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Bureau of Mines Information Circular/1988 
 
 Human Factors in Mining 
 
 By Mark S. Sanders and James M. Peay 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
Information Circular 9182 
 
 Human Factors in Mining 
 
 By Mark S. Sanders and James M. Peay 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 Donald Paul Hodel, Secretary 
 
 BUREAU OF MINES 
 
 David S. Brown, Acting Director 
 
ii 
 
 
 Library of Congress Cataloging-in-Publication Data 
 
 Sanders, Mark S. 
 
 Human factors in mining. 
 
 (Information circular/United States Department of the Interior, Bureau of Mines; 9182) 
 Includes bibliographies. 
 Supt. of Docs. No.: I 28.27 
 
 1. Mining engineering— Safety measures. 2. Human engineering. I. Peay, James M. II. 
 Title. III. Series: Information circular (United States. Bureau of Mines) ; 9182. 
 
 TN295.U4 
 
 622 s 
 
 622 '.8 
 
 87-600304 
 
CONTENTS 
 
 Abstract 1 
 
 Chapter 1.— Introduction 2 
 
 Definition of human factors 2 
 
 Basic model 3 
 
 What human factors is not 3 
 
 Road blocks to the application of human 
 
 factors 3 
 
 History of human factors 4 
 
 1940-50— war years -. 4 
 
 1950-60— birth of a profession 4 
 
 1960-80— recognition and expansion 4 
 
 1980— a household word 4 
 
 History of human factors in mining 4 
 
 1870-1950— early mechanization 5 
 
 1950-70— modern mechanization and the 
 
 coal act 6 
 
 1970— birth and growth of human factors 
 
 in mining 6 
 
 Coverage r*. 7 
 
 References 7 
 
 Chapter 2.— Human factors in the design 
 
 of systems 9 
 
 Characteristics of systems 9 
 
 Systems have a purpose 9 
 
 Systems are hierarchical 10 
 
 Systems operate in an environment 10 
 
 Components serve functions 11 
 
 Components interact 11 
 
 Systems, subsystems, and components have 
 
 inputs and outputs 11 
 
 How engineers really design 11 
 
 Stages in the design of systems 12 
 
 Stage 1: determine objectives and system 
 
 specifications : 12 
 
 Stage 2: define the system 12 
 
 Stage 3;- basic design 12 
 
 Stage 4: interface design . 16 
 
 Stage 5> facilitator design 18 
 
 Stage 6: testing 18 
 
 Discussion 18 
 
 References 18 
 
 Chapter 3.— Human capabilities and limitations . . 19 
 
 Who are miners 19 
 
 Human as an information receiver 20 
 
 Sight 20 
 
 Accommodation 20 
 
 Adaptation 20 
 
 Field of vision 20 
 
 Visual acuity 21 
 
 Detection of movement 21 
 
 Hearing 22 
 
 Sound localization 22 
 
 Tone and loudness discrimination 23 
 
 Masking . .- 23 
 
 Effect of age on hearing 23 
 
 Smell , 23 
 
 Human as information processor 23 
 
 Memory. 23 
 
 Decisionmaking 24 
 
 Attention 25 
 
 Page 
 
 Human as action taker 26 
 
 Reaction time 26 
 
 Stimulus reception time 26 
 
 Processing time 26 
 
 Response selection time 26 
 
 Movement time 27 
 
 Movement accuracy 27 
 
 Positioning movements 27 
 
 Continuous movements 27 
 
 Repetitive movements 27 
 
 Anatomical characteristics 27 
 
 Percentiles 27 
 
 Fallacy of the "average" person 27 
 
 Other limitations of anthropometric data 28 
 
 Static anthropometric data 28 
 
 Range of movement 28 
 
 Reach envelopes 28 
 
 Strength 29 
 
 Endurance 30 
 
 Circadian rhythms 30 
 
 Physiological adjustment 31 
 
 Shift work 32 
 
 Discussion 32 
 
 References 32 
 
 Chapter 4.— Human error and accidents 34 
 
 Human error 34 
 
 Broad classification of human error 35 
 
 Action classification of human error 35 
 
 Information-processing model of human 
 
 error 35 
 
 Warning-hazard classification of human 
 
 error 35 
 
 What is an accident 36 
 
 Human error and accidents 36 
 
 Theories of accident causation 38 
 
 Accident proneness theories 38 
 
 Job demand versus worker capability 
 
 theories 39 
 
 Psychosocial theories 40 
 
 Injury statistics 40 
 
 Industrywide comparisons 40 
 
 Comparisons with European countries 42 
 
 Costs of accidents 42 
 
 Discussion 44 
 
 References 44 
 
 Chapter 5.— Information displays 45 
 
 Choosing a display 45 
 
 Visual displays 46 
 
 Quantitative displays 46 
 
 Design features of quantitative displays .... 47 
 
 Scale markers 47 
 
 Numerical progression of scales 48 
 
 Design of pointers 48 
 
 Relative importance of design features 48 
 
 Qualitative displays 48 
 
 Signals and warning lights 49 
 
 Signs and labels 50 
 
 Typography 50 
 
 Pictorial signs and labels 51 
 
CONTENTS— Continued 
 
 Page 
 
 Auditory displays 51 
 
 Alarms 51 
 
 Speech 52 
 
 Intensity of speech 52 
 
 Intelligibility of speech 52 
 
 Preferred octave speech interface level 
 
 (PSIL) 53 
 
 Hearing protection and speech 53 
 
 Underground loudspeaker system: a case 
 
 study 53 
 
 Problems during introduction of the 
 
 system 53 
 
 Results of installation 54 
 
 Olfactory displays 54 
 
 Discussion 54 
 
 References 54 
 
 Chapter 6.— Design of controls, equipment, 
 
 and tools 55 
 
 Controls 55 
 
 Types of controls 55 
 
 Factors in control design 56 
 
 Identification of controls 56 
 
 Control-response ratio 59 
 
 Resistance 59 
 
 Deadspace 59 
 
 Backlash 59 
 
 Design of specific controls 59 
 
 Equipment design 60 
 
 Compatibility 60 
 
 Conceptual compatibility 60 
 
 Movement compatibility 60 
 
 Spatial compatibility 61 
 
 Placement of displays and controls 61 
 
 Arrangement of controls and displays 61 
 
 Standardization 61 
 
 Location of controls and displays 63 
 
 Special problems in equipment design 66 
 
 Seating for low-seam coal equipment 
 
 operators 66 
 
 Operator field of vision 70 
 
 Egress-ingress on surface mining 
 
 equipment 72 
 
 Designing for maintainability 77 
 
 Handtool design 78 
 
 Principles of handtool design 79 
 
 Maintain a straight wrist 79 
 
 Avoid tissue compression stress 79 
 
 Avoid repetitive finger action 79 
 
 Design for safe operation 79 
 
 Women and left-handers 79 
 
 Vibration-induced white finger 79 
 
 Discussion 80 
 
 References 80 
 
 Chapter 7.— Physical work 82 
 
 Work physiology 82 
 
 Muscle 82 
 
 Energy consumption 83 
 
 Cardiac output and aerobic capacity 83 
 
 Measurement of work 84 
 
 Page 
 
 Energy expenditure at work 86 
 
 Grades of physical work 86 
 
 Energy expenditures for common mining 
 
 tasks 86 
 
 Recommended energy expenditure levels 88 
 
 Manual materials handling 90 
 
 Materials handling accidents 91 
 
 Biomechanics of lifting 91 
 
 Effects of lifting posture 93 
 
 NIOSH recommended lifting load limits 94 
 
 Reducing the risk 95 
 
 Redesign the task 95 
 
 Redesign the workplace 95 
 
 Selection of workers 96 
 
 Training workers 96 
 
 Discussion 97 
 
 References 97 
 
 Chapter 8.— Environmental factors 99 
 
 Illumination 99 
 
 Measurement of light .' 99 
 
 Luminous flux 100 
 
 Illuminance 100 
 
 Luminous intensity and luminance 100 
 
 Reflectance 100 
 
 Contrast 100 
 
 Illuminance and performance 100 
 
 Illumination requirements 101 
 
 Glare 102 
 
 Noise 102 
 
 Measurement of noise 102 
 
 Frequency 103 
 
 Intensity 103 
 
 Indexes of noise intensity 103 
 
 Conditions in mining 103 
 
 Standards for noise exposure in mining 104 
 
 Hearing loss 104 
 
 Other physiological effects of noise 104 
 
 Effects of noise on performance 105 
 
 Controlling the noise problem 105 
 
 Hearing protection 107 
 
 Whole-body vibration 108 
 
 Vibration terminology 108 
 
 Effects of vibration on humans 108 
 
 Health effects 108 
 
 Performance effects 108 
 
 Vibration exposure standards 108 
 
 Vibration exposure of surface coal miners .... 109 
 
 Controlling vibration 109 
 
 Heat stress 109 
 
 Physiological response to heat stress 109 
 
 Indexes of head stress 110 
 
 Effective temperature (ET) 110 
 
 Wet-bulb-globe temperature (WBGT) Ill 
 
 Heat stress index (HSI) Ill 
 
 Heat stress conditions in mining Ill 
 
 Performance effects of heat stress Ill 
 
 How much is too much 112 
 
 Protection from heat stress 112 
 
Ill 
 
 CONTENTS— Continued 
 
 Page 
 
 Cold stress 113 
 
 Frostbite 113 
 
 Performance effects of cold 113 
 
 Protection from cold stress 114 
 
 Discussion 114 
 
 References 114 
 
 Chapter 9.-Training 116 
 
 Effectiveness of training 116 
 
 Training: what is required 117 
 
 Training requirements in the United States . . 117 
 
 Training requirements in other countries 117 
 
 Discussion 118 
 
 Training practices in the United States 118 
 
 Characteristics of successful safety programs ... 119 
 
 Management 119 
 
 Training and incentives 119 
 
 Accident reduction 119 
 
 Basic concepts in human learning 120 
 
 Learning versus performance 120 
 
 Performance feedback 120 
 
 Reward and punishment 121 
 
 Learning from models and examples 121 
 
 Methods of training 122 
 
 Classroom training 122 
 
 Part-task simulation 122 
 
 Full-task simulation 122 
 
 Simulated mine environments 122 
 
 Training sections in an actual mine 123 
 
 On-the-job training 123 
 
 Developing a training program 124 
 
 Assess training needs 124 
 
 Write goals and objectives 125 
 
 Determine criteria and evaluation 
 
 measures 125 
 
 Select training modes and media 125 
 
 Develop training materials 125 
 
 Evaluate effectiveness 126 
 
 Revise 126 
 
 Safety awareness programs 126 
 
 Consol's program 126 
 
 Elements of a successful program 126 
 
 Safety signs 126 
 
 Discussion 127 
 
 References 127 
 
 Chapter 10.— Motivation and organizational 
 
 development 128 
 
 Motivation 128 
 
 Motivation and performance 128 
 
 Motivation and needs 129 
 
 Page 
 
 A theory of motivation 129 
 
 Valence 129 
 
 Effort-performance (E-P) expectancy 129 
 
 Performance-outcome (P-O) expectancy 129 
 
 The model 129 
 
 Implications of the model 130 
 
 Organizational climate 131 
 
 Organizational development 131 
 
 Rushton autonomous work group 
 
 experiment 132 
 
 Background 132 
 
 Autonomous work groups 132 
 
 Results 132 
 
 Hecla team-building project 132 
 
 Background 132 
 
 Team building 133 
 
 Performance appraisal system 133 
 
 Safety activities 133 
 
 Supervisory skills training 133 
 
 Results 134 
 
 Cost 134 
 
 Texasgulf management training study 134 
 
 Background 134 
 
 Objective supervisory performance 
 
 appraisal 134 
 
 Leadership training 135 
 
 Supervisory skills training 135 
 
 Institutionalization 135 
 
 Results 135 
 
 Cost 135 
 
 Quality control circles 135 
 
 QC circles at the Captain Mine 136 
 
 Results 136 
 
 Discussion 136 
 
 References 136 
 
 Appendix A.— Static anthropometric data for 
 
 male and female military personnel 138 
 
 Appendix B.— Typical joint mobility data 
 showing 5th and 95th percentile male and 
 
 female limits 141 
 
 Appendix C— Examples of pictorial safety signs 
 
 recommended for use in the mining industry . . . 142 
 Appendix D.— Summary of selected data regarding 
 
 design recommendations for control devices .... 145 
 Appendix E.— Selected data on access space 
 
 required to perform maintenance tasks 146 
 
IV 
 
 ILLUSTRATIONS 
 
 Page 
 
 1-1. Basic human-hardware-environment system 3 
 
 1-2. Undercutting a coal face before mechanization 5 
 
 1-3. Early Harrison Pick cutting machine 5 
 
 1-4. Use of animals for hauling coal 6 
 
 2-1. Schematic diagram of haulage vehicle subsystem within the total mine system 10 
 
 2-2. Schematic diagram of inputs and outputs between subsystems of a system 11 
 
 2-3. Stages in the development of a system 12 
 
 2-4. Example of a column format used in task analysis 13 
 
 2-5. Example of an operational sequence diagram (OSD) used in task analysis 14 
 
 2-6. Example of a timeline used in task analysis 15 
 
 2-7. Graphic illustration of the results of a link analysis of a roof bolting operation 16 
 
 2-8. Example of an articulated plastic manikin for evaluation of engineering drawings 16 
 
 2-9. Three-dimensional manikin produced by CAP based on external anthropometric measurement inputs . . 17 
 
 3-1. Diagram of the eye 20 
 
 3-2. Field of vision and effect of eye and head rotation 21 
 
 3-3. Illustration of the concept of visual angle 21 
 
 3-4. Effect of caplamp and background illumination on detection of moving objects in the periphery 
 
 of the visual field 21 
 
 3-5. Illustration of principal structures of the ear 22 
 
 3-6. Illustration of the cochlea 22 
 
 3-7. Changes in hearing sensitivity with age for 1,320 underground coal miners 23 
 
 3-8. The load-haul-dump-return cycle in surface mining creates a situation highly conducive to lapse 
 
 in attention and alertness 25 
 
 3-9. Reaction time as a function of the number of response choices available 26 
 
 3-10. Arm reach envelope for movements using a number of hand-grasp positions in three-dimensional space 29 
 
 3-11. Foot reach envelopes for various types of pedal operations 29 
 
 3-12. Arm strength data 30 
 
 3-13. Maximum force exerted on a foot pedal and maximum torque applied to a 22-in-diameter steering 
 
 wheel by truck drivers 31 
 
 3-14. Endurance time as a function of the force maintained 31 
 
 3-15. Typical circadian rhythm for body temperature 31 
 
 4-1. One consequence of operator error 37 
 
 4-2. Relationship between age and disabling injury rate 38 
 
 4-3. Supervisor fatalities in coal mining as a function of experience at mine, experience in job 
 
 classification, and total mining experience 39 
 
 4-4. Percent of fatalities, nonfatal-days-lost, and no-days-lost injuries occurring in 1983 for each of the 
 
 major segments of the mining industry 41 
 
 4-5. Nonfatal-days-lost and no-days-lost injury rates for 1983 for each of the major segments of the 
 
 mining industry 41 
 
 4-6. Comparison of nonfatal-days-lost injuries from major accident categories for the major segments of 
 
 the mining industry in 1983 41 
 
 4-7. Fatality rate per 200,000 employee-hours for U.S. underground coal mines from 1931 through 1983 ... 42 
 
 4-8. Comparison of fatality data between U.S. and European underground coal mines 42 
 
 4-9. Average cost of a fatality in the mining industry, 1975-81 43 
 
 4-10. Average cost of a disabling injury in the mining industry, 1975-81 43 
 
 4-11. Example of characteristic effect of a fatal injury on production in an underground mine 44 
 
 5-1. Examples of quantitative displays 46 
 
 5-2. Illustration of several numeric scale concepts 47 
 
 5-3. Recommended format for quantitative scales under normal and low illumination conditions 47 
 
 5-4. Illustrations of coding methods for marking zones of instruments that are to be read qualitatively .... 48 
 
 5-5. Mean response time for detecting pointer in danger zone for three dial designs 49 
 
 5-6. Two patterns of dials used in a check-reading experiment 49 
 
 5-7. Definition of stroke width to height and width to height ratios for alphanumeric characters 50 
 
 5-8. Illustrations of stroke width to height ratios of letters and numerals 50 
 
 5-9. Examples of pictorial signs that caused confusion among mining industry employees 51 
 
 6-1. Common types of controls classified by type of information they transmit most effectively 56 
 
 6-2. Control station of a low-seam coal auger 57 
 
 6-3. Controls with different length lever controls 57 
 
 6-4. Example of operator-provided shape coding 58 
 
 6-5. Control knob shapes that are easily identified by touch while wearing gloves 58 
 
 6-6. Control shapes recommended for underground roof bolters 59 
 
 6-7. Movement compatibility relationships where dial and display are in same plane 60 
 
ILLUSTRATIONS— Continued 
 
 Page 
 
 6-8. Compatible control-display movements when controls and displays are in different planes 61 
 
 6-9. Common meanings of lever movements 61 
 
 6-10. Examples of spatial compatibility between a bank of controls and displays 61 
 
 6-11. Different arrangements of roof bolter controls from one manufacturer 62 
 
 6-12. Brake, clutch, and throttle control placement on eight 120-st-capacity and smaller haulage trucks 62 
 
 6-13. Location of service brake relative to steering wheel on four front-end loaders 62 
 
 6-14. Preferred vertical surface areas and limits for various types of control functions operated by a 
 
 seated operator 63 
 
 6-15. Recommended dimensions and layout of seated operator workstations 64 
 
 6-16. Recommended configurations of a vehicle cab 65 
 
 6-17. SAE J898a recommended practice for control locations for construction and industrial equipment 
 
 design 66 
 
 6-18. Recommended layout of a standing operator workstation 67 
 
 6-19. Recommended separation between adjacent controls for one- and two-hand operation 67 
 
 6-20. Examples of typical seating postures in low-seam coal mining equipment 68 
 
 6-21. Seating space envelopes for 95th percentile male and 5th percentile female operators in two cab 
 
 heights 69 
 
 6-22. Relationship between interior cab height and required interior cab length needed to accommodate 
 
 various sized people 70 
 
 6-23. Human-factored seat for low-seam mining equipment 70 
 
 6-24. Illustration of front and side visual limitations from the cab of a 150-st-capacity rear-dump haulage 
 
 truck 71 
 
 6-25. Plan view illustrating front and side visual limitations and blind areas from the cab of a 
 
 150-st-capacity rear-dump haulage truck 71 
 
 6-26. Typical installation of an improved visibility system for large haulage trucks 71 
 
 6-27. Fresnel lens blind area viewer used to enhance visual field of haulage truck oeprators 72 
 
 6-28. Improved field of view resulting from installation of system shown in figure 6-27 72 
 
 6-29. Plan view of visual attention locations identified for continuous miner operators 72 
 
 6-30. Human eye reference measurement instrument used to assess fields of visibility from operators' cabs . . 73 
 
 6-31. Excessively flexible lower section support on haulage truck ladder 74 
 
 6-32. Inappropriate height of first step of haulage truck ladder 74 
 
 6-33. Design recommendations for stairs and ladders 75 
 
 6-34. Stairs used on haulage trucks 76 
 
 6-35. Schematic diagram showing relationship of seat, steering wheel, and doorway on a typical tractor .... 77 
 
 6-36. Example of a well-designed access door 77 
 
 6-37. Concept of Bureau-sponsored four-spring-supported lower steps for large haulage trucks 77 
 
 6-38. Bureau-sponsored four-spring-supported lower steps colliding with a large rock 77 
 
 6-39. Bureau-sponsored hydraulic "power" step for egress and ingress from tractors, dozers, and shovels .... 78 
 
 6-40. Examples of common handtools designed to permit users to maintain straight wrists 79 
 
 7-1. Electromyogram recording of biceps muscle during static force application 83 
 
 7-2. Schematic representation of metabolic process that takes place during muscular work 83 
 
 7-3. Oxygen uptake during muscular work 84 
 
 7-4. Aerobic capacity of male miners by age group 84 
 
 7-5. Linear relationship between heart rate and oxygen uptake for six adult males 85 
 
 7-6. Underground worker hanging brattice cloth 85 
 
 7-7. Effect of weight of objects being lifted and lift posture on energy expenditure 87 
 
 7-8. Effect of work pace on energy expenditure for a lifting task 87 
 
 7-9. Energy efficiency of lifting various weights from different starting positions 87 
 
 7-10. Energy expenditure and activity profile for roof bolter helper 88 
 
 7-11. Recommended maximum work times for males and females performing tasks at various levels 
 
 of energy expenditure 89 
 
 7-12. Materials handling accidents by major activity or function 92 
 
 7-13. Illustration of basic muscle biomechanics and lever analog 92 
 
 7-14. Diagram of spinal column 93 
 
 7-15. Calculated lower-back muscle force and compressive forces acting on the L 5 -S! disk resulting from 
 
 lifting a timber post 93 
 
 7-16. Cutaway view of a ruptured L 5 -Sj disk pressing the spinal nerve 93 
 
 7-17. Comparison of lower-back compression forces associated with stoop-back and squat methods of 
 
 lifting a wide object .- 94 
 
 7-18. Incidence and severity of back injury as a function of the job severity index 96 
 
 8-1. Effect of adding additional background luminance on the speed of detecting holes in a floor at a 
 
 distance of 10 ft 101 
 
VI 
 
 ILLUSTRATIONS— Continued 
 
 Page 
 
 8-2. Sine wave sound pressure wave showing one cycle with corresponding changes in air pressure 103 
 
 8-3. Relative response characteristics of the A, B, and C sound-level meter scales and the human ear 
 
 at threshold 103 
 
 8-4. Typical noise levels of machinery in underground and surface mining 104 
 
 8-5. Hearing loss among underground coal miners, by age 104 
 
 8-6. Example of type of information contained in Mining Machinery Noise Control Guidelines 106 
 
 8-7. Typical noise-time histories in passenger and operator compartments of an untreated and noise- 
 reduction-treated mantrip 107 
 
 8-8. Vertical vibration exposure limits for the preservation of performance 109 
 
 8-9. Mechanical response of a person's body to vibrations when sitting in different seats 109 
 
 8-10. Time until young, fit, unacclimatized men collapse from exhaustion 110 
 
 8-11. Setup for manually obtaining temperatures used to compute wet-bulb-globe temperature Ill 
 
 8-12. Effects of ambient temperature on miners loading mine cars and drilling rock 112 
 
 8-13. Relationship between rate of unsafe behaviors and wet-bulb-globe temperature 112 
 
 9-1. Results of an experiment that demonstrates effectiveness of performance feedback on incidence 
 
 of safe behaviors 120 
 
 9-2. OBSAC part-task simulator held in instructor's lap in port seat of a haulage vehicle 123 
 
 9-3. Shuttle car training system full-task simulator 123 
 
 9-4. Instructional system design approach to development of training programs 124 
 
 10-1. Schematic representation of expectancy theory of motivation 130 
 
 10-2. Results of organizational development intervention at Lucky Friday Mine 134 
 
 10-3. Incidence rates of lost-time accidents for the Lucky Friday Mine, Star Mine, and other mines in the 
 
 Coeur d'Alene mining district 134 
 
 A-l. Standing body dimensions 138 
 
 A-2. Seated body dimensions 139 
 
 A-3. Body depth and breadth dimensions 140 
 
 B-l. Typical joint mobility data 141 
 
 TABLES 
 
 2-1. Methods of collecting task analysis information 13 
 
 4-1. Information-processing model of human error 35 
 
 4-2. Human error classification of accidents in South African gold mines 36 
 
 4-3. 1982-83 medical compensation costs paid per incident by a major coal company, by type of injury 
 
 sustained 43 
 
 5-1. Average times for qualitative and quantitative reading with three types of scales 48 
 
 5-2. Recommended letter heights for labels and signs for various distance conditions 51 
 
 5-3. Recommended heights of letters on emergency signs 51 
 
 5-4. Characteristics and features of certain types of audio alarms 52 
 
 5-5. Maximum distance between speaker and listener to carry on a satisfactory conversation 53 
 
 6-1. Common types of controls 56 
 
 6-2. Descriptions of common types of control resistance 59 
 
 6-3. Compatible directions of movement associated with various control functions 60 
 
 7-1. Effect of vertical starting position on energy expenditure 86 
 
 7-2. Grade of physical work based on energy expenditure level 86 
 
 7-3. Energy expenditures for four low-seam tasks 86 
 
 7-4. Average energy expenditures for mining tasks in South African gold mines 88 
 
 7-5. Common mine materials and their weights 91 
 
 7-6. Materials handling nonfatal-days-lost injuries in the mining industry, 1983 91 
 
 7-7. Objects involved in overexertion back injuries suffered by underground coal miners during 1981 91 
 
 7-8. Maximum lift frequency based on average vertical location and period of performance 95 
 
 8-1. Examples of average reflectances of rocks and minerals from underground metal and nonmetal mines . 100 
 
 8-2. Samples of illumination standards set by various countries for underground coal mining 101 
 
 8-3. Walsh-Healy noise criteria for underground and surface mining 104 
 
 8-4. Effects of noise control treatments installed on a diesel track dozer 105 
 
 8-5. Advantages and disadvantages of insert-type and muff-type hearing protection devices 107 
 
 8-6. Comparison of proposed WBGT threshold values 112 
 
 8-7. Equivalent temperatures based on windchill index 113 
 
 9-1. Content of underground and surface mine health and safety training, by type 118 
 
Vll 
 
 TABLES— Continued 
 
 Page 
 
 9-2. Sources of information for assessing training needs 125 
 
 10-1. Factors that influence performance-outcome and effort-performance expectancies 131 
 
 A-l. Standing body dimensions 138 
 
 A-2. Seated body dimensions 139 
 
 A-3. Body depth and breadth dimensions 140 
 

 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 
 
 °c 
 
 degree Celsius 
 
 kg-m 
 
 kilogram-meter 
 
 c 
 
 candle 
 
 kHz 
 
 kilohertz 
 
 c/in 2 
 
 candle per square inch 
 
 kJ 
 
 kilojoule 
 
 c/m 2 
 
 candle per square meter 
 
 km 
 
 kilometer 
 
 cal 
 
 calorie 
 
 L 
 
 liter 
 
 cal/min 
 
 calorie per minute 
 
 L/min 
 
 liter per minute 
 
 cm 
 
 centimeter 
 
 lb 
 
 pound 
 
 dB 
 
 decibel 
 
 lb-in 
 
 pound-inch 
 
 dBA 
 
 decibel, A-weighted 
 
 lm 
 
 lumen 
 
 deg 
 
 degree 
 
 lm/ft 2 
 
 lumen per square foot 
 
 op 
 
 degree Fahrenheit 
 
 lx 
 
 lux 
 
 fc 
 
 footcandle 
 
 m 
 
 meter 
 
 fL 
 
 footlambert 
 
 m/s 2 
 
 meter per square second 
 
 ft 
 
 foot 
 
 m 2 
 
 square meter 
 
 ft-lb 
 
 foot-pound 
 
 mg 
 
 milligram 
 
 ft/s 2 
 
 foot per square second 
 
 min 
 
 minute 
 
 h 
 
 hour 
 
 mL 
 
 milliliter 
 
 Hz 
 
 hertz 
 
 mL/(kg/min) 
 
 milliliter per kilogram per minute 
 
 in 
 
 in 
 
 mm 
 
 millimeter 
 
 in/oz 
 
 inch per ounce 
 
 M N/m 2 
 
 micronewton per square meter 
 
 in/s 2 
 
 inch per square second 
 
 oz 
 
 ounce 
 
 in 2 
 
 square inch 
 
 psi 
 
 pound (force) per square inch 
 
 J 
 
 joule 
 
 s 
 
 second 
 
 kcal 
 
 kilocalorie 
 
 sr 
 
 steradian 
 
 kcal/h 
 
 kilocalorie per hour 
 
 St 
 
 short ton 
 
 kcal/kg-m 
 
 kilocalorie per kilogram-meter 
 
 W 
 
 watt 
 
 kcal/(m 2 /h) 
 
 kilocalorie per square meter per hour 
 
 yd 
 
 yard 
 
 kcal/min 
 
 kilocalorie per minute 
 
 yr 
 
 year 
 
 kg 
 
 kilogram 
 
 
 
HUMAN FACTORS IN MINING 
 
 By Mark S. Sanders 1 and James M. Peay 2 
 
 ABSTRACT 
 
 There is a growing awareness among mining professionals that the human factor 
 plays a significant role in safety and productivity. Since the 1960's, the science of human 
 factors, or ergonomics, has been making inroads into the mining industry, and a con- 
 siderable amount of research has documented human-factor -related mining problems 
 and solutions. This Bureau of Mines report is directed toward summarizing the applica- 
 tion of human factors to improving safety, productivity, and the general physical and 
 psychological working conditions of miners. 
 
 The aim of this report is to familiarize the readers with the role of human factors 
 in the mining industry and the benefits that can accrue by systematically applying 
 available human factors principles and data. The text contains 10 chapters dealing with 
 human, equipment, and environmental factors. Each chapter builds on the previous 
 chapter; therefore, it is recommended that the chapters be read sequentially. However, 
 if the report is used as a supplemental text, say in a mining safety course, chapters 
 can be assigned in any order to supplement other readings. 
 
 1 Senior staff scientist, Essex Corp., Westlake Village, CA. 
 
 2 Supervisory engineering psychologist, Bureau of Mines, Pittsburgh Research Center, Pittsburgh, PA. 
 
CHAPTER 1.— INTRODUCTION 
 
 The mining industry has undergone and continues to undergo technological innovation at an increasingly rapid pace. 
 
 It was not too long ago that horses were still in the 
 mines, and people loaded ore and coal by hand. In 1950, for 
 example, almost one-third of the coal produced underground 
 in the United States was loaded by hand {24)} Although 
 many jobs still require high levels of physical labor, mech- 
 anization has greatly reduced the physical demands placed 
 on the mine worker. Today, mines are safer than at any 
 period in the past and safety is now an important part of 
 mine management. Coupled with the concern for safety is 
 management's ever present concern for productivity and 
 the resultant economic viability of the mining operation. 
 
 Over the last quarter century or so, there has been a 
 growing recognition within industrialized countries that 
 people are the key to both safety and productivity. Tech- 
 nology has done much to increase productivity and safety 
 in the mining industry. It has become obvious, however, 
 that as technology advanced, new demands were being 
 placed on the worker. More attention, not less, had to be 
 paid to how people and technology would work together. 
 How could equipment and tasks be designed to match the 
 capabilities and limitations of the people who had to operate 
 and maintain them? This is one of the questions addressed 
 by human factors. The Bureau of Mines launched its human 
 factors research program over a decade ago (19), and a con- 
 siderable body of knowledge now exists concerning human 
 factors in mining. 
 
 The purpose of this report is to introduce the reader to 
 human factors and its application in mining, to summarize 
 much of the current knowledge, and to illustrate the util- 
 ity of considering human factors in the design of equipment, 
 tasks, procedures, and environments within the mining 
 industry. 
 
 DEFINITION OF HUMAN FACTORS 
 
 Before attempting to define human factors, a word about 
 terminology is in order. Unfortunately, several terms are 
 used interchangeably to refer to the same scientific dis- 
 
 1 Italic numbers in parentheses refer to items in the list of references at 
 the end of this chapter. 
 
 cipline. The two leading terms are human factors and 
 ergonomics. A third term, human engineering, is somewhat 
 dated and seems to be declining in use. The term "human 
 factors" is used most often in the United States and Canada. 
 Both countries have professional associations that use the 
 term in their name (i.e., The Human Factors Society in the 
 United States and The Human Factors Association of 
 Canada in Canada). In the United States, however, the more 
 scientific sounding term "ergonomics" is often used in prod- 
 uct advertisements for such things as automobiles, com- 
 puter hardware, and chairs. 
 
 In the rest of the world, the term "ergonomics" is pre- 
 ferred; and in many countries, including the United 
 Kingdom, France, Federal Republic of Germany, Poland, 
 Israel, and Mexico, there are ergonomic professional 
 organizations. 
 
 Although most authors do not attempt to distinguish 
 the two terms, one book does try to make the distinction 
 (7). Reference 7 indicates that ergonomics traditionally 
 focuses on how work affects people, emphasizing physiolog- 
 ical responses to physically demanding work; environmen- 
 tal stressors, such as heat, noise, and illumination; complex 
 psychomotor assembly tasks; and visual monitoring tasks. 
 The goal is chiefly to reduce fatigue by designing tasks 
 within people's work capacity. In contrast, reference 7 
 argues that human factors traditionally is more interested 
 in the human-hardware interaction, focusing on behavior 
 of people as they interact with equipment, workplaces, and 
 their environment, as well as on human size and strength 
 capabilities relevant to equipment and workspace design. 
 The goal is chiefly to reduce the potential for human error. 
 
 Although this distinction may be correct in theory, in 
 practice there is so much overlap in focus, emphasis, and 
 goals that it is safer to consider the two terms synonymous. 
 In fact, it should be pointed out that it was the Human Fac- 
 tors section at Eastman Kodak that published the book en- 
 titled "Ergonomic Design for People at Work" (7X The term 
 "human factors" will be used in this report, but human fac- 
 tors and ergonomics will be considered synonymous. 
 
 What then is the definition of human factors? The 
 simplest definition is that human factors is designing for 
 
human use. The following is a more elaborate definition that 
 most people would find acceptable. Human factors is the 
 systematic application of relevant information about human 
 characteristics, abilities, expectations, and behaviors to the 
 design of machines, tools, facilities, procedures, and envi- 
 ronments that people use. The goal of human factors is to 
 enhance the operational efficiency, and the health and 
 safety of the people using the system. 
 
 BASIC MODEL 
 
 Human factors focuses on the human-hardware- 
 environment system. The basic system, one person and one 
 machine operating inside an environment, is shown in fig- 
 ure 1-1. This, of course, is an oversimplification. Most 
 systems involve more than one person and more than one 
 piece of hardware, and they operate within a changing en- 
 vironment. Systems are more fully discussed in chapter 2, 
 but this rudimentary model illustrates the basic elements 
 of concern to human factors. The person receives informa- 
 tion from the machine by way of displays. These displays 
 can be visual, auditory, tactual, and olfactory in nature. The 
 human processes the information and makes inputs to the 
 machine by way of control devices: push buttons, knobs, joy- 
 sticks, steering wheels, etc. The person and machine are 
 affected by, and receive information from, the environment. 
 The machine affects the environment, often at the direc- 
 tion of the person. Although people can directly influence 
 the environment, this is usually accomplished through some 
 hardware device. 
 
 As an example of this model, consider a worker operat- 
 ing a jackleg drill in a hard-rock mine. The person receives 
 information from the drill: hydraulic pressure from a gauge, 
 vibrations and feel of the drill, visual confirmation of the 
 bit penetrating the rock, and the sound of the drill. Based 
 on this information and previous experience and knowledge, 
 the worker manipulates the controls to successfully drill 
 the hole. Drilling the hole alters the environment. It puts 
 a hole where none existed before; noise, dust, and mist are 
 generated; and perhaps rocks on the floor are moved by the 
 support leg of the drill. These aspects of the environment 
 affect the worker by reducing visibility, creating new trip- 
 ping hazards, or perhaps causing a temporary, partial loss 
 of hearing. 
 
 
 Dust Environment Noise 
 
 c 
 o 
 
 a 
 
 c 
 
 I 
 
 3 
 O 
 
 a> 
 
 a. 
 
 E 
 
 «2 
 
 , 
 
 i 
 
 
 
 Machine 
 
 
 
 
 
 
 ' 
 
 
 
 
 
 G 
 
 Displays 
 
 Controls 
 
 s*4 
 
 V 
 
 
 
 
 
 , 
 
 i 
 
 
 
 *■ i luman 
 
 , 
 
 
 
 Obstacles Glare People Vibration 
 
 Figure 1-1.— Basic human-hardware-environment system. 
 
 WHAT HUMAN FACTORS IS NOT 
 
 Human factors specialists are concerned with the 
 human and the human's interactions with equipment and 
 environment. They are concerned with how best to present 
 information, configure controls, and design the hardware 
 so humans can operate it efficiently, comfortably, and safely. 
 They are concerned with how the environment affects 
 human performance, and how humans sense and respond 
 to the environment. They are interested in the human as 
 an information processor, decisionmaker, and energy source 
 for physical work. 
 
 These are just some of the concerns human factors 
 specialists have regarding the human-hardware-environ- 
 ment system. Equally important to the understanding of 
 human factors is understanding what human factors is not. 
 Unfortunately, when asked what human factors is, many 
 engineers, designers, and supervisors often tell what it is 
 not. 
 
 Human factors is not just the application of checklists 
 and guidelines. Although checklists can be helpful, they do 
 not constitute a human factors evaluation. The problem 
 with checklists is that they do not deal with interactions 
 between items and the tradeoffs that must be made between 
 competing criteria. Guidelines are just that, guidelines. Two 
 people using the same guidelines can produce vastly dif- 
 ferent designs {26). 
 
 Human factors is not using yourself as the model for 
 designing things. Just because it makes sense to you, or 
 fits your capabilities, is absolutely no guarantee that it will 
 make sense to, or fit, the people who will ultimately use 
 it. There is considerable information available to assist 
 in designing tools, procedures, equipment, etc., but one 
 thing readily apparent is that nobody is typical. Construct- 
 ing an ore chute so that you can safely walk under it does 
 not mean it is at a safe height for other people. Instructions 
 written to make sense to an engineer may totally confuse 
 someone else. 
 
 Finally, human factors is not just common sense. Of 
 course, human factors involves common sense, but it is more 
 than that. Probably one reason why human factors seems 
 like common sense is that human factors recommendations 
 often make intuitive sense after they are explained. It is 
 much like a mathematician's proof. Once it has been devel- 
 oped, it is obvious; but arriving at the proof was a highly 
 creative endeavor. Sometimes human factors information 
 even runs counter to what some would call common sense. 
 For example, it is common sense that increasing the inten- 
 sity of an alarm will make the person respond faster. This 
 appears true for simple responses, but it is not necessarily 
 true for complex responses. In fact, increasing intensity may 
 even cause the person to respond more slowly (29). Would 
 common sense have predicted that surface irregularities 
 could be detected more accurately when a person wears a 
 thin cloth glove than when the bare fingers are used alone? 
 It does not seem like common sense, but it is true (21). 
 
 ROADBLOCKS TO THE APPLICATION OF HUMAN 
 FACTORS 
 
 Although it may be intuitively obvious that human fac- 
 tors considerations in a system are central to maintaining 
 production and efficiency, people have been somewhat slow 
 in applying the principles to the design of workplaces and 
 equipment. There are at least five common misconceptions 
 
that serve as roadblocks, and are often encountered when 
 attempts are made to introduce human factors into an 
 organization. 
 
 1. All people are created equal. In fact, no two people 
 are exactly alike. Systems must be designed to accom- 
 modate the diversity in the population. When one size fits 
 all, you can bet that the one size will fit all— poorly. 
 
 2. People can be trained to overcome design deficiencies. 
 This is true to some extent, but training can be somewhat 
 unreliable. Under stress, people will respond the way they 
 think systems should work, which may not be how the 
 systems actually work. 
 
 3. Engineers and designers know how people think and 
 act. Engineers and designers may know how engineers and 
 designers think and act, but engineers and designers do not 
 necessarily think or act like everyone else. 
 
 4. Minor human factors deficiencies are not important. 
 Minor deficiencies often compound into major deficiencies. 
 Minor deficiencies also have a way of insiduously eating 
 into productivity and efficiency. Minor human factors defi- 
 ciencies are much like minor hydraulic leaks; neither one 
 can be ignored for long. 
 
 5. No serious incidents indicate no human factors prob- 
 lems. The Three Mile Island Nuclear Powerplant had 
 numerous human factors deficiencies in the control room, 
 and until the day the plant came within 60 min of 
 meltdown, it had no serious incidents. 
 
 HISTORY OF HUMAN FACTORS 
 
 To appreciate the current state of human factors, it is 
 instructive to know a little history about the discipline. 
 Some would say that human factors started when the first 
 cavedweller fashioned a rock to skin an animal, and formed 
 the rock to fit the hand comfortably. For all practical pur- 
 poses, the discipline of human factors started during World 
 War II. 
 
 1940-50— War Years 
 
 It became apparent during World War II that the new, 
 sophisticated equipment was exceeding operators' capabil- 
 ities. At one time during the war, more pilots were lost in 
 training than were lost in combat. Experimental psycholo- 
 gists were asked to collaborate with engineers in designing 
 various military hardware, including aircraft cockpits, 
 radar consoles, combat information centers, and binoculars 
 (10). 
 
 1960-80— Recognition and Expansion 
 
 As an indication of expansion during this period, the 
 membership of The Human Factors Society grew to over 
 3,000. Human factors expanded beyond the military-aero- 
 space industry and entered civilian government and indus- 
 trial organizations. It was during this period that the 
 Bureau launched its human factors research efforts to im- 
 prove safety in the mines. Human factors people were also 
 employed by civilian industries to design and evaluate 
 workplaces and consumer products. 
 
 1980— A Household Word 
 
 Advertisers have begun to use the terms "ergonomics" 
 and "human-engineered" in advertisements for cars, lawn- 
 mowers, truck seats, computer terminals, and even dental 
 chairs. The following is a partial list of companies employ- 
 ing human factors professionals (20): 
 
 Aluminum Company 
 
 of America 
 AT&T 
 
 Boeing Corp. 
 Clark Equipment Co. 
 Control Data Corp. 
 Deere & Co. Corp. 
 Eastman Kodak Corp. 
 Federal Express Corp. 
 FMC Corp. 
 Ford Motor Co. 
 General Electric 
 General Motors Corp. 
 Harris Corp. 
 Hewlett Packard Corp. 
 Honeywell, Inc. 
 
 Hughes Aircraft 
 IBM Corp. 
 International Harvester 
 
 Co. 
 Liberty Mutual Insurance 
 
 Co. 
 Lockheed Corp. 
 NCR Corp. 
 Northrop Corp. 
 Pitney Bowes 
 RCA 
 
 Rockwell International 
 3MCo. 
 
 Westinghouse Corp. 
 Xerox Corp. 
 
 Other professional organizations, including The Amer- 
 ican Society of Mechanical Engineers, Institute of Electrical 
 and Electronics Engineers, American Industrial Hygiene 
 Association, and Society of Automotive Engineers have 
 human factors or ergonomics subcommittees or technical 
 groups. There are now about 60 graduate programs in 
 human factors at universities in the United States (27). 
 
 This brief history points out the early thrusts and cur- 
 rent expansion of the human factors profession. The follow- 
 ing section provides a brief historical look at human factors 
 in mining, with an emphasis on the research activities of 
 the Bureau. 
 
 1950-60— Birth of a Profession 
 
 HISTORY OF HUMAN FACTORS IN MINING 
 
 After the war, human engineering or engineering psy- 
 chology laboratories (as they were called then) were estab- 
 lished by the Navy and Air Force. Activity was maintained 
 almost exclusively within the military-industrial complex. 
 During this period, the Soviet Union launched Sputnik, and 
 the race for space began. The industry that built planes and 
 guns now turned to space, and with that came human fac- 
 tors. The Ergonomic Research Society of Great Britain was 
 formed in 1950, and The Human Factors Society in the 
 United States was established in 1957. In 1960, the mem- 
 bership of The Human Factors Society was 500. 
 
 Human factors concerns are often stimulated by the in- 
 troduction of new technology into the workplace. In the min- 
 ing industry, new technologies have had their greatest im- 
 pact in the underground environment. On the other hand, 
 surface mining innovations have typically been in terms 
 of increased size and efficiency of earth- and ore-moving 
 equipment, and for the most part, have not involved the 
 introduction of revolutionary new technologies. 
 
 Underground mining, before mechanization, was back- 
 breaking, dangerous work: picks and shovels were state- 
 of-the-art. Miners could spend 3 to 6 h undercutting a coal 
 
face. As shown in figure 1-2, this was done lying on their 
 sides and using picks to make a horizontal slit 3 to 4 ft deep 
 at the bottom of the seam. 
 
 1870-1950— Early Mechnization 
 
 Mechanization of underground mining really began in 
 the 1870's. At the beginning of the decade, steam locomo- 
 tives were introduced underground. Early attempts were 
 made to mechanize loading, but they did not attract much 
 
 attention. In the latter part of the decade, cutting machines 
 were introduced to undercut the coal face. Figure 1-3 depicts 
 two miners operating an early Harrison Pick cutting ma- 
 chine. A little over a decade after cutting machines were 
 introduced, the first electrically driven drill was used. These 
 early machines were extremely noisy, vibrated so violently 
 that they caused internal injuries, and liberated more dust 
 and methane than could be handled by the ventilation 
 systems. Technology moved slowly in the mining industry 
 and by 1915, almost 40 yr after the introduction of cutting 
 
 Figure 1-2.— Undercutting a COal face before mechanization. (Courtesy of National Archives, Washington, DC) 
 
 Figure 1-3.— Early Harrison Pick Cutting macnine. (Courtesy of National Archives, Washington, DC) 
 
machines, only about one half of the Nation's coal output 
 was mined by such machines (6). It was not until 1930 that 
 the industry fully mechanized the undercutting operation. 
 Mechanical loading of coal increased during the 1920's and 
 1930's (28), but it was not until 1943-44 that more coal was 
 mechanically loaded than was loaded by hand (24). 
 Although electric locomotives were generally accepted in 
 the early 1900's, West Virginia still reported 1,600 animals 
 used for haulage in 1938. A common sight was the horse- 
 drawn mine car shown in figure 1-4. 
 
 During this early mechanization period, the Bureau was 
 established (1910) as part of the Department of the Interior. 
 It was initially set up as strictly an information-gathering 
 agency. Not until 1941 was the Bureau given authority to 
 enter and inspect underground coal mines. 
 
 1950-70— Modern Mechanization and the Coal Act 
 
 The next "revolution" in underground mining was the 
 introduction of continuous mining machines. Actually, ex- 
 perimental models were being tested in several mines dur- 
 ing the late 1940's. Initially, the industry was skeptical, 
 but as larger and more powerful machines were developed, 
 the skepticism slowly abated. The machines were widely 
 adopted in the late 1950's and early 1960's. Early continu- 
 ous mining machines were not much different in appearance 
 from machines in use today. 
 
 During this period, there was virtually no human fac- 
 tors research being conducted in the United States, despite 
 
 the growing recognition of human factors in the military 
 and aerospace industries. In Europe, however, some human 
 factors work was being done, but on a limited and frag- 
 mented scale. In 1969 the National Coal Board in England 
 established the Institute of Occupational Medicine, which 
 was chartered to conduct ergonomic research for under- 
 ground coal mining. 
 
 In 1968, a mining disaster in Farmington, WV, killed 
 78 workers. One year later, the U.S. Congress passed the 
 Federal Coal Mine Health and Safety Act of 1969. This act 
 gave enforcement powers to the Bureau and significantly 
 broadened its mandate regarding health and safety research 
 in coal mining. 
 
 1970— Birth and Growth of Human Factors in Mining 
 
 After the passage of the 1969 coal act, the Bureau began 
 sponsoring human factors research programs. The first for- 
 mal human factors project was a problem identification 
 study in underground coal completed in 1971 (19). That 
 study proposed research dealing with equipment design, 
 personal protective equipment, communications, illumina- 
 tion, noise, roof testing, and training. That was followed 
 a year later by a review of the human performance litera- 
 ture (11) in which only 49 documents (mostly European) 
 could be found that addressed mining-related tasks and 
 contained quantitative results or factual support for 
 conclusions. 
 
 Figure 1-4. — Use Of animaiS for hauling COal. (Courtesy of National Archives. Washington. DC) 
 
In the next few years, the Bureau sponsored projects to 
 address identified problems (19). One project investigated 
 the standardization of controls for underground electric face 
 equipment and focused on the development of design guide- 
 lines that would provide some degree of consistency in 
 control configurations for this equipment (15). Another proj- 
 ect involved machine canopies, in particular the fabrication 
 and evaluation of overhead protective structures for under- 
 ground equipment operators (1-2, 8-9, 17-18). A project 
 that dealt with optimized operator compartments integrated 
 and extended the results of earlier work by developing and 
 validating design guidelines for underground mining-equip- 
 ment operator compartments (3, 12, 22). The Inherently Safe 
 Mining Systems project developed and demonstrated equip- 
 ment modifications for improved safety in conventional and 
 continuous coal mining systems (13). 
 
 During the early and mid-1970's, a series of disasters 
 rocked the industry. In 1977 Congress passed another mine 
 safety and health act that extended the 1969 act to metal 
 and nonmetal mining, shifted enforcement to the Depart- 
 ment of Labor (Mine Safety and Health Administration), 
 and made provisions for mandatory training regulations. 
 Much of the early human factors work in underground coal 
 was applicable to underground metal and nonmetal mines 
 because the same equipment was used. Nevertheless, 
 differences did exist, and in the 1980's two human factors 
 problem identification studies were launched for the under- 
 ground metal-nonmetal industry (16, 25). 
 
 The majority of human factors research has been con- 
 ducted for the underground environment, but surface 
 mining has also attracted some of the attention of human 
 factors researchers. One area that received early attention 
 in surface mining was the problem of limited visibility (field 
 of view) from large haulage trucks (14, 23). In 1982, two 
 human factors problem-identification studies directed at 
 surface mining were published. One dealt with the mining 
 process itself (4), and the other with processing plants (5). 
 
 It is apparent from this brief historical review that 
 human factors research in the mining industry has been 
 a relatively recent development, spurred on by advances 
 in technology and the recognized need to improve safety and 
 productivity. As will be seen in subsequent chapters, there 
 is a large body of human factors data, principles, and 
 methods, developed outside the mining industry, that can 
 be brought to bear on problems encountered within the in- 
 dustry today. 
 
 COVERAGE 
 
 The remaining chapters will review in more depth 
 human factors concepts applicable to the mining industry 
 and review much of the quickly expanding human factors 
 in mining literature. Chapters 2, 3, and 4 present basic foun- 
 dational information: the role of human factors in system 
 design, including analytical tools used by human factors 
 specialists; a review of human capabilities and limitations 
 that form the basis for many design decisions; and the role 
 of human error in accidents. 
 
 Chapters 5, 6, and 7 deal with design of equipment and 
 tasks. Special emphasis is given to the design of work that 
 involves physical labor because, despite the advances in 
 mechanization, there still remain numerous tasks involv- 
 ing lifting, carrying, etc. Chapter 8 focuses on the environ- 
 ment and its impact on human performance. The four 
 
 environmental stressors discussed are illumination, ther- 
 mal conditions, noise, and vibration. The last two chapters 
 deal with topics traditionally subsumed under industrial 
 and organizational psychology, including training, motiva- 
 tion, and organizational development. 
 
 REFERENCES 
 
 1. Billmayer, H. Study of Low Coal Canopy Concepts (contract 
 H0346102, Bendix Corp.). BuMines OFR 70-76, 1975, 39 pp.; NTIS 
 PB 254 301. 
 
 2. . Development of Protective Canopy Concepts for 
 
 Underground Rail Haulage (contract H0357091, Bendix Corp.). 
 BuMines OFR 76-76, 1976, 85 pp.; NTIS PB 254 504. 
 
 3. . Fabrication and Evaluation of Optimized Operator Com- 
 partments (contract H0252048, Bendix Corp.). BuMines OFR 79-78, 
 1976, 34 pp.; NTIS PB 284 023. 
 
 4. Conway, E.J., and M.S. Sanders. Recommendations for Human 
 Factors Research and Development Projects in Surface Mining (con- 
 tract J0395080, Canyon Res. Group Inc.). BuMines OFR 211-83, 
 1982, 86 pp.; NTIS PB 84-143650. 
 
 5. Cross, B., and J. Schurick. Hazard Analysis and Safety 
 Economics in Mineral Processing Plants. Canyon Res. Group Inc., 
 Westlake Village, CA, 1982, 163 pp. 
 
 6. Dix, K. Work Relations in the Coal Industry: The Hand Load- 
 ing Era, 1880-1930. Inst, for Labor Studies, WV Univ., Morgan- 
 town, WV, 1977, 77 pp. 
 
 7. Eastman Kodak Co. Ergonomic Design for People at Work. 
 Volume I: Workplace, Equipment, and Environmental Design and 
 Information Transfer. Lifetime Learning, 1983, 406 pp. 
 
 8. Farrar, R. Design and Development of Protective Canopies for 
 Underground Low Coal Electric Face Equipment, Including Shut- 
 tle Cars. Final Report (contract H0220031, Bendix Corp.). BuMines 
 OFR 3(l)-75, 1973, 241 pp.; NTIS PB 240 541. 
 
 9. Farrar, R., R. Champney, and L. Weiner. Survey on Protec- 
 tive Canopy Design (contract H0242020, Bendix Corp.). BuMines 
 OFR 50-76, 1974, 163 pp.; NTIS PB 251 672. 
 
 10. Fitts, P. Engineering Psychology and Equipment Design. 
 Ch. in Handbook of Experimental Psychology, ed. by S. Stevens. 
 Wiley, 1951, pp. 631-674. 
 
 11. Fried, C. The Miner, His Job and His Environment: A Review 
 and Bibliography of Selected Recent Research on Human Perfor- 
 mance (contract H0122019, Natl. Bureau of Standards). BuMines 
 OFR 27-72, 1972, 192 pp.; NTIS PB 211 732. 
 
 12. Gunderman, R. Optimized Operator Compartments (contract 
 H0252092, Dresser Industries). BuMines OFR 71-79, 1979, 94 pp.; 
 NTIS PB 297 668. 
 
 13. Hamilton, D.D., J.E. Hopper, and J.H. Jones. Inherently Safe 
 Mining Systems. Executive Summary (contract H0111670, FMC 
 Corp.). BuMines OFR 124-77, 1977, 38 pp.; NTIS PB 271 150. 
 
 14. Hawley, K.W., and S.F. Hulbert. Improved Visibility Systems 
 for Large Haulage Vehicles (contract H0262022, MBAssoc). 
 BuMines OFR 100-78, 1978, 121 pp.; NTIS PB 286 065. 
 
 15. Hedling, W.G., and R.J. Kennihan. Standardization of Con- 
 trols for Underground Electric Face Equipment. Final Report (con- 
 tract H0230021, Applied Science Assoc. Inc.). BuMines OFR 
 45(l)-75, 1974, 279 pp.; NTIS PB 242 562. 
 
 16. Helander, M., and G. Krohn. Human Factors Analysis of 
 Underground Metal and Nonmetal Mines (contract H0308067, 
 Canyon Research Group Inc.). BuMines OFR 16-84, 1983, 99 pp.; 
 NTIS PB 84-158732. 
 
 17. Hermanson, W. Fabricate and Evaluate Protective Canopies 
 for 3-Foot Coal Seams (contract H0357090, Bendix Corp.). BuMines 
 OFR 42-77, 1976, 157 pp.; NTIS PB 265 073. 
 
 18. Hermanson, W., and H. Billmayer. Design and Development 
 of Protective Canopies for Shuttle Car, Loader, and Roof Drill (con- 
 tract H0242028, Bendix Corp.). BuMines OFR 4-76, 1974, 39 pp.; 
 NTIS PB 248 833. 
 
 19. Hitchcock, L., and M. Sanders (eds.). Survey of Human Fac- 
 tors in Underground Bituminous Coal Mining. Naval Ammunition 
 Depot, Crane, IN, 1971, 137 pp. 
 
20. Knowles, M. (ed.). The Human Factors Society 1983 Direc- 
 tory and Yearbook. The Human Factors Society, 1983, 279 pp. 
 
 21. Lederman, S. Heightening Tactile Impressions of Surface Tex- 
 ture. Ch. in Active Touch, ed. by G. Gordon. Permagon, 1978, pp. 
 205-214. 
 
 22. McGuirk, F.D., and G.A. Podgornik. Optimized Operator Com- 
 partment. Final Report (contract H0242033, Applied Science Assoc. 
 Inc.). BuMines OFR 126(l)-76, 1975, 50 pp.; NTIS PB 261 490. 
 
 23. Miller, W. Analysis of Haulage Truck Visibility Hazards at 
 Metal and Nonmetal Surface Mines, 1975. MSHA IR 1038, 1976, 
 19 pp. 
 
 24. National Academy of Sciences. Toward Safer Underground 
 Coal Mines. 1982, 190 pp. 
 
 25. Perry, T., N. Schwalm, and W. Crooks. Human Factors Anal- 
 ysis of Underground Work Areas and Tasks in Metal and Nonmetal 
 
 Mines (contract J0387230, Perceptronics Inc.). BuMines OFR 
 111(1)-81, 1981, 150 pp.; NTIS PB 81-236804. 
 
 26. Rogers, J., and R. Armstrong. Use of Human Engineering 
 Standards in Design. Human Factors J., v. 19, No. 1, 1977. pp. 
 15-23. 
 
 27. Sanders. M., and L. Strother. (eds.). Directory of Graduate 
 Human Factors Programs in the U.S.A. The Human Factors Soci- 
 ety, 1985, 57 pp. 
 
 28. Smith, C, and C. Ball (eds.). Mechannual 1939. Mechaniza- 
 tion Inc., 1939, 437 pp. 
 
 29. Van der Molen, M.. and P. Keuss. The Relationship Between 
 Reaction Time and Intensity in Discrete Auditory Tasks. Q.J. 
 Exper. Psych., v. 31, 1979. pp. 95-102. 
 
CHAPTER 2.— HUMAN FACTORS IN THE DESIGN OF SYSTEMS 
 
 Effective system design should include system definition, task analysis, efficient interface design, and field 
 testing. 
 
 As indicated in chapter 1, a central concept in human 
 factors is the system. Although various authors use different 
 definitions for the term, a very simple one is used here. A 
 system is an entity that exists to carry out some purpose 
 (2). 1 A system is composed of humans, machines, and other 
 things that work together (i.e., interact) to accomplish some 
 goal that these same components could not produce inde- 
 pendently. Using systems concepts serves to structure the 
 approach to the development, analysis, and evaluation of 
 complex collections of humans and machines. According to 
 Bailey (2) 
 
 The concept of a system implies that we recognize a 
 purpose; we carefully analyze the purpose; we under- 
 stand what is required to achieve the purpose; we 
 design the system's parts to accomplish the require- 
 ments; and we fashion a well-coordinated system that 
 effectively meets our purpose. 
 
 This chapter first discusses the major characteristics of 
 a system, using a haulage vehicle in an underground mine 
 as the focus. The chapter then traces the development of 
 a system and indicates the various human factors activities 
 that could be applied to insure the resulting system meets 
 its stated objectives. 
 
 CHARACTERISTICS OF SYSTEMS 
 
 In discussing the various characteristics of systems it 
 will be helpful to have an example that illustrates the 
 
 1 Italic numbers in parentheses refer to items in the list of references at 
 the end of this chapter. 
 
 various concepts. In underground mining, both coal and 
 noncoal, haulage vehicles are used to move the coal, or ore, 
 from the working face to a more permanent continuous 
 haulage system, usually a conveyor belt system or train. 
 Examples of such haulage vehicles are front-end loaders, 
 scoops, shuttle cars, and load-haul-dump (LHD) vehicles. 
 These vehicles are run by batteries, diesel motors, or elec- 
 tricity supplied by cable. They are operated by a single 
 operator, although the operator may have a helper to assist. 
 In some cases the vehicle picks up the coal or ore itself, as 
 in the case of a scoop or LHD; in other cases the vehicle 
 is loaded by another machine, as in the case of shuttle cars. 
 Given this basic concept of an underground haulage vehi- 
 cle, the following is a discussion of the characteristics of 
 systems. 
 
 Systems Have a Purpose 
 
 In Bailey's definition of a system (2), it was stressed that 
 a system has a purpose. Every system must have a purpose, 
 or it is nothing more than a collection of odds and ends that 
 coexist. The purpose of a system is the system goal or ob- 
 jective, but systems can have more than one purpose. The 
 goals of a system should be stated in general terms so that 
 they need not be changed every time something in the 
 system changes. Appropriate system goals for a haulage 
 vehicle would include 
 
 Haul ore (or coal) from the working face to the continuous 
 haulage system. 
 Load ore (or coal) from the floor. 
 Protect the operator from roof falls. 
 
10 
 
 It is important that the goals or objectives of the system 
 be clearly understood and agreed upon before designing, 
 developing, or evaluating a system. For example, the com- 
 mon typewriter keyboard (QWERTY, so named for the first 
 six keys of the first letter row) has been criticized as ineffi- 
 cient and slow. The most common letters are positioned for 
 the left hand, and common letter combinations require 
 awkward finger movements. Actually, when the goal of the 
 system is understood, the keyboard organization has a pur- 
 pose. When typewriters were first invented, fast typists 
 could easily jam the keys. The keyboard, therefore, was 
 actually designed to slow the typist down and to separate 
 common letter combinations (e.g., QU) so that the key bars 
 would not come from the same side of the machine and jam. 
 As this example illustrates, failure to understand the goals 
 of a system can lead to irrelevant evaluations. It must be 
 pointed out, however, that one can challenge the adequacy 
 and relevance of system goals. With the advent of element 
 balls, daisy wheels, and word processor printers, there is 
 no need to slow down typists because there are no keys to 
 jam. 
 
 Systems Are Hierarchical 
 
 A system can be considered to be a part of a larger 
 system and, when analyzed, the system itself can be com- 
 posed of more molecular systems (also called subsystems). 
 This is illustrated in figure 2-1, where a haulage vehicle 
 system is shown as one subsystem in the larger mine 
 haulage system, which in turn is one subsystem in the even 
 larger mine system. A closer look at the haulage vehicle 
 
 Total mine 
 
 Exploration 
 
 Extraction 
 
 y/Am&'/zi 
 
 Trains 
 
 Processing 
 
 Conveyors 
 
 =F 
 
 /ehicle'^^ 
 
 Propulsion [ 
 
 Steering 
 
 Braking 
 
 UM^WA 
 
 Sensing | 
 
 Information 
 processing 
 
 Action I 
 
 Memory 
 
 Figure 2-1 .—Schematic diagram of haulage vehicle subsystem 
 within the total mine system. 
 
 subsystem shows that it is composed of a vehicle subsystem 
 and an operator subsystem. Each of these in turn is com- 
 posed of more molecular systems, such as the propulsion 
 system or the steering system. When faced with the task 
 of describing or analyzing a system, one often asks: "Where 
 do you start?" and "Where do you stop?" The answer to both 
 these questions is: "It depends." 
 
 In describing and analyzing a system two decisions must 
 be made. First, one has to decide on the boundary of the 
 system; that is, what is to be considered part of the system 
 under study, and what is to be considered outside the 
 system? There is no right or wrong answer, but the choice 
 must be logical and result in a system that performs an iden- 
 tifiable function. Thus, one could focus on the haulage 
 vehicle as the system and consider conveyors and trains as 
 outside the system. Alternatively, one could focus on the 
 mine haulage system, with haulage vehicles as one sub- 
 system or component of the larger system. 
 
 In some systems it appears that the designers drew the 
 boundary of the system in such a way that the operator and 
 maintainer of the equipment were considered outside the 
 system. When this sort of design philosophy prevails, one 
 finds systems that are difficult to operate, require excessive 
 training, are prone to operator errors, and are difficult to 
 maintain. As a general rule, one should always include 
 operators and maintainers inside the system boundary to 
 help insure that the system is designed to accommodate and 
 facilitate human performance and safety. 
 
 The second decision that must be made is to set the limit 
 of resolution for the system. That is, how far down into the 
 system do you want to go? At the lowest level of analysis 
 are components. A component in one analysis may be a sub- 
 system in another analysis that uses a more detailed limit 
 of resolution. Focusing on the haulage vehicle as a system, 
 the analysis can be limited and the vehicle and operator 
 can be considered the components. Alternatively, the anal- 
 ysis could be extended to consider the vehicle and operator 
 as subsystems and things such as propulsion and steering 
 as the components. As with setting system boundaries, there 
 is no right or wrong limit of resolution. The proper limit 
 depends on why one is describing or analyzing the situa- 
 tion in the first place. 
 
 Systems Operate in an Environment 
 
 The environment of a system, whether a closed- or open- 
 loop system, is everything outside its boundary; therefore, 
 the environment of a haulage vehicle system includes the 
 roadways of the mine; other vehicles, objects, and people 
 in the area; the conveyor system; the loading machine: etc. 
 An open-loop system cannot sense its own actions and can- 
 not alter its course of action. On the other hand, a closed- 
 loop system can sense its own action and alter its course 
 based on that information. 
 
 Humans are inherently closed-loop systems. To illus- 
 trate the difference, a haulage vehicle, without a driver, 
 would be considered an open-loop system when the vehicle 
 rolls down a slope. There is no mechanism to feed back in- 
 formation to the system regarding its position relative to 
 obstacles in the environment or to take corrective action 
 to avoid them. The same haulage vehicle, with a driver 
 maneuvering down a roadway, is a closed-loop system. The 
 operator functions in the feedback loop, sensing the posi- 
 tion of the vehicle and the position of obstacles in the en- 
 vironment, and changing the course of the vehicle to avoid 
 the obstacles. 
 
11 
 
 Components Serve Functions 
 
 Every component (the lowest level of analysis) must 
 serve at least one function in the system. Further, these 
 functions must be related to the fulfillment of one or more 
 of the system's goals or objectives. One of the tasks of human 
 factors specialists is to aid in making decisions as to whether 
 humans or machines (including computer software) should 
 carry out a particular system function. For example, who 
 or what should limit the speed of a haulage vehicle system? 
 Should a speed governor be installed to automatically limit 
 speed, or should that function be given to the driver? Who 
 should be responsible for sensing the speed of the vehicle? 
 Can a human estimate speed accurately enough, or should 
 a speedometer be provided as a component in the system? 
 By understanding the capabilities and limitations of 
 humans, human factors specialists can provide valuable in- 
 formation to the decisions regarding allocation of function. 
 
 Humans serve various functions in systems (7). These 
 functions involve 
 
 1. Sensing (seeing, hearing, feeling), 
 
 2. Storage (memory), 
 
 3. Information processing (thinking), 
 
 4. Decisionmaking, and 
 
 5. Action (movement, speaking). 
 
 Components Interact 
 
 To say that components interact simply means the com- 
 ponents work together to achieve system goals. Each com- 
 ponent has an effect, however small, on other components. 
 One of the outcomes of a systems analysis is the descrip- 
 tion and understanding of these component and subsystem 
 interactions. 
 
 Systems, Subsystems, and Components Have 
 Inputs and Outputs 
 
 At all levels of a system there are inputs and outputs. 
 The outputs of one subsystem or component are the inputs 
 to another. It is through inputs and outputs that components 
 and subsystems interact. Inputs can be physical entities 
 (such as materials and products), electrical impulses, 
 mechanical forces, or information. As illustrated in figure 
 2-2, a haulage vehicle outputs information on speed from 
 its speedometer. That information becomes an input to the 
 operator subsystem. The operator subsystem processes the 
 information and outputs an action; e.g., stepping on the 
 brake. That mechanical force then becomes an input to the 
 braking subsystem of the vehicle. 
 
 Output 
 
 c=E> 
 
 Input Speedometer 
 
 Output 
 
 Input M 
 
 W* j ! Output 
 
 ll 
 II 
 
 Input 
 
 Accelerator 
 
 Figure 2-2.— Schematic diagram of inputs and outputs between 
 subsystems of a system. 
 
 An analysis of a system must specify all the inputs and 
 outputs required for each component and subsystem to per- 
 form its functions. Human factors specialists are especially 
 qualified to determine the inputs and outputs that are 
 necessary for the human component to successfully carry 
 out its functions. Failure to supply adequate and proper in- 
 puts or the facilities necessary to produce outputs will result 
 in degraded system performance. For example, how appro- 
 priate is an auditory warning of excessive speed in an 
 underground mine? Which is more appropriate for input- 
 ting steering commands to the vehicle, a wheel or a joystick? 
 
 From this short overview, it can be seen that systems 
 have a purpose and are made up of subsystems and com- 
 ponents interacting through inputs and outputs to perform 
 functions in support of system objectives. Systems operate 
 within an environment, but the definition of what is part 
 of the system and what is part of the environment is a some- 
 what arbitrary decision made to facilitate analysis and 
 evaluation. With this in mind, a discussion of the system 
 design process and the types of activities that human fac- 
 tors specialists conduct is presented. 
 
 HOW ENGINEERS REALLY DESIGN 
 
 Several earlier studies that addressed the question of 
 how engineers design and how they make use of human fac- 
 tors information in the design process were analyzed (8). 
 Forty-four mechanical and electrical engineers, each with 
 approximately 15 yr of experience, served as subjects in the 
 studies. Basically, a design problem was presented to the 
 engineers, and information was provided them during the 
 design process. The tasks, or design problems, included de- 
 signing a command-control console, a circuitboard tester, 
 an air traffic control radar-monitoring console, and test 
 equipment to check an electronic subsystem. Each problem 
 took several days to complete. 
 
 What this analysis (8) found was that "almost im- 
 mediately after examining the problem, they (the engineers) 
 started to design hardware without performing much delib- 
 erate, systematic analysis." Little or no consideration was 
 given to how the equipment was to be used by the operator, 
 the sequence of use, or which functions were most impor- 
 tant or most frequently used. No attempts were made to 
 allocate functions between people and hardware. In essence, 
 the engineers appeared to skip over the first two stages of 
 system development. The engineers relied overwhelmingly 
 on design solutions that they had used before. This 
 prevented them from considering novel approaches to the 
 designs. Further, there was a reluctance to modify their in- 
 itial designs, except in minor respects when new informa- 
 tion was made available to them. For example, halfway 
 through the process the engineers were told that instead 
 of four people to operate the console, only two could be used. 
 This resulted in only minor changes in the placement of 
 displays and controls, but no overall revision of the basic 
 design concept. 
 
 As far as the attitudes of the engineers toward human 
 factors was concerned, the analysis (8) concluded that: "One 
 of the most consistent findings of our research, confirmed 
 in each study with all subjects regardless of sophistication, 
 years of experience, or type of design problem, is that the 
 typical design engineer does not consider human factors in 
 his design." In questioning the engineers during the anal- 
 ysis, however, it was found that they had a strong, profound 
 interest in human factors and a dedication to consider 
 
12 
 
 human factors in their designs. These verbal statements, 
 however, were totally inconsistent with their actual be- 
 havior on the design problems. 
 
 Although this analysis was carried out over 15 yr ago, 
 the situation, while improved, is still not much different 
 today. Recently, one of the authors of this Information Cir- 
 cular was called upon to evaluate the human factors aspects 
 of a large demineralizer panel. The engineers who laid out 
 the displays on the console did not know what information 
 the operator needed to run the panel, the operating se- 
 quence, how often various displays would be used, or the 
 importance of various displays in operating the system. 
 Despite this, they had no misgivings about placing the 
 displays on the panel. 
 
 STAGES IN THE DESIGN OF SYSTEMS 
 
 Systems do not just spring into life; they go through a 
 process of development. Sometimes the process is structured 
 and the stages are easy to identify. More often, systems are 
 developed in a more fluid, unstructured manner, where it 
 is almost impossible to separate the various stages of their 
 development. When a manufacturer develops a new bucket- 
 wheel excavator for a surface mine, it is likely that the 
 stages of development are carefully planned and executed. 
 When the superintendent of a surface mine puts together 
 an all-purpose maintenance vehicle, the stages of develop- 
 ment are passed through more informally. Although the 
 same sorts of decisions and considerations may be involved, 
 the process is not as systematic or exhaustive as it is por- 
 trayed in this chapter. 
 
 Six stages in the design of a system are listed by Bailey 
 (2). These stages are depicted in figure 2-3. Dividing the 
 design process into stages gives the impression of a simple 
 linear process. In actual practice, however, the process is 
 iterative; that is, it cycles over and over, becoming more 
 detailed in each pass through the stages. Information devel- 
 oped in a later stage may influence decisions made in earlier 
 stages, thus requiring a reappraisal. The concept of a sur- 
 face mining all-purpose maintenance vehicle will be used 
 to illustrate the various stages in the design of a system. 
 
 Stage 1 : Determine Objectives and System 
 Specifications 
 
 As already discussed, one cannot design a system 
 without a clearly stated set of objectives. The objective of 
 the maintenance vehicle is to carry the required tools, equip- 
 ment, parts, and personnel to perform maintenance tasks 
 on equipment in the field. Performance specifications state 
 what the system must do to meet its objectives. These re- 
 
 STAGE I 
 Determine objectives 
 
 and 
 system specifications 
 
 STAGE 2 
 Definition of system 
 
 STAGE 3 
 Basic design 
 
 STAGE 4 
 
 Interface 
 design 
 
 STAGE 5 
 
 Facilitator 
 
 design 
 
 STAGE 6 
 Testing 
 
 Figure 2-3.— Stages in the development of a system (based 
 on stages suggested by Bailey (2) ). 
 
 quirements are derived from a careful study of user needs. 
 Typically, according to Bailey (2), the information is col- 
 lected using interviews, questionnaires, site visits, and work 
 studies. Usually, constraints are part of the system require- 
 ments. For example, a maintenance vehicle has to operate 
 in mud, in high winds, and in temperatures below freez- 
 ing. System designers must also deal with constraints 
 related to the human component of the system. These relate 
 to the skills, knowledges, and capabilities of the operators, 
 and the number of people required to operate the system. 
 For example, one constraint for the maintenance vehicle 
 might be that it can carry at least two people. 
 
 Stage 2: Define the System 
 
 The second stage involves listing the functions that the 
 system must perform to achieve the objectives and system 
 specifications defined in stage 1. Some functions of the 
 maintenance vehicle system would include 
 
 Transporting people and equipment to the worksite. 
 
 Fixing hydraulic leaks, 
 
 Welding broken parts, 
 
 Lifting objects weighing up to 1 st, and 
 
 Communicating with the base maintenance shop. 
 During this stage, people-related information would also 
 be collected. This would include information regarding the 
 availability of people and the basic characteristics of the 
 potential user population (operators and maintainers), such 
 as size, education, skills, and abilities. In some cases the 
 constraints of the system will be modified as information 
 concerning the available labor pool is obtained. For exam- 
 ple, it may not be feasible to use a highly technical system 
 if the operators lack the required skills to understand it. 
 
 Stage 3: Basic Design 
 
 In this stage the functions identified in stage 2 are 
 allocated to human or machine, and the resulting tasks of 
 the human are analyzed. Central to this activity is the proc- 
 ess of task analysis. Task analysis is the process by which 
 the human's functions are broken down into required ac- 
 tivities, and each activity is analyzed to determine human 
 and system requirements needed to successfully carry out 
 the particular activity. 
 
 Task analysis is probably the most important and fun- 
 damental process performed by human factors specialists. 
 Its use transcends system design and becomes the basic tool 
 for understanding the human component in any system. 
 Task analysis is as much an art as it is a science. It involves 
 a series of methodologies for collecting task data and various 
 formats for presenting the information. It will not be pos- 
 sible to cover all the facts of task analysis in this report. 
 The reader interested in more information can refer to 
 reference 9. 
 
 Table 2-1 lists the various methods that can be used to 
 collect task analysis information. Generally, more than one 
 method is used to insure that complete and accurate in- 
 formation is obtained. One of the most comprehensive 
 examples of task analysis for the mining industry was car- 
 ried out by Crooks (3) in which virtually all underground 
 metal-nonmetal unit operations were analyzed. Examples 
 of unit operations included feedleg drilling, rock bolting, 
 sand filling, slusher operation, track maintenance, timber 
 construction, and ore skip operation. The task analysis 
 team, with an •expert' - (supervisor, safety engineer, etc) 
 
13 
 
 present, conducted onsite observations of workers perform- 
 ing the various unit operations. The team followed up the 
 observations by conducting two-person, group interviews 
 with experienced workers away from their jobs. A minimum 
 of four workers were interviewed for each unit operation. 
 After completion of the interviews, technical conferences 
 with one or two supervisors were held to verify the com- 
 pleteness of the information collected. A total of 188 inter- 
 views were conducted to analyze 43 unit operations. Each 
 of the unit operations (e.g., feedleg drilling) was broken 
 down into tasks (e.g., prepares drill, drills, maintains drill), 
 and each task was further analyzed into activities (e.g., col- 
 lars hole, drills hole, removes bound steel). 
 
 Table 2-1.— Methods of collecting task analysis information 
 
 Observation Observe worker performing job. 
 
 Interview: 
 
 Observational Observe and interview worker while per- 
 forming job. 
 
 Individual Interview worker away from jobsite. 
 
 Group Interview more than one worker at same 
 
 time, away from jobsite. 
 
 Technical conference Interview subject matter experts or super- 
 visors regarding job of worker. 
 
 Checklist Worker checks tasks that are performed on 
 
 the job from a master list. 
 
 Questionnaire Open-ended questions that worker answers 
 
 regarding work tasks. 
 
 Diary Worker keeps a record of job activities 
 
 throughout day. 
 
 Motion picture Motion pictures are made of worker per- 
 forming specific tasks. 
 
 The type of information collected in a task analysis 
 depends on the purpose of the analysis. For example, task 
 analysis information can be used for determining training 
 requirements for a task, for assessing hazards and unsafe 
 conditions or procedures involved in a task, for designing 
 or modifying equipment or procedures, or for determining 
 the type and level of people needed to operate and main- 
 tain a system. As another example, a task analysis approach 
 to determine visibility requirements for operation of con- 
 tinuous miners, shuttle cars, and scoops in underground coal 
 mines was used by Sanders and Kelley (10). It is also worth- 
 while by way of illustration to point out that the following 
 
 task analysis data were collected by Crooks (3) for under- 
 ground metal-nonmetal tasks: 
 
 Minimum and maximum times to complete. 
 
 Amount of training required. 
 
 Percentage of time standing. 
 
 Physical energy level required. 
 
 Degree to which 12 classes of physical activities (such as 
 climbing, stooping, handling, talking) were present. 
 
 Degree to which six classes of visual requirements (such 
 as near acuity, depth perception, color vision) were present. 
 
 Generic classes of hazards involved (such as electrical, hot- 
 cold surfaces, sharp objects, explosives). 
 
 Common errors or accidents. 
 
 Principal visual features involved in performing the task. 
 
 Type of illumination usually present. 
 
 Worksites where the unit operation was performed. 
 This is a rather extensive list of information for a single 
 task analysis. Several of the items in this tabulation were 
 included because a primary purpose of the analysis was to 
 establish illumination requirements for the unit operations. 
 The various formats used for presenting task analysis 
 information depend, of course, on what information is col- 
 lected and on the purpose of the analysis. Common formats 
 include column format, operational sequence diagrams, and 
 timelines. ' 
 
 With a column format, the steps or activities compos- 
 ing a task are listed down the page, and the information 
 categories are listed across the top of the page. For each 
 step or activity, the required information is filled in across 
 the page. Figure 2-4 is an example of a column format. 
 
 Operational sequence diagrams depict the sequence of 
 steps and the interrelationships among the components of 
 a system in carrying out a particular task. Standard sym- 
 bols are used to present the information. Figure 2-5 pre- 
 sents an example of an operational sequence diagram for 
 handling an emergency in a steam generation plant (6). 
 Timelines depict the activities performed along a time 
 scale. Where several persons, or persons and machines are 
 interacting, a timeline presentation can graphically illus- 
 trate periods of overload and underload during the execu- 
 tion of a task. Figure 2-6 shows an example of a timeline 
 generated by a computer program developed by the Na- 
 tional Coal Board in England (11). 
 
 Direction 
 
 3. Position miner 
 in entry 
 
 Operator Task 
 
 Maneuver machine to line up 
 
 overhead paint markings with 
 a known point on either side 
 of the cutting head that will 
 yield the planned entry width 
 while keeping machine clear 
 of ribs and roof. 
 
 Tram to face while raising 
 
 or lowering cutting head to 
 starting elevation and while 
 lowering the gathering head. 
 
 Helper Task 
 
 Lift and pull cable into 
 place along the right 
 rib so that it is out of 
 the way of the crawler 
 tracks as the miner is 
 trammed forward and 
 back. 
 
 Comments 
 
 Foreman painted centerhne 
 on ceiling Bolt crew hung 
 a reflector on the last row 
 of bolts to show boundary 
 of safe roof. 
 
 Different operators take 
 different approaches to 
 starting point for cutting 
 operation (top, middle, or 
 bottom). Some would bump 
 into the middle of the face 
 and then tram back a few 
 inches and start head 
 rotation. 
 
 Controls 
 
 Tram levers. 
 
 Conveyor boom elevation lever. 
 
 Conveyor boom swing lever. 
 
 Tram levers. 
 
 Cutting head elevation lever. 
 
 Gathering head elevation lever. 
 
 Displays or feedback 
 
 View of roof and painted 
 
 centerline 
 View of reflector on last 
 
 row of bolts. 
 
 View of cutting head 
 position. 
 
 View of gathering head 
 
 position. 
 View of face relative to 
 
 machine. 
 Sound of cutting head 
 
 bumping into face. 
 View of ceiling paint marks 
 
 relative to cutting head 
 View of machine relative 
 
 to ribs. 
 View of helper and cable. 
 
 Figure 2-4.— Example of a column format used in task analysis. 
 
14 
 
 il 
 I 
 
 m 
 i 
 
 l 
 i 
 
 ^Telephones auxiliary 
 operator 
 
 Directs to verify that flash 
 evaporator valve is closed 
 to make related adjust- 
 ments, and to shut 
 city water supply to 
 flash evaporator tank 
 
 Figure 2-5.— Example of an operational sequence diagram (OSD) used in task analysis (6). (Copyright 1984. Electric Power Research institute. 
 
 Report NP-3659, "Human Factors Guide For Nuclear Power Plant Control Room Development." Reprinted with permission.) 
 
Surface simulation study on cam packing 
 2- shift production, 3-shift ripping 
 
 15 
 
 h min 
 - 
 
 External delays 
 
 ~ 10 ~. 
 - 20 A 
 ~ 30 A 
 "40 A 
 
 ~ 50 A 
 
 1 - A 
 I " 10 
 I " 20 -j 
 I - 30 A 
 I " 40 A 
 I - 50 
 
 2 - 
 
 Main gate rip 
 cam packing 
 
 Rip preparation, 
 protect cables 
 
 -L 
 
 Prepare scaffold 
 to drill 
 
 Complete advance 
 m/g end I AFC 
 2 ft 
 
 Cut on snake 
 tail to main- 
 Obtain drill rod, 
 drill II 4-ft holes 
 
 Stem and charge 
 6 holes 
 
 I 
 
 Advance roadhead 
 space and cam 
 loader 
 Fire 4 ft, 6 holes 
 
 Trim loose stone 
 
 Fill to cam feeder 
 Stem and charge 
 
 f 
 
 No. I machine 
 at main gate 
 
 Machine preparation 
 
 Cut on snake main 
 to tail 20 yd 
 
 0/C dozer doors 
 
 Advance r/h supports, 
 
 extend r cantilever 
 
 2 ft, advance 
 
 ^— Cut on snake 
 Wait.AFC standing 
 
 0/C dozer doors 
 
 Flit to buttock 20yd 
 
 Cut main to tail 
 
 Advance main 
 gate end 
 
 Cut main to tail 
 160 yd 
 
 Wait, AFC standing 
 fire main gate rip 
 
 Cut main to tail 
 160 yd 
 
 ^ 
 
 Cut into No. 2 
 
 No. 2 machine 
 at tailgate 
 
 Machine preparation 
 
 Cut on snake tail 
 to main 20 yd 
 
 Flit cleanup main 
 ■to tail 20yd- 
 
 Wait.AFC standing 
 
 Flit tail to main 20 yd 
 
 ^-Advance AFC 
 Advance tail gate end 
 
 Advance 16 powered 
 supports 
 
 Cut main to tail 20yd 
 Flit cleanup 
 
 -¥ 
 
 Wait AFC standing 
 
 Flit cleanup 
 Flit main to tail 20 yd 
 
 Change picks 
 
 Wait.No. I machine 
 to remove buttock 
 
 Figure 2-6.— Example of a timeline used in task analysis (11). (Courtesy of Butterworth scientific Ltd.) 
 
16 
 
 The information obtained from the task analysis phase 
 of system design represents the primary source of data for 
 the remaining stages of the design process. Again, it should 
 be pointed out that the design process and task analysis 
 are iterative in nature. As more and more details are de- 
 fined in the system, more and more details can be added 
 to the task analysis. This serves to verify system design deci- 
 sions and to point the way toward further refinements in 
 the system. 
 
 Stage 4: Interface Design 
 
 Based on the information collected and decisions made 
 in stage 3, the designer moves to a more molecular level 
 and begins designing the human-equipment and human- 
 environment interfaces. These include the layout of work- 
 spaces, controls, displays, human-computer dialogues, 
 forms, etc. This is the phase of design where decisions such 
 as the following are made: What type of display should be 
 used? How many scale markers need there be? What type 
 of control should be used? How much resistance should be 
 included in the control? How close together should the 
 switches be placed? 
 
 One human factors technique often used to develop op- 
 timized panels, workstations, and work areas is link anal- 
 ysis. The purpose of link analysis is to graphically depict 
 the frequency and/or criticality associated with each of the 
 various interactions occurring between the operator and 
 equipment and/or between one operator and another (5). The 
 links that are analyzed could be eye movements between 
 displays on a console, or between objects in the environment. 
 Hand movements between controls are often analyzed as 
 well. The objective is to modify the arrangement of the com- 
 ponents to shorten the distance between components con- 
 nected by frequently employed links. 
 
 Figure 2-7 shows the controls on an underground roof 
 bolting machine and the results of a: link analysis carried 
 out on the bolting operation (4). The thickness of the lines 
 connecting the controls indicates the relative frequency of 
 hand movements between the respective controls. One as- 
 pect that stands out is the long, relatively frequent link be- 
 tween the boom swing and the head sump controls. 
 
 Another tool used by human factors specialists to aid 
 in interface design is the mockup. Mockups are usually, but 
 need not always be, full-scale models of the equipment or 
 facility. They are usually made of inexpensive materials, 
 such as foam-core cardboard or plywood. The components 
 are represented by actual items of hardware or by draw- 
 ings and photographs of the items. Typically, various sized 
 operators pretend to operate the equipment under the 
 watchful eye of the human factors specialist. The specialist 
 observes behavior, questions the operators, and makes 
 measurements to determine things such as whether there 
 is enough room for the operator to work, whether the oper- 
 ator can reach all the controls and see all the displays, how 
 much of the enviroment around the equipment the operator 
 can see, whether there are safety hazards or bumping and 
 snagging hazards, whether there will be problems getting 
 into or out of the equipment, and whether the equipment 
 is laid out in an optimum manner to facilitate human 
 performance. 
 
 Short of constructing full-scale mockups, evaluations 
 can be made of the engineering drawings of the equipment 
 and workstations by laying two-dimensional, articulated 
 plastic manikins over the drawings. These manikins can 
 be manipulated through typical operator movement pat- 
 
 terns. The manikins come in various sizes that represent 
 various scale models (e.g., one-tenth or one-quarter) of large 
 and small people. Figure 2-8, for example, shows an inex- 
 pensive front-, side-, and top-view manikin (12). A study was 
 
 tram 
 '-Boom 
 swing 
 
 L Stab jack 
 
 Canopy 
 
 Head 
 sump 
 
 Feed 
 *- Power boost 
 — Drill rotation 
 
 Figure 2-7.— Graphic illustration of the results of a link analysis 
 of a roof bolting operation (4). 
 
 Figure 2-8.— Example of an articulated plastic manikin for 
 evaluation of engineering drawings (12). (Courtesy of s.p Rogere Cop.) 
 
17 
 
 made of the body dimensions of low-seam underground coal 
 miners, from which plans were presented for constructing 
 two-dimensional manikins representing small (5th percen- 
 tile), average (50th percentile), and large (95th percentile) 
 male and female miners (1). Such manikins can be used to 
 uncover design deficiencies early in the interface design 
 stage. They should not, however, be considered a substitute 
 for a full-scale mockup evaluation. 
 
 With the growing use of computers to aid the design 
 process, it is not surprising that several systems would be 
 developed to assist in the design of workstation layouts. 
 Most of these were developed within a military context. 
 However, one system, the crewstation assessment of reach 
 program developed for the Naval Air Development Center, 
 is being modified by the Bureau for use in evaluating the 
 design of underground mining equipment. The Bureau's 
 crewstation analysis program (CAP) is intended for use by 
 original equipment manufacturers and mining companies 
 
 for the initial design work on new machines, and to evaluate 
 existing machines. 
 
 By using CAP, a designer can define the workstation 
 (controls, seat, eye position, line of sight, and head clearance 
 point) in three-dimensional space, and provide dimensions 
 of a sample population or an individual. CAP then proceeds 
 to evaluate the workstation with respect to the accommoda- 
 tion of the computer-generated test subjects. 
 
 Most of the analysis sections of CAP require a sample 
 population for testing. CAP allows the user to input either 
 the actual external anthropometric measurements for one 
 or more individuals directly, or to generate a sample popula- 
 tion from the means, standard deviations, and correlations 
 of a set of anthropometric measurements using statistical 
 methods. The external measurements (fig. 2-9) for the sam- 
 ple are transformed into internal link lengths and link cir- 
 cumferences, and are used to create either a link-person or 
 a three-dimensional manikin as shown in figure 2-9. 
 
 Stature 
 
 Hip 
 breadth 
 
 Foot length 
 
 Bideltoid 
 diam 
 
 m-hand 
 ngth 
 
 Sitting, 
 height 
 
 Figure 2-9.— Three-dimensional manikin (left) produced by CAP based on external anthropometric measurement inputs (right). 
 
18 
 
 It is hoped that CAP and similar systems will expedite 
 the incorporation of human factors considerations in the 
 design of mining equipment. The use of such systems allows 
 designers to quickly and inexpensively experiment with 
 alternative design concepts, refining them and testing their 
 adequacy for accommodating the user population. 
 
 Stage 5: Facilitator Design 
 
 During this stage, the designer plans for a set of 
 materials that will encourage acceptable human perform- 
 ance (2). For example, preliminary selection requirements 
 are developed to help insure that people with the proper 
 skills and abilities are chosen to operate and maintain the 
 system. The designer also identifies where instructions, per- 
 formance aids, and training will be needed and best used. 
 (Chapter 9 deals with the development and evaluation of 
 training in the mining environment.) 
 
 Stage 6: Testing 
 
 The last stage of the design process is testing. The 
 development of a system cannot be considered complete 
 unless the system is tested and evaluated to insure that it 
 meets the objectives set forth in stage 1 and does not pro- 
 duce any unintended negative effects. Actually, testing 
 should be conducted throughout the development of the in- 
 terface and facilitator design stages. To wait until a system 
 is complete, before testing it, could result in an enormous 
 waste of resources. The earlier in the process problems are 
 discovered, the less costly it is to correct them. 
 
 Initially, testing is usually carried out in a laboratory 
 setting. These tests are primarily concerned with assess- 
 ing whether the system performs as the engineers expected. 
 Human factors specialists would assess the human perform- 
 ance aspects of the tests and look for potential problems in 
 interface design. Ultimately, the system would be field 
 tested in real-world environments using actual operators 
 and maintainers. Human factors specialists would observe 
 the operation and maintenance of the system, develop ob- 
 jective data collection forms and surveys, and interview the 
 users to assess human factors problems with the design of 
 the system. 
 
 Design and preparation for a field evaluation takes time 
 and thought. Simply putting a new system or piece of equip- 
 ment in a mine and returning in 6 months for opinions is 
 a sure way to kill the best of systems. The test participants 
 must be trained and briefed on the operation of the equip- 
 ment and the purpose of the evaluation. Their cooperation 
 must be solicited, and they must be made to feel a part of 
 the team. Not only should their opinions of the system be 
 collected, but also they must be given the opportunity to 
 suggest ways of improving the system. Further, the system 
 development team must be receptive to the suggestions 
 made. If the system is so far along that no real changes can 
 be made, regardless of the outcome of the field test, then 
 one should seriously question the utility of the test and 
 perhaps even the system itself. The testing stage of system 
 
 development is of prime importance to the design process 
 and not an afterthought performed merely to confirm the 
 obvious. 
 
 DISCUSSION 
 
 As pointed out at the beginning of the discussion of the 
 system design process, most things designed and developed 
 by mining companies do not go through the various stages 
 of design in a rigorous way; and for simple things, it is prob- 
 ably not necessary. Nevertheless, the processes of defining 
 what a system is to do, analyzing the tasks humans will 
 do, designing the interfaces to facilitate human performance 
 and safety, and field testing the system should be part of 
 any design effort, no matter how small or simple it appears 
 to be. The difference between designing a simple system 
 and a complex system should be in the degree of formality 
 and documentation required. The basic steps and considera- 
 tions outlined in this chapter should be incorporated to the 
 degree commensurate with the criticality and complexity 
 of the system being designed. 
 
 REFERENCES 
 
 1. Ayoub, M.M., N.J. Bethea, M. Bobo, C.L. Burford, D.K. Cad- 
 del, K. Intaranont, S. Morrissey, and J.L. Selan. Mining in Low 
 Coal. Volume II: Anthropometry (contract H0387022, Texas Tech 
 Univ.). BuMines OFR 162(2)-83, 1982, 123 pp.; NTIS PB 83-258178. 
 
 2. Bailey, R. Human Performance Engineering: A Guide for 
 Systems Designers. Prentice-Hall, 1982, 672 pp. 
 
 3. Crooks, W.H., K.L. Drake. T.J. Perry. N.D. Schwalm. B.F. 
 Shaw, and B.R. Stone. Analysis of Work Areas and Tasks To 
 Establish Illumination Needs in Underground Metal and Nonmetal 
 Mines. Volume I of II (contract J0387230, Perceptronics, Inc.). 
 BuMines OFR 11KD-81, 1980, 254 pp.; NTIS PB 81-236804. 
 
 4. Foster-Miller Associates. Design and Develop Standardized 
 Controls in Roof Bolting Machines— Preliminary Design (contract 
 H0292041). BuMines OFR 107-80, 1980, 63 pp. 
 
 5. Geer, C. Human Engineering Procedures Guide. U.S. Air Force 
 Aerospace Med. Res. Lab., Wright-Patterson AFC, OH, AFAMRL- 
 TR-81-35, 1981, 239 pp. 
 
 6. Kinkade, R., and J. Anderson (eds.). Human Factors Guide for 
 Nuclear Power Plant Control Room Development. Essex Corp.. San 
 Diego, CA, 1983, 385 pp. 
 
 7. McCormick, E., and M. Sanders. Human Factors in Engineer- 
 ing and Design. McGraw-Hill, 5th ed.. 1982. 615 pp. 
 
 8. Meister, D. Human Factors: Theory and Practice. Wiley Inter- 
 science, 1971, 415 pp. 
 
 9. . Behavioral Analysis and Measurement Methods. Wiley, 
 
 1985, 509 pp. 
 
 10. Sanders, M.S., and G.R. Kelley. Visual Attention Locations 
 for Operating Continuous Miners, Shuttle Cars, and Scoops. 
 Volume I (contract J0387213, Canvon Res. Group Inc. 1 . BuMines 
 OFR 29(l)-82, 1981, 142 pp.; NTIS PB 82-187964. 
 
 11. Simpson, G. and S. Mason. Design Aids for Designers: An 
 Effective Role for Ergonomics. Appl. Ergonomics, v. 14. No. 3. 1983. 
 pp. 177-183. 
 
 12. S.P. Rogers Corp. (Santa Barbara. CA). ADAM. Anthropo- 
 metric Data Application Mannikin. 1976, 5 pp. 
 
19 
 
 CHAPTER 3.— HUMAN CAPABILITIES AND LIMITATIONS 
 
 People are not infinitely adaptable; they have limitations. Recognition of these limitations is a step toward 
 designing for increased safety and productivity. 
 
 In chapter 2 the human-hardware environmental sys- 
 tem was presented. The human as a system component was 
 described as receiving information, processing it, and tak- 
 ing actions based on it. These three functions will serve as 
 the basis for organizing the diverse information in this 
 chapter. In addition to the information reception-processing- 
 .action aspects of humans, their anatomical and biological 
 characteristics also impose limitations and provide capa- 
 bilities that affect system effectiveness. The last section of 
 this chapter will address these topics. 
 
 WHO ARE MINERS 
 
 There has not been much literature describing the 
 characteristics of today's miners. What data exist, however, 
 point toward several consistent trends that are changing, 
 and will continue to change, the composition of the mining 
 workforce. The first trend is that miners are getting 
 younger. For example, the National Research Council of the 
 National Academy of Sciences (23) 1 reports that among 
 
 1 Italic numbers in parentheses refer to items in the list of references at 
 the end of this chapter. 
 
 underground coal miners, those under 30 yr of age increased 
 from 20% of the workforce in 1971 to 41% by 1979. This 
 trend is seen also in the superintendent and supervisor 
 ranks where average ages are dropping. 
 
 The second trend, associated with the first, is that newly 
 hired miners have less mining experience than miners in 
 the past. Companies do not have the substantial pools of 
 experienced miners from which to select, as they did in prior 
 years. 
 
 Today's young miners are also better educated than 
 miners in the past. The President's Commission on Coal 
 (24) estimated that three-fourths of entering miners have 
 at least a high school education, with many (one-third or 
 more) having some education beyond high school. 
 
 The proportion of female miners is also increasing. 
 Reflecting the changing social climate, women are being 
 hired to perform what in the past had been traditionally 
 male-dominated jobs. It is estimated that women will com- 
 pose 10% or more of the mining work force in the near 
 future. 
 
 These trends toward younger, more educated workers, 
 and increasing numbers of women in the workforce have 
 implications for training and equipment design that can- 
 not be ignored. 
 
20 
 
 HUMAN AS AN INFORMATION RECEIVER 
 
 People receive information about their environment 
 through their senses of sight, sound, smell, touch, and taste. 
 People, however, have certain built-in limitations and 
 characteristics that affect the range and amount of infor- 
 mation they can receive. Only the first three senses are 
 discussed in this section. 
 
 Sight 
 
 A simple diagram of the eye is shown in figure 3-1. Light 
 enters the eye through the transparent cornea and passes 
 through a clear fluid called aqueous humor. The light then 
 passes through the pupil, a circular aperture whose size is 
 changed by muscles attached to the iris. The iris is the part 
 of the eye that gives it its characteristic color (blue, brown, 
 etc.). The pupil is the black spot (actually a hole) in the 
 center of the eye. The iris regulates the amount of light 
 entering the pupil by enlarging (dilating) the pupil or by 
 constricting it. Light rays passing through the pupil are 
 refracted (bent) by the lens. The light is bent so that the 
 light rays are brought to focus on the back inside surface 
 of the eyeball called the retina. 
 
 Accommodation 
 
 The lens is adjustable in thickness to permit objects 
 located at different distances to be focused on the retina. 
 This focusing is done automatically by small ciliary muscles 
 attached to the lens. When focusing on objects close to the 
 eye, the muscles contract and cause the lens to increase in 
 thickness. When viewing objects far away, the muscles relax 
 and the lens becomes thinner. This process of changing focus 
 is called accommodation. 
 
 Everyone has an accommodation range; that is, the eye 
 can focus objects within a given range of distances. Objects 
 too close to, or too far away from, the eyes cannot be brought 
 into sharp focus. The shortest distance at which an object 
 can be brought into sharp focus is called the near point, and 
 the longest distance is called the far point. Age has a pro- 
 found effect on the power of accommodation because the lens 
 gradually loses its elasticity; therefore, the near point 
 gradually recedes, while the far point remains more or less 
 the same. (This is why older people who become farsighted 
 hold newspapers at arms' length to read them.) The average 
 near point, in inches, for various ages, as given by Grand- 
 jean (9), is as follows: 
 16 yr..3.2, 32 yr..4.9, 44 yr..9.8, 50 yr..l9.7, 60 yr..39.4. 
 
 The level of illumination is a critical factor in accom- 
 modation. When lighting is poor, the far point moves nearer 
 and the near point recedes, giving a smaller range of ac- 
 commodation. Both speed and precision of accommodation 
 are reduced. Contrast is also important; the more an object 
 stands out against its background, the quicker and more 
 precise the accommodation. This is why signs, to be readable 
 at long distances, should be well lit, clean, and have high- 
 contrast lettering. 
 
 The retina is the heart of the visual process. It is com- 
 posed of two types of light-sensitive receptors called cones 
 and rods. There are 6 to 7 million cones concentrated in an 
 area called the fovea, which is located around the optical 
 axis. This is the area of maximum visual resolution. Cones 
 require relatively high levels of illumination to become ef- 
 fective, and therefore are used primarily for daylight vision. 
 
 Sclerotic coat 
 (sclera) 
 
 Choroid coat 
 (choroid membrane) 
 
 Optic nerve 
 
 Ciliary muscle 
 
 Figure 3-1 .—Diagram Of the eye. (Adapted from reference 9. courtesy of 
 Taylor and Francis Ltd.) 
 
 In addition, cones are sensitive to differences in color and 
 give rise to color vision. 
 
 Outside of the foveal area, the concentration of cones 
 drops off markedly, while the concentration of rods increases 
 dramatically. Although rods are more sensitive to light than 
 are cones, they do not detect fine differences in shape or 
 color. They become the dominant sense receptor in poor 
 illumination. 
 
 Adaptation 
 
 As illumination levels change, the rods and cones must 
 adapt to these changing light levels. This process is called 
 adaptation. With decreasing levels of illumination, sensi- 
 tivity to light increases. Adaptation to darkness (dark adap- 
 tation) takes a comparatively long time. Going from bright 
 daylight into a dark room results in partial adaptation 
 within 5 to 10 min, with full adaptation taking 30 to 60 
 min. Hence, sufficient time must be given to acquire good 
 night vision. 
 
 Light adaptation is much faster than dark adaptation. 
 Initial reductions of 80^ in retinal sensitivity occur in 0.05 
 s, with full adaptation occurring in 1 or 2 min. The implica- 
 tion of this is that, if there is a bright light in an otherwise 
 dark environment, the eye will tend to adapt to that bright 
 light and hence lose sensitivity for viewing the darker 
 surroundings. 
 
 There is another phenomenon (Purkinje shift) related 
 to color perception that occurs as levels of illumination 
 change. At high levels of illumination, the eye is most sen- 
 sitive to green and yellow-green colors. As illumination 
 levels decrease, however, the eye becomes most sensitive 
 to blue-green colors. This is the reason that fire trucks in 
 many communities are painted a greenish shade rather 
 than red. 
 
 Field of Vision 
 
 The field of vision is that part of one's surroundings that 
 can be seen when both the eyes and the head are held still. 
 Figure 3-2 shows the field of vision and also indicates the 
 effect of moving only the eyes, only the head, or both {12). 
 This figure uses the concept of visual angle, which is illus- 
 trated in figure 3-3. Figure 3-3 also presents a formula for 
 computing visual angles of objects at various distances. The 
 further away an object is located, the larger it must be to 
 maintain a constant visual angle. Consideration of the field 
 
21 
 
 of vision is important in designing equipment to help in- 
 sure that needed information and displays can be seen 
 without excessive head movements. 
 
 With the eyes and head stationary, the area of distinct 
 vision is only about 1' of visual angle, corresponding to the 
 foveal region on the retina. Outside this area (middle and 
 outer fields of vision), objects become progressively blurred 
 and indistinct. In the middle field, movement and chang- 
 ing contrasts or levels of illumination are noticed. Objects 
 in the outer field must flicker or move to be noticed. 
 
 15° 15° 
 
 optimum optimum 
 
 35° max 
 
 40°max 
 
 ' 35°max 
 
 15° 
 
 optimum 
 
 Normal line 
 of sight 
 
 15° 
 
 optimum 
 
 EYE ROTATION ONLY 
 
 0° 
 optimum 
 
 65°max 
 
 60°max 
 
 60°max 
 
 Normal line 
 of sight 
 
 35 max 
 
 HEAD ROTATION ONLY 
 
 15° 15° 
 
 optimum y-+-»/ optimum 
 
 90° max 
 
 95°max 
 
 95°max 
 
 NORMAL LINE OF SIGHT 
 
 15° 
 optimum 
 
 Normal line 
 of sight 
 15° 
 
 optimum 
 
 Figure 3-2.— Field of vision and effect of eye and head rota- 
 tion. (Adapted from reference 9, courtesy of Taylor and Francis Ltd.) 
 
 Visual angle 
 
 Object 
 
 \- Length (L) 
 
 To compute angles up to 10° (800'): 
 visua | an,,. . <LǤHU 
 
 ( L and D must be measured in the same 
 units, i.e., inches, centimeters, etc.) 
 
 Figure 3-3.— Illustration of the concept of visual angle. 
 
 Visual Acuity 
 
 Visual acuity is the ability to see fine detail clearly. 
 Actually, there are several types of visual acuity. Minimum 
 separable acuity refers to the smallest space between parts 
 of a target that the eye can detect. This acuity is measured 
 using the standard eye charts consisting of different letters, 
 or "E's" facing different directions. Vernier acuity refers 
 to the ability to distinguish the lateral displacement (or off- 
 set) of one line from another such that if the displacement 
 did not exist, the two lines would form one continuous line. 
 Minimum perceptible acuity is the ability to detect a spot 
 or dot. Stereoscopic acuity refers to the ability to differen- 
 tiate two objects as being different distances from the eyes. 
 
 In all types of visual acuity, the more peripheral a target 
 is in the visual field, the poorer the acuity. The greater the 
 illumination and contrast of a target, the greater will be 
 the acuity. As a point of reference, under good illumina- 
 tion and contrast, the normal minimum separable acuity 
 is about 1 ' of visual angle (this corresponds to 20/20 vision). 
 
 Detection of Movement 
 
 Movement is perceived in two ways. First, a moving 
 object is kept in view by moving the eyes, and the person 
 receives information regarding the object's motion from the 
 eye movements. In the second case the eyes are stationary, 
 and the object's image moves across the retina. Under this 
 condition, the minimum velocity (movement threshold) that 
 can normally be detected is about 1 ' to 2 ' of arc per second. 
 The movement threshold can be reduced by an order of 10 
 if another stationary object is also present in the visual field. 
 This has implications in underground and surface mines 
 where stationary objects may not be visible at night. 
 
 The effect of adding general background illumination, 
 in addition to caplamp illumination, on the detection of mov- 
 ing objects in the peripheral visual field was reported by 
 Martin and Graveling (1 7). For each condition, the mean 
 peripheral detection angle was computed. The results in- 
 dicated an improvement in detection angle by adding only 
 5 lx of background luminance. Figure 3-4 summarizes the 
 
 Caplamp only 
 
 ' ' 
 
 • 1 i i 
 nly 
 
 1 ' 
 
 i i i i 
 
 — i — r- -i i 
 
 W/A 
 
 
 
 5-lx backgro 
 
 und o 
 
 %M^ 
 
 m. 
 
 Caplamp plus 5 lx 
 
 
 /^^^ 
 
 V/ /ft/, 
 
 ^ 
 
 450-lx control 
 
 
 
 
 
 ^^^ 
 
 'W/ 
 
 //// 
 
 Wa 
 
 
 
 
 i i i 
 
 • i 
 
 ii i i 
 
 i i i i 
 
 65 70 75 80 85 90 
 
 MEAN PERIPHERAL DETECTION ANGLE, deg 
 
 Figure 3-4.— Effect of caplamp and background illumination 
 on detection of moving objects in the periphery of the visual field. 
 
 (Adapted from reference 17, courtesy of Butterworth Scientific Ltd.) 
 
22 
 
 results. The 9 ° increase in detection angle, achieved by add- 
 ing background illumination to caplamp illumination, 
 translates into an increase in the visual field of approx- 
 imately 5 ft at a distance of 50 ft. 
 
 Hearing 
 
 Sound originates from vibrations of some source. The 
 vibration causes air molecules to move back and forth, 
 creating corresponding increases and decreases in air 
 pressure. The sound "waves," much like the ripples caused 
 by dropping a rock in a still pond, are sensed by the hear- 
 ing mechanism of the ear. 
 
 Figure 3-5 shows a diagram of the ear divided into three 
 anatomical divisions: outer ear, middle ear, and inner ear. 
 The outer ear consists of the pinna, which collects sound 
 energy and passes it through the auditory canal to the tym- 
 panic membrane (eardrum). The sound waves cause the ear- 
 drum to vibrate. This vibration is transmitted through the 
 middle ear by three, very small, interconnected bones or 
 ossicles (malleus, incus, and stapes). The stapes is attached 
 to the oval window of the cochlea. The cochlea, located in 
 the inner ear, is the organ that transforms the sound vibra- 
 tion into electrical impulses that are transmitted to the 
 brain for interpretation. 
 
 One point worth mentioning is that the air pressure act- 
 ing on the outer ear and middle ear sides of the eardrum 
 should be equal. To achieve this, there is a tube (the 
 eustachian tube) that connects the middle ear to the back 
 of the throat. When a person changes elevation rapidly, as 
 would be the case when descending or ascending a mine 
 shaft, the eustachian tube may close, and pressure may 
 build up on one side of the eardrum. This differential 
 pressure causes the eardrum to stretch and can be quite 
 painful. In addition, the stretched eardrum cannot vibrate 
 freely, and the affected person loses some of his or her sen- 
 sitivity to sound. This loss of hearing can be dangerous if 
 the person depends on sounds to alert him or her of danger. 
 The eustachian tube can usually be opened by chewing, 
 swallowing, or yawning. 
 
 Figure 3-6 illustrates the cochlea as it would appear if 
 one looked into it from the middle ear. The cochlea is filled 
 with fluid, and when the stapes of the middle ear vibrate 
 the oval window, a wave pattern is set up in the fluid. The 
 movements of the fluid force the basilar membrane to 
 vibrate, which in turn forces the small hair cells on the 
 organ of Corti to brush against the tectorial membrane. This 
 stimulates the hair cells, and electrical impulses are sent 
 to the brain. If a person is repeatedly exposed to loud noises, 
 the hair cells can be permanently damaged by hitting 
 against the tectorial membrane. The actual process of how 
 complex sounds are encoded in the cochlea and later inter- 
 preted by the brain is still largely a mystery. Several 
 theories are postulated, but none fully explains the com- 
 plex processes involved. 
 
 Sound Localization 
 
 The position of our ears enables us to tell what direc 
 tion a sound is coming from. This sort of information is ex 
 tremely beneficial in the work environment. Knowing what 
 direction a moving vehicle is coming from, or where the 
 creaks and groans of the "working" roof are emanating 
 from, can mean the difference between life and death. 
 
 The ear uses two cues to determine the location of a 
 sound. The first cue is the difference in time it takes the 
 
 Pinna 
 
 Oval window 
 Inner ear 
 
 Auditory 
 nerve 
 
 Cochlea 
 
 Basilar membrane 
 
 Round 
 window 
 
 Figure 3-5.— Illustration of principal structures of the ear. 
 
 (Adapted from reference 18, courtesy of McGraw-Hill) 
 
 Vestibular 
 
 membrane 
 
 Scala vestibuli 
 (space) 
 
 Tectorial 
 membrane 
 
 Auditory 
 nerve 
 
 Epithelial 
 hair cells 
 
 Organ 
 of Corti 
 
 Scala tympani 
 (space) 
 
 Basilar 
 membrane 
 
 Figure 3-6.— Illustration of the cochlea, looking into it from the 
 middle ear. 
 
 sound to reach each ear. A sound coming from the right side 
 of the listener will reach the right ear a fraction of a second 
 sooner than it reaches the left ear. The second cue is the 
 difference in sound intensity reaching each ear. A sound 
 from the right side of the listener is more intense in the 
 right ear than in the left ear because of the shadowing ef- 
 fect of the head. This is easily demonstrated by adjusting 
 the relative loudness of two speakers in a stereophonic 
 system. For example, increasing the loudness of the right 
 speaker makes the sound appear to move across the room 
 to the right. 
 
 Accurate localization, however, occurs only when the 
 sound source is situated to the right or to the left of the 
 listener. If the head is fixed, front-back and up-down 
 discrimination is poor. It is very important, therefore, that 
 the head be free to move, allowing the person to place the 
 sound source along a left-right line relative to the ears. 
 
 There are several design features that can alter the 
 ability to accurately locate sounds. If the sound is blocked 
 to one ear, localization is poor. For example, if a driver keeps 
 the left window of a vehicle cab down and the right win- 
 dow up, sounds will appear louder in the left ear even if 
 they are coming from the right side of the vehicle. (.This 
 
23 
 
 same phenomenon occurs with operator cabs that are open 
 on only one side.) Sound bounces off surfaces, making it ex- 
 tremely difficult to localize the actual source. This kind of 
 problem is especially acute in underground mines. Finally, 
 if a person has a differential hearing loss in one ear relative 
 to the other, his or her ability to localize sounds will be 
 impaired. 
 
 Tone and Loudness Discrimination 
 
 In the work environment, it is necessary to discriminate 
 between sounds in terms of tone (actually frequency) and/or 
 loudness (intensity). The loudness and tone of roof "talk" 
 can serve as an alert to an impending roof fall. Motor noises, 
 if correctly identified, can indicate mechanical problems. 
 Two types of discrimination can be defined. The first type 
 is a relative judgment in which there is an opportunity to 
 compare two or more stimuli to determine which is louder, 
 higher pitched, or simply whether they differ. The second 
 type is an absolute judgment in which no opportunity ex- 
 ists for comparison. In essence, one must compare the sound 
 to a sound one remembers hearing. In most work situations, 
 discriminations are absolute judgments. Unfortunately, the 
 ability of people to make absolute discriminations between 
 individual stimuli is not very great. In this connection, 
 reference 21 referred to "the magical number seven, plus 
 or minus two" (i.e., five to nine) as the number of absolute 
 discriminations people can make along a single dimension. 
 Thus, one would expect that people can discriminate five 
 or six sounds of different loudness or different tone. If dif- 
 ferent dimensions are combined (e.g., loud and soft inten- 
 sity with high and low frequency), the number of absolute 
 judgments can be increased tenfold or more. 
 
 Masking 
 
 The major limitation of the ear is its relative inability 
 to detect a signal in a noisy environment. When this occurs, 
 the signal is said to be masked by the noise. Masking will 
 be further discussed in chapter 8. 
 
 Effect of Age on Hearing 
 
 As one advances in age, hearing sensitivity declines. 
 The effect is greater for higher frequencies than for lower 
 frequencies. Figure 3-7 shows the deterioration in hearing 
 threshold with age for 1,320 underground coal miners (11). 
 As can be seen, the major loss of sensitivity occurs with fre- 
 quencies above 3 kHz (3,000 Hz). It is at frequencies above 
 3,000 Hz that important speech sounds are contained. Thus, 
 with advancing age, speech comprehension declines. The 
 presence of masking noise makes the situation even worse 
 for older individuals. It should be pointed out that the hear- 
 ing loss pattern observed in the miner population shows lit- 
 tle difference from that of nonminer populations (11). 
 
 Smell 
 
 CD 
 
 ■o 
 
 en 
 c/> 
 o 
 
 _i 
 
 e> 
 
 z 
 
 < 
 UJ 
 
 I 
 
 
 
 1 I 1 II 1 III 
 — Aoft 
 
 
 ^^^^ \<J8-24 
 
 10 
 
 — ~~ — V *"^^\ >v 
 
 
 ^^v \ V25-34 
 
 20 
 
 \v \ \^35-44 
 
 30 
 
 \\V^ 
 
 
 \ V-45-54 
 
 40 
 
 \ v^ 
 
 
 y- 55-64 
 
 50 
 
 \z. 
 
 en 
 
 Ill 1 1 1 1 III 
 
 0.5 I 2 3 
 
 FREQUENCY, kHz 
 
 4 5 6 
 
 Figure 3-7.— Changes in hearing sensitivity with age for 1 ,320 
 
 Underground COal miners. (Adapted from reference 1 1 , courtesy of National In- 
 stitute for Occupational Safety and Health) 
 
 (e.g., coffee, paint, banana, etc.). With respect to identify- 
 ing odors in terms of intensity only, about four different 
 levels can be identified. Another limitation of the sense of 
 smell is that a person adapts to an odor rather rapidly and 
 soon becomes unaware of its presence. 
 
 Many U.S. metal mines use a stench system to alert 
 miners of an emergency; a foul-smelling substance is re- 
 leased into the ventilation system. As will be discussed in 
 chapter 5, the selection and design of such systems are in- 
 fluenced by the limitations of the olfactory sense. 
 
 HUMAN AS INFORMATION PROCESSOR 
 
 In order to process information, three functions must 
 be present: (1) memory, the ability to store information; (2) 
 decisionmaking, the ability to evaluate alternatives and 
 select a course of action; and (3) attention, the ability to at- 
 tend to environmental features and numerous sources of 
 information. 
 
 The sense of smell is relied on to provide information 
 about hazardous things in the work environment such as 
 spilled or leaking chemicals, dangerous fumes, or the 
 presence of fire. The sense organ for smell is a small 2- to 
 3-in 2 patch of cells located in the upper part of each nostril. 
 A sense of smell is not very good when it comes to making 
 absolute identifications of specific odors. Untrained 
 observers can identify approximately 15 to 32 common odors 
 
 Memory 
 
 \ 
 
 Human memory can be conceptualized as consisting of 
 two components, a working memory and a long-term 
 memory. 
 
 Working memory receives inputs from sensory channels 
 (eyes, ears, etc.) and stores a coded representation of that 
 
24 
 
 information. A characteristic of working memory is that in 
 the absence of attention, information will degrade, and any 
 operations performed with this information will deteriorate. 
 
 The fragile nature of working memory can be easily 
 demonstrated. Ask someone to remember three random let- 
 ters (e.g., ZBL) while counting backwards by threes from 
 a given number (e.g., 834). After about 20 s of counting 
 backwards, ask the person to recall the letters. It is doubt- 
 ful whether he or she will be able to do so. The reason is 
 that the act of counting backwards prevents a person from 
 paying attention to the letters in working memory; that is, 
 it prevents rehearsing the letters. This same phenomenon 
 occurs when an instruction is given to an employee, and 
 before the instruction can be carried out, the employee is 
 distracted or receives other instructions. Without time to 
 encode and rehearse the instruction, it is very likely that 
 it will be forgotten. 
 
 Working memory also has a finite capacity for holding 
 information. It is generally recognized that the limit is 
 seven, plus or minus two (i.e., five to nine) pieces of unre- 
 lated information. This means that, from working memory, 
 people can recall five to nine unrelated digits, five to nine 
 unrelated words, or five to nine unrelated sentences. If 
 materials can be grouped into meaningful "chunks," then 
 more items can be recalled. But again, people would be ex- 
 pected to recall only five to nine chunks. For example, ask 
 someone to recall the letter string FB-IJF-KTV. If the let- 
 ters are grouped into meaningful chunks, the task is much 
 simpler; i.e., FBI-JFK-TV. For remembering letters and 
 digits (e.g., equipment part numbers), the optimum size of 
 a chunk appears to be three to four items. Errors can be 
 reduced if part numbers or numeric codes are divided into 
 optimum sized chunks. For example, a designation such as 
 834-431-212 is better remembered than 8-344132-12. 
 
 Some tasks involve receiving or processing a continuous 
 sequence of stimuli. An operator must make a different 
 response to each stimulus or series of stimuli, and he or she 
 is not expected to remember the entire string. Most equip- 
 ment operations are of this sort where a constantly chang- 
 ing sequence of stimuli require different responses. This 
 situation is called a running memory task. If an operator 
 is asked to recall the last few stimulus items, the memory 
 span will be much smaller than five to nine items, and is 
 often no more than two prior items. When trying to recon- 
 struct an accident scenario, it is common for the people 
 watching the sequence of events to be unable to recall what 
 actually happened. (Often, what they relate is what they 
 think should have logically happened, which may or may 
 not be what actually happened.) 
 
 Long-term memory is vast, yet imperfect. No computer 
 in existence can store as much information as is contained 
 in the long-term memory of an average adult. The problem 
 is that much of what is learned is forgotten and much of 
 what is recalled was never learned. What ultimately is 
 stored in long-term memory must first be stored in work- 
 ing memory where it is coded and organized for effective 
 storage in long-term memory. This coding and organization 
 requires that attention be paid to the information in work- 
 ing memory. 
 
 Methods for organizing and coding information can en- 
 hance long-term memory. For example, one method called 
 the method of loci is useful for remembering a list of se- 
 quential items (tasks to perform, instructions to follow). The 
 idea is to attach the items to a spatial map in memory. The 
 first step is to picture a sequence of actions that are per- 
 formed daily; for example, your coming to work. You form 
 
 a mental map; that is, you picture the sequence of events 
 and their location in your mind. You enter the company 
 gate, park the car in the parking lot, walk to the change 
 room, change clothes, get a cup of coffee at the coffee 
 machine, read the bulletin board, etc. The next step is to 
 tie each thing you need to remember to a location on your 
 mental map. This is done by visualizing the thing you need 
 to remember at that location. If the visual images are 
 bizarre, the sequence of things will be easier to remember. 
 When the items need to be recalled, you have only to men- 
 tally traverse your route to work and recall each chunk of 
 information stored at each location. With practice, this 
 technique is very effective because it uses visual imaging 
 to organize information in long-term memory. 
 
 Decisionmaking 
 
 Decisionmaking is a complex process by which people 
 evaluate alternatives and select a course of action. This 
 process involves seeking out information, estimating prob- 
 abilities of outcomes, and attaching values to the potential 
 outcomes. Examples of common types of decisions include 
 deciding what make and model of haulage truck to buy, 
 deciding whether to set a temporary roof support before 
 checking the integrity of the roof, deciding what caused an 
 electrical malfunction in a piece of equipment, and deciding 
 whether to come to work in the morning. 
 
 Unfortunately, people are not optimal decisionmakers 
 and often do not act "rationally;" that is, they do not act 
 according to objective probabilities of gain and loss. There 
 are a number of biases inherent in the way people seek in- 
 formation, estimate probabilities, and attach values to out- 
 comes, and these biases produce what, to some, may appear 
 to be irrational behavior. The following is a short list of 
 some of these biases (33) 
 
 1. People give an undue amount of weight to early evi- 
 dence or information. Subsequent information is considered 
 less important. 
 
 2. People are generally conservative and do not extract 
 as much information from sources as they optimally should 
 extract. 
 
 3. The subjective odds in favor of one alternative or 
 another are not assessed to be as extreme nor given as much 
 confidence as they optimally should be given. 
 
 4. As more information is gathered, people become more 
 confident in their decisions, but not necessarily more ac- 
 curate. For example, people engaged in troubleshooting a 
 mechanical malfunction are often overly confident that they 
 have entertained all possible diagnostic hypotheses. 
 
 5. People have a tendency to seek far more information 
 than they can adequately absorb. 
 
 6. People often treat all information as if it were of equal 
 reliability, even though it is not. 
 
 7. People appear to have a limited ability to entertain 
 more than a few (three or four) hypotheses at one time. 
 
 8. People tend to focus on only a few critical attributes 
 at a time and consider only about two to four possible choices 
 that are ranked highest of those few critical attributes. 
 
 9. People tend to seek information that confirms the 
 chosen course of action and to avoid information or tests 
 whose outcome would contradict the chosen course of action. 
 
 10. A potential loss is viewed as having greater conse- 
 quence, and therefore exerts a greater influence over deci- 
 sionmaking behavior than does a gain of the same amount. 
 
 11. People believe that mildly positive outcomes are more 
 likely than are mildly negative outcomes, but that highly 
 
25 
 
 positive outcomes are less likely than are mildly positive 
 outcomes. 
 
 12. People tend to believe that highly negative outcomes 
 are less likely than are mildly negative outcomes. 
 
 These biases explain, in part, why some workers will 
 engage in obviously dangerous behaviors to get a job done 
 faster or with less effort. These people do not perceive the 
 probability of serious injury to be as high as it might actu- 
 ally be, but are certain that they will gain by reducing the 
 time and/or effort required to do the job. They also tend not 
 to seek information that would contradict their perceptions 
 of the situation. 
 
 Attention 
 
 Attention in human information processing is used in 
 two different ways. The first is as a searchlight in which 
 various features of the environment are attended. In some 
 situations, one aspect or task must be attended and other 
 distracting stimuli ignored; this is called focused attention. 
 In other situations, numerous sources of information or 
 multiple tasks must be attended; this is called divided at- 
 tention. In both cases humans have limitations. Distractions 
 are caused by irrelevant stimuli, or not everything can be 
 attended, thereby important information, is missed. Under 
 stress or high levels of arousal (e.g., during an emergency), 
 fewer sources of information are attended, concentration 
 is given those thought most important. 
 
 A special problem related to maintaining attention oc- 
 curs when operators must perform a monotonous, repetitive 
 task, yet stay alert to infrequent but critical events. This 
 type of situation is called a vigilance task. The classic ex- 
 ample is a control room operator who monitors dials and 
 
 displays for hours on end, waiting for something to go 
 wrong. As time passes, the probability increases that the 
 operator will miss a signal or critical event. This inability 
 to maintain alertness is evident after the first 30 min. This 
 decrement is made worse if the operator is tired, or the task 
 is performed in an unfavorable environment of high tem- 
 perature and humidity. It was recognized (19) that surface 
 mine haulage-truck drivers work in a situation that is con- 
 ducive to a decrement in vigilance performance. The load- 
 haul-dump-return cycle is highly repetitive, and little 
 stimulation is received from driving in circles in an open- 
 pit mine (fig. 3-8). This lack of alertness makes the driver 
 unable to quickly respond to an unexpected situation and 
 more likely to make inappropriate actions to maintain the 
 truck on the roadway (e.g., steering corrections). 
 
 The second use of the term "attention" is as a resource. 
 When performing any task, different mental operations re-' 
 quire some amount of a person's limited processing resource. 
 Doing more than one task at a time (e.g., divided attention) 
 requires more resources than doing a single task. Atten- 
 tion, as a resource, is required to keep information in work- 
 ing memory, to obtain information from environmental 
 sources, and to perform mental operations on that informa- 
 tion. It is in this sense that attention is the "glue" that holds 
 the entire information-processing function together. 
 
 In general, the more similar two tasks are, the more 
 they compete for the same resources and the greater the 
 interference. It is much harder to read two different mes- 
 sages at the same time than it is to read one and listen to 
 the other. The more difficult the tasks, the greater the de- 
 mand on resources, and the less efficient is the ability to 
 do both tasks at the same time. A trolley operator can drive 
 the trolley and easily converse with a dispatcher on a 
 
 
 Figure 3-8.— The load-haul-dump-return cycle in surface mining creates a situation highly conducive to lapse 
 in attention and alertness. 
 
26 
 
 straight, clear track. As the operator goes through intersec- 
 tions, multiple switches, or dangerous sections of track, 
 however, his or her conversation with the dispatcher will 
 deteriorate. 
 
 Mental workload is a concept that relates to the dif- 
 ference between the attentional resources available and the 
 demands placed on those resources by the tasks being per- 
 formed. Hence, mental workload can increase if an oper- 
 ator's capacity is reduced or if task demands are increased. 
 There have been numerous studies aimed at developing 
 measures of mental workload, including subjective evalua- 
 tions of workload, physiological measures, and performance 
 measures. Although many seem promising, no single 
 measure has emerged as the standard, nor is this likely to 
 happen. Mental workload appears to be a multifaceted con- 
 cept that probably cannot be adequately captured by a 
 single measure. 
 
 HUMAN AS ACTION TAKER 
 
 When humans react to stimuli by making responses, 
 they are concerned with the speed with which the response 
 is made and the accuracy of that response. Response time 
 can be divided into two components: reaction time and 
 movement time. Reaction time is the time from onset of a 
 stimulus to initiation of a response. Movement time is the 
 time from initiation of response to completion of the re- 
 sponse. For example, a person stepping into the path of a 
 vehicle would be a stimulus to the driver of that vehicle. 
 The driver must sense the stimulus, process the informa- 
 tion, and select a response (e.g., turn the wheel or hit the 
 brake). These activities take time and constitute reaction 
 time. The driver must then execute the action, e.g., lift his 
 or her foot and depress the brake pedal. The time required 
 to lift the foot, move to the brake, and depress the brake 
 would be the movement time. 
 
 Reaction Time 
 
 Reaction time is influenced by numerous factors. To 
 organize the discussion of some of the more important ones, 
 reaction time will be divided into three components: stim- 
 ulus reception time, processing time, and response selec- 
 tion time. The overall mean reaction times of coal miners 
 to a stimulus light was found to be 0.259 s (3). The coal 
 miners were alerted before the light came on, and hence, 
 this value probably represents the lower bound estimate 
 for overall reaction time to a simple stimulus among miners. 
 Under more realistic conditions, however, reaction times 
 can be 10 times as long. 
 
 Stimulus Reception Time 
 
 The time it takes to perceive a stimulus depends only 
 slightly on the sense modality (seeing, hearing, touching, 
 etc.), but depends heavily on the intensity of the stimulus. 
 Auditory and touch reaction times are approximately 0.15 
 s; vision and temperature reaction times are 0.2 s; smell 
 reaction time is 0.5 s; and pain and task reaction times are 
 1.0 s. 
 
 For visually presented stimuli, the location in the field 
 of vision is also an important determinant of reaction time. 
 Reaction time is much faster to stimuli in the line of sight 
 than it is to stimuli located in the periphery of the visual 
 field. Anything that can make the stimulus more conspic- 
 
 uous, such as increased size, brightness, contrast, and dura- 
 tion, will decrease reaction time. Flashing lights are also 
 responded to faster than are steady lights, especially if they 
 are located in the periphery of the visual field. 
 
 Processing Time 
 
 Once a stimulus is received, it must be processed and 
 a decision made to respond or not to respond to it. A major 
 variable affecting processing time is the temporal uncer- 
 tainty of the stimuli; that is, if a person knows when a 
 stimulus will occur, reaction time is faster. For example, 
 one study found that reaction time for braking an auto- 
 mobile in response to an anticipated auditory stimulus was 
 0.54 s, while braking in response to an unanticipated stim- 
 ulus was 0.73 s (15). Another factor that influences process- 
 ing time is whether a person is engaging in another task 
 that could compete for attentional resources. In one study 
 (26), reaction times of up to 2.5 s were found for responding 
 to warning lights in the periphery while simultaneously per- 
 forming a tracking task. This is very close to the results 
 obtained by Summala (27), wherein the steering response 
 to the onset of a light at the side of the road was measured. 
 Subjects were not aware that they were in an experiment 
 and were totally unexpectant of the stimulus. The average 
 steering response (toward the center of the road) started less 
 than 2 s after the onset of the light, reached its halfway 
 strength at 2.5 s, and reached its maximum response at a 
 little more than 3 s. Thus, reaction times in the operational 
 environments should not be expected to be less than 2.5 s, 
 and design should probably be for reaction times of 3.0 s. 
 A haulage truck, for example, going 20 mph will travel 
 about 90 ft in 3 s. 
 
 Response Selection Time 
 
 Once a stimulus has been processed, an appropriate re- 
 sponse must be selected. The more choices available to a 
 person, the longer the reaction time. Figure 3-9 shows the 
 results of one study (5) that measured reaction time as a 
 
 2 3 4 5 6 7 
 CHOICES 
 
 S 
 
 Figure 3-9.— Reaction time as a function of the number of 
 
 response Choices available. (Based on data presented s> Dame- s 
 
27 
 
 function of the number of choices available. Another 
 variable that is important is whether a response is compati- 
 ble with a stimulus. The more compatible a response is' to 
 a stimulus, the faster the reaction time. (Compatibility is 
 discussed in more detail in chapter 6.) 
 
 or tapping. Probably the most important aspect of repetitive 
 movements is that such work requires pauses from time to 
 time, and it is difficult to maintain a constant rhythm over 
 time without rest breaks. 
 
 Movement Time 
 
 Factors affecting movement time include the distance 
 traveled, direction and type of movement, load being moved, 
 and type of action taking place at the end of the movement. 
 It has been estimated (32) that a minimum movement time 
 of about 0.3 s can be expected for most control activities. 
 If one adds this time to the simplest reaction time of about 
 0.2 s, the minimum control activation time (reaction plus 
 movement time) is approximately 0.5 s. 
 
 Generally, horizontal hand movements are faster than 
 vertical hand movements, and continuous curved motions 
 are faster than abrupt direction changes. Movement time 
 is not linearly related to distance traveled because higher 
 movement velocities (inches per second) can be attained 
 with longer movements than with shorter movements. 
 Generally, reaction time using the hand is approximately 
 20% faster than using the foot, and the preferred hand is 
 approximately 3% faster than the nonpreferred hand (14). 
 These sorts of considerations, of course, have implications 
 for the layout of equipment controls where speed of opera- 
 tion is critical. 
 
 Movement Accuracy 
 
 Several types of movements can be distinguished: posi- 
 tioning movements, continuous movements, and repetitive 
 movements. 
 
 Positioning Movements 
 
 Reaching for something or moving an object to another 
 location are examples of positioning movements. Accuracy 
 of blind positioning movements was assessed by Fitts (7), 
 and the results indicated that people are most accurate in 
 blind positioning if a target is straight ahead. Accuracy 
 decreased as the target moved to more peripheral positions 
 and was better for targets at and below shoulder height than 
 for those above shoulder height. In many mining situations, 
 operators are required to reach for a control without look- 
 ing at where they are reaching. To avoid groping or con- 
 tacting the wrong control, controls that will be operated 
 blindly should be placed in front of the operator, at a below- 
 shoulder height. 
 
 Continuous Movements 
 
 Continuous movements require accurate control over 
 the entire movement, as for example in drawing a line on 
 a piece of paper. One study of tremor in arm movements 
 (20) found that tremor was significantly greater (four to six 
 times) if the arm movements were in-out (away from-toward 
 the body) than if they were up-down or right-left. 
 
 Repetitive Movements 
 
 Repetitive movements involve successive performance 
 of the same action over and over, such as in crank turning 
 
 ANATOMICAL CHARACTERISTICS 
 
 It is no surprise to anyone that human bodies come in 
 a variety of sizes and shapes. The science of measuring body 
 dimensions is called anthropometry. Anthropometric data 
 are essential for designing equipment and workspaces that 
 will accommodate the worker population. Anthropometric 
 data include body dimensions and range of movement. 
 Before presenting some of the basic anthropometric data, 
 a review of some basic concepts and some of the limitations 
 of using such data is given. 
 
 Percentiles 
 
 Anthropometric data are usually reported as percen- 
 tiles; e.g., the 95th percentile standing height for male low- 
 seam coal miners is 73.7 in. Percentiles indicate the percen- 
 tage of a particular population that have values less than 
 the value given. Thus, it is known that 95% of male low- 
 seam coal miners are less than 73.7 in tall and 5% are 73.7 
 in or taller. The most commonly reported percentiles are 
 the 5th, 50th, and 95th. The 5th percentile value is the small 
 person, as only 5% of the population have values smaller 
 than the 5th percentile value. The 50th percentile value 
 represents the "average" person; half the population have 
 values less than the 50th percentile value and half have 
 values equal to or greater than the 50th percentile value. 
 The 95th percentile value, of course, represents the large 
 person. 
 
 When equipment or workstations are designed, they are 
 usually designed for the 5th to 95th percentile values, that 
 is, the middle 90% of the population. The reasons for this 
 is that accommodation of the extreme 5% at each end of a 
 distribution requires a disproportionate range of adjusta- 
 bility in a workspace. For example, the 5th to 95th percen- 
 tile sitting height spans a range of 4.2 in. The 1st to 99th 
 percentile sitting height, however, spans a range of 6.0 in. 
 Therefore, to accommodate the extra 10% of the population, 
 vertical seat height adjustment would have to be increased 
 almost 43%. 
 
 Fallacy of the "Average" Person 
 
 The term "average size" is often used, but in reality no 
 one is average on more than one or two body dimensions. 
 That is, a person who is average in overall standing height 
 may have short legs and a long upper torso, or long legs 
 and a short upper torso. Short people may have long arms, 
 and tall people may have short arms. In a classic study (10), 
 not a single person among 4,000 Air Force men could be 
 found within ±30% of the mean on 10 body dimensions. 
 
 The fact that the smallest person is not necessarily the 
 smallest on all dimensions, that the average height person 
 is not necessarily the average on all dimensions, and that 
 the largest person is not necessarily the largest on every 
 dimension has important implications for using anthro- 
 pometric data in design. First, one cannot simply add 
 dimensions together and expect to arrive at the correct 
 percentile value. For example, adding the 5th percentile 
 
28 
 
 fingertip-to-elbow length to the 5th percentile elbow-to- 
 shoulder length will not yield the 5th percentile fingertip- 
 to-shoulder length. The correct procedure is more com- 
 plicated, requires additional information, and is beyond the 
 scope of this report. 
 
 Second, if individual dimensions are used to design 
 workspaces, a larger proportion of the population will be 
 excluded than would be expected. For example, if an oper- 
 ator's compartment was designed so that hand controls and 
 foot controls could be reached by the 5th percentile person, 
 more than 5% of the population would not be able to reach 
 either the foot controls or hand controls, or both. The reason, 
 of course, is that the 5% excluded from reaching the foot 
 controls are not necessarily the same 5% excluded from 
 reaching the hand controls. If several individual 5th and 
 95th percentile dimensions are used, the proportion of the 
 population that would be excluded could be over 50%. 
 
 Other Limitations of Anthropometric Data 
 
 There are two classes of anthropometric data: static and 
 dynamic. Static anthropometric data are collected on sub- 
 jects who assume erect, rigid postures and are wearing no 
 clothes or only the minimum required for modesty. These 
 postures are not often those actually assumed in the work 
 environment. People do not sit erect when operating equip- 
 ment. Arm length is not an accurate measure of reach dis- 
 tance because it does not take into consideration extending 
 the shoulder, bending the waist, and twisting the torso. 
 Thus, one must be careful in applying static anthropometric 
 data to designing a real workplace. Dynamic anthropo- 
 metric data take into account normal work postures and 
 the interaction between body parts that affect movements 
 and reaches. Unfortunately, there are far less dynamic data 
 available than there are static data. 
 
 Virtually all static anthropometric data are collected 
 on people clothed in less than normal working attire. Winter 
 garments, gloves, heavy boots, etc., are usually not worn 
 when the measurements are taken. The designer, therefore, 
 must increase dimensions to accommodate any additional 
 clothing and any restriction in movement caused by the 
 wearing of such clothing. 
 
 There is an enormous amount of static anthropometric 
 data available on all sorts of populations, including truck 
 drivers, coal miners, and flight attendants. By far, the most 
 comprehensive data base is from the military. The impor- 
 tant point is that there can be systematic differences in body 
 dimensions between different occupational groups. For ex- 
 ample, underground low-seam coal miners were measured 
 and the results were compared with those of military per- 
 sonnel and long-distance truck drivers (2). The results 
 showed that male miners were significantly heavier and 
 tended to have larger circumferences of the torso, arms, and 
 legs than did the comparison populations. The miners, 
 however, did not differ reliably from the comparison groups 
 in terms of linear dimensions (i.e., height, arm length, leg 
 length, etc.). Female low-coal miners were found to have 
 larger shoulder, waist, biceps, and thigh circumferences 
 than did the comparison populations, but again linear 
 dimensions did not differ. 
 
 It is important, therefore, that the designer choose a 
 data base that closely represents the worker population for 
 which he or she is designing. Based on Ayoub (2), it seems 
 
 safe to use military personnel data for most design prob- 
 lems, keeping in mind the increased circumferences for 
 miner populations. 
 
 Static Anthropometric Data 
 
 Appendix A contains static anthropometric data for 
 male and female military populations (30). In using the data 
 for mining applications, one must keep in mind its limita- 
 tions. Allowances must be made for clothing, including 
 heavy jackets, hardhats, battery packs and self-rescue units 
 (for underground miners), and boots. Standing and sitting 
 heights will be increased, and clearance spaces will have 
 to be enlarged to accommodate the added bulk from clothing 
 and personal protective equipment. The data in appendix 
 A, therefore, should be considered as estimates and used 
 as rough indicators for equipment and workspace design. 
 
 Range of Movement 
 
 The human body is not infinitely flexible. Joints impose 
 limits on the range of movements possible— elbows pivot in 
 one direction only but shoulder joints can rotate in all direc- 
 tions. The range of a joint movement is measured in degrees 
 of angular motion. Appendix B contains data on common 
 joint movements, including the 5th and 95th percentile 
 range of movement for both males and females (32). The 
 data are based on college-aged subjects. From ages 20 to 
 60, the decline in range of movement is only about lO^r . 
 
 Reach Envelopes 
 
 The combination of joint mobility and anthropometric 
 dimensions define the envelope within which a person can 
 reach objects. In addition to mobility and anthropometrics, 
 the posture assumed by a person, the clothes worn, and the 
 actual manipulative task to be performed influence the 
 reach envelope. For example, the more reclined the sitting 
 posture, the shorter the arm reach envelope in the forward 
 direction. If a person simply has to activate a pushbutton 
 with his or her fingertips, the reach envelope will be 2 to 
 3 in. longer than if a knob must be grasped. A hand-grasp 
 manipulation reduces the reach envelope an additional 2 
 to 3 in (4). A winter jacket, zipped up, can also reduce reach 
 envelopes by 2 to 3 in (25). 
 
 Figure 3-10 shows a representative three-dimensional 
 reach envelope (18). Several hand positions were used to 
 generate the data. The cross-hatched areas represent those 
 areas that were reached by all hand motions studied (6). 
 
 In addition to reaching controls with the arm, the foot 
 is also used to activate controls. Foot-reach envelopes are 
 much more constraining than are arm-reach envelopes. 
 Figure 3-11 shows optimal and maximal vertical and for- 
 ward pedal-reach envelopes for seated operators (28). The 
 data assume a horizontal seat pan and pedals that do not 
 require excessive force for activation. If high levels of force 
 are required, the pedals should be moved closer to the seat 
 reference point, the point of intersection of the centerline 
 of the seat back and the centerline of the seat pan. The max- 
 imum areas indicated in figure 3-11 require quite a bit of 
 thigh and/or leg movement and hence should be avoided 
 for frequently used pedals. 
 
29 
 
 TOP 
 
 _Ti§^=. ^>^ T 
 
 T|gj \ T 
 
 -imm-J-2 
 
 FRONT 
 
 7 / \ \ 
 
 i m ¥y. I= 
 
 \ ■" 2§ t 
 
 ^— i^ ^^.2 
 
 
 SIDE 
 
 
 
 
 
 '"V 
 
 \ 
 
 
 
 
 
 
 \ 
 
 
 
 
 
 TV 
 
 
 
 
 
 f l) 
 
 V^ 
 
 1 
 
 % 
 
 h— ™ 
 
 .«• 
 
 W 
 
 Note: Grid lines represent 6 in 
 
 Figure 3-10.— Arm reach envelope for movements using a 
 number of hand-grasp positions in three-dimensional space 
 (cross-hatched areas depict regions reached under all conditions 
 
 Studied). (Adapted by McCormick and Sanders (73) from reference 6, courtesy of 
 McGraw-Hill) 
 
 Strength 
 
 Strength is defined as the maximal force muscles can 
 exert isometrically (against a fixed object) in a single, volun- 
 tary effort ( 16). The measured strength depends on the in- 
 trinsic muscle strength of a person, as well as the person's 
 motivation and the specific instructions given the person 
 as to how to exert the force. Figure 3-12 presents 5th percen- 
 tile arm strength data for four directions of motion at five 
 arm positions (13). As can be seen, pull-and-push movements 
 are strongest, and up-and-down movements are weakest. 
 
 Strength data are important to designers so that con- 
 trols and manual tasks are not designed to require more 
 force than can be exerted by workers. Traditionally, 5th 
 percentile values are used for design standards to insure 
 that a task can be performed by 95% of a population. 
 
 Strength is related to age and sex. Maximum strength 
 is reached in the middle to late twenties and declines slowly 
 but continuously from then on. At age 65, strength is about 
 75% of what it was in the prime years. Women generally 
 have less muscle strength than men. Overall, women's 
 strength is about 66% of that of men; the exact percentage, 
 however, is dependent on the specific muscle group meas- 
 ured and ranges from 50% to 80%. 
 
 It is important to keep in mind that most muscular ac- 
 tions relevant to a job require the integrated exertion of 
 many muscle groups. For example, pushing a pedal requires 
 turning the ankle and extending the knee and hips, while 
 
 15 
 
 -i r^n r— 
 
 Maximum area for 
 -• — Toe -operated controls 
 -a — Heel -operated controls 
 
 I 
 
 Near high 
 toe 
 
 Far high 
 toe " 
 
 KEY 
 Optimum area for 
 
 - Toe-operated controls 
 
 — Heel-operated controls 
 
 Floor 
 
 25 30 35 40 45 50 15 20 25 30 35 
 DISTANCE FORWARD OF SEAT REFERENCE POINT, in 
 
 45 
 
 Figure 3-11.— Foot reach envelopes for various types Of pedal operations. (Adapted by McCormick and Sanders (78) from reference 6, courtesy of 
 McGraw-Hill) 
 
30 
 
 ► Push 
 
 60 90 120 150 180 
 
 ELBOW ANGLE, deg 
 
 Figure 3-12.— Arm strength data. Shown are 5th percentile values for four directions of movement (up, down, pull, push) at five 
 
 arm positions. (Adapted by McCormick and Sanders (18) from reference 13, courtesy of McGraw-Hill) 
 
 stabilizing the pelvis and trunk on the seat. Reference 25 
 collected the maximum forces that truck drivers could exert 
 on pedals and the maximum torque that could be exerted 
 on a 22-in-diameter steering wheel. Figure 3-13 summarizes 
 the data as a function of time. Drivers were told to hold their 
 maximum exertion for 15 s. 
 
 Endurance 
 
 Endurance refers to the ability to continue exerting a 
 force over time. Unfortunately, the ability to hold maximum 
 forces is rather limited. The higher the force applied, 
 relative to the maximum force possible, the shorter the en- 
 durance time. Maximum exertions can only be held for a 
 few seconds, but an exertion that is 25% of maximum can 
 be held for several minutes. This relationship is shown in 
 figure 3-14. Reference 25, for example, found that the mean 
 maximum force dropped 12% to 15% in just 5 s, and after 
 15 s had decayed 21% to 24%. 
 
 Circadian Rhythms 
 
 The human body, contrary to popular belief, does not 
 maintain an utterly constant, homeostatic internal environ- 
 ment. It is now generally accepted that there are regular, 
 
 significant fluctuations througout the day in almost every 
 physiological measure. These fluctuations take on a rhythm 
 that repeats roughly each day, and therefore the term "cir- 
 cadian rhythms" has been coined to describe them. (The 
 term "diurnal rhythms" is also used.) 
 
 One of the more easily measured circadian rhythms is 
 that of body temperature. Body temperature does not re- 
 main constant at 98.6° F, but fluctuates about 1 ° F through- 
 out the day. Figure 3-15 shows the typical temperature cir- 
 cadian rhythm with the minimum value occurring in the 
 early hours of the morning, followed by a pronounced rise 
 over the early working hours, with a slower rise over the 
 rest of the day, and finally reaching a peak in the early 
 evening. 
 
 These biological circadian rhythms are internally reg- 
 ulated, but can be influenced by the external environment. 
 For example, the temperature rhythm can be shifted by 
 altering the sleep-wake cycle. The important fact about 
 these circadian rhythms is that they are correlated with 
 performance. For simple perceptual and motor skills, per- 
 formance closely follows the body temperature rhythm, with 
 lower performance between midnight and 8:00 a.m. and 
 peak performance in the late afternoon and early evening. 
 Tasks that show this cycle include visual scanning tasks 
 where a person is searching for targets (e.g., the type of task 
 
31 
 
 300 
 
 £ 200 
 
 T 
 
 95th percentile 
 
 50th percentile 
 
 5 th percentile 
 
 99.68 
 
 Max 
 
 5 10 
 
 TIME,s 
 
 Figure 3-13.— Maximum force exerted on a foot pedal and max- 
 imum torque applied to a 22-in-diameter steering wheel by truck 
 
 drivers. (Adapted from reference 25) 
 
 4 6 
 
 TIME,min 
 
 Figure 3-14.— Endurance time as a function of the force main- 
 tained (16). (Copyright 1970, by the Human Factors Society, Inc., and reproduced 
 by permission) 
 
 98.60 
 
 12 2 4 6 8 10 12 2 4 6 8 10 12 
 
 t- am. 14- p.m. H 
 
 TIME 
 
 Figure 3-15.— Typical circadian rhythm for body temperature. 
 
 (Adapted from reference 22, copyright 1983, by John Wiley & Sons Ltd., and reprinted by 
 permission) 
 
 a haulage truck operator would perform); physical tasks 
 such as manual materials handling; and reaction time 
 tasks. It was found by Monk and Folkard (22), however, that 
 tasks involving high working memory loads show a very 
 different time-of-day trend. These sorts of tasks would in- 
 clude immediate recall of materials presented as prose (as 
 in a book). In the case of these tasks, performance declines 
 over the normal working day, with poorest performance in 
 the early evening— almost the exact opposite of that found 
 for simple perceptual motor tasks. This indicates that dif- 
 ferent biological clocks may be involved with these two 
 types of functions. 
 
 Physiological Adjustment 
 
 When people alter their sleep-wake patterns, as when 
 they change work shifts, the circadian rhythms slowly ad- 
 just to the new schedule. This process of adjustment takes 
 a considerable amount of time, up to 12 days in the case 
 of the temperature rhythm. However, it does not take much 
 time to readjust the temperature rhythm to a normal day- 
 wake, night-sleep pattern. This readjustment can occur in 
 1 or 2 days. There is evidence that the biological clock 
 related to simple perceptual motor performance adjusts to 
 change slowly, while the clock related to complex mental 
 activity changes rapidly. 
 
32 
 
 Shift Work 
 
 DISCUSSION 
 
 Circadian rhythms impose certain biological limitations 
 on performance. These limitations are most important in 
 the context of shift work. It was reported by Tasto and Col 
 ligan (28) that 30% of miners were shift workers. Among 
 metal miners, the percentage on late shifts (second or third) 
 was approximately 40%. 
 
 Three basic types of shift schedules can be distinguished: 
 
 (1) permanent, where people always work the same shift; 
 
 (2) rapidly rotating, where people never have more than one 
 or two shifts in a row before changing to a different time; 
 and (3) slowly rotating, where people work one shift for a 
 week or more before changing. There seems to be two 
 schools of thought with regard to which system is preferred. 
 One school of thought advocates permanent shifts to max- 
 imize physiological adjustment. To be effective, however, 
 the workers must maintain their sleep-wake habits during 
 their days off. The second school of thought advocates rap- 
 idly rotating shifts so that no adjustment of the rhythms 
 occur. It is believed that the constant adjustment and re- 
 adjustment in permanent shift workers who revert to a nor- 
 mal day shift during their days off is more harmful than 
 if they work a few days totally out of synchronization with 
 their circadian rhythms. The disadvantages of this approach 
 are (1) night-shift performance involving simple perceptual 
 motor skills will be impaired; and (2) a sleep debt may 
 quickly build up, thus requiring 2 or 3 days off after each 
 short run of night work. It should be pointed out that if the 
 work at night involves complex memory and mental proc- 
 essing tasks, a rapidly rotating shift would result in better 
 performance than a permanent shift schedule because per- 
 formance on such tasks is best when out of synchronization 
 with the circadian rhythm. 
 
 With respect to mining, most tasks are probably of a 
 simple perceptual motor nature. For example, field studies 
 of shift work performance have found that error frequency 
 in reading meters (2), in nodding off while driving (22), and 
 in train drivers missing warning signals (8), is higher on 
 night shifts than it is on day shifts. Permanent shift sched- 
 ules would probably be best under such conditions, given 
 that workers try to maintain their sleep-wake patterns dur- 
 ing their days off, and that adequate sleep is obtained. It 
 should be pointed out that none of the experts endorse a 
 slowly rotating shift system. This is considered the worst 
 of both worlds. 
 
 The major detrimental effects of shift work are sleep 
 loss, disruption of social and family life, and increased 
 gastro-intestinal problems. It must be pointed out, however, 
 that not all studies are unanimous on these disadvantages. 
 Some report advantages of being home during the day with 
 family, and some report no gastro-intestinal problems. Sleep 
 loss, however, appears to be fairly common. As with so many 
 situations, shift work appears to take a heavy toll on some 
 workers, while others appear unaffected or may even prefer 
 it to "normal" work hours. For mining companies using 
 shift work, it is important to recognize the potential nega- 
 tive effects and select workers and a shift schedule to min- 
 imize these negative aspects. Shift workers, for example, 
 get about 25% less sleep than their day-working counter- 
 parts (29). There appears to be little evidence, however, that 
 life expectancy is reduced by shift work, or that sickness 
 is increased among shift workers. 
 
 In this chapter, an enormous amount of information and 
 data have been presented concerning limitations and cap- 
 abilities of humans as information receivers, processors, and 
 action takers. Some of this information has direct relevance 
 to mining, while much of it forms the basis for the design 
 recommendations contained in subsequent chapters. 
 
 The intent was not to provide an exhaustive discussion 
 of human capabilities and limitation, but rather to illustrate 
 the range of factors and abilities that affect human perfor- 
 mance. This basic background information should aid in 
 appreciating the following chapters on information displays, 
 controls, tools, equipment design, physical work, etc. When 
 people's capabilities are exceeded because of the task, equip- 
 ment, and/or environment, errors increase, accident fre- 
 quency increases, and productivity declines. People are not 
 infinitely adaptable; they have limitations, and recognition 
 of these limitations is a step toward designing for increased 
 productivity and safety. 
 
 REFERENCES 
 
 1. Ayoub, M.M., N.J. Bethea, M. Bobo, C.L. Burford. D.K. Caddel, 
 K. Intaranont, S. Morrissey, and J.L. Salan. Mining in Low Coal. 
 Volume II: Anthropometry (contract H0387022, Texas Tech Univ.). 
 BuMines OFR 162(2)-83, 1982, 123 pp.; NTIS PB 83-258178. 
 
 2. Bjerner, B., and A. Swensson. Shiftwork and Rhythm. Acta 
 Med. Scand., Suppl. 278, 1953, pp. 102-107. 
 
 3. Bobo, M., C. Burford, M. Ayoub, and K. Intaranont. Hazar- 
 dous Occupations Showni Not To Increase Performance Times. Occu- 
 pational Health and Safety, Mar. 1984, pp. 59-61. 
 
 4. Bullock, M. The Determination of Functional Arm Reach Boun- 
 daries for Operation of Manual Controls. Ergonomics, v. 17, 1974, 
 pp. 375-388. 
 
 5. Damon, A., H. Stoudt, and R. McFarland. The Human Body 
 in Equipment Design. Harvard Univ. Press, 1966, 231 pp. 
 
 6. Dempster, W. Space Requirements of the Seated Operator. U.S. 
 Air Force Wright Air Develop. Center, Dayton, OH, TR-55-159. 
 1955, 187 pp. 
 
 7. Fitts, P. A Study of Location Discrimination Ability. Ch. in 
 Psychological Research on Equipment Design, ed. by R. Fitts. Army 
 Air Force Aviation Psychology Program, Dayton. OH. RR-19. 1947, 
 pp. 87-113. 
 
 8. Folkard, S., T. Monk, and M. Lobban. Short and Long Term 
 Adjustment of Circadian Rhythms in "Permanent"' Night Nurses. 
 Ergonomics, v. 21, 1978, pp. 785-799. 
 
 9. Grandjean, E. Fitting the Task to the Man: An Ergonomic Ap- 
 proach. Taylor and Francis, 1981, 379 pp. 
 
 10. Hertzberg, H. Dynamic Anthropometry of Working Positions. 
 Human Factors, v. 2, 1960, pp. 147-155. 
 
 11. Hopkinson, N. Prevalence of Middle Ear Disorders in Coal 
 Miners. NIOSH, Cincinnati, OH, DHHA-PN-81-101. 1981. 39 pp. 
 
 12. Human Engineering Laboratory Detachment, U.S. Army 
 Missile Command (Redstone Arsenal, ALl Human Engineering 
 Design Data Dig., June 1978, 149 pp. 
 
 13. Hunsicker, P. Arm Strength at Selected Degrees of Elbow 
 Flexion. U.S. Air Force Wright Air Develop. Center. Davton. OH. 
 TR 54-548, 1955, 87 pp. 
 
 14. Huchingson, R. New Horizons for Human Factors in Design. 
 McGraw-Hill, 1981, 512 pp. 
 
 15. Johansson, G, and K. Runar. Drivers' Braking Reaction 
 Times. Human Factors, v. 13, 1971, pp. 23-27. 
 
 16. Kroemer, K. Human Strength: Terminology. Measurement, 
 and Interpretation of Data. Human Factors, v. 12, 1970, pp. 297-313. 
 
33 
 
 17. Martin, R., and R. Graveling. Background Illumination and 
 Its Effects on Peripheral Visual Awareness for Miners Using 
 Caplamps. Appl. Ergonomics, v. 14, 1983, pp. 139-141. 
 
 18. McCormick, E., and M. Sanders. Human Factors in Engi- 
 neering and Design. McGraw-Hill, 5th ed., 1982, 615 pp. 
 
 19. McDonald, B. Improved Truck Driver Alertness Technology 
 (contract S3361341, Midwest Res. Inst.). BuMines OFR 84-77, 1977, 
 25 pp., NTIS PB 266 852. 
 
 20. Mead, P., and P. Sampson. Hand Steadiness During 
 Unrestricted Linear Arm Movements. Human Factors, v. 14, 1972, 
 pp. 45-50. 
 
 21. Miller, G. The Magical Number Seven Plus or Minus Two: 
 Some Limits on Our Capacity To Process Information. Psychological 
 Rev., v. 63, 1956, pp. 81-97. 
 
 22. Monk, T., and S. Folkard. Circadian Rhythms and Shiftwork. 
 Ch. in Stress and Fatigue in Human Performance, ed. by R. Hockey. 
 Wiley, 1983, pp. 87-115. 
 
 23. National Academy of Sciences. Toward Safer Underground 
 Coal Mines. 1982, 190 pp. 
 
 24. President's Commission on Coal. Coal Data Book. GPO, 1980, 
 83 pp. 
 
 25. Sanders, M. Anthropometric Survey of Truck and Bus Drivers: 
 Anthropometry, Control Reach and Control Force. Canyon Res. 
 Group Inc., Westlake Village, CA, 1977, 63 pp. 
 
 26. Sharp, E. Effects of Primary Task Performance on Response 
 Time to Toggle Switches in a Workspace Configuration. U.S. Air 
 Force Med. Res. Lab., Wright Patterson AFB, OH, AFAMRL- 
 TR-190, 1967, 63 pp. 
 
 27. Summala, H. Drivers' Steering Reaction to a Light Stimulus 
 on a Dark Road. Ergonomics, v. 24, 1981, pp. 125-131. 
 
 28. Tasto, D., and M. Colligan. Shift Work Practices in the United 
 States. NIOSH, Cincinnati, OH, DHEW-PN-77-148, 1977, 62 pp.; 
 NTIS PB 274 707. 
 
 29. Tilley, A. The Sleep and Performance of Shift Workers. 
 Human Factors, v. 24, 1982, pp. 629-641. 
 
 30. U.S. Department of Defense. Human Engineering Design 
 Criteria for Military Systems, Equipment and Facilities. MIL- 
 STD-1472B, Dec. 31, 1974, 231 pp. 
 
 31. Van Cott, H., and R. Kinkade. Human Engineering Guide 
 to Equipment Design. Wiley, rev. ed., 1972, 752 pp. 
 
 32. Wargo, M. Human Operator Response Speed, Frequency, and 
 Flexibility: A Review and Analysis. Human Factors, v. 9, 1967, 
 pp. 221-238. 
 
 33. Wickens, C. Engineering Psychology and Human Perfor- 
 mance. Charles E. Merrill, 1984, 544 pp. 
 
34 
 
 CHAPTER 4.— HUMAN ERROR AND ACCIDENTS 
 
 Accidents may happen but they can be avoided. 
 
 On Monday, July 11, 1983, the 5 right section crew 
 arrived at the working section. Because of absenteeism, 
 most of the crew was composed of miners from the 18 left 
 section. Richman, 1 a shuttle car operator, was in the No. 
 2 entry with Nystrom, a maintenance worker. According 
 to Nystrom, Richman was going to move the shuttle car but 
 could not do so because the brake lock was set. Richman 
 asked Nystrom where the lock was located and Nystrom 
 pointed it out to him and released it. Richman also told 
 Nystrom that he had never operated this particular model 
 of shuttle car. The shuttle car he normally drove, although 
 manufactured by the same company, was structurally dif- 
 ferent. He trammed the shuttle car-to the section feeder to 
 become familiar with its operation. 
 
 After the test run, Richman moved the shuttle car 
 behind the continuous miner and asked Upton, the contin- 
 uous miner helper, to check his cable reel. Richman then 
 angled his car beneath the continuous miner tail conveyor 
 and loading began. Shortly thereafter, Richman got out of 
 the operator's compartment, swiveled the seat to tram 
 outby, and got back in. As he was looking toward the con- 
 tinuous miner over his right shoulder, the car started to 
 move; he said that he could not hold it. Richman saw Up- 
 ton on the opposite side of the shuttle car, along the rib, 
 and began yelling for him to get out of the way while try- 
 ing to brake and hit the panic bar. The shuttle car pinned 
 Upton against the rib and completely severed both his legs. 
 Upton died shortly thereafter. 
 
 What was the cause of this accident? Was it human 
 error? Was it equipment failure? Was it a combination of 
 both? Why was Upton standing where he was? Why couldn't 
 Richman stop the shuttle car? 
 
 As it turned out, the shuttle car showed no evidence of 
 brake failure or any other malfunction. It was the consen- 
 sus of the investigating team that when Richman became 
 aware of the machine's movement toward Upton, he at- 
 tempted to brake, but he engaged the tram rather than the 
 brake pedal. Here then is a clear case of human error; or 
 is it? The accident report also noted that the shuttle car's 
 brake and tram control pedals were the exact opposite of 
 
 those on the shuttle car Richman normally operated. Both 
 cars were made by the same manufacturer but were dif- 
 ferent models. Perhaps Richman made an error, but is he 
 to blame for it? 
 
 In this chapter the concepts of human error and acci- 
 dent will be explored. Theories of accident causation will 
 be discussed, and an analysis of mining accident statistics 
 will be made. 
 
 HUMAN ERROR 
 
 Human error is often used as a synonym for operator 
 error, although there are obviously other humans in the 
 system besides the operator. The operator's immediate 
 supervisor and the mine's manager are human, and they 
 too can err. Improper work procedures, poor management 
 policies, and inadequate supervision could all be causal fac- 
 tors in an accident, and all are caused by humans. Main- 
 tenance personnel are human, and their errors can be the 
 cause of accidents. The designer of the equipment may also 
 have erred, as perhaps was the case with Richman and Up- 
 ton previously described. Thus, to think of human error only 
 in terms of operator error is rather narrow and may be 
 counterproductive with respect to accident investigation and 
 prevention. 
 
 When some people talk of human error, there is a con- 
 notation of blame or cause, rather than considering human 
 error as simply an event whose cause is yet to be deter- 
 mined. One danger with the causal interpretation of human 
 error is that the resultant emotional atmosphere often 
 makes it difficult to rationally determine appropriate cor- 
 rective action. 
 
 In this chapter the term "human error" is considered 
 to be an event that can occur anywhere in the system. The 
 following definition is suggested by Conway and Sanders 
 (7):* An inappropriate or undesired human decision or 
 behavior that reduces, or has the potential to reduce, effec- 
 tiveness, safety, or system performance. 
 
 Names have been changed. 
 
 1 Italic numbers in parentheses refer to items in the list of refcreiu 
 the end of this chapter. 
 
35 
 
 In addition to defining human error, numerous inves- 
 tigators have attempted to develop classification systems 
 to describe the nature of human errors. Some of these 
 systems are simple, two-part classifications, while others 
 are more elaborate and follow from the basic components 
 of human information processing and performance. 
 
 Broad Classification of Human Error 
 
 One investigator (1 7) attempted to classify human errors 
 into the following broad categories: operator-induced errors, 
 design-induced errors, and system-induced errors. Operator- 
 induced errors are incorrect conscious or unconscious ac- 
 tions or decisions on the part of personnel who have the 
 training, experience, and tools necessary to make correct 
 decisions and actions. Design-induced errors are errors in- 
 duced by poor equipment design, fabrication, installation, 
 or operating procedures. System-induced errors result from 
 such things as system integration, operational practices or 
 procedures, management policies, and selection and train- 
 ing procedures. 
 
 An important point was made by Meister (17) with 
 respect to this classification of errors. Many errors made 
 by operators are not operator-induced errors, but could be 
 design- or system-induced errors. The accident described at 
 the beginning of this chapter is an example of just such a 
 case. 
 
 Action Classification of Human Error 
 
 Action models focus on the output of the human in terms 
 of decisions made and actions taken. The simplest classifica- 
 tion is that suggested by Swain and Guttman (27): errors 
 of omission, errors of comission, sequence errors, and tim- 
 ing errors. 
 
 Errors of omission involve failure to do something. The 
 following is an example of an error of omission that resulted 
 in a mining fatality (MSHA Fatalgrams, Jan. 2, 1981, 
 81-09). 
 
 An electrician was electrocuted while attempting 
 to position himself on the steel framework of a substa- 
 tion. There were several points to disconnect in order 
 to shut off power completely to the substation. In this 
 case something was missed. 
 
 Errors of commission involve the incorrect performance 
 of an act. The following is an example from MSHA 
 Fatalgrams (Sept. 29, 1980, 80-039). 
 
 The victim, sitting on the conveyor belt, called for 
 his partner to hit the start button just lightly to jog 
 the belt forward a few inches. The helper lost his 
 balance momentarily, hit the button hard and actu- 
 ally started the belt, rather than just jogging it for- 
 ward. The victim was drawn between the belt and a 
 steel support member 9 inches above the belt. 
 A sequence error occurs when a person performs some 
 task or step in a task out of sequence. A good example is 
 the following (MSHA Fatalgrams, July 25, 1980, 80-033). 
 A helper was killed when the crane he was oper- 
 ating overturned. The victim lifted a 24 ton block with 
 the boom extended 80 feet at a low angle. Instead of 
 raising the boom first, the victim rotated the crane 
 to the right 90 degrees, resulting in positioning the 
 near-flat extended boom at right angles to the crawler 
 tracks. This caused the crane to overturn. 
 A timing error occurs when a person fails to perform 
 an action within the allotted time, either too early or too 
 
 late. An example would be a shot firer who does not vacate 
 a blasting area fast enough after lighting fuses and is 
 caught by the blast. 
 
 Actually, both sequence and timing errors are errors of 
 commission, but are listed separately because their causal 
 factors are frequently different. As can be seen, this classi- 
 fication focuses on operator errors as defined by Meister (1 7). 
 
 Information-Processing Model of Human Error 
 
 Several authors use an information-processing model 
 to classify human errors. These models use an input, deci- 
 sion, and output classification scheme. The output element 
 overlaps the action classification discussed previously. One 
 information-processing model is shown in table 4-1. A prob- 
 lem with applying such a taxonomy is that often the same 
 objective error can be classified into several categories, 
 depending on the details of the situation. Such details are 
 not often obvious from the description of the error or acci- 
 dent. For example, a loading machine helper was scaling 
 down broken roof. Two temporary supports had been set. 
 A large piece of rock broke from the roof, drove out the two 
 supports, and fell on the miner. How does one classify this 
 based on table 4-1? Did the worker not detect the loose rock? 
 Did he detect it, but not classify it as dangerous? Did he 
 incorrectly estimate the protective capability of the sup- 
 ports? As can be seen, such classification systems often re- 
 quire more information than is available in an error 
 situation. 
 
 Table 4-1 .—Information-processing model of human error (8) 
 
 Inputs Sensing. 
 
 Detecting. 
 
 Identifying. 
 
 Coding. 
 
 Classifying. 
 Decisions Estimating. 
 
 Logical manipulation. 
 
 Problem solving. 
 Outputs Chaining. 
 
 Omissions. 
 
 Insertions. 
 
 Misordering. 
 
 Copyright 1972 by McGraw-Hill Book Co., and reprinted by permission. 
 
 Warning-Hazard Classification of Human Error 
 
 Closely related to the information-processing model of 
 human error is the classification scheme (15) used to 
 investigate human errors in South African gold mining 
 accidents. Table 4-2 presents the classification scheme 
 and lists causes of the various types of human errors. 
 This classification stressed the importance of perceiving 
 and recognizing warnings about hazards in the work 
 environment. 
 
 Error classifications, such as those described, can serve 
 several useful purposes: (1) facilitate the tabulation of er- 
 ror frequencies, (2) provide a general frame of reference for 
 studying human error, and (3) direct efforts at reducing the 
 incidence of errors. The classifications that have been 
 developed, however, are crude at best and have not served 
 the needs of either the scientist or the practitioner. Fur- 
 ther efforts at developing an error classification scheme 
 could probably be better spent in identifying the causes of 
 human error, and developing and validating preventive and 
 remedial strategies. 
 
36 
 
 Table 4.2— Human error classification of accidents in 
 South African gold mines (15) 
 
 Human error 
 Failure to perceive a warning 
 
 Failure to recognize a 
 perceived warning. 
 
 Underestimation of hazard . 
 Failure to respond to a 
 
 recognized warning. 
 Responded to warning but 
 
 ineffectively. 
 
 Inappropriate secondary warning 
 
 Cause 
 Inadequate inspection technique. 
 Neglecting to inspect. 
 Obstruction to line of sight. 
 Masking noise. 
 Other. 
 
 Mixture of these. 
 Inadequate information. 
 Lack of training. 
 Lack of experience. 
 Other. 
 
 Mixture of these. 
 Causes unknown. 
 Underestimation of hazard. 
 Other. 
 
 Negligence or carelessness. 
 Standard practice inappropriate. 
 Well-intended but ineffective direct 
 action. 
 Other. 
 
 Mixture of these. 
 Causes unknown. 
 
 Copyright 1974 by National Council, and reprinted by permission. 
 
 WHAT IS AN ACCIDENT 
 
 Before anything can be scientifically studied, it must 
 be defined. Although this may sound easy with respect to 
 accidents, in fact, definition has been a stumbling block to 
 accident research since its inception. Consider the follow- 
 ing example. A haulage truck operator fails to visually in- 
 spect the area in front of his or her truck before starting 
 out. In one case, the operator drives off and nothing hap- 
 pens. In another case, the operator runs over a person stand- 
 ing in front of the truck; and in yet another case, he or she 
 crushes a small vehicle as shown in figure 4-1, but no one 
 is hurt. Is the first case an accident? One might consider 
 it an error; but when does an error become an accident? 
 Must there be injury or property damage in order for an 
 accident to be considered an accident? 
 
 In defining the term "accident" it is necessary to dis- 
 tinguish between the act itself and the consequence of that 
 act. Two extreme definitions can be identified, but there 
 are many shades and blends of definitions between them. 
 For example, 200 different definitions of accidents were col- 
 lected by Benner (2). At one extreme, definitions take no 
 account of the consequences of the act, but rather define 
 an accident in terms of the characteristics of the act itself. 
 For example, a list of accident indicators was produced by 
 Suchman (26); the more indicators that were present, the 
 more the event was likely to be called an accident. The in- 
 dicators were 
 
 1. Low degree of expectedness. 
 
 2. Low degree of avoidability. 
 
 3. Low degree of intention. 
 
 At the other extreme are definitions that stress the con- 
 sequence of the act. For example, acts that result in injuries 
 are considered to be accidents. For the most part, the min- 
 ing industry has adopted the consequence-type definition, 
 and for all practical purposes defines accidents as synony- 
 mous with injuries. 
 
 If consequence is considered the principal element in 
 the definition of an accident, then the following conse- 
 quences must be distinguished: 
 
 1. Fatal injury. 
 
 2. Nonfatal injury that results in days lost from work. 
 
 3. Nonfatal injury that results in restricted work days. 
 
 4. Nonfatal, no-days-lost injuries (also called first-aid 
 injuries). 
 
 5. Property damage. 
 
 One might think that such categories would be clear 
 and unambiguous. However, when 14 mine safety person- 
 nel were asked to classify four injury cases as disabling, 
 nondisabling, or neither, the results indicated disagreement 
 with respect to whether an injury was disabling or non- 
 disabling (20). 
 
 One common belief is that chance or luck distinguishes 
 a fatal accident from a nonfatal accident. A little reflection, 
 however, reveals that some activities are more likely to 
 cause one type of consequence than another. For example, 
 a study of coal mine accidents in Great Britain over a 3-yr 
 period (19) found that, as would be expected, a greater pro- 
 portion of fatalities occurred in haulage and transport than 
 in handling materials and using handtools. The results were 
 just the opposite for nonfatal injuries. 
 
 Serious accidents (all those that resulted in at least 1 
 day of restricted or missed work activity) in underground 
 and surface mines from 1975 to 1982 were investigated by 
 Bennett and Passmore (3). The probability that an injury 
 would be severe increased in each succeeding year studied; 
 was lower for supervisory and maintenance personnel than 
 for all other job classifications; and was not any greater for 
 younger or more inexperienced miners than for older or 
 more experienced miners. 
 
 Several investigators have urged the use of near-miss 
 accidents as a source of information on accident causation. 
 The logic behind this is that there are more near-miss ac- 
 cidents than injury-producing accidents, and therefore more 
 data are available for study. It is assumed that only chance 
 and luck discriminate a near-miss accident from an actual 
 accident. An investigation of near-miss accidents in British 
 coal mines (23) was made by asking miners once per month 
 to describe any near-misses they experienced. Two problems 
 with this approach are (1) there may be selective recall, e.g., 
 the miners may tend to recall near-misses that they felt 
 responsible for and may tend to forget those that were 
 caused by forces over which they had no control; and (2) the 
 definition of a near-miss is vague, i.e., how near a miss does 
 it have to be to call it a near-miss. These types of problems 
 make it difficult to use near-miss data to estimate the 
 relative contribution of various causal factors because only 
 a sample of all near-misses are reported, and this sample 
 is very likely unrepresentative of the population of near- 
 misses actually occurring. 
 
 HUMAN ERROR AND ACCIDENTS 
 
 What percentage of accidents is caused by human er- 
 ror? This is a question that has vexed researchers for years. 
 Probably the most common answer one hears is that ap- 
 proximately 85% of accidents are due to human error. This 
 
37 
 
 Figure 4-1 .—One consequence of operator error. 
 
 figure came from an analysis of insurance company records 
 conducted by Heinrich (11). This percentage, however, 
 should not be taken too seriously. The percentage of acci- 
 dents one attributes to human error depends on how one 
 defines human error; the data source used to compile the 
 statistics; and the alternative causes, other than human er- 
 ror, included in the tabulation. 
 
 If one assumes that human beings are responsible for 
 their own actions and are therefore responsible for the er- 
 rors they make, then a higher percentage of accidents will 
 be attributed to operator error. On the other hand, if the 
 view is adopted that errors can be anticipated and they 
 should therefore be planned for and designed for, and that 
 when they do occur the fault should be traced to the 
 designer, then fewer accidents will be attributed to operator 
 error. 
 
 The typicial human-error-in-accident investigation clas- 
 sifies cause as either due to unsafe acts (i.e., operator error) 
 or unsafe conditions, or as due to operator error or equip- 
 ment failure. Such a simple classification results in a 
 foregone conclusion that a high percentage of accidents will 
 be attributed to the operator. Such analyses leave out the 
 all important question of what caused the operator to err. 
 Often the cause can be traced to faulty equipment design, 
 inadequate or improper instruction and training, or dan- 
 gerous management policies. 
 
 A review of the literature reveals widely disparate esti- 
 mates of the percentage of accidents due to human error. 
 For example, in 12 studies reviewed by Conway, Muckler, 
 and Peay (6), percentages were found ranging from 4.3% 
 to 90%. Half reported percentages equal to or exceeding 
 80%, while the other half reported percentages less than 
 or equal to 50% 
 
 A few studies have attempted to estimate the propor- 
 tion of accidents in the mining industry attributable to 
 human error. A study of underground transport accidents 
 in Great Britain (10) revealed that 44% of the accidents were 
 due to "lack of discipline or ordinary caution" and "bad 
 operator practice." Sims, Graves, and Simpson (23) categor- 
 ized haulage near-misses as caused by "man factors" (i.e., 
 human errors), "vehicle/load factors," or "environmental 
 factors." They reported that 49% of the incidents were 
 caused by "man factors." On the other hand, it was reported 
 by Snyder (24) that, based on Mine Safety and Health 
 Administration accident investigations, 63% of the 43 fatal 
 accidents involving supervisors from 1981 through July 
 1983 involved the victims doing things they knew, or should 
 have known, were unsafe. These acts included the victims 
 placing themselves in a hazardous position; standing or 
 working in areas where the roof was not supported or where 
 an approved roof control plan was not being followed; repair- 
 ing machinery in motion or electrical equipment that was 
 
38 
 
 known to be energized; supervising improperly conducted 
 blasting operations; or overseeing work in operations with 
 inadequate ventilation. 
 
 From an analysis of 92 underground mining accident 
 investigations, it was found by Sanders and Shaw (21) that 
 operator error was involved to some degree in 93% of the 
 cases, but was the primary cause of only 39% of them. 
 Across all 92 cases, the average percentage of cause attrib- 
 uted to operator error was 30.5%. 
 
 Lawrence (25), in his investigation of 405 South African 
 gold mining accidents, identified 794 errors associated with 
 the perception of, recognition of, and response to warnings. 
 His investigative model assumed that all accidents were 
 due to human errors, and his task was to categorize the er- 
 rors by type. These error classifications and causes are 
 shown in table 4-2. A careful reading of the causes listed 
 for a human error indicate that some of them would be con- 
 sidered, according to Meister (17), as design errors (e.g., 
 obstruction to the line of sight or masking noise), or system 
 errors (e.g., lack of training or inappropriate standard prac- 
 tice). The percentages of accidents assigned to his classifica- 
 tion of errors by Lawrence (15) were as follows: 
 
 Failure to perceive a warning 36% 
 
 Failure to recognize a perceived warning 4% 
 
 Underestimation of hazard 25% 
 
 Failure to respond to a recognized warning . . . 17% 
 
 Responded to warning but ineffectively 14% 
 
 Inappropriate secondary warning 4% 
 
 It appears that there is probably no one answer to the 
 question of the contribution of human error to accidents. 
 The best that can be said is that the answer depends on what 
 human error is considered to be, and whether the cause of 
 the error is taken into account. Overall, however, it can 
 probably be said that operator error is the primary cause 
 in no more than half of the accidents occurring in 
 underground mining. This conclusion is based on the results 
 of the studies by the Health and Safety Executive (10), 
 Sanders and Shaw (21), and Sims, Graves, and Simpson (23). 
 
 THEORIES OF ACCIDENT CAUSATION 
 
 There has been a wide array of accident causation 
 theories proposed. Each theory emphasizes the orientation 
 of its author, be it psychological, sociological, or statistical. 
 The varying theories can, however, be grouped into three 
 broad classes: accident proneness theories, job demand ver- 
 sus worker capability theories, and psychosocial theories. 
 
 Accident Proneness Theories 
 
 The oldest and probably the most influential accident 
 causation theory is that of accident proneness. In its pure 
 form it hypothesizes that some people are more prone to 
 have accidents than others because of a peculiar set of 
 constitutional characteristics. Further, accident proneness 
 is considered to be a relatively permanent feature of the 
 individual. 
 
 The support for this theory has come from statistical 
 comparisons between the distribution of accidents in a 
 population of workers and the distribution expected by pure 
 chance. What was often found was that more people than 
 would be expected had multiple accidents. More recent 
 authors have challenged these early statistical studies, 
 pointing out that to accept accident proneness one must 
 accept the underlying assumption that all people in a pop- 
 
 ulation of workers are exposed to the same job and envi- 
 ronmental hazards. The fact that more people have multi- 
 ple accidents than would be expected because of chance may 
 only indicate that some people are exposed to more hazards 
 on the job than others. 
 
 A more restricted view of accident proneness is that peo- 
 ple are more or less prone to accidents in given specific situa- 
 tions, and that this proneness is not permanent but changes 
 over time. This has been called the accident liability theory. 
 Thus, person A may be more accident prone than person 
 B in situation 1; but in situation 2, person B may be more 
 accident prone than person A. Further, person A may be 
 more accident prone than person B in situation 1, but this 
 proneness may decrease with time. 
 
 Two prime variables that relate to this formulation of 
 accident liability are age and experience. The problem, 
 however, is that it is often difficult to separate the effects 
 of the two variables; younger workers usually are also the 
 most inexperienced. Little relationship was found among 
 underground coal miners between age and either fatality 
 rates or permanent disabling injury rates (18). There was, 
 however, a very strong correlation between age and nonper- 
 manent disabling injury rates. Figure 4-2 depicts the rela- 
 tionship found. A young miner (18-24 yr old) was about three 
 times more likely to be injured than a miner 45 yr of age 
 or older, and about twice as likely to be injured than a miner 
 25 to 44 yr of age. 
 
 A number of researchers have suggested that younger 
 workers have accidents for reasons other than experience. 
 For example, inattention, lack of discipline, impulsiveness, 
 recklessness, misjudgment, overestimation of capacity, and 
 
 (T> 
 
 or 
 o 
 
 X 
 I 
 UJ 
 
 UJ 
 
 >- 
 o 
 
 UJ 
 
 o 
 o 
 o 
 o* 
 
 o 
 
 or 
 
 Ul 
 
 Q. 
 
 UJ 
 
 I- 
 < 
 
 or 
 
 >- 
 or 
 z> 
 —} 
 
 25 
 
 20 - 
 
 15 - 
 
 10 
 
 5 - 
 
 
 
 
 
 
 
 
 - 
 
 
 
 - 
 
 
 
 
 - 
 
 m 
 
 
 
 
 
 18-24 25-34 35 "44 
 AGE GROUP, yr 
 
 >45 
 
 Figure 4-2.— Relationship between age and disabling injury 
 
 rate (23). (Courtesy of National Academy Press) 
 
39 
 
 pride were implicated by Lampert (14) as factors that may 
 account for higher accident rates among younger workers. 
 
 Although not investigated by the National Academy of 
 Sciences (18), other investigators have found that accident 
 liability increases among older workers (e.g., over 50 or 60 
 yr of age). This increase may be due to deterioration in 
 motor skills, sensory functions, and mental agility (9). It 
 should be pointed out that Schaffer, Gavan, and Woodward 
 (22) found no such rise in accident liability at the upper age 
 range for operators of surface front-end loaders, haulers, or 
 trucks, nor for operators of underground shuttle cars or roof 
 bolting machines. 
 
 The amount of job experience is another transient fac- 
 tor that changes an individual's accident liability over time. 
 Virtually all investigators have found experience to be 
 closely related to accident liability. Further, it appears that 
 specific job experience is more important than general min- 
 ing experience. The number of days of experience at a new 
 job element (new mine, new job, new piece of equipment, 
 new task, etc.) were found to be related to fatal accidents 
 (28). The accident frequency on the first day was nearly 
 three times higher than the average frequency for the next 
 4 days. This conclusion was supported by Studenski (25) 
 when he found that 40% of mistakes that resulted in ac- 
 cidents at work occurred on rarely performed or entirely 
 new tasks. 
 
 Even among supervisors, experience is an important fac- 
 tor in accidents. Among coal mine supervisors who were 
 killed in the 9-yr period from 1973 through 1981, 31% had 
 2 yr or less of supervisory experience. Figure 4-3 shows a 
 more detailed analysis of 49 supervisors who died in coal 
 mine accidents from 1981 through July 1983. As can be 
 
 10 
 
 uuv\n , u , Q_ 
 
 UJ 
 
 H 
 
 13 5 
 < 
 
 10 
 
 £ 
 
 U\A, 171, F1M 
 
 H 
 
 V\ 
 
 J2L 
 
 Hffl 
 
 ^A\ArXA 
 
 
 
 J 
 
 / 
 
 PHM , U\7\ 
 
 -2 
 
 6 8 10 12 14 
 EXPERIENCE, yr 
 
 16 
 
 18 20 22 
 
 Figure 4-3.— Supervisor fatalities in coal mining as a function 
 of experience at mine (A), experience in job classification (8), 
 
 and total mining experience (C) (24). (Courtesy of U.S. Mine Safety and 
 Health Administration) 
 
 seen, experience in job classification and experience at mine 
 are highly related to accident frequency, while the relation- 
 ship of total mining experience to accident frequency is less 
 discernible. It indeed appears that accident liability fluc- 
 tuates with time, especially as related to age and specific 
 job experience. The notion that some people are naturally 
 more accident prone than others across all situations and 
 at all times is probably a less tenable position. 
 
 Job Demand Versus Worker Capability Theories 
 
 This class of theories is related in part to the accident 
 liability notion previously introduced. Simply put, accident 
 liability increases when job demands exceed worker capa- 
 bilities. For example, if a job requires greater psychomotor 
 skills than workers have, accidents are expected to increase. 
 The relationship between job experience and accident rates 
 can also be considered as examples of job demands exceeding 
 worker capabilities. With more experience, capabilities in- 
 crease and, hence, one would expect accidents to decrease. 
 
 Another line of evidence used to support this class of 
 theories is the relationship of fatigue to accidents. The 
 assumption is that with increased fatigue, capabilities are 
 reduced. Because it is difficult to measure fatigue, in- 
 vestigators have correlated accident frequencies with fac- 
 tors believed to be related to fatigue, such as day of week, 
 time of day, and time since shift started. 
 
 The problems with studies that have investigated day 
 of week, time of day, etc., are that they do not attempt to 
 equate the number of people actually working on each day 
 of the week, the hour of the day, etc.; and they do not at- 
 tempt to equate the type of work being performed on each 
 day of the week, the hour of the day, etc. For example, it 
 was noted by Adams, Barlow, and Hiddlestone (1) that fewer 
 accidents occur on Mondays and a greater number of ac- 
 cidents on Wednesdays. It may well be that absenteeism 
 is higher on Mondays than in the middle of the week. They 
 also reported a steady increase in the number of accidents 
 occurring 40 to 70 min after a break, with a consistent and 
 steady drop thereafter. One factor affecting this steady drop 
 after 70 min may be that another break may be in progress 
 because there are not many workers who fail to take a break 
 of some sort after 90 min of work. 
 
 Unfortunately, then, this line of research cannot be used 
 to support the job demand versus worker capability theories. 
 Some tangential evidence, however, came from a study by 
 Kephart and Tiffin (12) who investigated the visual require- 
 ments of 12 jobs and compared them to the workers' visual 
 capabilities. In 11 of the 12 jobs, the percentage of safe 
 workers (low-accident employees) was higher among those 
 whose capabilities exceeded the requirements than among 
 those whose capabilities did not exceed the requirements. 
 
 Related to the job demand-worker capability class of 
 theories is the adjustment to stress theory. This theory 
 states that accident rates will be higher in situations where 
 stress (physical or physiological-psychological) is placed on 
 the worker. In essence, the additional stress overloads the 
 workers and adds to the demands of the job so that their 
 capabilities no longer match the job demands. Physical 
 stressors include noise, poor illumination, and temperature 
 extremes. Physiological-psychological stressors could in- 
 clude anxiety, lack of sleep, illness, anger or remorse from 
 having a fight with a spouse, etc. The research data are 
 mixed with respect to the effects of these variables. Un- 
 doubtedly, some of the confusion arises because the jobs per- 
 formed, even with the stressors, are not demanding enough 
 
40 
 
 to exceed the worker' capabilities; or the workers slow down 
 and this reduces the overall demands of the job. 
 
 Psychosocial Theories 
 
 One theory, goals-freedom-alertness, holds that greater 
 freedom among workers to set reasonably attainable goals 
 is accompanied by high-quality work performance, and ac- 
 cidents are viewed as examples of low-quality work perfor- 
 mance. The idea is that by raising the level of alertness, 
 accidents will be reduced; and this alertness can be sus- 
 tained only within a rewarding psychological climate (13). 
 Kerr contends that in industry, both management and 
 unions interfere with this climate by telling people what 
 to do and what not to do, without asking them their ideas 
 about relevant and attainable goals. Sanders, Patterson, 
 and Peay (20) found some evidence supporting this theory 
 among underground coal miners. This study will be dis- 
 cussed further in chapter 10. 
 
 In addition to the goals' freedom-alertness theory, there 
 are some psychoanalytical theories that view accidents as 
 self-punitive acts caused by guilt, aggression, etc. 
 
 Overall, then, there does not appear to be any one really 
 good theory of accident causation. All have a ring of truth 
 to them, but by themselves do not explain the complexity 
 of the accident situation. 
 
 INJURY STATISTICS 
 
 Numbers seem to be so objective; it is possible to com- 
 pute the number of trip-and-fall injuries, compare them to 
 back injuries, look for trends over several years, and make 
 recommendations based on the "statistics." For some 
 unknown reason, putting a number on something makes 
 it more believable. Nothing is inherently wrong with this, 
 as long as the limitations of the numbers used are under- 
 stood. Consideration must be given to how the data were 
 collected, and what factors could have influenced the 
 numbers obtained. 
 
 Mining companies may collect, tabulate, and analyze 
 their own accident data. The Mine Safety and Health Ad- 
 ministration (MSHA) of the Department of Labor requires 
 mining companies to report accidents and fill out accident 
 forms so that MSHA can collect, tabulate, and analyze the 
 resulting data. The entire accident-reporting process, from 
 accident occurrence to reporting, is at best an unreliable 
 process that almost always fails to capture all the accidents 
 that actually occur. In addition, the data collected about 
 the accidents are often inaccurate and incomplete. 
 
 As already discussed in this chapter, the term "acci- 
 dent" has many definitions, and the definition accepted will 
 obviously influence the type and the number of incidences 
 reported. Even if accident and injury are accepted as syn- 
 onymous terms, there is still plenty of opportunity to lose 
 data. 
 
 Sanders, Patterson, and Peay (20) traced the injury- 
 reporting process to the last step, transmitting the data to 
 MSHA, and revealed several areas where injury data may 
 be lost. 
 
 Workers commit unsafe acts, a proportion of which lead 
 to injuries. Workers must then decide to report the injuries 
 to management. In cases of serious injuries, there is little 
 choice. With less serious injuries (e.g., cut or bruised fingers, 
 strained back, or dust in the eye), however, workers may 
 decide not to report injuries for any number of reasons (e.g., 
 
 they know management does not like workers who belly- 
 ache, they are afraid they may be laid off, their pride keeps 
 them from admitting to injuries, they feel they can treat 
 the injuries themselves, etc.). 
 
 After a worker reports an injury, management decides 
 if it is really an injury. Again, with minor injuries, manage- 
 ment may question whether an injury really occurred (e.g., 
 back strain) or may say, "Put a bandage on it and forget 
 it." If an injury is considered bona fide, management then 
 decides whether it is a lost-time injury. Surprisingly, there 
 is some ambiguity here. A worker can be told to go home 
 and take a few days off to recuperate, creating a lost-time 
 injury; or the worker can be given a temporary assignment 
 in the office or topside where recuperation can take place 
 while the employee is on the payroll, without a lost-time 
 injury. This practice often exists in industry. 
 
 At each of the steps in this process, an injury may drop 
 out and not be reported. Some companies may report more 
 injuries than do others because of differences in reporting 
 policies rather than in the underlying safety of the mines. 
 If injury statistics are used in a punitive fashion, then com- 
 panies are more likely to underreport incidences. 
 
 The accident data collected on an injury can also be a 
 problem area. There is considerable confusion as to how an 
 accident should be classified. Especially ambiguous is the 
 source of injury category that identifies the object, sub- 
 stance, exposure, or bodily motion that directly produced 
 or inflicted an injury. Often, the nature of injury can be am- 
 biguous, especially in the case of multiple injuries. The 
 specification of accident type becomes difficult when the ac- 
 cident sequence comprises a series of associated events. One 
 worker drops a wrench. The wrench strikes another worker 
 who is standing on a ladder. This worker falls off the lad- 
 der, and the ladder in turn falls on him or her. Should this 
 accident be classified as struck by falling object, and if so, 
 by wrench or ladder, or as fall from ladder? 
 
 The data collected usually concentrate on the individual 
 injured, recording his or her age, experience, activity at time 
 of injury, job title, etc. This is done whether or not the vic- 
 tim was the cause of the accident or simply the recipient 
 of another person's error. For example, if a continuous 
 miner operator (50 yr old with 15 yr of job experience) 
 crushes his or her helper (21 yr old with 1 yr of job experi- 
 ence) against the rib with the tail conveyor of the continuous 
 miner, the victim's injury is attributed to youth and inex- 
 perience, when it may well be the fault of the older, more 
 experienced operator. 
 
 With these limitations in mind, a review is made of some 
 of the following basic injury statistics in the mining 
 industry. 
 
 Industry-wide Comparisons 
 
 The major sectors of the mining industry can be grossly 
 categorized within a two-dimensional matrix: commodity 
 by type of mine. Although these dimensions can become 
 complex, as far as injury statistics are concerned, the situa- 
 tion is simplified by dividing commodity into coal, metal, 
 and nonmetal categories, and type of mine into underground 
 and surface. This rough classification scheme is used by 
 MSHA to tabulate its injury statistics. MSHA does, how- 
 ever, include finer breakdowns within each of these 
 categories. 
 
 Figure 4-4 presents injury data for 1983 (29) for the 
 various segments of the mining industry. Shown are the 
 
41 
 
 percentages of fatal, nonfatal-days-lost (NFDL), and no-days- 
 lost (NDL) injuries occurring in each industry segment. As 
 can be seen, underground coal mining accounted for approx- 
 imately 65% of all fatal injuries, 70% of all NFDL injuries, 
 and 50% of all NDL injuries occurring in the mining in- 
 dustry during 1983. These values are typical; similar values 
 canbefound in other years as well. It is not surprising then 
 that much more research effort has been directed toward 
 understanding the causes of injuries in underground coal 
 mining than in any other segment of the industry. 
 
 Figure 4-5 shows the injury rates (per 200,000 employee- 
 hours) for each segment of the industry for 1983 (29). As 
 can be seen, the main distinction is between underground 
 and surface mines, with smaller differences among com- 
 modities. This is reinforced in figure 4-6, which shows the 
 percentage of NFDL injuries attributed to the five main 
 accident-producing categories for each segment of the in- 
 dustry (metal and nonmetal have been combined). These 
 five categories (handling materials, machinery, powered 
 haulage, slips and falls, and handtools) accounted for the 
 following percentages of NFDL injuries in 1983: 
 
 Underground coal 83% 
 
 Underground metal-nonmetal 79% 
 
 Surface coal 93% 
 
 Surface metal-nonmetal 91% 
 
 For some categories, there is no apparent relationship 
 among the segments of the industry, such as for handtool, 
 powered haulage, and materials handling accidents. A 
 greater proportion of accidents involved machinery in 
 underground mining than in surface mining, probably due 
 in part to the proximity of people to machinery, often in 
 cramped work areas. A greater percentage of NFDL ac- 
 cidents were slips and falls in surface mines than in 
 underground mines. This is due in part to slips and falls 
 while mounting and dismounting large surface mining 
 equipment. The large percentage of "other" accidents in 
 underground mining was due to roof fall injuries. The 
 analogous situation in surface mining would be an injury 
 due to failure of a highwall, to which fewer people are 
 exposed. 
 
 80 
 
 60 
 
 40 
 
 o 
 H 20 
 
 KEY 
 
 I I Fatal injury 
 
 E3 Nonfatal-days-lost injury 
 
 H No-days-lost injury 
 
 si 
 
 rJ 1T-M 
 
 Coal Coal Metal Metal Nonmetal Nonmetal 
 
 underground surface underground surface underground surface 
 
 SEGMENT OF INDUSTRY 
 
 Figure 4-4.— Percent of fatalities, nonfatal-days-lost, and no- 
 days-lost injuries occurring in 1983 for each of the major 
 
 Segments Of the mining industry (29). (Courtesy of U.S. Mine Safety and 
 Health Administration) 
 
 uj 5 
 Q. 
 
 KEY 
 Nonfatal-days-lost injury 
 No-days-lost injury 
 
 _ B 
 
 Coal 
 
 Metal 
 
 Nonmetal 
 
 SEGMENT OF INDUSTRY 
 
 Figure 4-5.— Nonfatal-days-lost and no-days-lost injury rates 
 for 1983 for each of the major segments of the underground (A) 
 
 and Surface (B) mining industry (29). (Courtesy of US Mine Safety and 
 Health Administration) 
 
 40 
 
 CO 
 UJ 
 
 or 
 
 v> 20 
 
 Q 
 
 
 < 
 
 £ 40 
 u. 
 
 z 
 o 
 
 z 
 
 S 20 
 
 < 
 
 UJ 
 
 o 
 or 
 
 UJ 
 
 o. 
 
 A 
 
 | 
 
 
 KEY 
 EZlCoal 
 ■■ Metah nonmetal 
 
 
 
 
 
 
 
 
 
 
 B 
 
 
 
 
 
 
 
 
 
 
 
 $ 
 
 
 ^ 
 
 ^ 
 
 
 <v 
 
 *< 
 
 *> 
 
 SOURCE OF INJURY 
 
 Figure 4-6.— Comparison of nonfatal-days-lost injuries from 
 major accident catagories for the major segments of the under- 
 ground (A) and surface (0) mining industry in 1983 (29). (Courtesy 
 
 of U.S. Mine Safety and Health Administration) 
 
42 
 
 it appears that much of the variance in injury statistics 
 is due to the type of mine (underground or surface), and that 
 underground mining is more hazardous than surface min- 
 ing. Further, underground coal mines account for the ma- 
 jority of mining industry injuries. For this reason, statistics 
 from underground coal mining will be concentrated on and 
 data from other segments of the industry will be addressed 
 only where appropriate. 
 
 Underground coal mines have been traditionally viewed 
 as having high fatality rates. Compared with fatality rates 
 of other industries, this is true. Compared with other types 
 of underground mining, it may not be so. In 1983, for ex- 
 ample, the fatality rate was higher in both metal and non- 
 metal underground mining than in underground coal min- 
 ing. Figure 4-7 shows the fatality rate for underground coal 
 mining from 1932 to 1983 (18, 29-32). As can be seen, the 
 general trend has been one of declining fatality rates over 
 the recent past. 
 
 Comparisons With European Countries 
 
 It is difficult to make meaningful comparisons of U.S. 
 injury rates with those of European countries. For one thing, 
 mining conditions and methods are different. U.S. mines 
 are generally less deep than European mines; room-and- 
 pillar method is predominant in the United States, while 
 longwall is predominant in Europe; labor is distributed dif- 
 ferently in European mines than in U.S. mines; and the 
 social systems and market conditions are different. Another 
 problem is that reporting differences exist among countries. 
 A disabling injury in the United States, is an injury that 
 results in 1 day of missed work. In some European coun- 
 tries, an injury is not classified as disabling until 3 days 
 of work are missed. 
 
 The number of fatalities is the only measure, therefore, 
 that is directly comparable among countries. Even compar- 
 ing the number of fatalities, however, can be tricky because 
 of the need to take exposure into account. Comparing the 
 number of fatalities per 1,000 workers among countries 
 assumes that there are the same number of hours per shift 
 in different countries, which is not true (16). If one compares 
 U.S. underground coal mine fatalities per 100 million labor 
 hours with those of European countries, one finds that the 
 United States has a poorer record. This is shown in figure 
 4-8A. It should be mentioned that the fatality rate in the 
 United States has been dropping more rapidly than in Euro- 
 pean countries, and is now approaching the European levels. 
 
 What these statistics fail to present is the fact that U.S. 
 mines are more productive than European mines. Therefore, 
 when fatalities are computed per 100 million st of coal 
 mined, the picture is radically different, as shown in figure 
 4-8S. Here, the U.S. record is better than that of most Euro- 
 pean countries, but more rapid improvements in productiv- 
 ity are occurring in European mines, so that the differences 
 are becoming smaller. 
 
 COST OF ACCIDENTS 
 
 Determining the cost of accidents can be a complex and 
 unending process. The problem is determining which cost 
 factors to include in the calculations. One end of the spec- 
 trum could consider only the immediate medical compen- 
 sation costs associated with various types of injuries. For 
 example, medical expenses connected with underground 
 
 0.4 
 
 Federal Cool Mine Health and 
 Safety Act of 1969 
 
 1930 
 
 1940 
 
 1950 
 
 I960 
 YEAR 
 
 1970 
 
 I960 
 
 1990 
 
 Figure 4-7.— Fatality rate per 200,000 employee-hours for U.S. 
 underground coal mines from 1931 through 1983 (18, 30-32). 
 
 (Courtesy of National Academy Press and U.S. Mine Safety and Hearth Administration) 
 
 Ul X 
 Q_ Ld 
 
 UJ 
 
 UJ >- 
 
 n 
 
 £ i 
 
 o 
 o 
 
 1 50 
 
 IOO - 
 
 300 
 
 i° 
 
 <r 
 
 UJ 
 Q. 
 
 200- 
 
 IO0- 
 
 KEY 
 C^ United Kingdom 
 m Germany 
 HE] France 
 &&J European Common Market 
 
 1950-64 
 
 1965-69 1970-74 1975-77 
 
 PERIOD 
 
 Figure 4-8.— Comparison of fatality data between U.S. and 
 
 European underground COal mines (18). (Courtesy of National Academy 
 Press) 
 
 coal mine injuries over an 18-month period for one large 
 company were reported by Cain and Pettry (4\ Table 4-3 
 shows the dollar amounts paid for various types of injuries. 
 The 558 incidents cost this mining company approximately 
 $217,950 or an average of $390.58 per incident in medical 
 expenditures alone. 
 
 Anyone who thinks such figures represent the total cost 
 of injuries is naive. The most comprehensive analysis of ac- 
 cident costs was carried out by FMC Corporation under a 
 Bureau contract. A review of that effort was given by Phi 
 
43 
 
 Table 4.3—1982-83 medical compensation costs paid 
 
 per incident by a major coal company, by type 
 
 of injury sustained (4) 
 
 900 
 
 Incidents 
 
 15 
 
 154 
 
 35 
 
 15 
 
 26 
 4 
 29 
 46 
 10 
 32 
 168 
 24 
 
 558 
 
 Cost 
 
 Incident 
 
 $178.25 
 
 219.47 
 
 90.89 
 
 61.22 
 
 2,601.17 
 
 3,416.37 
 
 36.59 
 
 135.95 
 
 80.84 
 
 299.25 
 
 406.18 
 
 422.48 
 
 390.58 
 
 Type 1 
 
 $2,675 
 
 33,800 
 
 3,180 
 
 920 
 
 67,630 
 
 13,665 
 
 1,060 
 
 6,255 
 
 810 
 
 9.575 
 
 68,240 
 
 10,140 
 
 217,950 
 
 Abrasion 
 
 Bruise 
 
 Bruise and cut 
 
 Burn (minor) 
 
 Fracture: 
 
 Simple 
 
 Compound 
 
 Irritation-inflammation 
 
 Laceration 
 
 Puncture 
 
 Sprain 
 
 Strain 
 
 Other 
 
 Total or average . . . 
 
 1 Rounded. 
 
 and DiCanio (5). The study and resulting predictive model 
 considered the following cost factors: 
 
 1. Loss of personal income. 
 
 2. Compensation of wages from State, Federal, and union 
 funds for disabling injuries. 
 
 3. Benefits for injuries resulting in death or permanent 
 disablity. 
 
 4. Medical treatment and hospital care. 
 
 5. Immediate and postaccident production losses as a 
 result of a fatality or amputation injury. 
 
 6. The costs incurred by the investigation of a fatal 
 accident. 
 
 The cost elements excluded were loss of life, fines, costs 
 of lawsuits, loss of equipment, production loss due to a per- 
 manent shutdown, immediate loss of production due to the 
 disruptive effect of an injury serious enough to require 
 medical attention, potential postaccident loss of production 
 due to temporary replacement of an injured miner by a less 
 experienced one, and cost of long-term followup treatment. 
 The reason for these exclusions was simply that such costs 
 are not readily available for analysis. Thus, the FMC model 
 must be considered conservative at best. 
 
 Figure 4-9 presents the findings on the average cost of 
 a fatality for the various segments of the mining industry, 
 and figure 4-10 presents the average cost of a disabling in- 
 jury. As can be seen, the average cost of injuries has been 
 increasing faster than the inflation rate for the last several 
 years. The average industry cost in 1981 for a fatality was 
 $674,000 and the cost of a disabling injury was $177,000. 
 
 A significant portion of the costs incurred was due to 
 postaccident declines in production. In the case of fatalities, 
 all underground cases lost production from mine and sec- 
 tion closures immediately following the accident. Further, 
 in 73% of the cases, postaccident production level was sig- 
 nificantly lower than preaccident production level for up 
 to 5 months after normal operations resumed. Figure 4-11 
 shows a typical example of the effect of an accident on pro- 
 ductivity. In the majority of cases, the largest decline in 
 productivity was not in the section that had the accident. 
 After underground fatalities, for example, production 
 declines in a majority of the sections. This demonstrates 
 that a fatal accident affects all crews in a mine. 
 
 The immediate and long-term production loss for cases 
 involving fatal accidents in underground coal mining 
 ranged from 0.5% to 9.4% of annual mine production, with 
 a mean of 2.7%. At a price of $25.00 per short ton of coal, 
 
 300 
 
 1975 
 
 1977 
 
 1979 
 
 1981 
 
 YEAR 
 
 Figure 4-9.— Average cost of a fatality in the mining industry 
 
 1975-81 (5). (Courtesy of American Mining Congress) 
 
 250 
 
 — ' 1 ' 1 ' 
 
 KEY 
 o Underground coal 
 d Surface coal 
 200 |— A Underground metal-nonmetal 
 O Surface metal-nonmetal 
 
 </> 
 
 .2 I50 - 
 
 o 
 •a 
 
 ro 
 
 O 
 
 if) 
 O 
 O 
 
 — Average 
 
 
 1 975 
 
 1 
 
 1 
 
 977 1 979 
 
 YEAR 
 
 1981 
 
 Figure 4-10.— Average cost of a disabling injury in the mining 
 
 industry, 1975-81 (5). (Courtesy of American Mining Congress) 
 
44 
 
 200 
 
 ,-g I60h 
 
 O S 
 
 I- -5 
 
 o > 
 
 o 
 
 o c 
 
 Or 33 
 
 120- 
 
 80 
 
 40' — 
 -150 
 
 -50 
 
 WORK DAYS 
 
 100 
 
 Figure 4-1 1 .—Example of characteristic effect of a fatal injury 
 on production in an underground mine, where the vertical axis 
 represents production over preaccident levels and the preacci- 
 
 dent level equals 100 (5). (Courtesy of American Mining Congress) 
 
 the average mine lost $450,000 in production value from 
 a fatality. One case resulted in a loss of $2,000,000. 
 
 For fatal cases in underground metal mines, the pro- 
 duction loss ranged from 0.5% to 4.0% of annual produc- 
 tion, with a mean of 1.8%. There was no significant post- 
 accident loss observed after fatalities in surface mines. 
 
 DISCUSSION 
 
 This chapter stressed the complexity of accidents and 
 the role of human error in accidents. A total systems per- 
 spective was stressed in which human error itself could be 
 caused by inadequate equipment designs, management 
 policy, and the like. The need to dig deeper to uncover these 
 root causes was emphasized. A review of the major classes 
 of accident causation theories revealed no one really good 
 theory that accounts for all the data. Although accidents 
 appear to be decreasing in the mining industry, there will 
 continue to be a level of accidents and injuries considered 
 by many to be unacceptable. Unfortunately, there is still 
 much not known about the causes of mining accidents, and 
 there remains more questions than answers in the field. 
 
 REFERENCES 
 
 1. Adams, N., A. Barlow, and J. Hiddlestone. Obtaining Ergonom- 
 ics Information About Industrial Injuries: A Five-Year Analysis. 
 Appl. Ergonomics, v. 22, No. 2, 1981, pp. 71-81. 
 
 2. Benner, L. Accident Investigations— A Case for New Percep- 
 tions and Methodologies. Soc. Automotive Eng., Warrendale, PA, 
 SAE/SP-80/46 1/800387, 1980, 44 pp. 
 
 3. Bennett, J., and D. Passmore. Probability of Death, Disabil- 
 ity, and Restricted Work Activity in United States Underground 
 Bituminous Coal Mines, 1975-1981. J. Safety Res., v. 15, 1984, pp. 
 69-76. 
 
 4. Cain, R., and R. Pettry. Investigation of Medical Costs Cor- 
 responding to Various Injuries in the Coal Industry and Subsequent 
 Implications of the Need for Ergonomic Research. Paper in Pro- 
 ceedings of the 1984 International Conference on Occupational 
 Ergonomics, Toronto, Canada, May 7-9, 1984, pp. 103-119. 
 
 5. Chi, D., and D. Di Canio. Mine Accident Cost Data Base and 
 Some Implications. Pres. at Am. Min. Congr. Min. Conv., San Fran- 
 cisco, CA, Sept. 11-14, 1983, 8 pp.; available upon request from D. 
 Chi, BuMines, Pittsburgh, PA. 
 
 6. Conway, E., F. Muckler, and J. Peay. Human Errors, Injuries 
 and Accidents— A Review and Analysis. Paper in Proceedings of 
 the Human Factors Society 26th Annual Meeting, Seattle, WA, 
 Oct. 25-29, 1982, pp.453-466. 
 
 7. Conway, E., and M. Sanders. Reduction of Human Errors, 
 Injuries and Accidents as a Result of Training: A Literature Review. 
 Paper in Proceedings of the Second International Symposium on 
 Training in the Prevention of Occupational Risks in the Mining 
 Industry, Washington, DC, Nov. 9-13, 1981, pp. 371-382. 
 
 8. De Greene, K. Systems Psychology. McGraw-Hill, 1972. 593 pp. 
 
 9. Hale, A., and M. Hale. Accident Literature Review. Commit- 
 tee on Safety and Health at Work. Her Majesty's Stationery Office. 
 London, UK, 1972, 96 pp. 
 
 10. Health and Safety Executive (London, UK). Health and Safety. 
 Mines. 1980, 23 pp. 
 
 11. Heinrich, H. Industrial Accident Prevention. McGraw-Hill, 
 4th ed., 1959, 462 pp. 
 
 12. Kephart, N., and J. Tiffin. Vision and Accident Experience. 
 Natl. Safety News, v. 62, 1950, pp. 90-91. 
 
 13. Kerr, W. Complementing Theories of Safety Psychology. J. 
 Social Psych., v. 45, 1957, pp. 3-9. 
 
 14. Lampert, U. Age and the Predisposition to Accidents. Archives 
 des Maladies Professionelles, v. 62, 1974, p. 173. 
 
 15. Lawrence, A. Human Error as a Cause of Accidents in Gold 
 Mining. J. Safety Res., v. 6, 1974, pp. 78-88. 
 
 16. Marovelli, R. A Comparison of American Safety Performance 
 to Other Countries. Min. Congr. J.. Aug. 1981, pp. 45-51. 
 
 17. Meister, D. Human Factors: Theory and Practice. Wiley 
 Interscience, 1971, 415 pp. 
 
 18. National Academy of Sciences. Toward Safer Underground 
 Coal Mines. 1982, 190 pp. 
 
 19. Nussey, C. Studies of Accidents Leading to Minor Injuries 
 in the UK Coal Mining Industry. J. Occupat. Accidents, v. 2. 1980. 
 pp. 305-323. 
 
 20. Sanders, M.S., T.V. Patterson, and J.M. Peay. The Effect of 
 Organizational Climate and Policy on Coal Mine Safety (contract 
 H0242039, Naval Weapons Support Center). BuMines OFR 108 
 1976, 180 pp.; NTIS PB 267 781. 
 
 21. Sanders, M., and B. Shaw. Research To Determine the Fre- 
 quency and Causes of Human Error Accidents in Underground Min- 
 ing. Ongoing BuMines contract J0348042: for inf.. contact J.M. 
 Peay, TPO, BuMines, Pittsburgh, PA. 
 
 22. Schaffer, L., G.R. Gavan, and J.L. Woodward. Normalizing 
 MESA-HSAC Injury Data for Coal Mine Mobile Equipment 
 Operators (contract J0265015, Woodward Assoc.). BuMines OFR 
 96-79, 1977, 178 pp.; NTIS PB 299 542. 
 
 23. Sims, M., R. Graves, and G. Simpson. "Near-Miss" Accident 
 Recording and Psychological Assessment Techniques of Accident 
 Investigations in the British Coal Mining Industry. Paper in Pro- 
 ceedings of the 1984 International Conference on Occupational 
 Ergonomics, Toronto, Canada, May 7-9. 1984, pp. 203-215. 
 
 24. Snyder, K. Supervisors' Deaths Often Linked to Earlier Dis- 
 ruption of Routine. Mine Safety and Health, Winter-Spring. 1984, 
 pp. 2-13. 
 
 25. Studenski, R. Studies Into the Mechanism of Occupational 
 Accidents. Przeglad Gorniczy (Engl. Trans.), v. 9. 1978. pp. 398-402. 
 
 26. Suchman, E. A Conceptual Analysis of the Accident Pheno- 
 menon. Social Problems, v. 8, No. 3, 1961, p. 241. 
 
 27. Swain, A., and H. Guttman. Handbook of Human Reliabil- 
 ity Analysis With Emphasis on Nuclear Power Plant Applications. 
 Sandia Lab.. Albuquerque, NM, 1983. 700 pp. 
 
 28. Theodore Barry and Associates. Fatality Analysis Data Base 
 Development (contract S0110601). BuMines OFR 22-73. 1972. 253 
 pp.; NTIS PB 219 250. 
 
 29. U.S. Mine Safety and Health Administration. Mine Injuries 
 and Worktime Quarterly. Jan-Dec. 1983. 1984. 34 pp. 
 
 30. Mine Injuries and Worktime Quarterly, Jan. -Dec. 
 
 1982. 1983, 18 pp. 
 
 31. Mine Injuries and Worktime Quarterly. Jan. -Dec. 
 
 1981. 1982, 18 pp. 
 
 32. Mine Injuries and Worktime Quarterly. Jan.-Dec. 
 
 1980. 1981, 18 pp. 
 
45 
 
 CHAPTER 5.— INFORMATION DISPLAYS 
 
 Information displays can be simple or complex. 
 
 Humans receive information from the environment, 
 process it, and take actions based on their judgments about 
 the information; thereby making information central to 
 everything they do. Information is received by humans 
 either directly or indirectly. Directly perceived information 
 would be involved when a shovel operator looks out his or 
 her cab window and sees the position of the shovel over a 
 haulage truck, or when an underground coal miner hears 
 the creaks and groans of the roof "working." Although a 
 great deal of information is received directly, we must often 
 rely on indirect sources of information because some stimuli 
 are beyond human sensing limits or can be sensed better 
 or more conveniently if converted to another type of repre- 
 sentation. Examples of indirect information include a sign 
 warning of dangers that might not be perceived, a temper- 
 ature gauge on a piece of equipment indicating the tem- 
 perature of a fluid that cannot be seen or touched, a map 
 showing the overall layout of an underground mine that 
 could not be directly seen without removing 800 ft of over- 
 burden and boarding an airplane, or a buzzer warning of 
 a dangerous level of methane that cannot be sensed. 
 
 The concern in this chapter is with the choice and design 
 of indirect sources of information, i.e., information displays. 
 A display, therefore, is considered to be any technique or 
 process for presenting indirect information. The informa- 
 tion can be conveyed through the visual, auditory, olfac- 
 tory, or tactual senses. Because most information displays 
 are visual and auditory in nature, this chapter will concen- 
 trate on these types. 
 
 CHOOSING A DISPLAY 
 
 In evaluating various information displays for human 
 use, several criteria are relevant. 
 
 1. Speed at which humans can receive and process the 
 information presented. 
 
 2. Accuracy of interpretation. 
 
 3. Speed in learning to use the display. 
 
 4. Comfort. 
 
 5. Absence of fatigue from long-term use. 
 
 6. Performance level under degraded environments and 
 stress. 
 
 The choice and design of information displays that max- 
 imize these criteria depend greatly on the type of task or 
 tasks for which the information is required. People need 
 information to perform the following seven generic tasks. 
 Each task places unique demands on a display to present 
 information in a manner that will facilitate its use. 
 
 1. Quantitative reading. —Must determine a specific 
 numeric value, such as pressure, weight, or speed. 
 
 2. Qualitative reading.— Need only approximate a value, 
 trend, rate of change, or direction of change. For example, 
 an operator might only have to know that pressure is ris- 
 ing or holding constant, but not the specific pressure value. 
 
 3. Check-reading.— Compare one or more displays to a 
 standard. For example, are the tensions on two lines equal? 
 
 4. Setting an indicator.— Set an indicator to a desired 
 value. For example, setting a timer to 90 s. 
 
 5. Tracking.— Must follow or compensate for a continu- 
 ously fluctuating stimulus. For example, maintaining a con- 
 stant flow by opening and closing a valve in response to 
 varying hydraulic pressures. 
 
 6. Spatial orientations.— Must determine location in 
 physical space. For example, determining where one is in 
 a mine and how to get back to the lift. 
 
 7. Receiving instruction or warning.— Must obtain infor- 
 mation about how or why to do something. For example, 
 a worker needs to know how many bags of rock dust to leave 
 at each of five sites in a mine. 
 
 It is common for a display to serve multiple purposes. 
 An operator may have to read a specific value from display 
 (quantitative), but may also need to know if there has been 
 a change, over time, in the value and in what direction the 
 change has occurred (qualitative). The same display may 
 also be used for check-reading when comparisons are made 
 with other similar displays. Further, the operator may have 
 to use the information on the display to set an indicator, 
 if it is out of tolerance. Such multiple-use situations present 
 interesting tradeoffs for a designer of displays. A display 
 designed for check-reading, for example, may not be opti- 
 mum for quantitative reading or vice versa. 
 
 A fundamental decision in display design is the choice 
 of display mode, i.e., visual, auditory, olfactory, or tactual. 
 Actually, in all but the most unusual circumstances, the 
 
46 
 
 choice is between the visual and auditory modes. In general, 
 visual displays are more appropriate than auditory displays 
 when the information has the following characteristics: 
 
 1. Long. 
 
 2. Complex. 
 
 3. Will be referred to later. 
 
 4. Deals with locations in space. 
 
 5. Does not call for immediate action. 
 
 Visual information can usually be read and reread, and 
 can be read at the receiver's pace. Auditory information, 
 once presented, is usually gone and is presented at a pace 
 set by the sender rather than by the receiver. 
 
 Further, visual displays are more appropriate than aud- 
 itory displays in the following situations: 
 
 1. Auditory system of a person is overburdened with too 
 many auditory information sources. 
 
 2. The receiving location is too noisy. 
 
 3. The receiver remains in one position rather than mov- 
 ing about continually. 
 
 Auditory displays, on the other hand, are more appro- 
 priate than visual displays when the information has the 
 following characteristics: 
 
 1. Simple. 
 
 2. Short. 
 
 3. Will not be referred to later. 
 
 4. Deals with events in time. 
 
 5. Calls for immediate action. 
 
 The best situations for auditory displays include the 
 following: 
 
 1. The visual system of a receiver is overloaded with too 
 many visual displays. 
 
 2. The receiving location is too bright or too dark for 
 visual information to be seen. 
 
 3. The information needs to be received regardless of the 
 position of the operator's head, i.e., you do not have to look 
 at an auditory display. 
 
 As can be seen, auditory signals are especially appro- 
 priate for presenting warnings that are usually simple, 
 short, and require immediate action. 
 
 VISUAL DISPLAYS 
 
 Estimates are that humans receive as much as 90% of 
 the information originating outside their bodies through 
 their visual senses. How this information is presented is 
 extremely important (7). 1 Advances in technology, including 
 remote sensing devices, video displays, and even wristwatch 
 televisions, hold both promise and challenge for the designer 
 and user of future systems. The mining industry is mak- 
 ing advances in the utilization of advanced technology, but 
 for the most part still depends on the tried and true, 
 "medium" technology equipment and displays it has used 
 for years. There are some good reasons for this hesitation 
 by the industry to embrace high-technology equipment. For 
 one thing, currently designed mining equipment is rugged, 
 lasts a long time, and is expensive to replace. In addition, 
 it is used in some of the most inhospitable environments, 
 which can adversely affect the reliability of some high- 
 technology equipment 
 
 The emphasis of this chapter, therefore, will be on the 
 design of more traditional visual displays still being used 
 and introduced in mining equipment. 
 
 Quantitative Displays 
 
 Quantitative displays are intended to convey to a user 
 the specific numerical value of some underlying variable 
 being measured by a device. This variable can be change- 
 able, e.g., speed, pressure, flow; or it can be essentially static 
 and unchanging, such as a ruler used to measure length. 
 
 There are three basic types of quantitative displays: (1) 
 fixed scale with moving pointer; (2) moving scale with fix- 
 ed pointer; and (3) digital displays, also called counters. Ex- 
 amples of these are shown in figure 5-1. There are strong 
 indications that a digital display is usually superior to an 
 analog display (moving pointer or moving scale) if a precise 
 numerical value is required and if the value presented re- 
 mains visible long enough to be read (12). But, if an operator 
 were required to report a precise pressure value during an 
 emergency where pressure was dropping rapidly, a digital 
 display would not be the choice. Given ample opportunity 
 to read the numerals on a digital display, however, both 
 speed and accuracy can be greatly improved upon that ob- 
 tained with a moving pointer display, as shown by the 
 following data from Zeff (21 ): 
 
 Digital display 
 
 Circular, fixed scale, 
 moving pointer 
 
 Response time, s Errors 
 0.94 0.5% 
 
 3.54 
 
 6.5% 
 
 Fixed scale, moving pointer displays, however, are 
 superior to digital displays for qualitative readings, such 
 as when an operator needs to sense the direction or rate 
 of change in a variable. In general, fixed scale, moving 
 pointer displays are better than moving scale, fixed pointer 
 displays; this is especially true when a control is used to 
 set a value under the fixed pointer. The reason for this is 
 that with a moving scale, fixed pointer, the scale has to 
 
 1 FIXED SCALE, MOVING POINTER | 
 
 40 50 60 TO 
 
 Semicircular Vertical 
 or curved 
 
 MOVING SCALE, FIXED POINTER 
 
 Decrease Increase 
 
 Horizontal 
 
 5 6 1 
 
 _) 
 
 Increase Decrrose 
 
 40 50 
 
 A 
 
 Circular 
 
 Open window Vertical 
 
 DIGITAL DISPLAY I 
 
 Humumu 
 
 I2|7|9|4|g 
 Counter 
 
 3M578 
 
 Electronic 
 
 1 Italic numbers in parentheses refer to items in the list of references at 
 the end of this chapter. 
 
 Figure 5-1.— Examples of quantitative displays (12). (Courtesy of 
 
 McGraw-Hill) 
 
47 
 
 move in a direction opposite to that in which the values are 
 changing. Look at the moving scale, fixed pointer vertical 
 display shown in the middle row of figure 5-1. To increase 
 the value, the scale must move down, yet "down" is usu- 
 ally associated with decreasing values. The principal ad- 
 vantage of moving scale, fixed pointer displays can be seen 
 in the open window displays in the middle row of figure 5-1. 
 Such displays take up a minimum amount of panel surface 
 area, yet can display a very large range of values. Often, 
 the scale is moved around spools behind the panel face. 
 
 Design Features of Quantitative Displays 
 
 Figure 5-2 illustrates several important concepts in the 
 design of quantitative displays: 
 
 1. Scale range.— The numerical difference between the 
 highest and lowest value on a scale. 
 
 2. Numbered value interval.— The numerical difference 
 between adjacent numbers on a scale. 
 
 3. Graduation interval value.— The numerical difference 
 represented by adjacent graduation values. 
 
 4. Scale unit value.— The smallest unit to which the scale 
 is to be read. This may or may not correspond to the 
 graduation-interval value. The scale in figure 5-2 is to be 
 read to the nearest pound; therefore, 1 lb would be the scale 
 unit value. 
 
 The following design recommendations were gleaned 
 from Bailey (i), McCormick and Sanders {12), and Oborne 
 (13). 
 
 Scale Markers 
 
 It is generally considered a good design practice to pro- 
 vide scale markers for every scale unit value. Figure 5-3 
 illustrates the recommended dimensions for scale markers 
 under both normal and low illumination conditions, assum- 
 
 ing a viewing distance of 28 in. In some circumstances, plac- 
 ing a marker at each scale unit produces a cluttered scale 
 with inadequate space between markers. In such cases it 
 is usually better to require an operator to interpolate be- 
 tween markers. Interpolation to fifths yields satisfactory 
 accuracy in many situations. 
 
 Scale range 
 (0-90lb) 
 
 Graduation interva 
 value (2 lb) 
 
 Numbered 
 
 value interval 
 
 (10 lb) 
 
 Figure 5-2.— Illustration of several numeric scale concepts. 
 
 Basic sketches, measurements in inches 
 
 Major scale marker 
 
 HK 0.125 
 
 CM 
 CM 
 
 r— Intermediate 
 
 0, 2 5HV Cale mQrker 
 rMo= 71 Minor scale 
 
 i 1 ^ 1 
 
 n 
 
 marker- 
 
 0.09 J 
 
 Mill 
 
 HH 0.05 
 
 Hvlinimum separation between 
 centers [could be 0.035] 
 
 Major scale marker 
 
 Intermediate scale 
 marker 
 
 Minor scale 
 
 -H H— 0.035 [-Intermediate scale 
 
 Tl* i marker 
 
 ■ 0.030HV ... , 
 
 ■ wv/ov Minor scale 
 
 3|h h—0.025 I marker—, 
 
 ill 1 1 III 1 1 1 1 
 
 1 
 
 o.io-J 
 
 / 
 
 0.07 
 
 Minimum separation between centers 
 
 Actual Size 
 
 milium 
 
 milium 
 
 B 
 
 Figure 5-3.— Recommended format for quantitative scales under normal (A) and low (B) illumination conditions (adapted by McCor- 
 mick (12) from reference 7). (Courtesy of McGraw-Hill) 
 
48 
 
 If a normal viewing distance greater than 28 in is ex 
 pected, the dimensions given in figure 5-3 must be increased 
 to maintain the same visual angle to the observer. The 
 following formula will correct the dimension of interest: 
 
 Dimension at X in. = (dimension at 28 in.) x (X/28). 
 
 Numerical Progression of Scales 
 
 The numbered intervals on a scale should be in ones, 
 twos, or fives, and multiples of 10. For example, 10-20-30, 
 20-40-60, 50-100-150, or .5-1.0-1.5 would be acceptable. Pro- 
 gression by threes, fours, and sixes should be avoided. 
 Decimals make scales more difficult to use; but if used, the 
 zero before the decimal should be omitted. 
 
 Design of Pointers 
 
 There is general agreement that pointers should— 
 
 1. Have a tip angle of about 20°. 
 
 2. Meet, but not overlap, the smallest scale marker. 
 
 3. Be colored the same as the scale markings from the 
 tip to the center, and be colored the same as the background 
 from the center to the tail. 
 
 4. Be as close to the dial face as possible to minimize 
 parallax. 
 
 Relative Importance of Design Features 
 
 The effects of the following seven factors on speed and 
 accuracy of dial reading (fixed scale, moving pointer) were 
 assessed by Whitehurst (19): 
 
 Numerical progression . . By 8 or by 10. 
 
 Scale unit length 3.2 or 6.4 mm. 
 
 Pointer width 6.4 or 0.8 mm. 
 
 Marker width 0.8 or 1.6 mm. 
 
 Scale number location . . . Same side as pointer 
 
 or opposite side. 
 Scale orientation Vertical or 
 
 horizontal. 
 Clutter Added words or 
 
 nothing added. 
 
 It was also found in this study that the two most im- 
 portant factors affecting reading speed and accuracy were 
 numerical progression (by 10 was better than by 8) and scale 
 unit length. (The more widely spaced arrangement was bet- 
 ter than the narrowly spaced arrangement.) The other fac- 
 tors had little effect on performance. 
 
 Qualitative Displays 
 
 The task of a user in obtaining qualitative information 
 from a display is to assess the appropriate value of some 
 quantitative variable or to estimate its trend or rate of 
 change. Often, the display that is best for obtaining a quan- 
 titative reading is not the best for obtaining a qualitative 
 reading. For example, three displays for the speed of mak- 
 ing both qualitative readings (pointer above 60, say "high;" 
 pointer 40-60, say "OK;" and pointer below 40, say "low") 
 and quantitative readings were compared by Elkin (6). The 
 three displays compared were an open-window fixed pointer, 
 moving scale; and two moving pointer, fixed scales, one cir- 
 
 cular and the other vertical. The results of this study are 
 shown in table 5-1. The open-window display resulted in 
 the fastest times for quantitative reading and the slowest 
 times for qualitative reading. 
 
 Table 5-1 .—Average times for qualitative and quantitative 
 reading, with three types of scales (6), seconds 
 
 (Courtesy of U.S. Wright Air Development Center) 
 
 Type of scale 
 
 Qualitative 
 
 Quantitative 
 
 Fixed pointer, moving scale: 
 
 Open window 
 
 Fixed scale, moving pointer: 
 
 Circular 
 
 115 
 
 107 
 101 
 
 102 
 113 
 
 Vertical 
 
 118 
 
 
 
 If a quantitative scale can be divided into a limited 
 number of zones or ranges, color coding or shape coding can 
 be added to the dial to demarcate the regions, as shown in 
 figure 5-4. Response time for three dial designs, two of which 
 used coding techniques to represent danger zones, were com- 
 pared by Kurke (11). The task was to respond when the 
 pointer was in a danger zone. Figure 5-5 shows the designs 
 and the relative response times using the uncoded display 
 as the base (100%). As can be seen, a substantial decrease 
 in response time is realized by the addition of simple color 
 coding, and an even more dramatic decrease is effected by 
 using the more complex wedge design. 
 
 Check-reading an array of dials to determine if all con- 
 ditions are normal is really just a special class of qualitative 
 information seeking. Several persons have investigated ar- 
 rangements of dials to facilitate such check-reading activi- 
 ties, such as the study by Dashevsky (4). The general 
 wisdom is that such dials should be arranged in neat rows 
 and columns, with the normal positions of the pointers all 
 aligned in the 9 o'clock or 12 o'clock position (4). This ar- 
 rangement yields more accurate detection of deviant dials 
 than if the normal positions are not consistent. It was found 
 by Elkin (6), for example, that people made 350% more er- 
 rors when the dials were subgrouped as shown in figure 5-6 
 than when all the normal pointer positions were at 12 
 o'clock. 
 
 
 Normal 
 
 Cold 
 
 Normal 
 
 
 (green) 
 i 
 
 (yellow) 
 Caution \ 
 
 (green) 
 
 Caution 
 (yellow)^ 
 
 
 
 (yellow) >C3 
 
 S\\ Hot 
 / V-^(red) 
 
 Danger 
 (red) 
 
 Caution 
 
 Figure 5-4.— Illustrations of coding methods for marking zones 
 of instruments that are to be read qualitatively (12). (Counssyof 
 
 McGraw-Hill) 
 
49 
 
 A. No indication of 
 
 "danger H zones 
 
 (0-1,9-10) 
 
 1 00 pet 
 
 a. 
 
 Red line indicating 
 "danger" zones 
 
 C. Red wedge appears 
 when pointer is in 
 "danger" zone 
 74 pet 1 5 pet 
 
 Mean time as percentage of condition A 
 
 Figure 5-5.— Mean response time for detecting pointer in danger zone for three dial displays, where the mean response time is 
 shown as a percentage of dial design. (Adapted by McCormick and Sanders (12) from reference 11, courtesy of McGraw-Hill) 
 
 12 o'clock 
 pattern 
 
 Varied (subgroup) 
 pattern 
 
 © o © o 
 
 G © Q 
 
 o o o © 
 
 © © 
 
 o o o © 
 
 Q © O 
 
 © o o o 
 
 O O © 
 
 Figure 5-6.— Two patterns of 
 a check-reading experiment. Tht 
 in 350% more errors than did 
 
 dials used by Dashevsky (4) in 
 t subgroup arrangement resulted 
 the 12 o'clock arrangement. 
 
 SIGNAL AND WARNING LIGHTS 
 
 Signal and warning lights are often used in the mining 
 industry to indicate operation of equipment, such as con- 
 veyors or vehicles, and to attract attention to a potentially 
 dangerous situation, such as on an instrument panel or on 
 a barricade around a newly dug hole. Unfortunately, there 
 is little research relating to such signals, but some general 
 conclusions can still be made. 
 
 The detectability of a light depends on its size, lumin- 
 ance (i.e., brightness), contrast with its background, and 
 time available to detect it. A number of recommendations 
 were offered by Heglin (8) regarding the use of signal and 
 warning lights on instruments panels. 
 
 When should they be used— To warn of actually or poten- 
 tially dangerous conditions. 
 
 How many warning lights. —Ordinarily only one. (If sev- 
 eral warning lights are required, use a master warning or 
 caution light and a word panel to indicate the specific 
 danger condition.) 
 
 Steady-state or flashing.— Because they are distracting, 
 flashing lights should be reserved for emergencies. 
 
 Flash durations.— If flashing lights are used, flash rates 
 should be from 3 to 10 per second (4 is best), with equal in- 
 tervals of light and dark. 
 
 Warning-light intensity.— The light should be at least 
 twice as bright as its immediate background. 
 
 Light size.— The warning light should ordinarily be 1.5 
 times the size of other indicators on a console. Master warn- 
 ing or extreme emergency light should be twice the size of 
 other console indicators. 
 
 Location.— The warning light should be within 30° of the 
 operator's normal line of sight. 
 
 Color.— Warning lights are normally red because red 
 means danger to most people. (Other signal lights in the 
 area should be other colors.) 
 
 An extension of the idea of using lights to warn is us- 
 ing retroreflective material to draw attention to a poten- 
 tial danger. Retroreflective material (or paint) contains 
 minute glass spheres that return light directly back to the 
 light source. The amount of light that is reflected to the eye, 
 however, becomes less as the angle from the eyes to the ob- 
 ject and from the object to the light source increases. A par- 
 ticularly good application of retroreflective material is to 
 make underground miners more visible to equipment oper- 
 ators. The effect of various configurations of retroreflective 
 material on detectability was tested by Beith, Sanders, and 
 Peay (2). A one-fifth scale simulator was used in the study 
 Dolls with miniature functioning caplamps and retroreflec- 
 tive material on their helmets served as miners to be 
 detected at various viewing angles in various body postures. 
 
50 
 
 At the most severe viewing angle (i.e., 45° from the line 
 of sight), probability of detection almost doubled when retro- 
 reflective armbands and/or belts were added to the dolls. 
 
 SIGNS AND LABELS 
 
 Warning and information signs and labels are common 
 in the mining industry and some are even mandated by the 
 Code of Federal Regulations. Usually, signs convey impor- 
 tant safety information or warn of potential hazards and 
 dangers. It is important, therefore, that signs and labels 
 be designed and displayed to maximize their effectiveness. 
 Three attributes that are important in evaluating the ef- 
 fectiveness of signs and labels are visibility, legibility, and 
 comprehension. 
 
 First, a sign or label must be seen and distinguished 
 from its surroundings (visibility). The size, color, and place- 
 ment of a sign or label are important determinants of visi- 
 bility. Once a sign or label has attracted the attention of 
 the viewer and has been seen, its alphanumeric or symbol 
 characters must be easy to read or identify (legibility). This 
 depends on such features as the size and form of the char- 
 acters, and the contrast and illumination of the sign or label. 
 Finally, the message presented must be understood by the 
 viewer (comprehension). As will be seen, this can pose a real 
 problem with pictorial-symbol signs. 
 
 Typography 
 
 Two important characteristics of alphanumeric charac- 
 ters depicted in figure 5-7 are stroke width to height ratio 
 and width to height ratio. Various stroke width to height 
 ratios are illustrated in figure 5-8 for black letters on a white 
 background and for white letters on a black background. 
 Under good viewing conditions (normal illumination, no 
 time constraint), most people can adequately discriminate 
 alphanumeric characters over a wide range of stroke width 
 to height ratios. Under adverse conditions, however, this 
 variable becomes more important. The optimum ratio is 
 smaller (i.e., thinner letters), for white characters on a black 
 background (1:8-1:10) than for black characters on a white 
 background (1:6-1:8). This is due to a phenomenon called 
 irradiation in which white features appear to spread into 
 adjacent black areas. 
 
 Experimental evidence suggests that for capital letters, 
 a width to height ratio of about 1:1 is optimum, but that 
 it can be reduced to about 3:5 without serious loss in legibil- 
 ity. In general, alphanumeric characters that have uniform 
 stroke widths and strokes that do not have serifs (flourishes 
 and embellishments) are more legible than fancy nontradi- 
 tional styles. 
 
 An important variable affecting legibility of a sign or 
 label is the size of the characters or symbols used in rela- 
 tion to the anticipated viewing distance. To be equally leg- 
 ible, a sign or label must be made larger if it is moved 
 farther from the viewer. A simple formula for determining 
 the height of letters, given the viewing distance, importance 
 of the sign or label, and illumination and reading condi- 
 tions was developed by Peters and Adams (14). The formula, 
 however, should probably not be applied to viewing dis- 
 
 X - 
 
 Stroke width to height = Z:Y 
 Width to height = X'Y 
 
 Figure 5-7.— Definition of stroke width to height and width to 
 height ratios for alphanumeric characters. 
 
 Stroke 
 
 width to 
 
 height 
 
 ratio 
 
 Black on white 
 
 1 = 5 
 
 ABC 
 
 456 
 
 l<6 
 
 ABC 
 
 -456 
 
 1-8 
 
 ABC 
 
 -456 
 
 I MO 
 
 ABC 
 
 456 
 
 1 12 
 
 ABC 
 
 45 6 
 
 White on black 
 
 ABC 
 
 456 
 
 ABC 
 
 45 6 
 
 ABC 
 
 456 
 
 ABC 
 
 456 
 
 ABC 
 
 45 6 
 
 Figure 5-8.— Illustrations of stroke width to height ratios of let- 
 ters and numerals (12). (Courtesy of McGraw-Hill) 
 
 tances beyond 60 in, because the correction for importance 
 and reading condition may be inadequate. The formula is 
 as follows: 
 
 H = 0.0022D + K, + K„ 
 
 where H = height of letter, in, 
 D = viewing distance, in, 
 K, = correction factor for illumination and viewing 
 
 condition; 
 
 0.06 (abo\-e 1.0 fc, favorable reading 
 
 condition), 
 
 0.16 (above 1.0 fc, unfavorable reading 
 
 condition), 
 
 0.16 (below 1.0 fc, favorable reading conition), 
 
 and 
 
 0.26 (below 1.0 fc. unfavorable reading 
 
 condition), 
 and K 2 = correction factor for importance; 
 
 0.075 for emergency and warning signs. 
 
 0.000 for all other signs. 
 
51 
 
 Table 5-2 uses this formula to compute letter heights for 
 various representative viewing distances from 14 to 60 in. 
 For viewing distances beyond 60 in, under varying illumina- 
 tion conditions, letters on emergency signs should subtend 
 approximately 30' of visual angle. Table 5-3 summarizes 
 the recommendations. 
 
 Table 5-2.— Recommended letter heights for labels and 
 signs for various distance conditions, 1 inches 
 
 14 
 
 0.09 
 .19 
 .29 
 
 .17 
 .27 
 .37 
 
 28 
 
 0.12 
 .22 
 .32 
 
 .20 
 .30 
 .40 
 
 48 
 
 0.17 
 .27 
 .37 
 
 .24 
 .34 
 .44 
 
 60 
 
 0.19 
 .29 
 .39 
 
 .27 
 .37 
 .47 
 
 Distance in. 
 
 Unimportant, K 2 <0.0: 
 
 K, <0.06 
 
 K, <0.16 
 
 K, <0.26 
 
 Important, K 2 <0.075: 
 
 K, <0.06 
 
 K, <0.16 
 
 Ki <0.26 
 
 1 Based on formula by Peters (14). 
 
 Table 5-3.— Recommended heights of letters on emergency signs 
 
 Viewing distance, ft Letter height, in 
 
 10 1.04 
 
 20 2.08 
 
 40 4.16 
 
 100 10.44 
 
 *Exit 72 pet 
 
 No passageway, 
 dead end 27 pet 
 
 A 
 
 Danger from rotating 
 
 fan blades 47 pet 
 
 ♦Radiation hazard 
 
 present 38 pet 
 
 Fallout shelter 
 location 1 4 pet 
 
 *Eye wash location 68 pet 
 Eye irritant 
 located here 24 pet 
 
 A 
 
 •Corrosive hazard 71 pet 
 2 1 pet 
 
 Emergency hand 
 wash location 
 
 ♦Correct interpretation 
 
 Figure 5-9.— Examples of pictorial signs that caused confusion 
 among mining industry employees. Most frequent interpretations 
 are given below each figure with the percentage of subjects 
 choosing each response given (3). 
 
 of what it was intended to mean. Appendix C presents the 
 pictorial warning signs recommended by Collins (3) for use 
 in the mining industry, based on her tests of underground 
 and surface mine employees. 
 
 Pictorial Signs and Labels 
 
 Although written signs and labels are probably the most 
 commonly used method of providing safety and hazard in- 
 formation, pictorial or symbolic signs are becoming more 
 and more common in industry. The following advantages 
 of pictorial signs over written signs were cited by Collins 
 (3). They provide essential information— 
 
 1. More rapidly, 
 
 2. More accurately, 
 
 3. At a greater distance, 
 
 4. In less space, 
 
 5. Without being language specific, and 
 
 6. Without the need to read written language. 
 
 All these advantages, however, do not come free. The 
 development of pictorial signs that will be understood by 
 a viewing population is a difficult task. For example, 72 
 symbols to depict 40 different hazard and safety messages 
 appropriate to the mining industry were developed. The 
 comprehension of these symbols was tested among a diverse 
 group of 271 underground and surface mine employees (3). 
 Only 44% of the symbols were comprehended correctly by 
 more than 90% of the people. More than 25% of the sym- 
 bols were correctly comprehended by less than 75% of the 
 people. Similar difficulties and results were obtained by 
 Woo (20) in his evaluation of pictorial hazard signs on sur- 
 face mobile mining equipment. Figure 5-9 shows a few ex- 
 amples of pictorial signs that were not readily understood 
 by the mining population tested by Collins (3). In some in- 
 stances, workers interpreted the sign to mean the opposite 
 
 AUDITORY DISPLAYS 
 
 As pointed out at the beginning of this chapter, the 
 auditory channel is especially effective for presenting warn- 
 ing information. Such information is usually short, requires 
 immediate action, and must be received by people even if 
 they move about from one location to another. 
 
 To be effective, auditory information must be detected 
 by a listener. That is, an auditory signal must be heard 
 above any background noises in an environment. If there 
 is more than one auditory signal that must be responded 
 to, then a listener must discriminate between them. In some 
 cases, a listener must specifically identify a signal, such as 
 identifying a sound as a sticky intake valve or a loose fan 
 blade. 
 
 In addition to discussing auditory alarms, the topic of 
 speech communication is also addressed as a form of audi- 
 tory display. 
 
 Alarms 
 
 There are numerous types of auditory alarms available 
 today; table 5-4 lists some characteristics of various generic 
 types. To insure that an alarm will be heard above an am- 
 bient noise environment, the intensity of the alarm must 
 be higher than the intensity of the noise. 
 
 A procedure and rule of thumb for specifying the opti- 
 mum intensity for a signal or an alarm was suggested by 
 Deatherage (5). First, adjust the intensity of the signal un- 
 til it is just barely detectable in the noise environment at 
 
52 
 
 Table 5-4.— Characteristics and features of certain types of audio alarms (5) 
 
 (Copyright 1972 by John Wiley and Sons, and reprinted by permission.) 
 
 Alarm 
 
 Intensity 
 
 Frequency 
 
 Attention 
 getting 
 ability 
 
 Noise-penetration 
 ability 
 
 Diaphone (foghorn) 
 
 Horn . 
 
 Very high 
 
 Very low 
 
 Low to high 
 
 . . do 
 
 . .do 
 
 do 
 
 Medium to high 
 
 Good 
 
 . . do 
 
 Good, if intermittent 
 
 Very good if pitch rises 
 and falls. 
 
 Good 
 
 . .do 
 
 Fair 
 
 Good, if intermittent 
 
 Poor in low-frequency noise. 
 Good. 
 
 High 
 
 Whistle 
 
 Siren 
 
 Bell 
 
 . .do 
 
 ..do 
 
 . . do 
 
 Medium 
 
 Low to medium 
 
 Good, if frequency is 
 
 properly chosen. 
 Very good with rising and 
 
 falling frequency. 
 Good in low-frequency noise. 
 Fair if spectrum is suited to 
 
 Buzzer 
 
 Low to medium 
 
 Chimes and gong 
 
 Oscillator 
 
 ..do 
 
 Low to high 
 
 . . do 
 
 Medium to high 
 
 background noise. 
 Do. 
 Good if frequency is properly 
 chosen. 
 
 normal operator work positions. Turn the noise off and 
 measure the intensity of the signal at the entrance to the 
 ear (called the masked threshold). Repeat this with several 
 people and average the results. The rule of thumb is to set 
 the intensity of the signal midway between the masked 
 threshold and 110 dB. Thus, if a signal could just barely 
 be heard in noise at 50 db, then one would be confident of 
 its detection in noise if it were set at 80 dB. 
 
 In addition to setting the intensity of a signal above the 
 background noise level, the frequency of the signal can be 
 selected to maximize its detectability. The idea is to select 
 a signal frequency that corresponds to the lowest intensity 
 frequency region of the background noise. Also, where possi- 
 ble, it is best to select a signal frequency below the domi- 
 nant frequency of the background noise; this is because loud 
 noise of a given frequency tends to mask signals higher than 
 its frequency more than it masks signals lower than its 
 frequency. 
 
 Under some conditions, especially those involving very 
 high intensity noise, the use of hearing protectors can in- 
 crease the detectability of a signal. This occurs because the 
 hearing protection brings the noise and signal intensity 
 down so that the signal can be more easily detected. 
 
 McCormick and Sanders (12) provided the following list 
 of general design recommendations for auditory warning 
 and alarm signals which were gleaned from various sources: 
 
 Use frequencies between 200 and 5,000 Hz, and preferably 
 between 500 and 3,000 Hz, because the ear is most sensitive 
 to this middle range. 
 
 Use frequencies below 1,000 Hz when signals have to 
 travel long distances (over 1,000 ft), because high frequen- 
 cies do not travel as far. 
 
 Use frequencies below 500 Hz when signals have to "bend 
 around" major obstacles or pass through partitions. 
 
 Use a modulated signal (1 to 8 beeps per second or 
 warbling sounds varying from 1 to 3 times per second), 
 because it is different enough from normal sounds to de- 
 mand attention. 
 
 Use signals with frequencies different from those that 
 dominate any background noise to minimize masking. 
 
 If different warning signals are used to represent different 
 conditions requiring different responses, each should be 
 discernible from the others, and moderate intensity signals 
 should be used. 
 
 Where feasible, use a separate communication system for 
 warnings, such as loudspeakers, horns, or other devices, not 
 used for other purposes. 
 
 It should be pointed out that some of these recommen- 
 dations can create conflicting situations. For example, 
 because mining noise tends to be of low frequency, it would 
 be best to use a high-frequency signal, despite the fact that 
 high frequencies do not carry as far as low-frequency sounds. 
 
 Speech 
 
 Speech is the most common method for transmitting in- 
 formation between humans. With the development of reli- 
 able, inexpensive speech synthesis and recognition systems, 
 it may also become a common method for transmitting in- 
 formation between humans and machines. Speech is one 
 of the most complex, yet suitable forms of communication. 
 Although there are only about 40 speech sounds in the 
 English language, these can be put together to convey the 
 most complex of messages. 
 
 Intensity of Speech 
 
 Different speech sounds have different levels of speech 
 power (intensity). In general, the vowel sounds contain more 
 speech power than do the consonant sounds. The a as pro- 
 nounced in talk has approximately 680 times the speech 
 power of th as pronounced in then. Unfortunately, the less 
 powerful consonant sounds are the most important for 
 understanding speech. 
 
 The overall intensity of speech, of course, varies from 
 person to person. The following, however, are representative 
 intensities averaged over large samples of speakers: 
 
 Talking as softly as possible 46 ABA 
 
 Lecture or telephone conversation 66 ABA 
 
 Talking as loudly as possible 86 ABA 
 
 Intelligibility of Speech 
 
 Intelligibility is the extent to which a spoken message 
 is understood by a listener. How much of a message is under- 
 stood depends, among other things, on the nature of the 
 message and the expectation of the listener. The English 
 language is very redundant: one does not have to hear every 
 syllable to understand a word, nor even - word to understand 
 a sentence. Further, if a listener has some idea about what 
 a message will pertain to. the probability of understanding 
 the message increases. 
 
53 
 
 In the mining industry, speech communication often 
 takes place in noisy environments, such as processing 
 plants, or near large mining machines. Intelligibility under 
 such conditions is of critical importance for maintaining pro- 
 ductivity and safety. One way to increase intelligibility, 
 especially in the presence of noise, is to limit the size of the 
 vocabulary and make a list of words known to both the 
 listener and speaker. Rather than use them interchange- 
 ably, one of several words to mean the same thing, agree 
 on one term and use it consistently. For example, the words 
 "increase," "raise," "up," "advance," "augment," and "in 
 tensify" can all mean the same thing. Rather than use them 
 interchangeably, one word should be selected and used con- 
 sistently. When selecting standard vocabulary words, 
 consider potential confusion between words. For example, 
 rather than using "increase" and "decrease," it would be 
 better to use "raise" and "lower" because they are less 
 likely to be confused in a noisy environment. 
 
 In general, complete sentences have higher levels of in- 
 telligibility than do single words, and long words are more 
 intelligible than short words. Words commonly used every 
 day are more intelligible than uncommon words. A classic 
 example of increasing the length of a word to increase its 
 intelligibility is the use of the International Word-Spelling 
 Alphabet. Rather than telling a mechanic to get part 
 number ABE-136, one would say "Alpha-Bravo-Echo-one- 
 three-six." In a noisy environment, ABE is easily confused 
 with APE. 
 
 Preferred Octave Speech Interference Level (PSIL) 
 
 This index, reported by Peterson and Gross (15), gives 
 a rough evaluation of the effect a noisy environment has 
 on the transmission of speech. It is relatively easy to assess 
 and compute if the right equipment is available. A sound 
 pressure meter is needed that can measure intensity (sound 
 pressure in decibels) in three octave bands centered at 500, 
 1,000, and 2,000 Hz. The PSIL is simply the average of the 
 decibel levels of the noise in the three octave bands. This 
 technique is appropriate where the noise is relatively con- 
 tinuous and its spectrum (intensity at various frequencies) 
 is relatively flat. Given the PSIL, table 5-5 can be used to 
 determine the maximum distance that two people can be 
 
 Table 5-5.— Maximum distance between speaker and 
 
 listener to carry on a satisfactory conversation in various 
 
 intensity voices under ambient noise conditions defined by 
 
 the preferred octave speech interference level (PSIL) (18), feet 
 
 (Courtesy of National AcaHemv Press) 
 
 PSIL, 
 dB 
 
 40 
 
 45 
 
 50 
 
 55 
 
 60 
 
 65 
 
 70 
 
 75 
 
 80 
 
 85 
 
 90 
 
 95 
 
 100 
 
 105 
 
 110 
 
 120 
 
 NAP Not applicable. 
 
 Normal 
 
 32 
 16 
 
 8 
 
 5 
 
 3 
 
 1.75 
 .75 
 .5 
 NAp 
 NAp 
 NAp 
 NAp 
 NAp 
 NAp 
 NAp 
 NAp 
 
 Raised 
 
 >32 
 
 32 
 
 17 
 
 10 
 
 6 
 
 3 
 
 2 
 
 1 
 
 .5 
 
 NAp 
 
 NAp 
 
 NAp 
 
 NAp 
 
 NAp 
 
 NAp 
 
 NAp 
 
 Very 
 loud 
 
 >32 
 >32 
 >32 
 
 23 
 
 12 
 
 7 
 
 3.5 
 
 2 
 
 1 
 
 .6 
 
 NAp 
 
 NAp 
 
 NAp 
 
 NAp 
 
 NAp 
 
 NAp 
 
 Shout 
 
 >32 
 >32 
 >32 
 >32 
 
 24 
 13 
 
 7 
 
 4 
 
 2 
 
 1.25 
 .75 
 NAp 
 NAp 
 NAp 
 NAp 
 NAp 
 
 Max vocal 
 effort 
 
 >32 
 >32 
 >32 
 >32 
 >32 
 >32 
 >32 
 30 
 16 
 
 8 
 
 5 
 
 3 
 
 1.5 
 
 1 
 .5 
 NAp 
 
 apart and converse in a normal voice, raised voice, very loud 
 voice, or shouting voice. These limits represent distances 
 where 98% of the speech would be heard. Thus, in a proc- 
 essing plant where the PSIL was 80 dB, two people could 
 converse in a raised voice at 0.5 ft apart, in a very loud voice 
 at 1 ft, in a shouting voice at 2 ft, and with maximum vocal 
 effort at 16 ft. 
 
 Hearing Protection and Speech 
 
 It was found by Howell and Martin (9) that hearing pro- 
 tection did not degrade speech intelligibility for a listener. 
 This was confirmed in high-noise environments (90 dBA), 
 but a decrease in intelligibility in low-noise (70 dBA) envi- 
 ronments was found (1 7). Reference 9, however, found that 
 if those talking wore hearing protection, their speech was 
 reduced in both intensity and quality, and intelligibility ac- 
 tually decreased for the listener. The lesson here is that, 
 in noisy situations where people wear hearing protection, 
 extra effort must be made to speak loudly and clearly. Peo- 
 ple will think they are speaking more loudly than they 
 really are, and therefore must be made aware of this to com- 
 pensate for their misperceptions. 
 
 Underground Loudspeaker System: A Case Study 
 
 Results of adding a loudspeaker telephone system to an 
 underground longwall coal face in the Netherlands were 
 reported by Koene and Ruwette (10). The particular face 
 was approximately 790 ft in length with a working height 
 of approximately 3 ft. The face was equipped with the follow- 
 ing communication systems prior to installation of the 
 loudspeaker phones: 
 
 1. Dial telephones at the ends of the face. 
 
 2. Telephone sets at a number of points on the actual coal 
 face. (Face lights were flashed to signal a call, but there 
 was no way to determine which telephone should be 
 answered or who was being called.) 
 
 3. Elaborate signaling by flashing the face lights. 
 
 4. Messages transmitted verbally from person to person. 
 The loudspeaker telephones were installed every 60 to 
 
 70 ft. Each set incorporated two loudspeakers and a micro- 
 phone. Pressing of the microphone switch enabled transmis- 
 sion of a message through all the loudspeakers on the coal 
 face. A whistle signal could also be transmitted. 
 
 Problems During Introduction of the System 
 
 Koene and Ruwette (10) also indicated the following 
 social-psychological communications problems caused after 
 the system was installed: 
 
 1. Personnel were initially timid about using the system. 
 
 2. Because of the public nature of the communications, 
 greater control of language, criticism, and negative remarks 
 was required. 
 
 3. Supervisory staff had a tendency to intervene when a 
 lower ranking supervisor gave an instruction, thereby 
 undermining his or her authority. 
 
 4. There was a temptation to transmit messages encourag- 
 ing workers to work harder. This reduced the credibility 
 of the system. 
 
 5. The system was used like a regular telephone; the per- 
 son to whom the message was addressed was required to 
 reply. 
 
 6. Supervisors sought more information than was needed 
 to conduct proper operations. 
 
 These investigators indicate that, with proper instruc- 
 tion, these initial problems were reduced or eliminated. 
 
54 
 
 Results of Installation 
 
 With the loudspeaker system, one supervisor did the 
 work of the two required before the system was installed. 
 This was accomplished without increasing the distance 
 traveled by the supervisor to perform the job. The major 
 finding was that after installation, the duration of stoppages 
 per shift decreased from 160 to 128 min, a reduction of 20%. 
 Compared with all coal faces in the mine, the test site had 
 a lower percentage of utilization rate before installation (i.e., 
 percentage of time coal was being extracted). After installa- 
 tion, the percentage of utilization was higher than the over- 
 all mine average. There was clear evidence that the system 
 reduced the duration of stoppages by supplying necessary 
 information to everyone along the coal face. Better coordina- 
 tion of material transport and repositioning of props reduced 
 the number and duration of sucb stoppages. Response times 
 to emergencies were significantly reduced, and the 
 responses were more coordinated. 
 
 OLFACTORY DISPLAYS 
 
 Although olfactory displays are not very common, there 
 are applications where their use can be beneficial. In facil- 
 ities served by natural gas, for example, an odorant is added 
 to the naturally odorless gas to aid in the detection of leaks. 
 Another example of an olfactory display is the use of stench 
 systems in underground noncoal mines to warn of a fire or 
 other emergency. Miners, upon smelling the stench, evac- 
 uate the mine according to a prearranged plan. 
 
 Stench systems have been used for 60 yr in underground 
 mines. The odorant most commonly used, ethyl mercaptan, 
 however, is highly toxic and sometimes causes nausea 
 among the miners. In 1980, the Bureau embarked on a pro- 
 gram to develop an improved stench system (16). The 
 chemical tetrahyprothiophane (THT) was selected as the 
 odorant; it is widely used in Europe as a natural gas odorant 
 and is not as toxic as ethyl mercaptan. In a field test of the 
 new system, which included a new method for dispersing 
 the odorant, average penetration time (time from release 
 to detection at various locations within the mine) was 10.5 
 min compared to 19.6 min using the old system, a reduc- 
 tion of 46%. 
 
 DISCUSSION 
 
 Information is critical for safe, productive work; it is 
 necessary for guidance of decisionmaking and actions. Many 
 sources of information are not readily available so indirect 
 sources of information are relied on— information displays. 
 This chapter has reviewed some human factors considera- 
 tions in the design of medium-technology visual and audi- 
 tory displays, signal lights and signs, and has illustrated 
 that speed and accuracy are affected by how these infor- 
 mation sources are designed. 
 
 Although high-technology computer displays were not 
 dealt with, as their use in mining is still relatively small, 
 many of the same principles of design apply. Concern with 
 detectability, legibility, and comprehension still remain. 
 With many computer displays, information overload often 
 is an additional problem. Operators are presented with a 
 screen full of numbers and are expected to analyze and in- 
 terpret the meaning of the information presented. Much can 
 be done to improve such displays, including presenting only 
 the information the operator really needs to do the tasks, 
 
 use of color coding, and proper layout of information on the 
 screen. The human factors literature has really only 
 scratched the surface with regard to formatting computer- 
 displayed information. It is anticipated that in the future 
 more guidance on proper designs will be available. Until 
 then, as with other medium-technology displays, existing 
 human factors can be applied, keeping in mind the infor- 
 mation needs of the operator, supplying neither less nor 
 more than is required, and trying to do so in a manner that 
 requires the least amount of mental processing. 
 
 REFERENCES 
 
 1. Bailey, R. Human Performance Engineering: A Guide for 
 System Designers. Prentice Hall, 1982, 672 pp. 
 
 2. Beith, B., M. Sanders, and J. Peay. Using Retroreflective 
 Material to Enhance the Conspicuity of Coal Miners. Human Fac- 
 tors, v. 24, No. 6, 1982, pp. 727-735. 
 
 3. Collins, B.L. Use of Hazard Pictorials/Symbols in the Minerals 
 Industry (contract J0113020, NBS). BuMines OFR 44-84, 1983, 193 
 pp.; NTIS PB 84-165877. 
 
 4. Dashevsky, S. Check-Reading Accuracy as a Function of 
 Pointer Alignment, Patterning, and Viewing Angle. J. Appl. Psych., 
 v. 48, 1964, pp. 344-347. 
 
 5. Deatherage, B. Auditory and Other Sensory Forms of Infor- 
 mation Presentation. Ch. in Human Engineering Guide to Equip- 
 ment Design, ed. by H. Van Cott and R. Kinkade. Wiley, 1972. pp. 
 123-160. 
 
 6. Elkin, E. Effect of Scale Shape, Exposure Time and Display 
 Complexity on Scale Reading Efficiency. U.S. Air Force Wright 
 Air Devel. Center, Dayton, OH, TR-58-472, 1959, 142 pp. 
 
 7. Grether, W., and C. Baker. Visual Presentation of Informa- 
 tion. Ch. in Human Engineering Guide to Equipment Design, ed. 
 by H. Van Cott and R. Kinkade. Wiley, 1972, pp. 41-122. 
 
 8. Heglin, H. NAVSHIPS Display Illumination Design Guide. 
 Volume II: Human Factors. U.S. Naval Electronics Lab Center, 
 San Diego, CA, NELC/TD223. 1973, 313 pp. 
 
 9. Howell, K., and A. Martin. An Investigation of the Effects of 
 Hearing Protectors on Vocal Communication in Noise. J. Sound 
 and Vibration, v. 41, 1975, pp. 181-196. 
 
 10. Koene, G., and L. Ruwette. Communication at the Coal Face. 
 Eur. Coal and Steel Community, Ergonomic Res.. Doc. 97 70e RCE. 
 1970, 52 pp. 
 
 11. Kurke, M. Evaluation of a Display Incorporating Quantitative 
 and Check-Reading Characteristics. J. Appl. Psych., v. 40. 1956. 
 pp. 233-236. 
 
 12. McCormick, E., and M. Sanders. Human Factors in Engineer- 
 ing and Design. McGraw-Hill. 5th ed., 1982, 615 pp. 
 
 13. Oborne, D. Ergonomics at Work. Wiley, 1982. 321 pp. 
 
 14. Peters, G., and B. Adams. The Three Criteria for Readable 
 Panel Markings. Product Eng.. v. 30, No. 21. 1959. pp. 55-57. 
 
 15. Peterson, A., and E. Gross. Handbook of Noise Measurement. 
 General Radio Co., Concord. MA, 8th ed., 1978. 322 pp. 
 
 16. Pomroy, W.. and T. Muldoon. A New Stench Gas Fire Warn- 
 ing System. Pres. at 52nd Annual Tech. Session of the Mine Acci- 
 dent Prevention Assoc, of Canada. Toronto. Canada. May 25-27. 
 1983, pp. 83-91. 
 
 17. Prout, J.H.. P.L. Michael, and L.W. Saperstein. A Study of 
 Roof Warning Signals and the Use of Personal Hearing Protection 
 in Underground Coal Mines (grant G0133026. PA State Univ.i. 
 BuMines OFR 46-74, 1973, 238 pp.: NTIS PB 235 S54 
 
 18. Webster, J. Effects of Noise on Speech Intelligibility. Am. 
 Speech-Language-Hearing Assoc., Rockville. MD. ASHA Rep. 4. 
 1969, 16 pp. 
 
 19. Whitehurst, H. Screening Designs Used To Estimate the 
 Relative Effects of Display Factors on Dial Reading. Human Fac- 
 tors, v. 24, No. 3. 1982. pp. 301-310. 
 
 20. Woo, J. Perception of Hazard Pictorials on Surface Mobile 
 Mining Equipment. Trans Systems Co.. Vienna. VA. 19S0. 174 pp. 
 
 21. Zeff, C. Comparison of Conventional and Digital Time 
 Displays. Ergonomics, v. 8. No. 3. 1965. pp. 339-345. 
 
55 
 
 CHAPTER 6.— DESIGN OF CONTROLS, EQUIPMENT, AND TOOLS 
 
 Because of the unique operating requirements and environments of mining equipment, special attention must 
 be given to human factors considerations, whether in the design of operating controls, tools and access for 
 maintenance, or the equipment itself 
 
 In this chapter a broad overview of major human fac- 
 tors considerations and issues in the design of controls, 
 equipment, and tools will be presented. The benefits to be 
 gained by incorporating human factors into the design of 
 equipment, include increased safety, higher productivity, 
 and worker satisfaction and comfort. Special attention will 
 be given to the problems of seating on low-seam under- 
 ground equipment, restricted field of vision in underground 
 and surface equipment, egress and ingress in surface equip- 
 ment, and designing for ease of maintenance in all types 
 of mining equipment. 
 
 CONTROLS 
 
 Controls are the means by which humans communicate 
 with equipment, and the proper design of controls helps en- 
 sure safe, productive operation of that equipment. The Min- 
 ing Equipment Safety Laboratory of the Mine Safety and 
 Health Administration (MSHA) analyzed all fatal accident 
 reports involving underground coal mine mobile and elec- 
 trical face equipment for the years 1972 through 1979 (17)} 
 A total of 350 fatalities were investigated. Twenty-five 
 fatalities (an average of three per year) were attributed to 
 improper control design. Unknown is the number of non- 
 
 1 Italic numbers in parentheses refer to items in the list of references at 
 the end of this chapter. 
 
 fatal injuries caused, in whole or in part, by improper con- 
 trol design. It must be assumed, however, that it is higher 
 than the number of fatalities. 
 
 Types of Controls 
 
 There is a wide variety of control devices available, with 
 certain types best suited for particular applications. Com- 
 mon control types were classified by McCormick and 
 Sanders (20) as to the type of information they can most 
 effectively transmit (discrete vs continuous) and the amount 
 of force normally required to manipulate them (large vs 
 small). Discrete information is information that can only 
 represent one of a limited number of conditions, such as on- 
 off; high-medium-low; crusher 1, crusher 2, crusher 3; or 
 alphanumerics, such as A, B, and C; 1, 2, and 3. Continuous 
 information, on the other hand, can assume any value on 
 a continuum, such as speed (as to 60 mph); pressure (as 
 1 to 100 psi); or direction of motion. Table 6-1 lists the com- 
 mon types of controls classified by this scheme. Figure 6-1 
 illustrates some of the more common of these controls. 
 
 It is important that the type of control used be suited 
 to the type of information an operator wishes to communi- 
 cate to the equipment. For example, speed is generally 
 thought of as a continuous variable. Going slow or fast is 
 thought of as slowing down or speeding up; yet many pieces 
 of underground electrical equipment permit an operator to 
 
56 
 
 Toggle 
 
 Toggle 
 
 Rotory 
 
 switch 
 
 switch 
 
 selector 
 
 2- 
 
 3- 
 
 switch 
 
 position 
 
 position 
 
 2 
 
 Knob 
 
 For transmitting discrete information 
 
 Foot push- 
 button 
 
 For transmitting continuous information 
 
 CranK Wheel Lever 
 
 'Si 
 
 Pedal 
 
 Figure 6-1.— Common types of controls classified by type of 
 information they transmit most effectively (20). (Courtesy of 
 
 McGraw-Hill 
 
 Table 6-1 .—Common types of controls, 
 
 by type of information transmitted 
 and force required to manipulate (20) 
 
 Information 
 transmitted 
 
 Discrete: 
 Pushbuttons, including keyboards 
 
 Toggle switches 
 
 Rotary selector switches 
 
 Detent thumb wheels 
 
 Detent levers 
 
 Large hand pushbuttons 
 
 Continuous: 
 
 Rotary knobs 
 
 Multirotational knobs 
 
 Thumbwheels 
 
 Levers or joysticks 
 
 Small cranks 
 
 Handwheels 
 
 Foot pedals 
 
 Large levers 
 
 Large cranks 
 
 Manipulation 
 force required 
 
 Small. 
 
 Do. 
 
 Do. 
 
 Do. 
 Large. 
 
 Do. 
 
 Small. 
 
 Do. 
 
 Do. 
 
 Do. 
 
 Do. 
 Large. 
 
 Do. 
 
 Do. 
 
 Do. 
 
 (Copyright 1982 by McGraw-Hill, and reprinted by permission) 
 
 control speed only as a discrete variable: on-off. Slow speed 
 is achieved by repeatedly activating the tram controls to 
 inch the machine forward. 
 
 Factors in Control Design 
 
 Although controls differ in design, there are certain fac- 
 tors that apply to all types of controls and influence the 
 overall performance of an operator. Well-designed controls 
 that match the task requirements, and the capabilities and 
 limitations of an operator are easier to learn to operate, are 
 operated faster and more accurately, and result in fewer 
 errors and better operator acceptance. The major factors 
 that should be considered in the design or selection of con- 
 trols are identification, control-response ratio, resistance, 
 deadspace, and backlash. Spacing and general positioning 
 of controls are discussed in another section of this chapter 
 
 Identification of Controls 
 
 The ability to quickly and accurately identify the proper 
 control can often mean the difference between life and 
 death, especially in the mining environment where massive 
 pieces of equipment are set in motion with the flick of a 
 lever. An operator, while reaching for a boom-sump control 
 on a roof bolter machine, could accidentally activate the 
 boom swing and crush a person against a mine rib. Identi- 
 fication of the proper control is really a problem of control 
 coding, and the basic methods of control coding are shape, 
 texture, size, location, color, and labels. 
 
 The choice of a coding technique and the specific coding 
 values depend on the speed and accuracy requirements of 
 a task, whether an operator can look at the controls, what 
 the environmental conditions are (especially illumination), 
 whether an operator is wearing gloves, and the number of 
 controls that must be coded. 
 
 The most common method of control coding used on min- 
 ing equipment is location coding. For example, on one par- 
 ticular model of a machine, the tram control is third from 
 the outside, the boom swing is second from the outside, etc. 
 Two deficiencies, however, are often present in mining 
 equipment, which minimize the effectiveness of location 
 coding. First, there is often no standardization in control 
 placement from manufacturer to manufacturer, or even 
 from model to model within a manufacturer's line. Second, 
 controls are often very close together and are easily con- 
 fused. A good example of this is shown in figure 6-2. Some 
 manufacturers provide long and short lever controls, or bend 
 levers so that the controls are positioned in different planes 
 for easier discrimination as shown in figure 6-3. 
 
 Shape coding involves providing different shaped 
 handles or knobs on the equipment. Figure 6-4 shows a case 
 where operators had added a glob of electrical tape to one 
 handle in an array of handles to aid in identification; an 
 example of primitive shape coding. The shapes selected for 
 shape coding must be different enough from one another 
 to be identified by operators even when they are wearing 
 gloves. Figure 6-5 presents a set of shapes that have been 
 found by the U.S. Army to be identifiable by touch alone 
 even when wearing gloves (30). Further, to facilitate the 
 learning of a control function, it is helpful if the shapes 
 selected connote, or relate to, the function being controlled. 
 The shapes shown in figure 6-6 for the controls of roof 
 bolting machines were suggested based on opinions of 
 MSHA inspectors and equipment manufacturers (15). 
 
 One consideration often overlooked in the use of shape 
 codes is that of maintenance. If a control knob can be 
 removed or easily broken, it may be replaced by a dissimilar 
 knob, thus destroying the coding scheme. The welding of 
 knobs to control levels to prevent this problem is usually 
 a good idea. 
 
 Coding by texture (i.e., smoothness, rippledness. or 
 knurledness) and size is somewhat limited with respect to 
 the number of different values that can be detected. Size 
 coding probably has more application in the mining environ- 
 ment than texture coding because of the tendency of some 
 texture codes to become obliterated by dirt and muck and 
 the difficulty of identifying textures when wearing gloves. 
 If size coding is being used, probably no more than three 
 sizes should be employed. The largest size should be for 
 either the most frequently used or the most important 
 controls. 
 
57 
 
 Figure 6-2.— Control station of a low-seam coal auger. 
 
 Figure 6-3.— Controls with different length lever controls, which provides easier location discrimination. 
 
58 
 
 Figure 6-4.— Example of operator-provided shape coding. Electrical tape has been added to the fourth knob from the left to aid 
 in identifying the control. 
 
 e 
 
 Figure 6-5.— Control knob shapes that are easily identified by touch while wearing gloves (30). (Courtesy of us Army mbs* Command) 
 
59 
 
 Drill rotate 
 
 Canopy 
 
 r^^n 
 
 Auger clamp 
 or drill guide 
 
 Boom lift 
 
 Boom swing 
 
 Cable reel 
 
 Stabjack 
 
 Boom sump 
 
 Bolt torque 
 
 Figure 6-6.— Control shapes recommended for underground 
 roof bolter (15). 
 
 Coding by colors and labels requires visual confirma- 
 tion of the control choice. Operators do not often have the 
 luxury of looking at the controls each time they have to 
 activate them. One thing that everyone agrees on, however, 
 is that, at a minimum, every control (and display for that 
 matter) must be labeled. With labels, an operator can at 
 least determine the function of a control if the function has 
 been forgotten, although it is unlikely that an operator 
 could rely on labels as the primary coding method during 
 actual operation of the equipment. 
 
 If color coding is used, as for example on a control panel 
 in a processing plant, it is important that the colors chosen 
 are easily identified and that their meaning is the same 
 everywhere in the plant. For example, if a red pushbutton 
 means stop on one panel, it should not mean energize on 
 another panel. 
 
 A well thought out coding scheme is especially impor- 
 tant for complex equipment used in the mining industry. 
 Inadvertent activation of the wrong controls can be reduced 
 and often eliminated by the prudent application of control 
 coding techniques. 
 
 Control-Response Ratio 
 
 The control-response (C-R) ratio is the ratio of the move- 
 ment of a control device to the movement of a system 
 response. A large C-R ratio would indicate that a control 
 must be moved a large distance to cause a small system 
 response. A small C-R ratio indicates that a small control 
 movement results in a large system response. 
 
 Often, the problem with C-R ratios is that they are too 
 small; that is, a slight movement of a control may cause 
 a large swing of a boom conveyor or an abrupt increase in 
 tram speed. Such controls are difficult and dangerous to use. 
 One solution that is gaining acceptance is the use of pro- 
 portional controls to replace the detent on-off controls com- 
 monly found in underground hydraulic equipment. An ex- 
 ample of a proportional control is the accelerator pedal in 
 
 an automobile; the more you depress the pedal, the faster 
 you go. 
 
 The proper C-R ratio must be empirically determined 
 by testing various ratios and determining the speed and ac- 
 curacy of system control achievable with each ratio. 
 
 Resistance 
 
 There are several types of resistance that are inherent 
 in, or can be built into, controls. The main types are listed 
 in table 6-2. In general, a little elastic resistance is usually 
 desirable, but inertial resistance often causes a decline in 
 control precision. 
 
 Table 6-2.— Description of common types 
 of control resistance 
 
 Type Description 
 
 Elastic Spring loaded— the greater the displacement of 
 
 a control, the greater the resistance. 
 
 Static Resistance to initial movement is maximum but 
 
 drops off sharply as a control is moved 
 (sticky). 
 
 Coulomb Continued resistance to movement that is 
 
 unrelated to the velocity or displacement of a 
 control movement. Resists change in direction. 
 
 Viscous damping .... Like moving a spoon through thick syrup. The 
 faster one moves a control, the more 
 resistance is encountered. Resists quick 
 changes in direction and helps execute 
 smooth control movements. 
 
 Inertia Resistance to movement or change in direction 
 
 caused by the mass of the mechanism. 
 Resists quick control movements and any at- 
 tempt to slow down or speed up control 
 movements. 
 
 Deadspace 
 
 Deadspace in a control mechanism is the amount of con- 
 trol movement around the null position that results in no 
 response of the device being controlled. A little deadspace 
 is usually desirable, especially if vibration and buffeting 
 of an operator are present. Too much deadspace, however, 
 can be detrimental to operator performance. 
 
 Backlash 
 
 As described by McCormick and Sanders (20), the best 
 way to think of backlash is to imagine operating a joystick 
 or lever with a loose, hollow cylinder fitted over it. When 
 the cylinder is moved to the right, for example, it touches 
 the stick on the left. If you move the cylinder to the right 
 and then reverse direction, the stick does not start to return 
 to the left until the cylinder comes up against the right side 
 of the stick. Until the cylinder contacts the stick, the oper- 
 ator's control movements have no effect on the system. In 
 essence, then, backlash is deadspace at any control position. 
 
 Backlash is usually inherent in any system that uses 
 gears, because the gear teeth rarely mesh perfectly. When 
 a direction of movement is changed, there is a delay until 
 the gear teeth contact the opposite side of the gear-teeth 
 slots. Typically, operators do not handle backlash well, and 
 performance deteriorates with increasing amounts of it. 
 
 Design of Specific Controls 
 
 There are several good sources of design recommenda- 
 tions for common controls, such as knobs, levers, cranks, 
 
60 
 
 pedals, and wheels (8, 30, 32, 35). No attempt will be made 
 here to set forth all the detailed recommendations contained 
 in these sources. Appendix D, however, presents recom- 
 mended sizes, displacements, and resistances for many of 
 the common controls, including pushbuttons, toggle 
 switches, rotary selector switches, cranks, levers, and 
 pedals. 
 
 EQUIPMENT DESIGN 
 
 The focus of this section is on the integration of controls 
 and displays, and the layout of workstations, as aspects of 
 equipment design. In addition, some special problems will 
 be addressed, including operator field of vision, egress and 
 ingress, and designing for maintenance. 
 
 The proper design of equipment that matches the capa- 
 bilities and limitations of an operator, and provides the in- 
 formation and control functions needed by the operator to 
 perform a task will pay dividends over and over. Reduced 
 training time, less downtime, higher quality work, fewer 
 errors and accidents, and greater user satisfaction accrue 
 from well-designed equipment. The importance of such con- 
 siderations is stressed by Grandjean (11) and U.S. Air Force 
 Systems Command (29), for example. 
 
 There is a general misconception that people are adapt- 
 able; they can get used to anything. As with most mis- 
 conceptions, there is probably a grain of truth buried 
 somewhere in them. People are adaptable, but there is a 
 cost associated with forcing them to adapt. It takes energy, 
 both physical and mental, to adapt to the unfamiliar or 
 unexpected, and this leads to both physical and mental 
 fatigue— the ultimate consequences of which are obvious. 
 
 Consider the tradeoffs: Properly design a machine once 
 or require every operator who uses it to accommodate and 
 adapt. It is not easy but it is necessary to design equipment 
 so that (1) controls operate as expected, (2) operators can 
 reach controls and see displays, and (3) enough space ex- 
 ists to carry out the work in a safe and efficient manner. 
 
 Compatibility 
 
 Probably one of the most fundamental human factors 
 design principles is to design to meet user expectations. 
 Equipment should work in a natural, expected manner; that 
 is, it should be compatible with a user's expectations. 
 
 There are several types of compatibility: conceptual com- 
 patibility, movement compatibility, and spatial compatibil- 
 ity. As pointed out by McCormick and Sanders (20), some 
 compatible relationships are intrinsic in certain situations. 
 Turning a wheel to the right in order to turn to the right 
 is an example. Other compatible relationships are culturally 
 acquired. In the United States, for example, a light switch 
 is usually pushed up to turn it on, but in certain other coun- 
 tries it is pushed down. 
 
 Conceptual Compatibility 
 
 Conceptual compatibility deals with the meaning of 
 symbolic information. For example, red means stop and 
 green means go. This type of compatibility is most relevant 
 for the design of coding systems and symbolic signs. 
 
 Movement Compatibility 
 
 Movement compatibility refers to the direction of con 
 trol movement and the resultant system response. An ex 
 
 ample is turning a steering wheel to the right to cause a 
 vehicle to turn right. Figure 6-7 shows compatible relation- 
 ships for dial movement and display response where both 
 the dial and the display are in the same plane. The situa- 
 tion becomes more complicated when the control and the 
 display are in different planes as shown in figure 6-8. Both 
 figures 6-7 and 6-8 represent directions of motion that a 
 majority of people would expect without prior training or 
 experience (i.e., population stereotypes). The expectation is 
 stronger in some cases than in others. Figure 6-9 presents 
 common meanings associated with lever movements in dif- 
 ferent planes and directions. Lever controls are very com- 
 mon on underground and surface mining equipment; yet, 
 compatible relationships often are not observed. For exam- 
 ple, up-down movement of a lever may cause a boom to 
 swing left-right. Table 6-3 presents a list of common move- 
 ment stereotypes grouped by function, without regard for 
 spatial layout. 
 
 Table 6-3.— Compatible directions of movement 
 associated with various control functions (30) 
 
 Function Direction 
 
 On Up. right, forward, clockwise, pull (push-pull type 
 
 switch). 
 
 Off Down, left, rearward, counterclockwise, push. 
 
 Right Clockwise, right. 
 
 Left Counterclockwise, left. 
 
 Raise Up. back 
 
 Lower Down, forward. 
 
 Retract Up, rearward, pull. 
 
 Extend Down, forward, push. 
 
 Increase Forward up, right, clockwise 
 
 Decrease Rearward, down. left, counterclockwise. 
 
 Open valve Counterclockwise. 
 
 Close valve Clockwise. 
 
 (Courtesy of US Army Missile Command) 
 
 A 
 
 ► 
 
 t 
 
 Figure 6-7.— Movement compatibility relationships where dial 
 and display are in same plane. 
 
61 
 
 Figure 6-8. — Compatible control-display movements when con- 
 trols and displays are in different planes (11). (Courtesy of Taylor and 
 
 Francis Ltd.) 
 
 Backward 
 
 Less 
 
 Minus 
 
 Off 
 
 Up 
 
 Forward 
 
 More 
 
 Plus 
 
 On 
 
 Down 
 
 Left 
 
 Right 
 
 Less 
 
 More 
 
 Minus 
 
 Plus 
 
 Off 
 
 On 
 
 Left 
 
 Right 
 
 Less 
 
 More 
 
 Minus 
 
 Plus 
 
 Off 
 
 On 
 
 Down 
 
 Less 
 
 Minus 
 
 Off 
 
 Backward 
 
 Figure 6-9.— Common meanings of lever movements (adapted 
 
 from 11). (Courtesy of Taylor and Francis Ltd.) 
 
 Spatial Compatibility 
 
 Spatial compatibility refers to the physical location and 
 relationship between the controls and the displays they con- 
 trol. Figure 6-10 shows examples of arrangements of con- 
 trols and displays. Where the relationship between controls 
 and displays is not obvious, it is more likely that the wrong 
 control will be activated, user response time will be slowed, 
 and additional training time will be required to learn how 
 to operate the equipment. 
 
 Placement of Displays and Controls 
 
 To determine display and control placement requires 
 two questions to be answered. First, where in physical space 
 is it best to place controls and displays; and second, within 
 that space, how should the displays and controls be 
 arranged. 
 
 Poor 
 
 0/ 0)2 Q)3 
 
 0)4 0)5 0)6 
 
 4/ 
 
 4« 
 
 kz 
 
 k5 
 
 4j 
 
 k6 
 
 Better 
 
 0/ 
 
 0)2 
 
 Oj 
 
 0)4 
 
 0)5 
 
 0)6 
 
 
 4/ 
 
 42 
 
 43 
 
 *4 
 
 45 
 
 45 
 
 Best 
 
 Figure 6-10.— Examples of spatial compatibility between a bank 
 of controls and displays. 
 
 Arrangement of Controls and Displays 
 
 The arrangement of controls and displays obviously in- 
 volves spatial compatibility; but, beyond that, considera- 
 tion must be given to grouping displays and controls with 
 regard to how they are used. There are four basic principles 
 for arranging controls and displays: importance principle, 
 frequency-of-use principle, functional principle, and 
 sequence-of-use principle. 
 
 The importance principle states that controls and dis- 
 plays that are vital to the achievement of a task be placed 
 in an optimum location. The frequency-of-use principle 
 states that the most frequently used controls and displays 
 be given priority in a workspace. The functional principle 
 provides for the grouping of controls and displays by func- 
 tion, such as grouping together all controls that deal with 
 the tail conveyor of a continuous miner. Finally, the 
 sequence-of-use principle requires that controls and displays 
 be arranged to take advantage of frequently used patterns 
 or sequences of operation. 
 
 Obviously, one cannot satisfy all of these principles at 
 the same time; tradeoffs must be made. In general, the im- 
 portance and frequency-of-use principles are probably most 
 applicable in determining the general area in a workstation 
 to locate controls and displays, while the sequence-of-use 
 and functional principles apply more to the arrangement 
 of components within a general area. One thing does seem 
 clear, however; where there is a fixed sequence of opera- 
 tion, the sequence-of-use principle should take precedence 
 over the other principles. *• 
 
 Standardization 
 
 Transcending the preceding principles of arrangement 
 is the principle of standardization. Once an acceptable 
 
62 
 
 layout of components has been achieved, every effort should 
 be made to standardize that arrangement within a partic- 
 ular class of equipment and, where possible, across similar 
 equipment. In chapter 4, a fatal accident was described that 
 could be attributed to a lack of standardization between dif- 
 ferent models of the same manufacturer's equipment. Lack 
 of standardization probably represents the most serious and 
 pervasive problem with respect to equipment design in the 
 mining industry. 
 
 Figure 6-11 shows different arrangements of roof bolter 
 controls used by one manufacturer. A survey of surface min- 
 ing haulage trucks and front-end loaders by Conway and 
 Sanders (6) found eight different configurations for brake, 
 clutch, and throttle controls on 120-st-capacity and smaller 
 haulage trucks as shown in figure 6-12. In consideration 
 of the many different braking systems employed, standard- 
 ization of the major controls would be highly desirable, with 
 recommended locations for other controls if they were 
 employed. 
 
 Figure 6-13 shows the placement of the service brake 
 relative to the steering wheel in four front-end loaders found 
 at surface mines (6). Again, the need for standardization 
 is obvious. 
 
 When equipment layout is not standardized, an operator 
 must unlearn old habit patterns (e.g., hitting the brake with 
 the left foot) and learn new patterns (e.g., hitting the brake 
 with the right foot). The unlearning-learning is much more 
 difficult than learning a habit pattern the first time. With 
 practice, people can usually adapt; however, it is a well 
 known fact that in panic or stress situations, people will 
 often revert to old habit patterns or operate controls in the 
 stereotypically expected manner. There are no reliable 
 statistics available as to the number of accidents that were 
 caused, in whole or in part, by lack of standardization in 
 control-display layout. However, it was reported by White 
 (33) that 72% of crane operators admitted to making control- 
 input errors because of lack of standardization. 
 
 Roof Bolter A 
 
 1 Boom extend 
 
 2 Canopy 
 
 3 Fast feed 
 
 4 Rotate 
 
 5 Feed 
 
 6 Drop head 
 
 7 Stabjack 
 
 8 Drill guide 
 
 9 Boom swing 
 
 Roof Bolter B 
 
 1 Canopy 
 
 2 Boom tilt 
 
 3 Drill guide 
 
 4 Drop head 
 
 5 Feed 
 
 6 Rotate 
 
 7 Fast feed 
 
 8 Stabjack 
 
 9 Diverter 
 
 43 |rcJ 
 
 HE 
 
 
 ®— |"rs| 
 
 S B 
 
 © [rc| 
 
 HE ' 
 
 BEE 
 
 EBB 
 
 HE] H 
 
 KEY 
 
 © Steering column 
 
 A Accelerator or throttle (floor pedal) 
 
 B Service brake (floor pedal) 
 
 B/B Dynamic or service brake (combination floor pedal) 
 
 BS Rear brake (steering column mounted) 
 
 C Clutch (floor pedal) 
 
 RC Retarder (console mounted) 
 
 R Retarder (floor pedal) 
 
 RS Retarder (steering column mounted) 
 
 TB Trailing unit brake (steering column mounted) 
 
 Figure 6-12.— Brake, clutch, and throttle control placement on 
 eight 120-st-capacity and smaller haulage trucks (adapted frorr 
 6). 
 
 Brake to the left 
 of steering wheel 
 
 Brake to the right 
 of steering wheel 
 
 Brake left or 
 
 right of 
 steering wheel 
 
 Brake left and 
 
 right of 
 
 the center 
 
 Figure 6-1 1 .—Different arrangements of roof bolter controls 
 from one manufacturer (15). 
 
 Figure 6-13.— Location of service brake relative to steering 
 wheel on four front-end loaders (6). 
 
63 
 
 Location of Controls and Displays 
 
 The optimum location for controls and displays depends 
 on the posture assumed by an operator in a workspace. Most 
 design recommendations deal with the seated operator. 
 These recommendations assume an upright seated posture 
 typical of that found in computer consoles or truck vehicles. 
 Rarely dealt with are semireclining work postures often 
 found on low-seam mining equipment. The reclining posture 
 workstations are discussed in another section of this 
 chapter. 
 
 Figure 6-14 presents a diagram showing the preferred 
 vertical surface area for various classes of controls used by 
 a seated operator. The dimensions are indexed from the seat 
 reference point (SRP), which is at the midline of the seat 
 at the intersection of the seat back and seat pan. 
 
 Figure 6-15 presents an integrated picture of data rela- 
 tive to the design of seated workstations, including fields 
 of view, reach distances, and control and display place- 
 
 ments. Placing displays and controls in these recommended 
 areas helps insure that they can be seen and reached with 
 minimal delay, discomfort, and errors. 
 
 Vehicle cab design is similar to, but has important dif- 
 ferences from, the typical seated console workstation. Figure 
 6-16 presents recommendations for the design of vehicle 
 cabs. The Society of Automotive Engineers (SAE) has pub- 
 lished a recommended practice regarding the location for 
 controls in heavy construction equipment (27) as shown in 
 figure 6-17. This figure shows a 95th percentile male with 
 the seat in the most rearward position. A 4-in forward ad- 
 justment range on the seat will accommodate 90% of the 
 operator population. Figure 6-17 is indexed from the H-point 
 of the seat. The H-point is determined by using an anthro- 
 pometric, weighted device developed by SAE. Because most 
 people in the mining industry do not have access to H-point 
 data about truck seats, one can approximate the location 
 of the seat reference in figure 6-17 as 4.0 in to the rear and 
 2.2 in lower than the H-point. 
 
 42 
 
 5 36 
 
 Q_ 
 
 UJ 
 (J 
 
 UJ 
 (Z 
 UJ 
 
 u. 
 
 Ul 
 
 rr 
 ui 
 
 C/> 
 Ul 
 
 > 
 
 o 
 
 GO 
 
 < 
 
 Ul 
 
 o 
 
 CO 
 
 o 
 
 30 
 
 24 
 
 18 
 
 12 
 
 Maximum flat surface area for secondary controls 
 
 1 
 
 -24 -18 -12 -6 6 12 18 24 
 
 DISTANCE TO RIGHT AND LEFT OF SEAT REFERENCE POINT, in 
 
 Figure 6-14.— Preferred vertical surface areas and limits for various types of control functions operated by a seated operator (adapted 
 
 from 20). (Courtesy of McGraw-Hill) 
 
64 
 
 15° optimum eye rotation 
 35° max eye rotation 
 color limit 
 "ST 
 
 Standard 
 line of sight ~0 e 
 
 13 in min display distance, 
 20 in preferred 
 
 r visual limits, keep 
 above to avoid glare 
 
 Lower visual limit 
 
 ~~|~~ 5*15 
 
 Optimum control zone 
 between elbow and 
 
 shoulder height 
 
 6in_p 
 min | 
 
 1 
 
 eye rotation 
 
 Min to avoid seeing top, 54 in 
 
 Standard horizontal 
 
 line of sight- 0° 
 Optional eye rotation 
 Normal sight line, 15° 
 
 Note, 5th-95th percentile 
 operators 
 
 Adjust 
 8-IOin 
 
 Adjust 
 15-18 in 
 
 —15 in max* 
 -—26 in min 
 
 
 — 24 in min ~^ 
 
 KEY 
 
 A Typing typewriter keyboard lowest level should be 26 in, 
 
 upper row no higher than 31 in 
 B Display -control 
 C Display, setup control 
 D Emergency display, setup control 
 E Reference display adjust control 
 
 Figure 6-15. — Recommended dimensions and layout of seated operator workstations (32). (Copyright 1972 by John wiiey and Sons Ltd . and 
 
 reprinted by permission.) 
 
65 
 
 8 in min Wheel diam 15-18 in 
 \ Rim diam 0.75 - 1.5 in 
 
 30 in 
 
 25 in mm 
 
 elbow 18-21 in 
 clearance 
 
 W l/l WW fill 
 
 Footrest same angle as 
 normal accelerating position 
 
 n* 2by3in min clutch 
 
 HqZE- 2 in 
 S-Tin l—^g ^rake 
 
 \ Min 10 lb, max 201b 
 2 by 9 in min 
 
 28 in max 
 
 — to prime 
 
 displays 
 
 Desired up vision 
 
 to windshield 
 Standard horizontal 
 line of sight 
 
 Desired down vision, or 
 so driver can see 10 ft 
 60° in front of vehicle 
 
 4 in max travel 
 normal accelerator 
 10° operating position 
 
 28° min rest 
 
 4 in min in 
 
 Hn increments 
 
 8 in optimum. 
 4- 5 in max 10 in max 
 
 ( Note: 5th - 95th 
 percentile operators) 
 
 Figure 6-16. — Recommended Configurations Of a Vehicle cab (32). (Copyright 1972 by John Wiley and Sons Ltd., and reprinted by permission) 
 
66 
 
 48 
 c 40 
 
 ,_- 32 
 
 16 
 
 8 
 
 
 
 8 
 
 16 
 24 
 
 O 
 
 u_ 
 
 UJ 
 
 o 
 
 GO 
 
 Q 
 
 L-" 
 
 
 r-fi | i | l | 1 I l 
 
 /\ 
 
 ^ Maximum \ 
 
 - / 
 
 ^ \ Optimum \ 
 
 - 
 
 
 ^ A— — ^S^^oof Maximum 
 
 - 
 
 
 y.u "Kx^orbptimumV / - 
 
 
 
 
 
 — 
 
 
 A\^^<rl \ 1 /f^\f 
 
 
 — \ \ / /v\v — 
 
 ~ , 1 . 
 
 ,1.1,1,1,1." 
 
 40 
 32 
 
 J 24 
 
 5 | '6 
 o a: 
 rx w e 
 
 "-& 
 Su. o 
 
 2 O 
 ?W 8 
 
 <n ? 
 
 LU 
 h- 
 Z 24 
 UJ 
 
 o 
 
 321 
 
 8 8 16 24 32 40 48 
 DISTANCE FROM H POINT, in 
 
 i I ' I i 
 H point pivot line 
 
 401— i_l_i 
 
 Hand area illustrated 
 is on a horizontal 
 plane 9 in above H point 
 
 16 8 8 16 24 32 40 48 
 DISTANCE FROM H POINT 
 
 PIVOT LINE, in 
 
 Figure 6-17.— SAE J898a recommended practice for control locations for construction and industrial equipment design (27). (Copyngm 
 
 1974 by Society of Automotive Engineers Inc., and reprinted with permission) 
 
 With respect to standing workstations, figure 6-18 
 presents recommendations regarding placement of controls 
 and displays. 
 
 One final consideration in the placement of controls is 
 the distance between them; if they are too close together, 
 the wrong control is more likely to be activated. This is 
 especially true when operators are wearing gloves or work- 
 boots. If two controls must be operated simultaneously or 
 in rapid succession, too great a distance would slow perfor- 
 mance and even make it impossible to perform a task as 
 intended. Figure 6-19, based on work by Chapanis (5), 
 presents recommended control separations based on the type 
 of control, whether one or two hands (or feet in the case of 
 pedals) are being used, and whether the controls are oper- 
 ated in a random sequence, sequentially, or simultaneously. 
 The empty cells indicate combinations for which no reliable 
 data exist. Extra space should be added between controls 
 when operators wear gloves or boots (in the case of pedals). 
 
 Special Problems in Equipment Design 
 
 Four special problems in equipment design, especially 
 relevant to the mining industry, are discussed in the follow- 
 ing sections. The problems are seating for low-seam coal 
 equipment, operator field of vision, egress-ingress on equip- 
 ment, and access for maintenance and service. 
 
 Seating for Low-Seam Coal Equipment Operators 
 
 Judeikis (27) reported that of 350 underground coal mine 
 fatalities involving mobile face equipment, 24 (averaging 
 three per year) involved inadequate compartment size, 20 
 
 (2.5 per year) involved an operator leaning out of the cab. 
 19 (2.4 per year) involved not having an operator compart- 
 ment, and 13 (1.6 per year) involved poorly designed seats. 
 This represents a total of 76 fatalities related to improperly 
 designed operator compartments. 
 
 A major constraint in operator compartment design is 
 the operating height of many coal mines in the United 
 States. Many seams are less than 48 in high, and mine 
 heights are usually no higher than the seam height. As 
 pointed out by Aljoe (2), however, the practical working 
 height of a coal mine is considerably less than the mine 
 height because of overhead obstructions (e.g.. a roof sup- 
 port timber) and undulating floor conditions. The upshot 
 of this is that the height of an operator compartment may 
 be as little as 22 in, thus requiring the operator to assume 
 a reclined seating posture. Figure 6-20 shows three ex- 
 amples of typical seating accommodations in low-seam min- 
 ing equipment. 
 
 Figure 6-21 shows diagrams of the 95th percentile male 
 and 5th percentile female seating envelopes for two cab 
 heights: 42 and 22 in (4). These diagrams dramatically il- 
 lustrate the increased cab lengths, reduced reach envelope, 
 and restricted fields of vision resulting from a reclined 
 seating posture. 
 
 Figure 6-22 presents data on the interior cab length re- 
 quired for various interior cab heights to accommodate var- 
 ious sizes of operators. The data assume a 10 c seat pitch 
 and a 2-in helmet clearance space. As pointed out by 
 Cooksey (7), the data in figure 6-22 do not take into consid- 
 eration the space for a headrest or the additional cab length 
 needed to depress foot pedals. 
 
67 
 
 Keep lights above 
 to avoid glare 
 
 78 in maximum 
 overhead control 
 
 -IX 
 
 VVV\VUVUV\ 
 
 75 in 
 minimum 
 
 -r 7f k~— Standard door 
 — Reference displays 
 
 6ft£— Highest shelf 
 J— Emergency display 
 
 imum 
 yiew 
 30° 
 
 Optimum 
 control 
 
 -4fV 
 
 -20 in 
 minimum 
 
 Increase to 45 in 
 
 to operate controls 
 
 below 36 in 
 
 4in 
 
 3± 
 
 in 
 
 5ft v — 61 in continuous visual monitoring 
 'Sr-To see over console- phone 
 y\ mouthpiece 
 \ Setup controls 
 Display control 
 —Standard wall switch 
 
 45 in maximum for keyboard 
 <T\ (angle 0°- 15°) 
 1 41 in writing counter, minimum 16 in 
 deep (horizontal only) 
 Hand rails 
 38 in door knob 
 36 in standard workbench, 
 minimum 24 in deep 
 
 i ft. 
 
 — Maintenance controls, storage 
 Note, 5 th - 95 m percentile operator 
 
 / 
 
 Figure 6-18. — Recommended layout Of a Standing operator workstation (32). (Copyright 1972 by John Wiley and Sons Ltd., and reprinted with permission) 
 
 Number of body 
 
 members and 
 +-type of use 
 
 Knobs 
 
 Push buttons 
 
 Toggle switches 
 
 Cranks, levers 
 
 Pedals 
 
 Cdjs^_P# 
 
 c$ 
 
 
 
 
 
 Qfl 
 
 I, randomly 
 
 in 
 
 20) 
 
 2(l/ 2 ) 
 
 2(3/4) 
 
 4(2) 
 
 6(4) 
 
 I, sequentially 
 
 in 
 
 
 I 0/4) 
 
 l('/ 2 ) 
 
 
 4(2) 
 
 2, simultane- 
 ously 
 
 in 
 
 5(3) 
 
 
 
 5(3) 
 
 
 2, randomly, 
 sequentially 
 
 in 
 
 
 V 2 0/ 2 ) 
 
 3 / 4 ( 5 / 8 ) 
 
 
 
 Figure 6-19.— Recommended separation between adjacent controls for one- and two-hand (or foot in the case of pedals) opera- 
 tion, randomly, sequentially, or simultaneously. Minimum separations are given in parentheses, alongside preferred separations. 
 
 (Adapted by McCormick and Sanders (20) from reference 5, courtesy of McGraw-Hill) 
 
68 
 
 Figure 6-20.— Examples of typical seating postures in low-seam coal mining equipment. 
 
69 
 
 4 8 12 16 20 24 28 32 36 40 44 48 52 56 4 8 12 16 20 24 28 32 36 40 44 48 52 56 
 
 CAB DEPTH, in 
 
 4 8/16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 
 
 CAB DEPTH, in 
 
 A 
 
 Ankle point 
 
 K 
 
 B 
 
 Knee point 
 
 L 
 
 C 
 
 Hip point 
 
 M 
 
 D 
 
 Shoulder point 
 
 N 
 
 E 
 
 Shoulder extended 
 
 P 
 
 F 
 
 Elbow point 
 
 Q 
 
 Standard ling of sight 
 Upper line of sight 
 Lower line of sight 
 Warning display vision 
 Controls and display vision 
 Peripheral vision 
 
 R Maximum control reach 
 S Maximum control grip 
 T Maximum control grip 
 Z Minimum display distance 
 SRP Seat reference point 
 
 Figure 6-21 .—Seating space envelopes for 95th percentile male and 5th percentile female operators in 42-in (top) and 22-in (bottom) 
 
 Cab heights (4). (Courtesy of Canyon Research Group Inc.) 
 
70 
 
 45 
 
 15 
 
 w^ 50 ** 
 
 / 95 pet 
 
 40 
 
 50 60 70 
 
 INTERIOR CAB LENGTH, in 
 
 80 
 
 Figure 6-22.— Relationship between interior cab height and re- 
 quired interior cab length needed to accommodate various sized 
 people. Assumes a 10° seam pitch and 2-in helmet clearance (7). 
 
 (Courtesy of R. Cooksey, University of New England) 
 
 In an effort to reduce problems common to low-seam 
 operator compartments, the Bureau sponsored a research 
 project to develop a human-factored, state-of-the-art, low- 
 seam seat (13). Although the aim was to develop a seat for 
 the remote control of mining equipment, the design could 
 conceivably be adopted to on- vehicle operator compartments 
 as well. Figure 6-23 shows the seat and a schematic design. 
 The seat is easily adjustable and fits a wide range of opera- 
 tor body sizes. The seat surface is made of strips of woven 
 monofilament, open-mesh, polyester belting for strength, 
 durability, and comfort. The headrest is constructed of a 
 piece of standard seven-ply, neoprene conveyor belting 
 looped so the bias provides maximum flexing resistance in 
 the longitudinal direction. 
 
 Operator Field of Vision 
 
 Restricted field of vision from both surface and under- 
 ground equipment is a common problem in mining. Con- 
 way and Sanders (6) pointed out that restricted vision from 
 operators' compartments was a serious problem for haulage 
 trucks, front-end loaders, and dozers in surface operations. 
 A review of the literature, however, finds that almost all 
 the research and development effort has been directed 
 
 ** rf^ '^--//-Headrest 
 
 .Backrest angle adjustment knob 
 
 Figure 6-23.— Human-factored seat for lOW-Seam mining equipment (13). (Copyright 1 982 by the Human Factors Society Inc.. and reproduced by permission) 
 
71 
 
 toward haulage truck visibility problems. MSHA deter- 
 mined that lack of "visibility" was a contributing factor in 
 approximately 20% of fatal and nonfatal truck haulage 
 accidents during the years 1972 to 1975 (21). Poor or 
 restricted field of vision greatly contributed to operators 
 driving off haulage roads and over embankments, colliding 
 with other equipment and fixed objects, and running or 
 backing over individuals. 
 
 To illustrate the magnitude of the field of view problem 
 for haulage truck operators, figure 6-24 shows front- and 
 side-vision limitations for a 150-st-capacity rear-dump 
 haulage truck. As can be seen, an operator cannot see a 6-ft 
 person standing closer than 40 ft in front of the truck and 
 can only see the ground beyond 62 ft in front of the truck. 
 Figure 6-25 presents a plan view of the same truck and 
 shows the blind spots and the distances required to see an 
 8-ft object and the ground around the operator's cab. 
 
 Visibility plots such as those presented in figures 6-24 
 and 6-25 are good for illustrating field of vision problems, 
 but should not be considered as a totally accurate depiction 
 of an operator's visual field. A single plot does not take }nto 
 account different sized operators (and hence, eye heights); 
 
 105 ft 
 
 -Grade visibility 
 line 
 
 70 ft 
 1-6- 
 
 ft visibility line 
 
 ft 10 ft 16 ft 
 6"ft visibility line- 1 I 
 Grade visibility line-' 
 
 different seat adjustment positions and heights; and equip- 
 ment modifications, such as new components on the right- 
 side deck, shields over the engine, different tire sizes, etc. 
 All of these factors will change the shape and size of blind 
 spots. For example, a 3-in-diameter corner post in a cab 
 located 33 in from an operator's eyes will block an object 
 5.5 ft wide at a distance of 60 ft. 
 
 The Bureau sponsored research to develop improved 
 "visibility" systems for large haulage vehicles (14). The final 
 system consisted of fresnel lens, blind area viewers; a quick- 
 change left mirror; a rectangular convex right mirror; and 
 a ruggedized, closed-circuit television system (16). Figure 
 6-26 shows a typical system on a haulage truck. The fresnel 
 lens allows an operator to see objects as close as 5 ft to the 
 truck, as shown in figure 6-27. Figure 6-28 shows the im- 
 proved field of visibility using the new system of lenses, mir- 
 rors, and cameras. The improved system eliminated approx- 
 imately 85% of the forward and right blind area, and about 
 95% of the rear blind area. 
 
 In the underground mining environment, MSHA attrib- 
 uted 25 fatalities involving mobile face equipment from 
 1972 through 1979 to inadequate "visibility" from the 
 operator's cab (17). This represents an average of 4.6 
 fatalities per year as a result of restricted field of vision. 
 A system for assessing the visibility requirements for op- 
 erating continuous miners, shuttle cars, and scoops was 
 developed by Sanders and Kelley (25). They also developed 
 a methodology for measuring the adequacy of the actual 
 fields of vision for underground equipment. This method- 
 ology involved a task analytic approach for identifying the 
 important visual features needed to efficiently and safely 
 
 62 ft 40 ft ft 
 
 | L 6"ft visibility line 
 
 '-Grade visibility line 
 
 Figure 6-24.— Illustration of front and side visual limitations 
 from the cab of a 150-st-capacity rear-dump haulage truck (27). 
 
 (Courtesy of U.S. Mine Safety and Health Administration) 
 
 □ Totally visible to operator 
 H Viewing area 
 
 1—1 
 
 KEY 
 
 E2)Blind area until 8-ft object is visible 
 @ Blind area until ground is visible 
 
 Figure 6-25.— Plan view illustrating front and side visual limita- 
 tions and blind areas from the cab of a 150-st-capacity rear-dump 
 
 haulage truck (21). (Courtesy of U.S. Mine Safety and Health Administration) 
 
 Blind area viewers 
 
 TV monitor 
 
 Left rearyiew 
 mirror 
 
 Right rearvlew 
 curved mirror 
 
 Closed circuit 
 TV camera 
 
 Figure 6-26.— Typical installation of an improved visibility 
 system for large haulage trucks (16). 
 
72 
 
 Figure 6-27.— Fresnel lens blind area viewer used to enhance 
 visual field of haulage truck operators. A person standing a few 
 feet from the truck can be seen through the lens. 
 
 Figure 6-28.— Improved field of view resulting from installa- 
 tion of system shown in figure 6-27 (76). 
 
 operate the equipment. These visual features were trans- 
 lated into visual attention locations (VAL's) that should be 
 visible from an operator's cab. Figure 6-29 shows a plot of 
 the VAL's for continuous miner operations. (At each VAL, 
 several heights above the floor should be visible.) 
 
 The method of assessing a field of vision involved the 
 use of a human eye reference measurement instrument 
 (HERMI) shown in figure 6-30. By placing the instrument 
 in an operator's cab and taking pictures of the cab from each 
 VAL, one can easily determine if a VAL is visible from the 
 cab, and if not visible, what is obstructing the view. 
 
 Machine centerline - 
 Widest machine point •» 
 
 Necessary stopping 
 distance 
 
 *- U-Operator centerline 
 
 —Widest machine point 
 
 Figure 6-29.— Plan view of visual attention locations (VAL's) 
 identified for continuous miner operators. Several vertical heights 
 are represented at each VAL (25). 
 
 A sample of center- and end-driven shuttle cars for high- 
 and low-seam height applications, with canopies in both 
 high and low positions, was evaluated by Sanders and 
 Krohn (26) using these techniques. It was found that with 
 a canopy in the low position, the field of vision was increased 
 by placing the cab in the front of the car as opposed to the 
 center or rear of the car. It was also found that adding a 
 canopy did not reduce the field per se, as long as it did not 
 force operators to lower their eye position. The field of vi- 
 sion was degraded when the eye position was lowered, with 
 or without a canopy in place. 
 
 Across all configurations and canopy positions, six 
 VAL's were not visible from any machine tested. These 
 VAL's were located at floor level, on the opposite side of 
 the machine from the operator's cab. and from 2 ft to the 
 necessary stopping distance in front of the machine's direc- 
 tion of travel. This area, then, represents a blind area on 
 virtually all shuttle cars. It was recommended that mirror 
 systems be developed and retrofitted on current shuttle cars 
 to eliminate such blind spots. 
 
 Egress-Ingress on Surface Mining Equipment 
 
 Slips and falls while ascending and descending equip- 
 ment account for over one-third of all surface mining lost- 
 time accidents associated with the operation of haulage 
 trucks, front-end loaders, track dozers, shovels, and drag- 
 lines (18). A review of MSHA accident data by Gavan (10) 
 revealed that almost 2.000 slip and fall accidents occurred 
 on surface mine mobile equipment during 1978 and 1979 
 alone. These accidents averaged 15.3 lost days per incident. 
 
73 
 
 Figure 6-30.— Human eye reference measurement instrument (HERMI) used to assess fields of visibility from operators' cabs. 
 The white arcs represent the 95th percentile male and 5th percentile female eye positions allowing reasonable head and trunk flex- 
 ion (26). 
 
 Characteristic injuries are cuts, lacerations, contusions, 
 fractures, sprains, and strains. 
 
 The types of generic design problems that contribute to 
 the frequency of slip and fall accidents, according to Long 
 (18), include 
 
 1. Excessively flexible lower section supports for lower 
 steps or rungs on ladders (fig. 6-31). 
 
 2. Inappropriate distances from ground level to first step 
 (fig. 6-32). 
 
 3. Use of access paths that are not intended for that pur- 
 pose such as the tracks on dozers and shovels. 
 
 Added to these problems are the tendencies for mud, 
 snow, ice, and oil to accumulate on the step surfaces, and 
 the tendency of the operators to carry personal items with 
 them, making it difficult for them to use both their hands 
 to hold the rails when mounting or dismounting. 
 
 Figure 6-33 shows recommended design guidelines for 
 stairs and ladders that are applicable to surface mining 
 equipment egress-ingress systems. Figure 6-34 shows two 
 innovative stair designs for haulage trucks. In both cases, 
 stairs replaced conventional vertical ladders for easier and 
 safer egress and ingress. The pulldown stair design (figure 
 6-34, top) also has the safety feature that when the stairs 
 
 are down, the counterweight is clearly visible to the driver. 
 This reduces the chance of moving a truck when someone 
 is attempting to board. 
 
 In addition to stair and ladder design, Bottoms (3) 
 pointed out the need to consider the design and placement 
 of the doorways for egress and ingress. Figure 6-35 shows 
 a typical access path for entering a tractor. The door is 
 aligned with the steering wheel, thus requiring the operator 
 to maneuver around the wheel into the seat. Ideally, the 
 gap between the seat and steering wheel should be opposite 
 the doorway, as shown in figure 6-36. If this cannot be done, 
 the effective platform width (W in figure 6-35) should be 
 made as large as possible. Bottoms (3) also recommended 
 door widths of 26 in at or above waist level, and 16 to 26 
 in at foot level. The minimum size recommended is 22 in 
 at and above waist level, and 12 in at foot level. 
 
 The Bureau sponsored a research and development proj- 
 ect to improve egress-ingress systems for surface mining 
 equipment, as discussed by Long (19). Figure 6-37 shows 
 the spring-supported lower step concept for large haulage 
 trucks. This design consists of a lower first step that will 
 flex and withstand collisions, as shown in figure 6-38, and 
 still provide a semirigid mounting surface. 
 
74 
 
 Figure 6-31.— Excessively flexible lower section support on 
 haulage truck ladder, a common problem (18). 
 
 Figure 6-32.— Inappropriate height of first step on haulage 
 truck ladder (18). 
 
75 
 
 In. 
 
 Min 
 
 Max 
 
 A. 
 
 Angle of rise: 
 
 50° 
 
 75° 
 
 B. 
 
 Tread depth : 
 
 
 
 
 For 50° rise : 
 
 6 
 
 10 
 
 
 For 75° rise: 
 
 3 
 
 6 
 
 C. 
 
 Riser height: 
 
 7 
 
 12 
 
 D. 
 
 Height .step to landing: 
 
 6 
 
 12 
 
 E. 
 
 Width, handrail-handrail: 
 
 21 
 
 24 
 
 F. 
 
 Min overhead clearance: 
 
 5.5ft 
 
 
 G. 
 
 Height of handrail: 
 
 34 
 
 37 
 
 H. 
 
 Diam of handrail: 
 
 I.I 
 
 2 
 
 I 
 
 Min hand clearance: 
 
 3 
 
 
 In. 
 
 Min 
 
 Max 
 
 A. 
 
 Angle of rise: 
 
 75° 
 
 90° 
 
 B. 
 
 Rung or cleat diam: 
 
 
 
 
 Wood: 
 
 1.1 
 
 1.6 
 
 
 Protected metal: 
 
 0.8 
 
 1.6 
 
 
 Metal that may rust: 
 
 1 
 
 1.6 
 
 C. 
 
 Rung spacing: 
 
 9 
 
 
 D. 
 
 Height, rung to landing : 
 
 6 
 
 
 E. 
 
 Width between stringers: 
 
 12 
 
 
 F. 
 
 Climbing clearance width: 
 
 24 
 
 
 G. 
 
 Min clearance depth: 
 
 
 
 
 In back of ladder: 
 
 6 
 
 
 
 On climbing side. 
 
 36 for 75° 
 
 30 for 90° 
 
 H. 
 
 Height of string above landing: 
 
 33 
 
 
 I 
 
 Max height of climb: 
 
 
 10ft 
 
 Figure 6-33.— Design recommendations for stairs and ladders, in inches (30). (Courtesy of us. Army Missile Command) 
 
76 
 
 Figure 6-34.— Stairs used on haulage trucks instead of vertical ladders (6). Top, counterbalanced pulldown design; bottom, fixed 
 immovable design. 
 
77 
 
 Access path 
 
 Figure 6-35.— Schematic diagram showing relationship of seat, 
 steering wheel, and doorway on a typical tractor (W is effective 
 platform width) (3). This design requires the driver to maneuver 
 
 around the Steering Wheel. (Courtesy of Butterworth Scientific Ltd.) 
 
 Figure 6-36.— Example of a well-designed access door. The 
 door is aligned with the gap between the seat and the steering 
 wheel rather than being offset. 
 
 Rigid ladder 
 assembly 
 
 High-grip step 
 material (typical) 
 
 Pretension spring 
 assembly (typical) 
 
 Figure 6-37.— Concept of Bureau-sponsored four-spring- 
 supported lower steps for large haulage trucks (18). 
 
 Figure 6-38.— Bureau-sponsored four-spring-supported lower 
 steps colliding with a large rock (18). 
 
 The Bureau also supported a research and development 
 project to build a hydraulic lift "power" step for access to 
 an operator's cab. Its principal application is for track dozers 
 and shovels. Figure 6-39 shows a man and some materials 
 being transported via the power step. Both the spring- 
 supported steps and the power step have been field tested 
 with favorable results in terms of safety and reliability. 
 
 Designing for Maintainability 
 
 As mining equipment becomes larger and more complex, 
 increased demands are placed on the maintenance function. 
 Equipment must be routinely serviced to keep it in good 
 working condition and to reduce downtime. When equip- 
 ment fails, it must be fixed quickly and returned to service. 
 Unfortunately, equipment is not often designed for service- 
 ability or maintainability. Design problems with off- 
 highway equipment were discussed by Puffer (23) and 
 include poorly designed fluid level indicators that are so 
 difficult to read that they are ignored, filters that are so 
 difficult to reach and remove that they frequently are not 
 serviced on schedule, and filler caps that are located where 
 dust will accumulate and contaminate the system. 
 
 Complex maintenance procedures are required to fix 
 simple problems. On one 120-st-capacity e ] ectric drive rear- 
 dump truck, for example, to remove the wheel motor, it is 
 necessary to remove the truck bed, the entire rear axle 
 assembly, and the casing around the axle-wheel to expose 
 the motor. In another truck, to change four belts or certain 
 hoses, either the radiator or the engine block have to be 
 removed (18). Long also listed the following design problems 
 related to haulage truck maintenance. (These problems, 
 however, are not restricted to trucks, but are found with 
 most mining equipment.) 
 
 1. Poor access to machine parts or areas of the unit for 
 routine or unscheduled maintenance tasks. 
 
 2. Inadequate access openings to permit a person to reach 
 or climb in to repair or replace parts. 
 
 3. Need to remove or dismantle ancillary components in 
 order to gain access to the failed unit. 
 
78 
 
 ****** riifm 
 
 «L tORPORATiON 
 
 Figure 6-39.— Bureau-sponsored hydraulic "power" step for egress and ingress from tractors, dozers, and shovels (18). 
 
 4. Inadequate or no provisions for the safe handling of 
 heavy or large parts. 
 
 5. Inadequate tools to perform the required maintenance 
 tasks. 
 
 Often, if maintenance tasks were thoroughly analyzed 
 in the initial design stage, many of the problems would be 
 obvious and correctable. Unfortunately, maintenance pro- 
 cedures are often not even developed until after the equip- 
 ment is designed and fabricated. 
 
 This chaper does not cover the intricacies related to 
 designing for maintainability, such as designing fasteners 
 and connectors; covers, cases, and shields; or cables and 
 hoses. However, because inadequate access for removal and 
 replacement of parts and making periodic adjustments 
 ranks as one of the most prevalent maintenance design pro- 
 blems, information is supplied on access space. Appendix 
 E contains information regarding required work area 
 clearances needed to accommodate various working 
 postures, selected clearances for arms and hands, access 
 spaces required to operate typical handtools, and access 
 spaces required to grasp various sized objects with one or 
 two hands (30). 
 
 HANDTOOL DESIGN 
 
 In 1983, MSHA accident data revealed 1% to 10<* of all 
 nonfatal, lost-days accidents in the mining industry were 
 related to handtools (31). The problem can often be traced 
 to using the wrong tool for the task at hand. This is not 
 surprising when one considers the vast array of specialized 
 tools available. For example, Williams (34) described 25 dif- 
 ferent types of wrenches for various tasks. One can hardly 
 expect every maintenance person to carry a full complement 
 of such wrenches in addition to all the various types of ham- 
 mers, screwdrivers, etc., that are available. The result is 
 that one wTench often serves multiple purposes, including 
 acting as a hammer. 
 
 In the mining industry, as in most other industries, non- 
 powered handtools make up the bulk of handtool-related 
 injuries, often 75°t or more. The most commonly implicated 
 tools are hammers, wrenches, and knives. There is a body 
 of human factors literature related to the design of hand 
 tools that provides guidance with respect to size and weight, 
 handle design, and positioning of trigger switches. The in- 
 terested reader is referred to references 8 and 9. 
 
79 
 
 Principles of Handtool Design 
 
 This section discusses some general principles of hand- 
 tool design as given by McCormick and Sanders (20). It also 
 discusses the special problem posed by vibrating handtools 
 such as rock drills, pneumatic chipping tools, and chain 
 saws. 
 
 Maintain a Straight Wrist 
 
 The flexor tendons of the fingers pass through a tunnel 
 in the wrist and attach to the muscles in the forearm. This 
 tunnel is called the carpal tunnel because it is formed by 
 the transverse carpal ligament. When the wrist is bent, the 
 tendons bend and bunch up in the carpal tunnel. Repetitive 
 wrist bending, or the exertion of forces by the hand with 
 the wrist bent, can cause an inflammation of the tendon 
 sheaths of the wrist (tenosynovitis). In addition, the median 
 nerve also passes through the carpal tunnel and can be in- 
 jured by the same kinds of actions that cause tenosynovitis. 
 Injury to the median nerve is called carpal tunnel syndrome 
 and sometimes requires surgery to correct the problem and 
 relieve the pain. A common type of hand motion that can 
 lead to tenosynovitis is that of "clothes wringing" (28), in 
 which the wringing is done by a clockwise movement of the 
 right hand and counterclockwise action of the left. This type 
 of motion is involved when inserting screws in holes, and 
 looping wire while using pliers. In general it is better to 
 bend the tool than the wrist. Figure 6-40 shows examples 
 of tools that have been redesigned to permit straight- wrist 
 use. 
 
 Avoid Tissue Compression Stress 
 
 Often in the operation of a handtool, considerable forc< 
 is applied to the palm of the hand. Handles of pliers dig in 
 to the palm area; the palm is used to exert force on the top 
 of a screw driver; or the palm is used to pound a wrench. 
 All of these actions can damage unprotected blood vessels 
 and nerves in the hand. 
 
 Avoid Repetitive Finger Action 
 
 Excessive use of the index finger to operate triggers can 
 result in "trigger finger," where the person can flex the 
 finger but cannot extend it. In general, frequent use of the 
 index finger should be avoided, and thumb-operated con- 
 tacts should be used. 
 
 Design for Safe Operation 
 
 This includes the elimination of pinching hazards, sharp 
 corners, and edges; installation of braking devices in power 
 tools to stop the tool quickly when the trigger is released; 
 and the proper placement of on-off switches to reduce ac- 
 cidental activation and permit quick response times to turn 
 off the device. 
 
 Women and Left-Handers 
 
 The number of women in the mining industry workforce 
 is increasing. The major problem women have with hand- 
 
 ']/\^/\sW/\A/\AAAA<WAA>*<WWAM>\^^ 
 
 Figure 6-40.— Examples of common handtools designed to per- 
 mit users to maintain straight wrists. 
 
 tools is that their hands are too small to effectively operate 
 some tools, such as wire strippers, crimping tools, pliers, 
 and shears. The maximum grip strength can be applied 
 when the handle opening of a tool is 2.5 to 3.5 in; this ap- 
 plies to both males and females. The maximum handle open- 
 ing should not exceed 4.0 in in order to accommodate 
 smaller female hands. 
 
 Left-handers make up about 8% to 10% of the popula- 
 tion. Tools should be designed so that they can be used by 
 either left- or right-handed operators. Trigger positions and 
 stabilizing handles should be mounted to allow operation 
 with either hand. 
 
 Although it is often not possible for companies to design 
 and fabricate their own handtools, awareness of the basic 
 human factors principles can be valuable in selecting the 
 proper tools for a job and for training workers in the proper 
 use of handtools. 
 
 Vibration-Induced White Finger 
 
 The National Institute for Occupational Safety and 
 Health (NIOSH) estimated that over 100,000 workers in the 
 mining industry are potentially exposed to hand-arm vibra- 
 tion from pneumatic and motor driven tools (22). It is now 
 recognized that exposure to this sort of vibration can cause 
 a condition known as vibration-induced white finger (VWF). 
 Early stages of this syndrome are characterized by tingling 
 
80 
 
 or numbness in the fingers. As NIOSH points out, tem- 
 porary tingling or numbness during or soon after use of a 
 vibrating handtool is not considered VWF. The symptoms 
 must be more persistent and occur without provocation. 
 Other symptoms include blanching, pain, and flushing of 
 the fingers. These symptoms usually appear suddenly, and 
 are precipitated by exposure to cold. With continued ex- 
 posure to vibration, the signs and symptoms become more 
 severe and the pathology may become irreversible. 
 
 The recognition of VWF among miners dates back to 
 the early 1900's when Hamilton (12) described spastic 
 anemia of the hands among limestone quarry workers us- 
 ing pneumatic chipping hammers and drills. Studies by 
 NIOSH (22) found an incidence of VWF symptoms as high 
 as 83% in workers exposed to vibrating handtools in 
 foundries. 
 
 Despite considerable research, little is known about the 
 physiological basis of VWF or which specific vibration 
 parameters are most necessary to control. It is certain, 
 however, that progressive stages of VFW arise from the 
 cumulative effect of trauma to the hands from regular, pro- 
 longed use of vibrating handtools. 
 
 Redesign of a rock drill and air leg unit, and reducing 
 the level of vibration significantly, was reported by Rogers, 
 Eglin, and Hart (24). They were not successful in their 
 search for a glove material that would reduce the vibrations 
 transmitted to the hand. Attempts by manufacturers to 
 reduce vibration from chain saws has been very successful 
 and has contributed to a reduction of VWF cases among 
 chain-saw operators (2). 
 
 DISCUSSION 
 
 This chapter has briefly reviewed major human factors 
 issues in the design of hardware and has presented some 
 data, both in the chapter and in appendixes, that can be 
 used to evaluate and enhance the design of mining equip- 
 ment. More extensive data can be found in references 8, 30, 
 32, and 35. 
 
 The design of equipment is the culmination of a 
 systematic approach that should detail the task re- 
 quirements for the operator and maintainer, and incor- 
 porate considerations of human limitations into the final 
 design. A well-designed piece of equipment will result in 
 reduced training time, higher productivity, fewer accidents, 
 and greater worker satisfaction and comfort. 
 
 REFERENCES 
 
 1. Aljoe, W. How to Design Cabs and Canopies. Coal Min. and 
 Processing, Mar. 1983, pp. 61-67. 
 
 2. Axelsson, S. Progress in Solving the Problem of Hand Arm 
 Vibration for Chain Saw Operators in Sweden, 1967 to Date. Paper 
 in Proceedings of the Int. Hand Arm Vibration Conf. NIOSH, Cin- 
 cinnati, OH, 1977, pp. 77-170. 
 
 3. Bottoms, D. Design Guidelines for Operator Entry-Exit 
 Systems on Mobile Equipment. Appl. Ergonomics, v. 14, 1983, pp. 
 83-90. 
 
 4. Canyon Research Group Inc. (Westlake Village, CA). Human 
 Factors Design Guidelines for Personnel Carriers. 1982, 37 pp. 
 
 5. Chapanis, A. Design of Controls. Ch. in Human Engineering 
 Guide to Equipment Design, ed. by H. Van Cott and R. Kinkade. 
 Wiley, 1972, pp. 345-380. 
 
 6. Conway, E.J., and M.S. Sanders. Recommendations for Human 
 Factors Research and Development Projects in Surface Mining (con- 
 tract J0395080, Canyon Res. Group Inc.). BuMines OFR 211-83, 
 1982, 86 pp.; NTIS PB 84-143650. 
 
 7. Cooksey, R., G. Hartley, and A. Burks. Predictive Relation- 
 ships for Cab Dimensions in Low Coal Mining Machines. Paper 
 in Proceedings of the Human Factors Society 26th Annual Meeting, 
 Seattle, WA, Oct. 25-29, 1982, pp. 394-399. 
 
 8. Eastman Kodak Co. Ergonomic Design for People at Work. 
 Volume I: Workplace, Equipment, and Environmental Design and 
 Information Transfer. Lifetime Learning, 1983, 406 pp. 
 
 9. Fraser, T. Ergonomic Principles in the Design of Hand Tools. 
 Int. Labor Office, Geneva, Switzerland, OSHA Series No. 44, 1980, 
 91pp. 
 
 10. Gavan, G, P. Mate, D. Strassel, and K. Conway. Develop- 
 ment and Demonstration of Improved Truck Ladders (contract 
 H0282001, Woodward Assoc.). BuMines OFR 87-81, 1979, 335 pp.; 
 NTIS PB 81-223406. 
 
 11. Grandjean, E. Fitting the Task to the Man: An Ergonomic 
 Approach. Taylor and Francis, 1981, 379 pp. 
 
 12. Hamilton, A. Reports of Physicians for the Bureau of Labor 
 Statistics— A Study of Spastic Anemia in the Hands of Stonecut- 
 ters. Sec. in Effect of the Air Hammer on the Hands of Stonecut- 
 ters. Bull. 236, Industrial Accidents and Hygiene Series, No. 19, 
 U.S. Dep. of Commerce, Springfield, VA, 1918, pp. 53-66, NTIS PB 
 254-601. 
 
 13. Hartley, C, R. Cooksey, and A. Kwitowski. An An- 
 thropometrically Adjustable Seat for Low Seam Mining Applica- 
 tions. Paper in Proceedings of the Human Factors Society 26th An- 
 nual Meeting, Seattle, WA, October 25-29, 1982, pp. 389-393 
 
 14. Hawley, K.W., and S.F. Hulbert. Improved Visibility Systems 
 for Large Haulage Vehicles (contract H0262022, MB Assoc.). 
 BuMines OFR 100-78, 1978, 121 pp.; NTIS PB 286-065. 
 
 15. Helander, M., E.J. Conway, W. Elliott, and R. Curtin. Stan- 
 dardization of Controls for Roof Bolter Machines. Phase I. Human 
 Factors Engineering Analysis (contract H0292007, Canyon Res. 
 Group Inc.). BuMines OFR 170-82, 1980, 192 pp.; NTIS PB 
 83-119149. 
 
 16. Johnson, G.A. Improved Visibility System. Paper in Surface 
 Mine Truck Safety. Proceedings of Bureau of Mines Technology 
 Transfer Seminars, Minneapolis, Minn., June 25. 1980; Birm- 
 ingham, Ala., July 9, 1980; and Tucson, Ariz., July 24, 1980; comp. 
 by Staff, Bureau of Mines. BuMines IC 8828, 1980, pp. 22-39. 
 
 17. Judeikis, J. (MSHA, Triadelphia, WV). Personal communica- 
 tion, 1980; available upon request from M.S. Sanders, Essex Corp.. 
 Westlake Village, CA. 
 
 18. Long, D.A. Solving the Problem of Getting On and Off Large 
 Surface Mining Equipment. Paper in Safety in the Use and 
 Maintenance of Large Mobile Surface Mining Equipment. Pro- 
 ceedings: Bureau of Mines Technology Transfer Seminars, Tucson, 
 AZ, August 16, 1983; Denver, CO, August 18, 1983; and St. Louis, 
 MO, August 23, 1983, comp. bv Staff, Bureau of Mines. BuMines 
 IC 8947, 1983, pp. 3-16. 
 
 19. Improved Personnel Access for Surface Mining Equip- 
 ment. BuMines IC 8983, 1984, 20 pp. 
 
 20. McCormick, E., and M. Sanders. Human Factors in Engineer- 
 ing and Design. McGraw-Hill, 5th ed., 1982, 615 pp. 
 
 21. Miller, W. Analysis of Haulage Truck Visibility Hazards at 
 Metal and Nonmetal Surface Mines, 1975. MSHA IR 1038. 1976. 
 19 pp. 
 
 22. National Institute for Occupational Safety and Health. Vibra- 
 tion Syndrome. NIOSH 83-110, 1983, 21 pp. 
 
 23. Puffer, W. Designing for Reduced Repair Labor Costs. Soc. 
 Automotive Eng., Warrendale. PA, SAE Tech. Pap. 81099. 1981. 
 10 pp. 
 
81 
 
 24. Rogers, L., D. Eglin, and W. Hart. Rock Drill Vibration and 
 White Finger in Mines. Ch. in Vibration Effects on the Hand and 
 Arm in Industry, ed. by A. Brammer and W. Taylor. Wiley, 1982, 
 pp. 317-323. 
 
 25. Sanders, M.S., and G.R. Kelley. Visual Attention Locations 
 for Operating Continuous Miners, Shuttle Cars, and Scoops. 
 Volume I (contract J0387213, Canyon Res. Group Inc.). BuMines 
 OFR 29(l)-82, 1981, 142 pp.; NTIS PB 82-187964. 
 
 26. Sanders, M.S., and G.S. Krohn. Validation and Extension 
 of Visibility Requirements Analysis for Underground Mining 
 Equipment (contract J0318072, Canyon Res. Group Inc.). BuMines 
 OFR 154-83, 1983, 65 pp.; NTIS PB 83-252957. 
 
 27. Society of Automotive Engineers (Warrendale, PA). Recom- 
 mended Practice for Control Locations for Construction and In- 
 dustrial Equipment Design. Standard J898, 1974, 3 pp. 
 
 28. Tichauer, E. The Biomedical Basis of Ergonomics. Wiley, 
 1978, 99 pp. 
 
 29. U.S. Air Force Systems Command. Human Factors Engineer- 
 ing. Aeronautical Systems Div. AFSC DH 1-3, 1980, 582 pp. 
 
 30. U.S. Army Missile Command. Military Standardization 
 Handbook: Human Factors Engineering Design for Army Material. 
 MIL-HDBK-759A, 1981, 79 pp. 
 
 31. U.S. Mine Safety and Health Administration. Mine Injuries 
 and Worktime Quarterly, Jan.-Dec. 1982. 1983, 18 pp. 
 
 32. Van Cott, H., and R. Kinkade. Human Engineering Guide 
 to Equipment Design. Wiley, rev. ed., 1972, 752 pp. 
 
 33. White, T. Ergonomic Survey of Mobile Cranes. Appl. 
 Ergonomics, v. 4, 1973, pp. 96-104. 
 
 34. Williams, J. Selection of Hand Tools Leads to Efficient, Safe 
 Use. Coal Age, v. 80, 1975, pp. 108-112. 
 
 35. Woodson, W. Human Factors Design Handbook. McGraw- 
 Hill, 1981, 1049 pp. 
 
82 
 
 CHAPTER 7.— PHYSICAL WORK 
 
 Mining will always be a physically demanding occupation, but by proper design of the tasks and worksites 
 and through employee training, the incidence and severity of injuries can be reduced 
 
 Despite increased mechanization, mining remains one 
 of the most physically demanding occupations in the world. 
 For " .'Tiple, it was found by Van Rensburg (37) 1 that in 
 £• th rican gold mines with increased mechanization, 
 more people were working in less strenuous jobs, but the 
 physical demands of the tasks themselves were not reduced. 
 The high physical demands inherent in mining take their 
 toll in injury and productivity. Underground mining labor 
 is especially susceptible because of the cramped working 
 conditions and the presence of heavy objects that must be 
 lifted and carried. Rock dust sacks can weigh 50 lb; a 75-ft 
 roll of brattice, 60 lb; and a 6- by 10-in, 14-ft wood crossbar, 
 over 200 lb. With such loads, it is not suprising that back 
 injuries constitute the largest single type of lost-time ac- 
 cidents in the mining industry, accounting for approximate- 
 ly 25% of all lost-time injuries, 5,458 in 1981 alone (30). Fur- 
 ther, this type of injury accounts for more lost workdays 
 than any other single type. In 1981, for example, Peay (30) 
 noted that 40% of lost-time back injuries incurred by 
 underground coal miners resulted in more than 4 weeks of 
 lost time per individual. 
 
 In addition to the pain and suffering caused by injury, 
 physically demanding tasks take their toll on productivity 
 by fatiguing the worker. The more demanding the task, the 
 more rest the worker needs. 
 
 1 Italic numbers in parentheses refer to items in the list of references at 
 the end of this chapter. 
 
 This chapter will review the basics of work physiology 
 and manual materials handling, and the demands of com- 
 mon mining tasks. Recommended limits on physically 
 demanding work will be discussed, as well as human fac- 
 tors methods for reducing the risks involved in such work. 
 
 WORK PHYSIOLOGY 
 Muscles 
 
 Muscles in our bodies allow us to move and to perform 
 useful work. Approximately 40% of one's total body weight 
 is composed of muscle. Each muscle consists of large 
 numbers of muscle fibers ranging in length from 0.2 to 5.5 
 in. The diameter of an individual muscle fiber is about four 
 ten-thousandths of an inch, and a muscle can have a million 
 such fibers. 
 
 The most important characteristic of muscle is its ability 
 to contract; that is, it can shrink to about two-thirds of its 
 normal length. Each muscle fiber contracts with a certain 
 force, and the strength of the whole muscle is the sum of 
 the forces produced by these muscle fibers. Hence, the cross- 
 sectional area of a muscle determines its strength. A mus- 
 cle produces its greatest force at the beginning of its con- 
 traction when it is at its relaxed length. As a muscle 
 shortens, its power declines. 
 
83 
 
 Muscular contraction is initiated by an electrical im- 
 pulse. This electrical activity can be detected and measured 
 by a technique known as electromyography. Electrodes are 
 attached (taped) to the surface of the skin over the muscle 
 to be examined. The exact placement of the electrodes is 
 important to insure reliable and valid data. Skin electrodes 
 record the total electrical activity of the muscle. The 
 readings appear as rapid pen movements on a strip chart 
 recorder, much like those produced by a seismograph dur- 
 ing an earthquake. These recordings can be calibrated to 
 yield measurements of the force of the muscle contractions. 
 Figure 7-1 shows electromyograms (EMG's) of a biceps mus- 
 cle producing 15, 30, 45, and 60 ft-lb of static torque (22). 
 As can be seen, the higher the torque being produced, the 
 greater the electrical activity and the more "violent" the 
 pen recordings. 
 
 EMG's are usually processed electronically to yield a 
 simple integrated score. The use of this method, however, 
 requires well-trained technicians and precisely calibrated 
 equipment. 
 
 Energy Consumption 
 
 To perform work a muscle must expend energy. The 
 detailed process by which a muscle obtains the energy 
 needed to perform work is complex and beyond the scope 
 of this report. The interested reader can consult Astrand 
 and Rodahl (3) or Weiser (38). For the purposes of this report, 
 a somewhat simplified presentation will suffice, as given 
 by Grandjean (17). 
 
 Muscle work is accomplished by the transformation of 
 chemical energy into mechanical energy. Energy is released 
 in a complex series of chemical reactions. Figure 7-2 shows 
 a very simplified diagram of the process. A muscle get its 
 
 Static torque produced, ft~lb 
 
 60 
 
 45 
 
 30 
 
 
 Figure 7-1 .— Electromyogram recording of biceps muscle dur- 
 ing Static force application (22). (Copyright 1 973 by the Human Factors Society 
 Inc., and reproduced by permission) 
 
 Without O2 
 
 Lactic acid 
 
 J _Paytag_off _J With I 
 0, debt ^J 
 
 KEY 
 
 Energy flow 
 
 Chemical reactions 
 
 Figure 7-2.— Schematic representation of metabolic process 
 
 that takes place during muscular work ( 1 7). (Courtesy of Taylor and Fran- 
 cis Ltd.) 
 
 energy from the breakdown of high-energy phosphate com- 
 pounds into low-energy compounds; this process does not 
 require oxygen. The problem is that there are not a lot of 
 high-energy phosphate compounds available in a muscle, 
 and they must be regenerated to provide additional energy 
 for the muscle. This regeneration process requires energy 
 from other chemical reactions. 
 
 The main energy source for the regeneration process 
 during intense physical work is glucose, a sugar circulating 
 in the blood. Glucose is converted into pyruvic acid, and this 
 liberates energy for the regeneration process. The further 
 breakdown of pyruvic acid depends on whether sufficient 
 oxygen is present in the system. If pyruvic acid is being pro- 
 duced in small quantities, enough oxygen will be available 
 to break down the acid into water and carbon dioxide 
 (aerobic glycolysis). This breakdown is also a source of 
 energy for the regeneration process. 
 
 If, however, insufficient oxygen is available to break 
 down pyruvic acid, then the pyruvic acid is converted into 
 lactic acid, a metabolic waste product (anaerobic glycolysis). 
 This conversion releases a small amount of energy that can 
 also be used for the regeneration process. The build up of 
 lactic acid in a muscle, however, will cause it to cease con- 
 tracting. To eliminate the lactic acid, oxygen is needed to 
 first convert the lactic acid back to pyruvic acid and then 
 to water and carbon dioxide, thus releasing more energy 
 for regeneration of the high-energy phosphate compounds. 
 
 From this thumbnail sketch, it can be seen that at the 
 outset of physical work, a muscle does not need oxygen to 
 function. A sprinter, for example, can run a 100-yd dash 
 without taking a breath (14). This is because energy is 
 released from the breakdown of high-energy phosphate com- 
 pounds and from the breakdown of glucose to pyruvic acid 
 and pyruvic acid to lactic acid. At the completion of a run, 
 however, the sprinter would be breathing heavily, and his 
 or her heart would be pounding. The runner is said to be 
 in oxygen debt. That is, the body must take in oxygen, after 
 the muscular work has been completed, to convert the lac- 
 tic acid back to pyruvic acid and ultimately to water and 
 carbon dioxide. The energy released is used to regenerate 
 the high-energy phosphate components depleted during the 
 run. 
 
 The body does not respond immediately to the onset of 
 heavy work; it takes a couple of minutes until the body 
 mobilizes its forces to supply the working muscles with ox- 
 ygen. Figure 7-3 shows the oxygen uptake, over time, in 
 response to physical work. The initial lag creates an oxygen 
 deficiency that is made up during recovery, when the ox- 
 ygen debt is repaid. 
 
 Cardiac Output and Aerobic Capacity 
 
 The body mobilizes to supply increased quantities of ox- 
 ygen and glucose to the working muscle. Just breathing 
 deeper and faster, however, does little to increase the ox- 
 ygen supply in the blood; this because blood leaves the lungs 
 97% saturated with oxygen under normal healthy condi- 
 tions. The only way to increase the supply of oxygen to a 
 muscle is to pump more blood through the muscle. This is 
 done by increasing the heart rate (beats per minute) and 
 increasing the volume of blood pumped with each beat 
 (stroke volume). Combined, the overall cardiac output (liters 
 of blood per minute) increases. At rest, the cardiac output 
 is about 5 L/min. Coincidentally, the average adult body 
 contains only about 5 L of blood. In severe work, a fourfold 
 
84 
 
 2 - 
 
 0- 
 
 Z> 
 
 ° I 
 
 1 1 1 1 1 1 1 1 1 
 
 _ Adjustment Steady state 
 
 Recovery 
 
 / ■ \ 1 v 
 
 7 ^ 
 
 - o 2 >^~ 
 
 deficit/^ 
 
 X 
 
 ;/ 
 
 Rest 
 
 l.i.i. 
 
 ,O z debt/^ 
 
 I , I 
 
 6 
 TIME, min 
 
 IO 
 
 12 
 
 Figure 7-3.— Oxygen uptake during muscular work, showing 
 oxygen deficiency at the outset of work and the repayment of 
 the oxygen debt during recovery. 
 
 to fivefold increase in cardiac output, 20 to 25 L/min, can 
 take place. 
 
 There is a limit to the capacity of the body to increase 
 cardiac output and, hence, deliver oxygen to the muscles. 
 This leads to an important concept: maximum aerobic 
 capacity (V0 2 max). This is the maximum oxygen uptake 
 (consumption) the body is capable of delivering. Individuals 
 have different aerobic capacities because of such things as 
 their degree of physical training, age, sex, and ability of 
 their blood to carry oxygen. For discussion of how to deter- 
 mine an individual's maximum aerobic capacity, see 
 reference 21. The concept of maximum aerobic capacity is 
 important for determining safe levels of energy expenditure 
 over the course of a workday, which will be discussed later 
 in this chapter. 
 
 The aerobic work capacity of U.S. low-seam 
 underground coal miners was measured by Ayoub (4-5). The 
 results are shown in figure 7-4. Aerobic capacity declines 
 with age (the exception in the over 50-yr group is probably 
 due to the small sample of miners tested) and is lower for 
 females. In comparing these results with American Health 
 Association norms (1), the low-seam coal miners would be 
 rated about average in terms of cardiovascular fitness. As 
 shown in figure 7-4, the aerobic capacity of American low- 
 seam coal miners is below the levels of physical work 
 (aerobic) capacity of South African miners (28), and 
 Norwegian and Romanian miners (39). American miners 
 were also heavier than the other groups. 
 
 Ayoub (4) speculates that since low-seam coal miners 
 engage in tasks that require short intervals of work with 
 high energy expenditures, it is possible that these miners 
 become specifically trained in the anaerobic (without ox- 
 ygen) energy mode. 
 
 MEASUREMENT OF WORK 
 
 The basic unit of energy, heat, or work is the calorie. 
 A kilocalorie is equal to 1,000 cal and is the basic unit of 
 energy expenditure. 2 A kilocalorie is the amount of heat 
 
 KEY 
 
 I I American low-seam 
 coal miners 
 
 V/A Romanian miners - 
 South African miners 
 Norwegian workers 
 
 20-29 30-39 40 "49 
 
 AGE, yr 
 
 >50 
 
 2 The calorie is now obsolete and has been superseded by the joule (1 cal 
 = 4.2 J). Since most of the literature still uses kilocalories (1 kcal = 4.2 kJ> 
 it will be used in this chapter. 
 
 Figure 7-4.— Aerobic capacity of male miners by age group (4, 
 28, 39). 
 
 needed to raise 1 L (a little over a quart) of water, 1 °C (from 
 20° to 21 °C). In dietary circles, the term "Calorie" is equal 
 to 1 kcal. 
 
 To determine the energy requirements of a given task, 
 the amount of oxygen consumed by the person doing the 
 task needs to be known. Based on the typical Western diet, 
 it is known that for every liter of oxygen consumed, approx- 
 imately 5 kcal of energy is expended. That energy is used 
 by the muscles to perform work and is also given off as heat 
 during the various chemical reactions discussed previously. 
 Approximately 75% of the energy liberated by the body goes 
 to heat; only about 25% is used for work. This le%*el of effi- 
 ciency is better than a steam engine, but not quite as good 
 as an internal combustion engine. 
 
 Measuring oxygen consumption can be cumbersome, re- 
 quiring the person performing the task to wear a 
 mouthpiece, nose clip, and gas-measuring device on his or 
 her back. Flexible hoses connect the mouthpiece to the 
 measuring device. Fortunately, there is an easy way to 
 estimate oxygen consumption without actually measuring 
 it while performing the task. Heart rate and oxygen con- 
 sumption are linearly related within the range from 
 moderate to close-to-maximum work loads. 
 
 Once the specific linear equation relating heart rate to 
 oxygen consumption for an individual is known, oxygen con- 
 sumption can be estimated based on heart rate measured 
 while performing the task. It should be pointed out. 
 however, that factors such as heat, fatigue, and smoking 
 can distort the relationship between heart rate and oxygen 
 consumption. 
 
 Heart rate can be measured with a few wires attached 
 to the subject and a tape recorder or telemetry device the 
 
85 
 
 size of a cigarette package. The problem is that the equa- 
 tion relating heart rate to oxygen consumption is not the 
 same for everyone. Physical fitness is a major factor deter- 
 mining individual differences. Figure 7-5 shows examples 
 of heart rate-oxygen consumption relationships for various 
 adult men; the steeper the slope of the line, the better the 
 physical condition of the individual (20). 
 
 Therefore, to use heart rate to predict oxygen consump- 
 tion, an individual must be calibrated. This is done by hav- 
 ing the person perform a task at different levels of effort 
 (e.g., walking on a treadmill at different speeds), while both 
 heart rate and oxygen consumption are being measured. 
 From such data, the relationship can be determined. 
 
 There are two types of muscular effort, dynamic (rhyth- 
 mic or isotonic) and static (isometric). Dynamic effort is 
 characterized by an alternation of contraction and relaxa- 
 tion of a muscle. During dynamic effort, the alternating con- 
 traction and relaxation squeezes blood through the muscle, 
 thereby supplying the working muscle with glucose and 
 oxygen. 
 
 Static effort, in contrast, is characterized by a prolonged 
 state of contraction of the muscles. Examples of static ef- 
 fort are bending over at the waist and holding that posture 
 while repairing a piece of equipment, or holding the arms 
 out in front of the body while hanging brattice, as shown 
 in figure 7-6. During static effort, the blood vessels are com- 
 pressed by the muscle itself so that blood flow through the 
 muscle is reduced or stopped. The flow of blood is constricted 
 in proportion to the force exerted by the muscle. Grandjean 
 (17) indicates that blood flow is almost completely inter- 
 rupted if the effort is 60% of the maximum effort possible. 
 At 15% to 20%, blood flow should be normal. 
 
 _l 
 
 LU 
 XL 
 
 < 
 
 Q_ 
 
 3 
 
 CD 
 
 >- 
 X 
 
 o 
 
 80 120 160 200 
 
 HEART RATE, beats /min 
 
 Figure 7-5.— Linear relationship between heart rate and oxygen 
 
 uptake for Six adult males (20). (Copyright 1973 by the Human Factors Society 
 Inc., and reproduced by permission) 
 
 Figure 7-6.— Underground worker hanging brattice cloth with arms at full extension and static loading of shoulder muscle. 
 
86 
 
 The impaired blood flow allows waste products (prin- 
 cipally lactic acid) to build up in the muscle, leading to acute 
 pain and muscle fatigue. The maximum duration of a con- 
 traction is related to the force exerted. Exerting a force of 
 50% of maximum can be endured, at most, for 1 min. Forces 
 of 25% of maximum can be maintained for about 3 to 4 min, 
 while forces of 20% or less can be endured for 10 min or 
 more. 
 
 All tasks involve components of both static and dynamic 
 effort. The static component, however, is by far the most 
 fatiguing and should be reduced if possible. Static effort can 
 be decreased by reducing the effort required, switching com- 
 ponents of the task so that muscle groups can be alternately 
 flexed and relaxed, and inserting numerous small rest 
 breaks during the task. 
 
 ENERGY EXPENDITURE AT WORK 
 
 There are many factors that affect the energy expen- 
 diture involved in performing a task. With respect to lift- 
 ing objects, the principal ones are the following: 
 
 1. Body weight.— A task that requires a person to move 
 his or her body will require more energy the heavier the 
 weight of the person's body. Tasks that involve carrying 
 objects or picking up objects by squatting or bending at the 
 waist are examples of those affected by body weight. 
 
 2. Body posture.— For example, a squat lift requires more 
 energy than a stoop lift (straight leg, bent at the waist), 
 because more of the body must be lifted in a squat lift. 
 
 3. Weight of objects moved.— The heavier the load to be 
 moved, the greater the work performed, and hence the 
 greater the energy expenditure. Figure 7-7, based'on the 
 work of Brown (7), for example, shows the combined effect 
 of weight of load and lifting pos'ture on energy expenditure. 
 
 4. Work pace.— Work pace is defined as the number of 
 times an activity 'is- performed per unit of time. In normal 
 lifting, it is the number of lifts per minute. As shown in 
 figure 7-8, it appears that the relationship between work 
 pace and energy expenditure is essentially linear (18). 
 
 5. Distance traveled— The distance a load is moved, or the 
 distance over which a force is applied, is directly related 
 to energy expenditure. In normal lifting, it is the vertical 
 distance the load is lifted that is most important. 
 
 6. Temperature and humidity— In general, the higher the 
 temperature and humidity, the greater will be the energy 
 expenditure for tasks performed in such environments. Part 
 of this increase is due to a general increase in metabolic 
 rate in hot environments. 
 
 One additional factor that impacts energy expenditure, 
 and is especially important in normal lifting, is the vertical 
 heights of the beginning and end points of the lift. Lifting 
 the same distance, but starting at different heights, may 
 require the lifter to assume different body postures and may 
 involve differential movement of the body's center of grav- 
 ity, as illustrated by the data in table 7-1. Although the 
 same overall mechanical work is being performed, the 
 energy expenditure is greater for the task that starts out 
 at a lower height (task B), despite the fact that the work 
 pace is less. 
 
 Figure 7-9 shows the energy efficiency (energy per unit 
 mechanical work) for lifting various weights 20 in from 
 various starting positions (12). The most energy efficient 
 lifting occurs when the starting position is between 39 and 
 59 in above floor level. When the starting position is below 
 39 in the efficiency is greater the heavier the load. This is 
 
 true because the energy required to lift the body is constant, 
 no matter what the load. 
 
 Grades of Physical Work 
 
 Table 7-2 defines seven grades of work, including rest, 
 based on energy expenditure. Also included are associated 
 average heart rates and oxygen consumption values. The 
 data presented apply to reasonably fit adult males. 
 
 Energy Expenditures for Common Mining Tasks 
 
 In a survey of low-seam coal mining tasks, Ayoub (4) 
 identified the following jobs as most physically demanding: 
 roof bolter, bolter helper, miner helper, and timberman. 
 Table 7-3 shows the energy expenditure on these jobs and 
 for the task of shoveling; the grade of work to which each 
 corresponds is also shown. The energy expenditure for 
 shoveling is unusually high because this task is performed 
 at a rapid work pace at the coal face. In addition, it was 
 reported by Morrisey (24) that the energy cost of shoveling 
 increases as a worker is forced to assume a more stooped 
 posture, common in low-seam mines. At 60% of a normally 
 
 Table 7-1.— Effect of vertical starting position 
 on energy expenditure (27) 
 
 (Courtesy of National Institute for Occupational Health) 
 
 
 Task 
 
 
 A 
 
 B 
 
 Load lb . . 
 
 Work pace lifts/min . . 
 
 Vertical starting position in . . 
 
 Vertical ending position in . . 
 
 Mechanical work performed kg-m . . 
 
 Energy expenditure kcal/min . 
 
 10 
 
 25 
 
 36 
 
 66 
 
 86.6 
 
 3.56 
 
 10 
 21 
 '0 
 36 
 86.0 
 677 
 
 1 Floor. 
 
 Table 7-2.— Grade of physical work 
 based on energy expenditure level 1 (2) 
 
 (Reprinted with permission by American Industrial Hygiene Assoc ) 
 
 
 Energy expenditure, kcal 
 
 Heart rate, 
 beats/min 
 
 Oxygen 
 consumption. 
 
 
 Per min 
 
 Per 8-h day 
 
 L/min 
 
 Rest (sitting) 
 
 Very light work 
 
 Light work 
 
 Moderate work 
 
 Heavy work 
 
 Very heavy work .... 
 Unduly heavy work. . 
 
 1.5 
 1.6- 2.5 
 2.5- 5.0 
 5.0- 7.5 
 7.5-10.0 
 10.0-12.5 
 >12.5 
 
 720 
 768-1.200 
 1,200-2.400 
 2.400-3,600 
 3,600-4.800 
 4.800-6.000 
 >6.000 
 
 60- 70 
 
 65- 75 
 
 75-100 
 
 100-125 
 
 125-150 
 
 150-180 
 
 >180 
 
 0.3 
 0.32- .5 
 .5 -1.0 
 1.0 -1.5 
 1.5 -2.0 
 2.0 -2.5 
 >2.5 
 
 ' Assumes a reasonably fit adult male. 
 
 Table 7-3.— Energy expenditures for four low-seam tasks (4), 
 kilocalories per minute 
 
 Task and grade of work Expenditure 
 
 Shoveling, neavy worn 9.3 
 
 Helping, 1 moderate work 7.2 
 
 Timbering, moderate work 6.0 
 
 Roof bolting, light work 4.9 
 
 1 Includes both continuous miner and roof bolter helpers. 
 
87 
 
 10 20 30 40 
 LOAD, kg 
 
 Figure 7.7— Effect of weight of objects being lifted and lift 
 
 posture on energy expenditure (27). (Courtesy of National Institute for Oc- 
 cupational Safety and Health) 
 
 E 
 
 o 
 
 o 
 
 LjJ 
 
 <r 
 
 Q 
 Z 
 LlI 
 Q. 
 X 
 LU 
 
 >- 
 
 e> 
 q: 
 lu 
 
 z 
 
 UJ 
 
 8 
 
 ll.4-kg 
 cartons - 
 
 Average 
 
 4. 5 -kg cartons 
 
 6 8 10 12 14 16 
 WORK PACE, cartons/min 
 
 Figure 7-8.— Effect of work pace on energy expenditure for a 
 
 lifting task (18). (Copyright 1969 by the American Institute of Industrial Engineers, 
 and reprinted by permission) 
 
 Least 
 efficient 
 
 Most 
 efficient 5 10 1 5 20 
 
 WEIGHT, kg 
 
 Figure 7-9.— Energy efficiency of lifting various weights from different starting positions (12). (Courtesy of Butterworth Scientific Ltd.) 
 
88 
 
 erect posture, for example, energy expenditure was 13% 
 higher than in a fully erect posture. Table 7-4 presents 
 energy expenditure data collected in South African gold 
 mines on additional tasks. In handling rock dust bags (50-55 
 lb each) or arch sections (12 legs, 180 lb each; 6 crowns, 170 
 lb each), it was found by Sims (33) that the energy expen- 
 diture was approximately the same, 6.0 kcal/min (moderate 
 work). 
 
 Table 7-4.— Average energy expenditures for mining tasks 
 
 in South African gold mines (37), 
 
 kilocalories per minute 
 
 (Reprinted with permission by Chamber of Mines South Africa) 
 
 Task and grade of work Expenditure 
 
 Transport of explosives (25 lb), moderate work 6.85 
 
 Shoveling, moderate work 5.85 
 
 Mechanical loader operators, moderate work 5.20 
 
 Barring down, light work 4.75 
 
 Equipping: Pipes and tracks, light work 4.65 
 
 Tip operator, light work 4.43 
 
 Timbering, light work 4.40 
 
 Sweeping, light work 3.95 
 
 Pneumatic drill operator, light work 3.95 
 
 Stonewall building, light work 3.90 
 
 Pneumatic drill assistant, light work 3.15 
 
 Locomotive driver, light work 2.60 
 
 Winch driving, light work 2.55 
 
 bolter helper. As can be seen, energy levels peak at approx- 
 imately 11 kcal/min (very heavy work), but dip as low as 
 5.0 kcal/min (light work) elsewhere during the cycle. 
 
 Ayoub (4) calculated the total energy expenditure over 
 a 7.5-h shift (8 h minus 0.5 h for lunch) including idle time, 
 travel, and other activities for the workers they analyzed. 
 The results were as follows: Helpers (moderate work), 
 2,789-kcal expenditure for 7.5-h shift (average of 6.1 
 kcal/min); roof bolters (light work), 2,102-kcal expenditure 
 for 7.5-h shift (average of 4.7 kcal/min). 
 
 Although several tasks in mining require high levels 
 of energy expenditure over short time periods, the level of 
 work is generally in the light to moderate class. This, of 
 course, is because the workers intersperse rest breaks in 
 the work cycle or alternate between heavy and light activ- 
 ities. With the exception, perhaps, of shoveling, it appears 
 that high levels of cardiovascular fitness, although desir- 
 able, are not necessary to perform the majority of mining 
 tasks. Thus, females who generally have lower aerobic 
 capacities than men should be able to function well in 
 overall mining operations. As Ayoub (4) points out, how- 
 ever, females and small males may be limited because of 
 strength, as opposed to aerobic, capacity in their ability to 
 perform mining tasks as such tasks are performed today. 
 
 RECOMMENDED ENERGY EXPENDITURE LEVELS 
 
 When these values are reviewed, it must be remembered 
 that changes in the work pace or the method of carrying 
 out the task can significantly affect the energy expenditure 
 levels. Further, the energy expenditure during performance 
 of a task varies widely depending on the specific cycle of 
 activity. Figure 7-10, for example, presents the energy ex- 
 penditure levels during a work cycle for a low-seam roof 
 
 The National Institute for Occupational Safety and 
 Health (NIOSH) recommends that short-term energy expen- 
 diture levels (for 1 h or less) should not exceed 9 kcal/min 
 for physically fit males or 6.5 kcal/min for physically fit 
 females (27). The difference between the male and female 
 recommendations is due to the generally lower aerobic 
 capacity of females. 
 
 c 
 £ 
 
 S 15 
 
 LU 
 
 OL 
 
 Q 10 
 
 Z 
 
 LU 
 
 Q_ 
 
 X 
 
 LU 
 
 >■ 
 ^ 5 
 
 LU 
 
 z 
 
 LU 
 
 P r 
 
 c 
 3 £ 
 
 LU 
 
 !5 
 
 Z> 
 
 Z 
 LU 
 
 X 
 
 I o 
 
 14 
 
 16 
 
 18 
 
 2 4 6 8 10 12 
 
 TIME, min 
 
 Figure 7-10.— Energy expenditure and activity profile for roof bolter helper (4). 
 
 JO 
 20 
 
89 
 
 Long-term energy expenditure levels (averaged over a 
 workday) should not exceed 5.0 kcal/min for males and 3.5 
 kcal/min for females. These values correspond to approxi- 
 mately 33% of the average aerobic capacity of males and 
 females. NIOSH points out, however, that these guidelines 
 do not reflect the increased metabolic costs associated with 
 overweight or poorly conditioned individuals. 
 
 Based on the aerobic capacity of males and females, and 
 these NIOSH recommendations, the recommended maxi- 
 mum working time for tasks requiring various levels of 
 energy expenditure can be computed. Figure 7-11, for ex- 
 ample, shows recommended maximum working times for 
 
 males and females performing various low-seam mining 
 tasks. This figure gives maximum times for the 5th, 50th, 
 and 95th percentile males and females. The 5th percentile 
 represents the bottom 5% of the population in terms of 
 aerobic capacity and recommended work time. The 50th 
 percentile is the average, and the 95th percentile is what 
 can be expected by someone who is 5% from the top of the 
 population 
 
 Several authors have attempted to develop formulas to 
 predict the amount of rest required, or the amount of work 
 permitted before rest is required. Unfortunately, the for- 
 mulas do not always produce the same results. 
 
 O 
 O 
 
 LU 
 
 rr 
 
 z> 
 
 Q 
 
 15 
 
 10 
 
 i — i i i i 
 
 Task and ** 
 
 energy expenditure 
 (kcal/min) 
 
 "Shoveling (9.28) 
 
 KEY 
 
 — *95th percentile 
 
 — 50th percentile 
 
 — — — 5 th percentile 
 
 Timbering (6.0) 
 
 Bolting (4.9) 
 
 - 2 
 
 Helping bolter or miner (7.15) 
 
 j i ■ ■ i i 
 
 LU 
 < 
 
 LU 
 
 a. 
 x 
 
 LU 
 
 > 
 
 rr 
 
 LU 
 
 LU 
 
 10- 
 
 
 
 1 1 I I T 1 I I 
 
 B 
 
 i 
 
 1 III 
 
 1 1 1 1 1 
 
 1 1 
 
 Task and 
 
 
 
 
 
 energy expenditure 
 
 
 
 
 
 (kcal/min) 
 
 
 
 
 
 ^- Shoveling 
 
 (9.28) 
 
 
 
 
 — 
 
 Helping bolter ^** 
 
 
 or miner (7.15) 
 
 '^^"^ 
 
 
 ' • _^ 
 
 ^* • 
 
 
 Timbering (6.0) 
 
 
 '"* •* 
 
 •*"^*" 
 
 " • — 
 
 _ Bolting (4.9) 
 
 
 
 
 
 
 •^ 
 
 -- , w ^ • 
 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 -^ 
 
 •^■"^ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 • ^^^^-^^ • ^ 
 
 c 
 
 c 
 
 c 
 
 c 
 
 c 
 
 c 
 
 c 
 
 c 
 
 c 
 
 c 
 
 c 
 
 c 
 
 ~^"^fc 
 
 E 
 
 E 
 
 e 
 
 E 
 
 E 
 
 E 
 
 E 
 
 E 
 
 E 
 
 E 
 
 E 
 
 E 
 
 
 to 
 
 00 
 
 CM 
 
 0> 
 
 00 
 
 <r 
 
 O 
 
 CO 
 
 if) 
 
 CO 
 
 (0 
 
 (7) 
 
 
 
 If) 
 
 1 I... 
 
 OS 
 
 1 1 1 1 
 
 _L 
 
 CM 
 
 1 
 
 
 in 
 
 _l 
 
 10 
 
 l_ 
 
 0) 
 
 1 1 1 
 
 CM 
 
 1 
 
 ID 
 
 CM 
 
 1 I 
 
 5 -- 
 
 - 2 
 
 UJ 
 X 
 
 o 
 
 00 
 
 
 500 
 
 RECOMMENDED MAXIMUM WORK TIME, min 
 
 Figure 7-11.— Recommended maximum work times for males and females performing tasks in low-seam coal mines at various 
 levels of energy expenditure (4). 
 
90 
 
 One formula embraced by the American Industrial 
 Hygiene Association (AIHA) (2) is based on the assumption 
 that over an 8-h shift, average energy expenditures should 
 not exceed 5.5 kcal/min. Because at-rest energy expenditure 
 is 1.5 kcal/min, the 5.5 kcal/min figure really represents 
 an actual work expenditure of 4.0 kcal/min. The following 
 formula computes the needed rest allowance expressed in 
 terms of percentage of time working: 
 
 RT% = 
 
 W- 1.5 
 4.0 
 
 1 x 100, 
 
 where RT% = rest allowance 
 and W = energy expenditure during work, 
 kcal/min. 
 
 Murrell (26) presented another formula similar to the 
 AIHA formula, but which computes directly the number of 
 minutes of rest required. The formula assumes a maximum 
 average energy expenditure of 5 kcal/min. Murrell's for- 
 mula is as follows: 
 
 RT = 
 
 T (W - 5) , 
 (W - 1.5) 
 
 where RT = rest time, min, 
 
 T = work time, min, 
 and W = energy expenditure during work, kcal/min. 
 
 Application of these formulas to a male shoveling coal 
 in a low-seam mine (9.3 kcal/min) for 10 min yields the 
 following calculations: 
 
 AIHA formula-RT% = 
 
 9.3 - 1.5 
 515 
 
 1 x 100 = 95%, or 
 
 95% of 10 min work = 9.5 min rest, and 
 Murrell formula-RT = ^I'l^l) * = 5.5 min rest 
 
 Of equal or even greater importance than the amount 
 of rest is the arrangement of the rest periods. In general, 
 the greater the energy cost of a task, the more frequently 
 rest pauses should take place. There is less cumulative 
 fatigue and less demand on the heart and lungs with many 
 short rests (every 0.5 to 2 min) than with the same amount 
 of total rest time taken in fewer, but longer breaks. In ad- 
 dition, hot environments make extra demands on the cir- 
 culatory system, and hence the rest requirements are 
 greater than in cool environments. 
 
 Muller (25) presented a formula that attempts to predict 
 when to take a rest. Muller assumed that people have a 
 25-kcal energy reserve that is only tapped when work ex- 
 ceeds 5 kcal/min. His formula is based on taking a rest when 
 the 25-kcal reserve is used up. He further assumed that at 
 rest, the reserve is rebuilt at the rate of 3.5 kcal/min (5 
 kcal/min - 1.5 kcal basal metabolic rate). Hence, all rests 
 are 7 min long (i.e., 25/3.5). The formula is as follows: 
 
 WT = 
 
 25 
 
 (W-5) 
 
 where WT — work time, before rest is required, 
 
 and W = energy expenditure during work, kcal/min. 
 
 Application of this formula to a 9.3-kcal shoveling task 
 yields 
 
 WT = 
 
 25 
 
 (9.3 - 5) 
 
 = 5.8 min. 
 
 That is, after 5.8 min of work, a shoveler should rest for 
 7 min. For 10 min of work, he or she would require 1.7 rests 
 (10/5.8) of 7 min each for a rest total of 12 min. This can 
 be compared to the 9.5-min and 5.5-min values obtained by 
 applying the AIHA and Murrell's formulas, respectively. 
 Unfortunately, there are no objective data available to 
 determine which formula should be used to determine the 
 amount of rest required. The fact that most mining tasks 
 are self-paced, compensates in part for the heavy work loads. 
 However, workers cannot always be depended upon to take 
 rest breaks at the best times. Work-rest cycles can be em- 
 pirically determined by testing various combinations and 
 monitoring heart rate and oxygen consumption during the 
 work and rest phases. A good work-rest schedule should 
 result in significant recovery of heart rate during the rest 
 period and little increase in oxygen consumption during suc- 
 cessive work periods. One known fact is that people are poor 
 judges of when they require rest. Usually, by the time a 
 person feels tired, an inordinately long rest will be required 
 for recovery. A rest break should be taken before the need 
 for one is felt. 
 
 MANUAL MATERIALS HANDLING 
 
 Materials handling involves the lifting, pushing, pull- 
 ing, or shoveling of materials or components used during 
 equipment or mine maintenance activities. Generally 
 speaking, there is more manual handling of materials in 
 underground mining than in surface mining. This is due 
 to several factors, including a greater variety of supplies 
 used and the difficulty of using mechanical handling devices 
 underground. Unger and Connelly (35) cataloged materials 
 handling activities in underground mining into five 
 functions: 
 
 1. Production supply.— Handling materials from the sur- 
 face yard to locations near the working face. Examples 
 would include transporting rock dust bags, roof bolts, and 
 timbers. 
 
 2. Production end use.— Handling items during their end 
 use at the working face. Such work activities would include 
 erecting temporary curtains for ventilation, rock dusting, 
 roof bolting, and erecting cribbings. 
 
 3. Section move.— Handling materials from the surface 
 yard to the section being moved, including the handling dur- 
 ing the process of moving a mining section. Examples in- 
 clude moving haulage belts, transporting cables, moving 
 air lines, and moving longwall roof support. 
 
 4. Equipment maintenance.— Handling materials used 
 during maintenance of mine equipment. Examples include 
 extracting motors from continuous miners, replenishing 
 hydraulic oil, and splicing cables. 
 
 5. Mine maintenance.— Handling materials used in mine 
 maintenance. Examples of activities include maintenance 
 of roof, ventilation, rail track, and roadways. 
 
 Table 7-5 lists some common underground mine 
 materials and representative weights to give an idea of the 
 kinds of loads that are often manually lifted, pushed, and 
 pulled. 
 
91 
 
 Table 7-5.— Common mine materials 
 and their weights (75, 35), pounds 
 
 Table 7-7.— Objects involved in overexertion back injuries 
 suffered by underground coal miners during 1981 (31) 
 
 Roof support supplies: 
 Roof bolts, 5/8 in by 6 ft, 
 
 bundle of 10 55 
 
 Sheets, box of 25 25 
 
 Plates, 6 by 6 by 1/4 in, 
 
 bundle of 10 27 
 
 Roof jack, 6 by 6 in by 5 
 
 to 8 ft, closed 50-70 
 
 Wood crossbars, 6 by 8 
 
 in by 10 to 14 ft 160-225 
 
 Round wood post, 6 in 
 
 by 5 to 8 ft 48-76 
 
 Metal "H" beam, 6 by 6 
 
 in by 16 ft 320 
 
 Rock dust, 1 bag 50 
 
 Oil container, 5-gal (full) . . 40 
 
 Brattice roll, 75-ft 60 
 
 Trailing cable, 2- to 3-in 
 
 diam, 10 ft long 50-100 
 
 Concrete supplies: 
 
 Cement, 1 bag 80-90 
 
 Concrete block, 6 by 8 
 
 by 16 in 
 
 Rebar, 3/4 in by 6 ft, 
 
 bundle of 10 
 
 Rail supplies: 
 Rail: 
 
 30-lb, 30 ft 
 
 60-lb, 30 ft 
 
 Rail tie, 8 by 6 by 72 in 
 Belt supplies: 
 Belt roller, 6 by 42 in 
 Belt chain, 8 by 9 by 
 52 in 20-25 
 
 62 
 
 90 
 
 300 
 
 600 
 
 90-100 
 
 50 
 
 Materials Handling Accidents 
 
 Annually, materials handling is the leading accident 
 classification in coal, metal, nonmetal, stone, and sand and 
 gravel underground and surface mining and in all process- 
 ing and preparation plants. Table 7-6 shows the number 
 of materials handling nonfatal-days-lost injuries occurring 
 in the industry in 1983, as determined by MSHA (36). 
 Overall, materials handling accounted for 33.7% of all 
 nonfatal-days-lost accidents in the mining industry that 
 year. 
 
 Table 7-6.— Materials handling nonfatal-days-lost (NFDL) injuries 
 in the mininq industry, 1983 (36) 
 
 (Courtesy of U.S. Mine Safety and Health Administration) 
 
 Coal: 
 
 Underground 
 
 Surface 
 
 Preparation plants 
 Metal: 
 
 Underground 
 
 Surface 
 
 Mills 
 
 Nonmetal: 
 
 Underground 
 
 Surface 
 
 Preparation plants 
 Stone: 
 
 Underground 
 
 Surface 
 
 Mills 
 
 Sand and gravel surface . 
 Overall 
 
 NFDL 
 
 Share of 
 
 in- 
 
 all in- 
 
 juries 
 
 juries, % 
 
 2,432 
 
 35.1 
 
 439 
 
 28.8 
 
 236 
 
 36.8 
 
 162 
 
 24.0 
 
 103 
 
 31.6 
 
 175 
 
 35.6 
 
 82 
 
 33.7 
 
 50 
 
 33.3 
 
 236 
 
 41.2 
 
 16 
 
 21.9 
 
 254 
 
 32.2 
 
 376 
 
 36.3 
 
 164 
 
 29.9 
 
 4,725 
 
 33.7 
 
 Materials handling injury reports covering a 3-yr period 
 showed that 40% involved injury to the back (11). Finger 
 injuries while handling materials were the next most 
 prevalent (18%). It was also found that over half of the in- 
 juries (52%) involved overexertion; of these, 60% occurred 
 while lifting objects. Table 7-7, for example, lists the type 
 of objects underground coal miners were attempting to move 
 when they incurred back injuries because of overexertion. 
 (31). 
 
 Electric cables 
 
 Broken rock and coal . . . 
 
 Timbers and posts 
 
 Metal objects' 
 
 Belt conveyor systems . . 
 
 Wood objects 2 
 
 Steel rails 
 
 Bagged materials 
 
 Jacks 
 
 Mining machines 
 
 Roof bolts 
 
 Oil containers 
 
 Cement blocks 
 
 Buckets and cans 
 
 Metal covers and guards 
 
 Pry bars 
 
 Motors 
 
 Wheels 
 
 Boxes 
 
 Other 
 
 Total 
 
 100.0 
 
 1 Does not include metal objects such as rails, roof bolts, jacks, motors, etc., 
 which are listed separately. 
 
 2 Does not include timbers, posts, caps, and headers. 
 
 Materials handling accidents at 27 underground coal 
 mines during 1973 were analyzed (16). As shown in figure 
 7-12, the majority of injuries occurred in production supply 
 activities. This high number is probably due to several fac- 
 tors, including (1) materials are often handled several times 
 from the yard to locations near the face, thus increasing 
 exposure to injury; (2) many shipments of materials are 
 made on a daily basis, again increasing injury exposure; 
 and (3) materials are often banded or tied together in large, 
 heavy packages, thus increasing the risk of injury. 
 
 Biomechanics of Lifting 
 
 Because a majority of materials handling injuries result 
 in back injury from overexertion, and most of these occur 
 during lifting activities, a review of the basic dynamics of 
 lifting and back injury is in order. Biomechanics is the 
 science that, among other things, considers the actions of 
 the human body in bringing about controlled movements 
 and applying forces, torques, energy, and power to exter- 
 nal objects (32). 
 
 The basic principle of lifting involves the physics of 
 levers. When a load is held in the hands, the load as well 
 as the person's body mass creates rotational movements or 
 torques at the various joints of the body. The skeletal 
 muscles are positioned to exert forces at these joints to 
 counteract the movements due to the load and body weight. 
 The problem is that the muscles are positioned so that they 
 act through relatively small moment arms. Consider the 
 example depicted in figure 7-13 where a 10-kg (22-lb) weight 
 is held in the hand with the elbow at a 90 ° angle. For the 
 arm to maintain its position, the bicep muscle must exert 
 a force sufficient to overcome the weight of the load and 
 the weight of the forearm and hand. Based on anthropo- 
 metric data for an average male, the forearm weighs 
 approximately 4.4 lb. For the average male, the biceps mus- 
 cle is attached 2 in. from the point of rotation of the elbow, 
 the length of the forearm is approximately 14 in, and the 
 center of gravity of the forearm and hand is approximately 
 6.7 in. from the elbow. This is shown in simplified form in 
 the lower half of figure 7-13. 
 
92 
 
 140 
 
 120 
 
 100 
 
 [2 80 
 
 Z 
 UJ 
 
 9 
 o 
 
 O 60 
 
 40 
 
 20 
 
 I33((50%) 
 
 KEY 
 A Production supply 
 8 Equipment maintenance 
 C Section move 
 D Production end use 
 E Mine maintenance 
 Total accidents, 269 
 
 44(16%) 
 
 35(13%) 
 
 30(11%) 
 
 27(10%) 
 
 ° A B C D E 
 
 MINING ACTIVITY 
 
 Figure 7-12. — Materials handling accidents by major activity 
 or function. Data are from 27 coal mines during 1973. 
 
 b*® 
 
 MO kg 
 
 £. 
 
 Tf a ~~|f l 
 
 — d a -H 
 
 F M 
 Fa 
 
 Fl 
 Dm 
 
 Da 
 
 KEY 
 Muscle force 
 
 Force from weight 
 of arm and hand 
 
 Force from load 
 
 Distance of muscle 
 force 
 
 Distance of hand 
 and arm 
 
 Distance to load 
 
 Figure 7-13.— Illustration of basic muscle biomechanics and 
 
 lever analog (27). (Courtesy of National Institute for Occupational Safety and Health) 
 
 The moment or torque created by each load is the prod- 
 act of its force (a weight) and the distance from its center 
 of gravity to the rotation or pivot point. As with a teeter- 
 totter, to balance a light and heavy person, the light per- 
 son should sit at the end of the teeter-totter arm and the 
 heavy person nearer the pivot point. The light weight and 
 long distance compensate for the heavy weight and short 
 distance. 
 
 The force the biceps muscle in figure 7-13 must exert 
 to hold the 22-lb weight can be calculated using the follow- 
 ing formula: 
 
 (F M x D M ) = (F L x D L ) + (F A x D A ), 
 
 where: F = force, lb, 
 
 D = distance from the force to the pivot point, in, 
 
 M = muscle, 
 
 L = load being held, 
 
 and A = arm. 
 
 The solution is 
 
 (F M x 2) = (22 x 14) + (4.4 x 6.7) or F M = 169 lb. 
 
 Therefore, even in this simple situation, the biceps must 
 exert a force more than seven times the weight of the ob- 
 ject being held. In addition, when a muscle pulls across an 
 extended joint, it compresses the joint with about the same 
 magnitude of force. This is an important concept when con- 
 sidering low-back biomechanics. 
 
 The spine is made up of a series of bony vertebras 
 stacked up with flexible fibrous pads, called disks, between 
 each one. As shown in figure 7-14, the spinal column is 
 divided into five sections, and the vertebras in each section 
 are numbered for easy reference (19). 
 
 Most back injuries occur in the lower lumbar spine, and 
 the LvS, disk (sacrovertebral joint) has been used to repre- 
 sent the spinal stresses of lifting. Biomechanical models 
 have shown that during the lifting of a weight, the bending 
 moment at the L 5 -S, joint can become quite large due, in 
 part, to the weight of the upper body. For example, lifting 
 a 110-lb weight from the floor can produce a bending mo- 
 ment of approximately 1,732 lb-in at the L 5 -S, joint, accord- 
 ing to NIOSH (27). To counteract this moment, the muscles 
 of the lower back region (i.e., the erector spinae group) must 
 exert large forces because they operate on very small mo- 
 ment arms (approximately 2 in). Thus, to produce 1,732 lb- 
 in, the muscles must exert a force of 8801b. The large forces 
 generated by the lower back muscles are the primary 
 sources of compression forces on the Lj-Sj disk. The only 
 force that acts to diminish the compression forces of the 
 spine is intra-abdominal pressure. 
 
 Figure 7-15 shows the results of an analysis of the back 
 muscle force and compression forces resulting from lifting 
 a 100-lb timber in the posture depicted. The resulting mus- 
 cular force on the back in this situation was 1,148.5 lb and 
 the compression force on the L 5 -S, disk was 1.219.6 lb. 
 
 The amount of compressive force that the vertebras can 
 tolerate before experiencing microfractures is a function of, 
 among other things, age. sex, and prior compressive stresses 
 experienced. Data from cadavers of males under 40 yr of 
 age show a mean of about 1,485 lb of compression required 
 before microfractures occur. The value drops to approxi- 
 mately 880 lb for males 50 to 60 yr old. There is. however. 
 considerable individual differences in compression tolerance 
 within any age group. It has been estimated by Sonoda (34) 
 
93 
 
 Cervical 
 
 Atlas * 
 Axis 
 
 
 /I 
 
 Thoracic « 
 
 F be 
 
 Lumbar - 
 
 ■. y. 
 
 > -'- • y- 
 
 Sacral 
 
 y? 
 
 /r , 
 
 Coccygeal 
 
 *-/ 
 
 C4 
 
 T 4 
 T 5 
 
 '10 
 
 Jl2 
 
 L 2 
 
 Sacrovertebral 
 joint 
 
 Articular portion 
 of sacrum 
 
 Figure 7-14.— Diagram of spinal column showing division and 
 
 naming convention Of vertebras (19). (Courtesy of W.B. Saunders Co.) 
 
 Back muscle tension, F 2 
 (F 2 =l t l48.5lb) 
 
 w,=30lb 
 
 (738.2 lb) 
 
 rw N Reaction, R 
 ^ (R=l,2l9.6lb) 
 
 (970.8 lb) 
 
 F, = IOOlb 
 
 w | = Weight of head, neck, and arms (estimated as a 
 percent of total body weight) 
 
 w 2 = Weight of trunk (estimated as a percent of total body 
 weight) 
 
 F|=External weight lifted or held (timber) 
 
 Figure 7-15.— Calculated lower-back muscle force and com- 
 pressive (reactive) forces acting on L 5 -S, disk resulting from 
 
 lifting a timber post (6). (Copyright 1983 by the Human Factors Society Inc., 
 and reproduced by permission) 
 
 that the female spinal compression tolerance is about 17% 
 less than that of males due, in part, to the smaller force- 
 bearing area of their vertebras. 
 
 According to NIOSH (27), the following is the current 
 view on the genesis of a ruptured disk. Repeated compres- 
 sive stresses, especially from lifting, are sufficient to cause 
 microfractures in the cartilage end plates and subchondral 
 bone of the vertebras, which it is believed alters the me- 
 tabolism and fluid transfer to the disk. If this occurs, the 
 disk begins to degenerate, and its capacity to withstand fur- 
 ther compression loads decreases. The result is that the disk 
 squeezes out from between the vertebras and presses on the 
 spinal nerve root as shown in figure 7-16. This is commonly 
 called a slipped or ruptured disk. 
 
 If this scenario is correct, then assigning cause for lower 
 back pain to the immediate circumstance at the time when 
 the pain first developed may be overly simplistic. In fact, 
 most low-back injuries do not suddenly start with a jabbing 
 pain, although such cases are easily remembered. Most 
 often, the symptoms are slow to develop, with stiffness, dull 
 aching pain, and finally incapacitating discomfort that can 
 occur hours or days later. 
 
 Effects of Lifting Posture 
 
 The most important rule in lifting is to bring the torso 
 (really the L 5 -S! joint) as close as possible to the center of 
 gravity of the load before lifting. The closer the L 5 -S! joint 
 is to the load, the shorter the moment arm and the lesser 
 the force applied to the back. A second and subordinate prin- 
 ciple, is that the back should be kept straight and vertical 
 during a lift. In that posture, the compressive forces on the 
 spine are more or less evenly distributed over the load- 
 bearing surface of the vertebras. When the trunk is allowed 
 to bend forward, the forces are concentrated on the front 
 edges of the vertebras and tend to squeeze the disk toward 
 the rear of the vertebral column. 
 
 The best posture for lifting depends partially on the size 
 of the load being lifted. Small loads that can fit between 
 the knees when in a squat posture are best lifted with the 
 classical bent knee-straight back technique. With the load 
 between the knees, the torso is very close to the load center 
 of gravity, and the strain on the back is reduced. In addi- 
 tion, the back is kept vertical. Although this is often the 
 
 Normal 
 
 Ruptured 
 
 Figure 7-16.— Cutaway view of ruptured L5-S1 disk pressing 
 the spinal nerve (8). 
 
94 
 
 recommended lifting method, it may be easier said than 
 done. Often, people do not have the upper leg strength 
 needed to lift the load and the weight of the body. Because 
 the body must be lifted in this technique, it is one of the 
 most costly in terms of energy expenditure, and it quickly 
 induces fatigue if adequate rest periods are not taken. In 
 addition, this squat-lift technique requires flexibility and 
 ranges of motion in the hips, knees, and ankles that many 
 people do not possess. A systematic exercising and stretch- 
 ing program may be required to build the strength and flex- 
 ibility needed to use this type of lift. Finally, it is often not 
 possible to get close to the load being lifted to perform a 
 bent-knee lift because of obstructions. 
 
 When an object to be lifted is large (not necessarily 
 heavy), then the squat lift may be more dangerous than the 
 stoop-back lift technique, where knees are only slightly 
 flexed, and the person bends over at the waist to lift the 
 object. If a squat lift is attempted on a large object, the knees 
 will not fit around it, and the object will have to be lifted 
 in front of the knees. This places the load further from the 
 L^-Sj joint and increases the compressive forces on the disk. 
 Figure 7-17 shows a comparison of the two techniques while 
 lifting a wide box (29). The stoop-back lift results in about 
 two-thirds as much compression force as the squat lift. Ac- 
 tually, the difference would be greater if the person moved 
 in over the load even more than pictured in figure 7-17. 
 
 Thus, the best lifting technique, from a biomechanical 
 point of view, depends on the strength and mobility of the 
 lifter and the dimensional size of the object to be lifted. The 
 main idea is to keep the load close to the L 5 -S, joint. 
 
 Another technique of lifting, called asymmetric lifting, 
 is one to avoid. In this technique, the person brings the load 
 up along the side of the body with one hand. This not only 
 causes lateral (side-to-side) bending of the lumbar column, 
 but because of the natural arc of the lower back, also pro- 
 duces a rotation of each vertebra on its adjacent vertebra. 
 This is especially hard on the disks between the vertebras 
 and concentrates stress on the muscles used to stabilize the 
 spinal column. 
 
 disk compression = 
 183.3 kg 
 
 L 5~ s i 
 disk compression 1 
 
 278.5 kg 
 
 Body weight 
 above L 5 -S, 
 center of gravity 
 
 Stoop- back lift 
 
 Squat lift 
 
 Figure 7-17.— Comparison of lower-back compression forces 
 associated with stoop-back and squat methods of lifting a wide 
 
 Object (29). (Copyright 1974 by the American Institute of Industrial Engineers, and 
 reprinted by permission) 
 
 NIOSH Recommended Lifting Load Limits 
 
 NIOSH formulated a method for determining maximum 
 load limit recommendations for lifting tasks (27). A lifting 
 task is defined as "the act of manually grasping and rais- 
 ing an object of definable size without mechanical aids." 
 A lifting task, under this definition, takes normally less 
 than 2 s to complete. This is in contrast to a holding or 
 carrying task that requires sustained exertion. 
 
 The recommendations are intended to apply only for- 
 
 1. Smooth lifting; 
 
 2. Two-handed, symmetric lifting directly in front of the 
 body with no twisting during the lift; 
 
 3. Moderate width objects, e.g., 30 in or less; 
 
 4. Unrestricted lifting posture; 
 
 5. Good couplings (handles, shoes, floor surface); and 
 
 6. Favorable environments. 
 
 In addition, the recommendations do not include safety 
 factors to assure that unpredicted conditions are 
 accommodated. 
 
 Given the nature of the mining environment, many of 
 the characteristics of the lifting tasks listed are often not 
 present, especially in the underground environment. Pos- 
 ture is often restricted, floors are often slippery, environ- 
 ments are often hostile, and load widths are often larger 
 than 30 in. It is important, therefore, to consider the NIOSH 
 recommendations as best case limits. Any prudent mine 
 superintendent or supervisor should reduce the recom- 
 mended limits to compensate for unfavorable lifting 
 situations. 
 
 The NIOSH recommendations take into account five 
 parameters of the lifting task to determine the load limits. 
 Two limits are defined: the maximum permissible limit and 
 the action limit, which is one-third the maximum permis- 
 sible limit. Situations that are above the maximum per- 
 missible limit are considered unacceptable and require 
 redesign of the task. Situations below the action limit are 
 considered acceptable for most of the workforce. Situations 
 that fall above the action limit, but below the maximum 
 permissible limit are considered unacceptable, unless the 
 task is redesigned or a selection and training program is 
 used to upgrade the capabilities of the workforce. 
 
 The NIOSH (27) formula for determining the action 
 limits for a given lifting situation and the determination 
 follow. The maximum permissible limit is taken as three 
 times the action limit. Table 7-8 shows the maximum lift 
 frequency based on the average vertical location at the 
 origin of the lift and the period of time for which the lift 
 is performed. Horizontal location (H) = 6/H; vertical loca- 
 tion (V) = 1 - (0.01 x |V-30|); vertical distance traveled 
 (D) = 0.7 + (3/D); frequency of lift = 1 - (F/F^); and 
 constant = 90. 
 
 AL = 90 x H x V x D x F. 
 
 where AL = action limit, lb, 
 
 90 = constant, 
 
 H = horizontal location forward of midpoint be- 
 tween ankles at origin of lift, 6 to 32 in. 
 
 V = vertical location at origin of lift, to 70 in, 
 
 D = vertical travel distance between origin and 
 destination of lift, 10-in minimum. 
 
 F = average frequency of lift, lifts min. consid- 
 ering maximum lift frequency, F max (from 
 table 7-8), 
 and F max = maximum lift frequency that can be sus- 
 tained (.from table 7-8). lifts min. 
 
95 
 
 Table 7-8.— Maximum lift frequency based on average vertical 
 location and period of performance, lifts per minute 
 
 Av vertical location 
 
 in 
 
 >30 
 
 <30 
 
 
 
 1 h or less 
 
 18 
 15 
 
 15 
 
 More or less continuous 
 during shift 
 
 12 
 
 
 
 The maximum permissible lift is three times the action 
 limit. An example of determining the action limit and max- 
 imum permissible lift follows. 
 
 Situation.— A worker lifts 36- by 18- by 8-in rock dust bags 
 (50 lb each) from a scoop shovel on the ground and stacks 
 them three high on a bin pallet. The first tier is 6 in off 
 the ground, the second is 14 in off the ground, and the third 
 tier is 22 in off the ground. The task is performed for less 
 than 1 h at a rate of five bags lifted per minute. 
 
 Analysis.— Although the vertical location, V, at the origin 
 of the lift is the same throughout the task, the vertical 
 travel distance, D, varies from 6 to 22 in, depending on the 
 tier. One approach would be to perform the analysis on each 
 tier separately as if it were a separate task. Another ap- 
 proach, used here, is to determine an average travel 
 distance (i.e., 6 + 14 + 22 = 42, 42/3 = 14) and apply the 
 action limit formula to the average task. The horizontal 
 location, H, is estimated to be 6 in plus half the width of 
 the object (i.e., 6 + 18/2 = 15). 
 
 Calculations.— Constant is 90; horizontal location factor, 
 H, is 6/15 or 0.40; vertical location factor, V, is 1 - (0.01 
 x 30) or 0.70; vertical travel distance factor, D, is 0.7 + 
 (3/14) or 0.91; maximum frequency, F max , from table 7-8, is 
 15; and frequency of lift factor, F, is 1 - (5/15) or 0.67. Us- 
 ing the action limit formula, AL is determined as follows: 
 AL = 90 x 0.40 x 0.70 x 0.91 x 0.67, which yields 15.4 
 lb. The maximum permissible lift (3 x AL) is 46 lb. 
 
 Conclusion:— Since the rock dust bags weigh 50 lb, the 
 AL is 15.4 lb, and the maximum permissible lift is 46 lb, 
 this task would be unacceptable under the best of circum- 
 stances and the task should be redesigned. 
 
 REDUCING THE RISK 
 
 The risks inherent in a manual materials handling task 
 can be reduced by redesigning the task, redesigning the 
 workspace, selecting physically capable people to do the 
 task, training workers involved in normal materials han- 
 dling tasks, or a combination of these methods. 
 
 The following are methods for reducing the physical 
 stresses involved in manual materials handling tasks, the 
 fundamental concept being that active awareness of the 
 problem and a conscious effort to reduce the physical 
 stresses involved in the task can accomplish significant 
 results without incurring significant costs. 
 
 Redesign the task: 
 
 1. Use lifting aids (e.g., hoists, cranes, rollers, jacks, 
 conveyors). 
 
 2. Reduce weight of object. 
 
 3. Reduce frequency of lifting (lifts per minute). 
 
 4. Reduce duration of task (hours per shift). 
 
 5. Reduce the size of the object being handled. 
 
 6. Supply properly designed handles on the objects being 
 handled. 
 
 7. Maintain a predictable center of gravity in the load 
 being lifted. 
 
 Redesign the workspace: 
 
 1. Remove obstructions that prevent worker from getting 
 close to the object being lifted. 
 
 2. Provide ample space to maneuver and assume most 
 advantageous lift posture. 
 
 3. Begin lifts at about elbow height. 
 
 4. Reduce vertical travel requirements for lift. 
 
 5. Provide slip-resistant soles and floors. 
 
 6. Provide good lighting. 
 
 7. Maintain comfortable temperature, humidity, and 
 airflow. 
 
 Select workers: 
 
 1. Strength testing. 
 
 2. Aerobic capacity testing. 
 
 3. Clinical examination. 
 Train workers: 
 
 1. Hazard awareness. 
 
 2. Biomechanics of manual materials handling. 
 
 3. Reducing hazards. 
 
 4. Physical fitness. 
 
 Redesign the Task 
 
 The use of lifting aids is an obvious way to reduce the 
 physical strain on the job. Often, a little forethought can 
 make the use of such devices easier and safer to use. For 
 example, if materials are transferred at the cage or skip, 
 the area should be designed to accommodate lift trucks and 
 cranes. If components must be removed for maintenance in 
 a processing plant, fixtures should be installed so that tem- 
 porary winches can be attached. Floors should be smooth 
 so that rollers and dollies can be easily used. 
 
 Reducing the weight of the load is an obvious solution 
 to the problem, yet is often overlooked. The 50-lb rock dust 
 bags might be purchased in 25-lb bags. In addition, the 
 smaller bags would be more compact and hence permit the 
 worker to get closer to the load to lift it. To illustrate this 
 effect, if the width of the rock dust bags described in the 
 action limit determination were reduced from 18 to 12 in, 
 the action limit would increase from 15.4 to 19.2 lb. In ad- 
 dition to the overall weight, the center of gravity of the load 
 should be predictable and nonshifting. A box, half filled with 
 supplies that shift when lifted, places asymmetric loads on 
 the back and increases the probability of falls. The use of 
 baffles, dividers, or packing to stabilize the center of gravi- 
 ty is recommended. 
 
 The proper placement and design of handles can reduce 
 biomechanical strain and reduce the chances of dropping 
 the load. In general, handles should be placed above the 
 center of gravity, unless the height of the load would inter- 
 fere with the legs during walking. Many handles in use 
 today are unsatisfactory because of insufficient hand 
 clearance, sharp edges that can cut into a worker's hand, 
 and handle diameters that are too small. 
 
 Handle width should be at least 4.5 in with a 2-in 
 clearance all around the handle. If gloves are worn during 
 lifting, clearance should be at least 3 in, and the handle 
 should be 5.5 in. Handle diameter should be between 1 and 
 1.5 in. 
 
 Redesign the Workspace 
 
 Often, a simple rearrangement of the workspace will 
 permit a worker to get closer to an object when lifting and 
 releasing it. The use of platforms on which to stack mate 
 rials can bring the lifting task to elbow height and require 
 
96 
 
 little or no vertical movements. In the action limit deter- 
 mination, if the scoop shovel were lifted to the same height 
 as the stacked rock dust bags, and if the bags were stacked 
 on a pallet 22 in high (instead of 6 in), then the action limit 
 would be increased from 15.4 to 24.1 lb, and the maximum 
 permissible limit would be 72 lb. Thus, the task would be 
 acceptable. 
 
 Good lighting and slip-resistant soles and floors, of 
 course, reduce trip and slip-and-fall accidents. Comfortable 
 temperature, humidity, and airflow are especially impor- 
 tant for continuous physical activity since heat adds a con- 
 siderable burden to the circulatory system, and when added 
 to the strain from the physical task, can be dangerous. 
 
 Selection of Workers 
 
 Any methods for selecting workers for physically 
 demanding tasks should meet the following criteria: 
 
 1. Be safe (if a physical test of abilities is used). 
 
 2. Produce reliable results. 
 
 3. Be related to the specific demands of the task. 
 
 4. Be practical to administer. 
 
 5. Predict risk of future injury or illness. 
 
 Most of these are obvious; however, the methods used 
 to select workers must be related to the specific demands 
 of the job in order to eliminate accusations of bias in selec- 
 tion methods. Further, the job must be designed to reduce 
 the physical demands to the lowest practical level, and the 
 selection methods should be built around the redesigned job. 
 Failure to redesign a job, consequently excluding females, 
 might well be considered an act of discrimination. 
 
 Methods for selecting workers for physically demanding 
 tasks have centered around clinical examinations, strength 
 testing, and aerobic capacity testing. A clinical examina- 
 tion is a must for selecting workers for physically demand- 
 ing tasks. The purpose is to uncover any abnormalities that 
 might restrict the physical activity of a worker, and to iden- 
 tify those with prior episodes of back pain. It was reported 
 by Dillane (3) that the probability of an episode of back pain 
 increases by a factor of 3 to 4 after the first reported attack. 
 
 Some clinicians promote the use of lower-back X-rays 
 as a means of evaluating the risk potential to an individual 
 engaged in a lifting task. Current thinking, however, is that 
 such X-rays are of little practical value in predicting future 
 disability. Several studies, such as by NIOSH (27), report 
 no significant differences in the incidence of radiologically 
 identified abnormalities between workers with known his- 
 tories of back pain and those without. Such X-rays, however, 
 can be useful in conjunction with prior clinical examina- 
 tions to corroborate a suspected diagnosis. 
 
 Considerable attention has been given to the use of 
 strength testing as a means of selecting workers for 
 demanding lifting tasks. For continuous, high-energy tasks, 
 the measurement of aerobic capacity appears to be a valu- 
 able selection device. Specific methods for measuring 
 strength for preemployment testing are discussed by Chaf- 
 fin (8) and Kroemer (23). 
 
 Ayoub (6) reported the use of a job severity index ( JSI) 
 as a measure to match an individual with the demands of 
 a lifting task. The JSI is the ratio of a measure of job de- 
 mand to a measure of the capacity of the person perform- 
 ing the job under the job conditions. The measure of lifting 
 capacity is determined from formulas that predict the max- 
 imum weight an individual feels he or she can lift re- 
 peatedly without undue stress or overtiring. The formulas 
 take into consideration the following factors: sex, weight, 
 
 age, arm strength, back strengh, dynamic endurance, 
 shoulder height, and abdominal depth. 
 
 In a study of 101 jobs involving 385 males and 68 
 females, Ayoub (6) found that as the JSI increased, the in- 
 cidence and severity (days lost per incidence) of lower-back 
 injuries increased (fig. 7-18). JSI values below 1.0 indicate 
 that the worker's capability exceeds the demands of the job. 
 JSI values greater than 1.0 indicate that the job demands 
 exceed the capabilities of the worker. As can be seen in 
 figure 7-18, the number of incidents dramatically increases 
 with JSI values greater than 1.5, and the severity of in- 
 cidence dramatically increases with values greater than 
 2.25. 
 
 Training Workers 
 
 Although training for manual materials handling has 
 been practiced in some European countries since World War 
 II, there appears to have been few, if any, controlled studies 
 showing a drop in injury rates following training. Probably 
 what has kept up the interest is that employers feel a legal 
 or moral obligation to provide such training. The follow- 
 ing is the NIOSH recommended (27) content for a training 
 program on manual materials handling. 
 
 1. Risks to health of unskilled manual materials handling 
 (including accident experience of the organization). 
 
 2. Basic physics of manual materials handling. 
 
 3. Effects of manual materials handling on the body (in- 
 cluding anatomy of spine and muscles and joints). 
 
 4. Individual awareness of the body's strengths and 
 weaknesses (including how much can be handled safely and 
 comfortably). 
 
 5. How to avoid accidents (including task design varia- 
 bles, workspace layout, sizing up the load, planning the 
 activity). 
 
 OSJSK 0.75 0.75SJSKI.50 I.50SJSK2.2S E-25 < JSI 
 
 JSI RANGE 
 
 Figure 7-18. — Incidence and severity of back injury as a func- 
 tion of the job severity index (JSI). JSI values greater than 1 .0 
 indicate job demands exceed worker capabilities: values less 
 than 1.0 reflect worker capacities exceed job demands (5). 
 
 (Copyright 1983 by the Human Factors Society Inc.. and reproduced by permission) 
 
97 
 
 6. Handling skill (including actually lifting, carrying, 
 pushing, pulling materials handled on the job; the best way 
 to perform each task; and the principles involved). 
 
 7. Handling aids (including when to use them, how to use 
 them, how to improvise). 
 
 Examples of training materials for the mining industry 
 based on the components listed above were developed by 
 Connelly (10). 
 
 NIOSH (27) also pointed out that an adequate training 
 program must do more than just demonstrate the principles 
 using slides or films; participants must be actively involved 
 in the program. Teaching must extend beyond the classroom 
 back to the worksites to be effective. 
 
 Physical fitness training is another aspect of manual 
 materials handling training, although it is not listed in the 
 recommended course content by NIOSH. A 12-week pro- 
 gram in which sessions were held twice per week was 
 reported on by Chenoweth (9). The results showed small, 
 but reliable improvements in heart rate, blood pressure, 
 body weight, percentage of body fat, and flexibility. 
 
 DISCUSSION 
 
 Although manual materials handling injuries continue 
 to be the major category of lost-time injuries in mining, an 
 active awareness of the problem and an understanding of 
 the principles and dynamics involved can go a long way 
 toward reducing the hazards. Mining will continue to be 
 a physically demanding occupation, but by proper design 
 of the tasks and worksites and proper employee training 
 and selection, the incidence and severity of injuries can be 
 reduced. Proper task design will also contribute to a higher 
 level of productivity by reducing the level of fatigue 
 experienced by a worker. Much has been done to improve 
 the work environment, and much still remains to be done. 
 
 REFERENCES 
 
 1. American Heart Association (New York). Exercise Testing and 
 Training of Apparently Healthy Individuals: A Handbook for Physi- 
 cians. 1972, 93 pp. 
 
 2. American Industrial Hygiene Association Journal. Ergonomics 
 Guides: Ergonomics Guide to Assessment of Metabolic and Car- 
 diac Costs of Physical Work. Aug. 1971, pp. 560-574. 
 
 3. Astand, P., and K. Rodahl. Textbook of Work Physiology. 
 McGraw-Hill, 2d ed., 1977, 669 pp. 
 
 4. Ayoub, M.M., N.J. Bethea, M. Bobo, C.L. Burford, D.K. Cad- 
 del, K. Intaranont, S. Morrissey, and J.L. Selan. Mining in Low 
 Coal. Volume I: Biomechanics and Work Physiology (contract 
 H0387022, Texas Tech Univ.). BuMines OFR 162(l)-83, 1981, 175 
 pp.; NTIS PB 83-258160. 
 
 5. Biomechanics and Work Physiology in Low Coal. 
 
 Paper in Ergonomics-Human Factors in Mining. Proceedings of 
 Bureau of Mines Technology Transfer Seminars, Pittsburgh, Pa., 
 December 3, 1981; St. Louis, Mo., December 10, 1981; and Denver, 
 Colo., December 15, 1981; comp. by Staff, Pittsburgh Research 
 Center. BuMines IC 8866, 1981, pp. 3-16. 
 
 6. Ayoub, M., J. Selan, and D. Liles. An Ergonomics Approach 
 for the Design of Manual Materials Handling Tasks. Human Fac- 
 tors, v. 25, No. 5, 1983, pp. 507-515. 
 
 7. Brown, J. Lifting as an Industrial Hazard. Ontario Dep. of 
 Labor, Toronto, Canada, 1971, 16 pp. 
 
 8. Chaffin, D. Preemployment Strength Testing. J. Occup. Med., 
 v. 20, No. 6, 1978, pp. 403-408. 
 
 9. Chenoweth, D. Fitness Program Evaluation: Results With 
 Muscle. Occup. Health and Safety, June 1983, p. 14. 
 
 10. Connelly, D. A Manual Materials Handling (MMH) Train- 
 ing Program for the Mining Industry. Paper in Back Injuries. 
 Proceedings: Bureau of Mines Technology Transfer Symposia, Pitts- 
 burgh, PA, August 9, 1983; and Reno, NV, August 15, 1983; comp. 
 by J.M. Peay. BuMines IC 8948, 1983, pp. 74-80. 
 
 11. Conway, E., and W. Elliott. Back Injuries and Maintenance 
 Material Handling in Low-Seam Coal Mines. Paper in Back In- 
 juries. Proceedings: Bureau of Mines Technology Transfer Sym- 
 posia, Pittsburgh, PA, August 9, 1983, and Reno, NV, August 15, 
 1983; comp. by J.M. Peay. BuMines IC 8948, 1983, pp. 74-80. 
 
 12. Davies, B. Moving Loads Manually. Appl. Ergonomics, v. 3, 
 No. 4, 1972, pp. 190-194. 
 
 13. Dillane, J, J. Fry, and G. Kalton. Acute Back Syndrome. Brit. 
 Medical J., v. 2, 1966, pp. 82-84. 
 
 14. Edholm, O. The Biology of Work. McGraw-Hill, 1967, 267 pp. 
 
 15. Ellis, C. Accidents Related to Transportation and Materials 
 Handling. Paper in Proceedings of 14th Annual Institute of Coal 
 Mining Health and Safety Research. Polytechnic and State Univ., 
 Blacksburg, Va., Aug. 23-25, 1983, pp. 106-121. 
 
 16. Foote, A.L., and J.S. Schaefer. Mine Materials Handling 
 Vehicle (MMHV) (contract H0242015, MBAssoc). BuMines OFR 
 59-80, 1978, 308 pp.; NTIS PB 80-178890. 
 
 17. Grandjean, E. Fitting the Task to the Man: An Ergonomic 
 Approach. Taylor and Francis, 1981, 379 pp. 
 
 18. Hamilton, B., and R. Chase. A Work Physiology Study of the 
 Relative Effects of Pace and Weight in Carton Handling Tasks. 
 AIIE Trans., v. 1, 1969, pp. 106-111. 
 
 19. Jacobs, S., and C. Francone. Structure and Function in Man. 
 Saunders, 5th ed., 1965, 538 pp. 
 
 20. Kamon, E. Laddermill and Ergonometry: A Comparative 
 Summary. Human Factors, v. 15, No. 1, 1973, pp. 75-90. 
 
 21. Kamon, E., and M. Ayoub. Ergonomic Guides: Ergonomic 
 Guide to Assessment of Physical Work Capacity. Am. Ind. Hygiene 
 Assoc, Akron, Oh., 1976, 9 pp. 
 
 22. Khalil, T. An Electromyographic Methodology for the Evalua- 
 tion of Industrial Design. Human Factors, v. 15, No. 3, 1973, pp. 
 257-264. 
 
 23. Kroemer, K. Field Testing of Workers Involved in Material 
 Handling. Paper in Back Injuries. Proceedings: Bureau of Mines 
 Technology Transfer Symposia, Pittsburgh, Pa., August 9, 1983, 
 and Reno, Nev., August 15, 1983; comp. by J.M. Peay. BuMines 
 IC 8948, 1983, pp. 47-53. 
 
 24. Morrissey, S., N. Bethea, and M. Ayoub. Task Demands for 
 Shovelling in Non-Erect Postures. Ergonomics, v. 26, No. 10, 1983, 
 pp. 947-951. 
 
 25. Muller, E. The Physiological Basis of Rest Pauses in Heavy 
 Work. Q. J. Experimental Physiology, v. 38, 1953, p. 205. 
 
 26. Murrell, K. Human Performance in Industry. Reinhold, 1965, 
 306 pp. 
 
 27. National Institute for Occupational Safety and Health. Work 
 Practices for Manual Lifting. NIOSH Publ. 81-122, 1981, 183 pp.; 
 NTIS PB 82-178948. 
 
 28. Pafnote, M., I. Vaida, and O. Luchian. Physical Fitness in 
 Different Groups of Industrial Workers. Physiologie, v. 16, No. 2, 
 1979, pp. 129-131. 
 
 29. Park, K., and D. Chaffin. A Biomechanical Evaluation of Two 
 Methods of Manual Load Lifting. AIIE Trans., v. 6, 1974, pp. 
 105-113. 
 
 30. Peay, J. Introduction. Section in Back Injuries. Proceedings: 
 Bureau of Mines Technology Transfer Symposia, Pittsburgh, Pa., 
 August 9, 1983, and Reno, Nev., August 15, 1983; comp. by J.M. 
 Peay. BuMines IC 8948, 1983, p. 2. 
 
 31. Peters, R. Activities and Objects Most Commonly Associated 
 With Underground Coal Miners' Back Injuries. Paper in Back In- 
 juries. Proceedings: Bureau of Mines Technology Transfer Sym- 
 posia, Pittsburgh, Pa., August 9, 1983; and Reno, Nev., August 15, 
 1983; comp. by J.M. Peay. BuMines IC 8948, 1983, pp. 23-31. 
 
 32. Roebuck, J., K. Kroemer, and W. Thomson. Engineering An- 
 thropometry Techniques. Wiley, 1975, 459 pp. 
 
 33. Sims, M., L. Morris, R. Graves, and G. Simpson. Manual 
 Handling of Mining Materials. Paper in Proceedings of the 1984 
 Int. Conf. on Occupational Ergonomics, Human Factors Assoc, of 
 Canada. Toronto, Canada, May 7-9, 1984, pp. 103-118. 
 
98 
 
 34. Sonoda, T. Studies on the Compression, Tension, and Tor- 
 sion Strength of the Human Vertebral Column. J. Kyoto Prefect 
 Medical Univ., v. 71, 1962, pp. 659-702. 
 
 35. Unger, R., and D. Connelly. Materials Handling Methods and 
 Problems in Underground Coal Mines. Paper in Back Injuries. Pro- 
 ceedings: Bureau of Mines Technology Transfer Symposia, Pitts- 
 burgh, Pa., August 9, 1983; and Reno, Nev., August 15, 1983; comp. 
 by J.M. Peay. BuMines IC 8948, 1983, pp. 3-22. 
 
 36. U.S. Mine Safety and Health Administration Quarterly. Mine 
 Injuries and Worktime, January-December, 1983. 1984, 34 pp. 
 
 37. Van Rensburg, J. Energy Requirements of Different 
 Underground Mining Tasks With Specific Reference to the In- 
 
 fluence of Mechanization. Chamber of Mines, Johannesburg, South 
 Africa, Rep. No. 11/81, Mar. 1981, 61 pp. 
 
 38. Weiser, P. Interrelationships of the Motor and Metabolic Sup- 
 port Systems During Work and Fatigue. Ch. in Psychological 
 Aspects and Physiological Correlates of Work and Fatigue, ed. by 
 E. Swanson and P. Weiser. Charles C. Thomas, 1976, pp. 212-255. 
 
 39. Wyndham, C, and G. Sluis-Cremer. The Capacity for 
 Physical Work of White Miners in South Africa. South African 
 Medical J., v. 43, No. 1, 1969, pp. 3-8. 
 
99 
 
 CHAPTER 8.— ENVIRONMENTAL FACTORS 
 
 In addition to the obvious environmental factor of temperature, illumination and noise factors, as 
 well as others, affect the performance, health, comfort, and safety of miners. 
 
 Humans live and work in a wide range of environments, 
 each with its own set of particular characteristics that can 
 affect performance, health, comfort, and safety. Because the 
 list of such environmental factors is extensive, including 
 odors, dust, chemical fumes, radiation, and even insects, this 
 chapter will only concentrate on four factors that are tradi- 
 tionally covered in the human factors literature: illumina- 
 tion, noise, whole-body vibration, and climate (heat and cold 
 stress). For each of these factors, a brief discussion is pre- 
 sented covering the measurement of the factor, conditions, 
 found in mining, effects of the factor on humans, standards 
 that exist, and methods for reducing the negative effects 
 of the factor on workers. 
 
 ILLUMINATION 
 
 The topic of illumination is especially important in the 
 mining environment. Underground mines are completely 
 dependent on artificial sources of illumination, as are night 
 operations in surface mines. Because humans receive the 
 bulk of their information visually, the quantity and qual- 
 ity of illumination is critical to the safe and efficient per- 
 formance of our jobs. 
 
 Measurement of Light 
 
 Two major systems of units are currently used for the 
 quantification of light: English system and International 
 
100 
 
 System of Units (SI). The primary difference between the 
 English and SI systems is that the English system uses U.S. 
 standard measures for linear dimensions in the unit defini- 
 tions, while the SI system uses metric measures. Current 
 U.S. coal mine lighting regulations customarily use English 
 units; therefore, these will be used primarily in this section. 
 All standard systems of light units employ the follow- 
 ing basic concepts: 
 
 1. Luminous Flux (<(>, unit— lumens, lm).— The time rate 
 flow of light energy. 
 
 2. Illuminance (E, unit— footcandle, fc, or lux, lx).— A 
 measure of the density of luminous flux striking a surface. 
 
 3. Luminous Intensity (I, unit— candle, c).— A concept used 
 to describe how a light source distributes the total luminous 
 flux, or lumens, it emits into various portions of the space 
 surrounding the source. 
 
 4. Luminance (L, unit— candle per square inch, c/in 2 , or 
 candle per square meter, dm 2 ).— In physical terms, lumin- 
 ance is a concept used to quantify the density of luminous 
 flux emitted by an area of a light source in a particular 
 direction toward a light receiver, such as an eye. 
 
 5. Reflectance (q).— The ratio of reflected to incident light 
 energy, which may be defined as lumens emitted per unit 
 area divided by lumens incident per unit area. 
 
 6. Contrast.— The concept that the greater the luminous 
 and color contrasts of an object with its background, the 
 greater the object visibility. 
 
 Luminous Flux 
 
 Flux is a power quantity in the same manner as horse- 
 power or Btu per hour. The unit of luminous flux, the lumen, 
 is most frequently used to describe the total lighting power 
 of light sources. 
 
 Illuminance 
 
 Imagine a light source placed inside, at the center of 
 a sphere. The amount of light striking any point on the in- 
 side of the sphere is called illuminance. It is measured in 
 terms of luminous flux (per steradian) 1 per unit surface. One 
 lumen per square foot is equal to 1 fc, and 1 fc is equal to 
 10.76 lx. An accepted practice for some purposes is to con- 
 sider 1 fc equal to 10 lx, ignoring the fraction (23)} 
 
 The amount of illuminance striking a surface from a 
 light source follows the inverse square law, E = I/D 2 , where 
 D is the distance from the source. At 2 ft, a 1-c source would 
 produce 1/4 fc; and at 3 ft, it would produce 1/9 fc. 
 
 Luminous Intensity and Luminance 
 
 Some light striking a surface is reflected. The amount 
 of light (luminous intensity) per unit area leaving a sur- 
 face is called luminance. Luminance is defined in terms of 
 lumens (luminous flux per steradian) per square foot, or 
 footlambert. 
 
 Reflectance 
 
 The ratio of reflected luminous flux to the total incident 
 luminous flux is reflectance. Some surfaces reflect, while 
 others absorb almost all the luminous flux that strikes 
 
 them. Generally, dark-colored surfaces absorb more lum- 
 inous flux than do light-colored surfaces. 
 
 In actuality, no surface is a uniform diffusing surface. 
 The reflectance of 34 wet and dry rock and mineral samples 
 from underground metal and nonmetal mines was meas- 
 ured by Crooks (11). Table 8-1 presents some representative 
 data from that survey. Notice that wet samples show lower 
 average reflectance than dry samples. Over three-fourths 
 of all worksites measured by Crooks (11) had reflectances 
 of less than 30% . To illustrate the consequences of different 
 reflectivity on the amount of illumination needed, Crooks 
 and Peay (12) indicated that the lighting adequate for 
 development activities in dry dolomite would have to be in- 
 creased approximately 400% to achieve the same luminance 
 levels in wet sphalerite. 
 
 Table 8-1.— Examples of average reflectances 
 
 of rocks and minerals from underground metal 
 
 and nonmetal mines (11). percent 
 
 Sample description 
 
 Light brownish gray trona 
 
 Brownish gray trona 
 
 Feldspar with olivine, chalky surface . . . 
 Feldspar with pyrite, medium gray color 
 
 Dolomite 
 
 Almost pure sphalerite 
 
 Whitewashed shale (haulageway wall) . . 
 
 Quartzite 
 
 Chalcopyrite 
 
 Dry 
 
 Wet 
 
 59 
 
 28 
 
 38 
 
 19 
 
 61 
 
 38 
 
 39 
 
 24 
 
 59 
 
 44 
 
 16 
 
 9 
 
 82 
 
 61 
 
 17 
 
 11 
 
 14 
 
 8 
 
 1 The steradian is a measure of the unit solid angle at the center of a 
 sphere. There are 4 n or 12.57 sr in a sphere. 
 
 2 Italic numbers in parentheses refer to items in the list of reterences at 
 the end of this chapter. 
 
 Contrast 
 
 Althougn contrast is not a light measure per se. it is 
 a critical concept for determining visibility. If an object has 
 no contrast with its background, it will not be seen, regard- 
 less of how much illuminance is supplied. Luminous con- 
 trast is measured by the following formula: 
 
 Contrast - Q D J ect luminance - Background luminance . 
 Background luminance 
 
 With more light, the eye can see detail better and. hence, 
 less contrast is needed. For example, an object with lumin- 
 ance of 43.8 fL on a background having a luminance of 14.6 
 fL will be easier to see than an object with luminance of 
 4.5 fL on a background having a luminance of 1.5 fL. even 
 though both have contrasts equal to 2.0. Experiments have 
 shown that a 1% loss of contrast requires a 10% to 15% in- 
 creasejn illuminance to maintain the same visual perfor- 
 mance (15). 
 
 In addition to luminous contrast, color contrast also 
 enhances visibility, even if the luminous contrast is zero. 
 For example, a yellow target shows up against a blue back- 
 ground, even if the luminance of the two colors is the same. 
 
 Illumination and Performance 
 
 At the turn oi tne ceniui j . coal miners commonly suf- 
 fered from an eye disease called nystagmus. The symptoms 
 were uncontrollable oscillations of the eyeballs, headaches, 
 and dizziness. One of the main contributing factors was the 
 effect of working under very low levels of light for long 
 
101 
 
 periods of time. With the advent of electric caplamps, the 
 disease virtually disappeared. 
 
 The literature on mine lighting with respect to acci- 
 dents, production, and health was reviewed by Trotter (44). 
 With respect to accidents, several European studies were 
 cited that showed accident rates decreasing as much as 60% 
 when the overall level of illumination was increased. 
 Studies in industries other than mining supported the 
 general conclusions that increased levels of illumination 
 have a positive effect on accidents. 
 
 With respect to the effects of lighting on productivity, 
 numerous studies have been done using simple tasks, such 
 as threading needles, to show that increasing illumination 
 up to about 100 fc results in increased productivity and 
 decreased errors. Trotter (44) cited two studies relating 
 lighting to productivity in the mining environment. Adding 
 general area illumination resulted in an increase of 17% 
 to 26% in productivity, compared to similar sections of the 
 mine where only caplamps were used. 
 
 In the underground environment, caplamp illumination 
 results in notoriously poor peripheral vision, because the 
 beam is usually focused to a narrow spot. The addition of 
 general lighting in such situations greatly enhances pe- 
 ripheral vision and allows workers to see objects more 
 quickly and at greater distances. For example, the effect 
 additional background luminance had on the detection time 
 of various targets, such as simulated rock cracks, tripping 
 hazards, and rock movements was measured by Merritt (28). 
 In all cases, the provision of additional background lumin- 
 ance decreased detection time and errors. As an example, 
 figure 8-1 shows the average response time to detect holes 
 in the floor at a distance of 10 ft. With caplamp illumina- 
 tion only (0.055 fL), response time was 15 s. The provision 
 of additional background luminance with general area light- 
 ing decreased the response time to 1 s. 
 
 Thus, it appears that improved lighting can improve 
 safety, productivity, and the time needed to respond to 
 hazards. Recognition of these facts has prompted govern- 
 ment agencies to specify illumination requirements, which 
 are discussed in the following section. 
 
 Illumination Requirements 
 
 The setting of illumination requirements involves many 
 tradeoffs, including weighing the cost of increased illumina- 
 tion against the improvement in visual performance, and 
 balancing increased levels of illumination against the in- 
 crease in glare. Trotter (44) reviewed standards set by var- 
 ious countries for underground coal mining. The minimum 
 light levels specified vary considerably from country to 
 country, as shown in table 8-2. The data in table 8-2 are 
 given in terms of illuminance (i.e., the amount of light strik- 
 ing a surface). The United States and the Commission Inter- 
 Table 8-2.— Samples of illumination standards set 
 by various countries for underground coal mining (44), lux 
 
 
 Shaft 
 
 Loading 
 
 Around machines 
 
 Haulageways 
 
 Belgium 
 
 20- 50 
 
 20 
 
 25 
 
 10 
 
 British Columbia, 
 
 
 
 
 
 Canada 
 
 53 
 
 21 
 
 53 
 
 21 
 
 Czechoslovakia 
 
 15- 40 
 
 20 
 
 20 
 
 5 -10 
 
 Germany, Federal 
 
 
 
 
 
 Rep. of 
 
 30- 40 
 
 40 
 
 80 
 
 15 
 
 Hungary 
 
 40-100 
 
 40-60 
 
 20-50 
 
 2 -10 
 
 Poland 
 
 15- 50 
 
 15-30 
 
 NA 
 
 .5- 2 
 
 United Kingdom .... 
 
 70 
 
 30 
 
 NA 
 
 2.5 
 
 0.02 0.04 0.06 
 
 BACKGROUND LUMINANCE, fL 
 
 0.08 
 
 NA Not available. 
 
 Figure 8-1 .—Effect of adding additional background luminance 
 (area lighting) on speed of detecting holes in a floor at a distance 
 of 10 ft (28). 
 
 nationale de l'Eclairage (CIE), by contrast, specify minimum 
 levels in terms of luminance (i.e., reflected light). It is more 
 appropriate to state requirements in terms of luminance, 
 because it is reflected light that allows us to see objects; 
 and, depending on the reflectance of the surface, the same 
 amount of incident light can result in very different levels 
 of reflected light. Whitewashing an area, for example, can 
 greatly increase luminance without increasing the number 
 or intensity of light sources. 
 
 The United States requires 0.06 fL of luminance in work 
 areas and around equipment in underground coal mines. 
 Specific details of the requirements for underground coal 
 mines are contained in reference 45. The usual practice is 
 to plan illumination systems based on an assumed reflec- 
 tance of 0.04 in coal mines. A luminance requirement of 
 0.06 fL, with a reflectance of 0.04, yields an illuminance 
 requirement (light striking the surface) of 1.5 fc. The Mine 
 Safety and Health Administration (MSHA) requirements 
 recognize the problem of glare, especially in low-seam mines 
 (under 48 in), and have reduced the size of the area around 
 machines that must be illuminated to the minimum re- 
 quired luminance. 
 
 With respect to surface mining, MSHA proposed that 
 all exterior areas related to draglines, shovels, and wheel 
 excavators, where people regularly work and travel, be il- 
 luminated to 5.0 fc. This area extends out 20 ft in all direc- 
 tions from the machines. Areas beneath the boom, from 20 
 ft out from the main frame to the furthest point the equip- 
 ment can excavate or discharge material, must be illumin- 
 ated to 1 fc. 
 
102 
 
 Merritt (28) performed extensive research to determine 
 illumination requirements for underground metal and non- 
 metal mines. The recommendations are somewhat more 
 complex than the requirements for coal mines. For exam- 
 ple, he recommends 0.1284 fL at 8-ft viewing distance, 12 ° 
 off axis; and 0.05 fL at 6-ft viewing distance, 22.5° off axis. 
 It was believed that a more powerful caplamp could supply 
 the needed luminance. Recommendations for illumination 
 of mobile equipment operations include 0.10 fL on the floor, 
 20 ft in front of the machine. 
 
 In order to determine if an illumination system will 
 supply the proper amount and distribution of light, it is 
 necessary to simulate the situation and equipment, install 
 the lights, and take the required measurements. The 
 Bureau, however, has developed a computer model that uses 
 representations of mining machinery and data on lumi- 
 nance output characteristics of various lights to compute 
 the level and distribution of illumination in the work area 
 (19-20). The system is interactive so that different types of 
 lights and light positions can be tested quickly and easily. 
 
 Glare 
 
 Illumination engineers distinguish two types of glare: 
 disability glare and discomfort glare. Disability glare inter- 
 feres with visibility and reduces visual performance. Dis- 
 ability glare operates in two ways. In the first, a glare source 
 reduces the contrast of a visual scene by causing a scatter- 
 ing of light in the fluid of the eyeball. This scattering creates 
 a veiling brightness on the retina that in turn reduces con- 
 trast. The second mechanism by which a glare source re- 
 duces visual performance is due to transient adaptation. The 
 source causes a shift in the eye's adaptation or sensitivity 
 to light. The glare source causes the eye to become adapted 
 to a higher level of illumination and hence less sensitive, 
 which makes it harder to see low-contrast or dimly lit ob- 
 jects. The effect is similar to going into a dark movie theater 
 on a sunny day. 
 
 The disability glare factor (DGF) of various lighting 
 arrangements on underground coal mining equipment was 
 reported on by Whitehead (49). The DGF indicates the 
 percentage of visibility still left, given the effect of glare. 
 The higher the number, the less the disability glare effect. 
 For a continuous miner operator, DGF values in four work 
 positions varied from 1.8% to 100% using various light 
 sources. The average DGF across all positions and light 
 sources was 51%, a reduction of almost 50% in visibility 
 due to disability glare. An even poorer situation was 
 reported for a roof bolter operator, where the average DGF 
 was only 30%, i.e., a 70% reduction in visibility. 
 
 Discomfort glare increases eye fatigue and pain, and 
 causes distraction. The exact mechanism by which discom- 
 fort glare causes pain is not known, but probably has some- 
 thing to do with the muscles that constrict the pupil when 
 faced with a bright light. Actually, the absolute intensity 
 of the glare source is not important, but rather the dif- 
 ference in contrast between the source and the general adap- 
 tation level of the eye. A 200-W lightbulb would not cause 
 discomfort glare, outside, on a sunny day; but it would on 
 a dark moonless night. 
 
 Because discomfort glare is a subjective experience, 
 some people are more tolerant of discomfort glare, while 
 others are more sensitive. For example, Whitehead (49) 
 reported on sensitivity to discomfort glare among under- 
 ground coal miners. The results showed that the miners 
 were no more sensitive to discomfort glare than nonmin- 
 ing populations. 
 
 Trotter (44) listed the following ways to reduce glare in 
 the mining industry: 
 
 1. Avoid small sources of high luminance. The use of 
 frosted tungsten-filament bulbs rather than clear bulbs, for 
 example, increases the surface area of the source and thus 
 reduces glare. 
 
 2. Use large sources of low luminance. Fluorescent tubes 
 provide larger, low-luminance sources. The veiling bright- 
 ness effects of disability glare are the same whether the 
 glare source is small and of high luminance, or large and 
 of low luminance, provided that the illuminance at the eye 
 is the same. The large, low-luminance source, however, will 
 produce less discomfort. 
 
 3. Move luminance sources out of the field of view. A 
 source of light above the line of sight is less distracting than 
 one that lies to the side or below it. As a rule of thumb, the 
 angle between the horizontal line of sight and a line from 
 the eye to the light source should be greater than 30°. 
 
 4. Shield sources from direct view. As miners approach 
 a shielded light source, they cannot see the source directly. 
 When they are under the source, it no longer is in the field 
 of view. 
 
 5. Use prismatic lenses, filters, or cross polarizers. These 
 devices diffuse the light from the source, effectively increas- 
 ing its size and reducing its apparent brightness. 
 
 6. Keep differences in luminance small between visible 
 source and background. Use low-luminance sources in large 
 surrounds or direct some of the light to illuminate the area 
 beyond the source. 
 
 7. Keep background and surround luminances high. The 
 ratio of luminances of the task, the background, and the 
 environment should not exceed 10:3:1, with a 10:5:2 ratio 
 being very good. Generally, providing peripheral lighting 
 yields acceptable ratios. 
 
 8. Position work and lighting properly. A change in the 
 angle of a light source or the position of the task relative 
 to the position of the worker can reduce reflected glare. 
 
 9. Avoid specular surfaces. This relates to reflected glare 
 from shiny surfaces; use matte or rough surfaces instead. 
 
 10. Use light of the right quality. Color of illumination, 
 as for example the yellow of pressure sodium lamps, is 
 believed to penetrate dust and fog better than white, green, 
 or blue light. 
 
 NOISE 
 
 Since the advent of mechanized mining, noise has 
 become an integral part of the mining environment. As 
 equipment becomes more powerful, noise levels generally 
 increase. Noise as an environmental factor has important 
 implications for the worker population. The obvious implica- 
 tion is, of course, the potential for noise-induced hearing 
 loss. In addition, noise produces other health effects, in- 
 fluences work performance, and makes communications 
 more difficult. Noise is probably the most prevalent envi- 
 ronmental stressor in the mining industry, considering both 
 surface and underground operations. 
 
 Measurement of Noise 
 
 Noise, and sound in general, originates as vibrations. 
 The two primary characteristics of sound are frequency and 
 intensity. 
 
 _ 
 
103 
 
 Frequency 
 
 Sound waves are really alternating increases and de- 
 creases in air pressure caused by a vibrating source. Figure 
 8-2 shows the waveform of a simple sound source. The wave 
 is called a sinusoidal or sine wave. The height of the wave 
 above the midline, at any point in time, represents the 
 amount of above-normal air pressure at that point. Points 
 below the line represent the below-normal air pressure. One 
 complete cycle is shown in figure 8-2. The number of cycles 
 generated per second is the frequency of the sound and is 
 measured in hertz, which is equivalent to cycles per second. 
 Complex sounds can be decomposed into an additive set of 
 sine waves of various frequencies. 
 
 Intensity 
 
 The intensity of sound pressure level (SPL) of a sound 
 is defined using a logarithmic measure called the decibel. 
 It is really based on the ratio of two sounds, one of which 
 is an arbitrary standard set to represent dB. The formula 
 of SPL is as follows: 
 
 SPL (dB) = 20 log Pj/P,, 
 
 where P ; = the sound pressure (usually measured in 
 
 ^N/m 2 ) of the sound being measured 
 and P r = 0-dB reference level (usually 20 juN/m 2 ). 
 
 Notice that the 0-dB reference level cannot itself be zero 
 because the Pj-P r ratio would be infinity. The reference 
 level is set at an SPL roughly equivalent to the lowest in- 
 tensity, 1,000 Hz pure tone, that a healthy adult can just 
 barely hear under ideal conditions. Therefore, when the 
 sound pressure of the sound being measured equals the 
 reference level, the Pj-P r ratio equals 1.0, and the log of 
 1.0 equals zero, hence dB. 
 
 There are several implications of using the decibel scale: 
 (1) sounds can have intensities less than dB; (2) a dou- 
 bling of the power of a sound will increase the SPL by only 
 3 dB; and (3) signal-to-noise ratios are really just the dif- 
 ference between the SPL for noise and the SPL for signal. 
 
 Indexes of Noise Intensity 
 
 As discussed in chapter 3, the ear is not equally sen- 
 sitive to all frequencies of sound; it is more sensitive to fre- 
 quencies in the 2,000- to 6,000-Hz range, and less sensitive 
 to lower frequencies. To account for this differential fre- 
 quency sensitivity, sound pressure meters contain fre- 
 quency-response weighting networks that electronically 
 attenuate sounds of certain frequencies, and produce a 
 weighted total sound pressure level. The networks are 
 designated A, B, and C; and their relative responses, as 
 given by Jensen (26), are shown in figure 8-3, along with 
 the response characteristics of the ear at threshold. Of the 
 three scales, the A scale comes closest to approximating the 
 response characteristics of the ear. This scale is used by 
 MSHA to set environmental noise criteria. 
 
 Noise often varies in intensity over time. To account for 
 this, a time-weighted average of the noise exposure can be 
 computed. The Environmental Protection Agency recom- 
 mends the equivalent sound level (LgJ as the best measure 
 of the cumulative effects of noise. The equivalent sound 
 level is defined as the sound pressure level (usually 
 measured in decibels, A weighted) of a constant noise that, 
 
 Above-normal 
 air pressure 
 
 Below-normal 
 air pressure 
 
 Corresponding changes 
 in density of air molecules 
 
 Figure 8-2. — Sine wave sound pressure wave showing one cy- 
 cle with corresponding changes in air pressure. 
 
 10 
 
 CD 
 
 uJ 
 
 CO 
 
 o io 
 
 Q. 
 CO 
 
 UJ 
 
 cc 
 £20 
 
 UJ 
 DC 
 
 30 
 
 40_ 
 
 i i 1 1 1 1 1 — i — i i i 1 1 1 1 1 — i — i — i ii i 
 
 Sound level 
 meter scales 
 
 < // 
 
 // 
 
 I 
 I 
 
 / \ 
 
 ^ 
 
 \ 
 
 / 
 
 / 
 
 50 100 
 
 Approximate ear 
 response of threshold 
 
 L 
 
 -10 
 
 
 CO 
 
 
 •o 
 
 
 a* 
 
 
 
 3 
 
 
 UJ 
 
 
 X 
 
 
 1- 
 
 
 IJ 
 
 10 
 
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 >- 
 
 
 h- 
 
 
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 F 
 
 20 
 
 CO 
 
 
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 UJ 
 
 30 
 
 > 
 
 
 h- 
 
 
 < 
 
 
 _l 
 
 
 UJ 
 
 
 cc 
 
 1,000 
 FREQUENCY, Hz 
 
 10,000 
 
 .40 
 
 Figure 8-3.— Relative response characteristics of A, B, and C 
 sound-level meter scales and the human ear at threshold (26). 
 
 (Courtesy of National Institute for Occupational Safety and Health) 
 
 over the time period being measured, transmits to the 
 receiver the same amount of acoustic energy as the actual 
 time-varying sound. For example, if a person is exposed to 
 100 dBA for 1 h and quiet for the next 4 h, the L eq for the 
 total 5-h period would be 94 dBA. That is, 5 h of 94-dBA 
 noise is equivalent in acoustic energy to 1 h of 100 dBA and 
 4 h of quiet (less than 80 dBA). Sound pressure meters have 
 been developed that give direct readouts of L eq values. 
 
 Conditions in Mining 
 
 Figure 8-4 presents an overview of the noise levels 
 typically experienced in underground and surface mining 
 by operators of various types of equipment (18). As can be 
 seen, all the levels listed exceed 90 dBA. With the excep- 
 tion of longwalls, underground shuttle cars, and surface 
 trucks, all exceed 100 dBA. 
 
104 
 
 Standards for Noise Exposure in Mining 
 
 In the United States, the Walsh-Healy criteria for noise 
 exposure, shown in table 8-3, are the standards set for 
 underground and surface mining. Comparing these stand- 
 ards against the typical levels reported in figure 8-4 makes 
 it very likely that operators are exceeding recommended 
 noise exposure criteria. For example, the noise exposure of 
 over 700 underground coal miners was studied by Bobick 
 and Giardino (8). They found that 20% of the miners were 
 overexposed according to the Walsh-Healy criteria. 
 
 Table 8-3.— Walsh-Healy noise criteria for underground 
 and surface mining 
 
 Max noise Max expo- 
 level, dBA sure time, h 
 
 90 •. .. 8 
 
 92 6 
 
 95 4 
 
 97 3 
 
 100 2 
 
 102 1.5 
 
 105 1 
 
 110 .5 
 
 115 .25 
 
 Hearing Loss 
 
 As would be expected, daily exposure to high levels of 
 noise results in permanent hearing loss. The National In- 
 stitute for Occupational Safety and Health (31 ) conducted 
 a hearing survey of 1,500 underground coal miners who had 
 no history of significant nonoccupational noise exposure, 
 severe head trauma, or chronic ear infections, and had been 
 out of the working environment for at least 14 h. Figure 
 8-5 presents the results, showing the percentage of miners, 
 by age, who suffered hearing loss of 25 and 40 dB for the 
 frequencies of 1,000, 2,000, and 3,000 Hz (these are impor- 
 tant frequencies for speech perception). By age 50, approx- 
 imately half of the miners had a hearing loss in excess of 
 25 dB, and about 30% had a loss exceeding 40 dB. These 
 statistics were measurably worse than the national average. 
 
 Other Physiological Effects of Noise 
 
 Noise acts as a nonspecific physiological stressor. The 
 onset of a loud, unexpected noise will cause a startled 
 response. This usually involves flexion of the arms, arching 
 of the torso, and blinking. Although not harmful, it may 
 cause a person to be injured, or to injure others. Much of 
 the literature dealing with the physiological effects of noise 
 was reviewed by Antecaglia and Cohen (3). They reported 
 the following noise effects noted by various researchers: 
 
 1. Undue excitability and nervousness. 
 
 2. Reduced speed of eye movements to focus clearly on 
 objects. 
 
 3. Narrowing of the visual field. 
 
 4. Modification of the perception of color (partial deficiency 
 for perceiving red). 
 
 5. Increased secretions of corticosteroids (an indicator of 
 general stress). 
 
 6. Constriction of blood vessels, fluctuations in blood 
 pressure, and cardiovascular irregularities. 
 
 7. Increased gastric secretions. 
 
 _ 
 
 
 
 106 
 
 
 
 
 
 
 
 
 B 
 
 _ 
 
 - 
 
 107 
 
 JS 
 
 Q 
 
 
 'PA 
 
 
 
 
 
 102 
 
 ■ 
 
 N 
 
 O 
 
 Q 
 
 
 101 
 
 C i_ 
 <V V 
 
 §8 
 
 w 
 Li. 
 
 
 IOO 
 m 
 
 S5-S 
 
 I 2 
 
 S o> 
 
 o 
 
 
 
 
 94 
 
 
 93 
 
 i/i 
 
 M 
 u 
 
 3 
 w 
 
 - 
 
 Ul 
 
 O I 10 
 
 90 
 
 SO 
 
 70 
 
 6 8 8 8 8 8 
 
 OPERATING TIME PER SHIFT, h 
 Figure 8-4.— Typical noise levels of machinery in underground 
 
 (A) and surface (B) mining (18). (Courtesy of US Mm Safety and Hearth 
 Administration) 
 
 UJ 
 
 rr 
 
 o 
 
 80 
 
 70 
 
 60 
 
 50 
 
 E 40 
 
 < 
 UJ 
 
 X 
 V) 
 
 rr 
 
 UJ 
 
 30 
 
 20 
 
 10 
 
 Hearing loss > 25 dB 
 
 10 
 
 Hearing loss> 40 dB 
 I I 
 
 30 40 50 
 
 MINERS' AGES, yr 
 
 60 
 
 70 
 
 Figure 8-5. — Hearing loss among underground coal miners, by 
 
 age (18). (Courtesy of U.S. Mine Safety and Hearth Administration) 
 
 I 
 
105 
 
 It must be emphasized that these changes are, for the 
 most part, small. The long-range effect of continual noise 
 exposure has not really been addressed outside the realm 
 of hearing loss. There is some evidence of potential stress- 
 related problems, but the reports are few and sketchy at 
 best. 
 
 Effects of Noise on Performance 
 
 The effects of noise on performance depend heavily on 
 the task being performed. The more cognitively demanding 
 a task, the more likely it is that noise will adversely affect 
 performance. Performance of simple, routine tasks shows 
 little or no effect from noise, and in some cases even shows 
 a facilitative effect. One effect of high noise is that people 
 tend to funnel attention on a task, focusing on the most im- 
 portant aspects and ignoring peripheral aspects. This may 
 be fine for simple tasks, but where information may be com- 
 ing from many sources and directions, funneling increases 
 the probability of missing important information. 
 
 One important detrimental effect of noise, of course, is 
 that is masks auditory cues. If workers depend on sound 
 cues : or voice communications to perform their jobs effi- 
 ciently and safely, noise robs them of that valuable infor- 
 mation, and safety and performance will suffer. 
 
 Controlling the Noise Problem 
 
 Noise can be controlled at the source, along the path 
 from the source to the receiver (i.e., operator), and at the 
 receiver's ear. In the mining industry, most efforts at noise 
 control have been directed at reducing noise at the source 
 and at the receiver. Little effort has been directed toward 
 reducing noise along its path by using enclosures and bar- 
 riers. Some processing plants have used sound absorption 
 and acoustic enclosures to reduce ambient noise, but such 
 approaches are less feasible when the sound source is 
 mobile, such as a truck or drill (although treating the in- 
 side of a truck cab with absorbent material is often used). 
 
 Because sound is essentially caused by vibrating objects, 
 the aim of noise reduction programs has been to reduce the 
 vibrations of the machine or component generating the 
 noise. The discussion of sound-reduction techniques is 
 beyond the scope of this report. However, a few general prin- 
 ciples of noise control are discussed and the results of a few 
 noise-reduction programs in the mining industry are 
 presented in this chapter. 
 
 Low-frequency noise, the predominant type of noise in 
 many mining situations, is attenuated less than high- 
 frequency noise as it travels in air. In addition, low frequen- 
 cies are much harder to contain using barriers and enclo- 
 sures than are high frequencies because low frequencies 
 travel over and around obstacles and through small holes. 
 High frequencies, on the other hand, are more easily 
 deflected. Although harder to contain, low frequencies are 
 less harmful than high frequencies. 
 
 When an object vibrates at its natural frequency related 
 to its mass, it resonates. Resonance actually increases the 
 amplitude of the vibration and, hence, the noise. This is 
 dramatically demonstrated by wetting your finger and 
 gently rubbing around the rim of a stemmed glass, caus- 
 ing the glass to vibrate. By changing the speed and pressure 
 of the rubbing action, the resonant frequency can be found, 
 and the glass will emit a very loud tone. Be careful, 
 however; the resonance can increase the vibration to the 
 point of shattering the glass. 
 
 In the context of noise control, a piece of equipment 
 vibrating at its resonance frequency will emit loud noises. 
 The noise can be reduced by changing the natural frequency 
 of the equipment. For example, adding or removing mass 
 (e.g., bolting a plate to the machine), drilling large diameter 
 holes in very flat plates, or tightening loose bolts can reduce 
 resonance. 
 
 Because vibration causes noise, isolating the vibrating 
 machine from surrounding structures also can reduce noise. 
 Using vibration-isolation springs, pads, etc., for example, 
 often drastically reduces noise. Such isolation materials, 
 however, must be selected carefully because they could 
 change the natural frequency of a machine and cause the 
 equipment to resonate, thus actually enhancing the noise 
 output of the source. 
 
 Noise from fluids flowing through pipes is usually 
 caused by turbulences in the flow. Such turbulences can be 
 caused by abrupt pressure changes, such as opening and 
 closing a valve quickly, or by sharp bends or partial obstruc- 
 tions in the pipes that set turbulences in motion. Using 
 fewer or softer (less than 90°) bends and not placing bends 
 close together will often reduce flow-generated noise. 
 
 Noise generated by fans can be reduced by changing the 
 pitch and/or number of blades in the fan or by supplying 
 an uninterrupted, nonturbulent flow of air to the fan. Posi- 
 tioning a fan so that the intake side is close to corners or 
 baffles will cause a turbulent flow of air to enter the fan 
 and will increase noise. The purchase of a commercially 
 available silencer from the fan manufacturer is probably 
 the most cost-effective solution. 
 
 The Bureau has published a handbook of noise control(5) 
 that details specific noise control procedures for various 
 types of surface, underground, and preparation plant equip- 
 ment. Included are the noise characteristics of particular 
 mining machines, noise-control treatments, anticipated 
 reductions in noise level, cost, and commercially available 
 sources for noise reducing kits, components, etc., references, 
 and case history reports. As an example, figure 8-6 presents 
 a page from this handbook for diesel-powered rotary drills 
 used in surface mining. 
 
 A project to reduce noise exposure to operators of diesel- 
 powered track dozers was discussed by Daniel (13). One 
 dozer had no operator cab and only a rollover protective 
 structure (ROPS). The noise level at the operator's ear was 
 105.5 dBA. Through the series of modifications listed in 
 table 8-4, the overall noise level was reduced 11.5 dBA, to 
 
 Table 8-4.— Effects of noise control treatments installed 
 
 on a diesel track dozer equipped with ROPS only (13), 
 
 decibels (A-weighted) 
 
 
 Sound 
 
 Reduction from 
 
 Treatment 
 
 level 
 
 baseline 
 
 None (baseline) 
 
 105.5 
 
 NAp 
 4 
 
 Windshield 
 
 101.5 
 
 Absorption under ROPS 
 
 102.5 
 
 3 
 
 Exhaust muffler 
 
 104.0 
 100.0 
 
 1.5 
 
 Windshield and absorption 
 
 5.5 
 
 Windshield, absorption, and muffler 
 
 99.5 
 
 6 
 
 Windshield, absorption, muffler, and dash 
 
 
 
 seals and isolation 
 
 96.5 
 
 9 
 
 Windshield, absorption, muffler, dash seals 
 
 
 
 and isolation, and floor seals 
 
 95.5 
 
 10 
 
 Windshield, absorption, muffler, dash seals 
 
 
 
 and isolation, floor seals, and seat seals . . . 
 
 95.0 
 
 10.5 
 
 Windshield, absorption, muffler, dash seals 
 
 
 
 and isolation, floor seals, seat seals, tank 
 
 
 
 seal, and hydraulic valve cover 
 
 94.0 
 
 11.5 
 
 NAp Not applicable. 
 
106 
 
 DIESEL-POWERED ROTARY DRILLS 
 
 Owse< E*hau« {(( 
 
 Typical noise level 
 85-100 dBA 
 
 II) Hydraulic Ncise 
 
 Treatment 
 
 Quieted 
 
 noise 
 
 level, dBA 
 
 Cost and 
 labor 
 
 Status 
 
 Refer- 
 ence 
 
 Add mufflers(s) 
 to engine 
 exhaust 
 
 85-95 S100-S450 Commercially available Al 
 
 2 h for all models. C2 
 
 Modify existing 
 cab. 
 
 75-90 $500-$900 
 20-80 h 
 
 Local design and 
 fabrication required. 
 
 Ill 
 
 A4 
 Bl 
 B2 
 
 Add acoustic 
 cab. 
 
 70-85 $10,000$ 15.000 Commercially available 
 80-140 h for some models. 
 
 A2 
 A4 
 B2 
 
 n 
 
 Add enclosure for 
 engine with 
 mufflers. 
 
 75-90 $1.500-$8.000 
 140-280 h 
 
 Local design and B2 
 
 fabrication required. B4 
 
 Add partial barrier 
 at operator with 
 mufflers. 
 
 80-95 $500-$2.000 
 20-120 h 
 
 Local design and 
 fabrication required. 
 
 A4 
 Bl 
 B2 
 
 6. 
 
 Modify cooling fan 
 with mufflers 
 for models with 
 noisy fans. 
 
 85-95 
 
 $500-$2,000 
 20-120 h 
 
 Local design and 
 fabrication required. 
 
 B3 
 
 7. 
 
 ^ 
 
 Install item 5 along 
 with covers for 
 hydraulic valves, 
 dust collector for 
 blow air, and 
 isolated cen- 
 tralizer or drill 
 pipe snubber. 
 
 80-90 
 
 $5,000-$ 10.000 
 200-250 h 
 
 Local design and 
 fabrication required. 
 
 A3 
 A4 
 Bl 
 B2 
 B3 
 
 Recommendation* 
 
 Reduce engine noise using a muffler, cab, or barrier 
 as appropriate. 
 
 Acoustically treated noise level 
 75-90 dBA 
 
 Figure 8-6.— Example of type of information contained in Mining Machinery Noise Control Guidelines (5). 
 
107 
 
 94 dBA. This represents a one-sixteenth reduction in sound 
 power, and a one-half reduction in loudness. About 6 dBA 
 of reduction was obtained by providing a windshield, muf- 
 fler, and sound-absorption material under the ROPS canopy. 
 The remaining 5.5-dBA reduction resulted from carefully 
 sealing openings and isolating the dash from engine 
 vibrations. 
 
 As a final example, a Bureau project to reduce noise 
 levels in low-seam, underground coal mine, mantrip trolley 
 cars was reported on by Galaitsis and Bobick (17). Noise 
 levels were typically 90 to 100 dBA in such vehicles at nor- 
 mal operating speeds. The major noise sources were the 
 wheel-rail interface system and the drive motor and train. 
 The noise-reduction treatments included metal panel damp- 
 ing, soft spring seats, soft suspension arm bushings, suspen- 
 sion arm guideplate isolators, motor enclosures, motor 
 mounts, and helical gears. Figure 8-7 shows the results of 
 the treatment for the passenger and operator compartments, 
 with average reductions of 5 to 10 dBA obtained. (Note that 
 a decrease of 3 dB represents a reduction of sound power 
 by one-half.) 
 
 Hearing Protection 
 
 If noise cannot be reduced at the source or in its path, 
 then hearing protection should be worn by the exposed 
 worker to reduce the noise level reaching the vulnerable 
 structures of the inner ear. There are a wide variety of hear- 
 ing protectors available: earplugs, muffs, custom ear molds, 
 etc. The two most common types are insert-type and muff- 
 type protectors. Table 8-5 presents the advantages and 
 disadvantages of each (37). 
 
 Table 8-5.— Advantages and disadvantages of insert-type 
 and muff-type hearing protection devices (37) 
 
 Courtesy of Charles C. Thomas, Publisher, Springfield, IL 
 MUFF 
 
 Advantages More attenuation and less variable. 
 
 Single size. 
 
 Easily monitored for wearing compliance. 
 
 Usually more comfortable. 
 
 Persons with infected ears can wear them. 
 
 Harder to lose. 
 Disadvantages Uncomfortable in heat. 
 
 Harder to store or carry. 
 
 Suspension forces may decrease with bending, 
 and attenuation may vary. 
 
 Large size. 
 
 Expensive. 
 
 INSERT 
 Advantages .... 
 
 Small size. 
 
 Easily worn with other headgear. 
 Comfortable in hot environments. 
 Inexpensive. 
 
 Disadvantages More fitting time required. 
 
 Less attenuation and more variable. 
 Dirt may be inserted into the ear canal with 
 the plug. 
 
 Hard to monitor for wearing compliance. 
 Only persons with healthy ears can wear them. 
 
 Each type and make of hearing protection has slightly 
 different attenuation properties. Some give better attenua- 
 tion at lower frequencies, some at higher frequencies. It is 
 important, therefore, to select hearing protection that 
 matches the environmental noise characteristics for which 
 protection is sought. It must be pointed out, however, that 
 the attenuation curves published by manufacturers are usu- 
 ally generated under more or less ideal laboratory condi- 
 
 < 
 
 100 
 
 90 
 
 80 
 
 E A 
 
 i A ^ Untreated 
 
 UJ 
 
 > 70 
 UJ 
 I 100 
 
 3 
 
 O an 
 
 V) 90 
 
 80 
 
 70 
 
 ^j\AvV\ 
 
 Treated 
 
 EB 
 
 * JlI\ Jf 
 
 i i i 
 •- Untreated 
 
 r*V '- 
 
 ijVrV. _r-l/ \l 
 
 rij/v^/ rM »*, |A fit 
 
 
 * AJyr 
 
 Treated ^ 
 
 _i 1 i 
 
 vvr v : 
 
 10 
 
 20 
 
 TIME, s 
 
 30 
 
 40 
 
 Figure 8-7.— Typical noise-time histories in passenger and 
 operator compartments of an untreated and noise-reduction- 
 treated mantrip (17). 
 
 tions. These data do not take into account wearing habits, 
 fit, interference with safety glasses or hair, and other on- 
 the-job factors. For example, tests conducted with muff-style 
 protectors in the underground environment were reported 
 on by Nguyen (32). Whereas the manufacturer claimed at- 
 tenuation of 25 to 30 dBA, actual measurements showed 
 values of 10 to 16 dBA. In other tests, it was found that 
 suspension fatigue and cushion deterioration had only a 
 minor effect on attenuation, but leakage caused by safety 
 glass temples resulted in up to a 5-dBA loss in attenuation. 
 Insert-type protectors, if properly inserted, are not affected 
 by interference of eyeglass temples and hair, as are muff- 
 type protectors. 
 
 An objection often given by workers to wearing protec- 
 tion devices is that such devices reduce speech intelligibility 
 and make it more difficult to hear warnings and other aud- 
 itory signals. The evidence, however, indicates that wear- 
 ing hearing protection does not necessarily reduce speech 
 intelligibility. In high noise level conditions, above 80 dBA, 
 wearing hearing protectors reduces both noise and speech, 
 and brings them into a range where they can be more eas- 
 ily discriminated, hence, increasing intelligibility. The prob- 
 lem is that when people wear hearing protectors, they tend 
 to speak more softly than when not wearing them. Person- 
 nel have learned to change their voice levels to compensate 
 for a noisy environment, and the quieting effect of hearing 
 protectors cause the wearers to tbink it is quieter than it 
 really is. The upshot is that people must be instructed to 
 speak loudly, slowly, and distinctly in noisy environments 
 and to be cognizant of the effect of hearing protectors on 
 their speech intensity. Thus, hearing protection per se does 
 not decrease intelligibility for a listener, but it may reduce 
 the speaker's intensity. 
 
 Tbere is some evidence that wearing hearing protection 
 can reduce the ability to localize sounds. Approximately 
 50% more errors in sound localization were found by 
 
108 
 
 Atherley and Noble (4) when subjects were wearing protec- 
 tion. There was also a marked increase in left-right errors, 
 where the subjects reported a sound on the right as coming 
 from the left, or vice versa. 
 
 Hearing protection should not be considered a perma- 
 nent solution to a noise problem, but rather only a tem- 
 porary fix while efforts are being made to reduce the noise 
 level at the source or along its path. 
 
 WHOLE-BODY VIBRATION 
 
 Whole-body vibration is prevalent in both surface and 
 underground mining environments. In surface mining, 
 mobile equipment operators are exposed to vibration and 
 buffeting as they drive their vehicles over bumpy roads. In 
 underground mining, shuttle car and scoop operators, as 
 well as miners being transported by mantrip, are also ex- 
 posed to vibration and buffeting. Vibration was discussed 
 in chapter 6 in the context of handtools. Although handtool- 
 induced vibration, as any jackleg drill operator will confirm, 
 can shake your entire body, it is necessary to distinguish 
 that sort of vibration from the lower frequency, higher 
 amplitude vibration transmitted to the whole body by 
 mobile equipment. The physiological and performance ef- 
 fects of the two types of vibration are somewhat different. 
 
 Vibration Terminology 
 
 Vibration is primarily of two types, sinusoidal and ran- 
 dom. As was discussed in relation to noise, sinusoidal mo- 
 tion is regular and repeats itself at set intervals. Most 
 studies of the effects of vibration on humans use sinusoidal 
 wave patterns. Random vibration, as would be expected, is 
 irregular and unpredictable; most real-world vibration is 
 random. 
 
 Vibration occurs in different directional planes (up- 
 down, forward-backward, left-right), with the predominant 
 vibratory forces experienced in the mining environment in 
 the up-down plane. 
 
 As in the case of noise, whole-body vibration is discussed 
 in terms of frequency and intensity. In the case of sinusoidal 
 vibration, frequency is defined in hertz, and intensity is 
 defined in several ways: amplitude (measured in inches or 
 feet); displacement (inches or feet); velocity (inches or feet 
 per second); or acceleration (inches or feet per square sec- 
 ond). Sometimes acceleration is expressed in terms of 
 number of gravity (g) where 1 g = 386 in/s 2 or 32.17 ft/s 2 . 
 
 The situation becomes more complex with random vibra- 
 tion, because the frequency spectrum varies randomly. Fre- 
 quency is usually displayed in a power spectral-density plot, 
 showing the power density (gravity squared per hertz) in 
 each frequency band. Intensity is often expressed as root- 
 mean-square acceleration (e.g., RMS G) and is a measure 
 of the total energy across the frequency range. 
 
 Vibration transmitted to the body can be amplified or 
 attenuated as a consequence of body posture (e.g., standing, 
 sitting), muscle activity (e.g., relaxed or rigid), type of 
 seating, and the frequency of the vibration. Every object 
 has a resonant frequency related to its mass. When an ob- 
 ject is vibrated at its resonant frequency, the object will 
 vibrate at maximum amplitude, greater than the amplitude 
 of the original vibration. This is called resonance. Different 
 parts of the body have different resonant frequencies. The 
 following is a partial list of frequencies, in hertz: Vertebras 
 
 of neck and lumbar region, 2.5 to 5; trunk, shoulder, and 
 neck, 4 to 6; head and shoulders, 20 to 30; and eyeballs, 60 
 to 90. 
 
 It is generally agreed that frequencies between 4 and 
 8 Hz are most likely to cause damage to the back and spine 
 because of resonance of these body parts. 
 
 Effects of Vibration on Humans 
 
 The effects of vibration on humans can be divided into 
 two classes, health effects and performance effects. 
 
 Health Effects 
 
 Several studies have been conducted on individuals ex- 
 posed to whole-body vibration on the job: tractor drivers, 
 truck drivers, bus drivers, and heavy equipment operators. 
 All the studies suggest that low-frequency vehicle vibra- 
 tions are associated with increased incidence of lower-back 
 pain, disk and vertebra degeneration, gastrointestinal dis- 
 orders, and hemorrhoids. The problem is that not all of these 
 ailments can be attributed to vibrations alone; it is likely 
 that other factors, such as maintaining a fixed-seated 
 posture, irregular and poor eating habits, and physical lift- 
 ing associated with the job, may have contributed to some 
 of these disorders. It was reported by Cain and Pettry (10) 
 that at one coal company in 1983, 33^ of back injuries oc- 
 curred to persons employed in jobs where they were regu- 
 larly exposed to whole-body vibration, yet only 20^ of the 
 workforce were in such jobs. 
 
 Performance Effects 
 
 The primary performance effects of vibration are on 
 visual and manual tasks. Decrements in visual acuity oc- 
 cur most prominently with vibrations in the 10- to 30-Hz 
 region. Vibration does not seem to have much of an effect 
 on cognitive performance or speed-of-reaction time. Vibra- 
 tion leads to fatigue, partly because it causes muscles to 
 tense in order to steady the body or attenuate the vibra- 
 tion. This general fatigue can, of course, lead to reduced 
 cognitive-processing capability. It was reported by Grand- 
 jean (21) that vibration impairs driving efficiency and in- 
 creases errors, which may result in accidents. 
 
 Vibration Exposure Standards 
 
 Researchers have for years been trying to develop a 
 standard for human exposure to whole-body vibration. In 
 1974, the International Organization for Standardization 
 published a recommended exposure standard for % - ertical 
 and lateral vibration (24). Three criteria were established: 
 fatigue-decreased proficiency boundary (FDPl beyond which 
 working efficiency was postulated to decrease: health ex- 
 posure limit, which is equal to two times the FDP; and the 
 reduced comfort boundary tRCB). equal to FDP 3.15. Figure 
 8-8 shows the FDP criteria for vertical vibration. Curves 
 are shown for 8-h, 1-h. and 1- to 4-min exposures. The 
 criteria, although widely accepted, can only be considered 
 approximate. Evidence has accumulated that challenges the 
 validity of the criteria (48). and that indicates that fatigue 
 effects occur at lower levels and for shorter durations than 
 the criteria suggest. 
 
109 
 
 100 
 
 N 
 
 < 10 
 
 z 
 o 
 
 g 
 
 QL 
 hi 
 
 _i 
 til 
 o 
 
 S 1.0 
 
 : 
 
 i i i 1 1 1 1 1 1 i i i 1 1 
 
 1 1. 
 
 - 
 
 At any t point, health limit = 2 X FDP 
 Comfort limit = FDP/ 3.15 
 
 ' - 
 
 — 
 
 
 \ 
 
 ; 
 
 "N. 1-4 min/ / 
 
 
 -^ 
 
 ^\. 1h / / 
 
 - 
 
 - 
 
 
 " 
 
 - 
 
 ^\. 8h X 
 
 - 
 
 
 i i i i i i 1 1 1 i i i i i 
 
 i i 
 
 250 
 
 10 
 
 100 
 
 FREQUENCY, Hz 
 
 Figure 8-8.— Vertical vibration exposure limits for preservation 
 of performance (fatigue-decreased proficiency, FDP) (24). 
 
 (Copyright 1974 by the American National Standards Institute Inc., and reprinted with 
 permission) 
 
 m 
 
 2 
 
 i I «" 
 
 KEY 
 --- Contoured chair 
 
 — Standard driver's 
 seat 
 
 •— •• Suspension seat 
 
 160-lb man, normal \ 
 sitting position, accel- \ 
 eration measured at 
 belt 
 
 J. 
 
 2 4 6 
 
 FREQUENCY, Hz 
 
 Figure 8-9.— Mechanical response of a person's body to vibra- 
 tions when sitting in different seats (39). 
 
 Vibration Exposure of Surface Coal Miners 
 
 The vibration exposure of surface coal miners operating 
 equipment such as track dozers, scrapers, haulers, blasthole 
 drills, motor graders, and shovels was measured by Rem- 
 ington (36). This work indicated that about half of all sur- 
 face machine operators are exposed to vibration exceeding 
 the FDP criteria; only about 15% experience vibration ex- 
 ceeding the health exposure limit. The machines in which 
 operators were most likely to exceed the FDP criteria (prob- 
 ability = 0.87-0.90) were scrapers, dozers, and loaders. 
 Truck drivers were next most likely (probability = 
 0.56-0.58), followed by grader operators (probability = 0.32). 
 The operators of blasthole drills, shovels, and draglines were 
 exposed to very little vibration. Remington concluded that 
 although one would not expect to see many mine machine 
 operators with vibration-induced health effects, one would 
 expect to find significant numbers with impaired ability to 
 operate their machines safely and efficiently because of 
 vibration exposure. 
 
 Controlling Vibration 
 
 Vibration can be reduced at the source through engi- 
 neering modifications to the equipment, including better 
 suspension systems and component isolation. In addition, 
 shock-resistant seats can be installed to reduce the inten- 
 sity of the vibration reaching the operator's body. Figure 
 8-9 shows the transmission of vibration to a seated person 
 
 in three types of seats (39). As can be seen, the suspension 
 seat reduced the level of vibration considerably. The amp- 
 litude of vibration was actually increased when the person 
 sat in the contoured and standard seats. The cost of a good 
 pneumatic seat can accrue dividends in increased worker 
 health, comfort, and efficiency. 
 
 HEAT STRESS 
 
 Thermal conditions in mining run the gamut from bit- 
 ter cold, experienced by surface miners in the winter, to hot 
 humid conditions, experienced in deep underground mines. 
 Heat stress is probably more prevalent, and certainly more 
 dangerous, than cold stress. The body can tolerate cold 
 stress much better than heat stress, and the performance 
 effects of cold stress seem to be more restricted than is the 
 case with heat stress. 
 
 Physiological Response to Heat Stress 
 
 As discussed in chapter 7, the body oxidizes glucose t» 
 release energy and heat. The more physically demanding 
 an activity, the greater the amount of heat generated. This 
 is the process of metabolism, and it can increase heat pro- 
 duction 10 to 20 times greater than at rest. The body also 
 gains and loses heat from and to the environment. Heat is 
 gained or lost due to convection (the mixing of cool and 
 warm air and the transfer of heat by molecular contact of 
 
110 
 
 the air molecules), conduction (direct contact with another 
 object— usually so negligible that it is combined with con- 
 vection), and radiation (the transfer of heat by electro- 
 magnetic radiation— as is done by the sun or hot object not 
 in direct contact with the body). The body loses heat through 
 evaporation (the conversion of water to water vapor). Evap- 
 oration is the principal avenue of heat loss for the body, and 
 is regulated by producing sweat and diverting heated blood 
 to the skin for evaporative cooling. 
 
 The body attempts to maintain a state of internal ther- 
 mal equilibrium. That is, the body regulates blood flow and 
 sweat production to maintain a constant (or nearly constant) 
 core temperature. Core temperature is the temperature of 
 the deep body organs and is approximated by rectal 
 temperature. As the body gains heat, due to either increased 
 metabolism or by exposure to a hot environment, the heart 
 beats faster and pumps more blood with each beat (i.e., in- 
 creased cardiac output). In addition, the blood vessels in the 
 skin dilate to allow the heated blood from the core to flow 
 to the skin and to be cooled, especially by evaporation. 
 
 In addition to the cardiovascular response to heat stress, 
 the body produces sweat that keeps the skin moist and is 
 the principal medium for evaporative cooling. If the body 
 can dissipate the metabolic and environmental heat build- 
 up, no major problems occur. If not, serious physiological 
 consequences, including death, can ensue. 
 
 Excessive heat stress leads to heat cramps, heat exhaus- 
 tion, and heat stroke. Heat cramps are painful muscle 
 cramps caused by excessive sweat loss. The cramping can 
 occur during or after work, and usually affects those muscles 
 most involved in the work. 
 
 Heat exhaustion is caused by excessive loss of water. 
 The worker with heat exhaustion experiences dizziness, ex- 
 treme weakness or fatigue, nausea, and headaches. Heat 
 stroke is the most serious health problem and can often lead 
 to death. Basically, in heat stroke, the body's heat dissipa- 
 tion system cannot cope with the heat stress placed on it. 
 Either the sweat glands fatigue and cease producing sweat, 
 or the system simply cannot adequately dissipate the heat 
 load. Core temperature rises and the hot blood damages the 
 vasomotor control centers in the brain; liver and heart 
 damage can also occur. Blood vessels dilate and insufficient 
 blood is returned to the brain and heart, and the person 
 often will go into shock. Immediate medical attention is re- 
 quired to prevent death. 
 
 Figure 8-10, based on work by Bell (7), shows the 
 number of minutes unacclimatized workers can tolerate 
 various combinations of dry bulb temperature and relative 
 humidity. The data were generated by young, fit men step- 
 ping on and off a stepstool, 12 times per minute. The men 
 continued the activity until exhausted. As shown, at these 
 relatively high temperatures and this work rate, collapse 
 occurred in less than 2 h. 
 
 158 
 
 140 
 
 UJ 
 
 cc 
 
 3 
 
 a: 
 
 UJ 
 
 Q. 
 
 UJ 
 
 r- 
 
 122 
 
 104 
 
 86 
 
 .30 % relative 
 humidity 
 
 i. 
 
 20 40 60 80 100 
 
 COLLAPSE TIME, min 
 
 120 
 
 Figure 8-10. — Time until young, fit, unacclimatized men col- 
 lapse from exhaustion caused by stepping on and off a stepstool 
 12 times per minute. (Adapted by Bell (7) from reference 33.) 
 
 (Copyright 1982 by John Wiley and Sons, and reprinted by permission) 
 
 indexes have been universally accepted because each has 
 its own shortcomings. Despite this, a few indexes seem to 
 have acceptability, and several exposure limit standards 
 are based on them. Three of these indexes— effective tem- 
 perature, wet-bulb-globe temperature, and Belding-Hatch 
 heat stress index— are discussed in the following sections. 
 Jensen (27) compared these heat stress indexes and 
 found very high correlations between wet-bulb-globe tem- 
 perature and corrected effective temperature, but lower cor- 
 relations between these measures and the Belding-Hatch 
 heat stress index. Similar results have been reported by 
 Morris (30). 
 
 Effective Temperature (ET) 
 
 Indexes of Heat Stress 
 
 Heat stress is the total neat load on an individual from 
 environmental and metabolic sources. Heat stress is distin- 
 guished from heat strain, which is the biochemical, physi- 
 ological, and psychological adjustments made by an 
 individual in response to the stress (27). 
 
 Over the years, many attempts have been made to 
 develop indexes of heat stress by combining several envi- 
 ronmental and task variables into a single number to repre- 
 sent the heat load on an individual. None of a dozen or more 
 
 ET is an index of the warmth felt by the human body 
 on exposure to various combinations of air temperature, 
 humidity, and air velocity, using as a reference the tem- 
 perature of an environment with still, fully saturated (100*5 
 relative humidity) air. Thus, if a given combination of tem- 
 perature, humidity, and air velocity yields an ET of 85 c F. 
 that environment would give the same thermal sensations 
 as an environment of 85 " F, 100*5- relative humidity, and 
 no air velocity. As pointed out by Jensen (27). ET does not 
 include the effects of radiant heat (e.g.. the sun\ and hence 
 underestimates heat load in environments where radiant 
 
Ill 
 
 heat exists. Several investigations have proposed correc- 
 tions to ET to take into account the effects of radiant heat. 
 Another development in the ET index has been to relate 
 the environments to 50%, rather than 100%, relative humid- 
 ity, and to use equivalent skin wetness rather than ther- 
 mal warmth felt. This scale is called corrective effective 
 temperature (16). 
 
 Wet-Bulb-Globe Temperature (WBGT) 
 
 WBGT combines natural wet bulb temperature (NWB), 
 globe temperature (GT), and dry bulb temperature (DB) into 
 a single index using the following formula: 
 
 Indoor application-WBGT = 0.3 GT + 0.7 NWB, and 
 outdoor application-WBGT = 0.2 GT + 0.7 NWB + 0.1 
 DB. 
 
 Natural wet bulb temperature is obtained by wrapping 
 the end of a thermometer with wet gauze. This simulates 
 the evaporative cooling capacity of the environment, tak- 
 ing into account the air movement and relative humidity 
 in one measure. Globe temperature is obtained by placing 
 a thermometer inside a copper sphere that is painted black. 
 This measures the radiative heat load of the environment. 
 Dry bulb temperature is simply the temperature reading 
 from a dry thermometer suspended in the air. Figure 8-11 
 shows a typical manual setup for obtaining the temperature 
 readings necessary to compute WBGT. As will be seen, 
 WBGT is fast becoming the measure upon which exposure 
 standards are being based. There are electronic instruments 
 available that display WBGT directly, but they are expen- 
 sive. A simplified measure proposed by Botsford (9), called 
 the wet globe temperature (WGT), consists of a dial ther- 
 mometer with a heat sensor enclosed in a small copper 
 sphere, covered with a wet black cloth (a Botsball). It is 
 designed to take into account all the forms of heat exchange 
 that affect a person's response to a hot environment, i.e., 
 evaporation, conduction, convection, and radiation. 
 
 Wet bulb 
 thermometer 
 
 l4 in 
 
 Dry bulb 
 thermometer 
 
 Globe 
 thermometer 
 
 6-in copper ball 
 *3mjtm ft P-'* d b '°' k 
 
 Adjustable 
 tripod 
 
 Figure 8-1 1 .—Setup for manually obtaining temperatures used 
 to compute wet-bulb-globe temperature. 
 
 Heat Stress Index (HSI) 
 
 HSI was developed by Belding and Hatch (6). It is one 
 of the most comprehensive indexes available, but requires 
 many measurements and uses a relatively complex formula. 
 Basically, HSI is the ratio of the body's heat load from 
 metabolism, convection, and radiation to the evaporative 
 cooling capacity of the environment. The idea is that the 
 heat load from these sources must be dissipated through 
 evaporation. The ratio of heat load to evaporative cooling 
 capacity of the environment therefore indicates the relative 
 ease by which that heat load is dissipated. The index takes 
 into account environmental factors, such as temperature, 
 humidity, and air movement, but also includes metabolic 
 rate and clothing effects. 
 
 Heat Stress Conditions in Mining 
 
 For the most part, heat stresses in undergound mines 
 with adequate ventilation are not excessive. The major prob- 
 lem encountered in underground mining is high humidity, 
 which reduces the body's capacity to dissipate heat by 
 evaporation. Crooks (11) surveyed underground metal- 
 nonmetal worksites in the United States and found the dry 
 bulb temperature averaged 62 ° F and ranged from 37 ° to 
 79° F. Relative humidities, however, averaged 70%, and 
 ranged from 13% to 99%. Over 25% of the worksites meas- 
 ured had relative humidities over 90%. The warmer, more 
 humid, and slower airflows were found in production and 
 development sites, where the heaviest physical labor occurs. 
 It is in such sites that heat strain becomes excessive if 
 precautions are not taken. 
 
 The wet bulb temperature in South African gold mines 
 (much deeper than U.S. mines) was reported on by Van der 
 Walt (46). Average temperature has been increasing for the 
 last 20 yr, probably because of mining at even greater 
 depths. It was estimated that half the total underground 
 workforce in South African gold mines works in areas where 
 the wet bulb temperature is above 86 ° F. This corresponds 
 to a dry bulb temperature of 88 ° F and 90% relative humid- 
 ity, or 92° F and 80% relative humidity. It is no wonder 
 that from 1969 to 1980, 205 heat stroke accidents were 
 recorded in South African gold mines, with 39 resulting in 
 fatalities. 
 
 Performance Effects of Heat Stress 
 
 There are several specific effects of heat stress that 
 reduce a worker's capability to perform efficiently and 
 safely. Excessive heat reduces a person's capacity to per- 
 form physically demanding work. In addition, the physically 
 demanding work increases the overall heat stress placed 
 on the individual. This results in reduced work output. The 
 performance of miners loading mine cars and of drilling rock 
 as a function of ambient temperature was reported on by 
 Misaqi (29). The results, presented in figure 8-12, show that 
 as temperature increased, performance declined rapidly. 
 
 Heat stress also reduces one's ability to remain alert 
 during lengthy and monotonous tasks, and reduces the 
 ability to make quick decisions. In addition, heat stress can 
 also, at times, contribute to frustration, anger, and other 
 emotions. These effects, combined with slippery sweaty 
 palms, dizziness, and fogging of safety glasses, can lead to 
 higher accident rates in heat stress environments. For ex- 
 ample, an investigation of the incidence of unsafe behaviors 
 in a variety of industries as a function of WBGT was 
 
112 
 
 reported on by Ramsey (34). The results, shown in figure 
 8-13, indicate a U-shaped relationship, with the least inci- 
 dence of unsafe behavior occurring between 62.6° F and 
 73.4° F WBGT. Above or below this optimum range, unsafe 
 behaviors increased. The effect was most pronounced for jobs 
 requiring moderate workloads, which represent most min- 
 ing jobs. It is usually the case that reducing heat stress can 
 pay off for everyone: reducing physiological stress on the 
 workers, increasing productivity, and reducing accidents. 
 
 100 
 
 80- 
 
 tf 60- 
 
 *: 
 rr 
 o 
 
 5 
 
 40- 
 
 20 
 
 - 
 
 X ' X ' 
 
 i i 
 
 - 
 
 _ 
 
 
 V .Rock drilling 
 
 - 
 
 - 
 
 Loading mine^^. 
 cars-^ 
 
 
 - 
 
 - 
 
 i i 
 
 i i 
 
 - 
 
 78 
 
 83 88 93 98 
 
 AMBIENT TEMPERATURE, ° F 
 
 103 
 
 Figure 8-12.— Effects of ambient temperature on miners 
 loading mine cars and drilling rock (29). (Courtesy ot us Mine safety 
 
 and Health Administration) 
 
 How Much Is Too Much 
 
 The National Institute for Occupational Safety and 
 Health (NIOSH), as discussed by Dukes-Dobos (14), has pro- 
 posed exposure limits based on the WBGT. These are simi- 
 lar to recommendations that have been accepted by the 
 American Conference of Governmental Industrial Hygien- 
 ists (1), the American Industrial Hygiene Association (2), 
 and the International Organization for Standardization (25). 
 Table 8-6 compares these standards for 8-h exposures at 
 various levels of workload. It should be pointed out that the 
 corrections for high-velocity airflow have been challenged 
 by some investigators as not necessary (22). The various 
 standards are very much in agreement, although the desig- 
 nations of light, moderate, and heavy workload differ 
 markedly. 
 
 Table 8-6.— Comparison of proposed 
 WBGT threshold values (35) 
 
 (Reprinted with permission by Taylor and Francis, Ltd) 
 
 
 Resting 
 
 Light 
 
 Moderate 
 
 Heavy 
 
 Very heavy 
 
 ACGIH: 
 
 
 
 
 
 
 Temperature . . °F . . 
 
 NP 
 
 86 
 
 80 
 
 NP 
 
 77 
 
 Energy . . . kcal/h . 
 
 NP 
 
 100-200 
 
 201-350 
 
 NP 
 
 350-500 
 
 AIHA: 
 
 
 
 
 
 
 Temperature. . °F. . 
 
 90 
 
 86 
 
 80 
 
 NP 
 
 NP 
 
 Energy . . . kcal/h . . 
 
 100 
 
 200 
 
 300 
 
 NP 
 
 NP 
 
 OSHA: 
 
 
 
 
 
 
 Temperature. . °F. . 
 
 NP 
 
 '86, 2 90 
 
 '82. 287 
 
 '79, 284 
 
 NP 
 
 Energy . . . kcal/h . . 
 
 NP 
 
 <200 
 
 201-300 
 
 >301 
 
 NP 
 
 ISO: 
 
 
 
 
 
 
 Temperature . . °F . . 
 
 91 
 
 86 
 
 82 
 
 '77, 279 
 
 '73. 2 77 
 
 Energy . . kcal/h . . 
 
 <100 
 
 100-201 
 
 201-310 
 
 310-403 
 
 >403 
 
 ACGIH American Conference of Governmental Industrial Hygienists. 
 
 AHIA American Industrial Hygiene Association. 
 
 NP Nothing proposed. 
 
 OSHA Occupational Safety and Health Administration. 
 
 ISO International Organization for Standardization. 
 
 1 Low-velocity ventilation. 
 
 2 High-velocity ventilation. 
 
 1.0 
 
 V) 
 
 o 
 
 .8 
 
 \ 
 
 \ — 
 
 KEY 
 
 Heavy workload 
 Moderate workload 
 - — - Light workload 
 
 41 50 59 68 77 86 
 TEMPERATURE (WBGT), °F 
 
 95 
 
 Figure 8-13.— Relationship between rate of unsafe behaviors 
 and wet-bulb-globe temperature (34). 
 
 Standards are also available for intermittent work in 
 a hot environment. These, however, diverge markedly, ac- 
 cording to Henschel (22), because there are very few data 
 available to provide guidelines. The relative physiological 
 impact of short and long heat exposures is not known, nor 
 is the extent of the effect of the rest area temperature on 
 strain or if short rest and short work periods result in the 
 same strain as long rest and long work periods. However, 
 if the continuous work recommended exposure levels are 
 adhered to, even for intermittent work, one would be confi- 
 dent of erring on the side of safety. 
 
 Protection From Heat Stress 
 
 A number of measures can be taken to protect workers 
 from heat stress. At a minimum, workers exposed to hot 
 environments should be given specific training in the symp- 
 toms and mechanism of heat stress, and how to protect 
 themselves against heat stress. Work done in hot environ- 
 ments can often be redesigned to reduce physical activity 
 and hard labor. Work should be mechanized where possi- 
 ble and paced to give frequent rest periods, and the overall 
 exposure time to heat should be minimized. Heavy physical 
 work in surface mining can often be scheduled for cooler 
 times of the day. Cool rest areas should also be provided 
 to maximize the benefits of rest. 
 
113 
 
 Workers must be supplied with fresh drinking water 
 and encouraged to drink, even if they are not thirsty. As 
 it turns out, thirst is not a good indicator of dehydration. 
 Water must be replenished on a regular basis, in quantities 
 that match the sweat loss incurred. If the workers eat nor- 
 mal meals and snacks, salt need not be added to the drink- 
 ing water, nor should salt tablets be used. The use of salt 
 in hot environments has a long history, but current evidence 
 strongly discourages this practice. Ingestion of salt actually 
 retards the acclimatization process, leads to high blood 
 pressure, and does not mitigate the negative effects of heat 
 stress (41). Recommendations by the American College of 
 Sports Medicine suggest that fluid loss should be replaced 
 with water having a 2.5% glucose (sugar) content. The tem- 
 perature of the replacement water should be 45° to 55° F. 
 
 Workers should be specifically selected to work in hot 
 environments; the following characteristics among workers 
 increase the likelihood of experiencing heat stress in hot 
 environments: 
 
 1. The taking of alcoholic drinks or narcotic drugs. 
 
 2. The taking of antihistamines or diuretic drugs. 
 
 3. Cardiovascular diseases. 
 
 4. Sickness, especially if vomiting and diarrhea are 
 symptoms. 
 
 5. Body weight less than 110 lb (47). 
 
 6. Over 45 yr of age (41). 
 
 7. Poor physical condition. 
 
 The work area should be redesigned, if feasible, to in- 
 crease airflow by installing fans, ventilation tubes, or air 
 conditioning. To shade surface workers from the sun, tent 
 covers can be erected. 
 
 Proper clothing should be insisted upon. On hot sunny 
 days, lightweight cotton shirts and pants reduce the radiant 
 heat load, and facilitate evaporation by soaking up sweat 
 and bringing it to the surface. Head covering is important 
 outdoors. Clothing should be loose fitting and not interfere 
 with evaporative heat loss. Under extreme conditions, ice 
 jackets can be worn to increase tolerance to heat stress (42). 
 
 Probably the most promising approach to reducing the 
 ill effects of heat stress is to institute a systematic accli- 
 matization program for those who must work in hot envi- 
 ronments. The Republic of South Africa has been a leader 
 in developing and testing various methods for efficiently 
 and safely acclimatizing workers and identifying those who 
 are at high risk (38, 41 , 43). Acclimatization is required for 
 workers who have to work in wet bulb temperatures of 82 ° 
 F or above. In South African mines, 0.25 million men must 
 undergo acclimatization each year. The acclimatization pro- 
 cedure involves several components: (1) climatic room ac- 
 climatization; (2) ascorbic acid (vitamin C) supplements; (3) 
 microclimate suits; and (4) heat tolerance testing. 
 
 The climatic room acclimatization involves working for 
 4 h/d at a metabolic load that is increased progressively from 
 150 kcal/(m 2 /h) on the first day to 240 kcal/(m 2 /h) on the 
 eighth day. The climatic room is controlled at 89 ° F wet 
 bulb. Workers are monitored for abnormal reactions and 
 given treatment if needed. Strydom (41) found that this pro- 
 cedure reduced the acclimatization period from 12 to 8 days, 
 and required only 4 h/d as against full shifts. 
 
 Workers are also given 250 mg of vitamin C per day, 
 starting before acclimatization and continuing throughout 
 the process. Results showed that acclimatization time was 
 reduced from 8 to 4 days; and, in addition, fewer men were 
 found to be heat intolerant. Without vitamin C, 3% to 5% 
 of the men could not acclimate; with vitamin C, less than 
 1% could not be acclimated. 
 
 Use of ice jackets (microclimate suits) was found to 
 reduce the ill effects of heat stress without retarding ac- 
 climatization. Results showed that workers would become 
 acclimatized to heat while doing their normal underground 
 tasks wearing an ice jacket for 6 days. Finally, a procedure 
 for screening workers to identify those who do not need ac- 
 climatization (the hyper-heat-tolerants) and those who 
 would not respond to acclimatization has been developed. 
 
 In South African mines, despite increased average work- 
 ing temperatures (due to mining at increased depths), 
 Strydom (41) found that heat stroke cases have steadily 
 declined over the last 20 yr, due in great part to the 
 widespread use of systematic acclimatization procedures. 
 
 COLD STRESS 
 
 As the ambient temperature declines, the body takes 
 defensive actions to maintain its thermal balance. The first 
 defense is to constrict the blood vessels in the skin and ex- 
 tremities, thereby keeping the warm core blood away from 
 the cold surface. A second defense is shivering^hich serves 
 to increase metabolic heat production and hence reduce or 
 halt overall heat loss. Excessive fluid loss can also occur 
 in cold environments, and cold-induced dehydration may 
 persist for several days. 
 
 The body can tolerate more cold stress than heat stress. 
 Deep-body temperature can decline to 78° F before death 
 occurs. There have even been cases of people (usually 
 children) who have survived bodv cooling to 60 ° F if the 
 drop occurred rapidly. 
 
 Whereas there are a host of competing indexes of heat 
 stress, there is really only one index of cold stress: windchill 
 index (or temperature). Table 8-7 presents the temperature 
 equivalent of various combinations of local temperature and 
 wind speed as given by Siple and Passel (40). 
 
 Table 8-7.— Equivalent temperatures based on windchill 
 index (40), degrees Fahrenheit 
 
 (Reprinted with permission by American Philosophical Society) 
 
 Air temp °F. 
 
 Calm 
 
 5-mph wind 
 
 10-mph wind 
 
 20-mph wind 
 
 30-mph wind 
 
 40-mph wind 
 
 40 
 
 40 
 37 
 28 
 18 
 13 
 10 
 
 20 
 
 20 
 
 16 
 
 4 
 
 -10 
 
 -18 
 
 -21 
 
 10 
 
 10 
 6 
 
 -9 
 -25 
 -33 
 -37 
 
 
 
 -5 
 
 -21 
 
 -39 
 -48 
 -53 
 
 -10 
 
 -10 
 -15 
 -33 
 -53 
 -63 
 -69 
 
 -20 
 
 -20 
 -26 
 -46 
 -67 
 -79 
 -85 
 
 Frostbite 
 
 One common disability caused by exposure to cold is 
 frostbite; i.e., localized freezing of body tissue. Frostbite can 
 be either superficial, involving only the skin, or deep, 
 extending below the skin. At a windchill temperature of 
 -25 ° F, exposed flesh may freeze within a minute. A tem- 
 perature of 5 ° F and a 15-mph wind combine to create such 
 a condition. 
 
 Performance Effects of Cold 
 
 Cold, even if not severe enough to cause body cooling, 
 can still affect performance, especially that involving motor 
 skills and cognitive ability. For example, whenever hand 
 
114 
 
 skin temperature falls below about 68° F, manual dexter- 
 ity deteriorates rapidly. Tasks that require use of handtools 
 or small parts are most affected by the cold. Localized warm- 
 ing of the hands, however, can reduce the negative effects 
 of cold on performance. However, if the entire body is not 
 kept warm, general body shivering will interfere with the 
 performance of fine motor-hand coordination tasks. 
 
 The results dealing with the effects of cold in cognitive 
 performance are less clear cut than those on motor per- 
 formance. Cold is likely to decrease the performance of 
 complex mental tasks that contain an element of time 
 estimation (time seems to go more slowly in the cold), due 
 to the distraction caused by the cold stress. 
 
 Protection From Cold Stress 
 
 It appears that little acclimatization to cold takes place, 
 except in the case of extremely long-term exposures. The 
 best protection is clothing that remains dry and insulates 
 the worker against the cold. Localized warming of the hands 
 using heat lamps may be beneficial under certain condi- 
 tions. Adequate diet, high in carbohydrates, fats, and pro- 
 tein, is also important to fend off the effects of cold. 
 
 DISCUSSION 
 
 This chapter has briefly reviewed the effects of illumina- 
 tion, noise, whole-body vibration, and climate on miner 
 health and performance. It is important to remember that 
 in the mining industry, combinations of environmental 
 stressors exist. Mining machines generate noise and vibra- 
 tion and are often used in low-light environments. In many 
 cases, these environmental factors can produce levels of 
 stress that seriously degrade performance and compromise 
 employee health. Technologies are available for controlling 
 such environmental factors and their application is well 
 within the state-of-the-art. What is needed on the part of 
 the mining industry is a more active awareness of the 
 severity of the problem and a commitment to reduce it. 
 
 REFERENCES 
 
 1. American Conference of Governmental Industrial Hygienists 
 (Cincinnati, OH). Threshold Limit Values for Chemical Substances 
 and Physical Agents in the Workroom Environment With Intended 
 Changes for 1987-88. 1987, 114 pp. 
 
 2. American Industrial Hygiene Association (Akron, OH). 
 Heating and Cooling for Man in Industry. 2d ed., 1975, 147 pp. 
 
 3. Antecaglia, J., and A. Cohen. Extra Auditory Effects of Noise 
 as a Health Hazard. Sec. in Noise and Hearing Conservation. Am. 
 Ind. Hygiene Assoc, Akron, OH, 1981, pp. 11-15. 
 
 4. Atherley, G., and W. Noble. Effects of Ear Defenders (Ear 
 Muffs) on the Localization of Sound. Brit. J. Ind. Medicine, v. 27, 
 1970, pp. 260-265. 
 
 5. Bartholomae, R.C., and R.P. Parker. Mining Machinery Noise 
 Control Guidelines, 1983. BuMines Handbook, 1983, 87 pp. 
 
 6. Belding, H, and T. Hatch. Index for Evaluating Heat Stress 
 in Terms of Resulting Physiological Stress. Heating, Piping, and 
 Air Conditioning, v. 27, 1955, pp. 129-136. 
 
 7. Bell, C, M. Crowder, and J. Walters. Duration of Safe Ex- 
 posure for Men at Work in High Temperature Environments. 
 Ergonomics, v. 14, 1971, pp. 733-757. 
 
 8. Bobick, T., and D. Giardino. Noise Environment of the 
 Underground Coal Mine. MSHA IR 1034, 1976, 26 pp. 
 
 9. Botsford, J. A Wet Globe Temperature for Environmental Heat 
 Measurement Am. Ind. Hygiene Assoc. J., v. 32, 1971, pp. 1-10. 
 
 10. Cain, R., and R. Pettry. Investigation of Medical Costs Cor- 
 responding to Various Injuries in the Coal Industry and Subsequent 
 Implications of the Need for Ergonomic Research (Paper in Pro- 
 ceedings of the 1984 International Conference on Occupational 
 Ergonomics, May 7-9, 1984). Human Factors Assoc, of Canada, 
 Toronto, Canada, 1984, pp. 462-465. 
 
 11. Crooks, W.W., K.L. Drake, T.J. Perry, N.D. Schwalm, B.F. 
 Shaw, and B.R. Stone. Analysis of Work Areas and Tasks To 
 Establish Illumination Needs in Underground Metal and Nonmetal 
 Mines. Volume I of II (contract J0387230, Perceptronics Inc.). 
 BuMines OFR 11HD-81, 1980, 254 pp.; NTIS PB 81-236804. 
 
 12. Crooks, W. and J. Peay. Definition of Illumination Re- 
 quirements for Underground Metal and Nonmetal Mines. Paper 
 in Mine Illumination. Proceedings: Second International Mine 
 Lighting Conference of the International Commission on Illumina- 
 tion (CIE); comp. by K.L. Whitehead and W.H. Lewis. BuMines IC 
 8886, 1982, pp. 319-333. 
 
 13. Daniel, J.H., J.A. Burks, R.C. Bartholomae, R. Madden, and 
 E.E. Ungar. The Noise Exposure of Operators of Mobile Machines 
 in U.S. Surface Coal Mines, 1979. BuMines IC 8841, 1981. 24 pp. 
 
 14. Dukes-Dubos, F., and A. Henschel. Development of Permissi- 
 ble Heat Exposure Limits for Occupational Work. ASHRAE J., v. 
 15, 1973, pp. 57-62. 
 
 15. Eastman, A. A New Contrast Threshold Visibility Meter. Il- 
 luminating Eng., v. 63, 1968, p. 37. 
 
 16. Gagge, A., J. Stolwijk, and Y. Nishi. An Effective Tempera- 
 ture Scale Based on a Simple Model of Human Physiological 
 Regulatory Response. Am. Soc. of Heating, Refrigeration, and Air 
 Conditioning Eng., New York, 1970, 22 pp. 
 
 17. Galaitsis, A., and T. Bobick. Noise Control of an Underground 
 Mine Personnel Carrier. Noise Control Eng. J., v. 21, No. 1, 1983. 
 pp. 4-9. 
 
 18. Giardino, D., and L. Marraccini. Noise in the Mining 
 Industry-An Overview. MSHA IR 1129, 1981, 10 pp. 
 
 19. Goldstein, R. An Interactive Computer System for Evaluating 
 Coal Mine Illumination (contract S0271041, Mathematical Applica- 
 tions Group Inc.). BuMines OFR 110-80, 1980. 21 pp.; NTIS PB 
 81-125528. 
 
 20. Modifications Made to an Interactive Computer 
 
 System for Evaluating Coal Mine Illumination (contract H0282038. 
 Mathematical Applications Group Inc.). BuMines OFR 101-81, 
 1980, 27 pp.; NTIS PB 81-236754. 
 
 21. Grandjean, E. Fitting the Task to the Man: An Ergonomic 
 Approach. Taylor and Francis, 1981, 379 pp. 
 
 22. Henschel, A. Comparison of Heat Action Levels. Paper in 
 Proceedings of NIOSH Workshop on Recommended Heat Stress 
 Standards, ed. by F. Dukes-Dubos and A. Henschel. NIOSH. Cin- 
 cinnati, OH, DHHS. 81-108, 1980. pp. 21-31. 
 
 23. Kaufman, J.E. (ed.). IES Lighting Handbook: Reference 
 Volume. Illuminating Eng. Soc. of North America, 1981, 481 pp. 
 
 24. International Organization for Standardization (Paris, 
 France). Guide for the Evaluation of Human Exposure to Whole- 
 Body Vibration. ISO 2631, 1974, 15 pp. 
 
 25. Hot Environments-Determination of the Web Bulb 
 
 Globe Temperature (WBGT) Heat Stress Index. ISO-DIS 7243. 1981, 
 18 pp. 
 
 26. Jensen. P., C. Jokel, and L. Miller. Industrial Noise Control 
 Manual (Rev.). NIOSH. Cincinnati. OH. DHHS 79-117. 1978. 173 
 
 PP- 
 
 27. Jensen, R., and D. Heins. Relationships Between Several 
 Prominent Heat Stress Indices. NIOSH. Cincinnati. OH. DHHS 
 77-109, 1976, 372 pp. 
 
 28. Merritt, J.O., T.J. Perry, W.H. Crooks, and J.E. Uhlaner. 
 Recommendations for Minimal Luminance Requirements for Metal 
 and Nonmetal Mines (contract J0318022. Perceptronics Inc. I 
 BuMines OFR 65-85, 1983, 236 pp.: NTIS PB $5-215689. 
 
 29. Misaqi, F. Heat Stress in Mining. MSHA SM 6. 1977. 34 pp. 
 
 30. Morris, L., R. Graves, and A. Nicholl. An Ergonomic Ap- 
 proach to the Assessment of Thermal Conditions in the Mining In- 
 dustry. Paper in Proceedings of the Ergonomics Society Conference 
 1983, Coudau, UK, Sept. 15-18. 1983; ed. by K. Coombes. Taylor 
 and Francis. 1983. pp. 77-81. 
 
115 
 
 31. National Institute for Occupational Safety and Health (Cin- 
 cinnati, OH). Survey of Hearing Loss in the Mining Industry. DHHS 
 76-172, 1976, 145 pp. 
 
 32. Nguyen, P. Mine Company Finds Ear Muffs Overrated by 
 Manufacturer. Natl. Saf. Coun. Min. Newsletter, Nov. -Dec. 1984, 
 p. 6. 
 
 33. Oborne, D. Ergonomics at Work. Wiley, 1982, 321 pp. 
 
 34. Ramsey, J., C. Burford, M. Beshir, and R. Jensen. Influence 
 of Thermal Environment on Safety Behavior. Ergonomics, v. 25, 
 No. 6, 1982, p. 528. 
 
 35. Ramsey, J., and C. Chai. Inherent Variability in Heatstress 
 Decision Rules. Ergonomics, v. 26, 1983, pp. 495-504. 
 
 36. Remington, P.J., D.A. Andersen, and M.N. Alakel. Assess- 
 ment of Whole Body Vibration Levels of Coal Miners. Volume II: 
 Whole Body Vibration Exposure of Underground Coal Mining 
 Machine Operators (contract J0308045, Bolt Beranek and Newman 
 Inc.). BuMines OFR 1B-87, 1984, 114 pp.; NTIS PB 87-144119. 
 
 37. Sataloff, J., and P. Michael. Hearing Conservation. Charles 
 C. Thomas, 1973, 376 pp. 
 
 38. Schutte, P., J. Hitge, A. Kielblock, and N. Strydom. Produc- 
 tive Acclimatization: II. A Code of Practice for Heat Tolerance 
 Testing and Micro-climate Acclimatization (Rev.). Chamber of 
 Mines, Johannesburg, South Africa, Rep. 5/82, 1982, 17 pp. 
 
 39. Simons, A., A. Radke, and W. Oswald. A Study of Truck Ride 
 Characteristics -in Military Vehicles. Bostrom Res. Lab., 
 Milwaukee, WI, 1956, 123 pp. 
 
 40. Siple, P., and C. Passel. Movement of Dry Atmospheric Cool- 
 ing in Subfreezing Temperature. Proc. Am. Philosophical Soc, v. 
 89, 1945, pp. 177-199. 
 
 41. Strydom, N. Developments in Heat-Tolerance Testing and 
 Acclimatization Procedures Since 1961. Paper in Proceedings of 
 the 12th CMMI Congress, ed. by H. Glen. Geol. Soc. South Africa, 
 Johannesburg, South Africa, Chamber of Mines, 1982, pp. 235-241. 
 
 42. Strydom, N., D. Mitchell, A. Van Rensburg, and C. Van 
 Graan. The Design, Construction, and Use of a Practical Ice- Jacket 
 for Miners. J. South African Inst. Min. and Metall, v. 75, 1974, pp. 
 34-37. 
 
 43. Strydom, N., P. Schutte, and A. Kielblock. Productive Ac- 
 climatization: I. A Code of Practice for the Selection of Workers 
 Based on Physical Work Capacity (Rev.). Chamber of Mines, Johan- 
 nesburg, South Africa, Rep. 49/81, 1981, 7 pp. 
 
 44. Trotter, D. The Lighting of Underground Mines. Gulf, 1982, 
 216 pp. 
 
 45. U.S. Mine Safety and Health Administration. Handbook of 
 Underground Coal Mine Illumination Requirements. 1980, 30 pp. 
 
 46. Van der Walt, W. A Survey of the Incidence of Heat Stroke 
 in the Gold Mining Industry over the Period 1969 to 1980. Chamber 
 of Mines, Johannesburg, South Africa, Rep. No. 15/81, 1981, 41 pp. 
 
 47. Van Graan, C. Some Applications of Ergonomics in the South 
 African Mining Industry. South African Mech. Eng., v. 24, 1974, 
 pp. 282-289. 
 
 48. Wasserman, D. Occupational Vibration Studies in the U.S.— 
 A Review. Sound and Vibration, v. 14, 1980, pp. 21-24. 
 
 49. Whitehead, K.L., and W.H. Lewis. Paper in Mine Illumina- 
 tion. Proceedings: Second International Mine Lighting Conference 
 of the Commission on Illumination (CIE); comp. by K.L. Whitehead 
 and W.H. Lewis. BuMines IC 8886, 1982, pp. 1-10. 
 
116 
 
 CHAPTER 9.— TRAINING 
 
 Training is an important and expensive enterprise in the mining industry. 
 
 Human factors seeks to modify the job to fit the person, 
 while training seeks to modify the person to fit the job— in 
 this sense the two oppose one another. Conversely, a well- 
 designed (human-factored) job reduces the requirements for 
 training, and an effective training program can reduce the 
 human factors design requirements— in this sense they 
 complement one another. It would be impractical, if not im- 
 possible, to design a job in such a manner that no training 
 was required. By the same token, it would be extremely un- 
 wise to expect the training function to overcome all human 
 factors deficiencies present in the design of a job. The fact 
 is that both human factors and training are necessary for 
 efficient and safe operations. 
 
 Both human factors and training seek to change be- 
 havior; human factors does it through design, while train- 
 ing does it by modifying skills, knowledge, and attitudes. 
 In addition to the commonality of goals, human factors also 
 has a role in the design of effective training programs. A 
 training program can be viewed as any other system, and 
 human factors can contribute to the design of such a system. 
 Human factors has contributed to (1) the design of train- 
 ing hardware, such as simulators and training aids, (2) 
 determining training needs, and (3) evaluating the effec- 
 tiveness of the training programs. 
 
 Training is an important and expensive enterprise in 
 the mining industry. In 1983, for example, the U.S. mineral 
 industry employed over 400,000 miners and provided ap- 
 proximately 4.5 million hours of formalized health and 
 safety instruction. In addition, the U.S. mining industry pro- 
 vided over 80,000 miners with occupational training to 
 support organizational goals and comply with Federal and 
 State training requirements. The mining industry spends 
 
 approximately $200 million on new hire, refresher, and 
 occupational training per year (2D. 1 
 
 EFFECTIVENESS OF TRAINING 
 
 Assessing the effect of training on behavior is a difficult 
 task in the operational environment. Several problems pre- 
 sent themselves that make the interpretation of results dif- 
 ficult. First is the problem of defining what is meant by 
 training. Often, a training program involves several com- 
 ponents, including classroom training, on-the-job training, 
 and company support programs such as safety campaigns. 
 It is difficult to determine which components of a program 
 are effective and which are not. 
 
 A second problem is one of experimental control. Often, 
 a control group (i.e., untrained miners) is not used, mak- 
 ing it impossible to determine what the injury or produc- 
 tion rates would have been without the training. Usually, 
 only before- and after-training measurements are made. 
 Factors in the work setting, other than training, may have 
 changed at the same time that training was started and 
 could have influenced safety or productivity. 
 
 A third problem is that the measures used to evaluate 
 the effect of training may not be sensitive enough to detect 
 real changes in behavior. Both injury rate and production 
 rate are influenced by all sorts of factors, including luck, 
 or lack of it. A crew may be working more safely and more 
 efficiently, but because of extenuating circumstances (e.g., 
 
 1 Italic numbers in parentheses refer to items in the list of reference* at 
 the end of this chapter. 
 
117 
 
 poor roof conditions, equipment breakdown, outbreak of flu), 
 its safety and productivity records do not reflect the positive 
 effects of training. 
 
 With these problems in mind, a review is made of a few 
 studies that have attempted to assess the effects of train- 
 ing on behavior. One conclusion from the literature is that 
 generalized training is not as effective as training targeted 
 to change specific behaviors. A second conclusion is that 
 a coordinated, multifaceted program, involving classroom 
 training, on-the-job training, and followup, is more effec- 
 tive than a single-shot training experience. 
 
 The results of a maintenance training program in South 
 African mines were reported by Robertson (22). In a 3-week 
 course, rock cutter operators were trained to diagnose faults 
 in their machines using a step-by-step troubleshooting pro- 
 cedure, and to repair the malfunctions without aid from 
 maintenance workers. Maintenance worker involvement in 
 repairs decreased from 46% to 3%. Average repair times 
 were reduced by 21%, and productivity increased by 30%. 
 
 The outcome of a forklift training program targeted at 
 specific unsafe behaviors was discussed by Cohen (5). The 
 program involved a classroom presentation of incorrect and 
 correct ways to handle specific hazardous situations, group 
 discussion of the recommended behaviors, and a final test 
 in which all members of the group scored each other as they 
 performed a series of tasks using a forklift. In addition, on- 
 the-job daily feedback in the form of verbal and posted 
 summaries of group performance (percentage of correct 
 behaviors on the job) was given to the group. The super- 
 visor, in a positive, constructive, and confidential manner, 
 coached the workers on correct work procedures. Results 
 showed reductions in unsafe behaviors of 70% and 40% at 
 two separate companies where the program was applied. 
 
 A structured 2- to 3-day training program with on-the- 
 job training, using a continuous miner simulator, was 
 reported by Morris (19). After training, production increased 
 an average of 7.15 st per month, per unit-shift. 
 
 The results of a study conducted at four salt mines in 
 which supervisors were trained to use social reinforcement 
 (praise) to increase safe behaviors were presented by Uslan 
 (27). The training program was general in nature, rather 
 than targeted to specific behaviors. Eye, hand, and back in- 
 juries were monitored before and after training of the super- 
 visors. The results were mixed. Injuries declined at two 
 mines, remained relatively stable at one, and increased in 
 the other mine. The lack of clearcut results was probably 
 due, in part, to the nonspecific nature of the training, and 
 to the fact that the training was directed toward changing 
 the behavior of supervision rather than that of the workers. 
 
 TRAINING: WHAT IS REQUIRED 
 
 In the United States, miner training regulations are 
 described in the Federal Mine Safety and Health Act of 
 1977, as amended. In addition, some States have also es- 
 tablished regulations for miner training. A brief review of 
 the essential features of these requirements will be pre- 
 sented as well as a comparison with those set forth in other 
 countries. This section should not be considered a complete 
 review of existing regulations, nor should it serve as a 
 substitute for the actual regulation of governing bodies. 
 
 Training Requirements in the United States 
 
 The Federal training regulations for new underground 
 miners set forth a minimum of 40 h of training, of which 
 32 h are classroom training and 8 h are at the jobsite. Eight 
 hours of training must be received before a new miner can 
 go underground. For new surface miners, Federal regula- 
 tions specify only a minimum of 32 h of training, of which 
 8 h occur before miners begin their actual work assign- 
 ments. In addition, 8 h of annual refresher training is re- 
 quired of all miners. The topics required for training new 
 miners, newly employed experienced miners, and annual 
 refresher training are listed in table 9-1 for both under- 
 ground and surface mining (9). 
 
 Besides the Federal training regulations, some States 
 impose additional requirements. Of the 15 States that pro- 
 duce coal in the United States, only five have requirements 
 beyond the Federal regulations. Kentucky requires 90 work- 
 ing days of experience, within sight and sound of a certified 
 miner, followed by an examination for certification. Indiana 
 requires a 6-month apprenticeship with an experienced 
 miner before a new miner can work alone. Pennsylvania 
 requires 1 yr of apprenticeship under close supervision, 
 followed by an oral, practical examination. Illinois requires 
 a 1- to 2-yr (maximum) apprenticeship, followed by oral and 
 written examinations, and first-aid and mine rescue train- 
 ing; those with an associate degree in coal mine technology 
 or a bachelor's degree in engineering can waive 6 months 
 of apprenticeship. West Virginia requires 80 h of instruc- 
 tion, followed by an examination to qualify as an apprentice; 
 the new employee then works 6 to 8 months (maximum), 
 within calling distance of a foreman, assistant foreman, or 
 designated experienced miner (20). 
 
 Training Requirements in Other Countries 
 
 An excellent review of training requirements and prac- 
 tices in foreign countries was provided by McAteer (16). No 
 attempt will be made to provide all the details of the various 
 foreign training requirements here, only brief overviews 
 for a few of the major European countries will be given. 
 
 Great Britain has some of the most comprehensive train- 
 ing requirements of any country. New miners must receive 
 100 days of training before they can work underground, and 
 they cannot work within 30 ft of the face until they have 
 completed 120 days of training. To become a certified miner 
 requires 3 yr, including over 300 days of formal instruction 
 and 100 days of work under constant supervision. 
 
 The Federal Republic of Germany requires a 3-yr ap- 
 prenticeship, including formal schooling 3 days per week. 
 Six months of training is required before a miner is per- 
 mitted to work underground. In addition, 20 days of above- 
 ground training, under simulated mining conditions, is also 
 required. When workers are away from their jobs for 6 
 months, 20 days of training is required (10 classroom and 
 10 at the face) before they can resume work. 
 
 In Poland, prospective miners enter mining school at 
 the age of 14 or 15 and take 3 yr of classroom and job in- 
 struction. A 3-yr apprenticeship is required, including 200 
 h of training at a mine training center. Sixteen hours of 
 annual refresher training is required of all miners. 
 
118 
 
 Table 9-1 .—Content of underground and surface mine health and safety training, by type (9) 
 
 Topic 
 
 Introductory for — 
 
 New 
 miners 
 
 Newly em- 
 ployed expe- 
 rienced miners 
 
 Annual 
 
 refresher 
 
 for working 
 
 miners 
 
 UNDERGROUND 
 
 Statutory rights and responsibilities of supervisors 
 
 Self-rescuer and respiratory devices 
 
 Entering and leaving the mine, transportation, communication 
 
 Introduction to the work environment 
 
 Mine map, escapeways, emergency evacuation, barricading . . 
 
 Roof and ground control, ventilation plans 
 
 Health 
 
 Cleanup, rock dusting 
 Hazard recognition . . . 
 Electrical hazards .... 
 First aid 
 
 Mine gases 
 
 Health and safety aspects of assigned tasks . 
 
 Mandatory health and safety standards 
 
 Prevention of accidents 
 
 Explosives 
 
 SURFACE 
 
 Statutory rights and responsibilities of supervisors 
 
 Self-rescue and respiratory devices 
 
 Transportation and communication 
 
 Introduction to the work environment 
 
 Escape and emergency evacuation, firewarning and firefighting 
 
 Ground control, highwalls, water hazards, pits and spoil banks, illumination and night work 
 
 Health 
 
 Hazard recognition 
 
 Electrical hazards 
 
 First aid 
 
 Explosives 
 
 Health and safety aspects of assigned tasks 
 
 Mandatory health and safety standards 
 
 Prevention of accidents 
 
 France has no specific training requirements. However, 
 training usually includes 2 weeks of surface classroom train- 
 ing and an examination, 3 to 4 months of training at an 
 underground training face, and 2 to 3 months of working 
 under close supervision at an actual production face. 
 
 Discussion 
 
 From even this short overview of training requirements, 
 it is obvious that the U.S. requirements fall short of those 
 in other countries. Some authorities suggest that this ac- 
 counts, in great part, for the lower injury and fatality rates 
 per million labor-hours experienced by European countries. 
 The fact that so many countries do require extensive new- 
 miner training and apprenticeship suggests that more could 
 be done in the United States to instill good working habits 
 in new miners. 
 
 TRAINING PRACTICES IN THE UNITED STATES 
 
 In the previous section, training requirements in the 
 United States and other countries were discussed. In this 
 section, a brief overview of U.S. training practices is pre- 
 sented. In essence, this is how the mining industry is 
 meeting and, in many cases, exceeding the training require- 
 ments placed on it by the Government. Over the years, a 
 few studies have attempted to summarize the mining in- 
 dustry's training experiences. Training at over 300 mines 
 
 was reviewed by Adkins (7), while Digman (9) reviewed 
 classroom training practices at 14 sites. Major sources of 
 mine-related training in the United States were reviewed 
 by Short (24). Several general themes emerge from these 
 reports. 
 
 1. The first-line supervisor plays a central role in most 
 training programs conducted by the mines. 
 
 2. There is a danger that technical compliance with 
 Government training regulations assumes more importance 
 than the goal of reducing mine accidents. 
 
 3. There is tremendous diversity among programs in 
 terms of resources allocated, methods used, competency of 
 instructors, and use of followup methods. 
 
 4. Instructional skills among trainers seem to be less well 
 developed than are technical skills. 
 
 5. On-the-job training is used extensively , but is often dif- 
 ficult to monitor, correct, or improve when it is inadequate. 
 
 6. Training is provided by mine companies, vocational 
 schools, State agencies. Mine Safety and Health Adminis- 
 tration (MSHA), equipment manufacturers, consultants, 
 and trade associations, with mining companies providing, 
 far and away, the majority of the training. 
 
 7. It is difficult to demonstrate, statistically, that one 
 training method is better than another for reducing 
 accidents. 
 
 Keeping in mind the diversity of training that exists 
 in the mining industry. Adkins (1\ nevertheless, repre- 
 sented a typical new underground miner indoctrination 
 training experience. The description is worthwhile and is 
 
119 
 
 reproduced here to give a conception of the methods used 
 
 most often in miner training. 
 
 The process begins with the personal safety equip- 
 ment—hard hat, protective glasses, safety boots, leg 
 bands, belt and self rescuer. The new man is shown, 
 lectured on, and issued this equipment. Use of the self 
 rescuer is shown in film, on poster and demonstrated 
 by each individual, and then, as shown by too many 
 disasters, forgotten. Next comes a brief introduction 
 to the mine environment (including the geology, mine 
 plan, ventilation, roof control and mining methods) 
 through lectures aided by various slides, films or 
 tapes, posters, mock-ups, and charts. This will be 
 followed by a mine tour to illustrate and reinforce 
 what the new man has been told by the instructor in 
 the classroom. 
 
 Most new employee programs continue the indoc- 
 trination with lectures and demonstrations covering 
 the topics of oxygen deficiency and methane detection 
 devices and first aid. Films, posters, and simulation 
 devices are used to supplement the lecture presenta- 
 tions and to give the student an opportunity for 
 "hands on" experience, as feasible. More lectures from 
 various company departments on organizations and 
 policy, and from state and union representatives on 
 the local laws and working agreement, plus some 
 qualification testing, will constitute the balance of 
 new employee indoctrination. Other than exposure to 
 slogans and either monthly (the usual case) or weekly 
 safety meetings, the average miner will not receive 
 any more classroom training unless he needs annual 
 qualification or moves on to maintenance or supervi- 
 sion duties. 
 
 CHARACTERISTICS OF SUCCESSFUL 
 SAFETY PROGRAMS 
 
 There have been several attempts to identify character- 
 istics of successful safety programs. The approach taken has 
 been to either examine exemplary safety programs or to 
 compare companies having high and low accident rates. For 
 example, 192 Wisconsin factories with high and low acci- 
 dent rates were compared by Cohen {4); two successful task 
 training programs in two open-pit taconite mines were 
 described by Couillard (6); and safety directors of 12 coal 
 companies that had won awards for extended periods of 
 work without lost-time injury were interviewed (8). In ad- 
 dition to these studies, a review of the literature available 
 up to 1977 was provided by Cohen (3). 
 
 These various studies and reviews show remarkable con- 
 sistency with respect to the characteristics of successful 
 safety programs. One conclusion that stands out is that 
 there is more to a successful safety program than just train- 
 ing. For purposes of this presentation, the characteristics 
 of successful safety programs will be divided into three 
 classes: management, training and incentives, and accident 
 reduction. 
 
 Management 
 
 The most consistent finding in all the studies investi- 
 gating successful programs is management commitment. 
 Top management must be sincerely committed to reducing 
 
 injuries, and be willing to back up that commitment with 
 resources and support. Other management-related charac- 
 teristics of successful programs reported in the literature 
 follow. 
 
 1. Safety personnel were part of top management, and 
 adequate staff was available to carry out the safety func- 
 tion. The ranking safety official was not subordinate to pro- 
 duction personnel. 
 
 2. Active safety committees were supported by manage- 
 ment, and there were provisions for short, daily safety 
 meetings. 
 
 3. Close, frequent contacts between workers and super- 
 visors or foremen were evident, enabling open communica- 
 tion on safety and other job-related matters. 
 
 4. A more humanistic attitude toward disciplining vio- 
 lators of safety rules was evident. In disciplinary actions, 
 measures other than suspension were used more often. 
 
 5. There existed a well-developed selection and job place- 
 ment system that matched worker capabilities to job 
 demands. 
 
 Training and Incentives 
 
 Several factors emerged from the literature relative to 
 the conduct of training and safety incentive programs. 
 
 1. Formal training must be reinforced, on the job, by first- 
 line supervisors. 
 
 2. A mixture of different safety activities (e.g., training, 
 safety promotional campaigns, off-the-job safety activities, 
 inspections) is more effective than concentrating on only 
 a few. 
 
 3. Trainers must be trained to train. 
 
 4. The primary goal of training should be improved job 
 performance, of which safety is one part. 
 
 5. There must be a readiness to change and modify train- 
 ing programs to keep up with changing needs. 
 
 6. Training programs should be competency-based so that 
 workers are evaluated on their ability to perform their jobs. 
 
 7. Greater opportunities should be made available for 
 general and specialized job and safety training. 
 
 8. Greater efforts must be made to influence the safety 
 consciousness of workers by enlisting family and community 
 involvement in company safety campaigns. 
 
 Accident Reduction 
 
 Successful programs usually include activities designed 
 to reduce accidents, such as the following. 
 
 1. High levels of housekeeping and orderly workplace 
 conditions. 
 
 2. Application of engineering controls, as well as non- 
 engineering techniques, to reduce accidents. (Engineering 
 controls include good human factors design of equipment, 
 environments, and procedures.) 
 
 3. More frequent formal inspections of worksites. 
 
 4. Continual examination and modification of safety rules 
 to improve their effectiveness. 
 
 5. Well-developed procedures for reporting and investi- 
 gating accidents. 
 
 Undoubtedly, all of these factors contribute to a success- 
 ful program. Unfortunately, it is not possible to say which 
 factors are the most critical or which are simply the conse- 
 quence of others. Management commitment, however, is 
 
120 
 
 probably the most important factor, because all the others 
 are dependent on management approval. 
 
 BASIC CONCEPTS IN HUMAN LEARNING 
 
 There exists a vast amount of research literature, span- 
 ning more than 100 yr, that deals with human learning. 
 For the most part, the research involves laboratory studies 
 of relatively simple learning tasks. The applicability of 
 much of the literature to complex, real-world learning situa- 
 tions is tenuous. Over the years, there have been numerous 
 attempts at developing theories to explain human learn- 
 ing; but, unfortunately, none of them has accounted for all 
 the intricacies involved in the process. What has emerged 
 from the research literature and theory building is a set 
 of concepts and basic principles that appear to be valid in 
 a wide range of learning situations. The purpose of this sec- 
 tion is to introduce the more important concepts and prin- 
 ciples to provide a basis for understanding the learning 
 process and the role of training. 
 
 Learning Versus Performance 
 
 The learning process is never directly observed. Instead, 
 it is found that learning has taken place by observing an 
 individual's behavior prior and subsequent to experiences 
 called training. What this means is that it is not known 
 whether individuals have learned until they have per- 
 formed. The verbal statement, "I understand how to do 
 that," should not substitute for actual performance. A per- 
 son demonstrates the acquisition of a skill by performing 
 a skilled act. Any training method that does not provide 
 ample opportunity for the trainee to perform allows little 
 opportunity for the trainer, or trainee for that matter, to 
 determine what has been learned and what has not been 
 learned. 
 
 Performance Feedback 
 
 People usually do not make an effort to change or im- 
 prove their behavior unless they perceive that it needs to 
 be changed or improved. Job performance often deteriorates 
 so slowly that no one really notices. However, once workers 
 are made aware that their performance has deteriorated, 
 they usually improve quickly, assuming, of course, that they 
 have the skills and support necessary to improve. 
 
 To provide performance feedback requires that a per- 
 son's behavior be observed, quantified, and presented in a 
 meaningful way. For example, the mean time to complete 
 a task or number of reworks might be the type of perfor- 
 mance data to feed back to maintenance workers. The in- 
 cidence of unsafe behavior is an appropriate measure for 
 all workers. Whatever the performance measure used, it 
 must be observable so that it can be measured; quantifiable, 
 to permit the use of summary statistics; reliable, to the ex- 
 tent that everyone observing the behavior agrees whether 
 or not it occurred, or to what degree it occurred; and valid, 
 so far as it relates to the goal to be maximized, e.g., safety, 
 productivity, maintenance efficiency. 
 
 For example, a study in a bakery to assess the effec- 
 tiveness of training and performance feedback on the in- 
 cidence of safe behaviors was performed by Komaki (13). 
 The approach illustrates how performance feedback can be 
 used to modify behavior. First, accident reports were re- 
 viewed, hazards clearly defined, and workers closely ob- 
 
 served to determine which specific areas needed the most 
 attention. From this preliminary analysis, specific unsafe 
 behaviors were targeted for modification. This is an impor- 
 tant point; the training and feedback were not comprehen- 
 sive or general in nature, but rather dealt with a set of 
 explicit behaviors and situations. 
 
 To assess the effect of this program, baseline data were 
 collected for 5.5 weeks. During this period, the incidence 
 of safe behaviors was recorded. The intervention or treat- 
 ment involved a training component that consisted of a slide 
 presentation dealing with the hazards and tasks and showed 
 how to perform the tasks safely. A list of the safe behaviors 
 was given to each worker. This is also an important point; 
 training focused on what should be done, rather than just 
 what should not be done. Too often a safety training pro- 
 gram overstresses the negative, "don't do this, don't do 
 that," but never really tells the trainee what to do or how 
 to do it correctly. 
 
 In addition to the training, performance feedback was 
 given of the percentage of times safe behaviors were used 
 on the job. Workers were shown a graph of the results of 
 the baseline observations that indicated that they had been 
 performing safely about two-thirds of the time. The graph 
 was posted with an unplotted section to be completed as the 
 intervention phase progressed. The intervention phase 
 lasted for 11 weeks, at which time a reversal phase was 
 introduced. 
 
 During the reversal phase, feedback was discontinued, 
 but the list of safety reminders remained. Figure 9-1 shows 
 the results of the experiment. As can be seen, the incidence 
 of safe behavior improved dramatically during the interven- 
 tion period, and remained high until the performance feed- 
 back was discontinued during the reversal phase. In a subse- 
 quent study (14), the effect of safety training, apart from 
 performance feedback, was assessed. The study found that 
 while safety training alone resulted in improved perfor- 
 mance, training combined with feedback yielded even bet- 
 ter performance. Cohen (5), in a carefully developed study, 
 reported similar results for safe forklift operation. This 
 study, however, found that the incidence of safe behavior 
 remained high for months after feedback was discontinued. 
 This was attributed to the development of informal peer 
 
 RMrari 
 
 OBSERVATION PERIODS 
 
 Figure 9-1.— Results of an experiment that demonstrates ef- 
 fectiveness of performance feedback on incidence of safe 
 
 behaviors (13). (Copyright 1978 by the American Psychological Association and 
 reprinted by permission of the author) 
 
121 
 
 group norms that stressed and accepted the safe methods 
 of performing the job. In essence, the safe way became the 
 accepted, normal way of doing the work (the dream of every 
 safety director). 
 
 One of the most common findings about performance 
 feedback is that it affects motivation. Studies have shown 
 that compared to trainees given no feedback, those receiv- 
 ing some feedback were less bored, reported for training 
 more frequently on time, and had more favorable attitudes 
 toward the training. 
 
 The amount and the timing of feedback in the training 
 process is critical. Burdening a trainee with too much in- 
 formation may be as bad as not providing any information. 
 The new trainee may be able to absorb only a small amount 
 of information. Too much detail can be both confusing and, 
 because of initial inadequate performance, discouraging. 
 
 Reward and Punishment 
 
 A general axiom of human behavior is that people tend 
 to repeat behaviors that are rewarded (positive reinforce- 
 ment). The practical problem is that what is rewarding to 
 an individual is not always known. A person may engage 
 in a particular behavior for any of a number of reasons, such 
 as to receive positive recognition from a supervisor, to 
 reduce the time required to complete a task, to appear dar- 
 ing because he or she likes to take chances, or to receive 
 positive recognition from a work group engaging in the 
 behavior. To be effective, positive reinforcement should be 
 
 (1) given as soon as possible after a behavior has occurred, 
 
 (2) valued by the person, and (3) specific and directed to a 
 particular behavior. For example, being told by a supervisor 
 who is not respected that one has done a good job probably 
 would not be very reinforcing. Telling workers at the end 
 of shift that they did a good day's work would do little to 
 reinforce specific behaviors of individual workers. Providing 
 a year-end bonus is too far removed in time from the occur- 
 rence of the behaviors one is trying to reinforce to be very 
 effective. A bonus based on overall mine productivity or 
 safety probably is an ineffective reinforcer, because an in- 
 dividual worker cannot relate the reward to his or her 
 behavior. 
 
 One thing is certain, if a behavior has been reinforced 
 and reinforcement is discontinued, the behavior will disap- 
 pear. That is, the frequency of the behavior will decrease, 
 and eventually the behavior will subside. This is called ex- 
 tinction. It is important, therefore, that the work situation 
 be structured so that behaviors acquired during training 
 will be reinforced on the job by supervisors, coworkers, etc. 
 
 With respect to extinction of behaviors following cessa- 
 tion of reinforcement, it is well accepted that a behavior 
 will persist longer if the original reinforcement was inter- 
 mittent rather than continuous. In the real world, it is im- 
 possible for a supervisor to give positive reinforcement each 
 time a job is done well; and, in fact, it is probably better 
 that it not be done every time. Eventually, the supervisor 
 will not be able to reinforce the behavior; but, the behavior 
 will persist longer if the supervisor did not always reinforce 
 the worker in the past. 
 
 An example of the use of positive reinforcement to 
 change behavior comes from a study performed in four salt 
 processing plants by Uslan (27). First-time supervisors were 
 trained in the systematic application of positive reinforce- 
 ment in the form of verbal praise to increase the frequency 
 of safe work behaviors. The results indicated a reduction 
 
 in injuries at two sites and no reduction at the other two 
 sites. When the data were corrected for hours worked, a 
 third site showed a reduction in injuries. The results were 
 not overly dramatic; but, upon reflection, this is not sur- 
 prising. The problem was that the behaviors were the target 
 of the praise, but the number of accidents was the measure 
 used to assess the effects of the praise. The relationship be- 
 tween behaviors and accidents is not perfect. The reinforce- 
 ment may have been very effective in increasing the inci- 
 dence of safe behavior; but, due to other circumstances (e.g., 
 work practices, environmental conditions), accident rates 
 may not have decreased significantly. It is for this reason 
 that safety program effectiveness is better judged by assess- 
 ing the effect on behavior, rather than by tallying accidents. 
 An effective safety program would be expected to reduce 
 accidents, but assessing the effect on behavior provides a 
 more immediate and valid measure of effectiveness. Simi- 
 larly, a job skills training problem is better evaluated based 
 on behavior changes than on productivity. 
 
 The use of punishment is not the same as failing to rein- 
 force. The evidence suggests that punishment inhibits 
 behavior rather than eliminating it, as would be the case 
 for behaviors that are not reinforced. In the case of punish- 
 ment, a behavior that leads to the avoidance of the punish- 
 ment is reinforced. Often, failure to reinforce a negative 
 behavior may have a better long-range effect than would 
 a reprimand (punishment) from a trainer, even though the 
 reprimand gives the trainer some temporary relief or sat- 
 isfaction. There are at least three reasons for this. 
 
 1. Punishment may suppress a behavior, but the be- 
 havior may appear again if the source of punishment is not 
 present at a later time. 
 
 2. Punishment can be disruptive and have its effects on 
 larger behavioral segments than on an undesired behavior 
 itself. 
 
 3. Repeated punishment from the same person may have 
 the effect of altering the perception of that person, so that 
 he or she is avoided and loses his or her effectiveness as 
 a source of positive reinforcement. 
 
 Perhaps the most efficient use of punishment would be 
 to combine mild and informative punishment for an incor- 
 rect behavior with reward for a correct behavior. 
 
 Learning From Models and Examples 
 
 People learn vicariously through observing behavior of 
 others and the consequences of that behavior. The literature 
 on vicarious learning and its application to on-the-job train- 
 ing in the mining industry was reviewed by Thurlow (25). 
 The notion of a model involves a person or persons who set 
 a standard of performance that others try to attain. A model 
 can be a supervisor, coworker, relative, or famous person. 
 Research has found that people tend to favor models similar 
 to their own ability over those whose behavior they can 
 match only through great effort. People exposed only to high 
 standards are more likely to adopt them than people ex- 
 posed to conflicting standards. Further, the high standards 
 set by a model are less likely to be adopted by trainees if 
 the model imposes lenient standards on himself or herself. 
 
 The practical implications of this are that supervisors, 
 trainers, and other models should adopt a consistent stan-^ 
 dard of behavior; and they must be willing to meet that stan- 
 dard in their work. Telling workers to "do what I say, not 
 what I do," is unlikely to make much of a positive impres- 
 sion on them. 
 
122 
 
 METHODS OF TRAINING 
 
 Although there are many ways of categorizing training 
 methods, this section is organized by the degree to which 
 each method approximates the actual working conditions 
 under which a trainee will ultimately work. There are all 
 sorts of training methods, but this section will concentrate 
 on only six: classroom, part-task simulation, full-task 
 simulation, simulated mine environments, training sections 
 in an actual mine, and on-the-job training. This list is 
 ordered from the most removed from the actual work situa- 
 tion to the actual work situation itself. The objective of this 
 section is to present some data and examples of each of these 
 training methods as they apply to the mining industry. 
 
 Most mine training programs use several of these train- 
 ing methods; the most common combination is probably 
 classroom training followed by on-the-job training. 
 
 Classroom Training 
 
 Classroom training has always been a part of miner 
 training, and appears to be gaining additional popularity 
 as a prime method of presenting new-worker orientation 
 and safety training mandated by Government agencies. 
 Traditionally, classroom training involves a lecture- 
 discussion format, supplemented by films, slide presenta- 
 tions, and equipment mockups and models. Trainees may 
 or may not be tested to assess their level of learning. In some 
 cases, trainees may have an opportunity to practice a skill; 
 for example, putting on a self-rescue device. 
 
 The major shortcoming of classroom training is that, in 
 most cases, the trainee is a passive receiver of information 
 and has no opportunity to practice what has been learned 
 in a realistic setting. The major advantage is that a great 
 deal of information can be imparted to a large number of 
 people, inexpensively. Classroom training is probably best 
 suited for presenting overview and general orientation in- 
 formation, or for promoting group discussion and develop- 
 ing group norms and attitudes. 
 
 A survey of 108 apprentice miners in West Virginia (18) 
 showed that miners liked classroom training, thought it was 
 valuable, and preferred study within a group rather than 
 self-study. However, these same miners strongly preferred 
 self-paced instruction, which is difficult to implement in a 
 group situation. The miners recommended using short text- 
 books and tests for each part of a course, but felt that study- 
 ing was valuable even without examinations. They also 
 liked movies and felt they learned best when movies were 
 used. Unfortunately, this survey did not assess whether 
 movies, indeed, resulted in better learning. 
 
 Part-Task Simulation 
 
 Part-task simulation extracts from an entire task or job 
 a small part for training. Part-task simulators usually con- 
 sist of hardware devices that give a trainee an opportunity 
 to practice, over and over, one part of an overall task. An 
 example of a part-task simulator is the onboard simulator 
 of abnormal conditions (OBSAC) developed under a Bureau 
 of Mines contract (15). This device, shown in figure 9-2, is 
 used to train haulage truck drivers to recognize and respond 
 to abnormal equipment conditions. The OBSAC, which is 
 electrically connected to the mobile equipment via an 
 adapter kit, allows the instructor to control the readings 
 of certain gauges, actuate visual and audible alarms, and 
 degrade braking and steering performance. Functional 
 
 gauges of the OBSAC prototype include water temperature, 
 oil pressure, voltmeter, transmission-converter oil temper- 
 ature, transmission-clutch oil pressure, starting air pres- 
 sure, and brake air pressure. A digital stopwatch, part of 
 the console, enables the instructor to determine the reac- 
 tion time of trainees to observe an emergency or abnormal 
 condition and initiate the proper action. 
 
 The OBSAC training is blended into the general haul- 
 age, loading, and dumping procedures; that is, once a 
 trainee starts handling rock in a normal operating man- 
 ner, the instructor adjusts a gauge by a certain amount. 
 A good example is the engine oil pressure; the instructor 
 intentionally adjusts the gauge so that it does not rise upon 
 startup. If, on startup, trainees do not observe the engine 
 oil pressure within 5 s, they lose three points. During nor- 
 mal operation, the instructor may drop the reading 25 psi, 
 and if the trainee does not notice it within 15 s, he or she 
 loses points. 
 
 Field tests of OBSAC were carried out at two surface 
 minesites (1 1 ). The overall reaction to the OBSAC was very 
 favorable among the trainees because it vividly simulated 
 abnormal situations in a realistic operational setting. One 
 major advantage of this device is that abnormal conditions 
 are presented at will, and the reactions of the trainees are 
 observed under a variety of conditions. This part-task 
 simulator is somewhat unique in that it is operated in the 
 actual work environment. 
 
 Full-Task Simulation 
 
 Full-task simulations involve simulating all, or a signifi- 
 cant portion, of a job in a training environment. Typically, 
 such simulators are very expensive and complex. Their 
 main advantages are that they allow the instructor to 
 develop specific training exercises to meet the capabilities 
 of the students; they allow the students to practice exer- 
 cises over and over again; they provide integrative train- 
 ing; and they permit learning in a safe, standardized envi- 
 ronment where student errors will not destroy equipment 
 or endanger lives. 
 
 An example of a full-task simulator is the shuttle car 
 training systems (SCTS) developed under a Bureau of Mines 
 contract (23). Figure 9-3 shows a cutaway diagram of the 
 SCTS. It is designed to provide control, familiarity, and 
 practice in procedures associated with tramming, turning, 
 loading, and dumping. The system includes inby and outby 
 projector systems that show actual in-mine environmental 
 conditions, and are tied to the shuttle car controls. This 
 enables the trainee to perceive and judge the relationship 
 of the shuttle car to corners and intersections, and to ma- 
 neuver through work sections. The simulator also provides 
 bumping and pitching movement, as well as integrated 
 sounds and vibration system, all computer controlled. 
 
 Simulated Mine Environments 
 
 Part- and full-task simulators attempt to reproduce the 
 equipment used in mining, usually in an environment far 
 removed from the actual working environment. OBSAC is 
 an exception in that it is used in an actual mine environ- 
 ment. Full-task simulators often only reproduce the visual 
 aspects of an environment. Simulated mine environments 
 offer an opportunity to conduct training in a systematic, 
 planned fashion, without being concerned with production 
 demands, changing conditions, etc. In Europe, training 
 galleries (simulated mine environments^ are more common 
 
123 
 
 Figure 9-2.— OBSAC part-task simulator held in instructor's lap in port seat of a haulage vehicle (15). 
 
 Inby remedial 
 system 
 
 Curved screen 
 
 Outby 
 remedial 
 system 
 
 Outby projection 
 system 
 
 Bumping 
 and pitching Operator's 
 pit 
 
 Electronics 
 cabinet 
 
 Inby projection 
 system 
 
 Sloping Curved screen 
 floor. 
 
 Figure 9-3.— Shuttle car training system full-task simulator (29). 
 
 than in the United States. Some European mine rescue sta- 
 tions use them to train rescue teams. In some, smoke can 
 be pumped into the simulated mine for additional realism. 
 One example of a U.S. simulated underground mine was 
 built by U.S. Steel at its Cumberland Mine (12). It consists 
 of four entries and three crosscuts, and contains a power 
 center, fans, continuous miner, conveyor belt, shuttle car, 
 scoop car, and roof bolter. Students with no experience prac- 
 tice jobs such as rock dusting, posting, building stoppings, 
 
 and hanging brattice cloth. This simulated mine is also used 
 to train experienced miners in the use of new equipment, 
 and to develop teamwork in a section crew. 
 
 Training Sections in an Actual Mine 
 
 Several companies have allocated sections of their mines 
 strictly for training purposes, which is a cost-effective alter- 
 native to building a simulated mine environment. Here, 
 training can be conducted without the pressures and con- 
 straints inherent in using actual production sections for 
 training. An additional advantage is that efficiency is usu- 
 ally increased; that is, the necessary materials are avail- 
 able, and several trainees can engage in a task at one time, 
 while others observe. A trainee can be stopped when an er- 
 ror is made and instructed in the proper manner of perfor- 
 mance, without concern for productivity. The sequence of 
 training tasks can be controlled and need not be compro- 
 mised because of production demands. 
 
 On-the-Job Training 
 
 The most commonly used, and abused, method of train- 
 ing in the mining industry is on-the-job training (OJT). OJT 
 encompasses informal procedures, wherein a new worker 
 is assigned to an experienced worker to follow around and 
 learn the ropes. Such training is often unstructured, 
 
124 
 
 haphazard, and incomplete. The senior person may perceive 
 the new miner as a hindrance who is taking valuable time 
 away from the primary goal— productivity. OJT may include 
 a structured program where workers are assigned specific 
 sequences of tasks, and are monitored and evaluated by peo- 
 ple whose primary responsibility is training. 
 
 An example of structured OJT is the job safety skills 
 training (JSST) program at Monterey Coal Co. (17). The 
 training is conducted by a specially trained team on the 
 working section. JSST team members give close personal 
 attention to the safety performance and attitudes of in- 
 dividual miners in the unit as they go about their work 
 routines. As part of the training, a mock emergency is 
 staged (the foreman is injured) to force the workers to decide 
 for themselves what must be done. The focus is on building 
 teamwork and leadership rather than testing first-aid pro- 
 cedures. Monterey Coal reports a 50% reduction in nonfatal- 
 days-lost injuries since the program started. 
 
 OJT often generates high levels of motivation in stu- 
 dents; and, because the training is taking place in the ac- 
 tual work environment, transfer of training to everyday 
 work is almost assured. The major weaknesses of OJT are 
 that it often must take a back seat to production, and it is 
 limited by production demands. Thurlow (25) listed several 
 other limitations of OJT. 
 
 1. The optimum sequence of training tasks cannot be ar- 
 ranged without interfering with ongoing work. 
 
 2. Some tasks as encountered on the job are too complex, 
 fast-paced, or pressured to give an effective demonstration 
 or practice opportunity for the trainee. 
 
 3. The use of expensive equipment may be such an eco- 
 nomic loss that it may be difficult to find opportunities for 
 trainees to practice on the equipment. Trainees may then 
 be assigned to semiskilled duties that do not interfere with 
 the ongoing work, but also do not provide the planned train- 
 ing opportunities. 
 
 4. If the instructor is a production worker, attention to 
 production demands interferes with his or her capacity to 
 train. 
 
 5. Generally, no diagnostic measures are available 
 from OJT unless special provisions are made. Production 
 records have distinct limitations as indexes of employee 
 performance. 
 
 The cost-benefit ratio of OJT may not compare favorably 
 with off-production training sections. With training sec- 
 tions, more trainees can be trained by a single instructor 
 than is possible in a good OJT program. The cost of unstruc- 
 tured OJT is low, but so are the results. The costs of struc- 
 tured OJT programs are as high, or higher than when us- 
 ing training sites and a small cadre of instructors. And, of 
 course, there are greater dangers to life and property in- 
 volved in OJT as compared to using training sections. 
 
 Most mine training programs use several of these train- 
 ing methods; the most common combination is probably 
 classroom training, followed by OJT. 
 
 DEVELOPING A TRAINING PROGRAM 
 
 The development of a training program should be an 
 orderly, logical process to insure that the training addresses 
 the needs of the organization and meets the objectives set 
 forth for the training program. This logical, orderly process 
 is called instructional systems design (ISD) and has been 
 used by the military and large corporations for many years 
 to develop effective training programs. ISD is a series of 
 
 interrelated activities. Although each application of ISD 
 uses a slightly different set of activities, all have certain 
 features in common. Figure 9-4 depicts an ISD approach 
 to training development, and will serve as a model for 
 discussion. All ISD methodologies start by assessing train- 
 ing needs and writing training objectives. Somewhere in 
 the process, criteria and evaluation measures are developed 
 to assess the effectiveness of the training program. The 
 training program is developed, evaluated, and revised based 
 on objective performance data where appropriate. The 
 following is a brief discussion of each box in figure 9-4. For 
 a more complete discussion of the ISD approach, the reader 
 is referred to Goldstein (10) or Tracey (26). 
 
 Assess Training Needs 
 
 A potential training need can be defined as the dif- 
 ference between desired and actual performance. It must 
 be stressed, however, that all such discrepancies may not 
 be training related. In previous chapters, the importance 
 of task and equipment design has been discussed, as have 
 the effects of environment on human behavior. A discrep- 
 ancy between desired and actual performance is often cor- 
 rected more cost effectively through the application of 
 human factors design criteria than through training. There- 
 fore, in determining training needs, it is first necessary to 
 identify where behavior is not meeting expectation, and 
 then to determine the best course of action for reducing the 
 discrepancy: whether by means of human factors design 
 changes, training, or a combination of both. 
 
 Assessing the difference between desired and actual per- 
 formance requires that one know what is desired and what 
 is the level of actual performance. In some cases, both types 
 of information are collected separately and compared. For 
 example, a standard or expectation may have been devel- 
 oped that a particular maintenance job should take 2 h to 
 
 
 Assess 
 training needs 
 
 
 
 
 1 
 
 
 
 
 Write goals 
 and objectives 
 
 
 Determine criteria 
 
 and evaluation 
 
 measures 
 
 
 
 
 
 
 
 
 
 Select training 
 modes and media 
 
 
 
 
 
 
 
 
 
 > 
 
 
 
 
 
 
 Develop training 
 materials 
 
 
 
 
 
 
 
 
 Revise 
 
 
 
 ! 
 
 
 
 
 t 
 
 
 Evaluate 
 
 
 
 
 
 
 effect 
 
 veness 
 
 
 
 
 Figure 9-4.— Instructional system design approach to develop- 
 ment of training programs. 
 
125 
 
 complete; when, in fact, it is actually taking an average of 
 4 h. In those cases where specific standards against which 
 to compare performance do not exist, it is necessary to rely 
 on expert judgment. For example, a maintenance supervisor 
 would be asked if the performance of some of the mechanics 
 needs to be improved. 
 
 There are many sources of information that can be used 
 to identify potential training needs, some of which are listed 
 in table 9-2. It is usually best to use a variety of sources, 
 as each one taps different aspects and populations. 
 
 Table 9-2.— Sources of information for assessing training needs 
 
 Opinions 
 
 Statistics 
 
 Performance 
 measures. 
 
 Supervisor round-table discussions. 
 
 MSHA inspector discussion. 
 
 Worker surveys and questionnaires 
 
 Employee performance evaluations. 
 
 Accident reports. 
 
 MSHA inspector reports. 
 
 Industry statistics. 
 
 Absenteeism data. 
 
 Maintenance records. 
 
 Productivity records. 
 
 Job skill tests. 
 
 On-the-job observations. 
 
 Paper-pencil tests of job knowledge and procedures. 
 
 If used properly, accident data can be an excellent source 
 of training needs information. First, it must be recognized 
 that the data are incomplete; that is, many unsafe acts do 
 not result in accidents and, hence, are not a part of the data 
 base. Second, one must develop long-term trend informa- 
 tion based on meaningful categories, so that slowly increas- 
 ing trends can be identified. A tabulation of injuries by part 
 of body may not reveal as much information as a tabula- 
 tion of injuries by worker activity or type of accident. Safety 
 directors often do not keep long-term trend data, except 
 perhaps for total accidents; and they only identify a prob- 
 lem when there is a rash of similar accidents over a short 
 period of time. The slow buildup problems are often missed. 
 
 Write Goals and Objectives 
 
 Based on the assessment of training needs, the next step 
 in the process is to write the goals and specific objectives 
 of the training program. Goals are more comprehensive 
 than objectives. Each goal will have a number of objectives 
 associated with it. An effective, meaningful instructional 
 objective should meet the following three criteria (28): 
 
 1. Identify, as precisely as possible, what an individual 
 will be doing to demonstrate that an objective has been 
 reached. 
 
 2. Describe the important conditions under which an in- 
 dividual must demonstrate competence. 
 
 3. Define the criteria or standard of acceptable perfor 
 mance expected. 
 
 Specific objectives serve several purposes. First, they 
 help insure that both the instructor and the student under- 
 stand what is to be gained from the training. Second, they 
 focus the training on behaviors that are measurable. 
 
 Some examples of specific behavioral training objectives 
 include 
 
 1. Given four dirty and two clean respirator filters, the 
 student can pick out the four dirty filters. 
 
 2. For each of the three types of respirators used in the 
 mine, the student can list how often the filter must be 
 checked and replaced. 
 
 3. Given a type X respirator, the student can disassem- 
 ble and replace the filter in less than 1 min. 
 
 4. The student can identify each of the three types of 
 respirators used in the mine and indicate what each pro- 
 tects against. 
 
 In writing objectives, it is critical to specify what is 
 really important for the student to learn, rather than that 
 which is easy to measure. For example, it may not be im- 
 portant whether a person can name every part of a 
 respirator, although this is easily determined. What may 
 be more important is that the person can disassemble, in- 
 spect, clean, and reassemble the respirator in a specified 
 time. The latter objective is more difficult to measure, but 
 may be the critical behavior that one wants to develop. 
 
 Determine Criteria and Evaluation Measures 
 
 Evaluation measures flow directly from the objectives 
 and should be specified before the actual training materials 
 and programs are designed. Training directors often develop 
 the evaluation measures after they have developed the 
 training course. The problem with this is that the evalua- 
 tion measures may be based on the course content, which 
 may or may not be designed to meet the training objectives. 
 It is important to develop the evaluation measures direct- 
 ly from the objectives so that they can be used to evaluate 
 the training in determining if the objectives are being met. 
 Evaluation measures can include paper-and-pencil tests, 
 performance on a simulated task, on-the-job performance, 
 supervisor ratings, and student opinion surveys. 
 
 Select Training Modes and Media 
 
 The type of training modes and media used depends in 
 great part on what skill is being trained. Role playing, group 
 discussion, and case study are effective in training atti- 
 tudinal and decisionmaking skills. Simulators and on-the- 
 job training are effective for training perceptual and motor 
 skills. Movies and slides are effective for training percep- 
 tual skills and job knowledge. The proper mix of modes and 
 media must be carefully selected and should not merely be 
 whatever is available. 
 
 Develop Training Materials 
 
 Training materials can be developed in-house, pur- 
 chased from outside sources, or purchased from outside 
 sources and tailored to the specific needs and problems of 
 a particular mine. The Bureau's Pittsburgh (PA) Research 
 Center has compiled an extensive list of commercially avail- 
 able training materials appropriate to the mining industry 
 that is available to individuals and companies. In-house 
 development of materials includes slide presentations using 
 actual people and areas of the mine to illustrate training 
 points, videotapes of job procedures (7), posters summariz- 
 ing key points, and models and mockups of equipment to 
 demonstrate correct actions. 
 
 Effective training materials should include short tests 
 so that students and instructors can assess the progress be- 
 ing made during a training program. The training should 
 be divided into small modules so that students can digest 
 one module before going on to the next. This also gives the 
 student a sense of accomplishment when each module is suc- 
 cessfully completed. 
 
126 
 
 Evaluate Effectiveness 
 
 The evaluation measures, developed from the training 
 objectives, are used to test the trainees and assess whether 
 the training objectives were met. In addition, other evalu- 
 tion data are collected. Student opinions should be solicited; 
 they are an excellent source of data on how a training pro- 
 gram could be improved. Followup on the job is critical. 
 Training personnel should seek supervisor opinions as to 
 whether training has improved job performance and what 
 areas need to be stressed further in training. Accident, pro- 
 duction, and maintenance records should be reviewed to 
 assess any positive impact of the training. 
 
 Revise 
 
 Based on the evaluation data, changes are made to the 
 modes, media, and content of training programs. Objectives 
 should not be revised based on the evaluation; they should 
 be revised based on a reassessment of training needs. Every 
 training program will need to be revised at some time. 
 Materials go out of date, training needs change, and the 
 types of students change. All of these necessitate the con- 
 stant review and revision of a training program. 
 
 SAFETY AWARENESS PROGRAMS 
 
 Safety awareness programs typically include various 
 communications, promotional devices, and contests aimed 
 at increasing employee awareness of the importance of 
 working safely. Probably one of the most extensive aware- 
 ness programs is that undertaken by Consolidation Coal 
 Co. (2). The following sections briefly describe this program 
 and summarize the elements that contributed to its success. 
 
 Consol's Program 
 
 The Consol program was a four-pronged approach. It in- 
 volved (1) establishment of a corporate-wide safety depart- 
 ment and corresponding departments in each operational 
 region, (2) an intensive safety training program, (3) an all- 
 out safety engineering program, and (4) a safety communica- 
 tions program to heighten awareness among all employees. 
 
 A symbol (the A-OK hand signal: with index finger and 
 thumb forming a zero) and a slogan (Consol's Goal— Zero 
 Accidents) were selected and used consistently on all com- 
 munication and promotional materials. It was recognized 
 that to be effective, both the workers and their families had 
 to be involved. Family involvement was accomplished by 
 sending a quarterly safety newsletter to the families. In 
 addition, all sorts of promotional items were mailed to the 
 homes, including packets of sugar, salt, mustard, ketchup, 
 baggies, and handy wipes— all with the symbol and slogan 
 printed on them— to be packed in lunchboxes as reminders. 
 Potholders, Christmas wrappings, and toboggans were 
 given away, again all emblazoned with the safety symbol 
 and slogan. To keep the link between job safety and family 
 salient, safety posters were displayed at the mines with pic- 
 tures of employees' children and messages such as, "Dad, 
 work safely so you can give me away at my wedding" or 
 "Work safe, Dad, we need you at home." 
 
 In addition, the workers were also given safety slogan 
 items to maintain their awareness of the program, including 
 fishing knives, leg bands, belt buckles, caps, and retroreflec- 
 tive stickers for their helmets. Paycheck stuffers were in- 
 
 cluded to promote specific safety concerns. Extensive 
 signage was used at the minesites, including safety clocks 
 and thermometers. Even the jumpsuits of the mine rescue 
 teams had the safety symbol and slogan on them. 
 
 To complement the communications, safety awards were 
 given. Workers earned points for safe work performance and 
 could use them to purchase gifts. Jackets and caps were used 
 regionally to reward a good safety record. Gold pins were 
 given to superintendents whose operations had no lost-time 
 accidents for a year, and safety trophies were given to opera- 
 tions with 1 million work-hours without an accident. 
 
 In 1978 it was reported that the program was costing 
 approximately $200,000 per year, but during the first 6 yr 
 of the program, the accident frequency rate was reduced 
 by almost 60%. 
 
 Elements of a Successful Program 
 
 There are several aspects of the Consol program that 
 accounted for its success. These elements have also been 
 found to be essential for such programs in other industries 
 as well. First, and perhaps foremost, is top management's 
 total commitment to the program. Second, an awareness 
 program must be part of a larger safety program, with 
 strong emphasis on training and engineering-human fac- 
 tors approaches to accident reduction. Third, it is impor- 
 tant that the worker's family is made an integral part of 
 the awareness program. It has also been suggested that the 
 community be included. Fourth, a wide variety of devices 
 must be used to get the message across. Safety slogan items 
 must be changed periodically, and new items must be in- 
 troduced to keep interest high. The prizes and gifts must 
 be updated and expanded. 
 
 It is impossible to determine which specific aspects of 
 the Consol program were effective and which were not. In 
 all likelihood, it was the totality of the program that was 
 effective. It is much like analyzing how a dam holds back 
 water. Examining each individual stone would lead to the 
 conclusion that each stone, by itself, would not hold back 
 the water, yet all the stones together hold back the water 
 very effectively. 
 
 Safety Signs 
 
 Unfortunately, many companies rely on safety signs as 
 their primary method of increasing safety awareness. There 
 are some characteristics of effective signs that are worth 
 pointing out, in addition to those dealing with such issues 
 as attention-getting, visibility, and comprehensibility. 
 
 First, safety signs must reinforce other aspects of a com- 
 pany's safety program. Signs should correspond to aspects 
 being stressed in training or at weekly safety meetings. In 
 essence, signs should be part of a focused campaign aimed 
 at a select number of safety problems. For example, signs 
 may be directed toward the use of lockouts in electrical 
 maintenance work. The message would be stressed by super- 
 visors on the job and in safety meetings, better lockout 
 designs would be installed, new job procedures developed, 
 etc. 
 
 Second, the signs should be directed to specific safety 
 problems rather than general messages. The emphasis 
 should be on what to do. rather than just what not to do. 
 (Note that the Consol program used general be-safe type 
 signs; by themselves, they probably would not have been 
 very effective.) Signs showing specific actions are usually 
 more effective. It is usually agreed that, where possible, the 
 
127 
 
 consequences of not performing the action should be illus- 
 trated on the sign. For example, if the message on a sign 
 was to block the wheels of vehicles parked on an incline, 
 the sign might also show a runaway vehicle hitting a 
 person. 
 
 Third, signs should be placed where they are needed. 
 A block-the-wheels sign, for example, should be hung on 
 inclined roadways where vehicles are likely to be parked, 
 and on the vehicles themselves. It would do little good to 
 hang them in the clean room or lunch area. Related to the 
 place-them-where-you-need-them principle is that one 
 should not overdo the placement of signs. If there are safety 
 signs everywhere a worker looks, the signs may quickly lose 
 their significance and be ignored. 
 
 DISCUSSION 
 
 This chapter has reviewed training and similar 
 endeavors as they relate to the achievement of organiza- 
 tional goals— increased safety and productivity. The chapter 
 is not meant to be a how-to guide for developing training 
 programs, but rather as a survey of the utility, methods, 
 and lessons learned from the field. 
 
 Training often aims at redirecting and increasing moti- 
 vation. Chapter 10 deals with the topics of motivation and 
 organizational development which can be viewed as a 
 logical extension of the training function to embrace the 
 entire organization and the interactions of its parts. 
 
 REFERENCES 
 
 1. Adkins, J., R. Akeley, P. Chase, L. Marrus, W. Prince, R. 
 Rodick, C. Rogne, J. Saalberg, and L. Szempruch. Review and 
 Evaluation of Current Training Programs Found in Various Min- 
 ing Environments. Volume I, Summary (contract S0144010, Ben- 
 dix Corp.). BuMines OFR 110(l)-76, 1976, 67 pp.; NTIS PB 259 410. 
 
 2. Cochran, H. Safety Communications for Reducing Mine Ac- 
 cidents. Min. Congr. J., v. 64, No. 6, 1978, pp. 27-29. 
 
 3. Cohen, A. Factors in Successful Occupational Safety Programs. 
 J. Safety Res., v. 9, 1977, pp. 168-178. 
 
 4. Cohen, A., M. Smith, and H. Cohen. Safety Program Practices 
 in High Versus Low Accident Rate Companies: An Interim Report 
 (Questionnaire Phase). NIOSH, Cincinnati, OH, DHHS 75-185, 
 1975, 183 pp.; NTIS PB 298-332. 
 
 5. Cohen, H., and R. Jensen. Measuring the Effectiveness of an 
 Industrial Lift Truck Safety Training Program. J. Safety Res., v. 
 15, No. 3, 984, pp. 125-135. 
 
 6. Couillard, D.T., and B.C. Nelson. Task Training in the Iron 
 Mining Industry: Two Approaches. BuMines IC 8994, 1984, 11 pp. 
 
 7. Couillard, D.T., B.C. Nelson, and R.R. Tomassoni. Video- 
 Supplemented Task Training at the United States Steel Corp. 
 Minntac Mine, Mt. Iron, MN. BuMines IC 8999, 1985, 9 pp. 
 
 8. Davis, R.T. and R.W. Stahl. Safety Organization and Activities 
 of Award-Winning Companies in the Coal-Mining Industry. 
 BuMines IC 8224, 1964, 26 pp. 
 
 9. Digman, R.M., and J.T. Grasso. An Observational Study of 
 Classroom Health and Safety Training in Coal Mining (contract 
 J0188069, WV Univ.). BuMines OFR 99-83, 1982, 65 pp.; NTIS PB 
 83-210518. 
 
 10. Goldstein, I. Training: Program Development and Evalua- 
 tion. Brooks and Cole, 1974, 229 pp. 
 
 11. Hardy, K. Training With OBSAC. Paper in Proceedings of 
 TRAM 10 (Training Resources Applied to Mining), PA State Univ., 
 Aug. 14-17, 1983, pp. 46-52. 
 
 12. Hoover, R. Cumberland Training Center and Simulated Mine. 
 Min. Congr. J., v. 65, 1979, pp. 46-48. 
 
 13. Komaki, J., K. Barwick, and L. Scott. A Behavioral Approach 
 to Occupational Safety. J. Appl. Psych., v. 63, 1978, pp. 434-445. 
 
 14. Komaki, J., A. Heinzmann, and L. Lawson. Effect of Train- 
 ing and Feedback: Component Analysis of a Behavioral Safety Pro- 
 gram. J. Appl. Psych., v. 65, 1980, pp. 261-270. 
 
 15. Krupp, K., and J. Applegate. Haulage Truck Training System 
 (contract J0387221, Woodward Assoc. Inc.). BuMines OFR 61-85, 
 1983, 224 pp.; NTIS PB 85-215762. 
 
 16. McAteer, J., and L. Galloway. A Comparative Study of Miners' 
 Training and Supervisory Certification in the Coal Mines of Great 
 Britain, The Federal Republic of Germany, Poland, Romania, 
 France, Australia and the United States: The Case for Federal Cer- 
 tification of Supervisors and Increased Training of Miners. WV Law 
 Rev., v. 82, 1980, pp. 936-1016. 
 
 17. McGrath, J. Aggressive Safety Skills Training Gets Results 
 at Illinois Coal Mine. Mine Safety and Health, Spring-Summer, 
 1983, pp. 2-9. 
 
 18. Menzer, G, J. Curtin, and F. Bick. A Training Analysis Ap- 
 proach to the Education of Coal Miners. McDonnell Douglas 
 Astronautics Co., St. Louis, MO, MDC-E-1566, 1976, 145 pp. 
 
 19. Morris, C.W., and E. Conklin. Development and Fabrication 
 of a Continuous Miner Training System. Volume 2 (contract 
 H0377024, McDonnell Douglas Electronics Co.). BuMines OFR 
 140(2)-83, 1982, 79 pp. 
 
 20. National Academy of Sciences. Toward Safer Underground 
 Coal Mines. 1982, 190 pp. 
 
 21. Peay, J., W. Wiehagen, and G. Bockosh. The Human Element 
 in Mining— An Overview of Bureau of Mines Human Factors 
 Research. Paper in Proceedings of the 15th Annual Institute on 
 Coal Mine Health, Safety and Research, Aug. 28-30, 1984. VA 
 Polytechnic and State Univ., Blacksburg, VA, 1984, pp. 61-83. 
 
 22. Robertson, N. What Does Research Tell Us About Training? 
 Pres. at Assoc, of Mine Managers Meeting. Chamber of Mines, 
 Johannesburg, South Africa, February 1979, 12 pp.; available upon 
 request from M.S. Sanders, Essex Corp., Westlake Village, CA. 
 
 23. Seidle, N. Shuttle Car Operator Training System (contract 
 H0272039, ORI Inc.). BuMines OFR 59-85, 1984, 84 pp.; NTIS PB 
 85-215788. 
 
 24. Short, J., J. Harris, J. Waldo, and S. Barber. A Study to Deter- 
 mine the Manpower and Training Needs of the Coal Mining In- 
 dustry (contract J0395038, John Short and Assoc). BuMines OFR 
 14-80, 1979, 145 pp.; NTIS PB 80-164742. 
 
 25. Thurlow, R., J. Olmstead, and R. Trexler. On-The-Job Train- 
 ing and Social Learning Theory: A Literature Review. Human 
 Resour. Res. Organization Inc., Alexandria, VA, 1980, 56 pp. 
 
 26. Tracey, W. Designing Training and Development Systems. 
 Am. Management Assoc, 1971, 432 pp. 
 
 27. Uslan, S.S., H.M. Adelman, and R.S. Keller. Testing the Ef- 
 fects of Applied Behavioral Analysis and Applied Behavioral 
 Management Techniques on the Safe Behaviors of Salt Mine Per- 
 sonnel (contract J0166137, Salt Inst.). BuMines OFR 44-80, 1978, 
 41 pp.; NTIS PB 80-171309. 
 
 28. U.S. Occupational Safety and Health Administration 
 (Washington, DC). Training Guidelines: Request for Comments and 
 Information. OSHA 76-135, 1976, 11 pp. 
 
 29. Wiehagen, W. Current Research in the Application of Train- 
 ing Equipment Supporting Equipment Operator Training. Paper 
 in Mine Safety Education and Training Seminar Proceedings: 
 Bureau of Mines Technology Transfer Seminars, Pittsburgh, Pa.. 
 Dec. 9, 1980; Springfield, 111., Dec. 12, 1980; and Reno, Nev., Dec. 
 16, 1980; comp. by Staff— Pittsburgh Research Center. BuMines 
 IC 8858, 1981, pp. 46-58. 
 
128 
 
 CHAPTER 10.— MOTIVATION AND ORGANIZATIONAL DEVELOPMENT 
 
 The link between organizational climate and safety and productivity has become apparent. Work organiza- 
 tion concepts of bygone days are now only seen in photographs found in the National Archives. 
 
 Throughout this report, the effects of equipment and 
 environment on human behavior have been emphasized. 
 The topics have been rather technical, with a definite 
 engineering flavor. The importance of motivation has been 
 occasionally alluded to as a determinant of performance, 
 but it has not been discussed in depth; that is the purpose 
 of this chapter. 
 
 Chapter 8 discussed environmental factors, including 
 illumination, noise, vibration, and heat, that influence 
 behavior. In this chapter another environmental factor in- 
 fluencing behavior— organizational climate— will be dis- 
 cussed. The effects of organizational climate on behavior 
 are more psychological in nature than are the effects of the 
 factors discussed in chapter 8. In keeping with the emphasis 
 on changing the job to fit the person, this chapter will pre- 
 sent the process of organizational development, and specific 
 attempts made to alter the organizational climate in the 
 mining industry. 
 
 MOTIVATION 
 
 The term "motivation" is rather loosely used to describe 
 the drive, thrust, or energy behind an individual's behavior. 
 In addition, a goal-oriented function of motivation is in- 
 ferred. People are not just motivated; they are motivated 
 to do something or obtain something. Motivation, then, is 
 responsible for the intensity, direction, and persistence of 
 behavior. 
 
 Motivation and Performance 
 
 Motivation is related to performance, but it is not the 
 same thing as performance. Performance is a function of 
 ability and motivation. Many theories suggest the follow- 
 ing equation to express this relationship: 
 
 Performance = /"(ability x motivation). 
 
 The multiplicative relationship is important and implies 
 that, if either motivation or ability are zero, performance 
 will be zero. In essence, all the motivation in the world will 
 not yield satisfactory performance unless a person has the 
 ability to perform satisfactorily. The converse is also true: 
 a person with all the ability in the world will not perform 
 without the motivation to do so. 
 
 Ability refers to how well a person can perform at a 
 given time. As such, ability is considered to be a function 
 of aptitude, training, and experience. Thus 
 
 Ability = /"[aptitude x (training + experience^]. 
 
 Aptitude is an enduring, inalterable quality of an in- 
 dividual that imposes a fixed limit on his or her level of 
 potential performance. As such, aptitude determines 
 whether an individual can be brought through training 
 and/or experience to a specified level of performance. Notice, 
 this expression implies that without aptitude, all the train- 
 ing and experience will not give an individual the ability 
 to perform. 
 
 * 
 
129 
 
 One important implication of all this is that not all per- 
 formance problems that occur in organizations are caused 
 by low motivation. Problems can be caused by low aptitude; 
 inadequate training and experience; or poorly designed jobs, 
 equipment, and environments that exceed whatever abili- 
 ties people may have. 
 
 Motivation and Needs 
 
 For centuries, psychologists and philosophers have tried 
 to explain why some objects or outcomes seem to be desired 
 by people, while others are not. People have needs; and it 
 is assumed that if these needs are better understood, a bet- 
 ter understanding of why people act as they do follows. 
 
 There have been many attempts to classify human 
 needs. Probably the most influential theory of human needs, 
 and by far the most widely used classification system for 
 the study of motivation in organizations, is the hierarchical 
 classification scheme of Maslow {11-13)} He postulates five 
 categories of needs as follows: 
 
 1. Physiological needs, including the need for food, water, 
 air, etc. 
 
 2. Safety needs, including the need for security, stabil- 
 ity, and the absence from pain, threat, or illness. 
 
 3. Belongingness and love needs, which include the need 
 for affection, fellowship, love, etc. 
 
 4. Esteem needs, including both the need for personal 
 feelings of achievement or self-esteem, and the need for 
 recognition or respect from others. 
 
 5. The need for self-actualization, that is, the feeling of 
 self-fulfillment or the realization of one's potential. 
 
 According to Maslow, these five needs categories exist 
 in a hierarchy of importance, such that the lower or more 
 basic needs (physiological, safety) are inherently more im- 
 portant than the higher needs. This means that, before any 
 of the higher level needs will become important, a person's 
 physiological needs must be satisfied. Once the physiological 
 needs have been satisfied, their strength or importance 
 decreases, and the next higher-level need becomes the 
 strongest motivator of behavior. At the highest level of the 
 hierarchy, a slightly different thing occurs. For self- 
 actualization, increased satisfaction of the need leads to in- 
 creased need strength. The more you get, the more you 
 want— but, according to Maslow, this only occurs at the top- 
 level need. 
 
 Maslow does say that the hierarchy is not rigidly fixed 
 for all people. He clearly states that physiological needs are 
 at the bottom, and self-actualization needs are at the top; 
 but the order of the middle needs may vary from person to 
 person. 
 
 This theory suggests, for example, that as people are 
 promoted and their lower-level needs become satisfied, they 
 will become more concerned with self-actualization and 
 growth. If these higher order needs are not addressed, peo- 
 ple may become dissatisfied with their jobs. The theory also 
 suggests that if a person's job security is threatened, that 
 person will abandon all else in order to protect it. 
 
 Maslow, however, is not the last word on needs theories. 
 Some theorists take exception to parts of his theory because 
 the empirical evidence has not always supported it. Some 
 believe that there are fewer levels of needs, that all can be 
 o' erating at the same time, and that failure to satisfy a 
 
 1 Italic numbers in parentheses refer to items in the list of references at 
 the end of this chapter. 
 
 higher order need can cause a lower order need to increase 
 in importance. 
 
 A Theory of Motivation 
 
 Theories of human needs, such as that of Maslow, are 
 useful for explaining what outcomes will be attractive to 
 an individual; but they are not sufficient to explain the in- 
 dividual's behavior. The reason is that such theories do not 
 include many of the factors that are known to influence 
 motivation. There have been numerous theories of motiva- 
 tion over the years, but one has attracted considerable at- 
 tention and research support in the work environment; i.e., 
 expectancy theory (16). 
 
 Expectancy theory states that people will expend effort 
 (motivation) toward a performance goal if they perceive that 
 their efforts will result in attaining that level of perfor- 
 mance, and the attainment of that level of performance will 
 lead to desired outcomes. The theory utilizes three main 
 concepts: valence, effort-performance expectancy, and 
 performance-outcome expectancy. Each of these are ex- 
 plained, in reference to figure 10-1 (10), in the following 
 sections. 
 
 Valence 
 
 The valence of an outcome refers to the affective 
 response of a person to an outcome. An outcome can have 
 a positive valence, in which case the outcome is something 
 a person desires or wishes to attain; a neutral valence, as 
 when a person is indifferent to the outcome; or a negative 
 valence, as when a person prefers not to attain the outcome. 
 Examples of outcomes include a pay raise, working with 
 a friend, losing one's job, working in less hazardous and 
 more pleasant surroundings, being praised by one's super- 
 visor, gaining a sense of accomplishment, being ostracized 
 from a group, being injured, etc. 
 
 Effort-Performance (E-P) Expectancy 
 
 E-P expectancy is simply a person's estimate, in a given 
 situation, of the probability that he or she will attain a 
 performance level if he or she puts in the effort. Figure 10-1 
 shows two levels of performance, satisfactory and unsatis- 
 factory; but these could also represent alternative perfor- 
 mances, such as doing the job safely and unsafely. 
 
 Performance-Outcome (P-O) Expectancy 
 
 P-0 expectancy is the perceived probability that a level 
 of performance will lead to an outcome. Some outcomes are 
 certain to follow from performance, such as a feeling of 
 accomplishment when a difficult task is satisfactorily com- 
 pleted. Some outcomes will occur, regardless of the perfor- 
 mance level attained (e.g., outcome C in figure 10-1). Other 
 outcomes may or may not occur, depending on the situation. 
 
 The Model 
 
 Expectancy theory postulates that for each outcome that 
 can result from a level of performance, people multiply the 
 P-0 expectancy by the valence (V). These are summed for 
 all the outcomes attached to a performance level to obtain 
 an overall valence for the performance level. This overall 
 
130 
 
 Outcome 
 B 
 
 Expectancy 
 
 Performance 
 A 
 
 Outcome 
 B 
 
 Performance 
 B 
 
 KEY 
 
 Performance 
 
 A The intended performance, a 
 successful result from effort 
 
 B Performance other than that intended, 
 an unsuccessful result from effort 
 
 Outcome 
 
 Outcome 
 
 Outcome 
 
 Outcome 
 
 Outcome 
 B 
 
 Outcome 
 B 
 
 Outcome 
 
 Outcome 
 
 A An outcome sought as an end in itself 
 
 B An outcome sought as a prerequisite to other outcomes 
 
 C An outcome that can be obtained whether or not the 
 effort leads to the intended performance 
 
 Figure 10-1.— Schematic representation of expectancy theory of motivation (10). (Courtesy of Brooks and Cote) 
 
 valence is then multiplied by the E-P expectancy to deter- 
 mine the level of motivation a person will experience toward 
 attaining the performance level. This is done for various 
 performance levels, and the level of performance with the 
 highest motivation level is the one that a person, in theory, 
 will choose to attain. In formula format: 
 
 Motivation = (E-P) x [(P-O) x (V)]. 
 
 There are several implications of this model. People will 
 not pursue a performance if it is perceived that the attain- 
 ment of the performance will result in a net negative overall 
 valence, unless all other performance levels will result in 
 even more negative valences. Attaining a high level of pro- 
 ductivity may get the praise of a supervisor and maybe even 
 a promotion, but it may also result in the loss of friends 
 and being overly fatigued at the end of the day. Depending 
 on the P-0 expectancy and valence of each of these, the 
 overall valence could be positive or negative. On a smaller 
 scale, wearing safety glasses may result in fewer injuries 
 (positive valence), but it can also result in discomfort and 
 lower visual ability due to fogging (negative valence). 
 Whether people wear saftey glasses depends on their P-0 
 expectancies and valences for these and other outcomes. 
 
 Implications of the Model 
 
 Table 10-1 lists the major factors that influence E-P and 
 P-0 expectancies. People often have an inaccurate percep- 
 tion of a situation, which can lead to incorrect P-0 or E-P 
 expectancies. They may not understand the high probability 
 of an accident if certain unsafe procedures are followed, or 
 they may perceive that the safe way of doing a job is more 
 difficult or time consuming than an unsafe way. Proper 
 training can often correct such misconceptions. Training 
 can also alter E-P expectancies by increasing a person's self- 
 esteem and ability to perform the work. The way a work 
 group and supervisor reward performance also affects the 
 P-0 expectancies. If safe behavior is rewarded, then the P- 
 O expectancy for that outcome increases. If a person is 
 criticized for reduced production because he or she chose 
 to use a safe job procedure, P-0 expectancies will also be 
 affected. 
 
 P-0 expectancies are influenced by the valence of the 
 outcomes themselves. To most people, positive outcomes are 
 believed more likely to occur than negative outcomes. Peo- 
 ple also tend to discount the possibility that very negative 
 things (e.g., injury or death) will happen to them. Is it any 
 wonder that people will engage in behaviors that will save 
 
131 
 
 Table 10-1 .—Factors that influence performance-outcome (P-O) 
 and effort-performance (E-P) expectancies (10) 
 
 (Reprinted with permission by Brooks and Cole) 
 
 E-P 
 
 P-O. 
 
 Self-esteem 
 
 Past experiences in similar situations. 
 
 Actual situations. 
 
 Communications from others. 
 
 Past experiences in similar situations. 
 
 Attractiveness of outcomes. 
 
 Belief in self versus fate. 
 
 Actual situations. 
 
 Communications from others. 
 
 a little time (positive valence and high P-O expectancy), but 
 will expose them to danger of bodily harm (high negative 
 valence, but low P-O expectancy). 
 
 One goal of mine management, then, should be to struc- 
 ture a situation so that positively valenced outcomes occur 
 when desirable behaviors are performed, and that either 
 negatively valenced outcomes occur when undesirable 
 behaviors occur; or, at the least, positively valenced out- 
 comes do not occur. In addition, training should be aimed 
 at reinforcing the connection between performance and out- 
 come, and at increasing the expectancy that the perfor- 
 mance desired will be attained if effort is expended. 
 
 ORGANIZATIONAL CLIMATE 
 
 Organizational climate refers to the collective percep- 
 tions held by employees about aspects of their organiza- 
 tional environments. These perceptions have a psycholog- 
 ical utility in serving as a frame of reference for guiding 
 appropriate and adaptive task behaviors. Perceptions that 
 make up organizational climate include whether manage- 
 ment is perceived as caring about the individual workers; 
 whether management listens to workers' suggestions and 
 complaints; whether productivity is stressed more or less 
 than safety; whether the coworkers support one another and 
 work together, etc. 
 
 An important component of organizational climate that 
 he called safety climate or the concern for safety was 
 distinguished by Zohar (18). Organizational climate, in- 
 cluding safety climate, is assessed by the use of question- 
 naires administered to employees of a company. Usually, 
 a rating form is used to solicit perceptions on specific dimen- 
 sions. Zohar, for example, used a 49-item questionnaire to 
 measure safety climate, in which employees marked a 
 5-point scale for each item (strongly disagree-disagree- 
 neutral-agree-strongly agree). The questionnaire tapped 
 the following perceptions: 
 
 Perceived importance of safety training programs. 
 
 Perceived management attitudes toward safety. 
 
 Perceived effects of safe conduct on promotion. 
 
 Perceived level of risk at workplace. 
 
 Perceived effects of required work pace on safety. 
 
 Perceived status of safety officer. 
 
 Perceived effects of safe conduct on social status. 
 
 Perceived status of safety committee. 
 Zohar also found strong correlations between the scores 
 on the safety climate questionnaire and the rankings by 
 safety inspectors of the overall safety records of 50 
 companies. 
 
 One of the first studies to investigate the relationship 
 between organizational climate and accidents in the mining 
 industry was carried out by Sanders (15). Miners from 22 
 underground coal mines were administered questionnaires 
 
 that examined their perceptions of such things as decision 
 decentralization, shared autonomy, management receptive- 
 ness, production pressure, feedback, management support - 
 iveness and concern for working conditions, and worker 
 morale. 
 
 Using a sophisticated cross-lagged correlational design 
 that required testing at each mine approximately 6 months 
 apart, the following conclusions were made based on the 
 data: 
 
 1. When decisions are decentralized, when management 
 is flexible and innovative in trying new procedures and pro- 
 grams, and when morale is high, disabling injuries decrease. 
 
 2. As disabling injuries increase, feedback, continued 
 employee development, and consistency of orders improve. 
 That, in turn, appears to decrease injuries. 
 
 3. Production pressure appears to lead to an increase in 
 disabling injuries. The increase in disabling injuries, in 
 turn, leads to a decrease in production pressure. 
 
 A basic conclusion from this study was that certain 
 organizational climate and managerial practices affect in- 
 jury rates; and, further, that injury experiences have an 
 effect on other climate and managerial issues. Therefore, 
 in order to reduce accidents, one must not only focus on the 
 worker and the physical environments, but must also focus 
 on the broader organizational context and managerial prac- 
 tices within which the miner works. The techniques used 
 to change the broader organizational context and mana- 
 gerial practices are in the province of organizational 
 development. 
 
 ORGANIZATIONAL DEVELOPMENT 
 
 Organizational development (OD) is a long-term effort 
 that examines and alters management policies, practices, 
 and organizational dynamics in a systematic way for the 
 purpose of assisting a company to solve its major problems 
 and to achieve its major goals (1). OD recognizes that the 
 key unit in an OD activity is the ongoing work team, in- 
 cluding both the supervisor and his or her subordinates. 
 This is in contrast to the more traditional management 
 development approach that concentrates on the individual 
 managers and supervisors, rather than on the intact work 
 groups. 
 
 Another distinguishing feature of OD is the use of a 
 change agent to initiate and guide the OD activity. The 
 change agent is a third party, external to the particular part 
 of an organization that is initiating the OD activity. This 
 change agent usually does not make recommendations in 
 the traditional sense, but rather intervenes in the ongoing 
 processes of the organization, and assists the organization 
 in understanding and changing how it goes about solving 
 problems. 
 
 A final distinguishing characteristic of OD is that the 
 activities generally follow an action research model. Basi- 
 cally, an action research model consists of (1) a preliminary 
 diagnosis of an organization's (or work group's) problem, 
 (2) data gathering from the group to further diagnose the 
 source of its problems, (3) data feedback to the group that 
 summarizes the findings from the data gathering, (4) discus- 
 sion by the group of the findings, (5) action planning by the 
 group to solve the problems uncovered, (6) implementation 
 of the action plan, and (7) monitoring and evaluating the 
 action plan to insure that the problems are indeed being 
 solved. 
 
132 
 
 Actually, OD is more of a philosophy than a specific 
 methodology. OD activities take many different forms. To 
 provide an appreciation for OD, four OD projects that were 
 carried out in the mining industry will be reviewed: the 
 Rushton autonomous work group experiment, the Hecla 
 team-building project, the Texasgulf leader-match study, 
 and the use of quality circles by mining companies. 
 
 Rushton Autonomous Work Group Experiment 
 
 This project began in 1974 and was sponsored by the 
 Department of Commerce and the Ford Foundation. I' 
 represents probably the most comprehensive OD activity 
 initiated in the coal industry. The implementation and 
 results are fully detailed by Goodman (7). The Rushton 
 experiment was and is one of the more controversial OD 
 interventions, perhaps because of the extensive attention 
 it generated (3, 14, 1 7) and the problems it encountered. 
 
 Background 
 
 The Rushton Mine was owned by Pennsylvania Mines 
 Corp., which was part of Pennsylvania Power and Light. 
 The mine was located in central Pennsylvania and em- 
 ployed about 200 people. The workers were members of the 
 United Mine Workers of America (UM WA). The project can 
 be considered as being composed of two phases. The first 
 phase involved the OD intervention on three shifts (each 
 composed of eight-person crews) in one of the four working 
 sections of the mine. The second phase involved efforts to 
 expand the intervention to the other three working sections. 
 
 Autonomous Work Groups 
 
 The OD intervention involved setting up autonomous 
 work groups. Basically, the miners in a crew organized and 
 managed themselves. They performed all the different 
 tasks, traded individual job assignments periodically, and 
 learned all work conditions. Specifically, authority for daily 
 production decisions was delegated to the mining crew. The 
 foreman's job was to concentrate on safety, planning, and 
 coordinating activities (not on daily production decisions). 
 Key features of the plan were that each member of the crew 
 was to learn all other jobs in the section, and all the mem- 
 bers of the crew would receive the same top rate of pay. Fur- 
 ther, two additional workers were added to each crew to 
 do support work. 
 
 A joint labor-management committee, consisting of five 
 members from the union and five members from manage- 
 ment, was to supervise the day-to-day project activities. All 
 grievances were to go to the joint committee prior to going 
 through the traditional grievance procedure. In addition to 
 these efforts, an extensive training program was instituted, 
 and a gain-sharing plan (like a profit-sharing plan) was to 
 be instituted. This plan, however, was never implemented. 
 The training consisted of classroom training, 2 full days per 
 week for 3 weeks, covering the autonomous work group con- 
 cept, reviewing all job tasks, job safety analysis, and Federal 
 safety laws. Other changes, such as the introduction of dif- 
 ferent performance appraisal systems and department-wide 
 conferences, were also included. 
 
 Results 
 
 For the better part of 2 yr, the program worked well. 
 The crews organized and solved problems collectively. In- 
 
 formal leaders emerged and took over, while the foremen 
 devoted their time to safety measures. 
 
 The following are some quotes from the miners involved 
 during the period of the experiment: 
 
 Well, you're your own boss. You got your section 
 
 and run things our own way and talk things over 
 
 when you have to. 
 
 Before, when a timber was down, you'd say the 
 
 hell with it. Now you do something— it's your section. 
 
 If something's wrong, we fix it now. 
 
 We see that the work gets done, that the safety 
 
 law is kept up. We learn how to run all the equipment. 
 
 You want to come to work now. We all work together, 
 
 like a team. 
 
 But, fellow workers who were not involved in the pro- 
 gram called them the Communist crews. They were envious 
 of the freedom, flexibility, and higher pay of the experimen- 
 tal sections. The jealousy and suspicion among the other 
 miners at Rushton caused the UMWA local to withdraw 
 its support by a narrow vote in 1977. 
 
 Management went ahead with a modified version of the 
 program and tried to expand it to other working sections. 
 Lacking the support of the union, mine officials found it 
 hard to gain the same spirit of cooperation from the mines. 
 Miners who did not take part in the original experiment 
 balked at taking the initiative in making decisions regard- 
 ing their work. The foremen again took over the sections, 
 and again had the dual and sometimes conflicting respon- 
 sibilities for safety and production. 
 
 Although productivity did not shoot up as anticipated, 
 it did increase 3%. Job attitudes and safety, as measured 
 by the number of safety violations and inspectors' ratings, 
 shifted in a positive direction. However, accident rates 
 showed little, if any, change due to the intervention; but 
 they were low even before the experiment began. The level 
 of job skills in the workforce definitely increased; and, at 
 least among the miners involved in the experiment, a 
 greater sense of teamwork developed. Both the management 
 and the union felt that the project led to improved attitudes 
 toward each other; and these attitudes probably facilitated 
 the process of labor-management relationships during that 
 period. 
 
 HecJa Team-Building Project 
 
 During the period of March 1980 through May 1982, 
 the Bureau funded a demonstration project at the Hecla 
 Mining Co. Lucky Friday Mine, located in the Coeur 
 d'Alene region of northeastern Idaho (4). The purpose of that 
 project was to investigate the feasibility and effectiveness 
 of OD activities for the mining industry. The overall con- 
 tract consisted of the Hecla project and the Texasgulf proj- 
 ect (which will be discussed in a subsequent section). 
 
 The OD activities at the Lucky Friday Mine primarily 
 consisted of team-building and problem-solving activities, 
 as well as the necessary skills training required to support 
 those activities. A brief overview of the procedures used and 
 the results obtained at the Lucky Friday Mine is presented, 
 drawing heavily from Fiedler (4). 
 
 Background 
 
 The Lucky Friday Mine was a deep-vein, hard-rock mine 
 (silver and lead), employing about 270 miners represented 
 by the United Steelworkers of America. A comparison or 
 control mine, at which no OD interventions were made, was 
 
133 
 
 also included in the study. The comparison mine was the 
 Star Mine, also owned by Hecla Mining Co. and located 
 within a few miles of the Lucky Friday Mine. The Star Mine 
 employed about 360 nonunion miners. The safety records 
 of both mines were considered to be poor. 
 
 As is so often the case in field research, anything that 
 could go wrong did. During the intervention period, silver 
 prices increased 800% and then fell dramatically. Also dur- 
 ing the period, the Lucky Friday Mine experienced a 9-week 
 work stoppage that made assessment of the impact of the 
 OD intervention difficult. 
 
 Team Building 
 
 The primary intervention was through team-building 
 and problem-solving meetings in which a boss and his or 
 her immediate subordinates identified and resolved major 
 problems to make their unit more effective. Some of the 
 assumptions that underlie team building are (1) work teams 
 are the basic building blocks of an organization; (2) effec- 
 tive team functioning requires good leader-member rela- 
 tions, clear team goals, clarification of role expectations, 
 and individual and group problem-solving skills; (3) teams 
 can improve their performance by systematically solving 
 the major problems that confront them; and (4) enhancing 
 work team performance makes individuals more competent 
 and organizations more successful. 
 
 The classic or team-building, problem-solving approach 
 introduced at Hecla was governed by several principles. 
 
 1. Start team building, problem solving at the top of the 
 organization and work through all levels. 
 
 2. Focus attention on intact work teams consisting of 
 superiors and subordinates. 
 
 3. Focus on getting the job done; that is, find better ways 
 to accomplish the team's mission by solving major problems 
 and seizing opportunities. 
 
 4. Be data based; that is, discover problems, oppor- 
 tunities, and solutions through fact-finding and diagnostic 
 procedures. 
 
 5. Be interaction oriented; i.e., develop and implement 
 action plans to cause desired changes. Follow up and 
 evaluate actions to ensure a general team-building, 
 problem-solving framework, but use additional OD tech- 
 niques as they are appropriate. 
 
 The technique of team building involved a series of 
 meetings in which high-priority issues facing the team were 
 systematically examined and resolved. These meetings 
 usually were conducted with the aid of a consultant who 
 acted as a facilitator. Problems were defined and clarified, 
 alternative solutions were evaluated, preferred solutions 
 were implemented, and the effects of actions were monitored 
 for desired results. Team building had two expected out- 
 comes: the team's mission would be better accomplished, 
 and working relationships among team members would be 
 improved. 
 
 Five, day-long, team-building meetings with the presi- 
 dent and staff led to a formal statement of company philos- 
 ophy and goals. An agreement on corporate strategy related 
 to safety and productivity was developed. A statement of 
 each department's goals, functions, responsibilities, and 
 authority was also drawn up. 
 
 Team-building meetings were held with the top-manage- 
 ment team at the Lucky Friday Mine, as well as with the 
 operations team that included the shift bosses. These 
 meetings involved the mine manager, mine superintendent, 
 mine foremen, shift bosses, and auxiliary support super- 
 
 visors. These meetings dealt more intensively with issues 
 of organizational coordination, communication, and coopera- 
 tion. For example, support units were not delivering the 
 needed services; some individuals and work units were not 
 meeting others' expectations of what they should be ac- 
 complishing. The outcomes of these meetings were improved 
 methods for getting the job done and detailed strategies for 
 reducing mine accidents and injuries. 
 
 During the last phase of the project, team-building 
 meetings were held with shift bosses and their work crews. 
 The meetings addressed four main questions: 
 
 1. What is preventing us from doing the job in the way 
 we think it ought to be done? 
 
 2. What are we doing that helps us get the job done? 
 
 3. How can we get the job done more safely? 
 
 4. How can be make this a better place to work? 
 
 Performance Appraisal System 
 
 The development of a reliable and acceptable perfor- 
 mance evaluation system became the first accomplishment 
 of the project. This was essential for several reasons. First, 
 supervisors and managers needed feedback on the way in 
 which their own supervisors viewed their effectiveness in 
 dealing with production and safety problems. Second, an 
 appropriate performance system focused attention on the 
 areas of performance seen by management as important. 
 Thus, including safety as one of the prominent areas in 
 which supervisors and managers were judged had an almost 
 immediate effect on the emphasis lower level managers 
 placed on safety-related issues. Third, the project itself re- 
 quired data that would reflect changes in performance in 
 safety-related areas. The performance appraisal consisted 
 of three evaluation forms (one for managers, one for pro- 
 fessional and technical employees, and one for clerical per- 
 sonnel) based on a key traits and behaviors format. 
 
 Safety Activities 
 
 The OD project activities at Hecla included a review and 
 critique of Hecla's 40-h safety training course. The organiza- 
 tion's safety functions were also analyzed in various team- 
 building meetings. These resulted in specific changes, in- 
 cluding the following: 
 
 1. Reassignment of responsibility for the safety engineer- 
 ing, and safety inspection and enforcement. 
 
 2. Upgrading the mine safety person position from shift 
 boss to foreman rank. 
 
 3. Commitment to give safety training to each new 
 supervisor. 
 
 4. Commitment to develop a year-long schedule of safety 
 incentive programs at the Lucky Friday Mine. 
 
 Supervisory Skills Training 
 
 This aspect of training was given a high priority from 
 the outset. The most critical areas for training were con- 
 sidered to be in company policies, record-keeping practices, 
 standard production methods, and supervisory and leader- 
 ship skills. Part of this instruction was handled by a com- 
 mercially produced management training package. Other 
 needed skills were taught by Hecla staff members. 
 
134 
 
 Results 
 
 In terms of productivity (average tons per worker-shift) 
 and assay values of the silver and lead (a measure of the 
 amount of waste rock extracted), the results were mixed, 
 at best, and not very impressive. From the start of the OD 
 intervention until the 9-week strike, productivity and assay 
 values were dropping at Lucky Friday. After the strike, both 
 improved. One would be hard pressed, however, to attribute 
 this to the OD intervention. Figure 10-2 shows these results 
 using the 1979 preintervention period as a baseline of 100%. 
 
 With regard to safety, the results were more clear cut 
 and dramatic, as shown in figure 10-3. As can be seen, the 
 incidence rate of lost-time injuries was reduced by 46%, 
 decreasing from 21.1 injuries per 200,000 employee-hours 
 of exposure in 1980 to 11.4 injuries per 200,000 employee- 
 hours in 1981. In 1982, that rate was reduced even further 
 (to 4.0 for the month of January). The improvement in lost- 
 time injuries from 1980 to 1981 was the equivalent of 540 
 worker-shifts at the Lucky Friday. During this same time, 
 the accident rate at neither the Star Mine nor the other 
 district mines changed appreciably, although they did show 
 some signs of decreasing early in 1982. These results 
 strongly suggest that the OD intervention had a significant 
 effect on safety at the Lucky Friday Mine. Thus, the efforts 
 to reduce accidents appear to have been quite successful. 
 Mine Safety and Health Administration (MSHA) officials 
 responsible for the Idaho district expressed the belief that 
 the personnel at the Lucky Friday Mine were making ex- 
 ceptional progress toward improving their safety record. 
 
 Cost 
 
 The cost of the OD intervention project at Lucky Fri- 
 day Mine was approximately $200,000— not including the 
 time put into the meetings by Hecla management and 
 workers. Hecla has trained in-house consultants for con- 
 tinued OD interventions at its mines. 
 
 Texasgulf Management Training Study 
 
 The Texasgulf management training study was part of 
 the same Bureau contract that supported the Hecla team- 
 building project and is described in the same report by 
 Fiedler (4). Although most practitioners of OD would argue 
 that the intervention at Texasgulf was not really OD but 
 was more along the lines of traditional management train- 
 ing, the project is reviewed here rather than in chapter 9. 
 because it makes an interesting comparison with the in- 
 tensive OD-type intervention carried out at Rushton and 
 Hecla. 
 
 Background 
 
 The target site for the management training program 
 was a trona mine owned by Texasgulf and located near 
 Granger, WY. The mine employed about 500 workers, half 
 underground and half surface in the processing mill. Train- 
 ing was conducted for managers and supervisors of both 
 groups, starting in 1979. As was the case with the Hecla 
 project, Murphy's law prevailed. In 1980, the mine began 
 an effort to double its output. As a result, only 2 of the 15 
 key managers retained the same job they held at the begin- 
 ning of the study. 
 
 The intervention began with a series of interviews to 
 (a) familiarize the consultants with the organization, (b) 
 
 120 
 
 80 
 
 70 
 
 j-i 1 1 1 i i i 
 
 Intervention » 
 
 5 
 ■ 
 
 KEY 
 
 Productivity 
 Silver assay 
 Lead assay 
 
 1979 
 
 980 
 
 981 
 
 1982 
 
 Figure 10-2.— Results of organizational development interven- 
 tion at Lucky Friday Mine, showing productivity and assay values 
 of silver and lead as a percentage of 1979 baseline, preinterven- 
 tion period. 
 
 30 
 
 -Baseline 
 
 Intervention 
 
 o 
 o 
 
 key 
 
 □ Lucky Friday Mine 
 o Star Mine 
 A District mines 
 
 1 978 
 
 1 979 
 
 1 980 
 
 I98I 
 
 I982 
 
 Figure 10-3.— Incident rates of lost-time accidents for the Lucky 
 Friday Mine, Star Mine, and other mines in the Coeur d'Alene 
 mining district. 
 
 identify the major goals of management and supervisors, 
 and (c) develop a list of critical behaviors to construct a per- 
 formance evaluation scale for assessing the effects of the 
 intervention. The training program itself consisted of the 
 following four basic elements. 
 
 Objective Supervisory Performance Appraisal 
 
 A performance appraisal system was designed so that 
 managers and supervisors could become aware of their own 
 strengths and weaknesses, and those of their subordinates. 
 
135 
 
 The rating scales concentrated on supervisory behaviors- 
 how the supervisor acts, and how he or she can change in- 
 effective behaviors. This type of performance evaluation has 
 been found effective by other industries in motivating 
 employees to improve their behavior at work. 
 
 Leadership Training 
 
 The intervention used the leader match program 
 developed by Fiedler (6). This program is based on a gen- 
 erally accepted view in the leadership area that the 
 performance of leaders or managers depends both on their 
 personalities and on the specific situations in which they 
 operate. The method further assumes that it is generally 
 much easier to change critical components of the leader- 
 ship situation than one's personality or deeply ingrained 
 habits of interpersonal interactions with subordinates. 
 
 Leader match teaches individuals to diagnose their own 
 leadership styles, as well as to diagnose the leadership situa- 
 tions. The leaders are given detailed instruction on various 
 methods for modifying the situations to match their par- 
 ticular management approaches and personalities. The in- 
 struction is provided by a trainer who uses a detailed 
 manual, aided by videotaped illustrations, slides, and/or 
 transparencies. 
 
 This approach has been used by the U.S. Office of Per- 
 sonnel Management and the military services, as well as 
 by many organizations in the private sector. Validation of 
 this method is described by Fiedler (5). 
 
 Supervisory Skills Training 
 
 This training method used videotaped vignettes in ac- 
 tual and staged settings that taught the supervisor how to 
 deal with specific problems with employees. The problems 
 addressed included reinforcing safe behavior, correcting an 
 employee, overcoming resistance to change, handling an 
 irate employee, and creating a cooperative work team. 
 
 Institutionalization 
 
 Finally, to assure that the training would actually be 
 used and would remain a permanent part of the organiza- 
 tion, key personnel in the Texasgulf training department 
 learned to administer the training methods. 
 
 Results 
 
 Productivity (tons per worker-hour) changed in the 
 positive direction during the intervention. On average, the 
 Texasgulf Mine increased productivity by 1.7% during the 
 period of the intervention, whereas in the industry as a 
 whole, productivity decreased by 2.9% during this period. 
 The accident rate also improved during the last year of the 
 intervention, while the average for the industry remained 
 relatively constant. 
 
 The Texasgulf Co. commissioned an independent man- 
 agement consulting firm to conduct a company-wide job 
 satisfaction and attitude survey in 1979, prior to the begin- 
 ning of the intervention, and again in May of 1981, 4 
 months after the intervention had ended. Of particular in- 
 terest in this survey are the data relating to employee sat- 
 isfaction and dissatisfaction with the mine's safety efforts. 
 The comparison of the ratings of satisfaction prior and again 
 shortly after the intervention showed satisfaction decreased 
 only among administrative personnel and warehouse 
 
 workers who were not the focus of the management train- 
 ing program. Satisfaction increased most dramatically, by 
 23%, among the underground mine personnel, and 19% 
 among mill personnel, both of whom were involved in the 
 intervention. 
 
 Cost 
 
 The development of the management training program 
 and conduct of the study cost approximately $100,000, with 
 most of the money being spent on development of the video- 
 taped training modules and training manuals. This does 
 not include the training of the mine managers and super- 
 visors who attended all training sessions. Fiedler (4) con- 
 cluded that the management training program was far less 
 costly, and apparently no less effective in terms of the 
 criteria evaluated than was the more intensive OD inter- 
 vention carried out at Hecla's Lucky Friday Mine. 
 
 Quality Control Circles 
 
 In the last decade or so, there has been a steady and 
 dramatic growth of quality control (QC) circles in the United 
 States. QC circles are considered to be a Japanese manage- 
 ment innovation, but actually the original ideas underlying 
 the concept were introduced by U.S. experts in postwar 
 Japan. A brief review of some of the characteristics and 
 assumptions of QC circles follows, based on Goodman (8-9). 
 
 A QC circle is a group of up to about 10 workers who 
 voluntarily participate in improving a variety of perfor- 
 mance indicators (e.g., quality, downtime, scrap, or rejects). 
 The team meets on company time, and the foreman or a 
 designated senior worker acts as the team leader. Train- 
 ing is an important part of QC circles; time must be allo- 
 cated to teaching workers both elementary problem-solving 
 techniques and certain statistical data collection methods. 
 Most organizations that use QC's have a QC facilitator who 
 works with several circles in a given plant. Often a human 
 resources staff person, the facilitator has received special 
 training in working with groups. The facilitator's job is to 
 provide support and followup activities to insure that the 
 circle remains viable. While the circle leader runs the cir- 
 cle meetings, the facilitator helps the group when special 
 problems arise, interfaces with other groups in the organiza- 
 tion, and provides assistance to the team leader. 
 
 Several basic assumptions underlying the idea of quality 
 circles follow. 
 
 1. Joint problem solving should be a continuous process. 
 
 2. Problem-solving activities should improve quality, 
 costs, productivity, and safety. 
 
 3. QC circle involvement should increase the technical 
 and leadership skills of the work force. 
 
 4. Change should be more enthusiastically accepted be- 
 cause the workers will have been directly involved in pro- 
 posing improvements. 
 
 5. Recognition and participation in the problem-solving 
 process should be desirable to workers. 
 
 The benefits expected from the institution of QC circles 
 include the following. 
 
 1. For the worker, QC circles should provide a clear op- 
 portunity to participate, to become involved in work, and 
 to work with management. The circles should also provide 
 powerful mechanisms for training workers in a variety of 
 problem-solving, leadership, group-process, and presenta- 
 tion skills. In addition, QC circles should be designed to pro- 
 vide recognition for the workers. 
 
136 
 
 2. For the company, the benefits should be in increased 
 quality, lower downtime, greater organizational loyalty, and 
 the availability of the resources of all employees for solv- 
 ing problems. 
 
 3. The current state of knowledge of QC circles should 
 make introducing them relatively easy. 
 
 QC circles are not without costs, or disadvantages, in- 
 cluding the following. 
 
 1. For foremen, QC circles can just mean more work 
 placed on them by the company. Unless a foreman sees the 
 QC circle as beneficial to his or her work, the circle will 
 not be successful. As with some of the other OD changes, 
 the circle could increase the workload and stress on the first- 
 line supervisor. Some of this stress will be transferred to 
 other levels of management. 
 
 2. Most companies with QC circles use support person- 
 nel or QC facilitators. These individuals must receive 
 special training, which represents an additional cost of run- 
 ning the program. 
 
 3. Time is lost when workers meet; however, organiza- 
 tions using the plan find no drop in productivity because 
 of the motivational influence the circle meetings seem to 
 have. 
 
 QC Circles at the Captain Mine 
 
 The QC circle program at the Arch Mineral Corp. South- 
 western Illinois Coal Corp. Captain Mine, a surface coal 
 mine located near Percy, IL, was described by Chironis (2). 
 This program included a steering committee that set the 
 overall goals for the circles and monitored the program. The 
 steering committee consisted of four department heads, two 
 employees (union), and a facilitator who was individually 
 responsible for coordinating and directing the circles and 
 for training the circle leaders. Specifically excluded from 
 QC circle discussions were the topics of benefits and salaries, 
 employment policies, discharge policies, and grievances and 
 work rules. The circles were to concentrate on improving 
 teamwork, company communications, and morale. 
 
 An ideal group size for a QC circle is five to eight. At 
 the Captain Mine, 22 people volunteered to be in the cir- 
 cle; 7 were selected by drawing lots. Meetings were held 
 approximately once a week, with each meeting lasting 
 about 1 h. A project or problem was picked by the members 
 of the circle, and the leader advised management of the 
 selection. Typically, a number of problems were identified 
 and listed by the circle. A partial list of problems identified 
 by the QC circle of the Captain Mine included the following. 
 
 Excessive downtime because of truck failures. 
 
 Excess spillage off end of stacker. 
 
 Tendency for some jobs to be started but not finished. 
 
 Lack of walkways between new plant and breaker 
 building. 
 
 Lack of sufficient number of tractors. 
 
 Tendency for some chutes to plug up. 
 
 Insufficient housekeeping. 
 
 Insufficient orientation of new tipple employees. 
 
 Frequent misplacement of tools. 
 
 Insufficient organization of tipple supply yard. 
 Problem analysis is performed by the circles, with the 
 assistance of appropriate technical experts as needed. The 
 circle makes its recommendations directly to management 
 
 by using a formal management-presentation procedure. 
 This assures that management is fully cognizant of the prob- 
 lem selection, analysis, and recommended solution. 
 
 Results 
 
 QC circles have not been extensively used in the min- 
 ing industry, so that reports of results are not available. 
 Even in industries where QC circles are widespread, little 
 good data are available about their effectiveness. The Cap- 
 tain Mine did report several innovative solutions to prob- 
 lems identified, and a generally positive attitude toward 
 the program by both management and workers. Several ad- 
 ditional circles were formed at the Captain Mine. 
 
 DISCUSSION 
 
 The importance of motivation for safe and productive 
 work habits is known by everyone in the mining industry. 
 The link between organizational climate and safety and pro- 
 ductivity is becoming more apparent. Organizational devel- 
 opment as a means of positively altering the climate of an 
 organization has just started to make inroads into the min- 
 ing industry— and then only with large mining companies. 
 The years ahead should see increased use of team-building 
 and quality circle techniques, with more emphasis on 
 middle-sized companies. 
 
 REFERENCES 
 
 1. Bell, C, M. Chemers, and F. Fiedler. Organizational Develop- 
 ment Methods for Increasing Mine Safety. Paper in Mine Safety 
 Education and Training, Seminar Proceedings: Bureau of Mines 
 Technology Transfer Seminars, Pittsburgh, Pa., Dec. 9, 1980; 
 Springfield, 111., Dec. 12, 1980; and Reno, Nev., Dec. 16, 1980: comp. 
 by Staff. Pittsburgh Research Center. BuMines IC 8858. 1981. pp. 
 71-76. 
 
 2. Chironis, N. Quality Circles Raise Efficiency. Coal Age. Jan. 
 1983, pp. 80-85. 
 
 3. Coal Age. Rushton "Quality of Work" Experiment: Mixed 
 Results. Jan. 1980, pp. 19-21. 
 
 4. Fiedler, F.E., C.H. Bell, Jr., M.M. Chemers, and D. Patrick. 
 The Effectiveness of Organizations and Management Training on 
 Safety and Productivity in Metal/Non-Metal Underground Mining 
 (contract J0387230. Perceptronics Inc.). BuMines OFR 191-84. 1983. 
 296 pp.; NTIS PB 85-163285. 
 
 5. Fiedler. F., and L. Mahar. A Field Experiment Validating Con- 
 tingency Model Training. J. Appl. Psych., v. 64, 1979. pp. 247-254. 
 
 6. Fiedler, F.. L. Mahar, and M. Chemers. Leader Match IV. Pro- 
 grammed Instruction in Leadership for the U.S. Army. Dep. Psych.. 
 Univ. of WA. Seattle, WA, 1977, 241 pp. 
 
 7. Goodman, P. Assessing Organizational Change: The Rushton 
 Quality of Work Experiment. Wiley. 1979. 391 pp. 
 
 8. Goodman. P.. and R. Atkin. Labor-Management Problem Solv- 
 ing Groups. Carnegie-Mellon Univ., Pittsburgh. PA. 1982. 11 pp. 
 
 9. . New Concepts on Organizational Development. Paper 
 
 in Ergonomics— Human Factors in Mining. Proceedings: Bureau 
 of Mines Technology Transfer Seminars. Pittsburgh. Pa., December 
 3, 1981; St. Louis, Mo.. December 10. 1981: and Denver. Colo.. 
 December 15, 1981; comp. by Staff, Pittsburgh Research Center. 
 BuMines IC 8866, 1981, pp." 84-97. 
 
137 
 
 10. Lawler, E. Motivation in Work Organizations. Brooks and 
 Cole, 1973, 267 pp. 
 
 11. Maslow, A. Motivation and Personality. Harper and Row, 
 1954, 348 pp. 
 
 12 . Motivation and Personality. Harper and Row, 2d ed., 
 
 1970, 382 pp. 
 
 13. A Theory of Human Motivation. Psych. Rev., v. 50, 
 
 1943, pp. 370-396. 
 
 14. Mills, T. Altering the Social Structure in Coal Mining: A Case 
 Study. Monthly Labor Rev., Oct. 1976, pp. 3-10. 
 
 15. Sanders, M.S., T.V. Patterson, and J.M. Peay. The Effect of 
 Organizational Climate and Policy on Coal Mine Safety (contract 
 H0242039, U.S. Dep. Navy). BuMines OFR 108-77, 1976, 180 pp.; 
 NTIS PB 267 781. 
 
 16. Vroom, V. Work and Motivation. Wiley, 1964, 344 pp. 
 
 17. Wood, R. Safety and Productivity in Numbers. Coal Age, Sept. 
 1976, pp. 120-122. 
 
 18. Zohar, D. Safety Climate in Industrial Organizations: 
 Theoretical and Applied Implications. J. Appl. Psych., v. 65, 1980, 
 pp. 96-102. 
 
138 
 
 APPENDIX A.— STATIC ANTHROPOMETRIC DATA 
 FOR MALE AND FEMALE MILITARY PERSONNEL' 
 
 Figure A-1.— Standing body dimensions. 
 
 Table A-1.— Standing body dimensions, inches 
 
 Figure 
 
 
 5th percentile 
 
 95th percentile 
 
 refer- 
 ence 
 
 122.4- 
 lb male 
 
 102.3-lb 
 female 
 
 201.9- 
 Ib male 
 
 164.3-lb 
 female 
 
 1 . . 
 ? 
 
 
 Stature 
 
 Eye height 
 
 64.1 
 59.5 
 52.6 
 46.4 
 39.8 
 24.4 
 38.0 
 30.0 
 28.8 
 18.7 
 12.2 
 28.6 
 33.2 
 
 60.0 
 55.5 
 48.4 
 43.0 
 37.4 
 22.2 
 36.6 
 26.8 
 26.2 
 17.2 
 11.4 
 25.2 
 289 
 
 73.1 
 682 
 60.7 
 53.7 
 46.4 
 29.2 
 45.3 
 36.1 
 34.5 
 23.1 
 16.0 
 35.8 
 39.8 
 
 68.5 
 63.9 
 
 3.. 
 4.. 
 
 5. . 
 
 6. . 
 
 7 
 
 Shoulder (acromiale) height. . . 
 
 Chest (nipple height) 1 
 
 Elbow (radiale) height 
 
 Fingertip (dactylion) height . . . 
 Waist height 
 
 56.6 
 50.3 
 43.6 
 27.0 
 43.4 
 
 a 
 
 Crotch height 
 
 33.0 
 
 9.. 
 10 
 
 Gluteal furrow height 
 
 Kneecap height 
 
 31.9 
 20.7 
 
 11 
 
 Calf height . . . 
 
 14.4 
 
 1? 
 
 Functional reach 
 
 31.7 
 
 13. 
 
 Functional reach, extended . . . 
 
 36.5 
 
 Bustpoint height for women. 
 
 1 From U.S. Department of Defense MIL-STD-1472B. "Human Engineering Guide to Equipment Design." Dec. 31. 1974. 
 
139 
 
 15 |7 
 
 rThr.zs 
 
 19 20 
 
 1 13 
 
 Figure A-2.— Seated body dimensions. 
 
 Table A-2.— Seated body dimensions, inches 
 
 Figure 
 
 
 5th percentile 
 
 95th percentile 
 
 refer- 
 ence 
 
 122.4- 
 Ib male 
 
 102.3-lb 
 female 
 
 201.9- 
 Ib male 
 
 164.3-lb 
 female 
 
 14.. 
 15.. 
 16.. 
 17.. 
 18.. 
 19 
 
 
 Vertical arm reach, sitting .... 
 
 Sitting height, erect 
 
 Sitting height, relaxed 
 
 Eye height, sitting erect 
 
 Eye height, sitting relaxed 
 
 Midshoulder height 
 
 50.6 
 32.9 
 32.1 
 28.3 
 27.6 
 22.3 
 21.3 
 13.1 
 12.5 
 17.3 
 6.9 
 NA 
 19.6 
 15.6 
 21.6 
 17.9 
 17.9 
 43.5 
 
 46.2 
 31.1 
 30.5 
 26.6 
 26.1 
 21.2 
 19.6 
 12.1 
 11.6 
 15.7 
 6.4 
 4.1 
 18.5 
 15.0 
 20.9 
 17.1 
 17.1 
 39.2 
 
 58.2 
 38.2 
 37.3 
 33.3 
 32.5 
 26.7 
 25.7 
 15.8 
 15.1 
 20.5 
 11.0 
 NA 
 23.7 
 19.7 
 25.9 
 21.5 
 21.5 
 50.3 
 
 54.9 
 35.8 
 35.3 
 31.2 
 30.7 
 24.6 
 
 20.. 
 21.. 
 7? 
 
 Shoulder height, sitting 
 
 Shoulder-elbow length 
 
 Elbow-grip length 
 
 23.7 
 14.4 
 14.0 
 
 23.. 
 ?4 
 
 Elbow-fingertip length 
 
 Elbow rest height 
 
 18.7 
 10.6 
 
 25.. 
 26.. 
 ?7 
 
 Thigh clearance height 
 
 Knee height, sitting 
 
 Popliteal height 
 
 6.9 
 21.8 
 18.0 
 
 28.. 
 29.. 
 30 
 
 Buttock-knee length 
 
 Buttock-popliteal length 
 
 Buttock-heel length 
 
 24.9 
 20.7 
 20.7 
 
 31 
 
 Functional leg length 
 
 46.7 
 
 NA Not available. 
 
140 
 
 .33 
 
 Figure A-3.— Body depth and breadth dimensions. 
 
 Table A-3.— Body depth and breadth dimensions, inches 
 
 Figure 
 
 
 5th percentile 
 
 95th percentile 
 
 refer- 
 ence 
 
 122.4- 
 Ib male 
 
 102.3-lb 
 female 
 
 201.9- 
 Ib male 
 
 164.3-lb 
 female 
 
 32. . 
 
 Chest depth 1 . 
 
 7.5 
 NA 
 10.8 
 11.9 
 16.3 
 15.7 
 12.1 
 8.4 
 
 7.7 
 
 7.2 
 
 9.9 
 
 12.4 
 
 15.0 
 
 13.0 
 
 13.0 
 
 9.1 
 
 10.5 
 NA 
 13.5 
 14.5 
 19.6 
 21.1 
 15.1 
 10.5 
 
 10.7 
 
 33 
 
 
 Buttock depth 
 
 9.6 
 
 M 
 
 Chest breadth 
 
 12 4 
 
 35. . 
 36.. 
 37. . 
 38.. 
 39. . 
 
 Hip breadth, standing 
 
 Shoulder (bideltoid) breadth . . 
 
 Forearm-forearm breadth 
 
 Hip breadth, sitting 
 
 Knee-knee breadth 
 
 15.6 
 18.0 
 17.7 
 17.3 
 
 12.0 
 
 
 
 
 
 NA Not available. 
 
 ' Bust depth for women 
 
141 
 
 APPENDIX B.— TYPICAL JOINT MOBILITY DATA 
 SHOWING 5th and 95th PERCENTILE MALE AND FEMALE LIMITS 
 
 Male Female 
 
 Percentile 5th 95th 5th 95th 
 
 / Ankle extension (A) 18° 58° 36° 64° 
 
 Ankle flexion (B) 23° 47° 9° 29° 
 
 2 Knee flexion 
 
 129° 159° 121° 147° 
 
 
 r 3 
 
 Knee rotation 
 Medial (A) 
 
 Knee rotation 
 Lateral (B) 
 
 15° 55° 25° 63° 
 23° 63° 40° 72° 
 
 
 
 
 Percentile. 
 
 Male Female 
 5th 95th 5th 95th 
 
 ; 7 Forearm supination (A) 77° 149° 61° 117° 
 Forearm pronation (B) 37° 117° 77° 127° 
 
 8 Elbow flexion 
 
 26° 159° 140° 163° 
 
 9 Shoulder flexion (A) 168° 208° 151° 184° 
 Shoulder extension (B) 38° 84° 25° 58° 
 
 v& 
 
 ^ Hip flexion 
 
 92° 134° 56° 104° 
 
 10 Shoulder abduction (A) 33° 63° Unknown 
 Shoulder abduction (B) 106° 162° Unknown 
 
 Hip abduction (A) 
 Hip abduction (B) 
 
 33° 
 11° 
 
 73° 
 51° 
 
 Unknown 
 Unknown 
 
 Hip rotation, sitting 
 
 
 
 Lateral (A) 
 
 16° 45° 
 
 40° 72' 
 
 Medial (B) 
 
 16° 46° 
 
 25° 63 
 
 *f // Shoulder rotation 
 
 Lateral (A) 13° 55° 15° 52° 
 
 Shoulder rotation 
 
 Medial (B) 61° 133° 139° 181° 
 
 Figure B-1. — Typical joint mobility data. (Copyright 1972 by John Wiley and Sons, and reprinted by permission) 
 
142 
 
 APPENDIX C— EXAMPLES OF PICTORIAL SAFETY SIGNS RECOMMENDED 
 
 FOR USE IN THE MINING INDUSTRY 
 
 (DANGER) 
 
 I Electrical Explosion Flammable 
 
 Red border. 
 
 White 
 background 
 
 White and 
 red image 
 
 ( CAUTION ) 
 
 Fall Slip Trip 
 
 Black border 
 
 Yellow . 
 background 
 
 Black image 
 
 Entanglement Crush Poison 
 
 Corrosion Hot surface Pinch point 
 
 ^ ^ ^ 
 
 Cut or sever 
 
 ^ 
 
143 
 
 ( PROHIBITION ) 
 
 No smoking No open flame Do not touch 
 
 Red circle 
 
 Black image 
 white background 
 
 ® 
 
 (EGRESS- LOCATION) 
 
 Exit Directional arrow 
 
 Green 
 background 
 
 Green image §| ^»_«* L. ^^ ^J White 
 
 on 
 white doorway 
 
 (MANDATORY ACTION) 
 
 Eye protection Hard hat Ear protection 
 
 Safety gloves Safety shoes 
 
 Blue background 
 
 o 
 
 White image 
 
144 
 
 (SAFETY LOCATION INFORMATION) 
 
 First aid 
 
 Eyewash Safety shower 
 
 Green 
 background 
 
 White image 
 
 L_ White 
 background 
 
 Green image 
 
 (FIRE EQUIPMENT LOCATION) 
 Fire extinguisher Fire hose and reel 
 
 Red 
 background 
 
 White image 
 
145 
 
 APPENDIX D.— SUMMARY OF SELECTED DATA REGARDING 
 DESIGN RECOMMENDATIONS FOR CONTROL DEVICES 
 
 Device 
 
 Displacement 
 
 Resistance 
 
 Min 
 
 Max 
 
 Min 
 
 Max 
 
 0.125 in 
 
 15 in 
 
 10 oz 
 
 40 oz 
 
 0.5 in 
 
 NAp 
 
 NAp 
 
 NAp 
 
 1 in 
 
 NAp 
 
 NAp 
 
 NAp 
 
 NAp 
 
 2.5 in 
 
 NAp 
 
 NAp 
 
 NAp 
 
 4 in 
 
 NAp 
 
 NAp 
 
 NAp 
 
 NAp 
 
 4 lb 
 
 20 lb 
 
 NAp 
 
 NAp 
 
 10 lb 
 
 20 lb 
 
 30° 
 
 120° 
 
 10 oz 
 
 40 oz 
 
 15° 
 
 140° 
 
 10 oz 
 
 40 oz 
 
 30° 
 
 1 40° 
 
 10 oz 
 
 40 oz 
 
 NAp 
 
 NAp 
 
 NAp 
 
 4.5-6 in/oz 
 
 NAp 
 
 NAp 
 
 2 lb 
 
 5 lb 
 
 NAp 
 
 NAp 
 
 5 lb 
 
 10 1b 
 
 NAp 
 
 NAp 
 
 2.5 lb 
 
 8 lb 
 
 NAp 
 
 14 in 
 
 NAp 
 
 NAp 
 
 NAp 
 
 38 in 
 
 NAp 
 
 NAp 
 
 NAp 
 
 NAp 
 
 12 oz 
 
 32 oz 
 
 NAp 
 
 NAp 
 
 2 lb 
 
 20-100 lb 
 
 NAp 
 
 90°-120° 
 
 5 lb 
 
 "30 lb 
 
 0.5 in 
 
 NAp 
 
 NAp 
 
 NAp 
 
 1 in 
 
 NAp 
 
 NAp 
 
 NAp 
 
 NAp 
 
 2.5 in 
 
 NAp 
 
 10 1b 
 
 NAp 
 
 7 in 
 
 NAp 
 
 180 1b 
 
 NAp 
 
 NAp 
 
 4 lb NAp 
 
 NAp 
 
 NAp 
 
 10 lb 
 
 NAp 
 
 Hand pushbutton, 0.5-in min size: Fingertip operation 
 
 Foot pushbutton, 0.5-in min size: 
 
 Normal operation 
 
 Wearing boots 
 
 Ankle flexion only 
 
 Leg movement 
 
 Will not rest on control 
 
 May rest on control 
 
 Toggle switch, 0.125- to 1-in-diam control tip, 0.5- to 2-in-length lever arm 
 
 Rotary selector switch, 1- to 3-in length, 0.5- to 1-in width, 0.5-in depth: 
 
 Visual positioning 
 
 Nonvisual positioning 
 
 Knob, continuous adjustment, finger-thumb, 2 0.5- to 1-in depth, 0.375- to 4-in diam, 1.5- to 3-in hand- 
 palm diam 
 
 Crank, 2 0.5- to 4.5-in radius for light loads and 0.5- to 20-in radius for heavy loads: 
 
 Rapid, steady turning: 
 
 < 3- to 5-in radius 
 
 5- to 8-in radius 
 
 For precise settings 
 
 Levers: 3 
 
 Fore-aft (1 hand) 
 
 Lateral (1 hand) 
 
 Finger grasp, 0.5- to 3-in diam 
 
 Hand grasp, 1 .5- to 3-in diam 
 
 Handwheel, 2 7- to 21-in diam, 0.75- to 2-in rim thickness 
 
 Pedal, 3.5-in length, 2-in width: 
 
 Normal use 
 
 Heavy boots 
 
 Ankle flexion 
 
 Leg movement 
 
 Will not rest on control 
 
 May rest on control 
 
 NAp Not applicable. 
 
 1 When special requirements demand large separations, max should be 90°. 
 
 2 Displacement of knobs, cranks, and handwheels should be determined by desired control-display ratio. 
 
 3 Length depends on situation, including mechanical advantage required. For long movements, longer levers are desirable (so that movement is more linear). 
 
 4 For 2-handed operation, max resistance of handwheel can be up to 50 lb. 
 
 Source: McCormick, E., and M. Sanders. Human Factors in Engineering and Design. McGraw-Hill, 5th ed., 1982, 615 pp. 
 
146 
 
 APPENDIX E.— SELECTED DATA ON ACCESS SPACE REQUIRED 
 TO PERFORM MAINTENANCE TASKS 1 
 
 r— ©- 
 
 C. Width 
 
 D. Width 
 
 E. Height 
 
 F. Height 
 
 G. Length 
 
 H. Height 
 I. Length 
 
 Dimensions, in 
 Minimum Preferred 
 
 A. Height 48 
 
 B. Width 27 36 
 
 26 
 
 42 
 55 
 
 31 
 59 
 
 17 
 112 
 
 40 
 
 48 
 
 36 
 
 20 
 
 Dimensions, in 
 Minimum Preferred 
 
 J. Height for - - 
 
 Inspection 1 8 
 
 Using small 
 tools, making 
 minor adjust- 
 ments 24 
 
 Reasonable 
 
 arm 
 
 extension 32 
 
 K. Length 76 
 
 L. Crawl 
 through pipe 
 diam 25 
 
 M. Shoulder 
 width 
 
 N. Height 
 
 0. Square 
 Round 
 
 21 
 15 
 
 18 
 22 
 
 30 
 
 24 
 
 20 
 
 22 
 24 
 
 1 From U.S. Army Missile Command MIL-HDBK-759A, "Military Standardization Handbook: Human Factors Engineering Design for Army Mat- 
 erial," 1981. 
 
147 
 
 Opening 
 dimension 
 
 Dimension, in 
 A B 
 
 4.3 4.7 
 
 Task 
 
 Using common screwdriver, 
 with freedom to turn hand 
 through 180°. 
 
 5 1 45 Using pliers and similar 
 
 tools. 
 
 Using "T" handle wrench, 
 5.3 6.1 with freedom to turn hand 
 
 through 180°. 
 
 ft£=t 
 
 m 
 
 10.6 7.9 
 
 Using open-end wrench, with 
 freedom to turn wrench 
 through 60°. 
 
 B 
 
 4.7 6.1 
 
 Using Allen- type wrench 
 with freedom to turn 
 wrench through 60°. 
 
 3.5 3.5 Using test probe, etc. 
 
148 
 
 Opening dimensions 
 
 Dimensions, in 
 A B 
 
 Task 
 
 4.3 
 
 4.7 
 
 Grasping small objects 
 (up to 2 in or more 
 wide) with one hand. 
 
 W+1.8 
 
 Grasping large objects 
 (2 in or more wide) 
 with one hand . 
 
 W+3 
 
 Grasping large objects 
 with 2 hands, with 
 hands extended 
 through openings up 
 to fingers . 
 
 W + 6 
 
 Grasping large objects 
 with 2 hands, with 
 arms extended 
 through openings up 
 to wrists . 
 
 W+6 
 
 Grasping large objects 
 with 2 hands, with 
 arms extended 
 through openings up 
 to elbows . 
 
 Or sufficient to clear part if part is larger than 5 in 
 
149 
 
 75 pet of depth of reach (B) 
 plus 6 in 
 
 Y/////A 
 
 A. Both arms, 1 opening 
 
 4.5 in diam 
 
 5in diam 
 
 Add (3 in) for winter clothing 
 B. Arm to elbow C. Arm to shoulder 
 
 2 in 
 
 D. Empty (flat) 
 
 4in 
 
 E Empty (clenched) 
 
 Add 075in 
 for gloves 
 
 4in C 
 
 F. Holding small object 
 
 1.5-in diam 
 H. Push button access 
 
 l.75in 
 Clearance around object 
 6. Holding larger object 
 
 3.5-in diam 
 i". 2 -finger twist 
 
150 
 
 INDEX 
 
 Page 
 
 Ability 128 
 
 Access space 146-149 
 
 Accident causation: Theories of 38-40 
 
 Accident data analysis 125 
 
 Accident liability theory 38 
 
 Accident proneness 38 
 
 Accident reduction programs 119 
 
 Accident reporting 40 
 
 Accident scenario, reconstruction of 24 
 
 Accidents: 
 
 Age and 38 
 
 Back injury 82 
 
 Cab design and 66 
 
 Control design and 55 
 
 Cost of 42-44 
 
 Definition of 36 
 
 Fatigue and 39 
 
 Gold mining 35-36, 38 
 
 Handtools and 78 
 
 Haulage 37 
 
 Human error and 36-38 
 
 Illumination and 101 
 
 Job experience and 39 
 
 Material handling 91 
 
 Near miss 36 
 
 Supervisors 37, 39 
 
 Transport underground 37 
 
 Visibility and 71 
 
 Acclimatization: Heat stress and 113 
 
 Accommodation 20 
 
 Action research model 131 
 
 Acuity, visual 21 
 
 Adaption 20 
 
 Adjust to stress theory 39 
 
 Aerobic capacity 83-84 
 
 Age: 
 
 Accidents and ". 38 
 
 Accommodation and 20 
 
 Hearing and 23 
 
 Strength and 29 
 
 Alarms (see: Auditory displays) 
 Alphanumeric characters: 
 
 Size of 50-51 
 
 Stroke width to height ratio 50 
 
 Typography of 50-51 
 
 Width-to-height ratio 50 
 
 Anthropometric data 138-140 
 
 Anthropometry 27-28 
 
 Limitations of data 28 
 
 Aptitude 128 
 
 Arm reach envelopes 28-29 
 
 Attention 25-26 
 
 Auditory displays 51-54 
 
 Autonomous work groups 132 
 
 Backlash 59 
 
 Biomechanics: Of lifting 91-93 
 
 Body dimensions (see: Anthropometric data) 
 
 Canopy design 7 
 
 Cardiac output 83-84 
 
 Carpal tunnel syndrome 79 
 
 Character typography 50-51 
 
 Check-reading 48-49 
 
 Checklists 3 
 
 Circadian rhythms 30-31 
 
 Climate (see: Heat stress and cold stress) 
 
 Closed-loop system 10 
 
 Coding: Controls 56-59 
 
 Page 
 
 Cold stress 113-114 
 
 Performance and 113-114 
 
 Protection from 114 
 
 Color coding 48 
 
 Color contrast 100 
 
 Column format 13 
 
 Compatibility 60-61 
 
 Computer aids for design 17-18 
 
 Continuous movements 27 
 
 Contrast 100 
 
 Control-display compatibility 60-61 
 
 Control-response ratio 59 
 
 Controls: 
 
 Accidents related to 55 
 
 Arrangement of 61 
 
 Backlash and 59 
 
 Coding of 56-59 
 
 Control-response ratio 59 
 
 Deadspace and 59 
 
 Design criteria 145 
 
 Identification of 56-59 
 
 Placement of 61-66 
 
 Resistance in 59 
 
 Spacing of 66-67 
 
 Types of 55-56 
 
 Crewstation analysis program (CAP) 17-18 
 
 Deadspace 59 
 
 Decisionmaking 24-25 
 
 Disability glare factor 102 
 
 Displays: 
 
 Arrangement of 61 
 
 Criteria for evaluating 45 
 
 Placement of 61-66 
 
 Visual versus auditory 46 
 
 (see also: Information displays, and specific types) 
 
 Displays, auditory (see: Auditory displays) 
 
 Displays, olfactory (see: Olfactory displays) 
 
 Displays, visual (see: Visual displays) 
 
 Diurnal rhythms (see: Circadian rhythms) 
 
 Doorway placement: Surface equipment 73, 77 
 
 Drill, jackleg 3 
 
 Ear 22 
 
 Ear protection (see: Hearing protection) 
 
 Effective temperature 110-111 
 
 Egress: Surface equipment 72-74, 76-77 
 
 Electromyography 83 
 
 EMG 83 
 
 Endurance 30-31 
 
 Energy consumption 83 
 
 Energy expenditure: 
 
 Factors that affect 86 
 
 For common mining tasks 86-88 
 
 Grades of work and 86 
 
 Recommended levels of B8-S9 
 
 Equivalent sound level 103 
 
 Ergonomics (see: Human factors) 
 
 Eustachian tube 22 
 
 Evaluation testing 18 
 
 Expectancy 129-131 
 
 Expectancy theory 129-131 
 
 Experience: Accidents and 39 
 
 Extinction 121 
 
 Eye 20 
 
 Fatigue: Accidents and 39 
 
 Federal Coal Mine Health and Safetv Act 6 
 
 Feedback 120-121 
 
151 
 
 Page 
 
 Females: Handtools and 79 
 
 Field of vision: (see also: Visibility) 
 
 Low-seam equipment 66, 68-70 
 
 Underground equipment 71-72 
 
 Foot reach envelopes 28-29 
 
 Front-end loader controls 62 
 
 Frostbite 113 
 
 Functions, of humans in systems 11 
 
 Glare 101-102 
 
 Goals freedom alertness theory 40 
 
 Gold mining accidents 35-36, 38 
 
 Grip strength: Handle size and 79 
 
 Handles 95 
 
 Handling materials injuries 41 
 
 Handtool design 78-80 
 
 Accidents and 78 
 
 Handtool injuries 41 
 
 Harrison Pick machine 5 
 
 Haulage accidents 37 
 
 Haulage truck: 
 
 Maintainance problems 77-78 
 
 Controls 62 
 
 Drivers 25 
 
 Hazard recognition 35 
 
 Hearing 22-23 
 
 Discrimination 23 
 
 Intensity 23 
 
 Discrimination of tones 23 
 
 Localization of sound 22-23 
 
 Masking and 23 
 
 Hearing loss 104 
 
 Hearing protection 107-108 
 
 Heat cramps 110 
 
 Heat exhaustion 110 
 
 Heat stress 109-113 
 
 Acclimization program for 113 
 
 Conditions in mining Ill 
 
 Exposure standards 112 
 
 Indexes of 110-111 
 
 Performance and 111-112 
 
 Physiological effects of 109-110 
 
 Protection from 112-113 
 
 Unsafe behavior and 112 
 
 Heat stress index Ill 
 
 Heat stroke 110 
 
 Heat transfer 109-110 
 
 Human engineering (see: Human factors) 
 
 Human error 34-38 
 
 Accidents and 36-38 
 
 Classification of 35-36 
 
 Definition of 34 
 
 Types of 35-36 
 
 Human factors: 
 
 Definition of 2 
 
 History in mining 4-7 
 
 History of 4 
 
 In metal-nonmetal mining 7 
 
 In processing plants 7 
 
 In surface mining 7 
 
 Roadblocks to application 3 
 
 Human-hardware-environment system 3 
 
 Ice jackets 113 
 
 Illuminance 100 
 
 Illumination 99-102 
 
 Accidents and 101 
 
 Accommodation and 20 
 
 Measurement of 99-100 
 
 Performance and 100-101 
 
 Requirements for 101-102 
 
 Safety and 101 
 
 Page 
 
 Incentive programs 119 
 
 Information: 
 
 Continuous 55 
 
 Discrete 55 
 
 Information displays: Tasks performed with 45 
 
 Inherently safe mining systems 7 
 
 Injuries: Types of 41 
 
 Injury statistics 40-42 
 
 Comparisons to other countries 42 
 
 Industry-wide comaprisons 40-41 
 
 Inputs 11 
 
 International word-spelling alphabet 53 
 
 Job severity index 96 
 
 Joint mobility data 141 
 
 Ladders 73-77 
 
 Leader match program 135 
 
 Learning: Concepts of 120-121 
 
 Letters (see: Alphanumeric characters) 
 Lifting: 
 
 Aids to 95 
 
 Biomechanics of 91-93 
 
 Energy expenditure and 86-88 
 
 Posture and 93-94 
 
 Recommended limits 94-95 
 
 Reducing risks 95-97 
 
 Techniques of 94 
 
 Light (see: Illumination) 
 
 Lights: Signal, warning 49-50 
 
 Limit of resolution 10 
 
 Link analysis 16 
 
 Loading, hand 2 
 
 Loading, mechanical 6 
 
 Loudspeaker system 53-54 
 
 Luminance 100 
 
 Luminance ratio 102 
 
 Luminous flux 100 
 
 Luminous intensity 100 
 
 Machinery injuries 41 
 
 Magic number 7 plus or minus 2 24 
 
 Maintainability, equipment 77-78 
 
 Maintenance: 
 
 Access space requirements 146-149 
 
 Training for 117 
 
 Manikins 16 
 
 Mantrip trolley: Noise and 107 
 
 Manual materials handling (see: Materials handling) 
 
 Masking 23 
 
 Materials handling 90-97 
 
 Activities 90 
 
 Reducing risk 95-97 
 
 Materials, weights of 91 
 
 Memory 23-24 
 
 Mental workload 26 
 
 Metabolism 109-110 
 
 Method of loci 24 
 
 Miners, characteristics of 19 
 
 Mockups 16 
 
 Motivation 128-131 
 
 Definition of 128 
 
 Performance and 128-129 
 
 Theory of 129-131 
 
 Movement accuracy 27 
 
 Movement time 27 
 
 Movements: 
 
 Continuous 27 
 
 Positioning 27 
 
 Range of 28 
 
 Repetitive 27 
 
 Muscles 82-83 
 
152 
 
 Page 
 
 Needs: Hierarchy of 129 
 
 Noise: 102-108 
 
 Conditions in mining 103-104 
 
 Control of 105-107 
 
 Exposure standards 104 
 
 Hearing loss from 104 
 
 Hearing protection and 107-108 
 
 Indexes of 103 
 
 Measurement of 102-103 
 
 Performance and 105 
 
 Physiological effects of 104-105 
 
 Nystagmus 100 
 
 OBSAC 122-123 
 
 Olfactory displays 54 
 
 Olfactory sense 23 
 
 Open-loop system 10 
 
 Operational sequence diagrams 13-14 
 
 Organizational climate 131 
 
 Organizational development 131-136 
 
 Outputs 11 
 
 Oxygen debt 83-84 
 
 Pedals: Placement of 62 
 
 Percentiles 27 
 
 Pointer design 48 
 
 Positioning movements 27 
 
 Powered haulage injuries 41 
 
 Preferred octave speech interference level 53 
 
 Punishment 121 
 
 Purkinje shift 20 
 
 Quality control circles 135-136 
 
 Reach envelopes: 
 
 Arm 28-29 
 
 Foot 28-29 
 
 Low-seam equipment 66, 68-70 
 
 Reaction time -. 26 
 
 Reflectance 100 
 
 Repetitive movements 27 
 
 Resistance 59 
 
 Resonance 105, 108 
 
 Rest, amount required 89-90 
 
 Retina 20 
 
 Retroreflective material 49 
 
 Reward 121 
 
 Roof bolter: Energy consumption 88 
 
 Roof bolter controls 56, 59, 62 
 
 Rotary drills: Noise and 106 
 
 Rushton experiment 132 
 
 Safety awareness programs 126-127 
 
 Safety climate 131 
 
 Safety programs: 
 
 Characteristics of 119 
 
 Management and 119 
 
 Seating: Low-seam equipment 66, 68-70 
 
 Selection: For lifting 96 
 
 Shift work 32 
 
 Shuttle car 34 
 
 Training system 122-123 
 
 Signs 20, 126-127 
 
 Conceptual compatibility 60 
 
 Pictorial 51, 142-144 
 
 Size of letters 51 
 
 Typography 50-51 
 
 Simulation 122-123 
 
 Slip and fall injuries 41 
 
 Smell 23 
 
 Sound localization 107 
 
 Sound pressure level 103 
 
 Page 
 
 Sound-level meter scales 103 
 
 Speech 52-53 
 
 Hearing protection and 53 
 
 Intelligibility of 52-53, 107 
 
 Intensity of 52 
 
 Noise effects on 53 
 
 Spine 92-93 
 
 Stairs 73-77 
 
 Standardization 61-62 
 
 Static effort 85 
 
 Stench systems 23, 54 
 
 Strength 29-31 
 
 Strength testing 96 
 
 Supervisor accidents 37, 39 
 
 Systems: 
 
 Boundary of 10 
 
 Characteristics of 9-11 
 
 Definition of 9 
 
 Objectives 12 
 
 Specifications 12 
 
 Stages in design of 12-18 
 
 Task analysis: 12-16 
 
 Formats for presenting 13-15 
 
 Methods for collecting 13 
 
 Type of information collected 13 
 
 Team building 132-134 
 
 Temperature (see: Heat stress and cold stress) 
 
 Timelines 13, 15 
 
 Tool design (see: Handtool design) 
 
 Track dozers: Noise control in 105 
 
 Training 116-126, 
 
 128, 130 
 
 Cost in mining 116 
 
 Effectiveness of 116-117 
 
 Heat stress 112 
 
 Leadership 135 
 
 Management 134-135 
 
 Materials handling 96-97 
 
 Methods of 122-124 
 
 Needs assessment 124-125 
 
 On the job 123-124 
 
 Physical fitness 97 
 
 Practices in United States 118-119 
 
 Requirements for 117-118 
 
 Systems design 124-126 
 
 Transient adaptation 102 
 
 Transport accidents 37 
 
 Trigger finger 79 
 
 Trolley operators 25-26 
 
 Troubleshooting 24 
 
 Undercutting coal 4-5 
 
 Valence 129-131 
 
 Vehicle design 63-66 
 
 Vibration: Hand-arm 79-80 
 
 Vibration-induced white finger 79-80 
 
 Vibration, whole body 108-109 
 
 Control of 109 
 
 Effects of 108 
 
 Exposure standards 108-109 
 
 Surface miner exposure 109 
 
 Vicarious learning 121 
 
 Vigilance 25 
 
 Visibility: From haulage trucks 7, 71 
 
 Vision 20-22 
 
 Accommodation 20 
 
 Adaption 20 
 
 Detection of movement 21-22 
 
 Field of vision 20-21 
 
 Visual acuity 21 
 
153 
 
 Page 
 
 Visual angle 21 
 
 Visual displays 46-51 
 
 Color coding 48 
 
 Design of pointer 48 
 
 Numerical progress 48 
 
 Scale markers 47 
 
 Warning-signal lights 49-50 
 
 Page 
 
 Walsh-Healy noise criteria 104 
 
 Wet-bulb globe temperature Ill 
 
 Windchill index 113 
 
 Work physiology 82-84 
 
 Work-rest cycles 89-90 
 
 Workstation design: 
 
 Seated 63-66 
 
 Standing 66-67 
 
 U.S. GOVERNMENT PRINTING OFFICE: 1988 - 505-016/80,013 
 
 INT.-BU.OF MINES,PGH. ,PA. 28696 
 
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