purpose sound-measuring instruments are normally equipped with three frequency- weighting networks, A, B, and C,* that can be used to adjust the frequency response of the instru- ment. These three frequency weightings shown in Figure 23-4 were chosen because: 1) they approx- imate the ear’s response characteristics at different sound levels, and 2) they can be easily produced with a few common electronic components. Also 0° 90° 180° 270° 360° Pr Pr T T T P + Pz _— & z= X > A Q a H . 4 N PHASE a X = a x ~~ = 2 > Oo a (a) O° PHASE DIFFERENCE ,Pr=2P (Pr=P+6dB) Pr T Pr P —— w a > 7] 0 x PHASE a 2 = Oo n (b) 90° PHASE DIFFERENCE, Pr=1.4P (Pr=P+ 3dB) RPr w 7 a a o 2 S oO Nn (c) 120° PHASE DIFFERENCE, Pr=P (Pr=P +0dB) RA Py W P mT 2 4 BS wn / \ 0 / NM & Pr % > a a 2 S oO Nn “er (d) 180° PHASE DIFFERENCE , Pr=0 Figure 23-3. Combinations of Two Pure Tone Noises (p, and p,) Phase Differences 305 FLAT A 0 — -5 T a 2-10 + 8s T Q ELECTRICAL FREQUENCY RESPONSE 0-204 FOR THE ANSI WEIGHTING i CHARACTERISTICS w 25 = = - « 30+ w © -35+ “40+ 45 + 20 50 100 200 500 1000 2000 5000 10,000 FREQUENCY (cps) - Figure 23-4. Frequency-Response Characteristics for Sound Level Meters (4) shown in Figure 23-4 is a linear, overall, or flat response that weights all frequencies equally. The A-frequency weighting approximates the ear’s response for low-level sound, below about 55 dB re 0.00002 N/m?2. The B-frequency weight- ing is intended to approximate the ear’s response for levels between 55 and 85 dB, and the C-fre- quency weighting corresponds to the ear’s response for levels above 85 dB, In use, the frequency distribution of noise energy can be approximated by comparing the levels measured with each of the frequency weight- ings. For example, if the A- and C- weighted noise levels are approximately equal, it can be reasoned that most of the noise energy is above 1000 Hz because this is the only position of the spectrum where the weightings are similar. On the other hand, if there is a large difference be- tween these readings, most of the energy will be found below 1000 Hz. In many cases, such as in noise control pro- cedures, the information supplied by the A, B, and C frequency weightings do not provide enough resolution of frequency distribution of noise en- ergy. Hence, more detailed analyses are needed from analyzers having bandwidths ranging from octaves to only a few cycles in width. Frequency Bandwidths The most common frequency bandwidth used 306 for industrial noise measurements is the octave band. A frequency band is said to be an octave in width when its upper band-edge frequency f, is twice the lower band-edge frequency f,: f,=2f, (10) Octave bands are commonly used for measure- ments directly related to the effects of noise on the ear and for some noise-control work because they provide the maximum amount of information in a reasonable number of measurements. When more specific characteristics of a noise source are required, such as might be the case for pinpointing a particular noise source in a back- ground of other sources, it is necessary to use nar- rower frequency bandwidths than octave bands. Half-octave, third-octave, and narrower bands are used for these purposes. A half-octave bandwidth is defined as a band whose upper band-edge fre- quency f, is the square root of 2 times the lower band-edge frequency f;: f,= V2 1, (11) A third-octave bandwidth is defined as a band whose upper band-edge frequency f, is the cube root of 2 times the lower band-edge frequency f;: f= W2f, (12) The center frequency f,, of any of these bands is the square root of the product of the high and low band-edge frequencies (geometric mean): fu= YTL.f, (13) It should be noted that the upper and lower band-edge frequencies describing a frequency band do not imply abrupt cut-offs at these frequen- cies. These band-edge frequencies are convention- ally used as the 3-dB-down points of gradually sloping curves that meet the American Standard Specification for Octave, Half-Octave, and Third- Octave Band Filter Sets, S1.11-1966.° Comparing Levels Having Different Bandwidths Noise-measurement data (rms) taken with analyzers of a given bandwidth may be converted to another given bandwidth if the frequency range covered has a continuous spectrum with no prom- inent changes in level. The conversion may be made in terms of sound-pressure levels by L,(A) =L,(B) — 10 log 2B) P ) p( ) og Af(A) ’ where L(A) =the sound-pressure level, in dB, of the band having a width Af(A) Hz. where L, (B) = the sound-pressure level, in dB, of the band having a width Af(B) Hz. Sound-pressure levels for different bandwidths of flat continuous spectrum noises may also be con- verted to spectrum levels. The spectrum level de- scribes a continuous-spectrum wide-band noise in terms of its energy equivalent in a band one- hertz wide, assuming that no prominent peaks are present. The spectrum level L,(S) may be determined by L,(S)=L,(af) —10 logaf (15) where L, (Af) =the sound-pressure level of the band having a width of Af Hz, Af =the bandwidth in Hz. It should be emphasized that accurate conver- sion of sound-pressure levels from one bandwidth to another by the method described above can be accomplished only when the frequency bands have flat continuous spectra. (14) NOISE PROPAGATION CHARACTERISTICS The sound-power level supplied by the manu- facturer of noise-making equipment can be used to predict sound-pressure levels that will be pro- duced by the equipment in surrounding work areas if the acoustical characteristics of the work area are known. These calculations are complex if all factors are considered, but simple approximate solutions to general cases are often helpful to esti- mate levels. Noise Source in Free Field A free field has been defined as one in which the sound pressure decreases inversely with the distance from the source. These ideal acoustical conditions are rarely found in work environments because of the reflecting surfaces of equipment, walls, ceilings, floors, etc.; however, free-field con- ditions may sometimes be approached outdoors or in very large rooms. For standard free-field con- ditions, the sound-pressure level L, at a given dis- tance r from a small omni-directional noise source can be written in terms of the sound-power level Lp of the source as L,=Lp—20 log r—0.5 (16) where r is in feet, L, is in dB referenced to 0.00002N/m?, and Lp is in dB referenced to 1072 watts. Many noise sources have pronounced direc- tional characteristics; that is, they will radiate more noise in one direction than another. Therefore, it will be necessary for the equipment manufac- ‘turer to provide the directional characteristics of the source, as well as the power levels, to predict the sound-pressure levels. The directional charac- teristics of the source are generally given in terms of the directivity factor Q. Q is defined as the ratio of the sound power of a small, omnidirec- tional, imaginary source to the sound power of the actual source where both sound powers produce the same sound-pressure level at the measurement position. The directivity factor may be added to Equation (16) in the form L,=Lp—201logr—0.5+101og Q , (17) where 10 log Q is called the directivity index. Example: Predict the sound-pressure level that will be produced in a free field at a distance of 100 feet directly in front of a particular machine. A directivity factor of 5 is provided by the machine manufacturer for this location. The noise source has a continuous spectrum and a sound power of 0.1 watt. From Equation (17): L,= 10 log [10 —20 log 100—0.5+ 10 log 5 =10 (log 0.1 —log 1072) —20(2) —0.5+10(0.7) =10(—-1+12)—-40—-0.5+7 =76.5 dB re 0.00002 N/,,*. Noise Source in Reverberant Field In reverberant fields where a high percentage of reflected sound energy is present, the sound- pressure levels may be essentially independent of direction and distance to the noise source. Levels in these reverberant areas depend upon room dimen- sions, object size, and placement in the room, and upon the acoustical absorption characteristics of surfaces in the room. Additional complications may be present in the form of regions of enforce- ment and cancellation of sound pressure, standing waves, caused by strong pure-tone components be- ing reflected. Thus, it is extremely difficult to pre- dict sound-pressure levels at a particular point in a reverberant area. Scund Absorption The acoustical characteristics of a room are strongly dependent upon the absorption coeffi- cients of its surface areas. A surface that absorbs all energy incident on its surface is said to have an absorption coefficient of one, while a surface that reflects all incident energy has an absorption co- efficient of zero. The absorption coefficient de- pends upon the nature of the material, the fre- quency characteristics of the incident sound, and the angle of incidence of the sound. The absorp- tion coefficient is expressed in terms of the frac- 307 tion of the energy absorbed by the material under the conditions described. A rule of thumb that may be used to deter- mine the amount of noise reduction possible from the application of acoustically absorbent material on room surfaces is as follows: absorption units after absorption units before’ where the absorption units are the sum of the products of surface areas and their respective noise absorption coefficients. * © Absorption units are commonly expressed in terms of the sabin, which is the equivalent of 1 square foot of a perfectly absorptive surface. Transmission Loss (TL) of Barriers Sound transmission loss (TL) through a bar- rier may be defined as ten times the logarithm (to the base 10) of the ratio of the acoustic energy transmitted through the barrier to the incident acoustic energy. TL of a barrier may also be de- fined in terms of the sound pressure level reduc- tion afforded by the barrier. Unless otherwise specified, the sound fields are diffuse on either side of the barrier. The TL of a barrier is a physical property of the material used for a given wall construction. The TL for continuous, ran- dom noise commonly found in industry increases about 5 dB for each doubling of wall weight per unit of surface area, and for each doubling of frequency. Multiple wall construction with enclosed air spaces provides considerably more attenuation than the single-wall mass law would predict.” ® © However, considerable care must be taken to avoid rigid connections between multiple walls when they are constructed or any advantages in atten- uation will be nullified." ' Noise leaks which result from cracks or holes, or from windows or doors, in a noise barrier can severely limit noise reduction characteristics of the dB reduction= 10 log 308 barrier. In particular, care must be exercised throughout construction to prevent leaks that may be caused by electrical outlets, plumbing connec- tions, telephone lines, etc., in otherwise effective barriers. References 1. HALLIDAY, D., and R. RESNICK., Physics, (p. 512), New York: John Wiley and Sons, Inc. (1967). “American Standard Specification for Sound Level Meters, S1.4-1971,” American National Standards Institute, 1430 Broadway, New York, N.Y. 10016. “American Standard Specification for Octave, Half- Octave, and Third-Octave Filter Sets, S1.11-1966,” American National Standards Institute, 1430 Broad- way, New York, N.Y. 10016. BERANEK, L. L., Acoustics, New York: McGraw- Hill Book Co. (1954). “Performance Data Architectural Acoustical Ma- terials,” issued annually by Acoustical and Insulating Materials Association (AIMA), 205 W. Touhy Ave., Park Ridge, Illinois 60068 (Bulletin XXX issued 1970). “Sound Absorption Coefficients of the More Com- mon Acoustic Materials,” National Bureau of Stan- dards, U.S. Dept. of Commerce, Letter Circular L C 870. “Guide to Airborne, Impact and Structureborne Noise Control in Multi-Family Dwellings,” U.S. Dept. of Housing and Urban Development, Septem- ber, 1967, (U.S. Government Printing Office, FT/ TS—24). . “Field and Laboratory Measurements of Airborne and Impact Sound Transmission,” ISO/R 140 — 1960 (E), International Organization for Standardi- zation, 1 Rue de Varembe, Geneva, Switzerland. “Recommended Practice for Laboratory Measure- ment of Airborne Sound Transmission Loss of Building Floors and Walls,” American Society for Testing Materials (ASTM), 1916 Race Street, Phil- adelphia, Pennsylvania 19103, Designation E-90-70 (1970). BONVALLET, G. L., “Retaining High Sound Trans- mission in Industrial Plants,” Noise Control 3 (2), 61-64 (1957). . BERANEK, L. L., Noise Reduction, New York, N. Y.: McGraw-Hill Book Co. (1960). 2. CHAPTER 24 PHYSIOLOGY OF HEARING Joseph R. Anticaglia, M.D. INTRODUCTION The basic function of the hearing mechanism is to gather, conduct and perceive sounds from the environment. Sound waves, propagated through an elastic medium, liberate energy in a characteristic pattern which varies in frequency and intensity. The human voice and other ordinary sounds are composed of fundamental tones modified by harmonic overtones (refer to Chapter 23). Our hearing sensitivity is greatest in childhood, but as we get older, our perception of high tones wors- ens, a condition labelled “presbycusis.” The fre- quency range of the human ear extends from as low as 16 Hz to as high as 30,000 Hz. From a practical standpoint, however, few adults can per- ceive sounds above 11,000 Hz. The ear responds to alterations in the pres- sure level of sound. The amplitude of these sound pressure alterations determines the intensity of the sound. So great is the range of intensities to which the ear responds that a logarithmic unit, the deci- bel (dB), is commonly used to express the pres- sure level of sound. The subjective correlates of frequency and intensity are pitch and loudness. The translation of acoustical energy into per- ceptions involves the conversion of sound pres- sure waves into electrochemical activity in the inner ear. This activity is transmitted by the audi- tory nerves to the brain for interpretation. Al- though there are many gaps in our understanding of the precise mechanism of hearing, the following presentation will emphasize the peripheral proc- esses involved in hearing. PERIPHERAL MECHANISM OF HEARING Sound reaches the ear by three routes: air con- duction through the ossicular chain to the oval window; bone conduction directly to the inner ear; and conduction through the round window. Under ordinary conditions, bone conduction and the transmission of sound through the round window are less significant than air conduction in the hear- ing process. An example of bone conduction oc- curs when you tap your jaw. The sound you per- ceive is not coming through your ears but through your skull. Sound perception via air conduction is the most efficient route and it encompasses the external and middle ear conducting system which will be discussed in more detail. Conduction of Sound External Ear. Anatomically, the ear can be di- vided into an external portion (outer ear), an “air- filled” middle ear, and a “fluid-filled” inner ear (Fig. 24-1). The outer ear consists of the auricle and the external auditory meatus, or canal. The 309 auricle is an ornamental structure in man. Neither does it concentrate sound pressure waves signifi- cantly, nor does it function in keeping foreign bodies out of the ear canal. The two ears give us “auditory localization” or “stereophonic hearing,” namely, the ability to judge the direction of sound. One explanation is that sound waves arriving at the two auricles have a slight time lag, differing in intensity and timbre since in the far ear the sound must travel a greater distance. The external auditory canal is a little more than an inch in length and extends from the concha to the tympanic membrane. The skin of the cartilaginous portion of the ear canal secretes wax, which helps maintain relatively stable con- ditions of humidity and temperature in the ear canal. The ear canal protects the tympanic mem- brane and acts as a tubal resonator so that the intensity of sound pressure waves are amplified when they strike the tympanic membrane. The tympanic membrane (TM, eardrum) sep- arates the external ear from the middle ear. This almost cone-shaped, pearl-gray membrane is about a half-inch in diameter. The distance the ear- drum moves in response to the sound pressure waves is incredibly small, as little as one billionth of a centimeter.! Besides vibrating in response to sound waves, the eardrum protects the contents of the middle ear and provides an acoustical dead space so that vibrations in the middle ear will not exert pressure against the round window. Middle Ear. Medial to the eardrum is the special air-filled space called the middle ear. It houses three of the tiniest bones in the body: the malleus (hammer); the incus (anvil); and the stapes (stir- rup). The handle of the malleus attaches to the eardrum and articulates with the incus which is connected to the stapes. The malleus and the incus vibrate as a unit, transmitting the sound waves preferentially to the stapedial footplate, which moves in and out of the oval window. Below and posterior to the oval window is the round window whose mobility is essential to nor- mal hearing. Fig. 24-2 shows the two intratympanic mus- cles, the tensor tympani and the stapedius. The tensor tympani extends from the canal above the eustachian tube to the handle of the malleus. It moves the malleus inward and anteriorly, and helps maintain tension on the eardrum. The stapedius muscle inserts on the posterior aspect of the neck of the stapes. It pulls the stapes out- ward and posteriorly. The two muscles are antagonistic in their ac- tion, but contract only when stimulated by rela- CRURA OF STAPES FACIAL NERVE PROMINENCE OF LATERAL SEMICIRCULAR CANAL FOOTPLATE OF STAPES IN OVAL WINDOW INCUS VESTIBULE MALLEUS SEMICIRCULAR CANALS, UTRICLE, AND SACCULE ATTIC OF MIDDLE EAR (EPITYMPANIC RECESS) INTERNAL ACOUSTIC MEATUS COCHLEAR NERVE VESTIBULAR NERVE FACIAL NERVE PINNA EXTERNAL AUDITORY MEATUS (EAR CANAL SCALA VESTIBULI EAR DRUM COCHLEAR DUCT (TYMPANIC MEMBRANE) CONTAINING ORGAN > COCHLEA OF CORTI CAVITY OF MIDDLE EAR PROMONTORY ROUND WINDOW (22 4 CIBA EUSTACHIAN TUBE SCALA TYMPANI ©Copyright 1970 by CIBA Pharmaceutical Company, Division of CIBA-GEIGY Corporation. Reproduced with permis- sion from CLINICAL SYMPOSIA illustrated by Frank H. Netter, M.D. All rights reserved. Figure 24-1. Pathway of Sound Conduction Showing Anatomic Relationships. 310 Malleus mm ~N — Incus ——— = Stapedius Tensor tympani Stapes Auditory tube Ear drum Lockart R., Hamilton G., Fyfe F.: Anatomy of the Human Body. London, Faber & Faber, 1959, p. 463. Figure 24-2. Intratympanic Muscles Viewed from the Medial Wall. Faber & Faber, London. 311 tively loud sounds. Contraction of the muscles causes rigidity of the ossicular chain with a re- sultant decrease in the conduction of sound energy to the oval window. A limited protective function has been ascribed to this reflex contraction of the muscles although the aural reflex does not react fast enough to provide complete protection against sudden and explosive sounds. Also, exposure to steady state noise for long periods of time would cause the muscles to adapt or fatigue to the audi- tory stimulus.” The “eustachian or auditory” tube connects the anterior wall of the middle ear with the naso- pharynx. It is about an inch and a half in length and consists of an outer bony portion (one third of the tube which opens into the middle ear) and an inner cartilaginous part (two thirds of the tube which opens into the throat). The lumen of the bony part is permanently opened while that of the cartilaginous portion is closed except dur- ing certain periods such as swallowing, yawning, or blowing the nose. To hear optimally, the at- mospheric pressure on both sides of the eardrum should be equal. The act of swallowing, for ex- ample, forces air up the middle ear and thus equalizes the atmospheric pressure on either side of the tympanic membrane. Yet, the fundamental problem that the mid- dle ear must resolve is that of “impedance match- ing.” In other words, the ear must devise a mechanism of converting the sound pressure waves from an air to a fluid medium, without a signifi- cant loss of energy. This is a noteworthy accom- plishment since only 0.1% of airborne sound en- ters a liquid medium whereas the other 99.9% is reflected away from its surface. Stated differently, the intensity of vibration in the fluid of the inner ear is 30 decibels less than the intensity present Lawrence M., cited by De Weese D., Saunders W.: Text- book of Otolaryngology. St. Louis, C. V. Mosby Com- pany, 1968, p. 270, ed. 3; Courtesy of Dr. Merle Law- rence, Ann Arbor, Michigan. Figure 24-3. Loss of Sound Energy at the Air-Water Interface. at the eardrum (Fig. 24-3). The middle ear has two arrangements to narrow this potential energy loss. First is the “size differential” between the com- paratively large eardrum and the relatively small footplate of the stapes. The eardrum has an effec- tive areal ratio which is 14 times greater than that of the stapedial footplate. This hydraulic effect increases the force of pressure from the eardrum onto the footplate of the stapes so that there is approximately a 23 dB increase of sound intensity on the fluid of the inner ear. The “lever action” of the ossicles amplifies the intensity of sound as it traverses the middle ear by about 2.5 dB. Thus, the impedance matching mechanism of the middle ear is not perfect, but accounts for a 25.5 dB increase in the intensity of sound pressure at the air-liquid interface (Fig. 24-4). AREAL RATIO LEVER RATIO 1.31 TO | 2.5 db 14 TO | 23 db Lawrence M.: How we hear. JAMA 196:83, Copyright 1966, American Medical Association, Chicago, III. Figure 24-4. Impedance Matching Mecha- nism of the Middle Ear which Minimizes En- ergy Loss as Sound Is Transferred from Air to Fluid Medium. Journal of the American Med- ical Association. Perception of Sound Inner Ear. The labyrinth or inner ear is a com- plex system of ducts and sacs which houses the end organs for hearing and balance. It consists of an outer bony and an inner membranous lab- yrinth. The center of the labyrinth, the vestibule, connects the three semicircular canals and the cochlea. A watery fluid, perilymph, separates the bony from the membranous labyrinth while inside the membranous labyrinth are fluids called endo- lymph and cortilymph. The cochlea resembles a snail shell which spirals for about two and three-quarter turns around the bony column called the “modiolus” (Fig. 24-5). There are three stairways or canals within the membranous cochlea: the “scala vesti- buli;” the “scala tympani;” and the “scala media a HELICOTREMA (SCALA VESTIBULI WW CN APICAL ga TURN \ ho & Se + ~~ ks COCHLEA oT : . : Snel DUCT h INTERNAL Sd | (CONTAINS \ i ACOUSTIC BASILAR ENDOLYMPH) “5, MEATUS MEMBRANE ORGAN OF CORTI SCALA VESTIBULI — (CONTAINS PERILYMPH) COCHLEAR NERVE VESTIBULAR SCALA TYMPAN| — : MEMBRANE (REISSNER'S) (CONTAINS PERILYMPH) VESTIBULAR VESTIBULO- NERVE COCHLEAR NERVE (Vill FROM OVAL WINDOW OSSEOUS SPIRAL LAMINA MODIOLUS TO ROUND WINDOW ©Copyright 1970 by CIBA Pharmaceutical Company, Division of CIBA-GEIGY Corporation. Reproduced with per- mission from CLINICAL SYMPOSIA, illustrated by Frank H. Netter, M.D. All rights reserved. Figure 24-5. Cross Section of Cochlea. 313 Y VESTIBULAR MEMBRANE (REISSNER'S) DEFLECTION OF VESTIBULAR MEMBRANE BY PRESSURE WAVE TECTORIAL MEMBRANE ORGAN OF CORTI COCHLEAR DUCT a SPIRAL LIGAMENT SCALA VESTIBULI (FROM OVAL WINDOW) GANGLION — 7 a SCALA TYMPANI (TO ROUND WINDOW) o : DEFLECTION OF Lia BASILAR MEMBRANE AND ORGAN OF CORTI BY PRESSURE TRANSMITTED THROUGH os COCHLEAR DUCT . Aisa BASILAR MEMBRANE NERVE FIBERS OUTER HAIR CELLS OSSEOUS SPIRAL LAMINA INNER HAIR CELL ©Copyright 1970 by CIBA Pharmaceutical Company, Division of CIBA-GEIGY Corporation. Reproduced with per- mission from CLINICAL SYMPOSIA, illustrated by Frank H. Netter, M.D. All rights reserved. Figure 24-6. Transmission of Sound across the Cochlear Duct Stimulating the Hair Cells. 314 or cochlea duct.” A bony shelf, the “spiral lam- ina,” together with the basilar membrane and the spiral ligament, separate the upper scala vestibuli from the lower scala tympani. The third canal, the scala media, is cut off from the scala vestibuli by Reissner’s vestibular membrane. The scala media is a triangular-shaped duct within which is found the organ of hearing, namely, the “organ of Corti.” The basilar mem- brane, narrowest and stiffest near the oval win- dow, widest at the apex of the cochlea, helps form the floor of the cochlear duct. On the surface of the basilar membrane are found phalangeal cells which support the critical “hair cells” of the or- gans of Corti. The hair cells are arranged in a definite pattern with an inner row of about 3,500 hair cells and three to five rows of outer hair cells numbering about 12,000. The cilia of the hair cells extend along the entire length of the cochlear duct and are imbedded in the undersurface of the gelatinous overhanging tectorial membrane (Fig. 24-6). Inner Ear Fluids. The vestibular and tympanic canals contain perilymph and communicate with each other through a tiny opening at the upper- most part of the cochlea, the “helicotrema.” The perilymph has a high sodium concentration and a low potassium content whereas the opposite is true of endolymph. Since the transmission of neural impulses should be impossible in the high concentration of potassium found in endolymph, it has been shown that the fluid which bathes the organ of Corti — Cortilymph — has a different ionic content than that of endolymph, and fur- nishes a suitable medium for the normal function- ing of the hair cells and neural endings of the organ of Corti.* * The tectorial membrane appears to maintain a zero potential compared to the scala tympani while the endolymph has a positive potential and the organ of Corti, a negative potential. The posi- tive resting potential of the endolymph has been labelled the ‘“endocochlear or DC potential.” A change in the resting potential of the endolymph results from acoustical stimulation so that the scala media is negative relative to the scala tympani, “summating potential.” In short, the fluids of the cochlear duct supply nourishment to Corti’s organ, a system of remov- ing waste products, an appropriate medium for the transmission of neural impulses, and a means of eliminating noise that its own blood supply would produce. Transmission of Sound Waves in the Inner Ear. The two openings afforded by the oval and round windows are essential for sound pressure waves to pass through the cochlear fluids. The movement of the stapedial footplate in and out of the oval window moves the perilymph of the scala vesti- buli (Fig. 24-7). This vibratory activity travels up the scala vestibuli, but causes a downward shift of the cochlear duct with distortion of Reiss- ner’s membrane and displacement of endolymph and Corti’s organ. The activity is then transmitted through the basilar membrane to the scala tym- pani. When the oval window is pushed inward, 315 the round window acts as a relief point and bulges outward. Transduction. The conversion of mechanical en- ergy of sound into electrochemical activity is called transduction. The vibration of the basilar mem- - brane causes a pull, or shearing force of the hair cells against the tectorial membrane. This “to and fro” bending of the hair cells activates the neural endings so that sound is transformed into an elec- trochemical response. It remains to be clarified whether an electrical and/or chemical process stimulates the neural endings. Travelling Waves. In general, the hair cells at the base of the cochlea transmit high frequency sounds while those at the apex especially respond to low frequency tones. This results in the travel- ling wave phenomena in which there is a specific point of maximum displacement of the basilar membrane beyond which the wavelength and the amplitude become progressively smaller in char- acter. High pitched sounds travel a short distance along the basilar membrane before they die out; the opposite occurs with low pitched sounds. Nerve Conduction. Each nerve fiber connects with several hair cells, and each hair cell with several nerve fibers. The hair cells stimulate auditory neural endings and nerve fibers which stream out through small openings in the spiral lamina into the hollow modiolus (Fig. 24-5). The cell bodies of the nerve fibers form the spiral ganglia whose axons make up the cochlear (auditory) division of the eighth cranial nerve. The movement of the hair cells sets up action potentials, and coded in- formation from both ears are sent to the cochlear nuclei and thereafter to the temporal lobe of the brain where cognition and association takes place. Fig. 24-7 summarizes the peripheral mechanism of hearing. CLASSIFICATION OF HEARING LOSS Loss of hearing can be classified into the fol- lowing categories: 1. Conductive impairment; 2. Sensorineural impairment; 3. Mixed (both conduc- tive and sensorineural); 4. Central impairment; 5. Psychogenic impairment. Conductive Hearing Loss Any condition which interferes with the trans- mission of sound to the cochlea is classified as a conductive hearing loss. Pure conductive losses do not damage the organ of Corti nor the neural pathways. A conductive loss can be due to wax in the external auditory canal, a large perforation in the eardrum, blockage of the eustachian tube, inter- ruption of the ossicular chain due to trauma or disease, fluid in the middle ear secondary to in- fection, or otosclerosis, that is, fixation of the sta- pedial footplate. A significant number of conduc- tive hearing losses are amenable to medical or surgical treatment. Sensorineural Hearing Loss A sensorineural hearing loss is almost always irreversible. The sensory component of the loss involves the organ of Corti and the neural com- ponent implies degeneration of the neural ele- ments of the auditory nerve. DISTORT REISSNER'S MEMBRANE AND BASILAR 5. SHORT WAVES (HIGH 1. SOUND WAVES FREQUENCY, HIGH PITCH) IMPINGE ON ACT AT BASE OF COCHLEA | MEMBRANE OF COCHLEAR EAR DRUM, © SOUND. WAVES DUCT md mn SON AlNeD IT ORGAN Y 76 VIBRATE TRANSMITTED ney ow WITCH) | STIMULATING HAIR UP SCALA ACT AT APEX OF CELLS WHICH ARE IN 38 VESTIBULI IN COCHLEA CONTACT WITH THE 3 SIapes MEDIUM OF TECTORIAL MEMBRANE. AND OUT ITS CONTAINED IMPULSES THEN PASS OF OVAL PERILYMPH UP COCHLEAR NERVE 2. ossicigs. .. VINROW Ty, VIBRATE AS “ Ne A UNIT ) IH Brean” 6. WAVE TRANSMITTED ACROSS COCHLEAR DUCT «_ 7. WAVES DESCEND \ ~ y “SCALA TYMPANI N\ 8. IMPACT OF WAVE ON MEMBRANE OF ROUND WINDOW v CAUSES IT TO MOVE Me IN AND OUT AT ROUND WINDOW IN OPPOSITE PHASE TO OVAL WINDOW ©CIBA' » IN MEDIUM OF ITS CONTAINED PERILYMPH IN MEDIUM OF ENDOLYMPH, FROM SCALA VESTIBULI TO SCALA TYMPANI. (NOTE: WAVES MAY ALSO TRAVEL AROUND HELICOTREMA AT APEX OF COCHLEA) ©Copyright 1970 by CIBA Pharmaceutical Company, Division of CIBA-GEIGY Corporation. Reproduced with per- mission from CLINICAL SYMPOSIA, illustrated by Frank H. Netter, M.D. All rights reserved. Figure 24-7. 316 Transmission of Vibrations from Drums through Cochlea. ” A+ 171 HEARING LEVEL IN DB RE AUDIOMETER ZERO - 60 80 100 25 5 I0 20 40 60 80 TEST FREQUENCY 102 Hz -10 0 om & 20 Zz N AN NN J 6 40 << > we. wg \ = 9 60 23 < 80 w Ww rx 100 25 5 10 20 40 60 80 TEST FREQUENCY 102 Hz Figure 24-8. Audiograms Showing A) Conductive and B) Sensorineural Types of Hearing Loss. 317 Exposure to excessive noise causes an irre- versible sensorineural hearing loss. Damage to the hair cells is of critical importance in the patho- physiology of noise-induced hearing loss. Invari- ably, degeneration of the spiral ganglion cells and the peripheral nerve fibers accompany severe in- jury to the hair cells. Sensorineural hearing loss may be attributed to various causes, including presbycusis, viruses (e.g., mumps), some congenital defects, and drug toxicity (e.g., streptomycin). Mixed Hearing Loss Mixed hearing loss occurs when there are components and characteristics of both conductive and sensorineural hearing loss in the same ear. Central Hearing Loss A central hearing loss implies difficulty in a person’s ability to interpret what he hears. The abnormality is localized in the brain between the auditory nuclei and the cortex. Psychogenic Hearing Loss A psychogenic hearing loss indicates a ‘“‘non- organic” basis for an individual’s threshold eleva- tion. Two conditions in which such a loss may oc- cur are malingering and hysteria. AUDIOMETRY The pure tone audiometer is the fundamental tool used in industry to evaluate a person’s hear- ing sensitivity. It produces tones which vary in frequency usually from 250 Hz to 8,000 Hz at octave or half-octave intervals. The intensity out- put from the audiometer can vary from zero dB to 110 dB, and is often marked “hearing loss” or “hearing level” on the audiometer. Zero dB or zero reference level on the audio- meter is the average normal hearing for different pure tones and varies according to the “standard” to which the audiometer is calibrated. Zero refer- ence levels have been obtained by testing the hear- ing sensitivity of young healthy adults and averag- ing that sound intensity at specific frequencies at which they were just perceptible. It is to be dif- ferentiated from the 0.0002 microbar references for the sound pressure level measurements. If a person has a 40 dB hearing loss at 4,000 Hz, it means that for the individual to perceive a tone the intensity of that tone must be raised to 40 dB above the “standard.” The audiogram serves to record the results of the hearing tests. A graphic description of the faintest sound audible is obtained by plotting the intensity against the frequency. Examples of audi- ograms which indicate conductive and sensori- neural losses are shown in Fig. 24-8. In conduc- tive hearing losses, the low frequencies show most of the threshold elevation, whereas the high fre- quencies are most often involved with the sensori- neural losses. The recording of an audiogram is deceptively simple, yet for valid test results, one must have a properly calibrated audiometer, an acceptable test environment to eliminate interfering sounds, and a qualified audiometrician. When a marked hearing loss is encountered, bone conduction au- diometry and more sophisticated hearing tests are often helpful in diagnosing the site and cause of the hearing loss.” For more details concerning appropriate American National Standard Institute (ANSI) standards and the objectives of a good audiometry program, refer to the preferred read- ing list. EFFECTS OF EXCESSIVE NOISE EXPOSURE Since the ear does not have an overload switch or a circuit breaker, it has no option but to receive all the sound that strikes the eardrum. In industry, excessive noise constitutes a major health hazard. Such exposure can cause both auditory and extra- auditory effects. Auditory Effects Noise induced hearing loss (NIHL) can happen unnoticed over a period of years. At first, exces- sive exposure to harmful noise causes auditory fatigue or a temporary threshold shift (TTS). This shift refers to the difference in one’s hearing sensi- tivity measured before and after exposure to sound. It is called “temporary” since there is a return of the individual’s pre-exposure hearing level after a period of hours away from the intense sound. However, repeated insults of excessive noise can transform this TTS into a permanent thresh- old shift (PTS). In fact, studies substantiate that the hearing sensitivity of factory workers in heavy industry is poorer than that of the general popu- lation. Fig. 24-9¢depicts the stages of destruction PE § y Tm aie Lawrence M.: Auditory problems in occupational medi- cine. Arch. Environ. Health 3:2888, Copyright 1961, American Medical Association, Chicago, Ill. Figure 24-9. Stages of Destruction of the Organ of Corti. (A) The normal organ of Corti. (B) A stage of hair cell degeneration follow- ing the first subtle changes within the cyto- plasm of the cells. The internal hair cell re- mains intact. (C) Both inner and outer hair cells are gone, and the supporting structures are degenerating. (D) In the final stages, the entire organ of Corti is dislodged, leaving a denuded basilar membrane, which may be- come covered with a simple layer of eipthelial cells. (Arch. Environ. Health) 318 of the organ of Corti in a laboratory test animal that was overstimulated by loud continuous noise. Many factors influence the course of NIHL. The overall “decibel level” of the noise exposure is obviously important. If a noise exposure does not cause auditory fatigue, then such exposure is not considered harmful to one’s hearing sensitivity. Another consideration is the “frequency spec- trum” of the noise. Noise exposure which has most of its sound energy in the high frequency bands is more harmful to a worker’s hearing sensitivity than low-frequency noises. Another factor is the daily “time distribution” of the noise exposure. In general, noise which is intermittent in character is less harmful to hear- ing than steady state noise exposure. As the “total work duration” (years of employment) of a worker to hazardous noise is increased, so too does the incidence and magnitude of his NIHL. However, no report of “total” hearing loss has been attrib- uted to excessive noise exposure alone.® Finally, the “susceptibility” of the worker to hazardous noise must be considered, since not every individual will suffer identical hearing im- pairment if exposed to the same noise intensity over the same time period. A small percentage of workers will be highly susceptible or, on the other hand, refractory to the degrading effects of noise. The hearing loss from “acoustic trauma” should be differentiated from the insidious, irre- versible sensorineural NIHL that results after months or years of exposure to excessive noise conditions. Acoustic trauma refers to the loss of hearing secondary to head or ear trauma, or after exposure to a sudden, intense noise such as that of firearms or explosions. A conductive type of hearing loss results when the trauma causes a per- forated eardrum or disruption of the middle ear ossicles. The trauma can cause a sensorineural loss, but not infrequently, the hearing loss is tem- porary in nature. Besides causing hearing loss, hazardous noise levels can mask speech, be a source of annoyance, and occasionally degrade a worker’s job performance.’ Extra-Auditory Effects The extra-auditory effects of noise result in physiologic changes other than hearing. We are familiar with the reflex-like startle response of an individual to a loud, unexpected sound. Less com- monly noted are the cardiovascular, neurologic, endocrine and biochemical changes secondary to intense noise exposure. Subjective complaints of nausea, malaise, and headache have been reported in workers exposed to ultrasonic noise levels. Vasoconstriction, hyperreflexia, fluctuations in hormonal secretions, disturbances in equilibrium and visual functions have been demonstrated in laboratory and field studies. These changes have been for the most part transient in character, and it remains to be clarified whether such noise ex- posure has long lasting ill effects on the organism.® 319 SUMMARY The important function of the hearing mech- anism is to convert the mechanical energy of sound pressure waves into an electrochemical response. Excessive noise exposure can tax the physiologic limits of the hearing mechanism and cause an ir- reversible, sensorineural hearing loss. Noise is just one of many causes of hearing loss, so that a rele- vant medical history and a detailed history of a worker’s previous employment will eliminate many false conclusions concerning the cause of a work- er’s loss of hearing. References 1. von BEKESY, G.: “The Ear.” Scientific American, 415 Madison Ave., New York, N.Y. 10017, 197: 2 (1957). WEVER, E. and M. LAWRENCE: Physiologic Acoustics, Princeton University Press, Princeton, New Jersey 08540, pp. 179 (1954). ENGSTROM, H.: “The Cortilymph, the Third Lymph of the Inner Ear.” Acta Morphologica Neer- lando-Skandinavia, Heereweg, Lisse, Netherlands, 3: 195-204 (1960). LAWRENCE, M.: “Effects of Interference with Terminal Blood Supply on Organ of Corti.” Laryn- goscope, St. Louis, 76: 1318-1337 (1966). VAN ATTA, F.: “Federal Regulation of Occupa- tional Noise Exposure.” Sound and Vibration, 27101 E. Oviatte, Bay Village, Ohio 44140, 6: 28-31 (May 1972). GLORIG, A.: “Age, Noise and Hearing Loss.” Annals of Otology, St. Louis, Missouri, 70: 556 (1961). COHEN, A.: Noise and Psychological State. Pro- ceedings of National Conference on Noise as a Pub- lic Health Hazard, American Speech and Hearing Association, Rept. No. 4, Washington, D.C., pp. 74-88 (Feb. 1969). ANTICAGLIA, J. and A. COHEN.: “Extra-Audi- tory Effects of Noise as a Health Hazard.” Am. Ind. Hyg. Assoc. J., 210 Haddon Ave., Westmont, N.J. 08108, 31:277 (May-June 1970). Preferred Reading 1. Specifications for Audiometers. ANSI S3.6-1969, American National Standards Institute, New York (1969). Standard for Background Noise in Audiometric Rooms. ANSI S3.1-1960, American National Stan- dards Institute, New York. Guide for Conservation of Hearing in Noise. Sub- committee on Noise, 3819 Maple Avenue, Dallas, Texas, 1964. Background for Loss of Hearing Claims. American Mutual Insurance Alliance, 20 N. Wacker Drive, Chicago, Illinois, 1964. Guidelines to the Department of Labor's Occupa- tional Noise Standards. Bulletin 334, U.S. Dept. of Labor, Washington, D.C. KRYTER, K.: The Effects of Noise on Man, Aca- demic Press, New York, 1970. SATALOFF, J.: Hearing Loss, Lippincott Company, Philadelphia and Toronto, 1966. GLORIG, A.: Audiometry, Principles and Practices, The William & Wilkins Company, Baltimore, 1965. HOSEY, A. and C. POWELL, (Eds.): Industrial Noise, A Guide to its Evaluation and Control, U.S. Dept. H.E.W., Publication No. 1572 U.S. Govt. Printing Office, Washington, D.C. (1967). CHAPTER 25 NOISE MEASUREMENT AND ACCEPTABILITY CRITERIA James H. Botsford INSTRUMENTS FOR SOUND MEASUREMENT There is probably a greater variety of instru- ments for measuring noise than for any other en- vironmental factor of concern to industrial hygien- ists. Almost every measurement need can be sat- isfied with instrumentation available commercially today. Only those instruments more useful to the industrial hygienist will be discussed here. Sound Level Meters The standard sound level meter is the basic measuring instrument for the industrial hygienist. General Radio Co., Concord, Massachusetts. Figure 25-1. A Standard Sound Level Meter. 321 It consists of a microphone, an amplifier with calibrated volume control and an indicating meter. It measures the root-mean-square (rms) sound pressure level in decibels which is proportional to intensity or sound energy flow. Sound level meters of the same type differ mainly in external shape, arrangement of controls, and other convenience features that frequently in- fluence the selection made by a prospective user. A typical sound level meter is pictured in Figure 25-1. Standards for sound level meters’ * * specify performance characteristics in order that all con- forming instruments will yield consistent readings under identical circumstances. The more impor- tant characteristics specified are frequency re- sponse, signal averaging and tolerances. TABLE 25-1 Relative Response of Sound Level Meter Weighting Networks Frequency ~~ Weighted Response, dB Hertz A B C 31.5 —39 —17 -3 63 —26 —9 — 125 —16 —4 0 250 -9 —-1 0 500 —-3 0 0 1000 0 0 0 2000 1 0 0 4000 1 ~r 1 —1 8000 —1 =~3 -3 Reproduced with permission of General Radio Company, West Concord, Mass., from “Handbook of Noise Mea- surement,” 1967. Three weighting networks are provided on standard sound level meters in an attempt to dup- licate the response of the human ear to various sounds. These weighting networks cause the sensi- tivity of the meter to vary with frequency and in- tensity of sound like the sensitivity of the human ear, The relative responses of the three networks are shown in Table 25-1 where the A, B and C weightings mimic ear response to low, medium and high intensity sounds respectively. Entries in the table show relative readings of the meter for con- stant sound pressure level of variable frequency. These A, B and C meter response curves corre- spond to the 40, 70 and 100 phon equal loudness contours. The D-weighting network is provided on some sound level meters for approximating the “perceived noise level” used in appraising the of- fensiveness of aircraft noises. The A-weighting network is the most useful one on the sound level meter. It indicates the A- weighted sound level, often abbreviated dBA, from which most human responses can be predicted quite adequately.* Action of the indicating meter may be selected as “fast” or “slow.” Relatively steady sounds are easily measured using the “fast” response. Un- steady sounds can be averaged with the more slug- gish “slow” response to reduce meter needle swings. The speed of meter response affects the read- ings obtained for transient sounds. For example, General Radio Co., Concord, Massachusetts. Figure 25-2. A Sound Level Calibrator. 322 the level of a whistle toot lasting 1/5 second would be indicated no more than 2dB low on the “fast” scale. On the “slow” scale, the level of a toot lasting 1/2 second would read 3 to 5 dB low, American standard sound level meters are fur- nished in three types offering varying degrees of precision.’ Designated Types 1, 2 and 3 in order of increasing tolerances, the Type 2 generally measures within 2 or 3 dB of true levels which is satisfactory for most purposes. Errors are about half as large with the Type 1 or “precision” sound level meter and about twice as large with the Type 3 “survey” instrument. These errors can be re- duced somewhat by careful calibration. Calibrators The overall accuracy of sound measuring equipment may be checked by using an acoustical calibrator such as is shown in Figure 25-2. It con- sists of a small, stable sound source that fits over the microphone and generates a predetermined sound level within a fraction of a decibel. If the meter reading is found to vary from the known calibration level, the meter may be adjusted to eliminate this error. The acoustical calibration procedure supplements the electrical calibration incorporated in some meters to check the gain of all electronic components following the micro- phone. Sound level calibrators should be used only with the microphones for which they are in- tended in order to avoid errors and microphone damage. Impulse Meters The sound level meter is too sluggish to indi- cate peak levels of transient noises lasting a frac- tion of a second such as those produced by ham- mer blows or punch press strokes. Such noises must be measured with a special meter that in- dicates the peak level. Accessory impulse meters are available for connection to sound level meters and can be cali- brated to indicate the peak level of the sound at the microphone. One of these is shown in Figure 25-3. In taking such readings, it is necessary to General Radio Co., Concord, Massachusetts. Figure 25-3. A Noise Peak Meter for Con- nection to a Sound Level Meter. B&K Instruments, Inc., Cleveland, Ohio. Figure 25-4. A Precision Sound Level Meter with an Octave Band Filter Attached to the Base. 323 be sure that the upper sound pressure limit of the microphone is not exceeded as the indicated level will then be too low. The upper limit of the sound level meter can be extended by replacing the stan- dard microphone with a less sensitive one that is linear to higher levels. Such microphone substi- tutions affect the calibration of the sound level meter and must be taken into account when inter- preting readings. The sound level meter in Figure 25-4 is equipped with a circuit for measuring impulse noise according to a German standard. It has a rather slow rise time in order that the indication of impulsive sound will correlate with the loudness perceived by the ear. For impulses that rise abruptly, the reading with this circuit is lower than would be found with a true peak meter. However, the instrument shown has been provided also with an instantaneous peak reading circuit that will indicate the true peak. Frequency Analyzers It is often necessary to know the frequency distribution of the sound energy. It is important in noise abatement, for example, since the reduc- tion afforded by control devices varies with fre- quency. Such information is provided by one of the several types of sound spectrum analyzers available. They may be connected, to the sound level meter or other sound sensing system. The electrical signal from the microphone is filtered by the analyzer circuitry so that only signals within a limited frequency range are transmitted to the indicating meter. Measurement of sound pressure level in contiguous frequency ranges provides data for a plot of sound pressure level versus frequency. Octave band analyzers are the types most commonly encountered. An octave band filter set is shown attached to the lower end of a sound level meter in Figure 25-4. The frequency range of each band is such that the upper band limit is twice the lower band limit. Formerly, octave bands were described by these cut-off frequency limits such as 300 to 600, 600 to 1200, etc. Currently they are designated by the geometric mean of the cut-off frequencies which are called center fre- quencies. Thus, when the 1000 Hz band is men- tioned, it is understood that it extends from 710 to 1420 Hz. The center and cut-off frequencies of octave band filters in common use are shown in Table 25-2. Often bands narrower than octaves are re- quired for pinpointing the frequency of a tone. In such applications, the one-third and one-tenth octave analyzers are quite valuable. Some of these can be coupled to a graphic level recorder which tunes the analyzer through the frequency range and simultaneously plots its output on a moving paper chart. This equipment is very useful in de- termining sources of noise in machinery since sound of a particular frequency must be generated by mechanical events such as the meshing of gear teeth, passing of fan blades, etc. which are re- peated at the same rate, Accessory Equipment As most sound is generated by vibration of seme body, it is sometimes desirable to study the TABLE 25-2. Center Frequencies and Limits of Octave Bands. Traditional bands, Hz Preferred bands, Hz Lower Center Upper Lower Center Upper limit freq. limit limit freq. limit 19 27 38 22 31.5 44 38 53 75 44 63 88 75 106 150 88 125 177 150 212 300 177 250 355 300 425 600 355 500 710 600 850 1,200 710 1,000 1,420 1,200 1,700 2,400 1,420 2,000 2,840 2,400 3,400 4,800 2,840 4,000 5,680 4,800 6,800 9,600 5,680 8,000 11,360 Reproduced with permission of General Radio Company, West Concord, Mass., from “Handbook of Noise Mea- surement,” 1967. vibration as well as the sound. Accessory vibra- tion pickups are available for most sound level meters to make such vibration analysis possible. They are generally accelerometers for which the electrical output is proportional to the acceleration of the surface to which they are attached. Types sensitive to the velocity or displacement of the surface are also available. Complete vibration meters are supplied too, for greater convenience. The vibration signal may be examined for fre- quency content using any of the sound analyzers discussed earlier. In this way, vibration at a par- ticular frequency may be correlated with the sound of the same frequency it produces. Calibrators are available for checking the sensitivity of the vibra- tion pickup to reduce errors in measuring the acceleration of a surface. The cathode ray oscilloscope is useful for ob- serving the wave-form of a sound. It plots the sound pressure versus time on a television-type screen. From observation of the wave shape, it is sometimes possible to determine the mechanical process responsible for the noise. It is also pos- sible to observe the peak pressures of impulsive sounds. Cameras are available for photographing the face of the cathode ray tube to obtain a per- manent record of the wave form. A graphic record of sound level may be ob- tained by connecting a sound level meter to a graphic level recorder which plots the sound level on a moving paper chart. The pen speed of the recorder must be capable of following the fluctua- tions in sound level if an accurate record is to be obtained. The magnetic tape recorder can be used to store a sound for later analysis on replay. An instru- ment of broadcast quality must be used to obtain high fidelity reproduction of the sound on play- back. For analysis on replay, the recorder output should be connected to the analyzer input by means of a patch cord. Too much distortion will occur if the recording is played back through a loud-speaker and picked up with a microphone. If only the frequency content is of interest, then no precautions need be taken to keep track of level during recording and playback. However, if it is necessary to determine the true levels of the orig- inal noise on playback, careful recording of cali- bration tones must be undertaken. Generally, it is better to measure sound directly in the field if possible. Sound Monitors When sound level varies erratically over a wide range, it is difficult to describe the noise by meter readings. Therefore, statistical analyzers have been developed to assist in this process. They indicate the percentage of time that the sound level lies in certain predetermined level ranges. From these data, the mean level, standard deviation as well as other statistical indices may be calculated. Another type of monitor evaluates noise ex- posures according to the rules established by the American Conference of Governmental Industrial Hygienists (ACGIH ),* which will be described in a section that follows. These instruments may be exposed to varying noise for a work day and will indicate whether this exposure limit has been ex- ceeded. One: of the battery-powered, wearable types is shown in Figure 25-5. A different type of noise hazard meter recently developed integrates the effects of noise like the ear does." When exposed to non-impulsive noise of any duration, it indicates the amount of tempo- rary shift in hearing threshold that a group of normal ears would experience in the same expo- duPont de Nemours & Co., Wilmington, Delaware. Figure 25-5. A Battery-Powered Noise Mon- itor That Can Be Worn by a Workman. sure. Its reading is interpreted according to the theory that noise exposures producing little tem- porary hearing loss are not likely to produce much permanent hearing loss even after many repeti- tions, ACCEPTABILITY CRITERIA Criteria for the acceptability of noise are dic- tated by the effects which are to be avoided. The most important of these is hearing damage result- ing from prolonged exposure to excessive noise. Another undesirable effect is speech interference or interruption of communications by noise. An- noyance is a third undesirable effect of noise more difficult to assess. There are also certain non- auditory effects of noise we are just beginning to recognize, which are discussed later in this chapter. Hearing Damage The damaging effect of noise on hearing de- pends on (1) the level and spectrum of the noise, (2) duration of exposure, (3) how many times it occurs per day, (4) over how many years daily exposure is repeated, (5) the effects on hearing regarded as damage and (6) individual suscept- ibility to this type of injury. All of these factors must be considered in establishing limits of accept- able exposures to dangerous noise. Noise Evaluation. Early in the study of the effects of noise on hearing, it was learned that noise frequency as well as intensity influenced the effect produced. High frequency noise was found to be more damaging than low frequency noise of the same sound pressure level. Therefore, noise spectra were evaluated with standard octave band analyzers which were the only portable spectrum analyzers then available. As knowledge of noise effects grew, some in- vestigators began to feel that octave band analysis was a needlessly complicated evaluation of noise which could be replaced with the A-weighted sound level measured using a standard sound level meter. It seemed that the A-weighting network made the meter less sensitive to low frequency sounds to about the same extent that the ear is less susceptible to injury by these low frequency sounds, In these studies, the damage to be avoided was impairment of ability to understand “everyday speech” as defined by the medical profession.’ This medico-legal definition allows some observ- able change in hearing threshold$ not sufficient to affect ability to understand everyday speech significantly. Steady Noise. All day exposure to steady noise has been investigated to determine the level at which hearing damage begins after many years of redundant exposure. Such studies are the basis for the curves in Figure 25-6 which indicate the risk of hearing impairment associated with expo- sure to a steady noise level at work.® Each curve indicates on the vertical scale the percentage of workers that showed impaired hearing as defined by the medical profession after working continu- ously in the noise levels shown on the horizontal scale. To interpret the Figure, note that the upper 325 curve shows that in a group of 100 men aged 50 to 59 years, which has been exposed to 90 dBA at work for 33 years, 33 men should show evi- dence of impaired hearing, However, note that the lower flat portion of the same curve indicates that the general population and others not exposed to dangerous noise at work exhibit 22 cases of im- paired hearing out of every hundred. Therefore, near-lifetime exposure to 90 dBA at work seems to produce about 11 more cases of impaired hear- ing per hundred surviving than would otherwise have occurred. As the data generating the curves of Figure 25-6 are not so consistent as the precise lines would indicate, this difference of 11 percent- age points is about the smallest that can be con- sidered significant. For lower age groups exposed for shorter periods, the increase in prevalence of impaired hearing is much less pronounced. The curves of Figure 25-6 suggest 90 dBA as one limit for steady exposure to continuous noisc, a limit that has become rather widely accepted. Future standards may lower this limit. Intermittent Noise. Most occupational noises are intermittent rather than continuous. Interrupt- ing harmful noise allows the ear to rest and recover which reduces the likelihood of permanent dam- age.’ Such intermittent exposures have not been studied much because of the great complexities of exposure description. As a result, theories are re- lied upon to set limits for intermittent noise. The theory most generally accepted postulates that the hazard of noise exposure increases in pro- portion to the average temporary hearing loss which the exposure would produce in a group of normal ears. This theory arises out of the obser- vation that those noise exposures that ultimately produce permanent hearing loss also produce tem- porary hearing loss in normal ears. Conversely, those noise exposures that do not produce perma- nent hearing loss do not produce temporary hear- ing loss in normal ears. While the true relation between temporary and permanent hearing loss has not been established, it is logical to assume that those noise exposures that do not cause much temporary loss will not cause much permanent loss either. Any temporary threshold shift (TTS) that disappears before the next exposure to noise com- mences is considered acceptable. On the basis of this assumption, results of TTS studies have been used to define safe limits for all day exposures to steady noise. These limits agree with those established by permanent threshold shift studies. TTS studies have also indicated that inter- mittent noise is much less harmful than steady noise, The laws describing growth of TTS during exposure and recovery afterwards have been used to calculate exposures producing acceptably small amounts of TTS. Combinations of sound level, duration of exposure and degree of repetition that are considered acceptable for personnel exposures at work are shown in Table 25-3." This method for appraising noise exposures was derived from the report describing hazardous exposure to inter- mittent and steady-state noise prepared by the National Academy of Science-National Research ® o 1 ~ oO 1 0 o i 1 On Oo 1 Ad Ww g i AGE GROUP 50-59 ~~ 40-49 ~~ 30-39 20 // / 2 / 20- INCIDENCE OF IMPAIRMENT IN PERCENT OF POPULATIONS bd oO Oo L 4 29 1+ __ 1 1 i I I v NON GEN. 80 90 100 110 NOISE POP A-SCALE LEVEL IN DBA Guidelines for noise exposure control, Sound and Vibration 4:21, 1970. Figure 25-6. 326 Prevalence of Impaired Hearing and Sound Levels at Work. Council, Committee on Hearing, Bio-acoustics and Bio-mechanics, generally referred to as CHABA.*? Maintaining exposures within the limits CHABA recommended will allow few additional cases of impaired hearing to occur.'® TABLE 25-3. Maximum Permissible Sound Levels for Intermittent Noise When Occurrences Are Evenly Spaced Throughout the Day. "Total noise Number of times noise occurs per day duration Shady 1 3 7 15 35 75 160up 8 h. 89 89 89 89 89 89 89 6 90 92 95 97 97 94 93 4 91 94 98 101 103 101 99 2 93 98 102 105 108 113 117 1 96 102 106 109 114 125 125 (1% h) 30 m. 100 105 109 114 125 15 104 109 115 124 8 108 114 125 A-weighted 4 113 125 sound levels, 2 123 dBA Reproduced with permission from “Sound and Vibration” Bay Village, Ohio (4:16, 1970). To use Table 25-3, select the column headed by the number of times the noise occurs per day, read down to the average sound level of the noise and locate directly to the left in the first column the total duration of the noise permitted for any 24 hour period. It is presumed that the noise _ bursts are evenly spaced throughout the work day so that an opportunity for rest and recovery be- tween noise bursts exists. It is permissible to interpolate in the Table if necessary. able 25-3 shows that intermittency is as im- portant as duration and level. For example, it shows that a continuous noise level of 91 dBA can be tolerated for 4 hours; 101 dBA can be tolerated also for 4 hours if it is presented in 15 evenly spaced bursts lasting 16 minutes each. Thus, the interruption of the higher noise reduces the effect on hearing to that which would be pro- duced by a steady noise of equal duration 10 dec- ibels lower. So you might say that the interrup- tions are equivalent to a 10 decibel noise reduction. Impulsive Noise. Exposure limits for impulse noise are based on studies of the average TTS caused in normal ears by exposure to various im- pulses. Limits that will cause little TTS and, therefore, little expected permanent damage have been set.!* These limits are complicated to apply and, as a result, have not been widely used. However, an approximate method of determin- ing whether these limits are likely to be exceeded can be carried out with the sound level meter using 327 the C-weighting and “fast” meter response. To do so, set controls so that zero on the meter scale corresponds to a level of 130 dB. If the impulse does not cause the meter needle to jump above 125 dB (minus 5 on the meter scale), then it probably is not excessive.® ACGIH TLV for Noise. The noise exposure limits expressed in Table 25-3 are inconvenient to use in practice. So, a simplification of the table was adopted in 1970 by the ACGIH as a thresh- old limit value (TLV) for noise.” It is shown in Table 25-4. The simplification embodies the presumption that practically all noise exposures are interrupted at least a few times a day by meals or rest periods, machinery stoppages, etc. The limits of Table 25-4 correspond very closely to those of Table 25-3 for noises that occur three to seven times per day. Since these exposure limits do not take proper account of intermittency, they do not provide a true evaluation of hearing dam- age potential of the noise exposure. They are too liberal for absolutely continuous noise and too conservative for noise that is interrupted very fre- quently. If an exposure consists of two or more noise levels, the combined effect must be considered. To do so, it is necessary to compute the ratio of the duration of each level to the duration al- lowed by Table 25-4. The sum of these ratios for all noise levels involved in the exposure must not exceed unity if the exposure is to be accept- able. Noise levels below 90 dBA are not con- sidered in these calculations. The graph in Figure 25-7 is convenient for calculation of exposures involving several levels. For impulsive sounds, ACGIH proposed a limit of 140 dB peak which is quite conservative compared to the recommendations of Coles et al.'* TABLE 25-4 Threshold Limit Values for Non-impulsive Noise Adopted by the American Conference of Governmental Industrial Hygienists Duration Permissible per day, hours sound level, dBA 8 90 6 92 4 95 3 97 2 100 1%2 102 1 105 Ya 107 a 110 Ya 115 max. Reprinted with permission of American Conference of Governmental Industrial Hygienists, Cincinnati, Ohio from “Threshold Limit Values for Noise,” 1970. NCISE LEVEL 90 85 100 500 400 300 200 150 100 80 60 40 30 20 DURATION OF NOISE IN MINUTES 15 "Oy o, Figure 25-7. DBA 1o IN 105 "Hs Graphical Presentation of ACGIH TLV for Noise. To use the graph, locate the point corresponding to the noise level and duration; then read off the exposure ratio C/T from the diagonal lines interpolating if necessary. The ACGIH TLV for noise was accepted by the U.S. Department of Labor for promulgation under the provisions of the Occupational Safety and Health Act of 1970. It is being adopted also by many states for enforcement as part of their occupational health regulations. Non-occupational Exposures. All that has been said up to now about hearing damage ap- plies to the noise exposures at work. Medical evaluation of heating handicap from occupational noise exposure disregards changes in hearing that do not affect ability to understand everyday speech significantly. When it comes to the non-occupational ex- posures in transportation vehicles, public places, etc., none of these mitigating influences exist. Yet levels equalling those in industry are often encoun- tered and there is a tendency to apply industrial standards when appraising the hazard. Stricter standards of safety should be imposed for non- occupational exposures so that no change in hear- 328 ing whatsoever can occur. Dr. Cohen has recom- mended limits 15 dB below the limits shown in Table 25-4.1¢ Speech Interference Noise can mask or “blot out” speech sounds reducing the intelligibility of messages. Labora- tory studies of these effects have appraised the disruptive potential of the noise by its “speech interference level” which is the average sound pressure level of 500, 1000, and 2000 Hz octave bands.” The distances at which difficult messages can be conveyed reliably are shown in Table 25-5 as a function of speech interference level. Simple, redundant messages normally used at work can be understood at greater distances. The speech interference level is closely related to the A-weighted sound level. It is lower by 7 decibels for most common noises. Using this con- version, the speech interference effects of various noises may be estimated from A-weighted sound levels using Table 25-5. EXPECTED MANY COMPLAINT FEW RESPONS C ORGANIZED pr ACTION NONE THREATS MUCH SOME PREVIOUS EXPOSURE NONE DAY ONLY TIME NIGHT INDUSTRIAL COMMERCIAL RESIDENTIAL SUBURBAN § a 0 o I v Ll 2 COUNTRY 1/ DAY 2-4/0DAY 4-20/0AY 1-10/HOUR 10 -60/HOUR NN CONTINUOUS REPITITION IMPULSES NO IMPULSES PURE TONE TYPE NOISC WIDE BAND 30 40 so 60 70 80 90 A-WEIGHTED SOUND LEVEL IN DB Botsford J. H.: Using sound levels to gauge human response to noise. Sound and Vibration 3:16, 1969. Figure 25-8. Chart for Estimating Community Complaint Reaction to Noise. To use the chart, locate in the curved grid at the bottom the point corresponding to the sound levels of the noise under consideration (C-A is the difference between the C- and A- weighted sound levels). From this point, project directly upward into the first of the six correction sec- tions bounded by the horizontal lines. When entering a correction section, follow the lane en- tered until reaching a position opposite the condition listed at the left which applies to the neighborhood noise under consideration, and then proceed vertically, disregarding lanes, until the next section is reached. In this way, work up through the lanes of the correction sections until reaching the top where the community reaction to be expected is shown. 329 Annoyance Annoyance by noise is a highly subjective phenomenon which is very difficult to relate to the sound that causes it. Noises become more annoying as they get louder than the background noise on which they are superimposed. Noises that are unsteady or contain tones are most an- noying as are those that convey unpleasant mean- ing. Indoors, noise is likely to become annoying when the A-weighted sound level exceeds 30 dBA in auditoria or conference rooms, 40 dBA in pri- vate offices and homes, or 50 dBA in large offices or drafting rooms. Outdoors, a noise can be ex- pected to prove annoying if it exceeds the back- ground level by 10 dBA or more. A procedure for rating the annoyance poten- tial of a noise in the community is given in Figure 25-8.* It provides a method for estimating com- munity complaint reaction to a given noise con- dition. TABLE 25-5 Maximum Speech Interference Levels for Reliable Communication at Various Distances and Vocal Efforts. Distance, Vocal Effort feet Normal Raised Loud Shout 0.5 76 82 88 94 1 70 76 82 88 2 64 70 76 82 4 58 64 70 76 8 52 58 64 70 16 46 52 58 64 32 40 46 52 68 Reproduced with permission of General Radio Company, West Concord, Mass., from “Handbook of Noise Mea- surement,” 1967. Non-Auditory Effects Audible noise produces other effects which are just beginning to be examined.'® Laboratory studies have shown that noise reduces efficiency on some tasks, can upset the sense of balance, and can cause blood vessels to constrict, raising blood pressure and reducing the volume of blood flow. It causes the pupils of the eyes to dilate. Even when we are sleeping, noise can cause changes in electro-encephalograms and blood circulation without waking us. Noise can also cause fatigue, nervousness, irritability, hypertension and add to the overall stress of living. There is no convincing evidence so far that any of these effects become permanent and thus are deleterious to health. Very intense noise below 1000 Hz can be felt as well as heard. Airborne vibrations can stimu- late mechano-receptors throughout the body, in- cluding touch and pressure receptors and the ves- tibular organs. The respiratory system is affected by sounds in the 40 to 60 Hz range because of the resonance characteristics of the chest. Sounds too high in frequency to be heard by the normal ear produce no significant effect when they reach the body by air pathways. However, transmission of ultrasound into the body through fluid or solid media is more efficient and can produce cavitation of the tissue as well as deep burns. Intense sound below the audible frequency range can cause resonant vibration of the eye balls and other organs of the body. Dizziness and - nausea can result. Levels of 130 dB or more are 330 required to cause there effects, and are not often encountered in industry. SURVEY TECHNIQUES One should become thoroughly familiar with operation of noise measuring instruments through study of operating instructions before attempting to make noise surveys. Set up the equipment and check its operation before embarking. At inter- vals during the survey, batteries should be checked as well as overall instrument calibration. When transporting instruments, they should be protected from vibration and shock as much as practical. Instruments should also be protected from extremes of temperature. Overheating, such as might occur in the trunk of a car parked in the sunshine, can damage circuit components. Allow- ing the instrument to become very cold in a car parked overnight in the winter will result in con- densation of water vapor in the instrument when it is used in a heated space the next morning. Water condensed from the air can cause electrical leakage resulting in low readings. When conducting surveys, it is important to be assured that the meter indication is due to noise and not to other influences. One way of doing so is to listen to the meter output with a pair of headphones to learn whether the sound heard is the noise being measured. Wind blowing across the microphone causes a rushing sound that is registered on the meter. Use of a wind screen can minimize this effect. Electric and magnetic fields can also cause needle deflections. This interference may occur around welding on large assemblies and becomes apparent when the meter needle does not move in step with the loudness of the noise heard. These electro- magnetic effects can be reduced by reorienting the meter until minimum coupling with the electrical fields is obtained as indicated by minimum meter reading. One particularly troublesome location where electrical interference is observed is around electric furnaces. Here, the electrical interference and the noise are coincident so that it is easy to confuse these spurious signals with noise. When taking readings, one should obtain rep- resentative data. The microphone should be moved about to determine that standing waves are not present. If they are, a spatial average should be obtained. Exposure Surveys When conducting exposure surveys of various kinds, the most important consideration is to measure levels that are typical of those at the auditor’s location. It is not necessary, in fact it is undesirable, to measure sound right at the ear since diffraction around the head can alter the sound field. Tt is better to measure at some loca- tion a few feet away where exploration with the sound level meter indicates levels are the same as at the auditor’s location. When attempting to evaluate the potential for hearing damage, all factors of significance must be recorded such as sound level, duration, intermittency, etc., necessary to make proper evaluation of an exposure, using Table 25-3. If one is merely attempting to determine com- pliance with the regulatory limits shown in Table 25-4, then the ACGIH exposure evaluation pro- cedure must be followed. When noise levels are too variable to allow this procedure to be carried out with a sound level meter and stop watch, a noise monitor may be used. Several of these are commercially available to compute automatically the fractional exposure according to the prescribed methods. One of these monitors is shown in Fig- ure 25-5. Source Determination When attempting to locate sources of noise in a room or in a machine, the simplest approach is to probe the sound field with the sound level meter. The noise will increase as the source is approached and disclose its location. Extension cables can be used to remove the microphone from the meter for greater convenience in these explorations. Another aid to locating the original sources of noise is spectral analysis of vibrating parts, the frequency of the sound will be the same as the frequency of the part vibration. Thus, narrow band analysis will often reveal frequencies that can be correlated with repetitive mechanical events or multiples thereof. These clues point to the mechanical disturbances responsible for the noise. SUMMARY A complete array of instruments is available for measuring steady, intermittent and impulsive noises. Sound level meters, calibrators, frequency analyzers, and accessory equipment are provided by several suppliers. Sound exposure monitors which can be worn by roving workmen record individual patterns of exposure that could be as- sessed in no other way. Criteria have been established for avoiding permanent hearing loss resulting from steady, in- termittent and impulsive sounds. The Threshold Limit Value for noise, adopted by the American Conference of Governmental Industrial Hygienists, has been accepted widely. Non-occupational ex- posures require stricter limits to provide complete protection. Criteria for avoiding speech interference and complaints of annoyance are also available. Sev- eral non-auditory effects of noise are being studied, but no harmful effects that require safety criteria have been discovered yet. Techniques for survey- ing noise conditions are well developed so that any noise problem can be readily evaluated. References 1. Specification for Sound Level Meters, SI. 13-1971, American National Standards Institute, 1430 Broad- way, New York, New York, (1971). 2. General Purpose Sound Level Meters, 1EC/123 (1961), American National Standards Institute, 1430 Broadway, New York, New York. 331 3. Precision Sound Level Meters, 1EC/179 (1965), American National Standards Institute, 1430 Broad- way, New York, New York. 4. BOTSFORD, J. H.: “Using Sound Levels to Gauge Human Response to Noise.” Sound and Vibration, 27101 E. Oviatt, Bay Village, Ohio 44140, 3: 16 (Oct. 1969). 5S. Threshold Limit Values for Noise, American Con- ference of Governmental Industrial Hygienists, P. O. Box 1937, Cincinnati, Ohio 45201, (1971). 6. BOTSFORD, J. H.: “Noise Hazard Meter.” Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 32:92 (1971). 7. “Guides to the Evaluation of Permanent Impair- ment; Ear, Nose, Throat and Related Structures.” J. Amer. Med. Assoc., 535 North Dearborn St., Chicago, Illinois, 177: 489, (1961). 8. “Guidelines for Noise Exposure Control.” Sound and Vibration, 27101 E. Oviatt, Bay Village, Ohio 44140, 4: 21 (Nov. 1970). 9. WARD, W. D., A. GLORIG and D. L. SKLAR.: “Dependence of Temporary Threshold Shift at 4KC on Intensity and Time.” J. Acoust. Soc. Am., 335 E. 45th St, New York, New York 10017, 30: 944 (1958). 10. WARD, W. D.: “The Use of TTS in the Derivation of Damage Risk Criteria.” Int. Audiol. (Now Au- diology — Audiologie), Karger, A. G., Medical and Scientific Publishers, Arnold-Boecklin Strasse, 25- C.H.-4000 Basel 11, Switzerland, 5: 309 (1966). 11. BOTSFORD, J. H.: “Current Trends in Hearing Damage Risk Criteria.” Sound and Vibration, 27101 E. Oviatte, Bay Village, Ohio 44140, 4: 16 (April, 1970). 12. KRYTER, K. D.,, W. D. WARD, J. D. MILLER and D. H. ELDREDGE.: “Hazardous Exposure to Intermittent and Steady-State Noise.” J. Acoust. Soc. Am., 335 E. 45th St, New York, New York 10017, 39: 451 (1966). 13. BOTSFORD, J. H.: “Prevalence of Impaired Hear- ing and Sound Levels at Work.” J. Acoust. Soc. Am., 335 E. 45th St.,, New York, New York 10017, 45: 79 (1969). 14. COLES, R. R. A, G. R. GARINTHER, D. C. HODGE and C. G. RICE.: “Hazardous Exposure to Impulse Noise.” J. Acoust. Soc. Am., 335 E. 45th St., New York, New York 10017, 43: 336 (1968). . 15. KUNDERT, W. R.: General Radio Company, West Concord, Mass., 1970. 16. COHEN, A., J. ANTICAGLIA and H. H. JONES.: *“ ‘Sociocousis’ — Hearing Loss from Non-Occupa- tional Noise Exposure.” Sound and Vibration, 27101 E. Oviatt, Bay Village, Ohio 44140, 4: 12 (Nov. 1970). 17. WEBSTER, J. C.: “Effects of Noise on Speech In- telligibility.” Noise As A Public Health Hazard: (American Speech and Hearing Association, Wash- ington) 49: (1969). 18. GLORIG, A.: “Non-Auditory Effects of Noise Ex- posure.” Sound and Vibration, 27101 E. Oviatt, Bay Village, Ohio 44140, 5: 28 (May, 1971). Preferred Reading PETERSON, A.P.G. and E. E. GROSS, J.R.: Handbook of Noise Measurement, General Radio Company, West Concord, Mass., 1967. Sound and Vibration, Acoustical Cleveland, Ohio (Monthly). Noise as A Public Health Hazard, American Speech and Hearing Association, Washington, D.C. 1969. CHALUPNIK, J.D. (ed.) Transportation Noises, Univ. of Washington Press, Seattle, Washington 1970. KRYTER, K. D.: The Effects of Noise on Man, Aca- demic Press, New York, N.Y. 1970. WELCH, B.L. and A. S. WELCH (eds.) Physiological Effects of Noise, Plenum Press, New York, N.Y. 1970. BARON, R. A.: The Tyranny of Noise, St. Martins Press, New York, N.Y. 1970. Publications, Inc. or [I 2 i . La ) . . . I vs de \ ) N=. . - A RN Fa - i ’ CHAPTER 26 VIBRATION Robert D. Soule INTRODUCTION Exposure to vibration is frequently associated with exposure to noise in industrial processes since the two often originate from the same oper- ation. However, the adverse effects resulting from exposure to noise and to vibration are quite differ- ent in nature, the former having a more substan- tial basis than the latter for establishing a cause- and-effect relationship both qualitatively and quantitatively. As more information concerning industrial exposures to vibration becomes avail- able, particularly within the United States, and appropriate exposure criteria are established and standards adopted, the now common practice of taking noise surveys in industrial situations will likely be extended by the use of a vibration sensor to assist the investigator in evaluating the expo- sures of workers to both noise and vibration. The effects of exposure to noise have been thoroughly investigated and the results of these studies are reflected in current legislation. Al- though a significant amount of research is under- way on the relationship between exposure to vi- bration and the health and well-being of the per- sons exposed, sufficient evidence for the establish- ment of occupational health standards has not yet been developed. Therefore the purpose of this chapter is to acquaint the reader with the general principles in- volved in recognition, evaluation and control of workers’ exposure to vibration. Except to the extent necessary, the chapter will not discuss con- siderations of vibration in noise control efforts, since this is done in detail in Chapter 37. EFFECTS OF VIBRATION ON MAN The human body is an extremely complex physical and biological system. When looked upon as a mechanical system, it contains a num- ber of linear and non-linear elements, the mechan- ical properties of which differ from person to per- son. Biologically, and certainly psychologically, the system is by no means any simpler than it is mechanically. On the basis of experimental studies, as well as documented reports of indus- trial experience, it is apparent that exposure of workers to vibration can result in profound effects on the human body — mechanically, biologically, physiologically and psychologically. It should be noted at this point that relatively few studies of industrial exposures to vibration have been conducted in the United States; most of the available literature on documentations of effects of vibration in industrial situations has been 333 published in European countries. There have been considerable numbers of military and, relatively recently, agriculturally applied research programs in the United States. The application of such studies to general industrial situations is obviously limited. However, they have been valuable in de- termining some of the parameters of importance in investigating the response of people exposed to vibration and, for this reason, results of some of these studies will be discussed later in this chapter. HEAD UPPER TORSO N ARM — SHOULDER SYSTEM THORAX— ABDOMEN SYSTEM (SIMPLIFIED) STIFF ELASTICITY OF SPINA COLUMN J HIPS | Beh APPLIED TO SITTING | Ba LEGS | oa APPLIED TO et SUBJECT Figure 26-1. Simplified Mechanical System Representing the Human Body Standing (or Sitting) on a Vertically Vibrating Platform.! Reprinted from “Mechanical Vibration and Shock Mea- surements” courtesy of Briiel & Kjaer Instruments, Cleve- land, Ohio. When considering the effects of vibration on man, it is necessary to classify the type of vibration exposure into one of two categories on the basis of the means by which the worker contacts the vibrating medium. The first category is referred to as “whole body” vibration and results when the whole body mass is subjected to the mechanical vibration as, for example, from a supporting sur- face such as a tractor seat. The second category is usually referred to as “segmental” vibration and is defined as vibration in which only part of the body, far example the hand or hands operating a chain saw, is in direct contact with the vibrating medium and the bulk of the body rests on a sta- tionary surface. This classification of vibration does not necessarily mean that parts of the body other than those in direct contact with the vibrat- ing surface are not affected. If the whole body is considered as a mechan- ical system, at low frequencies and low vibration levels it may be approximated roughly by a sim- plified mechanical system such as that depicted in Figure 26-1. Results of some of the research studies con- ducted in the United States are presented in Fig- ures 26-2 and 26-3. * * These studies have shown that, for whole body vibration, the tolerance of a seated man is lowest in the frequencies between approximately 3 and 14 Hertz. As with any tangi- ble object, it is possible to apply externally gen- erated vibrations to the human body at certain frequencies and in such a way that the body be- comes more in resonance with the vibrating source than at other frequencies. These studies have indicated that such whole body resonances occur 2.0 HIP/ TABLE SHOULDER / TABLE o 15 | | 2 = HEAD / TABLE Zz f——" z - = 1.0 FR EN w J w . 8 \ NS gq NN, 05 F \ BELT/ TABLE ~. \_ KNEES BENT SN \ N N ~ \ N St —— 0 | biden dd. ] 1 | 2 3 4 6 8 10 20 30 40 FREQUENCY, HZ Figure 26-2. Transmissibility of Vertical Vi- bration from Supporting Surface to Various Parts of the Body of a Standing Human Sub- ject as a Function of Frequency.» + Reprinted from “Mechanical Vibration and Shock Mea- surements” courtesy of Briiel & Kjaer Instruments, Cleve- land, Ohio. 334 35 ™ EY / \ 30 HEAD/ ~~ SHOULDER } A / wh I | I 1 2.0 ! / o SHOULDER / / 4 TABLE / « / 15 , 3 / [= - / = = / HEAD/ uw - k / TABLE - - \ | w 1.0 [eT \ NT 8 Tee x Pn — 0.5 0 1 1 1 1 1 | | I 2 34 6 810 20 30 40 FREQUENCY, HZ Figure 26-3. Transmissibility of Vertical Vi- bration from Supporting Surface to Various Parts of a Seated Human Subject as a Func- tion of Frequency.** Reprinted from “Mechanical Vibration and Shock Mea- surements” courtesy of Briiel & Kjaer Instruments, Cleve- land, Ohio. in the frequency range 3-6 Hertz and 10-14 Hertz. The studies have also indicated the presence of resonant effects in some of the sub-systems of the body as a result of exposure to whole body vibra- tion. For example, resonance of the head-shoul- der sub-system has been found in the 20-30 Hz range; disturbances which suggest eyeball reso- nance have been indicated in the 60-90 Hz range; and a resonance effect in the lower jaw and skull sub-system has been reported for the 100-200 Hz range. The preceding discussion has dealt with me- chanical responses to vibration, however, there are pronounced physiological and psychological effects resulting from exposures to whole body vibration as well. Although these effects are rather complex and usually difficult to measure, the subjective responses of man to whole body vibration have been fairly well documented in the European liter- ature. A few causal relationships between the bio- mechanical effects of whole body vibration and consequent physiological changes in the body are apparent. These physiological observations have included evidence of a slight acceleration in the rate of oxygen consumption, pulmonary ventilation and cardiac output.” * ” # There is evidence of an inhibition of tendon reflexes and an impairment in the ability to regulate the posture, possibly by actions through both the vestibular and spinal re- flex pathways.” 1° Alterations have been recorded in the electrical activity of the brain and there has been evidence of effects on visual acuity and per- formance at various levels of motor activity and task complexity during exposure to whole body vibration.'" * These and other studies conducted in Europe have indicated that whole body vibra- tion has effects on the endocrinological, biochem- ical and histopathological systems of the body as well. The most extensive investigations of industrial exposures of workers to vibration have been con- cerned with repeated exposure to low frequency vibration transmitted through the upper extremi- ties of the worker; that is, during the use of hand- held power tools which incorporate rapidly rotat- ing or reciprocating parts. Such studies therefore consider the effects of “segmental” vibration on the worker. Unfortunately, most of these studies pre- sent only general descriptions of the clinical evi- dence of overexposure to vibration and very few contain any controlled observations by quantita- tive techniques; consequently there is a large vari- ability between the observations reported by dif- ferent investigators. However, the main features of what can be called a vibration syndrome are evi- dent. The clinical evidence of overexposure to vibra- tion during the use of hand tools can be conveni- ently grouped into four categories.’ These four types of disorders, in decreasing order of their ap- pearance in the published literature, are: 1. A traumatic vaso-spastic syndrome in the form of Raynaud’s phenomenon (discussed in more detail below); Neuritis and degenerative alterations, par- ticularly in the ulnar and axillar nerves, that is, a loss of the sense of touch and thermal sensations as well as muscular weakness or even paralysis, and abnormal- ities of the central nervous system; Decalcification of the carpal and meta- carpal bones; fragmentation, deformation and necrosis of carpal bones; and 4. Muscle atrophy, tenosynovitis. As indicated earlier, the prevalence of the dif- ferent symptom groups varies tremendously in the reports of different investigators. However, a fair estimate of the average overall prevalence of the vibration syndrome, at least as typified by the Ray- naud phenomenon, appears to be around 50%; that is, about half of the workers exposed to seg- mental vibration exhibit clinical symptoms char- acteristic of the Raynaud phenomenon. Raynaud’s Syndrome Raynaud’s syndrome or “dead fingers” or “white fingers” occurs mainly in the fingers of the hand used to guide a vibrating tool. The circula- tion in the hand becomes impaired and, when ex- posed to cold, the fingers become white and void of sensation, as though mildly frosted. The condition usually disappears when the fingers are warmed for some time, but a few cases have been suffi- 335 — ciently disabling that the men were forced to seek other types of work, In some instances, both hands are affected. This condition has been observed in a number of occupations involving the use of fairly light vibrating tools such as the air hammers used for scarfing and chipping in the metal trades, stone- cutting, lumbering and in the cleaning departments of foundries where men have a good deal of over- time work. Obviously, prevention of this condition is much more desirable than treatment. Preventive measures include directing the exhaust air from the air-driven tools away from the hands so they will not become unduly chilled, use of handles of a comfortable size for the fingers, and in some instances, substituting mechanical cleaning meth- ods for some of the hand methods which have pro- duced many of the cases of “white fingers.” In many instances, simply preventing the fingers from becoming chilled while at work has been sufficient to eliminate the condition. The appearance of the syndrome appears to be a function of the cumulative absorption of vibra- tion energy, its harmonic content and on personal factors such as the age of the worker. Vibration in the frequency range 40-125 Hz has been im- plicated most frequently in reported cases of vibra- tion disorders.’ '* In most studies it appeared that an exposure time of several months was gen- erally needed before symptoms appeared. With continued exposure there was a progressive di- versification and intensification of the symptoms; some improvement of symptoms has been re- ported, but rarely complete recovery, with cessa- tion of exposure to vibration. It is the opinion of many investigators in Europe that the vibration syndrome is a widespread and alarmingly com- mon occupational disorder.'* Symptoms of over- exposure are reportedly grave or moderately grave in about half of those affected, and in all cases result in a varying loss of working capacity. Results of the European studies of industrial vibration exposures are summarized in Table 26-1. These data were obtained from reports issued by investigators in several countries: Austria, Czecho- slovakia, France, Finland, Germany, Great Brit- ain, Italy, the Netherlands, Russia, Sweden and others. In general, these studies revealed abnor- mal changes in the vascular, gastric, neurological, skeletal, muscular and endocrine systems as well as definite effects on visual acuity and task per- formance. The presence of Raynaud’s syndrome was common to practically all studies of exposures to segmental vibration. It is beyond the intent of this chapter to discuss any of the hundreds of articles published in the literature on these studies; bibliographies on the subject have been published and should be reviewed by the interested reader.'® 1% As can be seen from Table 26-1 the vibration syndrome does indeed appear to be a widespread occupational disorder in European industry. It must be noted here again that similar studies in industries in the United States have been very limited. However, it is reasonable to assume that United States workers employed in occupations TABLE 26-1 EUROPEAN INDUSTRIES IN WHICH CLINICAL EVIDENCE OF OVEREXPOSURE OF WORKERS TO VIBRATION HAS BEEN REPORTED Industry Type of Common Vibration Vibration Sources Agriculture Whole body Tractor operation Boiler Making Segmental Pneumatic tools Construction ~~ Whole body Heavy equipment Segmental vehicles, pneumatic drills, jackham- mers, etc. Diamond Segmental Vibrating hand cutting tools Forestry Whole body Tractor operation Segmental chain saws Foundries Segmental Vibrating cleavers Furniture Segmental Pneumatic chisels manufacture Iron and steel Segmental Vibrating hand tools Lumber Segmental Chain saws Machine tools . Segmental Vibrating hand tools Mining Whole body Vehicle operators Segmental rock drills Riveting Segmental Hand tools Rubber Segmental ~~ Pneumatic stripping tools Sheet metal Segmental ~~ Stamping equipment Shipyards Segmental ~~ Pneumatic hand tools Stone Segmental ~~ Pneumatic hand dressing tools Textile Segmental ~~ Sewing machines, looms Transportation Whole body Vehicle operation (operators and passengers) similar to those listed in Table 26-1 are being potentially exposed to excessive levels of vibra- tion during their routine work activities. The Na- tional Institute for Occupational Safety and Health (NIOSH) has initiated a comprehensive program in which the occupational exposures to vibration in American industries is being investigated.'® VIBRATION EXPOSURE CRITERIA It is obvious from the preceding discussion that the occurrence of vibration disorders in a wide 336 cross section of industry is significant enough, both in terms of prevalence and magnitude, that ap- propriate standards for allowable exposure to vi- bration are desirable. However, at the present time there are no generally accepted limits for safe vibration levels and, in fact, the available litera- ture, because of the variability of reported find- ings, does not permit the reliable construction of a vibration exposure standard. All this is not to say that individual standards and criteria, as well as corrective methods for dealing with excessive levels of industrial vibration, have not been at- tempted; in fact, they have. However, the ap- proaches to establishment of criteria and/or im- 01 Pls z= / INTOLERABLE 00! \ \ / S11 UNPLEASANT DISPLACEMENT AMPLITUDE — INCHES _ .000I \ H~ PERCEPTIBLE .0000I | 2 4 6810 20 406080100 VIBRATION FREQUENCY -—CYCLES PER SECOND Figure 26-4. Subjective Responses to Vi- bratory Motion. The chart is based on the averaged values of various investigators and is valid for exposures up to a few minutes. The vertical arrows represent one standard deviation above and below the means. McFarland RA Human engineering and industrial safety. Reprinted from Vol. 1, F. A. Patty “Industrial Hygiene and Toxicology”, 2nd edition. Courtesy Interscience Pub- lishers, Inc., New York, N.Y., 1958. plementation of corrective methods have been quite variable even within a given country. Many studies have been conducted in which the subjective responses of exposed personnel to various levels of vibration have been documented. The results of experimental studies with human volunteers conducted by three different investiga- tors are presented in Figure 26-4.!7 It must be emphasized that these data and, in fact, all such data in which experimental exposures have been documented are useful only over a very limited time duration. Most of these studies have been conducted for military and/or aerospace programs and are concerned primarily with acute exposures; that is, relatively short duration exposure such as impact or shock type of vibrations encountered in military situations. The subjects selected for such studies, therefore, are normal young, physically fit men, such as pilots. There are obvious pitfalls, therefore, in using such information as a basis for establishment of standards for industrial exposures to vibration. In the occupational workplace the normal work force is comprised of persons consti- tuting a wide spectrum of characteristics. The in- dustrial worker can be female as well as male, is not necessarily as physically fit as the subjects used in experimental studies, and certainly encom- passes a greater range of age and other physical characteristics. Perhaps of more significance, how- ever, is the fact that these experimental investiga- tions represent acute or short-term exposures to vibration and certainly do not permit direct ex- trapolation to the typical industrial exposure which is comprised, for the most part, of exposure to relatively low frequency vibration of varying amp- litudes for extended periods of time. In the case of the industrial worker then, one must be con- cerned with the cumulative effects of exposure to vibration over a working lifetime which can be comprised of exposure to vibration for, in an extreme example, 40 hours per week, 50 weeks per year for 40 years. Suffice to say, therefore, that the types of human exposure studies that have been conducted in the United States have limited application in the industrial environment. Attempts have been made to establish vibra- tion exposure standards and, of these, perhaps the single best vibration exposure criteria guides are those proposed by the International Standards Or- ganization.'®* These criteria, presented in Figure 26-5 as a family of curves, are valid for vibra- tions transmitted to the torso of a standing or sit- OCTAVE PASS BAND 6.3 — A m/st NN 7 brood NON i ~ J 2 25 - o> TMIN. NV x — I5MIN, Zz ’ 30MIN. S — g 1.0 ~ ~~ th / x = ~N TN J / 4 ~_ 2h 8 0.63 — 2 _ NU or 0.4 — ~~ } 0.25 — 8h TTT Fri LL IL rT 04 063 10 16 25 40 63 10 16 25 40 63 HZIOO FREQUENCY —o Figure 26-5. Vibration Exposure Criteria Curves. The vibration levels indicated by the curves in Figure 26-5 are given in terms of RMS acceleration levels which produce equal fatigue-de- creased proficiency. Exceeding the exposure specified by the curves, in most situations, will cause noticeable fatigue and decreased job proficiency in most tasks. The degree of task interference depends on the subject and the complexity of the task. Reprinted from “Mechanical Vibration and Shock Measurements” courtesy of Briiel & Kjaer Instruments, Cleveland, Ohio. 337 ting person and are, therefore, to be considered a guide for whole body vibration. A tentative ISO vibration guide has been proposed for segmental (hand-arm system vibrations).’®* The ISO whole body vibration guide is based to a great extent on studies conducted in the aerospace medical re- search laboratories in formulating guides for short- term exposures, usually of a military nature and thus again may have only limited application in industrial work environments. The vibration levels indicated in Figure 26-5 are given in terms of the root mean square ac- celeration levels which produce equal “fatigue- decreased proficiency” over the frequency range of 1-100 Hz. Vibrations in frequencies below 1 Hz produce annoyances which are individually unique; for instance, cinetosis or air sickness. For frequencies above 100 Hz the vibrational percep- tions are mainly effective on the skin and depend greatly upon the influenced body part and on the damping layer; for example, clothing or shoes. It seems, therefore, practically impossible to state generally valid vibration exposure criteria for fre- quencies outside the range indicated in Figure 26-5, that is, 1-100 Hertz. Exceeding the ex- posures specified by the curves in most situations will cause noticeable fatigue and decreased job efficiency. The degree of task interference de- pends on the subject and the complexity of the task being performed. The curves indicate the gen- eral range for onset of such interferences and the time dependency observed. An upper exposure ! DISPLACEMENT considered hazardous to health as well as perform- ance is considered to be twice as high (6 decibels higher) as the “fatigue-decreased efficiency” boun- dary shown in Figure 26-5 while the “reduced comfort” boundary is assumed to be about 3 (10 decibels below) the illustrated levels. Again, these criteria are presented as recom- mended guidelines or trend curves, rather than firm boundaries of classified quantitative biological or psychological limits. They are intended solely for situations involving healthy, normal people considered fit for normal living routines and stress of an average work day. A program for estab- lishing vibration exposure based upon identifi- cation and characterization of exposed workers in industries in the United States and implementation of relevant studies to ascertain the extent of the industrial vibration hazard and determination of criteria for these standards to prevent adverse exposures to industrial vibration has been in- itiated.'® CHARACTERISTICS OF VIBRATION In general, vibration can be described as an oscillatory motion of a system. The “motion” can be simple harmonic motion, or it can be extremely complex. The “system” might be gaseous, liquid or solid. When the system is air (gaseous) and the motion involves vibration of air particles in the frequency range of 20 to 20,000 Hertz (Hz), sound is produced. For the purposes of this chap- ter, only the effects on the worker caused by mo- Figure 26-6. Reprinted from “Mechanical Vibration and Shock Measurements” Ohio. 338 AAA = Representation of Pure Harmonic (Sinusoidal) Vibration. courtesy of Briiel & Kjaer Instruments, Cleveland, tion of solid systems will be considered. The oscillation of the system may be periodic or completely random; steady-state or transient; continuous or intermittent. In any event, during vibration one or more particles of the system oscil- late about some position of equilibrium. Periodic (Sinusoidal) Vibration Vibration is considered periodic if the oscillat- ing motion of a particle around a position of equilibrium repeats itself exactly after some period of time. The simplest form of periodic vibration is called pure harmonic motion which as a func- tion of time, can be represented by a sinusoidal curve. Such a relationship is illustrated in Figure 26-6, where T = period of vibration. The motion of any particle can be character- ized at any time by (1) displacement from the equilibrium position, (2) velocity, or rate of change of displacement, or (3) acceleration, or rate of change of velocity. For pure harmonic mo- tion, the three characteristics of motion are related mathematically. Displacement The instantaneous displacement of a particle from its reference position under influence of har- monic motion can be described mathematically as: s=S sin (2= . )=S sin (2 = ft) =S sin ot where s=instantaneous displacement from reference position S=maximum displacement t= time T = period of vibration f =frequency of vibration o=angular frequency (2 = f) Of the possible vibration measurements, dis- placement probably is the easiest to understand and is significant in the study of deformation and bending of structures. However, only if the rate of motion, i.e. frequency of vibration, is low enough, can displacement be measured directly. Velocity In many practical problems, displacement is not the most important property of the vibration. For example, experience has shown that the veloc- ity of the vibrating part is the best single criterion for use in preventive maintenance of rotating ma- chinery. Although peak-to-peak displacement measure- ments have been widely used for this purpose, it is necessary to establish a relationship between the limits for displacement and rotational speed for each machine. Since the velocity of a moving particle is the change of displacement with respect to time, the particle’s velocity can be described as: _ds_ _ i" Lo T pT oS cos(wt) =V cos (ot) =V sin (at +3) where v = instantaneous velocity V = maximum velocity Acceleration In many cases of vibration, especially where mechanical failure is a consideration, actual forces 339 set up in the vibrating parts are critical factors. Since the acceleration of a particle is proportional to these applied forces and since equal-and-op- posite reactive forces result, particles in a vibrat- ing structure exert forces on the total structure that are a function of the masses and accelerations of the vibrating parts. Thus, acceleration measure- ments are another means by which the motion of vibrating particles can be characterized. The instantaneous acceleration, i.e., the time rate of change of velocity of a particle in pure harmonic motion, can be described as: a= at — »*S sin (ot) = A sin (ot+7) where a= instantaneous acceleration and A = maximum acceleration. Other terms, such as “jerk,” defined as the time rate of change of acceleration, are sometimes used to define vibration. At low frequencies, jerk is related to riding comfort of automobiles and elevators and is also important for determining load tie-down in airplanes, trains and trucks. However, from the equations and definitions pre- sented in the preceding discussion, it is apparent that, regardless of the parameter being studied, i.e., displacement, velocity, acceleration or jerk, the form and period of the vibration are the same. As noted above, the instantaneous magnitudes of the various parameters have been defined in terms of their peak values, that is, the maximum values obtained. This approach is quite useful in the consideration of pure harmonic vibration be- cause it can be applied directly in the above equa- tions. However, in the consideration of more com- plex vibrations it is desirable to use other descrip- tive quantities. One reason for this is that the peak values describe the vibration in terms of a quantity dependent only upon an instantaneous vibration magnitude, regardless of the previous history of the vibration. One descriptive quantity which does take the time history into account is the “average absolute value” defined as: | T S (average) = T JS |s| dt 0 Although the above quantity does take the time history of the vibration into account over one period, it has very limited practical usefulness. The root mean square (rms) value is a much more useful descriptive quantity which also takes the time history of the vibration parameter into ac- count. This quantity is defined as: 7 J sad o The importance of the rms value as a descrip- tive quantity lies mainly in its direct relationship to the energy content of the vibration. For ex- ample, in the case of pure harmonic motion the relationship between the various values is: Seis = m™ 1 Sims = 2 Y2 S Cavorage) “Ya S Or, in a more general form: Sims = F; S (average) = F. S The factors, F; and F,., are called “form fac- tor” and “crest factor,” respectively, and give an indication of the wave shape of the vibration being studied. For pure harmonic motion ™ and F.= V2=1414 There have been attempts to introduce the concept of “acceleration level” and “velocity level.” These terms, similar in concept to the sound pressure level used in expressing noise levels, indicate the acceleration and velocity in dec- ibels; that is, the logarithm of the ratio of the ac- celeration or velocity to a reference acceleration { ACCELERATION Figure 26-7. or velocity. Although several references have been proposed, the most common velocity reference value is 10 meters per second; i.e., 10™® centi- meters per second. The acceleration reference value is 107° meters per second squared or 107° centimeters per second squared. Suitable “standard reference values” for acceleration, velocity and displacement are still being studied. The discussion and certainly the equations which have been presented to this point have dealt exclusively with the periodic vibrations, and more specifically with pure harmonic periodic vibrations. It must be pointed out that most of the vibrations encountered in industry and in fact, practically anywhere, are not pure harmonic motions, even though many of them certainly can be character- ized as periodic. A typical nonharmonic periodic vibration is illustrated in Figure 26-7. VAAN Example of a Non-Harmonic Periodic Motion (Piston Acceleration of a Com- bustion Engine). Reprinted from “Mechanical Vibration and Shock Measurements” courtesy of Briiel & Kjaer Instruments, Cleveland, Ohio. By examining this curve and determining the peak absolute and root mean square values of this vibration as well as the form factor and crest fac- tor, it is obvious that the motion is not harmonic. However, on the basis of this information, it would be practically impossible to predict all of the vari- ous effects the vibration might produce in con- nected structural elements. Obviously, other meth- ods of description must be used; one of the most powerful descriptive methods is that of frequency analysis, which is based on a mathematical theorem first formulated by Fourier, which states that “any periodic curve no matter how complex may be looked upon as a combination of a number of pure sinusoidal curves with harmonically related frequencies.” As the number of elements in the series in- creases, it becomes an increasingly better approxi- mation to the actual curve. The various elements constitute the vibration frequency spectrum and in Figure 26-8 the non-harmonic periodic vibra- tion illustrated in Figure 26-7 is re-illustrated, together with two important harmonic curves which represent its frequency spectrum. A more convenient method of representing this spectrum is shown in Figure 26-9. This characteristic of periodic vibrations is evident in examining Figure 26-10. Their spectra consist of discreet lines when represented in the so-called “frequency do-- main”; random vibrations show continuous fre- quency spectra when represented in similar fashion. Random Vibrations Random vibrations occur quite frequently in nature and may be defined as motion in which the vibrating particles undergo irregular motion cycles that never repeat themselves exactly. Theoretically then, obtaining a complete description of the vi- 340 ACCELERATION Figure 26-8. Illustration of How the Waveform Shown in Figure 26-7 Can Be ‘Broken Up” into a Sum of Harmonic Related Sinewaves. Reprinted from “Mechanical Vibration and Shock Measurements” courtesy of Briiel & Kjaer Instruments, Cleveland, Ohio. ACCELERATION (RMS) ) 1, (=x) > (=73 FREQUENCY, f f, d= Figure 26-9. Examples of Periodic Signals and their Frequency Spectra. a) Description in the time domain. b) Description in the frequency domain. Reprinted from “Mechanical Vibration and Shock Mea- surements” courtesy of Briiel & Kjaer Instruments, Cleve- land, Ohio. brations requires an infinitely long time record. This, of course, is an impossible requirement and finite time records would have to be used in prac- tice. Even so, if the time record becomes too long, it also will become a very inconvenient means of describing the vibration, and other methods there- . 4 ACCELERATION ACCELERATION fo» — (RMS) T A roa TIME fo FREQUENCY ACCELERATION ACCELERATION (RMS) B TIME fo 2fo FREQUENCY ACCELERATION ACCELERATION ther (RMS) Cc TIME — fo 3ty Sf, Tho FREQUENCY (a) (b) Figure 26-10. Examples of Periodic Signals 341 and their Frequency Spectra. a) Description in the time domain. b) Description in the frequency domain. Reprinted from “Mechanical Vibration and Shock Mea- surements” courtesy of Briiel & Kjaer Instruments, Cleve- land, Ohio. fore have to be devised, and are commonly used. It is beyond the purpose and intent of this chapter to discuss the theoretical and mathematical models necessary to describe complex vibrations; this in- formation is presented in several well-written scien- tific and engineering texts. VIBRATION MEASUREMENTS Basic Elements In a Measurement System A wide variety of component systems, con- sisting of mechanical or a combination of mechan- ical, electrical and optical elements are available to measure vibration. The most common system uses a vibration pick-up to transform the mechan- ical motion into an electrical signal, an amplifier to enlarge the signal, an analyzer to measure the vibration in specific frequency ranges and a meter- ing device calibrated in vibrational units. Vibration Pick-ups The vibration pick-up measures the displace- ment, the velocity, or the acceleration of the vibra- tion. These parameters are all inter-related by differential operations so that it does not normally matter which variable is measured. If the result is desired in terms of velocity or displacement, elec- tronic integrators are added at the output of an accelerometer, an instrument which measures the acceleration of a mass due to the vibration signal. Accelerometers, the most common type of vibration pick-up, are normally smaller than velocity pick-ups and their useful frequency range is wider. An accelerometer is an electromechanical transducer which produces an output voltage sig- nal proportional to the acceleration to which it is subjected. The most common type of accelerometer is the piezoelectric type, such as the one shown in Figure 26-11, in which two piezoelectric discs HOUSING WV SPRING MASS PIEZOELECTRIC DISCS We OUTPUT TERMINALS BASE Figure 26-11. Sketch Showing the Basic Construction of the Bruel & Kjaer Compres- sion Type Piezo-Electric Accelerometers (Sin- gle-Ended Version). Reprinted from “Mechanical Vibration and Shock Mea- surements” courtesy of Briiel & Kjaer Instruments, Cleve- land, Ohio. 342 produce a voltage on their surfaces due to the mechanical strain on the asymmetric crystals which make up the discs. The strain is in the form of vibrational inertia from a moving mass atop the discs. The output voltage is proportional to the acceleration, and thus to the vibration signal, The upper limit of the accelerometer’s useful frequency range is determined by the resonant frequency of the mass and the stiffness of the whole accelerom- eter system. The lower limit of the frequency range varies with the cable length and the proper- ties of the connected amplifiers. The accelerom- eter’s sensitivity and the magnitude of the voltage developed across the output terminals depends upon both the properties of the materials used in the piezoelectric discs and the weight of the mass. The mechanical size of the accelerometer, there- fore, determines the sensitivity of the system; the smaller the accelerometer, the lower the sensitiv- ity. In contrast, a decrease in size results in an increase in frequency of the accelerometer reso- nance and thus, a wider useful range.** Other factors to consider in the selection of a suitable accelerometer include: 1. The transverse sensitivity, which is the sensitivity to accelerations in a plane per- pendicular to the plane of the discs. 2. The environmental conditions during the accelerometer’s operation, primarily tem- perature, humidity, and varying ambient pressure. Often two types of sensitivities are stated by the manufacturer — the voltage sensitivity and the charge sensitivity. The voltage sensitivity is impor- tant when the accelerometer is used in conjunction with voltage measuring electronics, while the charge sensitivity, an indication of the charge accumulated on the discs for a given acceleration, is important when the accelerometer is used with charge-measuring electronics. Preamplifier The preamplifier is introduced in the measure- ment circuit for two reasons: 1. To amplify the weak output signal from the accelerometer; and 2. To transform the high output impedence of the accelerometer to a lower, acceptable value. It is possible to design the preamplifier in two ways, one in which the preamplifier output voltage is directly related to the input voltage, and one in which the output voltage is proportional to the input charge, with the preamplifier termed a volt- age amplifier or charge amplifier, respectively. The major differences between the two types of amplifiers rest in their performance character- istics. When a voltage amplifier is used, the overall system is very sensitive to changes in the cable lengths between the accelerometer and the pre- amplifier, whereas changes in cable length produce negligible effects on a charge amplifier. The input resistance of a voltage amplifier will also affect the low frequency response of a system. Voltage amplifiers are generally simpler than charge amplifiers, with fewer components and are, therefore, less expensive. In selecting the appro- priate preamplifier for vibration work, these above- mentioned factors should all be considered. Analyzers The analyzer element in a vibration measuring arrangement determines what signal properties are being measured and what kind of data can be ob- tained in the form of numbers or curves. The simplest analyzer consists of a linear am- plifier and a detection device measuring some char- acteristic vibration signal value such as the peak, root mean square, or average value of the accelera- tion, velocity, or displacement. The phase response of a system must be taken into account, in addition to the frequency response in choosing the correct analyzer. A signal reaching the detection device may look completely different from the signal input to the linear amplifier, due to possible dis- tortions during linear attenuation of a complex signal’s various frequency components. Serious waveshape distortion of the signal may be avoided when the fundamental vibration frequency is higher than 10 times the low frequency limit of the measuring system, and the highest significant vi- bration frequency component has a frequency which is lower than 0.1 times the high frequency limit of the system.?° Phase response can be dis- regarded for measurement of only RMS values. In most practical cases it will be necessary to determine the frequency composition of the vibra- tion signal, which is done with a frequency ana- lyzer. Two types of frequency analyzers are com- monly available, the constant bandwidth analyzer and the constant percentage bandwidth-type ana- lyzer. If the vibrations are periodic, the con- stant bandwidth-type analyzer is preferred because the frequency components are harmonically re- lated. If the signal is not quite stable and only the first few harmonics are significant, such as charac- teristic of a shock signal, a constant percentage bandwidth-type analyzer is suitable. If the vibra- tion signal is random in nature, the type of ana- lyzer will depend on the use to be made of the measurement as well as the frequency spectrum itself. If the vibrations are periodic, the frequency spectra are presented in terms of the RMS value of the signal, defined earlier. In random vibrations, the RMS-value fluctu- ates during measurement because the averaging time is limited to a practical time limit and the time of observation is greater than the averaging time of the instrument. A decrease in averaging time will cause considerable fluctuations in the RMS values. Vibration Recorders Many types of metering or recording devices are available to exhibit the analyzer output. These are divided into three classes: the strip-chart recorder which prints the output on preprinted calibrated recording paper; the vibration meter which indicates some characteristic value (RMS, peak, etc.) on a precalibrated scale; and an oscil- loscope, which projects the wave form on a screen for analysis and measurement. When a strip-chart recorder is used, the aver- 343 aging time is determined by the writing speed of the recording pen, the input range potentiometer, and other internal properties of the recorder in- stead of observation time. The choice of averaging time affects the recording of a random vibration frequency spectrum, The oscilloscope presents measurements as a function of time, and makes possible the study of instantaneous values of vibration. An oscilloscope with slow sweep rates, long-persistence screen, and a DC amplifier is recommended for most studies. Accessories The accessories used with vibration meters are determined by customer needs and usually can be built into any specified instrument. Integrators to interconvert displacement, velocity, and accelera- tion can be specified in the basic circuit design of measuring devices. Often, a series of ranges can be requested for a frequency analyzer, depending on the accuracy of the measurements required. Additional analyzers including the third- octave-bandwidth, tenth-octave-bandwidtth, one- percent-bandwidth, and a wave analyzer are avail- able. Different recorders, dependent on desired output, can be used in conjunction with any ana- lyzer. For peak or high speed impacts, the signal can be recorded on tape and then replayed at varied speeds to give the optimum measurement on an electric output signal. A calibrator is an important accessory for checking the overall operation of a vibration- measuring system. The common calibrator is noth- ing more than an accelerometer, driven by a small, electromechanical oscillator mounted within the mass, operated at a controlled frequency and RMS acceleration. Provisions can be made for addi- tional calibration of transducers, insert voltage, and reciprocity. Field Measurements The arrangement of the vibration equipment for typical field use is shown in Figure 26-12. Sources of error in field measurements must be recognized by the investigator and avoided or min- imized, at least, Common sources of error are incorrect mounting, incorrect calibration, connect- ing cable noises, and thermal effects. In the field, consideration must be given to the location and mounting of the accelerometer in order to record the original motion and resonant frequencies of the structure. The vibration transducer should load the structural member as little as possible, since any loading effects will invalidate the measurement results. In most practical situations, the mass loading effect is negligible but can be checked by the formula: MS AR=AS (rom ) where AR = Response of structure with accel- erometer AS =Response of structure without accelerometer MS = Weight of the structure member to which the accelerometer is attached MA = Weight of the accelerometer FREQUENCY ANALYZER PRE - ® AMPLIFIER ® ACCELEROMETER | o 4 w o = ® . LEVEL RECORDER . ooo ® oo ® ° ) oe Figure 26-12. Arrangement of Equipment for Automatic Frequency Analysis. Reprinted from “Mechanical Vibration and Shock Measurements” courtesy of Briiel & Kjaer Instruments, Cleveland, Ohio. A number of methods can be used to mount the accelerometer, including mounting by means of a steel stud, an isolated stud and mica washer, a permanent magnet, wax or soft glue, or hand- held with a probe. Use of a steel stud gives the best frequency response, approaching the actual calibration curve supplied with the accelerometer. When electrical isolation is required between the accelerometer and vibrator, a mica washer is used because of its hardness and transmission charac- teristics. A permanent magnet also gives electrical isolation, but magnetic mass, and temperature ef- fects on the accelerometer can be introduced. Handheld probes are convenient but should not be used for frequencies higher than 1000 Hz where mass loading effects begin. Wax, because of its stiffness, gives a good frequency response but should not be used at high temperatures. Another source of error, cable noise, originates either from mechanical motion of the cable or from ground loop-induced electrical hum and noise. Mechanical noises originate from local capa- city and charge changes due to dynamic compres- sion and tension of the cable, affecting low-fre- quency readings. A ground loop (see Figure 26-13) induces a current and small voltage drop which adds directly to the sometimes weak accel- erometer signal. Insuring that grounding of the installation is made only at one point eliminates ground looping. In ordinary vibration measurements, tempera- ture effects need not be considered. However, measurements of very low frequency, very low am- plitude vibration will be disturbed by even small temperature changes due to the variance of the accelerometer output at a rate determined by the time constant of the accelerometer preamplifier input circuit. Calibration of a typical vibration measuring arrangement can be made directly from curves and figures supplied by the manufacturer. Special 344 measuring arrangements can be calibrated using a vibration calibrator. The following general outline points out the important considerations in a field measurement: 1. Determine placement of the vibration trans- ducer with consideration for possible mass loading effects. 2. Estimate the types and levels of vibrations likely at the mounting point. 3. Select a suitable vibration transducer con- sidering the mass loading effect, types of vibrations, temperature, humidity, acoustic and electric fields. 4. Determine what type of measurement would be most appropriate for the problem at hand. 5. Select suitable electronic equipment, con- sidering frequency and phase character- istics, dynamic range and convenience. 6. Check and calibrate the overall system. 7. Make a sketch of the instrumentation sys- tem, including types and serial numbers. 8. Select the appropriate mounting method, checking vibration levels, frequency range, electrical insulation, ground loops, and temperatures. 9. Mount the accelerometer, carry out the measurements, and record the results. Re- cord any octave band analysis of the vibra- tions, if necessary. Note the setting of various instrument control knobs. The apparent vibration level, similar to a back- ground reading, should be recorded by mounting the accelerometer on a nonvibrating object in the measured system. Apparent vibrations should be less than one-third of the measured vibrations for accuracy in the actual vibration measurements. Analysis should include measurements at dif- ferent points on the machine or system to deter- mine the areas of greatest vibration and their 10. INCORRECT GROUNDING (a) (b) CORRECT GROUNDING PRE AMPLIFIER ACCELEROMETER ISOLATION Figure 26-13. FREQUENCY ANALYZER Illustration of Ground-Loop Phenomena. a) This method of connection forms ground loop and should be avoided. b) No ground-loop is formed. Recommended method of connection. Reprinted from “Mechanical Vibration and Shock Measurements” courtesy of Briiel & Kjaer Instruments, Cleveland, Ohio. respective frequency components. Experience is the best guide in pinpointing vibration sources in familiar machinery. Since machine vibrations pro- duce noise, reduction of vibration often reduces noise problems as well. CONTROL OF VIBRATION Vibrations may be reduced by: 1. Isolating the disturbance from the radiat- ing surface; 2. Reducing the response of the radiating surface; and 3. Reducing the mechanical disturbance caus- ing the vibration. 345 Isolation Vibration isolators effectively reduce vibration transmission when properly installed. The vibra- tion of a machine on isolators is complex, since the machine can move along or rotate about its one vertical and two horizontal axes. The machine will have a resonant frequency for each of the six modes of vibration; thus, it is important that none of the six possible resonances occur at the fre- quency of the disturbance. To insure adequate isolation, the resonant frequency of the isolator should be less than half the disturbing frequency. For the vertical mode, which is usually the most important, the resonant frequency of the iso- lator is related to its static deflection under the weight of the machine by the following formula: _ 3.13 Yd d is the static deflection, inches f is the frequency, Hertz To find the stiffness required from the isolation mount (spring) when the desired frequency has been determined, the formula: K = 0.04 X MS X F,? can be used. K = Spring constant MS = Machine weight F,=Resonant frequency of the machine and isolation mount system. Since the degree of isolation increases as the resonant frequency is lowered, the equation indi- cates that isolation is improved as the static deflec- tion is increased. Transmission of vibration to an adjacent structure may also be reduced by making elec- trical connections less rigid. For piping, elec- trical connections, and ductwork flexible connec- tors may be used. When using enclosures, the housing should be anchored to the floor rather than the machine to eliminate transmission of the vibration to the enclosures. Another important consideration is that the vibration isolators be placed correctly with re- spect to the motion of the center of gravity of the machine, with the center of gravity located as low as possible. In cases of instability, i.e., “rocking”, the effective center of gravity may be lowered by first mounting the machine on a heavy mass and isolating the mass from the machine. Reduction of Surface Response (Damping) where kg/cm In cases where isolation of the vibrations is . not suitable, or is difficult to arrange, the principle of vibration absorbers may be used. By attaching a resonance system to the vibrating structure (which counteracts the original vibrations), the structure vibrations can be eliminated. Through mathematical differential equations it can be shown that by tuning the absorber system resonant fre- quency, it is theoretically possible to eliminate the vibration of the machine. Structural elements like beams and plates ex- hibit an infinite number of resonances. When sub- jected to vibrations of variable frequency, the ap- plication of separate dynamic absorbers to struc- tural elements becomes impractical. Since there is usually little inherent damping of resonant vibra- tions in the structural elements themselves, exter- nal arrangements must be made to reduce vibra- tions. External damping can be applied in several ways: 1. By means of interface damping (friction) 2. By application of a layer of material with high internal losses over the surface of the vibrating element 3. By designing the critical elements as “sand- wich” structures. Interface damping is obtained by letting two 346 surfaces slide on each other under pressure. With no lubricating material the “dry” friction produces the damping effect, although this commonly causes fretting of the two surfaces. When an adhesive separator is used, a sandwich structure results, a concept which will be discussed later. Mastic “deadeners” made of an asphalt base are commonly sprayed onto a structural element in layers, to provide external dampening. These deadeners are commonly made from high-polymer materials with high internal energy losses over certain frequency and temperature regions. To obtain optimum damping of the combination struc- tural element and damping material, not only must the internal loss factor of the damping material be high, but so must its modulus of elasticity (the ratio of stress to strain). An approximate formula (see Figure 26-14) governing the damping properties of a treated panel is given by: ) ( ) d, N. E, N = 14 (Ge N = Loss factor of the combination structure element + damping material N, =Loss factor of the damping material E, = Modulus of elasticity of the structural element E, =Modulus of elasticity of the damping material d, = Thickness of the structural element d, = Thickness of the damping material layer. The ratio ( d, 2 d, usually around 3:1 for best results. The third method of damping is the use of sandwich structures; a thick or thin layer of visco- elastic material is placed between two equally thick plates, or a thin metal sheet is placed over the viscoelastic material which is covering the panel. The damping treatment will be more effective if applied to the area where vibration is greatest, but the actual amount of treatment and the area of coverage are best determined by experiment. As a rule of thumb, the amount (density X thickness) of material applied should equal that of the sur- face to which it is applied. Since this can lead to using large amounts of damping material, the method of covering the damping material with a sheet metal overlay is often used. Studies®’ show that to a certain extent, the thickness of a layer is not the most important factor; but in cases of sandwich layers, symmetry is most significant. Sandwich layers often are preferred due to a greater dampening factor (Figure 26-14) than with single layer coatings. Reduction of Mechanical Disturbance Mechanical disturbances that produce vibra- tion can be reduced by reducing impacts, sliding or rolling friction, or unbalance. In all cases, either mechanical energy is cou- pled into mechanical-vibratory energy, or energy in some other form is transformed into mechani- cal-vibratory energy. These other forms of en- ergy include: varying electrical fields, varying hy- ) "is the most important factor, 1.0 << S = 2 uw © Z 0.l a Z o 0.01 50 100 200 400 800 1600 3200 6400 HZ FREQUENCY, f — Figure 26-14. Results of Loss Factor Measurements on a Sandwich Structure with a Thin Visco-Elastic Layer, and on a Plate Supplied with One Layer Mastic Deadening (d,/d, = 2.5). After Cremer and Heckl.*! Reprinted from “Mechanical Vibration and Shock Measurements” courtesy of Briiel & Kjaer Instruments, Cleveland, Ohio. draulic forces, aerodynamic forces, acoustic ex- linear characteristics a great number of citation, and thermal changes. extra response effects may take place. Often mechanical vibration can be reduced by: The reduction in shock severity which may be (1) proper balancing of rotating machinery, (2) obtained by the use of isolators results from the reducing response of equipment to a driving force, storage of the shock energy within the isolators and (3) proper maintenance of machinery. and its subsequent release in a “smoother” form. Limitations of Control Methods Unfortunately, since a shock pulse may contain In conjunction with the practical applications frequency components ranging from nil to near of isolators. and dampers, certain limitations infinity it is not possible to avoid excitation of the should be noted in the control of vibration: isolator-mass system. 1. Reduction in transmissibility can only Damping is a costly method of reducing the take place by allowing the isolator to de- response of a radiating surface, and is therefore flect by motion. Thus, certain space clear- generally avoided. Mechanical disturbances, pri- ances must be provided for the isolated marily dependent upon an effective maintenance equipment. program, are rarely eliminated completely. 2. If the resonant frequency of the isolation In conclusion, all vibration problems should be system is chosen incorrectly, the isolator approached by determining first if a quick, simple, may actually amplify the destructive char- and “common sense” solution is available. If a acteristics. Select a spring mounting so simple answer is not obvious, the quantitative that the natural frequency, F,, of the results of measurements become essential in the spring-mass system is considerably (at analysis and solution of the problem. As various least one-half) lower than the lowest fre- control procedures are tried, vibration measure- quency component in the force system pro- ments can be used to show the progress being made duced by the machine. and predict the correct steps in reducing vibrations 3. If the isolator produces unexpected non- further. 347 References 1. COERMANN, R. R., G. H. ZIEGENRUECKER, A. L. WITTVER and H. E. von GIERKE. “The Passive Dynamic Mechanical Properties of the Hu- man Thorax-Abdomen System and the Whole Body System.” Aerospace Med. 31, 443-455, 1960. DIECKMANN, D. A. “Study of the Influence of Vibration on Man.” Ergonomics 1, 346-355, 1958. RADKE, A. O. “Vehicle Vibration, Man's New En- vironment.” American Society of Mechanical En- gineers, paper no. 57-A-54, 1957. GOLDMAN, D. E. and H. E. VON GIERKE. “Effects of Shock and Vibration on Man.” Shock and Vibration Handbook. C. M. Harris and C. E. Crede (ed.), McGraw-Hill Book Co., New York, N. Y., Vol. 3, Chap. 11, pp. 44 & 51, 1961. COERMANN, R. R. “Investigations into the Effects of Vibrations on the Human Organisms.” Zschr. Luftfahrtmed. 4, 73, 1940. DUFFNER, L. R.,, L. H. HAMILTON and M. A. SCHMITZ. “Effect of Whole-Body Vertical Vibra- tion on Respiration in Human Subjects.” J. Appl. Physiol, 17, pp. 913-916, 1962. ERNSTING, J. “Respiratory Effects of Whole-Body Vibration.” 1.A.M. Report from the Royal Air Force, no. 179. Farnborough, England: Institute of Aviation Medicine, 1961. HOOD, JR., W. B.,, R. HL. MURRAY, C. W. UR- SCHEL, J. A. BOWERS and J. G. CLARK. “Cardiopulmonary Effects of Whole-Body Vibration in Man.” J. Appl. Physiol. 21, pp. 1725-1731, 1966. GUIGNARD, J. C. “The Physical Response of Seated Men to Low-Frequency Vertical Vibration: Preliminary Studies.” Report from the Flying Per- sonnel Research Committee. Farnborough, Eng- land: Institute of Aviation Medicine (Royal Air Force), (April) 1959. . LOEB, M. A. “Further Investigation of the Influ- ence of Whole-Body Vibration and Noise on Tremor and Visual Acuity.” Report from the U.S. Army Medical Research Laboratory (Fort Knox) no. 165, 1955. 348 11. 12. 20. 21. COERMANN, R. R,, E. B. MAGID and K. O. LANGE. “Human Performance Under Vibrational Stress.” Human Factors Journal 4, pp. 315-324, 1962; and In: Human Vibration Research, S. Lip- pert (ed.), Pergamon Press, New York, N. Y., pp. 89-98, 1963. LINDER, G. S. “Mechanical Vibration Effects on Human Beings.” Aerospace Med. 33, pp, 939-950, 1962. HASAN, J. “Biomedical Aspects of Low-Frequency Vibration: A Selective Review.” Work-Environ- ment-Health, Vol. 7, No. 1, 1970. AGATE, J. N. and H. A. DRUETT. “A Study of Portable Vibrating Tools in Relation to the Clinical Effects Which They Produce.” Brit J. Industr. Med. 4, p. 141, 1947. HUNTER, D. “The Diseases of Occupations.” Eng- lish University Press, London, pp. 782-792, 1955. . WASSERMAN, D. E. and D. W. BADGER. “The NIOSH Plan for Developing Industrial Vibration Exposure Criteria.” Journal of Safety Research 4, pp. 146-154, 1972. GOLDMAN, D. E. “A Review of Subjective Re- sponses to Vibratory Motion of the Human Body in the Frequency Range 1 to 70 Cycles per Sec- ond.” Project NM-004-001, Report 1, National Na- val Medical Research Institute, March, 1948. International Organization for Standardization. Technical Committee 108, Working Group 7. “Guide for the Evaluation of Human Exposure to Whole- Body Vibration,” August, 1969. International Organization for Standardization. Technical Committee 108, Working Group 7. “Guide for the Evaluation of Human Exposure to Seg- mental (Hand-Arm-System) Vibration.” Adoption pending. BROCH, J. T. “Mechanical Vibration and Shock Measurements,” K. Larsen & Son, Soborg, Denmark. CREMER, L. and M. HECKL. Koperschal. Springer Verlag, Berlin, Heidelberg, New York, 1967. CHAPTER 27 ILLUMINATION John E. Kaufman INTRODUCTION Lighting of the industrial environment pro- vides for the visibility of objects and awareness of space needed for man to perform in a produc- tive and secure manner. Not only should the lighting be properly designed and coordinated with the thermal, spatial and sonic designs, but it should be maintained through planned servicing procedures. The only means for determining whether a particular environment has been prop- erly designed and is correctly maintained is to perform periodic evaluations or surveys. In evaluating the lighting in any environment it is important to know how to make an effective meaningful survey and this can only be done with a basic understanding of lighting terminology, es- tablished recommendations for quantity and qual- ity of lighting, types of lighting equipment and design procedures, and finally survey methods and instruments to be used. LIGHTING TERMINOLOGY The lighting terms most often used in design and evaluation of illuminated spaces include: in- tensity, illumination level, luminance, reflectance, lamp and luminaire. Most often used units of measurement are: candela, lumen, footcandle and footlambert. For a more complete list of terms with their definitions see Section 1 of reference 1. Intensity Intensity, or more correctly luminous intensity, is an indication of how much light a source gives off in a given direction. The unit of luminous intensity is the candela (formerly “candle”). It is sometimes referred to as “candlepower.” Lumen The lumen is the unit of light output from a light source. For example, a 100-watt incandes- cent lamp emits about 1700 lumens initially in all directions, whereas a 40-watt cool-white fluores- cent lamp emits about 3200 lumens initially. By definition, a light source of one candela produces 4 = lumens. Illumination Level Illumination level is the amount or quantity of light falling on a surface and is measured in footcandles. 1f, for example, 100 lumens from a light source falls on one square foot of a table top, the illumination level on the table would be 100 footcandles. Also, a surface one foot from a source with an intensity of 100 candelas would have an illumination level of 100 footcandles. If the unit of surface area is in square meters rather than square feet, the illumination is mea- sured in lux. 349 Luminance Luminance, or photometric brightness, is a measure of the amount of light emitted or reflected from a certain area of a surface. Its unit is foor- lamberts when the area of surface is square feet. A surface emitting one lumen per square foot of surface has a luminance of one footlambert. A bare 40-watt fluorescent lamp has a luminance of about 2400 footlamberts, whereas the moon has a luminance of nearly 1170 footlamberts. If the unit of surface area is in square meters rather than square feet luminance is measured in candelas/square meter. Reflectance Reflectance is a measure of how much light is reflected from a surface. Actually it is the ratio of the luminance of a surface to the illumination on the surface (i.e., reflectance = luminance/illum- ination). A completely black surface has a 0 percent reflectance. A perfectly white surface has a reflectance of nearly 1.0 or 100 percent. Most surface finishes have reflectances of between 5 to 95 percent. Lamp Lamp is the term used for man-made light sources. Incandescent lamps are also called “bulbs” and fluorescent lamps, “tubes.” “Lamp” is also used for the name of a complete lighting device consisting of a lamp, shade, reflector, hous- ing, etc. Luminaire A luminaire is a complete lighting device con- sisting of one or more lamps together with parts to distribute the light, to position and protect the lamps and to connect the lamps to the power supply. PURPOSE OF LIGHTING The purpose of lighting in industry is to pro- vide efficient, comfortable seeing of industrial vis- ual tasks and to help provide a safe working en- vironment. Advantages derived from good light- ing include: fewer mistakes, increased production, reduction in accidents, improved morale and im- proved housekeeping. Lighting for Task Performance Visual tasks in industry vary in degree of difficulty depending on their size, their contrast (between detail and surround), their luminance and the time available for seeing. The smaller a task size the more difficult it is to see — for equal illumination a very small letter identification on a printed circuit board is harder to see than the type on this page. Tasks of low contrast, such as a gray stain on gray cloth are more difficult to see than higher contrast tasks such as a dark gray stain on white cloth. Also, it usually is easier to see an inspection task if more time is available for viewing. The factors of size, contrast and in many cases time, are inherent in a visual task. On the other hand task luminance is variable and can easily affect task visibility — the higher the luminance (the greater the illumination) the more visible the task. This is due to an increase in eye sensitivity with increased luminance. Lighting for Safety and Comfort Lighting adequate for seeing production and inspection tasks usually will be more than needed for safety alone. If task lighting is not provided throughout the working space, adequate surround- ing illumination is required to provide visibility of nearby objects which might be potential haz- ards or to see to operate emergency control equip- ment. In addition, lighting of ceiling and walls and the avoidance of glare will help provide a greater sense of well being and comfort, ILLUMINATION REQUIREMENTS FOR INDUSTRY Quantity of Illumination The difficulty of seeing tasks, based on con- trast, size and time for viewing as discussed above, is used as a basis for determining the levels of il- lumination for industrial areas. Research has shown that levels of illumination in the thousands of footcandles are required to see dark, low-con- trast tasks as easily as light-colored tasks of high contrast under low levels. For light-colored, high- contrast tasks, the levels required for good visi- bility are very low. However, there are many factors in addition to visibility that affect the con- cept of easier seeing which suggest a minimum of 30 footcandles be used for all areas where seeing is done regularly, even for the simplest seeing tasks.” The American National Standard Practice for Industrial Lighting® contains a tabulation of rec- ommended levels of illumination for specific vis- ual tasks and areas based on task characteristics and the visual performance requirements of young adults with normal eyes. According to the Amer- ican National Standard Practice for Industrial Lighting® “These lighting recommendations are in- tended to provide guides for lighting levels de- sirable from an overall operational standpoint rather than from safety alone and, therefore should not be interpreted as recommendations for regu- latory minimum lighting levels.” Table 27-1 is a sample of the type of recommendations listed and is included here to show its form. Task areas are shown with corresponding footcandle levels recommended for the tasks in the area, these levels to be used as the minimum value on the task when the lighting system and room surface have depre- ciated to their lowest before maintenance pro- cedures are effected (cleaning, relamping, paint- ing, etc.). Also, in some cases, as denoted by a double asterisk, supplementary lighting can be used. The levels recommended usually do not take 350 into account the wearing of safety goggles that materially reduce the light reaching the eyes. If they are worn, the level of illumination should be increased in accordance with the absorption of the goggles used. Quality of Illumination By definition, quality in lighting pertains to the distribution of luminances in a visual environ- ment and is used in a positive sense to imply that all luminances contribute favorably to comfort, safety, esthetics as well as ease of seeing. Exces- sively high luminances may produce glare and veiling reflections and affect eye adaptation. Im- proper distribution of luminances also may affect adaptation and cause shadows. Installations of very poor quality are easily recognized but those of moderately poor quality are not, even though there may be a material loss in seeing. TABLE 27-1. Levels of Illumination Currently Recommended® Footcandles Area on Tasks* Clothing manufacture (men’s) Receiving, opening, storing, shipping o.oo 30 Examining (perching) ............... 2000** Sponging, decating, winding, Measuring _.....oooooooiieiiiiiiaiieeaee 30 Piling up and marking ......__...__.._... 100 Cutting ooo 300** Pattern making, preparation of trimming, piping, canvas and shoulder pads .......................... 50 Fitting, bundling, shading, stitching... 30 Shops ooo 100 Inspection 500** Pressing o.oo 300% * Sewing ois 500** *Minimum on the task at any time. **Can be obtained with a combination of general light- ing plus specialized supplementary lighting. Care should be taken to keep within the recommended luminance ratios. These seeing tasks generally involve the discrimination of fine detail for long periods of time and under conditions of poor contrast. The de- sign and installation of the combination system must not only provide a sufficient amount of light, but also the proper direction of light, diffusion, color and eye protection. As far as possible it should eliminate direct and reflected glare as well as objectionable shadows. Glare. There are two general forms of glare — discomfort glare and disability glare — and both may be caused by bright light sources (electric and daylight) and by bright reflections in room surfaces. Glare from light sources and luminaires is known as direct glare; that from surfaces, as reflected glare. Discomfort glare, as its name implies, pro- duces discomfort and may affect human perform- ance, but does not necessarily interfere with vis- ual performance or visibility. In some cases ex- tremely bright sources (the sun) can even cause pain. Disability glare does not cause pain, but reduces the visibility of objects to be seen. An example is the reduced visibility of objects on a roadway at night caused by the glare of bright on- coming headlights. An industrial environment, then, will be rela- tively comfortable visually, if there is no glare, and seeing will be unimpaired if there is no dis- ability glare. The effects of glare can be avoided or minimized by mounting luminaires as far above or away from normal lines of sight as possible and by limiting their luminance and quantity of light emitted toward the eyes. In general, this can be done by shielding luminaires to at least 25 degrees down from the horizontal and preferably down to 45 degrees. In other words, the bright- ness of bare lamps preferably should not be seen when looking in the range from straight ahead to 45 degrees above the horizontal. For critical work- ing areas such as offices and laboratories the qual- ity criteria of the American National Standard Practice for Office Lighting* should be followed. Veiling Reflections. When reflected glare is pro- duced on or within the visual task itself it becomes a veiling reflection because in most cases it will veil the task (reducing its visibility) by reducing its contrast. In some cases these losses in con- trast are quite apparent; in others the losses are unnoticed yet may produce a marked reduction in visibility. The effects of veiling reflections may be reduced by increased levels of illumination and or by using layouts and luminaires designed to limit the light directed toward the task that will be reflected into the eyes. See the IES Light- ing Handbook. Luminance Distribution. The eyes function more efficiently and comfortably when the luminances within the visual environment are not too differ- ent from that of the seeing task. While performing a task the eyes become adapted to the luminance of the task. If however, the eyes shift to view a window or floor of higher or lower luminance and then back to the task, the visibility of the seeing task will be reduced until the eyes readapt to the task luminance. To reduce this effect, maximum luminance ratios are recommended as shown in Table 27-2. As an aid in achieving these reduced luminance ratios, the reflectance of room surfaces and equipment should be as listed in Table 27-3. Distribution, Diffusion and Shadows. In industrial areas where the locations of equipment and oper- ations are not known, it is desirable to provide uniform illumination such that the highest and lowest levels are no more than one-sixth above or below the average. This also will help maintain desirable luminance distributions as recommended above. Depending on the type of visual task and the operation, some tasks require directional lighting and others diffuse, but in both cases shading of the task should be avoided. Most tasks can be 351 TABLE 27-2 Recommended Maximum Luminance Ratios? Environmental Classification B A . Between tasks and adjacent darker surroundings S5tol 3tol 3tol . Between tasks and adjacent lighter surroundings 1to$5 1to3 1to3 . Between tasks and more remote darker surfaces 10to1 20to1l . Between tasks and more remote lighter surfaces 1to10 1to20 . Between luminaires (or windows, sky- lights, etc.) and surfaces adjacent to them * 20to 1 . Anywhere within normal field of view * 40to 1 *Luminance ratio control not practical. A—Interior areas where reflectances of entire space can be controlled in line with recommendations for optimum seeing conditions. B—Areas where reflectances of immediate work area can be controlled, but control of remote surround is limited. C—Areas (indoor and outdoor) where it is completely impractical to control reflectances and difficult to alter environmental conditions. TABLE 27-3 Recommended Reflectance Values® Applying to Environmental Classifications A and B we Reflectance* (percent) Ceiling 80 to 90 Walls 40 to 60 Desk and bench tops, machines and equipment 25 to 45 Floors not less than 20 *Reflectance should be maintained as near as practical to recommended values. satisfactorily illuminated by diffuse illumination, but tasks of inherently low contrast and of a three- dimensional nature often can be seen best using directional light to produce shadows and reflec- tions to improve contrast. Examples of such tasks are glossy black thread on matte black cloth and scratches on sheet metal. In the latter case it is especially important that the lighting be designed so that it will not produce reflected glare in the sheet metal. Color. For equal levels of illumination variations in the color quality of currently used “white” light sources have little or no effect upon clearness or speed of seeing. However, when contrast is low and color discrimination is important, source and surrounding surface colors should be selected carefully. INDUSTRIAL LIGHTING EQUIPMENT Light Sources Daylight and electric light are the two main sources of light for industrial areas. The use of daylight depends on building design orientation and site conditions as well as the availability of daylight at the location; however, because day- light is not always available electric lighting is provided. Illuminating Engineering Society, New York, New York. Figure 27-1. Electric light sources used for industrial appli- cation fall into three categories: incandescent (in- cluding tungsten-halogen), fluorescent and high- intensity discharge (including mercury, metal halide and high pressure sodium). Although all types can be used, there are certain applications for which some are better suited than others. For detailed information on their physical and operat- ing characteristics as well as industry averaged photometric data (lumen values) consult the IES Lighting Handbook. Luminaires There are two categories of luminaires for in- dustrial lighting — general and supplementary. General Luminaires are classified into five types according to their light distribution, as shown in Figure 27-1, and are used to provide general light- ing throughout an area or localized general light- ing, where the luminaries are located to provide higher levels at specific task locations yet provide some degree of general lighting. Each type of dis- Luminaire Classifications by Light Distribution: (a) Direct Lighting, (b) Semi-Di- rect Lighting, (c) General-Diffuse and Direct-Indirect Lighting, (d) Semi-Indirect Lighting and (e) Indirect Lighting. 352 i 7 I b ” a Illuminating Engineering Society, New York, New York. Figure 27-2. -d Cc Examples of Placement of Supplementary Luminaires: (a) Luminaire Located to Prevent Reflected Glare — Reflected Light Does Not Coincide with Angle of View. (b) Re- flected Light coincides with Angle of View. (c) Low-Angle Lighting to Emphasize Surface Ir- regularities. (d) Large-Area Surface Source and Pattern are Reflected toward the Eye. (e) Transillumination from Diffuse Sources. tribution has an application in industrial lighting, for example: direct types are the most efficient (but may produce disturbing shadows and glare unless units are of large size, mounted close to- gether and have some upward light), whereas at the other extreme indirect types are least efficient but produce more comfortable lighting. No one system can be recommended over all the others. Each should be evaluated based on the quantity and quality requirements of the space. Supplementary luminaires are luminaires used along with a general lighting system but are lo- cated near the seeing task to provide the higher levels or quality of lighting not readily obtainable from the general lighting system. They are divided into five major types from Type S-I to S-V, based on their light distribution and luminance charac- teristics. Each has a specific group of applications and locations, as shown in Figure 27-2, to best illuminate the seeing task involved. LIGHTING DESIGN In industrial areas where the primary function of the lighting installation is to provide illumina- tion for quick, accurate performance of visual tasks, the task itself is the starting point in the lighting design. Factors to be considered in the design process are listed below, but it should be recognized that the success of the design also de- pends on the accuracy of the information avail- able to the designer. 1. Visual Task. a. What commonly found visual tasks are to be lighted? How should the tasks be portrayed by the lighting? Should the lighting be dif- fuse or directional? Are shadows im- portant for a three dimensional effect? Will the tasks be susceptible to veiling reflections? Is color important? What level of illumination should be provided in accordance with the Amer- ican National Standard Practice for Industrial Lighting?® b. C. 353 Area in Which Task Is Performed. a. What are the dimensions of the area and reflectances of surfaces? What should the surface luminances be to minimize eye adaptation effects without creating a bland environment? Might the surfaces produce reflected glare? Is illumination uniformity desirable (general illumination or task illumina- tion)? Luminaire Selection. a. What type of distribution and lamp color quality is needed to properly por- tray the task (for diffusion, shadows or avoiding veiling reflections) and pro- vide a comfortable environment (vis- ually, thermally and sonically)? What type is needed to illuminate the area surfaces (for eye adaptation, for avoiding reflected glare)? What is the area atmosphere and there- fore the type of maintenance charac- teristics needed? What are the economics of the lighting system? Calculation, Layout and Evaluation. a. What layout of luminaires will portray the task best (illumination level, direc- tion of illumination, veiling reflections, disability glare)? b. d. b. What layout will be most comfortable (visually — direct and reflected glare, thermally)? c. What layout will be most pleasing esthetically? General Illumination When task locations are not known or a flex- ible arrangement of operations is desirable, light- ing is usually designed to provide general illumi- nation of the required amount throughout the area. This is also true where supplementary luminaires are used for task illumination alone. The calcu- lation procedure for designing general illumination A 90 C D 80 E S F : 70 72 | 0 70 5 67 a 3 63 0 60 = 57 - x E z a 50 Akt Zz Qo g OS le—1—t—2 3 4— © sol-cean CLEAN CLEAN CLEAN z LUMINAIRES ~~ LUMINAIRES LUMINAIRES LUMINAIRES ¥ ONCE AND PER 18 MONTHS PER 18 MONTHS PER 12 MONTHS RELAMP 100% RELAMP 100% RELAMP 50% RELAMP 33.1 3% ONCE PER ONCE PER ONCE PER ONCE PER 30[- 36 MONTHS 36 MONTHS 18 MONTHS 12 MONTHS 4 = a A—TEMPERATURE AND VOLTAGE 20 MN C —DIRT ON ROOM SURFACES Th B —DETERIORATION OF LUMINAIRE SURFACES i. 4 D —LAMP LUMEN DEPRECIATION (LLD) ~— == E—LAMP OUTAGES NOT REPLACED III or on names wo o 12 24 TIME IN YEARS Illuminating Engineering Society, New York, New York. Figure 27-3. Six Causes of Light Loss. Example above uses 40-watt T-12 cool white rapid start lamps in enclosed surface mounted units, operated 10 hours per day, 5 days per week, 2600 hours per year. All four maintenance systems are shown on the same graph for conven- ience. For a relative comparison of the four systems, each should begin at the same time and cover the same period of time. is the Lumen Method, where, with a uniform layout of luminaires, a relatively uniform level of illumination will be provided on a horizontal work- plane at a given distance above the floor. A de- tailed outline of this method can be found in General Procedure for Calculating Maintained Hlumination.* Task Illumination When task locations are known, Point Method procedures are used for design. Methods are 354 available’ for calculating illumination levels at spe- cific locations on horizontal, vertical and inclined surfaces, from all types of general or supplemen- tary lighting systems. Use of these methods is the most accurate means of checking illumination levels on tasks during the design stage. Maintenance As mentioned above, the success of the light- ing design is dependent on the accuracy of the information available to the designer, including the lighting servicing plan for maintaining the lighting from installation to end of life. Figure 27-3 illustrates the sizeable effects of various elements of light loss (temperature, voltage, dirt on luminaires and room surfaces, lamp depreci- ation and burnouts and deterioration of luminaire parts) on the level of illumination from initial operation (100 hours use) through various stages of servicing procedures. It is important to know or correctly assume thesc losses. It is equally as important to know the type of servicing plan so that minimum maintained levels can be de- signed for; so that during a lighting survey the surveyor will know if initial or lowest expected values are being measured, or whether the survey is somewhere between. Guidance for the use of light loss factors in design and information on lighting maintenance can be found in the IES Lighting Handbook. LIGHTING SURVEYS Evaluation of the lighting in an industrial en- vironment depends on the amount and type of information obtained during survey procedures Illuminating Engineering Society, New York, New York. Figure 27-4. and on the evaluator’s knowledge and understand- ing of industrial operations and their associated lighting recommendations. The material presented so far in this chapter deals with lighting recom- mendations. The following deals with the survey and evaluation. Measurable Quantities A lighting survey can be as simple or as com- prehensive as desired, but in any case three es- sential quantities are measured or determined: il- lumination (footcandles), luminance (footlam- berts) and reflectance (percent). For the more comprehensive surveys, temperature and voltage are also measured. Illumination readings are made at task locations for task lighting, at various locations on the hori- zontal work-plane for general lighting, and in some cases on various room surfaces to determine luminances and reflectances. Luminance readings are made of luminaires and room and task sur- faces. Reflectance determinations are made of room surfaces. Temperature is measured in the air near iuminaires. Voltage is mcasured at the luminaire input. Typical Photoelectric Meters Used in Lighting Surveys: (a) Pocket-Size Illumina- tion Meter, (b) Paddle-Type Illumination Meter with Operational Amplifier, and (c) Luminance Meter. Instruments Hlumination (Light) Meters. Figure 27-4a and b shows two typical illumination meters — a pocket- type and a more accurate paddle-type. The de- gree of accuracy required dictates the type of meter to be used, but in any case, instruments should be color corrected (to account for the response of the eye to light), cosine corrected (to compensate for light reflected from the light-detecting cell sur- face), calibrated for accuracy and with scale ranges so that no measurements are made below one-quarter full scale. A luminance meter (see below) can be used to measure illumination if a wn target of known reflectance is measured (illumi- nation = luminance = reflectance). Luminance (Brightness) Meters. Figure 27-4c shows a typical direct reading portable luminance meter. Again the degree of accuracy required dic- tates the type of meter to be used and its correc- tions, sensitivity and calibration. Luminance of surfaces also can be measured using an illumina- tion meter if the reflectance of the surface is known (luminance = illumination X reflectance). Reflectance can be measured directly using a Baumgartner reflectometer,’ however in field sur- veys, reflectance is usually determined by visual comparison of the unknown surface with color chips of known reflectance (Munsell Value Scales!) or by calculation using measurements (re- flectance = luminance = illumination). Survey Procedures The publication How to Make a Lighting Sur- vey,” developed by the Illuminating Engineering Society in cooperation with the U. S. Public Health Service, provides a uniform detailed lighting sur- vey form along with instructions for use. The sur- vey involves recording the following information: 1. Description of the illuminated area — room dimensions; colors, reflectances and condi- tion of room surfaces; and temperature surround- ing luminaires. 2. Description of the general lighting system — quantities, condition, wattages, lamps, distribu- tion, spacing and mounting. 3. Description of any supplementary lighting equipment used — as in 2, above. 4. Description of instruments used — manu- facturer, model and date of last calibration. 5. Illumination measurements — at specific locations, depending on type of lighting system used. 6. Luminance measurements — from specific work locations in normal viewing directions. 7. Answers to a series of questions concern- ing the lighting servicing procedure and a subjec- tive evaluation of the lighting. Evaluation of Results The measurements and other data recorded are used to determine: (a) illumination levels (for compliance with footcandle recommendations), (b) luminance values (for compliance with lumi- nance ratio limits for visibility and safety) and (c) an indication of the degree of comfort and pleas- antness in the area (from answers to related ques- tions). In addition, these data are useful in de- 356 termining if adequate maintenance or lighting ser- vicing procedures are in effect. Also, they can indicate if deficiencies exist and what changes can be made for improvement; (e.g., application of higher or lower surface reflectances, better use of color, different luminaire locations for uniformity and to avoid shadows and glare, more light on the ceiling and better control of the daylighting). It should be realized, of course, that the con- ditions existing during the survey may not be the same as those assumed by the designer in his de- sign procedure, and the surveyor and evaluators should be aware of this. References I. IES Lighting Handbook, fifth edition, Illuminating Engineering Society, New York, 1972. IES COMMITTEE ON RECOMMENDATIONS FOR QUALITY AND QUANTITY OF ILLUMI- NATION: Report No. 1, Illum. Eng., 53: 422 (1958). American National Standard Practice for Indus- trial Lighting, A 11.1 — 1965 (R 1970), Illuminat- ing Engineering Society, New York, 1970. American National Standard Practice for Office Lighting, A 132.1 — 1966, Illuminating Engineer- ing Society, New York, 1966. DAYLIGHTING COMMITTEE OF THE IES: Recommended Practice of Daylighting. /llum. Eng., 57: 517 (1962). LIGHTING DESIGN PRACTICE COMMITTEE OF THE IES: General Procedure for Calculating Maintained Illumination. Illum. Eng., 65: 602 (1970). LIGHTING SURVEY COMMITTEE OF THE IES. How to Make a Lighting Survey. Illum. Eng., 57: 87 (1963). Preferred Reading 1. Lighting Design & Application, Illuminating En- gineering Society, New York. Journal of the Illuminating Engineering Society, Illuminating Engineering Society, New York. ALLPHIN, W.: Primer of Lamps and Lighting, Sylvania Electric Products, Inc., 1965. 2. 2. 3. CHAPTER 28 NON-IONIZING RADIATION George M. Wilkening INTRODUCTION Current Interest in the Non-Ionizing Radiations Interest in the public health aspects of the non-ionizing radiations has increased many fold due to the expanded production of electronic products which use or emit radiation, e.g., lasers, microwave ovens, radar for pleasure boats, in- frared inspection equipment and high intensity light sources. All such sources generate so-called “non-ionizing” radiation, a term which is defined in the section entitled “Nature of Electromagnetic Energy.” Because of the proliferation of such electronic products as well as a renewed interest in electromagnetic radiation hazards, the Congress recently enacted Public Law 90-602, the “Radia- tion Control for Health and Safety Act of 1968.” PL 90-602 has as its declared purpose the es- tablishment of a national electronic product radia- tion control program which includes the develop- ment and administration of performance standards to control the emission of electronic product ra- diation. The most outstanding feature of the Act is its omnibus coverage of all types of both ioniz- ing and non-ionizing electromagnetic radiation emanating from electronic products, i.e., gamma, X rays, ultraviolet, visible, infrared, radiofrequen- cies (RF) and microwaves. Performance standards have already been issued under the Act for TV sets and microwave ovens; preparations are un- derway for the issuance of a laser standard. In similar fashion, the recent enactment of the federal “Occupational Safety and Health Act of 1970” gives due attention to the potential hazards of non- ionizing radiations in industrial establishments. For the purposes of this chapter more formal treatment is given to ultraviolet radiation, lasers, and microwave radiation than to the visible and infrared (IR) radiations. However, the informa- tion on visible and IR radiation presented in the section on “Laser Radiation” is generally applic- able to noncoherent sources. Nature of Electromagnetic Energy The electromagnetic spectrum extends over a broad range of wavelengtths, from less than 1072 cm to greater than 10° cm. The shortest wave- lengths are generated by cosmic and X-rays; the longer wavelengths are associated with microwave and electrical power generation. Ultraviolet, vis- ible and infrared radiations occupy an interme- diate position. Radio frequency waves may range from 3X 10° um to 3X10? um; infrared rays, from 3X 10* um to about 0.7 um; the visible spectrum, from approximately 0.7 um to 0.4 um; ultraviolet, from approximately 0.4 ym to 0.1 pm; and gamma and x radiation, below 0.1 um (see Fig. 28-1). The photon energies of electromag- netic radiations are proportional to the frequency of the radiation and inversely proportional to wavelength. Hence, the higher energies, e.g., 10% electron volts (eV) are associated with X-ray and gamma radiations, and the lower energies (e.g., 10~¢ eV) with RF and microwave radiations. Whereas the thermal energy associated with molecules at room temperature is approximately 1/30 eV, the binding energy of chemical bonds is roughly equivalent to a range of <1 to 15 eV. The nuclear binding energies of protons may be equiva- lent to 10° eV and greater. Since the photon en- ergy necessary to ionize atomic oxygen and hy- drogen is of the order of 10-12 eV it seems in order to adopt a value of approximately 10 eV as a lower limit in which ionization is produced in biological material. Hence, those electromagnetic radiations that do not cause ionization in bio- logical systems may be presumed to have photon energies less than 10-12 eV and, therefore, may be termed “nonionizing.” An extremely impor- tant qualification however is that non-ionizing radiations may be absorbed by biological systems and cause changes in the vibrational and rotational energies of the tissue molecules, thus leading to possible dissociation of the molecules or, more often, dissipation of energy in the form of fluores- cence or heat. In conducting research into the bioeffects of the nonionizing radiations the investigator has had to use several units of measurement in ex- pressing the results of his studies. For this reason Appendix A, containing definitions of many useful radiometric terms has been included. Appendix B provides a simple means for expressing radiant exposure and irradiance units in a number of equivalent terms. Since the eye is the primary organ at risk to all of the non-ionizing radiations, Appendix C has been added to provide the reader with a gen- eral scheme of absorption and transmission of electromagnetic radiations within the human eye. ULTRAVIOLET RADIATION Physical Characteristics of Ultraviolet Radiation For the purpose of assessing the biological effects of ultraviolét radiation the wavelength range of interest can be restricted to 0.1 um to 0.4 pum. This range extends from the vacuum ultraviolet (0.1 um) to the near UV (0.4 um). A useful breakdown of the ultraviolet region is as follows: 357 8S¢E Non-ionlzing Radiation IONIZING RADIATION “LIGHT RADIO FREQUENCIES HEAT CAMMA MICROWAVES XRAYS (VISIBLE | LP LF MF HF VHF UHF | SWF | ENF INFRA RED ULTRA VIOLET ad 1 1 1 1 1 3 1 1 1 100 10 1 10! 102 10-3 107¢ 10-3 10¢ (07 1 i 1 1 1 I 1 | 1 I Micrometers, um ¥ < > [SS =z 5 S : = & te vw o > oc «n © o - P 2 =z & s = ot Cr « Ss [= bd w "0 b= 8 > « 5 - Oo x 2 z se o © a o 8 a 2 = < ~ w o - < o 1 2 é 8 3 x : < P 3 1 } ! 1 i 1 Jd 1 od 1 1 1 1 1 ] 1 1 1 093 03 3 30 300 300) 3(10)* 331013 3¢0® 3007 3008 300° 3010/0 300)! 301002 30013 301014 301003, T T T T 1 1 f 1 | 7 T 71 T T T Tr T FREQUENCY, MHz 1 1 ! 1 1 i ld 1 Jd 1 J 1 1 J i 1 1 1 08 10% i0* 103 102 10 IC™ ©! 0? 10° 10°¢ 1073 0% 07 1078 10? 40° io! T y 1 T T T 1 T 1 1 7 7 T T T T 1 T WAVELENSTH, CM Mumford WW: Some Technical Aspects of Microwave Radiation Hazards. Proc. IRE 49:427-47, 1961. The Electromagnetic Spectrum. Figure 28-1. UV Region —Range, um. Photon Energy (electron volts) Vacuum <0.16 >7.7 Far 0.16-0.28 7.7-4.4 Middle 0.28-0.32 44-39 Near 0.32-0.4 3.9-3.1 The photon energy range for wavelengths between 0.1 pum and 0.4 um is 12.4 to 3.1 electron volts respectively. Certain transmission, absorption and reflectance characteristics of ultraviolet radiation are given in Tables 28-1 and 28-2. Representative Sources of Ultraviolet Radiation The major source of ultraviolet radiation is the sun, although absorption by the ozone layer permits only wavelengths greater than 0.29 um to reach the surface of the earth. Low and high pressure mercury discharge lamps and welding TABLE 28-1 Transmission, Absorption Characteristics of Ultraviolet Radiation A range, pm Transmission, Absorption Properties 0.3-0.4 Transmits through air — Partially transmits through ordinary glass, quartz, water. 0.2-0.32 Transmits through air, quartz. Absorbed by ordinary window glass. Ozone layer absorbs sun’s radiation at A less than 0.29 um. Absorbed by epithelial layers of skin and cornea. Poorly transmitted through air and quartz. Air and quartz completely absorb these A. Radiations can exist only in vacuum. 0.16-0.2 <0.16 and plasma torches constitute significant man- made sources. In low pressure mercury vapor discharge lamps over 85% of the radiation is usually emitted at 0.2537 um. At the lower pres- sures (fractions of an atmosphere) the character- istic mercury lines predominate whereas at higher pressures (up to 100 atmospheres) the lines broaden to produce a radiation continuum. In typical quartz lamps the amount of energy at wave- lengths below 0.38 um may be 50% greater than the radiated visible energy, depending upon the mercury pressure. Other man-made sources in- clude xenon discharge lamps, lasers and relatively new types of fluorescent tubes which emit radia- tion at wavelengths above 0.315 um reportedly at an irradiance less than that measured outdoors on a sunny day. Biological Effects of Ultraviolet Radiation The biological action spectrum for erythema (reddening) produced by ultraviolet radiation of the skin has been the subject of investigation for many years. The most recent data show that a maximum erythemal effect is produced at 0.260 pm with the secondary peak at approximately TABLE 28-2 Reflectance of 0.2537 um Radiation From Various Surfaces Material % Reflectance* Aluminum, etched 88 Aluminum foil 73 Chromium 45 Nickel 38 Stainless Steel 20-30 Silver 22 Tin-plated steel 28 White wall plaster 40-60 White paper 25 White cotton 30 White oil paints 5-10 White porcelain enamel 5 Glass 4 Water paints 10-30 *Values obtained at normal incidence. The percentage reflectance increases rapidly at angles greater than 75%. Reprinted from American Industrial Hygiene Journal, 3:1964, Akron, Ohio. Relative Erythema! Effectiveness 0 NN 240 250 260 270 280 290 30 310 320 Ngnometer Industrial Hygiene Highlights, vol. 1, p. 145. Figure 28-2. = Comparison of Standard Ery- themal Curve (S.E.C.) with Relative Erythemal Curve (S.E.C.) with Relative Erythemal Effec- tiveness Curves of Everett, Olsen and Soyer (E.O.S.) and Freeman, Owens, Knox and Hudson (F.0.K.H.) 359 0.290 pm.* ® Erythemal response to wavelengths above 0.32 um is predictably poor (see Fig. 28-2). The greatly increased air absorption of wave- lengths below 0.25 pm and the difficulty in ob- taining monochromatic radiations in this region probably account for the lack of definitive bio- effects data. This may change with the increase in the number of UV lasers available for research and study. Wavelengths between 0.28 um and 0.32 pm penetrate appreciably into the corium or dermis; those between 0.32 ym and 0.38 um are absorbed primarily in the epidermis, while those below 0.28 pm appear to be absorbed almost completely in the stratum corneum of the epidermis. Depending upon the total UV dose, the latent period for erythema may range from two to several hours; the severity may vary from simple ery- thema to blistering and desquamation with severe secondary effects. A migration of melanin gran- ules from the basal cells to the malpighian cell layers of the epidermis may cause a thickening of the horny layers of the skin. The possible long- term effects of the repeated process of melanin migration is not completely understood. The avail- able data seem to support the contention that some regions of the ultraviolet may produce or initiate carcinogenesis in the human skin. The experiments which have supported this contention indicate that the biological action spectrum for carcinogenesis is the same as that for erythema (see Fig. 28-3). A ——. i AEN LL \ ‘ Bactericidal ~~ \ = E. coli Relative Effectiveness - arbitrary units Cases of skin cancer have been reported in workers whose occupation requires them to be exposed to sunlight for long periods of time. The reportedly high incidence of skin cancer in outdoor workers who are simultaneously exposed to chemicals such as coal tar derivatives, benzpyrene, methyl cholan- threne and other anthracene compounds raises the question as to the role played by ultraviolet radia- tion in these cases. It is a matter of common knowledge that significant numbers of workers who routinely expose themselves to coal tar products while working outdoors experience a photosensiti- zation of the skin. Abiotic effects from exposure to ultraviolet radiation occur in the spectral range of 0.24 to 0.31 pm. In this part of the spectrum, most of the incident energy is absorbed by the corneal epithe- lium at the surface of the eye. Hence, although the lens is capable of absorbing 99% of the energy below 0.35 um only a small portion of the radia- tion reaches the anterior lenticular surface. Photon-energies of about 3.5 eV (0.36 ,m) may excite the lens of the eye or cause the aqueous or vitreous humor to fluoresce thus producing a dif- fuse haziness inside the eye that can interfere with visual acuity or produce eye fatigue. The phenom- enon of fluorescence in the ocular media is not of concern from a bioeffects standpoint; the condi- tion is strictly temporary and without detrimental effect. The development of photokeratitis usually has Keratitis Skin Carcinogenesis-man ( probable) 270 nls 280 320 Nanometers Figure 28-3. Action Spectra: Bactericidal, Hollaender; Keratitis, Cogan and Kinsey; Ery- themal, |.E.S. Lighting Handbook, 4th Ed.; Carcinogenesis, Rusch, Kline and Baumann. 360 a latency period varying from 30 minutes to as long as 24 hours depending upon the severity of the exposure. A sensation of “sand in the eyes” accompanied by varying degrees of photophobia, lacrimation and blepharospasm is the usual result. Blepharospasm is a reflex protective mechanism characterized by an involuntary tight closing of the lids, usually over a damaged cornea. Exposure Criteria The biological action spectrum for keratitis peaks at 0.28 um. At this wavelength, the thresh- old for injury has been determined to be approxi- mately 0.15 X 10° ergs.* It has been suggested that the corneal reaction is due primarily to selective absorption of UV by specific cell constituents; for example, globulin. Verhoeff and Bell® gave the first quantitative measurement of the ultraviolet energy necessary for threshold damage as 2 X 10° ergs/cm? for the whole UV spectrum. More recent data by Pitts et al.,*7 using 10 nm bands of radiation produced a threshold of approximately 0.5 X 10° ergs per square centimeter in rabbit eyes. The exposure criteria adopted by the American Medical Association based on erythemal thresh- olds at 0.2537 um radiation are as follows: 0.5 X 107° W/cm? for exposure up to seven hours; 0.1 X 107® W/cm? for exposure periods up to and ex- ceeding 24 hours.® Although these criteria are generally thought to be very stringent, they are nevertheless in common use. The American Conference of Governmental Industrial Hygienists? has published a “Notice of Intent” to establish Threshold Limit Values for ultraviolet radiation. The Notice states that the total irradiance of the unprotected skin or eye by ultraviolet energy in the 0.32 to 0.4 um wave- length range should not exceed 10~* W/cm? for a period of 16 minutes. For ultraviolet in a range from 0.2 um to 0.315 um, the radiant exposure should not exceed values which vary from 0.1 J/cm? to 1.0 J/cm? respectively. Measurement of Ultraviolet Radiation Various devices have been used to measure ultraviolet radiation; e.g., photoelectric cells, pho- toconductive cells, photovoltaic cells and photo- chemical detectors. It is common practice to em- ploy the use of selective filters in front of the de- tecting device in order to isolate that portion of the ultraviolet spectrum of interest to the investigator. A commonly used detector is the barrier or photovoltaic cell. Certain semiconductors such as selenium or copper oxide deposited on a selected metal develop a potential barrier between the layer and the metal. Light falling upon the sur- face of the cell causes the flow of electrons from the semiconductor to the metal. A sensitive meter placed in such a circuit will record the intensity of radiation falling on the cell. Ultraviolet photocells take advantage of the fact that certain metals have quantitative photo- electric responses to specific bands in the UV spec- trum. Therefore, a photocell may be equipped with metal cathode surfaces which are sensitive to certain UV wavelengths of interest. One of the drawbacks of photocells is solarization or deterior- 361 ation of the envelope, especially with long usage or following measurement of high intensity ultra- violet radiation. This condition requires frequent recalibration of the cell. The readings obtained with these instruments are valid only when meas- uring monochromatic radiation, or when the re- lationship between the response of the instrument and the spectral distribution of the source is known. A desirable design characteristic of ultraviolet detectors is to have the spectral response of the instrument closely approximate that of the bio- logical action spectrum under consideration. How- ever, such an instrument is unavailable at this time. Since available photocells and filter combi- nations do not closely approximate the UV bio- logical action spectra, it is necessary to standardize (calibrate) each photocell and meter. Such cali- brations are generally made at a great enough dis- tance from a standard source that the measuring device is in the “far field” of the source. Special care must be taken to control the temperature of so called standard mercury lamps because the spec- tral distribution of the radiation from the lamp is dependent upon the pressure of the vaporized mercury. A particularly useful device for measuring ul- traviolet is the thermopile. Coatings on the re- ceiver elements of the thermopile are generally lamp black or gold black to simulate black body radiation devices. Appropriate thermopile window material should be selected to minimize the effects of air convection, the more common windows being crystal quartz, lithium fluoride, calcium fluoride, sodium chloride and potassium bromide. Table 28-3 shows the sensitivity, impedance and response time of certain junction detectors.” Low intensity calibration may be made by exposing the thermopile to a secondary standard (carbon fila- ment) furnished by the National Bureau of Standards. TABLE 28-3 Sensitivity, Impedance and Response Time of Junction Detectors Response Type Sensitivity Impedance Time (Circular) ,V/uW cm™2 OHM (1/e) sec 1-junction: Const- Mang 0.005 2 0.1 4-junction: Cu-Const 0.025 5 0.5 4-junction: Bi-Ag 0.05 5 0.5 8-junction: Bi-Ag 0.10 10 1.0 16-junction: Bi-Ag 0.20 25 2.0 (linear) 0.05 10 0.5) 12-junction: Bi-Ag 0.05 10 0.5 Reprinted from Bulletin No. 3 (1964), p. 5, Eppley Laboratory, Inc., Newport, Rhode Island. Other UV detection devices include: 1) photo- diodes, e.g., silver, gallium arsenide, silver zinc sulfide and gold zinc sulfide (peak sensitivity of these diodes is at wavelengths below 0.36 um; the peak efficiency or responsivity is of the order of 50-70%); 2) thermocouples, e.g., Chromel-Alu- mel; 3) Golay cells; 4) superconducting bolo- meters; and 5) zinc sulfide Schottky barrier de- tectors.'! Care must be taken to use detection devices having the proper rise time characteristics (some devices respond much too slowly to obtain mean- ingful measurements). Also, when measurements are being made special attention should be given to the possibility of UV absorption by many ma- terials in the environment; e.g., ozone or mercury vapor, thus adversely affecting the readings. The possibility of photochemical reactions between ul- traviolet radiation and a variety of chemicals also exists in the industrial environment. Control of Exposure Because ultraviolet radiations are so easily absorbed by a wide variety of materials, appro- priate attenuation is accomplished in a straight forward manner. The exposure criteria given in the section entitled “Exposure Criteria” should be used for the specification of shielding require- ments. In the case of ultraviolet lasers no firm bioeffects criteria are available; however, the data of Pitts © may be used because of the narrow band UV source used in his experiments to deter- mine thresholds of injury to rabbit eyes. In using the data in the section “Exposure Criteria” it is important to remember that photosensitization may be induced in certain persons at levels below the- suggested exposure criteria. LASER RADIATION Sources and Uses of Laser Radiation The rate of development and manufacture of devices and systems based on stimulated emission of radiation has been truly phenomenal. Lasers are now being used for a wide variety of purposes, including micromachining,welding, cutting, seal- ing, holography, optical alignment, interferometry, spectroscopy, surgery, and as communications media. Generally speaking, lasing action has been ob- tained in gases, crystalline materials, semiconduc- tors and liquids. Stimulated emission in gaseous systems was first reported in a helium neon mix- ture in 1961.2 Since that time lasing action has been reported at hundreds of wavelengths from the ultraviolet to the far infrared (several hundred mi- crometers). Helium neon (He-Ne) lasers are typi- cal of gas systems where stable single frequency operation is important. He-Ne systems can oper- ate in a pulsed mode or continuous wave (CW) at wavelengths of 0.6328 micrometers (um), 1.15 um or 3.39 um, depending upon resonator design. Typical power for He-Ne systems is of the order of 1-500 mW. The carbon dioxide gas laser sys- tem operates at a wavelength of 10.6 um in either the continuous wave, pulsed or Q-switched modes. A Q switch is a device for enhancing the storage and dumping of energy to produce extremely high power pulses. The power output of CO,-N, sys- 362 tems may range from several watts to greater than 10 KW. The CO, laser is attractive for terrestrial and extraterrestrial communications because of the low absorption window in the atmosphere between 8 um and 14 um. Of major significance from the personal hazard standpoint is the fact that enor- mous power may be radiated at a wavelength which is invisible to the human eye. The argon ion gas system operates predominantly at wave- lengths of 0.488 um and 0.515 um in either a continuous wave or pulsed mode. Power gen- eration is greatest at 0.488 um, typically at less than 10 watts. Of the many ions in which laser action has been produced in solid state crystalline materials, perhaps neodymium (Nd*®+) in garnet or glass and chromium (Cr?+) in aluminum oxide are most noteworthy (see Table 28-4). Garnet (yttrium aluminum garnet) or YAG is an attractive host for the trivalent neodymium ion because the 1.06 wm laser transition line is sharper than that in other host crystals. Frequency doubling to 0.530 pm using lithium niobate crystals may produce power approaching that available in the fundamental mode at 1.06 pm. Also through the use of electro- optic materials such as KDP, barium-sodium nio- bate or lithium tantalate, “tuning” or scanning of laser frequencies over wide ranges may be accom- plished.’® The ability to scan rapidly through wide frequency ranges requires special consideration in the design of protective measures. Perhaps the best known example of a semi- conductor laser is the gallium arsenide types oper- ating at 0.840 um; however, semiconductor ma- terials have operated in a range of approximately 0.4 to 5.1 um. Generally speaking, the semicon- ductor laser is a moderately low-powered (milli- watts to several watts) CW device having rela- tively broad beam divergence thus tending to re- duce its hazard potential. On the other hand, certain semiconductor lasers may be pumped by multi kilovolt electron beams thus introducing a potential ionizing radiation hazard. TABLE 28-4 Certain Tons Which Have Exhibited Lasing-Action Wavelength Active ion pm Nd*+ 0.9-1.4 Ho*+ 2.05 Ert+ 1.61 Crit 0.69 Tm?+ 1.92 Ust+ 2.5 Pret 1.05 Dy*+ 2.36 Sm?*+ 0.70 Tm?+ 1.12 Biological Effects of Laser Radiation The body organ most susceptible to laser ra- diation appears to be the eye; the skin is also susceptible but of lesser importance. The degree of risk to the eye depends upon the type of laser beams used, notably the wavelength, output power, beam divergence and pulse repetition frequency. The ability of the eye to refract long ultraviolet, visible and near infrared wavelengths is an addi- tional factor to be considered in assessing the potential radiation hazard. In the case of ultraviolet wavelengths (0.2 to 0.4 um) produced by lasers the expected response is similar to that produced by noncoherent sources; e.g., photophobia accompanied by erythema, ex- foliation of surface tissues and possibly stromal haze. Absorption of UV takes place at or near the surface of tissues. The damage to epithelium results from the photochemical denaturization of proteins (see section entitled “Ultraviolet Radia- tion”). In the case of infrared laser radiation, damage results exclusively from surface heating of the cornea subsequent to absorption of the incident energy by tissue water in the cornea. Simple heat flow models appear to be sufficiently accurate to explain the surface absorption and damage to tis- sue. In the case of the visible laser wavelengths (0.4 to 0.75 um) the organ at risk is the retina and more particularly the pigment epithelium of the retina. The cornea and lens of the eye focus the incident radiant energy so that the radiant exposure at the retina is at least several orders of magnitude greater than that received by the cor- nea. Radiant exposures which are markedly above the threshold for producing minimal lesions on the retina may cause physical disruption of retinal tis- sue by steam formation or by projectile-like mo- tion of the pigment granules. ** In the case of short transient pulses such as those produced by Q-switched systems, acoustical phenomena may also be present.® There are two transition zones in the electro- magnetic spectrum where bio-effects may change from one of a corneal hazard to one of a retinal hazard. These are located at the interface of the ultraviolet-visible region and the visible near in- frared region. It is possible that both corneal and retinal damage, as well as damage to intermediate structures such as the lens and iris, could be caused by devices emitting radiation in these transitional regions. Figures 28-4 and 28-5 show the percent trans- mission of various wavelengths of radiation through the ocular media and the percent absorp- tion in the retinal pigment epithelium and choroid, respectively. These graphs illustrate why the retina PERCENT TRANSMISSION THROUGH OCULAR MEDIA PERCENT TRANSMISSION 5 3 8 88838838 400 S00 600 700 800 900 1000 i100 1200 1300 1400 1500 WAVE LENGTH (nm) Figure 28-4. Percent Transmission through Ocular Media. Percent transmission for light of equal intensity through the ocular media of human, monkey (rhesus), and rabbit eyes. From Geeraets, W. J. and Berry, E. R., Amer. J. Ophthal., 66, 15, 1968. PERCENT ABSORPTION IN RETINAL PIGMENT EPITHELIUM AND CHOROID CERT od SEY 100 1 » oe ~N ® © © 8 38 0 o o PERCENT ABSORPTION 400 S00 600 700 800 900 MEAN WMLUES (Light of equal intensity ond incident an the cornee ) === = Rabbit ( Dtch~ONs chills ) eee = Humon — o Monkey (Mhosvs) 1000 1100 1200 1300 1400 (300 WAVE LENGTH (nm) Figure 28-5. Percent Absorption in Retinal Pigment Epithelium and Choroid. Percent ab- sorption of light of equal intensity at the cornea in the retinal pigment epithelium and choroid for rabbits, monkey, and man. Redrawn to include correction for reflection from Figure 2 of Geeraets, W. J. and Berry E. R., Amer. J. Ophthal. 66, 15, 1968. is the organ at risk with visible wavelength-radi- ation whereas the cornea and skin surfaces are at risk with infrared and ultraviolet radiation. Sev- eral investigators '™ 1* noticed irreversible changes in electroretinograms, with attendant degeneration of visual cells and pigment epithelium, when al- bino and pigmented rats were exposed to high il- lumination environments. The biological significance of irradiating the skin with lasers is considered to be less than that caused by exposure of the eye since skin damage is usually repairable or reversible. The most com- mon effects on the skin range from erythema to blistering and charring depending upon the wave- length, power and time of exposure to the radia- tion. Depigmentation of the skin and damage to underlying organs may occur from exposure to extremely high powered laser radiation, partic- ularly Q-switched pulses. In order that the rela- tive eye/skin hazard potential be kept in perspec- tive, one must not overlook possible photosensiti- zation of the skin caused by injection of drugs or use of cosmetic materials. In such cases the max- imum permissible exposure (MPE) levels for skin might be considerably below the currently recom- mended values. 364 Exposure Criteria Permissible levels of laser radiation imping- ing upon the eye have been derived from studies of short term exposure and an examination of damage to eye structures as observed through an ophthalmoscope. Some investigators’ have ob- served irreversible visual performance changes at exposure levels as low as 10% of the threshold de- termined by observation through an ophthalmo- scope. McNeer and Jones ** ?° found that at 50% of the ophthalmoscopically determined threshold, the ERG B wave amplitude was irreversibly re- duced. Davis and Mautner®* reported severe changes in the visually evoked cortical potential at 25% of the ophthalmoscopically determined threshold. Since most if not all of the so-called laser exposure criteria have been based on ophthal- moscopically-determined lesions on the retina, the findings of irreversible functional changes at lower levels cause one to ponder the exact magnitude of an appropriate safety factor which should be ap- plied to the ophthalmoscope data in order to de- rive a reasonable exposure criterion. There is unanimous agreement that any pro- posed maximum permissible exposure (MPE) or threshold limit value (TLV) does not sharply di- vide what is hazardous from what is safe. Usually any proposed values take on firm meaning only after years of practical use. However, it has be- come general practice in evaluating a laser expo- sure to: 1. Measure the radiant exposure (J/cm?) or irradiance (W/cm?) in the plane of the cornea rather than making an attempt to calculate the values at the retina. This simplifies the measurements and calcula- tions for the industrial hygienists and ra- diation protection officers. 2. Use a 7 mm diameter limiting aperture (pupil) in the calculations. This assumes that the largest amount of laser radiation may enter the eye. 3. Make a distinction between the viewing of collimated sources; (e.g., lasers) and ex- tended sources (e.g., fluorescent tubes or incandescent lamps). The MPE for ex- tended source viewing takes into account the solid angle subtended at the eyes in viewing the light source; therefore, the unit is Watts/cm2.sr (Watts per square centi- meter and steradian). 4. Derive permissible levels cn the basis of the wavelength of the laser radiation; e.g., the MPE for neodymium wavelength (1.06 um) should be increased; i.e., made less stringent by a factor of approximately five than the MPE for visible wavelengths. 5. Urge caution in the use of laser systems that emit multiple pulses. A conservative approach would be to limit the power or energy in any single pulse in the train to the MPE specified for direct irradiation at the cornea. Similarly the average power for a pulse train could be limited to the MPE of a single pulse of the same dura- tion as the pulse train. More research is needed to precisely define the MPE for multiple pulses. Typical exposure criteria for the eye pro- posed by several organizations are shown in Table 28-5 and Table 28-6. These data do not apply to permissible levels at ultraviolet wavelengths or to the skin. A few supple- mentary comments on these factors are in order. There appears to be general agreement on maximum permissible exposure levels of radiation for the skin; e.g., the MPE values are approxi- mately as follows: for exposure times greater than 1 sec., an MPE of 0.1 W/cm? exposure times 107 to 1 sec., 1.0 W/cm?; for 10* to 10 sec., 0.1 J/cm? and for exposure times less than 10™* sec., 0.01 J/cm? The MPE values apply to visi- ble and infrared wavelengths. For ultraviolet ra- diations the more conservative approach is to use the standards established by the American Medical Association. These exposure limits (for germicidal wavelengths viz. 0.2537 um) should not exceed 0.1 X10™® W/cm? for continuous ex- posure. If an estimate is to be made of UV laser thresholds, then it is suggested that the more recent work of Pitts® 7 be consulted (see section entitled “Ultraviolet Radiation”). TABLE 28-5 Eye Exposure Guidelines for Laser Radiation as Recommended by Various Organizations Air Force* Army/Navy** ACGIH*** Wavelength and Pulse Duration Total Energy or Power Entering Total Energy or Power Over a 7 mm Aperture Total Energy or Power Over a 7 mm Aperture Eye (Pupil) (Pupil) Visible (0.4-0.7 um) Q switched 0.5X10°¢]J 1X 107° W/cm? 1X10" J/cm? (1 nsto 1 us) Long Pulse 1xX10°°J 1X10" J/cm? 1X107¢ J/cm? Continuous Wave Near Infrared (1.06 um) Q switched (10-100ms) 2.5%X10°¢J Long Pulse (0.2-2ms) 2.0xX10° J CW-YAG (2-10ms) 1X10 W CW-YAG (10-500ms) 5X10 W 1X 107® W(10-500ms) 2X 107 W(2-10ms) 1X107¢ J/cm? (1 ps to 0.1s) 1X10™° W/cm? (>0.1s) Infrared (10.6 pm) 8 W/cm? (<10ms) *See Reference 43 #*%%kSee Reference 45 **See Reference 44 365 1 W/cm? (50-250ms) 3 W/cm? (10-50ms) 1X10™* W/cm? 1X10 W/cm? TABLE 28-6 Maximum Permissible Exposure (MPE) for Direct Ocular Intra-beam Viewing for Single Pulses or Exposures (ANSI Z136)* Wavelength Exposure Time Maximum Permissible (um) (t in seconds) Exposure (MPE) Notes for Calculation and Measurement uv .200-.302 102—-3X%10* 3%x107% I mm limiting aperture. .303 102—=3 Xx 10¢* 4X10 .304 102—3X 10¢ 6X 1073 In no case shall the total irradiance, over .305 102-3 X10* 1.0X 102 all the wavelengths within the UV spectral .306 102—3X 10* 1.6 X10 region, be greater than 1 watt per square 307 102—-3X10* 25X10? centimeter upon the cornea. .308 102—=3X10* 4.0X107 \ Jeem~2 309 102-3X10* 63x10 10 0.1Wecm™ aSpecial Qualifications and Correction Factors Are Given in ANSI Document. bSpecial Qualifications, Correction Factors and Dimensions of Limiting Apertures Are Given in ANSI Document. *See Reference 46. Reprinted with advance permission of American National Standards Institute, N.Y., N.Y. Measurement of Laser Radiation The complexity of radiometric measurement techniques, the relatively high cost of available de- tectors and the fact that calculations of radiant exposure levels based on manufacturers’ specifica- tions of laser performance have been found to be sufficiently accurate for protection purposes, have all combined to minimize the number of measure- ments needed in a protective program. In the author’s experience, the output power of com- monly used laser systems, as specified by the manufacturers, has never been at variance with precision calibration data by more than a factor of two. All measurement systems are equipped with detection and readout devices. A general descrip- tion of several devices and their application to laser measurements follows. Because laser radiation is monochromatic, cer- tain simplifications can be made in equipment design. For example, it may be possible to use 366 narrow band filters with an appropriate type of detector thereby reducing sources of error. On the other hand, special care must be taken with high powered beams to prevent detector saturation or damage. Extremely short Q-switched pulses re- quire the use of ultrafast detectors and short time- constant instrumentation to measure power instan- taneously. Photoelectric detectors and radiation thermopiles are designed to measure instantaneous power, but they can also be used to measure total energy in a pulse by integration, provided the in- strumental time-constants are much shorter than the pulse lengths of the laser radiation. High cur- rent vacuum photo-diodes are useful for measur- ing the output of Q-switched systems and can operate with a linear response over a wide range. Average power measurements of CW laser systems are usually made with a conventional ther- mopile or photo-voltaic cells. A typical thermo- pile will detect signals in the power range from 10 . watts to about 100 milliwatts. Because ther- mopiles are composed of many junctions the re- sponse of these instruments may be nonuniform. The correct measure of average power is therefore not obtained unless the entire surface of the ther- mopile is exposed to the laser beam. Measure- ments of the CW power output of gas lasers may also be made with semiconductor photocells. The effective aperture or aperture stop of any measurement device used for determining the ra- diant exposure (J/cm?) or irradiance (W/cm?) should closely approximate if not be identical to the pupillary aperature. For purposes of safety the diameter should correspond to that of the nor- mal dark-adapted eye; i.e., 7 mm. The response time of measurement systems should be such that the accuracy of the measurement is not affected, especially when measuring short pulse durations or instantaneous peak power. Many calorimeters and virtually all photo- graphic methods measure total energy, but they can also be used for measuring power if the time history of the radiation is known. Care should be taken to insure that photographic processes are used within the linear portion of the film density versus log radiant exposure (gamma) curve. Microammeters and voltmeters may be used as read-out devices for CW systems; microvolt- meters or electrometers coupled to oscilloscopes may be used for pulsed laser systems. These de- vices may be connected in turn to panel displays or recorders, as required.?? 2 Calibration is required for all wavelengths at which the instrument is to be used. It should be noted that tungsten ribbon filament lamps are available from the National Bureau of Standards as secondary standards of spectral radiance over the wavelength region from approximately 0.2 to 2.6pm. The calibration procedures using these de- vices permit comparisons within about 1% in the near ultraviolet and about a half percent in the visible. All radiometric standards are based on the Stefan-Boltzmann and Planck laws of black- body radiation. The spectral response of measurement devices should always be specified since the ultimate use of the measurements is a correlation with the spec- tral response of the biological tissue receiving the radiation insult. Control of Exposure It stands to reason that certain basic control principles apply to many laser systems: (1) the need to inform appropriate persons as to the po- tential hazards, the procedures and engineering control measures required to prevent injury, the electrical hazard, particularly with the discharge of capacitor banks associated with solid state Q- switched systems; and (2) the need to rely primar- ily on engineering controls rather than procedures; e.g., enclosures, beam stops, beam enlarging sys- tems, shutters, interlocks and isolation of laser systems, rather than sole reliance on memory or safety goggles. The “exempt” laser system is an exception to these measures. In all cases, par- ticular attention must be given to the safety of unsuspecting visitors or spectators in laser areas. 367 “High powered” systems deserve the ultimate in protective design: enclosures should be equipped with interlocks. Care should be taken to prevent accidental firing of the system and where possible, the system should be fired from a remote position. Controls on the high powered systems should go beyond the usual warning labels; e.g., an integral warning system such as a “power on” audible sig- nal or flashing light which is visible through pro- tective eye wear should be installed. Infrared laser systems should be shielded with fireproof materials having an appropriate optical density (O.D.) to reduce the irradiance below MPE values. The main hazard of these systems is absorption of excessive amounts of IR energy by human tissue or by flammable or explosive chem- icals. Before protective eye wear is chosen, one must determine as a minimum the radiant exposure or irradiance levels produced by the laser at the dis- tance where the beam or reflected beam is to be viewed; one must know the appropriate MPE value for the laser wavelength; and finally one must determine the proper optical density of pro- tective eyewear in order to reduce levels below the MPE. Likewise, the visible light transmission characteristics should be known because sufficient transmission is necessary for the person using the device to be able to detect ordinary objects in the immediate field of vision. The minimum optical density required of protective eyewear is shown in Table 28-7. Table 28-8 lists the characteristics of most laser protective eyewear now available on the American market.* TABLE 28-7 Minimum Optical Densities Required of Protective Eyewear (ODyin = log, , H,/MPE or log,, E,/MPE) E,/MPE or H,/MPE OD 1=10° 0 10=10" 1 100=10? 2 1000=10? 3 10000=10¢ A 100000 =10° 5 1000000 = 10° 6 Where H, is equal to the emergent beam radiant exposure in Joules per square centimeter and E, is equal to the emergent beam irradiance in Watts per square centimeter. TABLE 28-8 Laser Eye Protection Goggles Based on Manufacturers’ Information} 1 OPTICAL DENSITY =log,, s———— Transmittance god oo Led , 0% < = BET Xo 5,985 oo, So Manufacturer Catalogue 2 g 5 8 3 g 3 g 28 gs 2 g g iz a s85E3 £257 Fea or Supplier Number 2 fe * ® = 7 vaAY <0 2%ggs S-=f W& American SCS—437,* 0.15 0.20 0.36 1 5 High No No 55 1,3.5mm' 90 % 10600 Optical Co. SCS—440 10600 580, 586% 02 2 3.5 4 27 — >0.2No 3525*%1,3.5mm 27.5% — 581, 587% 06 4.1 6.1 55 3 — >16No 35,25*%1,3.5mm 9.6% 6328 584 0 1 S 13 11 High >0.6 No 55 2,2 mm 46 % 10600 585 03 2 8 21 17 High >0.6 No 55 2,2 mm 35 % 6943-10600 598% 13 0 0 0 — — >14 No 25% 1,3 mm 23.7% 4550-5150 599 11 0 0 0 — — >14 No 35 1,25 mm 24.7% 4550-5150 680 0 0 0 0 0 50 No No 35 1,27mm 92 % 10600 698 13 1 4 11 8.5 High >14 No 55 2,2&3mm 5 % 10600 and 5300 Bausch 5W3754 15 02 0 0 0 =35 20 Yes 39 1,79 mm 43% 3300-5300 & Lomb SW3755 4 0 0 0 0.1 335 10 Yes 39 1,)7.9 mm 57 % 4000-4600 5W3756 0.8 12 15 56 48 =35 3 Yes 39 1,64 mm 6.2% 6000-8000 SW3757 09 45 77 12 5.7 =35 2 Yes 39 1,71 mm 4.7% 7000-10000 SW3758 1.9 18 22 48 7.5 335 2 Yes 39 I,76 mm 3 % 10000-11500 Control Data TRG-112-1 — 5 12 30 30 — No No 50 1,6 mm 22 % 6943 Corp. TRG-112-2 10 0 0 0 0 — No No 50 1,6 mm 31 % 4880 TRG-112-3 5 2 6 15 15 — No No 50 2,3 mm 5S % 6943-4880 TRG-112-4 — — ee — — High No No 50 1,5 mm 92 % 106000 Fish-Schurman Corp. FS650AL/18 0.34 3.8 10 >10 >10 — No No 30 1,6 mm 30 % 6943, 8400, 106000 Glendale NDGA** 1 05 2 16 16 High >20 No 25 Plastic 60 % 8400, 10600 Optical Co. R** 04 22 63 04 0.0 High 5 No 25 Plastic 19 % 6943 NH** 04 5 25 0.6 05 High >10 No 25 Plastic 19 % 6328 A¥* 15 0 0 0 0 High >12 No 25 Plastic 59 % 4880, 5143 NN** 0 0 0 0 0 High >12 No 25 Plastic 70 % 3320, 3370 Spectrolab _— 8 5 9 13 12 0 8 Yes 115 2,32mm <5 % Broadband *Spectacle Type. See reference 24. ** Available in goggles or spectacle type. CAUTION 1. designed for the specific laser in use. 2. of the eye protective devices. 3. take precedence over the use of eye protective devices. 4. Goggles are not to be used for viewing of laser beam. The eye protective device must be Few reliable data are available on the energy densities required to cause physical failure The establishment of engineering controls and appropriate operating procedures should The hazard associated with each laser depends upon many factors, such as output power, beam divergence, wavelength, pupil diameter, specular or diffuse reflection from surfaces, MICROWAVE RADIATION Physical Characteristics of Microwave Radiation Microwave wavelengths vary from about 10 meters to about one millimeter; the respective fre- quencies range from 30 MHz to 300 GHz. Certain reference documents,*® however, define the micro- wave frequency range as 10 MHz to 100 GHz. The region between 10 MHz and the infrared is generally referred to as the RF, or radiofrequency, region. Reference may be made to Figure 28-1 to determine the position occupied by microwaves relative to other electromagnetic radiations. Cer- tain bands of microwave frequencies have been as- signed letter designations by industry (see Table 28-9); others, notably the ISM (Industrial, Scien- tific, Medical) frequencies have been assigned by the Federal Communications Commission for in- dustrial, scientific and medical applications (see Table 28-10). For a more complete classification 368 of microwave frequency ranges, including a com- parison of American and Soviet designations, ref- erence should be made to Table 28-11. Sources of Microwave Radiation Microwave radiation is no longer of special interest only to those involved with communica- tions and navigational technology. Because of the growing number of commercial applications of mi- crowaves; e.g., microwave ovens, diathermy, ma- terials drying equipment, there is widespread inter- est in the possible new applications as well as an increased awareness of potential hazards. Typical sources of microwave energy are klystrons, mag- netrons, backward wave oscillators and semicon- ductor transit time devices (IMPATT diodes). Such sources may operate continuously as in the case of some communications systems or intermittently as in microwave ovens, induction heating equipment and diathermy equipment, or in the pulsed mode 0.30 ] 0 a 0.25 ] T 50 - ] a0 ] 30 -5- 0203 ] 25 ] ] E20 0.15 -10 - 0.125 ; 1S —154 C 0.10 : " a 7] ] I~ A 0097 —204] 10 0.08 ] 8 ] 9 0.07 b —25+ - 0.06 : PO 8 ] | » ] 0.05 7 z 1 - 30] 2 J . 6.5 0.04 " - | 6 w J 23 8-| OOOO $ ® +3 y = + = | —=aq yo— PL > 0.03- LEs 5.5 © cI? 24% Zz 0.025 4 8 a9 Q SF o a o -_— G 0.02 e iG Mumford, W.W.: Some Technical Aspects of Microwave Radiation Hazards. Proc. IRE 49:427-47, 1961. Figure 28-6. Transmission through a Grid of Wires of Radius r and Spacing a. TABLE 28-9 Letter Designation of Microwave Frequency Bands Band Frequency — MHz L 1,100- 1,700 LS 1,700- 2,600 S 2,600- 3,950 3,950- 5,850 XN 5,850- 8,200 X 8,200-12,400 Ku 12,400-18,000 K 18,000-26,500 Ka 26,500-40,000 TABLE 28-10 Industrial, Scientific, and Medical (ISM) Uses. ISM Frequencies Assigned by the FCC 13.56 MHz + 6.78 kHz 27.12 MHz = 160 kHz 40.68 MHz == 20 kHz 915 MHz =+ 25 MHz 2,450 MHz =# 50 MHz 5,800 MHz == 75 MHz 22,125 MHz + 125 MHz TABLE 28-11 Radiofrequency and Microwave Band Designations Band Designations USA USSR Wavelengths Frequencies Typical Uses* g Low frequency (LF) Long VCh 10%*10°m 30-300 KHz Radionavigation, radio beacon YE » | Medium frequency Medium (HF) 10°-10*m 0.3-3 MHz Marine radiotelephone, Loran, 28 (MF) AM broadcast © mM | High frequency (HF) Short 3 10%-10m 3-30 MHz Amateur radio, world-wide 2 broadcasting, medical dia- Rh , UHF thermy, radio astronomy Very high frequency Ultra-short 10-1m 30-300 MHz FM broadcast, television, air (VHF) (meter) traffic control, radionavigation Ultra high frequency Decimeter 1-0.lm 0.3-3 GHz Television, citizens band, (UHF) microwave point-to-point, “ Super microwave ovens, telemetry, Eg HF tropo scatter and meteoro- Mm logical radar © | Super high frequency Centimeter q (SHF)10-1 cm 3-30 GHz Satellite communication, air- S (SHF) borne weather radar, S altimeters, shipborne naviga- 2 tional radar, microwave = point-to-point Extra high frequency Millimeter 1-0.1 cm 30 GHz- Radio astronomy, cloud detec- (EHF) J 300 GHz tion radar, space research, HCN (hydrogen cyanide) emission *Modified after Table 1 in Reference 26 369 OLE LIMITED OCCUPANCY GENERAL WARNING 540 ALUMINUM LETTERS WARNING 1.0 RF RADIATION HAZARD oo 1 INSERT WARNING DATA OR INSTRUCTIONS IN THIS AREA ALUMINUM BORDER ALUMINUM LETTERS BLACK BACKGROUND |. PLACE HANDLING AND ROUTING INSTRUCTIONS ON REVERSE SIDE. . D=SCALING UNIT. . LETTERING RATIO OF LETTER HEIGHT TO THICKNESS OF LETTER LINES. wn UPPER TRIANGLE : 5 to! LARGE 6 to! MEDIUM LOWER TRIANGLE: 4 to! SMALL 6 tol MEDIUM 4. SYMBOL IS SQUARE, TRIANGLE ON RIGHT-ANGLE ISOSCALES DENIED OCCUPANCY DANGER RF RADIATION HAZARD DENIED OCCUPANCY KEEP OUT Derived from an ANSI C95.2 Standard. American National Standards Institute, New York, New York. Figure 28-7. Radio Frequency Signs. in radar systems. Natural sources of RF and mi- crowave energy also exist. For example, peak field intensities of over 100 volts per meter (V/m) are produced at ground level by the movement of cold fronts. Solar radiation intensities range from 107'* to 1077 watts per square meter per Hz (Wm™ Hz); however, the integrated intensity at the earth’s surface for the frequency range of 0.2 to 10 GHz is approximately 107 mW/cm®. This value is to be compared with an average value of 10* mW/cm® on the earth’s surface attributable to the entire (UV, visible IR and microwave) solar spectrum." Biological Effects of Microwave Radiation The photon energy in RF and microwave ra- diation is considered to be too low to produce photochemical reactions in biological matter. How- ever, microwave radiation is absorbed by biolog- ical systems and ultimately dissipated in tissue as heat. Irradiation of the human body with a power density of 10 mW cm? will result in the absorption of approximately 58 watts*” with a resultant body temperature elevation of 1°C, a value which is considered acceptable from a personal hazard standpoint. By way of comparison, the human basal metabolic rate is approximately 80 watts for a person at rest; 290 for a person engaged in moderate work. Microwave wavelengths less than 3 centi- meters are absorbed in the outer skin surface, 3 to 10 centimeter wavelengths penetrate more deeply (1 mm to 1 cm) into the skin and at wave- lengths from 25 to 200 centimeters, penetration is greatest with the potential of causing damage to internal body organs. The human body is thought to be essentially transparent to wavelengths greater than about 200 centimeters. Above 300 MHz the depth of penetration changes rapidly with frequency, declining to millimeter depths at frequencies above 3000 MHz. Above 10 GHz the surface absorption of energy begins to approach that of infrared radiation. Carpenter and Van Ummersen** investigated the effects of microwave radiation on the produc- tion of cataracts in rabbit eyes. Exposures to 2.45 GHz radiation were made at power densities rang- ing from 80 mW /cm?® to 400 mW /cm? for different exposure times. They found that repeated doses of 67 J/cm? spaced a day, a week or two weeks apart produced lens opacities even though the single threshold exposure dose at that power density (280 mW/cm?) was 84 J/cm*. When the single exposure dose was reduced to 50 J/cm? opacities were produced when the doses were administered one or four days apart, but when the interval be- tween exposures was increased to seven days, no opacification was noted even after five such weekly exposures. At the low power density of 80 mW /cm? (dose of 29 J/cm?) no effect developed, but when administered daily for 10 or 15 days, cataracts did develop. The conclusion is that mi- crowaves may exert a cumulative effect on the lens of the eye if the exposures are repeated suf- ficiently often. The interval between exposures is an important factor in that a repair mechanism 371 seems to act to limit lens damage if adequate time has elapsed between exposures. Certain other biological effects of microwave radiation have been noted in literature. One of these is the so-called “pearl chain effect” where particles align themselves in chains when sub- jected to an electric field. There is considerable disagreement as to the significance of the pearl chain effect. Investigators at the Johns Hopkins University" have suggested a possible relationship between mongolism (Down's Syndrome) in offspring and previous exposure of the male parent to radar. This suggested relationship was based on the find- ing that of two hundred sixteen cases of mongo- lism, 8.7 percent of the fathers having mongol off- spring versus 3.3 percent of the control fathers (no mongol offspring) had contact with radar while in military service. This possible association must be regarded with extreme caution because of many unknown factors including the probability of a variety of exposures to environmental agents (including ionizing radiation) while in military service. Soviet investigators claim that microwave ra- diation produces a variety of effects on the cen- tral nervous system with and without a tempera- ture rise in the organism." Claims are also made for biochemical changes, specifically a decrease in cholinesterase and changes in RNA at power den- sity levels of approximately 10 mW /cm®. The re- ported microwave effects on the central nervous system usually describe initial excitatory action; e.g., high blood pressure followed by inhibitory action, e.g., low blood pressure over the long term.* Electroencephalographic data have been interpreted as indicating the presence of epilepti- form patterns in exposed subjects. Other reported effects ranged from disturbances of the menstrual cycle to changes in isolated nerve preparations. What is often overlooked in any description of the biological effects of microwave radiation is that such radiations have produced beneficial effects. Controlled or judicious exposure of humans to diathermy or microthermy is widely practiced. The localized exposure level in diathermy may be as high as 100 milliwatts per square centimeter. Exposure Criteria Schwan®t in 1953 examined the threshold for thermal damage to tissue, notably cataractogenesis. The power density necessary for producing such changes was approximately 100 mW /cm? to which he applied a safety factor of 10 to obtain a maxi- mum permissible exposure level of 10 milliwatts per square centimeter. This number has been sub- sequently incorporated into many official stan- dards. The current American National Standards Institute C95 standard®® requires a limiting power density of 10 milliwatts per square centimeter for exposure periods of 0.1 hour or more; also an energy density of 1 milliwatt-hour per square cen- timeter (1 mWh/cm?) during any 0.1 hour period is permitted. The latter criterion allows for inter- mittency of exposure at levels above 10 mW/cm?, on the basis that such intermittency does not pro- duce a temperature rise in human tissue greater than 1 degree centigrade. More recently, Schwan?®® has suggested that the permissible exposure levels be expressed in terms of current density rather than power density, especially when dealing with measurements in the near or reactive field where the concept of power density loses its meaning. He suggests that a permissible current density of approximately 3 milliamps per square centimeter be accepted since this value is comparable to a far field value of 10 mW/cm? At frequencies below 100 KHz this value should be somewhat lower and for frequencies above 1 GHz it can be somewhat higher. The new performance standard for microwave ovens specifies a level of 1 milliwatt per square centimeter at any point 5 centimeters or more from the external oven surfaces at the time the oven is fabricated by the manufacturer. Five milli- watts is permitted throughout the useful life of the oven. Because Soviet investigators believe that effects on the central nervous systems (CNS) are more appropriate measures of the possibly detrimental effects of microwave radiation than are thermally induced responses, their studies have reported “thresholds” which are lower than those reported in Western countries. Soviet permissible exposure levels are several orders of magnitude below those in Western countries. The Soviet Standards for whole body radiation are as follows: 0.01 milliwatts per square centi- meter for five hours per day exposure, 0.1 milli- watts per square centimeter for two hours exposure per day and 1 milliwatt per square centimeter for a 15 to 20 minute exposure provided protective goggles are used. These standards apply to fre- quencies above 300 MHz. There appears to be no serious controversy about the power density levels necessary to pro- duce thermal effects in biological tissue. The non- thermal CNS effects reported by the Soviets are not so much controversial as they are a reflection of the fact that Western investigators have not used the conditioned reflex as an end point in their in- vestigations. Measurement of Microwave Radiation Perhaps the most important factor underlying some of the controversy over biological effects is the lack of standardization of measurement tech- niques used to quantify results. Unfortunately, there seems to be little promise that such standard- ization will be realized in the near future. The basic vector components in any electro- magnetic wave are the electric field (E) and the magnetic field (H). The simplest type of micro- wave propagation consists of a plane wave moving in an unbounded isotropic medium where the elec- tric and magnetic field vectors are mutually per- pendicular to each other and both are perpendicu- lar to the direction of wave propagation. Unfor- tunately, the simple proportionality between the E and H fields is valid only in free space or in the so-called “far field” of the radiating device. The far field is the region which is sufficiently removed from the source to eliminate any interaction be- tween the propagated wave and the source. The 372 energy or power density in the far field is inversely proportional to the square of the distance from the source and in this particular case the measure- ment of either E or H suffices for their deter- mination. Plane-wave detection in the far field is well understood and easily obtained with equipment which has been calibrated for use in the frequency range of interest. Most hazard survey instruments have been calibrated in the far field to read in power density (mW/cm?) units. The simplest type of device uses a horn antenna of appropriate size coupled to a power meter. To estimate the power density levels in the near field of large aperture circular antennas, one can use the following simplified relationship: *® _ 16P _ 4P W= i ay (near field) where P is the average power output, D is the diameter of the antenna, A is the effective area of the antenna and W is power density. If this com- putation reveals a power density which is less than a specified limit (e.g., 10 mW/cm?), then no further calculation is necessary because the equa- tion gives the maximum power density on the microwave beam axis. If the computed value ex- ceeds the exposure criterion then one assumes that the calculated power density exists throughout the near field. The far field power densities are then computed from the Friis free space transmission formula: GP _ AP yy = Nr? (far field) where A is the wavelength, r is the distance from the antenna and G is the far field antenna gain, and W, P, and A are as in the equation above. The distance from the antenna to the inter- section of the near and far fields is given by: 7D? _ A 8A 21° These simplified equations do not account for reflections from ground structures or surfaces; the power density may be four times greater than the free space value under such circumstances. Special note should be made of the fact that microwave hazard assessments are made on the basis of the average, not the peak power of the radiation. In the case of radar generators, how- ever, the ratio of peak to average power may be as high as 10°. Most microwave measuring devices are based on (1) bolometry, (2) calorimetry, (3) voltage and resistance changes in detectors and (4) radi- ation pressure on a reflecting surface. The latter three methods are self-explanatory. Bolometry measurements are based upon the absorption of power in a temperature sensitive resistive element, usually a thermistor, the change in resistance being proportional to absorbed power. This method is one of the most widely used in commercially avail- able power meters. Low frequency radiation of less than 300 MHz may be measured with loop or short whip antennas. Because of the larger wavelengths in the low frequency region, the field W= I, strength in volts per meter (V/m) is usually de- termined rather than power density. One troublesome fact in the measurement of microwave radiation is that the near field (reactive field) of many sources may produce unpredictable radiative patterns. Energy density rather than power density may be a more appropriate means of expressing hazard potential in the near field.*™ ** In the measurement of the near field of microwave ovens, it is desirable that the instrument have cer- tain characteristics; e.g., the antenna probe should be electrically small to minimize perturbation of the field, the impedance should be matched so that there is no backscatter from the probe to the source, the antenna probe should behave as an isotropic receiver, the probe should be sensitive to all polarizations, the response time should be adequate for handling the peak to average power of the radiation and the response of the instrument should be flat over a broad band of frequencies. In terms of desirable breed band characteris- tics of instruments it is interesting to note that onc manufacturer has set target specifications for the development of a microwave measurement and monitoring device as follows: frequency range 20 KHz to 12.4 GHz and a power density range of 0.02 to 200 mW/cm® = 1 dB. Reportedly,” two models of this device will be available: one a hand-held model with complete meter readout, the other a lapel model equipped with audible warning signals if excessive power density levels develop. Control Measures The installation of engineering controls is us- ually the most satisfactory means for controlling exposures to microwave radiation. The engineer- ing measures may range from the restriction of azimuth and elevation settings on radar antennas to complete enclosures of magnetrons in micro- wave ovens. The use of personnel protective de- vices has its place, but is of much lower priority importance to engineering controls. Various types of microwave protective suits, goggles and mesh have been used for special problems. In this con- nection Figure.28-6 showing the transmission loss through a wire grid may prove useful.*” Similarly, the general order of attenuation provided by vari- ous types of material (Table 28-12) may be of use in designing shields or enclosures.*' It has been shown recently*? that cardiac pace- makers, particularly those of the demand type, may have their function seriously compromised by microwave radiation. Furthermore, the radiation levels which cause interference with the pacemaker may be orders of magnitude below levels which cause detrimental biological effects. The most effective method of reducing the susceptibility of these devices to microwave interference seems to be improved shielding. Manufacturers of cardiac pacemakers are engaged in a major program to minimize such interference. The judicious use of appropriate signs and labels may prove useful in alerting people to the presence of dangerous microwave sources. Figure 28-7 illustrates the RF and microwave warning 373 signs adopted by the American National Standards Institute C95 committee. TABLE 28-12 Attenuation Factors (Shielding) Frequency Material 1-3 3-5 5-7 7-10 GHz GHz GHz GHz 60 X 60 mesh screening 20dB 25dB 22dB 20dB 32 X 32 mesh screening 18dB 22dB 22dB 18dB 16 X 16 window screen 18dB 20dB 20dB 22dB 14” mesh (hardware cloth) 18dB 15dB 12dB 10dB Window Glass 2dB 2dB 3dB 35dB 3%” Pine Sheathing 2dB 2dB 2dB 3.5dB 8” Concrete Block 20dB 22dB 26dB 30dB Presented at Am. Ind. Hyg. Conf., 1967: Palmisano, W., U. S. Army Environmental Hygiene Agency, Edgewood Arsenal, Md. Research Needs A major need is to conduct intermediate and long term bioeffects research at low (= 10 mW/ cm?) radiation levels. In this connection it is de- sirable to replicate certain of the Soviet work on CNS effects. Perhaps of greater importance is the need to standardize or at least coordinate all such research, particularly the measurement techniques used in the investigations. References 1. MATELSKY, I., “The Non-lonizing Radiations” In- dustrial Hygiene Highlights Vol. 1, Indus. Hygiene Foundation of America Inc., Pittsburgh, Pa., 1968. 2. Ibid, p. 145. 3. Ibid, p. 149. 4. COGAN, D. G. and V. E. Kinsey, “Action Spectrum of Keratitis Produced by Ultraviolet Radiation” Arch. Ophthal., 35, 670, 1946. VERHOEFF, F. H. and L. BELL, “Pathological Effects of Radiant Energy on the Eye” Proc. Amer. Acad. Arts and Sci., 51. 630. 1916. PITTS, D. G,, J. E. PRINCE, W. I. BUTCHER, K. R. KAY, R. W. BOWMAN, H. W. CASEY, D. G. RICHEY, L. H. MORI, J. E. STRONG, and T. J. TREDICI, “The Effects of Ultraviolet Radiation on the Eye,” Report SAM-TR-69-10, US.A.F. School of Aerospace Medicine, Brooks AFB, Texas, Feb. 1969. PITTS, D. G. and K. R. KAY, “The Photophthalmic Threshold for the Rabbit” Amer J. Optom., 46, 561, 1969. “Permissible Limit for Continuous Ultraviolet Ex- posure” Council on Physical Therapy, American Medical Assn., Chicago, Illinois 1948. The American Conf. of Govt. Industrial Hygienists, P.O. Box 1937, Cincinnati, Ohio 45201. “Bulletin No. 3” The Eppley Laboratory Inc., New- port, Rhode Island, 1964. RICHARDSON, J. R., and R. D. BAERTSCH, “Zinc Sulfide Schottky Barrier Ultraviolet Detectors,” 12. 13. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. Solid State Electronics, Pergamon Press, Vol. 12, pp. 393-397, 1969. JAVAN, A.,, W. R. BENNETT and D. R. HER- RIOTT, “Population Inversion and Continuous Op- tical Laser Oscillation in a Gas Discharge Contain- ing a He-Ne Mixture,” Phys. Rev. Lett, 6, 106, 1961. MILLER, R. C. and W. A. Nordland, “Tunable Lithium Niobate Optical Oscillator with Erternal Mirrors” Appl. Phys. Lett., 10, 53, 1967. WILKENING, G. M., “The Potential Hazards of Laser Radiation,” Proceedings of Symposium on Ergonomics and Physical Environmental Factors, Rome, Italy, 16-21, September, 1968, International Labor Office, Geneva. HAM, W. T., R. C. WILLIAMS, H. A. MUELLER, D. GUERRY, A. M. CLARKE and W. J. GEER- AETS, “Effects of Laser Radiation on the Mamma- lian Eye,” Trans. N.Y. Acad. Sci., (2) 28, 517, 1965. CLARKE, A. M., W. T. HAM, W. J. GEERAETS, R. C. WILLIAMS and H. A. MUELLER, “Laser Effects on the Eye,” Arch. Environ. Health, 18, 424, 1969. NOELL, W. K., V. S. WALKER, B. S. KANG and S. BERMAN, “Retinal Damage by Light in Rats,” Invest. Ophthal., 5, 450, 1966. KOTIAHO, A., I. RESNICK, J. NEWTON and H. SCHWELL, “Temperature Rise and Photocoagula- tion of Rabbit Retinas Exposed to the CW Laser,” Amer. J. Ophthal., 62, 644, 1966. McNEER, K. W., M. Ghosh, W. J. GEERAETS and D. GUERRY, “Erg After Light Coagulation,” Acta. Ophthal., Suppl., 76, 94, 1963. JONES, A. E., D. D. FAIRCHILD and P. SPYRO- POULOS, “Laser Radiation Effects on the Mor- phology and Function of Ocular Tissue,” Second Annual Report, Contr. No. DADA-17-67-C-0019, U.S. Army Medical Research and Development Command, Wash., D.C., 1968. DAVIS, T. P,, and W. J. MAUTNER, “Helium-Neon Laser Effects on the Eye,” Annual Report Contract No. DADA 17-69-C-9013, U.S. Army Medical Re- search and Development Command, Wash., D.C., 1969. SLINEY, D. H, F. C. BASON and B. C. FRE- ASIER, “Instrumentation and Measurement of Ul- traviolet, Visible, and Infrared Radiation,” Amer. Indus. Hygiene Assn. Journal, Vol. 32, No. 7, July, 1971. U.S. Dept. of Commerce, National Bureau of Stan- dards Technical Note 382, “Laser Power and Energy Measurements,” U.S. Govt. Printing Office, Wash- ington, D.C., 20402, October, 1969. Table 28-7, “Laser Eye Protection Goggles,” Com- piled by SCHREIBEIS, W.J., Bell Telephone Lab- oratories, Murray Hill, New Jersey, Jan., 1970. “Safety Level of Microwave Radiation with Respect to Personnel,” Committee C95-1, U.S.A. Stds. Inst. (now Amer. Nat'l. Stds. Inst.) New York, N.Y., 1966. CLEARY, S. F., “The Biological Effects of Micro- wave and Radiofrequency Radiation,” CRC Critical Review in Environmental Control 1, (2), 257, 1970. MUMFORD, W. W., “Heat Stress Due to R. F. Radiation,” Proceedings of 1.E.E.E., Vol. 57, No. 2, Feb. 1969, pp. 171-178. 374 28. 29. 30. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. CARPENTER, R. L. and C. A. VAN UMMERSEN, J. Microwave Power, 3, 3, 1968. SIGLER, A. T., A. M. LILLIENFELD, B. H. COHEN and J. E. WESTLAKE, “Radiation Expo- sure in Parents of Children with Mongolism (Down’s Syndrome)” Johns Hopkins Hospital Bull. 117, No. 6, 374-399, Dec. 1965. TOLGSKAYA, M. S. and Z. V. GORDON, Trans. Inst. of Labor Hygiene and Occupational Diseases of the Acad. of Med. Sci., 1960, 99. . ORLOVA, A. A., Proc. on Labor Hygiene and the Biol. Effects of Electromagnetic Radio Frequency Waves, 1959, 25. PRESMAN, A. S. and N. A. LEVITINA, Bull. Exp. Biol. Med. (Moscow) 1, 41, 1962. KHOLODOV, Yu. A., Proc. on Problems of the Biological Effects of Superhigh Frequency Fields, 1962, 58. SCHWAN, H. P., and K. LI, Proc. IRE, 41, 1735, 1953. SCHWAN, H. P., Biol. Effects and Health Implica- tions of Microwave Radiation, U.S. Govt. Printing Office, 1970. U.S.A. Standards Institute (now American National Standards Institute) C95.3, “Specifications for Tech- niques and Instrumentation for Evaluating Radio Frequency Hazards to Personnel,” New York, N.Y., 1968. WACKER, P., Biol. Effects and Health Implications of Microwave Radiation, U.S. Govt. Printing Office, 1970. Ibid, BOWMAN, R. General Microwave Corporation, 155 Marine Street, Farmingdale, New York, 11735. MUMFORD, W. W., “Some Technical Aspects of Microwave Radiation Hazards,” Proc. IRE, 40, 427, 1961. PALMISANO, W. A. and D. H. SLINEY, “Instru- mentation and Methods Used in Microwave Haz- ard Analysis,” U.S. Army Environmental Hygiene - Agency, Edgewood, Md., Presented at Amer. Indus. Hygiene Conf., 1967. KING, G. R.,, A. C. HAMBURGER, F. PARSA, S. J. HELLER and R. A. CARLETON, “Effect of Microwave Oven on Implanted Cardiac Pacemaker,” Jama 212:7, 1213, May 18, 1970. Department of the Air Force, AFM “Laser Health Hazards Control,” Wash., D.C., 1971. Departments of the Army and the Navy TB Med 279/NAVMED P-5052-35, “Control of Hazards to Health from Laser Radiation,” Washington, D.C., 24 Feb., 1969. “Threshold Limit Values for Physical Agents,” Amer. Conf. of Governmental Industrial Hygienists, Cincinnati, Ohio, 45202, 1970. American National Standards Institute, Z136 Stan- dards Committee “Safe Use of Lasers,” New York, in preparation. Preferred Reading CLARKE, A. M., “Ocular Hazards from Lasers and Other Optical Sources,” CRC Critical Reviews in Environmental Control, 1, (3), 307, 1970. CLEARY, S. F., “The Biological Effects of Micro- wave and Radiofrequency Radiation,” CRC Critical Reviews in Environmental Control, 1, (2), 257, 1970. APPENDIX A USEFUL RADIOMETRIC AND RELATED UNITS Unit and Term Symbol Description Abbreviation Radiant Energy Oo Capacity of electromagnetic Joule (J) waves to perform work Radiant Power P Time rate at which energy is emitted Watt (W) Irradiance or E Radiant Flux Density Watt per square Radiant Flux meter (WeM™) Density (Dose Rate in Photo- biology) Radiant Intensity I Radiant Flux or Power Emitted Watt per steradian per solid angle (steradian) (Wesr™) Radiant Exposure H Total Energy Incident on Unit Joule per square (Dose in Photo- Area in A Given Time Interval meter (Jem™2) biology) Beam Divergence d Unit of Angular Measure. Radian One Radian = 57.3° 27 Radians =360° APPENDIX B Conversion Factors A-Radiant Energy Units erg joule W sec wW sec g-cal erg= 1 1077 1077 0.1 2.39X 1078 joule = 10 1 1 10¢ 0.239 W sec= 107 1 1 10* 0.239 uW sec= 10 10—¢ 10° 1 2.39% 1077 g-cal= 4.19 X 107 4.19 4.19 4.19% 10° 1 B-Radiant Exposure (Dose) Units erg/cm? joule/cm? W sec/cm? pW sec/cm? g-cal/cm? erg/cm?= 1 1077 1077 0.1 2.39% 1078 joule/cm? = 107 1 1 10° 0.239 W sec/cm?= 107 1 1 10° 0.239 uW sec/cm? = 10 107 107 1 2.39% 1077 g-cal/cm?= 4.19 X 107 4.19 4.19 4.19 x10° 1 C-Irradiance (Dose Rate) Units erg/cm?ssec joule/cm?sec W/cm? uW/ cm? g-cal/cm?esec erg/cm?ssec = 1 1077 1077 0.1 2.39x10°® joule/cm?esec = 107 1 1 10° 0.239 W/cm? = 107 1 1 10° 0.239 uW/cm?= 10 10 107 1 2.39% 1077 g-cal/cm?esec = 4.19 x 107 4.19 4.19 4.19 x 10° 1 375 HIGH ENERGY X-RAYS, GAMMA RAYS; 99% PASS COMPLETELY THRU THE EYE, 1% ABSORBED. hed ve rf SHORT UV: ABSORPTION. PRINCIPALLY AT — | CORNEA. (INTERMEDIATE UV: ABSORPTION mth AT CORNEA AND LENS.) LONG UV, VISIBLE; TRANSMITTED THRU EYE AND FOCUSED ON RETINA. NEAR IR; PARTIALLY ABSORBED BY LENS, IRIS, AND MEDIA, PARTIALLY FOCUSED AT RETINA. FAR IR; ABSORPTION LOCALIZED AT CORNEA FOR SHARP H,O ABSORPTION WAVELENGTHS, OTHER WAVELENGTHS ABSORBED ALSO BY LENS AND IRIS. MICROWAVE; GENERALLY TRANSMITTED V/ITH PARTIAL ABSORPTION IN ALL = : PARTS OF THE EYE. Figure also appears in Bell Laboratories: Policies and Practices for Personnel Using Laser Devices. Murray Hill, New Jersey. Appendix C. General Absorption Properties of the Eye for Electromagnetic Radiation. 376 CHAPTER 29 IONIZING RADIATION Edgar C. Barnes INTRODUCTION Definition and General Description Ionizing radiation, in general, is any electro- magnetic or particulate radiation capable of pro- ducing ions, directly or indirectly, by interaction with matter. In the specific situation being con- sidered here, the industrial environment — and usually in considering radiation protection matters — that portion of the electromagnetic spectrum having frequencies in the ultraviolet portion and lower is excluded (see Chapter 28). Stated in more explicit terms, the International Commission on Radiation Units and Measurements (ICRU)! defines ionizing radiation as: “any radiation con- sisting of directly or indirectly ionizing particles or a mixture of both. Directly ionizing particles are charged particles (electrons, protons, alpha par- ticles, etc.) having sufficient kinetic energy to pro- duce ionization by collision. Indirectly ionizing particles are uncharged particles (neutrons, pho- tons, etc.) which can liberate directly ionizing particles or can initiate nuclear transformations.” Thus, ionizing radiation encompasses considera- tion both of atomic particles having a variety of physical and electrical characteristics streaming at velocities from nearly zero, to values approaching the speed of light, and of electromagnetic radia- tions (photons) having a wide range of energies streaming at the speed of light. Photons, which have no mass, are referred to as “particles” for theoretical reasons. In this chapter “radiation” implies “ionizing radiation.” In the industrial environment, the radiations of primary concern are: X, gamma, alpha, beta and neutron. X and gamma radiations may be called x rays and gamma rays. Also, alpha and beta radiations are called alpha and beta particles. Except for very small amounts from natural back- ground radiation, proton and some other kinds of radiation are not of concern unless there is equip- ment designed to specifically produce them. Re- search facilities, such as large accelerators, are not discussed in this chapter. X and gamma radiations both are penetrating electromagnetic radiations having wavelengths much shorter than that of visible light but they are of different origin. X rays originate in the extra nuclear part of the atom, whereas gamma rays are emitted from the nucleus in the process of nuclear transition or during particle annihila- tion. (Annihilation is the process by which a nega- tive electron and a positive electron, called a posi- tron, combine and disappear with emission of electromagnetic radiation.) 377 Ordinarily, useful x rays are produced in an evacuated tube by accelerating electrons from a heated filament to a metal target with voltages of 50 to 500 kilovolts (kV). Sometimes much higher or somewhat lower voltages are used. The elec- trons interact with orbital electrons of atoms in the target causing energy level changes that result in the emission of “characteristic” x rays, and also with the nucleus of the atom to produce electro- magnetic radiation having a “continuous” spec- trum (called bremsstrahlung). All radionuclides undergo a spontaneous trans- formation, called decay, during which radiation is emitted and a new nuclide, called a daughter (or decay product) is formed. The radiations are of a specific type (or types) and energy, or energy distribution, for each species of radionuclide. Tab- ulated data for many radionuclides are presented in Radiological Health Handbook .* Gamma rays are emitted by the nucleus of certain radionuclides during their decay. Each such radionuclide emits one or more gamma rays having a specific energy. Gamma rays also are produced by neutron interactions with nuclei. Alpha radiation consists of a stream of alpha particles, each particle being physically identical to the helium nucleus — two neutrons and two protons. They are emitted spontaneously during the radioactive decay of certain radionuclides, pri- marily those of higher molecular weight — bis- muth and higher. Because of the comparatively large size and double positive charge of the alpha particles, alpha radiation does not penetrate mat- ter readily. The more energetic radiation is com- pletely stopped by the skin. Inside the body, how- ever, it produces dense ionization in tissues. Beta radiation consists of a stream of beta particles, which are either electrons of negative charge or electrons of positive charge, called posi- trons, which have been emitted by an atomic nucleus — or by a neutron in the process of trans- formation. Radionuclides that spontaneously emit beta particles span the entire range of the elements. These nuclides emit particles having a maximum energy characteristic of that nuclide, along with many other particles of lower energy. Neutron radiation consists of a stream (flow) of neutrons. Radionuclides do not emit neutrons spontaneously, although a small number of very heavy radionuclides fission spontaneously with the emission of neutrons. Neutron radiation is pro- duced by various nuclear reactions, by nuclear fission and by interactions of alpha or gamma radiation with certain nuclei. Since neutrons are uncharged, the radiation readily penetrates matter. Neutrons decay into a proton and an electron with a half-life of 11.7 minutes. Neutron energies, ex- pressed in electron volts (eV) or the multiples kiloelectron volts (keV) and megaelectron volts (MeV), span a very wide range of values, and are commonly classified into three general groups — slow, intermediate and fast. The range of energies for each of these general groups is indefinite, dif- ferent ranges being selected according to specific needs. One such classification is <1 eV, 1 eV to 0.1 MeV and >0.1 MeV, respectively. There are also more specific classes, e.g., thermal, which are those essentially in thermal equilibrium with the medium in which they exist (mean value 0.025 eV at 20°C). Quantities and Units In quantitating radioactive materials, a unique situation exists because one property of primary interest is continually changing. As decay takes place, the activity, or number of nuclear disinte- grations occurring in a given quantity of material per unit time decreases exponentially. Therefore, a time dependent factor, half-life, becomes part of any quantitative evaluation. Each radionuclide has a definite half-life, however the range of half- lives for different radionuclides is very great, from fractions of a second to billions of years. Since the mass of material does not change significantly during this decay, the quantity of a radionuclide or of a radioactive material is usually specified in terms of its activity, with the exception that mass may be used in some situations (e.g., nuclear fuel manufacturing) where half-lives of the useful radionuclides are very long. Since activity in a given specimen (and the radiation from it) may come from one or more radionuclides, each decay- ing exponentially, the composition and activity must be specified as of a definite date, the accuracy (year, month, day, minute, second) depending on the relation of the half-lives to previous or sub- sequent periods of interest. The activity is com- monly expressed in curies (or its multiples) al- though for some measurements, disintegrations per minute (dpm) or per second (dps) are com- monly used. One curie equals 3.7 x 10 disin- tegrations per second. Another unique and complex situation exists in quantitating the effect of radiation on living organisms. The different kinds of radiation inter- act in a wide variety of ways both with living organisms (e.g., body tissues) and inanimate things (e.g., shielding). Furthermore, the inter- actions may be different for different energies of the same type of radiation; and the spatial dis- tribution of the interaction is not uniform. They all, however, impart energy to matter through which they pass; and for living organisms the absorbed dose — energy imparted in a volume element divided by the mass of irradiated mate- rial in that volume element — provides a common base for considering the degree of effect produced by specific amounts of any of the different types of radiation. The unit of absorbed dose is the rad. One rad equals 100 ergs per gram. The biological effect for equal absorbed doses 378 from different types and energies of radiation, however, is not constant. Therefore dose equiva- lent, which is the absorbed dose modified by perti- nent factors, particularly the “quality factor,” is used for radiation protection evaluations to take into account the difference in the biological effect of the different radiations. Values of the quality factor for commonly encountered radiations, suit- able for general use, have been determined (see page 391). The special unit of dose equivalent is the rem, which is the product of absorbed dose in rads and the applicable quality factor. For special situations, a factor in addition to the qual- ity factor may be used. Dose-limiting recommen- dations are expressed as maximum permissible dose equivalent in rems, commonly called “maxi- mum permissible dose (MPD).” A similar concept is expressed as a Radiation Protection Guide (RPG) by the Federal Radiation Council.* In some situations, it may be convenient and sufficiently accurate to express dose-limiting rec- ommendations for x and gamma radiation (or to make related measurements) in terms of ioniza- tion in air, at the point of interest. The measure of ionization produced in air by x or gamma radia- tion is called “exposure,” its special unit being the roentgen (R). It is customary, for radiation protection purposes, to consider that one R at the point of interest would be equivalent to a dose equivalent of one rem. A comprehensive collection of data, graphs and tables will be found in the Radiological Health Handbook.* Tt should prove to be a useful adjunct to this chapter, since extensive tables and graphs are not included here. Glossary This glossary includes a limited number of terms used in radiation protection practice. These definitions are mostly from reference (3) which contains definitions of other terms. References (2) and (3) also include pertinent definitions. activity (A). The number of nuclear disintegra- tions occurring in a given quantity of material per unit time. body burden. The total quantity of a radio- nuclide present in the body. body burden, maximum permissible. That body burden of a radionuclide which, if maintained at a constant level, would produce the maxi- mum permissible dose equivalent in the critical organ. bremsstrahlung. The electromagnetic radiation associated with the deceleration of charged particles. The term is also applied to the radiation associated with the acceleration of charged particles. controlled area. A specified area in which ex- posure of personnel to radiation or radioactive material is controlled and which is under the supervision of a person who has knowledge of the appropriate radiation protection practices, including pertinent regulations, and who has responsibility for applying them. curie (Ci). The special unit of activity. One curie equals 3.7 x 10'° disintegrations per second exactly. By popular usage, the quantity of any radioactive material having an activity of one curie. daughter. A nuclide, stable or radioactive, formed by radioactive decay. A synonym for decay product. dose. A general term denoting the quantity of radiation or energy absorbed in a specified mass. For special purposes, its meaning should be appropriately stated, e.g., absorbed dose. dose, absorbed. The energy imparted to matter in a volume element by ionizing radiation divided by the mass of irradiated material in that volume element. dose equivalent. The product of absorbed dose, quality factor, and other modifying factors necessary to express on a common scale, for all ionizing radiations, the irradiation incurred by exposed persons. dose equivalent, maximum permissible (MPD). The largest dose equivalent received within a specified period which is permitted by a regu- latory agency or other authoritative group on the assumption that receipt of such dose equiva- lent creates no appreciable somatic or genetic injury. Different levels of MPD may be set for different groups within a population. (By popular usage, dose, maximum permissible, is an accepted synonym.) exposure. A measure of the ionization produced in air by x or gamma radiation. It is the sum of the electrical charges on all of the ions of one sign produced in air when all electrons liberated by photons in a volume element of air are completely stopped in the air, divided by the mass of the air in the volume element. genetically significant dose (GSD). The dose which, if received by every member of the population, would be expected to produce the same total genetic injury to the population as do the actual doses received by the various individuals. half-life, radioactive. For a single radioactive decay process, the time required for the activ- ity to decrease to half its value by that process. half-value layer. The thickness of a specified substance which, when introduced into the path of a given beam of radiation, reduces the value of a specified radiation quantity by one- half. It is sometimes expressed in terms of mass per unit area. isotopes. Nuclides having the same atomic num- ber but different mass numbers. NOTE: this term is often used inaccurately as a synonym for nuclide. nuclide. A species of atom characterized by its mass number, atomic number, and energy state of the nucleus, provided that the mean life in that state is long enough to be observ- able. quality factor. A linear energy transfer depend- ent factor by which absorbed doses are to be multiplied to obtain the dose equivalent. rad. The special unit of absorbed dose. One rad equals 100 ergs per gram. radiation source. An apparatus or a material 379 emitting or capable of emitting ionizing radia- tion. Radiation Protection Guide (RPG). The radia- tion dose which should not be exceeded with- out careful consideration of the reasons for doing so; every effort should be made to en- courage the maintenance of radiation doses as far below this guide as practicable. Radioactivity Concentration Guide (RCG). The concentration of radioactivity in the environ- ment which is determined to result in organ doses equal to the Radiation Protection Guide. roentgen (R). The special unit of exposure. One roentgen equals 2.58 x 107! coulomb per kilo- "gram of air. sealed source. A radioactive source sealed in a container or having a bonded cover, where the container or cover has sufficient mechanical strength to prevent contact with and dispersion of the radioactive material under the condi- tions of use and wear for which it was de- signed. PHYSICAL ASPECTS OF IONIZING RADIATION Electromagnetic Radiation In the electromagnetic spectrum, gamma radi- ation spans an energy range from approximately 8 x 10% eV to 107 eV, the corresponding frequen- cies being 2 x 10" to 2.5 x 10*! hertz. X rays span a somewhat wider range of values, although there is no clear break at the lower energy bound- ary and at higher energies special equipment, such as an accelerator, is used for their production. A beam of x rays from x-ray equipment en- compasses a range of energies. The highest photon energy in the beam corresponds to the electron accelerating voltage, with the median being con- siderably below this value. The beam will include both photons having energies which are “char- acteristic” of the target material and photons hav- ing a continuous spectrum (bremsstrahlung), the proportion of the latter being greateg, at higher electron accelerating voltages. The energy spec- trum, or quality of the beam, may be expressed either in terms of an “effective energy” or in terms of its half-value layer. The accelerating voltage may be constant or may come from a pulsating generator, which influences the photon energy dis- tribution, the latter being designated in terms of peak voltage (kVp). Ordinarily, x-ray tubes and their housings are arranged so that there is shield- ing in all directions except for a “window” where the useful beam is emitted. The solid angle and shape of the useful beam is determined by the size of the window and by collimating devices, such as diaphragms and cones, made of shielding materials. Some low energy x rays are absorbed in the target, while others are removed from the useful beam by the material in the tube window and usually also by filters that preferentially absorb the less penetrating radiation. Accelerators used to produce high energy x rays are commonly ar- ranged for beam emission to accomplish a specific purpose. Sealed sources, consisting of a radionuclide encased in a metal capsule, are a common source of gamma radiation used in industry. They are used in radiography, measuring devices and a number of other special applications. The radio- nuclides in them are selected to provide radiation of the desired photon energy. Some emit photons of one energy, such as cesium-137 (.66MeV); others a range of energies, such as radium (.047 to 2.4 MeV due to retained daughters). There are two basic processes by which elec- tromagnetic radiation interacts with matter: scat- tering, in which the direction of the photon and its energy are altered; and absorption, in which the photon disappears with transfer of its energy to other radiations. Along the path of a primary beam of photons, there are interactions between the electric fields of these photons and the electrons in the material being penetrated which cause “scattering” of some of the primary beam photons. Further reactions ensue with a resulting 360° angular distribution of scattered photons having a range of energies down to nearly zero. The shape of this angular, and associated energy, distribution is a function of the energy of the original photons. For a mathe- matical treatment of scattering, see Principles of Radiation Protection.” Absorption of photons occurs primarily by three processes — the photoelectric effect, the Compton effect and pair production. These are also treated mathematically in the above book.” The photoelectric effect predominates for the lower energy photons, the Compton effect where the energy is greater than approximately 0.5 MeV, and for pair production a minimum of 1.02 MeV is required. The photoelectric effect involves an interaction between incident photons and the electrons in the shells around the nuclei. Electrons are ejected from the atoms with an energy equal to the differ- ence between the photon energy and the binding energy of the ejected electron. Subsequently, x rays or electrons are emitted as the shell vacancies are corrected, the x rays having a wide range of energies which are higher for the higher atomic number materials. The portion of photons inter- acting by the photoelectric process increases with increasing atomic number and decreasing energy. The Compton effect involves interactions of photons incident on orbital electrons. The photon gives up part of its energy to the electron causing it to recoil and the balance of its energy goes into a scattered photon. From conservation of energy and momentum, the angular relationships of the recoil electron, scattered photon and incident photon can be determined. The original photon energy determines the distribution of these angles; at lower energies, the angles at which electrons are scattered is greater. Pair production occurs by the interaction of a photon with the electric field surrounding a charged particle. The original photon disappears with the formation of an electron-positron pair. The photon energy must exceed 1.02 MeV and it is divided equally between the electron and the positron. The portion of incident photons which interact with a nucleus by pair production in- creases with increasing atomic number. As a beam of photons traverses matter, the scattering and absorption of photons by all proc- esses results in attenuation of the beam exponen- tially. This is expressed by the equation: I=1,e™ (1) where 1 is exposure rate at a depth x I, is exposure rate at zero depth nis the attenuation coefficient The value of the attenuation coefficient depends on the photon energy and the absorbing material. This coefficient may be expressed in terms of thickness, as a linear attenuation coefficient (cm™'), or as a mass attenuation coefficient (cm*g) obtained by dividing the linear coefficient by the density p of the absorbing material. Table 29-1 presents some of these values. More ex- tensive tables are available in reference (2). In matter being traversed by a beam of electromag- netic radiation, there is actually a higher intensity of photons at any point, particularly at great depth, TABLE 29-1 Mass Attenuation Coefficients Photon energy Mass attenuation coefficient in cm*/g for — MeV Aluminum Iron Lead Water Concrete 0.01 26.3 173 133 5.18 26.9 0.02 3.41 25.5 85.7 0.775 3.59 0.05 0.369 1.94 7.81 0.227 0.392 0.1 0.171 0.370 5.40 0.171 0.179 0.5 0.0844 0.0840 0.161 0.0968 0.087 1.0 0.0613 0.0599 0.0708 0.0707 0.0637 5.0 0.0284 0.0314 0.0424 0.0303 0.0290 10.0 0.0231 0.0298 0.0484 0.0222 0.0231 Reprinted from “Radiological Health Handbook”, U.S. DHEW, Public Health Service, 1970. 380 TABLE 29-2 Dose Buildup Factor (B) for a Point Isotropic Source Material MeV px 1 2 4 7 10 15 20 Water 0.255 3.09 7.14 23.0 72.9 166 456 982 0.5 2.52 5.14 14.3 38.8 77.6 178 334 1.0 2.13 3.71 7.68 16.2 27.1 50.4 82.2 2.0 1.83 2.77 4.88 8.46 12.4 19.5 27.7 3.0 1.69 2.42 3.91 6.23 8.63 12.8 17.0 4.0 1.58 2.17 3.34 5.13 6.94 9.97 12.9 6.0 1.46 1.91 2.76 3.99 5.18 7.09 8.85 8.0 1.38 1.74 2.40 3.34 4.25 5.66 6.95 10.0 1.33 1.63 2.19 2.97 3.72 4.90 5.98 Aluminum 0.5 2.37 4.24 9.47 21.5 38.9 80.8 141 1.0 2.02 3.31 6.57 13.1 21.2 37.9 58.5 2.0 1.75 2.61 4.62 8.05 11.9 18.7 26.3 3.0 1.64 2.32 3.78 6.14 8.65 13.0 17.7 4.0 1.53 2.08 3.22 5.01 6.88 10.1 13.4 6.0 1.42 1.85 2.70 4.06 5.49 7.97 10.4 8.0 1.34 1.68 2.37 3.45 4.58 6.56 8.52 10.0 1.28 1.55 2.12 3.01 3.96 5.63 7.32 Iron 0.5 1.98 3.09 5.98 11.7 19.2 35.4 55.6 1.0 1.87 2.89 5.39 10.2 16.2 28.3 42.7 2.0 1.76 2.43 4.13 7.25 10.9 17.6 25.1 3.0 1.55 2.15 3.51 5.85 8.51 13.5 19.1 4.0 1.45 1.94 3.03 4.91 7.11 11.2 16.0 6.0 1.34 1.72 2.58 4.14 6.02 9.89 14.7 8.0 1.27 1.56 2.23 3.49 5.07 8.50 13.0 10.0 1.20 1.42 1.95 2.99 4.35 7.54 12.4 Lead 0.5 1.24 1.42 1.69 2.00 2.27 265 (2.73) 1.0 1.37 1.69 2.26 3.02 3.74 4.81 5.86 2.0 1.39 1.76 2.51 3.66 4.84 6.87 9.00 3.0 1.34 1.68 2.43 2.75 5.30 8.44 12.3 4.0 1.27 1.56 2.25 3.61 5.44 9.80 16.3 5.1097 1.21 1.46 2.08 3.44 5.55 11.7 23.6 6.0 1.18 1.40 1.97 3.34 5.69 13.8 32.7 8.0, 1.14 1.30 1.74 2.89 5.07 14.1 44.6 10.0 1.11 1.23 1.58 2.52 4.34 12.5 39.2 * uX=mass absorption coefficient (p/p) X shield thickness (cm) X shield density (g/cm?). NOTE: For concrete use an average of aluminum and iron; e.g., B(con¢) = [B(iron) + B(Al)] +2. Reprinted from “Radiological Health Handbook”, U.S. DHEW, Public Health Service, 1970. than would be predicted solely by attenuation (equation 1) because of the presence of x rays and secondary or scattered photons. This increase in exposure rate, called buildup (B), is not easily calculated. It can be included as a factor B in the attenuation equation I=BIle™* and tabu- lated values of B for one set of conditions is shown in Table 29-2. Additional values appear in ref- erence (2). To assure proper accuracy, it is us- ually necessary to consider this buildup factor. Since absorption of energy is the physical quantity used in specifying absorbed dose, a mass energy absorption coefficient similar to the atten- uation coefficient is useful. Table 29-3 presents some of these values. More extensive tables will be found in Physical Aspects of Irradiation.’ 381 TABLE 29-3 Mass Energy-absorption Coefficients Photon Mass energy-absorption coefficient energy in cm*/g for MeV Water Air Bone Muscle 0.01 4.89 4.66 19.0 4.96 0.02 0.523 0.516 2.51 0.544 0.05 0.0394 0.0384 0.158 0.0409 0.1 0.0252 0.0231 0.0368 0.0252 0.5 0.0330 0.0297 0.0316 0.0327 1.0 0.0311 0.0280 0.0297 0.0308 5.0 0.0190 0.0173 0.0186 0.0188 10.0 0.0155 0.0144 0.0159 0.0154 Reprinted from ‘Radiological Health Handbook”, U.S. DHEW, Public Health Service, 1970. Shielding of radiation sources is commonly provided to reduce the exposure rate in occupied areas. For economy, the shield should be as close as possible to the radiation source. For discrete energies, the attenuation by a shield can be calcu- lated from the attenuation equation, including buildup. In practice, extensive data on attenua- tion (or transmission), presented in graphic form, is available and used for shielding calculations. This data is presented in a variety of ways and selection of the most useful form will simplify shielding calculations. Because attenuation is ex- ponential, the thickness of a “half-value layer” (HVL) for different shielding materials is a com- mon and convenient form to present such data. A shield thickness of 2 HVL reduces exposure rate by a factor of 4, 3 HVL by a factor of 8, etc. Table 29-4 presents such data for the gamma radiation from several radionuclides, as well as their specific gamma ray constants (exposure rate constants). The latter are useful in determining exposure rate at varying distances, in air, from a point source using the inverse square relationship between exposure rate and distance from the source. Additional values are included in refer- ence (2). Comprehensive shielding data for x rays appear in Safety Standard for Non-medical X-ray and Sealed Gamma-ray Sources,” and Medi- cal X-ray and Gamma-ray Protection for Energies up to 10 MeV ® Particulate Radiation Beta radiation is emitted by a large percentage of the radionuclides, frequently accompanied by x or gamma radiation. Each nuclide, which decays by beta particle emission, emits beta particles having a maximum energy characteristic of that nuclide along with many other particles of lower energy. The average of these energies is much less than the maximum and for different nuclides the ratios of maximum to average span a wide range of values. For different nuclides, the range of maximum energies is from a few keV to slightly over 4 MeV. In contrast to electromagnetic radi- 382 ation which is attenuated exponentially, beta radi- ation has a definite range as it traverses matter, the maximum being determined by its energy and the density of the material. If this distance is divided by density, a graph showing range in mg/cm? versus energy in MeV is applicable to all materials. Values for a given energy from the graph in Figure 29-1, divided by the density of the material being traversed (mg/cm*), gives the thickness of that material (cm) which will com- pletely stop that beta radiation. It should be noted that complete shielding for beta radiation is provided by reasonable thicknesses of commonly available materials. Correspondingly, measuring instruments must be selected which will not sig- nificantly impede the beta radiation, this being of particular importance at low energies. As beta radiation traverses matter, the electrons occasion- ally interact in a manner to produce electromag- netic radiation (bremsstrahlung), the amount of this radiation increasing as the beta energy and atomic number of the absorber increase. Alpha radiation is emitted primarily by the heavier radionuclides, The alpha particles are emitted at a specific energy characteristic of each nuclide. The energy range of these alpha particles from the different nuclides is predominantly be- tween 4 and 8 MeV. Alpha radiation, like beta, has a definite range in the materials it traverses. The distances traversed, however, are much shorter than for beta. The horny layer of the skin completely stops alpha radiation and air stops it in a few centimeters. Figure 29-2 is a graph show- ing the range in air for different energy alpha particles. Although neutrons are not emitted by radio- nuclides other than by a few that fission spontan- eously, there are several types of radioactive neu- tron sources available and in use. Of course, neutron radiation exists around the core of any nuclear reactor and it will be produced in the event of an accidental nuclear criticality incident. The radioactive neutron sources are sealed sources, normally of relatively small size. Their neutrons are produced by interactions of alpha or gamma radiation with nuclei of appropriate materials (target materials). Alpha emitting radionuclides having a high specific activity are mixed with or alloyed with the target material; and in sources using gamma interactions, the target material usu- ally surrounds the radionuclide. These sources emit neutrons with a maximum energy character- istic of the radionuclide and target material; and many more neutrons at lower energies, with a dis- tinctive energy spectrum. Characteristics of some radioactive neutron sources are shown in Table 29-5. When neutron radiation traverses matter it is attenuated by elastic and inelastic scattering, capture, and induced nuclear reactions. The ex- tent of these processes depends both on the energy (or energy spectrum) of the radiation and the specific nuclides in the matter being traversed. Moderation (slowing down) of the neutrons by elastic collisions progressively changes the energy spectrum. The probability of these interactions taking place is specified in terms of cross-sections, Sli/3m o2uey o — o oo T as i 1 epuben. po QO~O Nw « 10 “0 ¢£3asuy APR Radiological Health Handbook. U.S. Dept. of Health SOMO Nw 0°T o ONO Nw TI 1684 NR 168 ¢ i + sv § 2 [RR] § € z 168L9 8 ¢ ¢€ 29s v JAUNO XDUIANT TONY TIOTLNVd VINd Public Health Service, 1970. icle Energy Range Curve Education and Welfare Beta Part 383 29-1 igure F MEAN RANGE (CM) ENERGY (MEV) 40 4.5 50 55 6.0 6.5 7.0 7.5 8.0 l 4 1 , : ; li 4 == os pa peg Lome dE SA 4, i fmm] er ere, ; em Color Tr TT a : ob PRS Cf i 1 TT RANGE vs. ENERGY 20 === FOR ALPHA PARTICLES IN AR (STP) fmm fm r Free mr ef ee pe es ee} os be et ef ee ee. ———d- Fg tm a of md ees 1 — ae} 4am of emt + rt mei fm em bm ———— Fre po Se Y = = TL Coho Tory TTT 45 Fo = mo emer aera frame = eet wee] J oe tr ee mm fon eed en] be epee em te ee eee TL LL TL Td } 7 14.0 10 F—= por ¥ — = I Thm tm ee pe — a bv rrr rv pom ae Arr om 2 : — -— 0.5 rt 24 eae 4 ep pete aeereebe = - — : 1 2.5 + 1 — — ee cee b -— 4 it } | 1 Ep i I S| te ee ee eee pe ef fr tet af, : ! —+ itt. bee ee bee a ee ped eee yy 0 t- > “1 I 1 p : I oie — SIiS 1 Bi + i 20 0 0.5 1.0 1.5 2.0 25 3.0 3.5 40 ENERGY (MEV) fe — Radiological Health Handbook. U.S. Dept. of Health, Education and Welfare, Public Health Service, 1970. Figure 29-2. Alpha Particle Energy Range Curve. 384 MEAN RANGE (CM) with their area expressed in units of barns (1 barn=10 ~2*cm?). These various interactions re- sult in the production of secondary radiations, particularly gamma rays, which must always be considered when neutron radiation is present. The complexities of neutron interactions with matter do not permit adequate treatment of energy ab- sorption and shielding here (see Protection Against Neutron Radiation).? Dosimetry Dosimetry involves the evaluation of radiation, often complex as to its nature, energy, direction and quantity, in terms related to its effect on bio- logical systems or other matter. Theoretically, it would seem that measurements could be made to completely describe the radiation field itself at any point of interest including time variations, and from this, the dose or other quantity of in- terest determined. In practice, however, measure- ments are made at the place of interest in a man- ner which relates the measurement directly to the quality of interest — usually absorbed dose or TABLE 29-4 Data for Gamma-Ray Sources Atom- or tom Half-Value Tenth-Valve Specific Num- Half Gamma Layer Layer Ray Radioisotope ber Life Energy Conc. Steel Lead Conc. Steel Lead Constant MeV in in cm in in cm Rcm®/m Ci-h® Cesium-137 55 27y 0.66 1.9 0.64 0.65 6.2 2.1 2.1 3.2 Cobalt-60 27 5.24y 1.17, 1.33 2.6 082 1.20 82 27 40 13.0 Gold-198 79 2.7d 0.41 1.6 — 033 53 — 1.1 2.32 Iridium-192 77 74 d 0.13 to 1.06 1.7 0.50 0.60 5.8 1.7 2.0 5.0¢ Radium-226 38 1622 y 0.047 to 2.4 2.7 0.88 1.66 92 29 55 8.25¢ Reprinted with permission of National Council on Radiation Protection and Measurements from “NCRP Report No. 34”, (1971) Washington, D.C. a Approximate values obtained with large attenuation. b These values assume that gamma absorption in the source is negligible. Value is R/millicurie-hour at 1 cm can be converted to R/Ci-h at 1 meter by multiplying the number in this column by 0.10. ¢ This value is uncertain. 4 This value assumes that the source is sealed within a 0.5 mm thick platinum capsule, with units of R/mgh at 1 cm. TABLE 29-5 Data for Neutron Sources Max. Avg. Yield neutron neutronn/sec. x energy energy 107%/ Source Half-life MeV MeV curie 210py-ne 138.4 d 10.8 4.3 2.5 Ra DEF-Be 19.4y 10.8 4.5 2.5 2261 ne 1622 y 13.2 3.6 15 239pu-ne 24,400y 10.6 4.5 2.0 Reprinted from NBS Handbook 85-196, National Bureau of Standards, Washington, D.C. dose equivalent. To the maximum possible extent, there is a summation of the quantities of interest. Furthermore, due to the complexity of any bio- logical response to irradiation by various types and quantities of radiation, as well as their meas- urement, it is customary to utilize environmental measurements for radiation protection purposes, with precise determinations of dose and dose dis- tribution in biological systems limited to situations of special interest — usually abnormal exposures. 385 Thus, dose-limiting recommendations, although specified in terms of dose equivalent in the body, are commonly evaluated by strictly environmental measurements. There are a variety of detectors, with asso- ciated readout devices which are used for radia- tion monitoring or measurement. The most im- portant are: Geiger-Miiller (GM) tubes, ioniza- tion chambers, proportional counters, luminescent detectors, scintillation detectors, photographic emulsions, chemical reaction detectors, induced radiation detectors and fissionable materials. None are universally applicable and selection of the most appropriate detector or detectors for each radia- tion measurement (or type of measurement) be- comes a matter of great importance. These detec- tors, with associated readout equipment, are used to perform two distinctly separate functions — to measure the radiation in the environment (moni- toring or surveying); and to determine the activity or kind of radionuclide, or both, in solids or fluids, commonly samples from a larger quantity of ma- terial (analysis). G-M tubes detect ionizing events which take place within their sensitive volume, each event causing an output voltage pulse. These pulses may be counted or summed in various ways, usu- ally to give a count rate (counts per minute, cpm). Two types of G-M survey meters are in common use. One uses a cylindrical tube encased in a pro- tective metal shield with an opening on one side over which various absorbers can be placed. The other has the opening at one end of the cylinder where the tube has a very thin “window.” The output (cpm) is not proportional to exposure or absorbed dose rate for different types and energy of the radiation. Although scales on survey meters are frequently marked “R per hour,” these values are only true for the calibrating radiation. Sig- nificant errors can occur from use where the radia- tion is different than the calibrating radiation. When G-M tubes are used for analysis, proper calibration is likewise essential. Ionization (ion) chambers are commonly used to measure dose or dose rate (or exposure or ex- posure rate) from beta, gamma and x radiation. Ions formed by the radiation passing through a selected gas in a chamber are measured either by applying voltage continuously with measurement of the extremely low current flow or by using the chamber as a condenser which is first charged, then exposed to the radiation and the amount of discharge determined. The chamber walls, inter- nal components and gas filling are usually either air equivalent or tissue equivalent. Proportional counters usually consist of a gas filled cylinder (chamber) containing a central wire to which a potential is applied. The potential is selected so that the output voltage signals are proportional to the energy released by the radia- tion causing the ionization events in the chamber. This permits selective measurement of different radiations. These counters are commonly used to measure alpha or neutron radiation. The gas in the chamber may be either static or flowing. They may be used as survey meters or for analysis, in- cluding spectrometric analysis (measurement of radiation intensity as a function of energy). The alpha survey meters have a very thin “window” to minimize absorption of the radiation. Luminescent detectors are solids in which energy changes produced by radiation are stored so that subsequent processing will cause them to emit a quantity of light proportional to the energy change. Commonly used materials are metaphos- phate glass and calcium or lithium fluoride. The glass is processed by irradiation with ultraviolet and the fluorides by heating. The latter, called thermoluminescent dosimeters (TLD), are find- ing many uses because of good sensitivity with small pieces. They are used for personnel moni- toring, including neutron exposure evaluation. Scintillation detectors use the phenomenon of light production due to interaction of radiation with crystals or other phosphors (solid, liquid or gas). Light pulses from the scintillator are meas- ured with a photomultiplier tube and its asso- ciated electronic equipment. Since the light out- put and in turn the electrical signal is proportional to the radiation energy absorbed in the scintillator, these devices find a wide variety of uses. They are used as survey meters and for analysis, including spectrometric analysis. 386 Radiation produces a latent image in photo- graphic emulsions, resulting in darkening of the film when developed by usual techniques. Two general types of film are used, one in which the radiation (beta, gamma, x ray) produces a gen- eral blackening, and the other in which small tracks are produced by charged particles, usu- ally protons from fast or thermal neutron inter- actions in the film. The blackening due to gamma and x rays is not proportional to air or tissue absorbed dose at different energies, and various absorbers are placed adjacent to the film to mini- mize this aberration. Blackening due to beta radi- ation varies a small amount with energy. A major use of film for dosimetry has been in personnel monitoring badges. Using both shielded and un- shielded sections permits measurement of beta as well as gamma and x rays. Chemical reaction detectors are systems in which radiation produces a chemical change in a material in such a manner that a chemical analysis or indicator will measure the amount of change. An example is a system using a chlorinated hydro- carbon, such as chloroform, with water and a dye indicator to measure the acid formed due to ir- radiation. These detectors are not used extensively because of their low sensitivity. Induced radiation detectors are materials in which the radiation interacts to form radionuclides whose radiation can be measured. They are par- ticularly useful for detecting or measuring neutron radiation. A typical example is the use of indium foil for detection of neutron radiation exposures. Proper selection of foil materials permits evalua- tion of a neutron energy spectrum. Fissionable materials also are useful for neutron radiation detection and measurement. CATEGORIES OF RADIATION EXPOSURE Natural Radiation Individuals continually receive a dose from natural radiation that comes both from sources external to the body and from naturally occurring radionuclides deposited within the body. The ex- ternal sources are primarily cosmic radiation and gamma radiation from materials naturally present in the ground and in building materials. From foods, drinking water and in the air, several radio- nuclides are deposited in the body including uran- ium and its decay products, thorium and its decay products, radiopotassium and radiocarbon. Nat- ural radiation in the United States results in an estimated average annual dose equivalent to in- dividuals of about 125 mrem (100 mrem external and 25 mrem internal). It is unlikely to be less than 100 mrem for any individual and unlikely to be more than 400 mrem for any significant num- ber of people.’? Environmental Radiation In addition to natural radiation, environmental radiation from man-made sources adds a small increment of dose to the population generally. This dose comes from a wide variety and type of sources including: fallout from nuclear weapons testing; effluents from nuclear and other facilities processing or using radionuclides; luminous dial clocks or watches and signs; and electronic de- vices, such as television sets, using high voltages. The average annual dose equivalent to the popu- lation from these sources is estimated to be only a few percent of natural radiation, probably about five or six mrem per person per year. Medical Irradiation The planned exposure of patients to radiation is a category which involves a large percentage of the general population. Occupational exposures received incidentally by physicians and supporting staff are not considered part of this exposure cate- gory. Diagnostic and therapeutic procedures in- volve external irradiation with beta, gamma or x radiation, internal irradiation from ingested or injected radionuclides, and irradiation from im- planted sealed sources. Doses to individuals vary over an extremely wide range but usually involve only partial body irradiation. Average annual dose equivalent to the population members from these sources has been estimated to be between 50 and 70 mrem per year.'® Ordinarily, medical and occupational exposures are considered separ- ately. With the exception of a high dose due to an occupational accident, necessary medical expos- ures are not restricted because of occupational exposures. Occupational Irradiation Occupational radiation exposures arise from practically every type of radiation and radiation source. The major groups of occupationally ex- posed personnel are medical or para-medical workers and workers in the expanding nuclear energy programs. However, there are many ex- posures to radiation or radioactive materials throughout industry, in underground mining, and in many types of research. On the basis of occu- pational radiation exposure records of the U. S. Atomic Energy Commission and its contractors for 1967, the average annual occupational expos- ure is estimated at about 500 mrem per person to 100,000 adults (95% of them received less than 1 rem each).'® Assuming a similar dose to other workers, the estimated average annual dose equivalent to the population members is a fraction of a millirem per year. BIOLOGICAL ASPECTS OF IRRADIATION Somatic and Genetic Effects Irradiation of humans produces two types of effect — somatic and genetic. The somatic effect is the effect on tissues, organs or whole body. Independent of any somatic effect, irradiation of the gonads may cause genetic effects since muta- tions, which are caused by heritable changes in the germ plasm, may occur. Of course, only the irradiation prior to conception can have this in- fluence. Somatic effects vary over a wide range — from rapid death due to short term whole body exposures of 10,000 Roentgens or greater to slight reddening of the skin due to minimal exposure. Effects, including those of particular concern —neoplasms, cataracts and life shortening—may also be delayed for long periods. Within the body, cells react with varying degrees of sensitivity. Tis- sues also respond differently, depending on dose equivalent rate. Dose fractionation has an amel- iorating effect and there is repair of tissues and organs when time permits and the change is not irreversible. Partial body irradiation has much less effect than whole body irradiation. Age is a significant factor; for a given dose many effects are less as age increases. For equal absorbed doses, different types (and energies) of radiation do not produce the same degree of response. In the study of biological effects, the variation due to different kinds of radiation is referred to as “relative biological effectiveness” (RBE) — the ratio of absorbed doses that produce equal effect, with cobalt-60 gamma rays or 200-250 kV x rays used as the reference. This ratio is reflected indirectly in the quality factor used in radiation protection practice. Those somatic ef- fects (e.g., neoplasms) that are delayed for long periods of time may occur only in a small fraction of the exposed individuals — the probability of the effect occurring increasing with increased dose equivalent. Genetic effects are of general concern because radiation-induced mutations are added to the “load” of defective genes present in the popula- tion. Because of the presence of defective genes in all members of the population, it is not possible to identify an abnormality in an offspring with possible mutations caused by irradiation of the parent. Thus, genetic effects relate to population groups, not individuals. Because of this, the radia- tion exposure to the entire population group is the “matter of primary concern, and the genetically 387 significant dose (GSD) has been established as a measure of this population exposure. Further- more only gonadal exposures during the reproduc- tive period of a lifetime have an influence.” Thus, the age at which radiation exposures occur, as well as the dose equivalent, is of prime concern in relation to genetic effects. Acute and Chronic Exposures Practically all occupational irradiation involves chronic exposures, i.e., small weekly doses (e.g., <100 mrem) occurring over many months and years. Occasionally, due to an accident, an acute exposure may occur, i.e., a high dose (e.g., 25 rem) in a period of a day or less. Somatic re- sponse to acute exposure is different from and greater than that for an equal chronic exposure. In a lifetime of occupational exposure without any observable effect, an individual’s total dose can be large enough so that an equal dose given in a few hours would be seriously disabling or fatal. Effects of acute exposures may be early, delayed or secon- dary, and late. Early effects as a result of an acute whole body exposure are shown in Table 29-6. There is less effect for partial body expo- sures. Delayed effects may occur some time after the early effects have been ameliorated, the extent depending on the dose. In addition to possible loss of hair, one such effect of general concern (often misunderstood) is sterility. Permanent sterility occurs only with absorbed doses to the TABLE 29-6 Representative Dose-effect Relationships in Man for Whole Body Irradiation Representative absorbed dose of whole body X Or gamma radiation (rads) 5-25 Nature of Effect Minimal dose detectable by chro- mosome analysis or other spe- cialized analyses, but not by hemogram Minimal acute dose readily de- tectable in a specific individual (e.g., one who presents him- self as a possible exposure case) Minimal acute dose likely to pro- 75-125 duce vomiting in about 10% of people so exposed Acute dose likely to produce tran- 150-200 sient disability and clear hema- tological changes in a majority of people so exposed. Median lethal dose for single short 300 exposure The dose entries in this table should be taken as representative compromises only of a surpris- ingly variable range of values that would be of- fered by well-qualified observers asked to com- plete the right hand column. This comes about in part because whole body irradiation is not a uniquely definable entity. Mid-line absorbed doses are used. The data are a mixed derivative of ex- perience from radiation therapy (often associated with “free-air” exposure dosimetry), and a few nuclear industry accident cases (often with more up to date dosimetry). Also, the interpretation of such qualitative terms as “readily detectable” is a function of the conservatism of the reporter. Reprinted with permission of National Council on Radi- ation Protection, from “NCRP Report No. 39” (1971) Washington, D.C. gonads of 500-600 rads of x or gamma radiation; and a single dose of 50 rads may induce brief temporary sterility in many men and some women.'" Late effects as the result of acute ex- posure, such as leukemia, may occur many years after exposure, their probability increasing as dose increases. From chronic exposures, there are no secondary or delayed effects and the possibility of late effects is minimal. If chronic occupational doses are within the NCRP dose limiting recom- mendations, the probability of any late effect is so small that it has not been possible to establish clearly whether any such somatic effect exists. Internal and External Radiation Sources External radiation sources, i.e., those sources which are located external to the body, present an entirely different set of conditions than radionu- clides which have gained entrance to the body 388 with their attendant continuous irradiation of the cells and tissues in which they exist. Such radio- nuclides are called internal radiation sources — sometimes internal emitters. Entry of internal radiation sources into the body during occupational exposures is principally from breathing air containing particulate or gas- eous radionuclides, although ingestion may be a significant mode. Absorption through the skin is significant for some compounds of a few radio- nuclides, particularly tritium; and implantation under the skin may occur as the result of acci- dental skin puncture or laceration. Once inside the body, radionuclides are absorbed, metabolized and distributed throughout the tissues and organs according to the chemical properties of the ele- ments and compounds in which they exist. Their effects on organs or tissues depends on the type and energy of the radiation and residence time. Both radioactive decay and biological elimina- tion remove radionuclides from the body and its organs, these removal rates frequently being ex- pressed as half-lives. The net rate is designated as the “effective half-life.” While metabolically similar, the degree of effect from different radio- active isotopes of the same element will vary ac- cording to the type and energy of the radiation they emit and their radioactive half-life. Acute or early effects do not occur from internal radiation sources, with the possible exception of a very large intake of certain radionuclides. While radiation measurements can be made in the environment of workers which characterize their dose cquivalent from external radiation sources, no comparable environmental radiation measurement will reveal dose equivalent from ex- posures to internal radiation sources. Instead, evaluation (and control) is based on activity con- centrations in air or water, a specific relation be- tween these concentrations and the resulting dose equivalents for each radionuclide having been de- termined from human experience when available, or from calculations. Thus, practical dose-limiting recommendations are expressed in terms of maxi- mum permissible concentrations (MPC) for in- haled or ingested radionuclides. A similar. con- cept is expressed as a Radioactivity Concentration Guide (RCG) by the Federal Radiation Coun- cil.* For essentially insoluble gases producing beta or gamma radiation, such as the inert gases argon and krypton, the amount of the radionuclide that becomes an internal radiation source is so small that the external irradiation from an infinite cloud surrounding the individual will produce the greater dose equivalent. The effect from external radiation sources de- pends on the penetrating ability of the particular radiation. Thus, alpha radiation is of no concern externally, and beta is stopped in the outer tissues, the depth depending on energy. Very low energy x or gamma radiation is attenuated quite rapidly. The effect of radiation on any organ or tissue is dependent on the total dose equivalent from both internal and external radiation sources. Thus, the total dose equivalent must be considered when comparisons with the MPD are made. Theoretic- ally, it should be possible to sum these separate dose equivalents but in practice such quantitation is difficult, if not impossible. Therefore, it is cus- tomary to use the two different dose-limiting rec- ommendations conservatively. Critical Organs and Tissues The various tissues and organs of the body are not affected equally by equal irradiation. Their responses vary considerably and for radia- tion protection purposes it is essential that dose equivalent to the most sensitive organs essential to well being be given primary consideration. For uniform whole body irradiation, the blood form- ing organs (red bone marrow), the lens of the eye, and the gonads are more susceptible to sig- nificant effects and these are designated as “crit- ical organs.” Of course, for individuals past re- productive age the gonads are not a critical organ. For those internal radiation sources that do not irradiate the body uniformly the distribution and metabolic pattern for each radionuclide will de- termine which organs and tissues receive the larger dose. Again, for radiation protection pur- poses, any essential organ or tissue which is likely to be affected the most by the radiation from in- ternal radiation sources is of primary concern and these are also designated as critical organs. These critical organs (and tissues), sometimes desig- nated as limiting organs, are: lung, GI tract, bone, muscle, fatty tissue, thyroid, kidney, spleen, pan- creas and prostate. The total activity (curies) of a radionuclide in the body is designated as the “body burden.” Distribution may be inhomogeneous, with a large fraction in one or more organs or tissues. While the activity in the crititcal organ is the limiting factor, the body burden corresponding to the MPD for the critical organ indicates the total ac- tivity that should be present in the entire body. It is designated as the maximum permissible body burden. RADIATION PROTECTION CONSIDERATIONS Occupational and Public Exposures Occupational radiation cxposures involve a select age group of healthy individuals. Their ex- posures occur for periods not exceeding approxi- mately eight hours per day and 250 days per year. This group is a very small portion of the general population and they are trained in radiation pro- tection practices. In contrast, the general popula- tion necessarily includes the unborn, the very young, the sick or disabled; and their exposures can be continuous — 24 hours per day, 365 days per year. For these, and other reasons, dose- limiting recommendations for the general popu- lation are set at lower limits than for occupational exposure, commonly by a factor of 10 or greater. Dose-limiting recommendations applicable to the public are designated frequently as “dose limits,” those for occupational exposure as “maximum permissible dose equivalent (MPD).” The Fed- eral Radiation Council designates both as RPG's. Only those individuals whose duties involve ex- 389 posure to radiation should be classed as “occupa- tionally exposed” and their training in radiation protection should be assured. Dose Assessment To accurately determine the true dose equiva- lent to the critical organs of all occupationally exposed individuals is a desirable objective which in practice becomes impractical, if not impossible. Activities in the workplace are varied in space and time, the energy and frequently the type of radiation varies, parts of the body being irradiated change with time, irradiation may occur from both internal and external radiation sources, and meas- urement devices have varying degrees of accuracy. Environmental measurements, however, can be made in a manner such that they provide a con- servative evaluation of the dose equivalent to the critical organs and in turn assure that dose-limit- ing recommendations are not exceeded. This is accomplished by a combination of radiation sur- veys, area monitoring and personnel monitoring. If radiation surveys or other adequate data indi- cate that external irradiation will be less than one fourth of the applicable dose-limiting recommen- dation, personnel monitoring devices are not rec- ommended. Above this, suitably selected person- nel monitoring devices are required for evaluation of the radiation environment in which the individ- ual works. The dose equivalents indicated by these are normally conservative with respect to any critical organ dose equivalent, and for gen- eral control purposes their readings can be com- pared to the applicable dose-limiting recommen- dation. Personnel monitoring devices are nor- mally worn on the trunk of the body, but for some types of work they are required on extremities, particularly hands and forearms, as well. The dose-limiting recommendations permit higher doses here. Possible doses from small beams not intercepted by personnel monitoring devices must be cvaluated by other means. For exposures to airborne radioactive ma- terials, the activity concentration in the breathing zone of the worker, averaged over a 40-hour weekly period, is compared with the tabulated values of maximum permissible concentrations (MPC) for the radionuclides of concern (see page 390). These concentrations, if breathed 40 hours per week indefinitely, will produce a dose equiva- lent in the critical organ equal to the dose-limiting recommendation. If a valid determination of total dose equiva- lent to the whole body, the parts of the body, or the critical organ is required, such as after an abnormal cxposure or to establish a monitoring procedure, a detailed evaluation based on all per- tinent data should be made. To convert absorbed dose to dose equivalent, the rounded practical values of the quality factor in Table 29-7 may be used. Methods of calculat- ing a quality factor are described in reference (10). If neutron flux density and energy are mcasured or known, the dose equivalents may be found in Table 29-8. TABLE 29-7 Practical Quality Factors Radiation Type Rounded QF X rays, gamma rays, electrons or posi- 1 trons, Energy =0.03 MeV Electrons or positrons, Energy <0.03 1 MeV Neutrons, Energy <10 keV 3 Neutrons, Energy > 10 keV 10 Protons 10 Alpha particles 20 Fission fragments, recoil nuclei 20 TABLE 29-8 Mean quality factors, QF, and values of neutron flux density which in a period of 40 hours results in a maximum dose equivalent of 100 mrem. Neutron Energy QF Neutron Flux Density MeV cms 2.5% 107% (thermal) 2 680 1X1077 2 680 1X10 2 560 1X107° 2 560 1X10 2 580 1X107° 2 680 1X10 2.5 700 1X10 7.5 115 5X10 11 27 1 11 19 2.5 9 20 5 8 16 7 7 17 10 6.5 17 14 7.5 12 20 8 11 40 7 10 60 5.5 11 1X10? 4 14 2X10? 3.5 13 3X10? 3.5 11 4X10? 3.5 10 aMaximum value of QF in a 30-cm phantom. Tables 29-7 and 29-8 reprinted with permission of Na- tional Council on Radiation Protection and Measure- ments, from “NCRP Report No. 39” — (1971) Wash- ington, D.C. 390 TABLE 29-9 NCRP Dose-limiting Recommendations Maximum Permissible Dose Equivalent for Occu- pational Exposure Combined whole body occupational exposure Prospective annual limit Retrospective annual limit Long term accumu- lation to age N 5 rems in any one year 10-15 rems in any one year years (N—18) X5 rems Skin 15 rems in any one year Hands 75 rems in any one year (25/qtr) Forearms 30 rems in any one year (10/qtr) Other organs, tissues 15 rems in any one year and organ systems (5/qtr) Fertile women (with 0.5 rem in gestation respect to fetus) period Dose Limits for the Public, or Occasionally Ex- posed Individuals Individual or occasional Students 0.5 rem in any one year 0.1 rem in any one year Population Dose Limits 0.17 rem average per year 0.17 rem average per year Genetic Somatic Emergency Dose Limits—Life Saving Individual (older than 45 years if possible) Hands and forearms “100 rems 200 rems, additional (300 rems total) Emergency Dose Limits—Less Urgent 25 rems 100 rems, total Individual Hands and forearms Family of Radioactive Patients Individual (under age 45) Individual (over age 45) 0.5 rem in any one year 5 rems in any one year Reprinted with permission of National Council on Radi- ation Protection and Measurements, from “NCRP Report No. 39” (1971) Washington, D.C. The dose to the whole body or to the critical organs from internal radiation sources continues as long as the radionuclide is present. When in- take is stopped, the dose decreases with time — frequently exponentially. Where the effective half- life is long, the total dose equivalent is rather large in comparison to that produced during and shortly after the time of exposure. This total dose equivalent, integrated over a lifetime, is desig- nated as the “dose commitment.” It is useful in a number of different types of evaluations. Dose-Limiting Recommendations The National Council on Radiation Protection and Measurements (NCRP) is generally recog- nized as an authoritative source of radiation pro- tection information, data and criteria in the United States. NCRP Report No. 39° discusses radia- tion protection criteria in detail and presents their dose-limiting recommendations, which are shown in Table 29-9. The NCRP comment on the occu- pational limits is: “There will be occasions when the measured or estimated actual dose equivalent exceeds the prospective limit of 5 rems in a year. No deviation from sound protection is implied if the retrospective dose equivalent does not exceed 10 to 12 rems for dose increments well distributed over time or even 15 rems for exceptionally well- distributed increments. Repetition of retrospective dose equivalents in excess of planned limits is controlled by the long-term occupational accumu- lated dose equivalent.” The NCRP- recommenda- tions serves as the basis for various regulations and standards in which interpretations are made according to specific needs. Regulations of states, U.S. Atomic Energy Commission and other gov- ernmental agencies may not be the same as NCRP recommendations and must be consulted and used as applicable (see Chapter 9 and page 392). Similarly, NCRP has provided tabulated val- ues of maximum permissible body burdens and maximum permissible concentrations of radionu- clides in air and water for occupational exposures. Some of these values are shown in Radiological Health Handbook.* The complete tabulation is in NCRP Report No. 22" and a similar tabulation, with the derivation data and methods, is in a re- port of the International Commission on Radia- tion Protection.'? The various regulations also contain such tabulations, usually including values applicable to the general public. IRRADIATION BY EXTERNAL RADIATION SOURCES Exposure Control A basic concept in radiation protection prac- tice is the establishment of a “controlled area.” Access to these areas must be controlled and within them supervision and control of occupa- tional exposures is provided. Emergence of beams and escape of radioactive materials from these areas are also controlled. These areas are identi- fied by use of the standard radiation symbol*® with associated warning notices. This symbol, a pur- ple trefoil on a yellow background, also identifies any radiation source. Since the useful beam of x-ray equipment may inflict a year’s MPD in minutes or less, the design of industrial x-ray facilities must of necessity give proper consideration to the establishment of a suitably controlled area which will assure proper radiation protection for two groups of individuals — those who operate the equipment (occupation- ally exposed) and those in the environs, either normally or casually (not occupationally ex- posed). Where possible, the x-ray equipment should be within a room or other enclosure ar- ranged with controls outside and having interlocks 391 to prevent entry when equipment is energized. Shielding can then be provided so that the ex- posure rate outside the enclosure will be low enough to insure that the applicable MPD or dose limit will not be exceeded. Small devices or in- struments using x rays, such as laboratory equip- ment, usually can be totally enclosed with ade- quate shielding, but accessibility to the inside of the shield requires special consideration (inter- locks, etc.). Where work requires truly mobile or portable equipment, exposure time and distance ' from the equipment become the basic method for controlling exposure rates to values which will insure that no individual exceeds the applicable MPD or dose limit. Portable shielding can be an aid. American National Standard Z54.1-19637 classifies x-ray and sealed gamma-ray source in- stallations into three types: exempt, enclosed and open. Shielding design and operational require- ments are given. Although intended for medical installations, Medical X-ray and Gamma-ray Pro- tection for Energies up to 10 MeV*® may provide useful data; shielding data is also presented in reference (2). For accelerators, American Na- tional Standard Radiological Safety in the Design and Operation of Particle Accelerators'* estab- lishes safety requirements. In addition to x-ray equipment, there may be other sources of x rays in industry, such as high voltage (=10kV) electron tubes, which may re- quire shielding or other means of control to as- sure adequate radiation protection for workers (or the public). Gamma radiation, usually from a sealed source, is used for a variety of purposes in indus- try. The larger sources produce beams compar- able in exposure rate to x-ray equipment. Detailed descriptions cannot be given here, but rather a few general considerations. Gamma radiation can- not be turned off like x rays. This imposes a severe requirement on retention of the sealed source at a predetermined specific location where exposure control is assured or within appropriate shielding at all times. Procedures and surveys must guarantee this control. The integrity of the encapsulation or bonded cover of the sealed source must be assured at all times to prevent release of the radioactive material into the environment where it could be dispersed and inhaled or in- gested. Periodic tests, such as smears of the sealed source or its container, should be made. Appropriate testing of radium sources is particu- larly important because any failure will release radon gas which, with its daughters, can contam- inate the surrounding area. Exposure rates from sealed sources, in air, can be calculated from the specific gamma-ray constant (see page 382). As an approximation, the gamma exposure rate (R/hr) at 1 foot is 6CE, where C is the number of curies and E is the total energy per disintegration in MeV. As for x-ray installations, references (7) and (8) provide useful shielding information. Beta radiation sources, which are frequently built into some piece of equipment such as a thick- ness gauge, must be shielded and arranged so that access to the beta radiation is prevented. Of par- ticular concern is control of exposures during any maintenance procedures. Consideration must be given to any associated gamma radiation; and to the bremsstrahlung exposure rate, particularly for sources of high activity and energy. To permit escape of the beta radiation, the encapsulating material must be relatively thin, at least over the useful area of the source. Damage to this en- capsulation will permit release of the radionuclide to the environment where it can be dispersed and inhaled or ingested. Radioactive neutron sources are commonly small sealed sources of relatively substantial con- struction. Yield of neutrons is proportional to the activity in the source. See page 385 for neutron source data. Consideration must be given to gamma radiation as well as neutron radiation from them. If the radionuclide in them is radium, the gamma dose equivalent rate is higher than that from neutrons and the possibility of radon leak- age must be recognized. Leakage of any of the radionuclides used in these sources presents a hazard of considerable magnitude which necessi- tates care in use and periodic testing. Commonly used shielding materials are concrete, polyethy- lene, boronated polyethylene or boron in other materials such as aluminum. Shielding and other useful data will be found in Physical Aspects of Irradiation® and Protection Against Neutron Radi- ation”. External radiation sources involve a wide va- riety of equipment which cannot be described here. Descriptions and useful data will be found in Radiation Hygiene Handbook." Exposure Evaluation Applicable regulations (or NCRP recommen- dations) established the time period during which specific dose equivalents may be given to workers. Currently, most regulations permit a limit of 1.25 rem/quarter indefinitely to the whole body, go- nads, bloodforming organs and lens of the eye; or, for individuals whose previous radiation his- tory has been established, a limit of 3 rems/ quarter®* with an overriding yearly limitation of 5(N-18) rems, N being age in years. Separate quarterly and usually yearly limits, with higher values, are specified for extremities and skin. Exposure evaluations therefore must be related to these time periods, no matter whether meas- urements are made in rems (or R) per hour, per day, per week or per month. Administratively, daily or weekly limits are frequently used for general control. The evaluations to establish dose equivalent from external radiation sources are accomplished by conducting radiation surveys and monitoring the environment in which the individuals work. The radiation survey establishes the parameters that must be measured and depicts whether occa- sional or essentially continuous surveillance with measuring instruments is required. Proper instru- ments must be selected for the survey so that all possible types and energies of the radiation will be measured with reasonable accuracy. A wide *This was a former NCRP recommendation. 392 selection of instruments is available commer- cially® ** 17 but caution must be exercised to be certain their specified capability will fulfill the required needs. A comprehensive discussion of instrumentation is in Radiation Protection Instru- mentation and Its Application." Proper calibra- tion for the radiation to be measured is essential. The higher the instantaneous dose rates or poten- tial dose rates in the work area and the greater the complexity of the operations, the greater the need for continuous or frequent surveillance meas- urements; and correspondingly, closer control over the exposure time of the workers. Where abnormal situations may occur, area monitoring by permanently installed instruments at key loca- tions, with readouts under observation at a central location, will aid in detecting any significant changes of the radiation levels in the general en- vironment. Use of alarms may be indicated in extreme cases. Except where it can be assured that dose equivalent rates are consistently very low (<25% MPD), personnel monitoring devices must be used to measure the radiation incident on a work- er’s body (or extremities), integrated over pre- selected time periods. Film badges, available from commercial services,'""'" have been used exten- sively with time periods usually being from a week to a month. Currently, there is increasing use of thermoluminescent dosimeters (TLD) for these and longer periods. Where dose equivalent rates are high and variable, the dose accum- ulated during minutes or hours of exposure becomes critical and pocket dosimeters (ionization chambers) provide a convenient means of such measurement. There are two types, those that require an instrument for readout and those that can be read directly. The latter are particularly useful when the worker can read them frequently and limit his work period or procedures accord- ingly. A film badge or TLD is normally used in addition to the pocket dosimeter to provide a back-up for an off-scale reading. There may be discrepancy between the two readings because of different response characteristics. A pocket-size instrument with an alarm sensitive to either dose or dose rate is available and can be used if oper- ating conditions warrant. Indium foils may be added to film badges or other badges worn by workers if accidentally high neutron exposures may occur, the induced activity permitting a rapid qualitative check for a high neutron exposure. External irradiation of the body tissues or or- gans may occur from radionuclides deposited on the skin or in the clothing. To detect (or meas- ure) this requires a very careful probing over the entire body with a suitable instrument. A probe on a flexible cord is desirable; or where the con- tamination is limited to the hands or shoes, a “hand and foot counter” may be used. Although periodic medical examinations are desirable for many reasons, they cannot be used as a means of exposure evaluation unless dose equivalents are many times the MPD (see Table 29-6). A relatively new cytogenetic technique involving a determination of chromosome irregu- Wounds and Inhalation Skin Absorption Ingestion J J Upper Respiratory Tract T MN i | i." .---- |} WV Lung > Body (Storage) Fluids GI ! \ 1 | | | Vv Organs ' (other than \ lung), bone, : tissues ' . (Storage) | ! Vv \ Vv Exhalation Urine Feces Simplified Diagram of Metabolic Pathways of Radionuclides in the Body Figure 29-3. principal pathways - supplementary pathways decending on chemical and physical composition Radionuclide Pathways through the Body. 393 larities found in somatic human blood cells," al- though nonspecific, can provide a means of meas- uring dose equivalents slightly above the MPD, but use of this technique is severely limited due to the many man-hours required for cach de- termination. General administrative practices for radiation monitoring are presented in American National Standard Guide for Administrative Practices in Radiation Monitoring.** IRRADIATION BY INTERNAL RADIATION SOURCES Mode of Entry Internal radiation sources gain entry to the body by breathing gaseous or particulate airborne radioactive materials, by swallowing radioactive materials that have gotten into the mouth from contaminated lips, hands, foods, or liquids, and by absorption through or implantation under the skin. After entry, a rather complex distribution throughout the body may occur as indicated in Figure 29-3. Although there may be irradiation throughout the body, the organs or tissues where the residence time and concentration arc greatest receive most of the dose equivalent from alpha and beta radiation, while gamma dose is morc distributed. . When inhaled, a fraction of radioactive gases and particulates are retained and absorbed in ac- cordance with chemical and physical propertics (not radioactive properties), the balance being exhaled. The retained material is distributed along all respiratory passages — that deposited in the upper passages being subsequently swallowed after clearance by drainage or ciliary action. Re- tention of particulates in the several sections of the respiratory tract is a function of the particle size distribution, the larger particles (=10 pm dia.) not reaching the lung. Soluble materials, when deposited in the lung, are taken up in the blood stream, their subsequent distribution and excretion being determined by the metabolic pat- tern for that element. Insoluble materials arc re- tained in the lung with a relatively slow clearance rate (e.g., — 120 day half-life). Without specific data, ICRP recommends an assumption that 25% is exhaled, 50% is deposited in the upper respira- tory passages and 25% is deposited in the lungs, with all of that in the upper passages and half of that in the lungs being swallowed. Ingested materials, including those cleared from the respiratory tract, pass through the gas- trointestinal tract, with their absorption and ex- cretion being determined by solubility of the par- ticular chemical compound and metabolic pattern of the element. Embedded materials, unless very soluble, tend to remain in the tissues near the sight of entry with a slow clearance rate from that site. Those few materials which can be absorbed through the skin are promptly distributed throughout the body tissues. The tabulated values of MPC for air and water take all of these various ramifications into account except for embedded materials, yet for exposure control and exposure evaluation purposes some of the above factors require consideration. Exposure Control Work with radioactive materials that are not effectively contained necessitates the establishment of a well defined controlled area. Preferably it should be a room or other totally enclosed area which will prevent atmospheric dispersion of the radioactive materials to outside areas. Exhaust of air from the room through filters may be required. Movement of individuals or materials through the exit (entrance) should be controlled to prevent inadvertent transfer of radioactive materials out- side. Any liquids containing radioactive materials should either be retained for safe disposal at an authorized location or be put into a drain which fulfills pertinent requirements for release of radio- active materials to the environment. Only work- crs, properly trained, or visitors properly con- trolled, should be permitted entry. The degree of these controls will vary over a wide range for dif- ferent kinds of work depending on the activity (Ci) involved, the MPC of the radionuclides in air or liquid, the dispersion characteristics of the materials and the size or complexity of the opera- tions. . Within the controlled arca, the workers must be protected against breathing radionuclides in concentrations greater than the MPC averaged over a 40 hour week. Where exposure times are less or greater than 40 hours in a week, the tabu- lated MPC may be adjusted up or down propor- tionately. Although the MPC’s are set for 40 hours per week exposures indefinitely, most regu- lations require that each weck be considered sep- arately. For work with very small amounts of material, c.g., less than the activity in a few maximum permissible body burdens, rather simple exposure controls are required — perhaps gloves and a lab coat. As the activity and dispersibility increase, protective measures progress through ventilated hoods, specially designed exhaust hoods, total enclosures and glove boxes. Some of these are described in reference (15). Use of personal protective equipment such as coveralls, gloves, head covers and shoe covers may be indicated (see Chapter 36). Where the concentration of airborne radioactive materials cannot be ade- quately controlled by exhaust and enclosures, respiratory protective equipment approved for . radioactive materials is required.*’ Where abnor- 394 mal concentrations may occur, continuous air sampling devices with an alarm may be needed. Contamination of surfaces with radioactive ma- terials throughout the controlled area may require control, such measurements being made by count- ing smears taken on filter papers from 100 cm? areas. Clothing change rooms with shower facili- ties, located at the exit (entrance) of the con- trolled area, may be required to prevent spread of radioactive materials from the area and to assure removal of contamination from workers’ bodies. Possible remaining contamination is checked with an instrument probe. For a laboratory, many or all of these factors require consideration. American National Stand- ard Design Guide for a Radio-Isotope Laboratory (Type B)** is a general guide to these require- ments. Exposure Evaluation Except for an accident, internal radiation sources resulting from occupational exposures usu- ally accumulate gradually in the body of workers. Breathing airborne radioactive materials either intermittently or continuously is a prime source. Thus, a knowledge of the radionuclides and their average activity concentration in the air breathed by workers becomes important in any assessment of dose equivalent to critical organs or the corre- sponding bodily intake in relation to the MPC. Usually it is sufficient to assure that the weekly average airborne radioactivity concentration in the breathing zone of workers is less than the MPC, although other possible modes of entry should be considered. Hence, where dispersible radioactive materials are used, an air sampling program be- comes a necessity. This program may vary from an occasional spot check where concentrations are readily maintained at a small fraction of the MPC, to continuous sampling either at or near the breathing zone of workers where exposure may average near the MPC or equipment failures may produce abnormal conditions. Air sampling techniques and instruments dis- cussed in Chapters 13, 14 and 15 may be used for radioactive materials provided the sample is suitable for radioactivity analysis. Samplers using filter paper or membranes have found gencral ap- plication because the activity measurement can be made readily. For some situations, samplers which provide a size scparation are used. The samplers may be portable instruments with a sampling head that can be positioned or held near the breathing zone of workers, or be permanently mounted equipment. American National Standard Guide to Sampling Airborne Radioactive Materials in Nuclear Facilities** provides a complete guide to sampling airborne radioactive materials. Radionuclides are removed from the body by excretion in the urine and feces, the rate and par- titioning between the two depending on many factors including mode of entry into the body, elemental composition, solubility and rate of in- take. For many radionuclides, sufficient knowl- edge of excretion patterns and rates are available so that measurements of excretion rates can be quantitatively related to intake rates, or activity in the body, or both. Data obtained from analysis of urine or feces — frequently called bioassays — can serve as an assessment of previous and current intake rates to verify air sampling data. By dis- continuing current intake for a period, an estimate of the body burden or critical organ burden can be made from such excretion measurements usually a series of measurements over a period of a week or longer. When used to assess current intake rates it is common practice to establish, for each radionuclide, an “investigation level” or “check point.” These are discussed in Recom- mendations of the International Commission on Radiological Protection, Report of Committee IV on Evaluation of Radiation Doses to Body Tissues 395 from Internal Contamination Due to Occupational Exposure,** with very conservative values listed. For excretion rates or activity concentrations in the excreta which are below an appropriate inves- tigation level, it is assumed that exposure controls and evaluations have been adequate; but if above these levels, an examination of the adequacy of current practices is made. A further means of assessing the current status of a worker with respect to intake and retention of radionuclides is an in vivo determination of body burden or critical organ burden by measur- ing the gamma radiation being emitted from his body (or critical organ). The simplest of these is measurement of radioiodine in the thyroid by placing an instrument adjacent to the thyroid. For most radionuclides, a “whole body counter” is required. It consists of one or more measuring instruments which scan the whole body, usually in a well shielded enclosure to minimize the effect of background radiation.?” Such measurements re- quire skilled personnel and very sensitive measur- ing devices, properly calibrated. Such measure- ments can be made for radionuclides emitting x rays, such as uranium-235, plutonium-239 and americium-241, as well as for radionuclides emit- ting higher energy gamma radiation. As with external irradiation, medical examina- tions cannot be used to evaluate dose equivalent from internal radiation sources when exposures are at or below MPC, and the cytogenetic tech- nique (page 392) may be useful in a qualitative way at slightly higher exposures. PARTICULAR CONDITIONS Nuclear Criticality Safety A few of the heavier radionuclides which are capable of sustaining a nuclear chain reaction re- quire handling and processing techniques which will avoid the possibility of inadvertently forming a critical mass, with the attendant emission of in- tense radiation. The mass of these fissile materials at any one location or their geometric arrange- ment must be controlled with a high degree of confidence. Information about the basic limiting parameters used to assure nuclear criticality safety are in American National Standard N16.1*" Addi- tionally, all fissile materials are used under Atomic Energy Commission regulations and license — in which they are designated as “Special Nuclear Materials.” The regulations designate the masses of fissile materials below which nuclear criticality safety controls are not required and licenses spec- ify the limiting conditions of use for greater amounts. A standard symbol is used to identify fissile materials and areas in which they are used.*” It is similar to the radiation symbol with circular bars around it. Nuclear Reactor Industry The nuclear reactor industry presents an array of radiation protection problems much too com- plex to discuss in this Chapter. During mining of uranium ore there are exposures to radon gas and its daughters, as well as to uranium dust;** and similar problems occur during the processing to extract the uranium from the ore.” The uran- ium enrichment (in uranium-235) process involves various chemical forms of uranium including uran- ium hexafluoride, a gas. After enrichment, nuclear criticality safety controls become mandatory for all subsequent handling and processing. Fuel manufacturing® involves a chemical conversion process and various treatments of the resulting solids prior to loading into the fuel rods. The fuel rods are sealed and subsequent handling in- volves no further exposure to airborne radioactive materials. Fuel manufacturing and much of the previous processing involves only relatively minor external irradiation problems. In a nuclear re- actor facility, control of exposure to external radi- ation sources as well as control of fission and corrosion products which may become airborne becomes necessary. Fuel reprocessing plants take spent fuel, which is highly radioactive, and pass it through complex chemical processes to separ- ate the fuel materials (including plutonium) from the fission products, so that both external irradia- tion and complex airborne radioactive materials, including gases, require control and evaluation. Fuel manufacturing may include fuel elements that contain plutonium — requiring sophisticated con- trols to prevent release of plutonium. Throughout the industry, control and evaluation of releases of radioactive materials to the environment is essential. Transportation Radioactive materials are shipped by all nor- mal transportation methods including the U.S. Postal Service, railroads, airplanes, trucks and ships. There are some limitations on the types and quantities that will be accepted by some of these, particularly the Postal Service. Regulations of the U. S. Department of Transportation (DOT) are applicable to all interstate transport except for the Postal Service. There are separate regu- lations for the Coast Guard and Federal Aviation Agency, although these conform to the DOT Reg- ulations. Most states have regulations applicable to intrastate transport and a few cities have some regulations. Turnpikes, bridges and tunnels oper- ated by authorities may have separate regulations, limitations and requirements. Packaging of fissile materials and large quantities of radioactive ma- terials are subject to Atomic Energy Commission Regulations, 10 CFR 71 (see Chapter 9). Inter- national transport is subject to regulations of the International Atomic Energy Agency. In all cases the shipper is required to provide packaging which fulfills the requirements of the pertinent regulations except for small quantities that are exempted. For detailed packaging and labelling requirements, the regulations applicable to the mode of shipment should be consulted.” * Records Since some diseases and attendant disability that may be caused by exposure to radiation or radioactive materials can occur after many years of exposure or many years after exposure, reten- tion of suitable records relating to exposures and working conditions for long periods of time is desirable and usually required by regulations. Workmen's Compensation Laws usually permit 396 filing claims for radiation injury many years after exposure occurred, and for these adequate records will be required. A comprehensive presentation of information about records and their retention is in American National Standard N2.2.** Regulations The use of radiation and radioactive materials is subject to official regulation by various govern- mental agencies. Such regulations are discussed in Chapter 9. It is essential that any user of radia- tion or radioactive materials become intimately familiar with the details of all current rules and regulations applicable to his operations. Licenses, permits or notifications are commonly required. Before preparing a license application the person who will subsequently issue the license should be consulted. Because of the length, detailed provis- ions and variability of these rules and regulations, only a few general provisions have been mentioned in this chapter. References I. Radiation Quantities and Units 1CRU Report 19. International Commission on Radiation Units and Measurements, Washington, D. C. 20014 (1971). Radiological Health Handbook U. S. Dept. of Health, Education and Welfare, Public Health Serv- ice. U.S. Govt. Printing Office, Washington, D. C. 20402 (1970). American National Standard Glossary of Terms in Nuclear Science and Technology N1.1-1967. Amer- ican National Standards Institute, New York, N.Y. 10018 (1967). Background Material for the Development of Radia- tion Protection Standards, Report No. 1, Federal Radiation Council. U. S. Govt. Printing Office, Washington, D. C. 20402 (1960). MORGAN, K. Z. and J. E. TURNER. Principles of Radiation Protection, John Wiley and Sons, Inc. New York, N.Y. (1967). Physical Aspects of Irradiation 1CRU Report 10b. National Bureau of Standards Handbook 85, U. S. Govt. Printing Office, Washington, D. C. 20402 (1964). . Safety Standard for Non-medical X-ray and Sealed Gamma-ray Sources, Part 1. General, National Bu- reau of Standards Handbook 93. U. S. Govt. Print- ing Office, Washington, D. C. 20402 (1964). Medical X-ray and Gamma-ray Protection for Ener- gies up to 10 MeV, Structural Shielding Design and Evaluation, NCRP Report No. 34. National Council on Radiation Protection and Measurements, Wash- ington, D. C. 20008 (1970). Protection Against Neutron Radiation NCRP Re- port No. 38. National Council on Radiation Protec- tion and Measurements, Washington, D. C. 20008 (1971). . Basic Radiation Protection Criteria NCRP Report No. 39. National Council on Radiation Protection and Measurements, Washington, D. C. 20008 (1971). Maximum Permissible Body Burdens and Maximum Permissible Concentrations of Radionuclides in Air and Water for Occupational Exposure NCRP Re- port No. 22. National Bureau of Standards Hand- book 69. U. S. Govt. Printing Office, Washington, D. C. 20402 (1959). Recommendations of the International Commission on Radiological Protection, Report of Committee 11 on Permissible Dose for Internal Radiation (1959) ICRP Publication 2. Pergamon Press. Health Phys- ics 3:1, P.O. Box 156, East Weymouth, Ma. 02189 (1960). American National Standard Radiation Symbol rN 11. 12. 17. 18. 19. 20. 21. 22. 23. 24. 25. N2.1-1969. American National Standards Institute, New York, N.Y. 10018. American National Standard Radiological Safety in the Design and Operation of Particle Accelerators N43.1-1969. NBS Handbook 107, U.S. Govt. Print- ing Office, Washington, D. C. 20402 (1969). BLATZ, H. Radiation Hygiene Handbook, McGraw- Hill Book Co., Inc., New York, N.Y. (1959). Guide to Scientific Instruments, Science 174A4:9 (1971). Nuclear News Buyers Guide 1971, Supplement to Nuclear News. 14: No. 2, Feb. 1971. American Nuclear Society, Hinsdale, Ill. 60521. Radiation Protection Instrumentation and Its Appli- cation ICRU Report 20. International Commission on Radiation Units and Measurements, Washington, D. C. 20014 (1971). BENDER, M. A. Somatic Chromosomal Aberra- tions, Use in Evaluation of Human Radiation Ex- posures. Archives of Environmental Health 16:556, Chicago, Ill. (1968). American National Standard Guide for Administra- tive Practices in Radiation Monitoring N13.2-1969. American National Standards Institute, New York, N.Y. 10018 (1969). U. S. Bureau of Mines, Procedure for Testing Filter Type Dust, Fume and Mist Respirators for Permis- sibility Schedule 21B, June 1969. (30 CFR 14) U. S. Govt. Printing Office, Washington, D. C. 20402 (1969) American National Standard Design Guide for a Radio-Isotope Laboratory (Type B) NS5.2-1963. American National Standards Institute, New York, N.Y. 10018 (1963). American National Standard Guide to Sampling Air- borne Radioactive Materials in Nuclear Facilities N13.1-1969. American National Standards Institute, New York, N.Y. (1969). Recommendations of the International Commission on Radiological Protection, Report of Committee 1V on Evaluation of Radiation Doses to Body Tissues from Internal Contamination Due to Occupational Exposure 1CRP Publication 10. Pergamon Press, Long Island City, N.Y. 11101 (1968). Radioactivity ICRU Report 10c. National Bureau 397 of Standards Handbook 86. U. S. Govt. Printing Office, Washington, D. C. 20402 (1963). American National Standard Nuclear Criticality Safety in Operations with Fissionable Materials Out- side Reactors N16.1-1969. American National Stand- ards Institute, New York, N.Y. 10018 (1969). 27. American National Standard Fissile Material Symbol N12.1-1971. American National Standards Institute, New York, N.Y. 10018 (1971). American National Standard Supplement to Radia- tion Protection in Uranium Mines and Mills N7.1a- 1969. American National Standards Institute, New York, N.Y. 10018 (1969). American National Standard Radiation Protection in Uranium Mines and Mills (Concentrators) N7.1- 1960. American National Standards Institute, New York, N.Y. 10018 (1960). } American National Standard Radiation Protection in Nuclear Reactor Fuel Fabrication Plants N7.2-1963. American National Standards Institute, New York, N.Y. 10018 (1963). 26. 28. 29. 30. 31. Code of Federal Regulations. U. S. Govt. Printing Office, Washington, D. C. 20402. Department of Transportation 49CFR 170-179. Coast Guard 46CFR 146. Federal Aviation Agency 14CFR103. 32. Radioactive Matter, Publication No. 6, U. S. Postal Service, U. S. Govt. Printing Office, Washington, D. C. 20402. 33. American National Standard Practice for Occupa- tional Radiation Exposure Records System N2.2- 1966. American National Standards Institute, New York, N.Y. 10018 (1966). Preferred Reading Health Physics, Official Journal of the Health Physics Society. P.O. Box 156, East Weymouth, Mass. 02189. American Industrial Hygiene Association Journal. 66 South Miller Rd., Akron, Ohio 44313. Reports (various). National Council on Radiation Protec- tion and Measurements, Washington, D. C. 20008. American National Standards (various). American Na- tional Standards Institute, New York, N.Y. 10018. Reports (various). U. S. Dept. of Health, Education and Welfare, Public Health Service, Rockville, Maryland 20852. CHAPTER 30 PHYSIOLOGY OF HEAT STRESS David Minard, M.D., Ph.D. INTRODUCTION Industrial heat exposure often exceeds that encountered in the hottest natural climate. Be- cause hot industrial jobs usually require heavy work, the added burden of metabolic heat produc- tion may exceed the worker's physiologic capacity to regulate his body temperature, leading to im- paired performance or clinical signs of heat illness. The physiologist’s aim is to determine the dura- tion and intensity of work (internal heat load) in combination with heat exposure (external heat load), which can be tolerated without cxcessive heat strain on thermoregulatory systems. By rea- son of physical fitness, work capacity, age, health status, living habits, and level of acclimatization, men vary in ability to tolerate heat stress. The purpose of this chapter will be to discuss a) ho- meostatic control of body temperature by balanc- ing heat loss and heat gain, b) physiological in- dices of heat strain, ¢) acclimatization and other factors affecting heat tolerance, and d) clinical °F °C RECTAL 104+40 HARD EXERCISE 1024 3° 100 38 USUAL RANGE 37 98 OF NORMAL 36] | EARLY MORNING COLD WEATHER 96 DuBois, E. F.: Fever and the Regulation of Body Temperature. Range of Normal Rectal and Oral Temperatures [from DuBois (1)] Figure 30-1. illnesses resulting when adaptations fail. BODY TEMPERATURE REGULATION Thermal Homeostasis Man, and other homeotherms, regulate inter- nal body temperature within narrow limits by physiologic control of blood flow from sites of heat production in muscles and deep tissues to the cooler body surface where heat is dissipated through physical channels of radiation, convection and evaporation to the environment. When heat loss is in balance with heat production, inter- nal temperature is maintained at the regulated level. Homeostasis thus maintains a favorable and uniform internal temperature despite fluctuations in the thermal environment. Normal Range Figure 30-1" indicates the usual range in body temperature (rectal, oral) in normal persons as well as extreme upper and lower limits of normal. There are other sites in the lower esophagus and ORAL EMOTION OR MOD. EXERCISE A FEW NORMAL ADULTS MANY ACTIVE CHILDREN HARD WORK, EMOTION A FEW NORMAL ADULTS MANY ACTIVE CHILDREN USUAL RANGE OF NORMAL EARLY MORNING ETC. COLD WEATHER ETC. Springfield, Illinois, Charles C. Thomas, 1948. 399 in the ear canal for measuring internal temper- ature which reflect more promptly the responses to transient heating or cooling of the body. For pres- ent purposes central or “core” temperature, wher- ever measured, will be designated T.. Body Shell This term refers to the cooler superficial tis- sues (skin, subcutaneous tissues, extremities) sur- rounding the warm core. Temperature of the shell tissues, particularly the distal extremities, varies more widely than the core under ambient heat and cold, as reflected in changes of mean temperature of the skin surface, T,, which is a weighted aver- age taken at up to ten skin sites. The shell acts as a thermal buffer between the core and thermal environment. Under comfortable ambient condi- tions T. is 37° and T, is normally 33-34°C, but may approach to within a degree or two of T. under heat stress and decline to as much as 10- 15°C below T. in the cold. These changes in core to surface gradient are accompanied by alterations in rate of blood flow- ing from the warm core to the cool surface to meet changing needs in heat conductance, which is de- fined as units of heat transferred through the skin per unit time to the environment per degree of temperature gradient. Under heat stress T, rises, and core to skin gradient narrows. A greater vol- ume of blood must flow through the skin each minute to achieve the same rate of heat exchange as in a neutral environment. This is the basic cause for heat strain on the circulation, for which conductance is a useful index. Heat Production Energy required to sustain all body functions at rest and during work is derived by enzymati- cally controlled oxidative combustion of fuel sub- strates (carbohydrate, fat, protein), with CO,, water and nitrogen wastes forming end products. These reactions are exothermic, the heat produced in the body being essentially equal to that mea- sured when the same quantities of food substrates are oxidized at high temperature outside the body. This is the basis of indirect calorimetry in which heat produced metabolically can be mea- sured by the rate of oxygen uptake during rest or activity, one liter of O, being closely equivalent to a heat output of 5 kcal. Laboratory or field mea- surements of metabolic heat production are rela- tively simple, involving a system for measuring the volume of air breathed each minute and an instru- ment for measuring the difference in 0, concen- tration between inspired and expired air. Resting 0, uptake in an average man (70 kg body weight; 1.8m?* surface area) is about 0.3 1/min, equivalent to heat production at a rate of 1.5 kcal/min or 90 kcal/hr. In terms of surface area this is 50 kcal/m? hr, a unit referred to as I met, the metabolic rate of a man sitting at rest in a comfortable environment. There is little individual variation in resting metabolism when expressed in heat production per unit area. In terms of maximum capacity to perform work, however, there are wide differences, depending mainly on body size, muscular develop- ment, physical fitness and age. An important measure of work capacity is the maximum rate at which a man can take up oxygen during brief strenuous work effort. Maximum oxygen uptake (VO, max) among healthy workers ranges between about 2.0 and 4.0 1/min. Table 30-12 lists examples of work activity, the 0, requirement, the heat equivalent, and the TABLE 30-1 Oxygen Uptake, Body Heat Production, and Relative Energy Cost of Work in 70 kg Men Maximum Oxygen Uptake (1/ min) Oxygen* Body Heat** Low Medium High Activity Uptake Production (M) 2.5 3.0 35 (1/min) (kcal /hr) Percent VO, max Required Rest (seated) 0.3 90 12 10 8.5 Light Machine Work 0.66 200 26 22 19 Walking (3.5 mph on level) 1.0 300 40 33 28 Forging 1.3 390 52 43 37 Shoveling 1.5-2.0 450-600 60-80 50-66 43-58 (depends on rate, load and lift) Slag Removal 2.3 700 92 77 66 *From Passmore and Durnin (See Figure 30-2). **In lifting, pushing, or carrying loads, cranking, etc. the heat equivalent of the external work (W) is subtracted from the total energy output (0, uptake) to obtain heat produced in the body (M). w 0. uptake (work) — 0, uptake (rest) of work performance and thus reduces heat load of M. 400 Net efficiency of W, i.e, is 20% or less for most work. Skill acquired by practice increases efficiency TABLE 30-2 Heart Rate, Core Temperature, and Endurance Time AY Corresponding to Relative Energy Cost of Work M i Percent VO, max ’ At Rest 25 3313 50 75 100 Heart Rate (min) 60-80 90-100 105-110 120-130 150-160 180-190 Core Temperature (°C) 37 37.4 37.8 38.2 38.8 Continuous at Equilibrium (Unstable) Rise Endurance Time for Continuous Work >8 hr 8 hr 1 hr 15-20 min ~~ 4-6 min percent of VO, max required for this work in men of low (2.5 1/min), intermediate (3.0 1/min) and high (3.5 1/min) work capacity. A comparative index for estimating maximum work capacity among men is the heart rate (HR) attained during steady work at less than the maxi- mal effort (Table 30-2) which also indicates that the rise in T. is proportional to % VO, max. At work rates at 50% VO, max and above the oxygen supply to the muscle fails to meet the 0, demand, thus limiting endurance time. Succes- sive increments in energy requirement for work are supported by progressively greater proportions of the energy being supplied by anaerobic (i.e., TABLE 30-3 Symbols and Their Meaning for Physical Factors in the Thermal Environment and Physiological Factors in Heat Exchange Physical Factors Symbol Meaning T, Air temperature using dry bulb ther- mometer. T, Mean temperature of surrounding sur- faces (wall temperature). In presence of radiant heat, T, > T,. Air velocity (fpm or m/s). < Temperature of the 6” black globe. T, exceeds T, when T,> T,. Elevation of T, in equilibrium with radiant heat varies in- versely with convective cooling by V. With appropriate coefficients T, represents R + C. Pya I b Water vapor pressure of ambient air. Temperature of the wet bulb thermom- eter. Evaporative cooling under forced con- vection depresses reading of T\,, below T,, the degree varying inversely with Py,. In air fully saturated with water vapor (100% RH) Tw = T.. Effective Temperature Scale. An em- pirical index combining T, (or T,), Tu, and V into a single value based on sensory effect. * Ter °Cgr Effective Temperature in degrees Centi- grade. Physiological Factors Symbol Meaning T, Mean skin temperature. T. “Core” or central temperature (mea- sured in the rectum, esophagus, or near the tympanic membrane. Ps Water vapor pressure of wetted skin at skin temperature. A Total surface area of the body (m*). S Area of wetted surface. ~ X 100= % of wetted body surface. M Metabolic rate of body heat production (kcal/hr). Unit of M per m*/ hr. Resting M= 1 met or 50 kcal/m* hr met VO, max Maximum oxygen uptake. Also called maximum aerobic work capacity. SR Sweat rate (kg/hr). E Body heat loss by evaporation (kcal/hr). BF, Blood flow to the skin (I1/m?* min). C Conductance = M/A [kcal/m? hr per T.—T, degree of gradient] *ET Scales in the form of nomograms (Basic Scale for men stripped to the waist and Normal Scale for men lightly clothed) were derived from tests on men moving between two climate chambers, a test chamber with T,, T ,, and V fixed in various combinations, and a reference chamber with still air fully saturated held at temperatures rang- ing in different tests from 0 to 43°C. All combinations of T,, T,,, and V producing immediate thermal sensations which were equivalent to those experienced in the reference chamber were assigned the same Effective Tempera- ture, namely that of saturated still air at that temperature. 401 without 0,) splitting of muscle glycogen, the car- bohydrate energy storehouse, into lactic acid, which accumulates in the muscle, impairs contrac- tion and results in fatigue. During the rest period, the “oxygen debt” incurred during work is paid off, as indicated by 0, uptake remaining elevated and declining exponentially to the resting level as the accumulated lactic acid is oxidized or resyn- thesized into glycogen. Under heat stress, the re- covery period is longer to eliminate heat stored in the body during work. Heat Loss Under comfortable ambient conditions 25 per- cent of heat produced by metabolism (M) at rest is transferred from the skin surface to the cooler air by convection (C), 50 percent by radiative transfer to cooler surfaces in the surroundings (R), and the remaining 25 percent by warming inspired air, and by evaporation of 20 to 30 g/hr of mois- ture diffusing through the non-sweating skin. Res- piratory heat loss (8-10% of resting M) plays lit- tle role in temperature regulation and only heat loss through the skin will be considered here. Symbols and their meanings to designate the environmental and physiological variables used in this chapter are listed in Table 30-3. The foregoing sections may be summarized in the heat balance equation as expressed for temper- ature equilibrium below and in Table 30-4. M=*=R + C—E=0, in which R and C are rates of radiative and con- vective heat transfer. M and E are defined in Table 30-3. Table 30-4 indicates how the equa- tion applies under three different conditions of the temperature and vapor pressure gradient between skin and environment. It should be noted that when T, < T, and Py, approaches or equals Py, equi- librium is not possible either at rest or during work. TABLE 30-4 Heat Balance under Different External Temperature Gradients and Factors Limiting Endurance Time for Work External Heat Endurance Time Representative Gradient Example Balance Limited by: Environments T, > T, T,=25°C M=R+C+E Work Rate Temperate climate. Pui” > Pua Also thermally neutral work places. T.= Ty T,=35°C M=E Work rate and elevated Py, Tropical climate. Also Pus = Pa and/or low V canning, textiles, laundries, (Restricted evaporation) deep metal mines. Ts < Tg T;=45°C M+R+C=E Work rate and maximum Hot desert climate. Also Pus > > Pm capacity to sweat manufacturing of primary (Free evaporation) metals, glass, chemicals, etc. Hypothalamic Regulation of Body Temperature There is convincing evidence based on animal experiments that the temperature regulating center in man lies in a region at the base of the brain called the hypothalamus. The anterior portion contains the “heat loss” center which responds to increases in its own temperature, as well as to in- coming (afferent) nerve impulses from warm re- ceptors in the skin. It activates heat loss through increased blood flow to the skin and sweating (man) or panting (other mammals). A model of the thermoregulatory system for control of body temperature under heat stress is represented in Figure 30-2* as an analog of an engineering control system known as a propor- tional controller using negative feedback. Feed- back is negative because the error signal is the difference between the set point of the thermostat (input) and T. and/or Ty (output). It is a pro- portional controller because the central drive and effector responses (BFs and SR) are proportional to the error signal. In the absence of a heat load, central drive is zero, output and input being equal. The model predicts that when equilibrium is reached under a given heat load, the output of the 402 system (T., Ts) will stabilize at a level above the set point by an amount also proportional to the load. This deviation from the set point is known as the “load error.” In the presence of a load, a pro- portional controller does not restore the error sig- nal to zero. These characteristics of the model are also seen in thermoregulatory control under heat stress in man. Finally, effectiveness of the control- ler in temperature regulation depends on its gain, or sensitivity to an error signal. The gain factor is high in individuals with high heat tolerance, and increases in acclimatization. Subjective and Behavioral Responses to Heat Stress Subjective sensations of heat, perceived as neutral, warm, or hot, depend primarily on skin temperature. Heat discomfort, however, is the subjective evaluation of the thermal environment in terms of unpleasantness and depends not only on sensations of heat but also on, the level of physiological strain (SR, BF, T.). [Thermal com- fort scales (e.g., Effective Temperature Scale) de- fine limits of ambient temperatures, activity levels, and clothing under which heat balance can be maintained without thermal strain. | Heat Loss Center (Hypothalamus) Vasodilator & Nerve Pathways Heat Load Elevated M Elevated R+C : Sudomotor Controller i Central Drive Detector ] for Set Point Error preoptic] ! Conductance (BFs) Body Heat Te, Ts Hypoth 37.0° Signal |Neurons| and Content Skin 340° | Evaporative ! Heat Loss (SR) Feedback Elements (Central Receptors; Skin Receptors) CONTROLLING EFFECTOR PASSIVE SYSTEM SYSTEM SYSTEM Figure 30-2. Model of the System for Thermoregulatory Control of Body Temperature. *The model shown in Figure 30-2 is adapted from re- cent studies (Nadel er al.?) indicating that the central drive for sweating is the summation of effects from the elevation of T, and T, above their corresponding set points (37° and 34°C). The input from elevated T, however, is 10x greater in effect than that from elevated T,. Moreover, local heating or cooling of the skin aug- ments or suppresses local sweating from a temperature effect on the neuroglandular junction with a Q of 2.7 to 3.0. The summation model with the multiplicative factor for local skin temperature, "s), is given in the form SR= [qa (T,—37) +B (T,—34] ¢ (a =34/10 where Lis about 10, and e is the base of natural logarithms. These authors point out that SR is also inversely re- lated to skin wetness and directly to degree of acclima- tization. Immediate sensations of heat or the subse- quent discomfort from strain may lead to behav- ioral responses such as slowing or stopping work (reduced M), modifying clothing, or withdrawing to a cooler environment (reduced R+C). Such adaptive behavior, based on instinct or experience, serves as man’s first line of defense against severe or incapacitating strain. INDICES OF HEAT STRAIN Sweat Rate Under heat loads resulting in an error signal, effector outflow from the hypothalamus is trans- mitted via nerves to sweat glands of the skin which are activated by release of acetylcholine at the neuroglandular junction. Rate of secretion of individual glands, and the number of active glands recruited determines the total sweat rate. Under maximum central drive, the estimated 22 million eccrine glands can secrete sweat at peak rates of more than 3 kg/hr for up to an hour in highly acclimatized men, and can maintain rates of 1 to 1.5 kg/hr for several hours. When sweat can evaporate freely from the skin 403 (i.e., SR=E), evaporative cooling is regulated under steady state conditions of work and heat exposure to balance the heat load (M+R +C) up to the maximum rate of sweating (1 kg/hr). SR follows T, (Figure 30-3) which varies linearly with ambient temperature. Over a wide range of ambient temperatures from cool to moderately hot, Nielsen found that T. is constant under steady state conditions of work, the elevation of T. above 37°C depending solely on M. On the other hand, under constant ambient conditions SR varies with M, to which the elevation of T. is" proportional. The central drive for sweating is thus determined by work rate, M, but the actual sweat output is modulated by skin temperature to meet evaporative requirements under conditions from cool to hot up to the limits for sweating ca- pacity. Sweat Evaporation The evaporation of 1 g of sweat from the skin eliminates 0.58 kcal of body heat. Efficiency of body cooling by sweat, however, depends on the rate of evaporation, which is determined by the gradient between vapor pressure of wetted skin (P,.) and ambient air (P,,) multiplied by a root function of effective air velocity at the skin surface (V°¢) and s, the fraction of body surface, A, that is wetted. When evaporation of sweat is restricted, Ty} rises above that observed under less humid condi-| tions at the same T,. The heat loss center responds | by recruiting more sweat glands, thus increasing { the extent of wetted body surface, s.* If cooling needed to balance M +R + C under these conditions is thereby met, core temperature remains essentially unchanged. At higher levels *As a fraction of the total area of body surface, s can- not be measured directly. It is estimated from the ratio of the rate of evaporation required to balance M+R+C (Epoq) to the maximum rate at which sweat evaporation can occur (E_ .) at a given T, P_ , and air velocity. max Zone A Zone B Zone C . Time Limited Uncompensated Full Compensation Compensation Heat Storage “> rr A 214 A WC ry = S IO" —— Steady State A 8s, go - : Maximum S72 Pe Non -steady State Thermoregulatory “ oo O08F \ Ne - Response NY) o \® x \ Nn ~ 06 \S. Oo \'— 2 +1 » 04 he . o ' Upper Limit of ' = The Prescriptive Zone QO 40.0 Non- Highly —— LS. acclimatized Acclimatized -— L 180 3 © I ® 160 ® Lh = © — D ~ 140 3 > - > a 120 = “ = 2 1 1 1 1 7100 25 27 29 31 33 —— Effective Temperature(°C) Increasing Heat Stress Figure 30-3. Thermoregulatory Responses to Heat Stress in Zone A (Full Compensation), B (Time Limited Compensation) and C (Uncompensated Heat Storage). Graph illustrates the effector responses (SR, BF,), circulatory strain (HR) and the controlled variables (T., T.) in a highly acclimatized man working at one-third VO. max (M=2300 kcal/hr) at levels of heat stress up to his limits of tolerance. Responses under steady state conditions are linear with Effective Temperature in Zones A and B. In Zone C, the steady state is impossible. Dashed lines indicate continuous heat storage and show trends only of T., T,, SR and HR with increas- ing heat stress. (Semi-schematic representation based on data from refs. 7, 8, 9, 10, 11, 12, and 13.) of Py, or lower air velocities, s approaches A (the total body surface area) and at the point when s=A, the body surface is 100% wetted. Any further increase in sweat production does not con- tribute to cooling, but drips off the body and is wasted. Under higher levels of Py, with further restriction on E, body heat will be stored, raising both T, and T.. The response is a greater central drive for sweating. But as T, rises, P,. and evap- orative rate increase also. As a result, a new steady state may be established but at a cost of increased thermoregulatory strain, as reflected in further elevation of SR, BF, and HR. As seen above, sweat rate in the zone of free 404 evaporation varies linearly with heat load, and SR is proportional to M+R +C. In the zone of re- stricted evaporation when s/A approaches 1.0, SR =~ E and is proportional to the increase in T. and T.. Sweat rate is, therefore, an index of heat stress over the entire range of compensation. It is also an index of heat strain in the zone of time-limited compensation, where its rise parallels T. and HR. Sweat rate serves as a time-weighted average of heat stress. It is measured by the difference in body weight over a given time period corrected for weight gain by water and food intake and weight loss by urine and feces. A constraint on the use of SR as an index of heat stress (or strain) is that the level of sweating tends to decline with time of heat exposure, par- ticularly under restricted evaporation when skin is extensively wetted. As long as SR > E, the decline in sweat rate | does not interfere with heat loss, and might be regarded as an adaptive mechanism to conserve body water and electrolytes under conditions in which more sweat is produced than is useful. « Circulatory Strain Thermal conductance (C), referred to earlier as an index of BF,, is defined as co M/A T.— s The narrower the gradient for a given M, or the higher the M for a given gradient, the greater is the BF, required to transfer metabolic heat from core to the environment (Figure 30-3). In a thermally neutral environment, T is lower during work than at rest, reflecting a redistribu- tion of blood from skin blood vessels to those of active muscles. The reduced capacity and in- creased resistance of skin vessels and also of ves- sels in abdominal organs together with the pump- ing action of muscles maintain the return of ven- ous blood to the heart whose output increases in proportion to the % VO, max required by work. Under external heat loads both the central drive for increased conductance and the rise in local skin temperature dilate skin vessels, thereby increasing their blood capacity and reducing their resistance. BF, increases but at the cost of reduc- ing venous return of blood to the heart, resulting in less output per beat. To meet the oxygen re- quirements of working muscles, cardiac output can then be maintained only by further vasocon- striction in abdominal organs and an increase in heart rate (Figure 30-3). Thermoregulatory requirements for BF, thus compete for available cardiac output with energy requirements of active muscles. BFj, as estimated by C, increases from a quarter of a liter per min- ute at rest in a neutral environment to over two liters per minute in men working at 3-4 met under heat stress. Heart Rate as An Index of Circulatory Strain r Heart rate is responsive both to the increased cardiac output required by working muscles as well as the added circulatory strain imposed by heat exposure, and is a useful index of total heat load. Measured either by counting the pulse at the wrist or by using electronic devices for monitoring, HR is a valuable guide in assessing hazards to health of workers exposed to heat stress. Brouha® has used the term cardiac cost of work to indicate the total heart beats above the resting level dur- ing work, and the term cardiac cost of recovery, or “cardiac debt,” to denote the total number of beats above the resting level during the recovery period following work. The detrimental effect of heat stress on work performance is indicated by an increase in cardiac cost both of work and recovery. Reducing work [Kcal/m?-hr per degree of gradient] 405 load, increasing time of recovery or providing cool rest areas are alternative measures which manage- ment may elect to prevent excessive heat strain on workers. To ensure that men performing intermittent work in the heat will remain in thermal balance for the full shift without cumulative effects of strain, Brouha proposed a simple guide. Pulse rate is counted for the last 30 seconds of the first three’ minutes after rest begins. If the first recovery pulse, i.e., from 30 to 60 seconds, is maintained at 110/min or below and deceleration between the first and third minute is at least 10 beats/min, no increasing strain occurs as the work day progresses. Extensive testing to validate this guide in the man- agement of health problems of industrial heat stress seems highly warranted. The mean HR level observed during an entire work shift reflects sustained elevations and peak rates as well as recovery and resting rates and thus can also serve as a guide in assessing circulatory strain. Electronic devices for integrating total count or continuously recording individual heart beats are now generally available. Both methods were employed in a recent study of heart rate responses in steelworkers in a Pittsburgh steel mill. There was variance in the mean HR in five work- ers on the same shift depending on work capacity (VO, max) of the individual and in the same worker on different shifts depending on total heat load. HR in all workers ranged from 99 to 136/ min. The two workers with mean HR’s exceeding 120/min showed evidence of excessive strain as indicated by a high resting HR and impaired work performance during a standard exercise after the shift. The heart rate of men working at one-third VO, max will be 105-110/min (Table 30-2). On the basis that the combined effects of heat stress and work should not impose a greater circu- latory demand than from work alone, an upper value of 110/min as the mean HR for an 8-hour shift would appear to be a reasonable limit for work involving heat exposure. For men or women of lower work capacity (i.e., VO, max less than 3 1/min) the energy expenditure at this heart rate would be less, but the strain proportionally the same. In order to adopt the limit of 110/min. ex- pressed in Table 30-2 as a standard, extensive test- ing and validation in industry would be required. The aim would be to compare circulatory strain in workers performing jobs in which heat exposure and work rates vary in proportion, and in workers on jobs involving peak loads with those exposed to more uniform work stresses. Finally, it would be necessary to determine whether the level of 110/min is safe or should be lowered for male or female workers whose work capacity and heat tol- erance is limited because of age, physical fitness, acclimatization, or general health status. Core Temperature In Zone A (Figure 30-3) SR and BF; increase proportionally with the total heat load (M+R + C). T. is maintained at a uniform level which is determined only by M, and is independent of \ ambient temperatures at lower levels of external heat stress. Lind’ terms this the prescriptive zone to indicate the range of thermal environments in which men can work without strain on homeostatic control of core temperature. The upper limits of this zone are lower at high work rates because T. is higher (Table 30-2). By the same token, the limit would be similar for men differing in physical fitness but expending the same percent of their VO, max (Table 30-1). From data of Robinson® and others? 1 1112 the upper limit of the prescriptive zone in highly acclimatized men working at 300 kcal/hr is 31- 32°Cgrp. ’ For non-acclimatized men varying in physical fitness Lind'® recommends 27.5°Cyy (Figure 30- 3) as a realistic limit for this level of work. The wide latitude of heat stress between these limits clearly indicates the perplexing nature of the prob- lem of setting rational standards for industrial heat stress which will both protect workers of low heat tolerance and not restrict unduly work per- formance of those with higher heat tolerance. In a man performing steady work at 300 kcal/hr, T. is higher in Zone B than in the pre- scriptive zone in proportion to heat stress up to a limiting value of 39°C (Figure 30-3). This rep- resents the highest core temperature at which highly acclimatized men can attain a steady state of thermal balance, and then for only two hours or less. The upward inflection of T. in Zone B serves to maintain the core to surface-gradient as T, attains higher levels, but at a cost of thermo- regulatory strain on T.. In terms of the model (Figure 30-2), the load error of the control sys- tem as reflected in T. increases in proportion to the load. The maximum tolerable level of heat stress corresponding to the T. limit of 39°C was found by Robinson and others to be 34 to 35°Cyyp. Men less fit or less well-acclimatized for work at 300 kcal/hr would reach limiting levels for thermal balance at lower core temperatures and at corres- (pondingly lower levels of external heat stress. As a practical guide, the average core temperature of “men should not exceed 38°C for a work shift. | Transient increases to 39°C should be permitted / but only briefly, and with ample time for recovery in cooler areas. The border between Zones B and C marks the upper limit of man’s capacity to sweat, thus rep- resenting the maximum effector response of the thermoregulatory center. Hence, in Zone C, rates of heat loss fail to match rates of heat gain, lead- ing to heat storage with T,. and T,, rising contin- uously at rates proportional to the heat load. Storage may be further accelerated by fatigue or failure of sweating. No steady state during con- tinued work is possible. This is indicated by broken lines in Zone C which imply trends only and not the transient state. Under extreme heat (e.g., 40 to 45°Cyy) the core to surface gradient will be reversed, the blood returning from the skin heating the body core instead of cooling it. The rising body temperature accelerates metabolic processes (Q,, effect), further increasing the rate 406 of body temperature rise. Unless the man stops working and seeks relief, heat exposure in Zone C leads inevitably to his collapsing from circulatory failure or heat stroke. Voluntary tolerance time for work in Zone C ranges from a maximum of one hour to less than 20 minutes.*. Under intense radiant heat loads, skin temper- ature rises rapidly to the pain threshold (45°C). Under these conditions pain becomes the limiting factor in tolerance time rather than heat storage in deeper tissues. FACTORS IN HEAT TOLERANCE Heat Acclimatization Any man, however healthy, well-conditioned and motivated, who works for the first time under heat stress will develop signs of severe strain with abnormally high body temperature, pounding heart, and other signs of heat intolerance. On each succeeding day of heat exposure his ability to work improves as signs of strain and discomfort dimin- ish. After a week or two he can work without difficulty. The enhanced tolerance to heat ac- quired by working in a hot environment is called heat acclimatization. Figure 30-4 from Eichna et al.'® illustrates the principal physiological adjustments in thermal bal- ance which occurred in three highly conditioned young men with no previous heat exposure work- ing for one hour/day for ten days at 300 kcal/hr (3 met) in dry heat (T,, 50.5°C; Ty, 26.5°C; V, 450 fpm). T,., T,, and HR at rest in a cool en- vironment (large dots) and at the end of each 10 min period of work in the heat (small dots) are shown, with control tests at rest and working under cool conditions before and after ten days of work in the heat. Table 30-5 summarizes the authors’ data, including measurements of sweat rates and BF, calculated from conductance. The most significant change was a 10% in- crease in sweat output which was produced at a lower T, on hot day 10 compared with hot day 1. This increase in evaporative cooling with a steeper core to skin gradient was sufficient to compensate fully for the heat load, as indicated by the fact that core temperature was restored to within 0.1°C of that observed on cool day 1. In other words, con- ditions which had initially been nearly intolerable now fell within the “prescriptive zone” of full compensation, allowing the men to complete the work with no more difficulty than in the cool environment. Although BF, remained elevated on hot day 10, acclimatization reduced the circulatory load by 32%. Essential factors inducing acclimatization ap- pear to be sustained elevations of T. and Tj, above levels for the same work in cool environments for an hour, or preferably more, per day for one or two weeks. It seems well-established that acclimatization to wet heat increases tolerance to dry heat and vice versa. The reason why tolerance to wet heat is increased is not clear, because the increased sweat output, which may nearly double, is largely wasted. Heat conduction through the skin is enhanced, RECTAL TEMPERATURE HEART RATE SKIN TEMPERATURE DEGREES FAHR. 99 — 35 — 34 —33 — 32 — 3] DEGREES CENT. 100 96 96 94 92 DEGREES FAHR. ] 90 88 — 2 | 3 l 4 L HOT 5 ] 6 » l 8 l 9 | CooL a ENVIRONMENTAL DAYS Eichna, L. W., Park, C. R., Nelson, N., et al: Thermal regulations in a hot dry (dessert type) environment. Am. J. Figure 30-4. Physiol. 163:585, 1950. B (Time Limited Compensation), and C (Uncompensated Heat Storage). 407 Thermoregulatory Responses to Heat Stress in Zone A (Full Compensation), TABLE 30-5 Changes in Thermoregulatory Responses with Acclimatization (Eichna et al.) HR SR T. T, _ BF; Condition (min) (kg/m?hr) °C °C T.—T, (1/m?e 40) Initial cool day 111 0.079 37.8 30.9 6.9 0.35 Hot day 1 162 0.621 39.0 37.8 1.2 2.58 Hot day 10 118 0.692 37.9 36.4 1.5 1.76 Final cool day 103 0.083 37.7 31.1 6.6 0.37 Reprinted from American Journal Physiology, 163:585, (1950). however, which suggests a change in distribution of blood to the skin.” Whether the underlying change in acclimatiza- tion is greater sensitivity of the center to thermal inputs from skin or central receptors, a lower threshold of skin receptors to heat, an enhanced response of the sweat glands to the central drive, or some combination of these factors is still the basic problem of thermal physiology which re- mains under active study. Men who work at hot industrial tasks acquire levels of acclimatization commensurate with their average heat exposure. Unusual demands for work effort or sudden spells of hot weather may, however, overload their thermoregulatory capacity, leading to signs of overstrain. Heat acclimatiza- tion needs periodic reinforcement, such as oc- curs daily during the work week. Men may show some loss of acclimatization on the first day of the new shift after being idle for two days or over a weekend. After vacations of two weeks or longer, the loss of acclimatization is substantial, several days at work elapsing before heat toler- ance is fully restored. Some traces of acclimatiza- tion may be evident, however, as long as eight weeks following the last heat exposure. Seasonal changes in outside weather are re- flected in heat tolerance of workers,'® the lower level during cooler seasons owing largely to milder heat stress on the job, which parallels changes in outside weather temperature. Physiologic adjustments in acclimatization also include changes in sweat composition. Sweat is a dilute solution of electrolytes, principally sodium chloride. In unacclimatized subjects, sodium chlo- ride concentration in sweat (3 to 5 g/kg) is about half the concentration in blood plasma. In accli- matized subjects, sweat is not only more abundant but more dilute, the salt concentration falling to levels of 1 to 2 g/kg, reflecting an adaptive change in hormonal balance through secretion of aldo- sterone which acts to conserve body salt both by the kidneys and sweat glands. Surface Area to Weight Ratio In obese individuals as well as in those with stocky build the body surface area (A) to body weight (Wt) ratio is relatively low. Because heat loss is a function of A and heat production a function of Wt, a low A/Wt is a handicap for men performing sustained work in the heat. If lack- ing in acclimatization, physically unfit and obese men are at greater risk of succumbing to heat stroke. Age and Degenerative Diseases The healthy older worker (40-65 yrs) per- forms well on hot jobs if allowed to work at his own pace. Under demands for sustained work output in the heat, he is at a double disadvantage compared with younger men. First, VO, max declines 20-30% between ages 30 and 65, leaving the older worker with less cardiocirculatory re- serve capacity and second, under levels of heat stress above the prescriptive zone, the older worker compensates for the heat loads less effectively than the younger man, as indicated by his higher core temperature and peripheral blood flow for the same work output.’” This has been attributed to a delay in onset of sweating, and a lower sweat rate in older men, resulting in greater heat storage during work and longer time for recovery. Degenerative diseases of the heart and blood vessels intensify the age effect on heat tolerance by limiting the circulatory capacity to transport heat from body core to surface. Elderly men and women with chronic diseases of aging account for much of the excess in mortality reported in large northern cities during sustained heat waves.'® Men with long work experience in hot indus- tries, on the other hand, seem to be less at risk of dying from cardiovascular and other diseases than workers of similar age without a work history of heat exposure. In a recent unpublished bio- statistical study of 12,946 open hearth steel work- ers,’ the mortality rate for arteriosclerotic heart disease, and respiratory disease, as well as overall mortality rate were significantly less in this group than in the entire population of 58,829 steel work- ers. A self-selection process which eliminates those of low physical fitness and heat tolerance from jobs on the open hearth could not be ruled out. Water Balance Effective work performance in the heat de- pends on replenishing body water and salt lost in sweat. A fully acclimatized worker weighing 70 kg can secrete 6-8 kg of sweat per 8-hr shift. If water lost in sweat is not replaced by drinking, continued sweating ultimately draws on water both from tissue spaces and body cells as well, leading to the picture of shriveled skin, dry mouth and tongue, and sunken eyes recognized as extreme dehydration. Sweat loss of 1 kg of body water (1.4% of body weight) can be tolerated without serious effect. Water deficits of 1.5 kg or more during work in the heat deplete the volume of circulating blood, resulting in signs and symptoms of in- 408 creasing heat strain (elevated HR and T.; thirst and severe heat discomfort), resembling those seen in unacclimatized men. With water deficits of 2 to 4 kg (3 to 6% of body weight) work perform- ance is impaired. Continued work leads to incipi- ent signs of heat exhaustion. Therefore, to avoid excessive depletion of body water, sweating men should drink frequently at intervals of 30 min or less. Unacclimatized men should be encouraged to drink somewhat more than thirst dictates to avoid “voluntary” dehydration. Well-acclimatized men succeed much better in balancing water losses, even when sweating at high rates. Dehydration of more than 1 to 2% of body weight in acclimatized workers during a shift may signify greater heat loads than usual, or lack of access to water. Salt Balance Salt (NaCl) losses in sweat during work can usually be replaced at mealtime. The average American diet, which contains 10 to 15 g/day of salt, would meet the needs of an acclimatized worker producing 6-8 kg of sweat containing 1 to 2 g of salt per kg during a single shift. For the period of acclimatization supplementary salt dur- ing hot work might be needed by workers with no previous heat exposure. Although maximal sweat- ing rates in unacclimatized men are lower (4-6 kg/shift), salt concentrations are higher (3 to 5 g/kg sweat) than after acclimatization. At the higher sweat rate, an unacclimatized man may lose 18 to 30 grams of salt. Supplements in the form of 0.65-g salt tablets (preferably impregnated to avoid gastric irritation) may be taken if ample water is available. Better practice is to use salted water (0.1% or 1 tsp/gal) or to advise increased salt on food at mealtime. Salt supplements should be reduced or dis- continued after several days of heat exposure because salt loading suppresses normal hormonal mechanisms regulating salt and water metabolism under heat stress. Depletion of body salt may occur in unacclima- tized men exposed to heat who replace water losses without adequate salt intake in food. This leads to progressive dehydration because homeostatic con- trols are geared to maintain a balance between electrolyte concentration in tissue fluids with that in the cells. Deficient salt intake with continued intake of water tends to dilute tissue fluid, which suppresses the antidiuretic hormone (ADH) of the pituitary gland. The kidney then fails to re- absorb water and excretes dilute urine containing little salt. Thus homeostasis maintains the electrolyte concentration of body fluids but at the cost of de- pleting body water with ensuing dehydration. Un- der continued heat stress, symptoms of heat ex- haustion develop similar to those resulting from water restriction, but with more severe signs of circulatory insufficiency and notably little thirst. Absence of chloride in the urine ( <3 g/1) is di- agnostic of salt deficiency. On a short-term basis, sweating men drinking large volumes of unsalted water may develop heat cramps which are excruciatingly painful spasms of 409 those muscles used while working (arms, legs, or abdominal). Dilution of tissue fluid around the working muscle results in transfer of water into muscle fibers, causing the spasms. Treatment of the various clinical syndromes of water and salt depletion is similar; namely, replace- ment of depleted body water and, or salt by oral ingestion of salted liquids in mild cases or intra- venous infusion of saline in more serious ones. An excess of salt or water over actual needs is readily controlled by kidney excretion. These and other clinical entities resulting from failure to adapt to heat stress are described in Table 30-6, which is based on a nomenclature prepared jointly by com- mittees representing the U.K. and the U.S.?* For further details on etiology, signs, symptoms, treat- ment and prevention of heat illnesses, the reader is referred to Leithead and Lind.'* (See Table 30-6). Alcoholic Habits Many authors have noted an excessive alcohol intake by patients within hours or a day or two prior to onset of heat stroke. Others have described striking reductions in workers’ heat tolerance on the day following an alcoholic “binge.” It is known that alcohol suppresses ADH, leading to loss of body water in urine. Hence de- hydration may be a primary factor. Physical Fitness Physical conditioning alone does not confer heat acclimatization. The subjects of Eichna et al., (Figure 30-4) were all highly conditioned be- fore the test. Physical training without heat ex- posure, however, does improve heat tolerance, as indicated by somewhat lower heart rates and core temperatures in men exposed to heat after condi- tioning as compared with before. Sweat rates do not increase and skin temperature remains high. Physical conditioning enhances heat tolerance by increasing functional capacity of the cardiocircula- tory system. Two important changes are first, an increase in number of capillary blood vessels to muscle, thus providing a larger interface between blood and muscle for exchange of oxygen and waste products and second, increased tone of small veins from tissues other than muscle so as to reduce their capacity during exercise, thus in- creasing pressure in large central veins returning the blood to the heart. Cardiac output per minute during work can increase with less need to acceler- ate the heart. These factors combine to increase VO, max of the physically conditioned man, giving him a wider margin of safety in coping with the added circulatory strain of work under heat stress. The extent to which men might gain in heat tol- erance by acclimatization is not easily predictable, but those with a high level of physical fitness have the advantage. Selection and Periodic Examination of Workers Past performance in heat is perhaps the only reliable criterion on which to predict effectiveness of a worker’s future performance under heat stress. For new employees without previous heat expo- sure, screening procedures should include standard tests of physical fitness and heat tolerance. Heart rates attained during a stepping exercise at 332 oly TABLE 30-6. Classification, Medical Aspects, and Prevention of Heat Illness Category 1. Temperature Regulation Heat Stroke and Heat Hyperpyrexia Clinical Features Heat Stroke: 1) Hot dry skin: red, mottled or cyanotic. 2) High and rising T, 40.5°C and over. 3) Brain disorders: mental confusion, loss of consciousness, convulsions, coma as T, continues to rise. Fatal if treatment delayed. Heat Hyper- pyrexia: milder form. T, lower; less severe brain disorders, some sweating. 2. Circulatory Hypostasis Heat Syncope Fainting while standing erect and immobile in heat. 3. Salt and/or Water Depletion a) Heat Exhaustion 1) Fatigue, nausea, headache, giddiness. 2) Skin clammy and moist. Complexion pale, muddy or hectic flush. 3) May faint on standing with rapid thready pulse and low blood pressure. 4) Oral temperature normal or low but rectal tem- perature usually elevated (37.5-38.5°C). Water restriction type: Urine volume small, highly con- centrated. Salt restriction type: Urine less con- centrated, chlorides less than 3 g/1. b) Heat Cramps Painful spasms of muscles used during work (arms, legs, or abdominal). Onset during or after work hours. 4. Skin Eruptions a) Heat Rash (miliaria rubra; “prickly heat”) Profuse tiny raised red vesicles (blister-like) on affected areas. Pricking sensations during heat exposure. b) Anhidrotic Heat Extensive areas of skin which do not sweat Exhaustion on heat exposure, but present goose flesh appear- (miliaria ance, which subsides with cool environments. As- profunda) sociated with incapacitation in heat. 5. Behavioral Disorders a) Heat Fatigue — Transient Impaired performance of skilled sensorimotor, mental, or vigilance tasks, in heat. b) Heat Fatigue — Chronic Reduced performance capacity. Lowering of self-imposed standards of social behavior (e.g., alcoholic overindulgence). Inability to concen- trate, etc. Predisposing Factors 1) Sustained exertion in heat by unacclimatized workers. 2) Lack of phys- ical fitness and obesity. 3) Recent alcohol intake. 4) Dehydration. 5) Indi- vidual susceptibility. 6) Chronic cardiovascular disease in the elderly. Lack of acclimatization. 1) Sustained exertion in heat. 2) Lack of accli- matization. 3) Failure to replace water and/or salt lost in sweat. 1) Heavy sweating dur- ing hot work. 2) Drink- ing large volumes of wa- ter without replacing salt oss. Unrelieved exposure to humid heat with skin con- tinuously wet with un- evaporated sweat. Weeks or months of constant exposure to cli- matic heat with previous history of extensive heat rash and sunburn. Rarely seen except in troops in wartime. Performance decrement greater in unacclimatized, and unskilled men. Workers at risk come from homes in temperate climates, for long resi- dence in tropical lati- tudes. Underlying Physiological Disturbance Heat Stroke: Failure of the central drive for sweating (cause un- known) leading to loss of evaporative cooling and an uncontrolled accelerat- ing rise in T,. Heat Hyperpyrexia: Partial rather than com- plete failure of sweating. Pooling of blood in di- lated vessels of skin and lower parts of body. 1) Dehydration from deficiency of water and/ or salt intake. 2) Deple- tion of circulating blood volume. 3) Circulatory strain from competing demands for blood flow to skin and to active mus- cles. Loss of body salt in sweat. Water intake di- lutes electrolytes. Water enters muscles, causing spasm. Plugging of sweat gland ducts with retention of sweat and inflamma- tory reaction. Skin trauma (heat rash; sunburn) causes sweat re- tention deep in skin. Re- duced evaporative cooling causes heat intolerance. Discomfort and physio- logical strain. Psychosocial stresses probably as important as heat stress. May involve hormonal imbalance but no positive evidence. Treatment Heat Stroke: Immedi- ate and rapid cooling by immersion in chilled wa- ter with massage or by wrapping in wet sheet with vigorous fanning with cool dry air. Avoid overcooling. Treat shock if present. Heat Hyper- pyrexia: Less drastic cool- ing required if sweating still presentand T, < 40.5. Remove to cooler area. Recovery prompt and complete. Remove to cooler en- vironment. Administer salted fluids by mouth or give I-V infusions of nor- mal saline (.9%) if un- conscious Or vomiting. Keep at rest until urine volume and salt content indicate that salt and wa- ter balances have been re- stored. Salted liquids by mouth, or more prompt relief by I-V infusion. Mild drying lotions. Skin cleanliness to pre- vent infection. No effective treatment available for anhidrotic areas of skin. Recovery of sweating occurs grad- ually on return to cooler climate. Not indicated unless accompanied by other heat illness. Medical treatment for serious cases. Speedy re- lief of symptoms on re- turning home. Reprinted from “Heat Stress and Heat Disorders”, Leithead, C. S., Lind, A. R., (1964) published by F. A. Davies Co., Philadelphia, Pa. Prevention Medical screening of workers. Selection based on health and physical fitness. Acclimatization for 8-14 days by graded work and heat exposure. Monitoring workers dur- ing sustained work in se- vere heat. Acclimatization. Inter- mittent activity to assist venous return to heart. Acclimatize workers using a breaking-in sched- ule for 1 or 2 weeks. Supplement dietary salt only during acclimatiza- tion. Ample drinking wa- ter to be available at all times and to be taken fre- quently during work day. Adequate salt intake with meals. In unaccli- matized men, provide salted (0.1%) drinking water. Cooled sleeping quar- ters to allow skin to dry between heat exposures. Treat heat rash and avoid further skin trau- ma by sunburn. Periodic relief from sustained heat. Acclimatization and training for work in the heat. Orientation on life abroad (customs, cli- mate, living conditions, etc.) kg.m/min are now being used in selecting men for further acclimatization before assigning them to mining ore under high heat stress in the deep gold mines of South Africa.’ Those of low work ca- pacity, as indicated by a heart rate of over 140/ min, are eliminated for these tasks. Those with lower exercise heart rates, particularly if below 120/min, are considered the best candidates and undergo graded acclimatizing exercises for 4 hours/day for 8 days in hot rooms (T,,=31.7°C). A second screening at this stage eliminates those with oral temperatures persistently above 38.3°C. Through screening, acclimatization, and selective placement based on heat tolerance, together with careful supervision of workers, serious heat cas- ualties from heat stroke among the 100,000 or more men recruited yearly in this industry have been greatly reduced and productivity substantially increased. Operations of this magnitude do not exist in the United States, but the same principles are ap- plicable. On pre-employment examination, the physician can readily assess physical fitness using stepping exercises, or a bicycle ergometer to esti- mate VO, max. In terms of O, uptake per kg, a VO, max of 28 ml/kg min or less should be dis- qualifying. A standard test for heat tolerance is desirable but requires special facilities. Older workers, including both new applicants and those undergoing periodic evaluation, should be examined with particular attention to chronic impairments of the heart, circulation, and vas- cular system but also of the kidneys, liver, endoc- rines, lungs and skin. Significant disease of any of these systems should be disqualifying for new em- ployment on jobs involving severe heat exposure, or for those previously employed in such jobs if the disease is progressive despite treatment. Care- ful inquiry should be made on use of drugs, par- ticularly hypotensive agents, diuretics, antispas- modics, sedatives, tranquilizers, and anti-depres- sants, as well as the abuse of drugs, particularly amphetamines and alcohol. Many of these drugs impair normal physiological responses to heat stress, and others alter behavior, exposing the patient or fellow workers to safety hazards. Toxic agents in the work environment which reduce heat tolerance, notably carbon monoxide, must also be considered. History of repeated accidents on the job, poor work performance, emotional instability, or frequent sick absence should alert the physician to possible heat intolerance of the employee. Preferred Reading Books 1. BELDING, H. S.: “Resistance to Heat in Man and Other Homeothermic Animals.” (Chap. 13), Ther- mobiology (A. H. Rose, Ed.). Academic Press, London (1967). 2. BROUHA, L.: Physiology in Industry. Pergamon Press, New York, London (1960). 3. HARDY, J. D. (Ed.): Temperature: Its Measure- ment and Control in Science and Industry, Part 3. Reinhold Publishing Corp., New York (1963). 4. HARDY, J. D,, A. P. GAGGE, and J. A. J. STOL- WIIK (Eds.): Physiological and Behavioral Tem- perature Regulation. Charles C. Thomas, Spring- field, Illinois (1970). . 411 5. LEITHEAD, C. S. and A. R. LIND.: Heat Stress and Heat Disorders. F. A. Davis Co., Philadelphia (1964). 6. NEWBURGH, L. H.: Physiology of Heat Regula- tion and the Science of Clothing. W. B. Saunders, Philadelphia (1949). 7. WORLD HEALTH ORGANIZATION.: Health Factors Involved in Working under Conditions of Heat Stress. WHO Tech. Rep. Ser. No. 412, Gen- eva (1969). Journals I. American Industrial Hygiene Association Journal, 66 South Miller Rd., Akron, Ohio 44313. 2. Archives of Environmental Health, 535 No. Dear- born St., Chicago, Illinois 60610. 3. Ergonomics, Fleet St., London E. C. 4 (United Kingdom). 4. Journal of Applied Physiology, 9650 Wisconsin Ave., Washington, D.C. References I. DUBOIS, E. F.: Fever and the Regulation of Body Temperature. Charles C. Thomas, Springfield, Ill. (1948). 2. PASSMORE, R. and J. V. DURNIN.: “Human Energy Expenditure.” Physiol. Rev., 9650 Rockville Pike, Bethesda, Maryland 20014, 35: 801 (1955). 3. NADEL, E. R., R. W. BULLARD, and J. A. STOL- WIHK.: “Importance of Skin Temperature in the Regulation of Sweating.” J. Appl. Physiol., 9650 Wisconsin Ave., Washington, D.C., 3/: 80 (1971). 4. NIELSEN, M.: “Die Regulation der Korptemperatur bei Muskelarbeit.” Skand. Arch. Physiol., (now Acta Physiologica Skandinavica), (Editor) U. S. von Euler, 10401 Stockholm, Sweden, 79: 193 (1938). 5S. BROUHA, L.: Physiology in Industry, Pergamon Press, New York, London, p. 93 (1960). 6. MINARD, D., R. GOLDSMITH, P. H. FARRIER, JR., and B. J. LAMBIOTTE, JR.: “Physiological Evaluation of Industrial Heat Stress.” Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313. 7. LIND, A. R.: “A Physiological Criterion for Set- ting Thermal Environmental Limits for Everyday Work.” J. Appl. Physiol., 9650 Wisconsin Ave., Washington, D.C., 78: 51 (1963). 8. ROBINSON, S.: “Physiological Adjustments to Heat,” (Chap. 5), Physiology of Heat Regulation and the Science of Clothing. W. B. Saunders Co., Philadelphia (1949). 9. EICHNA, L. W., W. F. ASHE, W. B. BEAN, and W. B. SHELLEY.: “The Upper Limits of Environ- mental Heat and Humidity Tolerated by Acclima- tized Men Working in Hot Environments.” J. In- dustr. Hyg. Toxicol., (now Arch. of Env. Health), (Editor) Dr. John S. Chapman, American Med. Assoc., 535 No. Dearborn, Chicago, Illinois 60610, 27: 59 (1945). 10. EICHNA, L. W.,, C. R. PARK, N. NELSON, S. HORVATH, and E. D. PALMES.: “Thermal Regu- lations in a Hot Dry (Desert Type) Environment.” Am. J. Physiol., 9650 Rockville Pike, Bethesda, Maryland 20014, 163: 585 (1950). 11. WYNDHAM, C. H., W. v. d. M. BOUWER, M. G. DEVINE, H. E. PATERSON, and D. K. C. MAC- DONALD. “Examination of Use of Heat-Exchange Equations for Determining Changes in Body Tem- perature.” J. Appl. Physiol., 9650 Wisconsin Ave., Washington, D.C., 5: 299 (1952). 12. KAMON, E. and H. S. BELDING.: “Heart Rate and Rectal Temperature Relationships During Work in Hot Humid Environments.” J. Appl. Physiol., 9650 Wisconsin Ave., Washington, D.C., 3/: 472 (1971). 13. LIND, A. R.: “Effect of Individual Variation on Upper Limit of Prescriptive Zone of Climates.” J. 14. 15. 16. 17. Appl. Physiol., 9650 Wisconsin Ave., Washington D.C. 28: 57 (1970). LEITHEAD, C. S. and A. R. LIND.: Heat Stress and Heat Disorders., F. A. Davis Co., Philadelphia (1964). BELDING, H. S. and T. F. HATCH.: “Relation of Skin Temperature to Acclimation and Tolerance to Heat.” Fed. Proc., 9650 Wisconsin Ave., Washing- ton, D.C., 22: 881 (1963). DUKES-DUBOS, F. M., A. HENSCHEL, C. M. KRONOVETER, M. BRENNER, and W. S. CARL- SON.: “Industrial Heat Stress, Southern Phase.” USPHS Division of Occupational Health, Cincin- nati, Ohio, R.R.-5 (1966). LIND, A. R.: “Influence of Age and Daily Duration of Exposure on Responses of Men to Work in Heat.” J. Appl. Physiol., 9650 Wisconsin Ave., Washing- ton, D.C., 28: 50 (1970). 412 18. 20. 21. HENSCHEL, A., L. L. BURTON, L. MARGO- LIES, and J. E. SMITH.: “An Analysis of the Heat Deaths in St. Louis During July, 1966.” Am. J. Pub. Health, 1790 Broadway, New York, N.Y. 10019, 59: 2232 (1969). GUSTIN, J.: Disease Specific Mortality Patterns for Open Hearth Workers. Thesis for degree of M.S. (Hyg.) submitted to Grad. School of Public Health, Univ. of Pittsburgh (1971). MINARD, D.: “Nomenclature and Classification of Heat Disorders.” (editorial) Journal of the Amer- ican Medical Association (JAMA), 535 No. Dear- born St., Chicago, Illinois 60610, 191: 854 (1965). STRYDOM, N. B. and R. KOK.: “Acclimatization Practices in the South African Gold Mining Indus- try.” J. Occup. Med., 49 East 33rd St.,, New York 10016, 12: 66 (1970). CHAPTER 31 THERMAL STANDARDS AND MEASUREMENT TECHNIQUES Bruce A. Hertig, Sc.D. INTRODUCTION The Industrial Revolution brought with it un- deniable benefits to mankind, but not without certain costs. The opportunities for injury and sudden death that emerged included hazards un- known to the craftsmen in home-centered manufac- turing activities. Among the more dangerous pur- suits were those involving the production of basic materials, glass, metals, etc.: in short, the hot industries. Not only was there the ever-present danger of splashes, explosions and spills of molten material, but injuries and deaths mounted as the result of hard physical work in excessively hot environments. With the more enlightened current attitudes, one would assume that deaths and heat- illnesses are rare in the United States, but accurate data are not available on the frequency of heat casualties. Other chapters in this volume provide infor- mation related to the physiologic consequences of heat stress (Chapter 30) and possible measures which may be taken to reduce stresses caused by the thermal environment (Chapter 38). It is the purpose of this chapter to outline the philosophy and development of indices for rating severity of the thermal environment, to outline the methods of assessment of the several parameters involved in the indices, and to provide guidelines for appli- cation and interpretation of the indices. MEASUREMENT OF THE THERMAL ENVIRONMENT Measurement of the thermal environment re- quires selection and placement of instrumentation such that the data acquired will be meaningful in terms of heat exchanges between the worker and the environment. For this to be achieved effec- tively, the investigator must (a) understand the fundamental physical laws governing thermal ex- changes and (b) become familiar with the oper- ating principles and procedures of the instruments. Such understandings will help to avoid inappro- priate applications of instrumentation. Thermal Exchanges with the Environment The modes of heat exchange between man and the environment — evaporation, convection, radi- ation — have been covered qualitatively in Chap- ter 30, as have the environmental parameters which influence the rate of exchange. Quantita- tive relationships are developed in this chapter. Convection (C) is a function of (1) the tem- perature gradient between the skin and the am- bient air (or outer clothing), and (2) the move- ment of air past the surface. Stated algebraically: 413 C= f (T.—T,), Vv». In the Newtonian form and with the “Fort Knox” coefficients as revised by Hatch,'* the expression becomes C=1.0V* (T,—T,) where C= Convection, kcal/hr V = Air speed, meters/min T, = Air temperature, °C T,= Skin surface temperature, °C. The empirically obtained exponent of 0.6 applies to forced convection over vertical cylinders,® the geometric configuration that best corresponds to man in the working environment. The sign convention has been chosen such that when T, is higher than T,, C will be positive; thus heat gain to the man will be positive, and heat loss, negative. The coefficient includes the surface area for an “average” man (=1.8 m*). For a particular individual whose surface area may differ from average, the value of C may be adjusted by multi- plying by the ratio: actual area/1.8. The “Fort Knox” coefficients were developed on men essen- tially nude; the influence of clothing is considered by Belding in Chapter 38. Radiation, R, is a function primarily of the gradient from the mean radiant temperature of the solid surroundings to skin temperature. While radiative exchange, in reality, is a function of the fourth power of absolute temperature, a first order approximation is sufficiently accurate for estimat- ing R in the application outlined here.* [Note that the value of the coefficients in reference (4) also have been modified.?] R=11.3 (T\—T,) where R = Radiation, kcal/hr T, =Mean radiant temperature of the solid surroundings, °C. and T,= Skin surface temperature, °C. Evaporation, E, is a function of air speed, and the difference in vapor pressure between the perspiration on the skin (vapor pressure of water at skin temperature) and the air. In hot, moist environments, evaporative heat loss may be limited by the capacity of the ambient air to accept addi- tional moisture, in which case, Ex =2V" (PW,—PW,) where V = Air speed, meters/ minute PW, = Vapor press. of water on skin, mmHg PW, = Vapor press. of air, mmHg. In hot, dry environments E may be limited by the amount of perspiration which can be produced by the worker. The maximum sweat production that can be maintained by the average man throughout an eight-hour shift is one liter per hour, which is equivalent to an evaporative heat loss of 600 Kcal/hr. or (2400 Btu/hr). From the above, it is evident that four envir- onmental factors define the thermal exchanges: T., Tw, PW, and V. Physiological factors, e.g., Ts, metabolism (M), are dealt with elsewhere (Chapters 30 & 38). NOTE: Equations for C, R, and E,,,x in Eng- lish units (°F, ft/min, Btu/hr) are C=1.08 V°¢ (T,—T,), R=25 (Ty —Ty) and E.ux=4.0 Vos (PW,—PW,), respectively. Instruments Thermometry. Air temperature may be measured by a variety of instruments, each of which may have advantages under certain circumstances. 1. Mercury (or alcohol)-in-glass thermome- ters. The common glass thermometer is often used for determining air temperature. But because of its very common nature, sometimes the simplest of precautions are overlooked. Calibration. Thermometers may be in er- ror by several degrees. Each should be calibrated over its range in a suitable medium (usually a temperature-controlled oil bath) against a known standard, e.g., Bureau of Standards certified thermome- ter. Only thermometers with the gradua- tions marked on the stem should be used. Those with scale markings on a mounting board can be off by 10°; further the stem can shift relative to the mounting board. Range. 1t seems superfluous to specify that the range of the thermometer should be selected to cover the anticipated envir- onment. But if one is careless, a 0-50°C thermometer can be easily carried into a 60 °C environment where the mercury will break the capillary glass tube; this is not an unusual occurrence in practice. Separation of columns. Sometimes the liquid column in a thermometer will sep- arate. Before readings are taken, the con- tinuity of the column should be checked. Separated columns may be rejoined by shaking, or by heating in hot water (never a flame!). Type. If the thermometer is totally “im- mersed” in the air being measured, a total immersion instrument should be selected. A partial immersion thermometer will be the instrument of choice for wet bulb and globe thermometers and for the aspirated psychrometer. The depth of submersion for which a partial immersion thermometer is calibrated is usually indicated by a mark on the stem. Breakage. Glass thermometers are the simplest to use, most readily available and cheapest of the temperature instruments considered. Yet their fragility may prove to be a hazard in certain applications. The 414 mercury spilt from a broken thermometer may not be of consequence in a large, well- ventilated shop, but would certainly re- quire careful cleanup in an enclosed space, e.g., underwater chamber. 2. Thermoelectric thermometers. When two dissimilar metals are joined, and the temperature of the junction is changed, a small voltage is gen- erated (Seebeck effect)’. Two junctions in a cir- cuit, with one held at a known temperature (“ref- erence junction”), form the basic elements of a thermocouple. The current flowing in the circuit resulting from the electromotive force (e.m.f.) generated may be measured directly by a galva- nometer, or the e.m.f. balanced by a known source potentiometrically. The latter technique is pre- ferred, as the length of the thermocouple (hence its resistance) becomes of no consequence when current flowing becomes zero. Each thermocouple used with a current-measuring device must be calibrated individually. With a potentiometer, only samples from the spools of wire need be calibrated, and only then if extreme precision is required. Figure 31-1 provides a schematic ar- rangement of the components in a thermocouple system. Thermocouples of copper and constantan (a copper-nickel alloy) are commonly used for most environmental temperature ranges. They are easy to construct, and the wire for an individual couple costs only a few cents. However, the potentio- meter will cost several hundred dollars. The availability of small thermocouple wire, as fine as 40 gauge, makes the technique useful for measuring physiological temperatures, e.g., skin, ear canal, rectal, with the same recording or readout equipment as used for environmental tem- peratures. To prevent shorting out between junc- tions in the saline milieu of the body, thermojunc- tions used for physiological measurements should be electrically insulated. Thermocouples have these advantages over mercury-in-glass thermometers: (1) Adaptability to specific placement. Small junctions may be placed where the bulb of the thermometer would not be appro- priate, e.g., skin surface. (2) Remote reading. Thermojunctions may be placed at the measurement site, and read remotely — hundreds of meters away, if . necessary. (3) Simultaneous readings from several sta- tions may be read at one place with one potentiometer with a rotary selector switch in the circuit. (4) Low cost of thermocouples, once poten- tiometer is purchased. (5) Adaptability to continuous recording. (6) No hazards from breakage. (7) Equilibrium time with changing tempera- tures is almost instantaneous, whereas mer- cury-in-glass thermometers may require several minutes to reach a steady reading. On the other hand, disadvantages include: (1) High initial cost of potentiometer. (2) Bulk of potentiometer. B neeeeemsai== E 24 Laboratory for Ergonomics Research, Department of Mechanical and Industrial Engineering, University of Illinois at Urbana — Champaign. Figure 31-1. (3) Requirement for reference junction (usu- ally ice bath in Thermos bottle). (4) Requirement to run wires to measurement site. (5) Some technical skill required to construct thermocouples and use equipment. Lab- oratory training in techniques highly rec- ommended. 3. Thermistor thermometry. One of the “space age” gadgets is the thermistor: thermal re- sistor. Thermistors are semiconductors which ex- hibit substantial change in resistance in response to a small change in temperature. As the resist- ance of the thermistor itself is measured in thou- sands of ohms, the resistance imposed by lead wires up to 25 meters or so is immaterial, permit- ting remote readings, as with thermocouples. Readout equipment is battery-powered and rela- tively light and portable which is convenient for field studies. Advantages: . (1) Simple to use with minimum training. (2) Less bulky and complicated to use than thermocouples. (3) Requires no reference junction. (4) Output signal may be recorded. (5) Variety of probes available for special ap- plications. Disadvantages: (1) Cost of readout equipment about the same as potentiometer, but thermistor probes cost about $25.00 each. If the lead breaks, 415 Components in a Thermocouple System. it is not easily repaired, as are thermo- couples. (2) Thermistor probes, though they are called “interchangeable,” require individual cali- bration before use. Calibration of ther- mistor beads will shift somewhat with age, requiring annual or biennial recalibration. Comment: The advantages of the thermis- tor thermometer make it the instrument of choice for field use when mercury-in-glass thermometers are inappropriate. Regard- less of the type of thermometer used, shielding of the sensor against radiant ex- change may be required where walls are cooler or warmer than the air, or in direct sunlight. Heavy aluminum foil fastened loosely around the bulb provides effective shielding; however, it should not restrict the free flow of air around the sensor ele- ment. And finally, in asymmetric thermal fields readings at several locations in the occupied space may be required to pro- vide an adequate estimate of average air temperature. Anemometry. As noted above, heat transfer by convection and by evaporation are functions of movement of the ambient air. While the units associated with air motion — distance per unit time — suggest movement of the mass of air past a point, turbulent air with little net mass move- ment will be as effective in heat transfer as linear movement. Directional instruments, useful in ventilation engineering or meteorology, are usually not ap- plicable for assessment of heat stress. On the other hand, instruments which depend upon rate of cooling of .a heated element provide readings meaningful in terms of “cooling power” of the moving air, and are thus the instruments of choice. I. Thermoanemometers. Willson thermoanemometer. In use, two matched thermometers are mounted about 5 cm. apart in the environment. One of the thermometer bulbs is wrapped with a fine resistance wire. Cur- rent from a battery passing through the wire heats the bulb. The second thermometer is bare. The temperature differential between the heated and the unheated thermometers depends on the cur- rent through the wire (adjustable), and the air speed. The voltage is set between 2 to 6 volts, depending on the range of air speed encountered. At high air speeds, greater heat input is required to obtain sufficient differential between the ther- mometers for reliable readings. Knowing this temperature differential and the voltage, the oper- ator may find the air speed from the calibration curves supplied with each instrument. Achieving equilibrium requires 2 to 5 minutes. On the one hand, this provides an integrating effect in turbu- lent air, but on the other hand makes determina- tion of air speed at many locations tedious. Its design, however, assures relatively non-directional response. Alnor thermoanemometer. This instru- ment measures air motion by the rate of cooling of a heated thermocouple at the tip of the probe. One thermojunction is heated by a constant current supplied to a heater wire; the other junction is located in the air stream. The air speed governs the rate of heat removal from the heated thermo- couple, which in turn determines its millivolt out- put. The scale is calibrated directly in feet per minute. The low mass of the thermocouple permits almost instantaneous response of the instrument. An area may be surveyed quickly, but rapid fluc- tuations in air motion make mean speed estimates difficult. Batteries supply the power, making the instrument portable and self-contained. The ther- mocouple and heater supports restrict airflow somewhat; the probe should be slightly rotated to obtain the maximum reading. Anemotherm. The principle of operation of the Anemotherm is similar to the Alnor, though a heated resistance wire is used as one leg of a Wheatstone bridge instead of the heated thermo- couple circuit.” The Anemotherm also may be used to measure temperature and static pressure. Kata thermometer. Hill" developed the Kata thermometer to determine cooling power of the air, as a measure of efficiency of ventilation in factories, mines, etc. (Figure 31-2). It is essen- tially an alcohol-filled thermometer with an out- sized bulb. The bulb is heated in warm water until the column rises into the upper reservoir and is then wiped dry. The instrument is suspended in the air stream (it may be hand held, provided the body of the operator does not interfere with the flow of air); the fall of the column from the upper 416 UPPER RESERVOIR TIMING MARKS BULB SCALE _Jacm Hill, L.: The Science of Ventilation and Open Air Treat- ment. Part I, Med. Res. Count. Spec. Dept. No. 32, London, 1919. Figure 31-2. Kata Thermometer. to the lower mark etched on the stem is timed with a stopwatch. The cooling time of the Kata is a function of air speed and air temperature; the air speed is determined from nomograms accompany- ing the instrument. Katas are made in several ranges for high temperature environments, as well as the standard instrument for the comfort range (upper mark 38°C, lower mark 35°C). The bulb of the Kata must be silvered to reduce the effect of radiant heat exchange. The Kata is a good instrument for estimating accurately the cooling power of air motion at low speeds, <15 meters/min. The requirements for heating above ambient make it somewhat awkward for field work, though a Thermos of hot water may be carried. 2. Estimation of air motion. For investigators frequently called upon to make heat stress studies, it is well worth the effort to learn to judge air motion by “feel.” This permits a gross estimate of air movement without instruments on a survey or “walk through.” If no motion is felt, the air speed is below 10 to 15 meters/min (30-50 ft/ min). If a light breeze is felt, the speed will be about 15 to 30 meters/min. Breezes strong enough to cause movement of clothing, tousling of hair, etc., are in the range of 30-90 meters/min. Winds stronger than these are not often found within buildings, except in front of fans. Psychrometry. The amount of water vapor in the air (humidity) controls the rate of evaporation of water from skin surface and from other moist tissues, e.g., lungs, respiratory passages, conjunc- tiva of the eyes, etc. To understand the process of evaporation from these tissues into the ambient air, certain properties of liquid-vapor interfaces should be reviewed. Water, like other liquids, will tend to saturate the surrounding space with vapor. In an enclosed vessel, the amount of water vapor per unit volume in the space above the water is dependent only on the temperature of the system (assuming con- stant total pressure). In accordance with Dalton’s law of partial pressures, presence or absence of other species of gases in the space will have no effect on the amount of water vapor present. If all other gases are evacuated, the pressure developed is termed the true vapor pressure (or saturation pressure) of the liquid at the existing temperature. If the temperature is raised, saturation vapor pressure will increase. When the vapor pressure equals total atmospheric pressure, boiling occurs. In an open vessel where ambient air currents carry away the water vapor, continuous evaporation takes place. “Relative humidity” (RH) is defined as the amount of moisture in the air as compared with the amount that the air could contain at saturation at the same temperature. It is usually expressed as a percentage. Thus, the amount of moisture in the air at, say, 50% RH will vary depending on the air temperature. Since it is the amount of PSYCHROMETRIC CHART 40 50 60 70 eo 90 100 no 120 130 140 15% water vapor in the air (“absolute” humidity) which influences evaporation, the relative humidity cannot be used directly to compute evaporative loss. To illustrate this point: water vapor in air saturated at 0°C exerts a vapor pressure of about 5 mm Hg. This condition might prevail on a winter's day with freezing drizzle. When this air is inhaled into the lungs, it passes over mucous membranes coated with liquid water at 37°C, cor- responding to a vapor pressure of about 45 mm Hg. With this gradient of 40 mm Hg, evaporation occurs, quickly saturating the air, now warmed to 37°C. Thus, air at 100% RH enters at 0°, and air at 100% RH leaves at 37°, yet evaporation has occurred, and the moisture content differs greatly from inhaled to exhaled air. On exhala- tion, the air cools and the new moisture burden condenses out, creating a visible cloud. Given the relative humidity and the tempera- ture, the water vapor pressure may be determined. In fact, any two properties (temperature, total heat content, dew point, relative humidity, etc.) completely define the thermodynamic state of the air-water vapor mixture.” The psychrometric chart is a convenient graphical representation of the mathematical interrelationships of these param- eters (Figure 31-3 inset). The saturation line (100% relative humidity) marks the upper limit of moisture holding capacity of the air (Figure 31-3). Note that at saturation, the dry-bulb, wet- —448 . —4% Jaz <3 40 < —39 xr 220 © —36 w T Oo - oO 133% z 3 30 ¢ a - 50 & Jer a — 2 « 24a Ww L a —H21 a S- . @ seg J] « 2s” I & 7° -19 40 Je -13 Jo ORY BULB TEMPERATURE, F Powell, C. H., Hosey, A. D. (eds): The Industrial Environment — Its Evaluation and Control, 2nd Edition. Public Health Services Publication No. 614, 1965. Figure 31-3. Psychrometric Chart and Vapor Pressure Nomograph. bulb, and dew-point temperatures are equal. Sling psychrometer. This instrument consists of two thermometers clamped in a frame which in turn is fastened to a swivel handle. A cotton wick dipped in distilled water covers one thermometer; the other is bare. The terms “wet bulb” and “dry bulb” temperatures originated from this type of instrument. When it is rapidly whirled, water evaporates from the wick, cooling the bulb. The rate of evaporation from the wick is a function of the vapor pressure gradient, determining in turn the depression of the wet bulb thermometer read- ing below the dry bulb. The vapor pressure can be read directly from the psychrometric chart, or tables.” A few simple precautions should be observed in the use of the sling psychrometer. Usually one minute of swinging adequately cools the wet bulb to its lowest reading. It is advisable to check the reading, and then swing again for a few seconds. (Repeat if the temperature continues to fall.) There should be no obstructions in the path of the swinging thermometers. The use of distilled water prolongs the usefulness of the wick. When dirty, it may be restored by washing with detergent and thorough rinsing. It should also be noted that thermal radiation can cause rather large errors in both dry- and wet-bulb temperatures taken with a sling psychrometer. Motor-driven psychrometer. Several types of aspirated psychrometers are available, battery- powered for field use, as well as conventional lab- oratory instruments. These accomplish the same end as the sling psychrometer; air motion across the thermometer bulbs is created mechanically rather than whirling by hand. Hair hygrometer. Human hair absorbs and desorbs moisture with changes in atmospheric humidity. The length of hair under tension changes in turn with its moisture content. This motion is transmitted through a system of levers to a pointer indicating the relative humidity. Fitted with a pen, the pointer records the relative humid- ity on a revolving drum." Radiometry. Measurement of the mean radiant temperature of the solid surroundings (T,) for evaluation of thermal stress is most often effected by means of a blackened sphere, or Vernon globe.’ More precise measurements of the ra- diant field may be made by radiometers of various designs, or by surface pyrometry. For these more precise techniques, refer to other sources, such as Fanger,”' Gagge,'* or Longley et al.’* Vernon Globe (Black Globe). The Vernon Globe, or Black Globe, consists of a copper sphere about 15 cm. in diameter, the exterior of which is painted flat black. A hole for a thermometer (thermojunction or thermistor may be used) and a tab for a wire by which to hang it, complete the instrument (Figure 31-4). Copper toilet floats have been used with success, but spun spheres are usually preferred. To estimate the mean radiant temperature at some given point in an enclosure, the globe is placed at the desired location. The temperature of the globe is measured by the thermometer after 418 CONVECTION -—~———RADIATION Vernon, H. M.: The measure of radiant heat in relation to human comfort. J. Physiol. 70, Proc. 15, 1930. Figure 31-4. Vernon Globe (Black Globe). thermal equilibrium has been established, usually about 15 to 20 minutes. At equilibrium, heat loss (or gain) of the globe by convection is balanced by heat gain (or loss) by radiation. The mean radiant temperature at the globe location may be calculated by the equation: 4 4 To*=100 I 0) +2.48 V (T,—T.) 100 T,* = Vernon globe temp, “Kelvin V & T, =as before. where T,* =mean radiant temp, °Kelvin (273 + °C) T,* as calculated from this expression is an ef- fective wall temperature (absolute). It represents the temperature of a “black” enclosure of uniform wall temperature which would provide the same heat loss or gain as the environment measured. INDICES OF THERMAL STRESS The search for a scheme to integrate the sev- eral environmental, physiological and behavioral variables affecting heat transfer from man to the environment into a simple index has occupied scores of engineers and physiologists for decades. Recent reviews provide breadth and depth for an- alyses of the many rating scales which have been proposed.'*'® The purpose here is to outline those which have emerged as the most commonly en- countered in evaluation and control of industrial heat stress. Effective Temperature. The search for design cri- teria for thermal comfort in occupied spaces led to the development of the “Effective Temperature” scale (E.T.). This concept was introduced in 1923 by Houghten and Yaglou;'® their work was 150 130 120 120 10 10 : : # - 100 Instructions for use: Stretch 3 a thread or place a rule to rn join dry-bulb and wet-bulb &0 u temperatures. Note where this 0 g cuts appropriate air velocity 8 2 line and read effective tem- « a perature at this point on grid = 2 lines. g 80 «© 2 2 g 70 - 3 ; g » I 60 [so E40 E 30 "0 30 Powell, C. H., Hosey, A. D. (eds): The Industrial Environment — Its Evaluation and Control, 2nd Edition. Public Health Services Publication No. 614, 1965. Figure 31-5. Chart Showing Normal Scale of Corrected Effective (or Effective) Temperature. Instructions for use: Stretch a thread or place a rule to join dry-bulb and wet-bulb tempera- tures. Note where this cuts appropriate air velocity line and read effective temperature at this point on grid lines. 419 sponsored by the American Society of Heat- ing and Ventilating Engineers. Briefly, the ob- jective was to define the various combinations of dry-bulb temperature, air motion, and humidity which would provide the same thermal sensation to the occupants. Subjects were exposed first to one combination and then another of the param- eters (wall temperature was the same as air temper- ature T,=T,). On the basis of a large number of trials, nomograms were developed which charac- terized equivalent environments, expressed in terms of the temperature of a still, saturated en- vironment. Through the years, the original concept has been refined and modified by many investigators; among other things, methods of correcting for radiant heat exchange have been included. The early nomograms were psychrometric charts with lines of E.T. superimposed (see earlier editions of ASHVE Guide, e.g., 34th ed., 1956, for these forms of the E.T.). A separate nomogram was required for each air velocity. The present form of the scale incorporates the modifications into a single chart. Figure 31-5 shows the “normal” E.T. scale which relates to people wearing light weight summer clothing, similar to workers’ uni- forms. There is another E.T. scale for seminude men called the “basic” scale. Example: Given dry bulb=76°F, wet bulb =55°F, air speed=100 ft/min (English units used in the Chart), find E.T.=67. That is, the given environment would provide the same ther- mal sensation as one with dry- and wet-bulb tem- peratures of 67°F, and no air motion. (In reality, “still” air approximated 25 ft/min, or 8 m/min.) In spite of its widespread use, the E.T. has serious limitations, particularly as an index of heat stress: a. It was developed on transient thermal sensations. This tended to neglect the im- portance of sorption or desorption of moisture in the subject’s clothing. b. The scale was developed using clothed subjects in dress of that day. c. The subjects were sedentary. Later modifications were made to include the effect of metabolic rate. d. The scale was designed primarily for environments reasonably near the comfort zone. Extrapolation to thermally stressful en- vironments is tenuous. Heat Stress Index (HSI). The Heat Stress Index was developed by Belding and Hatch at the Uni- versity of Pittsburgh during the mid-1950’s.'" Their index combines the environmental heat (ra- diation and convection, R and C) and metabolic heat (M) into an expression of stress in terms of requirement for evaporation of sweat (E,.,). Stated algebraically: M=R=C=E,. The resulting physiologic strain is determined by the ratio of the stress (E,.,) to the maximum evaporative capacity of the environment, E,,.« (see above). Thus, the HSI is calculated: 420 HSI =-2r x 100 E,. and E,,.x may be computed by means of the equations given on pg. 274. A more convenient means is offered by a nomogram developed by McKarns and Brief’ (Figure 31-6). This nomo- gram is based on further revisions of the Fort Knox coefficients, which provide a 30 percent re- duction in R, C, and E,,, for the average man wearing light work clothing. The following equa- tions were used in the nomogram development: R=17.5 (T,—95) C=0.756 V** (T,—95) E..x=2.8 V" (42—PW,) where R = Radiant heat exchange, Btu/hr C = Convective heat exchange, Btu/hr E.... = Max exaporative heat loss, Btu/hr T. =Mean radiant temp. °F T, = Air temp. °F V = Air velocity, ft/min. PW, = Vapor press, mmHg. Caution: The original nomogram of Belding and Hatch is being widely reproduced in texts and handbooks even today, in spite of the availability for more than a decade of these revised coefficients. The sample solution outlined below and shown in Figure 31-6 illustrates the use of the nomo- gram. Example: Given T,=130°F, T,=100°F, T.,=80°F, V=50 ft/min, and M=2000 Btu/hr. Step 1. Determine convection. Connect 50 fpm (column I) with T,=100°F (column II). Read C=40 Btu/hr (column III). © Step 2. Determine E,,.,. From the psychro- metric chart (Figure 31-3), read dew point of ~~ 73°F from dry and wet bulb temperatures.’ Connect column I and column IV from V=50 to dew point=73 (line 2). Read E,..=620 (column V). Wh Step 3. Determine constant, K. Connect V=50, column I, with T,—T, (130-100) = 30, Column VI. Read K=22 (column VII). Step 4. Determine T,. Enter K=22 in lower diagram, column VII. Connect this to T,=130, column VIII. Read T,=155, col- umn IX. Step 5. Follow the slanting line to column X, read R=1050 Btu/hr. Step 6. Connect R=1050 with M =2000 (column XI); read R+M=3050 on column XII. Step 7. Enter C=30 in column III of lower figure; connect with R+M=3050, in column XII, read E,.,=3090 Btu/hr on col- umn XIII. Step 8. Enter E,,,=620 (step 2) on column V of lower diagram, and connect with E..,=3090 Btu/hr, column XIII. Read al- lowable exposure time =6 min. Air Evaporation Convection Dew point Air Temperature velocity, available {C), temperature, o.oo ature difference fpm (Emax) Buh F yn (1g - is) Btuh K F F (max of 2400) ¥ 140 S00 4501 (=1000) T% 1130 3 wf Foo } ser L70 (04120 FeO 3004+ +50 7 gagns f 7) 2504+ L 80 225 82 (80) 110_ot 30 2001 84 - 180 2 - ta le01 ¢ [ ©s5)4 10s 140 88 (86) 104 T15 (87) 103 120 ~~ fz} Loo 1 10 1004 Vo gl (89)+101 8.0 9 ~~ 91 a (90)- 100 _ pe 80 ~~ — - ; 6.0 70 - 125 92 (Mm199 5.0 ~~ a— — — — 4.0 g = —— (92498 55 | go —— 3.0 50 2 2.5 45 pry (93)497 2.0 35 1.5 30 9% +1.0 2 Broken lines indi- (94)L 9s cate solution to example in text. I Broken lines and also columns are ~ n o numbered to indicate steps in the solution, Radiation Wall Metabolism Evaporation Allowable Metabolism Convection Evaporation (R), temperature and Globe required exposure (M), (€), available, Btuh (tw), radiation, temperature (E eq), time, Btuh Buh (Emax), K F Btuh (tg), F Bru minutes Buh 5250 , T2500 T1500 2-1/4 | 0x 5000+ 2400 $1400 +0 4750 2-1/2 2300 11300 7 4500+ 2-3/4 2200 1200 200 4250 2100 1100 “0 «000+ ample TI st : 1900 900 600 3750 5 4500 ~~ 4 _—] 35004 1800 800 800 s04 J 5 1700 ra r +1000 30004} A 1500 600 +1 4 “wt 27501 0 0 1200 2500+ ~~ + 1400 400 L 1300 300 1400 wt 22504 “i 1200 1200 a ~- a— 000 30 ~~ 1600 Boos 20 1100, 100 20% 17501 120 tio Yo 1800 15001 [900 =i 42000 10} 1250 | 800 -200 10001 700 -300 2200 = 1 0 400 2400 500-- Lsoo 1-300 ya XX X XI VII XII IZ XI om xX McKarns, J. S., Brief, R. S.: Nomographs give refined Sytinss of heat stress index. Heat Pip. Air Condit. 38:113, 966. Figure 31 -8. Nomograph Developed by McKarns & Brief Incorporating the Revised Fort Knox Coefficients. 421 ©° o « Q 3 7 z 6 3 ad 2 34 ° £] ° 128 al <0 50 100 150 200 MET RATE C/M2/Hr. WET BULB TEMPERATURE °F ~ 80 McArdle, B., Dunham, W., Holling, H. E., et al: Med. Res. Coun. R.N.P. Rep. 47:391, 1947. Figure 31-7. Nomogram for the Prediction of the 4-Hour Sweat Loss of Fit, Acclimatized Young Men, Sitting in Shorts. The small inset chart gives the degrees F to be added to the wet bulb for metabolic rates between 50-100K Cals/m?2/Hr. 422 Computation of the HSI value yields: 3090 " HSI === X 100 = 500. In their original paper, Belding and Hatch pre- sented physiologic interpretations for various levels of HSI (Table 31-1). As can be seen, 500 greatly exceeds the maximum strain tolerable. The addition by McKarns and Brief of tolerance times for HSI’s in excess of 100 is a valuable contribu- tion. Predicted Four Hour Sweat Rate (P,SR). McArdle et al." developed a heat stress rating scheme based upon the sweat loss (in liters) that different environmental conditions would evoke: hence, the name “Predicted Four Hour Sweat Rate.” Figure 31-7 is the latest version of the nomogram, incorporating the effects of clothing and level of activity. TABLE 31-1. Evaluation of Values in Belding and Hatch HSI. Index of Physiological and Hygienic Implica- Heat Stress tions of 8-hr. Exposures to Various (HSI) Heat Stresses —20 Mild cold strain. This condition fre- —10 quently exists in areas where men re- cover from exposure to heat. 0 No thermal strain. +10 Mild to moderate heat strain. Where 20 a job involves higher intellectual func- 30 tions, dexterity, or alertness, subtle to substantial decrements in performance may be expected. In performance of heavy physical work, little decrement expected unless ability of individuals to perform such work under no ther- mal stress is marginal. 40 Severe heat strain, involving a threat 50 to health unless men are physically 60 fit. Break-in period required for men not previously acclimatized. Some decrement in performance of physical work is to be expected. Medical se- lection of personnel desirable because these conditions are unsuitable for those with cardiovascular or respira- tory impairment or with chronic der- matitis. These working conditions are also unsuitable for activities re- quiring sustained mental effort. 70 Very severe heat strain. Only a small 80 percentage of the population may be 90 expected to qualify for this work. Per- sonnel should be selected (a) by med- ical examination, and (b) by trial on the job (after acclimatization). Spe- cial measures are needed to assure adequate water and salt intake. Amel- ioration of working conditions by any feasible means is highly desirable, and may be expected to decrease the health hazard while increasing effi- 423 ciency on the job. Slight “indisposi- tion” which in most jobs would be insufficient to affect performance may render workers unfit for this exposure. 100 The maximum strain tolerated daily by fit, acclimatized young men. Adapted from Belding and Hatch, “Index for Evaluating Heat Stress in Terms of Resulting Physiologic Strains,” Heating, Piping and Air Conditioning, 1955. Example: Given Globe temperature=105°, wet bulb=80°, air speed=70 fpm, and me- tabolic rate (M)=100 kcal/m*=hr. From the small chart, find 4°F to be added to wet bulb to compensate for M above resting. En- ter right side of chart at T,,=84 (80+4). Follow 84 T,, line to intersection with 70 ft/min line. Connect this point with thread or straightedge to T,=105. Read P,SR where this transverse line cuts air speed = 70; read P,SR=1.2. This would result in rela- tively mild physiologic strain, as the upper limit of tolerance for fit, young men is about P.SR=4.5. Note that the chart is for men dressed in shorts. The index becomes less accurate in predicting strain as the upper level of tolerance is reached. Extrapolation to populations other than the standard “fit, young, acclimatized male” must be done with caution. Wet Bulb Globe Temperature Index (WBGT). This index was developed originally to provide a convenient method to assess, quickly and with minimum of operator skills, conditions which posed threats of thermal overstrain among military personnel.>” Because of its simplicity, it has been adopted as the principal index for a tentative , Threshold Limit Value (TLV) for heat stress (Figure 31-8) by the American Conference of Governmental Industrial Hygienists (ACGIH)*' Fundamentally, the WBGT index is an algebraic approximation of the E.T. concept. As such, it has all the built-in limitations of the E.T., but has the advantage that wind velocity does not have to be measured for calculating its value. WBGT is computed by appropriate weighting of Vernon Globe (T,), dry bulb (T,), and natural wet bulb (T,.,) temperatures. The natural wet bulb is depressed below air temperature by evap- oration resulting only from the natural motion of the ambient air, in contrast to the thermodynamic wet bulb, which is cooled by an artificially pro- duced fast air stream, thus eliminating the air movement as a variable. For outdoor use (in sunshine) the WBGT is computed: WBGT=0.7 (Taw) +0.2 (Ty) +0.1 (TD). For indoor use, the weighting becomes: WBGT=0.7 (Tw) +0.3 (T}). Originally the interpretation of the levels of WGBT was for military activities of recuits in the following manner: above 30°C (86°F) WBGT, activities to be curtailed; above 31°C (88°F) WBGT, suspended entirely. For those in the latter stages of training, and hence acclimatized to WBGT °C 35 30 251 ¢ LEGEND: L —— continuous work 7 tte 75% work 25% rest each hour —-— 50% work 50% rest each hour =--— 25% work 75% rest each hour yy 100 200 300 400 500 Kceal./ hr. | | | | 400 800 1200 1600 2000 BTU/ hr. light | moderate | heavy | work work work American Conference of Governmental Industrial Hygienists: Cincinnati, Ohio, 1971. Figure 31-8. Permissible Heat Exposure Threshold Limit Value. 424 40 198M the heat, the levels are 31.0° and 32.2°C (88° and 90°F), respectively. INTEGRATING INSTRUMENTS Many attempts through the years have been made to devise instrumentation for assessing simultaneously the four environmental factors of air temperature, air speed, humidity, and radiant temperature. One unit of this type, the modified Envirec was developed under a NIOSH contract. This instrument senses, indicates, and records on either magnetic tape or strip chart, the dry-bulb, thermo- dynamic wet-bulb and globe temperatures, and air velocity. Another useful instrument, the WBGT inte- grator was developed under another NIOSH con- tract. This instrument senses and indicates dry- bulb, natural wet-bulb, and globe temperatures. It will also integrate these measurements and give a direct readout of the WBGT Index for either sunlit or inside conditions in accordance with the previously stated equations. Instruments for inte- grating two or more parameters into a single read- ing include the Vernon globe discussed above; the globe temperature is used directly in the Corrected Effective Temperature of Bedford.** Also, the globe temperature, in conjunction with natural wet Botsford, J. H.: A wet globe thermometer for environ- mental heat measurement. Amer. Ind. Hyg. Assoc. J. 32:1-10, 1971. Botsford — A Wet-Globe In- strument ‘‘Botsball’. Figure 31-9. 425 bulb temperature, forms the basis of the WGBT Index discussed above. More recently, Botsford? has developed a wet- globe instrument based on a small (6-cm diam- eter) copper sphere fitted with a black cotton wick and water reservoir (Figure 31-9). While the Vernon globe integrates the effects of air tem- perature, mean radiant temperature and air mo- tion, wetting of the sphere introduces the fourth parameter. The device is maintained completely wet; man is not 100% wet unless E, x is low (see Chapter 38). The objective desired is that the stress readings obtained with the “Botsball” will correlate sufficiently well with physiologic strain that a given “Botsball” reading will have the same physiologic meaning in all combinations of en- vironmental parameters. The instrument has not been available long enough to determine whether this objective will be achieved, although, replac- ing the WBGT with the “Botsball” would be de- sirable because of its simplicity. The “Botsball” has a more advanced variant: the Botsball Cooling Capacity Meter. By addition of a heat source in the wet ball a constant 35°C surface temperature is maintained, to simulate hu- man skin temperature. The associated electronics translate the current required to maintain this temperature into a meter readout, either in terms of Cooling Capacity Index, with a range from 0 to 100, or in terms of cooling power expressed in watts or Btu/hr. Battery-powered or 110 AC models are available (see Appendix for man- ufacturer). This sophistication exacts a price: an order of magnitude greater in cost and loss of simplicity. The physiological meaning of the cool- ing power values obtained with this instrument will have to be established before its applicability can be evaluated. GUIDE FOR ASSESSING HEAT STRESS AND STRAIN For purposes of validating the applicability of the ACGIH TLV for heat stress as an index for establishing thermal standards NIOSH spon- sored a symposium. The participants of this symposium were asked to gather data in in- dustry by using a standard methodology based on the TLV requirements and described in the Guide for Assessing Heat Stress and Strains as prepared by Minard and Belding.>* Several indus- tries agreed to follow the procedures outlined to provide a substantial body of data for evaluating the tentative TLV. An instrumentation package consisting of the following instruments was recommended: 2 Bendix Hygro Thermographs Model 594; range +10° to +110°F 1 Bendix Psychron; range + 30° to +120°F 1 Botsford Wet-Globe Thermometer I Six-inch Globe Thermometer; range about 50° to 212°F I Natural Wet Bulb Thermometer; range about 20° to 100°F 1 Hot Wire Anemometer for measurement of air velocity. MERCURY THERMOMETER CA 20-100°F BOTSFORD WET - GLOBE > THERMOMETER —__—— 30-120°F = ~ THERMOMETER BULB 48" ABOVE FLOOR SUPPORT PLATE CA 24"x 6"x 1/4" 172-13NC “- p= 1/74 -20NC 125ml FLASK WITH DISTILLED WATER MERCURY THERMOMETER +» CA 50-2I2°F ONE-HOLE ~~ CORK STOPPER XI /2" COPPER TUBING, SOLDERED TO GLOBE 6" COPPER SHELL PAINTED MATTE BLACK 3/16 ROD »10- 32 NC THREAD or Minard, D., Belding, H. S.: Guide for Assessing Heat Stress and Strains. Industrial Health Foundation, Inc., En- gineering Ser. Bull. No. 8-71, 1971. Figure 31-10. One Hygro Thermograph records weather con- ditions outside the plant; the other is used as a reference monitoring station at a representative area within the plant. The Vernon globe and natural wet bulb are mounted together on a tripod for stationing at selected work sites (Figure 31-10). The Botsball is also shown in this arrangement, to encourage comparability studies. The psychrometer is used to take spot mea- surements of dry and (thermodynamic) wet bulb temperatures so that HSI or P,SR may be calcu- lated as well as WBGT. Sample data sheets are also provided so that information submitted by the diverse industries participating will be in com- parable form. The outcome of the pooled data will provide validation and/or modification of the tentative TLV so that an effective and fair stan- dard for heat stress may be written. WINDCHILL INDEX In recent years, it has become fashionable for weather reporters on radio and television to in- 426 Suggested Instrument Arrangement for Environmental Measurements. clude the Windchill factor. This index was devised by Siple** to assess the relative discomfort of cold in relation to the air temperature and wind speed. The basic concept recognizes that convection is the most important single avenue of heat loss under cold conditions. The Windchill effect can be read from Table 31-2 where it is expressed in equivalent air temperatures which achieve the same rate of cooling at different wind velocities. Example: Given T,=45°F and wind of 20 mph, read equivalent temperature = —27°F (at 0 mph). Note that equivalent tempera- tures are given for exposed flesh. Windchill values around 30°F are “cool;” — 10°F, “cold;” below —40°F, exposed flesh freezes quickly and “travel is dangerous.” SUMMARY The philosophy and development of indices for rating severity of the thermal environment has been discussed. The methods of assessment of the several parameters involved in the indices and guidance for their application and interpretation have been provided. Temperature, °F TABLE 31-2. Equivalent Temperatures on Exposed Flesh at Varying Wind Velocities Wind velocity, mph 0 1 2 3 5 10 15 20 25 23 47.5 53.5 57 60 65 67 68 69.5 —11 20 34.5 39 44.5 52 55 57 59 -27 0 11 18.5 28 38 42.5 45 47 —38 -235 = 9 0 11 25 30.5 34 36 —40* —40* —40 -165 — 5 11 18 23 25 —40* —40 -19 - 2 6 11 14 —40* -35 -15 - 6 0 3 —40 —29 —18 -12 - 8 —40* —40 —-30 —23 —18 —40* —40 —-35 -30 —40* —40* —40* tAdapted from Consolazio, Johnson and Pecora, Physiologic Measurements of Metabolic Functions in Man, McGraw- Hill Book Company, New York, 1963. *Less than value. References 1. MACHLE, W. and T. F. HATCH. “Heat: Man's Exchange and Physiological Responses.” Physiol. Rev. 27:200-227, 9650 Rockville Pike, Bethesda, Maryland 20014 (1947). HATCH, T. F. “Assessment of Heat Stress.” In Hardy, J. D. (Ed.) Temperature: Its Measurement and Control in Science and Industry. Vol. 3, pt. 3, 307, Reinhold, New York (1963). POWELL, R. W. Trans. Inst. Chem. Engrs. (Lon- don), 18:36, (1940). Quoted by Nelson, N., Eichna, L. W., Horvath, S. M., Shelley, W. B., and Hatch, T. F.: “Thermal Exchanges of Man at High Tem- peratures.” Am. J. Physiol. 151:626, 9650 Rockville Pike, Bethesda, Md. 20014 (1947). HAINES, G. F., Jr. and T. F. HATCH. “Industrial Heat Exposures—Evaluation and Control.” Heating and Ventilating, London (Nov. 1952). TEUTSCH, W. B. “Basic Physics of Thermoelectric Effects.” In Egli, P. H. (Ed.) Thermoelectricity, John Wiley, New York (1960). YAFFE, C. D,, D. H. BYERS and A. D. HOSEY (Eds.) Encyclopedia of Instrumentation for Indus- trial Hygiene. Ann Arbor, University of Michigan (1956). HILL, L. “The Science of Ventilation and Open Air Treatment.” Part I, Med. Res. Coun. Spec. Rept. No. 32, London (1919). MADISON, R. D. (Ed.) Fan Engineering, 5th ed., Buffalo Forge Co., Buffalo, New York (1949). MARVIN, C. F. Psychrometric Tables for the Ob- taining of Vapor Pressure, Relative Humidity, and Temperature of the Dew Point. U.S. Dept. of Com- merce, Weather Bureau, Washington, D. C. (1941). VERNON, H. M. “The Measurement of Radiant Heat in Relation to Human Comfort.” J. Physiol. 70, Proc. 15, (1930). FANGER, P. O. Thermal Comfort. nical Press, Copenhagen (1970). Danish Tech- . GAGGE, A. P. “Effective Radiant Flux, an Inde- pendent Variable that Describes Thermal Radiation on Man.” In Hardy, J. D., Gagge, A. P., and Stol- wijk, J. A. J. (Eds.) Physiological and Behavioral 20. 21. 22. 427 Temperature Regulation. Chapter 4, Charles C. Thomas, Springfield, Ill. (1970). LONGLEY, M. Y., R. L. HARRIS, JR., and D. H. K. LEE. “Calculation of Complex Radiant Heat Load from Surrounding Radiator Surface Tempera- tures.” Amer. Indust. Hyg. Assoc. J. 24:103-112, 66 South Miller Rd., Akron, Ohio (1963). BELDING, H. S. “The Search for a Universal Heat Stress Index.” In Hardy, J. D., Gagge, A. P. and Stolwijk, J. A. J. (Eds.) Physiological and Behav- ioral Temperature Regulation. Chapter 14, Charles C. Thomas, Springfield, Ill. (1970). . GIVONI, B. Man, Climate, and Architecture. Else- vier, London (1969). HOUGHTON, F. C. and C. P. Yaglou. “Determin- ing Lines of Equal Comfort.” J. Am. Soc. Heat. and Vent. Engrs. 29:165-176 (1923). BELDING, H. S. and T. F. HATCH. “Index for Evaluating Heat Stress in Terms of Resulting Phy- siological Strain.” Heat Pip. Air Condit. 27:129, Keeney Pub. Co., 6 N. Michigan Ave., Chicago, Ill. (1955). McKARNS, J. S. and R. S. BRIEF. “Nomographs Give Refined Estimate of Heat Stress Index.” Heat Pip and Air Condit. 38:113, Keeney Pub. Co., 6 N. Michigan Ave., Chicago, Ill. (1966). McARDLE, B., W. DUNHAM, H. E. HOLLING, W.S.S.LADELL, J. W. SCOTT, M.L. THOMSON, and J. S. WEINER. “The Prediction of the Physio- logical Effects of Warm and Hot Environments: the P.SR Index.” Med. Res. Coun. R. N. P. Rep. 47:391, London (1947). YAGLOU, C. P. and D. MINARD. “Control of Heat Casualties at Military Training Centers.” Arch. In- dust. Health 16:302-316 (1957). TLV’s. Threshold Limit Values for Chemical Sub- stances and Physical Agents in the Workroom En- vironment with Intended Changes for 1972. Am. Confer. of Gov. Indust. Hygienists, 1014 Broadway, Cincinnati, Ohio (1972). MINARD, D., H. S. BELDING and J. R. KING- STON. “Prevention of Heat Casualties.” J.A.M.A. 165:1813-1818, 535 N. Dearborn, Chicago, III. (1957). 23. BEDFORD, T. “Environmental Warmth and Its Measurement.” Med. Res. Coun. War Memo No. 17, London, HMSO (1946). 24. BOTSFORD, J. H. “A Wet Globe Thermometer for Environmental Heat Measurement.” 4.1.H.A. J. 32:1-10, 66 South Miller Rd., Akron, Ohio (1971). 25. MINARD, D. and H. S. BELDING. “Guide for As- sessing Heat Stress and Strains.” Industrial Health Foundation, Inc. Engineering Ser. Bull. No. 8-71 (1971). 26. SIPLE, P. A. and C. F. PASSEL. “Dry Atmos- pheric Cooling in Subfreezing Temperatures.” Proc. of the Am. Philosophical Society 89:177-199 (1945). 27. LIND, A. R. “Tolerable Limits for Prolonged and Intermittent Exposures to Heat.” In Hardy, J. D. (Ed.) Temperature: Its Measurement and Control in Science and Industry, Vol. 3, pt. 3, 337, Reinhold, New York (1963). 28. NIELSEN, M. “Die Degulation de Korpertempera- tur bei Muskelarbeit.” Skand. Arch. Fur Physiologie 79:193 (1938). 29. WYNDHAM, C. H.,, W. M. BOUWER, H. E. PATERSON and M. G. DEVINE. “Practical As- pects of Recent Physiological Studies in Witwaters- rand Gold Mines.” J. Chem. Met. Min. Soc. So. Africa 53:287 (1953). 30. Criteria for a Recommended Standard Occupational Exposure to Hot Environments. U.S. DHEW, HSMHA, NIOSH, HSM-72-10269. (1972). NIOSH Note The TLV diagram (Figure 31-8) combines three basic parameters: metabolic demands of the task (abscissa), an index of severity of the en- vironment (WBGT), and percentage of time that the individual may be permitted to perform the task. For example, a task requiring light to mod- erate light work of 200 kcal/hr, could be per- formed continuously in environments up to about WBGT=30°C, but only 25% of the time at WBGT =34°C. A heavier task, say 400 kcal/hr, could be performed in environments of WBGT only up to about 26°C. This recognizes the role played by metabolic heat production in the heat balance equation (see Chapter 30); a simple method for assessing this parameter can be found in the TLV text.>’ The basis for development of the TLV has been on the one hand the experi- ences of the services in protecting troops in train- ing against heat illness,*” and on the other hand, consideration of combinations of environments which do not cause deep body temperatures (Tore) to rise above 38°C (100.4°F); these were determined by Lind and were identified as the “Prescriptive Zone.”*" As is evident in Figure 31-11, the equilibrium level of deep body tempera- ture is dependent on the intensity of exercise, and independent of environment — up to a point. This effect was first noted by Nielson.>* The family of curves suggest that at the inflection points the en- vironmental stress has taxed the thermoregulatory system to its limit of thermal equilibrium at ac- ceptable levels is no longer possible. The philoso- phy applied in the TLV is that the environmental 101 + o lo a Ss A pH 4 100 + i o 8) w oc fe 99 + 50 60 70 8 90 EFFECTIVE TEMP. °F Lind, A. R.: Tolerable limits for prolonged and intermittent exposures to heat in Hardy, J. D. (ed): Temperature: Its Measurement and Control in Science and Industry. New York, Reinhold, 1963, vol. 3, p. 337. Figure 31-11. Levels of Rectal Temperature during Continuous Work at 100 Kcal/m2/hr (o), 167 Kcal/m*/hr (0) or 233 Kcal/m*/hr (4). At each rate of work there is a wide range of conditions in which the level of rectal temperature equilibrium is constant or nearly constant. 428 stress should not create a rise in deep body tem- perature over that in response to the work itself. This concept was also considered as most appro- priate for the protection of the workers’ health by an international scientific panel of the World Health Organization. Others have argued that daily demands on the body for temperature increases above the Prescrip- tive Zone have no deleterious effects. Indeed, in some industrial uses the upper limits of thermal stress are based on elevations of body tempera- tures rather than on environmental parameters.’ Application of the heat stress indices to hot industries has been attempted, not without some difficulties. Where the heat exposure is relatively uniform and lasts for prolonged periods e.g., mili- tary marching, driving an earthmoving vehicle, tending a weaving machine, the assessment of climatic and metabolic parameters is relatively simple. However, industries where duration of specific tasks may be measured in seconds, requir- ing maximal effort one minute, and minimal the next, and the environment may switch from intense radiant heat next to hot metal to ambient condi- tions of winter a few feet away, the assessment of the workers’ actual heat exposure becomes quite cumbersome. Under such conditions, a detailed time and motion analysis of the work has to be performed and time weighted averages have to be calculated both for the climatic exposure and work load. 429 Research is currently underway at NIOSH to provide simpler and more accurate methods for assessing WBGT values, as well as the metabolic demand of the task. APPENDIX Sources of Environmental Instrumentation Thermocouple wire: Driver-Harris, N.J., Leeds and Northrup, 4901 Stenton Ave., Philadelphia, Pa.; Revere Corp. of America, Wallingford, Conn. Thermistor thermometer: Yellow Springs Instrument Company, Yellow Springs, Ohio (Manufacturer. Avail- able only through scientific apparatus supply houses.) Sling psychrometer: Taylor Instrument Company, 95 Ames St., Rochester, N.Y. Motor-driven psychrometer: The Bendix Corp., En- vironmental Science Division, 1400 Taylor Ave., Balti- more, Md.; C. F. Casella Company, Ltd., Regent House, Fitzroy Square, London W.1, England. Hair hygrometer, recording: The Bendix Corp., En- vironmental Science Division, 1400 Taylor Ave., Balti- more, Md. Thermoanemometers: Alnor Instrument Co., 420 N. LaSalle St., Chicago, Ill.; Anemostat Corp. of America, P.O. Box 2128, Hartford, Conn.; Willson Products Div., The Electric Storage Battery Co., Reading, Pa. Kata thermometer: C. F. Casella and Co., Ltd., Re- gent House, Fitzroy Square, London, W.1, England. Vernon globe: (6-inch hemispherical spun copper blanks) Arthur Harris and Co., 212 N. Aberdeen St., Chicago, 111. Botsball thermometer: Howard Engineering Co., Box 3164, Bethlehem, Pa. I a a Trt CR SUR Te . v a - 2 } =a RR TR PT ey a ) : ET ; . Corsi SESE a L CHAPTER 32 ERGONOMIC ASPECTS OF BIOMECHANICS Erwin R. Tichauer, Sc.D. INTRODUCTION Biomechanics is the discipline dedicated to the study of the living body as a structure which can function properly only within the confines of both the laws of Newtonian Mechanics as well as the biological laws of life. Bomechanics is by no means a new pursuit. The mechanics of locomo- tion of many animals and birds were researched in depth as early as during the 17th century by Borelli." In the course of the next century, Berno- uilli* published a treatise on the “physiomechan- ics” of muscle movement. A contemporary of Ber- nouilli, Bernardino Ramazzini,* the father of oc- cupational medicine, discussed in his book “De Morbus Artificum” (about the diseases of work- ers) in remarkable detail the ill effects of poor posture and poorly designed tools on man. In the preface to the 1700 edition of his text he writes *“... Manifold is the harvest of diseases reaped by certain workers from the crafts and trades that they pursue; all the profit they get is injury to their health. That stems mostly I think, from two causes. The first and most potent is the harmful character of the materials that they handle, nox- ious vapors and very fine particles, inimical to human beings, inducing specific diseases. As the second cause I assign certain violent and irregular motions and unnatural postures of the body, by reason of which the natural structure of the living machine is so impaired that serious diseases grad- ually develop therefrom . . .” For nearly two centuries industrial hygiene and related disci- plines limited their scope of interest to the first set of occupational disease vectors as discussed by Ramazzini. They were easily identified and in many instances amenable to control by pro- cedures already then available to industrial hy- gienists. Simultaneously, however, positive and aggressive steps were taken to develop energetic- ally other fields of scientific endeavor basic to the maintenance of occupational safety and health. An unbroken chain of endeavors by physicists and physiologists since Lavoisier* provided the basic data necessary to develop metabolic studies and" ergonometry into reliable procedures, applicable to the measurement of effort expended by man at work. The publications of Benedict and Cathcart’ in 1913 and of Amar® in 1917 are among the first acquainting practitioners in industry with the ap- plication of ergometry to work measurement. Towards the end of World War I, the general interest in work physiology widened and deepened in the United States, Britain, France and Ger- © 431 these countries to forego their rather sheltered vic- torian style of life and to accept employment in ammunition factories and other occupations that up to then had been considered distinctly unfemi- nine. They performed jobs strange to them in an environment they had never known before; emo- tional and physiological considerations caused problems in efficiency, hygiene and safety, which in turn stimulated research, especially as related to the effects of heat” as well as light on both output and physical comfort of workers. By the end of the hostilities, both work physi- ology as well as industrial psychology had become firmly established albeit quite separate disciplines. The events of World War II and their social and economic after-effects gave impetus to the consolidation of a number of narrow specialties into a broad, unified and generally accepted sep- arate discipline dedicated to the academic as well as the applied study of man at work: Ergonomics. Also, the Ergonomics Research Society was founded in England. Its membership developed rapidly on a world-wide basis. However, in the immediate post-war years the practice of ergo- nomics was of prime importance to European countries where, as a matter of economic survival, consumer goods industries had to be rebuilt fast. Their working population was still untrained in the use of modern technology that had meanwhile developed in the United States. Workers were also generally undernourished and worn out from years of struggle and many of them were physi- cally handicapped. Thus, ergonomics was first ap- plied to overcome the serious and general prob- lems involved in fitting jobs to the physical and behavioral operating characteristics of individual workers. This involved a broader study of the relationship between man and his environment, the design of equipment and particularly the appli- cation of anatomical, physiological and psycho- logical knowledge to the solution of problems arising from equipment and environment. This new systems approach to problems common to occupational safety and health as well as indus- trial efficiency required new and deeper under- standing of the mechanics of the living body at work. .* * Occupational Biomechanics was added as a new tributary to the pool of general knowledge essen- trial to the understanding of the complex mecha- nisms of interaction between the worker and the industrial environment. The industrial environment as opposed to . work environment (including, e.g., farming) is many. Dire manpower needs forced the wortien of . - unique in several aspects. Firstly, it is entirely man-conceived, man-made and purposefully de- signed with one objective in mind: to maximize economic efficiency of human performance. Phys- iological performance and comfort of the working population, at least until recently, were only con- sidered inasmuch as they were conducive to higher levels of productivity. Thus, by implica- tion, those who are responsible for the mainte- nance of occupational safety and health have to overcome many biomechanical, physiological and behavioral hazard vectors likely to be overlooked in the design of the industrial environment. It is the purpose of this chapter to describe occupational biomechanics as a subdiscipline of ergonomics which can be applied by professionals active in the health as well as technological sci- ences for the purpose of achieving maximal phys- iological and emotional well-being of the working population, while at the same time enhancing the economic efficiency of industrial undertakings as a whole. In our modern industrial environment ef- ficiency is a by-product of comfort. The enterprise that manufactures no sore backs, shoulders, wrists or behinds is at a competitive advantage over one with suffering workers.'" The information provided in this chapter will be adequate for a general biomechanical evalua- tion of workplaces, machinery, handtools, chairs, lifting tasks and industrial work situations in general, = LS AL Ye TNE KJ] PPL RE — The Ergonomics Research Society: The Origin of Ergonomics. Loughborough, England, Echo Press, 1964. Figure 32-1. Illustration symbolizes the concept of modern ergonomics (biomechanics). Worker .is surrounded by external physiological and mechanical environments which have to be matched to his internal physiological and biomechanical environments. 432 THE ANATOMY OF FUNCTION Anatomy is concerned with the description and classification of biological structures. Syste- matic anatomy describes the physical arrangement of the various physiological systems (e.g., anatomy of the cardiovascular system); topographic an- atomy describes the arrangement of the various organs, muscular, bony and neural features with respect to each other (e.g., the anatomy of the abdominal cavity); and functional anatomy fo- cuses upon the structural basis of biological func- tion (e.g., description of the heart valves and an- cillary operating structures, description of the an- atomy of joints). As distinct and different from the aforementioned, the anatomy of function is concerned with the analysis of the operating char- acteristics of anatomical structures and systems when these interact with physical features of the environment such as is the case in the performance of an industrial task. Modern occupational bio- mechanics considers the worker as the monitoring link of a man-equipment-task system. In such a situation, man is enveloped by the “external me- chanical environment” (Figure 32-1) which is an array of machinery, levers, pushbuttons, and such other equipment as may pertain to the immediate working environment of the individual. Located inside of the human skin is the “internal biome- chanical environment” which may be presumed, at the risk of oversimplification, to be identical with the neuro-musculo-skeletal system. If the “motions and reactions inventory” demanded by the external environment is not compatible with the one available from the internal biomechanical environment, then discomfort, trauma and ineffi- ciency may ensue. The anatomy of function is the structural basis of human performance and thus provides much of the rationale by which the output mea- surements derived from work physiology and en- gineering psychology can be explained. Lever Systems Within the Human Body The musculo-skeletal system is an array of bony levers connected by joints and actuated by muscles. With few exceptions, lever classifications and taxonomy in both anatomy and applied me- chanics are identical. Each class of anatomical lever is specifically suited to perform certain types of movement and postural adjustments efficiently and without undue risk of accidents while it may be less suited to perform other equally specific maneuvers. Therefore a good working knowledge of location, function and limitation of anatomical levers involved in specific occupational maneuvers is a prerequisite essential for the ergonomic an- alysis and evaluation of most man-task systems. First Class Levers have force and load located on either side of the fulcrum acting in the same direction but opposed to any force supporting the fulcrum (Figure 32-2). This is exemplified by the arrangement of those musculo-skeletal structures as are involved in head movement in looking up and down. Then the atlanto-occipital joint acts as the fulcrum of a first class lever because the mus- cles of the neck provide the force necessary to extend the head. This is counteracted by gravity 433 FULCRUM Figure 32-2. The action of the muscles of the neck against the weight of the head is an example of a first class lever formed by ana- tomical structures. The atlanto-occipital joint acts as a fulcrum. acting on the center of mass of the head which is located on the other side of the joint, and hence constitutes an opposing flexing weight. First class levers are often found where fine positional ad- justments are required. In standing or the static holding of bulky loads, head movement in the midsagittal plane produces the fine adjustment of the position in the center of mass of the whole body necessary to maintain upright posture (Figure 32-3). Individuals suffering from impaired head movement (e.g., arthritis of the neck), should not be exposed to tasks where inability to maintain postural equilibrium constitutes a substantial haz- ard. Likewise, workplaces where free and unre- stricted head movement is difficult should be pro- vided with either chairs or other means of postural stabilization. Second Class Levers have the fulcrum located at one end, the force acts upon the other end but in the same direction as the supporting force of the fulcrum. The weight acts upon any point be- tween fulcrum and force in a direction opposed to both of them. Second Class Levers are opti- mally associated with ballistic movements requiring some force and resulting in modifications of stance, posture or limb configurations. The muscles in- Tichauer, E. R.: Ergonomics: The state of the art. Figure 32-3. Amer. Ind. Hyg. Assoc. J. 28:105-16, 1967. Myograms of the Sacrospinalis Muscle during a Lifting Task. It can be seen how activity in this muscle varies according to posture. (A) upright posture showing electro- silence in muscle. (B) failure to hold head upright in straight-back, bent-knee lift results in strong postural reactions recorded by the myogram. (C) straight-knee, bent-back lift, showing high strain in sacro-spinalis muscle. (D) straight-back, bent-knee, head-up lift, showing less stress in sacro-spinalis muscle.® serted into the heel by way of the achilles tendon (i.e., force), the weight of the body transmitted through the ankle joint, and the base of the big toe (i.e., fulcrum) are a good example of a sec- ond class lever system used in locomotion (Figure 32-4). Third Class Levers have the fulcrum at one end, the weight acts upon the other end, in the same direction as the supporting force of the ful- crum. The “force” itself acts upon any point be- tween weight and fulcrum but in a direction op- posed to both of them. Tasks which require the application of strong but voluntarily graded force are often best performed by this type of anatom- ical lever system. Holding a load with forearm and hand when the brachialis muscle acts upon the ulna with the elbow joint constituting the pivot is a typical example (Figure 32-5). Torsional Levers are a specialized case of the Third Class Lever (Figure 32-6). Here the axis of rotation of a limb or long bone constitutes the fulcrum. The force-generating muscle of the sys- tem is inserted into a bony prominence and pro- duces rotation of the limb whenever the muscle contracts. The “weight” is constituted by the in- 434 ertia of the limb plus any external torque oppos- ing rotation. An example is the supination of the flexed forearm. Here the fulcrum is the longitud- inal axis of the radius, the force is exerted by the biceps muscle inserted into the bicipital tuberosity of the radius while the opposing load may be the inertia of forearm and hand plus the resistance of, for example, a screw driven home. Tasks to be performed with strength and precision and at variable rates of speed are best assigned to tor- sional lever systems. An inexpensive anatomical atlas for artists constitutes a useful aid in task analysis and design whenever an evaluation of the effectiveness of the anatomical lever systems employed is under consideration. Range and Strength of Limb Movement The absolute range of limb movement is lim- ited by the mechanical configuration of the joints. For example, due to interference of the olecranon, it is impossible to extend the angle between fore- arm and upper arm beyond 180°. Likewise, the location of the point of insertion of the brachialis tendon into the ulna makes it impossible to flex the joint to an angle of less than 15°. This re- FULCRUM Figure 32-4. The Ankle Joint, as an Exam- ple of an Anatomical Second Class Lever Sys- tem. The fulcrum is located at the base of the big toe. sults in a total range of 165°. In occupational biomechanics, however, not the total but only the 435 effective range of movement is of significance (Figure 32-7). Muscles behave like extension springs. They can exert no force when fully con- tracted and exert maximal force when fully ex- tended. Between these two states, potential force varies linearly as a degree of extension. Further complexities are introduced into the system be- cause the “mechanical advantage” to which it can be applied varies with the degree of joint flexion. In physics “mechanical advantage” is defined as *“... ratio of the weight of the actual load raised to the force input required to perform,” [paraphrased from (11)1. Therefore, the mechanical advan- tage with which the potential force of the muscle can be applied does not vary linearly, but changes in proportion to the sine of the angle between the bony elements of the lever system. This results in a narrow angular range within which limb move- ment is strong as well as precise and outside of which not only effectiveness of motion decreases, but individual differences increase to such an ex- tent that performance becomes virtually unpredic- table. There are many compilations in tabular form available, useful in estimating range and strength of limb movement for a given work situa- tion.'> '*1* Partial recapitulation of the compre- hensive data presented in the references mentioned would not only be redundant but could also tempt readers to rely on fragmentary and insufficient in- formation as a basis for decision making. Most anthropometric reference works, however, were developed as aids in the design of specialized man- task systems such as the operation of motor ve- hicles,’ or military aircraft, and therefore some information might not be applicable without a degree of modification to generalized work situa- tions. Also many references state range of joint movement over the full angle and strength of movement in terms of maximum and therefore these data, with the help of an anatomical atlas or, better, an articulated plastic skeleton, should always be reduced to the “effective range” for a specific task or for a specialized working popula- tion (Figure 32-8). Kinetic Elements The functional aggregate of all anatomical structures involved in producing a simple move- ment of a joint about one of its axes is called a “kinetic element” (Figure 32-9). The basic structure of each kinetic element is a lever system consisting of at least two bones connected by a joint. The levers are moved by the contraction of muscles inserted into the bones. These muscles are arranged to oppose each other. The action muscle is termed ‘‘protagonist;” the opposer, “antagonist.” Contraction occurs in re- sponse to stimuli from the specific nerve supplying each muscle. The oxygen required for the energy release needed to bring about muscular contrac- tion is provided by arterial branches supplying protagonists as well as antagonists with blood. The waste products of the physiological combustion process incidental to energy release are carried away by venous or other drainage mechanisms. Thus, each kinetic element is made up of the fol- lowing constituents: <-&—— FULCRUM EIGHT a" FULCRUM Figure 32-5. An anatomical third class lever is formed between ulna and humerus. The brachialis muscle provides the activating force, the fulcrum is formed by the center of the trochlea of the humerus. 436 C A 9 A = the forearm flexed at U0 deg a = humerus B = The angle of the forearm extended when the efficiency of the biceps as an outward Here the muscles will pull the radius strongly against the C = Cross section X- Xthrough A showing why the biceps is an outward rotator of the The Biomechanics of the Arm-Back Aggregate under Industrial Working Conditions. New York, xx b= biceps c = attachment of biceps d = radius e = head of radius f = capitulum of humerus g = ulna rotator is reduced. humerus causing friction and heat in the joint forearm Tichauer, E. R.: American Society of Mechanical Engineers, 1965. Figure 32-6. A Torsional Lever System Exemplified by the Kinetic Element Made Up of Humerus, Radius and Biceps. A = HUMERUS B = ULNA C = HUMERO-ULNAR JOINT D = BRACHIALIS MUSCLE E = HAND Figure 32-7. The kinetic element formed between humerus, ulna and brachialis muscle can operate at best mechanical advantage only within a relatively narrow angle of fore- arm flexion. 1. bony; 2. articular; 3. muscular; 4. nervous; and 5. vascular. Only the simplest and most basic of all mo- tions such as, for example, reflex reactions, in- volve only one kinetic element. In the industrial environment, manipulative as well as locomotive maneuvers are normally performed by a “kinetic chain.” 437 Western Electric News Features, New York, 1965. Figure 32-8. The Use of a Plastic Skeleton for the Objective Analysis of Biomechanical Advantage of a Specific Working Posture. Possible stresses in the shoulder joint are measured with the mechanical analog along side. Kinetic Chains A kinetic chain consists of a number of serially interacting kinetic elements reacting to inputs and ARTERY / HUMERUS Figure 32-9. The Kinetic Element of Fore- arm Flexion and Extension. feedbacks perceived from within and without the body by sensory organs connected with the kinetic element in such a manner as to form a cybernetic, or self-regulating system. The first step in the bio- mechanical evaluation of a workplace is normally the identification of that kinetic chain which links sensory inputs or feedbacks from the workplace with the muscular output required to perform a specific task.'® To enumerate all anatomical struc- tures of a kinetic chain is not only cumbersome, but often unnecessary. Therefore, in industrial practice the description of a kinetic chain includes only major sensory organs and key kinetic ele- ments. The kinetic chain of “eye-hand coordination” is perhaps the most frequently used one in most industries (Figure 32-10). Here the main sensory input is perceived by the eyes. These track the visual target when moved by the small muscles Tichauer, E. R., Gage, H., Harrison, L. B.: The Use of Biomechanical Profiles in Objective Work Measurement. J. Ind. Eng. IV:20-27, 1972. Figure 32-10. The Kinetic Chain of Eye-Hand Coordination. (Figure 32-10/R) which rotate the eyeball. How- ever, binocular vision and thus, depth perception, exists only within the binocular visual cone of 60°. To bring binocular vision to bear upon an object positioned outside of this cone, it becomes neces- sary to rotate the head and thus the next kinetic element in the chain is formed by the sternomas- toid muscle (Figure 32-10/S) and its connection with the skull and the breastbone. Subsequent to visual evaluation of the work situation, a forward movement of the arm about the shoulder is pro- duced by the anterior belly of the deltoid muscle (Figure 32-10/A) which is antagonized and con- trolled by activity of the posterior belly (Figure 32-10/P) of the same muscle. To reach out, the triceps inserting into the ulna functions as pro- tagonist and this action is opposed and controlled by the brachialis, (Figure 32-10/T and 32- 10/B) which, in turn, originates from the hu- merus and inserts into the ulna. Fine positioning of the wrist is governed by, among others, a com- plex group of extensor muscles (Figure 32-10/E), originating from the elbow region and inserted into the phalanges of the fingers. Identification of such a kinetic chain makes it possible to compare, with- out physical experimentation, the anatomical complexity of motions performed under visual control in various directions, and to eliminate those which are likely to be the most fatiguing motions. In Figure 32-10 motion pathway B would be very easy to perform, requiring only the use of the brachialis muscle while motion path- ways A & B and P & T would very likely lead to early fatigue as such action demands the use of every element, sensory as well as motor, in the kinetic chain. Likewise, correct identification of the kinetic chain permits the spotting, and often the elimina- tion, of potential anatomical failure points in a man-task system. Anatomical Failure Points in Man-Task Systems Whenever, in a man-task system, an element in a kinetic chain is structurally overstressed so that the maintenance of economically acceptable production rates or product quality becomes im- possible without impairing the worker’s physio- logical or emotional well-being, then the kinetic element under consideration becomes an actual or potential anatomical failure point. Quite frequently, workplace design in accord- ance with established industrial engineering princi- ples is conducive to the generation of such failure points. The principles of work simplification and other work measurement and design techniques did not change at the same pace as the develop- ment of modern industrial technologies. Many reputable industrial engineering texts” still recog- nize only five different classifications of motion: finger; fingers and wrists; fingers, wrists and forearm; fingers, wrists, forearm and upper arm; and all of the above (1-4) plus a body motion or a change of posture. These texts or common usage!” further stipu- late “. . . required motions should be performed NEL = 439 within the lowest classification possible . . . any motion beyond the maximum for 4th class should be avoided if at all possible. The shorter the mo- tion, the less time and effort it will take to per- form it . . .” This approach has simply become untenable in this age of pushbutton-operated ma- chinery and miniaturization. Even the simplest of man-task systems, unless screened while still in the planning stage, for po- tential anatomical failure points, can adversely affect health as well as performance of large num- bers of workers.” For example, the ergonomic efficiency and safety of a screwdriving task de- pends primarily on the magnitude of the included angle between forearm and upper arm in habitual working posture. If workers are permitted to position themselves only a few inches too far away from the workplace, then the incidence of sore elbows at the workplace, be they classified as epicondylitis, bursitis, or by any other name, will increase dramatically (Figure 32-11). This can be explained and avoided by biomechanical an- alysis of the relevant kinetic element. The biceps is not only a flexor of the forearm but also, due to the mode of its attachment to the radius, the most powerful lateral rotator of the wrist (Figure 32-11/c). Whenever working posture is such that the angle between forearm and upper arm ap- proximates 90° (Figure 32-11), then this muscle operates at mechanical advantage. However, if a posture is assumed which increases this angle (Figure 32-11), then the biceps also jams the head of the radius against the capitulum of the humerus generating friction, heat, and ultimately conditions commonly classified as epicondylitis. This example is typical of the numerous work situations where effective occupational hazard con- trol can be exercised through identification of anatomical failure points in a man-task system. A kinetic element is a potential failure point when: a. the degrees of freedom of movement re- quired exceed those available from the lever system employed; b. the lever system has to perform for ex- tended periods of time at mechanical dis- advantage or under conditions of high stress concentration at the joint surfaces; c. the muscles employed are too small to maintain performance for prolonged in- tervals of time; d. the blood supply to the muscles is im- paired; and e. sensory feedback is defective or equivocal. ANTHROPOMETRY Industrial Anthropometry is the discipline concerned with the body measurements of man as they relate to the maintenance of occupational efficiency, safety and health. A number of excel- lent reference works containing complete sets of numerical data are available in this field,’* ** so that partial recapitulation of numerical material here would not only be redundant but, due to the necessary oversimplification in presentation, dan- gerously misleading. n w ( WORKERS USING SCREWDRIVERS CONTINUOUSLY) 0 a 85° * " 120° 130° INCLUDED ANGLE BETWEEN FOREARM AND UPPER ARM (IN HABITUAL WORKING POSTURE) TOTAL SORE ELBOW CASES OUT OF 38 PATIENTS SEEN AT THE ROYAL SOUTH SYDNEY HOSPITAL REHAB. CENTER b 0) 47 Figure 32-11. THE MECHANICAL ADVANTAGE OF THE BICEPS DEPENDS ON THE ANGLE OF FLEXION OF THE FOREARM. This muscle is not only a flexor, but also, due to the mode of attachment, the most powerful outward rotator of the limb. The worker who sits too far away from his work place has to overexert himself when using a screwdriver because the biceps operates at mechanical disadvantage. Sore muscles and excessive friction between the bony structures of the elbow joint are the results.'® In most cases anthropometry is concerned with the measurement of relationships between visible anatomical surface landmarks. In industrial prac- tice, most data are obtained by direct caliper measurement. The data gathered are statistically evaluated and made representative of the range of body measurements typical for the working population under study. To substitute means in lieu of ranges is a dangerous practice. Often a piece of equipment of a workplace dimensioned for average man will be too small for one-half of the working population, and too large for the other half. Likewise, due consideration should be given to the substantial differences in body di- 2 = CORONAL PLANE 8 = MID-SAGITTAL PLANE 9 = TRANSVERSE PLANE Jacob, S. W., Francone, C. A.: Structure and Function in Man. Philadelphia, W. B. Saunders Co., 1970, p. 8. Figure 32-12. The Basic Planes of Refer- ence for Biomechanical and Anatomical De- scription? 441 mensions as well as skeletal geometry of move- ment between males and females. Industrial Seating Many jobs require performance in seated pos- ture. Therefore, chairs are among the most im- portant devices used in industry. They determine postural configuration at the workplace. Poorly designed seating accommodations represent fre- quent and definitive occupational hazards. Well- designed working chairs do not only contribute to the physical well-being of the working popula- tion but also may add as much as approximately 40 productive minutes to each working day. Optimal dimensions for working chairs and benches are well established and can be obtained with ease from standard reference works (Fig. 32- 12).#* ** Numerical dimensions are of but limited value to the designer or user of industrial seating, unless they are supplemented by adequate knowl- edge of the relevant anatomical facts and biome- chanical considerations. To facilitate description of seated as well as other work situations based on anthropometric considerations, a uniform nomenclature of planes of reference suitable for the description of postures has been agreed upon by convention.’ ** A line in the coronal plane passing through the point of contact between the ischial tuberosities and the seating surface constitutes the “axis of support” (Figure 32-13) of the seated torso. This pro- duces a “2-point support.” Therefore, all coronal sections of the seating surface of the chair should be straight lines. A coronally contoured seating surface may restrict postural freedom at the work- place severely and, when poorly matched to the curvatures of the buttocks, may cause discom- fort. Likewise, improper contouring may interact with sanitary napkins and other devices worn by women during the menstrual period with the en- suing further reduction in physical well-being dur- ing an already trying time of the month. Working chairs should be “cambered” in the sagittal plane. The term “camber” describes the backward slant of the seating surface. A properly cambered seat prevents forward sliding of the but- tocks and encourages the use of the backrest. A rough texture of the seating surface further helps to prevent undesirable and fatiguing sliding. The frontal end of the seating surface should terminate in a “scroll” edge which does not cut into the back of the leg. Finally, the seating surface should be preferably porous or else constructed in such a manner as to permit adequate conduction of heat away from the contact area between but- tocks and chair. Especially undesirable are inter- acting combinations of multiple layers of loose garments made from synthetic fabrics and solid synthetic seat covers of, for example, vinyl plastic which will definitely affect female workers detri- mentally due to a considerable damming up of heat at the body surface. At the back of the leg, in the hollow of the knee, a sharp and easily distinguishable crease is located which is termed the “popliteal crease.” The distance from the popliteal crease to the floor when standing in a relaxed upright posture and Figure 32-13. A biomechanically — correct seating posture (A) contributes substantially to health, well-being and efficiency of the working population. When the popliteal height of the worker is less than the popliteal height of the chair (B) discomfort will ensue. Note deformation of thigh and buttocks in situa- tion (B). while normal working shoes are worn is termed the “popliteal height of the individual.” The height of the highest point of the seating surface above the floor is the “popliteal height of the chair.” If the popliteal height of the chair is equal or greater than the popliteal height of the individual concerned, then undesirable pressures may be exerted upon the back of the thigh. To 442 be comfortable, the popliteal height of the chair should be approximately 2-inches lower than the popliteal height of the individual. The seating surface should be short enough so that the distance between the front edge of the seat and the popli- teal crease is about 5 inches. This dimension is called “popliteal clearance.” In some industrial chairs, the depth of the seat can be regulated by adjustment of the backrest. If the backrest is moved forward, then the seat becomes shorter. This is a very desirable design feature contributing both to productivity as well as physical well-being. The lower border of the backrest should clear the iliac crest. Preferably the upper edge or the highest point of contact with the back of the seated individual should be at a level lower than the in- ferior margin of the rib cage. At least the top of the backrest should clear all but the “false” ribs. Many work situations require continuous and rhythmic movement of the torso in the sagittal plane, and then a backrest which is too high will produce bruises on the backs of a considerable portion of the working population. The best de- signed backrests are small, kidney shaped, and can swivel freely about a horizontal axis located in a coronal plane. Thus, they fit well into the hollow of the lumbar region and provide the needed support for the lower spine without detri- mental interference with soft tissues. It is often desirable, especially when much movement of the torso during work must take place, that the area of contact with the backrest does not extend be- yond that region of the back which overlays the tough and fibrous plate which constitutes the ori- gin of a large muscle; the latissimus dorsi. A backrest which is overly wide, under circum- stances when much materials-handling and twist- ing of the torso in the seated position takes place will make frequent and repeated contact with the breasts of female workers.?* This can produce great pain, especially during the premenstrual period when the breasts of many individuals are quite tender. Whenever backrests produce either bruising or only slight discomfort, workers pro- tect themselves. The painful effects of excessive interaction between chair and torso are commonly reduced by ad hoc devices such as pillows, brought from home and strapped to the backrest. Work sampling studies show that several hours every week may be wasted in an effort to keep such im- provised cushioning devices in place. Properly designed backrests are much cheaper than im- provisations, both in the long as well as in the short run.?” A frequent and sometimes dangerous response to chair-generated discomfort is temporary ab- senteeism from the workplace. When the level of personal tolerance has been exceeded, workmen simply “take a walk.” It is found occasionally that individuals involved in accidents are at the place of injury without authorization. Since no accident is possible unless victim and injury-pro- ducing agent meet at the same spot and at the same time, temporary absenteeism from the work- place may result in unnecessary exposure to po- tentially hazardous situations.” Some working chairs are equipped with coast- ers. These facilitate limited locomotion and ma- terials-handling without abandoning the seated posture. In many work situations, coasters help to reduce unnecessary torsional moments acting on the lumbar spine. In other circumstances, es- pecially in some cases of circulatory disturbance in the lower extremity, a chair equipped with coasters may stimulate muscular activity and con- sequently improve circulation in the leg. How- ever, coasters should only be used when they either contribute to the well-being of an individual or the efficiency of an operation. They constitute some hazard to safety. There is always the risk that the chair rolls accidentally away or is inad- vertently removed while the user gets up for a brief interval of time. Where possible, a cheap restraining device such as a nylon rope, a chain, or, in some circumstances, a rigid linkage between chair and workbench should be considered. Supervisors as well as workers should receive brief but formal instruction in the proper adjust- ment of working chairs. First, the height between seating surface and top of the workbench is ad- justed so that an optimal angle of abduction of the upper arms during activity can be maintained. The chairs should have design features permitting easy adjustment in discrete steps. A 3-step height adjustment is adequate for most populations and in most situations. Secondly, after the height of the seat with respect to the top of the worktable has been fixed, correct popliteal height is then established by means of an adjustable footrest. Footrails, because they cannot be easily adjusted, are less desirable, and may traumatize anatomical structures around the ankle joint and may inter- fere with the ease of access to foot pedals. Oc- casionally drawers located underneath work- benches may interfere with proper seat height ad- justment and should then be removed. There should be no need for adjustment of the camber in a well-designed working chair. Third, seating surfaces should be wide enough to permit some postural freedom. Arm rests are sometimes useful but in some situations, support for only one arm is needed. In such case, a chair with detachable arm rests should be provided. No one single chair design can possibly fit all work situations. Seating analysis should always be conducted in a thorough fashion, giving due weight to all relevant features of the task under consideration. It is highly desirable that standard reference works!" ** be available during consul- tation. In addition to the analysis of the seated pos- ture with respect to physical comfort and biome- chanical correctness, it is also necessary to con- sider the changes in kinesiology of the lower ex- tremity resulting from seated posture. The seated leg and foot can rotate only with diffculty and unless the popliteal height of the chair is extremely low, such as is the case in motor vehicles, opera- tion of foot pedals may become cumbersome and fatiguing. On the other hand, the seated “leg and thigh aggregate” can abduct and adduct volun- tarily, precisely and strongly without fatigue for long intervals of time. It is therefore frequently 443 advantageous to make use of this kind of move- ment in the design of machine controls (e.g., the knee switch of the sewing machine). In the seated posture, knee switches are generally superior to foot pedals. The Physical Dimensions of the Workplace In most industrial enterprises, productive ac- tivities are organized according to certain princi- ples of division of labor and thus broken down into a series of relatively simple and specific oper- ations; each one assigned to a different employee. Therefore, most members of the working popula- tion do spend practically the entirety of their pro- ductive time confined to a quite small area of the manufacturing plant which is termed “the work- place.” Thus, in many instances the term “work- place” is synonymous with “working environment” and includes everything except man himself. Thus, regular as well as protective clothing, climate, illu- mination, chairs, machines, tools, and the product worked upon must be considered in the ergonomic analysis of the industrial environment. Within the narrower framework of biomechanics, the physical relationship, in terms of distances and other linear dimensions is often of paramount importance to production efficiency as well as to physical and emotional well-being of the worker. Even small changes in the dimensions of the workplace may have large effects on occupational safety and health as well as on the economics of the productive process. In practice, the designer of workplaces must often operate within the constraints of accepted industrial standards. These aim at the attain- ment of maximal levels of production efficiency. Most of these standards were developed between 1917 and 1936."*" Unfortunately, the develop- ment of industrial standards relating to the di- mensions of the workplace lags behind the devel- opment in workforce and technology which has so radically altered the industrial environment during the last few years. Acceptance of recom- mended changes in workplace layout will normally depend on the ability of the analyst to convince all parties concerned that higher levels of efficiency accompanied by increased well-being are a normal “by-product” of work situations dimensioned to suit the anthropometric and kinesiologic capa- bilities of the workforce. Perhaps the most commonly used set of “norms” for workplace layout are the “Principles of Motion Economy” which were first enunciated by the Gilbreths,** improved by subsequent re- searchers and accepted today generally in the for- mat developed and presented by Barnes*® who uses as a subheading for that table the words “A Checksheet for Motion Economy and Fatigue Re- duction” (Table 32-1). Many of these principles of motion economy are still applicable in the form in which they were originally enunciated. However, others have become either redundant or, in some instances, outright hazards to safety and health. They were devised to optimize the inter- action between man and the workplace within the framework of technologies and industrial fur- niture available at the time of their conception. They aim principally at an increase of produc- N \ TABLE 32-1 Principles of Motion Economy A Check Sheet for Motion Economy and Fatigue Reduction These twenty-two rules or principles of motion economy may be profitably applied to shop and office work alike. Although not all are applicable to every operation, they do form a basis or a code for improv- ing the efficiency and reducing fatigue in manual work. Use of the Human Body Arrangement of the Work Place Design of Tools and Equipment Ballistic movements are faster, easier, and more accurate than permit good posture should be provided for every worker. . The two hands should begin as 10. There should be a definite and 18. The hands should be relieved of well as complete their motions at fixed place for all tools and ma- all work that can be done more the same time. terials. advantageously by a jig, a fixture, . The two hands should not be idle 11. Tools, materials, and controls or a foot-operated device. at the same time except during should be located close to the 19. Two or more tools should be rest periods. point of use. combined wherever possible. Motions of the arms should be 12. Gravity feed bins and containers 20. Tools and materials should be made in opposite and symmetrical should be used to deliver material pre-positioned whenever possible. ed should be made close to the point of use. 21. Where each finger performs some : 13. Drop deliveries should be used specific movement, such as in . tland and body mations should wherever possible. typewriting, the load should be e confined to the lowest classi- : distributed in accordance with the fication with which it is possible 14. Materials and tools should be inherent capacities of the fingers. to perform the work satisfactor- locaied to permit the best se- ily quence of motions. 22. Levers, crossbars, and hand ’ - wheels should be located in such Momentum should be employed 13. Provisions SANA The Kade Lior positions that the operator can to assist the worker wherever pos- Soo) illumination is the first manipulate them with the least sible, and it should be reduced virement for atisfactor visual change in body position and with to a minimum if it must be over- qui ti or sau y the greatest mechanical advan- come by muscular effort. perception. tage. . Smooth continuous curved mo- 16. The height of the work place tions of the hands are preferable and the chair should preferably to straight-line motions involving ting and standing aL AheTnate - sudden and sharp changes in di- ily possible. 17. A chair of the type and height to restricted (fixation) or “con- trolled” movements. 8. Work should be arranged to per- mit easy and natural rhythm wherever possible, 9. Eye fixations should be as few and as close together as possible. From “Motion and Time Study”, R. M. Barnes, John Wiley & Sons, Inc., New York, 1963. tive output per unit of time with fatigue reduc- tion and maintenance of product quality a secon- dary, albeit important, consideration. A second set of universally used, as well as misused, schemes of “normal” and “extended” reach and work areas’ must be considered limited in application as the schemes neglect anthropo- metric considerations necessary due to different ethnic compositions of diverse working popula- tions. They also neglect age and are based on an incorrect conception of the kinesiology of the up- per limb. However, there is still very much substance in the “Principles of Motion Economy,” the con- cepts of work areas, predetermined motion-time systems as well as other current industrial stan- dards; they are still useful and, when properly applied, of great potential value for the promo- tion of economic efficiency as well as occupational health. To adapt the above-mentioned industrial systems, standards and practices to current needs, the dimensions of the workplace should comply with the following set of rules:® 444 Rule 1: The dimensions of the workplace are de- termined by body measurement as well as range and strength of movement of the kinetic elements involved in a task. These should be obtained from reference works specifically aiming at the industrial environment." Workplaces should always be dimen- sioned to suit the full range of body mea- surements of that specific working popu- lation likely to be assigned to the task under consideration." Differences of sex, ethnic origin and ed- ucational or social background often ex- press themselves in specific types of mus- culo-skeletal configurations as well as spe- cific motion inventories and/or manipu- lative skills. Therefore, both dimensions as well as geometry of the workplace should take these characteristics into con- sideration if maximal efficiency and phys- ical well-being are to be obtained in com- petitive situations. Rule 2: Rule 3: MTM + 40%, WF 40% 70% 30% — 82% 47% Figure 32-14. § ESTIMATE VS PRODUCTION LEVEL | | RESTING METABOLIC cos1/100 UNITS MADE 100% S PRODUCTION COST 100% ¢ GRINDING COST 100 | PRODUCTION TIME 100% THRUST ON TOOL TN OD C A o “OPTIMUM POSITION If the dimensions of equipment do not suit the body measurements of work- ers, then displacement by as little as 2 inches from the optimum position of the operator may modify performance levels of man and/or equipment considerably. Rule 4: Rule 5: Optimal position of operator with respect to equipment controls should be ascer- tained by biomechanical analysis. Rela- tively small deviations from the optimum may produce drastic productive as well as physiological responses from the equip- ment operator (Figure 32-14). There- fore, both operator and supervisor should receive instructions about proper posi- tioning of individuals with respect to the physical features of the workplace. In repetitive work situations, task design should aim at maximal postural freedom. 445 Wherever feasible, a task should be equally well-performable in the seated as well as the standing posture. Such oc- casional changes during the working day are beneficial and therefore measurements of workbenches, chairs, trays, equipment, etc., should be selected in such a manner as to permit individuals to stand up or sit down without changing the angle of abduction of the upper arm, the angle of forward flexion of the upper arm, or the included angle between forearm and up- per arm (Figure 32-15). Rule 6: In work situations demanding a standing posture, all tasks, including materials- handling operations, should be perform- able without standing on the toes, torsion or sideways bending of the trunk. Rule 7: No work should be performed on a strip 3” wide from the border of the work- bench which is closest to the operator. The proximity of this area to the oper- ator’s body demands excessive retraction or abduction of the upper arm to bring \ / the hands into position. In addition, ex- are needed to achieve effective eye /hand A STI coordination (Figure 32-16). Under | such conditions, users of spectacles or individuals afflicted with slight arthritic conditions of the neck, who are frequently found in middle-aged and other working populations, can suffer considerable phys- ical discomfort. Likewise, in many women, the position of the breasts inter- feres with ease of visual scanning in this ua area. ‘Rule 8: Whenever workplaces must be designed on the basis of already accepted stan- Figure 32-15. When work is possible in dardized normal and extended reach either seated or standing position, then work- areas (Figure 32-17), then this informa- bench and seating design should permit tion should be supplemented by charts change of posture without change of muscu- which display optimal directions within lo-skeletal configuration. each area and identify such poinis as may be difficult to reach due to anatomical or kinesiological reasons. ®? Tichauer, E. R.: Industrial Engineering in the Rehabilitation of the Handicapped. J. Ind. Eng. XIX:96-104, 1968. Figure 32-16. (A & B) Visual problems combined with bad postural habits might cause a typ- ist to sit too close to the typewriter. This may put great strain on a neck with arthritic lesions (a). To educate the patient to sit eight inches further away from the typewriter helps to reduce stress on the cervical spine and assists with problems caused by farsightedness (b). Com- pressive stress between the sixth and seventh cervical vertebrae in “a” is approximately three times the force computed for “‘b.” : 446 Figure 32-17. of the wrist changes with the angle of abduc- tion. Adapted from (33). The natural motions pathway Rule 9: The dimensions of areas for temporary holding or storage of products in process should be computed on the basis of queu- ing theory. Frequently the following formula can be used to advantage:* where N =the required capacity of the area P =the greatest acceptable proba- bility that the area will become temporarily overloaded. This number is normally determined on the basis of a subjective management decision. R =the mean arrival rate of units per time divided by the mean processing rate. These values are normally available from the Motion and Time Studies De- partment. Rule 10: Source of incident or reflected light. should be located in such a manner as not to produce visual discomfort due to glare (Figure 32-18). WORK TOLERANCE Within the context of Ergonomics, work stress is defined as any action of an external vector upon the human body while work strain manifests itself as the physiological response to the application of stress.” Stress and strain need not occur at the same points. An increase in environmental tem- perature above normal is correctly called “heat stress” and the resulting increase in sweating rate is then identified as “heat strain.” Likewise, when lifting loads, the force exerted upon the musculo- skeletal system is termed “work stress” and the resulting increases of cardiac and metabolic activ- ity are each examples of “work strain.” The performance of any task, no matter how 447 Glare J 7 oe SN aN 70 TTANN Nes 77 VY O/ Jy “ \ AN 5 foot-candles on at eye v 7 10 ans es IN from glare source J ~ ! / Zz Fol AN 7 £5 3 roy \ \ se 2 N / $= c \ / g ° c \ LE g X = 5 ZN ° ON E & SL 20 53% © Le - 5 & | N ~~ “ Eo ° x 9 f- AN ne ce So wf) 69 /’ pon?” ” , _ 7 : sar - 1 NS =D 84% Line of vision Object to Eye be seen Figure 32-18. Glare becomes worse as it comes closer to the direct line of vision. From M. Luckiesh, Light, Vision and Seeing, copy- right 1944, D. Van Nostrand Co., Princeton, New Jersey. light, will impose some work stress and conse- quently by needs elicit physiological responses characteristic of work strain. Thus, neither work stress nor work strain per se are undesirable; un- less they become excessive and produce work- induced disease or diminished work tolerance. The general field of Ergonomics is concerned with five basic environmental stress vectors (climatotactic, biotactic, mechanotactic, chemotactic, particulo- tactic) (Figure 32-19). All but mechanotaxes are treated comprehensively elsewhere in this book. Therefore, only mechanotaxes, contact with things mechanical, is discussed in this chapter. Mechanotactic stress results in three types of strain (Fig. 32-20): 1. Terminal Strain: Death. 2. Instantaneous Trauma: apparent physical injury. 3. Cumulative Pathogenesis: The gradual de- velopment of ergogenic disease by repeated mechanotaxis applied for sufficiently long intervals of time; where each individual application of stress may be quite harmless in itself, but produces lesions through fre- quency and repetition of application. Contact with things mechanical, even light contact, may result in trauma. A long enough stay in bed may produce a very intractable lesion, the bed sore. Writer's cramp and the calluses on the hands of surgeons are other well-known examples of strain resulting from mechanotactic stress. Often excessive environmental stress leads to a reduction in work tolerance, long before in- jury or disease have become manifest. The estab- lishment of conditions conducive to high levels of work tolerance is of utmost importance for the maintenance of occupational health. An immediately ECOLOGIC STRESS VECTORS WITHIN THE INDUSTRIAL WORKING ENVIRONMENT —_————— — — T | | | 1 I ® é CLIMATOTACTIC BIOTACTIC ® CHEMOTACTIC PARTICULOTACTIC A) x \ \ \ \ \ | CUTANEOTACTIC VISCEROTACTIC 7 7 / / / / [sociotacTic] MICROBIOTACTIC| f° Tichauer, E. R. Potential of Biomechanics for Solving Specific Hazard Problems. Proc. 1968 Professional Confer- ence, American Society of Safety Engineers, Park Ridge, Illinois, 1968, pp. 149-187. Figure 32-19 The Scheme of Ecologic Stress Vectors Common to All Working Environments. Workstress is derived from contact with climate, contact with living organisms such as fellow man or microbe, contact with things chemical, contact with hostile particles such as silica, or asbestos and finally, contact with things mechanical.*® ~ ( MECHAN OTACTIC WORKSTRESS T \ | 1 1 1 \ | | | | | | | | | | I I | | I I | ® (INSTANTANEOUSLY TRAUMATOGENIC ) CUMULATIVELY PATHOGENIC TERMINAL | | | | | | ® VIBRATION FORCE PERCEPTUAL OVERLOAD \ Tichauer, E. R. Potential of Biomechanics for Solving Specific Hazard Problems. Proc. 1968 Professional Confer- ence, American Society of Safety Engineers, Park Ridge, Illinois, 1968, pp. 149-187. Figure 32-20. Mechanotactic Stress Vectors Leading to Hazard Exposure in the Industrial Environment: A. Instantaneous Traumatogenesis (e.g. an arm is torn off). B. Terminal (e.g. death occurs immediately). C. Cumulative Pathogenesis. This term describes the gradual develop- ment of disability or disease through repeated exposure to Mechanical Stress Vectors over extended periods of time.* 448 TABLE 32-2 Prerequisites of Biomechanical Work Tolerance by E. R. Tichauer Posture: Man-Equipment Interface: Effective Kinesiology: (P1): Keep the elbows down. (P2): Keep moments acting on the vertebral columns low. (P3): Avoid Covert Lifting Tasks. (P4): Scanning should require eye movement only and not necessitate simultaneous head motion. (P5): A musculo-skeletal configura- tion conducive to maximal biome- chanical efficiency should be main- tained. (El): Do not restrict circulation. (E2): Vibrations transmitted at the man-equipment interface should not lead to somatic resonance reactions. (E3): Moving parts of the body should not be constrained by rigid supports. (E4): Stress concentration on small skin areas or small joints should be avoided. (ES): Ergonomic check-lists should always be consulted whenever handtools are designed, modified, selected or evaluated. (K1): Avoid deviation of the wrist while moving or rotating the fore- arm, (K2): Avoid forward reaches exceed- ing 16 inches. (K3): When the motion element “transport loaded” has to be per- formed in the sagittal plane, then the movement should be directed towards the body and not away from it. (K4): Holding and manipulation are mutually exclusive operations. (K5): Motions should be terminated by positive external stops rather than by voluntary muscular action. ©Copyright, E. R. Tichauer, 1970 130 » / | —— RATED PERFORMANCE LEVEL 120 \, ZL \ NL ,/ —— WORK METABOLISM Ho x (TOTAL METABOLISM MINUS \ - X WORK METABOLISM ) % 100 Pm —4 \ 90 \ 80 70 Q SNS ELBOW HEIGHT pl OPTIMAL POSITION. —_— 0° 8° 23° 33° 4° ANGLE OF ABDUCTION. o" 1/8" 1" 2" 3" — DIFFERENCE IN ELBOW HEIGHT. Tichauer, E. R. Potential of Biomechanics for Solving Specific Hazard Problems. Proc. 1968 Professional Confer- ence, American Society of Safety Engineers, Park Ridge, Illinois, 1968, pp. 149-187. Figure 32-21. Effect of Angle of Abduction on Physiological As Well As Economical Working Efficiency of 12 Female Workers 20 to 32 Years of Age Engaged in Food Packing. Stick fig- ures indicate elbow height in relation to optimal position (horizontal line); first line of nu- merals, angle of abduction, in degrees; bottom line, difference in elbow height, in inches, from optimal position, statistically tested means are reduced to arbitrarily fixed “benchmarks” of 100 percent. Work metabolism (total metabolism minus work metabolism, dashed line) meas- ured by Wolff's method and instrument Performance levels (solid line).* 449 Work Tolerance Work tolerance is defined as the ability to per- form a task at acceptable economic levels with respect to both quality as well as quantity of out- put, while, at the same time, enjoying a full mea- sure of physiological and emotional well-being. The most important prerequisites of Biome- chanical Work Tolerance are presented in tabular form (Table 32-2), arranged into three sets each consisting of five “Prerequisites”: P: Five prerequisites relating to the mainte- nance of postural integrity and safety. E: Five prerequisites relating to the develop- ment and maintenance of nontraumato- genic man/equipment interfaces. K: Five prerequisites relating to the produc- tion of an effective as well as nonfatiguing kinesiology. fl Ol) \) ua 1] Tichauer, E. R. Potential of Biomechanics for Solving Specific Hazard Problems. Proc. 1968 Professional Conference, American Society of Safety Engineers, Park kidge, Illinois, 1968, pp. 149-187. Figure 32-22. Keeping the arm abducted brings large muscles into play. This, during protracted periods of work, may cause sore- ness over chest and shoulder in some un- trained individuals and therefore occasionally induce fear of heart disease or even an im- pending heart attack. Areas of potential sore- ness are circled. 450 Posture P1: Keep the elbows down. Unnecessary abduc- tion of the upper arm, especially if maintained for extended periods of time, may have several undesirable side effects. It may also be produced through carelessness in workplace design in sev- eral different ways. For instance, if chair height is poorly policed, then a seat height only three inches too low with respect to the work surface will produce an angle of abduction of the upper arm of approximately 45° (Figure 32-21).%" “7 When this is the case, then a wrist movement at the workplace normally performed by rotation of the humerus would require a physically demand- ing shoulder swing. The resulting fatigue over several hours may reduce the efficiency rating by as much as 50%. Also when the seat is too low, especially in assembly operations, the left arm is frequently used as a vise, and the right hand to manipulate objects. Then after an hour or two, particularly under incentive conditions, some vague sense of discomfort over the origin of the left pectoralis and deltoid muscles, which stabilize the abducted arm, may be felt. This can lead especially in elderly and overweight workers, or those with heart conditions, to an unjustified fear of an impending heart attack and all the ensuing undesirable emotional difficulties (Figure 32-22). P2: Keep moments acting on the vertebral column low. Lifting stress is not solely the result of the weight of an object handled. Its magnitude must be expressed in terms of “Biomechanical Lifting Equivalent” in the form of a “moment.” This re- lationship, when holding a load upright, can be roughly estimated by taking 8 inches as the thick- ness of the human body plus half the length of the load, again in inches. The sum will approxi- mate the distance of the center of mass of the load from the lumbar spine. Very often a light but bulky object (Figure 32-23) may impose a heavier lifting stress than a heavy load of great density. P3: Avoid covert lifting tasks. Physiologically a lifting task exists when, for any reason whatso- ever, a moment is applied to the vertebral column. This frequently includes situations where only body segments are moved but no object is lifted (Figure 32-24). Then man becomes an analog of the crane and the same mechanical considerations with respect to load supporting capacity apply to both. When bending over, the weight of the body seg- ment moved — in this case, the trunk — may impose a far greater lifting stress than the load itself. Likewise, there are work situations where everything is stacked high and closely arranged in semicircular fashion around the worker. This requires holding up of the arm and thus applying a torque on the shoulder joint for extended periods of time. This may produce pain in the lumbar region because the torque is transmitted through the stabilized shoulder via the vertebral column onto the lumbo-sacral joint. Other examples will be discussed in a separate section on back prob- lems. P4: Scanning should require eye movement only and not necessitate simultaneous head motion. Only under conditions of binocular vision is it possible to estimate correctly and/or easily true L —0" 12" ud - 36" — WwW 32LBS 18 LBS 8+ iL) W )- M. AZ 250 INCHPOUNDS Tichauer, E. R.: Potential of Biomechanics for Solving Specific Hazard Problems. Proc. 1968 Professional Con- ference, American Society of Safety Engineers, Park Ridge, Illinois, 1968, pp. 149-187. Figure 32-23. The “Moment Concept” Applied to the Derivation of Biomechanical Lifting Equivalents. All of the loads represented in the figure produce approximately equal bending moments on the sacro-lumbar joint (approximately 250 inch pounds). 8=approximate dis- tance in inches from the joints of lumbar spine to front of abdomen (i.e., a constant for each individual). L: length in inches of one side of a cube of uniform density lifted during the stan- dard task. W: the weight in Ibs the cube handled. Me: the biomechanical lifting equivalent (here approximately 250 inch pounds). or relative distances or sizes of objects. Binocular ~~ Man-Equipment Interface vision without head movement can take place only ~~ El: Do not restrict circulation. Both the designer within a cone of 60° included angle, the axis of as well as the evaluator of tools and equipment which is originating from the root of the nose and should be familiar with the location of the princi- is located in the midsagittal plane of the head (Fig- pal and vulnerable blood vessels. Otherwise circu- ure 32-25). Often head movement at the work- lation may be inadvertently impaired and localized place constitutes a “protective” reaction necessary ischemia can result. Of especial importance is the to reestablish binocular eyesight whenever the protection of the blood vessels in the hand. For visual target is located outside of the cone. Si- example, a poorly designed or improperly held multaneous eye and head movements take much scraping tool (Figure 32-26) may squeeze an time, and this may produce a hazard whenever important blood vessel, the palmar arch, between fast-moving equipment (motor vehicles, airplanes, handle and the hamate bone. Numbness and conveyors) are operated. Furthermore, whenever tingling of the fingers will follow. head movement is restricted (e.g., eyglasses or ~~ E2: Vibrations transmitted at the man-equip- arthritic lesions in the neck), then if objects of ment interface should not lead to somatic reso- manipulation are located outside the visual cone nance reactions. White Finger Syndrome, or inter- of 60°, problems of eye-hand-head coordination mittent blanching and numbness of the fingers, will ensue. sometimes accompanied by lesions of the skin, has P5: A musculo-skeletal configuration conducive to been identified for many years as an occupational maximal biomechanical efficiency should be main- disease associated with the operation of pneumatic tained. Unless the individual members of a kinetic =~ hammers and other vibrating tools.** ** Vibrations chain involved in the performance of a task are of low frequency and quite low intensity can make optimally positioned and aligned, with respect to the whole body, body segments or individual vis- each other as well as with any equipment controls cera vibrate at harmonic resonance frequencies.*’ employed, considerable work strain may result, The resulting symptoms may simulate a wide even under conditions of light work. Of especial range of musculo-skeletal and organic diseases importance in this respect are angles formed be- such as back pain, respiratory difficulties, cardiac tween long bones (Figures 32-11 & 32-14). distress or minor ailments such as visual disturb- 451 A - y G—- A = humerus B = socket of hip joint C = vertebral column D = shoulder joint E=am F = load G = muscles of the buttocks (gluteus maximus) H = muscles of the back (sacro-spinalis) 1 = lumbo-sacral joint J = spinous process of a vertebra K = trapezius muscle L = distance from the center of mass of combined body load aggregate to the joints of the lumbar spine Figure 32-24. IN LOAD-LIFTING, THE STRUCTURAL ELEMENTS OF MAN ARE ANALOG- OUS TO THE STRUCTURAL ELEMENTS OF A CRANE. The same mathematical techniques can be applied to predict performance of either of them.'* ances.'' Reliable literature’ and experienced expert advice should be consulted whenever vibra- tion transmittal between equipment and the human body is a possible cause of manifestations of ill health. E3: Moving parts of the body should not be con- strained by rigid supports. Where extensive move- ment of the trunk in the sagittal plane is required, an improperly located backrest will produce bruises. Likewise, a firm arm rest supporting a moving elbow will lead to swelling and inflam- mation. E4: Stress concentration on small skin areas or small joints should be avoided. In many indus- tries a trend towards miniaturization, mechaniza- tion and automation is conducive to the ever-in- creasing introduction of highly localized work stress. Often simple remedies will help to prevent penetration of the skin, calluses, or the aggrava- tion of joint disease. The tailor’s thimble is one good example. Often the introduction of simple cushioning devices such as foam rubber or springs underneath pushbuttons can reduce or eliminate trauma to the distal interphalageal joints of the fingers. Even the prevention of soreness of the fingertips may facilitate or accelerate training programs for the technologically obsolescent in a 452 pushbutton-oriented society. Finally, formfitting handtools or equipment handles often fit only one hand perfectly: the hand of the designer. When used by individuals with larger or smaller hand dimensions, contour features may cut into the body surface and produce localized stress con- centrations. ES: Ergonomic checklists should always be con- sulted whenever handtools are designed, modified, selected or evaluated. The most frequent, as well as most intense, contact between man and equip- ment occurs normally at the handtool interface. The design features of a nontraumatogenic hand- tool are complex and an ergonomic checklist is presented as a separate section of this chapter. Effective Kinesiology K1: Avoid deviation of the wrist while moving or rotating the forearm. Tools are occasionally de- signed in such a manner as to demand deviation of the wrist towards the ulna or the radius dur- ing operation (Figure 32-27). This affects both health as well as efficiency. The principal flexor and extensor muscles of the fingers originate in the elbow region and are connected with the pha- langes by way of long tendons. The extensor ten- dons are held in place by a confining transverse ligament on the dorsum of the wrist while the Milli-Sec. 500 _ 400 300 200 - 100 20 Degrees Saccadic Eye Movement Figure 32-25. 40 Head Rotation Binocular Field Convergence at 16" “EYE TRAVEL AND BINOCULAR VISION” (RELATED TO SPEED AND QUAL- ITY OF PERFORMANCE). flexor tendons on the palmar side of the hand pass through a narrow carpal tunnel which contains also the median nerve. Deviation of the wrist to- wards the ulna causes these tendons to bend and to become subject to mechanical stress underncath the ligament and in the tunnel. This is conducive to tenosynovitis. Likewise, this skeletal configu- ration favors ulnar drift of the extensor tendons which is highly undesirable when a hand is already afflicted with even very light arthritis. When such a tool is used in jobbing operations for only a few minutes every working day, then generally no ill effects are experienced. However, when continuous operation under production conditions is demanded, ulnar deviation constitutes a haz- ard to the health of the working population, and it should be remembered that it is much safer to bend the tool than to bend the wrist. If, how- ever, ulnar deviation is overcompensated so that the wrist becomes deviated towards the radius, then the hazard of “tennis elbow” is introduced. This risk is particularly high when a work situation demands the simultancous dorsiflexion and radial deviation of the wrist. Furthermore, deviation of the wrist reduces the range of rotation of the forearm and hand (Figure 32-28). As much as 50% of the useful range of motion may be lost through wrist deviation. Whenever screws have to be inserted or panels wired, the number of wrist movements necessary to perform that task will 453 have to be doubled because of the lost range of motion. This is conducive to carly fatigue and difficulties during training. K2: Avoid forward reaches exceeding 16 inches. Most systems of predetermined motion times in common use in industry for the purposes of work- place layout postulate that reach time is a lincar function of reach length." This, however, applies only to young individuals with a high degree of physical fitness. In a middle-aged working popula- tion, where the vertebral column exhibits already the signs of the normal wear and tear of life, in women during the premenstrual and menstrual period, and in individuals afflicted with light arth- ritic conditions of the vertebral column, a reach in the sagittal plane exceeding 16” constitutes a severe covert lifting task and causes reach time to increase proportionally to the square of the reach length (Figure 32-29). Under such condi- tions, certain groups of workers will not only be at a competitive disadvantage, but will suffer se- vere physical discomfort when trying to keep up with younger and more physically-fit workers. It is often easy to arrange the workplace in such a manner as to obviate excessive reach length. K3: When the motion element “Transport Loaded” has to be performed in the sagittal plane, then the movement should be directed towards the body and not away from it. The protagonist muscles of forward flexion of the upper arm oper- Tichauer, E. R.: Ergonomics: The state of the art. Amer. Ind. Hyg. Assoc. J. 28:106-16, 1967. Figure 32-26. Ergonomic Considerations in Hand Tool Design. A, the relations of bones, blood vessels, and nerves in the dissected hand. B, a paint scraper is often held so that it presses on a major blood vessel (P) and directs a pressure vector against the hook of the hamate bone (Q). C, in the live hand, this results in a reduction of blood flow to, among others, the ring and little fingers, which shows as a darkening on infrared film (R). D, a modi- fication of the handle of the paint scraper causes it to rest on the robust tissues between thumb and index finger (S), thus preventing pressures on the critical areas of the hand.” ate at biomechanical disadvantage. Their antago- nists are the large and powerful muscles of the back and this, in balance within the kinetic ele- ment, makes a sagittal forward reach per se an undesirable motions element. The transport of even a relatively light object, by means of the hand away from the body in the direction of the sagittal plane leads to early fatigue, loss of preci- sion of movement and ultimately great discomfort in the shoulder region. Such disposal movements are best performed at an angle of 45° to the sagit- tal plane or in the coronal plane (Figure 32-30). K4: Holding and manipulation are mutually ex- clusive operations. The arrangement of muscles, tendons and ligaments which make possible the 454 Figure 32-27. STRAIGHT-NOSE PLIERS PRODUCE STRONG BENDING MOMENTS IN THE WRIST. Neither the axis of rotation nor the axis of thrust correspond with the corres- ponding axes of the limb. A tool with a bent nose eliminates these faults.'® use of the hand for “work” is complex. The fully flexed wrist, among other reasons because of pre- tensing of the extensors of the fingers, does not permit an effective wraparound grasp (Figure 32- 31).** Under opposite conditions, when the wrist is fully hyper-extended, the configuration of the wrist joint, tension in the flexor muscles of the fingers, and the mechanical disadvantage of the small intrinsic muscles of the hand, do not permit the effective use of the distal phalanges for fine manipulative movements. When the wrist is fully extended, but not hy- per-extended, there is 100 percent grasping power, 50 percent holding power, and 50 percent manip- ulative effectiveness. In full flexion of the wrist, the hand is 100 percent effective in manipulation but has almost no holding power. The strong dependence of the effectiveness of the hand on skeletal configuration may produce situations where a machine control can be tight- ened or loosened effectively by a right-handed person, but can be completely unmanageable by a left-handed one. Often such job difficulties for left-handed people may be eliminated by creating a work situation without postural restraint as far as the wrist is concerned. Whenever a task re- quires a mixture of both holding and manipulation such as is frequently the case in the operation of vises, fixtures, dials to be adjusted, then these controls should be located so that they can be operated effectively by both the right as well as the left hand. Often a simple bend in a lever or the positioning of a dial at an angle will accom- 75° 90° 105° 30° Figure 32-28. Ulnar deviation of the wrist reduces normal range of pronation-supination from 180 degrees to 90 degrees, thus doub- ling the number of movements necessary to perform a pronation-supination task. Fatigue or, even worse, occupational trauma may en- sue. (Adapted from Industrial Engineering Handbook: H. B. Maynard, editor, McGraw Hill Book Co., 1963. p. 5-23). plish this. About 25% of the working popula- tion are left-handed. } K5: Motions should be terminated by positive ex- ternal stops rather than by voluntary muscular ac- tion. It is well-known that termination of hand movement with precision, especially when high speed is demanded or incentive conditions are in- volved, can lead to performance difficulties. Well- known systems of predetermined motion times make allowance for a “positive stop work factor,” recognizing the need to facilitate the precise ter- mination of hand movements by positive contact with an external stop. This important sensory facilitation can be achieved through diverse, phys- ically quite different devices (Figure 32-32). In each and every case it will reduce the need for voluntary control over precision of movement and often will reduce performance times. This is of especial importance to the young worker who is inexperienced, those with little innate manual dexterity and the elderly who are developing tremors or show the beginnings of not yet clin- ically important bone and joint disease. Espe- cially under incentive conditions, or where the possibility of dismissal because of failure to meet efficiency demands exists, these working popula- tions may develop emotional reactions such as nervousness, or abrasiveness, in contact with fel- low workers unless sensory facilitation produced at positive stops enables them to perform again at competitive levels. Not infrequently the absence of positive stops produces intense nervousness, especially when the job security of a worker de- pends on his ability to maneuver a fragile object into a narrow space. Such physiological responses 455 may include fluctuations and increases of heart rate and variations in respiratory parameters. Not all of the above-listed “Prerequisites of Work Tolerance” are applicable to all work situa- tions and all individuals. They provide, however, a convenient checklist for the analysis of existing or planned work situations in order to insure that human needs for peace of mind, physical comfort, occupational safety and health have not been sac- rificed for the sake of short-term expediencies such as the need to maintain high performance speed over short periods of time. Where the ma- jority of prerequisites of work tolerance are ap- plied (Table 32-2), there is a better labor-man- agement relationship. Likewise, improvement of the general physical and emotional health of the working population as well as an increment in economic efficiency, and higher levels of product quality will be observed. HANDTOOLS The basic tools used today by man as wéll as the basic machines were invented in the dawn of the prehistoric age and evolved over many thou- sands of years. However, the contemporary and very rapid rate of industrial and technological de- velopment demands frequently “instant” creation of new and specialized implements through effi- cient design rather than by evolution. This sec- tion considers both hand tools as well as equip- ment controls since the latter are merely the “tools” which permit the operation of machinery. Also, the functions of tools are varied and their shapes diverse. There are many principles of biomechanics and ergonomics which need to be considered in the selection and evaluation of al- most all kinds of tools, no matter how different their fields of application. Some of the material presented here has been mentioned elsewhere in this chapter. It is, however, by no means redun- dant, as such repetition where it occurs, empha- sizes the relevance of ergonomic and biomechan- ical factors upon the selection and evaluation of the most commonly used implements in indus- try, tools and equipment controls. Force Optimization The prime purpose of primitive tools was to transmit forces generated within the human body onto a material or workplace. In the course of artisanal and industrial development, this purpose was widened so that tools should now be designed to extend and reinforce range, strength, and ef- fectiveness of limbs engaged in the performance of a given task. The term “extend” as used here is not restricted to the meaning of magnification and amplification because often a tool makes possible a far finer movement than the unarmed hands would be capable of performing (e.g. tweezers, screwdriver) and sometimes it enables the application of a grip or grasp soft enough so as not to injure a workpiece as is the case in a suction tool so often used to transport small and fragile components. A micromanipulator of the “master-slave” type is another good example of a tool which serves as an attenuator rather than as an amplifier of human force and motion. TIME ya em Awareness of the "Hidden" Lifting Task Should Exist. Because of Higher Torques Exerted on the Lumbar Spine, o Sealed Job, instead of Being “light Work," May Be the Physiological Equivalent of a Severe Lifting Task. In Seated Work, the Rule 1s: “Get the Job Close to the Worker." (Adapted from! 43) A = Humerus 8 = Socket of Hip Joint C = Vertebral Column D = Shoulder Joint E = Arm F = load G = Muscles of the Buttocks (Gluteus Maximus) H = Muscles of the Back (Sacro-Spinalis) | = Lumbo-Sacral Joint J = Spinous Process of a Vertebro K = Trapezius Muscle L = Distance from the Center of Mass of Combined Body-Load Aggregate to the Joints of the Lumbar Spine 30 1.20 ~ 2 ————= y-02"- 6x +64 INTERQUARTILE RANGE OF REACHES BY PEOPLE OVER 40 YEARS NOMINAL MTM VALUES FOR REACH USED INTERQUARTILE RANGE OF REACHES BY YOUNG MEN A i Tichauer, E. R.: Industrial engineering in the rehabilitation of the handicapped. J. Ind. Eng. XIX:96-104, 1968. Figure 32-29. The Interquartile Range of 1200 Reaches in Sagittal Direction Performed by Individuals above 40 Years of Age Fitted Well to a Quadratic Equation. A control experiment where a like number of reaches was performed by young men showed agreement with MTM data. A system of predetermined motion times for the elderly worker remains still to be developed. In an endeavor to provide maximum mechan- ical advantage, equipment designers frequently maximize through effective use of the principle of the lever, the ratio of force output from the tool divided by the force input from the hand. This, however, can be easily overdone, because the force output should also provide sufficient sensory feed- back to the muscular-skeletal system in general and the tactile surfaces of the hand in particular. In a thread-tapping job, for instance, if this ratio is too large, the force applied may be excessive resulting in either stripped threads or broken taps and bruised knuckles. If, on the other hand, the ratio of force output over force input is too small, then an unduly large number of work elements will have to be repeated to complete a job such as is the case in the pounding of a large nail with too small a hammer. A tool should also produce an optimal stress concentration at a desired loca- tion on the workpiece. Thus, up to a certain limit, an axe should be as finely honed as possible to fell a tree with the minimum number of strokes, but the edge should not be so keen as to require frequent resharpening or to be fragile. Finally, the shape of the tool should be such as to insure that it is automatically guided into a position of optimal mechanical advantage where it will do its job best without bruising either hand or workpiece. The Phillips Screwdriver as com- pared with the ordinary flat blade tool is a good example of such efficient design. Distribution of Pressures and Stresses The use of handtools causes generation of a large variety of stress vectors at the man-equip- ment interface. These may be mechanical, ther- mal, circulatory or vibratory and have a tendency to be propagated to other points within the body. Thus, awareness that work strain and the result- ing trauma often show up at points quite remote from the locus of work stress application must be 456 Figure 32-30. direction away from the body and in the mid- saggittal plane is conducive to discomfort and early fatigue because of the strong antagonist activity in the latissimus dorsi muscle. The disposal of objects in a kept constantly in mind.** Contact surfaces be- tween the tool and the hand or other live tissues should be kept large enough to avoid concen- tration of high compressive stresses. Pressures should be distributed over sufficiently large skin areas so that both ischemia as well as mechanical trauma to nerves are avoided. Care should be exercised to avoid all but the mildest possible compression against those areas of the hand which overlie particularly vulnerable blood vessels and nerves (Figure 32-33). “Form-fitting” should be a feature employed only sparingly in the design of handles and all anthropometric factors of rele- vance should be considered so that the handle does not fit only the hands of the designer properly. Likewise, it is advantageous to use the tough tis- sue located at the vertex of the angle formed be- tween the spread thumb and index fingers as one of the skin areas capable of supporting large pressure and other physical stress.*" Whenever 457 finger grooving is employed as a device to facili- tate firm gripping of a tool, then it should be shaped in such a manner as not to lead to stress concentration on the interphalangeal joints when oversized or undersized hands must hold the im- plement (Figure 32-34). Therefore, the selector and evaluator of handtools should be provided with and trained in the use of an atlas of the anatomy of the hand and be fully familiar with shape and location of those anatomical structures which relate to the long term and short term safety of handtool usage. Consideration of Working Gloves Many undesirable results may stem from im- proper fit and/or design of working gloves. These may lead to low efficiency and certain health hazards; but a false impression may be generated that these discomforts, poor workmanship and in- creased tendency towards injuries, could be due to poor tool design. Unsuitable working gloves are likely to be associated with one or more of the following areas of concern resulting in hand- tool usage: 1. Loose gripping of tools. It is impossible to close the hand without causing the inter- phalangeal surfaces of the fingers to abut against each other (Figure 32-35). The skin between the fingers is particularly richly endowed with nerve end organs which transmit sensory feedback to the central nervous system. Strength of grip may well be dependent upon pressure be- tween the fingers. If the working glove is too thick in this region, high pressures at the interdigital surfaces may be generated before the hand is firmly closed about the tool handle or equipment control and these may then be insecurely grasped. Aware- ness of this lack of firmness of hold may cause many individuals to grip unneces- sarily tightly and firmly which results in increased fatigue and other undesirable side-effects. Also, if a working glove is too thick, the fingers may not be able to wrap around the handle sufficiently for a firm hold. The detrimental effect of overdesigned working gloves becomes most apparent when pulling cables or hold- ing firmly onto smooth rods. 2. Carpal tunnel considerations. The carpal tunnel is a channel in the wrist through which important nerves, blood vessels and tendons pass into the hand (Figure 32-36). Pressure, generated by overly tight or too stiff cuffs of working gloves, on the tunnel itself or on the areas im- mediately proximal or distal to it may result in one or more of the following: ulnar tenosynovitis; impairment of blood supply to the hand and, consequently, cold- ness, numbness and tingling of the fingers. The fit of working gloves should be checked before tool design or workload are considered as a possible cause for the aforementioned symptoms. There is a well-known disease entity, the “carpal tun- Figure 32-31. nel syndrome.” This can be aggravated through poorly designed working gloves; but may not have been caused by either gloves, tools or workplace design. Selection and Evaluation of Tools Based on Biomechanical Design Considerations Repetitive maneuvers and the resulting cumu- lative work stress are far more frequent causes of occupational trauma than spontaneous overexer- tion. Frequently observed in this connection is ten- osynovitis. This may be due to biomechanical overstress or an infectious process. Both overuse of the hand as well as unaccustomed usage are as- sociated with tenosynovitis and some consider it a “training disease.” Industrial physicians often resort to a medically-imposed restriction of per- formance levels once the disease has been diag- nosed. Tenosynovitis is most frequently observed on 458 The flexed wrist (A) cannot grasp a rod firmly, while the straight wrist (B) can grip and hold firmly. Conversely the flexed wrist (C) is well positioned for fine manipulation, but when extended (D) freedom of finger movement is severely limited. the back of the hand where it involves the exten- sor tendons. It is not a “training disease,” but a definite sign of overstress which should be cor- rected by changes in tool design or workplace layout. Whenever changes in the design of the working environment and implements are not feasible, then reduction in task demands such as lowering the required output or changes in work rhythm should be considered as possible means to reduce tenosynovitis. As another alternative, “job enlargement’** may be tried. Then members of the exposed working population will not be performing the “suspect task” throughout the en- tire working day, but will be rotated periodically to workplaces which are less conducive to exces- sive cumulative work stress imposed upon the wrist. Equipment used under circumstances where repetitive rotation of the wrist against resistance is required should allow the task to be performed without ulnar deviation. Ulnar deviation favors A 12 WEEKS 5% B 5 WEEKS DROPOUTS DURING TRAINING AVERAGE TRAINING TIME A I Tichauer, E. R.: Potential of Biomechanics for Solving Specific Hazard Problems. Proc. 1968 Professional Conference, American Society of Safety Engineers, Park Ridge, Illinois, 1968, pp. 149-187. Figure 32-32. Sensory facilitation of posi- tioning can be achieved in many ways, be it by enlargement of contact surfaces ‘“B”, or sometimes by the flairing of inlet holes. Such facilitation will result in the reduction of train- ing time as well as in an increased number of individuals capable of learning a new opera- tion without fatigue or discomfort. Adapted from (35). “drift” towards the ulna of the extensor tendons, exposing these and the surrounding tendon sheath to compressive stresses. Likewise, on the palmar side of the wrist, those tendons, nerves and blood vessels which pass through the carpal tunnel are subjected to similar stresses in ulnar deviation (Figures 32-27 & 32-36). A pre-existing risk of tenosynovitis, be it due to the anatomy of the operator, or due to work- ing conditions, may be enhanced whenever strong palmar flexion of the wrist is demanded concur- rently with ulnar deviation. Since tool-wrist-fore- arm configuration is often a function of the prox- imity of the worker to the workbench, or the lo- cation of the chair, close attention should be paid to these extraneous potential causes of handtool imposed work stress. Dorsiflexion of the wrist while the forearm is pronated should be avoided. This combination predisposes to radio-humeral bursitis (i.e., “ten- nis elbow”). To exert excessive stress on the el- 459 bow joint by this configuration, repetitive prona- tion and supination of the forearm need not be part of the task. Stresses on the radio-humeral joint, which may be potentially pathogenic, can be imposed also while the forearm is stabilized in pronation, such as when hammering overhead in an awkward position. Generally speaking, tool-hand configurations which are conducive to motions like “laundry wringing,” insertion of screws, looping of wires us- ing pliers, or repetitive manipulation of switches or controls rotating coaxially with long rods, such as those found on the steering handles of motor- cycles, require careful biomechanical analysis in order to avoid damage to forearm, wrist, and hand. Many of those strong muscles which flex and extend the fingers come from the elbow region and are connected by tendons to the phalanges. Be- cause of the peculiar construction of the tendon- tendon sheath system, a potential risk of “trigger finger” is imposed when any finger other than the thumb must be frequently flexed against resis- tance. This is true for both dynamic as well as isometric flexion. The level of exposure is in- creased when a tool handle is so large that the distal phalanx must be flexed before the more proximal phalanges can be flexed and preposi- tioned (Figure 32-37). “Trigger Finger” is the vernacular term for two different conditions, both having the same effect. Either overwork may result in the impression of a groove on the ten- don where it enters a guiding tunnel in the hand, or alternatively a nodule may arise on sheath or tendon and lock the mechanism when it is squeezed within the sheath. In either case, the flexor muscles are able to flex the finger against the resistance of the trigger mechanism, but the extensors are too weak to straighten it out after locking. The finger must then be extended by external manipulation and this extension is usually accompanied by a small click caused by the sudden release of a groove or nodule. All trigger-controlled hand or power tools should be subject to careful biomechanical an- alysis. Often triggers can be replaced by push- buttons which can be operated easily by the thumb. Unlike the other fingers, the thumb is flexed, abducted and opposed by strong short muscles located within the palm of the hand. It can therefore actuate pushbuttons and triggers repeatedly and strongly without fatigue. The handles of rotating tools should be posi- tioned at an angle of roughly 120° with the longi- tudinal axis of the tool. This angle is desirable because the axis of rotation of the forearm runs from the lateral side of the elbow through a point located roughly at the base of the ring finger (Figure 32-38). However, the optimal axis for transmission of thrust runs from the base of the index finger through the center of the capitulum of the humerus. It runs parallel with the longi- tudinal axis of the forearm and at an angle of ap- proximately 10° with the axis of rotation, while the “axis of grip” of the closed fist runs at an ULNAR NERVE Figure 32-33. angle of 70° with respect to the best line of thrust transmittal. If thrust is required for the effective operation of a tool, then the implement should be designed so that this force vector is directed towards the base of the thumb and the broad distal end of the radius (Figure 32-38). Thrust should never be applied so that it acts against the heel of the little finger because this would produce a bending mo- ment on the wrist which could cause fatigue, dis- comfort and, in extreme cases, trauma to nerves, tendons or blood vessels. It is often possible to design a rotating tool so that its tip emerges from the hand between the middle and the ring finger, or if thrust is required, between the index and the middle finger. This, in spite of its occasionally awkward appearance, pro- duces excellent results from the point of view of working comfort and endurance. Optimal musculo-skeletal configuration of the forearm may frequently be achieved by bending the tool instead of flexing the wrist. 460 rains Segre. MEDIAN NERVE ARTERIES MEDIAN NERVE Position of the Most Important Arteries and Nerves in the Palm of the Hand. Materials and Weights for Tools and Handles Tool weight should be determined according to the nature of the task to be performed. A tool housing vibrating components, especially pneu- matic and power tools, should be sufficiently heavy to possess inertia adequate to prevent transmis- sion of excessive vibration onto the human body. If this requires excessive weight, then recourse should be taken to suspension mechanisms and counterweights. The center of mass of heavy tools should be located as close as possible to the body of the operator in working posture and preferably on a transverse plane passing through the umbili- cus (Figure 32-39). Materials for tool handles to be operated by the ungloved hand should be poor conductors of heat and electricity. All han- dles should have a surface texture rough enough to permit secure gripping and avoid slipping in operation. Handles should be hard enough so that they will not allow chips, small components, grit or injurious materials to be imbedded. They Figure 32-34. Form-fitting hand tools often fit only the hands of the designer. When an over- sized or undersized hand grips a finger grooved handle, then undesirable pressure upon the surfaces of the joints may be exerted. should also be made of nonporous materials so that they will not soak up or retain oils or other liquids. *® Power Tools The operating mechanism of most power tools are either reciprocating (i.e., vibratory) or rotary. They are operated by either compressed air or by electricity. When selecting reciprocating or vibratory tools, the frequency and amplitude spectrum of the vibrations transmitted onto man should be evaluated.*® The risk of somatic resonance re- sponse is highest when amplitude exceeds 100 microns within a frequency band between 3 to 125 Hertz. This has already been discussed in general terms under the heading of “Man-Equip- ment Interface.” With respect to the operation and selection of hand tools, Raynaud’s Syndrome (i.e., White Fingers) provoked at critical fre- quencies or potential exacerbation of developing bone and joint disease, deserves careful consider- ation. When tools are activated by a rotating mech- 461 anism, the maximum torque transmitted upon the axis of rotation of the forearm should be below 12 inch-lbs. A 2-handed power tool should be designed with an angle of 120° between the grip- ping axes of both hands (Figure 32-40) for opti- mum operation when firmly held. Tools powered by electricity should not be operable without a ground line which uses the third or middle prong of the power plug. Make- shift conversion from 3-prong to 2-prong adaptors should be prevented by appropriate plug and socket design. MANUAL MATERIALS-HANDLING AND LIFTING Almost one-third of all temporarily disabling injuries at work are related to the manual handling of objects.” Many of these are avoidable and are the consequence of inadequate or simplistic bio- mechanical task analysis. The Elements of a Lifting Task Relative severities of materials-handling oper- ations and differences in lifting methods can only Basmajian, J. V.: Muscles Alive: Their Function Re- vealed by Electromyography, 2nd Edition. Baltimore, The Williams & Wilkins Co., 1967. Figure 32-35. The fingers buttress against each other when flexed.” be evaluated when all elements of a lifting task are considered together as an integral set (Table 32-3). All these elements are of different mechanical dimensions (Table 32-4) but, nevertheless, have one basic property in common. Any change in Figure 32-36. Through the carpal tunnel (A) pass many vulnerable anatomical structures: blood vessels (B) and the median nerve (C). Outside of the tunnel, but vulnerable to pres- sure are: the ulnar nerve (D) and a major artery, the palmar arch (E). 462 Tichauer, E. R.: Gilbreth Revisited. New York, American Society of Mechanical Engineers, 1966. Figure 32-37. Too wide a pistol grip on an electric hand drill prevents a firm grasp be- cause distal phalanx of a finger cannot be flexed strongly unless middle phalanx has been prepositioned by bending. A grasp around a handle which is too wide will pro- duce large compressive forces on joints and may lead to joint disease or trigger finger if tool is used often enough and long enough.™ magnitude of any element of a lifting task pro- duces a change in magnitude of metabolic activity. Thus, no matter what the dimensions of mechan- ical stress imposed upon the human body during materials-handling are, the physiological response will result in increased energy demand and release, conveniently measured in “calories.” Therefore, physiological response to biomechanical lifting stress has always the dimensions of work. Hence, the measurement of metabolic activity through computation of oxygen uptake per unit of time provides a convenient experimental method for the objective measurement of the relative severity of materials-handling and other chores. The current consensus’ assumes on the basis of an 8-hour working day, that the limit for heavy continuous work has been reached when oxygen uptake over and above resting level approaches 8 kilo-calories per minute. 6 kilo-calories per minute seems to be the upper limit for medium heavy continuous work while an increment of 2 kilo-calories per minute appears to be the dividing line between light and medium-heavy work (Table 32-5). However, application of metabolic measure- ment is often not possible. The procedure re- quires expensive equipment, great expertise and is often difficult to perform on the shop floor. Fur- thermore, the objective assessment of work stress through the analysis of respiratory gases is an ex post facto procedure. The job exists already and its energy demands are computed so that possible corrective action may be considered. It is, of course, much better to analyze a task objectively while both job as well as workplace layout are Figure 32-38. A= the hinge joint between ulna and humerus from the medial side B = the right forearm outwardly rotated C= the right forearm medially rotated a = humerus g b = trochlea of humerus ¢ = capitulum of humerus d = thrust bearing formed by capitulum and head of radius e = head of radius = radius g = ulna h = attachement of biceps i = axis of rotation of forearm j = optimal axis for thrust transmission /; THE CONSTRUCTION OF THE SKELETON OF THE FOREARM. 463 —— nn — UMBILICAL LEVEL Figure 32-39. the center of mass of a heavy two-handed powertool should be located in that transverse plane which passes through the umbilicus. The axis of action as well as Figure 32-40. the axes of the handles of a two-handed power tool should approximate 120 degrees to achieve optimal biomechanical posture. The included angle between still in the design stage. Recourse must then be taken to elemental analysis. By definition, a state of lifting exists whenever a moment — no matter in which direction — acts upon the vertebral column. A “moment” is de- fined as magnitude of the force times distance of application. The three “static moments” (Table 32-3/a) are easy to compute, either from draw- ings, from photographs, or by speculative analysis. Moments are conveniently expressed in foot- pounds, multiplying the force acting upon an ana- tomical structure with its distance from the point of maximal stress concentration. The heaviest article normally handled by man at work is his 464 own body. Only rarely do workers handle ob- jects weighing 150 lbs., and, in most instances, the mass of an object moved is quite insignificant when compared to the weight of the body seg- ment involved in the operation. For example, the majority of handtools or mechanical components in industry weigh considerably less than '2 Ib. but an arm, taken as an isolated body segment, weighs 11 lbs.?* #8 The sagittal lifting moment is the one easiest to compute and is of greatest severity when lift- ing loads and putting loads down right in front of the body. It is most conveniently derived by graphical methods. First, the weights of the body segments involved in a specific task are obtained from reliable tables. Then a “stick figure” of proper anthropometric dimensions (Figure 32-41) is drawn and the location of the center of mass for each body segment as well as for the load han- dled is marked. Finally, the sum of all moments acting upon a selected anatomical reference struc- ture (in this case the lumbo-sacral joint) is com- puted and becomes the sagittal biomechanical lift- ing equivalent of the specific task under considera- tion. The estimation of sagittal lifting equivalents is of great practical usefulness in the comparison of work methods. It is often necessary to decide if a task is better performed sitting as opposed to standing (Figure 32-42). A schematic sketch or a photograph is then a convenient aid to decision making. The masses involved, i.e., the torso above the lumbo-sacral joint plus neck, head, upper limb and the object manipulated are identical for each individual, in both the seated and standing postures. According to data by Abt,> the body mass in the case of a 110-Ib. female would be 45 Ibs. To this, the weight of the object handled, in this case, 20 1bs., is added. Then computing mo- ments,” °7 the distance from the lumbo-sacral joint to the center of mass of body segments and load combined equals approximately 1V2 ft. (Fig- ure 32-42/L). However, in the case of a seated individual, value “L” becomes approximately 212 feet. This is due to the forward leaning posture of trunk and the outstretched arm. Therefore the torque exerted on the lumbar spine now is in- creased to 146 ft.-Ibs. or nearly 50% more than when standing. This explains why, in so many instances, when unnecessary chairs are introduced in the work situation, workers, instead of being overjoyed, complain rightly about much increased work stress. Analyzing lifting tasks routinely in terms of moments tends to develop in supervisors a healthy and critical attitude toward cut and dried “cook- book rules of lifting.” The principle of “knees bent-back straight-head up” is well enough known. However, a simple diagram (Figure 32-43) shows that in many work situations sensible con- cessions must be made to the influence of body measurements on work stress. In Figure 32-43 “Mr. X,” long legs, short torso shows the anthro- pometric configuration of a typical male; while “Ms. Y,” relatively long torso and fairly short legs, has female body characteristics. It can be 3135! INCH LBS Figure 32-41. Graphic computation of the location of center of mass of whole body and body segments as well as of the sagittal moment acting upon the lumbo-sacral joint can be conveni- ently accomplished through the use of stick figures. This example shows that an improper working posture, a load weighing only 30 Ibs., combined with the mass of the various body segments involved in a lifting task, may produce a torque exceeding 3000 inch-Ibs., which is the lifting equivalent of a very severe task. readily seen that “Mr. X” does not benefit at all from application of the standard lifting rule sim- ply because his body build prevents him from get- ting under and close to the load. Therefore, dis- tance “L” in Figure 32-43/b is no shorter than distance “L” in Figure 32-43 /a; therefore, the mo- ments acting on the lumbar spine are the same in both cases. Ms. “Y,” however, due to a differently proportioned body, can get under the load and close to it. Thus, distance “L” now becomes much shorter and the moments on the lumbo-sacral joint 465 and therefore, also work stress, are approximately halved. Under such circumstances, provided that the height of the workbench cannot be changed, the standard lifting rule may be applied to the female, while in the case of the male, no benefit is derived. To the contrary, working in the “ap- proved lifting posture” may lull a male worker into a sense of false security. It has already been described earlier (Fig- ure 32-33) how a light but bulky object will often impose a lifting stress much greater than the one A = Humerus 8B = Socket of Hip Joint C = Vertebral Column D = Shoulder Joint E = Arm F = load G = Muscles of the Buttocks (Gluteus Maximus) H = Muscles of the Back (Sacro-Spinalis) + I = lumbo-Sacral Joint J = Spinous Process of a Vertebra K = Trapezius Muscle L == Distance from the Center of Mass of Combined Body-load Aggregate to the Joints of the Lumbar Spine Tichauer, E. R.: Ergonomics of Lifting Tasks Applied to the Vocational Assessment of Rehabilitees. Rehabilita- tion in Australia, Oct. 1967, pp. 16-21. Figure 32-42. A change from standing to seated working posture may move the centre of mass of the combined body load aggregate away from the lumbar spine and thus increase stress there. When changing from standing to seated work, reach length should be kept as short as possible.?? exerted by a heavier article of greater density. Indeed, the ergonomic problems resulting from recent trends in miniaturization and containeriza- tion have added a serious and perhaps sinister overtone to the age-old jocular question: “Which is heavier — one pound of lead or one pound of feathers?” The feathers, of course; they are so much bulkier! In many instances, however, other moments in addition to the sagittal one must be considered. Lateral bending moments assume importance whenever a job calls for ‘“side-stepping” (Figure 32-44) or the handling of materials on trays. Like- wise, consideration of torsional moments becomes necessary when materials are transferred from one surface or workbench to another (Figure 32-45). All moments like the other elements of a lift- ing task add up, not algebraically but vectorially. The magnitude of lateral and torsional moments is computed by procedures similar to the one de- scribed for the sagittal moment. Often a mathe- matical computation becomes unnecessary because trained ergonomists soon develop the knack to “guesstimate” rather correctly the magnitude of all three moments by looking at the worker, mo- tion pictures or a drawing of the workplace layout. It may be assumed that, when the vector sum of all three moments is 350 inch-lbs. or less, the 466 A B "WRONG" POSTURE "APPROVED" POSTURE Tichauer, E. R.: Ergonomics of Lifting Tasks Applied to the Vocational Assessment of Rehabilitees. Rehabilita- tion in Australia, Oct. 1967, pp. 16-21. Figure 32-43. Postural corrections in train- ing for lifting should be aimed at reducing torques acting on the spine. “X,”” an anthro- pometric male, does not benefit materially from the “approved” lifting posture because “L,” the distance from the center of mass of load to the fourth lumbar vertebra, does not shorten materially. ““Y,” an anthropometric female, does benefit from the “bent knees, straight back’ rule because she can get under the load. When matching worker and task, the measurements of the individual worker as well as the dimensions of the workplace should be considered.®? work is light and can be performed with ease by untrained individuals, male as well as female, ir- respective of body build. Moments above this level but below 750 inch-lbs. put a task into the classification of “medium-heavy” requiring good body structure as well as some training. Tasks above this but below 1200 inch-lbs. are considered to be heavy requiring selectivity in the recruitment of labor, careful training and attention to rest pauses. Whenever the vector sum of moments exceeds those stated before, then the work is very heavy in nature, cannot always be performed on a continuing basis for the entire working day and requires great care in recruitment and training. Figure 32-44. Side stepping induces heavy lateral bending moments acting on the spine. (from: SPARGER, C.—Anatomy and Ballet-by A. and C, Black Ltd., London, 1960). The gravitational components are elements of a lifting task which are always present. In physics work is defined as a product of force and the distance through which this force acts. Thus, lifting 10 Ibs. against gravity to a height of 5 feet will constitute 50 foot-lbs. of work. Likewise, pushing an object horizontally for a distance of 5 feet when 10 Ibs. of pushing force are required to perform this task throughout this distance will also result in 50 foot-lbs. of work. This definition, however, is not always applic- able from the standpoint of work physiology. For example, if an individual pushes with all his force against the wall and moves neither his body nor the wall, he has not accomplished any work in the sense of physics. Nevertheless, during the entire time while his muscles are under tension, his metabolic activities have increased, and the added energy demands of the living organism manifest themselves in the expenditure of additional cal- ories which, in physics, are assigned the dimensions of work. The event which causes such physiolog- ical work to be performed is called “isometric ac- tivity.” Isometric “work” is performed whenever a muscle is under tension, but produces no visible motion. Another kind of “physiological work” is “tension time.”"* This also results in an increased expenditure of calories and is performed whenever muscle is under tension for an interval of time. Tension time is always present and must always be taken into consideration whenever a materials- handling task is performed. It can be estimated simply by taking the weight of the object handled plus the weight of the body segment involved in the task, and multiplying this by the time the musculature is under tension. Both “isometric work” and “tension time” are assigned the dimensions of “impulse” which equal force multiplied by time. For the practical purposes of work stress estimation, “isometric work” and “tension time” are added algebraically together, and their sum, named the “isometric component” 467 . (as distinct from “isometric work) is in turn added vectorially to the other gravitational com- ponents (Table 32-3). A vector defined by the dimensions of im- pulse is obviously not additive with other vectors carrying the dimensions of work. To overcome this difficulty, a simple mathematical transforma- tion is useful.”® Dynamic work is defined as the product of the weight of an object handled multiplied by the ver- tical distance through which it is lifted upwards against gravity. It has the dimensions of work as defined by physics. Negative work is performed whenever an ob- TABLE 32-3 The Elements of a Lifting Task (a) Static (b) Gravitational (c¢) Inertial Moments Components Forces sagittal isometric acceleration lateral dynamic aggregation torsional negative segregation (d) Frequency of Task ject is lowered at velocities and accelerations of less than gravity so that work against the gravity vector is performed. To avoid complex computa- tions, it is practical under industrial working con- ditions to accept the recommendation by Kar- povich™ to assume that one-third of that work which would have been expended when lifting the same object over the same distance in an up- ward direction is approximately equal to the dy- namic work equivalent of the task. Finally, the inertial forces have to be consid- ered. Often acceleration over several inches of distance is too insignificant to demand numerical evaluation of this vector, provided that isometric activity is given due consideration. However, the forces involved in the aggregation and segregation of man and load do affect work stress to a high degree. In order to maintain equilibrium in upright posture, it is necessary that the center of mass of the body be located above a line passing through the sesamoid bones of the big toes. Whenever a load is lifted, then object and human body be- come one single aggregate and during the act of aggregation, the combination of load and body and the formation of a single center of mass exert forces upon vulnerable anatomical reference points. Likewise, during segregation the displace- ment of the center of mass of the body exerts forces on diverse anatomical structures. Inertial forces have the dimensions of mass multiplied by acceleration (i.e., force). Objects such as are commonly handled in industry are lifted (i.e., aggregated) over approximately three seconds, while release (i.e., segregation) is much faster requiring only a time interval of somewhat less than 1/25th of a second. Therefore the se- verity of a lifting task is greatest at the instant of " TOP VIEW x L = lumbo-sacral joint Figure 32-45 & 46 (A & B). Schematic Drawing of the Lifting Task Evaluated Quantitatively in the Text of Standing (A) and Seated (B) Position. Solid lines describe posture at beginning, broken lines posture at end of task. 468 load release. It was already mentioned that the severity of a lifting task can be reliably evaluated by theo- retical analysis. Under such circumstances, all the elements of a lifting task as listed in Table 32-3 are described quantitatively and the values then added as vectors. The addition of vectors, how- ever, demands that the quantities involved in the computation are of identical dimensions. There- fore it is necessary, prior to final computation, to reduce the elements of a lifting task to values with compatible dimensions. It was already established by the pioneers of work physiology’ ®' that the basic activity of the musculo-skeletal system lead- ing to increased energy demands, expressed in terms of calories (dimensions of work) would be isometric effort (dimensions of impulse). Work with rehabilitees caused researchers in the immediate period following World War II to assume that for computational purposes it would be desirable to reduce all elements of physical work to quantities having the dimensions of im- pulse (i.e., force X time). The soundness of this approach was validated by Starr.” To make all elements of a lifting task dimensionally compatible with isometric effort, the following operations are performed: 1. The vector sum of the three moments is divided by distance (moment arm) and multiplied by performance time. The total physiological effort equivalent of isometric dynamic and negative work is obtained from the formula: physiological effort equivalent = fmla+tgldt where t is performance time and a is ac- celeration other than gravity, while g is the acceleration due to gravity and m equals mass. 3. The inertial forces of acceleration, aggre- gation and segregation are multiplied by their time components. This converts all elements into equivalents of physiological effort with the isometric dimensions of IbF sec or Force lbs. multiplied by time. The following practical example will illus- trate in step by step fashion the mode of applica- tion of this approach to lifting problems. Solved Problems The lifting and transfer of a box weighing 30 Ibs. from a table to a sideboard without side-step- ping can be performed either seated or standing (Figure 32-46). When standing the object is picked up from a point in the midsagittal plane two feet in front of the midcoronal plane. It is put down in the mid- coronal plane two feet to the right from the mid- sagittal plane. Operation time amounts to two seconds per box and maximum height of lift is 3 inches. Frame by frame film analysis shows aggregation and segregation times to be 0.5 sec- onds and 0.04 seconds respectively, while seg- mental analysis (Figure 32-41) permits the as- sumption that the displacement of the center of gravity of the body in aggregation and segregation equals 2 inches. [SS] 469 When the worker is in a seated position, and the workbench interferes with knees and other an- atomical features, the worker must move further away from the task, and now the distances from the coronal and sagittal plane respectively will equal 30 inches. Performance, aggregation and segregation times are now 4 seconds, 0.6 seconds and 0.05 seconds respectively. The changed pos- tural configuration increases the displacement of the center of mass during aggregation and segre- gation from 2 inches to 3 inches and the maximum height of lift from 3 inches to 8 inches. For the purposes of comparative work stress evaluation, the following assumptions are made: I. Accelerations and decelerations are con- stant and equal in magnitude for all dis- placements. The path of the center of mass of the box approximates a straight line from pick-up point to the maximum height of lift. 3. Peak velocity of displacement is attained midway between aggregation and segrega- tion points, and is assumed to be twice the average velocity. 4. The load accelerates from 0 to peak velo- city and decelerates back to 0. Sagittal and lateral moments are obtained in IbF ft, by multiplying the weight of the box by its distance from the midcoronal and midsagittal plane respectively. To compute the torsional mo- ments, the mass of the box is multiplied by its acceleration and the resulting force multiplied by the distance. The weight of trunk and arms was neglected in these calculations because they are constant for both postures, and their inclusion would have increased the complexity of compu- tation considerably without materially increasing the accuracy for the purposes of estimation. The following symbols will be used through- out calculations: w = weight of the load m = mass of the load W = weight of the man M = mass of the man 1bF = pounds force 1 =reach of arm in ft. t = operating time in seconds. a=uacceleration and deceleration during the operation b= acceleration and deceleration during aggregation ¢ = acceleration and deceleration during segregation S = total path travelled during the operation in ft. h = height to which the load is lifted in ft. t’=aggregation time in seconds. t”” = segregation time in seconds. x = distance through which the center of gravity moves in aggregation and segregation. Subscript 1 denotes standing position. Subscript 2 denotes sitting position. [39] The numerical values of those parameters which describe adequately both lifting tasks, the standing and the seated one, for the purposes of quantitative analysis, are stated in Table 32-4. On the basis of these values, the elements of both lifting tasks are now computed as represented in Table 32-5. Now the values obtained are made isodimensional with physiological isometric effort for the purposes of computation as derived in Ta- ble 32-6. Finally, the total level of physiological effort for standing and seated work while per- forming the lifting task is computed by the meth- ods shown in Table 32-7. The results of this analytical exercise, provided that the frequency of lift is the same in both cases, shows clearly that in this case a standing working posture requires far less effort and that the provision of seating accommodations far from making the task easier, would require almost twice the effort expanded by a standing worker. As this chapter addresses itself specifically to biomechanics proper, a comprehensive treat- ment of lifting and materials-handling would ex- ceed the boundaries of the section and lead to overlap with other chapters. Nevertheless, occu- pational safety and health problems stemming from manual materials-handling are numerous and complex. Therefore, wide cross-reading on all aspects of manual materials-handling is recom- mended. By way of illustrative examples, culled from a larger number of equally excellent publi- cations, Astrand®® and others" are cited as a good source of reference on work physiology. McCor- mick deals in a comprehensive fashion with the. human factors aspects of lifting and back prob- lems while Snook" and Snook and Irvine® treat the psycho-physiological aspects of the problem extensively. Finally, the publications of the Na- tional Safety Council,” Himbury*® and Gri- maldi®® are recommended as general references which place the problem of manual materials- handling into proper perspective with respect to the overall problem of occupational safety and health. MEASUREMENT AND EVALUATION IN BIOMECHANICS Americans have always been a nation of prob- lem solvers. The history of this country in fields economical and social, as well as technological, bears ample witness to this. Thus it is but logical that all industrial, as well as technological develop- ment in this country stems from the need to over- come and solve problems of design, production, distribution and use of manufactured articles. However, the very concept of “problem solving” implies that an existing situation is unsatisfactory and must be improved. Therefore American in- dustry traditionally has subscribed to the “im- provement approach” as the principal avenue to- wards economic efficiency and viability of private enterprise. This, in many instances, has led to TABLE 32-4 Numerical Values of Parameters Describing Lifting Example Values Symbol Standing Sitting t t, =2.00 secs t,=4.00 secs t’ t’ =0.50 secs t, = 0.60 secs t” t'7=0.04 secs t7=0.05 secs l [,=2 ft. 1,=2.5 ft. h h,=1/4 ft. h,=2/3 ft. X x, =1/6 ft. x,=1/4 ft. S=2)/F+h S,=2]/2:+ (1) S,=2 Gor (2) 2 2 4 2 3 =2.8722 ft. =3.7784 ft. a=4S a, =4(2.8722) a,=4(3.7784) t? 22 42 =2.8722 ft/sec? =.9446 ft/sec? b=4x b,=4(1/6) b,=4(1/4) (t)? 0.52 0.6° =2.6664 ft/sec? =2.7777 ft/sec? c=4x c,=4(1/6) c,=4(1/4) (t”)? 0.04 0.05% =416.6250 ft/sec? =400.0000 ft/sec? 470 TABLE 32-5 Values of Elements of Lifting State in Their Proper Dimensional Units Values Elements Standing Sitting Sagittal Moment = wl Lateral Moment =wl Torsional Moment =mal Isometric + Dynamic + Negative Work ={'m|a+g|dt Acceleration Force =ma Aggregation Force =(m+M)b Segregation Force =(m+M)c Vector Sum of Moments = (sagittal moment)? + (lateral moment)? + (torsional moment)? }/2 wl, =30(2) =60 IbF ft wl, =30(2) =60 IbF ft ma, =.9316(2.8722)2 =5.3514 IbF ft J .9316(2.8722+32.2)dt =(.9316) (35.0722) (2) = 65.3464 1bF sec .9316(2.8722) =2.6757 IbF = (.9316+ 6583) (2.6664) =14.9049 IbF =(.9316+4.6583) (416.6250) =2328.8920 IbF Y60%+ 602+ (5.3514) 85.3514 IbF ft wl,=30(2.5) =75 IbF ft wl,=30(2.5) =75 IbF ft ma,l,=.9316(.9446) (2.5) =2.1997 IbF ft J .9316(.9446+32.2)dt = (.9316) (33.1446)4 =123.5100 IbF sec 9316 (.9446) =0.8799 IbF (.9316+4.6583) (2.7777) =15.5270 IbF =(.9316+4.6583) (400) =2235.96 IbF = Y(75)*+ (75)*+ (2.1997)? =106.0888 IbF ft TABLE 32-6 Values of Elements of Lifting in Physiological “Work” Units with Their Calculations Element Standing Sitting Work due to Moments =85.3514 (2) =106.0888 (4) = vector sum in IbF ft * t 2 2.5 l Isometric + Dynamic + Negative Work Acceleration Work =ma-t Aggregation Work =85.3514 1bF sec =65.3464 1bF sec =2.6757 (2) =15.3514 1bF sec = (14.9049) (.5) =7.4524 1bF sec =169.7420 1bF sec =123.5100 1bF sec = (0.8799) (4) =3,5196 1bF sec = (15.5270) (.6) =9.,3162 1bF sec =(m+M)b-t Segregation Work =(m+M) ct’ = (2328.8920) (0.04) =03.1556 IbF sec = (2235.96) (0.05) =111.7980 IbF sec uneconomic product design and manufacturing methods. Particularly prior to the development of rational methods of workplace design as are available today, it was accepted procedure to con- ceive products hastily, establish manufacturing processes intuitively, and then, on the shop floor, during actual production runs to review gradually deficiencies in product design or manufacturing methods. Such improvement normally takes place over several months or years. This approach was not only feasible, but also highly desirable during past decades when, for example, the “T” model - of the Ford remained in full production for ap- 471 proximately 30 years. In the past, this very same classical process of gradual improvement of prod- ucts as well as method was also applied success- fully to the reduction of health hazards and the redesign of stressful work situations. First evidence of work-induced trauma and occupational disease was obtained then the causes were identified and eventually removed. The effectiveness of “improvements” in both fields economical as well as occupational health are customarily measured in terms of “cost re- duction.” In many industries “cost reduction” is expected as a matter of course from supervisory TABLE 32-7 Physiological “Work” in LbF sec Physiological “Work” LL. in 1bF sec Description oo Standing Sitting Moments (Vector Sum) 85.4 169.7 Work (Isometric + Dynamic + Negative) 65.3 123.5 Acceleration 5.4 3.5 Aggregation 7.4 9.3 Segregation 93.2 111.8 Total 256.7 417.8 and engineering personnel during the first months or years of production of a new article. This helps produce a strong temptation among those who are responsible for “efficiency” to design products and work methods initially imperfect to provide opportunities for later cost reduction. This, of course, is false economy which may well lull management into a sense of false security while a competitive position is being lost. The trait of viewing “cost reduction” as the only index of managerial effectiveness is especially strong in enterprises which maintain effective cost accoun- tancy systems. There cost avoidance is occasion- ally actively discouraged because it is not easy to measure in terms of dollars and cents, while cost reduction shows up clearly in the ledger. Often the practitioner in ergonomics is chal- lenged to justify his activities in terms of savings accrued by the improvement of existing opera- tions. There are three main areas of evaluation of ac- tivity which are of prime interest to the practi- tioner in industry: (1) historical evaluation: (2) analytical evaluation: and (3) projective evaluation. Historical Evaluation The improvement and cost reduction ap- proaches outlined above are so firmly ingrained in industrial practice that quite often interest of manufacturing enterprises in biomechanics is in- itially triggered by a patently obvious breakdown in occupational safety and health resulting in in- creased manufacturing expense, poor personnel relationships, and a distorted image of corporate objectives, projected to consumers. The result is normally a request for historical evaluation of past activities and events. Such study is normally conducted within the framework of reference of the “four big C's” of any investigation of a break- down in occupational safety and health: 1. Cause. 2. Consequence. 3. Cost. 4. Cure. In most instances, the consequence and the cost are known; what remains to be discovered is the true cause and the cure. 472 In any such study, theoretical analysis is the most powerful tool available to the investigator. Experimental methods are often not only ex- pensive and lengthy, but also quite superfluous when applied to a critique of events of the past. In addition, the procedures of theoretical analysis offer a depth of scope and a degree of privacy and confidentiality not available whenever experimen- tation with man as a subject is conducted. The investigation is normally initiated by iden- tifying the environmental stress vectors (Figures 32-19 & 32-20) which may be implicated. When- ever mechanotaxis could be one of the possible vectors involved, then the next step would be to ascertain if the principles of motion economy (Ta- ble 32-1) or the prerequisites of biomechanical work tolerance (Table 32-2) were to some ex- tent disregarded in the design of products or work methods. Step by step, to check out pro- cedures with the aforementioned tables in hand is the best approach. At this juncture, it is often possible to suggest possible causes for the observed anatomical, physiological or behavioral failure and frequently, an inexpensive and easily applied corrective action may be suggested. It should however be constantly borne in mind that too simplistic an approach may prevent the de- tection of the actual anatomical failure points. The locus of observation of evidence of work strain is frequently quite remote in terms anatomical as well as in time from the point of application of work stress mechanism. This is, in fact, very often the case when less than due attention has been paid to the biomechanical prerequisites of work tolerance. Then the following questions should be asked: 1. Are the muscular constituents of the ki- netic element involved large enough to perform the task without undue fatigue? 2. Do hand tools, machine controls, or other mechanotactic vectors evident at the work- place interfere with adequate blood sup- ply to the muscle masses performing the actual work? 3. Are all kinetic chains working at adequate levels of mechanical advantage? 4. Are the sensory feedback mechanisms in the kinetic chain adequate to elicit some protective response by the worker to ex- cessive stress? Whenever the frequency of incidence of oc- cupational ill health or accidents increase, after a manufacturing process has been in safe operation for some time, then the following questions should be asked: WHAT CHANGES IN EQUIPMENT DESIGN, TOOLS USED, WORKING POPULA- TION EMPLOYED OR WORK METHOD AP- PLIED HAS TAKEN PLACE IMMEDIATELY PRIOR TO THE BREAKDOWN OF HAZARD CONTROL? A case study will illustrate the power of theo- retical analysis. A case study in historical evaluation of the bio- mechanical causes of a series of accidents. In a factory producing basic chemical materials, a sud- den and dramatic increase of “pedestrian acci- dents” was observed. Workers crossing aisles were hit by fork-lift trucks transporting materials on pallets. Common human-factors engineering approaches were explored, the trucks made more visible and zebra-striped, the aisles better lit and automatic warning horns were installed on some of the vehicles. However, none of these measures was of any avail. Then the question was asked: Why were so many workers crossing the aisles and walking around instead of being seated in comfort and safety at the workplace? Work samp- ling studies™ revealed two things: firstly, that the accident frequency was proportional to the density of pedestrian traffic in the aisles and, secondly, that from a certain date onwards brief periods of absenteeism from the workplace had increased dramatically in number and, consequently, more people were walking in the aisles at any instant. The time of this change of workmen’s bchavior coincided with the introduction of a new tool. A rather expensive electrical brush used to clean trays was replaced by a much cheaper and appar- ently far more effective paint scraper (Figure 32-26). As stated under the “Prerequisites of Biomechanical Work Tolerance” (Table 32-2) I-1, the new and cheaper tool interfered with the blood supply to the ring and little finger. The re- sulting numbness and tingling caused the individ- uals afflicted to lay down their tools at frequent intervals and to seek relief by exercising their hands. First, line supervisors tried to counteract the decrease in productivity by frequent admoni- tions. Now, in order to avoid arguments with their supervisors, workers simply made use of every conceivable opportunity for brief absences from the job. Trips to the washroom, the tool room, the store, etc., became rather frequent, and this was the true cause of the rapid increase in acci- dents unjustly ascribed to the fork-lift trucks. The first of the four big C's, the true cause of the accidents, had been identified as absence from the workplace produced by an ergonomically incorrect designed tool. It only remained to develop a cure. The handle of the paint scraper was redesigned (Figure 32-47). As a result, workers spent more time per day in productive activity and thus out- put and economy of operation increased, while at the same time, due to diminished exposure to vehicles in the aisles, accident rates returned to normal. Analytical Evaluation The procedures of analytical evaluation are most often called for when an already existing manufacturing operation is generally satisfactory but has to be improved, either in order to make it more competitive or to reduce training time, to eliminate operator discomfort and to enhance the health and well-being of the working population. Theoretical analysis applied as described in the aforegoing paragraph is the initial step in all an- alytical evaluation. However, very often this will not suffice and certain experimental measures must be employed. The simplest and perhaps most effective aid in this kind of study is cine- matography and subsequent frame-by-frame an- alysis. This will permit a detailed evaluation of 473 Figure 32-47. Redesigned Paint Scraper, Eliminating Interference with Blood Supply in the Fingers as Described in Figure 26. the worker's reaction to each event at the work- place, and to each contact with tool, machine, or manufactured article. Very often slow-motion viewing of the manufacturing operation will reveal biomechanical or ergonomic defects as well as re- flex reactions which cannot be detected with the naked eye because of the brief duration of many such events. The fact that the “hand is quicker than the eye” is well known to stage magicians who wish to deceive the spectators in the audience. The movie camera prevents self-deception by the work analyst. There is currently a strong trend towards the use of videotape for such purposes. This should be discouraged because the evolution of videotape is not adequate for the detection of fine details of expression, blanching of the skin, or frame-by-frame analysis. Furthermore, color videotaping is exorbitantly expensive while color film, especially in the Super-8 size, is economical and tells much more than a black-and-white picture. Finally, manufacture of a videotape from movie film is very inexpensive while the converse, i.e., the manufacture of a movie film from a videotape, is a very expensive operation. Fur- thermore videotape, being magnetic in nature, re- quires more careful storage and is sensitive to magnetic fields, and often gets accidentally erased. Motion picture analysis of the work situation should allow the viewing of the workplace at least in two different planes, if a realistic appreciation of all the parameters of the layout is to be ob- tained (Figure 32-48). When movie analysis alone is not adequate as a basis for process eval- uation, then recourse to other experimental tech- nologies must be taken. a. Dynamometry. This is a technique con- cerned with the measurement of the force- time relationship of strength of joint move- ment. It is employed with advantage in fatigue measurement when a lever system intrinsic to a specific kinetic element, made, by means of a mechanical device, to act against a measured force for a fixed num- ber of cycles or a fixed interval of time. Magnitude of excursion of joint movement as well as magnitude of force developed during the activity are both plotted against time. The ergograph commonly employed for the measurement of finger fatigue in industry (Figure 32-49)7® is one of the many useful types of dynamometers. The squeeze dynamometer (Figure 32-50)7° is applicable for the objective measurement of fatigue and work tolerance in squeezing operations of the whole hand, such as are demanded by wraparound grasps of power grips, must be evaluated. The mechanical form of dynamometer used in rehabilitation medicine or physiotherapy is not commonly applicable to industrial circumstances as it is only an indicator of maximal force de- veloped under conditions of a single squeeze. . Myography. Techniques of ergonometry and dynamometry permit the objective di- agnosis of whether an individual is fatigued or incapacitated with respect to the spe- cific job under analysis. Often, however, it is necessary to make a projective pre- diction about the likelihood of fatigue de- veloping sometime in the future, the possi- bility of overexertion of a single kinetic - - - Le Sot fs Nm] Tichauer, E. R.: Industrial Engineering in the Rehabilitation of the Handicapped. J. Ind. Eng. XIX:96-104, 1968. Figure 32-48. A realistic impression of the three-dimensional nature of a task can best be obtained by “mirror-box’ photography. This chronocyclegraph shows changes in the angle of abduction which influence effort levels in three coordinates.** 21d. 11b. Il | ii i {11 ; 0 h] 2 3 A . MINUTES No Load ill lik ill | \ | 0 1 A 1.0 1.1 MINUTES Munn, N. L.: Psychology — The Fundamentals of Human Adjustment, 3rd Edition. Boston, Houghton Mifflin Co., Figure 32-49. FINGER ERGOGRAPH AS DESIGNED BY MOSSO. The pointer at upper left traced a record of movements upon a smoked drum. The first and third fingers are held sta- tionary by being inserted into metal cylinders. Lifting is done by the second finger. 475 Figure 32-50. namometer Permitting to Explain Subject’s Performance Decay as a Function of Fatigue An Instrumented Hand Dy- Due to Shape of Tool Handles. (a) 1%2z-in. handle starting performance, normal pattern. (b) Fatigue pattern after 12 min. of activity. (c) Starting performance in subject with in- flamed tendon sheaths resulting in pro- nounced decay after 2 min. of performance. (d) After 8 min. a complete performance drop in subject c. (e) Subject with damage to ner- vous system. Original performance pattern showing early decay. (f) Same subject asin e, improved performance pattern after work tol- erance training.™ element, reduced work tolerance or other hazards to occupational safety and health. Then it is necessary to establish muscular input — biomechanical output relation- ships. Muscular effort involved in the per- formance of a specific task can conveni- ently be demonstrated by electromyog- raphy. A myogram is an electrical signal obtained from a contracting muscle. Under laboratory conditions, it may be advan- tageous to insert needle electrodes directly into the muscle investigated and record the potentials developed during exertion. This is the type of myogram preferred by phy- sicians for the purpose of clinical investi- gation of neuromuscular disease. In occu- pational biomechanics, however, bioelec- tricity is “assumed to be” merely the by- product of a muscular event which makes it possible to measure strength and sequenc- ing of muscle utilization through tech- niques non-invasive with respect to the human body. This limits industrial biome- chanical procedures to surface electrodes which are adhesive conductive discs similar to those employed in electrocardiography. Before application, the skin is cleansed with alcohol or a similar solvent and good electrical conductive contact between the human body and the electrode is insured by the application of a conductive jelly be- tween electrode and skin. The electrodes are placed so that they “triangulate” the 476 Figure 32-51. ography “Triangulating” the Biceps Muscle to Obtain a Maximal Integrated Myographic Signal. Electrodes for Surface My- individual muscle or muscle group under study (Figure 32-51). A differential am- plifier is then employed to magnify the action potentials so that they can be read on oscilloscopes or paper recorders. A dif- ferential amplifier uses three electrodes, one ground and two active electrodes. It aug- ments only the difference between the two active electrodes. As any interference is common to all three electrodes, it is not amplified. This “common mode” rejection makes imperative the use of differential amplifiers in an industrial setting where electrical interference from fluorescent tubes and all kinds of other apparatus is abundant. Due to the nature of the procedure, surface electrode myography records the summed signal from a number of action potentials simultaneously, depending upon the place- ment and size of the electrodes. Because of the brief intervals of time elapsing be- tween individual action potentials, which is sometimes on the order of a few microsec- onds only, readout devices and recorders may be “overdriven” with respect to speed and time. The signal is then not repre- sentative of the nature of the action po- tential but is conditioned and distorted as a function of the quality of the recording device (Figure 32-52). Even a change in the viscosity of the ink may produce a drastic change in the pattern of the tracing from the same amplifier reproduced on the same recorder. Therefore, in biomechanics, a conditioned type of myogram is em- ployed. It records the sum total of the peaks of the action potentials counted over a sampling interval of time. If the rate at which individual muscle fibers contract is twice as fast, the deflection of the recorder pen will be twice as large. This type of myogram, which is representative of the total number of muscle fibers contracting at any instant, is erroneously but neverthe- less commonly referred to as an “integrated myogram.” Due to the physiological “all or none law,” it is also representative of the effort ex- pended at any instant. As the signal pro- duced requires only a rather slow re- sponse capacity of the recorder, it is re- peatable and easily obtained with rela- tively inexpensive equipment (Figure 32- 53). It is thus possible to ascertain under field conditions if an undue amount of ef- fort is expended in the performance of a specific maneuver. Likewise, the inte- grated myogram shows if there is proper sequencing between muscles involved in an operation. There should always be a “peak and valley” relationship between protag- onist and antagonist muscles (Figure 32- 54). It cannot be too strongly emphasized that the industrial myogram is employed not to detect pathology, but to detect fatigue indi- cated by changes in the pattern of the myo- gram; to establish whether muscles function in the most desirable sequence and whether a specific muscle is actually involved in a specific productive operation. When the areas of application which define also the limits of usefulness of an integrated sur- DIRECT SURFACE MYOGRAM Biceps as Supinator Isometric Torque = app.l4 inch-pound Tichauer, E. R., Gage, H., Harrison, L. B.: The Use of Biomechanical Profiles in Objective Work Measurement. J. Ind. Eng. IV: 20-27, 1972. Figure 32-52. A Simultaneous Recording of the Biceps Muscle Firing Pattern Displayed on a Chart Recorder (Upper Half) and an Oscilloscope (Lower Half) at Exactly the Same Sensi- tivity and Speed. Only five points of similarity are evident, because the signal speed of the myogram exceeds the rise time and slew rate of commercial chart recorders.® 477 "INTEGRATED'' SURFACE MYOGRAM RU Biceps as Supinator | « = TED une — sometric Torque = app.lé inch-pounds J 4 i h Wo r 0.4 sec/cm Tichauer, E. R., Gage, H., Harrison, L. B.: The Use of Biomechanical Profiles in Objective Work Measurement. J. Ind. Eng. IV: 20-27, 1972. Figure 32-53. The Same Biceps Contraction Pattern as Shown in Fig. 52 Chart Recorder (Upper Half), Oscilloscope (Lower Half). However the signals here have been conditioned by summing all action potentials over time so that the trace now represents the analog of the firing rate, which is indicative of the total activity of the muscle mass at any instant during the sampling period. The signals are fully compatible with the frequency response of the chart re- corder. The integrated myogram produces repeatable and very reliable measurements of mus- cular activity levels. face myogram are kept clearly in mind, Preferred fields of application of electro- then this electrophysiological signal will be myography are the comparative evaluation found to be an eminently useful tool in the of handtool designs, of lifting stress when objective analysis of work situations. objects of different weight or shape are to There are, of course, other and perhaps be handled, etc. It is often a more con- even more precise approaches to electro- venient and reliable means of work and myography in fatigue study,” "7" but effort measurement than metabolic investi- many of these require the true laboratory gations. setting of a clinical or research institution. c. The Biomechanical Profile. It is often de- 478 . Ftd be deef ¥ no BICEPS MYOGRAM + nd oo [ ~~ ; eet irrTr PRONATOR TERES MYOGRAM | AN lb fr rh nator teres (antagonist) show peak and valley phasing Pe oy i — { FT Af £4 c I | i t 14 PRONATOR LEAD tre ‘ J & ' - A § : =. BICEPS LEAD $ Figure 32-54. Simultaneously recorded integrated myograms of biceps (supinator) and pro- indicative of proper sequencing of muscle conducive to high work tolerance. sirable to record simultaneously myograms and the readouts from dynamometers. The resulting tracing constitutes a “Biomechan- ical Profile” indicative of the nature of muscular effort-work output-work tolerance relationships. Such Biomechanical Profile permits the objective evaluation and prog- nostication of changes in functional ca- pacity resulting from modifications of man- equipment interfaces. Figures 32-55 and 32-56 illustrate the comparative evaluation of two machine controls. First a T-handle was attached to a rotating dynamometer, and subjects were asked to pronate the supinate against a set resistance. A biceps myogram, as indica- tive of the main supinatory effort, was re- corded simultaneously with an electrical signal proportional to the amplitude of forced the wrist into ulnar deviation (Fig- ure 32-55). The resulting Biomechanical Profile (Figure 32-56) now shows that, when a machine control requires the wrist to be rotated while in ulnar deviation, that the operator must expend twice the force to obtain half the output because the myo- gram is now twice as high while the dis- placement signature shows only half the amplitude. In other words the operator, when using the straight handle instead of the T-handle, would have to apply twice the effort to produce rotation. As the range of excursion of the shaft is halved, he would also have to perform twice as many maneuvers to achieve the same output. Clearly the T-handle is much superior and less injurious to operator health (Figure 32-57). the rotation of the shaft. This then consti- tuted a Biomechanical Profile in simplest form (Figure 32-56). Then a straight han- dle was substituted. This straight handle Projective Evaluation Whenever possible, a job should be ergonom- ically evaluated while it is still in the planning phase. This makes it possible to “design out” of 479 SNRY LET py handle used in (b) y Ve surface ICT eh) BU Figure 32-55. Kinesiometer Measuring Ro- tation of the Forearm Using (a) a Tool Handle Which Permits the Wrist To Be Kept Straight. A surface electrode simultaneously picks up a myogram of the biceps, which is one of the muscles rotating the forearm, and a potenti- ometer attached to the end of the tool shaft measures rotation of tool. (b) A tool handle which forces the wrist into deviation, which is uncomfortable and fatiguing.** the task, features, equipment and maneuvers which are potentially traumatogenic. It also makes it possible to make reliable predictions with respect to the work tolerance of a specific industrial popu- lation, duration of training, and counselling pro- cedures which should be employed while training is in progress. All projective evaluation, be it theoretical or experimental, must include an analysis which shows how sensory input from the workplace is transferred by the musculo-skeletal structure into manipulative output. The ergonomist, under such circumstances, should direct his efforts towards the development of the optimal kinetic chain for the performance of a given task. If projective evaluation demands experimen- tation, then the results of laboratory or field work should be presented in the form of a Biomechan- ical Profile, which, however, is far more complex than the one described in Figure 32-56. Also, un- less the task studied is physically heavy, the dyna- mometer will only be rarely used in projective evaluation. Instead the kinesiometer is employed. The kinesiometer measures the biomechanical parameters of manipulative movements. These are output measurements describing quantitatively the performance elements of a man-task system. In manipulative movement, most commonly dis- placement, velocity and acceleration of the object handled, are used as measures of output efficiency. Displacement is indicative of range and pattern of motion. Velocity serves as an index of both speed as well as strength. Finally, acceleration re- flects control over precision and quality of mo- tion.' Abnormal acceleration and deceleration “signatures” are invariably associated with im- range of rotation 180° rotation a] (a) Figure 32-56. ere Surface myogram of biceps (b) Biomechanical Profile of Forearm Rotation Using Tracing of Tool Rotation and Surface Myogram of Biceps. (a) Wrist straight. (b) Wrist deviated.* 480 WRIST STRAIGHT A = no complaint 36 B = soreness on dorsum of hand F—] C = carpal tunnel complaints 1 D = sore radial aspect of elbow Fl FF] 40° ULNAR DEVIATION TTTTTTT TTT | 4 4 Tichauer, E. R.: Potential of Biomechanics for Solving Specific Hazard Problems. Proc. 1968 Professional Conference, American Society of Safety Engineers, Park Ridge, Illinois, 1968, pp. 149-187. Figure 32-57. Subjective Physical Response Obtained from a Sample of 40 Volunteers Performing the Task Described in Fig. 56.* precise and unsafe movements due to the inability to terminate a motion at the correct place and time. A kinesiometer is described in Figure 32-58. It comprises a task board with lights installed on it and wired so that only one light is on at a time. A metal-tipped “tool” is mounted on a lightweight rod. As soon as the light is touched by the tool, it is extinguished and another bulb automatically switches on. With the help of a programming board, it is possible to generate a sequence of motions simulating an actual job closely, thus avoiding an expensive mock-up of a workplace which may exist at that stage only on the drawing board. The rod attached to the tool is connected to a set of potentiometers so that the movement of the tool in space generates voltage signals which are converted into electrical analogs of the vec- tor sums of each displacement, velocity and ac- celeration of the “tool tip” at any instant. Motion inventories can be programmed through inter- changeable patchboards to simulate occupational motion patterns for a wide range of industries, such as food processing, electronic assembly, or the needle trades. These biomechanical parameters are recorded simultaneously with the electrophysiological para- meters of the kinetic chain of the task (Figure 32- 59). These represent activity of the muscles mov- ing the eyes, the head and neck, the shoulder and 481 the extensors of the wrist. These tracings — al- together seven in number — displaced on the chart recorder constitute the complete Biomechan- ical Profile for this task. Figure 32-60 shows a subject completely electroded for testing. Optimal positioning of electrodes can be easily obtained when consulting standard reference works.™ The profile makes it possible to distinguish between individuals likely to develop either low or high work tolerance (Figure 32-61). In the example shown in Figure 32-61, two workers per- formed exactly the same task, a number of for- ward reaches in identical sequence. Although their production times were approximately equal, the effort required to produce these outputs was markedly different. The activity rate in the deltoid muscle, particularly at low velocity, was generally far higher in the individual with low work toler- ance while, at the same time, the wrist extensor signal remained unstructured. This is indicative of high effort, but disproportionately low output, and predictive of early fatigue. Also, it was seen from the tracings of neck muscle activity that too much scanning was done by the head instead of by the eyes. The lack of purposeful anticipatory eye scanning following a single head movement is also indicative of inferior performance and great discomfort when performing the task over lengthy periods of time. The remedy, of course, is train- ing for proper motion habits, after potentially discomfort-causing performance features have been identified. The Biomechanical Profile can also establish status and quality of the individuals training as well as identify many improper work mannerisms which can be eliminated through proper instruc- tion. Figure 32-62 shows “before practice” and “after practice” performance of the same individ- ual reaching sideways away from body and back. The untrained worker lacks coordination between scanning and wrist movements; the deltoid muscle is in constant tension, indicating that there is a violation of one of the basic prerequisites of work tolerance: Keep the Elbows Down (Table 32-2). The worker was counselled to look straight at the target, then to proceed to reach for it with- out further dependence upon further visual cor- rection, reserving the strongest activity of the wrist for the end of the sequence when time positioning takes place. In the “after practice” profile re- corded, eye and wrist movement are now in proper sequence. Deltoid activity has declined; thus, the level of effort has substantially decreased, work tolerance has increased, and productive out- put has nearly doubled. A kinesiometer can take many forms and can be adapted to a wide variety of jobs, from hand- tool operation to the measurement of the poten- tial traumatogenic effects of equipment displays, and to the measurements of lifting operations. This bridges the gap which since the beginnings of scientific management, industrial psychology and work physiology has plagued most practition- ers in industry. Workers as early as the Gilbreths had already fully established the scientific rationale behind the disciplines of ergonomics and biome- : The use of Biomechanical Profiles in Objective Work Measurement. J. Ind. Eng. IV: 20-27, 1972. The kinesiometer used in this experiment consists of a task board (A) and Tichauer, E. R., Gage, H., Harrison, L. Figure 32-58. a metal-tipped tool (B). When any of the 19 lights on the task board is touched by the tool it is extinguished and another bulb switches on. The tool movement generates voltage signals in three potentiometers (C). The output of this kinesiometer is converted by an analog compu- tation module (D). Also at (D) are the interchangeable patch boards which program the light patterns to simulate any occupational motion pattern. The chart recorder (E) displays the com- plete Biomechanical Profile. Signals are stored in analog form on a multi-channel tape re- corder (F) for computer processing.'* chanics as practiced today. Nevertheless, they strumentation have made it possible to develop. lacked instrumentation adequate to conduct ex- perimental investigations into the physical effort expended by individual muscles in the performance of a specific task. Likewise, the sequencing of action and effort levels of the various muscles involved in manipulative and other maneuvers were beyond the investigative technologies avail- able then. These pioneers were simply fifty years ahead of their time. True enough, the second in- dustrial revolution, due to the fact that the worker in industry is no longer a “free roaming animal” but is constrained to a relatively rigid posture and repetitive motion pattern throughout a long work- ing day, has produced, or aggravated, numerous known and previously unknown industrial ail- ments and complaints. However, the new tech- nologies, as a by-product, also produced the means of disability prevention. The solid-state technologies perfected during recent years and the ensuing miniaturization and improvements of in- 482 kinesiometers and biomechanical techniques which are effective tools of disability prevention raising both the levels of physiological and emotional well-being of the working population as well as the productive levels and the competitive posture of American enterprise. ACKNOWLEDGEMENTS Much of the research leading to the technol- ogies described in this chapter was supported by a grant from the National Institute for Occupa- tional Safety and Health, and to some degree by the Social and Rehabilitation Service of the De- partment of Health, Education and Welfare, under the designation of New York University as a Re- search and Training Center. Dr. Howard Gage helped with the review, and redrafting of the sec- tion on Ergonomic Evaluation of Handtools; while Dr. Ch. Saran assisted with the mathematical mechanics in the section on Materials — Handling. Tichauer, E. R., Gage, H., Harrison, L. B.: The use of Biomechanical Profiles in Objective Work Measurement. J. Ind. Eng. IV: 20-27, 1972. Figure 32-59. The kinetic chain constructed for industrial practice links the major sensory organs and key muscles required to perform a task. In Eye-Hand coordination, sensory input to the eyes is inferred by monitoring the small muscles (R) which rotate the eyeball. To see ob- jects outside a binocular visual cone of 60 degrees, the head must be moved, using (S) the sternomastoid muscles of the neck. Arm movement at the shoulder is produced by (D) the deltoid muscle. Wrist movement is produced by (W) the extensor muscles of the forearm.'¢ C. Gold designed much of the electronic instru- mentation described. My wife, Mrs. Helen Tich- auer, was of great help in literature search and in the drawing and development of illustrations. Fi- nally, the subsection on Projective Evaluation is based upon a paper'” “The Use of Biomechanical Profiles in Objective Work Measurement” by Tich- auer, Gage and Harrison. The painstaking care of Miss E. Schipper in preparation and revision of the manuscript is gratefully acknowledged. References 1. BORELLI, A.: De Motu Animalium, Volumes, (1679). 2. BERNOUILLI, J.: De Motu Musculorum, Physio- mechanicae Dissertatio, Venetiae, 2nd Edition (1721). 3. RAMAZZINI, B.: Essai sur les Maladies de Artisans. (translated from the Latin text De Morbis Artificum by M. de Fourcroy), Chapters 1 and 42 (1777). Romae, 2 483 4. 5. HUNTER, D.: The Diseases of Occupations, 84, Little Brown and Co., Boston (1969). BENEDICT, F. G. and E. F. CATHCART.: Mus- cular Work, a Metabolic Study With Special Ref- erence to the Efficiency of the Human Body as a Machine. The Carnegie Institution of Washington, Washington, (1913). AMAR, J.: Organization Physiologique du Travail. H. Dunod, Paris (1917). TICHAUER, E. R.: “Ergonomics: The State of the Art.” Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio, 28: 105-116 (March-April 1967). TICHAUER, E. R.: “Human Capacity: A Limiting Factor in Design.” The Institution of Mechanical Engineers Proc., Vol. 178, Part 1, No. 37, London, England (1963-1964). DUKES-DOBOS, F.: “Ergonomics in Science and Industry,” Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio, 3/: 561-71 (1970). PATER, A. F. and PATER, J. R. (Editors).: What They Said in 1969. Monitor Book Company, Inc., Beverly Hills, p. 25 (1970). Tichauer, E. R., Gage, H., Harrison, L. B.: The use of Biomechanical Profiles in Objective Work Measurement. J. Figure 32-60. Ind. Eng. IV: 20-27, 1972. Four sets of surface electrodes were placed on each subject, over the mus- cles comprising the kinetic chain, as pictured in Fig. 59. In each set, the third electrode acts as the ground. Electrodes were positioned according to standard muscle testing procedures, so that each myogram obtained represented a maximum amount of contracting muscle mass. All subjects were representative of the female working population commonly found perform- ing manual production work in industry.'® 11. UVAROV, E. B. and D. R. CHAPMAN.: 4 Dic- tionary of Science. Penguin Books, Inc., Baltimore (1958). WOODSON, W. E.: Human Engineering Guide for Equipment Designers. University of California Press, Berkeley, California, pp. 71, 73, 74, 264, 299. MORGAN, C. T,, J. S. COOK, S. CHAPANIS and M. W. LUND (Editors).: Human Engineering Guide to Equipment Design. McGraw-Hill Book Co., New York (1963). HERTZBERG, H. T. E. (Editor).: Annotated Bib- liography of Applied Physical Anthropology in Hu- man Engineering — R. Hansen, D. Y. Cornog and Yoh Company, WADC Technical Report 56-30, Wright Air Development Center, U.S.A.F., (1958). DAMON, A., H. W. STOUDT and R. A. McFAR- LAND.: The Human Body in Equipment Design. Harvard University Press, Cambridge, Mass. (1966). TICHAUER, E. R., H. GAGE and LL. B. HAR- RISON.: “The Use of Biomechanical Profiles in Work Measurement.” Industrial Engineering, 25 Technology Park, Atlanta, Norcross, Georgia 30071, 1V:5, 20-27 (May 1972). CARSON, B. G. (Editor).: Production Handbook, 2nd Ed., Sect. 14, Ronald Press, New York, p. 15 (1958). TICHAUER, E. R.: The Biomechanics of the Arm- Back Agregate Under Industrial Working Condi- 484 tions. The American Society of Mechanical En- gineers, ASME Publication No. 65-WA /HUF-1, 29 W. 39 St., New York, N.Y. (1965). DREYFUSS, H.: The Measure of Man-Human Fuac- tors in Design. Whitney Library of Design, New York, 2nd Edition. COUNT, E. W., et al.: “Dynamic Anthropometry.” Annals of the New York Academy of Sciences, 2 E. 63rd St., New York, N.Y. 10021, Vol. 63, Art. 4, 433-636. KROEMER, K. H. E.: Seating in Plant and Office. AMRL-TR-71-52, Wright-Patterson Air Force Base, Ohio, Aerospace Medical Research Laboratory (1971). GRANDIJEAN, E.: Fitting the Task to the Man — An Ergonomic Approach. Taylor & French, Lon- don (1967). JACOB, S. W. and C. A. FRANCONE.: Structure and Function in Man, W. B. Saunders Company, 218 W. Washington Square, Philadelphia, Penn. 19105, p. 8 (1970). DAMON, F. A.: “The Use of Biomechanics in Manufacturing Operations.” The Western Electric Engineer, 195 Broadway, New York 10007, 9 (4), 15 (1965). TICHAUER, E. R.: Gilbreth Revisited. American Society of Mechanical Engineers, ASME, 29 W. 39 St.. New York, N. Y., Publication 66-WA/BHF-7 (1966). HIGH WORK TOLERANCE DISPLACEMENT =D = apr 620" A f scl 1 LOW WORK TOLERANCE DISPLACEMENT =D =4??620" ° VELOCITY ACCELERATION , a 4 FS Y ise] a WRIST EXTENSORS i EYE MUSCLES —, NECK MUSCLES A Tichauer, E. R., Gage, H., Harrison, L. B.: The use of Biomechanical Profiles in Objective Work Measurement. J. Ind. Eng. IV: 20-27, 1972. Figure 32-61 (A & B). Biomechanical profiles can be used to distinguish between individuals who are likely to have low or high work tolerance. Two workers performed a number of forward reaches. The firing rate in the deltoid (A) muscle, particularly at low velocity, is commonly far higher for individuals of low work tolerance, left, while the wrist extensors’ myograms (B) of such workers are continuous and unstructured. Both of these factors are likely to be indicative of relatively high effort accompanied by poor efficiency of performance — the worker manipu- lates for fine positioning before arriving at the target. Neck muscles’ activity (C) show that the low tolerance worker does too much of the scanning with the head. The lack or presence of purposeful anticipatory eye scanning (D) is also a good predictor of sustained performance ability.1¢ 485 fro SUBJECT "J" a = DELTOID i 3 : 3 3 z SE WRIST EXTENSORS ¥ : ® AFTER PRACTICE Damon, A., Stoudt, H. W., McFarland, R. A.: The Human Body in Equipment Design. Cambridge, Mass., Harvard University Press, 1966. Figure 32-62. The state and quality of worker’s training can be measured by electromyo- graphic kinesiology, and the work habits which need retraining can be pinpointed. Before practice (left), the subject moves her eyes to search (1), then moves her wrist (2), looks again (3), finally does useful work with her wrist as she positions a second time (4). During the entire motion (which goes from the horizontal to a side target point), the deltoid (5) is under constant tension since the elbows are kept high as the shoulder is moved. The total motion consumes 4.7 seconds. The practiced performance (right) resulted from proper training. The subject carried out instructions such as: “keep the elbows down.” Deltoid activity is minimal (6); eye movement (7) is purposeful and efficient — Subject “J” looks first, scanning the entire visual field; the wrist (8) is then moved to the located target. The trained subject needs less than half the reach time.'” 26. BARNES, R. M.: Motion and Time Study. 5th Books, Division of Grossman Publishers, New York Edition, John Wiley and Sons, New York (1963). (1967). 27. TICHAUER, E. R. and R. A. DUDEK.: Introduc- 32. TICHAUER, E. R.: Industrial Engineering Tech- tion to Industrial Engineering for Physicians. Texas niques Appropriate in Young Economies. ‘Texas Technological College. Lubbock, Tex 1965) Technological College, Lubbock, Texas, (1963) M 2 wv ge, , as ( )s (Monograph) : onograph). . 28. GILBRETH, F. B.: Motion Study, Van Nostrand, ~~ 33. SCHMIDTKE, H. and F. STIER.: “An Experimen- New York, p. 234 (1911) tal Evaluation of the Validity of Predetermined 29 duc LC ’ . Elemental Time Systems.” Journal of Industrial En- Chen Ganev (loa, Su nermational Labour gineering, 25 Technology Park. Atlanta, Norcross, » . eorgia J . : ( . 30. TICHAUER, E. R,, J. F. T. CLOSE and R. B. 34. TICHAUER, E. R.: Biomechanical Prerequisites of MITCHELL.: Methods Engineering, Radio Univer- Work Tolerance. Copyrighted Lecture Notes, New sity Monograph 18.811G. The University of New York University, 400 E. 34th St, New York, N.Y. South Wales, Sydney, Australia (1965). 10016 (1971). 31. DREYFUSS, H.: Designing for People. Paragraphic 35. TICHAUER, E. R.: Potential of Biomechanics for 486 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 53. 54. 55. Solving Specific Hazard Problems. Proc. — 1968 Professional Conference, American Society of Safety Engineers, Park Ridge, Illinois, 149-187 (1968). TICHAUER, E. R.: “Human Factors Engineering.” 1971 McGraw-Hill Yearbook of Science and Tech- nology, McGraw-Hill Book Co., New York, 228- 238 (1971). SLESIN, S.: “Biomechanics.” Industrial Design, 130 E. 59th St., New York 10022, /8: No. 3, 36- 41 (April 1971). LORIGA, G.: Occupation and Health, Supple- ment, International Labour Organization, Geneva. Quoted by L. Teleky (1938). HAMILTON, A., J. P. LEAKE, et al.: Bureau of Labor Statistics Bulletin No. 236. U.S. Department of Labor, Washington, D.C. (1918). MAGID, E. G. and R. R, COERMANN.: “Human Response to Vibration,” Human Factors in Tech- nology, McGraw-Hill Book Co., New York, 86-119 (1963). Work — Environment — Health, 7:1, Institute of Occupational Health, Helsinki, Finland (1970). WOODSON, W. E. and D. W. CONOVER.: Hu- man Engineering Guide for Equipment Designers. 2nd Edition, University of California Press, Berke- ley, California (1964). TICHAUER, E. R.: “Industrial Engineering in the Rehabilitation of the Handicapped.” Journal of In- dustrial Engineering, 25 Technology Park, Atlanta, Norcross, Georgia 30071, XIX: (2): 96-104 (Feb. 1968). NAPIER, J. R.: ‘The Prehensile Movements of the Human Hand.” J. Bone J. Surg., 10 Shattuck St., Boston, Mass. 12115, 38-B, 902 (1956). DRILLIS, R., D. SCHNECK and H. GAGE.: “The Theory of Striking Tools.” Human Factors, Balti- more, Maryland 21218, 5 (5), (Oct. 1963). BINKHURST, R. A. and S. CARLSON.: “The Thumb-Forefinger Grip and the Shape of Handles of Certain Instruments.” Ergonomics, Fleet St., London E. C. 4 (United Kingdom), 5 (3): 467 (1962). HUNTER, D.: The Diseases of Occupations, Little Brown & Co., Boston (1969). American National Standard, Industrial Engineer- ing Terminology, Biomechanics, ANS1 Z94.1-1972, Secretariat, American Institute of Industrial Engin- eers, Inc., The American Society of Mechanical En- gineers, Published by the American Society of Mechanical Engineers, United Engineering Center, 345 East 47th Street, New York, New York 10017. TICHAUER, E. R.: “Some Aspects of Stress on Forearm and Hand in Industry.” J. Occ. Med., 49 East 33rd St, New York, 10016, 8 (2): 63-71 (Feb. 1966). Accident Facts, National Safety Council, Chicago, p. 31 (1969). CONSOLAZIO, C. F., R. E. JOHNSON and L. J. PECORA.: Physiological Measurement of Metabolic Functions in Man, McGraw-Hill Book Co., New York, 328 ff (1963). TICHAUER, E. R.: “Ergonomics of Lifting Tasks Applied to the Vocational Assessment of Rehabili- tees.” Rehabilitation in Australia, 403-411 George St., Sydney 2000, Australia, p. 16-21 (Oct. 1967). DEMPSTER, W. T.: “The Anthropometry of Body Action. Dynamic Anthropometry,” R. W. Miner (Editor), Annals of the New York Academy of Sciences., 2 E. 63rd St, New York 10021, 63 (4), 559-585 (1955). WILLIAMS, M. and H. T. LISSNER.: Biome- chanics of Human Motion, W. B. Saunders Co., 218 W. Washington Square, Phil, Penn., 19105 (1962). ABT, L. E.: “Anthropometric Data in the Design of Anthropometric Test Dummies. Dynamic An- thropometry,” R. W. Miner (Editor), Annals of the 487 56. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74. 75. 76. New York Academy of Sciences., 2 E. 63rd St., New York 10021, 63, Art. 4, 433-636 (1955). HERTZBERG, H. T. E. (Editor).: Annotated Bib- liography of Applied Physical Anthropology in Hu- man Engineering — R. Hansen, D. Y. Cornog and Yoh Company, WADC Technical Report 56-30, Wright Air Development Center, U.S.A.F. (1958). . BRAUNE, W,, O. FISCHER, J. AMAR and W. T. DEMPSTER.: Human Mechanics. Four mono- graphs abridged. Technical Documentary Report No. AMRL-TDR-63-123, U.S. A.F. (Dec. 1963). STARR, 1.: “Units for the Expression of Both Static and Dynamic Work in Similar Terms, and Their Application to Weight-Lifting Experiments.” J. Appl. Physiol., 9650 Wisconsin Ave., Washing- tion, D.C., 4: No. 21 (1951). KARPOVICH, P. V.: Physiology of Muscular Ac- tivity. W. B. Saunders Co., Philadelphia (1959). HILL, A. V.. Muscular Activity. Williams and Wilkins, Baltimore (1925). HILL, A. V., C. N. H. LONG and H. LUPTON.: “Muscular Exercise, Lactic Acid and the Supply and Utilization of Oxygen.” Proc. Roy. Soc. (Biol.), Royal Society, 6 Carlton House, Paris, London SW1, England, 96: 438 (1924). ASTRAND, P.O. and K. RODAHL.: Textbook of Work Physiology. McGraw-Hill Book Co., New York (1970). SIMONSON, E. (Editor).: Physiology of Work Capacity and Fatigue. Charles C. Thomas, Spring- field (1971). McCORMICK, E. J.: Human Factors Engineering, 3rd Edition, McGraw-Hill Book Co., New York (1970). SNOOK, S. H.: Group Work Capacity: A Tech- nique for Evaluating Physical Tasks in Terms of Fatigue. Liberty Mutual Insurance Co., Hopkin- ton (1965). SNOOK, S. H. and C. H. IRVINE.: “Maximum Acceptable Weight of Lift.” Am. Ind. Hyg. Assoc. J., 66 South Miller Rd., Akron, Ohio 44313, 28: 322 ff (1967). Accident Prevention Manual for Industrial Opera- tions, 6th Edition, National Safety Council, Chi- cago (1969). HIMBURY, S.: Kinetic Methods of Manual Han- dling in Industry. Occupational Safety and Health Series No. 10, International Labour Organization, International Labour Office, Geneva (1967). GRIMALDI, J. V. and R. H. SIMONDS. Safety Management. Richard D. Irwin, Homewood (1963). BARNES, R. M.: Motion and Time Study, 6th Edition. John Wiley & Sons, New York (1968). TICHAUER, E. R., R. B. MITCHELL and N. WINTERS.: A Comparison of the Elements ‘Move’ and ‘Transport’ in MTM and Work Factor.” Micro- tecnic, 23 ave. de la Gare, 1000 Lausanne, Vol. 16, No. 6 (1963). } MUNN, N. L.: Psychology — the Fundamentals of Human Adjustment, Third Edition, Houghton Mif- flin Company, Boston, Riverside Press, Cambridge, 438 ff (1956). TICHAUER, E. R.: Gilbreth Revisited, American Society of Mechanical Engineers, ASME, 29 W, 39 The Williams & Wilkins Co., Baltimore (1967). St., New York, N. Y., Publication No. 66-WA/ BHF (1966). TICHAUER, E. R.: Biomechanics of Lifting, Re- port RD-3130-MPO-69. Prepared for Social and Rehabilitation Service, U.S. Department of Health, Education and Welfare, Washington, D.C. (1970). MARTIN, J. B. and D. B. CHAFFIN.: “Biochem- ical Computerized Simulation of Human Strength in Sagittal Plane Activities.” American Institute of Industrial Engineers, Transactions, 345 E. 47th St., New York 10017, 4 (1), 19 (March 1972). GOODGOLD, J. and A. EBERSTEIN.: Electro- diagnosis of Neuromuscular Diseases. The Williams and Wilkins Co., Baltimore, Maryland (1972). 77. BASMAIJIAN, J. V.: Muscles Alive: Their Func- tions Revealed by Electromyography, 2nd Edition. The Williams and Wilkins Co., Baltimore (1967). 78. QUIRING, D. P, and J. H. WARFEL.: The Extremities, The Head, Neck and Trunk. Third Edition, Lea & Febiger, Philadelphia (1967). 79. KENDALL, H. O., F. P. KENDALL and G. WADS- WORTH.: Muscles: Testing and Function. 2nd Edition. The Williams and Wilkins Co., Baltimore, Maryland (1971). Preferred Reading I. American National Standard, Industrial Engineering Terminology, Biomechanics, ANSI 7Z94.1-1972, Sec- retariat, American Institute of Industrial Engineers, Inc., The American Society of Mechanical Engin- eers, Published by the American Society of Me- chanical Engineers, United Engineering Center, 345 East 47th Street, New York, New York 10017. Note: the glossary of this chapter contains definitions from the Standard. Practitioners of Biomechanics in in- dustry should acquire this publication in order to have available a complete reference to commonly used terms in Occupational Biomechanics. 2. FOSTER, WALTER, T., Anatomy. Foster Art Ser- vice, 430 W, 6th St., Tustin, California (1970). 3. Encyclopedia of Occupational Health and Safety, Vol. I and Vol. II. International Labour Office Geneva (1971). 4. OLISHIFSKI, J. B. and F. E. McELROY (Edi- tors).: Fundamentals of Industrial Hygiene. Na- tional Safety Council, Chicago, Illinois (1971). 5. Ergonomics in Machine Design. Vol. I and Vol. II. Occupational Safety and Health Series. Interna- tional Labour Office, Geneva (1969). 6. SINGLETON, W. T., J. G. FOZ and D. WHIT- FIELD (Editors).: Measurement of Man at Work: An Appraisal of Physiological and Psychological Criteria in Man-Machine Systems. Van Nostrand Reinhold Co., New York. 7. JOKL, E. (Editor).: “Biomechanics — Technique of Drawings of Movement and Movement Analysis.” Medicine and Sport, Vol. 2, Basel, Switzerland; S. Karger, New York (1968). 8. THOMPSON, CLEM W.: Kranz Manual of Kinesi- ology. 5th Edition. The C. V. Mosby Co., St. Louis (1965). 9. MURRELL, K. F. H. Ergonomics — Man in His ie Environment. Chapman and Hall. London 1969). 10. EDHOLM, O. G.: The Biology of Work. World University Library. McGraw-Hill Book Co., New York (1967). 11. JACOB, STANLEY W. and FRANCONE, CLAR- ICE ASHWORTH. Structure and Function in Man. 2nd Edition. W. B. Saunders Co., Philadelphia (1970). 12. BROWN, J. R.: Manual Lifting and Related Fields, An Annotated Bibliography, published by The La- bour Safety Council of Ontario and The Ontario Ministry of Labour. 13. WASSERMAN, D. E. and BADGER, D. W.: Vibra- tion and the Worker's Health and Safety, Technical Report #77, National Institute for Occupational Safety and Health, Physiology and Ergonomics Branch, 1014 Broadway, Cincinnati, Ohio 45202. Important Notice: The American Industrial Hygiene As- sociation (Technical Committee on Ergonomics) publishes from time to time “Ergonomics Guides” each one concerned with a specialized aspect of the field (e.g., Ergonomics Guide to Manual Lifting); all these should be considered indispensible references for daily practice. GLOSSARY Angle of Abduction Angle between the longi- tudinal axis of a limb and a sagittal plane (q.v.). 488 Antagonist A muscle opposing the action of another muscle. An active antagonist is essen- tial for control and stability of action by a prime mover (q.v.); e.g., the biceps and pro- nator teres are antagonists in pronation and supination. Anthropometry ~~ The measurement of man’s body dimensions, generally performed with calipers which measure the distance between specific anatomical reference points. For more details, see Dreyfuss: “The Measurement of Man,” Whitney Library of Design. Axis of Rotation The true line about which angular motion takes place at any instant. Not necessarily identical with anatomical axis of symmetry of a limb nor necessarily fixed. Thus, forearm rotates about an axis which ex- tends obliquely from lateral side of elbow to a point between the little finger and ring finger. The elbow joint has a fixed axis maintained by circular joint surfaces, but the knee has a moving axis at its cam-shaped surfaces articu- late. Axis of rotation of tools should be aligned with true limb axis of rotation. Sys- tems of predetermined motion times often specify such axes incorrectly. Axis of Thrust Line along which thrust can be transmitted safely. In the forearm, it coincides with the longitudinal axis of the radius. Tools should be designed to align with this axis. Ulnar or radial deviation which produces mis- alignment causes bending stress acting on the wrist. Biceps Muscle The large muscle in the front of the upper arm. Bicipital Tuberosity A protuberance on the medial surface of the radius to which the biceps attaches. Biomechanics ~~ The study of the human body as a system operating under two sets of laws: the laws of Newtonian mechanics and the biologi- cal laws of life. Brachialis Muscle ~~ Short, strong muscle origi- nating at lower end of the humerus (q.v.) and inserting into ulna (q.v.). Operates at mechanical advantage, powerful flexor of fore- arm, employed when lifting. Camber Generally refers to a tilt or curve. In seating design, the camber, or slope of the chair with respect to the horizontal is opti- mally 8° from front to back. Capitulum of Humerus A smooth hemispher- ical protuberance at the distal end of the humerus articulating with the head of the ra- dius. Irritation caused by pressure between the capitulum and head of the radius is called tennis elbow. Carpal Tunnel A passage in the wrist through which important blood vessels and nerves pass to the hand from the forearm. Ulnar or ra- dial deviation cause misalignment of the car- pal tunnel and irrigation of structures passing through it. Carpal Tunnel Syndrome A common affliction of assembly workers caused by compression of the median nerve in the carpal tunnel. Often associated with tingling, pain or numbness in the thumb and first three fingers. Reduces manipulative skills, particularly if thumb is involved, and frequently reduces work output. Deltoid Muscle The muscle of the shoulder responsible for extending the arm sideways, and for swinging the arm at the shoulder. Overuse of the deltoid muscle may cause fa- tigue, pain in the shoulder and unwarranted fear of heart disease. Distal ~~ Away from the central axis of the body. Distal Phalanx Colloquially known as the “knuckle,” the long bone of the finger or toe away from the central axis of the body (dis- tal). Frequently used as an anatomical ref- erence point in work analysis. Dynamometer ~~ Apparatus for measuring force or work output external to a subject. Often used to compare external output with asso- ciated physiological phenomena (electromyog- raphy, spirometry, etc.) to assess physiological work efficiency. Epicondylitis Inflammation or infection in the general area of an epicondyle; e.g., tennis elbow. Ergonomics ~~ A multidisciplinary activity deal- ing with the interactions between man and his total working environment plus such tra- ditional environmental elements as atmos- phere, heat, light and sound as well as all tools and equipment of the workplace. Extensor Muscles A muscle which, when ac- tive, increases the angle between limb seg- ments; e.g., the muscles which straighten the knee or elbow, open the hand or straighten the back. Extensor Tendon Connecting structure between an extensor muscle and the bone into which it inserts. Examples are the hard, longitudinal tendons found on the back of the hand when the fingers are fully extended. External Mechanical Environment The man- made physical environment; e.g., equipment, tools, machine controls, clothing. Antonym: internal (bio)mechanical environment, q.v. Flexor Muscles A muscle which, when con- tracting, decreases the angle between limb segments. The principal flexor of the elbow is the brachialis muscle. Flexors of the fingers and the wrist are the large muscles of the fore- arm originating at the elbow. Cf., extensor muscle. Foot-Pounds of Torque A measurement of the physiological stress exerted upon any joint during the performance of a task. The product of the force exerted and the distance from the point of application to the point of stress. Physiologically, torque which does not pro- duce motion nonetheless causes work stress 489 whose severity depends on the duration and magnitude of the torque. In lifting an object or holding it elevated, torque is exerted and applied to the lumbar vertebrae. Humerus ~~ The bone of the upper arm which starts at the shoulder joint and ends at the elbow. Muscles which move the upper arm, forearm and hand are attached to this bone. Iliac Crest The upper rounded border of the hip bone. No muscles cross the iliac crest and it lies immediately below the skin. It is an important anatomical reference point be- cause it can be felt through the skin. Seat backrests should clear the iliac crest. Inertial Moment Related to biomechanics, that moment of force-time caused by sudden ac- celerations or decelerations. Whiplash of the neck is caused by an inertial moment. In an industrial setting, side-stepping causes appli- cation of a lateral inertial moment on the lumbosacral joint, which may cause trauma, pain, and in any case will lower performance efficiency. The inertial moment is one of the seven elements of a lifting task. Internal Biomechanical Environment The mus- cles, bones and tissues of the body, all of which are subject to the same Newtonian force as external objects in their interaction with other bodies and natural forces. When de- signing for the body, one must consider the forces that the internal mechanical environ- ment must withstand. Ischemia ~~ Lack of blood flow. Loss of sufficient replacements to maintain normal metabolism in the cells. Caused by blockage in the circu- latory system or failure of the cardiac system. Blockage may be by internal biological agents such as arterial wall deposits or by external en- vironmental agents such as poorly designed tools or workplaces which press against arter- ies and occlude them. Depending on the degree of ischemia, numbness, fatigue and tingling may be evidenced in the limbs. At the workplace, loss of precision in manipulation may lead to reduced efficiency, poor quality and possibility of accidents. Ischial Tuberosity ~~ A rounded projection on the Ischium. Itis a point of attachment for several muscles involved in moving the femur and the knee. It can be affected by improper design of chairs and by situations involving trauma to the pelvic region. When seated, pressure is borne at the site of the ischial tuberosities. Chair design should provide support to the pressure projection of the ischial tuberosity through the skin of the buttocks. Isometric Work Referring to a state of mus- cular contraction without movement. Al- though no work in the “physics” sense is done, physiologic work (energy utilization and heat production) occurs. In isometric exercise, muscles are tightened against immovable ob- jects. In work measurement, isometric mus- cular contractions must be considered as a major factor of task severity. Kinesiology ~~ The study of human movement in terms of functional anatomy. Kinetic Chain ~~ A combination of body segments connected by joints which, operating together, provide a wide range of motion for the distal element. A single joint only allows rotation, but kinetic chains, by combining joints en- able translatory motion to result from the rotary motions of the limb segments. Familiar- ity with the separate rotary motions and their limitations is necessary for comprehension of the characteristics of the resultant motion. By combining joints whose axes are not parallel, the kinetic chain enables a person to reach every point within his span of reach. Man-Equipment Interface ~~ Areas of physical or perceptual contact between man and equip- ment. The design characteristic of the man- equipment interface determine the transfer of information and motor skill. Poorly designed interfaces may lead to localized trauma (e.g., calluses) or fatigue. Latissimus Dorsi ~~ A large flat muscle of the back which originates from the spine of the lower back and inserts into the humerus at the armpit. It adducts the upper arm, and when the elbow is abducted, it rotates the arm medially. It is actively used in operating equip- ment such as the drill press where a down- ward pull by the arm is required. Lumbar Spine Lowest section of the spinal col- umn or vertebral column immediately above the sacrum. Located in the small of the back and consisting of five large lumbar vertebrae, it is a highly stressed area in work situations and in supporting the body structure. Lumbosacral Joint ~~ The joint between the fifth lumbar vertabrae and the sacrum. Often the site of spinal trauma because of large moments imposed by lifting tasks. Mechanotactic Stress ~~ Stress caused by contact with a mechanical environment. Mechanotaxis ~~ Contact with a mechanical envi- ronment consisting of forces (pressure, mo- ment), vibration, etc. One of the ecological stress vectors. Improper design of the me- chanotactic interface may lead to instantane- ous trauma, cumulative pathogenesis, or death. Median Nerve A major nerve controlling the flexor muscles of the wrist and hand. Tool handles and other objects to be grasped should make good contact with the sensory feedback area of this nerve located in the pal- mar surface of the thumb, index, middle, and part of ring finger. Mid-Sagittal Plane A reference plane formed by bisecting the human anatomy so as to have a right and left aspect. Human motor func- tion can be described in terms of movement relative to the mid-sagittal plane. Popliteal Clearance 490 Moment ~~ Magnitude of the force times distance of application. Moment Concept ~~ The concept based on theo- retical and experimental bases that lifting stress depends on the bending moment exerted at susceptible points of the vertebral column rather than depending on weight alone. Musculo-Skeletal System ~~ The combined system of muscles and bones which comprise the in- ternal biomechanical environment. Olecranon Fossa ~~ A depression in the back of the lower end of the humerus in which the ulna bone rests when the arm is straight. Palmar Arch Blood vessel in the palm of the hand from which the arteries supplying blood to the fingers are branched. Pressure against the palmer arch by poorly designed tool han- dles may cause ischemia of the fingers and loss of tactile sensation and precision of move- ment. Distance between the front of the seating surface and the popliteal crease. This should be about 5” in good seat design to prevent pressure on the popliteal artery. Popliteal Crease (or Line) The crease in the back of the leg in the hollow of the knee when lower leg is flexed. Important anatomical landmark. Popliteal Height of Chair ~~ The height of the highest part of the seating surface above the floor. Popliteal Height of Individual ~~ The height from the crease in the hollow of the knee to the floor is called the “popliteal height” of the individual concerned. Pronation ~~ Rotation of the forearm in a direc- tion to face the palm downward when the forearm is horizontal or backward when the body is in anatomical position. An important element of industrial demanded motions in- ventory, it is performed by muscles whose efficiency is a function of arm position. Proximal Describing that part of a limb which is closest to the point of attachment. The elbow is proximal to the wrist which is prox- imal to the fingers. Radial Deviation Flexion of the hand which deflects its longitudinal axis toward the radius. It causes the head of the radius to press against the capitulum of the humerus, and may lead to irritation of the elbow (“tennis elbow’). Tool design should minimize radial deviation. Strength of grasp is diminished in radial devia- tion. Radius The long bone of the forearm in line with the thumb. It is the active element in the forearm during pronation and supination. It also provides the forearm connection of the wrist joint. Raynaud’s Syndrome ~~ Constriction of the blood vessels of the hand from cold temperature, emotion, or unknown causes. Afflicts women predominantly and affects both hands simul- taneously. Hands become cold, blue and numb and lose fine prehensile ability. On recovery, hands become red accompanied by burning sensation. Easily confused with one-sided numbness and tingling caused by poor tool de- sign and resulting pressure. Sagittal Plane A plane from back to front vertically dividing the body into right and left portions. Important in anthropometric definitions. Mid-sagittal plane is a sagittal plane symmetrically dividing the body. Sensory Feedback Use of external signals per- ceived by sense organs (e.g., eye, ear) to indi- cate quality or level of performance of an event triggered by voluntary action. On the basis of sensory feedback information, deci- sions may be made; e.g., permitting or not per- mitting an event to run its course; enhancing or decreasing activity levels. Sensory End Organs Receptor organs of the sensory nerves located in the skin. Each end organ can sense only a specific type of stimu- lus. Primary stimuli are heat, cold, or pres- sure, each requiring different end organs. Knowledge of end organ distribution is of im- portance to the safety engineer. For example, there are few heat receptors on the outer sur- face of the forearm, so that the skin may be severely burned before heat is sensed. Sternomastoid Muscles ~~ A pair of muscles con- necting the breastbone and lower skull behind the ears, which provide support for the head. When operating together, the right and left sternomastoids pull the head forward and downward, and when operating singly, each turns the head to the opposite side. They op- pose the semispinalis muscles and stabilize the head. In the workplace, the worker's head position should be nearly vertical to minimize activity of the semispinalis and sternomastoid muscles. The sternomastoid is also function- ally important in head scanning. Supination ~~ Rotation of the forearm about its own longitudinal axis. Supination tends to turn the palm upward when the forearm is horizontal and forward when the arm is in anatomical position. Supination is an impor- tant element of available motions inventory for industrial application, particularly where tools such as screwdrivers are used. Efficiency in supination depends on arm position. Work- place design should provide for elbow flexion at 90 degrees. Tendons Fibrous end sections of muscles. It attaches to bone at the area of application of tensile force. When its cross-section is small, stresses in the tendon are high, particularly because the total force of many muscle fibers is applied at the single terminal tendon. The site of many industrial diseases caused by trauma, biomechanically improper movements, 491 or failure of lubrication, the tendon must be protected in tool and workplace design. Tennis Elbow Sometimes called epicondylitis. An inflammatory reaction of tissues in the lateral elbow region. In an industrial environ- ment it may follow effort requiring supination against resistance (as in screwdriving) or vio- lent extension of the wrist with hand pronated. Can frequently be avoided by assuring that the axis of rotation of a tool or machine con- trol coincides with the orthoaxis of rotation of the forearm. Tenosynovitis ~~ A disease of the wrist. Inflam- mation of the tendon sheaths of the wrist often associated with continual ulnar deviation dur- ing rotational movements (e.g., screwdriving) or by other overwork or trauma. In industry, extensor sheath inflammation is more frequent. Work tolerance is reduced because of pain during wrist and finger movement. Trauma An injury or wound, generally caused by a physical agent. Cuts, bruises and abra- sions are obvious examples of trauma, but trauma may be present even though it is not visible; e.g., strained muscle. The causes of trauma must be anticipated in workplace de- sign or tool design. Protective devices and special clothing (work shoes, gloves) are used to avoid trauma. Triceps The large muscle at the back of the upper arm that extends the forearm when contracted. Trigger Finger Also know as snapping finger. A condition of partial obstruction in flexion or extension of a finger. Once past the point of obstruction, movement is eased. Caused by thickening of a tendon or localized reduc- tion of the tendon sheath. In the workplace, flexing against strong antagonists and flexing of the distal phalanx without middle phalanx movement is suspected. Tool handles should be designed for trigger operation by the thumb. Ulna One of the two bones of the forearm. It forms the hinge joint at the elbow and does not rotate about its longitudinal axis. It terminates at the wrist on the same side as the little finger. Task design should not im- pose thrust loads through the ulna. Ulnar Deviation ~~ A position of the hand in which the wrist is bent toward the little finger. Ulnar deviation is a poor working position for the hand and causes nerve and tendon dam- age. It reduces the useful range of pronation and supination by approximately 50%, and work performed in ulnar deviation proceeds at low efficiency. Handtool design should avoid ulnar deviation. Viscerotaxis ~~ One of the ecologic stress vectors. A form of chemotaxis concerned with the in- ternal contact of chemical agents within the body. Chemical exposure via the gastrointes- tinal tract, the pulmonary system, and the uro- genital systems are examples of viscerotaxis. Work Strain The natural physiological response reaction of the body to the application of reaction of the body to the application of work stress. The locus of the reaction may often be remote from the point of application of work stress. Work strain is not necessarily traumatic but may appear as trauma when excessive, either directly or cumulatively, and must be consid- ered by the industrial engineer in equipment and task design. Thus, increase of heart rate is non-traumatic work strain resulting from physical exertion, but tenosynovitis is patho- Work Stress 492 logical work strain resulting from undue work stress on the wrists. Biomechanically, any external force acting on the body during the perform- ance of a task. It always produces work strain. Application of work stress to the hu- man body is the inevitable consequence of performance of any task, and is therefore only synonymous with “stressful work conditions” when excessive. Work stress analysis is an integral part of task design. CHAPTER 33 THE INFLUENCE OF INDUSTRIAL CONTAMINANTS ON THE RESPIRATORY SYSTEM George W. Wright, M.D. INTRODUCTION Those persons responsible for evaluation and control of the industrial environment for the pur- pose of preventing respiratory injury should have (1) knowledge of the anatomy of the respiratory system, (2) an understanding of the factors govern- ing entry, deposition, removal and retention of gases and particles presented to the system and (3) some knowledge of the way in which tissues of the respiratory system react to gases and particles. The type and severity of tissue response is related to the dose and the nature of the specific agent present. Air, which looks dirty or has an offensive odor may, in fact, pose no threat what- soever to the tissues of the respiratory system. In contrast, some gases essentially odorless or at least not offensive, and some particles even when pres- ent in numbers too small to make the air appear dirty, can cause severe and serious tissue injury. Information about these matters provides an es- sential motivation to the industrial hygienist and his co-workers and gives them a more balanced approach to their activities. Lack of such knowl- edge converts a responsibility which should be most interesting and rewarding into a series of rather dull activities. The progenitors of man evolved in an environ- ment which probably contained a higher concen- tration of particles and noxious gases than exists now. One could anticipate therefore, that man might retain some ability to overcome such haz- ards or his genetic precursors would not have survived during that distant period. The fact is, man does possess anatomical and physiological mechanisms which protect the tissues from injury by many airborne agents. The multiple branch- ings and tortuous course of the narrow passage- ways through which air is conducted on its way to the deeper portions of the lungs favor the depo- sition of particles upon the more resilient surface of the proximal conducting tubes, rather than the fragile, more distal gas exchanging surface. The entire surface of the air-containing parts of the lung is covered by a thin layer of fluid which, not only serves as a protective layer, but also as a carrier or vehicle upon which particles are trans- ported from the lung to the pharynx via the mucociliary escalator, This mechanism, plus that of the phagocytic system, is extraordinarily effi- cient in removing particles or storing them within cells, the macrophages, which are capable of toler- ating many kinds of particles without injury. The surface cells of the lung replicate at a high rate and when they are injured, they are rapidly re- 493 placed by normal cells. Recovery from tissue in- jury via these regenerative forces is often surpris- ingly complete. These various mechanisms of up- per airway deposition, surface protection, particle transport and cell regeneration make it possible for man to tolerate surprisingly high concentra- tions of airborne particles and noxious gases. Nevertheless, the system can be overwhelmed with subsequent persistent injury depending upon the concentration and the kind of gases and air- borne particles to which it is exposed. This chap- ter is aimed at setting forth the principles govern- ing the reactions of the respiratory system to the environment. It is not a compendium of occupa- tional respiratory diseases, nor is it in any sense a textbook of pulmonary anatomy and physiology. PERTINENT FEATURES OF THE ANATOMY AND PHYSIOLOGY OF THE RESPIRATORY SYSTEM The human lung is much like a fish’s gill, de- veloped in the course of our evolution in a posi- tion inside rather than outside the body. It is a gas-exchanging mechanism comprised of a large membrane, on one side of which blood flows and on the other side of which there is a gas phase. A high gradient for oxygen and CO, exchange is maintained by the flow of venous blood over one side, and by the pumping of air into and out of the lungs, thus maintaining an optimum concentration of oxygen and CO, in the gas phase overlying the other side of the membrane. The gas-exchang- ing surface is comprised of blood capillaries over- laid by a very thin single cell layer having an effec- tive surface of approximately seventy square meters. Blood is brought to this membrane via pulmonary arteries and conducted away from it via the pulmonary veins. A second system of tubes, the bronchial system, conducts air to and from the gas phase contained in the alveoli, the thin walls of which contain the capillaries. The heart pumps blood through the system, and the muscles of respiration move the chest bellows, and thus pump the respired air to and from the gas phase in the alveoli. One of the marvels of ani- mal construction is that this highly complex and effective system is housed in a relatively small space and is protected from mechanical injury by being contained within the chest cavity. In this discussion we will be concerned chiefly with the air-conducting system and the terminal air spaces or alveoli, the walls of which constitute the mem- brane separating the gas from the blood phase. The air-conducting system begins with the nose, mouth and pharynx. The mouth and oral- pharynx are a globular, open chamber. The nasal and naso-pharyngeal chambers, in contrast, con- tain ridges or projections, the turbinates. The pas- sages through the nose are semi-separate, narrow and tortuous and this causes the airstreams travers- ing this system to be turbulent and to change di- rection frequently, and to be so narrow that the center of the moving airstream is close to the wall of the passages. This arrangement favors deposi- tion of the particles and makes for a more effective gas absorbing surface in this region than exists in the mouth and oral pharynx. A single tube or airway, the trachea, emerges from the pharynx. This tube divides into the right and left bronchus, each of which further divides into branches entering each lobe of the two lungs. The bronchial system undergoes twenty-three branchings, each of slightly smaller diameter than its parent. The walls of the bronchial tubes be- come progressively thinner and at the seventeenth branching, small out pouchings or chambers — the alveoli — begin to appear. Subsequent branch- ings have walls composed essentially of alveoli. Progressing from the trachea toward the ultimate end structures, all divisions devoid of alveoli are called bronchi or bronchioles. When a few alveoli appear in the wall of the conducting system, the tube is designated as a respiratory bronchiole and, when many are present, the tube is an alveolar duct. The ultimate structure at the very end is a wider chamber, the atrium, and from this room only alveoli project. Air conduction or mass movement of air tra- verses all bronchi and bronchioles, but at the alve- olar duct, or some more distal point, mass move- ment of air ceases. Further movement of gas molecules into the alveoli, or from the center of the alveoli to the surface of the alveolar mem- brane, is by diffusion. The anatomical point at which the transition from mass movement of air to pure diffusion occurs is uncertain and probably varies with depth of breath. The location of this interface where mass movement of air ceases and diffusion becomes the only mechanism for more distal movement of particles is of some impor- tance. Particles larger than 0.5 microns do not diffuse, but move through the airways by being entrained in mass movement of air. Hence, par- ticles larger than 0.5 microns penetrate the lung only where mass movement of air occurs and the majority that are deposited fall on the walls of the conducting tubes. Based upon position, some un- doubtedly fall by gravity effect into the alveolar openings and thus onto the alveolar surface. A relatively small proportion of the total particles larger than 0.5 microns in diameter entering the lung actually reach the alveolar surface. The surface of the nasal passage is approxi- mately 160 cm? and in most places the air flows through channels approximately one millimeter in diameter. These dimensions, plus the fact that the air stream changes its direction several times and is turbulent at various points during its passage through the nasal structures, makes the nasal pas- sageway effective as a filter for airborne particles 494 and also as a gas absorber, particularly for those gases such as sulphur dioxide which have a rather high solubility in the fluids covering the inner sur- face of the nose. In adults, the trachea is approxi- mately twenty millimeters, the third or fourth branching of the bronchi five millimeters, and the sixteenth branching 0.5 millimeters in diameter. Further branchings arrive at a tube approximately 0.4 millimeters in diameter. The conducting tubes become slightly wider during each inspiration and narrower during expiration. The frequent change of direction of the branching air tubes and their small diameter greatly favors the deposition of particles from the air passing through them. Thus, those airways proximal to any point in the con- ducting system act as a filter protecting those pas- sages located more distal to that point. The nasal passages and the air conducting tubes are lined by a mucous membrane having most important characteristics. The surface of the mem- brane is covered by mucous, a liquid which arises in part from cells making up the surface of the membrane, and in part from secreting glandular structures located beneath the surface of the mem- brane, but connected to that surface by a tubular structure. The mucous forms a sheet overlying the tissue surface and would rather rapidly fill the lumen of the conducting system if it were not for the fact that a mechanism exists for propelling the mucous from the deeper parts of the lung towards the pharynx, where it either can be swallowed or expectorated. The majority of the cells making up the surface of the mucous membrane lining the nasal passages and conducting tubes bear a multitude of cilia on their luminal surface, located just underneath the mucous blanket. The cilia beat rhythmically in a fashion which propels the over- lying mucous sheet in the direction of the mouth and thus constantly removes the secretions. The mucous blanket serves two obvious purposes. First of all, it acts as a protective layer on top of the delicate cells which line the respiratory conducting system. Equally important, the blanket provides a vehicle for removal of particles which are con- tinuously deposited upon it from the overlying air mass. Thus the mucociliary escalator system be- comes a very potent mechanism whereby the lung undergoes continuous self-cleansing. The mucocil- iary apparatus extends from the pharynx down through the fifteenth or sixteenth generation of branching. The surface of subsequent branchings, including that of the alveoli, is lined by a thin lig- uid film, which according to recent studies, is con- stantly being replaced but at a far slower rate than that of mucous secretion. This thin lining prob- ably is removed by a push from the film-forming cells combined with a pull by its attachments to the mucociliary sheet. In essence, there is a con- tinuous cleansing phenomenon provided by re- moval of a film of varying thickness and composi- tion, extending all the way from the alveolar surfaces up to the pharynx. A second cleansing mechanism is provided by phagocytic cells, the macrophages, which are found primarily in the alveolated parts of the lung. The origin of the macrophages is not certain, but the evidence suggests there are always some present, and these can be enormously and rapidly aug- mented by local cell division and, via the blood stream, by cells of a similar nature formed in other parts of the body. Macrophages are large enough to engulf particles measuring as much as fifteen microns in their largest aspect. These cells also form clusters around even larger particles and produce giant multinucleated cells. The macro- phage individually or in clusters, may live for a long period of time with their engulfed particles, provided the nature of the particle is not such as to cause the death of the macrophage. Some macrophages, since they are mobile, find their way out onto the mucociliary escalator and are ex- creted together with their engulfed particles by that cleansing mechanism. A third mechanism of lung cleansing is pro- vided by the lymphatic system. There is a liquid filled space between the capillary blood vessels and the surface of the alveoli, into which particles can penetrate or perhaps be carried by phago- cytic cells. This liquid filled space is in direct continuity with the lymphatic tubular system which provides for the flow of a liquid, the lymph, in a direction paralleling the bronchi and directed to- wards progressively larger tubes. Ultimately the lymph is discharged into the venous system, but enroute it passes through aggregates of lymphoid tissue cells, including the large aggregates or lymph nodes at the lung root. Some of the particles that penetrate into this tissue space just below the alveolar surface ultimately appear in and are held by these collections of lymphoid cells. Other particles appear to traverse the lymph nodes and ultimately are discharged into the venous system. The exact mechanism of this transport of par- ticles and their storage is unknown. A substantial proportion of the particles suspended in the in- haled air remain airborne and leave the lung dur- ing exhalation. Those particles which are de- posited on the surface of the conducting and more distant portions of the airway are removed by the mucociliary escalator, engulfed by macrophages, pass into the lymphatics, become retained in the lymph nodes or enter the blood stream and some portion of the total remain free in the tissues of the lung. It is worth noting that particles deposited on the distal portions of the mucociliary escalator can traverse the distance from the fourteenth or fif- teenth generation of bronchi up to the pharynx within as little as thirty minutes. Cleansing of this portion of the air-conducting tubes therefore is quite rapid. Those particles deposited in a more distal area move much more slowly; it may take days or weeks in order to be cleared or seques- tered. Some particles, either naked or engulfed by macrophages, simply remain indefinitely on the surface or in the interstitial tissues between the alveoli. Bands of smooth muscle encircle the conduct- ing system throughout its entire length. The utility of this muscle tissue is unclear but because of its presence, the lumen of various portions of the conducting system can be markedly narrowed 495 when this muscle contracts. The mucous pro- ducing cells can respond quite rapidly to stimuli of various kinds with an augmentation of flow of mu- cous. Under the influence of some kinds of stim- ulation, the mucous membrane becomes engorged with blood retained in the capillaries and by an excess production of interstitial tissue fluid. These various mechanisms lead to some degree of nar- rowing of the airway and consequent elevation of resistance to airflow through the conducting sys- tem. These phenomena likewise can be reversed quite rapidly, either by removing the stimulus or by applying appropriate drugs. The muscular sys- tem is under the control of nerve impulses and the same appears to be true, to some degree at least, of the mucous secreting glands and possibly even of the ciliary action. The surface cells, blood vessels, lymphatics and conducting tubes, especially those that are thin walled, are supported by an interlacing network comprised of strands of collagen, reticulin and elastic tissue, termed the connective tissue. This tissue also has its substrate of cellular components, chiefly fibroblasts. The replication rate of this tissue is slower than that of the surface cells or blood vessels, but can proceed in an orderly fash- ion. If injured, however, the replacing tissue may lose its properly organized structure, and in- stead form masses of fibrosis or scar tissue. The precise mechanism whereby this occurs is uncer- tain. As will be discussed later, some kinds of particles evoke a rather marked fibrosis and per- sistent cellular reaction, while other particles are quite inert and produce little or no such reaction. This brief account of the anatomy and physiology of the conducting system and alveolar structures should be of help in understanding the manner in which the respiratory system reacts to inhaled gases and particles. Behavior of Gases Which Enter the Respiratory System Gases are made up of particles of molecular size which move both by mass transfer, as in the flow of gas along a tube, and also by diffusion under the influence of the gravitational forces be- tween molecules. If one breathes back and forth into a bag containing a foreign gas of low solu- bility, the mass movement of air and diffusion forces will lead to an even distribution of gases through the lung-bag system within three or four minutes of quiet breathing, and within a matter of a few seconds if one takes rapid deep breaths. If the foreign gas has a high index of solubility in the fluids lining the conducting system and the gas is of relatively low concentration, the major por- tion of the inhaled gas may be absorbed in the upper airways, especially in the nose, and the concentration of the gas reaching the depth of the lung will be lower than at the point of entry. This is particularly true during breathing through the nose. For this reason, gases such as SO, will predominantly affect the nose and upper air- ways, whereas gases of low solubility, such as nitrogen dioxide, will affect the airways rather evenly throughout their entire length. Some gases, as for example nitrogen and carbon monoxide, appear to be totally inert insofar as their influence on the cellular structure of the respiratory system is concerned. Other gases such as phosgene, ni- trogen dioxide, sulphur dioxide, and ozone may have a profound effect on the tissues dependent upon the concentration presented to the cells mak- ing up the tissues at the point of contact. Behavior of Particles Which Enter the Respiratory System If, by suitably gentle technique, one digests the lungs of fifty- to sixty-year-old individuals, includ- ing those who may have worked in the dusty trades, one will obtain a residue which can be assumed to have come from exogenous sources via the airborne route over the years. These tiny particles have a most interesting size range. Many will be found to be so small as to be visible only by electron microscope magnification, while others, generally those larger than 0.5 microns in dia- meter, can be visualized by appropriate illumina- tion and 450x magnification. Of this entire popu- lation of particles retained over a period of many years, approximately half will be smaller than 0.5 microns in diameter. Of those that are larger, almost all will be between 0.5 and 5.0 microns in diameter. Fewer than 0.2 of a percent of the total will be larger than 5 microns in diameter, and less than 0.002 percent will be larger than 10 microns in diameter. If one defines a fiber as a particle having an aspect ratio such that the length is three or more times its diameter, one will observe fibers for the most part to be less than fifty microns in length, although some may be as much as two hundred microns long. Even so, the diameters of these fibers will be distributed as indicated above. If, in contrast, one samples the ambient air to which the general public or those who work in the dusty trades are exposed, one finds particles of these dimensions, but in addition, many of much larger diameter and length. It is incumbent upon us, therefore, to reach an understanding of why it is that the long term retention of particles is limited to the sizes just described, in spite of the fact that millions of particles of greater diameter become airborne and, therefore, have the poten- tial for entry into the respiratory system. The ex- planation for this arises from our knowledge of the behavior of particles suspended in air (aero- sols) and the anatomical and physiologic peculi- arities of the lung as described in the preceding paragraphs. For the immediately ensuing paragraphs we will consider particles to be of a non-fiber charac- ter. Particles can vary markedly as to shape and, dependent on composition, as to density; both of these factors play a role in the behavior of par- ticles in air suspension. For our purposes we will consider all particles as being spheres of unit dens- ity with the understanding that there could be some variation between particles as to speed of settling, depending on their shape and density. For this part of the discussion we will also think of particles as being far larger than those of molecu- lar size. In this respect the major point would be that those particles larger than 0.5 microns will exhibit essentially zero diffusion activity, and even 496 those down to 0.1 will have minimal such reac- tion. Those of electron microscope size down to .01 microns and lower will respond to molecular bombardment, and thus exhibit a considerable diffusion activity. Several physical forces are conducive to the removal of particles from an airborne suspension and their deposition upon surfaces of the respira- tory system. Particles suspended in a moving air stream possess inertial forces tending to maintain the direction of motion of the particle. When the air column changes its direction, as at a branching point of the conducting system, or in the tortuous passages of the nose, the entrained particle will tend to continue in its previous direction and be precipitated upon the surface. This effect is di- rectly proportional to the size of the particle, the speed of the air stream, and thus of the particle, and inversely proportional to the radius of the tube. Gravitational forces also remove particles from the air stream and precipitate them on the surface of the respiratory system. The terminal settling velocity of a particle is directly related to its density, the gravitational con- stant and to the square of the particle diameter. It is inversely related to air viscosity. Since the gravitational constant and air viscosity are the same at all times, the terminal velocity is in fact predominantly related to particle density and di- ameter. The degree to which deposition on the basis of gravity will occur is thus related to these two factors, plus the distance through which the particle must fall and the time permitted for the event to occur. Particle deposition by diffusion is limited es- sentially to those particles having a diameter smaller than 0.5 microns and, in fact, smaller than 0.1 micron. The smaller the particle the more rapidly diffusion movement can occur. The electron microscope size particles are relatively uninfluenced by any deposition force other than that of diffusion, and the fact that such large numbers of electron microscope sized particles are found in the lung residue indicates that diffusion can play a major role in the deposition of this size particle. Electrostatic and thermal forces have been thought possibly to play a role in de- position of particles in the lungs, but this is still uncertain. On the basis of known behavior of particles in air suspension and the anatomical arrangement of the conducting tubes, it was predicted that par- ticles larger than ten microns in diameter would be removed completely in the passage of the air stream through the nose and upper airways and that particles between five and ten microns in diameter would be deposited primarily in the up- per airways on the mucociliary escalator. Only those particles in the range of one to two microns would be likely to penetrate into the deeper por- tions of the lung where some deposition in the alveoli might occur by gravity. Particle deposition would, on the basis of these calculations, be least for those particles having a diameter of 0.5 mi- crons. Deposition of particles smaller than this might be increased by diffusion, particularly in the most distal portions of the air system. Numerous actual experimental determinations have confirmed this general distribution of loca- tion of deposition. For nasal breathing it has been shown that particles larger than ten microns in diameter are almost completely removed and few, if any, reach the conducting tubes of the lungs per se. Some smaller particles also are deposited in the nose, but the majority of these pass through and then are deposited, dependent primarily upon their diameters, along the upper or lower airways. It can be seen from these studies that particles greater than three microns in diameter will have very little opportunity to penetrate deeply and be deposited in the most distal portions of the con- ducting tubes, where the cleansing action and mucociliary apparatus would be less effective. Since almost 100% of the particles larger than three microns in diameter would fall on the muco- ciliary escalator and be removed, there is a reas- onable explanation for the fact that so few parti- cles of larger size are found in the lung residue after a lifetime of exposure to aerosols of ambient air which undoubtedly contained particles of larger size. A fiber, defined as a particle the length of which is three or more times its diameter, repre- sents a special case in terms of deposition. As is true of other particles, the settling velocity of a fiber is dependent primarily upon its diameter. One can think of a fiber as being a string of non- fibrous particles insofar as the settling velocity is concerned. In a moving air stream, fibers tend rather strongly to align their length parallel to the direction of air flow. Those fibers that are straight and rigid will therefore present an end-on aspect essentially that of their diameter. Fibers that are curved, curled, or bent in a U shape will have an end-on aspect equal to the width of the curl or curvature. Insofar as interception is concerned there thus will be a much greater chance for de- position of the non-straight fibers, a factor of con- siderable importance in the narrow airways and in the boundaries of air flow close to the surface. It has been demonstrated that curly fibers pene- trate to the deeper portions of the lung much less readily than do straight fibers of equivalent diam- eter. Length becomes important also to the de- gree that the fibers are distributed in a random way in the moving air stream. Thus a fiber one hundred microns long oriented at right angles to the direction of flow will have a much greater change of impacting on the surface than will those oriented parallel to the direction of flow. While one does observe an occasional fiber two hundred microns long in the lung dust residues, by far the majority are shorter than fifty microns in length. Factors Governing the Reaction of the Lung to Gases and Particles The recognition of whether or not a lung re- action in response to a stimulus has occurred is to a high degree dependent upon the tools and cri- teria used for such recognition. This is a matter of great importance and often ignored when deter- mining the significance of a specific reaction with respect to whether or not the cellular changes 497 have led to impairment in terms of function, life expectancy, and employability. Cell death and replacement by replication characterizes the or- ganism from conception to death. Physical factors and external agents, such as bacteria and viruses, constantly influence the orderly progression of cell death and replacement during the state that we call good health. From time to time these external agents may exert an influence of sufficient magni- tude to interfere with function or life expectancy, and these episodes are thought of as representing disease. When one examines the body of a healthy per- son, utilizing the light microscope one can always find some areas of inflammation and scarring and mild disorder of cell replication which is termed metaplasia. As one examines tissues with the elec- tron microscope, one can recognize alterations of cell structure under circumstances which the light microscope will not recognize. During life one is usually limited to the use of less refined tools in order to recognize the presence of abnormalities, and in general our concept of disease is based upon these tools. Such tools are coarse to the degree that the quantitative aspects of abnormality must reach a certain extent before they will dis- close the presence of injury. There is thus a quan- titative aspect as well as a qualitative aspect in our concept of disease. There is a further factor in- volved in deciding whether or not an injury is meaningful and thus deserves the appellation of disease. This has to do with whether or not the impairment is of sufficient magnitude to interfere with life and normal pursuits which make up one’s life style. For example, some scars representing the end stage of injury are found in the lungs of every adult. Nevertheless, when these scars are minor in extent they do not in any way interfere with function or shorten the life expectancy of the person. In the light of these statements, it is im- perative that one realize there is no sharp line of demarcation between being healthy or ill, normal or diseased, injured or uninjured. We can speak in rather broad terms of the way in which gases and particles may or may not injure the lung, but one must bear in mind that the quantitative aspects are probably more important under most circumstances than are the qualitative ones. The above comments are germane to a bal- anced understanding of the factors that govern the import of tissue reaction to external agents. Three characteristics determine whether or not tissue injury will occur and be of an extent great enough to impair function, or shorten life. These factors are (1) the nature of the agent, (2) the quantity or dose of the agent brought to bear in action upon the tissues, and (3) the reactivity of the tissues, oftentimes referred to as the host-factor. Particles and gases vary as to their inherent physical and chemical nature, and this influences whether or not injury occurs. There are some gases as for example nitrogen, and particles such as carbon and most silicates, which under almost all circumstances are essentially inert in terms of evoking tissue reaction. Such particles, when re- tained in the lung, are engulfed in macrophages and ultimately come to reside in the tissue, or in lymph nodes where the reaction is either non- existent, or at most a mild foreign body inflamma- tory process. Under unusual circumstances of ex- ceedingly high concentration, as for example ni- trogen under several atmospheres of pressure, or carbon particles in extra-ordinarily excessive amounts, a cell reaction of greater significance may occur. In contrast, there are some gases such as phosgene and particles such as free crystalline silica, which, because of their inherent quality, are biologically quite active and when present in high enough concentrations can evoke a biological reaction of important magnitude. Bacteria are a special case because these particles, when de- posited in the lung, may either be destroyed by macrophages or may grow in large enough num- bers to produce disease. In ordinary life pursuits most particles and many gases are inert or rela- tively inert in the concentrations commonly met with. On the basis of much evidence, it is generally held that there is a dose or quantity of potentially biologically active particles that will be tolerated without overt evidence of tissue reaction. In terms of an important reaction, this is certainly the case. In terms of recognition of a cellular reaction such as macrophage accumulation in the lung, or subtle changes recognized only by electron microscope or biochemical disturbance of cell structure or func- tion, there is some question as to whether or not this is true. It must also be recognized that the cell reaction to the agent may be an appropriate one and considered a normal reaction rather than an abnormal one. For example, premature death of a cell and its replacement by a normal cell can be thought of as a normal body mechanism for tolerating exogenous agents. In the same sense, the phagocytic action of macrophages with storage of inert particles therein is a normal body func- tion and can scarcely be considered an injury. For our purposes, all injury of a meaningful sort is dose related. This appears to be the case, at least in’ the minds of most students of the prob- lem, even with respect to carcinogenesis. The host factor plays an important role, but unless the dose can be accurately measured it is very difficult to quantitate the host reactivity. There are striking examples of true allergic hy- persensitivity causing a person to react violently to doses of allergen readily tolerated by the non- allergic. There is also a considerable variation from individual to individual in terms of their immune responses and cellular responses, which is not on an allergic basis. This ordinarily is re- ferred to as hyperreactivity and it accounts for the fact that more serious tissue injury may de- velop in one individual than in another even though the dose administered to both individuals is the same. This is an important phenomenon because it requires us either to set safe levels for specific agents in terms of the effect on those who are most reactive, or it requires us to find some means of excluding from contact with such agents, those people who are hyper-reactors. Taking into consideration these three major factors it is no wonder that there is considerable 498 personal variation in terms of whether or not dis- ease occurs in response to deposition of particles or exposure to gases, and that there should be some confusion in the minds of the uninformed with respect to the fact that some gases and par- ticles can exist in high concentrations without ensuing disease. VARIOUS WAYS IN WHICH THE RESPIRATORY SYSTEM CAN REACT TO AIRBORNE PARTICLES AND NOXIOUS GASES All parts of the respiratory system can be in- jured with consequent impairment of function as a result of the inhalation of certain kinds of gases and particles. Among the manifestations of such injury or stimulation are (1) changes of resistance to airflow through the conducting tubes, (2) hyper- secretion of mucous, (3) paralysis of the mucocil- lary escalator, (4) mobilization of macrophages in the tissues and air spaces of the lung, (5) cell injury with consequent acute inflammatory proc- esses or pulmonary edema, (6) chronic inflamma- tion of a granulomatous nature, (7) the develop- ment of pulmonary fibrosis or scar tissue, and (8) cell transformation or carcinogenesis. As indicated at the outset of this chapter, it would not be ap- propriate to discuss all these in detail, but some comments with respect to each of these will be useful. Changes of Resistance to Airflow An increase of resistance to airflow, either of an acute and reversible nature or of a chronic and persistent nature, may develop as a result of in- halation of certain noxious gases and particles. It has been shown that deposition of finely divided particles or the inhalation of certain gases such as SO, or hydrochloric acid mist will appreciably in- crease the resistance to airflow and that this is readily reversible following removal of the stimulus or by the use of appropriate drugs. The site of the stimulation is both in the nose and along the course of the tracheo-bronchial tree. It is presumably caused by contraction of the circular smooth muscle plus some engorgement of the mucosa with consequent anatomical nar- rowing of the lumen of the conducting system. It is probable that all kinds of finely divided par- ticles may do this to some degree. The dose re- quired for this reaction is usually quite large ex- cept in those persons truly allergic. If a specific allergen is deposited in the nose or upper airways, the sensitized person will respond with rapid and oftentimes very severe bronchial narrowing. In this instance the dose may be extremely small. It is also of interest that in this circumstance the particle size can be quite large. Most pollens are greater than ten microns in diameter. These are readily deposited in high concentration in the nose and upper airways where they trigger the acute response. The ability to cleanse these areas by. the mucociliary escalator removes the pollens and terminates the episode. Perhaps the most exquisite example of this in an industrial setting is the severe asthmatic response of those who have been sensitized to toluene-2, 4-diisocyanate (TDI). wi adie Hypersecretion of Mucous Many gases and most particles are irritating to the mucosa of the nose and conducting system of the lungs. When the dose is sufficiently large and the stimulus strong enough, there is an out- pouring of mucous from the appropriate cells, leading to cough and an increase of sputum. Acute short term exposures produce a reaction that is fully reversible and in all probability this should be considered a normal phenomenon and not a disease manifestation. There is some evidence, especially among heavy cigarette smokers, that a persistent stimu- lation by irritant gases and particles will produce persistent hyper-secretion and enlargement of the mucous secreting glandular system. This is to some degree reversible on removal of the stimulus, but in some individuals there appears to be a per- sistent hypertrophy and hypersecretion even after the stimulus is removed. The excess secretion leads to chronic productive cough and this condi- dition is termed chronic bronchitis. The accumu- lation of secretions in the lumen of the air tubes and the thickening of the mucosa consequent to hypertrophy of the glandular system causes a re- duction in the lumen of the air tubes and therefore an increase of resistance to airflow. Such indi- viduals not only have chronic cough and excess sputum production, but also evidences of chronic obstructive airway impairment. There is contro- versy as to whether this occurs as a result of in- dustrial exposure to gases and particles, but it is generally agreed that industrial environments characterized by high levels of irritant gas or particles aggravate chronic bronchitis. Paralysis of Mucociliary Escalator There is evidence in experimental animals that gases such as SO, and NO, paralyze, at least temporarily, the cilia and thus interfere with the effective removal of mucous secretions. There is some evidence that in response to certain doses there may be a stimulation of the cilia. Recovery from this kind of paralysis appears to be rapid and there is no evidence to indicate that persistent or permanent paralysis of cilia occurs under ordinary life circumstances. The combination of daily ex- cess mucous production and impairment of ciliary action, however, leads to an excessive accumula- tion of mucous in the conducting tubes. This in turn leads to an increase in resistance to airflow and to inadequate cleansing of the lung with the result that colonization of bacteria can occur with greater ease. As a result, acute bronchitis or pneu- monia may ensue. Prolongation of the “residence time” of some biological agents also may occur and be an important influence in causing tissue injury. Mobilization of Macrophages Though essentially all of the particles larger than ten microns, and a large proportion of those two to five microns, lodge on the mucociliary es- calator and thus are removed, a substantial pro- portion of those under five microns, and particu- larly those that are under two microns in diameter, will penetrate far enough out into the lung to be deposited beyond the mucociliary escalator and in 499 the alveolous bearing portion of the lung. Under normal circumstances there are relatively few macrophages in this portion of the lung at any one time. These are present in part for the purpose of sequestering, removing or digesting foreign ma- terial taken into the lungs from the general envi- ronment. When greater numbers than usual of particles are deposited, there is an augmentation of the macrophage population and in some cir- cumstances the numbers can become very large. This macrophage response is a normal function and cannot, in itself, be considered to constitute a disease. Macrophages engulf the particles either as single cells or functioning as clusters of cells and retain the particles for the lifetime of the macro- phage. The exact life of the macrophage is un- known, but it is measured in weeks and prob- ably in months. Presumably when the macro- phage dies and the particles are released, they are rephagocytized by another macrophage. When inert particles are injected intratrach- eally into the lungs, there is an initial massive out- pouring of macrophages in the regions where the particles are distributed. Over an ensuing period of weeks and months the number of macrophages becomes less and the number of free particles in the lung tissue becomes smaller. One can at this later time observe numerous macrophages filled with particles lying on the surface of the alveoli or in the interstitial tissues and large numbers of particles may be seen in the regional lymph nodes. Fibers shorter than ten to fifteen microns also are phagocytized. Segments of longer fibers may be incorporated in one or more macrophages or entirely surrounded by a cluster of macro- phages. At any one time, particles, including fi- bers, may be seen entirely outside of macrophages even years after they have been introduced into the lung. It is not known whether they have never been phagocytized or are at that moment between periods of residence within a macrophage. Macrophage reaction is clearly a very im- portant one for removal and sequestration of par- ticles. It is tempting to speculate that the macro- phage surrounds the particles and either coats the particle or, by surrounding it with its own protein, breaks the direct contact between the surface of the particle and other cells in the tissues and therefore renders the particle innocuous. There are some circumstances, as for example, {ree crystalline silica, where those particles small enough to be phagocytized by the macrophage actually kill the macrophage within a matter of a few days. The released particles are rephagocy- tized and again kill the macrophage. The impor- tance of this phenomena will be discussed under the paragraph on pulmonary fibrosis. Cell Injury with Acute Inflammation or Pulmonary Edema Acute cell injury is limited essentially to re- action to noxious gases rather than to particles. Exception to this would be a consideration of bacteria as particles. Gases such as phosgene and nitrogen dioxide and to a lesser degree sulphur dioxide or sulphurous acid mist will, dependent upon the concentration, produce anything from a mild irritation manifested by hypersecretion of mucous to a severe reaction characterized by death of the cells lining the airways and most distal por- tions of the lung. In the latter circumstances the lining cells of the conducting tubes are destroyed with the exception of the most basal layer of cells. From this basal layer there is the potential for a reconstitution of the normal cell system lining the conducting tubes. In the alveolar bearing areas, cell injury may lead to destruction of the alveolar surface cells and also of the capillary cell wall with a resultant pouring out of blood plasma or whole blood leading to hemorrhagic pulmonary edema. Depending upon the severity of the reaction, there can be a very rapid outpouring of liquid with death virtually due to drowning in the accumula- tion of fluid in the deep portions of the lung. With lower concentrations of these gases, the death of the cells making up the alveolar wall is slower and there is a delayed pulmonary edema occurring four to six hours after the exposure. This can be just as fatal as the more acute and sudden reaction. When there is a still lower intensity of exposure, the walls of the alveoli may maintain their physical integrity and gradually be reconstituted in a nor- mal fashion. It is of interest that when particles are inhaled, their distribution within the lung is localized or patchy in nature. The same is true for the inhalation of gases, if the period of inhala- tion is rather brief, as for example, only a few minutes rather than hours. For this reason not all parts of the lung are involved equally in the severe reaction, and a patchy distribution of pulmonary edema is the rule. If the individual survives the acute reaction, the subsequent course is one of recovery with little or no residual injury. This kind of chemical pneumonia in its earliest stage is a hemorrhagic edema, but in the later stage there is an outpouring of leukocytes and sometimes ac- tual bacterial infection supervenes followed by lobar or bronchial pneumonia. In some unusual circumstances, as for example, exposure to the salts of beryllium, there may be a more gradual or sub-acute development of the chemical pneu- monia. Experiments have shown an astonishing ability of animals to recover from this kind of acute cell injury with reconstitution of lung tissue that has in all facets the appearance of normal lung tissue. Chronic Inflammation of a Granulomatous Nature This is sometimes termed “chronic interstitial lung disease” and it occurs in individuals exposed to some salts of beryllium, farmers exposed to moldy hay and in certain other occupations such as the handling of bagasse and removal of bark from trees. The exact nature of this disease from an etiologic point of view is uncertain, but it would appear to be predominantly a hypersensitivity re- action with the development of a chronic inflam- matory disease in the distal parts of the lung. The nature of the injury is such as to lead to more or less persistent changes which can fluctuate in se- verity and be reversed to some degree by steroids. Occasionally the injury is such as to lead to the 500 development of pulmonary fibrosis. In some cir- cumstances the exciting agent is thought to be a thermomycete. In all of these cases there appears to be a rather high degree of individual suscepti- bility. Depending on the extent of the disease, clinical manifestations can either be absent or severe. Pulmonary Fibrosis A classical example of pulmonary fibrosis sec- ondary to the inhalation of particles is the reaction to the inhalation of substantial amounts of free crystalline silica. The hypothesis for pathogenesis of this disease, silicosis, having the strongest sci- entific support is as follows. The particles of free silica, when deposited beyond the mucociliary escalator and picked up by the macrophages, ap- pear to kill the macrophage and in the process release a material capable of stimulating the con- nective tissue of the lung to produce fibrous scars. This clearly is a dose-related disease. There are two kinds of scar production, prob- ably based on two separate mechanisms. The par- ticles of silica appear to be collected in focal areas in the lungs inside the macrophages and, at the death of the macrophage, they release the fibro- genic agent which leads to the development of a nodular kind of dense connective tissue character- ized by a proliferation of fibrous tissue elements and the laying down of a central area of collagen. These focal points of fibrosis, scattered through the lung, characterize what is termed simple dis- creet nodular silicosis. In many individuals this is the only reaction that occurs. In some such individuals, however, a second reaction characterized by the development of a massive irregular scar sometimes reaching five or more cm. in diameter develops. The nodular character is lost and the predominant feature is the large mass of scar tissue. Around the peri- phery the reaction is more cellular in nature. In contrast to the simple discreet nodular reaction, which appears to be self-limited after removal from exposure to dust, the massive scars tend to continue to enlarge and hence the term “progres- sive” massive fibrosis. It is postulated that the discreet nodular lesion is the reaction to a fibro- genic material released locally and hence its dis- creet focal character. In contrast the progressive massive fibrotic lesion is thought to be caused by coalescence of the simple nodular lesions plus the laying down of large amounts of gamma globulin. In other words, the progressive massive fibrosis is in part an immunological reaction and hence its progressive nature. There is not full agreement with this hypothesis. It is of considerable interest that the coal miner, whose nodular lesion is very different from that of the silicotic nodule in that far less scar tissue develops in the “coal worker nodule,” nevertheless may go on to develop the large scars of progressive massive fibrosis. The same can apparently occur following unusually heavy exposure to iron oxide or to pure carbon black. It would appear that progressive massive fibrosis is an immunological reaction and thus is a manifestation of hyper-reactivity or an unusual host factor. In contrast to the nodular lesion produced by the focal collection of free crystalline silica and the reaction to silica in the lung, the reaction to asbestos fiber is of a quite different nature. In this case, the very short fibers, less than five microns long, are phagocytized by the macrophage and appear to reside in the macrophage without harm- ing it. Longer fibers which cannot be totally en- closed within the macrophage and remain naked in the lung tissue or on the surface of the alveolus lead to a cellular reaction which is of a granulo- matous nature. If the reaction becomes mature enough, actual fibrous tissue is laid down in a non-nodular manner creating a pattern distinctly different from that of silicosis. Progressive mas- sive fibrosis does not appear to develop as a re- sult of exposure to asbestos, but the question of whether or not the granulomatous and fibrotic reaction to the asbestos fiber is progressive even after removal from exposure is unsettled. The re- action to asbestos fiber is not as focal and is much more generalized than is the reaction to free crys- talline silica. In all of these examples where ex- tensive scar tissue forms, lung substance is lost and a restrictive type of pulmonary function impair- ment occurs. Because of the focal nature, with normal intervening lung tissue, the silicotic reac- tion is accompanied by less impairment of blood gas exchange than occurs in the more generalized kind of tissue reaction characterizing the response to inhalation of asbestos fibers. Carcinogenesis There are numerous cell types in the lungs, most of which undergo division or replication with- in the lung in order to replace the senile and dying cells or, under intermittent stress, to augment cer- tain cell types such as the macrophage. The epi- thelial or lining cells of the airways and alveoli are estimated to replace themselves completely every few weeks. It is probable that this rate of replica- tion is accelerated under the stimulus of surface cell injury or irritation. Normally, cell division proceeds in an orderly fashion with the continuous development of identical, normally formed and constituted cells. In response to the influence of irritation and other factors, the cells may gradually change their character and organization and under- go metaplasia. If tHe alteration is of a particular kind, the cells lose their customary organization and orderly replication and undergo malignant transformation. The frequency with which this happens is unknown, but in some individuals the cancerous cells survive, become established and propagate to produce clinical malignant tumors. It is known that some kinds of inhaled particles foster the development of metaplasia and cancer. For example, the frequency of lung cancer is ex- cessively high in workers exposed to particles of chromium, nickel, asbestos, uranium and other agents. Cigarette smoke, a complex of irritating gases, including nitrogen dioxide, when combined with small particles and hydrocarbons, has carcin- ogenic action. While single agents have been shown to be carcinogenic in experimental ani- mals, a much higher yield of tumors is obtained if agents are combined. For example, if the 501 surface cells of the bronchi are caused to replicate in an accelerated manner by SO, or trauma, benzo (a) pyrene becomes a potent carcinogen, even though it is a weak one when used alone. It would appear that cells are more vulnerable to malignant transformation when they are replicating at a high rate. The concept of co-carcinogen action and multi-factorial influences in carcinogenesis seems to be well established. That there is a host factor as well is very likely. RESIDENCE TIME AND COMBINED EXPOSURE Two other concepts with respect to the action of particles deposited on the surface of the lung need to be pointed out in order to establish a bet- ter understanding of the possible biological effects of dust and gases. While the deposition of parti- cles on the surface of the proximal conducting air- ways protects the more distal air tubes and favors particle removal by the mucociliary apparatus, there is an appreciable “residence time” of such particles. During that period of minutes to hours, the biological effects leading to chronic bronchitis, metaplasia and lung cancer could be initiated. If co-existing gases paralyze the cilia and reduce their effectiveness, the residence time would be prolonged. A second potentiating effect might occur by reason of the fact that particles, which might or- dinarily be inert, can become carriers by having biologically active agents adsorbed upon their sur- face. This might concentrate the active agent and prolong the effect when the coated particle is de- posited in the lung. These two factors might play a role not only in carcinogenesis but also in the other biological effects discussed in this chapter. The importance of taking into account multiple co-existing expos- ures is becoming more and more apparent and reveals a heretofore inadequately appreciated re- sponsibility of the industrial hygienist. Preferred Reading 1. CORN, M.: “Nonviable Particles in the Air,” Air Pollutions” Vol. 1, 2nd Edition (Stern, A. C., edi- tor), p. 47., Academic Press, New York, N. Y., (1968). HATCH, T. F. and P. GROSS.: Pulmonary Depo- sition and Retention of Inhaled Aerosols, Academic Press, New York, N.Y., (1964). Inhaled Particles and Vapours, Proceedings of an International Symposium, C. N. Davies, (ed.), Pergamon Press, New York, N. Y., (1961). Inhaled Particles and Vapours II, Proceedings of an International Symposium, C. N. Davies, (ed.), Pergamon Press, New York, N. Y., (1967). Inhaled Particles and Vapours 111, Proceedings of an International Symposium, W. H. Walton, (ed.), Unwin Brothers Limited, The Gresham Press, Old Woking, Surrey, England, (1971). LIEBOW, A. A. and D. E. SMITH.: The Lung, The William & Wilkins Co., Baltimore, Md., (1968). Morphology of Expiramental Respiratory Carcino- genesis. Proceedings of a Biology Division, Oak Ridge National Laboratory Conference, Conf — 700501, National Technical Information Service, U. S. Department of Commerce, Springfield, Vir- ginia 22151, (1970). ro gm wg RT =. - -. mac mag : = - RIT PYRE ay TIEny CHAPTER 34 OCCUPATIONAL DERMATOSES: THEIR RECOGNITION, CONTROL AND PREVENTION Donald J. Birmingham, M.D. INTRODUCTION Occupational diseases of the skin comprise a broad assortment of skin changes caused by an infinite number of substances or conditions en- countered in the work environment. Because of the varied clinical displays, they are appropriately termed “occupational dermatoses,” but other titles as industrial dermatitis, occupational eczema, oc- cupational contact dermatitis, and professional eczema are also used. More specifically related to cause are such descriptive titles as cement eczema, chrome dermatitis, chrome holes, fiberglas derma- titis, oil acne, rubber itch, and tar cancer, among others. These disorders have plagued mankind since antiquity, but little was written about them until 1700 when Ramazzini published his classical text entitled, “De Morbis Artificum,” (A Treatise of the Diseases of Tradesmen). Contained within this book are descriptions of occupational skin diseases which remain remarkably accurate today. In 1755, Percival Pott described cancer of the scrotum among chimney sweeps. This was probably the first report dealing with an occupationally induced cancer. Throughout the 18th and 19th century, interest in occupational diseases of the skin was prominent in England, France, Italy and Ger- many. As industrialization spread to other coun- tries, more people were employed and occupa- tional diseases, including those affecting the skin, occurred in greater numbers. With the advent of World War I, industry expanded enormously in the United States and with it there developed a strong interest in diseases of occupation which has led to better understanding of the work haz- ards, the diseases they produce, and what could be done to control them. That occupational skin disease is an important sector in dermatology is without question. How- ever, these disorders are equally important in the field of occupational medicine, industrial hygiene, occupational health nursing and to the insurance companies. This is readily understood because dermatoses are by far the most common of the occupational diseases, numbering no less than one- half to three-fourths of all industrial illnesses re- ported. They are no less important to the working population, who number between 73 and 80 mil- lion. About one-third of this number, 23 million, work in big industry. The remaining 40 to 50 mil- lion work in small plants (500 employees or less). Anyone who works is a potential candidate for an occupational skin disease. If he works in a large industrial plant, the chance of developing a skin 503 ailment is less because the medical, nursing and hygienic services are keyed to prevent occupa- tional diseases. Conversely, work in a small plant often is attended by greater risk to health because protective measures generally are poor in quality, if present at all. In any event, it has been esti- mated that 1% of the working population suffers from occupational skin disease during the course of the year. Thus, with our present employment level, we can expect the occurrence of between 730 and 800 thousand cases. The resulting eco- nomic impact of this disease frequency is un- known, but it is estimated that the amount of money required to compensate for lost time and medical care associated with occupational derma- toses each year is in excess of 150 million dollars. Further, there is no way of calculating the dollars lost because of occupational diseases which result in job changes, loss of efficiency and production, or the rehiring and retraining of help. DEFENSE MECHANISMS OF THE SKIN The skin is the largest organ of the body. It has approximately 20 square feet of surface area for potential contact with foreign substances in nature and in the industrial environment. It is a multi-functioning organ whose anatomical and physiologic properties subserve protection by reg- ulating body heat, receiving sensations, secreting sweat, manufacturing pigment, and replenishing its own cellular elements. Each of these functions is important in the maintenance of a healthy skin and any deviation from normal can alter the health of the skin and sometimes that of the entire body. The structure or anatomical design of the skin is protective because of its thickness, resiliency, and the capacity of certain of its layers to inhibit the entrance of water and water-soluble chemicals. Its thickness and elasticity protect the underlying muscles, nerves and blood vessels. Additionally, the thickness and color of the skin afford protec- tion against the effects of sunlight and other sources of physical energy. Structurally, skin is composed of two layers — the epidermis and the dermis. Epidermis has two essential levels — an outermost stratified layer of horn cells called the “stratum corneum” and the inner living cells from which the horn cells arise. Stratum corneum cells are shed, yet replenished continually because the inner living epidermal layer keeps reproducing cells which eventually become stratum corneum cells. In short, the epi- dermis has its own self-support system. The stratum corneum layer is essential for protection, Surface layer Keratin layer Epidermal cells Basal cells Sebaceous (oil) gland Dermatology Department, Wayne State University, Detroit, Michigan. Figure 34-1. being thickest on the palms and soles. Chemically, it is a complex protein structure which is rela- tively resistant to mild acids, to water and water- soluble chemicals; but vulnerable to alkaline agents, strong detergents, desiccant chemicals, and solvents (Figure 34-1). In the lowermost region of the epidermal layer “are the basal cells from which all of the epidermal cells arise. Nestled within the basal cell layer are melanocytes or pigment-producing cells which furnish protection against ultraviolet radiation. This comes about through a complex enzyme reaction leading to the production of pig- ment or melanin granules which are engulfed by the epithelial cells which, in turn, migrate to the upper level of the skin and eventually are shed. Melanin serves as a protective screen against sun- light because the granules absorb photons of light. This mechanism occurs naturally throughout the lifetime of an individual. Sunlight and certain chemicals stimulate pigment formation and, at times, its activity can be inhibited. Dermis is thicker than epidermis and is com- posed of elastic and collagen tissue which provide the skin with its resiliency. Invested also in the dermis are sweat glands and ducts which deliver sweat to the surface of the skin; hair follicles in which hairs are encased; sebaceous or oil glands which excrete their products through the hair fol- licle openings on the skin; blood vessels; and nerves. Body temperature is regulated by the excre- tion of sweat, circulation of the blood, and the 504 Diagram of the Skin's Protective Layers. central nervous system. Blood is maintained at a relatively constant temperature even though the body can be exposed to wide ranges of tempera- ture variations. Sweat facilitates greatly the cool- ing of the overheated skin surface by evaporation. At the same time, dilation of the blood vessels within the skin also permits heat loss. Conversely, when the body is exposed to severe cold, blood vessels will contract to conserve heat. Nerve end- ings and fibers present in the skin participate in the receptor and conduction system which allows the individual to differentiate between heat, cold, pain and sense perception. This latter quality al- lows one to discriminate between dryness or wet- ness, thickness or thinness, roughness or smooth- ness, hardness or softness. Secretory elements within the skin are the sweat glands and the sebaceous glands. Perspira- tion or sweat contains products from the body’s metabolic function, but 99% of sweat is water. Excessive or inadequate sweating can be harmful not only to the skin, but to the general health. Sebaceous or oil glands are situated in the dermis and connect to hair follicles which exit on the surface of the skin. They manufacture an oily substance called “sebum,” whose precise physio- logic function is not well-understood. Present in normal amounts, it appears to offer some surface protection to the skin. Over-function of these glands is associated with acne. Coating the outer surface of the keratin layer is a waxy type of mixture composed of sebum, breakdown products of keratin, and sweat. It is believed that the emulsion-like mixture impedes somewhat the entrance of water and water-solu- ble chemicals, but its actual protective quality is minimal. It does assist in maintaining the surface pH of the skin, which is normally in the range of 4.5 to 6. Its protective capability is minimized because it is easily removed by soaps, solvents and alkalis. None the less, it is continually re- plenished under normal conditions and does con- stitute an extra layer of protection which must be removed before keratin cells can be attacked. Absorption of materials through the skin oc- curs when the continuity of the skin is disrupted by an abrasion or a laceration or a puncture. Ab- sorption of fat-soluble chemicals, fats and oils can occur via the hair follicle which contains the hair bulb and a portion of the hair shaft. Some sub- stances as organophosphates are absorbed directly through the intact skin; further, skin permits the ready exchange of gases, except for carbon mon- oxide. Sweat ducts offer little, if any, avenue for penetration. From the above it is evident that the skin has its own built-in defense mechanism. How- ever, many direct and indirect causes of occupa- tional skin disease can alter this normal defense pattern. CAUSES OF OCCUPATIONAL DERMATITIS Indirect or predisposing factors which lead to the development of an occupational dermatosis are generally associated with race, age, sex, tex- ture of the skin, perspiration, season of the year, lack of cleanliness and allergy. An outstanding example of how racial char- acteristics predispose to the development of an occupational dermatosis is seen in the marked reaction of the red-head or blond, blue-eyed, light complexioned individual to sunlight. The con- verse is seen in the resistance to sunlight or ultra- violet displayed by dark or melanotic skin. This racial difference is true in the case of sunlight and in the handling of certain chemicals as tar and pitch which react with sunlight, but dark skin is not universally resistant to the industrial environ- ment. It has been noted that young workers develop occupational dermatoses more readily that the older workers. This is not a predisposition associ- ated with any peculiar structure of their skin, rather it is the direct result of their frequent dis- regard for exercising caution in handling injurious “materials at work. Women are just as prone as men to develop occupational skin diseases. In manufacturing plants they work at many of the same jobs and come into contact with chemicals — organic and inorganic, solvents, machine oils, plastics, etc. Women have a natural tendency to be more fas- tidious in their cleansing habits at work; but, as a group, they also experience additional exposure to cleansers, detergents, waxes and other agents in the household. Workers with naturally dry skin are less able to tolerate the action of solvents and detergents. Those with oily skins can resist solvents more readily, however, they also are predisposed to 505 developing acne-like lesions induced by cutting oils. Insoluble oils collect within the hair follicle openings and irritate that area sufficiently to cause an inflammation of the hair follicle. Permitted to continue, oil acne will result. Although sweating is a normal physiologic ac- tion, in excess it is often detrimental. Increased perspiration in the armpits and in the groins may cause a breakdown of the skin surface which al- lows chemicals and bacteria to be more active at those sites. Excessive perspiration also can cause prickly heat, particularly among workmen exposed to high degrees of temperature. Occupational dermatitis is generally more com- mon during warm weather. When the work area is hot, workmen become lax in the use of pro- tective clothing and, thereby, overexpose them- selves to hazardous substances. Warm weather also means greater exposure to sunlight, poisonous plants and insects, the effects of which may or may not be related to the job. Keeping the skin free of harmful agents en- countered at work is readily accomplished by fre- quent washing and the proper use of protective devices. However, workmen with poor cleansing habits are prone to develop an occupational skin disease. These same individuals tend to wear soiled work clothing for prolonged periods of time. This practice enhances the amount of con- tact between the skin and chemical contaminants in the soiled clothing. It is a natural tendency on the part of many people to believe that all dermatitis is based on allergy. Among the working population, allergy accounts for about 20% or less of all the occu- pational dermatoses seen. Certain individuals known as “atopics” are born with a predisposition for the development of allergic diseases such as hay fever, asthma, hives and eczema. However, these people are no more disposed to allergic con- tact dermatitis in industry than are nonallergic workmen. Certain industrial or environmental substances are well-known allergens, but these ma- terials can cause a contact allergy in anyone. When one develops an occupational contact allergy it does not mean that he has to quit work. By using good protective measures, he can generally con- tinue at his job. However, there are certain peo- ple who develop such a high level of allergic reac- tion that they must seek other types of work. Direct Causes In order of their importance and frequency, the direct causes of occupational dermatitis can be classified as chemical, mechanical, physical and biological. Chemical Organic and inorganic chemicals are the major dermatoses hazards present in the work environ- ment. They constitute a never-ending list because each year the chemical spectrum gains additional agents capable of injuring the skin. Chemicals act as primary irritants or allergic sensitizers or photosensitizers. A primary irritant is a substance which, if permitted to contact the skin in sufficient concentration for a sufficient length of time, will produce a demonstrable effect upon the skin at the site of contact. In short, a primary irritant will affect the skin of anyone. Some irritants are strong or absolute in their action; for example, chromic acid, nitric acid, sodium hydroxide or chloride of lime can produce their effect within moments after contact, or at least within a few hours following initiation of contact. Other sub- stances act as relative or marginal irritants and require several contacts before any of their effects are seen; for example, prolonged exposure to soap and water or to soluble cutting fluids or mild sol- vents as acetone. About 80% of all occupational dermatoses are caused by primary irritants. Most inorganic and organic acids act as primary irritants. Cer- tain inorganic alkalis as ammonium hydroxide, calcium chloride, sodium carbonate, sodium hy- droxide are skin irritants. Organic alkalis, par- ticularly the amines, also are active irritants. Me- tallic salts, notably the arsenicals, chromates, mer- curials, nickel sulphate and zinc chloride, produce severe irritant effects on skin. Organic solvents represent a large number of substances, such as the chlorinated hydrocarbons, petroleum base compounds, the ketones, the alcohols, terpenes, among others, which irritate skin because of their solvent qualities. Primary irritants damage skin because they have an innate chemical capacity to do so. Many primary irritants are water-soluble and, thereby, actively able to react with certain tissue within the skin. Even the water-insoluble compounds which comprise many of the solvents react with the lipid clements within skin. We do not know the precise mechanism of primary irritation on the skin, but some useful generalizations serve as indices to explain the activity of groups of materials in the irritant category. Keratin Solvents All of the alkalis, organic and inorganic, in- jure the keratin layer when concentration and ex- posure time is adequate. These agents soften the keratin cells and succeed in removing many of them. At the same time, they bring about consid- erable water loss from this layer resulting in dry, cracked skin which prepares the way for secondary infection and also, at times, for the introduction of allergic sensitization. Fat and Oil Solvents Just as organic solvents dissolve oily and greasy industrial soils, they remove the surface lipids and disturb the keratin layer of cells so that they can no longer maintain their water-holding capacity. Workmen exposed each day to the ac- tion of the organic solvents develop exceedingly dry and cracked skin. Protein Precipitants Several of the heavy metal salts precipitate protein and denature it. Best known for this ac- tion are the salts of arsenic, chromium, mercury and zinc. Reducers Salicylic acid, oxalic acid, urea, as well as other substances, in sufficient concentrations, can actually reduce the keratin layer so that the latter is no longer protective and an occupational der- matosis results. 506 Keratin Stimulants Several chemicals stimulate the skin so that it undertakes peculiar growth patterns which may lead to tumor or perhaps cancer formation. Cer- tain petroleum products, a number of the coal tar based materials, arsenic, and some of the chlor- inated hydrocarbons can stimulate the epidermal cells to produce these effects. Primary irritant chemicals are commonly en- countered in industry; they account for about 80% of all of the occupational dermatoses seen; they attack the skin in various ways; strong irritants can injure the skin in a matter of moments or hours; weak or marginal irritants may require several days. Because a workman must come into contact with a primary irritant does not mean that he will necessarily develop an occupational derma- titis. Exposure to irritant materials can be con- trolled when proper precautions are taken. Sensitizers Chemicals which cause allergic contact derma- titis are far fewer in number than are the primary irritant substances. Best known among the aller- genic agents are such plant toxins as poison ivy, poison oak, and poison sumac. Other well-known cutaneous sensitizers are the alkaline dichromates, epoxy resin systems, hexamethylene tetramine, phenolformaldehyde resins, among others. A sen- sitizer does not cause visible change on the skin following first contact; but after several contacts, which may require days or sometimes months, it causes specific changes in the skin so that further contact on the same or other parts of the body will induce a dermatitis. Allergic contact derma- titis is rarely seen amongst workers before the fifth or seventh day after exposure is initiated, whereas primary irritant dermatitis can occur within a few hours or a few days. Only in a few instances, as for example, when exposed to poison ivy or epoxy resin systems or phenol-formalde- hyde plastics, do large numbers of workers become allergically sensitive. Photosensitivity There are two forms of photosensitivity der- matitis — phototoxic and photoallergic. Excess exposure to sunlight or artificial ultraviolet can injure the skin through a phototoxic effect. Many workmen are exposed to various forms of natural and artificial light, for example, farmers, police- men, road builders, telephone and electric line- men and sailors. Additional to exposures from ‘natural and artificial light sources are numerous chemicals, plants and drugs which react with se- lected wavelengths of natural and artificial light to cause phototoxic or photoallergic dermatitis. The best-known industrial chemicals with this ca- pacity are derivatives of coal tar, as anthracene, phenanthrene, and creosote; and certain dyes — acridine, eosin and rose bengal. Further, a host of topically applied and ingested drugs can inter- act with specific wavelengths of light to produce these effects. Examples of these are certain chlori- nated compounds (present in soaps for antibac- terial purposes), tranquilizers of the phenothiazine type and drugs related to sulfonamid and some antibiotics. Mechanical Causes Anyone who works experiences some type of a mechanical trauma involving friction or pressure. Friction may result in an abrasion or, more com- monly, a callus, produced by repetitive types of hand motions or through using a certain type of tool. Those who work with pneumatic tools may experience untoward effects of the hands and forearms, depending on the type of tool being used. High frequency tools can produce what is called “painful white fingers,” a disorder accom- panied by spasmodic pain in the fingers of the hand operating the tool. Heavier pneumatic instru- ments, like hammers, riveters and chisels, can cause painful tendinous or muscle or bone injury to the hands and forearms. Physical Causes Heat, cold, sunlight, artificial ultraviolet and ionizing radiation are capable of injuring the skin. Jobs involving exposure to high temperature in- duce excessive sweating and prickly heat. High levels of heat may also cause systemic symptoms and signs as heat cramps, heat exhaustion and even heat stroke. Burns of the skin can result from electric shock, sources of ionizing radiation, mol- ten metals and glass, and solvents or detergents being used at elevated temperatures. Low temperatures may induce frostbite and permanent damage to blood vessels. The ears, nose, fingers and feet are common sites for this type of cold injury. Electric and telephone line- men, highway maintenance workers, farmers, fishermen, policemen, postmen, among other out- door employees, may experience this type of skin injury. Many people who work outdoors are exposed to sunlight and increasing numbers come into casual or prolonged contact with artificial ultra- violet sources as molten metals and glass, welding operations and the plasma torch. A newer light source is found in operations using the laser ap- paratus. Since these monochromatic beams can injure skin and other biologic tissue, appropriate protective devices should attend their use. Numerous ionizing radiation sources are be- ing used in industry. Alpha radiation, though not injurious to skin, is dangerous if inhaled or in- gested. Beta radiation can injure skin and the body in general if inhaled or ingested. Gamma radiation and x-rays are well-known skin and sys- temic hazards when sufficient exposure occurs. X-ray diffraction instruments pose a potential source of skin injury to those employed in the operation of these devices. Biologic Causes Bacteria, viruses, fungi and parasites attack the skin and sometimes produce systemic disease of occupational origin. Animal breeders, agricul- tural workers, bakers, culinary employees, florists, horticulturists, laboratory technicians and tannery workers are among the ones who may develop an occupational dermatosis or a systemic disease caused by one of the biologic agents. Where these substances are known to be connected with the work, all necessary precautions for preventing 507 disease must be exercised. A common type of skin infection seen among workmen is caused by staphylococci invading the site of a previous wound. Clinical Types of Occupational Dermatoses Several clinical variations of occupational skin disease are known to occur; however, the lesions produced on the skin rarely are characteristic of a specific chemical. Nevertheless, certain types of skin changes do suggest contact with certain classes of agents, for example: (a) Acute contact derma- titis is generally caused by a primary irritant or a sensitizing chemical, a poisonous plant or a photosensitizing agent. (b) Acne-like skin dis- cases usually mean contact with petroleum oils and greases, tar or pitch or certain chlorinated hydrocarbons which induce chloracne, for ex- ample, chlorinated diphenyls and triphenyls, chlor- inated diphenyl oxide, among others. (c) Pig- ment changes in which there is a loss or gain in pigmentation. Several complex phenolic com- pounds present in germicidal agents have caused loss of skin pigment. Some examples are tertiary butyl phenol, tertiary amyl phenol, tertiary butyl catechol. Conversely, petroleum oils, asphalt, pitch, photoreactive chemicals and sunlight pro- duce gains in pigment formation. (d) New growths. Sunlight, x-ray, tar, arsenic trioxide, impure par- affins and certain shale oil fractions are known to cause skin tumors, which may become cancerous. (e) Ulcers. Arsenic trioxide, chromic acid, sodium chromate, potassium dichromate, lime, thermal burns and forceful injury can cause ulceration of the skin. These five examples of occupational skin changes (dermatoses) are presented in a decreas- ing order of frequency. To recognize them and understand their causation requires a familiarity with diseases of the skin and the environmental factors which influence their development. It in- volves understanding the nature of the lesion, the site of the cruption, the course of the disease and the correct interpretation of any clinical tests found necessary to aid in the diagnosis. Occupa- tional skin problems are best managed by physi- cians familiar with them. PREVENTION OF OCCUPATIONAL SKIN DISEASE Dermatoses caused by substances or condi- tions present in the work environment are largely preventable, but only through the conjoint effort of management, supervision and the workman. That such can be accomplished is best demon- strated in large industrial plants, while the con- verse is demonstrated in hundreds of small work establishments where little, if any, interest is shown in preventive measures. Two major approaches to the control of occupational diseases, in general, or dermatoses, in particular, are: (a) environmen- tal control measures and (b) personal hygiene methods. . Engineering Controls The best time to introduce engineering con- trols is when a plant is being designed. At that time, control measures can be integrated more readily into the operations than after the plant has been built. Ideally, operations would be con- ducted in entirely closed systems, but not all in- dustrial processes lend themselves to this approach. When closed systems are used, raw materials can be brought to the manufacturing site in sealed cars or containers and their contents emptied into stor- age tanks or bins, and later cycled through re- torts or other reaction apparatus, meanwhile pre- venting contact with the material being processed. If this type of control system is unattainable, it is generally possible to install local systems which collect the irritant dusts, vapors, fumes and mists. In any event, it is recognized that elaborate venti- lation systems are costly and most plants cannot afford this method of control. Smaller plants may have many devices intended for control purposes, but experience shows generally that small plants depend more upon personal hygiene practices than on environmental control measures. Personal Hygiene If a workman is to minimize contact with harmful agents, he must have access to facilities for washing his hands and be furnished other means of keeping clean at work. It is up to the plant to provide adequate washing facilities and good cleansing materials. Washbasins must be well designed, conveniently located and kept clean, otherwise they will be used infrequently, if at all. The farther a workman must walk to cleanse his skin, the less likelihood there is of his doing so. Inconveniently located washbasins invite such un- desirable practices as washing with solvents, min- eral oils or industrial detergents, none of which were intended for skin cleansing. For workmen to keep their skin reasonably free of injurious agents, they must use washing facilities at least three times a day — during work, before lunch, after lunch and before leaving the plant. Work- ing with toxic chemicals and radioactive sub- stances requires the daily use of showers. Many industrial hand cleansers are available as plain soap powders, abrasive soap powders, abrasive soap cakes, plain soap cakes, liquids, cream soaps and waterless hand cleaners. Work- men generally like powdered soaps because they gain a sense of having removed soils because of the frictional element. Most powdered cleansers with abrasives will remove tenacious soils, but waterless cleaners have become very popular be- cause they remove greases, grimes, tars, paint and some plastics with relative ease. However, care must be exercised in selecting waterless cleaners because many of them contain excess alkalis and solvents, which cause excessive drying of the skin and sometimes contact dermatitis. Management should have more than a passing interest in providing good washing facilities and good cleansing products. All too frequently, the cleansing agents are purchased by people having no familiarity with their quality. The practice usually results in procuring industrial hand cleans- ers which are cheapest in price. Disposable hand towels are desirable because 508 they can be discarded after use. They are an ex- cellent replacement for the old fashioned machin- ist waste. Protective Clothing It is not necessary that all workmen wear pro- tective clothing, but for those jobs in which its use is required, good quality clothing should be ob- tained. Manufacturers now provide a large selec- tion of protective garments of rubber, plastic films, leather, cotton or synthetic fibers designed for spe- cific purposes. For example, we now have access to different clothings which protect against acids, alkalis, extreme exposures of heat, cold, moisture, oils and the like. When such garments must be worn, management should purchase and control the use of the protective gear. They should see to it that the clothing is serviced and laundered often enough to keep it protective. When workmen are required to purchase their own protective cloth- ing, they generally buy the cheaper materials with little thought being given to the purpose for which it is intended. Further, if work clothes are laun- dered at home, it can cause contamination of fam- ily wearing apparel with chemicals, fiberglas or other dusts. Protective clothings include hair covers as caps and nets, coveralls, smocks, aprons, sleeves, gloves and shoes. Protective sleeves and gloves are helpful devices, but care must be exercised in their use. Unless they are made of tear-away fab- ric or film, a sleeve or glove may cause serious injury to an arm or a hand. Cotton or leather gloves are useful for protecting the hands against friction and dusts. Synthetic rubber gloves are used for protection against acids and alkalis. Neo- prene dipped cotton gloves will protect against most liquid irritants. Some workmen do not like to wear rubber gloves because the rubber causes the hands to perspire excessively. Gloves with built-in liners are probably less efficient and com- fortable than plain plastic or rubber gloves which can be worn over replaceable cotton liners. Each workman requiring this type of protective gear can have three or four pairs of washable cotton liners which can be changed when his hands become saturated with perspiration. Major manufacturers of protective clothings have descriptive catalogs which provide useful information in selecting the best protective apparel for certain exposures. Barrier Creams Generally speaking, a barrier of protective cream is the least effective way of protecting skin. Nevertheless, there are instances when a protec- tive cream may be the best method available for preventing contact with harmful agents, for ex- ample, if the face cannot be covered by a shield or gloves cannot be worn. There is no all-purpose protective cream. Several manufacturers com- pound a variety of products, each designed for a certain type of protective purpose. Thus, there are barrier creams for protecting against dry sub- stances and those which protect against wet ma- terials. Using a barrier cream to protect against a solvent is not as effective as using an impervi- ous glove; however, there are compounds which offer some protection against solvents, providing the creams are used with sufficient frequency. To use a protective cream correctly, it must be applied on clean skin at the beginning of the work shift, removed and reapplied at the break, removed at lunch, reapplied after lunch, again in the afternoon and, of course, removed at the close of the work shift. When barrier creams are used, they should be selected because of a particular need by work- men who cannot wear other types of equipment. They should not become the substitute for protec- tive clothing. In summary, management is responsible for furnishing the facilities and products required to keep the work-place safe. Similarly, the workman has certain responsibilities in a prevention pro- gram. He must wear protective clothing if it is required; he must wash with frequency if he is working with irritant or toxic chemicals. If he develops an occupational dermatitis in spite of his attempts to prevent its occurrence, he should re- port immediately to the plant dispensary or to his physician for prompt diagnosis and medical treat- ment. 509 References 1. RAMAZZINI, B.: Diseases of Workers. Translated from the Latin Text De Morbis Artificum of 1713 by W. C. WRIGHT. Hafner Publishing Company, New York, 1964. SCHWARTZ, L., L. TULIPAN and D. J. BIR- MINGHAM: Occupational Diseases of the Skin (3d ed). Lea & Febiger, Philadelphia, 1957. BIRMINGHAM, D. J.: Occupational Dermatoses. In Dermatology in General Medicine. T. B. FITZ- PATRICK (ed) et al. McGraw-Hill, Inc., New York, 1971. GAFAFER, W. M. (ed): Occupational Diseases — A Guide to Their Recognition. Public Health Ser- vice Publication No. 1097. U. S. Gov't. Printing Office, Washington, 1964. WHITE, R. P.: The Dermatergoses or Occupational Affections of the Skin (4th ed). H. K. Lewis, Lon- don, 1934. AMERICAN MEDICAL ASSOCIATION: Occupa- tional Dermatoses (A Series of Five Reports). Re- port by Advisory Committee on Occupational Der- matoses of the Council on Industrial Health, A. M.A, Chicago, 1959. ADAMS, R. M.: Occupational Contact Dermatitis. J. B. Lippincott Company, Philadelphia, 1969. BIRMINGHAM, D. J.: Occupational Dermatoses. Progress in Dermatology. Vol. 3, No. 2: 1-8, (Sept.) 1968. CHAPTER 35 PRINCIPLES FOR CONTROLLING THE OCCUPATIONAL ENVIRONMENT Jack E. Peterson, Ph.D. INTRODUCTION Hazards and potential hazards in the occupa- tional environment can be purely mechanical in nature, or they can take the form of materials which are capable of causing fire or explosion, or of producing injury by inhalation, skin or eye con- tact, or by ingestion. Physical forms of energy such as noise, non-ionizing and ionizing radiation, and heat are also potential hazards. Most basic to the control of any hazard is the concept that it can be controlled. Once the hazard is defined properly and the need for and the degree of necessary control is determined, then the only re- quirements are imagination, trained personnel and money to put the control methods to work. The basic principles for controlling the occu- pational environment consist of substitution, iso- lation and ventilation. Not all basic control prin- ciples are applicable to every form of hazard, but all occupational hazards can be controlled by the use of at least one of these principles. Ingenuity, experience and a complete understanding of the circumstances surrounding the control problem are required in choosing methods which will not only provide adequate control, but which will con- sider installation, operating and maintenance costs and personal factors such as employee acceptance, comfort and convenience. Furthermore, hazards, costs and benefits can change with time so that hazard control systems need continuous review and updating. The aim, then, must be not only to de- vise efficient hazard control methods, but to eval- uate the effectiveness of those methods at regular intervals. SUBSTITUTION Usually, when one thinks of controlling a hazard he thinks automatically of adding some- thing to do the controlling. For example, an en- gineer is more likely to think of controlling a va- por hazard by ventilation than by substituting a less hazardous material for the one which is caus- ing the problem. Yet, substitution of less hazard- ous materials or process equipment, or even of a less hazardous process, may be the least expensive as well as the most positive method of controlling an occupational hazard. Unfortunately, substitution is not a technique easily taught. No one can sit down with a slide rule, pencil and paper and decide how to best use substitution to eliminate an occupational hazard. Instead, the principle of substitution is demon- strated best with examples so that by analogy the 511 student may apply what he has learned to his par- ticular problem. Process One of the main hazards to our atmospheric environment results from the use of gasoline-pow- ered internal combustion engines in nearly all of our automobiles. Control of this source of air pol- lution is being attempted in many ways, from the passage of laws to the modification of gasoline to the substitution of a less hazardous process. Sub- stitute processes range from diesel engines to elec- tric motors, and even include the greatly increased use of mass transit systems. That there is no agreement on the best “less hazardous process” (or in fact, that process substitution is necessary) indicates that more study is needed and problem solutions may be political as well as scientific. Choosing a substitute process is not always difficult. For instance, dipping an object into a container of paint almost always creates much less of an inhalation problem than does the process of spraying that object. Cutting is usually less noisy than breaking or snapping; mechanical stirring causes less material to become airborne than does sparging; generating electric power from nuclear energy causes less air pollution than does the use of fossil fuel, but hydroelectric power is less pol- luting than either; and distillation usually causes fewer problems than does crystallization. After considering many examples of process substitution, one principle appears to stand out: the more closely a process approaches being con- tinuous (as opposed to intermittent), the less haz- ardous that process is likely to be. This principle is a fairly general one and applies to energy haz- ards such as noise, as well as to the more familiar material hazards. This principle is not always use- ful, but its application should be considered when- ever hazard control by process substitution is at- tempted. Equipment Where the process itself does not need to be changed to reduce hazards, the needed control often can be achieved by substituting either equip- ment or materials handled, or both. Substituting equipment is nearly always less expensive than substituting processes and often can be done “on the job.” On the other hand, finding a substitute material may be easy or may require extensive research and/or process changes. For these rea- sons, equipment is substituted more often than either processes or materials. Equipment substitution is often the “obvious” solution to an apparent hazard. An example might be the substitution of safety cans for bottles to store or contain flammable solvents, or the substi- tution of safety glass for regular window glass in the sash of a “fume” hood. Examples such as these can be multiplied indefinitely because they are obvious on inspection. One of the main requirements for efficient equipment substitution is the awareness of alter- nates. Persons concerned with hazard reduction must familiarize themselves with all kinds of “safety” equipment as well as with the processes and process equipment in their jurisdiction. For example, sideshield safety glasses are unlikely to be substituted for regular spectacles unless some- one knows the need for, as well as the existence of, the side-shield glasses. Unless someone knows that neoprene gloves are being ruined by contact with chlorinated hydrocarbons, and also knows that polyvinyl alcohol gloves are available and impervious to this kind of attack, a substitution is unlikely. Realistic suggestions for process equipment substitution are often based on a background in both engineering and industrial hygiene, but even without an extensive background, a fresh look at an old process or problem can pay large dividends. The man who gets out and around within a plant, a company, a city or a nation is likely to observe new solutions to problems and thus is likely to be able to apply them elsewhere. Good equipment substitution is based on common sense, ingenuity, keeping up with the state of the art, and the ex- perience of working with people, processes, and the equipment used by both. Material After equipment substitution, material substi- tion is the technique most often used to reduce or to eliminate hazards in the occupational en- vironment. Examples abound. The substitution (forced by a tax law in 1912) of red for white phosphorus in matches drastically reduced both an industrial and a “general” hazard. Substitu- tion of perchloroethylene for petroleum naphtha in the dry cleaning industry essentially eliminated a serious fire hazard. Using tritium-activated phos- phors instead of radium-based paint for watch and instrument dials has reduced the hazards associ- ated with the manufacture of the dials, and in ad- dition has reduced by a small amount the back- ground radiation experienced by the general pub- lic. Removing beryllium phosphors from fluores- cent lamps not only eliminated a hazard to the general public, but also eliminated a more serious hazard to the men manufacturing such lamps. Many years ago the principal cold cleaning solvent was petroleum naphtha. Because of its fire hazard, a substitute material was sought. Car- bon tetrachloride appeared to be ideal because of its low flammability, good solvent power, and low price. Experience and a great deal of research, however, showed that a serious fire hazard had been traded for a perhaps even more serious vapor inhalation hazard. Today, carbon tetrachloride is 512 being supplanted by several other chlorinated hy- drocarbons, notably 1, 1, 1-trichloroethane, tri- chloroethylene, perchloroethylene and methylene chloride. Each of these substitutes is far less toxic and far less hazardous to handle than is carbon tetrachloride, although each has its own hazards. In addition, the fluorinated hydrocarbons are being used more and more despite their expense, mainly because their inhalation and fire hazards are so low. The principle of material substitution carries with it the same type of reward and the same po- tential hazards as other kinds of substitution. Sub- stitution of a different material can reduce or eliminate hazard, but one hazard can be substi- tuted for another inadvertently. A careful watch must be kept for unforeseen hazards that may crop up when any kind of substitution is used. An ex- cellent source of information about the toxic prop- erties and hazards of materials and their substitutes is the Hygienic Guide series published by the American Industrial Hygiene Association. ISOLATION Isolation is the term applied when a barrier is interposed between a hazard and those who might be affected by that hazard. The barrier may be physical, or distance or time may provide the iso- lation considered necessary. Stored Material Stored material rarely poses an overt hazard, and therefore, whether it is raw material or fin- ished product, those concerned are likely to take it for granted and to assume that it poses no threat. This assumption can be dangerous. When flammable liquids are stored in large tanks above ground, common practice is to group the tanks on a “tank farm” but to isolate each tank from the others by means of a dike made of earth or concrete. If a major spill does occur, the (possibly flaming) liquid is restrained by the dike from coming close enough to other storage tanks to affect them. For more positive protection, tanks are buried to interpose an even more formidable barrier between their contents and the general environment. A further example is to restrict the volume of material stored in a single container. This exemplifies the use of isolation to reduce a hazard by imposing many small barriers rather than one large one between the contents and the environment. Where the principal hazard of a liquid arises from inhalation rather than from fire, the imposi- tion of a physical barrier becomes much more dif- ficult than simply building a dike. When the quan- tities are relatively small (up to a few tens of gallons, perhaps) the best storage technique uses both isolation and ventilation. An example of this practice is the more and more common use of ventilated storage cabinets in laboratories.> Such cabinets are usually made of fire resistant material and air is drawn through them constantly by means of a fan which discharges out-of-doors. This type of arrangement interposes both a physical and a ventilation barrier between the contents of storage vessels and the laboratory environment and in ad- dition, may free much valuable hood space for other than storage use. Solids usually are stored either in original con- tainers (bags, cans, or drums), bins, or simply in piles which may even be out-of-doors. Except in unusual cases, solids rarely pose problems in stor- age which compare in magnitude with those of liquids and gases. Outside storage piles can be unsightly and can be the source of air pollution problems; in such cases a physical barrier is the usual answer. The barrier may be as simple as a tarpaulin or as complex as a storage building with several kinds of materials handling equipment. Equipment Most equipment used in processing operations is designed to be safe if it is used properly. On the other hand, there are times and cases where this is far from true. Equipment that is operated under very high pressure, for instance, may well pose a severe hazard even when operated cor- rectly. In such cases, the proper action to take is to isolate the equipment from the occupational environment. Usually physical barriers are used and the barriers may be very formidable ones, indeed. Extensive use may be made of armor plate as well as reinforced concrete, mild steel, and even wood. Viewing the work area may be done by remote controlled television cameras, simple mirrors or periscopes. Equipment isolation may be the easiest method of preventing hazardous physical contact, for in- stance with hot surfaces. Insulating a hot water line may not be economical from a strictly mone- tary standpoint, but may be necessary simply be- cause that line is not sufficiently isolated from people by distance. Inhalation hazards can often be reduced markedly by equipment isolation. One example is that of isolating pumps. Nearly all pumps used in industry can lcak and will do so, at least oc- casionally. Proper planning should take this fact into consideration, perhaps by arranging vessels and piping so that pumps handling hazardous ma- terials can all be located in one arca. That area, then, can be isolated physically from the remainder of the process cquipment. If, then, the pump room (and/or cach pump) is ventilated properly, minor leaks will be of no consequence, and major ones will be repairable without a serious inhala- tion hazard to the mechanic. Process Process isolation is usually thought to be the most expensive of the isolation methods of hazard control, and thus is probably the least used. Never- theless, with today’s space-shot-perfected tech- niques, some extremely complex processes and equipment have been shown susceptible to remote control, and in principle there is probably no proc- ess which cannot be operated remotely if the ex- pense of remote operation is justified. Process isolation techniques were given great impetus when men sought ways in which to handle radioisotopes safely. They found that the hazard from external radiation sources could be atten- uated with shielding and distance, but both of these techniques required the development of very 513 sophisticated methods of remote operation. Mas- ter-slave manipulators were designed to allow di- rect “handling” of equipment from very remote locations and this, in turn, accelerated the devel- opment of different viewing methods, complex electronic systems, and the theory and philosophy of remote operation. The modern petroleum processing plant is an example of the use of remote processing. Many of the newer plants are based almost completely on centralized control with automatic sampling and analysis, remote readout of various sensors, on-line computer processing of the data, and per- haps actual computer control of process equip- ment. These techniques were not developed with hazard control uppermost in mind; instead, econ- omy of operation was the spur, but safety was a by-product. Computer-controlled processing also appears to be gaining acceptance in the chemical industry. For the most part, this change has been in re- sponse to economic pressures because, despite their high initial costs, computer-controlled con- tinuous processing plants can be operated with much less expense than that associated with man- ual operation, and at the same time produce a superior product. Such plants enjoy the advan- tages of remote operation and also those of con- tinuous processing with attendant relatively low volumes of materials actually being handled. This combination can result in a very low hazard po- tential. Process isolation, however, by its very nature can pose some rather extreme hazards. That is, when human intervention is required, the potential hazard may rise abruptly from near zero to near certainty. In such cases, full use must be made of techniques of isolating the man from his en- vironment. Workmen Isolating workmen from their occupational en- vironment has been used since antiquity, and will continue to be necessary in the foreseeable future. The first blacksmith to don an apron of hide was using this principle just as certainly as is the present day radioisotope handler with his plas- tic airsupplied sealed suit and its connecting “tun- nel.” Pliny, the Elder, wrote about the use of pig’s bladders by miners to reduce the amount of dust inhaled* and today advertising men extol the virtues of masks made of polyurethane foam to accomplish the same thing. Using personal protective equipment of any sort exemplifies the principle of isolating man from his occupational environment. Protective equipment for workers should usually be designed for emergency or temporary use, but this does not always hold true. Experts in the safety field stress the continual use of some sort of eye protection if only because loss of vision is such an extreme penalty to pay for a moment’s inattention. Hard hats and safety shoes with steel toecaps are other examples of protective equipment designed to be cheap insurance against severe loss. Some kinds of personal protective equipment are so ubiquitous as to be almost a badge of the trade. The butcher’s apron, the chef’s tall hat, the welder’s helmet, the first baseman’s glove, the logger's boots and the fullback’s shoulder pads are all devices designed to help isolate man from his occupational environ- ment. Today it is possible to isolate anyone from practically any environment for nearly any length of time. We can send men through the vacuum of space to the moon, for instance, or send them to the depths of the sea, completely protected from rather extreme environments. Nevertheless, even though essentially complete protection is possible, it is rarely used. Completely isolating a man from his occupa- tional environment is difficult and expensive; therefore, when worker isolation is necessary, it is usually partial rather than complete. Even par- tial isolation can result in discomfort (consider wearing a gas mask all day, for instance), and in such cases other techniques of controlling the en- vironment should be considered seriously. Face shields, ear plugs, rubber gloves and the like should always be available if their use is warranted, but the aim of the engineers and planners should be to make their continual use unnecessary. Further- more, all emergency protective equipment should be inspected periodically and tested if necessary to assure that it will perform its intended function in use. Testing of protective equipment and planning for its proper use (see Chapter 36) are both very complex fields. By its nature, most equipment of this type is designed for use at times when all of the hazards are not delineated readily — where, in fact, the real hazards may never be known. For instance, canister-type gas masks have been re- garded as suitable for respiratory protection in emergencies provided that the air still contains enough oxygen to sustain life. Chemical reac- tors, tanks, sewers and buildings on fire don’t al- ways provide enough oxygen to sustain life, and therefore, injuries do occur from asphyxiation. Furthermore, the canister on the mask may not be designed to protect against the air contaminant(s) actually present and again people are injured despite their gas masks. While the traditional gas mask still has uses, in many cases it should be re- placed by one of the supplied-air type which can be worn. in an oxygen-deficient atmosphere which contains unknown concentrations of unknown gases, vapors and particulates. This type of mask will do a good job in such atmospheres provided that it fits,” that the reservoir contains sufficient air for the necessary time, and that the regulator is. functioning properly. Gas masks are not the only pieces of protec- tive equipment that actually may not protect in the emergency where they are used, but they ex- emplify the idea that obtaining equipment for pro- tection is no guarantee that the equipment will be effective. Judicious testing of equipment de- signed to isolate man from his occupational en- vironment is a necessity. VENTILATION Ventilation (see Chapters 39 and 42) can be 514 used to insure thermal comfort as well as to keep dangerous vapors from the breathing zone of a worker. It can be misused in an attempt to blow away radiant heat or used properly to control the dust hazard from a grinder. Ventilation equipment is found everywhere, much of it designed, engi- neered, and used improperly, even though a simi- lar expenditure of time, effort and money could well have resulted in adequate or better-than-ade- quate control of the occupational environment.® From the point of view of the engineer, venti- lation systems can be either local or general in nature, and they can attempt control mainly by exhausting or supplying air properly. These desig- nations cannot, of course, be absolute because, for instance, local supply for one area is general sup- ply for any other part of that room or building. Nevertheless, the intention of the planner will con- trol this discussion. Local Exhaust and Supply Localized ventilation systems nearly always at- tempt to control a hazard by directing air move- ment. The velocity of the moving air may also be a consideration, but except in high velocity- low volume systems, it is used only to assure that the direction of movement is the correct one. There are two main principles governing the correct use of local exhaust ventilation to control airborne hazards. The first is to enclose the proc- ess or equipment physically as much as possible. The second is to withdraw air from the physical enclosure (hood) at a rate sufficient to assure that the direction of air movement at all openings is always into the enclosure. All other considera- tions are secondary. If these principles are fol- lowed, no airborne material will escape from the enclosure so long as the enclosure is intact and the ventilation system is operating properly. There are times where no enclosure is possible and where control of airborne hazards must be ac- complished simply by the direction and velocity of air movement. These cases are not exceptions to the basic principle because, at the point where control must be assured, if the direction of air movement is always into the hood there will be control of materials suspended in that air. Simi- larly, if an air-tight enclosure were to be used, then no air need be moved to assure control of a vapor or an aerosol, but the principles have not been violated. Three of the problems associated with local exhaust systems stand out. First, and most obvi- ous, is that of poor design. All too many venti- lation systems appear to have been laid out by someone who has no knowledge of how to handle air properly. These systems abound in abrupt expansions and contractions, in right-angle entries, in the overuse of blast gates to attenuate problems, and so on. Since the advent of the ACGIH Ven- tilation Manual,” poor exhaust or supply system design has had no excuse because good technique is so easily available. The second problem is that of inadequate ex- haust. It is exemplified by the exhaust system which has been added to from time to time, until nothing associated with the system works at all well. The solution is simply to make sure that all systems, old as well as new, are well engineered. The third problem of local exhaust systems is that of inadequate supply. People who are will- ing to install extra hoods at the drop of a hat (probably adding them to an already overloaded exhaust system) almost uniformly seem to feel that adequate supply air is a luxury or frill which they can do without. This tendency is accentuated by the widespread knowledge of a “rule of the thumb” which states that so long as the number of air changes per hour in the building is less “X” there is no need for a separate supply system. (The value of “X” varies from thumb to thumb, but is likely to be from 2 to 4.) This rule assumes that the building isn’t “tight” and that infiltration of air will equal or exceed that exhausted. Almost all buildings “leak” a little, and some leak a lot of air. Nevertheless, another principle of controlling the occupational environment by local exhaust is “always supply at least as much air as will be exhausted.” A mechanical air supply system can and will do many things that infiltra- tion cannot. A mechanical system can supply air that is filtered (and thus clean), tempered (warmed or cooled as necessary) and in the proper location to eliminate drafts and to avoid excessive disturbance of air at the faces of local exhaust hoods. None of these benefits can be gained by counting on infiltration for supply. Local supply in itself is used occasionally to effect control or to assist in control of local ex- haust. A combination of supply and exhaust, for instance, is sometimes used as a “push-pull” sys- tem to control vapors from large open tanks,* the supply air being used to “push” vapors into the exhaust system. If properly engineered, such sys- tems can work well and can effect control by the movement of much less air than would be neces- sary if only exhaust were used. The main use of local supply systems is not, however, to control hazardous vapors but, in- stead, to reduce heat stress problems. For this application, air is usually supplied on an individ- ual basis and each man is allowed to control the direction and/or the velocity of air impinging on his work station. The air used is not cooled, but is supplied at high velocities (up to 500 fpm); it cools by sweat evaporation and by convection, if its temperature is below the man’s skin tempera- ture (as is usually the case). General Exhaust and Supply General exhaust and supply systems attempt to control the occupational environment by dilu- tion. This principle can be used for many types of problems, ranging from hazardous vapors to locker room odors to problems of dust, humidity and temperature. A principle of general ventila- tion is that it be used to control problems that inherently are widespread. That is, it makes sense to use general exhaust and supply ventilation to control ‘the temperature and humidity of all the air in an office building, but it does not make sense to try to control the fume generated by one welder with an exhaust fan located in the opposite wall. General ventilation is almost always unsuccessful 515 when used to control “point” sources of airborne contaminants, and in addition, is very wasteful of air when used for such purposes. Even local systems must have air to exhaust, and usually that air is supplied by a general sys- tem — one that is not associated with any particu- lar hood or exhaust port. Some dilution of air contaminants will take place because of the gen- eral supply system, but its main purpose is simply to provide air to be thrown away by the exhaust system. Air moving equipment can be expensive, and air filtering and tempering equipment can be even more so. Therefore, some engineers attempt to save money by recirculating some exhaust air back into the supply system. While this practice is standard in office buildings, it is rarely applic- able in factories and shops because the air handled by the exhaust system cannot usually be cleaned adequately. Once-through systems, therefore, are standard except where the contaminant in the exhausted air is an easily handled particulate with a low inhalation toxicity. Sawdust, for example, is usually low in toxicity (although some woods are sensitizers), and the particles may be large enough to be removed easily from an air stream. In such a case, recirculation of some part of the exhaust air could be considered. Inadvertent recirculation of exhausted air is a growing occupational health problem. When ex- haust stacks and supply inlets are not separated adequately, part of the exhaust air will be cap- tured by the inlet and recirculated to the building. This problem is prevalent in buildings designed by architects who are more concerned with the ap- pearance of a roofline than they are with the health of those who will work in the building.” The problem also occurs between buildings, espe- cially when roof elevation differences are not great, and elsewhere when little or no attention has been paid to the possibility of recirculation. Recent work has shown that the best way to prevent recirculation is to discharge exhaust air in such a manner that all of it will escape from the “cavity” which forms as a result of wind moving over and around buildings.’ "' The intake can then be located at any convenient place, usually close to the roof, with assurance that re- circulation will be negligible. Unfortunately, the prediction of cavity height above a roof is not yet an exact science, but enough is known so that intelligent decisions can be made. The recircula- tion problem must be considered whenever highly toxic, highly hazardous, or highly odorous mate- rials are discharged by an exhaust system, whether or not a mechanical supply system is present. EDUCATION The first and most basic principle of almost any discipline is that knowledge is needed in order to apply that discipline to practical problems. Some knowledge comes with experience, but ex- perience can be a poor teacher. More or less formal education can supplement experience and can direct it into the most productive channels. Nearly all people with line responsibility in indus- ‘ try, and many with staff responsibility, can become involved with controlling the occupational envi- ronment. All of these people can profit from edu- cation in this area. Management Few managers become involved directly in the practical aspects of hazard control, yet very little hazard control is done without management back- ing. Managers exist mainly to motivate people (or to allow people to motivate themselves), but even expert motivators cannot channel activity into areas of which they are ignorant. Education of management should deal much more with the “why” of hazard control than with the how, when, where or whom. There has been very little effort to formalize the education of managers in most industries; usually they are taught about hazards in meetings, conferences and personal chats by men who work for them. Informal education is better than no education at all, but the present best hope is the recent proliferation of short courses prepared and presented for representatives of high echelon man- agement. A short course is the easy way to obtain quite a lot of valuable information with a small expenditure of time. This approach has been used successfully in the field of hazard control and much more use of it should be made in the future. Short courses for managers should identify hazards in broad areas; details should be reserved for examples. The courses should concentrate particularly on the costs and benefits of controlling the environment, but should not completely ne- glect humanitarian aspects. Legal requirements which must be met should also be a part of the course content, but where a “carrot” exists, its use will almost always produce better results than will a club. Particularly for managers, the car- rots (rewards) should be searched out, found and emphasized. Engineers At least a portion of the work of every indus- trial hygienist can be traced to equipment and/or process design failure. In many “failure” cases the person who designed the equipment or proc- ess simply was not aware of the potential conse- quences of the failure, or that such a failure was possible. Examples range from the purchase of equipment noisy enough to be hazardous, to the use of carbon tetrachloride or benzene as solvents, to the specification of gasoline-powered lift trucks for an enclosed warehouse, to the omission of a necessary fire door. In general, these failures arise from ignorance rather than from malice or from a “devil-may-care” attitude. Furthermore, the de- cision which resulted in a failure probably was made by someone quite far removed from the consequences of the decision — a planner, per- haps, or an engineering designer. Educating engineers in regard to environmental hazards has, in the past, taken place mainly on the job by association with more experienced people. In recent years a few short courses have been given to supplement on-the-job training, but all too often any remedy applied is both too little and too late. 516 The logical place for engineers to be exposed to the knowledge that the environment abounds with hazards is when they are students at the un- dergraduate level. What is necessary then is not a program designed to turn these people into industrial hygienists or safety engineers, but in- stead, a course or courses which tend to open their eyes to the consequences of decisions they may make in their professional capacity. Under- graduate engineers (and most graduate engineers, for that matter) simply are not aware that it is perfectly possible to write noise specifications for much equipment; that carbon tetrachloride and benzene have excellent, much less hazardous, sub- stitutes; that LPG fueled lift trucks generate much less carbon monoxide than do gasoline-powered lift trucks, that electric lift trucks are available and entirely suitable for most lift truck tasks; or when and where to install fire doors. The hazard gamut is so large that the typical short course can only scratch the surface, and a semester-long ex- posure stands a much better chance of getting the idea across. Several colleges and universities already offer one or more courses surveying the fields of indus- trial hygiene for undergraduates especially in en- gineering curricula. With such courses as the foundation, short courses later in professional life should be able to keep engineers reasonably well up to date on environmental hazard control provided, of course, that they regularly read the literature related to the field. Supervisors In most circumstances, the further a supervisor is from actual control of a process, the more he deals with men and the less he deals with things. Supervisors usually work only through other peo- ple and consequently, they become aware of most environmental hazards from other people, or through their actions. In the case of an obvious hazard within his jurisdiction, a supervisor either can deal with the hazard with his own resources or he can solicit aid from others. Generally, which action to take is rather obvious, but some of the hazards posed by the occupational environment are subtle rather than obvious, and most super- visors are not equipped to deal with the subtle variety at all. Education of supervisors usually should be process and process equipment oriented. The aim of the education should be to teach them about the subtle hazards that may be found in the en- vironment of their employees and when and under what circumstances to request aid in solving the problems those hazards pose. Supervisors who are knowledgeable and well informed about haz- ardous processes, operations and materials are often able to control hazards early enough so that outside aid is not necessary except for periodic checks or reviews. Workmen Traditionally, little effort has been made to teach workmen about either the equipment or the materials that they handle. In the past few dec- ades, safety engineers have shown over and over again that there are direct benefits to be gained from teaching workmen about the physical haz- ards in their environment and how to avoid those hazards. More recently, industrial hygiene engi- neers have begun, usually in periodic safety meet- ings, to teach workmen about the hazards of ma- terials and energies and, perhaps not surprisingly, have found similar benefits. Hazards associated with the occupational en- vironment impinge first on the men who work di- rectly with materials, process equipment and proc- esses. As these men are the first affected, they may well be the first to recognize adverse effects, and if so, if they are knowledgeable about the effects of the materials and energies they work with, they may be able to pinpoint problems be- fore those problems become severe. The main arguments against educating work- ers about the real and potential hazards of the materials and energies to which they are exposed have been that such knowledge would create ap- prehension, cause malingering, and give the unions another club to hold over the head of management. Where worker education has been used, how- ever, groundless fears have evaporated, attendance has improved, and unions have been more cooper- ative, especially in matters concerning the health and safety of workmen. An aware workman can often anticipate and circumvent hazards before they become serious to him, his fellow workers, or to the physical facili- ties. Furthermore, once the source of a hazard has been found, workmen, rather than supervisors or engineers, quite often have the best ideas of how to eliminate the problem with the least effort and expense. And finally, aware workmen often can be used to assist in industrial hygiene sur- veys,'? thereby freeing the industrial hygiene en- gineer for perhaps more productive tasks. References 1. STERN, A. C.: Air Pollution: Volume III, Aca- demic Press, Inc.,, New York, 1968. 2. PETERSON, J. E. and J. A. PEAY: Laboratory Fume Hoods and their Exhaust Systems, Air Cond. Heat. Vent. 5:63 (1963). 3. CROLEY, J. J. Jr.: Specialized Protective Clothing 517 Developed at the Savannah River Plant. Am. Ind. Hyg. Assoc. J. 28:51 (1967). 4. PATTY, F. A.: Industrial Hygiene & Toxicology, Volume 1. General Principles, p. 2, Interscience Publishers, Inc., New York, 1958. 5. BURGESS, W. A. and B. HELD: Field Fitting Tests for Respirators, Natl. Safety News 100:41 (1969). 6. KANE, J. M.: Are There Still Local Exhaust Ven- tilation Problems? Am. Ind. Hyg. Assoc. J. 28:166 (1967). 7. Industrial Ventilation: A Manual of Recommended Practice. American Conference of Governmental Industrial Hygienists (12th edition), P.O. Box 453, Lansing, Michigan, (1972). . 8. HAMA, G. M.: Supply and Exhaust Ventilation for the Control of Metal Pickling Operations, Am. Ind. Hyg. Assoc. J. 18:214 (1957). 9. CLARKE, J. H.: The Design and Location of Build- ing Inlets and Outlets to Minimize Wind Effect and Building Re-entry of Exhaust Fumes, Am. Ind. Hyg. Assoc. J. 26:242 (1965). 10. HALITSKY, J.: Estimation of Stack Height Re- quired to Limit Contamination of Building Air In- takes, Am. Ind. Hyg. Assoc. J. 26:106 (1965). Il. RUMMERFIELD, P. S., J. CHOLAK and J. KERE- IAKES: Estimation of Local Diffusion of Pollutants from a Chimney: A Prototype Study Employing an Activated Tracer, Am. Ind. Hyg. Assoc. J. 28:366 (1967). 12. PENDERGRASS, J. A.: Planning Industrial Hy- giene Studies to Utilize Plant Personnel, Am. Ind. Hyg. Assoc. J. 25:416 (1964). Preferred Reading I. PATTY, F. A.: Industrial Hygiene & Toxicology: Volumes I and 11, Interscience Publishers, Inc., New York, 1958. 2. HEMEON, W. C. L.: Plant and Process Ventilation, 2nd Ed., Industrial Press, Inc., New York, 1963. 3. [Industrial Ventilation: A Manual of Recommended Practice, American Conference of Governmental Industrial Hygienists (12th Edition), 1972. 4. CRALLEY, L. V,, L. J. CRALLEY and G. D. CLAYTON: Industrial Hygiene Highlights, Indus- trial Hygiene Foundation of America, Inc., 1968. 5S. McCORD, C.: A Blind Hog's Acorns. Cloud, Inc., New York, 1945. 6. HAMILTON, A. and H. HARDY: Exploring the Dangerous Trades, Little, Brown & Company, Inc., Boston, 1943. 7. JOHNSTONE, R. T. and S. E. MILLER: Occupa- tional Diseases and Industrial Medicine, W. B. Saun- ders Company, Inc., Philadelphia, 1960. CHAPTER 36 PERSONAL PROTECTIVE DEVICES Harry F. Schulte GENERAL PHILOSOPHY It is one of the fundamentals of industrial hy- giene that personal protective devices are ‘last resort” types of controls, to be used only where engineering controls cannot be used or made ade- quate. It should be noted that this fundamental is stated unequivocally in the standards adopted under the Occupational Safety and Health Act. There are many jobs in industry which are short- term or which must be conducted where exhaust ventilation or other control measures cannot be employed on short notice. Protective devices are also extremely important as a second line of de- fense against inadvertent or unexpected conditions. Thus, when a man dons a respirator or a face shield before opening a container of toxic material he does not expect to need this equipment, but he is prepared and protected if the toxic material escapes its confinement. Personal protective devices appear to be very simple to provide and use in contrast to such equip- ment as exhaust ventilation or sound absorbing barriers. It is the purpose of this chapter to show that this is not necessarily true, and to provide the reader with essential information on the selection and correct manner of use of personal protective devices. In making a selection of equipment to be used the employer is advised to consider the wishes of the workers who must use the equipment, since worker acceptance is the key factor in a successful protective equipment program. For this reason the comfort factor should be given con- siderable weight at the expense of costs but not of protection. Full discussion of the use of the devices with the employees, training in their use and instructions for care and maintenance are very important. For example, handing a man a respira- tor and telling him to use it is not only an ineffec- tive technique, but it can be very dangerous. PROTECTION AGAINST INHALATION HAZARDS Where Used There will always be a temptation to resort to respirators as a cheap substitute for a ventilation system. If this is done it is clear that management has not carefully considered the alternatives since reliance on, and effective use of, respirators is definitely not cheap. A careful study may be re- quired to determine that no other effective control measures can be used. Respirators are designed to protect only against certain specific types of sub- stances and in certain concentration ranges, de- pending on the type of equipment used. Many other factors should be considered carefully in 519 making the decision that other engineering con- trols are not practical. Nevertheless, there are many places where respirators can and should be used with full knowledge of their limitations and requirements. Approval Systems and Schedules The U. S. Bureau of Mines gave its first ap- provals of oxygen breathing apparatus in 1918 and gradually extended this activity to include all types of respirators. Each approved respirator and each approved filter, canister or cartridge bears an approval stamp or mark. Approvals are issued according to a series of “schedules” which describe the tests to be performed on each type of respirator and the standards it must meet to re- ceive approval. Lists of approved devices are is- sued periodically by the Bureau and supplements are added to include newly approved devices. The last complete list of approved devices was issued by the Bureau of Mines as Information Circular No. 8436 and included devices approved up to December 31, 1968.2 Supplements were issued in January 1970 and February 1971. The approval schedules themselves are subject to occasional reviews and new schedules are de- veloped to meet the needs for protection against new hazards or to reflect the development of new kinds of devices. Where respirators are used reg- ularly, these schedules should be consulted since they set forth the precise information to be ob- tained in the test procedures as well as the limita- tions of the tests. Prior to 1971 the U. S. Depart- ment of Agriculture performed tests and issued approvals on respirators to be used in working with pesticides. This function has now been taken over by the Bureau of Mines. With the passage of the Occupational Safety and Health Act and the subsequent formation of the National Institute for Occupational Safety and Health (NIOSH), the approval system has been in the process of change. In 1972 NIOSH took over the approval function from the Bureau of Mines for aboveground uses. Considerable research is now underway to expand the scope of the approval tests and to develop more satisfactory procedures to meet the changing and expanding needs. Particle-Removing Air Purifying Respirators Applications and functions. These devices are de- signed to protect the wearer against inhalation of material dispersed in air as distinct particles — as a dust or fume in the case of solid particles or as a mist or fog in the case of liquid droplets. They consist, principally, of a facepiece with some type mechanical filter. The material to be protected against may be a nuisance dust such as sawdust, a pneumoconiosis-producing dust such as silica or coal dust, a toxic dust like lead oxide, a metal fume like cadmium, a highly toxic dust like beryllium oxide or a radioactive dust such as plutonium. These examples range in their degree of protection required from relatively minor to extremely high. Respirators to meet this range of requirements differ chiefly, but not solely, in the efficiencies of their filters. Limitations. The user of any air purifying respira- tor must be certain that the atmosphere contains adequate oxygen and that the only harmful ma- terials present are those which can be removed by the respirator to be worn. There are many ways in which air can leak around the filter, seri- ously reducing the protective capability of the respirator. Failure of the filter to seat properly in its holder, leaking valves and imperfect sealing of the respirator to the wearer’s face are all significant. Some of these factors can be controlled by proper design but all require good and frequent inspec- tion and maintenance. Facepieces. There are two basic types of face- pieces used on air purifying respirators — half masks and full face masks. The half masks do not cover the eyes and hence offer no eye protection nor do they interfere as much with vision as do the full face masks. The half mask must contact a rather complex facial surface and the possibility of leaking is greater than in the case of the full face mask. Obviously, faces vary considerably in their dimensions from one individual to another and since a given respirator is usually made in only one size, a successful fit for the respirator cannot be made on all persons. Recently some manufacturers have begun making some respira- tors in several sizes. Where this choice is not available, it is essential that the employer stock several different models of respirators, usually from several different manufacturers. A fitting program, to be discussed later, is required to pro- vide adequately fitted respirators. A serious problem with full face respirators is obtaining an adequate seal for the worker who must use corrective glasses. Where the temples of conventional eyeglasses emerge from the face- piece, there is a serious place of leakage. Some masks provide methods of mounting a special set of corrective lenses inside the respirator facepiece. Half masks are usually held on the face by means of a single set or a double set of elastic bands. The double sets of straps are practically a necessity in assuring a reasonable face fit and each set should fasten to separate suspension points on the respirator. Full face masks, being much heavier, are supported by a head harness which should have at least five adjustable straps. Most respirator facepieces contain valves to direct the flow of air from outside, through the filter, into the nose and then back outside. Valve- less respirators are being used, but are not ap- proved for use with hazardous materials. The most important valve is the exhalation valve which opens during expiration allowing expired air to pass directly outside the mask. It closes during 520 inhalation and must close positively and quickly to prevent toxic material being drawn into the face- piece. The inhalation valve is located close to the point where the filter attaches to the facepiece. It opens during inhalation to allow air to be drawn in through the filter and closes during ex- halation to prevent the passage of moisture-laden expired air through the filter. Some approved respirators do not have inhalation valves. Obvi- ously, all valves should offer minimal resistance to air flow, but low resistance is particularly im- portant in the exhalation valve. Resistance to ex- halation is much less tolerable than is resistance to inhalation. Filters. Filtration by fibrous filters is the method universally used in respirators for removing parti- cles from the air. The filter material may be a loosely or tightly packed mass of fibers of cotton, wool, synthetic fibers, glass or mineral fibers, or it may be a paper made of these materials. The filter efficiency is influenced by the particle size, shape and density of the aerosol and by a number of other factors determined by the filter and the respirator. The diameter of the fibers used in the filter is important since higher collection efficiencies are obtained with finer fibers. The tightness with which the fibers are compressed is another factor leading to higher efficiency. As a filter is used in a dusty atmosphere its efficiency usually increases with time since the layer of collected dust becomes an additional filter. It should be noted that all of these factors leading to increased filter efficiency also lead to increased resistance to breathing. This limits the extent to which these factors can be used to obtain higher particle removal efficiency. The only way to compensate for high filter resis- tance is by providing large filter surface areas. Thus, many filters are folded in various ingenious ways to achieve large surface areas in small spaces. Filters may be incased in “cans” or holders to protect the folded filter. There are approval schedules for respirators for protection against (1) pneumoconiosis-pro- ducing and nuisance dusts, (2) toxic dusts (not significantly more toxic than lead), (3) metal fumes (not significantly more toxic than lead), (4) chromic acid mist, (5) dusts significantly more toxic than lead and (6) various combinations of these. A summary of some of the requirements for approval are given in Table 1 taken from the ATHA-ACGIH Respirator Manual.® Special Purpose Respirators. Because of recogni- tion of the necessity of maintenance and regular servicing and cleaning of respirators, there has been increased interest in the possibility of single- use respirators. These could be discarded when breathing resistance became excessive or the respi- rator became dirty or damaged. Some simple res- pirators of this type have been used in the past — a surgeon’s mask is an example — but they have never been approved because of their low efficien- cies and lack of exhalation valves. Recently sev- eral manufacturers have begun making single-use masks, and one has been approved under a new TABLE 36-1 U.S. BUREAU OF MINES APPROVAL SCHEDULES AND TESTS TEST CONDITIONS AND PERFORMANCE REQUIREMENTS FOR DISPERSOID RESPIRATORS Dispersoids Maximum Covered by Maximum Final Respirator Concentration Duration ~~ Allowable Resistance for Protection of Dispersoid, of test, Leakage, to Air Flow, against Test Dispersoid mg/m? hr mg mm of H,O Pneumoconiosis- Silica dust; geometric producing and mean not more than nuisance dusts 0.6 1; 0,=1.9 50 = 10 1.5 3.0 50 Toxic dusts (not Litharge, —75%; free significantly metallic lead, —25% ; more toxic geometric mean not 1S +5 1.5 0.43 50 than lead) more than 0.6 yu; 0, =1.9 (Pb) Metal fumes (not Freshly generated lead significantly fume 15 +5 5.2 1.50 50 more toxic (Pb) than lead) Chromic acid Electrolytically generated mist chromic acid mist I15+5 5.2 1.0 50 Pneumoconiosis- Mist formed by atomizing producing and a silica dust-water nuisance mists suspension 10 +5 5.2 5.0 50 Various combina- tions of above types of dis- persoids Respirator must meet requirements for each type." “For example, the protection against dusts not significantly more toxic than lead, the respirator must meet the re- quirements for the first two items in this table, that is, for pneumoconiosis-producing and nuisance dusts and for toxic dusts not significantly more toxic than lead. From RESPIRATORY PROTECTIVE DEVICES MANUAL published by American Intustrial Hygiene Association and American Conference of Governmental Industrial Hygienists, 1966. Bureau of Mines approval schedule recently adopted for such masks. Replacement (and dis- posal) costs must be balanced against cleaning and maintenance costs. Nuisance dust masks, including some not car- rying Bureau of Mines approvals, may still have some use in industry. These may be useful in woodworking shops, on workers operating ma- chines on dusty roads and farms, and for workers sensitive to pollens in certain seasons. Their costs are likely to be lower than those for approved masks and the reasons for their lack of approval should be given careful consideration. Thus a mask may fail to meet approval standards because of high breathing resistance, and this is likely to make it unacceptable for long wearing by workers. On the other hand, a mask may be a simple de- vice for which no approval schedule exists, and it may be adequate, highly acceptable and useful to the librarian required to clean dust from stacks of books. Such masks must be kept strictly separate from masks used for genuine protection against hazardous materials. A new type of respirator which is being em- ployed where high efficiency must be combined 521 with low breathing resistance is the powered filter respirator. In this device a battery-powered pump forces air through the filter, and by way of a hose, into the facepiece. The rechargeable battery, pump and filter are carried in a compact unit worn on the belt or other harness. For heavy work requiring large air volumes and low resis- tance to breathing in atmospheres containing highly toxic materials, this powered filter device is prov- ing both useful and popular. Workmen cleaning coke ovens and uranium miners are among those who are using this respirator. Gas and Vapor-Removing Air Purifying Respirators Applications. These respirators are designed to protect the wearer against the inhalation of ma- terials in the air that are present in the form of gases or vapors. Respirators for protection against such materials are equipped with a container or canister filled with a sorbent which absorbs, ad- sorbs or reacts with the hazardous gas in the at- mosphere. Some sorbents are highly specific for a particular compound and so the respirator con- taining only this sorbent gives no protection against any other material. Other sorbents take out whole classes of compounds such as acid gases or organic vapors. Limitations. Like the particulate removing respira- tor, the gas removing device is useless unless ade- quate oxygen is present. Unless the device is spe- cifically equipped with a filter in addition to the sorbent, it will not offer adequate protection against any hazardous particulate substances. Leakage around canisters can also occur as around filters but this is less likely. Leakage around the facepiece is also possible but, since these respira- tors usually offer less resistance to breathing than filter types do, there is a slightly smaller chance of this type of leakage. Once a sorbent canister is opened and used, the sorbent may absorb mois- ture or other deleterious materials from the air and deteriorate even without further usage. For respirators designed for use under highly dangerous conditions some canisters are equipped with devices which change color when sorbent de- pletion approaches. For respirators designed for use under less hazardous conditions the odor of the gas penetrating the canister is the only warning. For these reasons simple gas removing respirators are most frequently designed for a single usage in dealing with a specific situation. Facepieces. Essentially the same information re- lating to facepieces on particulate removing respi- rators applies also to gas and vapor removing respirators. Because many gases and vapors are also irritating or damaging to the eyes, full face respirators are much more frequently required than half masks. Half mask respirators usually carry relatively small sorbent canisters which can be used only for short periods in relatively low con- centrations of gas. Even with the full facepiece and its head harness, the sorbent canister for heavy duty usage may be too heavy to be supported on the facepiece. It may be worn on a chest harness or strapped to the belt. The canister is then con- nected by a hose to the facepiece. Sorbents. As previously noted, some sorbents may be used only in dealing with specific chemical compounds or with classes of compounds. Thus manufacturers have specific sorbents for ammonia or chlorine. Many canisters contain combinations of materials to assure absorption of a specific compound. It is important to note whether pro- tection against the substance required is claimed on the canister of the device to be used. Obvi- ously, it is not always possible to include the com- plete list of all such compounds on each canister, and the canister may effectively remove some ma- terials not listed. A list of sorbents for a large number of materials is given in the Respirator Manual. The Bureau of Mines makes approval tests on only a limited number of common indus- trial toxic chemicals. Since there is usually little warning of impend- ing canister failure, the instructions of the manu- facturer must be carefully followed regarding the length of time the device can be worn and the cir- cumstances of its use. The effectiveness of a can- ister depends on the presence of a reactive chem- ical and canisters usually deteriorate with time. Here again, the manufacturer’s instructions re- 522 garding shelf life should be followed and outdated canisters should be discarded. Types. Gas masks are full facepiece units with large canisters. The names of the substances against which the mask gives protection are writ- ten on the canister and, in addition, the canisters are given specific colors for identification pur- poses.” Chemical cartridge respirators are half mask respirators with small cartridges and are used for protection against the inhalation of atmospheres that are not immediately dangerous to life. Those used for protection against organic vapors are limited to use in concentrations not exceeding 0.1% by volume of such vapors; they are not satisfactory for all organic compounds. Mouth- piece respirators are small, compact devices for self-rescue in short term emergency situations (Figure 36-1). Instead of a facepiece this device fits in the mouth with a clip to put on the nose to force breathing through the mouth and the respirator. Various combinations of filter and vapor re- moving respirators are available. A widely used device of this type is the universal gas mask which contains a filter plus sorbents for organic vapors, acid gases, ammonia and for the oxidation of car- bon monoxide. This mask is used where the na- ture of the contaminants cannot be completely identified or where it is known that the atmosphere Supplied by and used with permission of Los Alamos Scientific Laboratory University of California Los Alamos, New Mexico Figure 36-1. Mouthpiece Respirator — Self Rescue Device. contains several of the above materials. It is the best respirator for protection against oxides of ni- trogen in moderate concentrations. It must be remembered that it offers no protection when there is little or no oxygen present. Some manufactur- ers use the same basic facepiece for a variety of applications and various filters and canisters can be used on the same unit. Figure 36-2 illustrates air purifying respirators. Atmosphere Supplying Respirators Applications. When a lack of oxygen is known or suspected or when a very high degree of protection is required the only suitable device is the atmos- phere supplying respirator. This consists of a source of air or oxygen which is fed through a hose to a mask or a helmet. Intermediate mixing and regulating equipment may be required. Sup- plied air devices offer essentially no resistance to breathing, and the atmosphere supplied may be cool and more acceptable than that from other types of respirators. Facepieces. A variety of facepieces are used with atmosphere supplying respirators. Half masks and full face masks are similar to those previously de- scribed although the valves are somewhat different. In addition to these, helmets may be used which cover the entire head and a cover may extend down to the waist as in the abrasive blasting hood. Another type of facepiece is the air supplied face shield. In this, the air is supplied by a hose to a perforated or slotted tube at the top of the face shield and the jets of air are directed downward past the eyes, nose and mouth. It is difficult to adjust this device to avoid entraining contaminated air and blowing it into the breathing zone. There are other combinations of atmosphere supplying equipment with hoods, blouses and complete clothing Hose types. There are several varieties of the hose types including the hose mask with blower, hose mask without blower and the air-line respirator. The hose mask with blower can be used in any Supplied by and used with permission of Los Alamos Scientific Laboratory University of California Los Alamos, New Mexico Figure 36-2. Air Purifying Respirators. Front Row — Half Masks Second Row — Full Face Masks Rear — Universal Gas Mask. 523 atmosphere provided that enough respirable air is supplied to the wearer by means of the blower. The blower must be hand operated and the blower operator serves as an observer capable of rescuing the wearer in case of accident. The hose mask without blower is used under conditions not im- mediately dangerous to life and from which the wearer can escape without the aid of the res- pirator. The air-line respirator (see Figure 36-3) consists of a source of compressed air to which the facepiece is connected by means of a small diam- eter hose. In the line is a pressure reduction valve and some type of flow regulating device. This equipment is used for protection in atmospheres that are not immediately dangerous to life or health or from which the wearer can escape with- out the aid of the respirator. There are two basic types or modes of opera- tion of air-line respirators — continuous flow and demand. In the first, the air is fed to the facepiece continuously and a positive pressure is maintained inside the mask at all times and any leakage will be outward. Considerably more air is used than is consumed in breathing. In the demand type a valve which regulates the flow of air opens only when a slight negative pressure is produced inside the mask as a result of inhalation. Thus, only air used in breathing is drawn from the source. Since a negative pressure is produced inside the face- Supplied by and used with permission of Los Alamos Scientific Laboratory University of California Los Alamos, New Mexico Figure 36-3. Airline Respirator. 524 piece it must fit tightly to the face or contaminated air will be drawn in. Usually the demand type has a by-pass valve so the wearer can switch to continuous flow if he desires. A newer variation is the pressure-demand type of flow regulation. In this, a small positive pressure is always main- tained in the facepiece even on inhalation. The demand valve opens to supply air when the posi- tive pressure decreases to a certain level as a result of inhalation. Thus leakage is always out- ward if a poor fit of facepiece to face is obtained. Self-contained breathing apparatus. In this appa- ratus the wearer carries his own supply of air or oxygen and so he is able to move about without attaching hoses which limit his travel distance and maneuverability. Since the wearer is limited to the supply of air which he can carry, several methods are used to conserve this supply. De- mand and pressure-demand valves may be used in the same manner as in the air-line respirator. A bypass for continuous flow is also provided, but can be used only for very short periods or the supply will be quickly exhausted. Either air or oxygen may be used in this type of apparatus. Another type of device uses recirculation to conserve the oxygen supply. In this unit the ex- haled air is not expelled but passes through an absorber which removes carbon dioxide and then enters a breathing bag. Here it mixes with fresh oxygen from the gas cylinder and then passes back to the facepiece for rebreathing. Oxygen only en- ters the breathing bag when the pressure in the bag drops below a fixed value. Since the oxygen con- tent of exhaled air is still about two-thirds of that of inhaled air, it is only necessary to make up this difference from the tank and thus the recirculating type can be used for much longer periods for the same quantity of oxygen carried. Both de- mand and recirculating equipment are marked for use only for a specified period of time ranging from thirty minutes to three hours. A third type of self-contained breathing appa- ratus uses a chemical source of oxygen which is liberated when carbon dioxide and moisture are absorbed from the exhaled air. A breathing bag is provided to mix the incoming oxygen with the purified exhaled air. This apparatus can be used for thirty minutes only and includes a timer to warn of the approaching limit (see Figure 36-4) Once the canister is opened it cannot be rescaled for further use even if it has been used for only a few minutes. Like all chemical cart- ridges it has a limited shelf life even if unopened. Combination types. One variety of air-line respi- rator utilizes a small cylinder of compressed air worn on the user as an emergency device. If any- thing happens to the regular air supply the wearer simply disconnects his air line, automatically switching to the small cylinder supply and unhur- riedly leaves the hazardous area. In place of a compressed gas supply, a filter or a sorbent can- ister may also be used for emergency conditions. Even with these devices air-line respirators are not approved for use in atmospheres immediately dan- gerous to life. Sources of air or oxygen. The hose mask simply Supplied by and used with permission of Los Alamos Scientific Laboratory University of California Los Alamos, New Mexico Figure 36-4. Self-Contained Breathing Apparatus. uses air drawn from a source outside the contami- nated atmosphere. The air-line respirator may use a compressed gas cylinder of air or oxygen or a compressor which picks up outside air. If the compressor is driven by a gasoline or diesel en- gine extreme care must be taken to see that the engine exhausts away from the pump intake and no exhaust gases enter the breathing air system. Water-lubricated compressors, or those not re- quiring internal lubrication, are the best sources of compressed air for these devices since heating may cause breakdown of lubricating oil forming carbon monoxide. Oil-lubricated compressors, if used, should be equipped with thermal overload switches to turn them off if overheating occurs. In any case, the compressor should be followed by a trap and filter to remove dirt, oil and water from the air line. If a regular building supply is to be used for an air-line respirator the system must be checked repeatedly to be certain that it does not contain even small concentrations of carbon mon- oxide.® A new alternative source of oxygen for the self-contained breathing apparatus is liquid air or liquid oxygen. Several devices using this oxygen source have been approved by the Bureau of Mines. Air from this source is cooler and may have a “fresher” odor than compressed air. Maintenance. All types of respirators require 525 maintenance and cleaning. The highly complex atmosphere supplying devices must be inspected for signs of wear and deterioration and to make certain that all of the parts are functioning prop- erly. Other types of respirators are simpler but still require regular inspection. Rubber parts de- teriorate with time and exposure to ozone and other gases. Hence, hoses, facepieces and valves must be inspected regularly and parts or whole respirators replaced when necessary. All respira- tors should be brought in for cleaning occasionally and emergency devices cleaned after every use when cylinders of gas or canisters are replaced. Emergency devices and self-contained breathing apparatus should be inspected monthly since they are usually to be used under very hazardous con- ditions. When respirators are used routinely they should be brought in regularly to be dismantled, washed and dried, inspected and parts replaced as necessary, new filters or canisters put in and the whole reassembled and stored in a clean place. Special Topics Worker Acceptance Factors. Good equipment is ineffective if the equipment is not accepted and used by the workers. Hence, factors leading to such acceptance must be carefully considered by management. All respirators are uncomfortable and irksome to wear but consideration of the com- fort factor in respirator selection can do much to gain worker acceptance in using respirators when they are needed. Low breathing resistance is im- portant, and while the Bureau of Mines specifies maximum values of permissible resistance, there are still differences among approved respirators. If face fit can be obtained only by very tight strap tension, the respirator cannot be worn long and its use will be avoided. A particularly important point is management’s interest in the program. If every effort is made to provide conditions where respirators are not necessary then they will be better accepted when they are necessary. Regular cleaning and maintenance is evidence of manage- ment’s interest. An educational program in respi- rator use is essential. Training. Respirators are complex devices and cannot simply be handed to the worker with the assumption that they will be used properly. When the worker is told to use a respirator he should see the various devices available to him and have their method of operation explained including all essential parts. He should then try on the device and test the fit of the facepiece. This may be done by covering the exhalation valve, if possible, and then exhaling sharply or by closing the intake ports and inhaling. Most manufacturers include instructions for leak testing with the respirators and these directions should be followed. The worker should be taught to inspect the respirator before each use. The subject of training is dis- cussed at considerable length in the Respirator Manual” and is an extremely important topic. Where considerable numbers of respirators are worn, it is advisable to designate a specific indi- vidual to be responsible for fitting and training. Heat problems. All respiratory equipment is very uncomfortable and fatiguing to use under hot con- ditions. Supplied air equipment such as air-line respirators may be most satisfactory under such conditions and complete supplied air suits may be necessary. A small compact vortex cooler is avail- able which can be worn on the belt or harness to supply cool air. Communications. Some voice communication is possible while wearing a respirator but sounds are muffled and attempts to talk loudly may loosen the face fit. With most full face masks it is possi- ble to replace the exhalation valve with a combi- nation valve and speaking diaphragm which per- mits much better voice transmission. When good communication over considerable distance is ne- cessary, it is possible to equip the full facepiece with a battery operated microphone transmitter which transmits to an outside speaker or to re- ceivers or earphones worn by others. Codes and sources of information. As noted, the Bureau of Mines issues approvals for all types of respiratory protective devices and the approval schedules which can be obtained from the Bureau contain full information on how the respirators are tested and the standards they must meet. The Bureau has also issued a list of dust respirators approved for use in coal mines.® The American National Standards Institute has issued its Amer- ican National Standard Z88.2-1969 entitled Prac- tices for Respiratory Protection which contains much useful information.” The most complete publication in this field is the Respiratory Pro- tective Devices Manual published by the American Industrial Hygiene Association and the American Conference of Governmental Industrial Hygien- ists. The National Safety Council has recently published a series of articles on respiratory pro- tection in National Safety News.» A Respirator Program for Industry The important elements of the successful plant respirator program have been discussed in pre- vious sections of this chapter. Here they will be summarized to provide a means for checking to be certain that all factors are covered in a particu- lar situation. Determination of need. This will require knowl- edge of the hazards anticipated in carrying out a particular job. An estimate will be required of the possible concentrations of toxic material that could be produced; whether existing engineering con- trols, such as ventilation, can adequately meet the needs; the anticipated duration of the required protection and any limitations imposed by the job. The latter includes the intensity of the physical ac- tivity required and whether or not the worker must be able to move about without encumbering hoses. Obviously, the determination of the need for respiratory protection is a technical decision and can best be made by an industrial hygienist. Selection of equipment. Much of the same infor- mation required in establishing the need for respi- ratory protection is required here also. In addi- tion, one must have a knowledge of the types of devices available for the particular circumstances encountered. Since it is impossible to expect each plant to have on hand every type of device manu- factured, equipment kept on hand must be pur- 526 chased in advance on a basis of surveys and studies of anticipated needs. Here, there is a re- quirement for close cooperation between the per- son in charge of the respirator program and the plant's purchasing and stores department. Pre- liminary education of appropriate persons in this department may be necessary since their tendency will be to stock items on a basis of price without regard to important distinctions between different pieces of equipment. Training. This is very important and requires con- tinuous study and updating of knowledge by the person giving the training. The latter should be the person responsible for selection of respirators to be carried in stores, or at least he should be in very close touch with this aspect, since his direct contact with workers using protective devices makes him aware of their needs. Supervision and enforcement. The support and en- couragement of supervisors, such as foremen, are essential to the program. The foremen, particu- larly, should be asked to participate in fitting and training even though they may have little occasion to use respiratory protective devices. This pro- vides an opportunity to demonstrate the impor- tance of the activity and gains their support for the program. Without this support many workers will not use the equipment correctly nor care for it adequately. Inspection. Industrial hygienists and safety engi- neers in the plant must include regular inspection of the condition of respirators as one of their rou- tine duties. It is particularly important that emer- gency devices such as those mounted on walls or in cabinets be checked regularly. The most im- portant inspections, particularly of smaller devices, are those given by the worker himself. His train- ing must include information on the importance of this and how to do it adequately. Maintenance. In most plants there should be a central cleaning station where respirators are brought in regularly for cleaning and replacement of worn or damaged parts. In very small plants this may be done by the worker himself with the aid of the safety engineer, industrial hygienist or plant nurse. Storage. New respirators should be stored in their original container in a clean, cool dry place be- fore being issued. Cleaned respirators if not im- mediately reissued should be placed in a dust-tight container, such as a plastic bag. The worker also should be instructed to store his respirator prop- erly after it is issued to him. A respirator crammed into a tool kit can be permanently distorted in shape so that it cannot fit. Dust accumulated on the interior of the mask is readily breathed in and wearing such a mask may be a cause of more exposure than failing to wear it. Management interest. Top management should give some evidence of support of the program. This may be done, in part, through the plant paper or magazine or through shop bulletins or other means of indicating interest or concern. It is the responsibility of the person in charge of the pro gram to keep management informed about the program if he is to obtain their interest and sup- port. PROTECTION AGAINST NOISE The previous section of this chapter has dealt at considerable length with the subject of respira- tory protection. Much of this is also applicable to devices used to protect against noise and other hazards. With hearing protective devices, both ear plugs and ear muffs, there is a need for ex- perimentation in trying different types of devices to meet specific needs. Since the noise hazard is not as acute as the respiratory hazard more experi- mentation is justified. Both plugs and muffs at- tempt to prevent the penetration of sound through the outer ear to the inner ear; however, some sound also reaches the inner ear by conduction through bone and tissue. Thus, any protective de- vice is limited in the degree of protection which can be achieved. In sound fields in excess of 120 decibels no protective device will give adequate protection for continuous exposure. When ear protectors are first used by a worker, he experiences a sensation that his own voice is very loud since outside noises are reduced. As a result, he tends to speak softer making it more difficult to communicate with others especially if they are wearing protectors also. Noises signaling dangers around the worker may be muffled and their warnings not heeded. Ear Plugs or Insert Devices Ear plugs are small conical or cylindrical de- vices made to fit into and seal the ear canal against the entrance of sound. The more closely the plug approximates the shape of the ear canal the more positively it will seal. Plugs are usually made of a soft pliable material like soft rubber or plastic so they can be inserted into the ear canal with positive force without being uncomfortable. Many models have soft flanges which can seal the canal even if contact with the body of the device is in- complete. Attempts have been made to improve the usefulness and acceptability of ear plugs by introducing models with “valves” or perforations which were to allow passage of sound of certain frequencies or to block loud but not soft sounds. None of these has been successful and the plain plug remains the best. Since fitting to the ear canal is important some manufacturers make plugs for individual ears by making casts or impressions of the ears and then moulding and curing a plastic material in the shape of the impression. While such devices would appear to have a great advan- tage in effectiveness and comfort, this is not al- ways the case. Malleable wax material is available which can be moulded into the ear and discarded after use. Wadded cotton has often been used, but actually is comparatively ineffective. Cotton impregnated with wax or vaseline is much more effective. A very fine glass wool material has been introduced in recent years, often called Swedish Wool after its country of origin. This material can be rolled into plugs and gives almost as good protection, if prop- erly used, as a good commercial plug. Dispensers for this material can be installed and the material is more acceptable to many workers than regular ear plugs. The degree of sound attenuation provided by 527 ear plugs varies in different frequency bands or octaves. For good, well-fitted plugs this varies from 25 decibels in the low frequency or low pitched sounds to 40 decibels at frequencies over 1000 Hertz. Fitting of the plugs is very important in achieving good results. Most plugs come in several sizes and the correct size must be chosen to fit the individual's ear canal. Frequently differ- ent sizes are needed for the two ears. Fitting by the Medical Department is a good way of achiev- ing this part of the program’s purpose. The physi- cian can examine the ear canal carefully for size and at the same time detect any ear infections or canal irregularities which may rule out the use of car plugs. Some persons simply cannot wear ear plugs. Ear Muffs Ear muffs are much like communications type earphones in appearance although the ear cup is usually deeper. They are equipped with a head- band which may go over the head or around the back of the neck. The latter type permits the wearing of a hat but usually offers slightly less hearing protection. They may also be mounted on a helmet or hard hat. The degree of attenuation obtained varies with the sound frequency and may range from 20 decibels at low frequency to 45 decibels at high frequency. There is a standard method of measuring attenuation by muffs, but it is complex and requires special equipment. Most users will have to rely on the attenuation data sup- plied by the manufacturer. To attain good protection the muff should seal over the ear and the seal may be made of foam rubber or liquid-filled or grease-filled cushions. The latter two are somewhat more effective and comfortable. Large cup volumes and small cup openings lead to greater attenuation. Proper fitting is important with muffs, but is not quite so individual a matter as with plugs. The worker should be offered a choice of several models to achieve the best fit and to gain his acceptance of the device. Where communication is necessary in a high noise level environment, ear muffs can be equipped with earphones and battery operated radios. The microphone can be muffled and mounted directly in front of the mouth. Plugs or Muffs? Good ear plugs may give slightly higher atten- uation in the very low frequency range while muffs give better attenuation in the middle ranges. Above 1000 Hertz there is little from which to choose on a basis of the degree of protection af- forded. Plugs are more acceptable to some work- ers while muffs are preferred by others. Where exposure to noise is intermittent, muffs are some- what more easily removed and replaced when needed. Plugs are easier to carry than muffs, but for the same reason are more easily lost. They are also less expensive. Muffs are more comfortable for use in cold weather. Both plugs and muffs deteriorate with time and should be inspected fre- quently. Evaluation If ear protection is required, there should also be a medical program which includes audiometric testing of exposed workers. Results of such test- ing will determine whether continued exposure is advisable even if protective devices are used. Ob- viously, every attempt should be made to control the noise by engineering methods and eliminate the need for personal protective devices. One author puts the case as follows — “When the only possible control method is ear protection, it is important — rather it is essential — that the ear protection program be continually monitored by knowledgeable and enthusiastic people who are dedicated to the task of protecting the hearing of noise-exposed employees.”*! PROTECTION OF SKIN AND BODY This section deals with the subject of what is usually called protective clothing and includes pro- tection of the various parts of the whole body either completely or partially as may be required. The term, protective clothing, is a correct one although much protective clothing offers no more direct bodily shielding than would be offered by ordinary street dress. Since street clothing might be ruined or rendered unsuitable for street use if worn in the shop, the shop clothing provided is ‘“‘protec- tive” of one’s ordinary clothing. Chemicals, dirt, heat and cold are the chief hazards against which protective clothing are used. Certain rather spe- cialized occupations require unusual types of pro- tection including firemen, aircraft crews, missile fuel handlers, astronauts and divers. In general, this section is not directed to these specialized vocations but much of what we have learned about protective clothing comes from experience in pro- viding protection for workers in such unusual en- vironments. There is a wide variety of materials available today to meet the requirements of many types of conditions. Fabrics such as cotton, glass fibers, Orlon, Nylon, Dynel and even Teflon are available for jackets and coveralls. These can be made im- pervious by coating with various plastics, rubber or Neoprene. Plastics are also available in sheet form and can be made into clothing with glued or heat-sealed seams. Respiratory protective devices often are worn with protective clothing and, in many cases, become an integral part of such clothing (see Figure 36-5). While some protective clothing is supplied and cleaned by the worker it is more commonly done by the employer, especially if the wearing of such clothing is a requirement of the job. In many cases, work clothing cannot and should not be taken home since such clothing could become a hazard to persons handling it there. This is par- ticularly true of workers handling radioactive materials, pesticides, beryllium and other highly toxic materials. If the employer is responsible for cleaning the clothing he, too, must decide whether to send it to a commercial laundry or to set up his own cleaning facility. For clothing contaminated with ordinary dirt, soil, grease and perspiration, a commercial laundry may be an acceptable method of handling the problem. In. many cases, one or more plant laundries will have to be provided depending on the variety of ex- posures encountered. 528 Supplied by and used with permission of Los Alamos Scientific Laboratory University of California Los Alamos, New Mexico An Air Ventilated Blouse with Integral Respirator. Figure 36-5. There is also the problem of maintenance and of replacement. Garments must be inspected be- fore or after cleaning and worn garments dis- carded. Those not meeting standards of cleanli- ness required may have to be recycled. For ra- dioactive materials, this may mean monitoring of each garment with a special instrument. Where the exposure is to certain chemicals, it may mean periodic tests on occasional selected garments after cleaning. Training in the use of protective clothing is important, especially with complex gear. Even with simple laboratory coats and coveralls, work- ers should be given some instructions in how to care for such garments and how and when to turn them in for cleaning and replacement. For complex garments, especially those including res- piratory protective equipment, regular training and refresher courses should be given. Here again, some one person should be in charge of selection, storage, maintenance and training in the use of such equipment. An important element in this training is that dealing with the methods of putting on and taking off this clothing. Special standard- ized techniques may be necessary where clothing has or could have become heavily contaminated. If care is not exercised, contaminating materials can be brought into contact with the worker’s skin or transferred to his street clothing. Separate lock- ers for work clothing and street clothing are neces- sary when hazardous materials are handled. These lockers may be on opposite sides of the shower room. Protection Against Contamination Situations included in this category are those where there is no immediate danger to the skin from contact with the contaminating material, but where it is undesirable to have the worker expose himself in his street clothing. This includes the mechanic or machinist exposed to dirt and grease, the operator handling toxic dusts, the laboratory employee handling various chemicals that could damage his clothing and the person working with radioactive materials or bacteriological agents. The emphasis in all of these cases is on limiting the spread of the contamination. When the worker leaves his job, he should not transfer the hazard- ous or undesirable material to clean parts of the plant or to places outside the plant. Clothing for these applications is often called anti-contamina- tion or anti-C clothing. It should be noted that also within this category of jobs are those where extreme cleanliness is required for the protection of the product being made. In that case, the aim is to prevent the spread of contamination from street clothing or the worker to the product. The same requirements and procedures also prevail here. Garments worn in these situations are princi- pally of cotton or synthetic fibers and usually are not impervious to liquids or dusts. The mechanic and the chemical plant operator usually wear cov- eralls. If the material is difficult to remove he may also wear gloves and some type of cap. Footwear may consist of a pair of shoes which are left in the plant. In working with more dangerous material like toxic dusts or radioactive materials more strict regulations are necessary. Here a complete change of clothing including socks and underwear is needed and showering is essential. For heavily contaminated work’special attention must be given to sealing all openings in the clothing. For dirty jobs which are not done routinely, openings may be sealed with masking tape and two suits of cov- eralls may be worn. If possible, the clothing should be designed to minimize the number of openings, decorative buttons and folds as these items col- lect contamination and make it difficult to re- move. Many workers wear full coverage clothing all day in doing their routine jobs. They may also wear surgeon's gloves or similar types to give the required sensitivity in handling objects, but these are not satisfactory if the work subjects the gloves to abrasion. Head covering in this case is usually a simple cloth cap although a hard hat may also be required on certain jobs. In addition to shoes worn only in the plant, special shoe covers may 529 also be required. These may be of heavy cloth, plastic coated cloth, plastic or rubber. These are particularly important to the worker who must move from one department or operation to an- other. By changing shoe covers he prevents the spread of the particular type of hazardous material in one department to another where a different material may be handled. Rooms where workers remove heavily con- taminated clothing must be well ventilated since removing contaminated clothing can cause sus- pension of the contaminant in the air where it be- comes hazardous to everyone in the room. For the same reason, chutes and bins where contami- nated clothing is deposited should have exhaust ventilation. For limiting contamination, consider- ation should be given to the possibility of using disposable clothing made of paper or plastic, par- ticularly on very dirty jobs. Cleaning costs should be balanced against the costs of replacement and disposal. In making this evaluation careful con- sideration should be given to the disposal cost as this is often neglected. Protection Against Corrosive Chemicals Included in this category are situations where the contaminant can have an immediately damag- ing effect on the skin. These include exposures to strong acids and acid gases, alkalis, some or- ganic chemicals and strong oxidizing agents. Also included are those requiring protection against very heavy contamination where ordinary anti-C clothing would permit skin contamination to levels where complete removal would be difficult. Clothing in this category is usually impervious to liquids, gases and vapors and may be made of fab- rics impregnated with rubber or plastic. Rubber “frog suits” have been used for work in heavy concentrations of dangerous radioactive materials. The worker may be required to shower with the suit on and then shower to clean himself after carefully removing the suit using standardized procedures. Respiratory protective equipment is almost always required in conjunction with this clothing. It may be worn under the clothing or it may be an integral part of the clothing. An air line may be attached directly to the clothing for ventilation or it may go directly to a respirator. The head cover is usually part of the clothing in the form of a hood. Gloves must be impervious and may also be an integral part of the clothing. Wearing impervious clothing imposes serious limitations on the amount of time the worker can wear the clothing and the strenuousness of his activity. Unless the clothing is ventilated with an air line, perspiration will rapidly accumulate in- side the clothing and the body temperature may increase except in cold environments. These con- ditions impose a serious stress on the worker. Air-ventilated clothing is much more comfortable and permits wearing the clothing a longer period of time although it may limit the movements of the worker. Air-ventilated clothing must be studied and evaluated carefully because improper de- sign can result in only parts of the clothing being ventilated. The air line must discharge through several openings to supply the various parts of the suit. Where workers must work in impervious clothing for long periods close medical surveillance is required. Protection Against Skin Penetration Certain materials will pass through the intact skin and produce systemic toxic effects without necessarily doing any damage to the skin or caus- ing pain. Situations involving these materials in- clude exposure to hydrogen cyanide, missile or rocket propellant and the radioactive form of hydrogen known as tritium, either in elemental form or as water vapor. The clothing requirements for these exposures are practically the same as those discussed in the previous category. They are grouped separately because the effects produced can be very serious and there is little or no warn- ing of failure of the protection. Thus, there is more need for frequent inspection and testing of the clothing worn in this type of exposure situa- tion. Respiratory protection is always required. Protection Against Heat and Cold For mild exposure to heat the clothing should be light and well ventilated. At higher tempera- tures most clothing restricts the body's ability to remove body heat by evaporation of perspiration and forced ventilation of the clothing is necessary for prolonged work at elevated temperatures. Obviously, the design of clothing for protection against heat and cold emphasizes thermal insula- tion and the principles on which such design is based are well known. If there is a great deal of radiant heat, as around a furnace or flames, alum- inized plastic, cloth or asbestos may be used to provide a reflective surface. Air supplied clothing is particularly useful since the supplied air may be heated or cooled to maintain thermal equilibrium. Air for breathing may also be heated or cooled and very cold air may be tempered if taken in through a hose wrapped around the worker’s body under the in- sulating clothing. For work at very low temper- atures, particular attention must be paid to pro- tection of the fingers, toes, ears and nose since they are the parts most difficult to keep at an ade- quate temperature and frostbite may result from exposure. Thick gloves which are necessary greatly limit manual dexterity and electrically heated gloves may be required under some condi- tions. There are special pieces of protective gear used to protect parts of the body against heat, flame and sparks. The welder’s leather apron and his face mask are examples. Foundry workers wear leather leggings to protect their legs against spilled molten metal. They also wear special foundrymen’s shoes called Congress shoes which can be pulled off quickly if hot metal is spilled into the shoes. There are many other devices used for the pro- tection of the individual worker against falls, fall- ing objects, flying particles, burns and injuries, such as safety hats, shoes, gloves, goggles, etc. They are not covered in this chapter since they are considered to be strictly “safety” items. See Chapter 47 for a general discussion of these items. 530 EMERGENCIES By its very nature, personal protective equip- ment is important in dealing with emergencies. Mine explosions and cave-ins, industrial fires, nat- ural disasters and gas leaks all present occasions when men must receive protection against severe and unusual conditions while saving life and prop- erty. Engineering controls such as ventilation are completely inadequate and usually inapplicable in such situations; therefore complete reliance must be placed on protective clothing and respiratory protective devices. Some of the same devices used in the daily plant activities may be applicable but in most cases it will be necessary to use more spe- cialized devices such as self-contained breathing apparatus or fire-resistant clothing. Equipment for dealing with emergency situa- tions must be stored where it is readily available and yet not be placed where it can be damaged by the accident causing the emergency. This re- quires careful analysis to anticipate the possible emergencies and accidents which can arise. An important characteristic of emergency protective devices is that they are stored which means that they are actually used very rarely. Since much equipment suffers deterioration even during stor- age, it is necessary to set a regular schedule of inspection and testing of each device. Most such devices are fairly complex and re- quire trained persons for their use. An untrained person attempting to rescue an injured man in a building filled with toxic vapors is very likely to become a casualty himself. Men must be trained in how to function in an emergency and in the use of all emergency equipment. Retraining exercises must be given at regular intervals since instruc- tions are easily forgotten, equipment is changed, and personnel may be transferred. The essential beginning of any emergency planning is a thor- ough analysis of the possibilities of accidents. This analysis, in itself, may lead to the correction of unsafe conditions. STANDARDS AND INFORMATION The approval schedules of the Bureau of Mines for respiratory protective equipment are stan- dards in a sense as has already been noted. The American National Standards Institute has pre- pared consensus standards on many items of pro- tective equipment and these are listed in the bibliography of the chapter. There are needs for additional standards for some equipment and for the revision and updating of many existing stan- dards. The process of producing standards is a lengthy one, and changes and improvements in the various devices are being introduced continuously. There must be a willingness to experiment and test new and nonstandard devices under non-haz- ardous conditions in order to secure improve- ments in protection and acceptability. In addition to the written standards there are various guidebooks to the selection, use and main- tenance of personal protective devices prepared by organizations concerned with health and safety. These are listed at the end of the chapter and the appropriate guide should be consulted by anyone ’ responsible for supervising the use of these de- vices. Such guides have been prepared by the National Safety Council, the American Confer- ence of Governmental Industrial Hygienists, the American Industrial Hygiene Association, the In- ternational Atomic Energy Agency and others. Most manufacturers of protective equipment fur- nish information on the degree of protection which can be achieved by their devices and on their proper use, care and maintenance. References 1. Occupational Safety and Health Administration Stan- dards, Personal Protective Equipment, Federal Reg- ister, 36:10590 (No. 106, May 29, 1971). 2. SCHUTZ, R. H. and E. J. KLOOS. Respiratory Protective Devices Approved by the Bureau of Mines as of Dec. 31, 1968, Information Circular #8436, Bureau of Mines, Pittsburgh, Pa. 3. Respiratory Protective Devices Manual, ACGIH, p. 91, 1963. 4. Ibid., pp. 56-58. 5. American Standard Safety Code for Identification of Gas Mask Canisters, K13.1-1961, American Na- tional Standards Institute, 1430 Broadway, New York, 10018. 6. VENABLE, F. S. and E. D. POLICK. “Your Compressed Air: Fit to Breathe?,” National Safety News, 89:28-32, 1964. 7. Respiratory Protective Devices Manual, AIHA- ACGIH, Chapter 13. } 8. SCHUTZ, R. H. Approved Dust Respirators for Coal Mines, Information Circular #8509, Bureau of Mines, Pittsburgh, Pa. 9. American National Standard Practices for Respira- tory Protection, 7.88.2-1968, American National Standards Institute, 1430 Broadway, New York, 10018. 10. “Series on Respiratory Protection,” National Safety News, April-December 1971. 11. BONNEY, T. B. Industrial Hygiene Highlights, p. ATHA- 531 208, Industrial Hygiene Foundation, Pittsburgh, Pa., 1968. Preferred Reading American Industrial Hygiene Association Journal Health Physics National Safety News Industrial Hygiene Highlights Annals of Occupational Hygiene (British) Staub (German) Additional Reading Additional Standards from the American National Standards Institute: American National Standard for Occupational and Educational Eye and Face Protection, 787.1-1968. American National Standard Safety Require- ment for Industrial Head Protection, Z89.1- 1969. American National Standard for Men's Safety- Toe Footwear, Z41.1-1967. Respirators and Protective Clothing, International Atomic Energy Agency, Safety Series #22, Vienna, 1967. HYATT, E. C. “Current Problems and New De- velopments in Respiratory Protection,” Am. Ind. Hyg. Assoc. J. 24:295-304, 1963. HYATT, E. C. Evaluation of Respirator Perform- ance by DOP Man Tests, Paper given at the Am. Ind. Hyg. Conf., Toronto, Ontario, May 1971 (To be published). Industrial Noise Manual, American Industrial Hy- giene Association, Chapter 10, 1966. PLUMB, E. E., E. L. MENDENHALL and M. C. ROBBINS. “Evaluation of Protective Clothing and Equipment for Operations in Oxygen-Rich or De- ficient Atmospheres Approaching — 100°F,” Am. Ind. Hyg. Assoc. J. 27:29, 1966. CROLEY, J. J. “Protective Clothing — Responsi- bilities of the Industrial Hygienist,” Am. Ind. Hyg. Assoc. J. 27:140, 1966. CHAPTER 37 CONTROL OF NOISE EXPOSURE Vaughn H. Hill DEFINITION OF PROBLEM Measure Noise Level From an engineering control standpoint, the first step in a hearing conservation program is to measure the noise levels in all working areas. Areas in which the noise level does not exceed 90 dBA* need not be considered further since noise reduction is not required. Determine Exposure Time In areas where the noise level does exceed 90 dBA, a study should be made to determine the actual worker exposure time. Then using this ex- posure time and the measured noise level, one can determine whether or not the government stan- dards are exceeded. Details regarding the use of government criteria are given in Chapter 25. It may be desirable to use a dosimeter to determine the actual daily noise exposure for comparison with government criteria. Dosimeters are discussed in Chapter 25. Evaluate Extent of Hazard If the combination of noise level and expos- ure time indicate that government criteria are ex- ceeded, an evaluation should be made to deter- mine the most economical solution to the problem. Considerations for making such an evaluation are: (1) reduction of noise level, (2) reduction of ex- posure time, (3) segregation of worker from noise, (4) substitution of more quiet machine or process or (5) provision of worker with personal protection such as ear muffs or plugs. Under the Occupational Safety and Health Act this latter op- tion is available only if others fail. Usually all of the following will be involved in making the best evaluation: (1) management, (2) medical, (3) personnel, (4) manufacturing, (5) engineering and (6) maintenance. This chapter will be lim- ited to the problem of reducing noise in working environments. CONSIDERATION OF ALL POSSIBLE MEANS OF NOISE CONTROL In a subject as broad as industrial noise con- trol, it is impractical to discuss all possible solu- tions to all problems. Therefore, typical problems of the type occurring most commonly in industry will be discussed with the hope that the reader will acquire an understanding of the principles of noise control that will guide him in solving a much wider variety of problems. The mode of attacking a noise problem is somewhat analogous to that of controlling any *Note: This figure may be changed by regulation or law. Check for the current standard requirement. 533 environmental hazard. Appropriate control mea- sures include such things as change in plant lay- out and design, substitution of less hazardous method, reduction of the hazard at its source, and reduction of the hazard after it has left its point of origin. In analyzing a noise problem one must con- sider that sound from a source can travel by more than one path to the point at which it becomes objectionable. Therefore, noise flow diagrams such as shown by Figure 37-1 are a definite aid to accurate analysis of a given problem. For instance, this shows that sound sources inside en- closures can have (a) direct radiation of sound through openings in the enclosure, (b) sound radiation from the enclosure due to solid borne vibration from the source and (c) indirect radi- ation from the enclosure, that is, airborne from the source to the inside of the enclosure and sub- sequent reradiation from the outside of the en- closure. The problem is to determine which paths carry the most sound energy and then select ap- propriate methods of obtaining the desired reduc- tions along those paths. It has proved helpful to follow a planned method of analysis so that no possible control measure is overlooked. The following outline can be used in making such an analysis: Noise Control Analysis Outline I. Plant Planning II. Substitution A. Use quieter equipment B. Use quieter process C. Use quieter material III. Modification of the Noise Source A. Reduce driving force on vibrating sur- face 1. Maintain dynamic balance 2. Minimize rotational speed 3. Increase duration of work cycle 4. Decouple the driving force B. Reduce response of vibrating surface 1. Add damping 2. Improve bracing 3. Increase stiffness 4. Increase mass 5. Shift resonant frequencies C. Reduce area of vibrating surface 1. Reduce overall dimensions 2. Perforate surface Use directionality of source Reduce velocity of fluid flow Reduce turbulence mmo SOLID-BORNE PATHS NOISE SOURCE AIRBORNE rn INSIDE_ENCLOSURE I GENERAL TO AIR 1H WORKL— = « DIRECTLY NOZZLE-\ [1 opeNINGS SAND BLASTING ENCLOSURE |..soLiD TO AIR AIR TO SOLID TO AIR “DIRECTLY TO AIR OPENINGS AIR TO SOLID TO AIR SOLID TO AIR INSIDE DUCT (FROM BEARING NOISE) AIR TO SOLID / ) TO AIR(DUCT) | * <1 _soLip To AIR L (DUCT) t=] ~ ~AIR-DIRECTLY DOWN AIR TO SOLID _|— bucT TO AIR =~ r~-9}-=SOLID TO AIR (BLOWER) = | ! BLOWER ST TEED voice FROM FAN 7 IU JI ~~17CuUT OFF CAN -= COMBINE WITH J BEARING NOISE DIRECTLY | HERE. TO AIR AIR INLET BLOWER DIRECTLY TO / AR AIR TO - =SO0LID TO AIR “soLID TO AIR TUMBLING SOLID TO AIR RADIATION FROM TOOL I DIRECTLY TO AIR I (NOISE FROM AIR | § EXHAUST) I | | } J——WORK 0 he Hr RIVET HAMMER i (CHIPPER) SOLID TO AIR (RADIATION FROM DIRECTLY TO AIR WORK) PNEUMATIC HAMMER Tyzzer, F. G.: Reducing industrial noise. Amer. Ind. Hyg. Assoc. J. 14:264-95, 1953. Figure 37-1. 534 Noise Flow Diagrams. “3 | ‘a =) g - ww > “ wi 0 [+4 =D wv wv wl x a 10 Qo z = oO wv 20 = < - wi ox x 130 o 8 S 4 GC 2 << uw 1 >= = 0.5 > 0.25 5 $0.25 x 0.1 0.2 0.5 1 2 o * DISTANCE r Figure 37-2. CURVES FOR DETERMINING THE SOUND PRESSURE LEVEL IN A ROOM RELATIVE TO THE SOUND POWER LEVEL wn [=] 100 200 500 1,000 2,000 5,000 10,000 20,000 "14°08 LNVLSNOD WOO 5 10 20 50 100 FROM ACOUSTIC SOURCE IN FT Curves for Determining the Sound Pressure Level in a Room Relative to the Sound Power Level. IV. Modification of the Sound Wave A. Confine the sound wave B. Absorb the sound wave 1. Absorb sound within the room 2. Absorb sound along its transmis- sion path. Examples of many of these possible control measures will be illustrated in this chapter. Plant Planning Noise specifications. An immediate step essential to those concerned with noise control is to stop buying new noise problems. Minimum essential designs for processes and equipment must involve light, high speed machines, high pressures, high flow velocities, light building structures and mini- mum floor space. All of these can lead to noise problems if limits are not specified. Noise specifi- cations are a must for new equipment. To prop- erly use noise specifications one must understand Figure 37-2. This graph shows the relationship between sound power level (L,) and sound pres- sure level (L,) and their relationship to distance 535 from the source (r), directivity factor (Q) and room constant (R). L, is total energy of the sound source and is independent of the distance or environment. It is calculated, not measured. See Chapter 23 (“Phys- ics of Sound”) for further discussion. L, is sound energy flow per unit area at some distance (r) from the source. It varies with dis- tance from the source, directivity and room con- stant. Therefore, these environmental conditions must be specified when expressing noise in terms of sound pressure level. Free field radiation. When a sound source is in a free field (where there are no reflections) it will diminish with the square of the distance from the source. The relation between L, and L, in this case is shown by Figure 37-3. L, can be measured with a sound level meter or analyzer. Room constant (R). R is a measure of the ability of a room to absorb sound. It can be calculated as follows: FREE FIELD NOISE RADIATION POINT SOURCE — NONDIRECTIONAL ; A 10 = om ©, m > 0 Lu - wi ox a wn -10 J oz oa. = NL 3 -20 NN wv NU LJ = S < 30 = - 1 RE 10 20 ¥ DISTANCE r FROM ACOUSTIC SOURCE IN FT. L, = L, + 20 Logigr +05 - T Figure 37-3. Free Field Noise Radiation Point Source — Nondirectional. R=_C Si . For hemispherical radiation, such as shown at 1=% ft the upper right, or in areas where the sound source where S; = total area of room bounding sur- faces in sq. ft. a= average sound absorption coefficient of room bounding surfaces _S al + S, a+... Sy an S,+S.=...... S. where S|, S,, etc. = area of each absorbing sur- face in sq. ft. a 2, a 2, etc. = corresponding of absorption R can be estimated from Figure 37-4 as an alternative to the calculation. Directivity factor (Q). Q is a measure of the de- gree to which sound is concentrated in a certain direction rather than radiated evenly in a full spherical pattern. Directivity factors for typical radiation patterns are shown in Figure 37-5. They are actually portions of spherical radiation pat- terns as related to the surface area of a sphere which is 4712. For spherical free field radiation, that is, where there are no reflections, the radiation pattern is illustrated at the upper left of Figure 37-5 and 0=1. coefficients 536 is near the center of the floor in a large room the same sound source would produce twice the con- centration of sound energy at a point on the sur- face of the hemisphere as it would on the surface of a sphere of the same radius. The surface area of the hemisphere is 4x1?/2 and Q=2. Similarly, if the sound source is near the in- tersection of the floor and a wall of a room such that 1/4 spherical radiation exists as shown at the lower left, the radiating area can be expressed by 4=r?/4 and Q=4. Similarly, if the sound source is near the intersection of the floor and two walls of a room such that 1/8 spherical radiation exists as shown at the lower right, the radiating area can be ex- pressed by 4xr?/8 and Q=8. The source might also have a directional noise radiation pattern indicated by the vendor. If so, this would have to be taken into account in addition to the environmental radiation pat- tern discussed above. This is a simplified presentation of directivity, but should be sufficient for most industrial situa- tions. Noise measurements made in the vendor’s test laboratory can be modified to estimate the 20,000 10,000 7,000 5,000 3,000 2,000 1,000 700 500 300 RR NEANRNIAN Room constant R in sq ft 200 100 70 50 10,000 3 5 7 2 3 S 7 100,000 1,000,000 Room volume V in cu ft ROOM CONSTANT FOR TYPICAL ROOMS Beranek, L. L. (ed): Noise and Vibration Control. New York, McGraw-Hill, p. 277. Figure 37-4. levels in the purchaser's intended environment by the use of Figure 37-2. The power level of the noise source will be the same in both locations. The sound pressure level in the purchaser’s environment will be the difference be- tween L, — L, in the vendor's shop as compared to L, — L, in the purchaser’s environment. L, is determined from previous calculations by working through Figure 37-2 and the measured L,,. Then L, for the purchaser’s environment can be determined by working through Figure 37-2 for the new conditions. Substitution. Sometimes it is possible to substitute a quieter machine, process or material. It is very 537 Room Constant for Typical Rooms. likely that noise was not considered at the design stage of existing projects (plants). For new proj- ects it will probably be less expensive to buy quiet equipment than noisy equipment that will require noise reduction treatment. Figures 37-6 through 10 illustrate some substitute possibilities. Quieter materials. The materials used in the con- struction of buildings, machines, pipes, chutes and containers have a vital relation to noise control. Some materials and structures have high internal damping; others have little and ring when struck. These latter are the potential trouble makers and should be avoided where the possibility of vibra- tional excitation is involved. Ringing can be re- DIRECTIVITY FACTOR (Q), SPHERICAL RADIATION Q-=1 1/4 SPHERICAL RADIATION Q-4 SIMPLIFIED RELATIONSHIPS 2 1/2 SPHERICAL RADIATION Q-=2 1/8 SPHERICAL RADIATION Q-=38 duPont de Nemours & Co., Wilmington, Delaware. Figure 37-5. duced by damping the material or reducing the exciting impact by means of resilient bumpers. Figures 37-11 and 12 illustrate the use of quieter materials. Damping will be discussed later in this chapter. Modification of the Noise Source There are two basic noise sources: (1) vibrat- ing surfaces and (2) fluid flow. In either case, usually, the nearer the source one can affect treat- ment, the less expensive will be that treatment because it will be minimum in size. Direct sound away from area of interest. Many industrial sound sources are directional, that is, they radiate more sound in one direction than in others. Common examples of directional sources are intake and exhaust (vent) openings, partially enclosed sources, and large sheet metal surfaces. It is sometimes possible to utilize directionality of the source to provide noise control in a particu- lar region of the sound field. This type of control is achieved by directing the source so that a mini- mum in the sound field occurs at the point or area of interest. A typical example is a vertical vent stack that directs the sound above the populated 538 Directivity Factor (Q), Simplified Relationships. area, or a vent stack cut off at an angle to direct the sound to one side. When the sound source is in a room it is not possible to achieve worthwhile noise reduction by source direction when the point of interest lies in the reverberant portion of the sound field. For enclosed areas containing little sound absorption the reverberant field may extend to within a few feet of the source, and direction of the source will have little effect on the sound levels throughout most of the area. Under these condi- tions there will be some advantage in directing the source to an area of highly absorbent material, for this effectively reduces the source strength as far as the remainder of the room is concerned. Figure 37-13 is an example where sound has been di- rected away from the point of interest. Reduce vibrating surface. This type of noise source will consist of a driving force, coupled to a sound radiating surface. Control at the source may then consist of reduction of the driving force, reduction of the radiating surface response to the driving force or reduction of the radiating efficiency of the vibrating surface. Reduce driving force. The driving (vibration ex- Ingersoll Rand, Allentown, Pennsylvania. Figure 37-6. QUIETER EQUIPMENT — CENTRIFUGAL COMPRESSOR: This high speed centrifugal multi stage compressor has a heavy cast case which encloses the impellers and interstage cooling system. It also encloses the noise so that operating areas around the com- pressor do not exceed 90 dbA provided motor and external piping noise is controlled. This compressor is a good example of a machine well designed for noise control. citing) force is often the result of unbalance or ec- centricity in a rotating piece of equipment. Such forces increase with increase in rotational speed, therefore the speed should be kept to a minimum. Figure 37-14 is an example of the effect of speed reduction. A large machine running at slower speed might be a better selection as far as noise is concerned. Certainly eccentricity and balance Figure 37-7. A rubber toothed type belt with flanged grooved pulleys was used to drive a pump. Noise levels were too high in the octave bands above 2400 Hz. The grooved pulleys and toothed belt were replaced with a V-belt drive. Reductions of more than 15 dB were obtained in the octave bands above 2400 Hz as shown below. The frequency distribution of noise created by should be checked to be sure they are within nor- mal tolerance. Good alignment, lubrication, and bearing maintenance are also important in mini- mizing noise. Figure 37-15 shows the noise re- duction achieved by improving maintenance on a blower system. Driving forces can also be caused by reciprocating members such as pistons or rams. Impact type driving forces are produced in QUIETER EQUIPMENT — V-BELT DRIVE. a toothed belt drive is dependent on the tooth passage rate — the higher the speed, the higher the frequency. If a toothed type belt must be used, the noise could have been reduced by enclosing the belt and pulleys. The enclosure should be lined with sound absorbing materials which is effective for the frequency range of interest. 600- 1200- Frequency — Hz 20- 75- 150- 300- 2400- 4800- 9600- — octave band 75 150 300 600 1200 2400 4800 9600 19,200 Noise Reduction 0 6 17 18 25 in dB 5 4 4 Vibra Screw Incorporated, Totowa, New Jersey. Figure 37-8. QUIETER EQUIPMENT — VI- BRATION ISOLATED HOPPER. An 8 ft. dia. hopper with electric solenoid type vibrator was creating excessive noise. A live bottom bin by Vibra Screw was installed as shown below and a noise reduction achieved as shown here. The noise reduction is due to the fact that the cone only is vibrated, there is much less vibratory power required and there is no metal to metal impacts. Frequency—Hz— octave band—center frequency of band 63 125 250 500 1000 2000 4000 8000 Noise Reduction—dB 7 6 20 22 16 12 12 9 most metal or plastic fabricating operations such as punching, forging, riveting and shearing. Be- cause of the short duration of most impact forces, considerable noise reduction can be achieved by modifying the system to provide a smaller force over a longer period of time. Figure 37-16 shows how this can be accomplished with a punch. Figure 37-17 illustrates this principle on a 48” shear. Here the cutting blades are segmented and skewed to give a shear type cut. Impact type forces can also be reduced by providing resilient bumpers at the point of impact. Examples of this method include lining tumbling barrels, chutes, hoppers, stock guides, etc. Figures 37-11 and 12 illustrate this method of control. It is a rare case where a machine causes 540 sufficient vibration of a building to cause the building to radiate noise in excess of 90 dBA. However, a common pitfall about equipment mounting should be pointed out here. It is becom- ing common practice to mount machines and their drives on a common base of steel weldments. This is fine for alignment and shipment, but for vibra- tion producing machines such as cutters, pulver- izers, grinders, blowers, compressors, the steel base can become a serious noise radiator. This prob- lem can easily be overcome by constructing the steel base so that after installation it can be filled with nonshrinking concrete or sand. If it is de- sired to vibration-isolate the equipment, the iso- lators should be between the concrete filled steel base and the building floor. The heavy base is also desirable in this case so that center of gravity of the equipment will be lower, that is, nearer the level of the vibration isolation mounts. For sta- bility’s sake the level of the isolators should be as close as practical to the vertical center of gravity of the vibrating machine. Since good vibration isolators are readily available and manufacturing instructions for selection and installation are ade- quate for most cases, further discussion will not be given here. Vibration isolation is usually not necessary except near offices or control rooms or where process equipment dictate the need. Vibra- tion isolation of equipment can cause the more serious problem of pipe line failure at the flexible joints in the lines required by the increased vi- bration of the isolated equipment. Reduce response of vibrating surface. The re- sponse of a vibrating member to a driving force can be reduced by damping the member, improv- ing its support, increasing its stiffness or increas- ing its mass. When the frequency of the driving force is equal to the natural frequency of the mem- ber being vibrated, large surface displacements arc usually developed. This condition is known as resonance. Most mechanical structures have a family or series of resonances which are rather widely spaced in the low frequency range but are more closely spaced at higher frequencies. Be- cause of the large surface displacements developed at resonance, there is usually increased noise radi- ation. Resonant vibration may be limited effec- tively by damping, decoupling or detuning by shift- ing the natural frequency. Optimizing a damping treatment is usually a complicated procedure best left to the experts if the cost can be justified. For many industrial problems it is satisfactory to use a simple rule of thumb approach. For the rough treatment typical of industrial environments, con- strained layer damping is usually preferred. This means covering the vibrating surface with a thin sheet of damping material plus an outer covering of sheet metal. The sandwich so formed is cemented (both surfaces) and bolted together on 6” to 8” centers. The rule of thumb is that for vi- brating panels having a thickness of up to 16 gauge, use an outer steel plate (restraining plate) of the same gauge as the vibrating plate. For vibrating plates of 16 gauge to 8” thick, use a restraining plate of 16 gauge steel. For vibrating plates of 18” to V4” thick, use a 8” thick re- FIGURE 37-9 An Elliott No. Elliott No. 115,000 was substituted. 1380 tube cleaner (2-7/8" dia ) created discharge of the turbine drive as shown by the drawing. achieved is shown in the table. DOWEL PIN - 2 RE MUFFLER UNIT THRUST BEARING 5088 FRONT BE AR'NG ASSEM o 203 Heo 37 1/2027 12009 THAUST WASHER MACHINE COURLING “AR PLATE REAP PEARING ASSEM, FAUDLE [FRONT CLATE foloya SHELL 2 5 RQTOR BODY ASSEMBLY PART * A ~|=|=|=-laj=|=|=|n~n]|=|n]—= aE PART No n5000-8.2%a excessive noise. A new design, The new design had a built in muffler for the air Noise reduction DISC PLUG: 1 REQ'D 'D BOOY DIAM Z 77 SHAFT THRD 37g", © HOSE CONN 3,4 'N.RAT. TYPE "DBT" -MUFFLED AIR DRIVEN MOTOR (EXTRA Lows Ko70R) FOR DATE - ke SE- //500¢ BY Cr ELLIOTT COMPA SPRINGFIELD OHIO NEWARK N J o 7 ENGR CHANGE wz Elliott Company, Springfield, Ohio. Figure 37-9. An Elliott No. 1380 tube cleaner (2-78” dia.) created excessive noise. A new design, Elliott No. 115,000 was substituted. The new design had a built-in muffler for the air discharge of the turbine drive as shown by the drawing. Noise reduction achieved is shown in the table. straining plate. For vibrating plates of 14” thick or heavier, use a ¥4” thick restraining plate. The common damping materials are damping felt, elas- tomeric damping sheeting and sheet lead. All ma- terial selected should be compatible with the tem- perature and environmental conditions involved such as exposure to chemicals and oils. It is to be noted that the flat unsupported surfaces are the ones radiating the most noise. Corners of box- like structures, reinforcing bosses, etc., are so rigid they probably do not require damping. This sim- plifies the damping treatment because it eliminates many double curved surfaces which would be difficult to laminate. Manufacturers of damping materials can advise regarding the most effective use of their materials. Do not hesitate to use the heavy restraining plates suggested above. They make the panel significantly stiffer and reduce not only resonance but the driven response as well. The extra weight and stiffness might be the most important factor in reducing the noise. Figure 37-18 illustrates constrained layer damping and 541 damping by means of filling structure with sand. Figure 37-19 illustrates noise control by increased mass and stiffness. Reduce efficiency of noise radiating surface. The sound energy generated by vibrating surfaces de- pends not only upon the velocity of surface motion but also upon the area of the radiating surface. Because the displacement of most surfaces is lim- ited by the constrained edges, the surface velocity will decrease with frequency, and the area must increase if constant sound output is to be main- tained. Therefore, the effective radiation of low frequency sound is usually limited to large sur- faces. Conversely, any surface of more than sev- eral square inches can effectively radiate sound at frequencies above 1000 Hz. In general, any regu- larly shaped area with one dimension greater than one-fourth wavelength can effectively radiate sound at the frequency corresponding to that wavelength in air. Surfaces radiating low frequency sounds can sometimes be made less efficient radiators by di- Ingersoll Rand, Allentown, Pennsylvania. Figure 37-10. QUIETER EQUIPMENT — PORTABLE AIR COMPRESSOR: The Ingersoll Rand portable air compressor shown above was designed with noise control as a specification. All functional components of this diesel — engine powered machine including engine, compres- sor, mufflers, fuel tanks, receiver separator tank and frame are completely enclosed in an alum- inum, glass fiber, sheet steel sandwich-panel material. Improved cooling by increased air flow through mufflers was required for this enclosed machine. The noise reduction achieved by this design is shown below. Frequency — Hz — octave band center frequency of band 63 125 250 500 1000 2000 4000 8000 Noise reduction in dB 8 13 24 17 10 10 10 14 viding them into smaller segments or otherwise re- create a serious noise problem. For example, ducing the total area. The use of perforated or ~~ where compressed air is used to clean or wipe a expanded metal can often result in less efficient product, such as blowing water from a freshly ex- sound radiation from sheet metal guards and truded plastic, the noise source is the sonic velocity cover pieces. of the gas passing through the pressure reducing Turbulent fluid flow. A very common industrial ~~ valve. The noise source is not the air velocity noise source is high velocity fluid flow. The strange ~~ which wipes the water from the plastic. This prob- thing about it is that usually the velocity required lem (and many more similar ones) can be solved by the industrial process is not high enough to by placing a muffler just downstream from the Figure 37-11. QUIETER EQUIPMENT — RESILIENT LINING FOR TUMBLING BARREL. The tumbling of steel balls against the steel ~~ will be reduced by a considerable amount. One shell of a ball mill can produce excessive noise. such mill lined with rubber produced the noise re- By lining the steel with resilient material this noise ~~ duction shown below. Frequency — Hz — octave band — center frequency of band 63 125 250 500 1000 2000 4000 8000 Noise reduction — in dB 3 4 6 7 11 12 15 19 542 RESILIENT HAMMER HEAD NM) STRIKING SURFACE NEOPRENE RUBBER CAP Figure 37-12. QUIETER MATERIAL — RESILIENT HAMMER HEADS: Rotary dryers com- monly use hammers (Knockers) on the outside of the dryer shell to prevent product buildup on the inside. The metal to metal impact noise produced is usually objectionable. This noise can be reduced by providing resilient heads for the hammers. By providing sufficient striking area between hammer and shell, the resilient facing material can usually be made to transmit the desired vibration to the dryer shell without causing the objectionable metal to metal im- pact noise. In one case, the overall noise level was reduced 28 dB. Common materials used for the face of hammers are Adiprene®, neoprene, nylon, Fabreeka and rawhide. NOTE: Lempco Automotive, Inc., supply nylon hammer heads and Garland Mfg. Co. supply rawhide hammer heads. valve as shown by Figure 37-20. The muffler is = accomplishes this achieves a gradual pressure drop to remove noise from the sonic velocity in the and expanding volume such that sonic velocities valve. Then with the nozzle downstream from the are not reached. The valve consists of a stack of muffler designed for minimum velocity to do the plates as shown by Figure 37-21 and each plate job, there should be no noise problem. Velocities has small gas passages as shown by Figure 37-22. as high as 10,000 ft. per minute can be used with- ~~ The high pressure gas enters from below as the out excessive noise, and even this velocity may not stem rises. When the stem passes by the ID of a be needed for many processes. The rule is, for plate, the gas flows through the tortuous path to low noise don’t use velocities higher than neces- the plate O.D. where it is at the low pressure level. sary. In particular, don’t use sonic velocities. Be- ~~ As the valve stem rises, more plates (and pas- ware of gas pressure reducing valves. sages) are exposed and more volume of gas passes. Where the ratio of upstream to downstream LMS is called the “Drag Valve.” It can be de- absolute pressures is 1.9 or greater, sonic velocity ~~ Signed for any desired noise level and gas flow. and excessive noise is produced — unless the re- For existing pressure reducing valves or for duction is controlled through the use of a special applications where quiet valves cannot be used valve which avoids sonic velocity. A valve which due to dirty gas or lack of economic justification, 543 +'x24"X 40" AUTO SAFETY GLASS —— J BEFORE W 100 a BEFORE— - Ww 90 [4 2 @ w 8o x AFTER a OVER-375 75 150 300 600 1200 2400 4800 2 ALL 75 1s0 300 600 1200 2400 4800 9600 2 Oo n OCTAVE BANDS—Hz AIHA Noise Committee: Industrial Noise Manual, 2nd Edition. Detroit, American Industrial Hygiene Associa- tion, 1966 Figure 37-13. NOISE SHIELD — DIRECT SOUND AWAY FROM POINT OF INTEREST. The use of shields between a noise source and an employee is usually quite effective when both the source and the employee are close to the shield and when the noise is pre- dominantly high frequency. An example is shown on the punch press which uses com- pressed air jets to blow foreign particles from the die. The installation of 4” thick safety glass shield gave the reduction shown in the graph. other means of noise control are available. If commercial mufflers can be used, the noise can be controlled as shown by Figure 37-23. If muf- flers cannot be used, external pipe covering can be applied as shown by Figure 37-24. This last treatment is not as economical as it might appear since sound can travel long distances down pipes with little attenuation and the pipe covering might be quite expensive. In addition, the sound might produce excessive vibration in downstream equip- ment and cause failure of such things as heat ex- changers and packed columns or cause excessive noise radiation from suction bottles, etc. To select mufflers for the usual type pressure reducing valves one must estimate the noise level just downstream from the valve. Unpublished work by K. U. Ingard provides a convenient method for doing this. Figure 37-25 shows that by relating the ab- solute pressure drop ratio and the gas flow in lbs. | — FILTER | — Blower > o z m | =] 20 db-re 0.0002 MICROBAR 0 375 75 150 300 600 75 150 300 600 1200 1200 2400 2400 4800 4800 9600 NOISE REDUCTION OCTAVE BANDS—Hz AIHA Noise Committee: Industrial Noise Manual, 2nd Edition. Detroit, American Industrial Hygiene Associa- tion, 1966. Figure 37-14. MINIMIZE ROTATIONAL SPEED. The blower for a vapor collection sys- tem produced excessive noise while moving 3600 cfm at 2.8” static pressure. It ran at 3450 rpm and had a 12.5” diameter material wheel. It discharged into a cylindrical filter consist- ing of 1.5” thick glass fiber compressed to 0.75”. A quieter fan was selected and the noise reduction achieved is shown on the graph. The new blower ran at 900 rpm and had a 32.265” diameter air wheel. A material wheel was not required since only air and oil vapor were being handled. per minute, the overall sound power can be de- termined. Then by means of Figure 37-26 the octave band power levels can be determined. In Figure 37-26 the zero line corresponds to the overall power level as determined from Figure 37-25. The frequency scale used in Figure 37-26 is normalized to the frequency f, =0.2 ¢/d where c is the speed of sound in the gas and d the equiva- lent valve diameter. The frequency f represents the center frequency of the corresponding octave band. To illustrate the use of Figure 37-25 and 26, consider the following example: Effective port area of valve =1 sq. in. Mass flowrate =50 Ib. per minute Gas = air at 190°F Upstream pressure =100 psig Downstream = 48 psig 544 L + LL CONCRETE cenmo) TN pon II MOTOR =i < o - on ® 3 o 10 w wo it wo 0 » 375 75 150 300 600 1200 2400 4800 a 75 150 300 600 1200 2400 4800 9600 pr 4 OCTAVE BANDS-Hz AIHA Noise Committee: Industrial Noise Manual, 2nd Edition. Detroit, American Industrial Hygiene Associa- tion, 1966. Figure 37-15. REDUCE DRIVING FORCE — IMPROVED MAINTENANCE (BLOWER). An exhauster running at 705 rpm, 6” static pres- sure, and 13,800 cfm was badly out of balance and the bearings needed replacing. As a re- sult the blower produced excessive noise. After balancing and installing new bearings the noise was reduced as shown by the graph. Determine the octave band power levels gen- erated at the valve discharge and the octave band sound pressure levels in the 3” line just down- stream from the valve. From Figure 37-25 at 50 Ib. per minute and a pressure ratio of 2.1 the overall power level (L,) would be 127 dB. The equivalent valve port diam- eter for an effective area of 1 sq. in. is — ~. [41 "12 a= =1.13" d= From Keenan & Kaye Gas Tables, C=1248 ft. per sec. for air at 190°F. Then: 1] when A=1 T _2C_2X1248_ 2X 1248X12 _ f= = ino nC 2650 Hz 12 Checking the frequency ranges of the octave bands, we find that 2650 falls in the 6th octave band which has a frequency range of 1400 to 2800 Hz and a center frequency of 2000 Hz. Now referring to Figure 37-26 for f/f =1 545 SINS vl A Vv | | ll Ll Oo O 14 ac Oo Oo TH le TIME —e= TIME —e= AIHA Noise Committee: Industrial Noise Manual, 2nd Edition. Detroit, American Industrial Hygiene Associa- tion, 1966. Figure 37-16. REDUCE DRIVING FORCE — SEGMENTED PUNCH AND SHEAR CUT. lllus- tration of Stepped Punches for Punching Sev- eral Holes at One Stroke of the Press. Schematic illustration of blanking operation, showing the effect of shear angle on the punch. The force-time diagram for each con- dition is shown. and a pressure ratio of 2.1, the octave band L. for the 6th octave band would be 127-7 or 120 dB. To obtain L, for the other octave bands, con- sider them relabeled as follows: For the 7th octave band f/f, =2 For the 8th octave band f/f, =4 For the 5th octave band f/f, = 12 For the 4th octave band f/f, = V4 etc. The next step is to determine from Figure 37- 26 the number of dB to be subtracted from the overall L, to obtain the octave band power levels. This would result in the values shown in column 5 of Table 37-1. Subtracting column § from col- umn 4 gives the octave band power levels shown duPont de Nemours & Co., Wilmington, Delaware. Reduce Driving Force — 48” Film Cutter with Skewed, Segmented Blades. Figure 37-17. Figure 37-18. REDUCE RESPONSE OF VIBRATING SURFACE BY DAMPING (EXTRUDER GEAR CASE). duPont de Nemours & Co., Wilmington, Delaware. The casing of a 2000 HP extruder gear was radiating excessive noise. The gear cover was 38" steel. The base was 1” steel with 1” thick 9” deep ribs. Measurements with an accelerometer showed that the 38” steel and the 1” steel were vibrating at approximately the same intensity. This indi- cated that all surfaces should be damped. The 38” steel was damped with 4” damping felt No. 11 N (by Anchor Packing Co.) plus an outer covering of %4” steel. The sandwich (38” steel + v4” felt+ 14” steel) was bolted together on 8” centers. The irregularity of the 1” steel of the base made constrained layer damping (as used on the cover) impractical. Instead, Y4” steel plate was welded to the 9” deep ribs and the voids filled with sand. The photographs below show the gear before and after treatment. The table below shows the noise reduction achieved after treatment of only one of three units in the room. Frequency — Hz — octave band — center frequency of band 63 1 25 250 500 1000 2000 4000 8000 Noise reduction — in dB X X X 4 17 26 24 18 546 LYS Figure 37-18. (BEFORE) ————— 5 i | #1 amt] a — 0 (AFTER) Figure 37-18. Studebaker — Worthington Inc., New York, New York. Figure 37-19. REDUCE RESPONSE OF VIBRATING SURFACE BY INCREASED STIFFNESS AND MASS (CENTRIFUGAL COMPRESSOR). These two photographs show a Worthington multi stage high speed centrifugal compressor which had noise control in mind during the design stage. Note the heavy cast construction of this machine. To meet the environmental criteria of 90 dBA, the only parts that require acoustical covering are the gear case cover and the steel interstage piping couplings. Here is another case where extra weight in the machine indicates economical noise control without the inconvenience of enclosure. 549 24 COMPRESSED TEXTILE FIBERS AIR SUPPLY LINE AIHA Noise Committee: Industrial Noise Manual, 2nd Edition. Detroit, American Industrial Hygiene Associ- ation, 1966. Figure 37-20. ABSORB THE SOUND WAVE — ALONG ITS TRANSMISSION PATH. An air ejector is used to strip waste textile fibers from perns. The curve shows the noise re- duction achieved 3 feet from the ejector by means of the dissipative muffler. The air sup- ply line is ¥2”, the pressure 100 psi, and a 1” dissipative muffler was used. Notice that the noise levels in the 75 to 150 and 150 to 300 cps octave bands were increased slightly, which is characteristic of this type of muffler. The noise of this problem is due to the pres- sure reduction at the valve and not the vel- ocity of air exhausting from the pipe. This is z oS apparent since the pipe size is the same at 5 he the inlet and discharge of the muffler. 3 in column 6. The next step is to determine the yo 0 sound pressure level (L;) in the 3” pipe just down- 2 stream from the valve. This can be determined by wo the following formula. nw 375 7% 150 300 600 1200 2400 4800 o ks 150 300 600 1200 2400 4800 9600 L,=Ly - 10 log,, D = where D = area of the pipe in sq. ft. OCTAVE BANDS-Hz For 3.37 pipe L,=L;— 10 log 0.0491 =L.,+ 13 dB This means that the octave band levels of Column AL 4 QUILET NL N | NL ns AS / 77 7995 q 2 SO FR — JA LIT RN 77 " S \ NL 0oom i —,e—_ NN KT Figure 37-21. 2 Ll o LLL TOSS @ Control Components, Los Alamitos, California. Reduce Velocity of Fluid Flow and Use Quieter Equipment — Quiet Pressure Reducing Valve. 550 6 would have to be increased by 13 dB to obtain the octave band sound pressure levels that would have to be contained by the pipe walls or pipe walls plus covering, or would be the basis for se- lecting a muffler to reduce noise transmission down the pipe. Streamline the flow. Once the velocity of a gas stream has been reduced to a minimum, additional reduction might be achieved by streamlining any obstructions in its path. The higher the velocity the more important it is to streamline the flow path. PRESSURE REDUCING VALVE Figure 37-22. REDUCE VELOCITY OF FLUID FLOW AND USE QUIETER EQUIP- MENT — QUIET PRESSURE REDUCING VALVE. The “Drag Valve’ shown in the draw- ing at left and described on page 14 is a pressure reducing valve which can provide the desired pressure drop but at the same time limit the maximum velocity thru the value to minimize the vibration and erosion and limit the noise reduction to most any desired level. The photograph at left shows a typical plate which illustrates the tortuous path the gas must take in passing from the inside (high pressure) to the outside (low pressure). For one design where 300 PSIG air was being vented to atmosphere, the noise reduction shown below was achieved as compared to venting through the more common orifice type valve. Frequency— Hz—octave band— center fre- quency of band 63 125 250 500 1000 2000 4000 8000 16000 31500 Noise reduc- tion—in dB 24 19 28 17 18 25 34 34 29 25 ii DIRECTION OF GAS FLOW Modification of Sound Wave Enclosures or partial enclosures. When enclosing a sound source with an unlined enclosure, the noise level inside the enclosure will build up to a con- siderably higher level than that measured without the enclosure. To avoid a lengthy calculation of this reverberant buildup, one can line the enclo- sure. If this is done so that the average sound absorption coefficient inside the enclosure is at least 0.70, the reverberant buildup will be insignif- icant. This allows one to select materials for the en- closure which have a transmission loss (TL) equal MUFFLER -— 4 | 6 duPont de Nemours & Co., Wilmington, Delaware. Figure 37-23. CONFINE THE SOUND WAVE — MUFFLE AND ACCOUSTICAL LAGGING: Cover valve and piping between valve and muffler with 2” fiberglas (3 to 4 Ib/cu ft plus an outer covering of Coustifab 488C). For unusually high pressure drops and flows, 16-gage steel weather covering might be required. 551 PRESSURE REDUCING VALVE | Vo ANNAN NNN; - b - NNNNNNAN vA DIRECTION OF GAS FLOW duPont de Nemours & Co., Wilmington, Delaware. Figure 37-24. CONFINE THE SOUND WAVE — ACOUSTICAL LAGGING ONLY: Cover valve and downstream piping as described on Figure 23. This method might require the cov- ering of a considerable amount of piping (100 ft or more). In this case, one must be careful not to excite equipment located downstream from the valve. Exceptions of such equipment would be thin-welled heat exchangers, separators, and spray towers. to the difference between the noise level without the enclosure and the desired noise level with the enclosure. It is good practice to add 5 dB to this difference as a factor of safety. Table 37-2 lists the TL of the more common building mate- rials. This method assumes that the enclosure of the noise source is complete and well sealed. If the enclosure is not complete and well sealed refer to Figure 37-27 for estimating the effect on TL of the leaks or openings. Figure 37-28 shows some common seals and fasteners used for acous- tical enclosures. If openings are needed for ven- tilation or feeding materials into or out from the enclosure, mufflers should be installed at these openings to maintain the desired TL of the rest of the enclosure. If the desired TL is not very great, partial enclosures, that is, enclosures with fairly large openings might be sufficient. The ef- fectiveness of a partial enclosure can be deter- mined by calculating the percent open area as compared to a complete enclosure, and then re- ferring to Figure 37-27. Absorb sound wave. In general, sound absorbing materials are soft and porous. They are porous so that the sound wave can enter the material but the material must have a high enough flow resis- tance to reduce the amplitude of the sound wave. If the material is too dense (has too high a flow resistance) the sound will be reflected. If the material is not dense enough (flow resistance too low) the sound wave will pass through unchanged. Materials are rated in their ability to absorb sound by their sound absorption coefficient («). This is the percent of incident sound which is absorbed in striking it. Table 37-3 lists the sound absorbing coefficients of various materials. The Acoustical Materials Association periodically pub- lishes such data for materials manufactured by their members. 552 It is important to note that « varies with fre- quency. Figure 37-29 illustrated this for 6 1b/ft.? Fiber glass. Notice that below 1000 Hz, a drops off markedly for ¥2” thick material. At 1” thick- ness this drop in « occurs below 500 Hz. For 3” material the drop in « occurs when the frequency is less than 250 Hz. The point is, when using « in a noise control problem it is important to use a at the frequency of interest. Room Absorption Noise control by absorption in room bounding surfaces is very limited in effectiveness and rela- tively expensive due to the large surface areas which must be treated. Seven to 10 dB is prob- ably the maximum reduction that can be expected, and in most cases 5 dB would be the best one could accomplish. Room absorption can only re- duce the reverberant buildup in a room and there- fore is not very effective for the worker if he must be close to the noise source. Room absorption is most effective where (a) the room has little or no sound absorbing material in it before treatment, (b) the room has multiple noise sources (4 or more), each producing about an equal amount of noise, and (c) the noise of any one machine alone does not exceed the criteria. If these con- ditions exist and room absorption appears to be the most attractive means of noise control, the reduction can be estimated as follows: Noise Reduction in dB=10 log,, oe 1 where A, =total number of absorption units (sabins) in the room before treat- ment A,=total number of absorption units (sabins) in the room after treat- ment. £SS TOTAL POWER LEVEL (Lw)IN dB re |I0~2 WATTS 160 150 140 130 120 10 3 4 5 6789I0 VALVE NOISE ( CHOKED VALVES) 20 40 60 80 100 MASS FLOW=- LBS / MIN. Ingersoll Rand, Allentown, Pennsylvania. Figure 37-25. Valve Noise (Choked Values). 200 300 500 700 1000 VALVE NOISE OCTAVE BAND POWER LEVEL ZERO dB CORRESPONDS TO THE TOTAL Lw OF FIGURE NO.l| J 0 w p= o 2 PRESSURE 42-0 E RATIO 25 20 E a’ = [2.5 ak -30 EB oe El 4 42 WE az -40 E Qed Ee f =frequency oc = f,=0.2 Cg © i LL LLL | 1 | | e ‘a ‘a 2 | 2 4 8 16 /, fy Ingersoll Rand, Allentown, Pennsylvania. Figure 37-26. Valve Noise (Octave Band Power Level). A sabin is a measure of the sound absorption of a surface and is the equivalent of one sq. ft. of a perfect absorptive surface. This formula is presented in monograph form in Figure 37-30. The total number of absorption units mentioned above is the sum of all the room surface areas multiplied by their respective ab- sorption coefficients. Absorption due to other materials and people should also be included in the calculation. Absorption along Transmission Path The most common example of noise absorp- tion along the transmission path is the commercial muffler. Figure 37-31 illustrates the three most common types. The most common one shown by the upper sketch is the straight through lined duct type. It is very effective provided the lining is effective for the frequency of the sound involved, the length is adequate and the ID does not exceed 6”. Th performance of such a muffler can be estimated as follows: Noise Reduction in dB per foot of length= P+ 12.6 5 where « = absorption coefficient of the lining material at the frequency of interest P = perimeter of the duct in inches A =cross sectional area of the duct in sq. inches To simplify the use of this formula, Table 37-4 shows the value of 12.6a'* for various absorp- tion coefficients. If the ID must be greater than 6” or if the noise reduction required makes it necessary to use a longer muffler than desirable, then the configuration shown by the center sketch of Figure 37-31 can be used. Here the absorptive center portion makes it possible to have relatively narrow flow passages through the mufflers. This provides good performance even where muffler length must be minimized. Where mufflers having absorption linings can- not be used, the combination resonant, reactive, and dispersive type mufflers shown by the bottom sketch of Figure 37-31 can sometimes be used. The performance of these mufflers is strongly de- pendent on gas flow through them, and prediction of performance in a given application is very diffi- cult. It is recommended that this type mufflers be bought on a performance guarantee. 554 30db REALIZED NOISE ATTENUATION -db 90 80 70 60 50 [44 Oo nN Oo Oo NN Oo wo PERCENTAGE OF BARRIER AREA 1 REPRESENTED BY CRACKS OR — OTHER OPENINGS 0 0.1% | % 2% — | 5% _— pe 10% / IN Vy 20% 7 30% | / | 40% I / 50% 10 20 30 40 50 60 BARRIER TRANSMISSION LOSS-db 42 db POTENTIAL Figure 37-27. Effect of Leaks. 555 STEEL HOUSING ANGLE FRAME HEAVY SPONGE NEOPRENE, JARROW PRODUCTS NO. Cslo-424 OBSERVATION WINDOW 4 FLOOR -- 2"t0 4" hp BASE SEAL SECTION A-—A TYPICAL ENCLOSURE METAL BENT BACK AT ENDS TO FORM DOUBLE THICKENED EDGE EPOXY CEMENT— METAL PANEL NEOPRENE SEAL, PAWLING PRODUCTS CORP. NO. 1-02-00334 ANGLE FRAME OR ATLANTIC INDIA RUBBER CO. X212 METAL PANEL FACE OF MASONRY WALL PAWLING RUBBER CORP. TYPE NO. 1-10-01392 EPOXY CEMENT—{ 2 CLEAR POLISHED WIRE GLASS, SPEC SBIG, TYPE D WINDOW SEAL SECTION C-C ATLANTIC INDIA RUBBER CO. TYPE NO. X-1156 MOUNTING SEALS SECTION B-B 5 i6 T i6 16 T 6 Nl A SASH LOCK te am TYPE NO. 1487 DRAW ACTION TYPE = “F HAGER HINGE CO. SESSIONS NO. 491110 NO. X-287 NO. X-288 ATLANTIC INDIA RUBBER CO. SB NO.1-10-01453 NO.I-10-02687 PAWLING RUBBER CORP. on | 2 RE 25" HOOK LOCK TYPE LINK LOCK TYPE 32 . SIMMONS FASTENER CORP. NO. 10246 JARROW PRODUCTS, INC duPont de Nemours & Co., Wilmington, Delaware. Figure 37-28. TYPICAL ACCESS DOOR SEALS AND FASTENERS. Note: An enclosure built to house a noise source must have all cracks and openings tightly sealed in order to reduce leakage of noise. The enclosure below illustrates applicable principles of sealing and fasten- ing base, wall, door, and observation window. It should not be considered a complete enclosure design because of possible need for ventilation, accoustical lining, etc. 556 Sound absorption material ~~ Perforated tube DISSIPATIVE MUFFLER - STRAIGHT-THROUGH TYPE | | Perforated surface o VS. £ AND THICKNESS (6 LB. FIBERGLAS) Acoustical packing Center body 0 125 250 500 1000 2000 4000 Inlet end of center body not perforated Owens-Corning Fiberglas, Toledo, Ohio. Figure 37-29. Effect of Material Thickness and Frequency on Absorption. DISSIPATIVE MUFFLER - CENTERED-BODY TYPE >. == Baffle and tubes »> duPont de Nemours & Co., Wilmington, Delaware. Figure 37-31. Mufflers. NONDISSIPATIVE MUFFLER MONOGRAPH FOR DETERMINING EFFECT OF ROOM ABSORPTION DECIBEL REDUCTION 0 | 2 3 4 5 6 7 9 10 1] 12 13 Lo i | 1 | 1 | 1 | 1 | 1 J: [ T [ TT rrr rrr | 2 3 4 5 6 7 8910 15 20 ABSORPTION RATIO a, /a, AIHA Noise Committee: Industrial Noise Manual, 2nd Edition. Detroit, American Industrial Hygiene Association, 1966. Figure 37-30. Monograph for Determining Effect of Room Absorption. 557 TABLE 37-1 OCTAVE BAND SOUND PRESSURE LEVEL DETERMINATION Relation of Octave Band Overall Overall to Octave Band L,in Number f/f, P,/P, Octave Band L,, L. 3” pipe 8 4 2.1 127 dB —-6 121 134 7 2 " " -5 122 135 6 1 " " -7 120 113 5 1% " " —11 116 129 4 Va " " -19 108 121 3 8 " " —-27 100 113 2 Us " ! —-37 90 103 TABLE 37-2 Sound Transmission Loss of General Building Materials and Structures Thick- ness Wt. Ib/ Item Material or Structure Inches sq ft 125 175 250 350 500 700 1000 2000 4000 A Doors 1 Heavy wooden door—special 212 12.5 30 30 30 29 24 25 26 37 36 hardware — rubber gasket at top, sides and bottom 2 Steel clad door — well sealed 42 47 51 48 48 45 46 48 45 at door casing and threshold 3 Flush — hollow core — well 14 21 27 24 25 25 26 29 31 sealed at door casing and threshold 4 Solid oak — with cracks as 1% 12 15 20 22 16 ordinarily hung 5 Wood door (307 X84”) spe- 3 7 31 27 32 30 33 31 29 37 41 cial soundproof constr. — well sealed at door casing and threshold. B Glass 1 1 1%2 27 29 30 31 33 34 34 34 42 2 Va 3 27 29 31 32 33 34 34 34 42 3 15 6 17 20 22 23 24 27 29 34 24 4 1 12 27 31 32 33 35 36 32 37 44 C Walls — Homogeneous 1 Steel sheet — fluted — 18 4.4 30 20 20 21 22 17 30 29 31 gage stiffened at edges by 2X4 wood strips — joints sealed 2 Asbestos board — corrugated 7.0 33 29 31 34 33 33 33 42 39 stiffened horizontally by 2 X 8 in. wood beam — joints sealed 3 Sheet steel — 30 ga .012 Va 3 6 11 16 21 26 Sheet steel — 16 ga .0598 25 13 18 23 28 33 38 558 TABLE 37-2 (Cont’d.) Sound Transmission Loss of General Building Materials and Structures Thick- ness Wt. Ib/ Item Material or Structure Inches sqft 125 175 250 350 500 700 1000 2000 4000 5 Sheet steel — 10 ga .1345 5.625 18 23 28 33 38 43 6 Sheet steel Va 10 23 28 38 33 41 38 46 43 48 7 Sheet steel 8 15 26 31 39 36 42 41 47 41 S51 8 Sheet steel a 20 28 33 38 43 48 53 9 Sheet Aluminum — 16 ga .051 734 5 8 13 18 23 28 10 Sheet Aluminum — 10 ga .102 1.47 8 14 19 24 29 34 11 Plywood Va 73 20 19 24 27 22 12 Plywood 5 1.5 8 14 19 24 29 34 13 Plywood Ya 225 12 17 22 27 32 37 14 Sheet Lead Xs 3.9 32 33 32 32 32 15 Sheet Lead 8 8.2 31 27 37 44 33 16 Glass fiber board — 1 Va 5 5 5 5 5 4 4 4 3 6 Ib/cu ft 17 Laminated Glass Fiber (FRP) IB 26 31 38 37 38 D Walls — Nonhomogeneous 1 Gypsum wallboard —two 12” 1 4.5 24 25 29 32 31 33 32 30 34 sheets cemented together — joints wood battened 2 Gypsum wallboard—four 2” 2 8.9 28 35 32 37 34 36 40 38 49 sheets cemented together — fastened together with sheet metal screws — dovetail-type joints paper taped 3 Ya” plywood glued to both 3 2.5 16 16 18 20 26 27 28 37 33 sides of 1 X 3 studs 16 in. O.C. 4 Same as 3 above but 12” gyp- 4 6.6 26 34 33 40 39 44 46 50 SO sum wallboard nailed to each face 5 Va” Dense fiberboard on both 412 3.8 16 19 22 32 28 33 38 50 52 sides of 2X4 wood studs 16 in. O.C. — Fiberboard joints at studs 6 Soft type fiberboard (3%) on both sides of 2 X 4 wood studs 16 in. O.C. — Fiberboard joints at studs nn 4.3 21 18 21 27 31 32 38 49 53 7 ¥2” gypsum wallboard on both ~~ 4% 5.9 20 22 27 35 37 39 43 48 43 sides of 2X4 wood studs 16 in O.C. 8 Two 38” gypsum wallboard § 8.2 27 24 31 35 40 42 46 53 48 sheets glued together and ap- plied to each side of 2X4 wood studs 16 in. O.C. 9 2” glass fiber (3 Ib/cu ft) + 4 4 13 26 31 lead — vinyl composite (0.87 1b/sq ft) 559 TABLE 37-2 (Cont'd.) Sound Transmission Loss of General Building Materials and Structures Thick- ness Wt. Ib/ Item Material or Structure Inches sqft 125 175 250 350 500 700 1000 2000 4000 10 38” steel +2.375 in. polyure- 38 52 55 64 77 thane foam (2 Ib/cu ft) +X; steel 11 Same as 10 above but 212” 37 51 56 65 76 glass fiber (3 1b/cu ft) instead of foam 12 14" steel+1” polyurethane 38 45 57 56 67 foam (2 Ib/cu ft) +0.055 in. lead vinyl composite (1.0 Ib Ib/sq ft) E Masonry 1 Reinforced concrete 4 53 37 33 36 44 45 50 52 60 67 2 Brick — common 12 121 45 49 44 52 53 54 59 60 61 3 Glass Brick—33% X 478 X 8 3% 30 36 35 39 40 45 49 49 43 TABLE 37-2 Sound Transmission Loss of General Building Materials and Structures Weight Loss in Decibels at Indicated Frequencies, H, Item Material or Structure Lbs/Ft> 128 192 256 384 512 768 1024 2048 4096 E Masonry 4 Concrete block — 4” hollow, no surface treatment 27 29 32 35 37 42 45 46 48 5 Concrete block — 4” hollow, one coat resin-emulsion paint 30 33 34 36 41 45 S50 55 53 6 Concrete block — 4” hollow, io one coat cement base paint Ed 37 40 43 45 46 49 54 56 55 [=] 7 Concrete block — 6” hollow, rd no surface treatment < 28 34 36 41 45 48 51 52 47 8 Concrete block — 8” hollow, < no surface treatment 8 18 24 28 34 37 39 40 42 40 9 Concrete block — 8” hollow, one coat cement base paint 30 36 40 44 46 48 S51 50 41 10 Concrete block — 8” hollow, filled with vermiculite insulators 20 29 33 36 38 38 40 45 47 11 Concrete block — 4” hollow, 21 26 28 31 35 38 41 44 43 no surface treatment 12 Concrete block — 4” hollow, one coat resin-emulsion paint 13 Concrete block — 4” hollow, two coats resin-emulsion paint 14 Concrete block — 4’ hollow, one coat cement base paint 15 Concrete block — 4” hollow, two coats cement-base paint 16 Concrete block — 6” hollow, 22 27 32 36 40 43 46 45 43 no surface treatment 26 30 32 34 37 42 43 46 44 24 31 33 35 38 42 44 47 44 23 30 35 38 42 43 44 48 43 34 38 40 42 45 47 49 S51 46 Expanded Shale Aggregate 560 TABLE 37-2 (Continued) Sound Transmission Loss of General Building Materials and Structures Loss in Decibels at Indicated Frequencies, H, Weight Item Material or Structure Lbs/Ftz 128 192 256 284 512 768 1024 2048 4096 17 Concrete block — 4” hollow, 30 36 39 41 43 44 47 54 50 no surface treatment 18 Concrete block — 4” hollow, 30 36 39 41 43 44 47 54 49 one coat cement base paint on face o 19 Concrete block — 6” hollow, g 37 46 50 S50 50 53 56 56 46 no surface treatment & 20 Concrete block — 6” hollow, <« 37 50 54 52 53 55 57 56 46 one coat resin-emulsion paint each face g 21 Concrete block — 8” hollow, A 40 47 53 54 54 56 58 58 50 no surface treatment 22 Concrete block — 8” hollow, two coats resin-emulsion paint each TABLE 37-3 Sound Absorption Coefficients of Materials The absorption coefficient («) of a surface which is exposed to a sound field is the ratio of the sound energy absorbed by the surface to the sound energy incident upon the surface. For instance, if 55% of the incident sound energy is absorbed when it strikes the surface of a material, the a of that material would be 0.55. Since the « of a ma- terial varies according to many factors, such as frequency of the noise, density, type of mounting, surface condition, etc., be sure to use the « for the exact conditions to be used and from per- formance data listings such as shown below. For a more comprehensive list of the absorption co- efficients of acoustical materials, refer to the bulle- tin published yearly by the Acoustical Materials Association, 335 East 45th St., New York, N. Y. 10017. Coefficients Materials Frequency 125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz Brick — glazed Sand — dry — 4” thick Sand — dry — 12” thick Sand — wet — 14 1b water per cu ft 4” thick Water Glass Fiber — mounted with impervious backing — 3 lb/cu ft, 1” thick Glass Fiber — mounted with impervious backing — 3 1b/cu ft, 2” thick Glass Fiber — mounted with impervious backing — 3 lIb/cu ft, 3” thick Steel (Estimated) Brick, unglazed Brick, unglazed, painted Carpet, heavy, on concrete Same, on 40 oz hairfelt or foam rubber (carpet has porous backing) Same, with impermeable latex backing on 10 oz hairfelt or foam rubber Concrete Block, coarse Concrete Block, painted Concrete, poured 0.01 0.01 0.01 0.01 0.02 0.02 15 35 .40 .50 .55 .80 .20 .30 .40 .50 .60 75 .05 .05 .05 .05 .05 15 .01 .01 .01 .01 .02 .02 14 55 .67 97 .90 85 .39 78 94 .96 85 -.84 43 91 99 98 95 93 .02 .02 .02 .02 .02 .02 .03 .03 .03 .01 .05 .07 .01 01 .02 .02 .02 .03 .02 .06 14 37 .60 .65 .08 24 57 .69 71 73 .08 27 .39 34 48 .63 36 44 31 29 39 25 10 .05 .06 .07 .09 .08 .01 .01 .02 .02 .02 .03 561 TABLE 37-3 (Continued) Sound Absorption Coefficients of Materials Coefficients Materials Frequency 125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz Fabrics Light velour, 10 oz per sq yd, hung straight, in contact with wall .03 .04 11 17 24 35 Medium velour, 14 oz per sq yd, draped to half area .07 31 .49 75 .70 .60 Heavy velour, 18 oz per sq yd, draped to half area 14 35 55 72 .70 .65 Floors Concrete or terrazzo .01 .01 .015 .02 .02 .02 Linoleum, asphalt, rubber or cork tile on concrete .02 .03 .03 .03 .03 .02 Wood 15 11 .10 .07 .06 .07 Wood parquet in asphalt on concrete .04 .04 .07 .06 .06 .07 Glass Large panes of heavy plate glass 18 .06 .04 .03 .02 .02 Ordinary window glass 35 25 18 12 .07 .04 Gypsum Board, ¥2” nailed to 2 X4’s 16” o.c. 29 .10 .05 .04 .07 .09 Marble .01 .01 .01 .01 .02 .02 Openings Stage, depending on furnishings 25— 75 Deep balcony, upholstered seats .50 — 1.00 Grills, ventilating 15 — 50 To outside 1.00 Plaster, gypsum or lime, smooth finish on tile or brick .013 .015 .02 .03 .04 .05 Plaster, gypsum or lime, rough finish on lath .14 .10 .06 .05 .04 .03 Same, with smooth finish .14 .10 .06 .04 .04 .03 Plywood Paneling, 38” thick 28 22 17 .09 .10 11 Water Surface, as in a swimming pool .008 .008 .013 .015 .020 .025 ABSORPTION OF SEATS AND AUDIENCE Values given are in Sabins per square foot of seating area or per unit Materials Frequency Audience, seated in upholstered seats, per sq ft of floor area Unoccupied cloth-covered upholstered seats, per sq ft of floor area Unoccupied leather-covered upholstered seats, per sq ft of floor area Chairs, metal or wood seats, each, unoccupied .60 49 44 15 125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz 74 .88 .96 93 85 .66 .80 .88 .82 79 54 .60 .62 58 79 19 22 39 38 39 Preferred Reading — Books TABLE 37-4 SOUND ABSORPTION COEFFICIENT 1. VS. 12.6a'* Sound Absorption 2 Coefficient 12.6a 2 0.50 eee 4.78 0:85 ..cicnsiecccioreinarmeennnsnameners 5.46 0.60 eee 6.16 0.65 eee 6.89 0.70 eee 7.65 0.75 i idumirrivaresiimmmericsenvinemnns 8.43 0.80 eee 9.16 0.85 eee 10.02 0.90 ca.connenssrinesinporannminnnsioan 10.87 BERANEK, L. L. — Noise and Vibration Control, McGraw-Hill Book Co., New York, 1971, HARRIS, C. M. — Handbook of Noise Control, McGraw-Hill Book Co., New York, 1957. HARRIS, C. M. and CREDE, C. E. — Shock and Vibration Handbook, Volume 2, McGraw-Hill Book Co., New York, 1961. Preferred Reading — Periodicals 562 Sound and Vibration — Published monthly by Acoustical Publications, Inc., 2710 E. Oviatt Road, Bay Village, Ohio 44140. Journal of Sound and Vibration — Published bi- monthly by Academic Press, Inc. (London) Limited. CHAPTER 38 CONTROL OF EXPOSURES TO HEAT AND COLD Harwood S. Belding, Ph.D. HEAT Introduction At this point we expect the student to have acquired an understanding of the several elements which act to determine the stress of hot environ- ments (Chapter 31) and of the physiological ef- fects of heat exposures on the body (Chapter 30). The task in this section is to identify methods of control of occupational exposures to heat. These methods must be adapted to the nature of the heat stress and, if chosen properly, can be ex- pected to ameliorate resulting physiologic strains. Control of heat hazards has been discussed in several publications. Engineers may wish to con- sult more comprehensive publications issued by the American Industrial Hygiene Association' and the American Society of Heating, Refrigerating and Air Conditioning Engineers. These offer some details not provided here, in particular on thermal control of large factory spaces by venti- lation. Engineering aspects of ventilation are also given in Chapter 39. Earlier, Hertig® and Hertig and Belding* discussed methods of heat control. Wason® provided a comprehensive treatment of many aspects of the subject. The ultimate goal of heat control engineering may be to create a climate of work in which true thermal comfort prevails. However, this seldom is achievable when large furnaces or sources of steam or water are present in the work area. In compromising with his ideal of providing comfort, the engineer may rationalize his shortcomings with the knowledge that man evolved as a tropical ani- mal; he is well-endowed with physiologic mechan- isms to cope with substantial levels of heat stress, particularly if he is acclimatized. It has even been suggested that some exercise of these natural mechanisms among well individuals may, as in the case with physical exercise, have beneficial effects (Chapter 30). This type of justification of hot working conditions is less warranted when jobs demand use of mental or perceptual facilities or of precise motor skills. In such cases thermal discomfort can distract attention; also, heat toler- ance of physically inactive workers is less in some respects than for those whose duties require physi- cal activity. . Analysis of the Problem and Options for Control Before initiating control measures the engineer will wish to partition the components of the heat stress to which the worker is exposed, or in plan- ning a new operation, is expected to be exposed. This information may be used not only as a basis for rational selection of the means of control, but also may be used, together with similar data ob- 563 tained following adoption of control measures, to demonstrate the effectiveness of corrective actions that have been taken. It is evident that the heat stress for the individual worker depends on: (1) the bodily heat production, (M), of the tasks which he performs (2) the number and duration of exposures (3) the heat exchanges as affected by the thermal environment of each task; namely exchanges by radiation (R), convection (C) and evaporation (E), as affected by air temperature (Ta), temperature of solid surround (Tw), air speed (v), and water vapor pressure of the skin (Pws) and the air (Pwa) (4) thermal conditions of the rest area (5) the clothing that is worn. Items 1 and 2 represent elements of behavioral control; 3 and 4, environmental control; and 5 may be regarded as a combination of both. The approach toward control may involve modification of one or more of these determin- ants of the heat stress. The challenge is to select specific methods for attack which will be both feasible and effective. Serious errors can result from resorting to some single pet engineering solution. Consider the consequences of ducting outside air to the task site. This air usually is blown at the worker at a temperature as warm as the upper reaches of the shed where the ducts have been installed. This will enhance cooling by evaporation of sweat, but if the air is warmer than the skin (35°C, 95°F), it will increase the convective heat load. Consideration of the trade oft between needed heat loss and increased heat gain is essential. And, provided that the plant air is reasonably clean, the same goal might be achieved less expensively with portable fans. How- ever, in such a situation the real mistake may be the failure to recognize that the heat problem de- rives from radiant load from a furnace and this is not decreased by air movement. This mistake has been made less frequently in recent years, but elaborate ducting across the ceilings of older plants exists as evidence of inappropriate action to control radiant heat loads. Let us examine means and effectiveness of the five listed modifiers of the heat stress. (1) Decreasing the physical work of the task. Metabolic heat can comprise a large fraction of the total heat load. However, the amount by which this factor may be reduced by control is quite limited. This is because an average sized man who is simply standing quietly while pushing buttons will produce heat at a rate of 100 kcal/hr whereas one who is manually transferring fairly heavy materials at a steady pace will seldom have a metabolic rate higher than 300 kcal/hr and usually not more than 250 kcal/hr. Obviously, control measures, such as partial mechanization, can only reduce the (M) component of these steady types of work by 100 to 200 kcal/hr; nevertheless mechanization can also help by mak- ing it possible for the worker to be more isolated from the heat source, perhaps in an air condi- tioned booth. Tasks such as shovelling which involve meta- bolic heat production at rates as high as 500 to 600 kcal/hr require that rest be taken one-half to two-thirds of the time simply because of the physical demands of the labor. Thus, the hourly contribution of (M) to heat load will seldom ex- ceed 300 kcal/hr. It is obvious that mechaniza- tion of such work can increase worker productiv- ity by making possible a decrease in the time necded for rest. (2) Modifying the number and duration of exposures. When the task in a hot environment involves work that is a regularly scheduled part of the job, the combined experience of workers and management will have resulted in an arrange- ment which makes the work tolerable most of the time for most of the workers. For example, the relief schedule for a task which involves manual transfer of hot materials may involve two workers only because of the heat, and depending on the duress, these workers may alternate at five-minute or up to hourly intervals which have been de- termined empirically. Under such conditions over- all strain for the individual will be less if the cycles are short.” Where there is a standardized quota of hot work for each man, it is sometimes lumped at the beginning of the shift. This ar- rangement may be preferred by workers in cooler weather; however, there is evidence that the strain of such an arrangement may become excessive on hot days. The total strain, evidenced by fewer heart beats, will be less if the work is spread out. The stress of hot jobs is dependent on vagar- ies of weather. A hot spell or an unusual rise in humidity may create overly stressful conditions for a few hours or days in the summer. Nonessen- tial tasks should be postponed during such emer- gency periods, in accordance with a prearranged plan. Also, assignment of an cxtra helper can importantly reduce heat exposure of members of a working team. However, there is danger in this practice when unskilled or unacclimatized work- ers are utilized in this role. Many of the critically hot exposures to heat faced in industry are incurred irregularly, as in furnace repair or emergencies, where levels of heat stress and physical effort are high and largely unpredictable, and values for the components of the stress are not readily assessable. Usually such exposures will force progressive rise in body tem- perature. Ideally such physiologic responses as body temperature and heart rate would be monitored and used as criteria for limiting such exposures on an ad hoc basis. Practically, how- ever, the tolerance limits must be based on ex- 564 perience of the worker as well as of his supervisor. Fortunately, for most workers most of the time individual perception of fatigue, faintness or breathlessness may be relied upon for bringing exposures to a safe ending. The highly motivated individual, particularly the novice who desires acceptance, is at greater risk. In the same spirit, foremen should respect the opinion of an em- ployee when he reports that he does not feel up to work in the heat at a particular time. Non-job personal factors such as low grade infection, a sleepless night or diarrhea (dehydration affects sweating) which would not affect performance on most jobs, may adversely affect heat tolerance. Perhaps the best advice that can be offered for control of irregular exposures is (a) that formal training and indoctrination of effects of heat be provided supervisors and workers; and (b) that this include advice to the effect that each exposure should be terminated before physical distress is severe. There is abundant cvidence that the physiological strain of a single exposure which raises internal body temperature to 39°C (102.2°F) is such as to contra-indicate further exposures during the same day; it may take hours for complete recovery. More work can be achieved during several shorter exposures and with less overall strain. (3) Modifying the thermal environment. The cnvironmental engincer will usually identify im- portant sources of heat stress in a qualitative sense, without resorting to elaborate measure- ments. Thus, his experience will suggest that when air is static and the clothes of the workers be- come wet with sweat it will help to provide a fan. Nevertheless, there arc advantages in quanti- tative analysis of the heat stress (and where pos- sible determination of physiological strains) on workers. The effects of various approaches to control can then be predicted and improvements in thermal conditions at the workplace can be documented for higher levels of management based on measurements made before and after action has been taken. We cite concrete examples to illustrate how the quantitative analytic approach may be used. CASE I. First is a casc which is encountered frequently under ordinary conditions of hot weather. Let us assume a laundry where the humidity is high (Pwa=25 mm Hg) despite the operation of a small exhaust fan on the wall. There is no high level heat source so Tw is about the same as Ta. In the simplest situation we take Ta and Tw equal to the temperature of the skin, which, under heat stress, may be assumed to be 35°C (95°F). This means heat exchange by R and C is zero.* Let ys examine the casc on the basis that expos- ure is continuous and the average physical work is moderate (M =200 kcal /hr). The heat load to be dissipated, Ereq, is then, M+R +C=Ereq 200+ 0+0=200 *In this case R+C is changed by about 17 kcal/hr for cach °C of deviation of Tw and Ta from Tsk. The workers wear only shorts or shorts and halter. The air speed is low, 20 m (65 ft.) per minute. Analysis in accordance with Chapter 31 for the seminude condition yields indication of maximum cooling by evaporation of sweat, Emax. Emax =2.0 v*¢ (42 —Pwa), where 42 mm Hg is Pws of completely wetted skin at 35°C; or Emax=2 x 6.0 (42-25) =200 kcal/ hr (approx.) Nominally, a worker under these conditions would be just able to maintain bodily heat balance if he kept his skin completely wet. To do this he would have to sweat extravagantly, which means some dripping. It is easy to see why the workers wear as little clothing as possible. Wearing a long- sleeved work shirt and trousers would reduce Emax by about 40 percent, or to 120 kcal/hr. The resulting excess of heat load over Emax would result in rise of body temperature and it can be estimated that the ordinary limit of toler- ance would be reached in about an hour. When, as in this case, the heat load is itself moderate, the attack of the control engineer should be aimed at increasing Emax. In most such situa- tions the management or the workers might find it expedient to bring in fans for spot “cooling.” Note that since Emax is 0.6 power function of air speed, tripling of air movement across the skin would result in doubling of Emax. In this case an increase from 20 m/min to 60 m/min is easily achieved and it is predicted that such air speed will raise Emax to 400 kcal/hr. Sweat would be reduced to about 0.35 liters/hr and would be evaporated easily; the skin would no longer be dripping wet. It is clear that this control measure has limitations. For example, if air speed were already 60 m/min tripling would produce a wind which might disrupt operations. A more effective permanent approach would be to replace the small exhaust fan with exhaust hoods opening over the principal source of mois- ture. This would work well in a dry climate, but in a humid one the make-up air from outside might have such a high Pwa as nearly to cancel the value of hoods. It is obvious that in Case I the use of mechanical air conditioning would prove expensive. CASE II. This is selected to show how the wearing of clothing can be advantageous and the presence of high air speed a liability under very hot, dry conditions. Assume Ta=45°C (113°F), Tw=55°C (131°F), v=100 m (300 ft.) per minute and Pwa, 10 mm. We use the same M as in Case I. Long-sleeved shirt and trousers are worn. * *The formulae used are explained in Chapter 31 and summarized here. NUDE kcal /hr CLOTHED 11(Tw—35) R 6.6 (Tw—35) 1.0 vO'6 (Ta—35) C 0.6 vos (Ta—35) 2.0 vO6 (42 —Pwa) Emax 1.2 v6 (42 —Pwa) Tw is approximated from temperature readings of a six- inch blackened globe, Tg, using Tw=Tg+ 0.24 v05 (Tg—Ta); vis in m/min; “35” is assumed Tskin; “42” is Pws of completely wet skin at Tskin of 35°C. 565 " M+R+C=Ereq 200+ 130+95=425 Emax=610 kcal/hr Suppose the worker wore only shorts under these circumstances. R, C and Emax would be in- creased: M+R + C=Ereq 2004220+160=580 Emax=1010 kcal/hr The total heat load is increased about 155 kcal/ hr. The specific cost of baring the skin would be about 0.26 liter per hour, raising the total re- quirement of sweating to 1.0 liter per hour, as compared with 0.71 liter per hour when wearing shirt and trousers. Thus under conditions where Tw and Ta are above 35°C and Pwa is low, the wearing of cloth- ing reduces heat stress and strain. In examining the above model it will be apparent that there is an optimum amount of clothing in such situations. This is the amount which reduces Emax to a value only slightly in excess of Ereq. The long-sleeved shirt and trousers happen to be just about right for this purpose under the given conditions. With low Pwa as in a semi-arid area, a more satisfactory solution probably might be reached through installation of an evaporative cooler. In Case 11, inside temperature was usually 5°C hot- ter than outside, due to process heat and insula- tion on the roof of the shed. Assuming outside Ta usually does not exceed 40°C (104°F) and Pwa is about 10 mm Hg, outside air drawn through a water spray washer in large volume theoretically could be reduced to prevailing out- of-door wet bulb temperature, namely 22°C (72°F), though in practice probably only 80 percent efficiency could be achieved. Most of the wash water could be recycled. Pwa of the con- ditioned air would be raised from 10 to 20 mm Hg. The temperature of the work space might actually be reduced by this means to 30°C. If so, the components of heat load for clothed workers would be reduced by 35 percent from Ereq=425 to Ereq = 280; Emax would still permit free evap- oration of sweat. M+R + C=Ereq 200+ 130—=50=280 Emax=420 kcal /hr CASE 111. This case is chosen to illustrate the dramatic reduction in heat load achievable by provision of appropriate shielding when radiation from a furnace is substantial. Practical examples of the reduction in radiant heat load achievable by these means are provided by Lienhard, Mc- Clintock and Hughes," by Haines and Hatch,” and by others.” '* This case is chosen from the first of these references, because the situation is real, and physiological and environmental data are available. The task is that of skimming dross from molten bars of aluminum. The worker stands at the task. Manipulation of a ladle involves mod- erate use of shoulder and arm muscles and re- quires an M of about 200 kcal ‘hr. The environ- mental temperatures before the corrective action were reported as Tg=71.7°C (161°F), Ta=47.8°C (118°F) and Twb=30.5°C (87°F). Air was forced from an overhead duct at 275 m/min (900 fpm).* Note that the humidity was very high (Pwa=24 mm Hg) which is character- istic of the local climate. In terms of heat load and Emax the situation was: M + R + C =Ereq 200+870+220=1290 Emax = 630 kcal/hr It is obvious from the deficiency of evaporation and the enormous load that the workers, despite full clothing and a face shield, were able to per- form this task only for a few minutes at a time. Heat exhaustion was not uncommon (and might partly be attributable to the difficult hot condi- tions prevailing in the nearby rest area). Engineers undertook control of this heat ex- posure by interposing finished aluminum sheeting between the heat source and the worker. Infra- red reflecting glass at face level permitted seeing the task and space was left for access of the arms in using the ladle. As a result of these measures it was recorded that both Tg and Ta were reduced to 43°C (110°F). The same air speed was pres- ent as before and if we assume the same Pwa we obtain: M +R + C =Ereq 200+50+140=390 Emax =630 kcal/hr By this action to reduce R the heat load was brought to a level that is reasonable for prolonged work, but did not completely eliminate the heat stress. The predicted requirement for sweating to maintain heat balance was reduced from the previ- ously impossible-to-sustain level of 2.1 liters/hr to about 0.7 liter/hr. (The before and after aver- age levels actually observed for two workers were not far from these predictions, namely 2.1 and 1.1 liters/hr. The same two subjects also showed a marked reduction in heart rate, as a result of the changes, from an average of 146 to 108 beats/ min.) The percent reduction of the radiant load can be taken as a measure of the effectiveness of the reflective shielding, and in this instance approxi- mates 85 percent. Large errors in the estimate of R are possible at extremely high globe tempera- tures, but in this case it appears that the maximum relief one could expect from shielding was achieved. Haines and Hatch® reported smaller re- ductions in R of 51 to 74 percent from interposing a sheet of aluminum at eleven different work sites in a glass factory. Others! have shown reduction of 90 percent or more under ideal conditions not likely to prevail on the plant floor. Control of Radiation: Further Considerations. While in Case III we have dealt with some aspects of control of R by shielding, the two other classi- cal approaches of industrial hygiene engineering, namely control at the source and control at the man, offer possibilities which must be considered. Application of insulation on a furnace wall can reduce its surface temperature and thereby the *High speed air jets (8-inch to 12-inch diameter) are frequently used for purposes of man-cooling. These directly affect air speed over only a small portion of the body. Directed downward, the speed measured near the legs may be only 10 to 20 percent of that at the head. The head represents only 10 percent of the body surface, the legs 40 percent. 566 level of R. A by-product of such treatment is sav- ing in fuel needed to maintain internal furnace temperatures. Application of a polished metallic surface to a furnace wall will also reduce R. How- ever, a polished metallic surface will not maintain its low emissivity* if it is allowed to become dirty. A layer of grease or oil one molecule thick can change the emissivity of a polished surface from 0.1 to 0.9. And the emissivity of aluminum or gold paints for infrared is not necessarily indi- cated by their sheen. If the particles are smaller than about one micron they emit almost like a black body. (The same is true for fabrics coated with very fine metallic particles.) Equal or even more effective reduction of R is achievable with non-reflective barriers through which cool water is circulated. The engineer is frequently baffled in shielding by the fact that access to the heat source is re- quired for performance of the task. We have seen various solutions to this problem. One is a curtain of metal chains which can be parted as required and which otherwise reduces emission like a fireplace screen. Another is a mechanically activated door which is opened only during ejec- tion or manipulation of the product. And finally, remotely operated tongs may be provided, taking advantage of the fact that radiant heating from an open portal is limited to line of sight and falls off as the reciprocal of the square of the distance from the source. (4) Thermal conditions of the rest area. Brouha® states “It is undeniable that the possi- bility of rest in cool surroundings reduces consid- erably the total cost of work in the heat.” This is demonstrated by responses of heart rate and body temperature of two groups of men doing the same job with and without access to an air condi- tioned space for recovery (Figure 38-1). There is no solid information on the optimum thermal conditions for such areas but we have laboratory data which support setting the temperature near 25°C (77°F). This feels chilly upon first entry from the heat, but adaptation is rapid. The placement of these areas is of some im- portance. The farther they are from the work- place the more likely that they will be used in- frequently or that individual work perio: will be lengthened in favor of prolonged rest periods. *Emissivity is the capacity to radiate relative to a black body, which has a capacity of 1.0. Bright metal sur- faces are poor emitters, having emissivities of less than 0.1. Absorptivity of materials for radiant energy is equivalent to their emissivity i.e., a black body is a perfect absorber. Reflectivity is 1.0 minus the emissiv- ity. These characteristics are dependent on spectral wavelength, which is shorter for bodies at higher tem- peratures. The radiation dealt with here is in the infra- red range, of longer wavelength than visible light. The emissivity and absorptivity of unpolished surfaces in this range are close to those of a black body, regardless of color. Thus light-colored oil paint will emit as a black body, as will skin, regardless of its color, and as will clothing. The near side of a polished metallic shield (1) will reflect back 90 percent of the energy which impinges from a furnace and (2) will emit from its far side only 10 percent of the energy that was ab- sorbed. To be doubly effective in this way a shield must be exposed to air on both sides. 99.8 996 | a ER 0 ——— [WORKING NoT! AIR- eee \RESTING ~~ __|/conpiTIoNED 99.4 7 99.2 x Foo / / ™ 99.0 v7 > i \ SN - —— Lv] NN 98.8 Va +— 1 _ S AIR- > NN == 7 CONDITIONED ] J 1 98.6 / 98.4 LUNCH HRS IST WORK| IST REST|2ND WORK|2ND REST[3RD WORK[3RD REST [4TH WORK|4TH REST PERIOD | PERIOD | PERIOD | PERIOD | PERIOD | PERIOD | PERIOD | PERIOD ~I130 E \ N £120 NOT AIR— \ \ 2 CONDITIONED N \ = 10 ISAFETY LIMIT LN \ Lud “ N Se \ © So NN oY = TO NN \ \ x “ No AIR- \ \ W 90 ~ SJ CONDITIONED 80 | LUNCH | 8 9 10 I 12 2 3 a TIME. 8am —4pm Brouha, L.: Physiology in Industry, 2nd Edition. New York, Pergamon Press, 1967. Figure 38-1. Average Heart Rates and Body Temperatures at Beginning and End of Suc- cessive Work and Rest Periods. Group with lower levels of responses rested in an air condi- tioned room. 567 Incidentally, the same principle applies for positioning of water fountains. When they are remote from the worker, substantial dehydration is more apt to occur. The proper temperature for drinks under hot conditions is often asked. There is no scientific answer, but most men will not willingly drink fluids that are close to body temperature. They welcome chilled water and seek chilled soft drinks and ice cream when these are available in rest areas. (Actually a liter of intake at 8°C (46°F) will contribute to body cooling by extracting 30 kcal of body heat; a half pint of frozen sherbet will remove about the same amount.) Experienced workers recognize that frequent intake of small amounts of fluid is better than large draughts. (5) Clothing: (a) Conventional work cloth- ing. Heat exposures may be controlled through selective wearing of clothing, as illustrated by Cases I and II. In Case II we illustrated effects of an ordinary work shirt and trousers in reducing heat transfer by radiation, convection and evapo- ration by about 40 percent from the values ap- plicable to seminude men.'! Design as well as thickness can be exploited. Note that air move- ment under clothing, that is provided for by loose fit and generous openings, will have twice as much effect on Emax as it does on C (see coefficients). On the other hand, in dry environments with high air speed, tighter fit may be employed to re- duce gain by C without critical reduction of Emax. Additional thickness may be exploited for further reduction of gain by R+C and may be of par- ticular value when alternating between extremes of heat and cold in open sheds in wintertime. In such situations long underwear may be advanta- geous because it acts as a “heat sponge.” Thick- ness can also be an advantage in clothing for fire fighting. (b) Aluminized reflective clothing. We have reported effects of wearing aluminum-coated clothing on heat exchanges." Somewhat to our surprise our samples provided only about 60 per- cent reduction of radiant heat gain as compared with the 40 percent available from ordinary work clothing. At high humidities (Pwa=20 mm Hg and above) a full aluminized suit, consisting of long coat, full trousers, spats and hard hat, rep- resented a greater handicap for prolonged use than ordinary work clothing. Subjects became overheated because the suit interferred with evap- oration of their sweat. In a trial where only the front of the body was exposed to the high level radiant source, we found that an aluminized apron and similar reflective covering for the front of the legs provided nearly as much protection as the full suit and permitted necessary evaporation. (¢c) Thermally conditioned clothing. Numer- ous ideas have been incorporated in special cloth- ing for maintaining comfort in extreme heat (or cold). Some systems supply appropriately cool air from a mechanical refrigerator to points under a jacket or coveralls. When air from a remote’ source is used there are two problems. One is the gain of heat through the walls of the supply tub- ing. This problem has been solved in some cases 568 by using porous tubing which will leak an appro- priate amount of supply air to keep the wall of the tubing suitably cool. The other problem is distri- bution of the air through the suit. With a simple, single orifice it is difficult to cool a sufficient area of skin; cooling limited to the face or trunk is usually not enough. Provision of several orifices, though better, will create bulk and restrict mo- bility. In fact, the restriction of movement re- sulting from tethering the worker to supply line will often contraindicate this type of system. The vortex tube source of cool air has been used successfully in some situations.” The device is carried on the belt. Air introduced tangentially at high velocity is forced into a vortex, which re- sults in two separable streams of air, one cold which is distributed under the suit, ‘the other hot which is discarded. Compressed air requirements to operate the vortex system are large. Self-contained sources of conditioned air which can be back-packed have also been developed. One contains a liquid which is sealed into a finned container. After being cooled in a deep freeze the container is placed in the pack. A small bat- tery-driven fan circulates air across the fins and into the suit. A single charging of this device may extend tolerance for relining furnace walls from several minutes to 30 or 60 minutes. More sophisticated devices employ a closed fluid-filled system and a fairly elaborate network of small tubing for distribution. The nuisance factor must be considered with all such devices. Men will not go to the trouble of donning them unless they recognize more than a marginal advantage. On the other hand, with such devices it has sometimes been possible to change hot tasks which required long rest pauses into continuous duty operations involving fewer workers. Checklist The emphasis of this section has been on ra- tionalization of the options for control of heat exposures, based on consideration of all elements of specific situations. Often there are several op- tions which may be capitalized upon simultane- ously without conflict. In other cases trade-offs must be weighed. Table 38-1 is a checklist which may be helpful in considering options which have been discussed in the text. COLD Introduction Protection of the body against excessive cool- ing has not received popular attention of occupa- tional health workers to the extent of protection against heat, even though many workers are ex- posed to cold conditions. This is despite the fact man has much more innate ability to adapt to heat, attributable to his well-developed sweating mechanism. In cold, he can only resort to con- striction of skin blood vessels or shivering. If nude, at rest ,and in still air the dermal vasocon- striction will avail to provide heat balance only down to about 28°C (82°F). Man’s adaptation to cold has been based on his ingenuity in pro- TABLE 38-1 CHECKLIST FOR CONTROLLING HEAT STRESS AND STRAIN Item Components of Heat Stress M, body heat production of task Actions for Consideration reduce physical demands of the work; powered assistance for heavy tasks R, radiative load interpose line-of-sight barrier furnace wall insulation metallic reflecting screen heat reflective clothing cover exposed parts of body C, convective load if air temperature above 35°C (95°F) reduce air temperature reduce air speed across skin wear clothing Emax, maximum evaporative cooling by sweating increase by decreasing humidity increasing air speed Acute Heat Exposures R, C and Emax air or fluid conditioned clothing; vortex tube duration and timing exposure limit shorten duration each exposure; more frequent better than long to exhaustion self-limited, based on formal indoctrination of workers and foremen on signs and symptoms of overstrain recovery Individual Fitness for Work in Heat air conditioned space nearby determine by medical evaluation, primarily of cardiovascular status careful break-in of unacclimatized workers water intake at frequent intervals non-job related fatigue or mild illness may temporarily contraindicate exposure (e.g. low grade infection, diarrhea, sleepless night) viding himself with insulative clothing and heated shelter. Clothing Requirements The same heat balance equation that is used for heat exposures is applied also for cold. Equilib- rium is achieved when M+R + C=E, but in cold weather R and C are minus quantities. E will re- flect activity of the sweat glands as needed to balance the equation. When not overclothed, E is still present to the extent that body water dif- fuses through the skin (about 15 grams per hour with cooling value of 10 kcal per hour) and the lungs. The lung loss is also about 15 g per hour when inactive, but increases in proportion to ven- tilation of the lungs during activity. There are also small losses in warming cold inspired air,™ which are neglected in this treatment. Minimum com- bined losses by E are commonly assumed to be about 25 percent of M when clothing requirements are being considered. Thus, 0.75.M is the heat available for loss by (R+C) when heat balance is being maintained without recourse to excessive sweating. Over the thermal range of interest, Newton’s Law of Cooling is applicable; this states that heat loss will be proportional to the thermal gradient divided by the insulation. In this instance: Ts—Ta (R+C)= Insulation’ Ts and Ta are skin surface and air temperature, respectively. In the equilibrium state, and since (R+C)=0.75 M, insulation requirement for a known thermal gradient may be expressed as: (Ts—Ta) 0.75 M The unit used for describing insulation needs or insulation value with respect to clothing of man is the clo.*'* In this unit the insulation required is: _5.55(Ts—Ta) Ielo=—"G=sM The value 5.55 is the coefficient which applies where Ts and Ta are in °C and M is in kcal per square meter of body surface per hour. Application of the equation is illustrated in answering the question: How much insulation is required to maintain comfort for a man seated at rest (M=50 kcal/m2+hr) at 21°C (70°F)? The “The unit was selected to represent the approximate in- sulation value of a business suit. One clo will maintain a thermal gradient of 0.18°C over an area of one square meter when the thermal flux is one kcal/hr. where insulation required = 569 skin temperature for comfort is known to average about 33°C, so 5.55(33-21) _ 38 The total insulation need may be met from two sources, both of which fundamentally involve im- mobilization of a layer of “still air” (under prac- tical conditions one-quarter inch of “still air” is worth about 1 clo). The first source is the film of air which always overlies the outside of the cloth- ing, or the surface of the skin when it is bare). This insulation of air, Ia, is worth about 0.7 clo when the body is inactive and is exposed to the natural convection present in a room. Ia varies as a power function of the reciprocal of air speed: at 30 m (100 ft) per minute it is 0.5 clo, at 100 m (330 ft) per minute it is 0.3 clo. The second source of insulation must be the clothing itself, Icl. Thus, the clothing needed at 21°C would be I clo in still air, because Ia contributes 0.7; at 100 m per minute the clothing per se would have to be worth 1.4 clo. Iclo= 7 When at rest as in the example, each added clo of insulation will protect to a 6.8°C (12°F) lower temperature. This means a total require- ment for thermal equilibrium of 4.8 clo while sitting at 0°C (32°F). On the other hand when working at a fairly hard M of 200 a total of only 1.2 clo should suffice for heat balance at the tem- perature; i.e., 5.55(33/150) =1.2. The require- ments for various levels of work at various tem- peratures are shown in Figure 38.2. The disparity of requirements for work and rest gives rise to one of the biggest problems for workers who are out- of-doors for prolonged periods in cold weather. The tendency of the inexperienced is to overdress. The result is copious sweating in the body’s at- tempt to maintain heat balance while working. The heavy clothing will not permit sufficient evap- orative cooling. A substantial amount of the sweat is accumulated in the clothing and continues to evaporate during subsequent rest, thus counteract- ing available insulation at a time when it is most needed. When in sunlight the net heat loss by (R+C) 14 — 12 S M IS HEAT PRODUCTION IN CAL./ m2 hr. e 10 — - ['4 2 = 8 <. x 8 — eS re Ww a SZ " S P cB w 6 4 i.) WY © & I > ONS = QS WV b » < S A We o YG oe We E 3 ok po 5 4 oo nS 6 B ” 2 0 o 5

    (A), flowrate (Q) can be calculated according to Equation 1. j FLOW —— es) PITOT TUBE eee NNN Ce SECTION ENLARGED TO SHOW DETAIL Dwyer Instruments, Inc.: Bulletin No. H-100. Michigan City, Indiana, p. 3. Figure 40-6. The Pitot Tube Connected to an Inclined Manometer. PITOT TUBE STATIONS INDICATED BY O EQUAL CONCENTRIC p——————————— A AREAS oO oO Oo O oO oO O oO B oO oO Oo Oo rl A © Le \ ° CENTERS OF /f Eat cfc |I6to64 EQUAL NZ CENTERS AREAS RECTANGULAR AREAS OF AREAS RECTANGUL AR DUCT ROUND DUCT Dwyer Instruments, Inc.: Bulletin No. H-100. Michigan City, Indiana, p. 3. Figure 40-7. Traverse of a Round and Rectangular Duct Area. 591 In cases when accuracy is not a prime consid- eration, a single centerline reading can be taken at least 10 diameters of straight duct downstream from the nearest interference. This VP should be adjusted by multiplying by 0.81, or the velocity should be multiplied by 0.90. When it is not possible to find undisturbed traverse locations 8.5 to 10 diameters downstream, alternate locations should be selected on the basis of a 5:1 ratio between downstream and upstream interferences. Depending on the situation and need for accuracy, multiple points for traverse can be selected and those points within 10% agreement averaged and used to determine velocity and air flow. Limitations. There are fewer limitations for Pitot tubes than for other air velocity measuring devices. Whereas they can be used in corrosive or variable temperature conditions, the impact and static openings can become clogged with particulate matter. Also, as with the other instruments dis- cussed, corrections should be made if the tem- perature is == 30°F from standard, the altitude is greater than 1000 ft., and the moisture content is 0.02 Ib./Ib. or greater. They cannot be used to measure low velocities (less than 600 fpm) and require an inclined manometer which must be level and free from vibration. They are not applicable for use in small diameter ducts (less than 3 inches) or in orifice type openings. Aneroid Gauges The most common and best known of the aneroid gauges is the magnehelic gauge. Aneroid gauges can be used for total, static, and, in con- junction with a Pitot tube, velocity pressure mea- surements. They are small, extremely portable, and not as sensitive to vibration and leveling as liquid filled manometers. Since the inches of water pressure is a function of the location of an indicat- ing needle on a dial, they are extremely easy to read. Magnehelic gauges are commercially avail- able in ranges from 0 to 0.5” WG. (500-2800 fpm) to 0 to 150” WG. (2000-125,000 fpm) (Table 40-1). The principal limitations are accuracy and calibration. Accuracy is usually below = 2% full scale. Since they are mechanical, there is a need to calibrate these devices periodically. Manometers Manometers range from the simple U-tube to inclined manometers already mentioned. A range of sizes and varieties of U-tube manometers are available and they may be filled with a variety of media ranging from alcohol to mercury. Readings can be converted to inches of water simply by cor- recting for differences in density (e.g., 1 inch of mercury is equal to 13.61 inches of water). When extreme accuracy is not essential or in high pressure systems, U-tube manometers will suffice. However, for accuracy and in low pres- sure systems, inclined manometers are required. Static Pressure Measurements Instrumentation and taps. Instruments used in measuring static pressure include the static leg of the pitot tube as well as any pressure measuring device connected to a hole in the side of a duct. 592 U-tube manometers and Magnehelic gauges are quite acceptable. Whereas the exact location of the hole is not extremely critical, the type of hole is. Generally, the holes should not be located in points where there is some basis for turbulence or non-linear flow such as the heel of an elbow. Holes should be flush with the inside of the duct with no projections or burrs. Thus, holes should be drilled and not punched. The location of holes 90° apart will allow for the averaging of multiple readings to provide an improved estimate of static pressure. Taps can range in complexity from a simple soft rubber hose held tightly against a {5 inch hole, to soldered pet cocks for use in high pressure applications. Applications. Static pressure measurements at strategic points in a system provide invaluable in- formation as to the performance. These measure- ments are neither difficult to obtain nor do they require expensive or delicate instrumentation. Estimation of air flow by the throat suction method* provides a fairly accurate estimation of flowrate of an exhaust opening if the coefficient of entry can be determined. Coefficient of en- tries for various hoods are given on Figure 2 of Chapter 42. Measurements are made between one and three diameters of straight duct from the throat of the exhaust inlet (point where the hood is connected to the branch duct). It is advisable to take multiple readings 90° apart. The flowrate in cfm can then be determined according to equa- tion 6: Equation 6: Q=4005 CeAy SP, Where: Q =Rate of flow in cfm Ce =Ratio of actual flow to theoret- ical flow (Figure 2 of Chapter 42) (Entry loss in” WG) A =Cross-sectional area of duct in ft* SP, = Average static pressure reading in inches of water Static pressure comparisons provide a means of either continuously or periodically monitoring the performance of a system. Additional informa- tion may be required, but strategically located static pressure taps can flag malfunctioning equip- ment, clogged ducts, dirty or broken filters, dented exhaust hoods, and changes in fan static pressure. The permanent installation of manometers immediately downstream from exhaust hoods con- trolling a hazardous material or critical process is advisable, as is the placement of such devices across a filter to determine the need for shaking, cleaning, or maintenance. Other Measuring Devices There are a number of other devices for mea- suring fluid flow, but their application is restricted to either laboratory use or the calibration of air sampling devices. Some are discussed briefly be- low: Orifice meter”. An orifice meter is simply a restric- tion in a pipe between two pressure taps. There are several types of orifice meters used, but the sim- plest and most common is the square edged orifice. If it is properly constructed, the orifice plate will be at right angles to the flow, and the surface will be carefully smoothed to remove burrs and other irregularities. Orifice meters are seldom used as permanent flow meters in ventilation systems be- cause of their high permanent pressure loss. They are more typically used in the ventilation labora- tory for calibration purposes. Permanent head loss will vary from 40 to 90 percent of the static pres- sure drop across the orifice as the ratio of orifice diameter to pipe diameter varies from, 0.8 to 0.3. Detailed discussions of orifices and orifice equa- tions can be found in reference 11. Venturi meters’. A Venturi meter consists of a 25° contraction to a throat, and a 7° re-expansion to the original size. This differs from the orifice meter where the changes in cross section are abrupt. The advantage of the Venturi over the standard orifice is that the permanent reduction in static pressure is small, because the velocity head in the throat is largely reconverted to static pres- sure by the gradual enlargement. A well designed and constructed Venturi will have a permanent static pressure loss of only 0.1 to 0.2 inches of H,O as compared to 0.4 to 0.9 for the orifice plate. Venturi meters are used in conjunction with a manometer as an in-line flow measuring device. A more detailed explanation of the Venturi is of- fered in reference 11. CALIBRATION OF INSTRUMENTATION All too often the need for calibration is not applied to devices for measuring air flow and ve- locity, yet as a group, with the exception of the Pitot tube, they require periodic calibration. Gen- erally, air flow measuring instrumentation is based on electrical or mechanical systems which are sen- sitive to shock. In addition, use of these instru- ments in corrosive or dusty atmosphere affects their reliability. A calibration wind tunnel as shown in Figure 40-8 represents the method of choice for calibrat- ing the devices described in this section. Reference 12 is an excellent treatment of the design and use of the calibration wind tunnel. A well designed wind tunnel must have the following compo- nents’: 1. A satisfactory test section. Since this is the location of the probe or sensing ele- ment of the device being calibrated, the gas flow must be uniform, both perpendicular and axial to the plane of flow. Streamlined entries and straight runs of duct are essen- tial to eliminate pronounced vena contracta and turbulence. 2. A satisfactory means of precisely metering air flow. A meter with adequate scale grad- uations to give readings of = 1% is re- quired. A Venturi or orifice meter rep- resent optimum choices since they require only a single reading. 3. A means of regulating air flow. A wide range of flows are required. A suggested range is from 50 to 10,000 fpm. There- fore, the fan must have sufficient capacity 593 to overcome the static pressure of the en- tire system at the maximum velocity re- quired. A variable drive provides for a means of easily and precisely attaining a desired velocity. Meters must be calibrated in a manner similar to how they are used in the field. Vane actuated devices should be set on a bracket inside a large test section with a streamlined entrance. Low ve- locity probe type devices may be tested through appropriate openings in the same type of tunnel. High velocity ranges of probe type devices and impact devices should be tested through appro- priate openings in a circular duct at least 8.5 diameters downstream from any interference. Straighteners as shown in Figure 40-8 will reduce this requirement to 7 diameters. NOTE: Devices must be calibrated at multiple velocities throughout their operating range. AIR FLOW SYSTEM SURVEYS System Start-up vs. Design Basis Any ventilation system, be it local exhaust for contaminant control or general for comfort, is de- signed in terms of removing or distributing a speci- fied quantity of air at a specified velocity at a total system pressure which is the sum of the parts. An initial survey of the system is the only time a valid comparison can be made between the design basis and optimum system performance. Sketch of the system. A sketch not necessarily to scale but representative of dimensions should be drawn noting such items as hoods, elbows, branch- ings, air cleaner, fan and stack. Supply ducts, plenums, and diffusers should be shown for gen- eral systems. Figure 40-1 and 40-2 represent gross simplifications of this concept. The sketch should be considered as part of the permanent record on which future changes in the systems may be recorded. Specific air flow measurements. Measurements in terms of air flow, velocity, and static pressure must be made to determine that the system is ade- quately balanced and performing according to the design basis. These measurements include: 1. Static pressure measurements at: a) hoods b) up and downstream of the air cleaner ¢) up and downstream of the fan 2. Air flow in cfm at: a) hoods (throat suction method) b) branches and mains (Pitot tube) ¢) up and downstream of fan (Pitot tube) 3. Supply, capture, and conveying velocities at: a) diffuser outlets (supply velocity) b) face or opening of hood (capture velocity) ¢) branches and mains (conveying velocity) 4. Fan performance a) fan speed in rpm b) horsepower (BHP) calculated using cfm (Q), total pressure (TP), and mechanical efficiency (ME) of fan. " 3hp motor with variable drive 500 to 3670 rpm Alternate damper Orifice —see detail 32 \ 5 1/2" diam L Plastic tube Streamline inlet Straighteners CALIBRATION WIND TUNNEL Fan Manometer - 6 "incline 15 vertical po 7 ——— 20" 6 wte—1 1" ¥ ; /" N Screen . Pipe taps I~ Ne \ 7 diam \ §~ Flonge i ! 35" ¥ 203/4"sq : 1 | bs \_grocker on rod Sharp edged orifice 1/8 steel plate 1 Transparent plastic TEST SECTION ORIFICE DETAIL For low velocity meters with large area in test air stream American Conference of Governmental Industrial Hygienists — Committee on Industrial Ventilation: Industrial Ventilation Manual, 11th Edition. Lansing, Michigan, 1970. Figure 40-8. The Calibration Wind Tunnel. . . _(Q) (TP) for the singular purpose of removing some con- Equation 7: BHP =—~% re taminant from the work environment. Visualiza- The locations of the measurements must be identified on the sketch and a record kept for fu- ture comparisons. A sample form can be found in reference 4. The measurements obtained should agree with- in 10% of the design basis. If not, system modi- fication should be made until such agreement is obtained. Other Checks. Local exhaust systems are installed tion techniques using smoke tubes or candles can be most helpful in verifying the system exerts a sphere of control over a sufficient area to prevent excessive exposures to operating personnel. Air evaluation for specific contaminants is also recom- mended to verify the system will control contami- nants to levels known to be safe. Air samples taken in the breathing zone of operating person- nel will be most helpful in assessing the adequacy of contaminant control. 594 As with the previous measurements, photo- graphic records of smoke tests and the results of air evaluation tests should be maintained for fu- ture reference. System Operation vs. System Start-up Once systems are started up and determined to perform satisfactorily, the degree of evaluation can be reduced as long as good records of start-up or initial conditions have been made. Experience with air flow systems clearly indicates periodic sur- veys are required to assure system performance is adequate. Operating personnel cannot be relied upon as an “indicator” of system performance. Also, ventilation systems are rarely an integral part of the operation in terms of quality and production, and all too often receive inadequate maintenance. For most systems simple velocity measure- ments at exhaust hoods and supply ducts will pro- vide a crude indication of system performance when compared with start-up evaluations. For local exhaust systems, the throat suction method applied to exhaust hoods and static pressure differ- entials for air cleaners and fans will suffice in con- firming the system is performing satisfactorily. The throat suction method will provide valid information unless: 1. The hood entry has been modified/dam- aged; 2. There are obstructions ahead of the point of measurement; or 3. The system has been modified. However, a reduction in throat suction can pro- vide valuable information, such as an indication that there has been: 1. Accumulations of material in an elbow, branch, or main, thus clogging or restrict- ing air flow. Build-up in the elbows result from impaction, while build-ups in straight runs result from insufficient conveying ve- locity or overloading the system. 2. A change in blast gate setting if the sys- tem is balanced using blast gates. 3. Additional branches and hoods added to the system. “Adding on” to a system is a real temptation. It is not sound economics when it renders the entire system deficient. 4. Excessive build-up on the filter. It is best to monitor filter build-up by attaching a static pressure measuring device across the filter. 5. Reduced fan output resulting from belt slippage, damaged or worn rotor, or build- up on the fan blades. Data Handling and Recording The sketch of the system made at start-up or for the initial air evaluation survey and the re- sults of the ensuing air flow survey must be re- corded and filed in such a manner that future air flow surveys can be conducted in a similar man- ner. The periodicity of air flow surveys can only be determined by such conditions as: 1. Nature of the materials being controlled. The more hazardous the materials, the more frequently the system should be checked. 595 2. Nature of the system. A blast gate system will require more frequent checks than other systems. 3. The degree of maintenance. Air flow sur- veys can be used to indicate the need for more frequent and improved maintenance. Reference 4 provides a sample of a diagram, check list and additional information regarding checking and testing systems. References 1. Occupational Safety and Health Standards. Fed- eral Register, Subpart G. 1910.94 Ventilation, Wash- ington, D. C., May 29, 1971. 2. Industrial Ventilation — A Manual of Recom- mended Practice. American Conference of Govern- mental Industrial Hygienists, 11th ed., Section 2, Dilution Ventilation, Cincinnati, Ohio, 1970. 3. SCHULTE, H. F., E. C. HYATT, H. S. JORDAN and R. N. MITCHELL. “Evaluation of Laboratory Fume Hoods.” Am. Ind. Hygiene Quarterly, 15:195, Chicago, Illinois, 1954. 4. Industrial Ventilation — A Manual of Recom- mended Practice. American Conference of Govern- mental Industrial Hygienists, 11th ed., Section 9, Testing of Ventilation Systems, Cincinnati, Ohio, 1970. 5. Operating Instructions for the Alnor Series 6000-P Velometer. Alnor Instruments Co., Chicago, Ill, 1970. 6. TUVE, G. L. and D. K. WRIGHT. “Air Flow Mea- surements at Intake and Discharge Openings and Grilles.” Heating, Piping and Air Conditioning 12:501, 10 South LaSalle St., Chicago, Illinois, 1940. 7. LIPPMAN, M. and G. W. FISCHER. Ch. 7 Air- Flow Measurements. The Industrial Environment — Its Evaluation and Control. USPHS, Washington, D. C., 1965. 8. AMCA Standard 210-67. Air Moving and Condi- tioning Association, Inc., 205 W. Toughy Ave., Park Ridge, Illinois, 60068. 9. Heating, Ventilation, and Air Conditioning Guide. ASHRAE, ASHRAE, Inc., New York, 1963. 10. Air Velocity Measurements. Dwyer Bulletin H-100, Dwyer Instruments, Inc., Michigan City, Indiana, 46360, 1970. 11. BRANDT, A. D. Industrial Health Engineering. John Wiley and Sons, New York, 1947. 12. HAMA, G. “A Calibration Wind Tunnel for Air Measuring Instruments.” Air Engineering, 9:18, Detroit, Michigan, 1967. Preferred Reading In addition to References 2, 4, 6, 9, 10, 11, and 12, the following represent selected sources which can contribute to the reader’s knowledge of the subject title. Heating and Cooling for Man in Industry, American Industrial Hygiene Association, 1st edition, Ch. 11 Testing, 1970. ASHRAE Guide and Data Book — Systems. Ch. 38 Testing, adjusting, and balancing; and Ch. 39 Preventive Maintenance, 1970. ASHRAE Guide and Data Book — Handbook of Fundamentals. Ch. 13 Measurements and Instru- ments, 1967. “Fundamentals Governing the Design and Operation of Local Exhaust System.” ANSI Z9.2 — 1971. Section 9, Operation and Maintenance; and Sec- tion 10, Checking Operation of Local Exhaust Sys- tems. American National Standards Institute, 1430 Broadway, New York, New York 10016. “Velometers and Other Air Velocity Measuring Instruments.” Bulletin No. 72-60-10M269. Alnor Instrument Co., 402 N. LaSalle St., Chicago, Illi- nois 60610. Hastings Air Meter Bulletin. Hastings-Raydist Co., P.O. Box 1275, Hampton, Virginia 23361. 596 Meriam In- “Meriam Pitot Tubes.” Bulletin 51. Cleveland, strument Co., 10920 Madison Ave. Ohio 44102. Anemotherm Air Meter Bulletin. Anemostat Prod- ucts, P. O. Box 1083, Scranton, Pa. 18501. CHAPTER 41 LOCAL EXHAUST SYSTEMS John E. Mutchler INTRODUCTION Local exhaust systems are employed to cap- ture air contaminants — dusts, fumes, mists, va- pors, hot air and even odors — at or near their point of generation or dispersion, to reduce con- tamination of the breathing zone of workers. Local ventilation is frequently used and is gener- ally the preferred method for controlling atmos- pheric concentrations of airborne materials that present potential health hazards in the work en- vironment. As discussed in Chapter 39, this type of ventilation is preferred over general exhaust ventilation for the following reasons: 2 1. If the local exhaust system is properly de- signed, the control of a contaminant can be complete; therefore, the exposure of workmen to contaminants from the sources exhausted can be prevented. With general ventilation the contaminant concentration has been diluted where the exposure oc- curs, and at any given workplace this dilu- tion may be highly variable, and therefore inadequate at certain times. 2. The volume of required exhaust is usually much less with local ventilation; therefore, the required volume of make-up air is less. A saving in both capital investment and heating and cooling costs is realized. 3. The contaminant is concentrated in a smal- ler volume of air; therefore, if a dust col- lector or other air pollution control device is needed, it is less costly. As a first ap- proximation the costs of air pollution con- trol are proportional to the volumetric rate of air handled. 4. Many local exhaust systems can be de- signed to capture large settleable particles or at least confine them within an en- closure, and thus greatly reduce the labor required for housekeeping. 5. Auxiliary equipment in the workroom is better protected from the deleterious ef- fects of the contaminant, such as corro- sion and abrasion. 6. Local exhaust systems usually require a fan of higher pressure characteristics to overcome pressure losses in the ventilation system. Therefore, the performance of the fan system is not likely to be grossly af- fected by wind velocity or an inadequate supply of make-up air. This is in contrast to general ventilation which can be affected severely by seasonal factors or an inade- quate supply of make-up air. 597 COMPONENTS OF A LOCAL EXHAUST SYSTEM A local exhaust system consists of four ele- ments as shown in Figure 41-1: 1) hoods, 2) ducts, 3) air cleaning device (cleaner) and 4) air moving device (fan). Typically, the system is a network of branch ducts connected to hoods or enclosures, main ducts, air cleaner for separating solid contaminants from the air stream, an exhaust fan, and a dis- charge stack to the outside atmosphere. Hoods A hood is a structure designed to enclose or partially enclose a contaminant-producing oper- ation and to guide air flow in an efficient manner to capture a contaminant. The hood is connected to the ventilation system via a duct which removes the contaminant from the hood. The design and location of the hood is crucial in determining the success of a local exhaust system. Ductwork The function of the ductwork in an exhaust system is to provide a channel for flow of the con- taminated air exhausted from the hood to the point of discharge. The importance of the ductwork design is underscored in the following points: a. In the case of dust, the duct velocity must be high enough to prevent the dust from settling out and plugging the ductwork. b. In the absence of dust, the duct velocity should strike an economic balance between ductwork cost and fan, motor and power costs. c. The location and construction of the duct- work must provide sufficient protection against external damage, corrosion and erosion, to provide a long, useful life for the local exhaust system. Air Cleaner Most exhaust systems for contaminants other than hot air need an air cleaner. Occasionally the collected material has some economic reuse value, but usually this is not the case. To collect and dis- pose of the contaminant is usually inconvenient and an added expense. This subject is discussed in greater detail in Chapter 43; it is beyond the scope of this chapter to elaborate on the details of air cleaning for ex- haust gas streams. Obviously, the growing con- cern with air pollution control, and attainment of air quality goals by legal restriction of emissions from sources of atmospheric discharge, place new importance on the air cleaning device within a local exhaust system. HOOD A ==" v ~ eNTRY | — Figure 41-1. Air Moving Device Centrifugal fans are the mainstay of air mov- ers for local exhaust systems. Wherever practic- able a fan should be placed downstream from the collector so that it will handle clean air. In such an arrangement, the fan wheel can be the back- ward curved blade type which has a relatively high efficiency and low power cost. For equivalent air handling the forward curved blade impellers run at somewhat lower speeds, and where noise is a factor, this may be important. Where chips and other particulate matter have to pass through the impeller, the straight blade or paddle wheel type fan is best because it is least likely to clog. Fans and motors should be mounted on sub- stantial platforms or bases and isolated by anti- vibration mounts. At the fan inlet and outlet the main duct should attach through a vibration iso- lator — a sleeve or band of very flexible material, such as rubber or fabric. : When the system has several branch connec- tions, consideration should be given to using a belt drive instead of direct connected motor. The need for increased air flow at a future date can then be accommodated, to some degree, by ad- justing the fan speed. The subject of air movers is covered in greater detail in Chapter 42. PRINCIPLES OF LOCAL EXHAUST When applying local exhaust ventilation to a specific problem, control of the contaminant is more effective if the following basic principles are followed: 1. Enclose the source as completely as prac- ticable; 598 FAN DUCT CLEANER Elements of a Local Exhaust System 2. Capture the contaminant with adequate velocities; 3. Keep the contaminant out of worker’s breathing zone; 4. Supply adequate make-up air; and 5. Discharge the exhausted air away from air inlet systems. Enclose the Source A process to be exhausted by local ventilation should be enclosed as much as possible. This will generally provide better control per unit volume of air exhausted. This principle is illustrated in Figure 41-2. Nevertheless, the requirement of ad- equate access to the process must always be con- sidered. An enclosed process may be costly in terms of operating efficiency or capital expendi- ture, but the savings gained by exhausting smaller air volumes may make the enclosure worthwhile. Capture the Contaminant with Adequate Velocities Air velocity through all hood openings must be high enough to contain the contaminant and, moreover, remove the contaminant from the hood. The importance of optimum capture and control velocity is discussed further in the following sec- tions. Keep the Contaminant Out of Worker’s Breathing Zone Exhaust hoods that do not completely enclose the process should be located as near as possible to the point of contaminant generation and should provide air flow in a direction away from the worker toward the contaminant source (see Figure 41-3). ADVANTAGES OF ENCLOSURE - * \ \ OPEN PLATING TANK LARGE AIR VOLUME ENCLOSED, MECHANIZED PLATING TANK SMALL AIR VOLUME ~ / CH Figure 41-2. Advantages of Enclosure. A NL AIR FLOW “it SOURCE WORKER ) (A) BAD i NA 3 [atm \ A ar —7 NN FLOW 7 WORKER “1 ) ol TANK { (B) SOMETIMES ACCEPTABLE Figure 41-3. 599 HOT PROCESS (C) ACCEPTABLE Use and Misuse of Canopy Hoods. This item is closely related to the character- istics of blowing and exhausting from openings in ductwork and is also considered in more detail in the following sections. Provide Adequate Air Supply Every cubic foot of air that is exhausted from a building or enclosure must be replaced to keep the building from operating under negative pres- sure. This applies to local exhaust systems as well as general exhaust systems. Additionally, the in- coming air must be tempered by a make-up air system before being distributed inside the process- ing area. Without sufficient make-up air, exhaust ventilation systems cannot work as efficiently as intended. Discharge the Exhausted Air Away from Air Inlets The beneficial effect of a well-designed local- exhaust system can be offset by undesired recircu- lation of contaminated air back into the work area. Such recirculation can occur if the ex- hausted air is not discharged away from supply air inlets. The location of the exhaust stack, its height, and the type of stack weather cap all can have a significant effect on the likelihood of con- taminated air re-entering through nearby windows and supply air intakes. This subject is treated in more detail in Chapter 42. FUNDAMENTAL CONCEPTS IN LOCAL EXHAUST VENTILATION Capture and Control Velocities All local exhaust hoods perform their function in one of two ways. One way is by creating air movement which draws the contaminant into the hood. The aii velocity created at a point outside a non-enclosing hood, which accomplishes this ob- jective, is called “capture velocity.” Other exhaust hoods essentially enclose the contaminant source and create an air movement which prevents the contaminant from escaping from the enclosure. The air velocity created at the openings of such hoods is called the “control velocity.” The determination of the two quantities, con- trol velocity and capture velocity, is the basis for the successful design of any exhaust hood. The air velocity which must be developed by the exhaust hood at the point or in the area of desired control is based on the magnitude and direction of the air motion to be overcome and is not subject to direct and exact evaluation (see Table 41-1). Many empirical ventilation standards, especially concerning dusty equipment like screens and con- veyor belt transfers, are based on “cfm per foot of belt width” or similar parameters. These are called exhausted rate standards. They are easily applied, are usually based on successful experi- ence, and usually give satisfactory results if not extrapolated too far. In addition, they minimize the effort and uncertainty involved in calculating the fan action of falling material, thermal heads within hoods, air currents, etc. However, such standards have three major pitfalls: 1. They are not fundamental. 2. They presuppose a certain minimum qual- ity of hood or enclosure design although it may not be possible or practical to achieve the same quality of hood design in a new installation. 3. They are valid only for circumstances sim- TABLE 41-1 RANGE OF CAPTURE VELOCITIES* Condition of Dispersion of Contaminant Capture Velocity, Released with practically no velocity into quiet air. Released at low velocity into moderately still air. Active generation into zone of rapid air motion. Examples fpm Evaporation from tanks; 50-100 degreasing, etc. Spray booths; intermittent 100-200 container filling; low speed conveyor transfers; welding; plating; pickling. Spray painting in shallow booths; 200-500 barrel filling; conveyor loading; crushers. Grinding; abrasive blasting, 500-2000 Released at high initial velocity into zone of very rapid air motion. In each category above, a range of capture velocity is shown. The proper choice of values de- pends on several factors: Lower End of Range Room air currents minimal or favorable to capture. Contaminants of low toxicity or of nuisance value 1 2 only. 3. Intermittent, low production. 4. Large hood — large air mass in motion. Upper End of Range 1. Disturbing room air current. 2. Contaminants of high toxicity. 3 . High production, heavy use. 4. Small hood — local control only. *Comm. on Industrial Ventilation, Industrial Ventilation, 12th edition, ACGIH, p. 4-5. 600 ilar to those which led to their adoption. It should be clear then, that the nature of the process generating the contaminant will have an important role in determining the required capture velocity. Air Flow Characteristics of Blowing and Exhausting The flow characteristics at a suction opening are much different from the flow pattern on a supply or discharge opening. Air blown from an opening maintains its directional effect in a fashion similar to water squirting from a hose. The effect is so pronounced that it is often called “throw.” However, if the flow of air through the same open- ing is changed such that it operates as an exhaust or intake opening with the same volumetric rate of air flow, the flow becomes almost completely non- directional and its range of influence is greatly re- duced. As a first approximation, when air is blown from a small opening, the velocity thirty diameters in front of the plane of the opening is about 10% of the velocity at the discharge. However, the same reduction in velocity is achieved at a much smaller distance in the case of exhausted open- ings, such that the velocity equals 10% of the face velocity at a distance of one diameter from the exhaust opening. Figure 41-4 illustrates this point. For this reason, local exhaust hoods must not be applied for any operation which cannot be conducted in the immediate vicinity of the hood. Air Flow into Openings Air flow into round openings was studied ex- tensively by DallaValle.® His theory of air flow into openings is based on a point source of suc- tion which draws air from all directions. The velocity at any point in front (distance X) of such a source is equivalent to the quantity of air (Q) flowing to the source divided by the effective area 30D a 22° 10% OF FACE VELOCITY AT 30 DUCT DIAS. APPROX. SPREAD OF AIR JET Figure 41-4. 601 of the sphere of the same radius. Conversely, Q=VA A=4rX? So, Q=V(12.57 X?) Where Q=air flow, cfm V = velocity at point X, fpm X = centerline distance, ft A =pipe area, ft? ~=13.1416, dimensionless constant Postulating that a point source is approximated by the end of an open pipe, Dalla Valle* and Brandt* determined the actual velocity contours for a circular opening, as shown in Figure 41-5. These contours, or lines of constant velocity, are best described by the following equation: Q=V (10 X2+A) Effects of Flanging Flanges surrounding a hood opening force air to flow mostly from the zone directly in front of the hood. Thus, the addition of a flange to an open duct or pipe improves the efficiency of the duct as a hood for a distance of about one diam- eter as shown in the following equation: Q=0.75V (10 X2+A) For a flanged opening on a table or bench: Q=0.5V (10 X2+A) Table 41-2 illustrates other hood types and gives the air volume formulae which apply.? Slots Caution must be used in applying the gener- alized continuity equation when the width to length ratio (aspect ratio) of an exhaust opening ap- proaches 0.1, since the opening becomes more like a slot. Using the same line of reasoning as D FAN EXHAUSTING in 10% OF FACE VELOCITY AT | DUCT DIA. BLOWING \ —D Air Flow Characteristics of Blowing and Exhausting. TABLE 41-2 INDUSTRIAL VENTILATION* HOOD EXHAUST VS. CAPTURE VELOCITY w HOOD TYPE DESCRIPTION ASPECT RATIO -~ AIR VOLUME ” SLOT 0.2 OR LESS Q=3.7 LVX 2 w ~ o> FLANGED SLOT 0.2 OR LESS Q=2.8 LVX » w 0.2 OR GREATER 2 PLAIN OPENING =V(IO +A X AND ROUND Q=-v{10% ) A=WL (sq.ft.) FLANGED OPENING 0-2 OR SREATER Q=0.75V(I0X? + A) AND ROUND H BOOTH TO SUIT WORK Q=VA= VWH rd A Ww Q=1.4 PVD CANOPY TO SUIT WORK P=PERIMETER Bp D= HEIGHT *Comm. on Industrial Ventilation, Industrial Ventilation, 12th edition, ACGIH, p. 4-4. DallaValle, Silverman® considered the slot to be a line source of suction. Disregarding the end, the area of influence then approaches a cylinder and the velocity is given by: _Q 27XL L =length of slot, ft. X = centerline distance, ft. ~=3.1416, dimensionless constant V= Where: Correcting for empirical versus theoretical con- siderations, the design equation which best applies for freely suspended slots is: _Q V=37XL 602 Flanging the slots will give the same benefits as flanging an open pipe so that only 75% of the air is required to produce the same velocity at a given point. Therefore, for a flanged slot: _ Q V=33 XL Air Distribution in Hoods To provide efficient capture with a minimum expenditure of energy, the air flow across the face of a hood should be uniform throughout its cross section. For slots and lateral exhaust applications this can be done by a “fish tailing” design. An eas- ier method of design is to provide a velocity of 2,000-2,500 feet per minute into the slot with a low velocity plenum or large area chamber behind it. For large, shallow hoods, such as paint spray % of diameter American Conference of Governmental Industrial Hy- gienists — Committee on Industrial Ventilation: Indus- trial Ventilation — A Manual of Recommended Prac- tice, 12th Edition. Lansing, Michigan, 1972. Figure 41-5. Velocity Contours for a Circu- lar Opening. booths, lab hoods, and draft shake-out hoods, the same principle may be used. In these cases un- equal flow may occur with a concentration of higher velocities near the take-offs. Baffles pro- vided for the hood improve the air distribution and reduce pressure drop in the hood giving the plenum effect. Where the face velocity over the whole hood is relatively high or where the hood or booth is quite deep, baffles may not be re- quired. Entrance Losses in Hoods The negative static pressure that is exhibited in the ductwork a short distance downstream from the hood is called the “hood static pressure,” SP. This term represents the energy needed to: 1. Accelerate the air from ambient velocity (often near zero) to the duct velocity; 2. Overcome the frictional losses resulting from turbulence of the air upon entering the hood and ductwork. Therefore, SP, =VP +h, where VP = velocity pressure in the duct and h, =hood entry loss The hood entry loss, h, is expressed as a function of the velocity pressure, VP. For most types of hoods h,=F,VP, where F, is the hood entry loss factor. For plain hoods where the hood entry loss 603 is a single expression, F,VP, the VP referred to is the duct velocity pressure. The hood static pressure can be expressed as: SP, = VPauct + he or SP, hl VPuct + FLVPauet = ( 1 + Fu) VPayct However, for slot and plenum or compound hoods there are two entry losses; one through the slot and the other into the duct. Thus, SP, = het + VPayct + heauct = For X VP + VPauet + Faucet X VPauet. The velocity pressure resulting from acceleration through the slot is not lost as long as the slot ve- locity is less than the duct velocity, as is usually the case. Another constant used to define the perform- ance of a hood is “coefficient of entry,” C.. This is defined as a ratio of the actual air flow to the flow that would exist if all the static pressure were present as velocity pressure. Thus, _ Qactual _4,005 AY VP __/VP Qvp = SP, 4,005 A Y SP, SP, This quantity is constant for a given shape of hood and is very useful for determining the flow into a hood by a single hood static pressure read- ing. The coefficient of entry, C,, is related to the hood entry loss factor, F,, by the following equa- tion only where the hood entry loss is a single ex- pression: e 1 Ce 1+F, Page 4-12 (Figure 4-8) of Industrial Ventilation provides a listing of the entry loss coefficient (C.) and the entry loss (h.) in terms of velocity pres- sure (VP). Most of the more complicated hoods have coefficients obtained by combining some of these simpler shapes. Static Suction One method of specifying the air volume for a hood is to specify the hood static pressure, SP, and duct size. The hood static pressure at a typical grinding wheel hood is two inches of water. This reflects a conveying velocity of 4500 feet per minute and entrance coefficient (C.) of 0.78. For other types of machinery where the type of ex- haust hood is relatively standard, a specification of the static suction and the duct size is given in Alden® and other reference sources. Specification of the static suction without duct size is, of course, meaningless because decreased size increases ve- locity pressure and static suction, while actually decreasing the total flow and the degree of control. Therefore, static suction measurements for stan- dard hoods or for systems where the air flow has been measured previously are quite useful to es- timate, in a comparative way, the quantity of air flowing through the hood. Duct Velocity for Dusts and Fumes The air velocity for transporting dusts and fumes through ductwork must be high enough that the particles will not settle and plug the ducts. This minimum velocity, called “transport velocity,” is typically 3,500 to 4,000 linear feet per minute. At these velocities, frictional loss from air moving along the surface of the ducts becomes significant; therefore, all fittings, such as elbows and branches, must be wide-swept, gradual, and with smooth in- terior surfaces. The cross-sectional area of the main duct generally will equal the sum of the areas of cross sections for all branches upstream, plus a safety factor of approximately twenty per- cent. When the main duct is enlarged to accom- modate an additional branch, the connection should be tapered and not abrupt. Local exhaust systems for gases and vapors may have lower duct velocities (1,500 to 2,500 feet per minute) because there is little to settle and plug the ducts. Lower velocities reduce markedly the frictional and pressure losses against which the fan must operate, thereby realizing a saving in power cost for the same air flow. EXHAUST HOODS AND THEIR APPLICATIONS The local exhaust “hood” is the point at which air enters the exhaust system, and the term is used in a broad sense to include all suction openings, regardless of their shape or their physical disposi- tion. Hoods in the context of this discussion em- brace all types of such openings including sus- pended, canopy-type hoods, booths, exhausts through grille work in the floor or bench top, slots along the edge of a tank or table, the open end of a pipe, and, in a general sense, exhaust from most enclosures. Hoods ventilate process equipment by captur- ing emissions of heat or air contaminants which are then conveyed through ductwork to a more convenient discharge point or to air pollution con- trol equipment. The quantity of air required to capture and convey the air contaminants depends upon the size and shape of the hood, its position relative to the points of emission and the nature and quantity of the air contaminants. Exhaust hoods should enclose as effectively as practical the points where the contaminant is re- leased. They should create air flow through the zone of contaminant release of such magnitude and direction so as to carry the contaminated air into the exhaust system. Exhaust hoods and en- closures may also serve the important function of keeping materials in the process by preventing their dispersion. Hoods can be classified conveniently into three broad groups: enclosures. receiving hoods, and ex- terior hoods. Booths, such as the common spray- painting enclosure, are a special case of enclosing hoods and will be discussed separately. Enclosures Enclosures normally surround the point of emission or contaminant generation, either com- pletely or partially. In essence, they surround the contaminant source to such a degree that all dis- persive actions take place within the confines of the hood. Because of this, enclosures require the lowest exhaust rate of the three hood types. A typical enclosed hood is illustrated in Figure 41-6. Enclosure hoods are economical and efficient. ['hey should be used whenever possible, especially when the contaminant is a hazardous material. 604 Materials having high toxicity or corrosiveness and fine dusts must be effectively controlled for workers’ health and safety. Hoods handling these materials should be carefully designed so as not to accumulate the contaminants. Booth Type Hoods Booths are typified by the common laboratory hood or spray painting booth in which one face of an otherwise complete enclosure is open for ac- cess. Air contamination takes place inside the en- closure and air is exhausted from it at such a rate as to induce an average velocity through the open- ing that will be sufficient to overcome escape ten- dencies of the air within it. The three walls of the booth greatly reduce exhaust requirements, but not to the extent of a complete enclosure. A list of several enclosure hoods and their application is shown in Table 41-3. TABLE 41-3. ENCLOSURE HOODS AND THEIR APPLICATIONS Hood Application Booth Laboratory Paint and metal spraying Arc welding Bagging machines Bucket elevators (complete enclosure) Vibrating screens Storage bins Mullers — Mixers Crushers Belt conveyor (transfer points) Packaging machines Abrasive blast cabinets Machine Enclosure Receiving Hoods The term “receiving hoods” refers to those hoods in which a stream of contaminated air from a process is exhausted by a hood located spe- cifically for that purpose. Two common types of receiving hoods are canopies and grinding hoods. Canopy hoods frequently are located directly above various hot processes. A canopy hood is shown in Figure 41-7. They receive contaminated air which rises into the hood primarily by reason of its own buoyancy. This type of receiving hood is similar to an exterior hood in that the contami- nated air originates beyond the physical boun- daries of the hood. The fundamental difference between receiving and exterior hoods is in the way air moves to the hood; i.e., the entire air flow is induced by the receiving hood, but flows more freely to the exterior hoods. However, canopy hoods are adversely affected by crossdrafts and are less efficient than total enclosures. They cannot be used to capture toxic vapors if people must work in a position between the source of contamination and the hood. Contaminants from a grinding or polishing wheel are too heavy to be captured by conven- tional air-flow patterns created by exhaust hoods. CASING EXHAUSTED AT TOP ~~ BELT WIDTH A REMOVABLE PANEL BETWEEN THE FEED AND THE RETURN RUN OF BELT ELEVATOR CASING BELT SCRAPER LOADING LEG Figure 41-6. Hence, this type of hood is also located in the pathway of the contaminant. Heavy particulates are released into the hood by inertial forces from the grinding (or polishing) wheel. If hood space is limited by the process, baffles or shields may be placed across the line of throw of the particles to remove their kinetic energy. Then, lower air ve- locities are required to capture and carry the par- ticles into the hood. A typical grinding wheel hood is shown in Figure 41-8. Some common receiving hoods are listed in Table 41-4. Exterior Hoods Exterior hoods must capture air contaminants being generated from a point outside the hood itself — sometimes relatively far away. These differ from enclosures or receiving hoods in that they must “reach” beyond their own dimensions and capture contaminants without the aid of na- tural phenomena (e.g., natural drafts, buoyancy 605 A Typical Enclosed Hood. TABLE 41-4. RECEIVING HOODS AND THEIR APPLICATIONS Hood Application Grinding Surface grinders Stone and metal polishing Woodworking Shapers, stickers, saws, Stone cutting Sanding Portable Canopy jointers, molders, planers Granite and marble cutters and grinders. Granite surfacing Belt and drum sanding operations Hand grinding, chipping Hot processes evolving fuines CANOPY L_ — 0.40 TANK Q=1.4 PDV where Q=RATE OF AIR EXHAUSTED, cfm, P=PERIMETER OF SOURCE, ft. D=VERTICAL DISTANCE BETWEEN SOURCE AND CANOPY, ft. V=REQUIRED AVERAGE AIR VELOCITY THROUGH AREA BETWEEN SOURCE AND CANOPY, fpm. Figure 41-7. inertia, etc.). Exterior hoods must create direc- tional air currents adjacent to the suction opening to provide exhausting action. They are sensitive to external conditions and may be rendered com- pletely ineffectual by even a slight draft through the area. They also require the most air to control a given process. Of the three hood types, exterior hoods are the most difficult to design. They are used when the mechanical requirements of a proc- ess will not permit the obstruction that total or partial enclosure would entail. This class of hood includes the numerous types of suction openings located adjacent to sources of contamination which are not enclosed. These hoods include ex- haust slots on the edges of tanks (see Figure 41-2) A Canopy Hood. 606 or surrounding a work bench, exhaust duct ends located close to a small area source, large exhaust hoods arranged for lateral exhaust across an ad- jacent area, exhaust grilles in the floor or bench work below the contaminating action, certain can- opy hoods and large propeller exhaust fans on outer walls adjacent to a zone of contamination. A more complete list of external hoods and their applications is given in Table 41-5. VENTILATION STANDARDS AND REGULATIONS Regulations resulting from the Occupational Safety and Health Act of 1970 include several standards for local ventilation, both for the pre- GRINDER OR POLISHER Side opening should be minimum. Ya maximum is desirable. 1 Cleanout door ———e 4 2 0— Adjustable tongue. Not more Tr than Y, from belt. Hinged side panel for maintenance For housing may extend to floor. heavy dust accumulations 45° Figure 41-8. vention of fire and explosion and for controlling hazardous materials in the workroom to prevent illness or injury. In late 1972, such regulations included specific ventilation requirements for: Abrasive blasting; Grinding, polishing and buffing; Spray finishing operations; Open surface tanks; Welding, cutting and brazing; Gaseous hydrogen; Oxygen; Flammable and combustible liquids in stor- age rooms and enclosures; and 9. Dip tanks containing flammable or com- bustible liquids. The bases of these OSHA standards have been the consensus-type standards developed by organi- zations such as the American National Standards Institute and the National Fire Protection Asso- ciation. It is quite likely that the number and specificity of ventilation standards will increase with time, both under the regulations of the Occu- pational Safety and Health Administration and by the added interest in occupational health and safety at all levels of government, It is important to understand that standards and codes define minimum standards of ventila- tion. Most of these have developed as “rule-of- thumb” values, usually based on successful ex- perience. As a result, they tend to be inflexible and can be inadequate for design purposes. If not NAN PE WUD 607 A Grinding Wheel Hood. TABLE 41-5 EXTERNAL HOODS AND THEIR APPLICATIONS Hood Application Slot Open tanks Push-Pull Plating tanks Cementing and lay-up tables Down draft Floor or bench type grinding, welding, low fog painting Side draft Some open surface tanks Shakeout grates Small canopy Wall fan (hood) Cool to warm processes Some plastics operations Feed mill used with caution, especially in new installations they can cause a false sense of security and re- sult in excessive expense when it is found neces- sary to modify or replace inadequate ventilation equipment. References 1. AMERICAN IRON and STEEL INSTITUTE. Committee on Industrial Hygiene, Steel Mill Venti- lation, AISI, 150 East 42nd Street, New York, New York, 1965. 2. AMERICAN CONFERENCE OF GOVERNMEN- TAL INDUSTRIAL HYGIENISTS. Committee on Industrial Ventilation, Industrial Ventilation — a Manual of Recommended Practice, ACGIH, P.O. Box 453, Lansing, Michigan, 12th Edition, 1972. . DALLAVALLE, J. M. “Velocity Characteristics of Hoods Under Suction,” ASHVE Transactions, 38, p. 387, 1932. BRANDT, A. D. Industrial Health Engineering, John Wiley and Sons, New York, New York, 1947. 608 5. SILVERMAN, L. “Velocity Characteristics of Nar- row Exhaust Slots.” Industrial Hygiene and Toxi- cology J., 24, 267, 1942. ALDEN, JOHN L. Design of Industrial Exhaust Systems, The Industrial Press, New York, New York, 1949. CHAPTER 42 DESIGN OF VENTILATION SYSTEMS Engineering Staff* George D. Clayton & Associates INTRODUCTION Not too many years ago the design of venti- lation systems was an art, but with the accumula- tion of knowledge today it has “come of age” and may be classified as an engineering science. Vari- ous “rule-of-thumb” methods have been replaced with new rules based on theory, supported by ex- perimentation, and validated by experience. When properly designed and installed, a good ventilation system often can add to productivity and the gen- eral well-being of workers. In some cases, a sys- tem with adequate collection devices can recover enough valuable materials to pay for itself in a reasonably short time. It should be emphasized that in industrial hygiene the primary purpose for designing a ven- tilation system is to protect the health and well- being of workers. The design of any ventilation system should include consideration of materials that will with- stand normal mechanical abuse inherent to the en- vironment in which it is operated. Frequently, extra design capacity in fans, control equipment and motors which allows for future expansion of the system at minimum cost is desirable. There are generally two types of ventilation systems: (1) general, and (2) local exhaust. For the purpose of this chapter make-up air is con- sidered part of local exhaust ventilation. GENERAL VENTILATION General ventilation refers to the commonly encountered process of flushing a working en- vironment with a constant supply of fresh air. General ventilation differs from local ventilation in that it is a dilution process rather than strictly an exhausting process. General ventilation may be accomplished by natural infiltration of air, or with the aid of some type of air moving device. Office Buildings For office buildings to maintain comfortable work conditions, the proper environmental at- mosphere must be achieved. This usually occurs as a result of a properly designed general ventila- tion system. Whereas the design criteria for local exhaust systems are relatively clear-cut, this is not necessarily the case for general systems. Here de- sign is based on human comfort requirements, noise considerations and ease of distribution of fresh air. *The following staff members participated in writing this chapter: Donald K. Russell, Quentin Keeny, John E. Mutchler and George D. Clayton. 609 Worker Comfort. The comfort of office workers is subject to the following environmental condi- tions: 1. Air temperature; 2. Humidity; 3. Radiant heat; 4. Concentrations of tobacco smoke; 5. Concentration of body odors; and 6. Air movement. Before designing any general ventilation system, the aforementioned conditions must be measured or estimated. Then a fresh air flowrate can be calculated which will reduce undesirable air quali- ties to tolerable levels. Comfort Zone. Various indices have been devised by investigators to describe a “comfortable” en- vironment. A comfort chart has been developed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. which uses wet- and dry-bulb air temperatures as parameters (See Figure 42-1). The comfort zone is that com- bination of environmental conditions which is thermally neutral to the human body. Specifically, the comfortable temperature range for office work- ers is 68 — 74°F during the winter months and 75-82°F in summer with moderate humidities. A summary of minimum ventilation requirements for various conditions is included in Table 42-1. Odor Control. Air exchange rates are dictated in part by the concentration of body and tobacco odors in a room. These concentrations are af- fected by air supply, space allowed per person, odor absorbing capacity of the air conditioning process, temperature and relative humidity. Conditioning of Air. Comfort conditions can be met by the proper selection of air conditioning equipment. Such equipment can maintain proper conditions of temperature, humidity, and odor levels when comfort indices have been determined. The subject of air heating and conditioning is be- yond the scope of this chapter; however, the reader is urged to consult the references listed at the end of this chapter, specifically 5, 6 and 7, for more information. To summarize briefly, the criteria for design calculations for general office ventilation systems include the determination of worker comfort, zone parameters (temperature, humidity), tolerable odor levels, space allowed per person in room and the odor-absorbing capacity of the air conditioning unit to be installed. In addition, it should be stressed that fan noise is an extremely important 90 1 | | T AIR MOVEMENT OR TURBULENCE 15 TO 25 FEET PER MINUTE é 9 80 & / \ XE ER, 1 W N NY] S are h R 70 3 RIN < N NA XN AS @ R KOC Ww Q 5 Pd VAS re OA XX NX NG SPN x £3 KAP E AE Wy Ww TWA YR (8 ~ 0% 045 KR APRN AR ol Wi 0 vi AUS ZU XS 5 3 OE N Q | OS SY \ V 52 OSPR {gx ~ A NO ANMSHAEA WV 3 \ \A AN 3 GN 0 so AT NN NN -— po -— 1 - oo" OM TD > ANA ZO os | vib 60 A) \ 40f + 7) 59 ih 50 60 70 80 90 100 DRY BULB TEMPERATURE F American Conference of Governmental Industrial Hygienists — Committee on Industrial Ventilation: Industrial Ventilation — A Manual of Recommended Practice, 12th Edition. Lansing, Michigan, 1972. Figure 42-1. Comfort Chart for Still Air (from: Industrial Ventilation Manual). Notes: 1. Ef- fective Temperature (dashed) lines indicate sensation of warmth immediately after entering conditioned space. 2. Solid lines 3, 4, 5, and 6 indicate sensations experienced after three hour occupancy. 3. Both sets of curves apply to people at rest and normally clothed. 610 TABLE 42-1. Summary of Minimum Outdoor Air Requirements for Ventilation Under Various Conditions Type of occupants Requirements Requirements Air space based on based on per person primary* impressions of (cubic feet) impresso~e occupants (cfm per person)(cfm per person) Heating season with or without recirculation. Air not conditioned. Sedentary adults of average socio-economic status Laborers Grade school children of average class Grade school children (low income) Grade school children (medium income) Grade school children (high income) 100 25 23 200 16 11 300 12 vine 500 7 >5 200 23 N- 100 29 ruse 200 21 15 300 17 500 11 200 38 200 18 inge 100 22 vine Heating season. Air humidified by means of centrifugal humidifier. Total air circulation 30 cfm per person. Sedentary adults 200 12 Summer season. Air cooled and dehumidified by means of a spray dehumidifier. Total air circulation 30 cfm per person. Sedentary adults 200 >4% 6% *Impressions upon entering room from relatively clean air at threshold odor intensity. fCorresponding to an air quality of fair to good. i Values provisionally restricted to the conditions of the tests. “The Industrial Environment and Its Control,” J. M. DallaValle, p. N.Y. 1948. design consideration of office ventilation systems. Usually a forward-curved blade fan is chosen over the more efficient backward-curved blade fan sim- ply because of noise considerations. More de- tailed information on fans and noise problems are given in a later section of this chapter and in sev- eral references? > * + °, Industrial Buildings General ventilation systems employed in in- dustrial buildings are of two types — natural and mechanical. Natural Ventilation. The two forces which are responsible for natural ventilation are wind and thermal head. Realizing this, in the past, architects devised sawtooth and monitor type roofs to achieve maximum ventilation and lighting, although with greater use of mechanical ventilation, these build- ing designs are slowly becoming outdated. More recently, windows such as the double hung sash and center-pin-swing-hinge type have been utilized to achieve maximum natural air flow. In build- ings such as warehouses, powerhouses and pump- rooms, where few people are employed, wall or roof openings generally provide enough fresh air for good ventilation. Mushroom, gooseneck, or louvered penthouse roof ventilators are reasonably 611 105, Pitman Publishing Corporation, New York, effective supply ports regardless of wind direction. Mechanical Ventilation. Although general venti- lation by natural means is the most economical, it is limited in usefulness. Ventilation by mechan- ical devices (i.e., fans) is seldom limited, and, when used in conjunction with ductwork, air can be distributed to all parts of the building. Equip- ment and design considerations for general venti- lation systems of this type are discussed in the fol- lowing section and later in this chapter. Design Considerations. General ventilation sys- tems are used in industry in conjunction with local exhaust ventilation systems to achieve maximum effectiveness (for additional discussion see Chap- ter 39). Besides providing for a comfortable at- mosphere in which to work, general ventilation systems may be employed to control vapors within acceptable limits from organic liquids of low-level toxicity. This is successfully accomplished by dilution. Table 42-2 lists the dilution air volumes for several commonly used solvents. Threshold Limit Values (TLV) represent guides to allowable toxic material concentrations in air. When the maximum allowable concentrations of the con- taminant are known and the generation rate has been estimated, the quantity of dilution air re- TABLE 42-2. Dilution Air Volumes for Vapors (based on 1971 TLV Values which are shown as ppm in parentheses) Cu. ft. of air (STP) required for dilution to TLV* Liquid Per Pint Evaporation Per Pound Evaporation Acetone (1000) 5,500 6,650 n-Amyl acetate (100) 27,200 29,800 Isoamyl alcohol (100) 37,200 43,900 Benzol (25) Not Recommended n-Butanol (butyl alcohol) (100) 44,000 52,200 n-Butyl acetate (150) 20,400 22,200 Butyl cellosolve (50) 61,600 65,600 Carbon disulfide (20) Not Recommended Carbon tetrachloride (10) Not Recommended Cellosolve (2-Ethoxyethanol) (200) ** 20,800 21,500 Cellosolve acetate (2-ethoxyethyl-acetate) (100) 29,700 29,300 Chloroform (50) ** Not Recommended 1-2 Dichloroethane (50) ** (ethylene dichloride) Not Recommended 1-2 Dichloroethylene (200) 26,900 20,000 Dioxane (100) 47,300 43,900 Ethyl acetate (400) 10,300 11,000 Ethyl alcohol (1000) 6,900 8,400 Ethyl ether (400) 9,630 13,100 Gasoline Requires special consideration Methyl acetate (200) 25,000 26,100 Methyl alcohol (200) 49,100 60,500 Methyl butyl ketone (100) 33,500 38,700 Methyl cellosolve (25) Not Recommended Methyl cellosolve acetate (25) Not Recommended Methyl ethyl ketone (200) 22,500 26,900 Methyl isobutyl ketone (100) 32,300 38,700 Methyl propyl ketone (200) 19,000 22,400 Naptha (coal tar) (100) Naptha (petroleum) (500) 30,000-38,000 Requires special consideration 40,000-50,000 Nitrobenzene (1) Not Recommended n-Propyl acetate (200) 17,500 18,900 Isopropyl alcohol (400) 13,200 16,100 Isopropyl ether (500) ** 5,700 7,570 Stoddard solvent (200) 1,1,2,2-Tetrachloroethane (5) 15,000-17,500 20,000-25,000 Not Recommended Tetrachloroethylene (100) 39,600 23,400 Toluol (Toluene) (200) ** 19,000 21,000 Trichloroethylene (100) 45,000 29,400 Xylol (xylene) (100) 33,000 36,400 *The tabulated dilution air quantities must be multiplied by the selected K value. **See Notice of Intended Changes in TLV List for 1971. The K value is merely a safety factor between 3 and 10 (usually 6) which is multiplied by the dilution air quanti- ties to assure air concentrations well below the TLV. © “Industrial Ventilation — A Manual of Recommended Practice” 12th Edition, American Conference of Govern- mental Industrial Hygienists, Committee on Industrial Ventilation, Lansing, Michigan, 1972. 612 quired may be calculated using the equations given in Chapter 39. Although this method of ventila- tion may be used effectively to deal with low tox- icity gases and vapors, it is not advisable to treat particulate contaminants or toxic vapors or gases with general ventilation. Whenever possible, local exhaust systems should be used to minimize the total amount of hazardous material released. LOCAL EXHAUST VENTILATION Local exhaust systems are primarily concerned with contaminant control at the point of emission and/or dispersion (for additional information see Chapter 41). As mentioned earlier, local exhaust systems usually complement (rather than replace) general ventilation systems. The components of all local exhaust systems are similar, but the total design of each system is unique. The components include a hood, ductwork, an air moving device, an air cleaning device, and special fittings. The processes to which these components are applied are numerous and varied. Therefore the size, shape and material of construction of each com- ponent will vary with the contaminated air being handled. Hood Design The design of any local exhaust system begins with the proper selection of an exhaust hood. Over the years, many types of hood designs have evolved, with only one purpose in mind — to confine or capture the contaminant with a mini- mum rate of air flow into the hood. In most in- stances, the more complete the hood enclosure, the more economical and effective the installation will be. Exhaust hoods are designed to work in one of two ways: (1) they can induce an air move- ment which draws the contaminant into the hood or (2) they can enclose the contaminant source and induce an air movement which prevents the contaminant from escaping the enclosure. In either case, a certain air velocity in front of the hood is required for effective removal of contamination. This required air velocity in front of the hood must be determined before the exhaust system can be designed. Unfortunately, the determination of required air velocity is not subject to direct and exact evaluation. In the past, three methods have been used to approximate a required velocity: (1) eval- uation of and comparison with existing operations, (2) experimental tests, and (3) calculations based on theoretical air requirements. These methods and practical experience enable the design engineer to estimate a required air velocity in most cases. Tables 41-1 and 42-3 are helpful for estimating required control velocities. Hood types. Exhaust hoods can be categorized as enclosures, receiving hoods, or exterior hoods. Enclosures, such as paint-spray booths, sur- round the point of emission either completely or partially. They are the most effective hoods to use, but they are seldom utilized for any manual operations where workers must also be enclosed. Receiving hoods are used on processes where contaminants may be conveniently “thrown” into the hood. For example, inertial forces carry air 613 contaminants from a grinding wheel into a hood located in the pathway of the particles. If the hood cannot be located directly 1. t.i2 path of the escaping particles, baffles or shields may be placed across the line of throw of the particles to destroy their kinetic energy. Then, lower air velocities will suffice to capture and carry them into the hood. Unlike enclosures and receiving hoods, exterior hoods must capture air contaminants that are generated from a point outside the hood. Exterior hoods require the most air to control a given proc- ess, are most sensitive to external conditions, and thus are the most difficult to design. Hood Design Considerations. Before designing a hood, several principles should be considered. Some of the most important ones are listed below: a. An attempt should be made to minimize or eliminate all air motion in the area of the contaminant source. This will reduce the amount of air needed to be exhausted and subsequently reduce system power and equipment requirements. b. Air currents which necessarily exist should be utilized by the hood whenever possible. c. The hood should enclose the process as much as possible without endangering workers’ safety. d. When enclosure is impractical, the hood should be located as close to the con- taminant source as possible. The air ve- locity created by an exhaust hood varies inversely with the square of the distance for all but long, slot-type hoods. e. The hood should be located so that the contaminant is removed away from the breathing zone of the worker. f. The use of flanges and baffles should be considered. Flanges can increase hood effectiveness and may reduce air require- ments by 25%. g. Use of a hood larger than required should be considered. Large hoods can reduce danger of “spills” by diluting them rapidly to safe levels. It has also been shown that small hoods require higher capture veloci- ties to be as effective as large hoods. Exhaust Duct Design The design of an exhaust duct system is the second stage of a total ventilation system design. Initially, a rough duct layout should be prepared which shows branches, expansions, contractions, elbows, air moving and air cleaning devices. Us- ing this as a basis, pressure drop calculations can be made and duct sizing can be estimated. Transport Velocity. At this stage of design, the required exhaust rate for each hood has been de- termined. The problem now is to determine the minimum transport-velocity — i.e., the air velocity required to move the contaminant through the duct system. Information pertaining to transport ve- locities may be obtained by the following methods: (1) by reference to data published in the litera- ture (See Tables 42-4 and 42-5). (2) by actual laboratory tests with the material to be conveyed, or (3) by theoretical considerations involving particle size, density and shape. TABLE 42-3 Minimum Control Velocities and Exhaust Rates for Typical Specific Operations Where both control velocity and exhaust rate are given, the air volume exhausted shall be based.on the method which requires the larger volume. Control Velocity, Exhaust Rate, Operation fpm Control Velocity Basis cfm Exhaust Rate Basis Abrasive blasting Cabinets 500 Openings in enclosure Re Rooms 60-100 Downdraft in room —_ Bagging Paper bags 100 Openings in enclosure pe Cloth bags 200 Openings in enclosure re Pulverized sand 400 Point of origin _ Barrel filling 100 Point of origin 100 Per sq. ft. barrel top, semi-enclosure Bin and hopper 150-200 ~~ Openings in enclosure 0.5 Per cu. ft. bin volume Belt conveyors Transfer point Belt speed <200 fpm 150 Openings in enclosure 350 Per ft. belt width >200 fpm 200 Openings in enclosure 500 Per ft. belt width Belt wiper 200 Per ft. belt width Bottle washing 150-250 Face of booth or enclosure openings — Bucket elevators ee 100-200 Per sq. ft. casing cross section Tight casing required Core sanding lathe 100 Point of origin — Foundry screens Cylindrical 400 Openings in enclosure 100 Per sq. ft. circular cross section Flat deck 150-200 Openings in enclosure 25-50 Per sq. ft. screen area Foundry shakeout Enclosure 200 Openings in enclosure 200 Per sq. ft. grate area Side draft ee 350-400 Cool castings per sq. ft. deal 00500 grate area Downdraft 400- Hot castings 250 Cool castings per 5. &, 600 Hot castings grate area Furnaces, melting Aluminum 150-200 Openings in enclosure — Brass 200-250 Openings in enclosure — Granite cutting Hand tool 200 Point of origin no Surfacing machine 1500 Point of origin — All tools 1500 Face of enclosing hood Grinding General —_— See applicable American National Standards 200 Per sq. ft. plan area of bench downdraft grille Disc and portable ee 400 Per sq. ft. plan area of floor downdraft grille Swing frame 150 Face of booth Kitchen range 100-150 Face of canopy _ Laboratory hood 100-150 Face of hood, door open. Less for “air supplied” hoods — Metallizing Toxic material 200 Face of booth Additional respiratory protection required Nontoxic 125 Face of booth — Nontoxic 200 Point of origin — Mixer 100-200 Openings in enclosure — 614 TABLE 42-3 Continued Minimum Control Velocities and Exhaust Rates for Typical Specific Operations Where both control velocity and exhaust rate are given, the air volume exhausted shall be based on the method which requires the larger volume. Control Velocity Exhaust Rate, Operation fpm Control Velocity Basis cfm Exhaust Rate Basis Packaging machines 100-400 Openings in enclosure 25 Per sq. ft. plan area of enclosure 50-150 Face of booth 75-150 ~~ Downdraft es Paint spray 100-200 Face of booth ee Pharmaceutical coating pans 100-200 At opening of pan — Quartz fusing 150-200 Face of booth _— Rubber calendar rolls 75-100 Openings in enclosure — Silver soldering 100 Point of origin ro Steam kettles 150 Face of canopy —_—— Tanks Open surface 50-150 See applicable American National Standards Closed 150 Manhole or inspection opening Welding, arc 100-200 Point of origin —_— 100 Face of booth —_— Woodworking See applicable American National Standards TABLE 42-4 each junction of two air streams the static suction Classification of Transport Velocities for Dust Collection Minimum Transport Material Velocity, fpm Very fine, light dusts 2000 Fine, dry dusts and powders 3000 Average industrial dusts 3500 Coarse dusts 4000-4500 Heavy or moist dust loading 4500 and up The minimum transport velocity is not used for duct design; rather, a design velocity is esti- mated which includes a safety factor based on practical considerations. These include consider- ations for material buildup, duct damage, corro- sion, duct leakage, etc. As shown in Tables 42-4 and 42-5, transport velocities for dust-laden air vary from 2000 fpm to 4500 fpm or higher.® Balance Methods. After the preliminary duct lay- out has been made, the duct system pressure losses can be calculated. Two methods are used to “bal- ance” the system — that is, adjust the duct de- sign so that the total system will function properly. Each method has advantages and disadvantages as described below. The first is known as the “Static Pressure Bal- ance” method. Some texts® refer to this as “Air Balance without Blast Gate Adjustment” because it is a procedure for achieving desired air flow without the use of dampers or blast gates. At 615 necessary to produce the required flow in one stream must match the static suction needed to produce the required flow in the other stream. Because there are no blast gates for workers to tamper with, this method is usually selected for use where highly toxic materials are to be con- trolled. The other method is “Balance with Blast Gates.” This type of system uses adjustable blast gates to balance the system and thus achieve the desired air flow at each hood. Calculations begin at the branch of greatest resistance. Pressure drops are calculated through the various sections of the main, on up to the fan. This design method is theoretically superior to the “Static Pressure Bal- ance” method in that it is flexible enough to allow air volume changes without duct redesign. How- ever, if blast gates are tampered with by unauth- orized personnel, ducts may become plugged and the exhaust system rendered ineffectual. Pressure Losses. Pressure losses in an exhaust duct system occur as a result of (1) hood entry, (2) special fittings, (3) duct friction, and (4) air cleaning devices. Various methods and charts are available to aid in estimating pressure losses from these sources.”® Because most charts and refer- ence tables are based on standard air (0.075 Ib./cu. ft.) corrections for altitude, temperature, and density must be made if conditions vary greatly from standard (See Table 42-6). Design calculations are based on volumes increased by the reciprocal of the density factor. System pres- sure losses will decrease directly as d, the density factor. TABLE 42-5 Examples of Transport Velocities Material, Operation, or Industry Velocity, fpm Minimum Transport Material, Operation, or Industry Minimum Transport Velocity, fpm Abrasive blasting 3500-4000 Aluminum dust, coarse 4000 Asbestos carding 3000 Bakelite molding powder dust 2500 Barrel filling or dumping 3500-4000 Belt conveyors 3500 Bins and hoppers 3500 Brass turnings 4000 Bucket elevators 3500 Buffing and polishing Dry 3000-3500 Sticky 3500-4500 Cast iron boring dust 4000 Ceramics, general . : Glaze spraying 2500 Brushing 3500 Fettling 3500 Dry pan mixing 3500 Dry press 3500 Sagger filling 3500 Clay dust 3500 Coal (powdered) dust 4000 Cocoa dust 3000 Cork (ground) dust 2500 Cotton dust 3000 Crushers 3000 or higher Flour dust 2500 Foundry, general 3500 Sand mixer 3500-4000 Shakeout 3500-4000 Swing grinding booth exhaust 3000 Tumbling mills : 4000-5000 Grain dust 2500-3000 Grinding, general 3500-4500 Portable hand grinding 3500 Jute Dust 2500-3000 Lint 3000 Dust shaker waste 3200 Pickerstock 3000 Lead dust 4000 with small chips 5000 Leather dust 3500 Limestone dust 3500 Lint 2000 Magnesium dust, coarse 4000 Metal turnings 4000-5000 Packaging, weighing, etc. 3000 Downdraft grille 3500 Pharmaceutical coating pans 3000 Plastics dust (buffing) 3800 Plating 2000 Rubber dust Fine 2500 Coarse 4000 Screens Cylindrical 3500 Flat deck 3500 Silica dust 3500-4500 Soap dust 3000 Soapstone dust 3500 Soldering and tinning 2500 Spray painting 2000 Starch dust 3000 Stone cutting and finishing 3500 Tobacco dust 3500 Woodworking Wood flour, light dry sawdust and shavings 2500 Heavy shavings, damp sawdust ~~ 3500 Heavy wood chips, waste, green shavings 4000 Hog waste 3000 Wool 3000 Zinc oxide fume 2000 Material in Tables 42-3, 42-4 & 42-5 is reproduced with permission from ANSI Z9.2 copyright 1971, by the American National Standards Institute, copies of which may be purchased from American National Standards Institute at 1430 Broadway, New York, N.Y. 10018. Hood Entry Losses A loss in pressure occurs when air enters a hood opening. This loss is indicated by the co- efficient of entry for the hood, C.. This coefficient represents the ratio of actual to theoretical flow; ie, C.=1.0 for a theoretically “perfect” hood. Several examples of entry coefficients are shown in Figure 42-2. The design equation used in determining the static suction at the hood throat is derived from the classical orifice theory. For standard air it becomes: Q=4005 A C.Y SP, (1) where: Q =air flow rate, ft*/min. A =area of opening, ft* C.=entry coefficient, dimensionless 616 SP, = static suction at hood throat, in. w.g. Static suction, SP, is related to hood entry loss according to the following equation: SP,=h.+ VP (2) where: VP = velocity pressure in throat, in. w.g. h. =hood entry loss, in. w.g. Velocity pressure (for standard air) may be calcu- lated using the following equation: 0s) 4005 3) where: VP =velocity pressure, in. w.g. V =air velocity, fpm ve=( Letting F be the fraction of the throat velocity [7] SQuARE_ To ROUND TAPER DESIRABLE STANDARD GRINDER HOOD Ce= 0.78 ~] i TRAP OR SETTLING CHAMBER Ce = 0.63 (APPROX) (— DIRECT BRANCH- BOOTH Ce =0.82 R=D/2 NE 4 BOOTH PLUS ROUNDED ~ DOUBLE (INNER cone) HOOD Ce =0.70 (APPROX) ee SHARP-EDGED ORIFICE Ce = 0.60 PLAIN DUCT END Ce = 0.72 7 FLANGED DUCT END Ce= 0.82 CH — ORIFICE PLUS FLANGED DUCT (MANY SLOT TYPES) Ce =0.55 (WHEN DUCT pr: ENTRANCE VELOCITY = SLOT VELOCITY) Ce = 0.97 American Conference of Governmental Industrial Hygienists — Committee on Industrial Ventilation: Industrial Ventilation — A Manual of Recommended Practice, 12th Edition. Lansing, Michigan, 1972. Figure 42-2. Hood Entry Loss Coefficients. Air Density Correction Factor, d TABLE 42-6 Sea —1000 Level _ Altitude, ft. 1000 2000 3000 4000 S000 6000 7000 8000 9000 10,000 Barometer .H& 3102 29.92 28.86 27.82 26.82 25.84 2490 23.98 23.09 2222 21.39 20.58 “Wg 422.2 407.5 3928 378.6 365.0 351.7 3389 3264 3143 302.1 291.1 280.1 Air Temp. —40 1.31 126 1.22 1.17 1.13 1.09 1.05 1.01 097 093 090 0.87 F 0 1.19 115 1.11 1.07 1.03 099 095 091 0.89 085 0.82 0.79 40 1.10 1.06 1.02 099 095 092 0.88 0.85 082 079 0.76 0.73 70 1.04 1.00 096 093 0.89 0.86 0.83 080 077 0.74 0.71 0.69 100 0.98 095 092 0.88 0.86 0.81 078 0.75 0.73 0.70 0.68 0.65 150 0.90 0.87 0.84 0.81 0.78 0.75 0.72 0.69 0.67 0.65 0.62 0.60 200 0.83 0.80 0.77 0.74 0.71 0.69 0.66 0.64 0.62 0.60 0.57 0.55 250 0.77 0.75 0.72 0.70 0.67 0.64 0.62 0.60 0.58 0.56 0.58 0.51 300 0.72 0.70 0.67 0.65 0.62 0.60 0.58 0.56 0.54 0.52 0.50 0.48 350 0.68 0.65 0.62 0.60 0.58 0.56 0.54 052 0.51 0.49 0.47 045 400 0.64 0.62 0.60 0.57 0.55 0.53 0.51 0.49 0.48 046 0.44 042 450 0.60 0.58 0.56 0.54 0.52 0.50 048 0.46 045 043 0.42 0.40 500 0.57 0.55 0.53 0.51 0.49 047 045 0.44 043 041 0.39 0.38 550 0.54 0.53 0.51 0.49 047 045 044 042 041 039 0.38 0.36 600 0.52 0.50 0.48 0.46 045 0.43 041 040 0.39 0.37 035 0.34 700 0.47 046 044 043 0.41 039 038 037 035 034 033 0.32 800 0.44 0.42 040 0.39 0.37 036 035 033 032 031 030 029 900 0.40 0.39 0.37 0.36 0.35 0.33 0.32 031 0.30 0.29 028 0.27 1000 0.37 0.36 0.35 0.33 0.32 031 030 029 0.28 027 0.26 0.25 Standard Air Density, Sea Level, 70 F=0.075 1b./ft.? “Industrial Ventilation — A Manual of Recommended Practice” 12th Edition, American Conference of Govern- mental Industrial Hygienists, Committee on Industrial Ventilation, Lansing, Michigan, 1972. > pressure loss in entry, and combining equations, he= (Fu) (VP) (4) Whenever a hood is made combining basic shapes, Equation 4 applies only to the parts and not to the hood as a whole. Losses from Special Fittings Pressure is lost when air travels through the various fittings in an exhaust system. Elbows, branch entries, enlargements and contractions are the main fittings to be considered. Pressure loss across these fittings is conveniently expressed as a fraction of the velocity pressure, VP. Tables giv- ing pressure regain and loss values (fractions) for expansions and contractions are included, see Ta- bles 42-7 and 42-8." Resistance of elbows and branch entries may also be expressed in terms of equivalent feet of straight duct (of the same diameter) that will pro- duce the same pressure loss as the fitting. An example table (Table 42-9) is included. Duct Friction Losses Many graphs are available which give friction losses in straight ducts. However, most graphs are 618 based on new, clean duct. The chart included here (see Figure 42-3) allows for a typical amount of roughness, and is more practical for use in gen- eral application. Four quantities are plotted on the chart. If any two are given, the other two can be read directly from the chart. Additional Pressure Losses In addition to the pressure losses mentioned above, the pressure drop across collection equip- ment (if used) must be known in order to insure proper operation. This can vary widely, but us- ually data are available from the manufacturer to minimize guess work. Where data are unavail- able, comparisons with known values for similar equipment should be used. Dust collection equip- ment is covered more extensively in Chapter 43. Design Suggestions. A few suggestions pertaining to duct design and location are listed below: a. Duct mains should be arranged in such a way that smaller branches enter the main near the high-suction end — closer to the fan inlet. b. Long runs of small diameter duct should be avoided. .0l .02 03 04 .06 08 || 2 3 4 6 8 | 2 3.4 6 8 10 2000 C-DTT RA > 2% re) o|| o| o oo ot oH,04+-0 0 o 1000 900 800 700 600 500 400 Ol Oo o 200 100 90 80 70 60 CU FT OF AIR PER MINUTE 50 40 30 -\ 3 20 ® ° a. = © ¥ oo +aHe-0lol-—2 12 10 B® Oo’ Oo | 0 |0 2 21 3 21% 92 395%] | 0 .02 03 04 06 08 . 2 3 4 6 8 | 2 3 4 6 810 FRICTION LOSS IN INCHES OF WATER PER 100 FT Figure 42-3. Friction of Air in Straight Ducts for Volumes of 10 to 2000 Cfm. ‘(Based on Standard Air of 0.075 Ib per cu ft density flowing through average, clean, round, galvanized metal ducts having approximately 40 joints per 100 ft.) Caution: Do not extrapolate below chart. 619 TABLE 42-7. Static Pressure Regains for Expansions A ~~ 40min eli - [73 . — oo Within duct At end of duct Regain (R), fraction of VP difference Regain (R), fraction of inlet VP raper angle Diameter ratios Dz/D; ops) jaichh Diameter rotios 5/0, degrees |.25:1| 15:1 |1.75:1| 2:1 |2.5:/ L/D L2:1 | 13:1 | 19:1 | 15:1 16:1 | L7:1 3/2 |0.92 |088 (084 |(08/ [0.75 0:1 037 (039 |0.38 (035 |03/ (0.27 5 088 (084 |0.680 | 076 |0.68 1.5 0.39 |046 (0.47 |046 [0.44 |0.9/ 0 0.85 |Q76 |0.70 |0.63 (0.53 20:/ 0.42 |049 |0.52 0.52 |0.5! |099 15 0.83 |070 |062 (0.55 (043 3.0:/ 044 052 (0.57 |0.59 |0.60 |0.59 20 08! (0.67 (0.57 (048 |0.43 4.0:/ 045 [0.55 (0.60 |0.63 |063 |Q64 25 080 |065 |Q53 (0.44 |0.28 35.0: 047 |a56 |0.62 (0.65 |0.66 |0.68 30 0.79 (0.63 |0.5/ (04! (0.25 75: 048 |0.58 (0.64 |0.68 [0.70 |0.72 Abrupt 900.77 |0.62 |0.50 | 0.40 (0.25 | | Where: SA = SR - RIVE)® Where: SR = SR +RIVR-VR) ® hen SB =0 (atmosphere) SK will be () The regain (R) will only be 70% of value shown above when expansion follows a disturbance or elbow (including a fan) by less than 5 duct diamelers. “Industrial Ventilation — A Manual of Recommended Practice” 12th Edition, American Conference of Govern- mental Industrial Hygienists, Committee on Industrial Ventilation, Lansing, Michigan, 1972. c. Extending an exhaust system to reach an isolated hood increases fan power con- sumption. To avoid this problem, it may be more economical to install a separate system for that hood. d. If possible, locate the fan near the middle of an array of exhaust hoods rather than at one end. e. If long rows of equipment are to be served, the main header duct should be located near the middle of the system to equalize runs of branch duct. f. Ductwork should be located so that it is readily accessible for inspection, cleaning and repairs. : g. Ductwork should be out of the way of elevators, lift-trucks, cranes, etc., to avoid mechanical damage. h. Duct cleanout areas should be provided. AIR MOVING DEVICES Various power-driven machines are capable of creating the required flow of air in an exhaust sys- tem. These machines are generally known as “air moving devices.” Included under this general head- ing are fans, turbo-compressors, ejectors and posi- tive displacement blowers. As mentioned in Chapter 39, the air moving device manufacturer, to gain acceptance for his product, generally must earn membership in the Air Moving and Conditioning Association (AMCA). Membership is contingent upon sub- jecting his product to the AMCA test code for air moving devices. In addition, the manufacturer must furnish a prospective buyer of his product, certain data relative to the product and its applica- tions. This information should include the follow- ing. ¢ 1. Classification according to static pressure limitations Multirating tables — performance curves Specifications — AMCA standards Drive arrangement Designations for rotation and discharge Dimensional data Materials and methods of construction Sound level ratings Accessories 10. Temperature limitations. Fans are the most commonly used exhausters in the field of industrial ventilation. They are di- vided into two main classifications: axial flow or propeller type, and radial flow or centrifugal type. A summary of fan types is given in Chapter 39. A list of fan types appears below. XIAN R LN Axial Flow Fans Centrifugal Fans 1. Propeller 1. Radial Wheel 2. Duct 2. Forward-Curved 3. Tube Axial Blade 4. Vane Axial 3. Backward-Inclined 5. Axial Centrifugal Blade 4. Airfoil 620 TABLE 42-8. Static Pressure Losses for Contractions [——— — / 3 @ a — Tapered contraction SR =SR-(VR -VR)-LIVR-VR) Taper ongle a 2 2 L(loss) 5 0.05 10 0.06 15 0.08 20 0.10 25 o./l 30 0./3 45 0.20 60 o30 over 60 Abrupt contraction Note: In calculating SP for expansion or conteaction use algebraic signs: VP is(4) ond beso SP is (+) in discharge duct from fon SP is (=) In inlet duct to fon @ -@ Abrupt contraction SR=SR-(VR- ve)-K(ve) Ratio “74, | x 0.1 0.48 0.2 0.46 0.3 0.42 04 0.37 0.5 0.32 06 026 07 0.20 A =guct area, sq ft “Industrial Ventilation — A Manual of Recommended Practice” 12th Edition, American Conference of Govern- mental Industrial Hygienists, Committee on Industrial Ventilation, Lansing, Michigan, 1972. Turbo-compressors and positive displacement blowers are used in systems having relatively low volume and high velocity and high static pressure. Turbo-compressors are typically used for indus- trial vacuum-cleaning systems where air must be transported through small diameter ducts at high velocities. Positive displacement blowers are used where a fixed quantity of air is required to be supplied or exhausted through an increasingly long duct, as in pneumatic conveying. Both exhausters can handle only clean, filtered air, due to the rigid design tolerances of their moving parts. Ejectors are used in exhaust systems handling gases which are too hot, corrosive, abrasive, or sticky to be handled by a fan. Because ejectors are mechanically very inefficient, they require a much higher horsepower expenditure than equiva- lent fan installations. Fan Laws and System Curves Before selecting the proper fan, it is necessary to be familiar with the fan laws and system curves. These are listed in Table 42-10. A fan or system curve shows graphically all possible combinations of volumetric flow and static 621 pressure for a given system. Because the fan and system can each operate only at a point on their own curve, the combination can operate only where their curves intersect. See Figure 42-4) If the fan speed is changed, the operating point will move up toward the right (increased speed) or down toward the left (decreased speed) on the system curve. (See Figure 42-5) Fan Selection A fan is chosen on the basis of its character- istics and the requirements of the system to which it will be applied. Each fan is characterized by five features: 1) volume of gas flow, 2) pressure at which this flow is produced, 3) speed of rota- tion, 4) power required, and 5) efficiency. These quantities are measured by the fan manufacturer with testing methods sponsored by the Air Mov- ing and Conditioning Association or the American Society of Mechanical Engineers. Test results are plotted to provide the characteristic fan curves supplied by most fan manufacturers. The designer chooses the fan he needs from multirating tables. Each different entry in the table has a unique performance characteristic — TABLE 42-9. Equivalent Resistance in Feet of Straight Pipe | — 20minf~— . Ye 0 of— Xe . » A Pipe ties of ay O 750 | 200 | 250 | 30° 45° 3" 5 3 3 2 3 4" 6 4 4 3 5 5" 9 6 5 4 6 6" 12 7 6 5 7 7" 13 9 7 6 9 8" 15 10 8 7 11 0" 20 14 11 9 14 12" 25 7 14 11 17 14" 30 2/ 7 13 2/ 6" 36 24 20 16 25 18" 4/ 28 23 18 28 20" 46 32 26 20 32 24" 57 40 32 30" 74 5/ 4/ 36" 93 64 52 40" 105 72 59 48" 130 89 73 * For 60° elbows — 0.67 x loss for 90° 45° elbows — 0.5 x loss for 90° 30° elbows — 0.33 x loss for se “Industrial Ventilation — A Manual of Recommended Practice” 12th Edition, American Conference of Govern- mental Industrial Hygienists, Committee on Industrial Ventilation, Lansing, Michigan, 1972. that is, each entry describes a corresponding per- formance curve. Usually the fan required will have characteristics between two values given in the table. A linear interpolation is necessary to determine the right fan size, speed, horsepower, etc. needed to do the job. (See Table 42-11.) Noise Vibration Control The possibility of noise problems arising in exhaust systems should not be overlooked at any stage of the design process. If the system has been designed improperly, or if the wrong fan has been chosen, it is likely that a noise or vibration prob- lem will arise. It is usually a simple matter to foresee such problems and prevent them from oc- curring. The potential source of noise in any exhaust system is the fan. It is a pliable piece of equip- ment, is often forced to operate at high speeds, and is inherently prone to vibrate. Fan vibration is of two types: aerodynamic or mechanical. Aerodynamic vibration varies distinctly with the volume of air drawn through the fan. This usually occurs when fans are operated at a point to the left of the peak of their static pressure curves. If the system pressure estimate is low, a smaller fan than actully needed may be specified, and forced to operate at a point other than the one for which it was selected. This type of vibration may also be caused by poor inlet connections to the fan. If possible, inlet boxes and inlet elbows should be avoided, or at least vaned to reduce fan inlet spin. (When air is forced to flow through a sharp turn as it enters the fan, it tends to load just part of the fan wheel and pulsation can occur.) Similarly, good outlet design will minimize pulsa- tion. Mechanical vibration cannot be foreseen by the design engineer except in cases where the structural support for the fan is inadequate. Fre- quently fans are supported on mounts having a natural vibration frequency near that of the fan. Under such conditions vibration is almost impos- sible to stop. The best support to use is an iner- tial mass such as a concrete pad supported by steel springs. The most common mount is the integral base — a structural steel platform built to fit TABLE 42-10. Fan Laws (Q=CFM P = Pressure) 1. Variation in Fan Speed: Constant Air Density—Constant System (a) Q: Varies as fan speed. (b) P: Varies as square of fan speed. (c) Power: Varies as cube of fan speed. 2. Variation in Fan Size: Constant Tip Speed—Constant Air Density Constant Fan Proportions—Fixed Point of Rating (a) Q: Varies as square of wheel diameter. (b) P: Remains constant, (c) RPM Varies inversely as wheel diameter. (d) Power: Varies as square of wheel diameter. 3. Variation in Fan Size: At Constant RPM—Constant Air Density Constant Fan Proportions—Fixed Point of Rating Varies as cube of wheel diameter. 2 Varies as square of wheel diameter. (c) Tip Speed: Varies as wheel diameter. (d) Power: Varies as fifth power of diameter. 622 4, Variation in Air Density: Constant Volume—Constant System Fixed Fan Size—Constant Fan Speed (a) Q Constant. (b) P Varies as density. (c) Power: Varies as density. 5. Variation in Air Density: Constant Pressure—Constant System Fixed Fan Size—Variable Fan Speed : Varies inversely as square root of density. Constant. (c) RPM: Varies inversely as square root of density. (d) Power: Varies inversely as square root of density. 6. Variation in Air Density: Constant Weight of Air—Constant System Fixed Fan Size—Variable Fan Speed (a) QO Varies inversely as density. (b) P: Varies inversely as density. (c) RPM: Varies inversely as density. (d) Power: Varies inversely as square of density. FAN SP POINT OF OPERATION CFM Figure 42-4. under the fan and motor, supported on steel spring or rubber-in-shear mounts. When the integral base is used, fan inlet and outlet vibration-elimination connections are required. In addition, a flexible conduit supplying power to the motor is essential. The type of fan chosen for an exhaust system has a great influence on noise levels. For instance, axial flow fans are louder than centrifugal, and radial blade centrifugal fans are louder than other centrifugal types. The relatively new, airfoil-blade wheel centrifugal fans are the most quiet fans available today. This type is a modification of the backwardly-inclined-blade wheel. Fans are now available with silencers to match the fan's aerodynamic characteristics. (Until re- cently fans and silencers were not designed to op- erate as an aerodynamic and acoustical unit.) Silencers impose additional resistance, the loss for which must be allowed in design calculations. In addition, streamlined duct transitions before and after the silencer must be considered. Silencers should always be installed on the clean air side of the system. Finally, flexible duct-fan connections should be considered. Whenever fans are rigidly con- nected to ducts, the system can carry the fan’s sound and vibration to remote areas. Use of duct lining can also reduce noise levels, but it is gen- erally not used on medium to high velocity sys- 623 Fan and System Curves. tems. Low velocity air conditioning systems us- ually employ linings to some degree. MAKE-UP AIR For a ventilation system to work effectively, the air exhausted from a room should be replaced in an amount at least equal to the exhausted vol- ume. For best results, the supply air should ex- ceed the exhaust volume; common practice is to allow 10% excess make-up air. The actual amount of make-up air needed depends upon the type of process involved, the amount of air ex- hausted, and the age and construction of the build- ing. ; The process to be exhausted may require low air exchange rates — six per hour or less. If ex- change rates are small enough and the building is old and not tightly constructed, there may be no need for other make-up air. However, if the process calls for high air change rates, e.g., 60 per hour, or the building is modern and tightly sealed, then make-up air is definitely required. A nega- tive pressure in a building is a common result of inadequate provision for make-up air. Importance of Make-up Air. There are many reasons for providing make-up air; the most im- portant ones are involved with the proper func- tioning of men and equipment. Make-up air should be provided for the following reasons: SP FAN CURVES Mes POINTS OF Jk OPERATION CFM Fan and System Curves. Figure 42-5. To insure that exhaust hoods operate properly. Exhaust volumes needed for proper operation of hoods may be dras- tically reduced under negative building pressures. If the exhaust system uses pro- peller fans, the flow may actually be re- versed, entering instead of exhausting. To insure proper operation of natural stacks. Some combustion exhaust stacks operate on natural drafts as low as 0.01 in. w.g. Under negative building pressures, flue gases, such as carbon monoxide, will not be able to leave via the stack. These gases may eventually infiltrate work areas and cause potential health hazards. To eliminate high velocity cross drafts. A negative pressure as low as 0.01 to 0.02 in. w.g. may result in high velocity drafts through doors and windows. Drafts can: cause discomfort for workers; bring in or stir up dust; disrupt hood operation. Drafts also tend to cause uneven heating and adverse humidity conditions as well as poor temperature control. To eliminate differential pressure on doors. A negative pressure of 0.05 to 0.10 in. w.g. is enough to make doors difficult to open. This situation is not only unpleasant for employees to deal with daily, but can 624 also lead to injury from slamming doors. The location and application of make-up air equipment also requires careful consideration. The following recommendations should be considered: 1. 2. Equipment. The fresh air intake should be located as far as possible from contaminant sources. Exhaust stacks should be tall enough and properly located so that waste air will not re-enter the plant make-up air system. Avoid the use of canopy type weather caps. By forcing air downward, weather caps on stack heads reduce the advantages gained by increasing stack height. Where necessary, make-up air should be filtered to protect equipment, prevent plug- ging, and provide maximum heat exchange efficiency. The equipment used for providing and tempering make-up air is similar to or iden- tical with that used for conventional heating and cooling systems. For heating make-up air, there are three basic equipment types: 1) heat exchang- ers using steam or hot water, 2) direct-fired heat- ers which burn gas or oil, and 3) open-flame heaters. 1. Steam heating coils are among the most common types of make-up air heaters. Moreover, if an ample steam supply is available, this type of heating may result in TABLE 42-11. Typical Fan Multirating Table Veloc- _ | . Outlet ity 1!in.SP 2in. SP Vol- veloc- pres- ume, cfm ity, 3 in. SP 4 in. SP 5 in.SP 6 in SP 7 in. SP 8 in. SP 9 in. SP sure, rmp bhp rpm bhp fpm in. WC rpm bhp rpm bhp rpm bhp rpm bhp rpm bhp rpm bhp rpm bhp 2,520 3,120 3,530 4,030 4,530 5,040 5,540 6,040 6,550 7,060 7,560 8,060 8,560 9,070 9,570 10,080 10,580 11,100 11,600 12,100 12,600 15,120 1,000 1,200 1,400 1,600 1,800 2,000 2,200 2,400 2,600 2,800 3,000 3,200 3,400 3,600 3,800 4,000 4,200 4,400 4,600 4,800 5,000 6,000 0.063 437 0.63 595 1.27 0.090 459 0.85 610 1.55 0.122 483 1.05 626 1.87 0.160 513 1.33 642 2.18 0.202 532 1.61 666 2.56 0.250 572 2.00 688 2.97 0.302 603 2.36 712 3.43 0.360 637 2.79 746 3.99 0.422 670 3.27 762 4.62 0.489 708 3.81 795 5.32 0.560 746 4.42 833 6.05 0.638 866 6.96 0.721 900 7.93 0.808 0.900 0.998 1.100 1.210 1.310 1.450 1.570 2.230 1,010 11.00 1,078 12.70 1,148 14.65 1,213 728 735 746 759 774 797 816 840 866 892 920 943 964 2.00 2.30 2.72 3.17 3.63 4.12 4.66 5.33 6.05 837 842 847 858 876 890 910 926 954 2.66 3.10 3.57 4.12 4.63 5.30 976 5.93 999 6.73 1,017 943 950 964 4.60 5.21 1,030 5.82 1,040 6.50 1,052 7.38 1,068 8.17 1,088 7.83 1,032 9.08 1,095 6.72 963 8.78 1,050 9.97 1,125 7.70 993 9.32 1,068 11.00 1,142 8.71 1,020 10.40 1,097 12.10 1,168 9.80 1,053 11.48 1,120 13.30 1,188 6.29 6.92 1,125 8.18 7.75 1,134 8.96 8.60 1,145 9.93 9.50 1,160 10.88 10.50 1,171 11.98 11.60 1,188 13.06 12.75 1,210 14.28 14.02 1,228 15.50 15.35 1,248 16.93 16.70 1,270 18.42 1,038 12.25 1,108 14.15 1,170 14.90 1,240 18.80 1,292 19.46 1,162 13.60 1,138 15.40 1,200 17.35 1,270 19.70 1,320 21.70 1,168 16.90 1,230 19.05 1,283 21.50 1,348 23.50 1,198 18.58 1,258 20.55 1,322 22.50 1,373 25.40 1,232 20.30 1,290 22.50 1,355 23.80 1,405 27.40 1,270 21.00 1,321 24.40 1,383 25.65 1,432 29.60 1,301 24.20 1,355 26.40 1,410 28.80 1,462 31.80 1,513 34.60 1,622 45.90 1,208 10.15 1,270 11.67 1,210 11.18 1,279 12.82 1,230 12.25 1,288 13.92 1,245 13.50 1,298 15.10 1,257 14.70 1,310 16.48 1,277 15.98 1,328 17.80 1,292 17.36 1,340 19.15 1,310 19.00 1,360 20.90 1,335 20.75 1,380 22.60 1,355 22.35 1,405 24.40 1,380 23.15 1,430 26.40 1,405 26.10 1,450 28.45 1,430 27.95 1,478 30.60 1,450 30.15 1,500 32.90 1,482 32.40 1,528 35.20 1,555 37.80 1,670 49.00 1,702 51.50 Design of Local Exhaust Systems “Air Pollution Engineering Manual”, Public Health Service, U.S.D.H.E,W., Cincinnati, Ohio 1967, data from New York Blower Company, 1948. the lowest fuel cost. The major drawback to steam coils is their potential to freeze and burst when the outside air is below freezing. 2. Direct fired heaters may be used where safety regulations permit (i.e., where there are no fire or explosion hazards). Here natural gas or liquified petroleum gas is burned directly in the air stream. Direct fired heating is used extensively for tem- pering make-up air. 3. Open flame, or indirect-fired heaters pro- vide a heat exchange surface between the combustion chamber and the air being heated. The gaseous products of combus- tion are sent out through a flue. The draw- back to this heating system is that conden- sation occurs on the heat transfer surface on every startup when using cold, outside air. Finally, when natural infiltration can effectively provide all the required make-up air, infra-red unit heaters can be used. Heating costs can be minimized if good en- gineering judgment is used in the make-up air supply design. The following recommendations should be considered: 1. Make-up air should be mixed with warmer building air before it reaches the work zone. 625 2. If possible, air should be delivered directly to the work zone. Make-up air should be introduced in the plant below the 8-10 foot level. In this way, the workers are constantly exposed to fresh air, and better circulation of air is achieved. 3. Sometimes it is possible to design a make- up air system that serves a dual purpose. Supply air may be used for spot cooling during warm weather, or in winter, waste heat can be recovered by cooling process equipment, motors, generators, etc. with this air. 4. Internal waste heat from a building can be recovered by using recirculated air to temper make-up air. Supply Duct Design. The principles and methods involved in designing the supply duct are the same as explained earlier for the “Balance with Blast Gate” method. The difference is that the major portion of the ductwork is on the pressure side of the fan instead of the exhaust side. Also, only clean air will be handled by this ductwork. Design velocities are based solely on econom- ical factors; minimum transport velocities are not critical here. Velocities in the range of 2000 fpm are commonly used as they are most feasible. Supply air systems are made up of rectangular ducts and branch takeoffs to save space. Light gauge construction materials are used with me- chanical joints because leakage is of little con- sequence. EXAMPLE PROBLEM To assist the reader in better comprehension of this chapter, an example is presented herewith illustrating the various considerations a design en- gineer must give to a specific problem. This ex- ample is presented purely for illustrative purposes — no consideration has been given to the possi- bility that interfering machinery, trusses, etc. may alter the final design. The problem: Design an exhaust system to control particulate residue from a 16-inch industrial disc sander. The system, shown in Figure 42-6, in- cludes a disc sander, ductwork, fabric dust collec- tor, and fan. The following assumptions are derived from information presented earlier in this chapter. 1. Q=440 cfm. The air volume required to properly exhaust the disc sander. ALL ELBOWS GR = 2D sLoT pr AROUND DISC SLOT AREA=0.18"ft2 SLOT DISC TABLE A —f ® Figure 42-6. 16" DISC SANDER 626 2. v=3500 fpm. The transport velocity re- quired for this system. 3. Hood losses =1.0 slot VP+ 0.25 duct VP In addition, assume that the pressure loss across the dust collector is 2 inches of water. It is required to design an appropriate local exhaust system for the sander and select an appro- priate fan. The first step in designing the system is to de- velop a systematic approach to the problem. Table 42-12, taken from the “Industrial Ventila- tion Manual,” assists in the orderly design of a ventilation system. At the top of this table are columns numbered 1-19. The required informa- tion is inserted into the various columns as shown. An explanation of how the various data shown in the table were obtained is presented in the section of this chapter entitled “Explanation of Answer Chart.” To assist the reader in following the various steps necessary to solve this problem, please refer to column numbers and to the diagram. ®— STACK FAN ~0) FABRIC COLLECTOR LOSS = 2" WG Controlling Dust from a 16” Disc Sander. TABLE 42-12. Answer Chart — A Worksheet for Answers to Problem 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 GT cumxcan M0 GUGLT Col. 9 100 Col. 14 Col. 15 Col. 16 junction Resistance Resistance in Air volume Length of duct in feet in inches inches No.of Dia. Area CFM Vel. water gauge entry hood of water cor- br.or duct duct in in in straight Number of equiv. total per of one loss suct. hood static gov. rected main in in. sq. ft. branch main FPM runs elbows entries length length 100 run VP (VP)(VP) suct. press. SP CFM A-B 5 0.1364 475 3500 23° 2-90° 12° 35" 4.0 1.40 0.76 .25 1.25 0.95 Slot 0.18 2640 0.44 1.0 0.44 2.79 Collector 2.0 4.79 C-D 5 0.1364 475 3500 10 1-90° 6 16 4.0 0.64 0.76 5.43 =SP in D-E 5 0.1364 475 3500 10 10 4.0 0.40 0.76 0.40 =SP out Column Entry Explanation 1 A-B Considering section of duct from point A to B. 2 5 ‘Example states that Q=440 cfm and v=3500 fpm. Using this information, choose duct diameter of 5”. This diameter gives Q=475 cfm at v=3500 fpm — see Column 5. 3 0.1364 The area of a 5” circular duct is 0.1364 sq. ft. 5 475 Duct diameter=5" and duct velocity=3500 fpm. Hence, the air volume in the duct is 475 cfm. 6 3500 Determined previously. 7 23 The length of straight pipe between points A and B is 23 feet. 8 2/90° From A to B there are two 90° elbows. 9 12 The equivalent length of each elbow is 6 feet. (See Table 42-10.) 10 35 The total length of straight pipe equivalent from A to B is 35 feet. 11 4.0 Friction loss is read directly from Figure 42-3 knowing duct diameter and air volume. 12 1.40 To determine total resistance of run from A to B, take 1/100 of the product of Column 10 x Column 11. 13 0.76 Convert from velocity to velocity pressure VP= (2005) 14 0.25 Entry loss was given in problem statement. 15 1.25 The hood loss is 1 velocity pressure. This represents the amount of energy needed to get air to flow into the hood. NOTE: Because the 1 velocity pressure has been added on here, it will not be considered when calculations are made on the slot. 1 Slot Considering slot opening only. 3 0.18 Given slot area in example description. 6 2640 Know slot area and air volume to be moved. Velocity can be determined from v=Q/A =475/0.18 =2640 fpm. 13 0.44 Velocity pressure conversion as before. 14 1.0 This entry loss is given in problem statement. 17 2.79 Combining all duct and slot losses Column 12+ Column 16 + Column 16 —2.79 in. w.g. 1 Collector Considering only the collector. 12 2 Given that the pressure drop across the collector was 2 in. w.g. 17 4.79 The cumulative resistance in the system to this point. 1 C-D Considering the duct between points C and D. 12 0.64 Resistance from duct friction is 0.64 in. w.g. 627 TABLE 42-12 Continued Answer Chart — A Worksheet for Answers to Problem Column Entry Explanation 17 5.43 Cumulative resistance in the system up to the fan. Quantity represents inlet static pressure. 1 D-E Considering only the straight length of duct from the fan. 12 0.40 Duct resistance. 17 0.40 Static pressure after the fan. It is important to note that in filling out Table 42-12, you start your design in Column No. 1 and complete the design horizontally through Column No. 17 in this particular problem. EXPLANATION OF ANSWER CHART Start entries in Column 1 and go across hori- zontally to Column 17. Columns 14, 15, and 16 need to be filled in only where air initially enters duct (i.e., through a hood). Section A-B will be considered in detail. Fan static pressure is calculated from the fol- lowing equation: Fan SP=SP (Fan Inlet) +SP (Fan Outlet) — VP (Fan Inlet) =5.434+0.40—0.76 =5.07 in. w.g. The fan and motor selected should be able to handle a static pressure of 5.25 to 5.5 inches of water. References 1. AMERICAN CONFERENCE OF GOVERN- MENTAL INDUSTRIAL HYGIENISTS, Commit- tee on Industrial Ventilation, Industrial Ventilation 628 — A Manual of Recommended Practice, A.C.G.I.H., P.O. Box 453, Lansing, Michigan, 12th Edition, 1972. HEMEON, W.C.L., Plant and Process Ventilation, 2nd Edition, The Industrial Press, New York, 1963. . AMERICAN IRON AND STEEL INSTITUTE, Committee on Industrial Hygiene, Steel Mill Venti- lation, A.1.S.1., 150 East 42nd Street, New York, New York, 1965. U. S. DEPARTMENT OF HEALTH, EDUCA- } TION, AND WELFARE, PUBLIC HEALTH SERVICE, Air Pollution Engineering Manual, Cin- cinnati, Ohio, 1967. AMERICAN BLOWER CORPORATION AND " CANADIAN SIROCCO COMPANY, LTD., Air Conditioning and Engineering, 2nd Edition, The American Blower Corporation, Detroit, Michigan, 1955. . AMERICAN SOCIETY OF HEATING, REFRIG- ERATION AND AIR CONDITIONING ENGI- NEERS, INC., ASHRAE Guide and Data Book — Applications, ASHRAE, Inc., New York, 1966. AMERICAN INDUSTRIAL HYGIENE ASSOCIA- TION, Heating and Cooling for Man in Industry, American Industrial Hygiene Association, 66 South Miller Rd., Akron, Ohio., 1970. . AMERICAN NATIONAL STANDARDS INSTI- TUTE, Fundamentals Governing the Design and Operation of Local Exhaust Systems, AN.S.1. Z-9.2 Committee, 1040 Broadway, New York, New York. CHAPTER 43 CONTROL OF INDUSTRIAL STACK EMISSIONS Engineering Staff* George D. Clayton & Associates INTRODUCTION Simply defined, pollution is the wrong sub- stance in the wrong place at the wrong time. Air pollution existed long before man discovered fire. Volcanic eruptions, dust storms, forest fires and other natural phenomena have released millions of tons of pollutants into the air since the beginning of time. With the advent of the industrial revolution, continuous exposure to a variety of gaseous and particulate materials became commonplace. The synergistic effects of these chemicals on health has led to several air pollution disasters throughout the United States. The first recorded episode oc- *The following staff members participated in writing this chapter: George T. McCollough, Delno Malzahn, John E. Mutchler and George D. Clayton. curred in Donora, Pennsylvania in 1948, when 20 people died during a five-day atmospheric in- version. In addition to health effects, pollutants in the air can cause extensive economic damage. The poisoning of livestock by lead and zinc, the de- struction of crops by sulfur dioxide, ozone and fluorides, and the damage to neighborhoods by smoke, dust and gaseous pollutants combined carry an economic price tag ranging between 10 and 60 billion dollars per year. One estimate given for the personal cost to a resident living in a relatively polluted community is $84 per year. This figure includes only those costs resulting from the maintenance of the household itself. The cost to industry of reducing emissions to the level required by the Clean Air Act will entail Estimates of Potential and Reduced Emission Levels and Associated Costs TABLE 43-1. Stationary Sources [298 Metropolitan Areas] Quantity of Emissions? (Thousands of Tons per Year) Control Costs (Millions of Dollars) Source Year Part SOx CO HC F Pb Investment Annual Solid Waste 1967 1,110 —_— 3,770 1,400 — — Disposal FY 76 W/O? 1,500 ee 5,450 2,020 — — FY 76 W? 185 een 414 293 — — 201 113 Stationary Fuel 1967 3,247 11,416 — _ = — Combustion FY 76 W/O 3,867 14,447 en —_— rr FY 76 W 930 4,697 —_— —_— — — 2,432 1,006 Industrial 1967 4,601 5,156 7,520 1,412 53 20 Processes FY 76 W/O 6,053 6,229 10,040 1,736 73 30 FY 76 W 453 1,720 539 849 9 10 3,877 1,095 TOTAL 1967 8,958 16,572 11,290 2,812 53 20 FY 76 W/O 11,420 20,676 15490 3,756 73 30 FY 76 W 1,568 6,417 953 1,142 9 10 6,510 2,214 1Emission abbreviations are: particulates (Part), sulfur oxides (SOx), carbon monoxide ) ( fluorides (F), and lead (Pb). Blanks in the table indicate the emission levels meet the applicable regulation or that emissions are negligible or do not exist. 2Estimates without implementation of the Clean Air Act, for fiscal year 1976. 3Estimates with implementation of the Clean Air Act, for fiscal year 1976. From “The Economics of Clean Air, Senate Document No. 92-67” annual report of the Administration of the EPA to Congress. 629 (CO), hydrocarbons (HC), a total investment of $6.5 billion by 1976, accord- ing to one estimate. By that year the associated total annual control cost including depreciation, operating and maintenance costs will amount to an estimated $2.2 billion (Table 43-1). LEGISLATION Federal air pollution legislation was enacted because of the inconsistency of local air pollution control regulations and the increasing deteriora- tion of the nation’s air quality. The first Federal legislation concerning air pollution (Public Law 84-159) was enacted in 1955; it authorized a pro- gram of research and technical assistance to the states. This legislation was amended and strength- ened in 1963, 1965 and again in 1966. The Air Quality Act of 1967, more commonly called the “Clean Air Act” represented a major shift in the enforcement level of air pollution regulations. Introduced into this Act was the con- cept of “air quality control regions” within a sin- gle state or interstate area. The state or states hav- ing jurisdiction in a particular region were em- powered to set standards of air quality, based on desired ambient air levels and guided by criteria published by the Department of Health, Education and Welfare. Initial and ongoing emission stan- dards were also established so that compliance would insure the attainment and maintenance of desired air quality. Within three years, the discrepancies arising in ambient standards among different air quality regions and the lack of national air quality stan- dards led to the Clean Air Amendments of 1970. Under these amendments, states are required to adopt implementation plans (emission limitations) for the entire air region, with priority to be given to development of plans for areas where air pollu- tion is most serious. National emission standards or limits have been established for certain new or newly-modified stationary sources for particulate, sulfur dioxide, sulfuric acid, nitrogen dioxide and plume opacity. In addition, national emission standards for hazardous chemicals such as beryl- lium, mercury and asbestos were set on existing sources. CONTROL CONSIDERATIONS The aggregate demands for improvement of air quality created by the existence of health hazards, economic damage, public pressure and legal re- quirements would seem to place industry in a posi- tion of “clean-up or shut-down.” The degree of control necessary to fulfill these demands dictates the efficiency and sophistication of required abate- ment systems. Once the required collection efficiency is de- termined for a single emission source, five basic factors of the source process must be characterized before proper design of an appropriate system can be undertaken: 1) The chemical and physical properties of the atmospheric effluent must be measured. These include size, density, shape, size- spectrum, chemical composition and cor- rosiveness. 630 2) The carrier exhaust gas must be character- ized, including temperature, humidity, density and pressure. 3) Estimation of process factors such as vol- umetric flowrate, velocity and particulate gaseous concentrations must be made. 4) Construction factors including equipment size, layout, materials of construction and safety requirements must be determined. 5) Operational factors, such as maintenance, utility and disposal costs must be obtained. Comparative cost data for collector designs is based on a variety of process variables. Emis- sion abatement costs increase as the total volume of gas to be treated is increased. Careful analysis of the equipment included in the collector system, plus the installation and maintenance costs, must be made for an optimum design choice between alternative systems. Table 43-2 presents curves to obtain preliminary cost estimates. It is impor- tant to note that the installed cost may exceed the cost of the collection device as shipped by the manufacturer by a factor ranging between 100 and 400 percent. Equipment modification and the substitution of process materials can often be the most effec- tive means of solving air pollution problems. Sub- stantial reduction of the loading in effluent air streams can be brought about by replacement of raw materials or fuel types used. For example, conversion from coal to natural gas as a combus- tion fuel dramatically reduces sulfur dioxide and particulate emissions. Modifications to the plant design which sup- press contaminant formation at the source are, of course, the ideal solution. In addition, any de- sign change which concentrates the contaminant loading to the collecting device into a smaller air volume, reduces the size and cost of the collector needed, since most collecting devices are designed on the volume rate of air to be handled and are relatively insensitive to changes in contaminant loading. Good plant layout, construction and house- keeping can be an effective system for contaminant suppression. The prevention of leaks, periodic vacuuming and “hosing down” procedures and the elimination of open piles of chemicals are a few of the many possible methods for lowering emissions within the plant area. The engineer, after carefully studying the costs related to such factors as: 1) the need for con- trols; 2) the degree of control required; and 3) potential process changes, has available to him a variety of types, designs and manufacturers of control devices. Proper selection of the optimum system requires a thorough understanding of the characteristics of process factors, along with a fundamental knowledge of the principles associ- ated with each type of control equipment. Table 43-3 includes a summary of the charac- teristics of particles and the effective range of certain collection devices. Table 43-4 includes the operating mechanisms and minimum size data for 90% collection efficiency. For a more detailed discussion, the equipment types are divided into TABLE 43-2. Cost Estimates of Dust Collecting Equipment 1.00 { : NN \ \ 75 NN Se NN H Q N A NN Q \ NN ~~ , 3 NN rf NN 25 ~~ nt 2 ¢ * [~~ NN a ~~ tf re TS ~~r ~~ 0 Rn g ~ N Mm Yo ©Q © O00 OO oS O00 © RS S88 8% § RORY SE CFM — THOUSANDS A—High temperature fabric collector (continuous duty) B—Reverse jet fabric collector (continuous duty) C—Wet collector (maximum cost range) D—Intermittent duty fabric collector E—High efficiency centrifugal collector F—Wet collector (minimum cost range) G—Low pressure drop cyclone (maximum cost range) H—High voltage precipitators six broad, general categories: 1) mechanical sep- arators; 2) filtration devices; 3) wet collectors; 4) electrostatic precipitators; 5) gas adsorbers; and 6) combustion incinerators. Mechanical Separators These devices impart either inertial or gravi- tational forces on the particle to remove it from the carrier stream. The range of particle sizes consistent with effective collection efficiencies is 15 to 40 microns in diameter; a sharp dropoff of collection efficiency occurs with particles smaller than 15 microns in diameter. Industrial use is limited to applications where the particulate is very coarse or the separator is used in series with other devices. The many varieties of mechanical separators can be divided into three broad categories: gravity chambers, cyclone collectors and impingement separators. Gravity Chambers. These chambers are the oldest and least efficient method of dust collection. They consist of a low-velocity enclosure where the larger contaminant particles are removed by the force of gravity. Particles smaller than 40p in diameter usually pass through, uncollected. 631 I—High voltage precipitators (minimum cost range) Note 1: Cost based on collector section only. Cost does not include ducting, water require- ment, power requirement or exhausters (unless exhaust is integral part of secon- dary air circuit.) “Industrial Ventilation — A manual of Recommended Practice” 12th Edition, Committee on Industrial Ventila- tion, American Conference of Governmental Industrial Hygienists, Lansing, Michigan. Collection efficiency is related to the terminal settling velocity, U,, and is expressed in the fol- lowing equation: _ 100 U; A, ! Q n="% collection efficiency by weight U, =particle terminal settling velocity, ft./min. A, =horizontal area of chamber, ft> Q =volumetric flowrate of gas, ft*/min. where: An increase in the effective horizontal area, A, through the use of horizontal baffles, or a de- crease in volumetric flowrate and velocity profile, favorably affects collection efficiency. Advantages of gravity settlers include: low initial cost (between 5¢ and 25¢ per cfm), sim- ple construction and a slight pressure drop. These advantages are offset by an inability to remove particles smaller than 40 microns in diameter and large space requirements. Gravity chambers are most useful as a pre- cleaning stage before treatment by a higher col- lection efficiency device. The removal of large- TABLE 43-3. Properties of Aerosols (Imp) (Imm. (lem) 0.0001 0.001 001 01 1 10 100 1,000 10,000 | Zz 3e3e8] 2 een] 7 reves] 2 recen| Iie ;aeses| 2 3436s] 234368] 2 3 [ I I I Mao [1250 | [rrdedu elm lall le] [5] 1 10 100 1,000 10.000 2,500 | 625 [LIL] [almrten ox] x Equivalent I hooreheal Math rele le 2 pd rt Sizes Rngstrom units, A | boo 70/0{ wo @lwolallzlels |x] | | (Used very infrequently) | U.S. Screen Mesh [olde] on | "PTR IT 2 +] a LT clad I Visible I I Electromagnetic ————— X-Rays —— -- —»te ~ Ultraviolet - —-—»+e s+ Near Infrared »t«— ———— Far Infrared — ———+ — Gas Sold: rT I Fume- Ce * co — Dust ——— --—— fp —— — — — Jochnical Despersonds | | iquid: fee a} Mist { — je I. — Spray — em | Soil semi him of og i iy -=-~t- Clay —— Silt -{ »==— Fine Sand —s+e- Coarse Sand > —— Gravel ——— er ie eT — Corwen Alwaphurc eee em Smog - - =e Clouds and Fog — ee Mist Orie +-—Rain— -- = oT . Rosin Smoke - | TE Fertihzer, Ground Limestone —+] EB) 1011 Smokes - te - Fly Ash —— —————» - Tobacco Smoke te Coal Dust — —— ~~» jo . Metallurgical Dusts and Fumes - OP HI r- 0, C0, CH r= Aminomum Chloride Fume -=+=+—— Cement Dust ——{ we] a I Sulfuric _' _ - I 5) | ncentrator Mist Buch Sond | ie Contact oo dq Carbon Black Soifuric Mist Coal - fe——Paint Pigments — —4 Flotation Ores — [ Typical Particles LR “Zinc Oxide Fume—t =~ Insecticide Dusts J ” — AESEARCH INSTITU! Gas Ompersoids @ ne Ce te} -— Ground Talat MENLO PARK CALIFORNIA Adoleculer fe —— Spray Dried Milk —— i " #EU ViScERily ole 4 YC. fe— —— Alkali Fume —— —» lens -— -— Fl ~ Milled Flour —— — fod rm "Sumo oot | cee bem re—Sea Salt Nuclei — Nebulizer Drops —= r«——+ Hydraulic Nozzle Drops — + Lung Damaging 1 Rome Bross Pa st Red Blood Cell Diameter bo Ze 103 3 te—— Viruses ——= te—————— Bacteria —4———+Human Hair T —_-A A EL Sieving— 7 —— a + ——Microscop - rain. t——— Electron Microscope —————— - --}-= , , distnbution set oe [oe Le on EER Analysis = -- calibration T y — | th $ te Visible to Eye —- te 1 Light Scattering" ee —— —— Machine Tools (Micrometers, Calipers, etc.) — — ~~ ->ye—— Electrical Conductivity —] = =m m—a EPP — === = ——1—Settling Chambers — — 1 - be — -— ~~~ - —Centrifugal Separators ———— T oa | | rr r= — Myo Scubbersf— - — y yoeso# | | |eemm———t——— — ———Cloth tors oo. Gas Cleaning [Son Ooh Solace I I Equipment te — - — Common Ai Filters— Tot mm ma +——High Efficiency Air Filters —{—— — - =f«— -|—— Impingement Separators ————— | J | I Thermal on ete — {Mechanical Separators— = a keen I Electrical Precipitators | I T Co - 12 - 1 ~ 10 -9 -8 ~-7 -6 9 -4 - 3 -2 -1 1 2 ae | Monee 0107, 10°, 10°, 107, 107, 10751107) 10; 10107 107 10° 0', 10°, 00, 0 225 C. s o i i z i : ! Terminal 1atm. Setting Velocty, 3 - of -3 -2 -1 o ' ] Gravitational cm/sec. 23 8 10 2 5 10 pas 107, ,J105;,,, 107,105,100, , 0°, s 10’ 1s 25 a S HE doa Lobe dba dae aie ly dooce cg) for spheres, re _ _ o _ _ _ - _ jr py yy or ware || ETON Number jo, 21074107’ 40°) 7107) 10°) poy 107107] 0°; 107; 10°; 107107] 107) 10°, 10' | 10f | 10° 10* " 210 NRT IP HRD 1, 10, BO, 1D, HD 105107 19, 10°, I | EN Cc Setting Velocity, -10 -9 -8 -7 -6 3 4 3 -2 - 1 0 ane [ey a ys ey geno Wan dey apg Wen sand ey 2 MF 2 yaaa d Py 1,,,100 1002 107,10, 10° __ 10° 107’ 10° 10° 10° 1 Particle Diffusion Latm, 32 | 832° 'b32" "saz 332 i832 8 a2 esad 2 esa3lz 7 esa sz esan|a 107, ,],10 Coefficient,’ — 11 11 TH 111 Fn 11 r= laa do aaa alt 1111 Lava ads Lyin all 1 cm */sec. » 10° 10°" 10” 10° 10° 10°" 10" 10°"? Fe 1100 bgt hell Lert herd lade! leneld Lanedt Deer *Stokes Cunningham 2 sasenl 2 34568) 2 34568) 2 3ase8] 2 3 asen| HERE 2 3456 nl 2 3asesl 2 factor included 0.0001 0.001 1 et Ger or 3 (Imp) 0 o1 ! 10 100 x 19900 Dut not included for water " ! Particle Diameter, microns (u) PREPARED AY CE LAPRE Reprinted by permission of Stanford Research Inst. J. 5, 95 (1961). Characteristics of particles and particle dispersions. Courtesy Stanford Research Institute. Source: “Air Pollution Manual”. Part 1I, p. 13, American Industrial Hygiene Association, Akron, Ohio. 632 TABLE 43-4, General Classification of Particulate Collectors Particle Diameter Control Device Class Force for 90% Removal in Microns Settling Chamber Mechanical Gravity 50 Impingement Separator Mechanical Inertial Impingement 25 Cyclone (Small Diameter) Mechanical Centrifugal >5 Cyclone (Large Diameter) = Mechanical Centrifugal 25 Baghouse Filtration Inertial Impingement + >1 Electrostatic + Diffusional Panel Filters Filtration Inertial Impingement + >1 Electrostatic + Diffusional Mat Filters Filtration Inertial Impingement + 10 Electrostatic + Diffusional Deep Filter Beds Filtration Inertial Impingement + 1 Electrostatic + Diffusional Spray Chamber Scrubber Inertial Impingement 25 Packed Tower Scrubber Inertial Impingement 5 Cyclone Scrubbers Scrubber Inertial Impingement + 5 Centrifugal Venturi Scrubber Inertial Impingement + >1 Centrifugal Wet Inertial (Mechanical) Scrubber Inertial Impingement + 5 Centrifugal Orifice Scrubber Inertial Impingement + 5 Centrifugal Single-Stage High Voltage Electrostatic Electrostatic Attraction >1 Precipitators Two-Stage Low Voltage Electrostatic Electrostatic Attraction >1 Precipitators Source: “Air Pollution Manual”. Part II, p. 13, American Industrial Hygiene Association, Akron, Ohio. size particulates which may prove erosive to a second-stage cleaner optimizes the system by in- creasing the efficiency and life of the second col- lector. Impingement Separators. Impingement separators encompass a large, heterogeneous group of collec- tion devices, all of which are based on the inertial force of a particle to accomplish its removal from the carrier gas stream. The separator utilizes a network of baffles to collect or concentrate the particulates, as depicted in Figure 43-1. As the particles moving in the gas stream approach a stationary target, the air will deflect around the impingement target, carry- ing with it the lighter particles. The inertial force of the heavier particles causes them to cross the fluid streamlines, strike the target, and be re- moved, as shown in Figure 43-2. The target efficiency of impingement is the percentage of particles which collide with the stationary object. This value can be obtained graphically from the separation number, N, which is a dimensionless value obtained from classical hydrodynamics and reported graphically in Fig- ure 43-3. — D,? Vv Pp Ne=38.D, 633 where: N,=Separation number, dimensionless D, =particle diameter, feet V =relative velocity gas to target, ft./sec. pp = particle density, 1b./ft.? w=gas viscosity, Ib. /ft.-sec. D, =target diameter, ft. The collection efficiency increases with in- creasing particle size, gas velocity and particle density; but overall efficiency is quite low, in the range of 50-80%, with particles smaller than 20 microns uncollected. Optimum designs, therefore, utilize small openings between baffles and high gas velocities. Advantages of impingement separators in- clude: low cost (from 15¢ to 30¢ per cfm), simple construction and trouble-free operation. Disad- vantages include low overall efficiency, erosion of baffles and corrosion. Impingement collectors find use throughout industry as: precleaners for more elaborate de- vices, collection devices where large particles are involved and devices that concentrate the partic- ulates, in a smaller percentage of the gas stream. Cyclone Collectors. The most prevalent type of mechanical collector in use today is the cyclone. It operates on the principle of creating a vortex from the inlet gas stream velocity. CLEANED AIR AIR _ LA I % Me mL 2 ni! ~ ps INLET. mL o_ RE rere DUST CIRCUIT American Industrial Hygiene Association: Air Pollution Manual. Akron, Ohio, 1968, part Il, p. 34. Figure 43-1. The entrained particles are drawn outward by centrifugal force, where they impinge on the wall surface and are removed by gravity to a collection point. The air flows in a double vortex, spiraling downward at the outside periphery and returning upward through the inside regions as shown in Figure 43-4. During cyclonic separation, the gas stream velocity may increase several times over the inlet conditions. The separation mechanism is similar 634 Flat Lower Impingement Separator. to gravitational settling except that the force acts centrifugally instead of gravitationally, resulting in an increased force on the particle. In small- diameter cyclones, this value may reach upwards of 2500 times the force of gravity. One typical equation for calculation of the size of particles collected is listed below: 9.0 D NEN = PY 22N, V; (pp — pe) PARTICLES IN THIS REGION WILL IMPINGE ON TARGET PARTICLE TRAJECTORY FLUID STREAM LINE Stern: Air Pollution, 2nd Edition. Academic Press, p. 401. Figure 43.2. Physics of Impingement. © O Oo Oo a 7 ® 3 oS // Nn Oo a oO DH Oo -RIBBON nN ol Oo O FA | /~/— SPHERE PERCENT TARGET EFFICIENCY " f——-CYLINDER oOo oO 0.0 O.l 1.0 10 100 SEPARATION NUMBER Stern: Air Pollution, 2nd Edition. Academic Press, p. 401. Figure 43-3. Target Efficiency of Impingement. 635 ZONE OF MOST EFFICIENT SEPARATION Air Pollution Engineering Manual, Department of Health, Education and Welfare, 1967, p. 93. Figure 43-4. A Simplified Cyclone Collector. where: D,.=diameter of particle collected at 50% efficiency pL =gas viscosity, lbs./sec.-ft. b=cyclone inlet, ft. N.=number of turns within the cyclone (approximately 5) Vi=inlet gas velocity, ft./sec. py = particle density, Ib./ft.* pe = gas density, 1b. /ft.”. Caution is recommended in applying this equa- tion to a design problem since the cyclone may be a poor classifier by particle size duc to the vari- ation of factors such as radius of rotation, distance from the wall and tangential velocity. In design consideration, the factor of primary importance is the cyclone’s radius. Collection effi- ciency increases as the radius is reduced. This is due to the increased centrifugal force created on the particle. Pressure drop increases with effi- ciency. Small diameter or high efficiency cyclones have seen increased application in the last few years. Often, an arrangement of cyclones in parallel is used to handle high-volumetric flowrates rather than one large-diameter cyclone. Cyclones have widespread use due to several inherent advantages: low initial cost (from 10¢ to 50¢/cfm) for simple construction, moderate pres- sure drop and low maintenance requirements. Disadvantages include: low collection efficiencies for particles below 5 microns and erosion from impingement of particulate. matter. . Filtration Devices “tag RIE a Er Filtration is an effective technique for control- 636 ling emissions in the form of dust or fume from a carrier stream. Collection efficiencies of over 99.9% have been recorded in some applications. Three classes of filters exist: mat filters, ultrafil- ters and fabric filters. Of the three, the latter is the most important for industrial applications of air pollution control. Mat filters are extremely porous, containing 97-99% void space. They have limited life and are usually used as process air cleaners. Ultra- filtration involves deep filter beds used for high efficiency removal requirements such as radio-ac- tive wastes. Baghouses or panel filters utilize fab- rics to effect separation and are common through- out industry for a multitude of applications. Fabric filters are employed in two basic de- signs, panel filters and baghouses. Panel filters are composed of individual filters, one or two inches thick. These panels filter out the particulate, as the gas flows through the medium. Baghouses are composed of long sleeves of fabric, up to 45 feet in length. These bags filter the air as it passes through the cloth. Periodic cleaning is important to both types to prevent excessive pressure drops from developing. Some mechanisms used for re- ducing the filter buildup of particulates are me- chanical shaking, reverse air jet and low-frequency sound generation. A typical baghouse is shown in Figure 43-5. The fabric weave often has interstices on the order of 100 microns, yet collection efficiencies of over 90% are reached on particles of one micron in diameter. Obviously, the filtering mech- anism cannot be simple sieving. The theory of fabric filtration is not well developed. Empirically, the cloth openings quickly fill, as large-diameter particles “bridge over” the openings. Forces of electrostatic attraction appear to exert the great- cst influence, but other forces, such as Brownian diffusion, impingement and gravitational settling may contribute to the overall process. The cake of particles that develops becomes the filtering medium. As this cake grows thicker, increasingly smaller particles are collected and the pressure drop increases. Periodic cleaning must be performed to limit the pressure drop to design levels. The pressure drop through a fabric filter and the cost of the device are the two most important factors in the design of a collection system for fabric filters. Generally, an increase in cloth area will enhance efficiency, lower the pressure drop and lengthen the fabric life through a reduced cleaning interval, but it also increases the cost of the device. Three variables of design are used to deter- mine the ultimate pressure drop in the system: I. Filter ratio, which is the ratio of carrier gas volumetric flowrate to filter area; 2. Type of cloth and weave selected; 3. Time period of cleaning and method uti- lized. The pressure drop is the sum of the resistances of the cloth and the filter cake amd cam be calcu- * lated from the following formula: AP; = AP; —~ AP; = K, L; ve Shaker mechanism Filter bags Cell plate NS Outlet pipe Clean air side Inlet pipe Baffle "plate Dusty air side Hopper American Industrial Hygiene Association: Air Pollution Manual. Akron, Ohio, 1968, part Il, p. 48. Figure 43-5. where: AP, = Pressure drop at time t due to dust cake, Ib.;/ft.? AP, = total filter resistance at time t, 1b. /ft.? AP; =initial filter resistance of cleaned filter, 1b.;/ft.> . : Ib.; sec.” K, = proportionality constant, Bb Tt «m . L.=dust concentration in carrier gas, Ib.,,/ft.? t=time since cleaning V = superficial filtering velocity, ft./sec. The filter ratio affects the pressure drop by determining the loading rate on the filter. A ratio of three cubic feet per minute per square foot of cloth area is an average value for common dusts. Excessive loading leads to rapid filter buildup. This, in turn, requires a shorter cleaning interval and lowers the life of the cloth. The resistance of the cleaned cloth is determined by material and weave pattern. The selection of cloth type depends on the 637 Single Compartment Baghouse Filter. temperature of the gas stream and the abrasive characteristics of the particulate. Table 43-5 illus- trates some of the more common fabric materials. Advantages of fabric filters include: 1) Upwards of 99% collection efficiency for virtually all particle sizes; 2) Moderate power requirements; and 3) Dry disposal of collection efficiency. Disadvantages include: 1) High cost (between 30¢ and $2.50/cfm); 2) Large space requirements; 3) High maintenance and replacement costs; 4) Control of moisture in the dusts; and 5) Cooling for high temperature gas streams. Wet Collectors Wet collectors or scrubbers effect separation of both particulate and gaseous phase contami- nants. Particle removal is accomplished by mech- anisms similar to those operating in mechanical separators. In a wet collector the particles first impinge upon discrete droplets or sheets of liquid, and then subsequent separation of the liquid re- moves the particulates from the gas stream. Re- moval of gaseous components takes place by the TABLE 43-5 Properties of Fiber Materials Used as Filters Physical characteristics Maxi- Normal mum Relative resistance mois- usable ture temper- to attack by Oth . Relative Specific content ature Organic ther Fiber strength gravity (%) (°F) Acid Base solvent attribute Cotton Strong 1.6 7 180 Poor Medium Good Low cost Wool Medium 1.3 15 210 Medium Poor Good ee Paper Weak 1.5 10 180 Poor Medium Good Low cost Polyamide (nylon) Strong 1.1 5 220 Medium Good Good® Easy to clean Polyester (Dacron) Strong 1.4 0.4 280 Good Medium Good? — Acrylonitrile (Orlon) Medium 1.2 1 250 Good Medium Good — Vinylidene chloride =~ Medium 1.7 10 210 Good Medium Good oe Polyethylene Strong 1.0 0 250 Medium Medium Medium _ Tetrafluoroethylene ~~ Medium 2.3 0 500 Good Good Good Expensive Polyvinyl acetate Strong 1.3 5 250 Medium Good Poor —_— Glass Strong 2.5 0 550 Medium Medium Good Poor resistance to : abrasion Graphitized fiber Weak 20 10 500 Medium Good Good Expensive Asbestos Weak 3.0 1 500 Medium? Medium Good — “Nomex” nylon Strong 1.4 5 450 Good Medium Good Poor resistance to moisture “Air Pollution” 2nd Edition, Stern, A. C. ed., Academic Press, New York, N. Y., 1968. aExcept phenol and formic acid. bExcept phenol. cExcept heated acetone. @Except SO, principle of absorption. This process proceeds through diffusional movement of the gas compo- nent towards the liquid upon which it absorbs by a concentration gradient across the interface re- gion. Wet collectors find industrial applications where one or more of the following conditions exist: 1) 2) Polluting gaseous components need to be controlled; Combustible situations would occur if dry collection were used; 3) A humid gas effluent is encountered; and 4) Cooling of the effluent is desired. Gas Absorption. Gas absorption occurs either through a chemical reaction with the contacting liquid or by simple physical equilibrium of solu- bility. In a system where a reaction occurs, equi- librium between the gas and liquid phases for a component is impossible, since in the liquid phase a reaction removes the component from solution. This allows for separation of the component in excess of equilibrium values. In a system involving simple gas solubility in water, Henry's Law can be used to calculate the equilibrium mole fractions in the liquid and vapor phases. P,=H Xa 638 where: Pj, = partial pressure of gas A H=Henry’s Law constant Xs =mole fraction of gas A dissolved in the liquid. Mass transfer of the gas to the liquid controls the rate at which this equilibrium is approached. A concentration profile exists across both the liquid and gas interface (Figure 43-6). This driv- ing force causes the molecules of the absorbent gas to diffuse from an area of higher gas concen- tration to an area of lower concentration, the inter- face. Since the gas phase diffusion is usually the rate-determining step, the flux at the interface can be determined by the following equation: Na = Kg A PAY where: Nj =moles transferred per hour, m/hr. Ke =mass transfer coefficient, hr./1b.¢* P =total pressure, lb.;/ft.? A =interface area, ft.? AY =driving force, 1b.;. Gas Absorption Equipment. Absorption equip- ment operates on the principles of gaseous or liquid dispersion. Packed towers, venturi scrub- bers and spray towers operate by liquid dispersion. Tray towers and sparging equipment operate by _ - CONCENTRATION PROFILE 7 CONCENTRATION ——= DISTANCE Concentration vs. Position in Liquid and Gas. Figure 43-6. gas dispersion. Particle Collection. Particle collection proceeds by a two-step process. First, the particle is con- tacted by a liquid droplet and is “wetted”; then the wetted particles are removed from the carrier gas. In some collectors, the liquid serves only to clean the impingement surfaces. Mechanisms for wetting the particle include: 1) Impingement upon liquid droplets; 2) Brownian diffusion; 3) Condensation of water around a particle as the gas dips below its dewpoint; and 4) Electrostatic attraction between the drop- let and the particle. The wetted particles are removed through im- pingement and/or centrifugal force, depending on the type of device. The wetting of the particle increases its mass, allowing it to be readily re- moved by inertial force. Overall design and col- lection efficiency equations are not well developed and depend on the type of equipment. Decreasing water droplet size and increasing relative gas velocities will improve collection efficiency. Particle Collection Equipment. All types of wet scrubbers including those that are used for gas absorption remove particulates to some degree. Generally, those devices that utilize high energy contact between the gas stream and small spray droplets achieve the greatest particle collection ef- ficiency. A list of wet collecting devices is in- cluded below: spray chambers cyclone-type scrubbers orifice-type scrubbers mechanical scrubbers mechanical-centrifugal collectors venturi scrubbers packed towers wet filters. Simplified drawings of several of the devices are depicted in Figures 43-7 through 43-10. Discussion of Wet Collectors. Water pollution problems are always associated with wet scrubbers SONA LI BD pt 639 GAS OUT ENTRAINMENT SEPARATOR _ LIQUID IN —_— LIQUID OUT Stern: Air Pollution, 2nd Edition. Academic Press, p. 474 Figure 43-7. and should be considered when evaluating possible systems. It is often necessary to settle out the particulate sludge with flocculants and to adjust the pH before the water can be returned on-stream. Other problems include: freezing of process water, corrosion and increased opacity of the plume due to condensing liquid. Advantages of a wet col- lector include: 1. constant pressure drop 2. dust removal problems eliminated 3. treatment of high temperature and humid gases 4. compact design 5. moderate costs (between 25¢ and 75¢/cfm). Electrostatic Precipitators Electrostatic precipitation is a collection proc- ess that utilizes a field of charged gas ions to charge the particle followed by attraction to a collection electrode. This device is sometimes called the Cottrell Process, after Frederick Gard- ner Cottrell, who invented and designed the first electrostatic precipitator. Three processes are involved in the operation of all electrostatic precipitators: particle charging, particle collection and removal of collected ma- terial. If particle charging and collection are sep- arated, a two-stage precipitator results; otherwise, the unit is a single-stage precipitator. Most indus- trial use is of the latter design, as shown in Figure 43-11. Particle charging occurs through the formation of a highly-charged region of unipolar gas ions called the corona field. The corona field forms from the electrical voltage potential between the electrodes. If this voltage potential becomes too large, sparking will occur and the corona field will Spray Tower. PISTRIBUTOR™\ WATER IN ARS Ne the SUITABLE PACKING MEDIA RE RK oy ha Ne American Conference of Governmental Industrial Hygienists — Committee on Industrial Ventilation: Ventilation — A Manual of Recommended Practice, 12th Edition. Figure 43-8. be disturbed. The particles flowing through the corona field charge themselves by collision with charged gas ions and move towards the oppositely charged electrode where collection occurs. Re- moval from the electrode is effected by a mechan- ical shaker. There is no theoretical limit to the size of the particles that can be collected. Collection effi- ciencies are related to the size of the equipment, with efficiencies of over 99% obtainable. The following equation can be used to calculate the efficiency of collection: - _ —AEE, a Ef=100— 100 exp gy x RXR QO 0 XR J XR0K 2 x YR 3 OUTLET 0 NR WA RK NW J (XX 0 » ( a XX 0 4 RR & RYT fog X STEEL CYLINDRICAL JACKET CORROSION RESISTANT LINING WHERE REQUIRED SUPPORT PLATE DUST AND WATER OUT Industrial Lansing, Michigan, 1972, p. 474. Packed Scrubber. 640 where: Ef=percent efficiency A =surface area of collecting electrodes, ft* V = volumetric flowrate, ft.®/min. E, = charging field, volts /ft. E, = collecting field, volts/ft. a= particle radius, ft. n= gas viscosity, 1b./hr. ft. From the equation, it can be seen that an increase in voltage and surface area coupled with a decrease in volumetric flowrate gives optimum operating conditions. Initial cost for an electrostatic collector runs LIQUID IN GAS IN VENTURI «oe, %.0, Be MIXTURE TO ENTRAINMENT SEPARATOR Stern: Air Pollution, 2nd Edition. Academic Press, p. 474 (9, 10) and p. 440 (11). Venturi Scrubber. Figure 43-9. GAS OUT GAS IN — ADJUSTABLE CONE Stern: Air Pollution, 2nd Edition. Academic Press, p. 474 (9, 10) and p. 440 (11). Figure 43-10. from 80¢ to $2.50/cfm, with erected cost approxi- mately 1.7 times the initial cost. Power costs are quite low, since energy is required only to sep- arate the particle without having to do work on the carrier gas. Electrostatic precipitators have many advan- tages, including: high efficiency dry collection of dusts low pressure drop ability to collect mists and corrosive acids low maintenance costs low operating costs SVN IBS ft Doyle Impingement Scrubber. 641 7. collection efficiency can be adjusted by unit size 8. ability to handle gases up to 1500°F. Disadvantages include: 1. high initial cost (between 80¢ and $2.50/cfm) 2. frequent need for a precleaner 3. large space requirements 4. difficulty in collecting materials with extremely high or low electrical resistivity. Gas Adsorbers Adsorption is a useful process for controlling highly odorous, radioactive or toxic gases. This process involves retention of molecules from the s phase onto a solid surface. Van Der Waals’ orces, ionic attraction, secondary chemical bonds and capillary condensation — all have a role in the adsorption of the gas onto the solid surface. Two general types of adsorbers exist: fixed bed and regenerative. In addition, recirculation may be utilized 10 increase the effectiveness of the de- vice. Fixed -bed' adsorbers are economical only when the average contaminant concentration is less than a few parts per million. Regenerative adsorbers are designed to handle much heavier loadings with the additional advantage of recovery of the contaminant solvent which may have a high economic value. A typical fixed bed adsorber is shown in Figure 43-12. The mechanism of adsorption progresses in three distinct steps: 1) The adsorbent moves to the solid surface; 2) Physical bonding occurs; and 3) Adsorbent is removed through treatment with steam, hot brines or other methods. In design of adsorbent systems, increased re- moval efficiency is often obtained if conditions of high pressure and low temperature are maintained. The high efficiency of adsorbers is offset by the many associated problems. Equipment costs may run as high as $35.00 per pound of vapor re- moved with operating costs running about five dollars per pound of vapor removed. Other prob- HIGH VOLTAGE INSULATOR COMPARTMENT TO CLEAN GAS MAIN DIRTY GAS MAIN SUPPORT TE INSULATOR STEAM COIL a HIGH TENSION ! SUPPORT FRAME —————"r TRI | COLLECTING ’ ILECTRODE PIPES ~~ GAS DEFLECTOR CONE SHELL —J| w | HIGH TENSION | HH HH ELECTRODE ELECTRODE || = [| N WEIGHT — | | / | — COLLECTED DUST OUT Stern: Air Pollution, 2nd Edition. Academic Press, p. 474 (9, 10) and p. 440 (11). Figure 43-11. Tube-Type Electrostatic Precipitator. 642 CONE SHELL HOUSING CARBON VAPOR-LADEN AIR IN Z= CONE SHELL HOUSING CYLINDRICAL SHELL HOUSING VAPOR-FREE AIR OUT 9 msn WIRE SCREEN CONES Air Pollution Engineering Manual, Department of Health, Education and Welfare, 1967, p. 197 and p. 172. Figure 43-12. lems include corrosion and particulate contamina- tion of the device. Combustion Incinerators Combustion incineration is a process that utilizes oxidation reactions for emission control. Combustion afterburners find numerous industrial applications and can be used for any of the fol- lowing situations: . odor control 2. reduction in opacity of the plume 3. conversion of carbon monoxide to carbon dioxide 4. reduction of organic vapors and particulate emissions. Combustion devices come in two types, direct flame and catalytic combustion. Direct flame in- cineration involves the burning of additional fuel to reach temperatures high enough for destruction of the gas or aerosol mixtures. Complete com- bustion yields H,O and CO,, whereas incomplete combustion may produce even more offensive compounds than originally found. A typical direct flame incinerator is shown in Figure 43-13. Catalytic combustion utilizes a catalyst, nor- mally a noble metal, to lower the activation energy of the oxidizing reactions to reduce the temperature and fuel costs required for oxidation. Combustion may even become self-sustaining if the concentra- tion of combustibles in the gas stream is suffi- ciently high. In designing or operating a flame combustion device, care should be taken to see that the tem- perature, residence time and turbulent mixing are sufficient for complete oxidation. One satis- factory method of achieving this goal is to admit the contaminant gases into a throat where the burner is located. High velocities can be obtained for thorough mixing of the gases in the region of highest temperature. A retention time of 0.3 to 0.5 second and operating temperature ranges be- tween 850°F-1500°F have been found to be satisfactory for most applications. Efficiencies of 643 Fixed Bed Adsorber. 98% or higher can often be obtained in a well- designed incinerator. The decision of whether to use flame or cata- lytic combustion is based on economic considera- tions and operational characteristics. Costs for flame and catalytic combustion vary widely, de- pending on the amount, types and concentration of pollutants to be burned. Some of the opera- tional differences are listed below: 1) Generation of nitrogen oxides is reduced using catalytic combustion; 2) Catalysts require periodic cleaning and re- generation; 3) Integration of catalysts into the design of equipment permitting heat recovery is much easier. SUMMARY This chapter has stressed the standard pollu- tion control equipment in existence today: me- chanical separators, filtration devices, wet collec- tors, electrostatic precipitators, gas adsorbers and combustion incinerators. These devices are listed and evaluated for comparison in Table 43-6. One area which has been neglected is the water pollution and solid waste potential of air pollution control devices. Obviously, devices which reduce atmospheric emissions must eventually ac- cumulate materials that must be disposed of by other means. A frequent argument against the use of wet collectors is the resulting liquid waste. In many cases the collected materials can be used productively. They may be recycled back into the process stream, put to use in another plant application or (rarely) sold. All too frequently, however, the liquid wastes are simply discharged to city waste treatment systems, or directly into the waterways, while solid wastes are hauled away to landfills or incinerators. The design of any air pollution control sys- tem must include consideration for potential pol- lution effects. A control system for one specific GAS BURNER PIPING BURNER 9. = BLOCK Figure 43-13. airborne contaminant may involve more than just the design of an air pollution control device. An evaluation of the overall waste disposal system for the total operation may result in numerous addi- tional modifications before all potential pollution sources are adequately controlled. Preferred Reading 1. STRAUSS, W. Industrial Gas Cleaning, International Series of Monographs in Chemical Engineering, Volume 8, Pergamon Press, New York (1966). STERN, A. C. Air Pollution, Volume Ill — Sources of Air Pollution and Their Control, Environmental 644 REFRACTORY LINED STEEL SHELL BURNER PORTS REFRACTORY RING BAFFLE YN IN— N INLET FOR J CONTAMINATED AIRSTREAM Air Pollution Engineering Manual, Department of Health, Education and Welfare, 1967, p. 197 and p. 172. Direct-Fired Afterburner. Science Monograph Series, New York (1968). DANIELSON, J. A. Air Pollution Engineering Man- ual, U. S. Department of Health, Education and Welfare, Public Health Service, Cincinnati, Ohio (1967). LUND, H. F. [Industrial Pollution Control Hand- book, McGraw-Hill Book Company, New York (1971). Air Pollution Manual, Part 11: Control Equipment, American Industrial Hygiene Association, 66 South Miller Road, Akron, Ohio 44313 (1968). Journal of the Air Pollution Control Association, Pittsburgh, Pennsylvania. Academic Press, TABLE 43-6. Comparison of Pollution Control Equipment Device To Control Advantages Disadvantages Costs Examples Mechanical Medium to large 1) Low initial cost 1) Low efficiency Low initial 1) Gravity Separators diameter 2) Simple construction 2) Erosion of components cost (5¢-25¢ Chambers particles 3) Ease of operation 3) Cannot remove small per cfm) 2) Impingement 4) Use as precleaners particles Separators 4) Large space require- 3) Cyclone ments Collectors Filtration Dusts, fumes 1) High collection 1) High costs High costs 1) Fabric Filters Devices efficiency on 2) Large space (30¢-$2.50 2) Mat Filters small particles requirements per cfm) 3) Ultrafilters 2) Moderate power 3) Must control moisture requiréments and temperature 3) Dry disposal of gas stream Wet High-tempera- 1) Constant pressure drop 1) Disposal of waste Moderate 1) Spray Collectors ture, moisture- 2) Elimination of dust water may be expen- (between Chambers laden gases removal problems sive and troublesome 25¢and75¢ 2) Cyclone, Ori- 3) Compact design per cfm) fice, Venturi Scrubbers 3) Mechanical Scrubbers 4) Mechanical- Centrifugal Collectors Electrostatic All sizes of 1) High efficiency 1) Often requires High initial 1) Single-stage Precipitators particles—even 2) Dry dust collection precleaner costs—Ilow Precipitators very small mists 3) Low pressure drop 2) Large space require- operating 2) Two-stage which form 4) Can collect mists and ments costs & low Precipitators free-running corrosive acids 3) Cannot collect some maintenance liquids high/low resistivity costs Gas Adsorbers Combustion Incinerators Highly odorous, radioactive or toxic gases Odors, plume opacity, carbon monoxide, organic vapors 1) Contaminant solvent may be recovered 1) Capable of reaching high efficiency operation 2) Catalytic combustion reduces NO, pollutants materials 4) High initial cost 1) High equipment & operating costs 2) Corrosion 3) Contamination 1) Must burn additional fuel or add catalyst 2) Incomplete combustion can further complicate original problem 3) Catalysts require periodic cleaning & regeneration High equip- ment and operatingcosts Vary widely depending upon application 1) Fixed Bed 2) Regenerative 1) Direct Flame 2) Catalytic Combustion 645 CHAPTER 44 CONTROL OF INDUSTRIAL WATER EMISSIONS Thomas J. Powers INTRODUCTION Industry uses water for almost every conceiv- able purpose from nuclear shielding to washing down floors. Every water use is important and each source of used water must be known and evaluated. By far the greatest volume of indus- trial water use is for heat exchange. The smal- lest water use is in products such as beverages and water-based latex paints. Man cannot use water without adding some- thing to it. That “something” may be heat, sus- pended materials or dissolved substances. The more water is used, the more materials are added to it until its usefulness is impaired and a condi- tion of pollution exists. Industrial water use must be so managed that pollution is avoided. Control of water emissions from industry to WATER SUPPLY | [WATER TREATMENT HEAT EXCHANGE ' WASTE Figure 44-1. 647 —= BOILER ~~ PROCESS = HOUSEKEEP [—= the environment requires a thorough knowledge of the volume of water used per unit time and the quality of the used water. Adequate control also demands a knowledge of the quality standards for both emitted water and receiving water. Water emissions may best be identified and categorized by the service from which the used water originates. There would then be used water from (Fig. 44-1): 1. Treatment of incoming water 2. Sanitary services 3. Boiler operation 4. Housekeeping 5. Heat exchange 6. Unit processes 7. Roof and yard drainages. Having identified all used water sources and SANITARY SERVICES STORM DRAINS ro WASTE WASTE Origins of Industrial Water Emissions. quality, the environmental engineer must review the control methods most applicable and economic for each waste water source. Combinations of waste waters are quite often possible and desir- able, but careful analysis of the water quality and the control methods are necessary to indicate compatibility. Modern small industry will probably find it most economic to purchase potable water from a public supply and to purchase waste water treat- ment services for those wastes which are com- patible with biologic systems. Extreme caution must be used on the potable water supply to avoid any cross-connections. It is also necessary to know accurately the waste water flowrate and quality so that design is adequate to insure con- trol of water emissions to meet standards. The discussions presented here are not refer- enced. The author has presented a list of excel- lent texts which answer almost all of the specific questions which might arise. The references in the texts will guide the reader to articles covering almost every type of waste water problem encoun- tered in industry. Throughout this chapter emphasis is placed on the necessity for proper measurement of waste flows, proper sampling and accurate analyses to- gether with laboratory experiments to arrive at sound judgments. There is no substitute for sound engineering based on facts derived in this manner. IDENTIFICATION OF USED WATER SOURCES Wastes from Water Treatment Treatment of incoming water to achieve the water quality necessary for each use is a necessity for many industries. Whenever solids must be removed, a waste water source results. Clarifier Underflows. Ordinary sedimentation us- ing coagulants such as aluminum or iron salts and flocculant aids is practiced widely on water from surface sources. The settled material removed from the bottom of the settling tank is called sludge and is usually about 8% solids and 92% water. The composition of the solids is the same as the solids in the incoming water plus the coagu- lant hydrates and filter aids. The sludges can be further dewatered by settling in ponds, by vacuum filtration or by centrifugation. The water result- ing from further dewatering should be recycled to the raw water source. The only water lost is to the sludge cake, usually 50% to 75% of the cake weight. Water softening is the removal of calcium and magnesium ions from the water and can be ac- complished by a cation exchanger or by the treat- ment of the water with lime followed by soda ash. The settled sludge from lime-soda softening will contain calcium carbonate and magnesium hy- droxide. By recycling the sludge in the process a final concentration for disposal might contain up to 25% solids and 75% water. Further dewater- ing can yield up to 50% solids. Sedimentation, even with flocculant aids, sel- dom results in a water with less than 20.0 mg/1 of suspended solids. Usually sedimentation is fol- 648 lowed by filtration to remove particles down to about 20 microns. Filter Backwash. Filter backwash is a waste water which contains the solids washed from a filter usually in a concentration about ten times the concentration fed to the filters. This water should be recycled back to a sedimentation tank inflow so that the water is not lost and the solids be- come a part of the sedimentation tank underflow sludge. Filters are also used to separate precipitated iron from well water which has been aerated to oxidize the ferrous iron to the ferric state. The wash water from these filters should be ponded and the water returned to the system. lon-Exchange Regeneration. Water treatment by ion-exchange is widely used for water softening where a cation exchange material removes the calcium and magnesium by replacement with so- dium. The regenerant is common NaCl and the waste water resulting from regeneration contains CaCl,, MgCl, and the excess NaCl used. The waste water volume resulting from regeneration is usually about 4 bed volumes and the frequency of regeneration depends on the amount of calcium and magnesium in the incoming water. Complete demineralization using both cation and anion exchangers produces water very close to distilled water. The regenerants may be am- monium hydroxide, caustic, sulfuric acid or hy- drochloric acid. The cation exchange replaces all cations with hydrogen giving an acid water which is degassed to remove CO, and SO,, and the anion exchanger then replaces regenerant anions with hydroxyl ion. The regenerant streams contain all of the substances contained in the original water less the acid gases blown out plus the excess of regenerant added. The waste volume is usually of the order of 6 bed volumes per re- generation. The regeneration brines from ion-exchange water treatment are of no value and cannot be recycled; they are true waste waters. Waste Waters from Sanitary Services Every industry must provide potable water ap- proved by the State Health Department for sani- tary services. Drinking water, washbasins, laun- dry, toilets, showers (including safety showers) and kitchens should be furnished with potable water. The environmental engineer should con- stantly be on the lookout for cross connections between potable and non-potable sources. Wher- ever it is necessary to use potable water as an alternate in a non-potable system, the potable water should be delivered to a head tank and re- pumped to the non-potable system (Fig. 44-2). A suitable color code for each water system can help prevent erroneous connections. Toilets, wash- rooms and showers should be sewered separately together with laundry and kitchen wastes, to a segregated system called the sanitary sewer. Drinking fountains, safety showers and eye baths are usually placed strategically for workmen’s maximum convenience and need not be sewered to the sanitary system. The waste water resulting from sanitary ser- NONPOTABLE WATER POTABLE WATER SUPPLY HEAD TANK Figure 44-2. vices will be about 20 gallons per person per shift. The waste water should be limited to 100 mg/1 of suspended solids and a B.O.D. of about 120 mg/l. If laundry and kitchen wastes are added, the volume will be about 30 gallons per person per shift. Waste Waters from Boiler Operation Many industries operate boilers to produce process steam and plant heat. These boilers are usually low pressure boilers (150 psi) and do not require demineralized water for make-up, but almost all use internal boiler treatment. The chem- icals added to boiler feed are for the purpose of holding compounds in solution as water is evap- orated and to prevent water entrainment in the steam. Boiler Blow-Down. In order to maintain the solids in the boiler at a manageable level it is necessary to purge the boiler periodically. This is called boiler blow-down. Naturally this represents a con- siderable heat loss which can be minimized by exchanging the heat to the boiler feed. The re- sulting water is highly mineralized and must be considered a waste. The total dissolved solids will be 3500-5000 mg/1. Ash Sluice Water from Combustion of Coal. Most low pressure coal fired boilers are stoker fed and seldom require fly ash control. Ashes are usually sluiced with water to an ash pit. The overflow water from ash handling is alkaline and must be considered as waste water. If fly ash is collected, 649 Dt PUMP Equipment to Avoid Cross-Connections. it also is usually sluiced to a pit. Boiler Cleaning Solutions. Fouled boiler tubes result in decreased efficiency and must be cleaned periodically (1-2 years). Chemical cleaning is widely used and the low pressure boiler can be cleaned using hydrochloric acid which contains substances to inhibit its attack on metallic iron. Many industries require that the cleaning con- tractor haul spent cleaning solutions off-site al- though in some instances the spent solutions are discharged to the ash pit where residual alkali neutralizes some of the acid and iron is pre- cipitated. High pressure boilers require more sophisti- cated cleaning methods using organic materials such as citric acid and versines since hydrochloric acid should not be used on stainless type steels. These spent cleaning solutions contain copper and nickel chelates and require separate handling. Waste Waters from Housekeeping Almost every industry maintains service hoses which are used to wash down equipment and floors. This is not only for appearance but also for personnel safety and product quality control. The food industries in particular must shut down all production periodically and remove all traces of putrescible substances from materials handling equipment and floors. It is common practice to run production for two shifts and use the third shift for a complete clean-up. Service hoses with 50 psi water pressure will deliver from 15 to 30 gpm. Several hoses being used at a time will result in a considerable flow from the building. The engineer should attempt to minimize wa- ter use and yet accomplish the purpose. Leaving hoses running is a very common mistake which must be corrected constantly. Water Used for Heat Exchange As stated previously the use of water as a heat exchange medium is by far the greatest industrial water use. Once-through cooling is extensively practiced because it is the simplest and cheapest system as long as sufficient water is available. Heat has become known as a pollutant because of the changes in the water biota due to increased temperatures. Heat added to surface waters is slowly transferred to the atmosphere until the water and air above it reach equilibrium. Once-through cooling adds very little to a water except heat; however, a 20-25°F rise in the water temperature is common. Cooling Towers. Heat exchange water which is in short supply or which may cause thermal pol- lution is recovered for re-use by causing the heat to be rapidly dissipated to the atmosphere through use of cooling towers. The recycle of cooling water over cooling towers necessitates treatment of the water to prevent scale and corrosion in the heat exchange piping. The cooling tower will lose about 2.0% of the water by evaporation, about 1.0% by entertainment and 10% by the purge required to maintain a constant solids content (Fig. 44-3). The purge loss will contain about 1000 mg/1 of total solids, plus the amount of zinc, chromium and other chemicals added to condition the water. COOLING HOT PRODUCT HOT WATER _ COOLED PRODUCT Figure 44-3. COOLED WATER Barometric Condensers. It is quite common to use a steam jet to pull a vacuum on a distillation or evaporation process. One source of heat ex- change water which may not be included in the cooling water system is the barometric quench condenser (Fig. 44-4). This type of condenser can contain sizable quantities of product if a small vacuum leak develops in the system. It is advisable to use an inner-after condenser rather than the quench condenser when the product being handled is a major pollutant (Fig. 44-5). Product Heat Exchangers. Heat exchangers which are used to cool a product should have readily accessible water sampling points downstream from the units. A small leak in a tube can account for a sizable product loss even though the pressure is greater on the water side. The velocity of the water past a pin hole leak can create a suction, causing product to enter the cooling water stream. Unit Processes The water which comes in direct contact with raw materials, intermediates, by-products or prod- ucts is called process water. The inadvertent loss of materials to heat exchange equipment and clean-up of floors has previously been discussed. Raw Material Purification. Many raw materials are transported by water and unwanted impuri- ties are washed or dissolved away. Many exam- ples of this water use are found in the food indus- try. Sugar beets are sluiced to screens ahead of slicers. The flume water washes dirt and debris from the beets and also dissolves some sugar de- pending on the condition of the beet. The quality of the process water from the can- ning industry can be directly related to the con- dition of the vegetables or fruit as received. TOWER AIR OUT SPRAY BAFFLES AR IN WELL | PUMP Cooling Tower. 650 COOLING WATER SURFACE CONDENSER vo VACUUM LINE Lot WATER PRODUCT ouT BAROMETRIC SEAL AN CONDENSATE STEAM STEAM JET — WATER QUENCH WASTE (QUENCH + STEAM CONDENSATE) Figure 44-4, Reaction Vessel Cleaning. One of the most im- portant waste water sources from unit processes is the clean-up of vessels from batch reactions. These waters are usually quite concentrated, are discharged intermittently and often require spe- cial handling. Raffinates. Solvent extraction of materials from water is a common industrial process. The water remaining after the extraction is called a raffinate. As a rule these are strong wastes containing by- products, some product and some solvent. Vent Gas Scrubbers. Whenever gases are released from a process they are usually scrubbed with water. If the gas is valuable, such as hydrogen, it may be scrubbed to remove impurities and re- covered for use. Many vent gases such as chlorine, hydrogen cyanide, hydrogen sulfide or phosgene may be dangerous and must be removed by effi- cient scrubbing equipment (see Chapter 43). The water wastes from vent scrubbers can be the most important waste water to measure and evaluate 651 Barometric Quench Condenser. for control. Condensates. Whenever steam is used or is formed in a process it is generally condensed using a heat exchanger or a quench condenser. Many conden- sates are pure water and can bé re-used, but al- most all condensates are subject to receiving im- purities. Continuous monitoring of condensates is a must to achieve process control as well as con- trol of water emission. Roof and Yard Drainage The design of the sewer system should provide a segregation of water run-off from factory roofs and yards. Raw materials and products are often lost to roofs or grounds. Pressure reaction vessels with frangible reliefs often vent materials to roofs. Tank car loading is bound to result in some spills. Storage tanks develop leaks. If control of water emission is to be achieved the environmental en- gineer cannot overlook roof and yard drainage. These waste waters should be monitored and the necessary controls installed and maintained. COOLING WATER IN VACUUM l LINE SURFACE 1 CONDENSER vo STEAM STEAM JET WATER PRODUCT OUT CONDENSATE SURFACE CONDENSER ——, WATER IN BAROMETRIC SEAL NL STEAM WATER ouT (CONDENSATE) Figure 44-5. CONTROL METHODS FOR WATER EMISSIONS Waste Inventory In considering the control of industrial water emissions it is well to remember that things hap- pen in industry. A good philosophy to follow in design is that if it can happen, it will. One of the most valuable and useful tools in the control of water emissions is impervious storage facilities into which high concentration, low volume and intermittent waste waters may be inventoried and from which waste may be monitored, recycled or treated to achieve control. Where land is at a premium, waste inventory can be achieved by pumping to holding tanks. It may be advisable to inventory each process waste separately near the production equipment and feed from these at a steady rate to the proper control method. The chemical industry has used waste storage 652 Barometric Inner Condenser. of brines with controlled discharge to streams at high flows for many years. Raw Material Change As is the case in control of air pollutant emis- sions it is sometimes necessary and feasible to avoid the production of a waste by changing the raw material. For instance, a tannery might change from salted hides to fresh hides and avoid the problem created by washing salt from the preserved hides. If the purification of the raw material creates a waste water problem it may be possible to have the supplier remove the impurity prior to shipping. Process Change There are many processes which have inherent losses to water. Most of these are in the wet proc- ess industries where raw materials are dissolved in water or transported by water. It is possible in some instances to change the process and relieve the losses to the waste water. The environmental engineer should review each process with process engineers to minimize water contact and the pro- duction of waste materials. Major process changes may take years to accomplish and be very costly, but if a waste can be avoided or made into a useful product, the long term economics can be favorable. Direct Burning The direct burning of organic residues from industrial processes is a common method of ulti- mate disposal. Minimizing water and concentrat- ing the waste water stream to more than 10% organic content permits the use of direct burning at reasonable cost. A very good example of this is the waste liquor from sulfite pulp mills. Both fluidized bed combustion and direct burning have been used. Wet combustion using air or oxygen to 300°C resulting in pressures up to 1750 psi has also been used on sludges in some municipalities, but has not yet been used extensively on strong industrial wastes. Vaporization and Catalytic Burning The catalytic burner is used extensively to control odorous air emissions (Chapter 43) and can also be used to destroy organic matter if the water waste is first vaporized. This technique has been used on nonrecoverable solutions of lower alcohols. Control of Water Emissions by Recycle The containment and utilization of waste wa- ters by recycle is common to most industries. Wa- ter conservation practices such as counter-current washing and the re-use of cooling water does not mean the reduction of pollutants but rather a con- centration in a smaller volume. Recycle of water usually entails the addition of chemicals to control corrosion, scaling and bacterial growths. However, the recycle of weak solutions which contain raw materials, intermedi- ates or product may be an economic necessity and should be investigated thoroughly. Subsurface Disposal The loss of polluted water to fresh ground water must be avoided. This is not easy and re- quires a knowledge of subsurface geology and hydrology. Sewers collecting acid wastes must be designed to carry that waste without loss to the ground. Sewers subject to hot water release must not break due to thermal shock. Dyked areas which might retain polluted water should be made impervious. Disposal by deep well is an engineered method of ultimate disposal which is politically and geo- logically possible in many parts of the country where porous and permeable sedimentary forma- tions containing connate brines exist. The waste waters which have been so disposed are usually brines or waters containing highly toxic or odorous materials which cannot be treated effectively and which should not be allowed to pollute the ground or surface water. The chemical and oil refining industries have used deep well disposal in Texas, Indiana, Ohio, Louisiana and Florida. The depth of these wells is usually 1500 to 6000 feet. 653 While deep well disposal is not exactly a last resort method, most State agencies will demand a review of alternate control techniques. The vol- ume of waste water a formation can accept safely is finite. The deep formation disposal capacity is a valuable resource and should be reserved for those wastes which must not be allowed to invade man’s environment. If deep well disposal is being considered, a competent hydrologist or geologist should be em- ployed to develop a feasibility report and pre- liminary costs. Starting with the State Water Pol- lution Control agency, all regulatory agencies must approve. The design of surface equipment and the well design cannot be trusted to inexperienced engineers. Drilling of the well and its completion should be closely supervised by an engineer knowl- edgeable in these matters. Too many failures have been the result of poor design and execution. Treatment to Standard Quality Very seldom is it possible to eliminate, contain or destroy waste waters to a degree which will permit release to public waters without treatment of some sort to meet a quality standard. Most municipal waste water treatment plants control the quality of industrial waste discharge to municipal sewers through ordinances establishing limits on pH, suspended solids and biochemical oxygen demand. Industries producing waste wa- ters exceeding the standards are required to pre- treat the waste or to pay a surcharge or both. San- itary sewage is described as having pH 6-9, sus- pended solids — 350 mg/l, B.O.D. — 300 mg/l. In addition to the control of these three para- meters, it is necessary to restrict the waste waters from industry to those wastes containing sub- stances which are compatible with the treatment process being used. Practically all municipal waste water treatment systems use biologic processes. Since the municipality must also treat to a stan- dard quality it cannot afford to receive wastes which will upset or poison the biologic process. Substances highly toxic to bacteria must not be al- lowed to reach the treatment process. Other sub- stances which may not be toxic but which have a high chlorine demand may also be refused. Physical and Chemical Treatment Methods: Neu- tralization. The first treatment step toward con- trol will probably be neutralization to achieve an effluent stream having a pH between 6-9. Aside from proper inventory, neutralization may be the only treatment needed in some instances. On the other hand, neutralization may cause precipita- tion of insoluble materials and require further treatment. It is also possible to use the neutraliz- ing power of one waste when properly mixed with another. The cheapest alkali usually available is finely ground limestone, CaCO,, and next is CaO, which should be slaked to Ca(OH),. One source of waste Ca(OH), is from the manufacture of acetylene from calcium carbide. Laboratory ex- periments should be performed to develop the most economic neutralization system. Screening. The use of coarse and fine screens to remove large suspended particles is a first treat- ment step in many industries, especially the food industry. Screening may also be the only pretreat- ment required before discharage to a municipal system. Fine screens remove those particles which may overload skimming and sludge hand- ling equipment in further treatment steps. Some- times screenings will be of some value as stock feed but mostly they are hauled off-site for burial or spreading on the land. Sedimentation-Flotation. Solids removal by set- tling is the universal primary treatment step. All set- tling systems should be designed, although many small industries dig a hole in the ground and hope for miracles. Flow-through settling ponds are used extensively in the mineral processing industries. These ponds must be designed to give adequate solids storage for long periods of time before set- tling capability is lost. Dual ponds permit the use of a fresh pond while the filled pond is being excavated. Where land is costly, the use of designed clari- fiers permits the continuous use of a stable settling capacity and the dewatering of solids for off-site disposal. Clarifiers are usually designed to receive water at 600-1000 gallons per square foot per day. Flocculation chambers can also be included so that coagulants and flocculants can readily be applied to upgrade not only the solids removal efficiency but also hydraulic capacity. It is usually most economical to remove as many settleable and colloidal materials as possible in the primary set- tling step. Here again laboratory experiments with various coagulants and flocculants guide the en- gineer’s judgment of the best system and engineer- ing paraineters. A well designed and properly operated clari- fier should deliver an effluent of about 25 mg/l suspended solids. Sludges from the underflow of clarifiers will usually contain about 5-8% solids. The accumu- lation of inorganic sludges in dyked areas is com- mon industrial practice. Dewatering by vacuum filters, sand beds or centrifuges permits hauling sludges off-site or, in the case of organic solids, prepares them for sanitary landfill or incineration. The safe disposal of sludges from waste water treatment can account for 50% of the total treat- ment cost and therefore requires detailed study. In some cases the character of the solids in a waste water may cause the engineer to select flotation as the solids-separation process. Oily and greasy materials having a specific gravity close to water can be made to trap other particles and, by using dissolved air under pressure, the fine bub- bles which are released to a flotation tank cause the suspended materials to rise to the top of the tank where they can be skimmed off readily. Laboratory experiments can quickly evaluate flotation efficiency and the effectiveness of adding coagulants. Most water treatment equipment sup- pliers have flotation equipment which can be en- gineered after design parameters are established. Chemical Treatment. The use of chemicals for neutralization and as aids in the sedimentation process has been mentioned. Chemicals are also used to precipitate undesirable ions such as mer- 654 cury and other heavy metals, fluorides and phos- phates. Hexavalent chromium can be reduced by SO, and precipitated as trivalent chromium. The use of chlorine as a disinfectant for mu- nicipal waste water prior to discharge is a requisite in most states. Chlorination of industrial wastes for disinfec- tion may be important in some industries where the dissemination of disease organisms to the en- vironment is likely. The most important use of chlorine in industrial waste treatment is as an oxi- dant to destroy highly toxic or odorous substances. The standard treatment of cyanides from the plat- ing industry is oxidation by alkaline chlorination. One pound of cyanide requires 7.35 pounds of chlorine. Chemical oxidation using chlorine, ozone or permanganate will cost more than 50 cents per pound of organic matter destroyed. This cost usually dictates that chemical oxidation be used only as a final polishing method after the bulk of the organic matter has been removed by some less expensive method. Adsorption. There has been a renewed interest in the use of activated carbon for the removal of soluble organic materials from waste waters. Ac- tivated carbon has a broad spectrum of pore size, but is most effective in the removal of larger mole- cules (C, and above). The cost of granular acti- vated carbon is usually more than 30 cents per pound. It is evident that at least ten regenerations must be effected if the adsorption cost is to be made competitive with chemical oxidation. Here again the use of activated carbon is usually lim- ited to threshold treatment. Extraction. Solvent extraction is a production tech- nique used extensively in the chemical industry. The extraction of phenol from water using caustic- washed benzene is a classic example. Since most solvents are soluble in water to some degree, it is then necessary to strip the solvent from the waste. An ideal situation might be the use of water-insol- uble waste from one process to extract the water- soluble waste material from another process water. Biological Waste Treatment Methods General. Bacteria can utilize an amazing num- ber of organic compounds as the carbon source in their metabolism, which is the basis for many sys- tems to remove organic materials from water. By providing an environment conducive to bacterial growth one can achieve rapid utilization of com- plex mixtures of soluble organic materials. End products of bacterial carbon utilization are carbon dioxide and protein. Since biological treatment depends on the pro- duction of protein, it is necessary that nitrogen and phosphorus in a usable form be available to build protein molecules. All living cells require carbon, nitrogen, oxygen and phosphorus. Oxygen can come from the free oxygen dissolved in water in which case the biologic system is called aerobic. If the oxygen comes from a combined source such as NO, or SO, the system is anaerobic. Anaerobic Biological Treatment. Anaerobic bac- teria use combined oxygen, and the entire system is one of reduction. The end products of anaero- bic bacterial action are CO,, CH,, NH,, H,S and fatty acids. The CO, is in excess of the NH, pro- duction and the NH; combines with the CO, to form ammonium bicarbonate. Material equiva- lent to one pound of Chemical Oxygen Demand (COD) fed to the anaerobic process should yield about 5.6 cubic feet of CH,. The use of anaerobic treatment by industry has been restricted largely to the food industry. Too often the industry has used merely an open pond and let nature take its course. Improper design and control have resulted in the uncon- trolled production of H,S and amino acids caus- ing odor nuisances. Properly designed and contained anaerobic treatment plants can remove effectively and cheap- ly as much as 90% of the B.O.D. from a strong organic waste. Proper mixing, recycled solids, off-gas containment and temperature control are requisite to achieve 90% removal in as little as 24 hours retention time. Anaerobic treatment should be considered for any waste which has a B.O.D. of more than 2000 mg/l. Temperature should be maintained at about 95°F. Usually anaerobic treatment is followed by aerobic treatment for two reasons. The anaerobic process develops considerable non-settleable solids and produces acetic and propionic acids. The aerobic process then metabolizes the organic acids and flocculates the colloidal particles. The best example of anaerobic treatment is the stabilization of the organic matter contained in municipal waste water treatment plant sludges. The digester effectively removes about 50% of the total organic matter contained in sludges. The gas from a well-operated digester will contain about 65% methane and 34% CO, with variable amounts of H,S. An interesting adaptation of the anaerobic process is the removal of nitrogen from a waste water containing nitrates. A low molecular- weight carbon source such as methanol is fed to an acclimatized system to reduce the nitrate to gaseous nitrogen. The single carbon minimizes sludge production, but other soluble organics can be used. Sludge lagoons can be rendered odorless if sufficient sodium nitrate is present in the water over the sludge. Aerobic Biological Treatment. Aerobic biological treatment of high volume, low organic, industrial waste waters is quite common, primarily because of low cost. Oxygen from air can, through bio- logic oxidation, be made to oxidize a pound of carbon for about 10 cents, including amortization and operation of the facilities. The cheapest chemical methods range upward from 50 cents per pound of carbon oxidized. Then too, bacteria can readily metabolize materials such as acetates which are extremely difficult to oxidize chemically. Many methods are used to accomplish bio- logical oxidation. (a) The earliest method was the oxidation pond which is still effective in warm climates if sufficient surface area and depth are provided. Without continuous sludge removal, a pond quick- ly becomes anaerobic on the bottom. Sufficient 655 retention time for solids permits the flow-through part of the pond to remain aerobic. Many pulp and paper mills have used aerated ponds to as- sure sufficient oxygen and minimize the land area needed. All biological reactions are temperature dependent, so in order to maintain effective treat- ment the water should remain above 50°F or the retention time required to achieve a standard qual- ity becomes too great and economy is lost. An- other factor in the retention time is the amount of biological solids kept in suspension. The aerated pond usually has no more solids in suspension than one half the B.O.D. concentration. With proper depth for sludge, observations on oxidation ponds have led engineers to design for about 50 lbs. B.O.D. loading per acre per day. (b) The trickling filter was an outgrowth of the old contact tank. It was observed that bio- logical slimes adhered to surfaces in natural streams. The contact tank was merely a tank filled with large stones into which the waste water was directed and operated on the fill and draw principle. The slimes on the rocks obtained oxy- gen from the air drawn into the tank on the dis- charge cycle. By spraying the waste water and permitting it to trickle down through a bed of stones, the process permitted more air to contact the waste and hence increased the loading as well as the oxidation efficiency. There is no filtering action as such in the so-called trickling filter. Soluble organics are converted to protein; colloidal matter, if present, can be absorbed in the slimes. The slimes adhering to the media will become anaerobic next to the media surface. As the slimes become thicker, they slough away from the media and become suspended solids in the effluent. The development of the rotary distributor further increased the usefulness of the trickling filter by insuring complete and uniform distribu- tion over the entire rock surface. The use of plastic shapes which provide a known surface-volume relationship have improved removal efficiencies and have permitted the use of increased depths so that these units have become known as oxidation towers. The trickling filter should not be used on wastes which have a high suspended organic solids content. Solids absorbed in the slimes can quickly go anaerobic, and the odors can be a nuisance. The oxidation tower has its best place in the rapid conversion of soluble materials to insoluble protein. In this case the indicated removals are in the neighborhood of 50%. The unit then serves to pre-treat medium strength wastes ahead of ac- tivated sludge. Rock trickling filters can seldom be loaded to more than 50 Ibs. B.O.D. per day per 1000 cu. ft. of media. The plastic media-units have been used with loadings of 500 Ibs. B.O.D. per day per 1000 cu. ft. (c) Activated sludge is a process in which flocculated biological slimes are settled and re- turned to the aeration tank to maintain a high ratio of acclimatized sludge mass to carbon. The activated sludge process has been the subject of much research since 1914. Each year investigators have added a little to our under- standing of the process until we now can formu- late the various relationships and design facilities with a fair amount of accuracy. With highly concentrated waste waters con- taining rapidly metabolized substances the main problem is to dissolve oxygen as fast as the bac- teria can use it. A well acclimated return sludge will convert soluble organic material to protein as rapidly as oxygen is made available. A limited oxygen supply will increase the time of conver- sion to the point that the protein growth phase is still in progress at the end of the aeration tank. When this condition occurs sludge will be lost over the settling tank weirs and effluent quality is poor. An overloaded activated plant is ex- tremely difficult to manage and usually goes from bad to worse because of the inability to condition properly the return sludge so that flocculation takes place before reaching the settling tanks. Accurate evaluation of waste waters and lab- oratory experimentation are necessary to define the design and operation of an efficient activated sludge system. Recommended Reading I. ECKENFELDER, W. WESLEY, JR.: [Industrial Water Pollution Control. McGraw-Hill Book Com- pany — New York, 1966. (Laboratory procedures to develop design criteria with excellent recent references.) 2. NEMEROW, NELSON M.: Liquid Wastes of In- dustry. Addison-Wesley Publishing Co., Reading, Mass., 1971. (Theories, Practices and Treatment — replete with specific industry references.) 3. Principles of Industrial Waste Treatment. John Wiley & Sons, New York, 1955. (General review of industrial waste problems and solutions.) 656 CHAPTER 45 CONTROL OF INDUSTRIAL SOLID WASTE P. H. McGauhey C. G. Golueke SCOPE OF INDUSTRIAL WASTE GENERATING ACTIVITIES The Problem of Definition In reducing to comprehensible terms the vast spectrum of residues of resource utilization which comprise solid waste, it is necessary to resort to some scheme of classification. At the broadest level of definition, relating wastes to the general sector of human activity in which they originate has been the most common approach. Thus municipal, agricultural, and in- dustrial wastes commonly appear in both the lit- erature and the language of solid waste manage- ment as categories which by implication, at least, are essentially of the same order. That they are not in fact of the same order is of little significance when the primary concern is for municipal wastes. However, when industrial waste is the problem, some distinctions between the three classes must be clearly understood. 1. Municipal Wastes. The domestic and com- mercial activities which generate municipal wastes are characteristic of cultural and social patterns which are national in scope. Thus, with some variations in regional and climato- logical factors which result in ashes in one community and year-round grass trimmings in another, the term “municipal wastes” has an identifiable meaning without great refinement of definition. Agricultural Wastes. In the case of agricul- tural wastes there is currently some confusion of definition. Some individuals still consider the term to include everything from crop resi- dues left in the fields to animal manures and the residues produced in processing food and fiber grown on the land. However, much of agriculture is organized and managed in the same manner as are factories. Land is pre- pared, and many crops are harvested, with sophisticated machinery. Thousands of ani- mals are concentrated in milk, egg, and meat production enterprises. The distinction be- tween a processing plant utilizing farm prod- ucts as its raw material and one processing crude petroleum, for example, is quite arti- ficial. Therefore, except for plant residues left in the fields and animal wastes deposited in the pastures, it seems appropriate to in- clude much of what is now classed as agricul- tural waste in the industrial waste category. In fact there is already a trend to consider animal manures as a source of industrial pol- lution.? 657 3. Industrial Wastes. Although, as previously noted, there is a certain logic in classifying solid wastes as municipal, agricultural, and industrial, the logic breaks down when control of industrial wastes is the problem of concern. Consequently, in terms of control there is no way to define “industrial wastes” in the con- text of the simple classification cited. It is everything that is not included in “municipal wastes” and a large percentage of what is included in “agricultural wastes.” Therefore, it can best be isolated only in relation to cer- tain types of human activity. Nature of Human Activity Involved in Industry The range of human activities which might be described by the word “industry” is so broad and varied that essentially the only thing all in- dustries have in common is that they generate residues they do not want. Although in the ag- gregate these unwanted residues comprise indus- trial solid waste, no one approach can resolve the waste control problem it presents, for the simple reason that there is no single identifiable prob- lem. There are, however, types of activity which generate broad types of industrial solid waste problems, each amenable to some typical ap- proach although not to a universal solution. For the purpose of this discussion these activities are divided into three classes: 1) extractive industries; 2) basic industries, and 3) conversion and fabri- cating industries. Obviously these three classes are not mutually exclusive. Processing, for example, may be a feature of any type of industry, but each class has identifiable characteristic waste generating fea- tures which differentiate it from the other two. INDUSTRY AS A GENERATOR OF SOLID WASTES Extractive Industries The normal concept of an extractive industry is, as the name implies, one in which raw ma- terials are taken from the earth and marketed in essentially their original state with little or no value added by manufacture or processing. Con- sequently it is to be expected that the solid wastes generated by such industries are but components or products of the earth. Four extractive indus- tries, namely mining, quarrying, logging, and farm- ing are of particular significance as generators of solid wastes. A fifth, the petroleum industry, is a major contribution to industrial solid waste prob- lems, but not in the extraction process itself. Mining. In terms of the quantity of solid wastes generated, mining probably exceeds all other industries, estimates ranging as high as 1.6 billion tons per year.> * Shaft and tunnel mining of coal and metal ores necessitates bringing to the surface large quantities of earth materials associated with the particular min- eral sought, or overlaying it. Convenience, economics, and sheer weight and volume of materials dictate that these tailings be dis- carded near the mine head. Thus the major waste problem is fundamentally the local cre- ation of an extremely large pile of inert ma- terial which is usually unsightly, destructive of the land resource it occupies, and may con- tribute to water pollution by leaching over a long period of time. Sometimes this waste pile is a menace to human life as well, as a result of instability due to fine particles, which may run as high as 40 percent.” A notable example is the 1966 tragedy in Aberfen, Wales, where 150 persons (mostly school children) were killed by a slide of an 800- foot-high pile of coal mine waste. Mine tailings are proving to be stockpiles of valuable resources, albeit by inadvertence rather than design.** A major example is the early discarding of tungsten and vanadium ores in iron mining operations. When later a use was found for these metals, more wealth was extracted from the waste pile than was originally generated from iron. However, this secondary extraction did little to diminish the size of the original heap of wastes. Concentration of solid wastes often occurs at locations which are relatively close to the mine where crushing, flotation, and other processing of ores is essential to the extraction process. Such secondary waste concentrations are generally smaller than those at the mine head but they are by no means insignificant in volume. For example, about 1.3 tons of wastes are generated for each ton of pelletized iron ore processed.” However, they still rep- resent materials taken from the earth’s crust and simply relocated and concentrated on the land surface. Quarrying. Quarrying is often classified sep- arately from underground mining. Open pit, or strip mining and the quarrying of glass sand, stone, and sand and gravel are typical of this type of extractive industry. In com- parison with other types of mining, sand and stone quarrying displaces and concentrates smaller amounts of unwanted materials (ap- proximately 0.5 to 5.0 percent).® Otherwise the solid waste problem is the same; i.e., inert earth materials piled on the surface. Al- though quarrying wastes may be deplored by citizens on the basis of effects on nearby prop- erty values, or of aesthetics or other emotional response, quarrying is more an environmental problem of noise, dust, traffic, and aesthetics than one of solid waste generation. Logging. As a generator of solid wastes the harvesting of timber differs from mining and 658 quarrying in that its residues are organic. Hence, in a matter of years rather than of geologic time they are returned to the soil by the biochemical processes of nature. It is es- timated that traditional logging procedures leave in the woods some 30 to 40 percent of the original weight of the tree, or about one ton of debris per 1,000 board feet of logs harvested.” As a solid waste problem this material is scattered over a wide area, is un- sightly, constitutes a fire hazard to the forest, may be a reservoir of tree-destroying diseases and insects, and represents a wastage of nat- ural resources. 4. Farming. The solid waste generating aspects of farming include both plant and animal wastes, the estimated per capita production averaging 43 to 60 1b./day.*® Plant residues of significance include unharvested or unhar- vestable crops, vines, straw and stubble, and orchard prunings. Here a variety of solid waste control problems accrue largely as a re- sult of air pollution and other environmental considerations. Unfortunately, burning of cer- tain seed grass stubble is necessary to control plant diseases. Straw and stubble plowed into soil increase the cost of nitrogen fertilizer to offset the carbon surplus. Unharvested prod- ucts such as melons and tomatoes produce unpleasant odors and may attract insects and rodents. Tree prunings are both a physical problem and a reservoir of crop and tree- destroying pests if burning is not allowed. Burning of sugar cane remains an economic and technological necessity in eliminating leaves prior to processing. Disposal of manure and dead fowl con- stitutes an extremely difficult problem to the poultry and egg production industry. Al- though the wastes are organic and capable of incorporation into soil by natural processes, they are concentrated in location, 10,000 to 100,000 birds being housed in a single loca- tion. Moreover, they are aesthetically objec- tionable, uneconomical to collect, and un- wanted by agriculturists. The same situation exists in dairy and animal fattening installa- tions, the latter of which involve as many as 20,000 animals in a single operation and may soon involve 100,000. Concentration of de- composable wastes, pollution of water, fly pro- duction, aesthetics, and economic and techno- logical problems of collection and disposal are among the solid waste problems generated by animal husbandry as an extractive aspect of the farming industry. In evaluating extractive industries as genera- tors of wastes, the four examples cited have sev- eral things in common. They concentrate wastes at specific locations on the surface of the earth; the wastes are normal products of the earth and its living things; and they do little to multiply the basic value of the product. They differ, however, in nature, some being inert materials whereas others are biodegradable organic matter. Con- sequently, no single approach to solid waste con- trol can overcome the problems man associates with the wastes of extractive industry. Basic Industries For the purpose of this analysis, basic indus- tries are considered those which take raw materials from extractive industry and produce from them the refined materials which other industries con- vert into consumer goods. Basic industries differ from extractive in several ways, the most signifi- cant being in the value added by manufacture. Products of the basic sector of industry are such things as metal ingots, sheets, tubes, wire, and structural shapes; industrial chemicals; coke; paper and paperboard; plastics materials; glass; natural and synthetic fabrics; and lumber and plywood. From the farming industry there is a tendency for fiber to go into basic industry, and food to con- version industries or directly into commercial channels. Exceptions might be the hulling of rice and the production of raw sugar from sugar cane, although these two might better be classed as con- version industries. The solid wastes generated by basic industries may be said to differ from those generated by extractive industries in three major aspects: They are more diverse in composition; they differ markedly from the normal mineral and plant resi- dues found in nature; and the industry itself gen- erates a fraction of its own wastes. The solid waste generated by any type of industry in its business offices is, of course, considered a part of the nor- mal commercial component of municipal wastes. Eight basic industries are perhaps the major generators of solid wastes in their class: metals, chemicals, paper, plastics, glass, textiles, wood product, and power. 1. Metals. Blast furnace slag and ashes from the smelting of iron ore probably rank second only to mining wastes in volume of waste pro- duced by industry. Slag produced in steel pro- duction is estimated to be more than 1,000 tons per day per furnace, or about 21 percent of the steel ingot production'®''. Similarly, the smelting of copper and the production of aluminum result in significant amounts (more than 5 million tons each in 1965)'*!? of waste materials essentially of an inert nature, although subject to leaching if carelessly dis- carded in the environment. Like extractive industry wastes, basic metal wastes are con- centrated at the points of generation. Here, however, the similarity begins to lessen. Min- ing wastes, for example, tend to occur in areas remote from any community which does not depend almost entirely upon mining for its livelihood. In contrast, smelting is more likely to be done in a community which through the years has diversified until it harbors many di- verse urban interests. Thus both the physical freedom to create a large pile of slag at the smelter site and the willingness of people to accept it, become serious aspects of the prob- lem of control of solid wastes from the metals industry. At the second level of the basic metals industry, where ingots are formed into 659 shapes, smaller amounts of mill scale and spalls characteristic of the metal being proc- essed appear as solid wastes. At this level of industry new types of solid waste appear: trimmings from the product itself; residues from the on-site use of other refined products associated with the process (e.g., lime sludges from the neutralization of spent pickling liquor); and miscellaneous wastes from the handling and shipping of the item produced. Chemicals. For variety of wastes the chemical industry exceeds all other basic industries and generates some of the most economically and technologically difficult problems of solid waste management. The nature of these prob- lems in any particular chemical plant, of course, depends upon the processes and the products involved. Producers of less exotic materials such as portland cement, carbon black, and lime have tended to locate in areas remote from urban communities. Their princi- pal solid wastes have been air-transported par- ticulates, deposited over a large downwind area, plus ashes and mineral residues accumu- lating at the plant site. In contrast, such in- dustries as petro-chemicals have generally lo- cated in urban centers or have been overrun by urban expansion. The same may be said of producers of sulfuric acid, fertilizers, and many other basic chemicals. The range of waste materials generated by the more complex chemical industries is too extensive to catalog in detail in this summary. However, it includes off-specification material, tars, process sludges, and a vast variety of chemical residues. Although roughly one-third of industrial wastes are generated by the chem- ical processing industries,'* the wastes are sig- nificant because of their particular chemical properties and their environmental effects. Generally, solid wastes from the more sophisticated chemical processes are generated in a liquid stream which, in many cases, has been discharged to the ocean or to surface streams, or injected into deep underground strata. Nevertheless, some are generated di- rectly in the solid state. These include chem- ical residues, precipitated sludges, and the miscellaneous refuse associated with the im- port of necessary processing materials and shipment of the finished products. In the en- vironmental climate of the 1970’s an increas- ing fraction of air-borne particulates and wa- ter-borne process brines and sludges will have to be collected as solids and controlled by solid waste management techniques. Paper. Although much public attention has been directed to paper as a waste material, most of the problems associated with its orig- inal production have been in the context of water pollution rather than solid waste control. As a generator of solid wastes the production of paper and paperboard is similar to other basic industries in that residues of materials used in the process and residues of the product itself must be dealt with. In the first category are such things as tree bark, wood fiber, paper pulp, and inert filler, which are not difficult to remove from transporting water; and process chemicals and wood extractives which can be isolated as solids only with difficulty, at con- siderable expense. As in the case of basic chemicals, both components of this first cate- gory of residues are destined to be controlled as solids if they are allowed to become wastes. The second category of wastes — residues of the product — consists primarily of trim- mings of paper or paperboard, plus wastage occasioned by malfunction of the processing equipment. Much of this material may be re- processed; some may be incinerated or depos- ited in landfills as are similar residues from the paper fabricating industry and from com- mercial and domestic sources. The total volume of solid waste produced by the basic paper industry, although not insig- nificant, is not as much of a management prob- lem as is the separation of dissolved solids from liquids in the waste stream which has historically been a water pollutant. Plastics. In the case of plastics, the residues associated with production of the basic ma- terial are essentially a problem of the chemical industry. Much of this material then goes di- rectly to the conversion and fabricating indus- tries, but some is converted by basic industry into sheets and other forms used by fabricators. Wastes from this segment of the industry are largely trimmings from the product itself. No estimate is available of the amount of such solid waste, but it is undoubtedly only a small fraction of the overall plastics disposal prob- lem of a community. Glass. Solid wastes generated by basic produc- ers of glass include slag from the purifying of glass sand, plus miscellaneous containers and residues from products used in coloring and laminating glass, cullet (glass fragments) from breakage during manufacture and trimming of sheets, off-grade, resin coated fibrous glass, and residues from on-site crating of glass for ship- ment to conversion and fabricating industries. Except in situations where cullet of various colors becomes mixed, the major fraction of solid waste from the basic glass industry is reused and hence does not appear as a waste requiring control measures. Textiles. Basic textile industries vary in the nature and spectrum of solid wastes generated, depending upon the type of material being processed. Trash from the ginning of cotton may be generated at the extractive industry level or as an intermediate step between extractive and basic industries. It is a fraction of the original cotton plant and is generally concen- trated as a waste in comparatively small frac- tions of the total at a number of dispersed loca- tions in cotton farming communities. Wastes specifically characteristic of the cotton textile mill are more commonly such things as strap- ping and burlap used in baling, plus comber wastes and fibers damaged during storage or 660 shipment which are generally reutilized in the industry.!* Linen textile manufacturers likewise must dispose of plant residues and materials used in shipment of the raw flax. Fiber, twine, dirt, and wool fat characterize the wastes from pre- paring wool for textile processing. In addition to waste fibers, synthetics generate special wastes in the form of containers used in ship- ping chemicals from the basic chemical pro- ducers. Residues from spinning, weaving, and trim- ming operations occur with all types of fabrics. Dye containers and residues from on-site prep- aration of cloth for shipment are a fraction of the overall solid waste generated by the basic textiles industry. 7. Wood Products. Tree bark, sawdust, shavings, splintered wood, and trimmings constitute the major solid wastes of the lumber producing industry. In weight they amount to some 10 percent of that of the original tree in the for- est, or about 1.26 tons per 1,000 board feet.'” Conversion of wood to plywood sheets con- tributes plywood trimmings, knots, and glue containers to the overall solid waste of the wood products industry at its basic level. Wood ashes are typical wastes of this industry as a result of on-site burning of wastes for power production or to dispose of sawdust and other wood wastes. Typically, sawmills are located in smaller communities and are notable for their untidy appearance. Broken cable, discarded machin- ery, and miscellaneous debris often character- ize the environment of a wood processing plant, albeit out of scale with the amount of such wastes generated. Air pollution and aesthetic considerations may be expected to intensify the solid waste control problems of the basic wood products industry as particulates now discharged to the atmosphere by burning become converted to solid wastes in response to restrictive legis- lation. 8. Power. Fly ash, bottom ash, and boiler slag accompany the production of power by burn- ing of coal. Production of these three wastes by the U.S. power industry in 1969 was 21, 7.6, and 2.9 million tons, respectively.'® Often such power plants are located in metropolitan areas, hence the objection to air-borne fly ash, dust, and ash heaps confronts the power pro- ducing industry with solid waste problems. Where high ash coals are utilized, the volume of ashes and clinkers may approach that of the original coal consumed, although, of course, its dry weight is generally appreciably less than 20 percent of that of the coal from which it was derived. As generators of solid waste, basic industries such as those herein cited have several things in common. With few exceptions, they draw upon more than one extractive industry for raw materials; a fraction of the raw materials they refine appears as a solid waste; they utilize refined products of other basic industries and of conversion industries, importing in the process things such as shipping containers which become wastes for which they must assume responsibility; a fraction of their own product must be handled as a waste; and a con- siderable value is added by manufacture, or proc- essing by the basic industry. In comparison with a purely extractive industry, a basic industry pro- duces more categories of solid waste, some of which it can recycle directly in its own processes. However, in comparing one basic industry with another, the things they have in common are not reflected in any similarity of waste generated. Hence no common approach to solid waste con- trol characterizes the problem of basic industries. Conversion and Fabricating Industries It is beyond the scope of this chapter to at- tempt any listing of the myriad enterprises which convert the products of basic industry into the goods which characterize our economy and our standard of living. Value added by manufacture is a maximum in the conversion and fabricating industries. As generators of solid waste, such industries also have many things in common. Particularly significant is the extent to which the output of one type of industry comprises a combi- nation of raw materials and solid waste for an- other. For example, one modest sized industry en- gaged in converting plate glass to windows and mirrors in the Los Angeles area estimates its cost of disposing of crating materials received from its suppliers at one thousand dollars per month. A second common characteristic of the con- version and fabricating industries is that residues of the basic materials they utilize generally con- stitute the greatest fraction of the waste they gen- erate. Moreover, unlike a basic industry which may directly recycle the trimmings and rejects of its own product, the conversion or fabricating in- dustry must rely on some secondary enterprise to take such of its residues as are reclaimable. Thus broken glass, metal trimmings, imperfect castings, and similar salvable residues can seldom be utilized directly by the conversion industry which gener- ates them. To illustrate the type of solid waste problems associated with the conversion and fabricating in- dustries, such broad categories of industry as pack- aging, automotive, electronics, paper products, hardware, soft goods, food processing, and con- struction may be cited as typical, though by no means all inclusive. 1. Packaging. For the purpose of this summary, production of packaging materials is classed as basic industry, hence only the conversion of packaging materials to containers is consid- ered. However, the scope of this sector of the industry is itself extremely broad and varied as regards the nature and resource value of the waste it produces. Aluminum, steel, glass, plastics, cardboard, corrugated paperboard, plastic-paper laminates, and paper with or without any of a broad range of coatings are among the materials used by the container industry. Whether or not an appreciable num- 661 ber of these items appear in any industrial waste stream depends, of course, upon the range of activities engaged in by a single com- pany or plant. Recoverability of residues often depends upon the cleanness and uniformity of the waste material. For example, conversion of glass to containers generates an appreciable amount of cullet; however, whether this is recoverable or useless, generally depends upon the extent to which colored and clear glass is mixed in the waste. Nevertheless it may be said that, at the industrial level, wastes from the packaging industry are primarily fractions of the material converted, although the range of possible materials is unlimited. A secondary waste of any individual pack- aging plant is packages passed along to it by its suppliers, together with residues on its own on-site shipping preparations. Automotive. There are two major waste-gen- erating sectors of the automotive industry. One makes and ships specialty components; the other assembles the components into a finished vehicle. Conversion and fabricating industries in the first of these categories produce such things as tires, generators, carburetors, radios, speedometers, wheels, bumpers, hub caps, lamps, bearings, and other of the dozens of systems or devices that go to make up an automobile. In each of these the solid waste generated is a function of the special activity of the individual industry, and comprises resi- dues of the materials used and the packaging received from suppliers. Painting and upholstering of automobile bodies adds both container and material resi- dues to the solid waste stream of the manu- facturer. However, by far the greatest com- ponent of the automobile assembly plant waste is the discarded packaging and shipping ma- terials associated with the delivery of compo- nents from other industrial suppliers. In fact, there is probably no other sector of industry which compares with automobile assembly in the amount of solid wastes it inherits from its relationship with other industrial activities. Electronics. Like the automotive industry, the electronics industry includes both a compo- nents and an assembly sector. Plastics, glass, wire and sheet metal scrap and residues of a variety of other basic products appear as solid waste of the many industries associated with production of electronic components. How- ever, in comparison with the waste from most other conversion and fabricating industries, the actual amount is relatively small. Packaging materials, particularly card- board, corrugated paperboard, polystyrene foams, and padding materials utilized in ship- ping electronic components is the major waste generating problem of the assembly activity of the electronics industry. Shipping of the assembled equipment is generally in specially designed containers, the manufacturing wastes of which are ascribable to the packaging in- dustry. 4. Paper Products. Conversion of paper into products used in commerce and by the public "largely results in solid waste in the form of paper trimmings. Facial and toilet tissue, pa- per towels and napkins, and similar products yield a high quality waste which may or may not be salvable through a secondary enterprise, depending upon whether white and colored paper residues are mixed together in the con- version process. Conversion of kraft paper into bags, for example, yields a readily salv- able waste. Publishing of books and maga- zines, which might be classed as a fabricating industry in the context of solid waste genera- tion, is a major source of filled paper residues which are commonly disposed of as solid wastes. Hardware. The term “hardware” rather than “hard goods” is used herein because the latter embraces many classes of basic as well as con- version and fabricating industries. ‘“Hard- ware” is confined further herein to the metals industry which produces the machines and tools (with the exception of the automobile), and the utensils and gadgets used by all classes of industry and by the public. Solid waste from such hardware industry includes residues from boring and machining of metals; trim- ming and sizing of plates, tubes, and structural shapes; and miscellaneous residues from cast- ing and forging processes. It also includes plating, etching, and similar liquid borne wastes which, like similar wastes from the basic chemical industry, must eventually be managed in the solid form. Soft Goods. Conversion of such materials as textiles, leather, and plastics into articles of commerce constitutes the soft goods industry in the context of conversion and fabrication. As is characteristic of all industries in this clas- sification, residues of the material processed represent the major item of solid waste gen- erated, with incoming and outgoing goods yielding secondary wastes associated with ship- ping. Food Processing. As a waste generating in- dustry, food processing presents problems somewhat different from other conversion in- dustries. Like extractive and basic industries concerned with material of plant and animal origin, food processing produces wastes which are subject to the normal recycling processes of nature. However, they are generated sea- sonally and in large amounts at locations which may be either urban or intermediate between farm and city. With the exception of a few residues such as rice hulls, food wastes are putrescible, attractive to insects, and occur in a semi-liquid or liquid state. Preparation of fruits and vegetables for canning yields a slurry of such things as leaves, soil, skins, peelings, pits, seeds, and cores, along with spoiled, out- sized, and damaged fruit. In California alone this type of cannery waste totaled 750,000 tons in 1967.” Washing and cooking opera- tions yield a companion stream of water-borne 662 dissolved and suspended solids. Because of water pollution problems, these solids increas- ingly are being removed from water for dis- posal by solid waste management techniques. Processing of fish and animals for market- ing or canning likewise generates putrescible liquid and semi-liquid wastes. The solids con- tent of these waste streams, along with bones and other inedible fractions, are destined to be handled as solid wastes as water quality ob- jectives become more restrictive. Because the food processing industry is linked directly to extractive industry without an intermediate basic refining, containers com- ing to the plant are reused in the fields and orchards. Furthermore, shipment of the fin- ished product makes use of containers already prepared by the packaging industry. Conse- quently, wastes from the food processing in- dustry are predominantly fractions of the ma- terial processed. 8. Construction. Among the most significant gen- erators of solid waste is the construction indus- try. In its purely fabricating activities its waste products are typical residues of the materials it employs — lumber, plasterboard, wire, pa- per, cement bags, sheet metal scrap, etc. How- ever, unlike other industries in the conversion and fabricating category, most construction wastes result from peripheral activities essen- tial to its production phase. Demolition of buildings, breaking up of pavement, and prep- aration of site produce very large volumes of such materials as earth; rock; broken concrete, tile, brick, lumber, and plaster; tree stumps, poles, and piling; and miscellaneous rubble. The eight foregoing examples by no means cover the full range of activities which might be classed as conversion and fabricating industries. They illustrate, however, that the wastes generated by this class of industry are primarily residues of the materials they process or convert into con- sumer goods, and that the measures necessary to move products from one sector of industry to an- other impose a secondary solid waste burden on the receiver. More important, it is significant that at this most complex level of industrial solid waste generating activity the value added by manufac- ture is greatest. This suggests that the economic capability of conversion and fabricating industries should generally be greater than that of a basic or an extractive industry as such. Moreover, con- version and fabricating industries tend to be ac- tivities of a diverse urban community. Therefore, social pressure for solid waste control can be ex- pected to be exerted most heavily upon such in- dustries, especially since their products, along with the associated packaging, constitute the major solid waste which the citizen himself ultimately casts off. MANAGEMENT OF SOLID WASTES Earlier in this chapter it was found conveni- ent to arrange industry into three categories, each having specific waste generating characteristics. These categories were presented in ascending or- der of magnitude of value added by manufacture, responsibility for creating wastes, and degree to which their activities are conducted in urban com- munities. To evaluate each category, and type of industry within that category, as a generator of wastes it was necessary to treat extractive, basic, and conversion and fabricating industries as dis- crete entities. In the real world of industry, how- ever, these three may be only sectors of a single large industry which owns and operates every as- pect from raw material source to the finished con- sumer product. Thus the conclusion that no com- mon waste management technique is appliable to all types of industry in a single category, although valid, is complicated by the fact that industry may be stratified vertically along ownership lines as well as horizontally along functional lines. To get at the general problem of solid wastes manage- ment in such a complex situation, it is convenient to consider waste control approaches in relation to the source of solid wastes rather than the composi- tion of the waste itself. Disposal as a Condition of Production The simplest situation in solid waste control applies especially to an extractive industry in which the feasibility of operating at all is contin- gent upon satisfactory control of its solid wastes. In such a circumstance a mining, quarrying, or logging operation might be undertaken by indus- try only when waste control is not an economically overwhelming consideration. Feasibility may, of course, be based on geographic or topographic conditions, property holdings, access, or regula- tion by public law or public policy. It does not necessarily imply environmental perfection, al- though there is a tendency (1971) for aesthetics to be given increasing weight where public interest or public opinion is a factor. Uneconomical con- ditions, whether natural or man-imposed in a wastes management context, generally have dis- couraged an extractive industry operating entirely on its own resources. However, in an industry which covers the whole range from extraction to conversion, extraction of raw material may well be operated at a loss in order to produce profits at the higher industrial level where value added by manufacture is sufficient to offset losses. More- over, control of solid wastes by an industry of this sort may be subject to considerable upgrading in technique and cost without causing the system to fail economically. Nevertheless, in such activi- ties as mining there is no choice but to dispose of wastes upon the land, albeit under conditions acceptable to society. In the case of farming as an extractive indus- try, constraints imposed by solid waste manage- ment have seldom been insurmountable unless ur- ban environmental conditions are required of the farmer. Generally, he is not part of an industrial complex which can take a loss continually at the extractive level. Thus if society asks too much in the name of solid waste control or other environ- mental context, the agriculturist, unless subsidized, ceases operations and converts his land to urban development. Incidental Residues Produced By An Industry As noted in a preceding section, processing, 663 converting or fabricating activities within several types of industry result in slag, ashes, clinkers, and similar solid residues, as well as air-borne par- ticulates or liquid carried process sludges, gener- ated at the site of operation. For air and water- borne solids, control measures may include elec- trostatic precipitators, bag filters, wet scrubbers, sedimentation, chemical precipitation, or other conventional waste treatment processes. Disposal of bulky worthless solids involves simple deposi- tion on the land in some location and under some conditions, acceptable to the public. More val- uable incidental wastes may, however, be reclaim- able or convertible to useful resource materials if the level of cost is acceptable. For example, about 14 percent of power plant solid wastes were uti- lized outside the power industry in 1969.'¢ Other measures which may assist in controlling the resi- dues produced incidental to industrial output may include such expedients as abandoning on-site gen- eration of power, or making changes in process. Abandonment of an entire plant, especially one with obsolescent processes, is a measure some- times taken by industry confronted with solid wastes which are a by-product of its fundamental processes. Product Residues Generated By A Basic Industry When refinement rather than conversion of raw materials is the goal of production, product wastes occasioned by spillage, breakage, or mal- function of process may be managed by direct recycling within the plant. The same is true of metal trimmings, cullet, and paper trimmings in industries producing metal, glass, or paper as basic products. Residues From Materials Conversion Or Fabricating Cullet, metal trimmings, packaging materials, and other residues resulting from the conversion of basic industrial products into consumer goods cannot be directly reused by the waste producer. To him they represent a solid waste, some of which might be salvaged or reused economically; some of which he shall have to pay someone to remove for disposal. Metal scrap, clear glass, and uncoated corrugated paperboard are typical of the material which might be returned to more basic industries for reprocessing. Similar trimmings from plastics, fiberboard, laminated plastic-paper, lumber, cloth and a host of other materials are generally useless and are relegated to the landfill or incinerator. Waste From Interindustry Transfer Packaging and shipping of basic materials or finished products, a necessary part of industrial activity, require that most industries accept vari- ous amounts of materials, which immediately be- come a waste, in order to acquire the materials necessary to their enterprise. Thus each industry helps to create a solid waste management problem for those with which it does business. In general. the waste-to-product ratio goes up from basic to conversion industry, reaching its maximum value at the conversion industry-to-consumer level. Most of the waste generated by interindustry transfer of materials and components is waste, although there are instances where intra- or inter-industry prac- tices work to hold down waste production. Where producer and fabricator are favorably located with respect to each other, such things as cable spools and protective packaging for television tubes are commonly reused repeatedly for their original purpose. Special Problem Materials Waste materials which present especially diffi- cult problems of management at present (1972) include both natural and synthetic products. Or- ganic wastes, particularly food processing wastes, are a nuisance because they are putrescible, whereas plastics are a nuisance because they are not. Process sludges of a wide variety of activity, ranging from industrial waste treatment to saline water reclamation, present an unsolved problem both because of their high liquid content and be- cause they are so newly recognized as solid waste problems that no economic technology for con- verting them to drier solids has been developed. CONTROL OF INDUSTRIAL SOLID WASTES In the preceding section attention is directed to the internal management of solid waste gener- ated at various levels in the industrial scale. How- ever, to determine what methods of control are needed in solving the overall problem of indus- trial solid wastes, it is first important to under- stand the relationship of industrial practice to the generation of society’s total solid waste problem. To a significant degree it is true that the entire industrial effort of the nation is dedicated to the production of solid wastes. The product of ex- tractive industry is the raw material of basic indus- try; and the product of basic industry feeds the conversion and fabricating industry. Each sector of the system discards what it cannot pass along to the next in line. Finally, the entire product of the conversion and fabricating industry becomes the solid waste of all sectors of society — industry, commerce, and citizens. The rate at which the overall system functions governs the economy of the nation and depends upon the acceptance of goods by the consumer at the top of the scale. This encourages industry to mistake the act of physical acceptance of goods by the citizens for actual consumption of these goods. The next logical step is to create through advertising a dis- satisfaction on the part of the consumer so that he discards his purchases gon the basis of obsoles- cence rather than loss of utility. Thus it is clear that quite aside from any question of whether in- dustry is giving the public what it demands, or the public is accepting what industry persuades it to demand, the overall waste generation of the com- mercial and municipal sectors of society is a func- tion of what flows from industry into these sectors. Carried to its logical conclusion, this system would eventually convert all nonrenewable re- sources into discarded wastes unless reuse and re- cycling are a matter of industrial practice and pub- lic policy. Therefore it seems logical to conclude that public agencies, industry, and education of the public each play a role in industrial solid waste control. 664 Role of Public Agencies in Industrial Solid Waste Control In the absence of any public agency concerned with overall environmental quality, solid waste control would be a problem of individual enter- prises in specific locations rather than one con- fronting the entire sector of human activity loosely described as “industrial.” Thus, for example, a mining operation with land area for spoils would have no disposal problems, whereas waste dis- posal might be the most compelling problem of a less fortunately situated operator. Without pub- lic constraints, wastes generated incidental to pro- duction, and residues of materials conversion as well, might be hauled to some public or private dump and so pose no problem other than that of cost to the generating industry. The same may be said of particulates discharged to the atmosphere, or of process brines and sludges discharged to the water resource. Industry would, of course, share in any ulti- mate disaster that wastes might bring upon man- kind, but in the interval industry's wastes like those of everyone else would react only to degrade the general environment. In such a situation, responsi- bility for deciding what sort of a world society wants accrues to the public; and implementing public goals is the function of public agencies. Therefore, some agency of the public must decide what constitutes an environmental problem, at what level the problem is to be tolerated, and what measures should be taken to alleviate it. In the context of problems associated with in- dustrial solid wastes public agencies play a role in four distinct areas: public health, environmental quality, resource conservation, and economics. 1. Protecting Public Health. The concept that industrial solid waste poses a threat to public health apart from that of municipal refuse is of quite recent origin. It developed from a realization that air pollution is a menace to human health and that industrial pollution of water has health implications beyond that of historical water-borne disease. Constraints im- posed on industry in the interests of health of workers and citizens in general are, therefore, currently reflected in the concept that air and water pollutants should be separated from their transporting media and dealt with directly as solid wastes. As with municipal refuse, how- ever, industry is expected to handle its putres- cible organic residues in such a manner as to keep down insect and rodent vectors of disease. Thus, the role of the public health agency in industrial solid waste control is essentially regulatory. 2. Attaining Environmental Objectives. Envi- ronmental objectives which call for clean air, pure water, freedom from nuisance and affront to the aesthetic sensibilities of man, and a healthy ecological balance in nature are per- haps the major concern of public agencies in relation to industrial (and other) solid wastes. At the local level attainment of such objectives may be the responsibility of the health de- partment, but at the federal level and in many states protection of the environment is a role assigned to some agency with broader regula- tory powers than the department of health. It is the role of this agency to determine where and under what conditions wastes may be de- posited on land, burned, or otherwise disposed of by those who generate them. In carrying out this role the agency, in the long run, con- tinuously must strike a balance between the environmental perfection desired by an emo- tional public and the industrial freedom con- sidered necessary to an ever-expanding and changing civilization to arrive at a point at which environmental objectives are attainable at an acceptable reduction in our level of civilization. Implementing Resource Conservation Policies. Resource conservation is a matter of public concern which has been assigned to numerous agencies with various powers and specific in- terests for more than half a century. In rela- tion to solid waste, conservation has been in- terpreted’™'® in terms of both land resources and the value of resource materials in the solid waste. Thus, a public agency, alone or in con- cert with other public agencies, might decree in one case that a spoils dump or a slag heap in a certain location would be destructive of a land resource either by physical occupancy of land or by environmental degradation. In another case the conclusion might be that a properly constructed landfill in a particular location would create a new land resource. Concern for the resource value of residues such as glass, metal, and paper wastes from the conversion and fabricating industries might lead a public agency to any of several alternate decisions. For example, the decision might be that enhancement of land resources is im- portant enough to justify sacrificing resource residues as landfill material. In contrast, there might be reason to decide that resource resi- dues should be stockpiled in a fill for reclama- tion at some future date; or that they should immediately be recycled in the interest of re- source conservation regardless of cost. Both the multiplicity of public agencies having interest in land use and in resource conservation, and the scope of possible policy decisions, gives the public agencies a broad and flexible role in determining the conditions industry must meet in managing its solid wastes. Overcoming Economic Constraints. In the matter of economic constraints, public agen- cies may play either of two important roles. They may force industry into actions regard- ing solid waste control previously thought to be too costly by regulatory actions directed to resource conservation, environmental quality, or any other objective. At the other extreme, they may establish economic incentives for ac- tion by industry. It is not likely that regulation of what con- version and fabricating industries must do with their solid wastes will be a deciding factor. 665 Instead, a requirement that resource materials be recycled will strike at the consumer-waste hinge of the system and so feed back through the entire industrial equilibrium. That is, it will change the kind of materials required by the conversion industry and, consequently, what basic industry produces and what amounts of specific raw materials are ex- tracted. In the matter of economic incentives, tax breaks or tax penalties,’® demonstration grants for exploring new processes, direct subsidy of recycling, and equalization of freight rates for new and scrap metal* are examples of actions which might be taken by public agencies under appropriate public policy. The result might be both a change in the nature of solid waste generated by industry, and in the ultimate fate of such wastes. Role of Industry in Industrial Solid Waste Control Because industry accounts for a very large fraction of the total solid wastes of society and the processes by which many wastes are generated are proprietary to industry, it is logical to expect that industry should play a significant role in the control of its wastes and, consequently, of the total waste load upon the land. The Matter of Options. If all discarded material is considered as waste, the mining and basic metals industries appear as the major source of industrial waste. To deal with such things as mine tailings and blast furnace slag, however, man has few op- tions. Thus at the lower end of the scale the role of industry in solid waste generation is relatively fixed. Similarly, the small value added by process- ing at the extractive level limits feasible disposal methods, unless higher levels of industry or gov- ernment subsidize waste control. Further up the scale, however, such rigidity no longer pertains. The material to be used for any given purpose, as well as the resulting waste- to-product ratio, is a function of the inventiveness and ingenuity of man. Competition for markets encourages the producer of consumer goods to use that ingenuity in finding better processes and cheaper materials and production methods. Con- straints imposed by public policies concerning re- sources, environment, and waste management may likewise react to this same end. Therefore, at the higher end of the scale the role of industry in the overall waste problem is not fixed by circumstance. Reducing the Amount of Waste. Better processes and cheaper materials do not lead necessarily to a lesser amount of wastes generated. In fact, it is possible that quite the opposite might result. Therefore, industry’s role in controlling the amount of solid waste society generates is one of looking to its own design and materials selection activities with consideration for the final disposition of its product in the environment. The concept that purchase is synonymous with consumption of goods leads logically to a limitation of the objectives of design to such traditional fac- tors as ease of manufacture, saving in cost of fab- *In Minnesota the 1970 freight rate for scrap was $4.25/ ton as contrasted with $1.84 for raw material.2® rication, appeal to the buyer, novelty, and obso- lescence. Responsibility for solid waste control and for resource conservation, however, now re- quires that degradability of synthetic materials, ease of dismantling for segregating component ma- terials, minimum number of types of material, and other materials recovery considerations or disposal objectives be among the specifications designers should seek to meet. Role of Public Education It is particularly important that people under- stand the inter-relationships within industry and the dependence of our level of civilization upon industrial activity. An informed public plays an especially sig- nificant role in the control of industrial solid wastes, both because public opinion is respected by industrialists and because public attitudes are the basis of policy legislation which creates the institutions which carry out public policy. Public education is both important and urgent at such times in history as the 1970’s when prophets of doom abound, and citizens are bombarded daily with propaganda and with naive and simplistic answers to complex environmental problems. References 1. LOEHR, R. C.: Alternatives for the Treatment and Disposal of Animal Wastes. J. Water Pollution Con- trol Federation, 43(4):668 (April 1971). DEAN, K. C. and R. HAVENS: Stabilization of Mining Wastes from Processing Plants. Proc. Sec- ond Mineral Waste Symposium. U. S. Bureau of Mines and IIT Research Inst., Chicago, Illinois, March 28-29, 1970. 3. McNAY, L. M.: Mining and Milling Waste Dis- posal Problems — Where Are We Today? Proc. Second Mineral Waste Symposium. U. S. Bureau of Mines and IIT Research Inst., Chicago, Illinois, March 28-29, 1970. 4. NAKAMURA, H. R., E. ALESHIN, and M. A. SCHWARTZ: Utilization of Copper, Lead, Zinc and Iron Ore Tailings. Proc. Second Mineral Waste Symposium. U. S. Bureau of Mines and IIT Re- search Inst., Chicago, Illinois, March 28-29, 1970. 5. COCHRAN, W.: Grace Mine Iron Ore Waste Dis- posal System and Estimated Costs. Information Circular 8435. U. S. Department of Interior, Bu- reau of Mines, 1969. 6. TIENSON, A.: Aggregates. Proc. Second Mineral Waste Symposium. U. S. Bureau of Mines and IIT Research Inst., Chicago, Illinois, March 28-29, 1970. 7. California Solid Waste Management Study 1968 and Plan 1970. Report by the California State Depart- ment Public Health (U. S. Public Health Service Publication No. 2118), 1971. 8. BLACK, R. J., A. J. MUHICH, A. J. KLEE, H. L. HICKMAN, JR., and R. D. VAUGHAN: Tle Na- tional Solid Waste Survey; An Interim Report. U. S. Department of Health, Education, and Wel- fare, 1969. 9. New Jersey Solid Waste Management Plan. Report prepared by Planners Associates, Inc. for Bureau of Solid Waste Management, Department of Environ- mental Protection, State of New Jersey, 1970. 10. BRAMER, M. C.: Pollution Control in the Steel Industry. Environmental Science and Technology. 5(10):1004 (October 1971). 11. BAKER, E. C.: Estimated Costs of Steel Slag Dis- posal. Information Circular 8440. U. S. Depart- ment of Interior, Bureau of Mines, 1970. ~~ 666 12. VOGELY, W. A.: The Economic Factors in Mineral Waste Utilization. Proc. Mineral Waste Utilization Symposium. U. S. Bureau of Mines and IIT Re- search Inst., Chicago, Illinois, March 27-28, 1968. 13. WITT, P. A., JR.: Disposal of Solid Wastes. Chem- ical Engineering. 78(22):62 (October 4, 1971). 14. LIPSETT, C. H.: Industrial Wastes and Salvage. Vol. 1. Second Edition. The Atlas Publishing Co., New York, 1963. 15. Idaho Solid Waste Management 1970 Status Report and State Plan. Idaho Department of Health, April 1970. 16. Ash Collection and Utilization — 1969. Ash at Work. 2(2):2. (Published by National Ash Assoc., Washington, D. C.), 1970. 17. GOLUEKE, C. G. and P. H. McGAUHEY: Com- prehensive Studies of Solid Waste Management. First and Second Annual Reports. Sanit. Eng. Re- search Lab., Univ. of Calif. (Berkeley). U. S. Public Health Service Publication No. 2039, 1970. 18. GOLUEKE, C. G. and P. H. McGAUHEY: Com- prehensive Studies of Solid Waste Management. Third Annual Report. Sanit. Eng. Research Lab., Univ. of Calif. (Berkeley). U. S. Government Printing Office Stock No. 5502-0023, 1971. 19. SOLOW, R. M.: The Economists’ Approach to Pol- lution and Its Control. Science. 173-498 (August 6, 1971). 20. BRADLEY, P.: Mining the Nation’s Scrap Heaps. Waste Age. 2(2):21 (March-April 1971). Recommended Reading 1. Abstracts, Excerpts, and Reviews of the Solid Waste Literature. Volumes I through V. Sanitary En- gineering Research Laboratory, University of Cali- fornia Richmond Field Station, 1301 S. 46th Street, Richmond, California 94804. 2. Comprehensive Studies of Solid Wastes Manage- ment. (Research Grant EC-00260 University of California.) SW 3 rg, Public Health Service Pub- lication No. 2039, U. S. Government Printing Office, Washington, D. C., 1970. 3. Waste Age. Three Sons Publishing Co., 6311 Gross Pt. Rd., Niles, Illinois 60648 ($10 per year). 4. Solid Waste Management-Refuse Removal Journal. 150 E. 52nd Street, New York, New York 10022 ($6 per year). 5. Compost Science-Journal of Waste Recycling. 33 E. Minor Street, Emmaus, Pennsylvania 10849 ($6 per year). 6. Chemical Engineering. 330 W. 42nd Street, New York, New York 10036 ($6 per year). 7. Proceedings of the First and Second Mineral Waste Symposiums. First Symposium, 1968; Second Sym- posium, 1970. IIT Research Institute, P., O. Box 4963, Chicago, Illinois 60680 ($15 per Proceeding — 2 separate volumes). 8. A Review of Industrial Solid Wastes. Open File Report (TO 5.0/0), Environmental Protection Agency, Publications Distribution Unit, 5555 Ridge Avenue, Cincinnati, Ohio 45213. 9. Intergovernmental Approaches to Solid Waste Man- agement R.O. Toftner and R. M. Clark, Washing- ton. U. S. Government Printing Office, 1971. 10. Proceedings of the 1968 and 1970 National Incin- erator Conferences. American Society of Mechan- ical Engineers, 345 E. 47th Street, New York, New York 10017 (2 volumes). 11. Solid Waste Management: Abstracts and Excerpts From the Literature, Public Health Service Publi- cation No. 2038, Bureau of Solid Waste Manage- ment, U. S. Government Printing Office, Washing- ton, D. C., 1970. (Volumes 1 and 2 cited in item 1) SW 2 rg. CHAPTER 46 CONTROL OF COMMUNITY NOISE FROM INDUSTRIAL SOURCES Lewis S. Goodfriend INTRODUCTION There are many potential sources of com- munity noise in an industrial plant. However, there are only six general classes of noise sources: a) power generating units, b) fluid control sys- tems, c) process equipment, d) atmospheric inlets and discharges, e) materials handling, and f) plant traffic. Although not a source, architectural and engineering deficiencies also contribute to com- munity noise by allowing plant noise to escape into the community. Within each of the above classes, there are several types of machines or processes that create the noise. The actual noise source within each machine or process is due to one of a very lim- ited number of physical noise generating mecha- nisms. Before describing each of the major industrial noise source categories, the physical generating mechanisms will be outlined, after which the ma- chines, processes and systems in industry that generate community noise will be described. This will be followed by a discussion of the response of people to noise in the community and the methods for delineating or comparing community noise levels. The chapter concludes with a presen- tation of methods of reducing industrial noise in the community and the outlook for future needs and methods of noise control. NOISE GENERATION The noise generating mechanisms which oc- cur in industrial machinery are: impact, gas flow phenomena, perturbations in fluid flow, combus- tion, friction, dynamic imbalance of reciprocating and rotating machines, and magnetic excitation. Each type will be discussed briefly with respect to the types of industrial machinery and processes and their particular systems of noise generation, transmission paths, and radiators. Impact The most familiar of the industrial impact phenomena are probably those from the forge hammer and the punch press. These produce in- tentional impacts which occur as a direct result of the energy in a flywheel or force of gravity on a drop hammer’s mass being expended on the workpiece. Other sources of impact include: repetitive chipping and scraping, bulk handling of small parts, e.g., tumbling, and the use of negative clear- ances in some processes. Another class of im- pacts is unintentional. This occurs when poor ma- chine design, installation, or maintenance permits over-travel of machine elements. 667 Gas Flow Phenomena The sound of escaping air or steam is prob- ably the most familiar gas flow noise. However, other conditions associated with gas flow, such as turbulent flow and flow around obstacles, can pro- duce noise. Where the obstacle is a sharp edge, it is possible to generate intense tones. Similar intense acoustic signals are generated by flow across spaced obstructions such as stiffeners in a duct. Flow across the face of a cavity will pro- duce noise which can be amplified by other parts of the mechano-acoustic system. Air flow causes noise. The hissing noise made by a high-pressure air line open to the atmosphere and the swishing noise of the air flowing past the open window of a car are both examples of air flow noise. There are two separate mechanisms at work here. In the open air-line case, the sound is generated by the non-uniform flow. In other words, the eddies or turbulences within the air stream generate noise, and the larger the differ- ence in velocity between the air stream and the stagnant surrounding air, the more noise which is generated. In the second case, the obstacles in the air stream cause vortices downstream of the obstacle. Since it takes time for the vortices to form, be shed and be followed by another, a peri- odic system, the sound generated is characterized by tonal quality. Noise from such air flow gen- erators can be amplified many times to produce intense whistles as will be discussed later. The usual sources associated with noise generation by air flow include fans, obstacles in air streams, leaks and open bypass valves in the air handling system, whether of high or low pressure. The siren effect is responsible for many types of gas flow noise. A siren basically is a device which emits puffs of air in a cyclic pattern. Clas- sically, it consists of an air supply and a rotating disc with holes that match one or more holes in the air supply. When the holes of the disc are aligned with those of the air supply or “wind box,” air can escape freely. At other times, the air is essentially cut off. The repetitive release of air makes a sound of tonal character. The volume of air released at each matching of the holes deter- mines the intensity of the noise produced. The siren effect is responsible for the noise of compres- sor inlets and air turbine discharges. Also, a similar sound is made by a power saw’s teeth which cause perturbations in the air near the blade as the teeth pass fixed portions of the saw. A special type of gas flow phenomenon which generates flow noises is the production of large volumes of hot, turbulent gases as a result of com- bustion of fuels, whether solid, liquid or gaseous. The expansion of the gas as it is produced and heated causes intense local acoustical disturbances. This gives combustion noise its distinctive low- pitch rumbling sound. Where combustion takes place unevenly, the noise is rough and uneven. In some instances the acoustic signal is so strong as to extinguish the flame which is reignited by a pilot flame or the heat of the burner, and this cyclic behavior can generate serious vibration, often resulting in structural damage. The noise is often an intense low frequency pulsation. Friction Another source of noise generation is friction. Although we generally associate energy losses due to friction with heat, friction causes two kinds of noise generation. The first is a series of miniature impacts as the imperfections in one surface are forced over another surface without any lubrica- tion. The sound is somewhat like that from air noise and the sound output is a function of sur- face smoothness and speed. The second type of friction noise is stick-slip noise. Here, the friction causes a moving part to stop or slow down im- perceptibly and as the driving force builds up, the friction is overcome and the parts slip by each other for an instant. Then, they grab again. This action produces high stresses in the parts and the sticking and slipping phases occur at high speeds, thereby producing an intense, high frequency phe- nomenon. Where the combination of part size and shape permit effective radiation of this type of sound, an intense sound will be radiated. Dynamic Imbalance Almost any kind of dynamic imbalance in high speed machinery will cause mechanical vi- brations. Where the appropriate acoustical con- ditions exist, the vibrations will be converted into acoustical energy. This energy may be radiated efficiently by some machine parts and housings. Typical sources are fans, pumps, engines, (both reciprocating and turbine) and compressors. Im- balance forces may be transmitted through bear- ings. Although bearing noise is partly friction noise, bearings can generate noise by the impact of imperfections in the bearings on other bearing parts at high speed. This causes vibrations which are readily converted to sound by the castings and housings. Generally, bearing noise is not a major source. Magnetic Excitation Although electrical machines are not generally considered as noise generators, motors, generators and transformers are capable of being major noise sources. The magneto-acoustic forces occur as a result of the magnetic forces on conductors and rotor and stator. Since there is no magnetic bias field like that due to the permanent magnet in a loudspeaker, the magnetic fields developed at both the positive and negative swings of the power sup- ply line voltage in AC machines cause an unidi- rectional force. Thus, for each cycle of the line frequency there is a magneto-acoustic force of twice the frequency. Because of non-linearities in the magnetic and mechanical systems, the acoustic output can have a high harmonic content. The 668 radiated sound can, therefore, be rich in mid-fre- quency components. In some transformers and motors, the maximum levels occur for signals at six and eight times the line frequency. In addition to the magnetic excitation, motors and generators produce noise from the radial blade fans used to cool the device by forcing air through or across the casing, and from the shear produced in the air as the slots on the rotor pass those on the stator. Noise Amplification and Radiation Except for a few of the sources mentioned such as fans, sirens, and air hoses, little noise would be radiated from equipment if it were not for subsystems which may be resonant or are effi- cient radiators. The most familiar resonant sub- system is the organ pipe. Without the pipe tuned to a resonance frequency desired, the noise made by the jet edge would be weak and would have little tonal quality. The pipe causes sound which has traveled to the far end to be reflected and transmitted just in time to reinforce the pressure variation at the jet, where a new, stronger signal is transmitted from the jet. The process repeats until an equilibrium situation occurs and a tone is radiated. There are other factors influencing the sound output of an organ pipe type of generator, such as the spacing of the nozzle and jet and their relative angular positions. Cavities with small necks produce the familiar whistle when air is blown across the mouth. Cast- ings can “ring like a bell,” and machined parts such as gears can produce bell-like tones. Sheet metal panels can resonate over a wide frequency range, vibrating as either plates or membranes. The theory for these subsystems is presented in most vibration texts. Some specialized subsystems include machine shafts at the critical speed, gas furnace burners, cup burners, in which the source is inside the resonant structure, and machine room floors consisting of lightweight structural members. Efficient radiators, formed by large surface area flexible bodies, may be combined with reso- nant subsystems. A small acoustical resonant sub- system, one side of which is formed by a large steel sheet, will drive the steel sheet as the coil in a loudspeaker drives the paper cone. The steel sheet will radiate the noise very effectively. EXTERIOR SOURCES OF INDUSTRIAL NOISE Power Sources Furnaces and heaters provide the energy for a variety of industrial processes including the refin- ing and fabricating of metals, generation of elec- tricity, petro-chemical processes and a variety of kilns. In some new combined cycle plants, the hot gases operate gas turbines and then the same gases at lower temperature and velocity heat water in heat recovery boilers, the steam from which operates one or more steam turbines. Also, fossil fuel boilers generate steam for a wide variety of industrial processes. The basic process in all cases is combustion which by its nature produces ther- mal and pressure perturbations in the air which propagate as sound waves. Because of the slow rate of flame-front propagation and the high en- ergy release involved in the combustion, the per- turbations, and thus, the sound waves produced, are of low frequency and high intensity. Furnace and boiler noise is often mixed with induced or forced draft fan noise, but where com- bustion is rough, the low frequency rumble is often clearly distinguishable. The pressure pulsa- tions can readily shake windows and cause doors to rattle against their stops. Both steam and gas turbine systems radiate considerable noise from both turbine casing and the connected ducts and piping. The gas turbine’s inlet and discharge are often open to atmosphere. Without mufflers they generate noise which is gen- erally unacceptable. The inlet radiates the intense noise at compressor blade-passing frequency and the discharge radiates the combustion noise. The inlet blade-passing sound is a high pitched signal like a siren. The exhaust noise is like the sound of jet aircraft exhaust. Electrical power transmission systems can cause three types of acoustical noise that can eas- ily be heard in many rural and suburban locations at levels quite high, with respect to the ambient noise. These are substation transformer hum, high voltage corona and switch-gear and circuit breaker operations. Transformer noise is usually highest in level at light loads occurring generally late at night. Transformer noise is characterized by the pure tone harmonics of 120 Hz. As the load on the transformer is adjusted, the signal changes character. In open country, substations can be heard for distances up to half a mile or more. The levels at 1000 feet can run in the 45 dB (A) range. Corona noise which sounds like frying has a range of 50 to 70 dB (A) below the lines, and ap- proaches these levels at houses along the transmis- sion line right-of-way. It is highest in level when the corona discharge is most severe, during periods of high humidity, rain and fog. The noise from air quenched circuit breakers is an explosive sound like a gunshot. When the circuit breaker operates, air at over 800 pounds per square inch gauge is used to cool and quench the breaker gap as the breaker opens. The result is a high pressure acoustic pulse which can run as high as 95 dB (A) at 1500 feet. Fluid Control Systems Pumps, both within and outside of buildings in industrial plants, generate high level noise. Generation of noise in pumps is caused by sud- den changes in any of the flow parameters, vol- ume, velocity and pressure, by turbulence, and by the mechanical noise generated by the bearings, seals, couplings and loose parts. The noise is transmitted along piping and conduit and is read- ily radiated from the pump casing, equipment en- closures and lightweight structural and building shell components. Compressors generate noise at the inlet be- cause of the rapid changes in velocity that occur as the inlet is either opened or closed in a recipro- cating compressor or as the blades pass the cutoff in a centrifugal compressor. In axial flow com- pressors, the noise originates through the inter- 669 action of the fixed and rotating blades at the blade passing frequency. This noise is radiated from the casing of the compressor, connected structural members, and housing elements as well as from the downstream piping and ducting. Fans and blowers generate noise in a manner similar to compressors, but work at lower static pressures. Many fans are exhaust or induced draft devices which are ducted on one side, but open directly to atmosphere on the other side. The noise generated by a fan will, in general, be a minimum at the most efficient operating point for the fan. Materials-handling blowers have an additional noise source, the interaction of the blade and the material itself, e.g., the scrap blower in a paper-board plant. Any obstruction in a fluid flow system causes a change in velocity and can generate vortices at the trailing edge of the obstacle. In addition, many flow control devices obstruct the flow, e.g., fire dampers, and may generate severe turbulence downstream. This results in the generation of vor- tex noise, turbulence noise, and in some cases, in- tense pure tones due to the interaction of the vor- tices with some resonance condition in the pipe or duct. Process Equipment The term process equipment encompasses a wide range of systems and machines. Typical ex- amples will be given, but it should be fairly easy to compare any process or machine to the list of sources, radiating systems and resonators in order to determine the acoustical system responsible for the noise associated with the particular device or system in question. There are numerous sizes of mills ranging from table-mounted units to those enclosed by a large building, with basically the same process in each. A number of heavy hard rods, balls or knives within the mill, work upon the material to be milled, dividing the substance under the pressure of the balls, rods or knives until the material is reduced in size to the range desired. It may then be separated by size using vibrating screens, me- chanical separation or flotation separation. In any case, the housing of the mill is acted upon by a large number of impacts. Because of the large relative area, the housing radiates the milling sound quite well. Connected with the mill are sets of gears, belts and bearings, which also gen- erate large forces because of the energy being transmitted is high. Thus, a mill may generate bearing and gear noise in addition to the sound of the milling itself. Crushers, particularly ore and stone crushers, require large amounts of power which is released in the destruction of the bonds holding together the particles of the material being worked. The result is a rapid series of high energy impacts. Crushers are often located out-of-doors or in light- weight sheds, and in either case radiate low fre- quency noise as well as bearing and drive equip- ment noise from the crusher structure, enclosure, or building. Saws Circular saws generate noise by siren action as the teeth pass fixed elements in the saw and as they pass into and out of the material being worked. Saws also ring in the manner of a gong, due to a plate resonance which can be excited readily by the teeth as they strike the work and by the siren tone. Even if used indoors, saws can generate noise which radiates into the community. Cooling Towers Among the major outdoor noise sources are the cooling towers used as heat exchangers in in- dustrial processes, power generation and air con- ditioning. The cooling water is sprayed into an air stream resulting from the action of a powerful fan or blower. The water flows over a “fill” ma- terial which enhances evaporation by providing a large surface area for contact with the air stream. The combined heat transfer due to evaporation and conduction provide the required cooling. The noise generated by the fans and blowers is similar to what can be effected from such fans. However, they often generate low frequency noise because of low speeds and few blades. These conditions are dictated by the fact that these are low static pres- sure, large volume devices of great physical size. Another component which generates cooling tower noise is the water splash. This contributes a dis- tinctive high frequency sound to cooling tower noise. When the fans are turned off, the splashing noise can be quite annoying. Flare Stacks In the petro-chemical field the disposal of waste gases is often accomplished by burning them at the top of a tower where the products of com- bustion can mix with ambient air and can diffuse sufficiently to reduce both concentration and tem- perature. The result is that the combustion takes place in the open at the top of a tower, providing clear line-of-sight sound propagation to the neigh- boring community. The sound is generated both by steam injection often used to suppress smoke, luminosity and instability of combustion, and by combustion instabilities often related to moderate and high wind velocities, flowrates and port char- acteristics. Mechanical Power Transmission The transmission of mechanical power can readily generate high noise levels as a result of friction and impact noise sources. Slight imper- fections in gear teeth cause acoustically significant perturbations in the force transmitted. These per- turbations are often amplified by resonators in the gear-shaft system and are effectively radiated by the machinery housing. The mechanical perturba- tions also shock-excite some components such as gears which then are free to vibrate at their reso- nance frequency. Here again, the part and its associated structure and housing may radiate the sound into the community. Belted systems can generate noise by several means, the most common of which is friction noise. In general, belt generated noise is not a major problem until other noise sources are elim- inated. Chain drive systems are basically impact generators as long as they are well lubricated, but if not lubricated, they can become friction noise generators and in some cases, the friction load on the bearings increases the bearing noise. 670 Bearings in transmission systems are usually designed to minimize friction. However, poor maintenance and overloading can soon turn bear- ings into high level noise sources. Since they are attached to the structure and often the machine housing, they can cause considerable noise to be radiated into the community. High Pressure Atmospheric Inlet and Discharge Rapid pressure fluctuations such as those oc- curring at the discharge of a diesel engine, or the inlet of a compressor, are radiated from the inlet or discharge as acoustic signals. The signal us- ually has a tonal quality or contains a pure tone (and harmonics) at the rate at which the port(s) open or close. At the engine discharge, the pulsa- tions may have initial pressures at many times atmospheric pressure. In compressors, the large volume involved often leads to high velocities in attached piping. The pulsations from the com- pressor inlet are transmitted as high velocity per- turbations down the pipe to the atmosphere where the pulses look very much like the exhaust pulsa- tions from an engine. Continuous flow discharge from steam, air and gas lines, and blow down from high pressure ves- sels and piping systems generate high level noise through turbulent mixing of the jet with the am- bient air. At pressure about twice atmospheric, the flow from an air line becomes sonic; that is, the velocity at the outlet is at the speed of sound. At pressures above this, the velocity remains sonic, but the nature of the flow changes and can be si'personic downstream. In either case, high acous- tic pressures arc generated. The noise level is a function of the eighth power of the Mach Number below sonic velocity and depends mainly on the square of the pressure ratio across the opening above sonic velocity. The exact level is influenced, however, by the temperature (second power), molecular weight and compressibility factor for the gas (both inversely as the second power). Materials Handling The noise caused by materials handling is among that most often heard outside of many plants. Fork-lift trucks and front loaders and a variety of cranes moving around the yard gener- ate noise with their motors and-sometimes with their loads. Electrically operated cranes of large capacity can be heard over large distances late at night and are sources of complaint mainly because of the pure tone component. Conveyors make noise from two major sources, the material con- veyed striking the sides of the chute or enclosure, and the bearings and rollers on which the moving belt, or in some cases, the material themselves move. Belt conveyors impose large loads on the bearings and rollers and these, in turn, can gen- erate noise which is readily radiated by the en- closure and structure. The sound of the large number of wheels of the skate-wheel conveyor, because of the nature of the wheels and the struc- ture, can radiate at levels which may exceed ac- ceptable community goals. Large vibrating shakers used to empty hopper cars radiate low frequency signals into the com- munity by means of the large radiating area of the side of the car. The noise is often a maximum level below 30 Hz and can rattle doors, windows and the china and glassware in a house at several hundred feet. The noise level at the house is us- ually 80 dB or more at the exciting frequency. At this level, no earth vibrations will be measured and the signal may only be heard by a skilled observer when the area is noisy at higher fre- quencies. This is due to the reduced sensitivity of the ear at low frequencies, as well as the mask- ing of low frequency noise and tones by high fre- quency noise. However, the low frequency acous- tic waves cause the walls of the building to vibrate and, in turn, cause relative motion between doors, windows and shelves and the rest of the structure. High frequency vibrators (actually 60 and 120 Hz) will also radiate effectively when attached to large sheet metal hoppers. However, the noise level can be six to 15 dB higher when internal springs and rubber dampers break or slip out of position. Other out-of-doors noise sources are the impact of large parts on other parts of loading platforms, the operation of dockside and platform elevators, and the use of powered material handling tools. Plant Traffic One of the most difficult noises to define and control in a modern industrial plant is traffic noise. The sources are trucks for the delivery and shipping of goods, rail cars in the shipping and classifying yards, and the employee automobile traffic. These sources might be only a moderate contributor during the day, but at night they may stand out against a much quieter ambient noise level. This will be particularly true where the plant operates a second shift and plant noise drops in level just before the outward flow of cars. Also early morning deliveries, before plant opening, can cause distinctive and annoying noise. Architectural Deficiencies The design of industrial plants must take into account the types of noise that will be generated within the plant. Openings made in the plant to install new equipment create a problem to be dealt with carefully. Among the most important items to consider are the adequacy of the basic structure and enclosure, and the prevention of any openings through which noise can escape inad- vertently. Plant ventilation must be accomplished without allowing the vent openings to act as trans- mission paths between the internal noise and the community. THE RESPONSE OF THE COMMUNITY TO INDUSTRIAL NOISE The noise which is heard in a given location from sources far and near, including readily iden- tified noises such as passing cars or barking dogs, is the ambient noise for that location. Removal of, or shutting down, all local sources under in- vestigation leaves the only sound arriving at the measuring location the background ambient noise. The background ambient noise in a community usually consists of distant transportation noise. Acceptability of Noise in the Community Noise in the community may or may not be 671 acceptable to the workers and citizens in the area. Without some “acceptable” noise to mask the more distant sounds and day-to-day activities of our neighbors, we should find life intolerable. Thus, the ambient noise serves a useful social func- tion, as long as it stays within certain bounds. Noise becomes unacceptable in any particular sit- uation when it is distracting, especially during creative activity and when it interferes with sleep or with speech communication. It is also unac- ceptable when it interferes with the ability to hear speech or the sound portion of television, radio or recorded programs. Industrial noise can prob- ably be acceptable at these relatively high levels, 50 dB (A) or more, out-of-doors when it meets certain criteria: a) itis continuous, b) it does not interfere with speech communi- cation (on the patio, at the dinner table, or in the office), it does not include pure tones or impacts, it does not vary rapidly, it does not interfere with getting to sleep, and it does not contain fear-producing ele- ments. There are many other parameters which in- fluence the acceptability of noise by individual residents or groups of residents exposed to any particular noise. Thus, although physical measure- ment of the sound level is important, it cannot ef- fectively predict the response of any specific neigh- borhood or community to a particular noise source. In fact, the relationships as will be deter- mined later, between the community and the op- erator of the noise source, and the responsiveness of the local political authority, may have a greater influence on acceptability of a noise than the noise level or quality. Measurement and Evaluation Both the A-weighted sound level and octave band analyses have been the major physical meth- ods for measuring noise for purposes of evaluat- ing its effect on the community. Octave band an- alysis permits the comparison with contours such as the noise rating chart or a municipal code. Studies have shown that even though it was de- signed for another purpose, the A-weighting does rank human response to noisiness and loudness quite well over a wide range of levels. Other schemes using manipulation of octave band data such as the Perceived Noise Level (PNL or PNdB)' or loudness? in sones have been used with some success for particular applications. The PNL is derived from equal noisiness contours similar to equal loudness contours but with a sharp increase in sensitivity in the range 1500 and 8000 Hz. In an effort to provide a single reading com- parable to the A-weighted measurement, the D- weighted curve based on the 40 Noys perceived noisiness contour has been used. None of the methods used except Composite Noise Rating (CNR),* based on the Noise Level Rank Curves (Figure 46-1) have shown any re- lation between noise and the community re- sponse.* Recent efforts to use single number c) d) e) f) Octave-Bend Sound-Pressure Level in dBre 0.0002 pbar 100 NN ~~ 90 NY . NINN 80 NN | NN — 70 opr 60 \ N\ NN. ~~ | i 50 \ NIN ~~ re f ee A RN ~~ —— ~~ d 30 SIS Te SL 20, i ol SY - 7 Rl + ’ En “ Frequency in Hz Figure 46-1. Noise Level Rank Curves. measures such as the A-weighted level alone or Noise Pollution Level (NPL) have not been successful.” A new effort using the A-weighted level modified by the same factors used in CNR has been proposed by Eldred and tested in a num- ber of situations. Called “Normalized Community Noise Equivalent Level (NCNEL), this measure is based on the daily time history of the noise exposure expressed in terms of the A-weighted reading occurring in three periods: day, evening, and night. A table of adjustments covering the nature and extent of the exposure, the ambient 672 levels against which the noise is heard and the attitude of the persons exposed, is used to adjust measured values, (Table 46-1). When the adjust- ments are made, the NCNEL may be plotted on a chart that indicates the expected range of re- sponse of those exposed. Noise Pollution Level (NPL),* which is cur- rently quite popular, attempts to use the statis- tical properties of the noise exposure to describe its noisiness. NPL is defined as L.,+2.56Xs where L., is the energy average of the noise as indicated on a level recorder or on a statistical analyzer. Here, s is used as the standard devia- tion of the noise levels from a large number of one second samples taken during the measuring period. Unfortunately, NPL does not distinguish between the quiet residential background on which are superimposed many children at play and passing neighbors’ cars versus the rather steady but high noise level of a downtown commercial area. There is not enough information in the sta- tistics alone to describe the noises that do or do not cause a large standard deviation. One com- mon treatment of data is the use of the tenth and ninetieth percentile of the measured levels to indi- cate the nature of the noise exposure. The 90 percentile values are considered to be the back- ground ambient (the noise levels are above this value 90 percent of the time, while the 10 per- centile values are those of the intrusions). The spread between the two is related to the standard deviation, but the absolute levels indicate its ef- fect on speech communication. Effect of Social-Political Environment The response of a community or neighborhood to an industrial noise is, as has been noted above, not necessarily related to the level of the noise. There are many influences, not the least of which is an interaction between the industry and the municipal council and the citizens. It is sometimes two-sided and sometimes three-sided, but it is in- variably a process of accommodation on each side. Whenever an industry proposes to locate a plant in a municipality, it has decided to do so on the basis of at least a preliminary investigation of the site. Corporate officials will have talked to local officials and there is some anticipation on both sides that the industry will provide jobs and tax income to the community and that the munici- pality will welcome the industry by accepting the gaseous, particulate, and liquid wastes and the increase in street traffc. However, after the in- itial decision to build a plant is made, the company must submit plans for zoning approval at one or 90 80 Daytime ~— — —Nighttime © > 3 70 © / 1 5 «8 —7 90 2 EF 50 £ 2 >< —Lio [a Q 60 = Nl d] 2 = =< 7 ‘WN 3 x =~ \ \ 2 0° \ 3 3S 50 \~ N | o£ [SX N oO NS I~ — ST = = TT : 40 == ~~ ~ ~~ h 30 3s 63 123 2%0 300 1000 2000 2000 2000 18000 . L i 1 1 1 1 | el ! 2 8 100 2 Ss 1000 2 8 10000 t Frequency in Hz U.S. Environmental Protection Agency: Noise from Industrial Plants, Report NTID 300.2. Washington, D.C. Figure 46-2. Example of Community Statistical Noise Spectra Obtained from Daytime and Nighttime Surveys. L,, L;, and L,, percentile values were obtained from 100 samples with one second integration time. 673 TABLE 46-1 Level Rank Chart. To Obtain Composite Noise Rating of a Noise Exposure (CNR), the Sound Spectrum is Plotted on the Chart and the High- est Level Rank Band Penetrated, Determine the Level Rank. The Level Rank is Then Adjusted One or More Steps According to the Table. LEVEL RANK CORRECTIONS FOR CNR a) Very Quiet Suburban +1 Suburban 0 Residential Urban —-1 Urban Near Some Industry —-2 Heavy Industry Area -3 b) Daytime Only -1 Nighttime 0 c) Continuous Spectrum 0 Pure Tone(s) Present +1 d) Smooth Temporal Character 0 Impulsive +1 e) Prior Similar Exposure 0 Some Prior Exposure —-1 f) Signal Present: 20% of Time —-1 5% of Time -2 2% of Time -3 more public meetings. Officials must answer ques- tions from municipal officials and the public. The process may have to be repeated four or five times. Finally, the plans must go to the municipal gov- erning body where public and local officials can repeat the process. Some citizens groups have been known to arrive with lawyers and experts, while the company arrives with top officials and its experts. After appropriate parrying, each side offers some accommodation, and then the govern- ing body may decide to approve the plans or ask for resubmittal. In all of these proceedings, noise is likely to be an important consideration. When the decision to accept the plant is given, the com- pany involved may withdraw its plans and seck another site in a different municipality because it has sensed the hostility of the community that it will have to live with for many years. Even where the approval is granted, the municipality still main- tains control. When the plant is completed it can- not be occupied without a certificate of occu- pancy. This must be issued by the building in- spector who will have been monitoring construc- tion. If he and the other officials are not satisfied, no Certificate of Occupancy will be issued until the “deficiencies” are ‘“‘corrected.” Finally, the municipal and state health officers and the state labor department must approve the plant and its operations. Thus, the process of accommodation works to maintain some moderation of the noise radiated into a community neighboring an industrial plant (Figure 46-3). Even where a plant has existed for many years in reasonable harmony with its neighbors, a change in the plant that allows an increase in sound levels in the neighboring com- munity is likely to cause an immediate response on the part of the neighbors. In some cases this results in demands for lower noise levels than ex- 674 isted prior to the change. In some cases the inter- personal relations between plant officials and neighbors may result in continuing skirmishes that preclude any satisfactory accommodation on the part of the parties involved. Even when the plant offers to buy neighboring homes at a premium, some neighbors may refuse, even if almost all of the remainder of the neighbors have left what was a substandard housing area. In some locations, single individuals have kept up such fights with major industries and have forced local officials to take legal action for viola- tions of local health statutes even though the en- forcement results from a personal vendetta. In general, the accommodation process has main- tained the noise levels in communities across the country at levels just below that at which neigh- bors will complain (Figure 46-4). These noise levels may be higher than is socially desirable, but often they are also just below the noise from trans- portation noise sources, nearby highways, truck routes, and parkways. The current effort to abate transportation noise may leave industrial noise as the major noise source in some areas. With the industries now clearly setting the ambient level, it may be that a new round of accommodation will occur. THE CONTROL OF INDUSTRIAL NOISE SOURCES Industrial noise sources expose both the em- ployees within the plant and the neighbors in the community. Often the same machine producing levels of 90 to 100 dB (A) around the machine indoors can be heard in the nearby residential neighborhood at levels from 40 to 60 dB (A). Some industrial noise sources as outlined earlier are out-of-doors and may or may not expose em- ployees to hazardous noise levels, but because they can generate high levels of noise they can be heard at distances up to a mile from the plant. Close to the plant the noise levels may be well above the ambient, and can be unacceptable. The following section discusses the general methods of quieting industrial noise sources, and in some cases, men- tions specific hardware. The first requisite for a noise reduction pro- gram is a carefully done noise survey. Made at or near the plant boundary or closer, it should be possible to identify the major contributors to the noise in every direction around the plant. It may be necessary to make some measurements dur- ing a shutdown, and others close to small ma- chines, to examine how much noise they might contribute to the total sound level in any given direction. With this information, the amount of noise reduction required at each machine may be evaluated. From the physics of the situation it is clear that if three or four different sources con- tribute about equal energy at a given point at the plant boundary, and thus, in the community be- yond, all must be quieted to some degree. Clearly, if four machines generate roughly the same noise with about the same spectrum, eliminating the noise from two will only cause a three dB drop in level, and shutting down three would yield about Weekend Weekday Weeknight Weekend Weekday Weeknight Key SCALE [LLL EE FE o 0 500 1000 1500 2000 2500 FEET Community Noise Levels in dB(A) 1 2 3 4 5 6 7 8 9 1011 12 13 46 54 45 39 41 43 - ~ 48 41 41 51 43 50 59 44 42 42 40 44 40 41 44 39 53 43 52 61 46 40 43 45 43 40 41 41 42 49 42 Piant Property Line Noise Levels in dB(A) a e f | m q ccaa x v U 50 62 59 68 55 41 44 40 60 65 52 49 64 61 68 59 49 50 49 66 .68 55 51 64 63 69 53 48 41 46 61 65 54 Industrial Noise Source Residential Area Railroad Track Highway Measurement Location U.S. Environmental Protection Agency: Noise from Industrial Plants, Report NTID 300.2. Washington, D.C. Figure 46-3. Example of a Noise Survey around an Industrial Plant. Levels were measured directly with a sound level meter. 675 Community Reaction Vigorous community | action Several threats of legal Ve oction, or strong appeals to local officials to stop noise Widespread complaints » or single threat of J legal action / / / / / Sporadic complaints - / eo oc / / 7 7 7 ~~ No reaction, although noise is generally noticeable 1 ] Envelope of 90% of Data / Windows Partially Open TA \ oe [X) [Xx ° ° ~~ ° Data Normelized to: / Residential Urban Residual Noise / Some Prior Exposure No Pure Tone or Impluses | ] | 1 1 45 50 -55 60 65 70 75 80 85 90 Norinalized Community Noise Equivalent Level in dB | l 1 | ] J 10 15 20 25 30 35 40 45 50 55 Approximate Noise Exposure Forecost in dB L 1 ] | 1 ! 1 1 J 85 90 95 100 105 110 15 120 125 Approximate Composite Noise Rating in dB U.S. Environmental Protection Agency: Noise from Industrial Plants, Report NTID 300.2. Washington, D.C. Figure 46-4. Relationship of Normalized Community Noise Levels and Other Human Re- sponse Scales and the Expected Community Response. (From Community Noise, U. S. Envi- ronmental Protection Agency Report NTID 300.2). six dB reduction. Thus, a careful examination of the options is in order after the data are as- sembled. Once the decision to quiet a given machine is made, detailed sound measurements and a study of the entire machine on a systems basis is in order. The sources within the machine must be identified, the various transmission paths for acoustic energy must be found by both inspection and measure- ment (acoustical and vibration), the radiators must be located, and finally, the resonators or feedback mechanisms must be found. When this study is completed, it will probably be clear what measures will provide the most noise abate- ment at the least cost. It may be possible to mod- ify the source, leaving the path and radiators alone, or it may be possible to operate on two, three, or more of the system elements to varying degrees yielding an optimized-cost treatment of the system to produce a specific minimum required noise reduction. Source Noise Reduction Intentional impacts are used in forging, shear- ing and stamping. The desired result is achieved 676 only by an impact. Source reduction is difficult, although in shearing and stamping, die design and rate of operation do have a major influence on the noise. Also, the nature of the metal being worked strongly influences die design and noise output. Increasing the total time for the actual work on the material will usually reduce the sound output. This may reach a limit when the total stroke time is used for work. Any further change leads to a reduction in output. Many parts of presses and shears radiate the noise unnecessarily. It is pos- sible to enclose partially some automatic presses; and large radiating surfaces, including belt and chain guards, can be damped as described below. The use of plastic shields and snap-out barriers close to the stamping dies should permit a reduc- tion of several dB at the operator’s position. Unintentional impacts can be found by in- specting the clearances with the machine oper- ating with illumination from a stroboscopic light source just off synchronism with the machine. Extreme care must be used not to touch parts that look like they are “standing still.” It may be necessary to provide viewing ports or to use mirrors to make the required inspection, but the results may be surprising. Rods and levers that appear to clear other parts when the machine is “turned over by hand” will whip at high speed with some being in mechanical resonance. Others may just be inadequately designed for the task. Rat- tling case parts can also be spotted by use of the strobe lamp. The obvious answer is redesign of the part, either using a more suitable section to prevent flexure or better connection at “crank-to- lever arm” connections that whip sideways. Each situation is different, and some will tax the design- er’s ingenuity. The problem is basically mechan- ical design, not acoustical. Gas flow noise sources can often be controlled through the use of mufflers. Mufflers for high pressure lines are made in sizes for pipes from V8 inch diameter up to 60 inches in diameter. They can provide extremely large reductions in noise level when correctly designed and made. The sizes from 2%% inches up are often called snubbers and are offered in a wide range of styles including steam and water separator units. Units for com- pressor inlet and engine discharge are designed to operate in the appropriate temperature range while handling the pulsations encountered in the respective services. These differ from units de- signed to quiet continuous high pressure super- sonic gas flow discharges where a special inlet diffuser section is required. In every case the muffler must be designed to withstand the high forces that occur both on the casing and on the internal baffles and tubing. Also, they must be fabricated from appropriate materials for the ser- vice intended. Small and miniature mufflers find application on production line valve discharges. Spool valves are particularly easy to quiet using small units. The number of unintentional discharges through disconnected lines or bypass valves is surprising. In some cases these can be capped, thus prevent- ing wastage. In other cases slight changes in process control can be made to eliminate the dis- charge. Another solution to valve discharges to atmos- phere is to manifold the discharge lines to a header which may serve as a muffler because of the large expansion ratio from the inlet pipe to the header. In other cases the collected discharge can be piped away to an outlet where the residual noise will be no problem or a single muffler of appropriate size used. In some instances it is clear that the use of high pressure air is unnecessary, but it is used be- cause it is available. A pressure reduction device (regulator) at or near the machine can reduce the sound output considerably. Valve noise in high pressure systems and the noise from centrifugal compressors radiated by the piping can best be eliminated by “lagging” the piping or valve.” The use of a two- to four-inch thick medium density mineral wool or glass fiber “spacer” covered by a one 1b./sq. ft. jacket of lead can yield high frequency noise reductions of 30 to 50 dB. Higher reduction values may be ob- tained, but it is difficult to cover every valve and 677 pipe support. Actually, flanking transmission us- ually begins to predominate beyond about 50 dB of reduction. The jacket may be sheet metal or any appropriate weather resistant material pro- viding the required weight. Asphalted roofing felt, leaded vinyl and leaded neoprene have been used in some applications. The control of perturbations in fluid flow is usually a job for the machine designer. This in- volves the design and spacing of the fixed and sta- tionary blades in compressors, the blade shape and cutoff design in centrifugal pumps and blowers and fans, and the nature of flow control in posi- tive displacement pumps. In general, these de- vices lose efficiency rapidly when changes are made from the optimum design. However, casing de- sign to minimize cavitation in pumps can yield lower noise output. Use of pressure equalization chambers, snubbers and mufflers in both liquid and gas systems and lagging have been the ac- cepted methods to date. In fans and blowers every effort made to re- duce the tip speed of the unit does help to reduce noise, but tip speed alone is not an adequate index of fan noise output. Noise in fans and blowers may be increased by having ‘struts or braces in the air stream such that, with axial flow units, the blades cut the wakes made by the obstruction. This can produce intense tones when the blade- passing frequency coincides with the vortex shed- ding frequency of the air-flow obstruction system. In low pressure air handling systems noise gener- ated by turbulence at turns, dampers and mixing boxes can usually be avoided by good design. However, air conditioning style mufflers can be used. These are usually a series of sound absorb- ing baffles on six to 12 inch centers. The sheet metal work is relatively light for residential and commercial building use. Special industrial grade mufflers are available, fabricated from heavier gauge metal with better assembly. Here again, material of construction is governed by the envi- ronment and the gas handled. These mufflers have sometimes been applied to cooling tower inlets. Cooling tower discharges may be equipped with mufflers, but their effect on the fan characteristics may be so great as to raise the source noise and yield no net effect on the sound output. One way to eliminate noise is to get rid of the source by modifying the process or system. Many industries faced with problems related to cooling tower noise use wells and return the water to the ground after passing it through a heat exchanger. In many cases local streams used for process water have been used for cooling, but current and pro- posed restrictions on thermal pollution will keep cooling towers in the picture for some time to come. The use of natural draft cooling towers solves most of the noise and discharge tempera- ture problem, but these are large and costly struc- tures. A change in design and operation can often effect the appropriate noise reduction, sometimes at a cost in efficiency. In one case, when night operation of one cell of a three cell cooling tower caused neighbors to complain, the electrical cir- cuits were modified, the motors rewound for two- speed operation and two cells were operated at about half-speed at night. The fan noise varies as the fifth power of velocity and operating two units only brings it back up three dB. This yields a net drop of about 12 dB. Another case of changing processes is to switch from deep drawing to spinning for fabrication of large objects of circular section. A change from oil fired combustion with high pressure air for atomization and combustion to gas firing with a totally-enclosed muffled burner has been used suc- cessfully on single and multiple burner furnaces. Also, the switch from induced draft operation where muffling hot stack gases is difficult, to a forced draft system with inlet mufflers, results in considerable noise reduction. The noise radiation formerly from the top of the stack now takes place at ground level where buildings act as bar- riers. Mechanical damping, most familiar as auto- mobile undercoating, can reduce the amplitude at resonance frequencies in a panel or even in struc- tural members, thus reducing radiation and feed- back to the source, and in turn, reducing the driv- ing forces. Damping can be effected by applied coatings of mastic or fibrous materials such as jute or wood fibers and foams. Also, friction be- tween two metal surfaces not adhered to one an- other over their entire surface is used. Air trapped within the space between two plates may provide added damping. The most effective damping may be obtained with a thin layer of elastomeric damp- ing compound between the sheet to be damped, and a thin constraining layer, such as metal foil or a lightweight metal sheet. Although damping is conventionally applied to large metal enclosures, it may also be used to control resonance of gears and sheaves by applying damping to the web or “spokes” as a constrained layer or a filler com- pound for hollow parts. With some components it may be possible to apply a damping disc or other mating form on one or both sides of a reso- nant part. Considerable noise is generated by loose parts, rattling covers, worn bearings, and broken equip- ment. Reductions on the order of six to 10 dB may be achieved through maintenance alone, and in some cases, spectacular results are possible when cases are resealed or even just screwed back onto the structure. Transmission Path Noise Control It is sometimes difficult to determine what part of a system is the source and what is the transmis- sion path. Sometimes the decision is arbitrary. In any case, a muffler may be used along the path or at the end of a line to eliminate not only noise generated at a given machine, but flow disconti- nuity noise generated at turns, dampers and valves along the way. It is sometimes necessary, espe- cially in the case of high temperature exhausts, to split the muffling between a unit near the engine and one near the discharge. The unit near the engine will reduce the input to the exhaust pipe and minimize the possibility of shock wave forma- tion, and the discharge unit will remove any noise 678 signals introduced along the way and clean up any small shocks formed. As mentioned above, manifolds are useful for collecting the discharge from several small lines and can act as mufflers. This does not always work because of resonances with the header or manifold. Appropriate baffles and inlet diffusers inside the header or manifold will prevent problems with resonance. Inside plants, and out of doors, large bar- riers® and partial enclosures provide considerable attenuation of noise, provided the barrier or en- closure is located close to the source and is not negated by reflections from a wall behind the equipment. Barriers with acoustical material on the surface facing the source wtih similar material on the wall behind can be quite effective. Enclo- sures are similar to barriers until they are fully sealed. Fully sealed enclosures provide varying degrees of noise reduction determined by the fre- quency of the noise and the transmission loss (TL) of the panel material. The TL is generally higher for more massive materials. However, even a one-to-four pound per square foot material such as damped sheet metal or cement asbestos board will yield a reduction in the A-weighted sound levels of 20 to 30 dB. If the seal on an enclosure is broken for ventilation, the TL will be reduced greatly, unless a vent muffler is installed. Such mufflers are produced as standard hardware by several manufacturers who also manufacture com- plete enclosures, and duct and blow-off mufflers. The vent mufflers may be equipped with fans having explosion-proof motors as required. The use of acoustically absorbing material similar to acoustical ceiling tile can provide some reduction for interior noises heard out of doors and for some out-of-doors operations such as at loading docks. The materials used for industrial application must be fire resistant and should be applicable to large areas. Spray-on materials were popular for some time, and the recent trend away from asbestos fibers toward open cell urethane foams and cellulose materials should also provide appropriate results. Sheets of mineral or glass fiber board with perforated or decorative open- faced material (expanded metal) are also useful although they require structural support. The perforated metal must have relatively small holes on close centers, typically no more than one-half inch centers and holes from 0.06 to 0.15 in diam- eter. The holes and spacing should yield an open area of more than 15 percent, preferably 30 to 40 percent. The most effective acoustical materials will have high sound absorption coefficients in the frequency range in which the noise levels are highest. However, good high frequency absorp- tion is usually desirable. For industrial applica- tions it is not sufficient to look at the “Noise Reduction Coefficient” because this is the average of the individual coefficients for the test frequen- cies 250, 500, 1000, and 2000 Hz, and since the noice to be controlled is in the 2000 to 4000 Hz range (air discharges and cleaning jets), the sound absorption values at 2000 and 4000 Hz are critical to the noise reduction. An interesting and useful facet of area noise control with acoustical material is that the entire ceiling and walls of the plant need not be covered. A coverage of 60 percent spread over the entire area of the ceiling is almost as effective as the entire ceiling and usually a lot less expensive. Wall treatment near the source of noise is always effective. Examples have indicated 12 dB reduc- tion at remote locations due to corner treatment close to a machine. There are some situations where muffling, en- closure, or machine modification are not readily feasible, but moving the machine is quite simple. Moving a small positive displacement blower from one side of a plant building to another can yield 20 to 30 dB reduction at the fence on the side of the building facing its original location. This works as long as the other side does not face a residential area also. This uses the plant as an acoustical barrier. There are numerous applica- tions of this barrier effect, and they are an eco- nomical way of accomplishing the desired pur- pose. It may take some ingenuity. As an ex- ample, many plants face highways and other trans- portation complexes, while the rear faces nearby residential zones. Although routine plant design does not locate major items of equipment along the face of the plant, it may turn out to be a reasonable design; suitable decorative screening is a low price to pay for the acoustical benefit. Because plant buildings are designed for the protection of employees and equipment from the weather, they often do not include noise control considerations. Louvers, windows and doors may all serve to provide effective ventilation and ma- terials flow. However, they also permit noise flow from the interior to ‘the neighboring community. There is much to favor gravity flow ventilation, and employees in some plants resist the use of mechanical ventilation unless it is accompanied by air conditioning. However, closing up the louvers or using acoustically treated louvers and forced draft ventilation with muffled fans will solve many noise problems. Curtain wall plants using corru- gated sheet skins that are not sealed, or damped, may let sound out through both the wall and leaks. Plant design must account for the high noise levels inside and the large radiating area provided by the walls. Also, loading dock and plant storage yards where active materials handling is carried out at night may require some planning in order to control noise. The use of perimeter storage sheds as barriers can effect noise control. Administrative Procedures for Noise Control Traffic noise, especially for the end of the sec- ond shift and early morning arrival, can readily be effected through an education or training pro- gram for the employees. This must be a positive and continuing program and make use of appro- priate traffic control systems within the parking lot and around the plant. In some cases the use of multiple exits help. The problem of employees’ talk at side yards adjacent to neighboring residen- tial property can also be controlled through a continuing education and internal public relations program. 679 PLANT NOISE ABATEMENT A number of sources discussed at the begin- ning of this chapter require a multistep approach or multielement approach in order to quiet the entire system. Steam power stations, for instance, require noise control of fans, blowers for forced and induced draft, materials handling systems, burner noise in fossil fuel systems, and steam and gas turbines when those facilities are used. Heat- ers and furnaces in petro-chemical and process in- dustries may require mufflers for the high pressure blowers, cooling blowers and the burners them- selves. Transformers are extremely difficult to quiet internally, although premium transformers are available which provide a modest amount of noise reduction. The most common technique today is to build partial enclosures around the transformers using special sound absorbing concrete blocks which are “tuned” to absorb the transformer gen- erated signals. Circuit breakers have received moderate at- tention with respect to quieting, but because they are not activated frequently they should not be a consistent problem. Location in an appropriate area is probably the most convenient method of handling them. Corona noise is currently under study. Another area in which a multielement approach must be used is in process industries where each machine or process element must be examined for noise generating capability and then quieted ac- cording to need. Large mills located inside build- ings may cause no community noise problems so long as the building is well sealed. In some cases, the building supports the mill and radiates the noise. On the other hand, rock crushers located within a sand and gravel operation may be totally exposed to the neighbors. In this situation, a par- tial enclosure of appropriate sound absorbing and transmission loss material combined in one shell would reduce the noise sufficiently to eliminate community complaints. Such materials are com- mercially available. Items such as switch valves, blow down lines and high pressure air or gas by- pass lines should all be equipped with appropriate mufflers. Material handling devices such as fork lifts, motors, and cranes can be quieted by attention to the engine inlet and discharge mufflers. Electri- cally operated overhead cranes may require a small motor enclosure with forced air cooling if the unit is to operate out-of-doors at night and not be heard by neighbors. Conveyors are sub- ject to both quieting through maintenance and im- provement in bearings, or they may require par- tial or total enclosure. Conveyors that carry ma- terials adjacent to or through a community over- head, may require a partial enclosure with only the top open. These are but a few examples of the applica- tion of noise reduction techniques to the outdoor noise generators discussed at the beginning of this chapter. However, an examination of each piece of equipment or each process in the larger system or process being studied should make clear those methods of noise control which are appli- cable and those which may be applicable if the effort is warranted. FUTURE OUTLOOK FOR INDUSTRIAL NOISE CONTROL As the citizens in the community become more conscious of noise and more aware of the noise in their environment, it appears that there will be an increasing demand for a quieter envi- ronment. Not every community today wants to increase its tax base at the expense of new indus- trial plants and their prospective noise sources. It thus appears that more stringent noise control requirements currently exist and are becoming commonplace. In the light of the potential need for more stringent requirements, it is heartening to note that the knowledge in the field of industrial noise control is increasing and that a large body of tech- nology is available to industrial machinery and industrial plant designers to achieve the desired acoustical goals. The payoff is an economic one. It costs money to carry out the design and devel- opment work for quieter machines and plants. The cost is not reasonable unless all industries within a given product area are required to meet the same criteria. This is discussed in detail in studies by the Environmental Protection Agency 680 in its report to Congress. For a discussion of the Environmental Noise Control Act of 1972 as passed by the House of Representatives see the October 18, 1972, issue of the Congressional Rec- ord, p. #10287. References 1. KRYTER, KARL D.: The Effects of Noise on Man, Academic Press, New York, pp. 270-331, 1970. USA Standard Procedure for the Computation of Loudness of Noise, ANSI S3.4, AMERICAN NA- TIONAL STANDARDS INSTITUTE, INC., New York, 1968. PARRACK, H. O.: “Community Reaction to Noise,” Chapter 36, Handbook of Noise Control, C. M. Harris, (Editor), McGraw-Hill, New York, 1957. Community Noise, U.S. ENVIRONMENTAL PRO- TECTION AGENCY, Washington, D. C., 1971. ROBINSON, D. W.: The Concept of Noise Pollu- tion Level, NPL Ero Reports, AC38, National Physical Lab., Teddington, England, 1969. ROBINSON, D. W.: “Towards a Unified System of Noise Assessment,” Journal of Sound and Vi- bration, Vol. 14, 1971. SCHULTZ, T. J.: *Wrappings, Enclosures, and Duct Linings,” Chapter 15, Noise and Vibration Control, L. L. Beranek, (Editor), McGraw-Hill, New York, 1971. KURZE, U. and L. L. BERANEK.: “Sound Propa- gation Outdoors,” Chapter 7, Noise and Vibration Control, L.L. Beranek, (Editor), McGraw-Hill, New York, 1971. 2. CHAPTER 47 SAFETY Frank E. Bird, Jr. HISTORICAL PERSPECTIVE Neil Armstrong’s first step on the lunar sur- face on July 20, 1969, climaxed the stunning suc- cess of one of the greatest scientific achievements ever accomplished by man to that date. What made the Apollo XI program possible was a com- bination of loss control disciplines and engineering skills that brought about the design and assembly of the most reliable flight products ever produced. Of all contributions to this success, the applica- tion of a system approach was probably the over- riding key. At all stages of design, manufacture and operation, the man-machine-environment sub- systems were considered as interrelated, interde- pendent components of the overall system. The meaning of safety in aerospace no longer represented the simple “freedom from hazard for man” as defined by Webster in the intercollegiate dictionary. Safety had come to mean “freedom from the man-machine-media interactions that result in: damage to the system, degradation of mission success, substantial time loss or injury to personnel.” In effect, the desire to insure the gross safety of the system and the ultimate mis- sion’s success brought about a level of total safety confidence never before realized in the annals of industrial management.? With the accomplishments of space safety achievements well known, it is appropriate to take a brief look backward at the occupational safety movement to understand in part the direc- tion taken in the past. The compensation-oriented specialist, largely influenced by attention focused on the appalling rate of death and disability asso- ciated with machinery and equipment, concen- trated his attention on the man sub-system, with traumatic injury prevention as his primary tar- get. To the early safety practitioner, the terms “accident” and “traumatic injury” were almost synonymous. While occupational disease, fire and property damage control were philosophically as- sociated with industrial safety, actual accident pre- vention practices were largely devoid of these considerations. Without doubt, the injury-oriented safety ap- proach, with its concentration on the sources of trauma, brought about a tremendous reduction in death and disabling injury over the years, as dis- cussed in the next section of this chapter. How- ever, failure to recognize the total safety interre- lationships of the occupational system’s man- equipment-material-environment components has created other major problems, resulting in un- precedented pressures and controls on industry by external agencies. Products liability, air, stream, 681 and noise pollution are some of today’s major problems highlighting the need to put loss control programs in tune with technological advances of our space age. With this historical perspective in mind, let us set the stage by discussing the terms “safety” and “accident” as they are considered by an ever increasing number of safety leaders today. The word “safety,” as used by loss control specialists, has broadened considerably in recent years be- cause of the space age influences mentioned ear- lier. It has more appropriately come to mean “freedom from man-equipment-material-environ- ment interactions that result in accidents.” Simi- larly, the practical application of the term ‘“acci- dent” has also evolved to the broader meaning of “an undesired event resulting in personal physical harm, property damage or business interruption.” The meaning of physical harm in this definition includes both traumatic injury and disease as well as adverse mental, neurological, or systemic ef- fects resulting from workplace exposures.? Atten- tion has been focused on the need to consider the “accident” as a “contact” with a source of energy (electrical, chemical, kinetic, thermal, ionizing radiation, etc.) above the threshold limit of the body or structure; or contact with a substance that interferes with normal body processes. ? Advocates of this view point out that the term “accident” is purely descriptive and has little etiological connotation in its use, while associa- tion with the word “contact” as used above gives more specific direction to control methodology. Utilizing this line of thinking, safety program ac- tivities can be directed at the PRE-CONTACT, CONTACT or POST CONTACT stages of acci- dent or loss control. For optimum results, the modern safety specialist will design his program to include considerations at all three levels of the control process, with a logical concentration of effort at the PRE-CONTACT stage. As we con- sider the broader implications of these newer meanings of “safety” and “accident” we more clearly see the important relationship of the safety and environmental health disciplines and the in- creased import of interface between related spe- cialists. THE LOSS PROBLEM: THE HUMAN SIDE Death and Disability While accidental injury rates in American in- dustry have decreased through the years, the death and disability loss problem remained gross enough as late as 1970 that our nation selected occupational safety as a major legislative target. In 1970, occupational accidents claimed the lives of 14,200 workers and injured 2,200,000 people to the extent they were unable to return to work the day following their injury. To express the general trends over the past 35 years, the death and disabling injury rates from 1945 to 1970 are shown in Table 47-1. TABLE 47-1. Statistics on Work Fatalities and Disabling Injuries Employed Fatalities Injuries Labor Per Per Force 100,000 Disabling 100,000 Year (millions )Fatalities Workers Injuries Workers 1945 53 16,500 32 2,000,000 3,788 1950 60 15,500 27 1,950,000 3,211 1955 63 14,200 23 1,900,000 3,055 1960 66 13,800 21 1,950,000 2,964 1965 71 14,100 20 2,100,000 2,954 1970 80 14,200 18 2,200,000 2,824 THE LOSS PROBLEM: THE ECONOMIC SIDE Injury Costs The National Safety Council estimated that wage losses of workers due to accidents in 1970 were $1,800,000,000, while related insurance ad- ministrative costs were approximately $1,300,- 000,000 and medical costs, $900,000,000. In ad- dition, other costs such as the money value of time lost by workers (other than those with dis- abling injuries) who are directly or indirectly in- volved in accidents, and the value of the time needed to investigate accidents and write up ac- cident reports amounted to the tidy sum of $4,000,000,000.2 Other Costs The number of legal suits involving accidents of people on the premises of the businessman, and product defects that resulted in injury, mush- roomed in the past five years, presenting manage- ment with another big loss drain that exceeded $885,000,000 in 1970. Sources such as industrial associations and insurance records available on limited types of property damage, lead to the conservative estimate that building damage, tool and equipment damage, product and material damage, production delays and interruptions resulted in over $4,500,000,000 during 1970. Fire property damage alone added another $1,100,000,000 making a total property damage loss of $5,600,000,000 for 1970.* Total Accident Costs The economic drain from accident losses is summarized in Table 47-2 as conclusive evidence of the tremendous loss problem faced by indus- trial America. THE LOSS PROBLEM: SOURCE OF WORK INJURIES The majority of injuries that cause workers to lose time but do not result in death, permanent total, or partial disability are referred to as tem- porary total injuries. State labor departments report that nearly half of this large group of com- 682 pensable work injuries result from two major sources -— handling objects and falls. On the other hand, machinery accidents account for only 6 per- cent of the temporary total injuries, but give rise to 19 percent of the injuries that cause permanent partial disability. This fact clearly indicates why emphasis on mechanical safeguarding and the elimination of catch points on moving machinery should be given emphasis in any safety program. The motor vehicle is as much a culprit on-the-job as it is off-the-job, and accounts for 18 percent of fatal, permanent total cases but only a very small percent of the permanent partial and tem- porary total injuries. The chart below reveals the major sources of work injuries by their severity types.’ TABLE 47-2. 1970 Accident Losses $1,800,000,000 $1,300,000,000 $ 900,000,000 $4,000,000,000 Workers’ loss of wages Insurance administrative costs Medical Costs Other costs related to above (time lost, investigation time, etc.) Liability costs Property damage costs (including fire loss) Total loss $ 885,000,000 $5,600,000,000 $14,485,000,000 TABLE 47-3. Source of Compensable Work Injuries Fatal Perma- Perma- Tem- All nent nent porary Cases Total Partial Total % % % % Source of Injury of Cases of Cases of Cases of Cases Total o.oo. 100.0% 100.0% 100.0% 100.0% Handling objects, manual 22.6 13.9 9.6 28.5 Falls... 20.4 17.4 18.5 21.2 Struck by falling, moving objects ...... 13.6 9.3 19.3 11.1 Machinery i. 3.1 19.2 6.3 Vehicles 20.7 7.1 6.9 Motor 18.0 4.3 5.2 Other 2.7 2.8 1.7 Stepping on, striking against objects ................. 6.9 2.3 5.6 7.6 Hand tools .............. 6.1 1.5 8.1 53 Elec., heat, explosives .............. 2.5 7.7 2.2 2.6 Elevators, hoists, CONVEYOIS ..ccccoennnne 2.2 3.6 3.8 1.5 Other co. 8.4 20.5 6.6 9.0 Source: Reports From State Labor Departments Tables 1, 2 and 3 from National Safety Council “Acci- dent Facts” 1972, Chicago, Illinois. THE PRE-CONTACT STAGE OF ACCIDENT CONTROL In considering the “accident” as a “contact” with a source of energy above the threshold limit of the body or structure, it is logical that sufficient effective action at the pre-contact stage of acci- dent control could prevent most accident contacts from happening. Such action would eliminate the very potential for personal harm or property damage. Recognizing that it is neither economically feasible nor practical to prevent all exposures to accident sources, action at this stage of loss con- trol could include considerations to reduce or minimize the effects of such contacts at other stages in the loss process if and when they were to occur. A well-organized modern safety pro- gram would place great emphasis on such activi- ties as good facility inspections, safety rules and regulations, group safety meetings, supervisory training, general promotion, hiring and placement practices, job analysis, job observation, skill train- ing, personal communications, work standards, design engineering and maintenance and purchas- ing standards. Since space does not permit a discussion of each of these and other important pre-contact stage program activity areas, the author has chosen the representative few that follow. They indicate well the need for a close inter-relationship of the safety and environmental health disciplines, and clearly highlight the enormous benefits of extended efforts at the pre-contact stage of accident con- trol. Facility Inspection Why Inspect for Hazards? Every piece of equip- ment will wear out in time. Even with ideal care and usage, normal deterioration is inevitable. Ma- terials and tools may be placed in unsafe positions or they may be abused and damaged. While one can speculate that a perfect pre- ventive maintenance engineering program should negate these problems, the question is, “Who has one?” Unless hazardous conditions are steadily “drained off” by regular hazard inspections, the average plant is continually “flooded” with haz- ards or sources of accidental contacts that have potential for personal harm and property damage. The Occupational Safety and Health Act of 1970 has the purpose “. . . to assure as far as possible every man and woman in the nation safe and healthful working conditions and to preserve our human resources . . .” The Act also says that each employer “. . . shall furnish to each of his employees employment and a place of employ- ment which are free from recognized hazards . . .” It would seem appropriate at this point to define the word “hazard” as a potential source of harmful contact. The word harmful in this con- text includes traumatic injury and occupational disease exposures; adverse mental, neurological or systemic effects; and property damage. While inspections may be of the FORMAL or INFORMAL variety, the formal type provides management with the most effective tool for the systematic detection and correction of hazardous conditions. What to Inspect. Although every plant has different operations, equipment and physical layouts, there are certain important items that are quite common to most and deserve special mention. The following list presents the major categories of items that one should generally con- sider in making a safety inspection. 683 Atmospheric Conditions: Relates to dusts, gases, fumes, vapors, illumination, etc. Pressurized Equipment: Relates to boilers, pots, tanks, piping, hosing, etc. Containers: Relates to all objects for stor- age of materials, such as scrap bins, dis- posal receptacles, barrels, carboys, gas cylinders, solvent cans, etc. Hazardous Supplies and Materials: lates to flammables, explosives, acids, caustics, toxic chemicals, etc. Buildings and Structures: Relates to win- dows, doors, aisles, floors, stairs, roofs, walls, etc. Electrical Conductors and Apparatus: Relates to wires, cables, switches, controls, transformers, lamps, batteries, fuses, etc. Engines and Prime Movers: Relates to sources of mechanical power. Elevators, Escalators and Manlifts: Re- lates to cables, controls, safety devices, etc. Fire Fighting Equipment: Relates to ex- tinguishers, hoses, hydrants, sprinkler sys- tems, alarms, etc. Machinery and Parts Thereof: Relates to power equipment that processes, machines or modifies materials, e.g., grinders, forg- ing machines, power presses, drilling ma- chines, shapers, cutters, lathes, etc. Material-Handling Equipment: Relates to conveyors, cranes, hoists, lifts, etc. Hand Tools: Relates to such items as bars, sledges, wrenches, hammers as well as power tools. Structural Openings: Relates to shafts, sumps, pets, floor openings, trenches, etc. Transportation Equipment: Relates to au- tomobiles, trucks, railroad equipment, lift trucks, etc. Personal Protective Clothing and Equip- ment: Relates to items such as goggles, gloves, aprons, leggings, etc.’ Detection System Compcenents The specific hazards and unique aspects of each industrial operation require the safety spe- cialist to adopt a system of formal hazard detec- tion that best meets his specific requirements. While there may be tremendous variation in his methods, he should attempt to fulfill two essential objectives. The first is to see that certain special items or parts are inspected at a frequency in ac- cord with the criticality of the item to prevent hazardous conditions of significant severity. These special items or parts are frequently referred to as critical parts and could include such items as: Re- gases, 10. 11. 12. 13. 14. 15. gear covers - shafts workpoint guards chains railings cables safety valves wires limit switches handles stand-up switches eyebolts speed controls lifting lugs gears grind wheels cables drill points foundations cutting points belts steps — rungs drives brackets Special inspections of critical parts are us- ually much more frequent than general inspec- tions and may be handled differently, even within the same plant. Frequently there are several dif- ferent forms and inspection methods to meet the unique problems associated with the use and ap- plication of items being inspected. The second important objective in any good program is to conduct regular, thorough general inspections of the entire facility. Several key guide- posts essential to accomplishing this goal are as follows: (1) the critical parts inspection program for an area, or a checklist of hazards common to the area, should be reviewed before starting; (2) previous inspection reports should be reviewed carefully to help familiarize an inspector with all related problems in the area; (3) a good inspec- tor will look for off-the-floor and out-of-the-way items as well as those right on the beaten track; (4) the good inspector will be methodical and thorough, and his notes will clearly describe spe- cific hazards and their exact location; (5) a good inspector will classify each hazard by its “potential and loss severity” to aid management in its reme- dial decisions (see hazard classification below); (6) the good inspector will lend appropriate em- phasis to those hazards (class “A”) with imminent chance for loss of life or body part, seeking inter- mediate temporary remedy for these “critical” hazards immediately and diligently following up their permanent remedy promptly after his inspec- tion is complete. Hazard Classification While a system of hazard classification has been used successfully by fire engineers for many years, application of this specific technique in gen- eral industry is relatively new. The extensive suc- cessful use of this tool in the aerospace program has unquestionably provided the motivation for its rapid adoption by an increasing number of com- panies in general industry. Since hazards do not all have the same potential for causing harmful effects, it is logical that a system for classifying them by their degree of probable loss severity potential can have considerable value. The fol- lowing simple classification system has proven quite successful and is very similar to the one used by OSHA inspectors to assist them in establishing the gravity of violations: Class “A” Hazard — A condition or practice with the realistic potential for causing loss of life or body part, permanent health disability, or extensive loss of structure, equipment, or material. Example 1: Barrier guard missing on large press brake used for metal shearing operation. Example 2: Maintenance worker observed in unventilated deep pit with running gasoline motor ser- vicing large sump pump. Class “B” Hazard — A condition or practice with potential for causing serious injury or ill- ness resulting in temporary disabilities, or property damage that is disruptive but less se- vere than class “A”. 684 Example 1: Slippery oil condition ob- served in main aisleway. Example 2: Broken tread at bottom of of- fice stairs. Class “C” Hazard — A condition or practice with probable potential for causing non-disab- ling injury or illness or nondisruptive property damage. Example 1: Carpenter without gloves ob- served handling rough lum- ber. Example 2: Worker complained of strong odor from rancid cutting oil circulating in large lathe at north end of shop. Classifying hazards into these three categories helps to put remedial planning in proper perspec- tive, aids in motivating the action of others on the more serious conditions, and focuses hazard con- trol attention on the critical areas requiring the greatest concentration of time, effort and re- sources. Job Analysis Job analysis” is a tool that enables the super- visor to teach and direct his employees syste- matically in order to obtain optimum job efficiency. Since efficiency demands maximum use and con- trol of the men, equipment, machines and environ- ment involved in any job, the potential sources of traumatic injury and environmental health ex- posures are evaluated along with all other factors associated with production and quality control. Once completed, a good job analysis provides the blueprint to teach any worker how to do a critical job the safe, productive way. The actual prepara- tion of a job analysis provides another enormous opportunity to detect actual or potential sources of occupational injury or health problems at the pre-contact stage of accident control. Methodology. Jobs that are determined to be serious risks to safety, quality or production be- come the “critical few” first targets for analysis. Selection may be based on the frequency or se- verity of past loss history or the potential for loss. The regular maintenance and updating of the analysis is an important aspect of any job analysis program. A job analysis is best prepared by ac- tual observations of a worker or workers doing the job. When infrequently performed jobs prevent the observation method of conducting a job an- alysis, the technique of group discussion can be employed as an alternative. The four basic steps in conducting a job an- alysis are: (a) determining the job to be analyzed, (b) breaking the job down into a sequence of steps, (c) determining key factors related to each job step, and (d) performing an “efficiency check.” The final step involves determining that each step of the job is done in the best and most efficient way. This final step frequently involves a job procedure or methods change, a job en- vironment change or a technique to reduce the number of times the job must be done. The sav- ings alone that result from the accomplishment of this step have consistently proved to be justi- fication for introduction of the program. JOB ANALYSIS Instruction Standard DIVISION Engineering DEPARTMENT Maintenance occupation Painter JOB ANALYZED Painting a Chair DATE EFFECTIVE Nov. 1, 1970 CODE NO. EM-72 SEQUENCE OF STEPS (NOT TOO FINE OR TOO BROAD) KEY QUALITY OR PRODUCTION FACTORS (CLEARLY TELL WHAT TO DO AND WHY) KEY SAFETY FACTORS (CLEARLY TELL WHAT TO DO AND WHY) Select work area. Bring tools and supplies to work area. Prepare work area. Remove old paint from chair with paint remover. Sand chair with sandpaper. Apply first coat of paint. Apply second coat of paint. Clean up area and tools. Store tools and supplies. Should be as dust-free as possible to prevent dust from sticking to painted surface while wet. This can damage finish, requiring re- work. Have all needed tools at hand before starting to avoid delay. Place chair on newspapers to .avoid delays caused by cleaning up spills. Be sure all paint is removed from cracks and crevices so final fin- ish will be uniform. Otherwise, re-sanding may be necessary to smooth out rough surfaces. Sand all surfaces with OO sand- paper until smooth to the touch for best results. Wipe off dust. Dust left on surface will make finish rough, requiring re-sanding. Coat of paint should be light and applied with even strokes to mini- mize brush marks for most attrac- tive results. Same as #6. Clean brushes thoroughly in paint thinner; then shake out thinner. Paint left in brush can ruin brush for further use if it is allowed to harden. Brushes should be hung up by the handle to keep weight off the bristles. The weight of the brush on the bristles can deform them and ruin the brush. Area should be well ventilated so that toxic fumes do not accumulate, possibly causing serious illness. Be sure all cans of thinner, paint remover, and paint are tightly closed when not in use to minimize the dangers from fire or explosion. Use at least six layers of paper to absorb spilled paint remover and paint. Both of these can cause extensive damage to the floor. Follow directions on paint remover container and do not allow smoking or open flame in area to prevent fire or explosion. Gloves should be worn while sanding to prevent abrasions and splinters. Follow directions on paint con- tainer. Same as #4, NO SMOKING OR OPEN FLAME. Same as #6. Dispose of all papers and wipe any spilled paint from floor or other surfaces. Papers left on floor can present fire or tripping hazards. All paint, thinner, and remover must be tightly sealed both to preserve them and to prevent escape of fumes which could cause fire or explosion. International Safety Academy, Macon, ‘Georgia. Job Analysis — Instruction Standard (Form) Figure 47-1. 685 There are two basic approaches in doing a job analysis. One that has been used extensively in the past is the “Job Safety Analysis” technique that produces an end product dealing purely with safety. While there are unquestionable merits for treating this important subject in this manner, the author personally favors the complete ap- proach referred to as “Proper Job Analysis,” “Total Job Analysis” or just plain “Job Analysis,” as the individual plant designates. This latter ap- proach seems to have more appeal to manage- ment people at all levels, since it is based on the new concept of safety as one of the many insep- arable parts of the supervisor's job. Figure 47-1 is an example of this approach. Benefits. While there are many benefits that come with a Job Analysis program, none is more im- portant than the peace of mind that a concerned management group has in knowing that it has pro- vided a tool to insure that the actual potential sources of traumatic injury and environmental health exposures have been carefully analyzed and evaluated for all critical jobs. Where complete elimination of hazards de- tected is not economically feasible or practical at the time a job analysis is accomplished, the com- pleted job analysis provides the guidelines to ac- complish the job safely by following the clearly defined method of procedure. Engineering Controls Most hazardous conditions can be predicted or anticipated at the design, purchase, mainte- nance or work-standard development stages of plant operation. Unsafe conditions, such as inad- equate guards and devices, inadequate warning systems, fire and explosion hazards, projection hazards, congestion and close clearances, hazard- ous atmospheric conditions, and inadequate il- lumination or noise are good examples of the more common causes of accidents that can be pre- vented by effective engineering at the pre-contact stage of accident control. Control Points. The design engineer naturally be- comes a key to the control of hazardous condi- tions in any plant. Local standards that require the interface of engineers with safety and environ- mental health specialists at all stages of facility or equipment design and development provide the best avenue to prevention or control of potential injury or health problems at the point of optimum effectiveness. Additional local standards requir- ing the approving signature of safety and environ- mental health specialists on all drawings or plans increase the possibility that proper consideration was given this important subject. In addition to all other guides suggested or re- quired by the state, local government, associations, and local plant establishments, the Occupational Safety and Health Act of 1970 provides the en- gineer with a comprehensive source of minimum required standards. The person(s) or department responsible for the purchase of materials/products/equipment also plays a major role in hazard prevention and control. Again, closely organized formal contact between purchasing personnel and those responsi- 686 ble for safety and health management at all stages of purchasing, planning and acquisition becomes a very important key to accident control. The required use of safety data sheets by suppliers on all materials with potentially hazardous properties can be an effective guide to decision-making in purchases, as well as provide local specialists with valuable information to develop safe-practice guides when the use of such potentially hazardous material cannot be avoided. Maintenance and industrial engineering per- sonnel are also among the vital few who play so important a role in the creation and control of a safe and healthful industrial environment. Local standards requiring safety and health considera- tions in all phases of related work activities must be designed into the job commitments of these key people. Safety and health personnel can main- tain control of such standards by periodic audits and required approvals on such items as work per- mits and job standards being created. Minimize Loss by Energy Control. Engineering considerations at the precontact stage can be di- rected toward the control of the energy exchange that could cause personal harm or property dam- age. Some of the various avenues open to prevent injurious loss through this means are: I. Eliminate a potential injurious energy type by substitution or use of an alterna- tive source; e.g., use of electrical motors instead of shafts and belts in powering machinery, or use of a solvent with a higher TLV than the one proposed. 2. Reduce the amount of energy used or re- leased; e.g., reducing the temperature of a hot water system to reduce the danger of scalds to personnel in shower rooms, or slowing the speed of vehicles in a plant by periodic bumper pads in the road. 3. Separate the energy from persons or prop- erty that could be exposed by time or space; e.g., barricaded and locked safety space provision around radioactive iso- tope usage, or placing electric power lines outside of a building in a less accessible location. 4. Interpose barrier between energy and peo- ple or property potentially exposed; e.g., personal protective equipment, bumper guard on loading dock, cement base guard on column, or insulation on noise-emitting machine.® 5. Modify the contact surfaces of materials or structures to reduce injurious effects to people or property; e.g., placement of shock absorbing material on low ceiling point of stairway to minimize risk of head injury. 6. Strengthen the animate or inanimate struc- ture to support the energy exchange; e.g., program of weight control and physical conditioning for railroad conductors to prevent spraining ankles while getting on and off moving cars, or reinforcing railroad cars to resist loads dropped on cars acci- dentally during crane handling.” THE CONTACT STAGE OF ACCIDENT CONTROL The safety or health specialist must be con- stantly alert to needs and applications of the principles of deflection, dilution, reinforcement, surface modification, segregation, barricading pro- tection, absorption and shielding at the contact stage of accident control. While many applica- tions of these principles are visually anticipated and provided for through effective engineering at the pre-contact stage, many others will escape the average system’s design considerations. One must also keep in mind that the energy exchanges in- volved with normal wear and tear, as well as ab- normal usage, will require continual repair and replacement of related materials, structures or equipment. The use and application of personal protective equipment provides one of the best ex- amples of safety countermeasures at this stage of accident control. Personal Protective Equipment Four important considerations deserve special attention when the decision has been made that a need exists for personal protective equipment. 1. Selection of the proper type of protective device. 2. Employee fitting of the equipment and in- struction on its proper use. 3. Enforcement of standards created. 4. An effective system of equipment sanita- tion and maintenance. Proper selection involves a determination of the degree of protection desired, the practicality of its application for the job, the acceptance by the worker, as well as the elements of maintenance and cost. Of course, we must always be conscious that equipment selected meets the required stan- dards of performance. Manufacturers whose prod- ucts meet the standards of the Bureau of Mines and/or N.I.LO.S.H., the National Fire Protection Association, American National Standards Insti- tute and other standards organizations, will usually include an approval marking or label on the product. To assure proper use, one should make sure that workers understand why protection is neces- sary, so they will want to use it. In addition, special attention should be given to the ease and comfort with which it can be used, so that it will be used. Personal protective equipment can be mis- used or disused to varying degrees depending on a variety of program factors. It, therefore, behooves the safety and health specialist to constantly recog- nize that this approach to hazard control should always be secondary to a sincere effort to eliminate the exposure. For additional coverage of this sub- ject the reader is referred to Chapter 36 on “Per- sonal Protective Devices.” Eye and Face Protection. Eye and face protection is required by the Occupational Safety and Health Act of 1970 “. . . . where there is reasonable prob- ability of injury that can be prevented by such equipment.” Some of the typical operations where eye hazards exist are the pouring or handling of molten metals or corrosive liquids, cutting and welding, grinding, milling, chipping, sand blasting 687 and electric welding. It is not only necessary for the operator to wear such protection, but it may also be required by any person near the operation, including other workers, supervisors, or visitors. The ANSI Standard Z87 gives specifications for design as well as functional requirements. Speci- fications are given for types providing impact pro- tection against flying objects, those providing pro- tection against fine dust particles or liquid splashes, and those providing protection against glare, in- jurious radiation and impact. Respiratory Protection. The Occupational Safety and Health Act of 1970 (OSHA) requires respira- tory protection for the control of occupational hazards caused by breathing air contaminated by harmful dusts, fogs, fumes, mists, gases, smokes, sprays, or vapors which cannot otherwise be kept from contact with people. The potential extent of health problems that occur from misuse or dis- use of respiratory equipment is so severe that every engineering means possible should be exhausted to avoid personal contact with harmful air contami- nants. When necessary, selection of respirators should be according to the guidance of the American National Standard Practices for Respiratory Pro- tection Z88.2-1969. Some respirators are used to purify the air from contaminants, while others are used to supply fresh air to the worker. Selec- tion involves the nature of the operation or proc- ess and the nature of the air contaminant, its con- centration, and its physiological effects upon the body. One should also remember that some air contaminants can affect the skin, too, providing a double hazard. Other factors to consider include length of the exposure and the length of time the protective device must be worn. Work in hazardous locations (such as tanks) requiring respirators to supply fresh air requires special safety precautions. For instance, in the event of equipment failure, it is essential to know the time required for escape, and the procedure for emergency escape. Standards also include the requirements for additional men to be present for special communication arrangements, and for the availability of rescue equipment and personnel in areas where self-contained breathing apparatus is used in atmospheres immediately hazardous to life or health. Other Protective Devices. OSHA states that “Hel- mets for the protection of heads of occupational workers from impact and penetration from falling and flying objects and from limited electric shock and burn shall meet the requirements and specifi- cations established in American National Standard Safety Requirements for Industrial Head Protec- tion Z89.1-1969” and that “Safety toe footwear for employees shall meet the requirements and specification in the American National Standard for Men’s Safety Footwear Z41.1-1967.” The Occupational Safety and Health Act also refers to ANSI Standards for rubber insulating gloves, rubber matting to be used around elec- trical apparatus, rubber insulating blankets, and rubber insulating sleeves to protect people work- ing around electricity. A wide variety of additional protective devices of special material is available and includes ap- rons, jackets, leggings and coats for protection against heat and splashes of hot metal in opera- tions such as steelmaking and welding. Special protectors have been designed for almost all parts of the body, to protect against cuts, bruises and abrasions. Many types of hand and arm protec- tors are available. The material used in gloves de- pends upon what is being handled. Impervious clothing is available to protect against toxic substances, dusts, vapors, moisture, and corrosive liquids. It ranges from aprons, bibs and gloves to full garments containing their own air supply. Natural rubber, neoprene, vinyl and other plastics are used to coat material used in this equipment. By taking all the necessary steps to select, fit, enforce and maintain an effective personal pro- tective equipment program, the safety or health specialist will have taken another giant step at the contact stage of accident control to prevent trau- matic injury and environmental health problems. THE POST-CONTACT STAGE OF ACCIDENT CONTROL There is a tremendous reservoir of informa- tion to prove that the severity of losses involving physical harm and property damage can be mini- mized by the application of one or more counter- measures at the post-contact stage of accident control. These could include prompt first aid and rehabilitation in cases of physical harm, and prompt reparative action and salvage in cases of property damage.” In addition to these countermeasures, the prompt investigation of any accident loss pro- vides a significant opportunity to prevent similar future losses by remedying the causes involved. Emergency care and accident investigation are briefly discussed below, and represent two major post-contact measures to control accident losses. Emergency Care The logic of utilizing prompt emergency care as an effective countermeasure to reduce death and disability in industry is supported by many occupational medicine specialists. There is no way of knowing how many lives might have been saved last year had this care been more readily avail- able. When we consider that one in every four disabling injuries involved some permanent loss of body part, the importance of this vital subject becomes even more evident. Expert consultants returning from Viet Nam have publicly asserted that, if seriously injured, their chances of sur- vival would be better in the zone of combat than in most American cities. Excellence of prompt emergency care proved to be the major factor in the phenomenal decrease of death rates for bat- tle casualties who reached medical facilities from 4.5% in World War II to less than 2% in Viet Nam." The author suggests that the size of the death- and-disability problem in American industry jus- tifies a much greater concentration of attention by everyone on this important post-contact acci- 688 dent control countermeasure. The emergency care requirements listed below are suggested as minimum for any general industrial establishment. 1. The existence of a properly-equipped cen- tral first aid area for the treatment of all general injuries. 2. The presence on all shifts of certified first aid attendants or medical professionals. 3. The existence and organization of a plan for handling serious or unusual cases. 4. The provision for assistance of a medical specialist to treat specific types of injuries. 5. The existence of an established, trained rescue or ambulance team on each shift. 6. The existence of an in-plant training pro- gram for key employees in urgently-neces- sary first aid cares. 7. Adequate distribution on the premises of “critical” first aid supplies to meet needs required by special exposures. Authoritative sources give strong indication that a soon-to-be-released comprehensive study of first aid training and its effects on safe behavior, made in Toronto, Canada, will prove a significant correlation between the two. In effect, it is be- lieved that this research will reveal that first aid training has significant value in the prevention of accidents and should be employed as a strong mo- tivational factor in pre-contact accident control. Accident Investigation An accident investigation report is basically the supervisor’s analysis and account of an acci- dent, based on factual information gathered by a thorough and conscientious examination of all fac- tors involved. The time for accident investigation is always as soon as possible. The less time between the accident and the investigation, the better and more accurate the data which can be obtained. Facts are clearer, more details are remembered, and the conditions are nearest those at the time of the ac- cident. Accident investigation report forms may differ from company to company, but the infor- mation they seek is fairly standard. An increas- ing number of companies use forms that provide a selection of numbered choices in the causal and remedial sections. Forms such as these are de- signed to minimize the amount of writing by the supervisor and to facilitate computerization of the data for analysis. The form displayed in Figure 47-2 at the end of this chapter is representative of the more common ones. The author would like to emphasize that many forms captioned “Acci- dent Report” are really injury investigation re- ports. Their very design prohibits their use as a tool to gain valuable information on other acci- dents resulting in costly property damage that under slightly different circumstances could also have involved personal injury. Obtaining Good Data Reporting Cooperation Essential. No matter how conscientious a front line supervisor might be, he cannot investigate an accident unless he is aware of it. Since most accidents do not result in the dramatic “big loss,” it is not difficult for workers to hide a large quantity of valuable data that SUPERVISOR’S ACCIDENT INVESTIGATION REPORT COMPANY BRANCH 2 DEPARTMENT - - - EXACT LOCA - DATE OF OCCURRENCE DATE REPORTED - ade req Ache 3-7-69 2: 3-7-9 INJURED'S NAME = 7, PROPERTY DAMAGED - 4 y . OF BODY ESTIMATED COSTS ACTUAL COSTS c 3 ! - s (50. 3 755 To OF INJURY NATURE OF DAMAGE - Z / INFLICTING INJURY OBJECT/EQUIPMENT/ INFLICTING DAMAGE WITH MOST OF OBJECT/EQUIPMENT/SUBSTANCE MOST CONTROL OF OBJECT/EQUIPMENT/SUBSTANCE 2 a: - ~ THE ACCI : ATTACH ACCIDENT DI FOR ALL VEHICLE ACCIDENTS. ~ - D E S Cc R I P T | 0 N /— CIR] acd Q-20-069.- LOSS SEVERITY POTENTIAL PROBABLE RECURRENCE RATE XI Major [] Serious [J Minor WK Frequent [J Occasional [J Rare WHAT ACTION HAS OR WILL BE TAKEN TO PREVENT RECURRENCE? PLACE X BY COMPLETED. - Z0==ZMmM - E 3 \ 3 Bh : . i Nee oo . it i wr . ’ = . ) ) ’ - - Er - \ oo Bh Ie N BN - - y } - - Re. ~ l 3 ) ’ a ~ y 5 - ro - = ~ . . - - r o - ) . - a =a - oo . - i Lan ) ) 4 Site in i: CHAPTER 48 DESIGN AND OPERATION OF AN OCCUPATIONAL HEALTH PROGRAM Jon L. Konzen, M.D. GENERAL COMMENTS AND OBJECTIVES An occupational health program has as its chief goal the preservation and, if possible, the improvement of the health of the work force. This work force includes everyone from the chief executive officer to the newest unskilled worker. Such a program must contain the basic ele- ments of prevention, acute clinical care, rehabili- tation and counseling. The scope of an individual program will depend on the size of the business or industrial organization, its geographic location, the potential hazards inherent in the operation, and the philosophy of management and labor. It is important that the scope of a program be defined in writing. This is true whether the plan is for a small single establishment involving only a few workers or a large multi-plant corporate pro- gram. The scope should include the basic objec- tive of the program, the duties, authority and reporting relationships within the organization. Above all, the scope should clearly indicate that management understands and fully supports the program. Without the complete understanding, philosophical and financial support of manage- ment the best conceived program has little chance of success. Occupational health programs involve multiple disciplines including occupational medicine, occu- pational health nursing, industrial hygiene, safety and health physics. These health professionals who are members of management must work closely not only with each other, but must have an effective relationship with other management members. This is especially true when working with members of the personnel and labor relations groups. This can be accomplished if the primary objective — the health of the worker — is con- tinually kept in mind. This will have a positive effect not only on the worker, but it will favorably influence personnel and labor relations in such areas as workmen's compensation, sickness, ab- sence and group insurance. Two additional objectives are frequently being assigned to or closely coordinated with the health program in industry. One is to determine and make recommendations regarding possible effects of facility operations on the surrounding commu- nity. The second objective is to determine the health effects of the products on the consumer. The extent of the health involvement in these latter objectives will be dependent on the size, scope and level of the operation. 693 PRESERVATION OF EMPLOYEE HEALTH Administration General. Management plays a major role in any health program in industry, whether this be at the corporate level or at the plant level. The manage- ment must be fully aware and agree with the pro- gram, realize that it is preventive in nature and understand that it is not simply a tool to reduce compensation costs or improve the safety record. Management must be willing to give both the au- thority and the responsibility for carrying out the program to the chief health professional in the organization. Position of Health Professionals in the Management Hierarchy 1. The physician should report to a senior member of management at both the plant and cor- porate level. The plant physician should report to the plant manager. The medical director at the corporate level should report either to the presi- dent or a senior vice-president. 2. The occupational health nurse, if there is a full-time physician, should report both admin- istratively and technically to the physician. If the physician is associated with the company on a part-time basis, the nurse should report to him functionally on technical matters, but may report to the personnel manager administratively. 3. The industrial hygienist may report both at the plant and at the corporate level to the med- ical organizations or directly to the same report- ing level as the physician. The reporting relation- ship is best determined on an individual company basis with consideration being given to the needs, philosophy, expertise and the full or part-time status of the personnel involved. 4. The safety professional has traditionally reported to the Personnel Department. As safety activities expand in the plant and the community, the reporting relationship must be re-examined and, if necessary, realigned to meet modern re- quirements. 5. The first aid personnel would report tech- nically to the plant physician and administratively to the Personnel Department. 6. Para-medical personnel, who are also called physician's assistants, would report directly to the plant physician both technically and admin- istratively, since a majority of such personnel are employed in plants with a full time physician. 7. The reporting relationships of other health professionals such as thc health physicist and the psychologist should be determined in a similar manner as outlined for the industrial hygienist. It must be emphasized that whatever the re- porting relationship, each health professional must be responsible for planning, justifying and admin- istering his own budget. There is a close interface among the disciplines of occupational medicine and nursing, industrial hygiene, safety, psychology and health physics. These disciplines may best serve the company and its employees through consolidation under one health professional, both at the local and corporate level. Basic Concept of the Program Pre-placement Health Evaluation. The pre-place- ment health evaluation should be an evaluation rather than “an examination.” It has been tradi- tional in many companies to carry out a pre- employment physical examination which consists of “seeing the doctor,” a chest X ray and a uri- nalysis. This examination was frequently used to “weed out” hernias, bad backs or other obvious physical disabilities. The examination frequently had no other use. A more rational approach to the pre-employ- ment evaluation is to consider it a placement eval- uation for intelligent assessment of the health status of the individual. In this era of wide med- ical coverage most job applicants have a reason- able knowledge of their health status. For this reason cither an automated or a check-off type history will give the reviewing medical personnel sufficient information to categorize the man’s health status without further examination. Another approach to pre-employment evalua- tion is to combine the health questionnaire with a selected battery of tests to monitor specific organ systems such as cardiopulmonary, hemotologic and urinary systems. Paramedical personnel frequently can carry out at least part of the pre-placement evaluation! The results from such programs sug- gest that these types of pre-employment screening are as effective as the traditional doctor/applicant encounter in delineating health status of the appli- cant and in determining his physical capabilities to perform a job. In industry where there are known hazards, it may be prudent to carry out in addition to the questionnaire and screening tests on selected organ systems, the. traditional encounter with the physician so that a man’s health can be further categorized. The examination will be used for job placement and as a baseline for further peri- odic health examinations based on work exposure. Selective Job Placement. Practically no worker comes to a place of employment without some physical defect. Therefore, the pre-employment examination results should play a major role in the intelligent placement of a worker. If the physical requirements of the job are considered in relation to the physical limitations of the worker, it will frequently prevent accidents, ill health and increase productivity. Blanket policies should not be established for accepting or not accepting applicants with certain physical condi- tions. The individual's physical capabilities should be matched with the work he is expected to per- 694 form. This will permit utilization of a willing worker with some physical defects. Periodic Health Evaluations Based on Job Ex- posure. The purpose of the periodic examination should be clearly defined and a program devel- oped with the approval of management. The pur- pose of the periodic examination is to evaluate the health condition of the individual with emphasis placed on specific “target organs” which may be affected by actual or potential environmental ex- posures. Such a periodic health monitoring pro- gram will rely heavily on a carefully planned check-off questionnaire, selected tests such as au- diometry for noise, spirometry for airborne par- ticulate, and blood determinations for specific metals and/or chemicals. If all of the test para- meters are normal, the physician may eliminate the personal examination and only review the record. Such a procedure lends itself to multi- phasic screening. A reasonable alternative is to broaden the scope of the periodic examination to make it a complete health appraisal of all body systems with emphasis on organ systems which may be harmed by the environmental exposures. The complete health appraisal is the more ideal approach; how- ever, it may not be possible to carry out an in- depth health appraisal on all personnel. Environmental Hazards in the Work Environment. Almost any environment has either potential or actual environmental hazards that need to be rec- ognized, measured and monitored. Management and the health professionals must have a high index of suspicion in order to identify potential or actual environmental hazards. Physical agents, airborne particulate and vapors alone, or in com- bination, even at low concentrations, may be haz- ardous. First, one must consider the raw materi- als, the level of exposure to the worker and their potential to do harm. Next, consideration must be given as to how these raw materials are modified through intermediate steps and the exposures cre- ated. Finally, the finished product must be re- viewed to determine possible effect on the worker. Each step from raw material to finished product must be evaluated under normal conditions and also under emergency conditions, such as spills, bursting or breaking. An effective industrial hygiene baseline and periodic monitoring program can be developed by the industrial hygienist based on the above con- siderations. It is important to assess the exposures in re- lation to the severity and length of the exposure. On this assessment, a rational approach to control by engineering methods can be undertaken. If it is demonstrated that the environment can be hazardous to health and that good engineering control cannot be effected, then an effective per- sonal program must be initiated. Such a program must take into consideration the proper protec- tive equipment, educational program to instruct the worker with regard to the hazards, and the necessity of wearing the protective equipment consistently and properly. Integration of Environmental and Physical Ex- amination Data. After in-plant environmental con- trol has been achieved through engineering mea- sures, or the much less desirable method of per- sonal protective devices, continued surveillance of both the environment and the worker is neces- sary. The environment should be sampled peri- odically or, if necessary, continuously to provide an adequate characterization of breathing zone and general work area exposure concentrations. It is not adequate simply to measure the work at- mosphere and on that basis conclude that there is no hazard to health “because the exposure is below the TLV.” The environmental exposure data must be in- tegrated with the physical status data in a manner that considers length of exposure, average con- centrations and peak exposures. The medical sur- veillance must evaluate the individual's physical condition in light of naturally occurring disease and the possibility of normal transitory physio- logical alterations in certain function studies. The periodic medical surveillance will generate con- siderable data on the exposed workers with em- phasis on organ systems most likely to be affected by a given exposure. We must characterize the exposures and physi- cal findings in terms of the individual and the group. This characterization may be simple for the small operation with few potentially hazardous exposures. In large complex operations the char- acterization may involve a computerized, epidemi- ologically coordinated system. This system would utilize industrial engineering to characterize a worker's location and movements, continuous in- dustrial hygiene monitoring to characterize the atmospheric exposures and multiphasic screening methods to examine the worker. Personnel Duties of the Health Professionals. Plant Physician — The physician is the med- ical officer of the plant. In this capacity, he is responsible for advising management concerning the health condition of the workers, the health hazards that may exist in the plant and the safe- guards to protect the health of the worker. In order to do his job effectively he must be fully cognizant of what the plant makes, how it is made, what raw materials are utilized, the potential and actual health hazards associated with this manu- facturing and the physical requirements of the various types of jobs. The physician must have this information so he can adequately carry out the pre-placement health appraisals, periodic health examinations and the health education pro- grams. Most physicians who practice clinical medicine require additional orientation in the area of pre- ventive occupational health programs. Sources of additional information for the development of a good occupational health program can be obtained from the organizations noted in the preferred reading list at the end of this chapter. Informa- tion concerning specific hazards, including the necessary industrial hygiene and medical moni- toring as well as the required control measures can be obtained from the standards published by 695 the Department of Labor in the Federal Register, the ten regional offices of the Occupational Safety and Health Administration (OSHA), U. S. De- partment of HEW’s National Institute for Occupa- tional Safety and Health (NIOSH) regional of- fices, the company’s insurance carrier, the firm supplying the particular chemical or material and private consultants in occupational medicine and industrial hygiene. The plant physician, whether part or full time, should tour the plant a minimum of once a month to review the in-plant environment and the effec- tiveness of environmental control. He should di- rect the attention of management and, if there is one, the corporate medical director to conditions which may cause adverse health effects to the work force. The doctor should follow up until adequate controls are effected. The physician, as the chief health officer of the plant, is responsible for de- termining the significance of occupational and en- vironmental sources of disease. The plant physician is not expected to render any specialized treatment such as major surgery, treatment of severe eye injuries or other conditions beyond his field of training or experience. These cases should be referred to recognized medical specialists preferably those certified by the boards of the various specialties. However, all cases of occupational injury or disease should be examined by the plant physician at frequent intervals re- gardless of who is rendering the actual treatment. Employees’ physical impairments or diseases which are non-occupational are also an important phase of the plant physician’s responsibilities. The physician should consult with the employees who seek his advice regarding non-occupational condi- tions, but should confine treatment to that which is necessary to relieve the emergency condition or to enable the employee to finish his shift. These employees should be referred promptly to their family physician. In some isolated areas the plant physician may care for both occupational and non- occupational related health conditions of the work- ers and possibly their families. In these situations there must be clear ground rules established be- tween the physician, the company and the local medical society regarding delivery of health care. It is the plant physician’s responsibility to no- tify the local health department in cases of report- able communicable diseases. All pre-placement, periodic, transfer and re- entrance health examinations are to be conducted or reviewed by the plant physician. All examina- tions should be conducted in privacy with only the patient present. Employees should not be ex- amined “en masse.” All female employees should be examined in the presence of a third party, pre- ferably a nurse. The plant physician should arrange and par- ticipate in First Aid courses for key plant person- nel given under the auspices of the American Red Cross or other similar service organizations. The plant physician should be responsible for and supervise the keeping of accurate, com- plete and legible medical records. The records of each individual employee are confidential. The local company physician, in accordance with ap- plicable policy, should determine the nature and amount of medical information that can be re- leased to others. Medical personnel should not discuss an applicant’s or an employee’s health or medical records with other personnel except as required in the performance of their duty. Spe- cific medical records of injury or occupational disease must be made available under the 1970 Occupational Safety and Health Act, and in cases involving workmen’s compensation. Portions of the medical records dealing with occupational ill- ness and injury must be discussed with the plant safety supervisor in order that he can carry out his functions. The physician’s opinions and recommenda- tions should be based entirely upon the facts as determined by careful investigation of each inci- dent, case or condition. Any biased judgment or opinion which might be used to further the com- pany’s or the employee’s interest at the expense of the other party is considered unprofessional and highly inappropriate. Occupational Health Nurse — The occupa- tional health nurse is a part of the management team. As a health professional it is important that she be objective in all of her professional duties. The nurse should be trained, and if appropriate, certified to conduct the specialized in-plant test- ing required in the program. Her duties can be grouped in the areas of prevention, treatment, re- habilitation and education. In the area of prevention, she plays a vital role in the pre-placement and periodic health ex- amination programs by conducting preliminary testing and assisting in the completion of medical questionnaires. Her duties may include prelim- inary review of test results to screen out the obvi- ous normal findings. This will permit the doctor to better utilize his time in reviewing the abnormal findings. A good industrial nurse can handle many of the minor accidents and injuries which occur in any industrial setting. These treatments are car- ried out under the direction and written orders of the physician. It is most important that every health facility have a set of written orders defin- ing the limits and responsibilities of the nurse with regard to treating the patient, and that the occu- pational health nurse is currently licensed to prac- tice in the state in which she is employed. The nurse plays a key role in rehabilitation of the injured worker by supervising appropriate ex- ercises, whirlpool or heat treatments in the unit. This rehabilitation will aid in the early return to work of the injured employee. The nurse plays a vital role in the educational program to inform the employee of potential health hazards of work and the signs and symptoms of over-exposure. Frequently she fits and instructs the worker in the proper use of personal protec- tive equipment. The nurse can serve as an effective health counselor for personal physical and mental health problems. She can be especially effective in the areas of alcohol and drug abuse. The keeping of good clinical medical records 696 as well as the records prescribed under the Occu- pational Health and Safety Act fall largely to the nurse. She must have knowledge of the in-plant environment so she can intelligently assess com- plaints. This will permit proper recordkeeping and assist in early recognition, and prompt med- ical management of occupationally related health conditions. Small plants frequently employ only part-time nursing service. The nurse coverage should be scheduled to cover more than one shift in a multi- shift operation. Her period in the plant should be long enough to accomplish all her duties. In most operations, each plant visit should be at least two hours in length. Industrial Hygienist — The industrial hygien- ist in most companies will be located at either the central office or at a divisional office location. A few organizations have a qualified industrial hy- gienist located at the plant level. Many compa- nies must rely on outside industrial hygiene con- sultation through their insurance carrier, state agencies or private consulting firms. The duties of the industrial hygienist are to make the corporate management aware of poten- tial in-plant environmental hazards, measure these hazards, recommend appropriate engineering con- trol and periodically monitor the controlled envi- ronment. The industrial hygienist, physician and nurse must work closely together to achieve the proper control of the environment and maintain it. The industrial hygienist’s specialized knowledge in the area of toxicology will be of great benefit to the physician and the nurse. He will often act as a liaison between the medical group and the actual plant production people in areas of com- mon concern. Safety Coordinator — The safety coordinator has the prime responsibility for the safety program of the plant. The two major areas of this respon- sibility are employee education in safe work prac- tices and property safety. The safety supervisor must work closely with the Medical Service of the plant to review all accidents and illnesses so unsafe conditions can be corrected and the affected employees be re-edu- cated promptly to prevent further accidents. First Aid Personnel — In all plants, and espe- cially those without full nurse coverage, employees should be selected and trained as first aid person- nel to provide emergency first aid when trained professionals are not present in the plant. These employees should attend and obtain certification from an approved first aid course such as is given under the auspices of the American Red Cross or other similar service organizations. The course must meet the standards for first aid training under the 1970 Occupational Safety and Health Act. The coordination of training these employees is the responsibility of the plant physician. Other Health Professionals — Other health professionals who may be involved in plant oper- ations from time to time include the health physi- cist and the doctor’s assistant. The need for these personnel will be governed by the size and type of operation. The use of a physician’s assistant must be governed by the availability of proper physician supervision. Facilities The location, size, layout and equipment of an in-plant medical facility should be based on the size of the operation, the number of employees and the activities of the plant. It is especially important in new plant design to plan for possible future expansion. The medical facility should be located on the first floor of a multi-floor complex with consider- ation given to proximity of elevator service which will accommodate a wheeled stretcher. An elec- tric cart to serve as an in-plant ambulance may be necessary if the plant is unusually large. The medical facility should be located within easy access to the work areas. There should be a sec- ond entrance to a driveway which is free of archi- tectural barriers where an ambulance can readily load an ill or injured employee. The size of the unit is governed by the extent of the in-plant program. There are various form- ulas for determining unit size, but a reasonable rule of thumb is to include approximately 1 to 1.5 square feet for each employee up to 1000 em- ploy 2s. Over 1000 employees, the square footage per employee can be appropriately reduced. The layout of the unit should permit wheeled stretchers to negotiate all turns and enter all rooms. It is important to remember that these units serve several functions: prevention, treat- ment and rehabilitation. In large units where there is one or more full time nurses as well as a full time physician, the floor plan should be de- signed to separate the preventive activities from the treatment activities. Various layouts have been devised for this purpose. There is no one best layout. | Privacy in an in-plant medical unit should equal that of the private physician’s office. Privacy can be accomplished even when examining large numbers of pre-placement or periodic applicants. One commonly used method is to have two or three small dressing cubicles adjacent to the ex- amining room. Each one of these cubicles has two doors. One door leads from the hall into the cubicle. The second door opens into the physi- cian’s examining room. The patient enters the cubicle, closes the hall door, locks it, disrobes and awaits the physician. The physician controls the movement from the cubicle into the examining room since no door knob is placed on the cubicle side of the door. The larger units may have specialized rooms for minor treatment of illness or injury, a spe- cial room where minor suturing can be carried out under good aseptic conditions and a ward for ob- servation of patients. It is most important that if there is more than one bed in a room that each bed be enclosed entirely by a cubicle curtain. All units, regardless of size, must have facilities for hand washing, toilet rooms and storage. In very small plants where there are fifty or less em- ployees, the medical unit which is to serve pri- marily for first aid and health counseling may consist of only one room. The room requires a sink, dressing cabinet, industrial treatment chair, examination table, desk and files for maintaining 697 the confidential medical records. All other pre- ventive, treatment and rehabilitative activities would be carried out at a nearby medical facility. For a plant of 200 individuals or less, a three- room unit consisting of a doctor’s office/examin- ing room, minor treatment room and nurse’s of- fice/waiting room would be suitable. The doctor’s office/examining room would also be used as a major treatment room for a severely injured pa- tient prior to transport to the hospital. Each treatment and/or examination room should have running water, adequate lighting and ventilation. In a small plant which employs less than 200 workers, where the physician does not come to the plant for other than monthly inspections, it may be appropriate for the nurse to carry out the preliminary health testing at the plant. The results would be forwarded to the physician’s pri- vate office for completion of the examination. Most equipment commonly used in preliminary testing such as the mechanical sight screener, spirometer, audiometer and audiometric booth are not usually found in the average physician’s pri- vate office. Blood can be drawn either at the physician’s office or in the plant. X-ray studies would be made at an outside facility. The effectiveness of the occupational medical program is usually increased by carrying out as much of the preventive, rehabilitative and educa- tional program as possible in the plant. This would include all parts of the examination with the possible exception of X ray. Such a program would require frequent plant visits by the physi- cian. The training, background and length of time that the medical personnel are at the plant should determine the type and sophistication of emer- gency and therapeutic medical equipment and drugs that will be maintained on the premises. Records The medical records which must be maintained on an individual must characterize his health at the beginning, periodically throughout and at termination of employment. A record of all occu- pational injuries, illnesses and treatments must be maintained. It is customary to have a pre-placement health examination form which includes a check-off health questionnaire that reviews the patient’s past environmental exposures, family history, personal medical history and provides a section to record the objective medical findings. In designing such a form it is important to consider the educational status of the average applicant so that the history portion can be completed by the applicant with a minimum of assistance from the medical person- nel. Newly designed forms should be computer compatible even if there are no immediate plans to use data processing equipment for storage, re- trieval or use of the records. A similar questionnaire and selected testing procedure approach may be used for the periodic health evaluation. _ The forms should be designed with sufficient room so that all data can be entered easily and re- viewed at a glance. The abnormal findings should stand out. There should be sufficient area for comment and elaboration of all abnormal find- ings. Laboratory and other testing data may be displayed in tabular form. Internal Statistical Reports. 1t is useful to have internal statistical reporting covering the costs, patient load and the various tests that arc per- formed. An objective review of this data will per- mit an evaluation of the effectiveness of the pro- gram, enable determination of accurate costs for medical services and assist in realistic budget development. Occupationally Related Accidents and Illness In- vestigation Reports. Early determination of the causes of occupational injury and illness is as- sisted by an intelligent accident or illness report that is completed jointly by the first-line super- visor, the plant safety coordinator and the medical service. If each of these disciplines intelligently and accurately complete their portion of the report, unsuspected problem areas may be identified and controlled. They will assist in reducing accidents by making the entire plant more aware of the in-plant environment. It will also demonstrate to the employees that the company takes the matter of their health and safety seriously. Such reports with certain modifications can be used as work- men’s compensation reports and the Occupational Safety and Health Administration Form #101. Records for Compliance with the 1970 Williams- Steiger Occupational Safety and Health Act. The Occupational Safety and Health Act of 1970 states that all illnesses and injuries which require more than simple first aid must be recorded within six days after the illness or injury becomes known. OSHA Form 100 or an equivalent form or method approved by the Secretary of Labor may be used. The law further requires that an accident report be completed on each recordable injury or illness. OSHA Form 101 is provided for this purpose. Annually a summary which can be completed on OSHA Form 102 must be posted in a conspicu- ous place for not less than thirty days. This form must be posted not later than the first of February of the year following the covered period. Some selected plants will be requested to complete OSHA Form 103 for submission to the Depart- ment of Labor. This is a more detailed summary of the information reported on OSHA Form 102. The details for recordkeeping requirements are summarized by the Department of Labor in the booklet RECORDKEEPING REQUIREMENTS UNDER THE WILLIAMS-STEIGER OCCU- PATIONAL SAFETY & HEALTH ACT OF 1970. Industrial Hygiene Records. Industrial hygiene sampling records must be available for review by the Secretary of Labor or his representative. The samples should be taken in sufficient numbers and locations to characterize in-plant exposure to people. Industrial hygiene reports which are made to management should be more than a list of nu- meric values. The report should interpret the data from the standpoint of ceiling values, time weighted exposures and excursion peaks. The reports should discuss the corrective action which would be appropriate in relation to the exposures. It should be emphasized that the acceptable ex- posure concentration used in industrial hygiene, commonly called threshold limit values, are guide- lines for reasonable exposures and are not absolute safe or unsafe limits. These levels should be dis- cussed in terms of the standards which have been and are continuing to be published by the Secre- tary of Labor. The Federal Register should be consulted on a continuing basis for published changes. Industrial Hygiene There are three basic types of industrial hy- giene surveys from a physician’s standpoint. These include baselining of an operation, periodic mon- itoring of an operation and emergency monitoring of an operation. Baselining is an in-depth eval- uation to characterize exposures throughout the manufacturing facilities. To carry out such a sur- vey it is usually appropriate for the hygienist and frequently the physician to make a preliminary walk-through survey of the facilities to review raw, intermediate and end products of a manu- facturing operation in order to identify actual and potential exposures under normal and abnormal conditions. After the walk-through has been com- pleted and evaluated, the industrial hygienist will move in with the appropriate equipment and com- plete the baseline survey. Periodic monitoring of the plant is carried out in essentially the same way except the initial walk-through may be eliminated and the number of individual samples required usually can be reduced. The third type of indus- trial hygiene survey is the emergency survey. Med- ical review of the first-line supervisor's accident report may require immediate evaluation and sampling to determine if a particular operation or exposure is creating a hazardous condition. Such emergency surveys can be kept to a minimum if the baseline and periodic surveys are well planned and executed. It is most important that the physician and industrial hygienist be consulted during initial planning and pilot stages of a new process or op- eration so that necessary environmental control and medical monitoring can be included in the economic feasibility study. It is possible that when the environmental concerns are considered, a product line may be unprofitable. Environmental and occupational health are necessary costs of doing business. There should be a procedure by which the plant or corporate engineering coordinates with the medical and industrial hygiene services so that sufficient environmental consideration is given to a process change and to the purchase of new prod- ucts and equipment. This will assure that en- gineering controls will be added or modified in order to control any potential environmental haz- ards. It is an old axiom that minimal changes in the process can cause maximal environmental problems. Safety Safety must play a major role in a well rounded health program (see Chapter 47). A 698 safety program should cover not only property, machine guarding, fire safety and the like, but must include the education of management as well as the work force in safe working procedures. The safety program begins when the worker is first employed. It is important to have on-the-job training programs that are directed to the indi- vidual to inform him of safety hazards in his particular job, as well as an indoctrination in the general aspects of safe work practices. This will require that a comprehensive job safety analysis be performed on all operations. Further, there must be a systematic inspection of new, revised and existing production and safety equipment to identify potential safety hazards and to assure compliance with governmental requirements. An- other important task of the safety supervisor is a systematic accident investigation program coordi- nated with first-line supervision and the medical service. Special Programs Programs Directed at Specific Hazards. The pre- placement and periodic examinations mentioned earlier in this chapter are important but not all inclusive parts of special programs to protect workers from specific hazards in the work place. The examinations are limited to assisting in iden- tification of workers who should not be exposed to certain hazards and reveal early adverse health effects. Special programs will vary in number and complexity depending on the hazard, type of ex- posure and number of workers involved. All the special programs have certain things in common which include recognition of the hazard, measure- ment of the hazard, control of hazard by engineer- ing or personal protective devices, medical moni- toring of the workers and education of the em- ployee with regard to the health and safety im- plications presented by the hazard. It cannot be stressed too vigorously that the educational part of the program and its resulting motivational in- fluence is one of the most important parts of any special program. If the worker cannot be properly motivated to cooperate in the protection of his health, costly industrial hygiene engineering, con- trol devices, personal protection equipment and medical monitoring will have only limited effec- tiveness. The employee does have specific respon- sibilities under Public Law 91-596 (OSHA) to achieve and maintain safe and healthful working conditions. Some of the more common specific hazard control programs include hearing conservation against noise; eye protection against flying partic- ulate; respiratory protection against such airborne agents as lead, silica, asbestos, cotton and solvent vapor; thermal stress protection against heat or cold; and dermal protection against skin sensitiz- ers or irritants (see Chapter 34). Immunization programs directed at such job related diseases as tetanus and in certain industries, typhoid, are often indicated. A well rehearsed and frequently re- viewed tank entry program which incorporates segments of other hazard control is a common requirement in industry. Medical Disaster Control. Medical disaster, either man-made or natural, can occur. All office com- 699 plexes and plants should have plans which will permit rapid evaluation, effective first aid, evacu- ation and transportation of injured personnel to a definitive treating facility. The elaborateness of the disaster control plan will depend on the size of the operation. Alcohol and Drug Abuse. Programs to combat alcohol and drug abuse are important and neces- sary. These specialized programs require an inter- disciplinary effort between personnel and medical departments and the community. Such programs should clearly define company policy, and include the detailed procedure for handling personnel in- volved in these abuses. These programs should be designed to treat drug and alcohol problems in the same manner as other chronic diseases. Consultation to Management on Group Insurance Benefits. Management should review the group health insurance benefit plan with the medical service. Medical expertise will be of assistance in formulating the most comprehensive plan for the least amount of money. Absentee Control. Absentee control is a by-prod- uct of a good medical program. Early recognition of job-related and non job-related conditions can assist in rapid treatment and early return to the job. A day-to-day evaluation of sickness absence takes a careful, well thought out form to obtain the necessary confidential medical information and establish a good rapport between the private physician and the company medical service. The program will aid in preventing unwarranted and excessively long sickness absences. It will assist the plant physician in intelligently placing the re- turning worker if job change is necessary. Occupational Mental Healtht. Mental health is an area of increasing concern of industry today. An emotionally affected worker who is troubled by home or work problems is not an efficient or safe worker. It is most important that the medical service programs train first-line supervision to recognize symptoms of emotional ill health, and refer employees promptly to the medical service. This will permit professional evaluation and coun- seling. If necessary, prompt referral to specialized mental health care can effectively be carried out by the medical service. It should be emphasized that the first-line supervisor should not try to diag- nose or ‘treat” emotional illness, but should promptly refer the employee. Evaluation and counseling take time in the medical facility, but this service can render great dividends in terms of the individual as well as his value to the company. Possible Health Effect of the Facility Operation on the Community Effluents from a Facility. Effluents which are emitted from a plant to the atmosphere, to waste water, or by solid waste disposal must be monitored for legal reasons and to pro- tect the health of the community. It is important to sample these effluents at the source of emis- sion, as well as in the community since many ma- terials may undergo a chemical change which would render them either more or less hazardous. Frequently emissions may be relatively unique to a particular facility operation. For this reason, there must be close cooperation between the en- vironmental engineering group and the medical group so that representative samples are obtained, and meaningful evaluation of the samples are carried out. At times by using toxicological con- sultation, the physician may be able to advise on the health effect of materials. At other times, it may be necessary to carry out animal studies or, in extreme cases, to evaluate the health effect on the community by epidemiological studies. Social Impact of Opening or Enlarging Operations in a Community. The social impact of a plant on the community, particularly if it is a small com- munity, may be appreciable. The medical service should be consulted during the initial planning stages of a new or enlarged facility to assist in the determination of adequate medical coverage for the in-plant operations and to assess the impact of the influx of a work force on the local medical support. In particularly small or isolated com- munities, it may be necessary to work with the local medical society in order to either encourage, and at times financially support expansion of local medical services, or offer comprehensive medical service to the employee and his family through the company. Possible Health Effect of Products on the Consumer Health Evaluation of New or Modified Products. For years many large progressive companies have carried out a joint effort with toxicologists and medical personnel to conduct studies on new or modified products from the conceptional stage through final product marketing. It is becoming increasingly clear that such procedures will have to be incorporated in product development pro- grams of still more industries. Possible health effects must be considered as part of the normal product development process. The possible health effect evaluations of new or modified prod- ucts may take place within the company or may be contracted to a variety of institutions who are equipped to carry out toxicological literature re- views, animal studies, human studies and limited field testing. Whether evaluations are carried out within the company or through consultants, it is most im- portant that a team within the company represent- ing medical, technical and toxicological expertise be established to determine the need, scope and design of any research study. Evaluation of Present Products. At times it is necessary to carry out a critical health effect eval- uation of products which have been marketed for various periods of time. These health effect eval- uations will utilize the same techniques as used for new or modified products. In addition, the health history of employees exposed to the finished prod- uct would be of value in assessing the health ef- fect. An additional important tool in determining health effect on the consumer is an objective and representative analysis of customer complaints from a health standpoint. It is important when using customer complaints to carefully document the adverse health effects in relation to the use or 700 misuse of the product. It is also important to de- velop mechanisms which will surface customer complaints effectively in all areas where the prod- uct is marketed. Preferred Reading 1. ALCOHOLICS ANONYMOUS WORLD SER- VICES, INC.: Box 459, Grand Central Post Office, New York, N. Y. 10017 (see Publications List). 2. AMERICAN ACADEMY OF OPTHALMOLOGY & OTOLARYNGOLOGY: Guide for Conservation of Hearing in Noise, 15 Second Street, S.W., Roch- ester, Minn. 55901 — 1969. 3. AMERICAN ASSOCIATION OF INDUSTRIAL NURSES, INC.: “Guide for Training Courses for Audiometric Technicians in Industry,” Occupa- tional Health Nursing (official Journal of AAIN), 79 Madison Avenue, New York, N. Y. 10016 — 1967 (see Publications List). 4. AMERICAN CONFERENCE OF GOVERN- MENTAL INDUSTRIAL HYGIENISTS: Docu- mentation of Threshold Limit Values, P. O. Box 1937, Cincinnati, Ohio 45201 — Revised edition, 1971. 5. AMERICAN CONFERENCE OF GOVERN- MENTAL INDUSTRIAL HYGIENISTS: Thres- hold Limit Values for Chemical Substances and Physical Agents in the Workroom Environment With Intended Changes for 1972. 6. AMERICAN INDUSTRIAL HYGIENE ASSOCIA- TION: Hygienic Guides of American Industrial Hy- giene Association, 66 South Miller Rd., Akron, Ohio. 7. AMERICAN MEDICAL ASSOCIATION, COUN- CIL ON OCCUPATIONAL HEALTH: Archives of Environmental Health, 535 North Dearborn St., Chicago, Ill. 60610 (see Publications List). 8. AMERICAN NATIONAL STANDARDS INSTI- TUTE, INC.: American National Standards List, 1430 Broadway, New York, N. Y. 10018. 9. AMERICAN PUBLIC HEALTH ASSOCIATION: American Journal of Public Health (“Local Health Officer’s Guide to Occupational Health”) 1015 18th St., N.W., Washington, D.C. 20036. 10. INDUSTRIAL HEALTH FOUNDATION: Indus- trial Hygiene Highlights, Volume 1, 5231 Centre Avenue, Pittsburgh, Pa. 15232 — 1968. 11. INDUSTRIAL HEALTH FOUNDATION: Indus- trial Hygiene Digest (Medical Series Bulletins), 5231 Centre Avenue, Pittsburgh, Pa. 15232 — 1968. 12. INDUSTRIAL MEDICAL ASSOCIATION: Jour- nal of Occupational Medicine, 150 North Wacker Drive, Chicago, Illinois 60606 — September, 1971 (see Publications List). 13. JOHNSTONE, R. T. and S. E. MILLER: Occu- pational Diseases and Industrial Medicine, Saunders, Philadelphia, Pa. — 1960. 14. LEVINSON, H. ET AL: Men, Management and Mental Health, Harvard University Press, Cam- bridge, Mass. — 1966. 15. MAYERS, M. R.: Occupational Health — Hazards of the Work Environment, The Williams & Wilkins Co., Baltimore, Maryland — 1969. 16. NATIONAL COUNCIL ON ALCOHOLISM: Suite 1720, Two Park Avenue, New York, N. Y. 10016 (Catalog of Publications). 17. NATIONAL SAFETY COUNCIL: Accident Pre- vention Manual for Industrial Operations, 425 North Michigan Avenue, Chicago, Illinois 60611 — 6th Edition, 1969. 18. NATIONAL SAFETY COUNCIL: Fundamentals of Industrial Hygiene, 425 North Michigan Ave- nue, Chicago, Illinois 60611 — 1971. 19. NEW YORK CHAMBER OF COMMERCE: “Drug Abuse as a Business Problem — The Problem De- fined with Guidelines for Policy,” 65 Liberty St., New York, N. Y. 10005. 20. 21. 22. 23. 24. PATTY, F. A., Editor: Industrial Hygiene and Tox- icology, Interscience Publishers, Inc., N. Y., Vol- ume I (General Principle) — 1958; Volume II Toxicology) — 1962. SATALOFF, J.: Hearing Loss, J. B. Lippincott Company, Philadelphia — 1966. THE CHRISTOPHER D. SMITHERS FOUNDA- TION: “Alcoholism in Industry — Modern Pro- cedures 1969,” 41 East 57th Street, New York, N. Y. 10022. STEWART, W. W., Editor: Drug Abuse in Indus- try, Halos & Associates, Inc., Medical Book Divi- sion, 9703 S. Dixie Hwy., Miami, Fla. U. S. DEPARTMENT OF HEALTH, EDUCA- TION AND WELFARE, N.I.LO.S.H.: “Occupational Diseases, A Guide to Their Recog- 701 nition,” P.H.S. Publication #1097 — 1964. “Community Health Nursing for Working Peo- ple,” P.H.S. Publication #1296, Superintendent of Documents, U. S. Government Printing Office, Washington, D. C. 20402. 25. U. S. DEPARTMENT OF LABOR, O.S.H.A.: “Compliance Operations Manual,” O.S.H.A. #2006 — January, 1972. “A Handy Reference Guide — The Williams-Stei- ger Occupational Safety and Health Act of 1970.” “Recordkeeping Requirements under the Williams- Steiger Occupational Safety & Health Act of 1970.” “Guidelines to the Department of Labor’s Occupa- tional Noise Standards,” Bulletin 334, U. S. Gov- ernment Printing Office, Washington, D. C. 20402. EE RE rT . > “I vee T TRE TE RT ——— CHAPTER 49 THE DESIGN AND OPERATION OF OCCUPATIONAL HEALTH PROGRAMS IN GOVERNMENTAL AGENCIES Victoria M. Trasko BACKGROUND Responsibility for occupational health and safety programs is dispersed among various fed- eral and state governments. Goals are basically the same — the prevention and control of occupa- tional injuries and illnesses, and the general im- provement of the health of workers and the work- ing environment; but missions are restricted to specific areas of authority or concern. For ex- ample, at the Federal level, health aspects of such programs have been viewed traditionally as the responsibility of the Public Health Service; safety aspects, the U.S. Department of Labor; and mine safety and health, the U.S. Bureau of Mines. Functions of federal agencies have been con- fined to research and development, technical as- sistance to states and others, dissemination of in- formation, and to various degrees, training and promotion of improved occupational health and safety programs at the state level. To these tra- ditional functions has been added enforcement of national safety and health standards under re- cently enacted legislation. The role of state agen- cies, which have legal responsibility for health and safety of employed workers, is provision of direct services to industry in the solution of occupational health and safety problems. The application of research and of standards of good practice, and supervision of the health of its employees while at work is regarded as the responsibility of man- agement. Over the years, a spirit of cooperation has existed among federal and state governments, and industry and labor which contributed greatly to the progress made in reducing the toll of occu- pational injuries and diseases which characterized the early decades of this century, and in making the job environment a safe and healthy place in which to work. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE National Institute for Occupational Safety and Health The National Institute for Occupational Safety and Health (NIOSH) was established within the Department of Health, Education and Welfare (HEW) by the Occupational Safety and Health Act of 1970, PL 91-596 (see Chapter I) to carry out the functions specifically assigned to it, and the research and educational functions assigned to the Secretary of HEW and delegated to NIOSH. NIOSH formally came into being with the re- designation of the Bureau of Occupational Safety 703 and Health, Public Health Service. It is now lo- cated administratively within the Health Services and Mental Health Administration of HEW. The reconstituted Bureau itself had its origin in the establishment of the Office of Industrial Hygiene and Sanitation by the Public Health Service in 1914, and has been active as a continuous organ- ization entity. The passage of the Occupational Safety and Health Act of 1970 provided for the first time a specific legislative base for occupa- tional safety and health research and training ac- tivities. In addition to broad responsibilities under PL 91-596, NIOSH has been delegated responsibilities for carrying out the health provisions of the Fed- eral Coal Mine Health and Safety Act of 1969, PL 91-173. Organization and Functions. NIOSH has its headquarters offices in Rockville, Maryland, and maintains primary research laboratories and other program functions in Cincinnati, Ohio, with spe- cialized field laboratories at Salt Lake City and Morgantown, West Virginia. Staffs are also main- tained in each of the 10 HEW Regional Offices. The “Statement of Organizations, Functions and Delegations of Authority” (printed in the June 30, 1971, issue of the Federal Register), assigns the following major functions to the Insti- tute: “Plans, directs, and coordinates the national program effort to develop and establish recom- mended occupational safety and health standards and to conduct research, training, and related ac- tivities to assure safe and healthful working condi- tions for every working man and woman: “(1) Administers research in the field of oc- cupational safety and health, including the psy- chological factors involved; (2) develops inno- vative methods and approaches for dealing with occupational safety and health problems; (3) pro- vides medical criteria which will ensure, insofar as practicable, that no employee will suffer di- minished health, functional capacity, or life ex- pectancy as a result of his work experience, with emphasis on ways to discover latent disease, es- tablishing causal relationship between diseases and work conditions; (4) serves as a principal focus for training programs to increase the number and competence of persons engaged in the practice of occupational safety and health; (5) develops and coordinates the appropriate reporting proced- ures which assist in accurately describing the na- ture of the national occupational safety and health problems; and (6) consults with the U.S. Depart- ment of Labor, other federal agencies, state and local government agencies, industry and employee organizations, and other appropriate individuals, institutes and organizations with regard to pro- motion of occupational safety and health.” Program activities are carried out through the Offices of the Director, Extramural Activities, Ad- ministrative Management, Planning and Resource Management, Research and Standards Develop- ment, Manpower Development and Health Sur- veillance and Biometrics. These offices are lo- cated in Rockville, Md. and Cincinnati with staffs including Associate Directors for the spe- cific areas. Operating programs are carried out primarily in Cincinnati by the Divisions of Laboratories and Criteria Development, Field Studies and Clinical Investigations, Technical Services, Occupational Health Programs, Training and (at Morgantown, West Virginia) by the Appalachian Laboratory for Occupational Respiratory Diseases. Staffs are diversified and include physicians, nurse consultants, hygienists, engineers, chemists, toxicologists, statisticians, physicists, physiologists and psychologists as well as other specialized per- sonnel. Prior to the passage of the Occupational Safety and Health Act of 1970, NIOSH was engaged in a broad program encompassing research and field investigations on occupational diseases, technical and consultative services, and short term training. Specific functions and activities include: environ- mental studies of uranium mines and medical studies of uranium miners to clarify the relation- ship to lung cancer of occupational exposure to radioactive ore; prevalence study of chronic chest disease problems in soft coal miners; long-term study to determine the occurrence of asbestosis and lung cancer in workers in the asbestos prod- ucts industry; toxicologic and pathologic research on materials anticipated or encountered in the occupational environment, including determina- tion of acute, subacute and chronic toxicity, safe limits of exposure, modes of action and tests for hypersensitivity; development of improved ana- lytical and field sampling methods; studies of ef- fect of heat on well being or work performance; national noise study; engineering, medical and nursing assistance and consultative services to states, federal agencies, and other groups; survey of employee health services in 7,000 general hos- pitals; a research grants program; and a technical information service. The following additional activities as author- ized by the Occupational Safety and Health Act of 1970 are being carried out: conduct of research for developing criteria for recommendations of new occupational safety and health standards for submission to the U.S. Department of Labor for promulgation; conduct of a grant program for support of demonstrations and training as well as of research at universities, state and local agen- cies, and other public and non-profit institutions; hazard evaluations in work places upon receipt of written requests from employers and represent- atives of employee groups; conduct, directly or by grants or contracts, of research, experiments 704 or demonstrations relevant to occupational safety and health, including studies of behavioral and motivational factors involved; conduct, directly or by grants, education programs to provide an ade- quate supply of qualified personnel to carry out the purposes of the Act; maintenance of an ana- lytical and instrument calibration service for the Department of Labor; publication of an annual listing of all known toxic substances and the con- centration levels at which such toxicity is known to occur; with the U.S. Department of Labor, re- view of state plans and grants; and consultation to the Secretary of Labor on various other pro- visions of the Act including the collection and compilation of national health and safety statistics. Implementation of the Coal Mine Safety and Health Act of 1969. (See also under Bureau of Mines.) NIOSH responsibilities under the Act include: (a) operation of the medical examination program in which over 60,000 underground coal miners have been provided chest X rays through contracts with coal operators or directly by NIOSH. The Morgantown facility serves as the X-ray receiving station and processes the X rays: (b) development of mandatory health standards for the protection of life and the prevention of occupational diseases of miners, including stan- dards on noise, which are then transmitted to the Department of Interior for publication and en- forcement; and (c) the conduct of studies, re- search, experiments, and demonstrations to pre- vent or control occupational diseases originating in the coal mining industry. For example, the Na- tional Study of Coal Workers’ Pneumoconiosis was conducted to provide basic research informa- tion for epidemiologic purposes. Approximately 10,000 miners in 31 selected mines in 10 states were given medical examinations. A considerable amount of research is underway on the develop- ment of techniques for prevention and control in- cluding identification of hypersusceptibles and the determination of relationship between the coal mine environment and occupational diseases. In- terim standards for respirable dust exposure have been published. The Morgantown facility, which conducts much of the research, has also been designated the certification laboratory for safety equipment and sampling instruments. As authorized by the Act, the Secretary of HEW appointed a Coal Mine Health Research Advisory Council which meets periodically to ad- vise on research priorities. Payment of Black Lung benefits authorized by the Act is the responsibility of the Social Se- curity Administration. By June 1971, the SSA had received 297,162 claims, processed 267,042, and approved benefits for 126,396 miners or their widows, totalling more than $313 million. U.S. DEPARTMENT OF LABOR Occupational Safety and Health Administration The Occupational Safety and Health Admin- istration (OSHA) was formed in April, 1971 to carry out the functions assigned to the Secretary of Labor in the Occupational Safety and Health Act of 1970. It is headed by the Assistant Sec- retary for Occupational Safety and Health, an Office established by the Act. By order of the Secretary of Labor (Federal Register, May 12, 1971), all safety and health responsibilities, per- sonnel, and facilities assigned to the Employ- ment Standards Administration (formerly called the Wage and Hour Administration) were trans- ferred to the Assistant Secretary for OSHA. The former Bureau of Labor Standards was absorbed by the newly created Administration. Responsibilities of OSHA are carried out through 1) the Federal and State Operations, 2) Office of Standards, and 3) Office of Training and Education. Field operations are conducted on a decentralized basis under 10 Regional Adminis- trators who report directly to the Assistant Sec- retary for Occupational Safety and Health. They will supervise 50 area offices. Field staffs include safety engineers, safety officers and industrial hy- gienists who serve as safety and health compliance officers. The Act also established the Occupational Safety and Health Review Commission, consisting of three members appointed by the President, to adjudicate disputes arising from the enforcement of the Act. This Commission is an independent agency and is not in the Department of Labor. Major Responsibilities of OSHA under the Occu- pational Safety and Health Act of 1970 include the promulgation, modification and enforcement of occupational safety and health standards; in- spections and investigations of premises of indus- trial establishments; issuance of citations and pro- posing penalties for job safety or health viola- tions; conduct of programs (with HEW) for the education and training of employees and employ- ers in recognition and prevention of unsafe or un- healthful working conditions in covered employ- ments; operation of the grants program to states to assist in identifying their needs and for develop- ing plans, and to assist in the enforcement of fed- eral safety and health standards or equally effec- tive state standards; formulation of regulations re- quiring employers to keep and make available to the Secretary of Labor and the Secretary of HEW records on certain employer activities, employee exposures to potentially toxic substances or harm- ful physical agents, and records and reports of work-related deaths, injuries and illnesses. In- terim standards with which all employers subject to the Act must comply, entitled “Occupational Safety and Health Standards” and consisting of certain National Consensus Standards and Es- tablished Federal Standards have been promul- gated (Federal Register, May 29, 1971, Part II). Other Functions and Responsibilities. OSHA is also delegated responsibility for implementing and enforcing the safety and health aspects of other Acts including the following: The Walsh-Healy Public Contracts Act was passed in 1936, and applies to contracts for materials and supplies exceeding $10,000. It conferred on the Department of Labor responsibility for protect- ing safety and health of workers, and authority to promulgate safety and health standards with which employers must comply. Safety inspectors in- 705 spect the establishments of contractors, and those who do not comply with rules and regulations are not permitted to bid upon future government contracts. McNamara-O’Hara Service Contract Act applies to contracts for service to the federal government exceeding $2,500. Federal Construction Act was passed in 1969, and applies to federal and federally assisted or fi- nanced construction contracts exceeding $2,000. The Longshoremen’s Act enacted in 1959, em- powered the Department of Labor to establish safety and health standards for longshoremen and shipyard workers. Other functions of OSHA include supervision and direction of a federal employees safety pro- gram through the Federal Safety Council; conduct of safety training courses for governmental per- sonnel, industry, and unions; and assistance to states and others in the development of safety codes and improvement of employment standards through better administration and legislation. Bureau of Labor Statistics The Bureau of Labor Statistics is the fact- finding agency of the Department in the field of labor economics and statistics. The collection and compilation of work-injury statistics is the im- mediate responsibility of the Division of Indus- trial Safety. Annual mail surveys of work injuries which provided the basis for frequency and se- verity rates per 1,000,000 hours worked have been conducted for many years on a voluntary basis in a sample of industries. Rates have been published for industry groups and by states. In 1970, 17 states participated in the collection and tabula- tion of the annual reports. Under the Occupational Safety and Health Act of 1970, the Secretary of Labor, in consulta- tion with the Secretary of Health, Education and Welfare, is authorized to develop and maintain a program of collection, compilation and analysis of statistics on work-related injuries and illnesses, other than minor injuries requiring only first-aid treatment. The Bureau of Labor Statistics was delegated the responsibility of carrying out this program (Secretary of Labor’s Order 12-71; Fed- eral Register, Wednesday, May 12, 1971), as well as the provision regarding grants to states to assist them in developing and administering pro- grams dealing with occupational safety and health statistics. With the passage of these provisions, the federal government was authorized for the first time to collect and compile statistics on work- related injuries and illnesses on a national basis. Regulations of the Secretary of Labor entitled “Recordkeeping Requirements under the Wil- liams-Steiger Occupational Safety and Health Act of 1970” have been published and disseminated to employers subject to the Act. The regulations require employers to keep rec- ords on reportable injuries and illnesses as defined, and to file an annual report as prescribed with the Secretary of Labor, upon request. Because of em- phagis on lack of statistics on occupational illnesses during the hearings prior to the enactment of the Act, the system designed specifies seven categories of reportable work-related illnesses. Bureau of Employees’ Compensation The Bureau administers the Federal Em- ployees’ Compensation Act applicable to Federal civilian employees; the Longshoremen’s and Har- bor Workers’ Compensation Act which covers pri- vate maritime employment on navigable waters in the United States, and also applies to employment in the District of Columbia; and several other Acts covering military and other personnel. DEPARTMENT OF THE INTERIOR Bureau of Mines The Bureau of Mines has responsibility for protecting the safety and health of workers em- ployed in the coal, metal and non-metallic mining industries. The Bureau has been in operation since 1910 when, as a result of a series of coal mine disasters, it was established in the Department of the Interior. Its major functions then were limited to the study of safe methods and appli- ances best adapted to prevent mine accidents and disasters. Subsequent legislation provided author- ity for coal mine inspection (1941) and in 1952, enforcement of the Mine Safety Code, including the closing of mines if imminent danger existed. The Bureau also carries out functions dealing with inspections and enforcement of health and safety standards, delegated to the Secretary of Interior, in the Federal Metal and Nonmetallic Mine Safety Act of 1966, and the Federal Coal Mine Health and Safety Act of 1969. The Bureau is composed of a headquarters in Washington, D.C., and a field organization of district offices, technical sup- port centers and field health groups. The Bureau through its Health and Safety Activity conducts programs of mine research and development, approval and testing of mining equipment and protective devices, certification of respirators, mine inspections and field investiga- tions, safety education and training, and mine ac- cident statistics analysis. It is responsible for the formulation and enforcement of health and safety standards. The Bureau has worked closely with NIOSH, HEW, in research and studies of dust diseases over the years. Responsibilities of the Bureau under the Fed- eral Coal Mine Health and Safety Act of 1969 include annual inspections and investigations in coal mines; development, promulgation and re- vision, as necessary, of improved mandatory safety standards (in consultation with HEW, and others) and the promulgation of mandatory health stan- dards transmitted by NIOSH, HEW; enforcement of the Act’s interim mandatory safety and health standards together with the Interim Compliance Panel, established by the Act to hold hearings and review permit requests from Coal operators for temporary periods of noncompliance with interim respirable dust standards; establishment of specifi- cations for personal sampling equipment; evalua- tion of dust measuring instruments and those ap- proved for usage under the Act; and expansion of education and training programs in recognition and prevention of accidents or unsafe working conditions. The Secretary of the Interior in co- ordination with the Secretary of HEW and of 706 Labor is authorized to make grants to states to assist in developing and enforcing effective coal mine health and safety laws, among other func- tions. Under the Act, operators are required to carry out respirable dust sampling programs in coal mine atmospheres by devices and in a manner approved by the Secretary of the Interior and the Secretary of HEW. The samples are transmitted to the Bureau’s Pittsburgh Dust Laboratory where they are weighed automatically. Some 30,000 samples are processed monthly. Data are computerized out of the Denver Office and results sent to the Districts and coal mine operators. A periodic sampling scheme has been developed which per- mits the Bureau to maintain control on exposures in working sections of mines, and at the same time, provide environmental data for epidemiologic purposes. The Act also provides that operators make arrangements in advance for obtaining emergency medical assistance and transportation of miners requiring such assistance; selected agents of the operator be trained in first aid; and coal mines to have adequate supplies of first-aid equipment at strategic locations at and near working places. The Secretary of the Interior may also require oper- ators to provide potable water and sanitation fa- cilities. Mandatory safety standards are being pro- posed for the prevention of explosions from in- flammable gases that may be found in under- ground coal mines. These include methane, car- bon monoxide, hydrogen sulfide and others. Other Federal Agencies A number of other federal agencies have vested authority in some aspect of occupational safety and health. For example, the Department of Transportation, through its assistant Secretary for Systems Development and Technology, has responsibility for the regulation of the transpor- tation of hazardous materials in interstate and foreign commerce and the conditions under which hazardous chemicals may be shipped by carriers. Through the Hazardous Materials Regulations, it also controls the transportation and packaging of radioactive materials. The Department of Commerce, through the Bureau of Standards, contributes greatly to the evaluation of the industrial environment through its research and central national services in broad program areas, covering basic, material, and tech- nological measurements and standards. The Department of Defense was established by the National Security Act Amendments of 1949, which also provided that the Departments of the Army, Navy and Air Force be military departments within it. Each of the three depart- ments have in operation extensive occupational medicine, safety, industrial hygiene and environ- mental health programs conducted for the pro- tection of the safety and health of their own em- ployees in the various installations, bases, repair shops and shipyards in the United States. In the Department of the Army, occupational safety and health activities are responsibilities of the Army Environmental Hygiene Agency; in the Department of Navy, of the Industrial Hygiene and Safety Branch; and in the Department of the Air Force, of the Bio-environmental Engineering Program. Activities also cover radiological health aspects, air pollution, hearing conservation pro- grams, disaster preparedness, acoustics and re- search into allied areas. The Atomic Energy Act, amended in 1959, provides for the establishment of the Federal Ra- diation Council to advise the president on radia- tion matters affecting health, the formulation of standards, and the establishment of cooperative programs with the states. The Food and Drug Administration, HEW, has enforced the 1960 Federal Hazardous Sub- stances Labeling Act designed to protect con- sumers from the misbranding of hazardous sub- stances used in industry and in the home. Federal Employee Health Services The Occupational Safety and Health Act of 1970 requires each federal agency to establish and maintain a comprehensive safety and health pro- gram for its employees, consistent with the Depart- ment of Labor’s safety and health standards re- quired of industry. Most federal agencies have established such programs. However, depending upon appropria- tions, activities and number of employees, extent of services provided varies widely. Agencies may operate their own programs, or they may contract for care with the Division of Federal Employee Health, Public Health Service, or with private medical sources. The Civil Service Commission, through its Bureau of Retirement, Insurance and Occupational Health, also promotes government- wide occupational health and safety programs for federal employees in those establishments that have not as yet arranged for such services. STATE AND LOCAL AGENCIES Occupational Health Programs Until the passage of the Federal Occupational Safety and Health Act of 1970, direct legal re- sponsibility for the health and safety of employed workers rested with state governments. The first state industrial hygiene programs were established in 1913 in the New York Department of Labor and Ohio Department of Health. Growth in initi- ation of additional programs lagged until 1936 when Social Security funds were made available for expansion of public health programs including industrial hygiene. The mounting silicosis prob- lems of the 1930’s also influenced the creation of several programs. Other major events that pre- cipitated their development were World War II and the designation of federal grants-in-aid from 1947 to 1950. During these three years, state and local programs reached an all-time high. The withdrawal of these funds and decreases in state appropriations resulted in retrogression of occu- pational health activities reflected in a loss of per- sonnel and discontinuance of some programs. However, not all programs were affected to the same degree. Because of the basic expertise of industrial hygiene staffs, many units were given 707 additional responsibilities in areas of air pollution control and radiological health which helped to stabilize financial situations. State occupational health programs are at crossroads once more. The implementation of the Occupational Safety and Health Act of 1970 may well alter the operating patterns of both state health and labor agencies. Administration. Primary objectives of a state gov- ernmental program in occupational health are the provision of direct services in the recognition, evaluation and control of occupational health haz- ards and the promotion of basic preventive health services for workers in all places of employment. The design and operation of programs will necessarily vary widely from state to state, de- pending upon extent of industrialization, size and type of industrial establishments, administrative support, program resources, and legislative and political mandates, among other factors. Most state and local occupational health units operate as subdivision of environmental health bureaus in departments of health. A few are independent units. The establishment of the Environmental Protection Agency as a separate federal agency may well influence state counterparts to break away from the health department. Should this be the case, as in Pennsylvania, the Occupational Health activity is likely to be transferred also. When in a state labor agency, the industrial hy- giene activity functions either as a separate ad- ministrative entity, or in a division of industrial safety. Regardless of where the program operates, provision should be made for adequate financing, staffs, facilities and equipment. Personnel. A broadly-based program requires many disciplines including industrial hygienists, engineers, physicists, chemists, physicians, nurses and supporting auxiliary staff. For an effective minimum environmental program, staff should in- clude at least one administrator, well-trained in industrial hygiene, one full-time field industrial hygienist, one specially trained chemist, and at least one secretary-stenographer. An approximate rule-of-thumb for field industrial hygienists is one per every 35,000 workers in areas with heavy industries; and in less industrialized areas, the recommended ratio is one per every 50,000 workers. In view of the perennial shortage of qualified and trained personnel, consideration should be given to the use of technicians and industrial health aides who could, under proper supervision, perform many of the routine tasks necessary in work environment control. Recruitment of per- sonnel could come from qualified junior college or high school graduates. In addition to on-the-job training, these individuals should be given an op- portunity to attend short-term training courses, and if indicated, time to attend and work towards a degree at some local college. Budgets. Budget allocations should be provided for: salaries of personnel (which should be ade- quate in order to recruit and retain qualified per- sonnel) ; travel; field and laboratory instruments, both for new and replacements; allowances for manuals, books and professional journals, print- ing, postage and communications; and allowances for special consultation services in areas for which the occupational health agency lacks personnel and/or capabilities. Legislation and Regulations. For effective oper- ation of a program, specific statutory authority regarding investigations of occupational health hazards is generally desirable. Such legislation should include right of entry, inspections, investi- gations, rule making and promulgation, and en- forcement powers. In actual practice, a diversity of situations exist. In some states, the authority is derived from broad powers of state health departments and labor authorities; in other states, it is specific, but may vary in extent of vested re- sponsibilities. In others, authorities overlap or are divided between two or more departments. The situation regarding state rules and regu- lations governing health and safety at work places is generally described as “chaotic.” In some states, regulations may be general in scope, in others specific for industry or processes or segments of the workforce, and in others absent altogether. Separate regulations dealing specifically with pre- vention and control of occupational health haz- ards exist in a few states or may be combined with accident prevention. “Occupational Safety and Health Standards,” which were promulgated by the U.S. Department of Labor in 1971, take prece- dence over the existing, inadequate state laws and regulations, and may well bring order and uni- formity in regulations governing safety and health of workers. Functions and Activities. The operation of state occupational health programs is based on the philosophy that corrective measures in industry for the protection and improvement of the health of workmen are accomplished largely by private efforts and funds. The important task for the state or local occupational health agency is to point out to industry how to solve its own health prob- lems. The types of services which the occupa- tional health agency can provide alone or in co- operation with other groups are extensive and will depend upon the agency’s resources and occupa- tional health problems in the area. As a rule, in inaugurating a program, the first step is the development of an occupational pro- file of the area. This includes obtaining informa- tion on the characteristics of the labor force, types and locations of industries, prevalence of occupa- tional diseases and injuries, availability of com- munity resources, and functions of other agencies with responsibility for health and safety of workers. Associated with the profile is the “prelimi- nary” or ‘“walk-thru” survey of a well-designed sample of industrial establishments. By this means, information is collected on potential health hazards and their control, availability of preven- tive health services to workers, extent of safety activities, adequacy of sanitation facilities, house- keeping practices, general ventilation and illumi- nation. Frequently, advice on control of obvious hazards can be offered on the spot. Such surveys 708 also offer the program administrator an opportun- ity to become acquainted with the industries in the area under his jurisdiction. A well-balanced program includes both en- vironmental, including industrial hygiene, and medical and nursing components. Following are examples of functions comprising the environ- mental component: 1. Routine inspections, surveys and techni- cal studies of work places for identification of hazards and their control. Surveys and studies usually require the collection of air samples for contaminant evaluation and materials for labora- tory analysis, field measurements of noise, vibra- tion, ionizing and non-ionizing radiations, heat, extremes of pressures, illumination and ventila- tion. 2. Supportive laboratory services including the calibration of instruments. 3. Follow-up on compliance with recommen- dations made for improvement or control of health hazards. 4. Professional investigation of reported or suspected occupational diseases with recommenda- tions for elimination or control of causative agents to prevent their recurrence. 5. Consultation services on industrial hygiene matters at request of management, labor, physi- cians, nurses and others. 6. Review and examination of engineering plans for plant alterations and installation of en- vironmental control equipment. 7. Development and distribution of occupa- tional health materials such as periodic bulletins, information sheets, etc., to employers, employee groups and others concerned. 8. Maintenance of adequate records and re- ports including lists of new industries coming into the area. 9. Maintenance of cooperative working rela- tionships with other official agencies such as state departments of labor, mine inspectors, state fire marshalls and industrial commissions on matters relating to health and safety at the work place. 10. Writing of needed or improved and up- dated regulations governing health and safety at the work place or providing assistance to the agency authorized to promulgate such rules and regulations. Examples of medical and nursing services that can be offered to industry include: 1. Medical consultation to management, labor and private physicians on recognition and diagnosis of occupational diseases. 2. Cooperation with medical societies and in- dividual physicians in the stimulation of proper preplacement examinations in industry. 3. Medical consultation in industry regarding health services for in-plant medical departments. 4. Promotion of nursing services in industry and nursing consultation to plant nurses in im- provement of health services or to first-aid workers regarding emergency first-aid procedures. 5. Promotion of and assistance with estab- lishing cooperative preventive health services for workers in small plants. 6. Assistance with establishment of employee health services for workers in governmental state or municipal jurisdictions. 7. Consultation to community health agencies regarding extension of public health services to the working population and assistance with their implementation. 8. Participation in joint medical and environ- mental studies of workers exposed to specific health hazards. Status of Currently Operating Programs. In ac- tual practice, occupational health programs rang- ing from token to relatively sophisticated activities operate in practically all the states. Administra- tion is as diversified as the scope of the programs. Ten units are located in state departments of labor, 42 in state departments of health, one in a Department of Environmental Resources (Pa.) and some 40 in local health departments. In sev- eral states, programs operate in both health and labor agencies. The smallest units usually consist of part-time or at most, one full-time industrial hygienist working alone, with reliance on others for laboratory support. Larger units may also be staffed by chemists, physicians, consultant nurses, health educators, statisticians and supporting auxiliary staff. Where air pollution and/or radi- ological health is part of the unit, staffs include various specialists in these areas. Best developed phases of programs deal with engineering services. Because of continuous loss of personnel, medical and nursing activities are responsibilities of only a small number of units. On the other hand, about one-half of the state units continue to have responsibilities in areas of radiological health and air pollution control. Ac- tivities range from provision of laboratory ser- vices, monitoring of air and fall-out materials, studies of community air pollution in collabora- tion with other agencies, to full direction of both community and occupational aspects. In a num- ber of instances such responsibilities have consti- tuted a drain on the occupational health activities, whereas in others they have given the program more visibility. Major Constraints. As is typical of many govern- mental agencies, problems of most currently oper- ating units center on inadequate budgets, man- power shortages, inadequate legislative authority, inadequate salaries, poor leadership and lack of administrative support. The lack of quantitative data on prevalence of occupational diseases is also frequently mentioned as a handicap in ob- taining funds, but as a rule this is not a deterrent to many of the more effective programs. Con- siderable knowledge exists on the kinds of occu- pational diseases and potential health hazards that are associated with specific occupations and industries, and this can be used as a guideline in setting up priorities. Factors Contributing to Effectiveness of Operating Programs. These include strong leadership; sup- port of the department and legislature; good bud- get justification and program planning; periodic self-appraisals of goals, accomplishments and needs; professionally competent and dedicated staffs; adequate salaries, retirement and health benefits; opportunity for graduate training, self- advancement, and self-expression as in writing ar- ticles for publication; participation of staff in ac- tivities of professional organizations; good public relations, and rapport with industry and labor; mutual inter-change of problem referrals between the occupational health unit and the labor author- ity; foresight and resources to tackle new prob- lems; prompt response to requests for service; and high caliber of technical services provided. Impact of Occupational Safety and Health Act of 1970. 1t is too soon to determine the impact of the Occupational Safety and Health Act of 1970 on the existing state and local occupational health units. Governors in most of the states have designated the agency or agencies to receive grants for planning and conducting occupational safety and health programs. According to the “Directory of Governmental Occupational Safety and Health Personnel, January 1972” (available from NIOSH), labor authorities were so designated in 32 states and Puerto Rico; state health depart- ments in 4 states (Kentucky, Massachusetts, Okla- homa and South Dakota) and both state labor authority and the health department in 8 states (Connecticut, Hawaii, Louisiana, Michigan, New Hampshire, New Mexico, Tennessee and Vir- ginia). In 5 other states, designated agencies vary. For example, in West Virginia, 4 different agencies were named, including the State Health Department. In Texas, the Occupational Safety Division (counterpart of a state department of labor) of the State Department of Health was so designated. References 1. General Service Administration: United States Gov- ernment Organization Manual — 1970/71. Re- vised July 1, 1970 (Revised annually). Govern- ment Printing Office, Washington, D.C. 20402. $3.00 per copy. 2. AMERICAN CONFERENCE OF GOVERNMEN- TAL INDUSTRIAL HYGIENISTS: Transactions of 1970 and 1971 Meeting. 3. HEIMANN, HARRY and VICTORIA M. TRAS- KO: “Evolution of Occupational Health Programs in State and Local Governments.” Public Health Reports, Volume 79, No. 11, November 1964. 4. TRASKO, VICTORIA M.: Occupational Health and Safety Legislation — A compilation of State Laws and Regulations. PHS Publication No. 357, Revised 1970. U. S. Government Printing Office, Washington, D. C. 20402. 5. REPORT OF COMMITTEE ON FEDERAL, STATE AND LOCAL OCCUPATIONAL HEALTH PROGRAMS, “A Look at Occupational Health as a State Activity.” In Transactions of the Thirtieth Annual Meeting of the American Conference of Governmental Industrial Hygienists. 1968. (See also Committee Report in 1971 Issue.) American Conference of Governmental Industrial Hygienists. 6. Local Health Officials Guide to Occupational Health: Prepared by Subcommittee on Occupational Health, American Public Health Association, 1015 Eighteenth Street, N.W., Washington, D. C. 20036. Price per copy $2.00. 709 CHAPTER 50 AN INDUSTRIAL HYGIENE SURVEY CHECKLIST Robert D. Soule Previous chapters have discussed in detail both the theoretical and practical aspects of the various interrelated considerations of which the industrial hygiene profession is comprised. In conducting any given industrial hygiene survey, the investi- gator must follow a prescribed set of procedures incorporating the “scientific method” of problem solving. In its simplest form, this method can be described as consisting of five distinct phases: recognition and definition of the problem, design of studies, quantification of the problem (i.e., data acquisition), evaluation of data, solution of the problem. The experienced industrial hygienist uses this approach, often without full awareness of its being used; a person relatively inexperienced in the practice of industrial hygiene requires some means of identifying and using the sequence of steps of the method. It is the purpose of this chapter, therefore, to present in simple checklist format, the various steps required in conducting an industrial hygiene survey. Although designed primarily for the “neo- phyte” in industrial hygiene, such a procedural outline has value to the experienced industrial hy- gienist as well, since it minimizes the possibility of overlooking various aspects of a study and maximizes the overall efficiency of the survey. Chapters in this Syllabus which discuss in detail the various points presented in this check- list are indicated by the numbers in parentheses following the specific items. AN INDUSTRIAL HYGIENE SURVEY CHECKLIST [J Determine purpose and scope of study (2, 8,9, 10). Comprehensive industrial hygiene sur- vey? Evaluation of exposures of limited group of workers to specific agent(s)? Determination of compliance with spe- cific recognized standards? Evaluation of effectiveness of engineer- ing controls? Response to specific complaint? Oo0oo0oogoao [J] Discuss purpose of study with appropriate representatives of management and labor. [J] Familiarize yourself with plant operations (2, 10). [[] Obtain and study process flow sheets and plant layout. [[] Compile an inventory of raw materials, intermediates, by-products and products (2, 4, 10). 711 Review relevant toxicological informa- tion (7, 8, 17, 48). Obtain a list of job classifications and the environmental stresses to which workers are potentially exposed. Observe the activities associated with job classifications (32). Review the status of workers’ health with medical personnel (17, 48). Observe and review administrative and engineering control measures used (35, 36). Review reports of previous studies. Determine subjectively the potential health hazards associated with plant op- erations (7-10, 17, 24, 26-34). Prepare for field study. Determine which chemical and physical agents are to be evaluated (7, 23, 25, 26-34). Estimate, if possible, range of contami- nant concentrations. Review, or develop if necessary, samp- ling and analytical methods, paying par- ticular attention to the limitations of the methods (e.g., sensitivity, specificity, (11-16, 18-21, 25-29, 31, 40). Calibrate field equipment as necessary (11, 12). Assemble all field equipment. Obtain personal protective equipment as required (hard hat, safety glasses, gog- gles, hearing protection, respiratory pro- tection, safety shoes, coveralls, gloves, etc.) (36). [J Prepare a tentative sampling schedule. Conduct field study (9, 10, 13, 15, 16, 25, 26, 27, 28, 29, 31, 32). Confirm process operating schedule with supervisory personnel. Advise representatives of management and labor of your presense in the area. Deploy personal monitoring or general area sampling units. For each sample, record the following data: oo ooo oo a Od Od O OO0ooaod Sample identification number. Description of sample (as detailed as possible). NN =— 3. Time sampling began. 4. Flowrate of sampled air (check frequently. 5. Time sampling ended. 6. Any other information or observa- td OOo O00 Oona a tion which might be significant (e.g., process upsets, ventilation system not operating). Dismantle sampling units. Seal and label adequately all samples (filters, liquid solutions, charcoal or silica gel tubes, etc.) which require subsequent laboratory analyses. Interpret results of sampling program. Obtain results of all analyses (14, 18, 19, 20, 21, 22). Determine time-weighted average ex- posures of job classifications evaluated (8,9, 10). Determine peak exposures of workers (8,9, 10). Determine statistical reliability of data, e.g., estimate probable error in deter- mination of average exposures. Compare sampling results with applic- 712 OJ 0 ood Oo od tl Ll Ll 0 able industrial hygiene standards. Discuss survey results with appropriate rep- resentatives of management and labor. Implement corrective action comprised of, as appropriate: Engineering controls (isolation, venti- lation, etc.) (35-46, 52). Administrative controls (job rotation, reduced work time, etc.) Personal protection (36). Biological sampling program (17, 48). Medical surveillance (17, 48). Determine whether other occupational safety and health considerations warrant further evaluation: Air pollution? (43) Water pollution? (44) Solid waste disposal? (45) Safety? (47) CONVERSION FACTORS AND EQUIVALENTS (Arranged Alphabetically) 1 acre =4047 m? 1 atmosphere =14.7 1b/in? =29.92 in Hg =760 mm Hg =1.013 x 100 9¥0¢s c 1 bar = 10° dynes/cm? 1 B.t.u.=0.252 kilocalories =778 foot-pounds (ft-1b) 1 B.t.u./min= 12.96 ft-1b/sec. 1 B.t.u./hr-ft>=0.0003154 watts/cm?* 1 calorie =4.186 Joules 1 calorie/sec-cm?= 13.272 B.t.u./hr-ft? = 4.186 watts/cm? 1 candela = Footcandles X D? (Distance in feet from source to illuminated object) _ lumens 12.57 ft. (area of a sphere of 1 ft radius) °C (Centigrade) = [°F (Fahrenheit) —32] + 1.8 1 centimeter/second (cm/sec) =1.97 ft/min =0.0224 mile/hr =1.9685 ft/min 1 cubic centimeter (cm?) = 0.0610 cubic inch (in?) 1 cubic foot (ft*) =28.32 liter =7.481 gallons (gal) 1 cubic foot (ft*) of air at 70°F and 1 atmosphere weighs 0.075 1b 1 cubic foot (ft*) of water (H,O) at 62°F weighs 62.32 1b 1 cubic meter (m®) =35.315 cubic feet (ft*) = 1000 liters (1) 1 dyne/cm2=0.0021 Ib/ft? 1 electron Volt (eV) =1.6 X 107" ergs °F (Fahrenheit) =1.8 X °C (Centigrade) +32 1 foot (ft) =30.48 cm 1 ft of water (H,0) = 0.4335 Ib/in? 1 footcandle = 1 lumen incident /ft? = 10.764 lumen incidents/m? _ 1 lumen “1 lumen/ft? =10.76 LUX (surface area in sq. meters) 1 lumen (reflected or emitted) ft.2 =1 foot candle (reflected or emitted) 1 gallon (gal) = 3.785 liter 1 gal (US.) of H,O at 62°F weighs 8.33 1b. 1 gram = 15.43 grains = 10° milligrams (mg) 1 gram-calorie = 0.00397 B.t.u. 1 foot lambert = 713 1 gram/cm?®= 62.43 lb/ft? =8.345 1b/gal 1 Hertz=1 cycle/sec 1 horsepower (hp) =0.707 B.t.u./sec = 550 ft-1b/sec =0.75 kilowatt =2545 B.t.u./hr 1 inch (in) =2.540 cm 1 in. of mercury (Hg) =0.4912 Ib/in? =13.57 in H,0 1 Joule= 107 ergs =0.239 calories °K (Kelvin) =273+ °C 1 kilogram (kg) =2.205 pounds (lb) 1 kilometer (km) =1000 m =0.6214 mile 1 liter= 1.057 quarts (U.S., liquid) =0.03531 ft? = 1000 cubic centimeters (cm? or cc) Lumen =Footcandles X Area (sq. ft.) = candela X 12.57 ft? =Foot lamberts X sq. ft. area reflecting or emitting light flux. 1 meter (m) =3.281 feet (ft) =39.37 inches (in) = 10° microns (un) = 10° millimeters (mm) = 10? centimeters (cm) 1 milligram (mg) = 10° micrograms (ug) 1 mg/m®=0.000437 grains/ft* 1 millimeter (mm) Hg=1.36 cm of H,O 1 ounce (oz) =28.35 grams Pi (=) =3.1416 1 pound (1b) =453.6 grams =16 ounce (0z) 1 pound/square inch (Ib/in%) =2.31 ft. H,O °R (Rankine) =460+ °F 1 square foot (ft?) =0.0929 square meter (m?) 1 square inch (in?) = 6.452 square centimeters (cm?) 1 square kilometer (km?) = 0.3861 square mile (mile?) (U.S) 1 Volt=1 Joule/coulomb 1 Watt=1 Joule/sec pe TET TE ETP A TERT : 3 . ) 3 . . . | al « a : . | i | $ oo EE — } “2 o + . . oo a pe . I \ \ . a . 1 5 . | i - ih / A . 1 . - . ) i N - tr IN ~ : . nF ACCIDENT CONTROL. See SAFETY. AEROSOLS, direct reading instruments for, 181 properties of, 181 source devices, 134 toxicity, 69 AIR CONTAMINANTS, batch mixtures of, 123 effects on respiratory system, 155 flow dilution systems, 126 properties of, 577 sampling techniques for gases and vapors, 167 sizing, 155 threshold limit values, 98 types, 139 AIR FLOW, 573 devices for air movement, 581, 620 fundamentals, 575 instruments for, 583 make-up air, 580, 623 measurements, 589 systems, evaluation of, 583, 584 surveys, 593 AIR POLLUTION, legislation, 630 stack emission control, 629 AIR QUALITY ACT OF 1967, 630 AMERICAN CONFERENCE OF GOVERNMENTAL INDUSTRIAL HYGIENISTS, 53, 84, 86 heat stress guide, 425 TLV for noise, 327, 526 ultraviolet radiation, 361 AMERICAN INDUSTRIAL HYGIENE ASSOCIATION, 86, 526, 531 AMERICAN NATIONAL STANDARDS INSTITUTE, 81, 86, 530 ANALYTICAL CHEMISTRY, 26, 207 classical methods, 26 industrial hygiene in, 207 instrumental methods, 27 ion exchange, 217 separation processes, 207, 221 solvent extraction, 208 ANALYTICAL METHODS, 26 atomic absorption spectrophotometry, 241 batch extraction, 211 batch technique, 219 column chromatography, 219 continuous extraction, 211 countercurrent distribution, 211 electrochemical, 28, 183 emission spectroscopy, 247, 254 exclusion chromatography, 221 fluorescence spectrophotometry, 238 gas chromatography, 257 gas-liquid chromatography, 262-264 gel permeation chromatography, 221 gravimetric, 27 infrared spectrophotometry, 27, 235 ion exchange extraction, 217 liquid-liquid partition chromatography, 27, 221 solvent extraction, 208 thermal diffusion, 221 thin layer chromatography, 219, 221 ultraviolet spectrophotometry, 27, 229 visible light spectrophotometry, 27, 224 volumetric, 26 ) x-ray diffraction, 28 x-ray fluorescence, 28 zone refining, 221 INDEX ANATOMY OF FUNCTION, 433 anatomical failure points, 439 glossary of terms, 488 kinetic chains, 437 kinetic elements, 435 lever systems, 433 limb movement, 439 ANTHROPOMETRY, 440 definition of, 440 glossary, 488 industrial seating, 441 selection and evaluation of tools, 458 workplace dimensions, 443 BIOCHEMISTRY, 31 carbohydrate metabolism, 42 detoxification processes, 46 energy production, 31 enzymes, 34 hemoglobin structure, 32 lipid metabolism, 41 mitochondrial oxidative phosphorylation, 44 monitoring, 46 protein synthesis, 36 waste removal, 45 BIOMECHANICS, 431 anatomy of function, 433 anthropometry, industrial, 439-441 definition, history, 431 evaluation, 472-479 glossary, 488-492 handtools, selection and evaluation, 458 materials-handling and lifting, manual, 461 measurement, 470 motion economy, principles of, 444-47 work tolerance, 447 CALIBRATION, 101 collection efficiency, 101-102 flow and volume, 104 instruments, 101, 104 methods and procedures, 103 sample stability, 102 sensor response, 102 standards for, 102 techniques, 104 types of, 101 CHEMISTRY, review of, 19, 61 analytical, 26 inorganic, 19 organic, 22 CLEAN AIR AMENDMENTS OF 1970, 630 CLOTHING. See PROTECTIVE CLOTHING. CODES. definition of, 85 enactment of, 88 respiratory protective devices, 526 COLD, exposure to, 569 protective clothing for, 569, 572 windchill index, 426 COLLECTION DEVICES, 142 Sw *