the INDUSTRIAL ENVIRONMENT
~—its EVALUATION & CONTROL
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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.
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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-
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Bureau of Labor Standards, 1969.
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Legislation: A Compilation of State Laws and Reg-
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EDE, L. and M. T. BARNARD. A Report on State
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CRALLEY, L. V,, L. J. CRALLEY and G. D.
CLAYTON. [Industrial Hygiene Highlights: “Epide-
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CLAYTON. Industrial Hygiene Highlights: “Intro-
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America, Inc., Pittsburgh, Pa., 1968.
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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.
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“Occupational Safety and Health Act of 1970.”
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American National Standards Institute, Inc., 1430
Broadway, New York, New York 10018.
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432, “Regulations Establishing Threshold Limits in
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Westmont, N.J. 08108, 1967.
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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
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| I | [
SPHERICAL PLUMB BOB
[
Ni
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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
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£
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5 0.90
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cs 0.85
oO
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oO
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£
QL
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2 0.75
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oO
5
€ 0.70
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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
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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-
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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.
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—
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.
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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 | |
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Zz f——"
z -
= 1.0
FR EN
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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
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Micrometers, um
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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,
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icle Energy Range Curve
Education and Welfare
Beta Part
383
29-1
igure
F
MEAN RANGE (CM)
ENERGY (MEV)
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ENERGY (MEV)
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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
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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,
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POWELL, R. W. Trans. Inst. Chem. Engrs. (Lon-
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L. W., Horvath, S. M., Shelley, W. B., and Hatch,
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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
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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
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21.
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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-
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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
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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
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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
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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,
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BENEDICT, F. G. and E. F. CATHCART.: Mus-
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AMAR, J.: Organization Physiologique du Travail.
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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
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England (1963-1964).
DUKES-DOBOS, F.: “Ergonomics in Science and
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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
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Technological College. Lubbock, Tex 1965) Technological College, Lubbock, Texas, (1963)
M 2 wv ge, , as ( )s (Monograph) :
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SLESIN, S.: “Biomechanics.” Industrial Design,
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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.,
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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
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HUNTER, D.: The Diseases of Occupations, Little
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American National Standard, Industrial Engineer-
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Secretariat, American Institute of Industrial Engin-
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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
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TICHAUER, E. R.: “Ergonomics of Lifting Tasks
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tees.” Rehabilitation in Australia, 403-411 George
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DEMPSTER, W. T.: “The Anthropometry of Body
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WILLIAMS, M. and H. T. LISSNER.: Biome-
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218 W. Washington Square, Phil, Penn., 19105
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ABT, L. E.: “Anthropometric Data in the Design
of Anthropometric Test Dummies. Dynamic An-
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STARR, 1.: “Units for the Expression of Both
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KARPOVICH, P. V.: Physiology of Muscular Ac-
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HILL, A. V.. Muscular Activity. Williams and
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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
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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-
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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
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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).
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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
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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 - -
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INJURED'S NAME = 7, PROPERTY DAMAGED - 4
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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
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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
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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
*