ML20137L926

Heat Stress Mgt Program for Nuclear Power Industry, Interim Rept

ML20137L926
Person / Time
Site:	Fort Saint Vrain
Issue date:	12/31/1985
From:	Balint L, Bernard T, Kenney W GENERAL PUBLIC UTILITIES CORP., PENNSYLVANIA STATE UNIV., UNIVERSITY PARK, PA, WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
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ML20137L904	List: ML20137L900 ML20137L926
References
PROC-851231, TAC-59787, NUDOCS 8601280138
Download: ML20137L926 (194)

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Heat Stress Management Program for the Nuclear Power Industry prepared by Westinghouse Electric Corporation with Pennsylvania State University GPU Nuclear Corporation December,1985 prepared for Electric Power Research Institute

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k Heat Stress Management Program for the Nuclear Power Industry RP2166-5 Interim Report Prepared by WESTINGHOUSE ELECTRIC CORPORATION Research and Development Center Pittsburgh, PA 15235 Principal Investigator l Thomas E. Bernard with contributions by PENNSYLVANIA STATE UNIVERSITY Noll Laboratory for Human Performance Research University Park, PA 16802 RP2166-3 l

i W. Larry Kenney and GPU NUCLEAR CORPORATION inree Mile Island Nuclear Generating Station Middletown, PA 17057 RP2166-6 Larry Balint Prepared for Electric Power Research Institute 3412 Hillview Avenue Palo Alto, CA 94304 i EPRI Project Manager John F. O'Brien Nuclear Engineering and Operations Nuclear Power Division

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LEGAL NOTICE This report was prepared by the organizations named below as an account of work sponsored by the Electric Power Research Institute Inc. (EPRI). Neither EPRI, members of EPRI the organizations named below, nor any person acting on behalf of any of them: (a) makes any warranty, express or implied, with respect to the use of any information, apparatus, method, or process disclosed in this report or that such use may not infringe privately owned rights; or (b) assumes any liabilities with respect to the use of, or for damages resulting from the use of, any information, apparatus, method, or process disclosed in this report.

Organization (s) that prepared this report: Westinghouse Electric Corporation, Pittsburgh, PA: Pennsylvanta State University, University Park, PA; GPU Nuclear Corporation Middletown, PA i

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ABSTRACT A program for managing heat stress in work situations has been developed. The program content is based on current industrial practices, current literature, surveys of nuclear power plants, and other EPRI research.

The objective of the program is to control the effects of heat stress through (1) evaluation, (2) countermeasures, (3) training, and (4) medical evaluation.

The evaluation scheme is presented as a decision tree that includes the effects of clothing, work demands (metabolism), and environmental factors. The counter g measures, which are suggested through the use of the decision tree, cover engineering controls, work practices, and personal protection. A complete training program is presented, with recommendatioh, for content, types of training and frequency. The medical evaluation includes a simple checklist for oreliminary ,

evaluation of personal risk factors. If risk factors are present, an cottonal exercise test can identify the level of relative heat tolerance.

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ACKNOWLEDGMENTS All EPRI-member nuclear stations helped the project by completing a detailed questionnaire on heat stress, and four stations graciously hosted a two-day site visit. The project was monitored by a Technical Advisory Group, which included:

H. F. (Hank) Pauley Duke Power Company Donnie R. Butler Tennessee Valley Authority Joseph L. Danek Florida Power and Light Ted Hogan, Ph.D. Comonwealth Edison Company James A. Kegebein Visucom Productions, Inc.

James B. Lancour, Ph.D. Georgia Power Company Bradley A. Parfitt GPU Nuclear Corporation William A. Pillsbury, M.D. Baltimore Gas and Electric Company Leonard A. Sagan, M.D. Electric Power Research Institute Howard R. Schumacher Sacramento Municipal Utility District Richard L. Warner Southern California Edison The group met twice with the authors and reviewed draf ts of the document. Their contributions were important to the success of the project.

1 In addition, valuable experience was provided by Dr. Suzanne H. Rodgers-(consultant) Dr. Jerry D. Ramsey (Texas Tech University), and Dr. David M. Kiser (Eastman Kodak Company). They also reviewed the technical direction of the program and commented on a draft of the document.

Dr. John F. O'Brien was the EPRI Project Manager. His guidance and support provided invaluable assistance to the project.

Within Westinghouse, Dr. Lewis F. Hanes provided management support, Dr. Albert A.

Spritzer commented on medical evaluation, and Dr. Mary C. Culver gave editorial assistance. Mrs. Betty Palocsko typed the original manuscript, and the Word Processteg Center suffered through the many revisions.

In support of the Pennsylvania State University activities, 51 men and women participated in heat stress experiments, which were diligently supervised by Debra A. Lewis and Ruth K. Anderson. Charles A. Ryan and N. Scott Demo provided technical support and Dr. Eliezer Kamon provided consultation. ,

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PREFACE The Heat Stress Management Program was prepared as an aid for nuclear utilities in which workers may be subject to the effects of heat stress. It is designed to control heat stress in order to protect workers and enhance performance.

Although the program was planned for the nuclear industry. it is applicable to all types of industries. The methodology is comprehensive and adaptable.

The program as presented in this interim report is ready for implementation. A demonstration of the program is planned at a nuclear site. A final report will then be issued to incorporate any additions or modifications suggested by the-

demonstration.

The report is organized so that important background topics are covered in the first four sections (Sections 1 - 4). A detailed overview of the report has been included in Section 1.5 along witn a recommendation concerning the personnel who

) need to read each section.

Section 5 explains the evaluation methodology developed for the program. Sections

) 6 - 8 cover countermeasures. Section 9 describes a medical evaluation process developed at the Pennsylvania State University under EPRI contract RP2166-3. A comprehensive training program is presented in Section 10.

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l i CONTENTS Section P_qgg 1 INTA000CTION 1-1 1.1 Program Goals 1-1

1.2 Background

1-2 1.3 Heat Stress in Nuclear Power Stations 1-3 1.3.1 Causes of Heat Stress.

1-3 1.3.2 C'ircumstances Associated with Heat Stress 1-4 1.4 Heat Stress Management 1-5 1.4.1 Evaluation and Countermeasures 1-5 1.4.2 Training Program l 1-6 1.4.3 Heat Stress Advisor 1.5 Document Description 1-6 l

1-9 1.5.1 Introduction

! 1.5.2 Heat Exchange and Thermophysiology 1-9 4

1-9 1.5.3 Recognition and Treatment of Heat Illness 1-10 1.5.4 Current Standards and Practices

, 1-10 1.5.5 Evaluation of Heat Stress 1-11 1.5.6 Engineering Controls i

1-11 1.5.7 Work Practices

] 1-11 1.5.8 Personal Protection j 1-12 1.f.9 Medical Evaluation for Heat Stress 1-12 f 1.5.10 Training 1-12 2

HEAT EXCHANGE AND THERM 0 PHYSIOLOGY

} 2-1 2.1 Heat Transfer 2-1 2.1.1 Metabolism 2.1,2 Convection 2-2 2-2 2.1.3 Radiant. Heat '

2.1.4 Evaporation 2-3 2-3 2.2 Physiological Responses to Heat Stress 2.2.1 Cardiovascular Responses 2-5

) 2.2.2 Sweating Responses 2-5 2.2.3 Body Temperature 2-6 2-6 5

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2.2.4 Acclimation 2-7 l 2.2.5 Hydration 2-9

) 3 RECOGNITION AND TREATMENT OF HEAT ILLNESS 3-1 3.1 Heat Rash 3-1 3.2 Heat Cramos 3-3 3.3 heat Syncope 3-3 3.4 Heat Exhaustion 3-4 1 3.5 Heat Stroke 3-5 4 CURRENT STANDARDS AND PRACTICES 4-1 4.1 Evaluation Methods 41 1

4.1.1 Standards for Heat Stress Evaluation 4-1 4.1.2 Armed Forces 4-5  !

! 4.1.3 Evaluation Methods Used in Industry 4-6 l 4.1.4 Comments on Evaluation Methods 4-8

4.2 Current Practices to Manage Heat Stress 4-8 4.2.1 Engineering Controls 4-9 i

4.2.2 Work Practices 4-12

!- 4.2.3 Personal Protection 4-16 1

5 EVALUATION OF. HEAT STRESS 5-1 5.1 Description of Required Data 5-1 5.1.1 Environment 5-1 f 5.1.2 Clothing 5-5

) 5.1.3 Metabolism 5-6 1 5.2 Data Gathering 5-8 I

5.2.1 Job / Location Identification 5-8 5.2.2 Environmental Data Collection 5-10 I

5.3 Evaluation of Heat Stress 5-13 5.3.1 Use of Decision Tree 5-13 5.3.2 Order of Priority 5-15 5.4 Reconenendations for Countermeasures 5-16 5.4.1 General Recommendations 5-16 5.4.2 Specific Reconnendations ~ 5-17 6 ENGINEERING CONTROLS 6-1 6.1 Effects of Engineering Controls on Evaluation 6-1 6.1.1 Goals of Engineering Controls 6-2 6.1.2 Reevaluation of Heat Stress 6-3 Y

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6.2 Metabolism 6-3 6.2.1 Evaluation of Metabolism by 7ask Analysis 6-3 6.2.2 Reduction of the Metabolism 6-6 6.2.3 Evaluation of Reduced Metabolism 6-7 6.3 Air Temperature and Humidity 6-7 6.3.1 Ventilation 6-8 6.3.2 Central Air Conditioning 6-10 6.3.3 Local Air Conditioning 6-11 6.3.4 Selection of Air Cooling Method 6-12 6.4 Air Velocity 6-12 6.5 Radiant Heat 6-13 6.5.1 Insulating Hot Surfaces 6-14 6.5.2 Changing Surface Emissivity 6-14 6.5.3 Shielding 6-15 6.6 Maintenance 6-15 6.7 Estimating the Changes in W8GT Due to Engineering Controls 6-16 6.7.1 Air Temperatun 6-16 6.7.2 Air Velocity 6-17 6.7.3 Natural Wet Bulb 6-17 6.7.4 Globe Temperature 6-17 6.7.5 Recalculation of W8GT 6-20 7 WORK PRACTICES 7-1  ;

7.1 Self-0etermination 7-1 7.1.1 Self-pacing 7-1 7.1.2 Self-limitation 7-2 7.2 Fluid Replacement 7-2 7.2.1 Replacement Schedule 7-3 7.2.2 Barriers 7-3 7.2.3 Replacement Fluids 7-4 7.3 Acc11mation 7-4 7.4 Scheduling Hot Work 7-5 1.5 Stay Times and Recovery 7-5 7.5.1 Stay Times 7-6 7.5.2 Estimation of W8GT for Stay Times 7-9 7.5.3 Recovery Times 7-9 7.6 Clothing 7-11 7.7 Buddy System 7-12 vi

k 7.8 Personal Monitoring 7-12 7.8.1 Body Temperature 7-12 7.8.2 Heart Rate 7-13

} 8 PERSONAL PROTECTION 8-1 8.1 Circulating Air Systems 8-1 8.1.1 Principle of Operation 8-1 ,

l 8.1.2 Types of Circulating Air Systems 8-2 8.1.3 Use of Circulating Air 8-4

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8.2 Ice Cooling Garments 8-9 -

8.2.1 Principle of Operation 8-9 8.2.2 Types of Ice Cooling Garments 8-9 8.2.3 Reconniended Methods 8-10

, 8.3 Liquid Cooling Systems 8-14

8.3.1 Principle of Operation 8-14 4

8.3.2 Types of Liquid Cooling Garments 8-15 8.3.3 Reconsiended Method of Use 8-16

! 8.4 Reflective Clothing 8-18 I

8.4.1 Principle of Operation 8-18 8.4.2 Types of Reflective Clothing 8-18 8.4.3 Reconenended Methods of Use 8-18

9 MEDICAL EVALUATION FOR HEAT STRESS 9-1 9.1 Physician's Guide for Evaluating Workers for Hot Jobs 9-2

.j 9.1.1 Background 9-2

{ 9.1.2 Medical Evaluation Checklist 9-7 9.2 Heat Tolerance Exercise Test 9-9 l

9.2.1 Background 9-9 j 9.2.2 Exercise Test 9-10 9.2.3 Intepre:ation 9-11 l 9.3 Recomendations 9-12 4 9.4 Hypothetical Application 9-12 10 TRAINING 10-1 I 10.1 Background 10-1 10.2 Overview of Training Program 10-2 10.3 Formal Training 10-3

, 10.3.1 Objectives 10-3 10.3.2 Content 10-4 i 10.3.3 Delivery 10-9 10.3.4 Program Development 10-10 j vit

10.3.5 Activities 10-11 10.3.6 Training Costs 10-11 4

10.3.7 Other Considerations 10-11 10.4 Workplace Meetings 10-17 10.4.1 Objective 10-12 10.4.2 Content 10-12 ,

i 10.4.3 Format , 10-12 10.4.4 Program Development 10-13 10.4.5 Training Costs 10 13

, 10.5 Heat Stress Alert 10-14

{ 10.5.1 Objective 10-14 10.5.2 Content 10-14 i 10.5.3 Format 10-14 j 10.5.4 Costs . 10-15 i

i 11 REFERENCES 11-1 l

APPEN0!X l HEAT STRESS CON 0! TION DESCRIPT!0MS ANO COUNTERMEASURES A-1 i

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LIST OF ILLUSTRATIONS F1qure P,,, age 2-1 Time Course of Body Temperature for Cycles of Work and Rest 27 Where the Recovery is Adequate 2-2 Time Course of Body Temperature for Cycles of Work and Recovery 2-8 Where the Recovery is M Sufficient 2-3 Adjustments of Body Temperature, Heart Rate, and Sweat Rate 2-8 During Acclimation by Oaily Exposures to Heat Stress 41 Body Core Temperature as a Function of Metabolism and 4-3 Environmental Heat Stress with the 5th Percentile ULPZ 4-2 Heat Stress Action Levels as Proposed by Otfferent Organizations 4-4 4-3 Schematic Curve Illustrating the Relationship 8etween Stay 4-15 Time and W8GT 5-1 Environmental Assessment Fors 5-9 5-2 Decision free for Evaluation of Hot Environments with 5-14 Condition Numbers that are Keyed to Further Infornation in the Appendix (The Cecision Tree is Also included in the Appendix Along with a Version for 'F) 6-1 Task Analysts Form for Listing the Individual Tasks that 6-4 are Performed in Completing a Job Described in the Environmental Assessment (Figure 5-1) 6-2 Floor Plugs Removed in Turblee Butiding to Aid General Ventilation 6-9 63 Portable Fan used to Cool Workers 6-14 6-4 Illustration of Method to Approximate Angles for Radiant 6-19 Heat Treatments in Order to Estimate fg 1-1 As Used by One Nuclear Site, Heat Stress Survey Results are 7-10 Posted as W8GT ('F) for Different Locations, and Information on Minimum and Maximum Stay Times can be obtained from Posted Procedure Sheets , ,

81 Vortex Tube used to Supply Cooled Air from a Compressed Air Source 8-3 8-2 Example of 4 01stributton free for 01 rect feed Circulating 8-3 Air System 8-3 A Otstribution Vest for Direct Feed Circulating Air Cooling Systems 8-4 8-4 Vortex Tube Hanging From Inlet Air Hose Away From the User 8-8 in

8-5 An Ice Cooling Garment with Insulating Jacket 8-10 8-6 A Chest Designed to Freeze Ice Packets by using Gas Released 8-11 from a Liquid N2 Dewar 8-7 Modular Liquid Cooling Garment 8-15 8-8 Integrated Liquid Cooling Garment 8-16 9-1 Candidate Checklist that can be used as an Initial Evaluation 98 for Heat Stress intolerance a

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LIST OF TA8LES Table _Pajte 3-1 Sunnary Table of Heat 01sorders 3-2 3-2 Distinguishing Features of the Two Types of Heat Exhaustion 3-5 4-1 Tabulation of Countermeasures Recommended in Six Heat 4-10 Stress Evaluation Documents 5-1 Categories of Air Velocity 5-4 5-2 Tyr,1calClothingEnsemoles(withreferenceabereviations) 5-5 5-3 Table of Metabolisms for Otfferent Activities 5-7 6-1 Maximum Air Velocities for Comfort Around a Working Person (9) 6-13 6-2 Estimation of T mb IPO* pI *b for 01fferent Air velocities 6-17 7-1 Schedule of Reacclimation after 01fferent Periods Away 7-5 From Heat Stress Exposures 7-2 RangesofStayTimesinMinutes(or"h"forHours)for 7-7 OffterentW8GTS(andBotsballReadings)In'Cand'Fby ,

Combinations of Clothing Ensemele and Metabolism (NL means greater than 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />) 73 Ranges of W8GT in 'C ('F) for Different Ranges of Stay Times 7-8 in Minutes (or "h" for Hours) by Combinations of Clothing Ensemble and Metabolism 7-4 HeartRateRecoveryPatternstoIndicateLevelofStress(See},1) 7-14 8-1 Recomended Maximum Air Temperatures for Supplied Air Entering 8-6 Circulating Air Cooling Systme 4r Indefinite Stay Times at 0tfferent Metabo11ses 8-2 Approximate Service Time Increments (STI) in Minutes for Ice 8-13 Garments that Start at 6'C (20'F) Per Kilogram (or found) of Ice 9-1 Sten Height and Stepping Frequency for a Stool Stepping Exercise 9-11 92 Test Sample Percentiles from EPRI RP2166-3' Associated with 9-11 the HRgg Score xi

SUMMARY

EFFECTS OF HEAT STRESS a worker subjected to heat stress will experience increases in body temperature, heart rate, and sweating as normal responses to the exposure. These responses '

nean that the worker also has significantly increased the risk of heat illness, fatigue, accident, and judgment errors. Depending on the conditions of the exposure, heat stress can cause decrements in work performance, Icst time accidents, damage to equipment, and fatalities.

About 355 of plant employees account for most of the heat stress exposures, but almost all workers exposed have noted a drop in their ability to work and felt that their safety could be jeopardized. This meant that there were decreases in performance before any signs of heat tilnesses. There were also reports of nausea, weakness, and faintness, which are signs of heat exhaustion. While the entreme effects are not consen, as evidenced by the good safety record of the industry, control of heat stress leads to improved worker health and safety and performance.

PROGRAM DESIGN Methods to control heat stress have been proposed by government agencies, industries, universities, and the armed forces. These methods were used to

~ ~ provide the framework for a comprehensive heat stress management program that was designed for the nuclear industry but can be applied to other industries. The program is to be directed by a person at the site, called a Heat Stress Advisor.

All the information needed to implement the program is contained in this document.

The principal parts of the program are evaluation, countermeasures, training, and medical evaluation.

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EVALUAfION The evaluation is performed by the Heat Stress Advisor. It includes 5 generstly accepted measure of the environment (W8GT, wet bulb globe temperature) with an estimate of air velocity, an estimate of the work demands (metabolism), and a notation of clothing requirements. With this information, the appropriate i countermeasures are identified through a decision tree. From the countermeasures l Indicated by the decision tree, the Heat Stress Advisor selects those that best j suit the constraints of the situation and the site philosophy.

COUMTEaMCASURES .

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The document provides detailed descriptions of the commonly accepted counter.

eessures, which are grouped inte three general categories: engineering controls,

.ork practices, and personal protection. The engineering controls are intended to change the level of heat stress by changing the environment. Work practices control the effects of heat stress by adjusting the way work is performed. l Personal protection provides an individual with protection from heat stress.

TRAINING PROGRAM ,

l The training program is designed to fit into annual employee training. It complements the countermeasures by providing the basic information on heat stress, !

heat illnesses, heat stress hygiene practices, and the site %ountermeasures.

There are also provisions for workplace meetings and an occasional reminder through a heat strest alert.

Mf0!CALEVALUATIO$ .

The medical evaluation process is designed to identify individuals who may be at risk for heat intolerance. An exercise test is described for the few who may be heat intolerant. The test will in11cate their tolerance in relation to workers in general.

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BENEFITS l

The Heat Stress Management Program will give the site a process for controlling s heat stress using accepted strategies. With the program, workers will be more productive and able to work with lower risk of heat illnesses and fewer accidents involving personnel and equipment.

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Section 1 INTRODUCTION 1.1 PROGRAM GOALS Heat stress is a comoination of environmental conditions work demands, and clothing requirements that tend to increase body temperature. The greater the stress, the greater is the tendency to increased body temperature. Heat stress can diminish work performance and adversely affect .vorker health and safety. In fact. entreme exposures have been fatal. While the injurious effects of heat stress are recognized and controlled in the nuclear power industry, as evidenced by its good safety record, further gains in worker well-being and productivity can be achieved through a program of heat stress management. The purpose of this document is to help a nuclear plant site develop such a program.

The program has two goals. The first goal is improved worker safety and health.

Since a person's mental and physical performance drops under heat stress, the result is more frequent sistakes and/or decreased obtlity to do the work. In the end, the worker commits uasafe acts with the potential for injury to himself and others. Also, his chances of suffering a heat-related illness increase.

The second goal is increased productivity. As a result of the program, productivity improvements should be seen in greater worker efficiency, lower radiation exposure, and/or reduced costs. Worker efficiency includes reduction in nonproductive activities and increased performance on the job. Lower radiation esposures will accompany worker efficiency as a result of less nonproductive time spent in radiation areas and less time needed to complete a task. Cost reductions can occur with a decrease in errors and in lost time due to heat illnesses.

ine program manages heat stress through three means: (1) environmental assessment,(2) countermeasures,and(3)employeetraining. The environmental assessment process provides the evaluation tools that enable a person to select appropriate countermeasures. Countermeasures include engineering controls, work practices, and personal protection. Training addresses the causes and effects of heat stress, heat illnesses, and the prevention of overemposure to heat stress, 11

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Other features of the program include backgecund information for medical t

evaluation and detailed treatmert methods for the medical staff. I i

l 1.2 BACKGROUNO i  ;

) In 1971, the Electric Po.er Research Institute (EPRI) sponsored a study of human l factors issues in power plant maintenance (RP1126). The study identifled heat

, stress as a major cause of reduced worker capability. Thereport(NP1567)(1) j documented high temperatures in tha work environment, heavy .ork demands, and cerscral protective gear as the causes of increased sweating, htqher body l tea:eratures, and elevated heart rates in the workers, in other words heat strain.

j !t concluded that heat stress factors resulted in noticeable worker heat strain manifested in decreased performance and increastJ potential for heat related j 111resses.

I, Ouring interviews for the study, most workers described situations in nich their  !

ability to work and their personal safety were comoromised by the heat and

! humidity, especially in comoination with vapor barrier clothing. Their drop in performance occurred before any signs of heat illness, but they had repeated i incidents of nausea, weakness, and faintness -- all signs of heat exhaustion.

Although utilities have very few reported incidents of Meat illnesses, the  !

workers' physical and mental performance is progressively compromised by increasing levels of heat stress, i

j To counteract the impairment due to heat stress EPR! Sponsored another project in I

1979 to develop and test a personal cooling garment (RP1705) (2). By wearing a specially designed ice vest, personnel studied in this project more than doubled their work time in laboratory tests and field trials. Because this approach was l successful and utilities e pressed interest in managing heat stress, a broader j project was indicated. '

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in 1963. EPR! Sponsored a project with the Westinghouse Electric Corporation  !

Research and Development Center entitled "A Program for Preventing and Mitigating ,

f Heat Stress for Nuclear Po.er Plant Workers" (RP2166 5). The project objective was to develop a program of heat stress management that can be readily implemented L at a nuclear power plant site. Important contributions to this program in the  !

l areas of medical screening and personal monitoring are the result of i research [

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and development effort by the Pennsylvanta State University under EPRI project l I

RP2166-3("HeatStress: Medical Screening and Personal Monitoring of Power Plant  ;

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Workers *). GPU Nuclear Corporation provided additional knowledge to the project under RP2166-6 (" Utility Technical Advisor Participation in EPRI Heat Stress Research").

The information contained in this document is a synthesis of data gatnered by personnel from the three EPRI projects. The data comes from current heat stress practices in industry and the military, the open literature, laboratory tests, a mail-out questionnaire to nuclear power stations, and site visits to four nuclear stations. The project team evaluated the data sources and integrated the relevant data into the Heat Stress Management Program with the advice of a Technical Advisory Group (TAG), which was composed of utility representatives fast 11ar with nuclear power stations. At two meetings, the TAG reviewed project progress and proviced direction for the project. This report was also reviewed by the TAG.

1.3 NEAT STRESS IN NUCl. EAR POWER STATIONS Results from the mail-out questionnaire provide a picture of heat stress as it exists in the nuclear power industry. More than half the total numoer of exposures to heat stress at a nuclear power station are received by one-third of the plant employees. Other plant employees account for another 15% of the esposures.

The most exposed group are the maintenance workers, especially those doing mecnsnical maintenance. Operations and health physics personnel are also affected by heat stress. Contractor personnel receive about 30% of the heat esposures, which is about the esposure expected for the number of contractors involved.

1.3.1 Causes of Heat Stress The chief causes of heat stress in the nuclear power industry are the environment, clothing requirements, and metabolism (work demands). Usually, there is some combination of these causes, tuch as plastic suits worn over cotton coveralls during periods of high work demands.

The environmental causes are the high temperatures, high humidities, and hot surfaces of the nuclear steam systems. Heat losses and steam leaks account for much of the high air temperature and humidity during operations. The outside environment can also make work areas hot and humid, adding to the plant heat sources. Another environmental source is radiant heat from hot surfaces, which occurs when the plant is at or near operating temperatures, 13

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] Clothing requirements represent the second cause of heat stress. While it is J necessary to protect the worker from radiological contamination, protective clothing has undesirable consequences. Such clothing reduces mobility and visual t j acuity, but the most significant problem is the restriction of body cooling by l sweet evaporation. Cotton co.>eralls allow some cooling by evaporation, but double t

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coveralls or vapor barrier clothing greatly reduces the important cooling power of }

sweat.

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i Heavy work or high metabolism is the third cause of heat stress. In this case, i f the waste heat from the chemical reactions (metabolism) that occur in working l mseles must be dissipated. Both the envirorment and protective clothing make it 1 1 '

] harder for the body to dissipate the estra heat caused by work. Heavy work is wsually associated with climbing ladders and stairs, turning valves, and lifting i

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or moving heavy objects, all of which are typical maintenance and operations work. '

an additional cause of heat stress is the lack of acc11mation to heat stress among

{ sow of the workers. This is most likely to occur when they have not been i f recently exposed to heat stress and therefore have not fully developed their j tolerance.

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1.3.2 Ctrcumstances Associated with Heat Stress l The conditions associated with heat stress Can be best defined by location in the  !

I plant, type of work, plant status, time of year, and clothing requirements. ,

Most examples of the heat stress (about two-thirds) occur in the containment building or drywell, depending on the reactor type. Within these areas, the most I likely jobs are refueling and reactor cooling (or rectreulation) pump j maintenance. Other jobs associated with heat stress include steam generator ,

l repair, work around the pressurt2er, repairs on the control rod drives, and valve operation and maintenance.

The turbine and auxiliary but1 dings provide about the same number of heat stress

! conditions, but both are a distant second to the containment butiding in this .

j respect. Jobs involving valve operation and maintenance as well as repairs to i steam leaks are also mentioned frequently ~with regard to heat stress.

1 Heat stress is most liktly to occur when the plant is at or near operating temperatures. It will also occur during hot statdown, in the early part of an 4 14 t

l outage, and when the plant is being heated up at the end of an outage. When the I

plant is in an extended outage. heat stress is also reported during the hot weather of the summer months.

Double cotton coveralls or vapor barrier suits are frequently cited as the cause of heat stress. About one-half of all heat stress jobs require the use of heavy l

protective clothing, and two-thirds of these also require respiratory i protection. Due to the contaminated steam loop, BWRs have reported more heat stress jobs that require protective clothing and filter respirators than PWRs.

1.4 HEAT STRES$ MANAGEMENT t

A program for heat stress management was developed from currently accepted 3 practices (see Section 4) and the needs of the nuclear power industry. The l program is described in this document. Key components of the program are (1) a

! systematic evaluation of heat stress with recommendations for effective countermeasures, (2) a training program for those workers who may be exposed to heat stress and their supervisors, and (3) a Heat Stress Advisor who is responsible for the administration of the heat stress program.

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1.4.1 Evatustien and Countermeasures An estimate of the heat stress must be developed first. This requires an assess-ment of the environmental factors by measuring air teeperature, wet bulb tempera-ture, globe temperature, and air motion. Metabolism is estimated based on typical activities. Because clothing plays an important role in heat exchange, the evalu-ation also considers several clothing ensembles.

Once the heat stress is evaluated, a decision tree presented in Section 5 guides the user to a set of countermeasures that are appropriate to the condition.

The countermeasures fall into three categories: engineering controls, work prac-j tices, and personal protection. For any given condition, several specific i

countermeasures are suggested, which can be tailored to the specific site l constraints. In general, the engineering controls are methods that can be implemented to change the environment so as to reduce the heat stress. Work practiccs are changes in the way the work is performed to control the exposure to ,

heat stress. Personal protection includes devices that can provide protection against the heat stress and allow longer work times.

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Engineering controls are always encouraged for the management of heat stress .

because they actually lower the level of heat stress {moosed on the worker by the job. These controls can be either temporary or permanent. In cases where engineering controls are not possible, the decision tree indicates work practices [

f and, if necessary, personal protection.

l 1.4.2 Training Program

The crimary targets of a training program in heat stress are the workers exposed

{ to heat stress and their supervisors. In addition, the emergency response team l and the plant nurse or other staff responsible for first aid need to be proficient ,

in recognizing and treating heat illnesses.

i for general training, emphasis is on a basic understanding of the causes of heat

} stress, the physiological responses, hygiene practices, and heat llinesses. Addf-I tional training is necessary for heat stress countermeasures used in the plant.

The purpose of training is to teach the worker how to deal with heat stress -

erNsures and especially how to recognize when he is nearing an overexposure.

) Knowledge of the causes of heat stress and the physiological responses to it j provides the foundation for understanding hygiene practices and recognizing

symptoms.

i i

] The first aid treatment of heat illnesses occurs at the plant. Because early I treatment is important, the people responsible'for first aid must vi x how to

recognize and treat the most conson and the most serious forms of 4l t illnesses.

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1.4.3 Heat Stress Advisor '

l An effective Heat Stress Management (HSM) Program must have a person who ts  ;

l responsible for implementing the program and who has strong senior managemrat support. This person is referred to as the Heat Stress Ady'isor (HSA). Th* HSA i

{ should be an individual rather than a conmittee because one person at the s'te 3

should have detailed and integrated knowledge of the HSM Program, but it 19 not ,

] necessary or practical to have more than one with the same depth of inf',r1 nation.

i i

The most logical candidate is a person responsible for industrial hygiene. If there is a separate safety function, a person with this responsibility is an L

) alternative. The next logical location for the HSA is within the Radiation j Protection organtration.

}

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The HSA should be recognized by plant management as having the heat stress management duties. If the site has a safety committee. the HSA can interface with it as he or she would for any other health and safety issue.'

1.4.3.1 Responsibilities. The responsibilities of the HSA are:

. Understanding the HSM document

. Interfacing with plant management and personnel

. Evaluating the workplace for heat stress

. Recommending countermeasures

. Ensuring the proper functioning of the countermeasures Ensuring that the proper training is available Understanding the HSM Document. The HSA must be familiar with all the information contained in this document in order to understand the interrelationships among the causes and results of heat stress exposures, how the countermeasures control the exposures, and what information others will need. He may be the only person who nas a complete and integrated view of ,

heat stress management at the site.

Interface. Along with understanding the tools for heat stress management, the HSA is responsible for developing the justification for specific countermea-

sures. The countermeasures require the approval of plant management and I

supervisors, and the participation of the affected workers.

Evaluation. Before countermeasures can be reconuended, the heat stress is evaluated. This requires making temperature measurements and estimates of air movement and metabolism. The evaluation is accomplished by using a decision tree that incorporates the collected heat stress data. The end result of using the decision tree is a description of the causes of heat stress and the types of countermeasures that can be used effectively.

Reconuendations. This document reconuends the types of countermeasures that are appropriate for the heat stress condition defined through the. decision

• 8ecause the HSA and other personnel may be either men or women, an effort has been made to use gender-free language. However, to avoid the akwardness of he/she, the masculine pronoun has been used generically in this report.

1-7

i tree. The HSA reviews these alternatives in light of the constraints imposed by the site management and facilities, and then selects the best system of countermeasures to protect the workers while meeting the constraints.

Implementation. Once the countermeasures have been selected, the HSA is responsible for overseeing their implementatio_n. This requires coordination -

among the different plant organizations that are required to participate in the establishment of a countermeasure.

The HSA also follows up on.the countermeasures to determine if they are being l

used correctly, if they are working as anticipated, and if improvements or l adjustments are necessary. He takes the necessary actions to improve the

, effectiveness of the countermeasures or reevaluates the selection.

Training. The HSA consults on the development and delivery of the heat Stress ,

training and may be given responsibility for all the training. He is also available for workplace meetings or other forums for informal training as requested.

4 1.4.3.2 Time Commitment. The time required of the HSA is divided into two areas:

the startup period and program maintenance. For program startup, the following a.

tivities will require about 25 days of effort. The activities are:

I . Study the HSM document (2 days)

) . Initial evaluation (3 days) '

l .

Implementation of countermeasures (15 days)

. Setup training program (5 days)

Program maintenance includes:

Evaluation of new situations

'iupport (e.g., surveillance) of current program e Review of countermeasures in use i The mainterance activities can require between 1 and 5 days per month depending on the re' quired involvement of the HSA in the established countermeasures.

4 J

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1.4.3.3 Consultation Support. The HSA has adequate information in this report to implement a Heat Stress Management Program. He may, however, require supporting consultation. One time is for evaluation of the effects of proposed engineering controls. He may also involve an expert in heet stress to review an original script for heat stress training. Another time that the HSA may want to consult with a heat stress expert is when unique conditions may be considered such as emergency planning for extreme conditions.

1.5 DOCUMENT DESCRIPTION This report provides all the information necessary to develop a Heat Stress Management (HSM) Program at a nuclear power station. It is divided into ten sections that provide detailed information on different aspects of the program.

To assist readers in selecting which sections may be of interest, the ten sections have been outlined below in terms of Audience, Purpose, and Content. It is expected that the HSA will read the entire document. ~

1.5.1 Section 1: Introduction Audience. Everyone interested in the Heat Stress Management Program, including:

. Corporate management

• Station superintendent e

Department managers for maintenance, health physics, and operations Heat Stress Advisor (person responsible for HSM Program)

Trainer for health and safety issues e

Nurse or first aid director Corporate medical director and plant physician Purtose. To provide the framework for the HSM Program. Topics cove ed are:

Heat stress in the nuclear industry Establishing an HSM Program Content. Background material:

Past EPRI activities a

Sources of heat stress e

Role of Heat Stress Advisor 1.5.2 Section 2: Heat Exchance and Thermophysiology Audience,

e. Trainer for health and safety Nurse or first aid director e

Corporate medical director and plant physician Heat Stress Advisor l 1-9 1

Purcose. To explain the causes of heat stress and the normal physiological responses to heat stress.

Content. The causes of heat stress, illustrated through the four avenues of heat gain and loss:

• Hetabolism

. Convection

• Radiation

• Sweat evaporation 1.5.3 Section 3: Recognition and Treatment of Heat Illness Audience.

Nurse or first aid director

. Trainer for health and safety Heat Stress Advisor Corporate medical director and plant physician Purcose. To ensure that the common manifestations of excessive heat exposure are recognized.

Content. Discussion of five heat illnesses:

. Skin rashes

• Muscle cramps

. Faintress

. Exhaustion

. Heat stroke Each is discussed in terms of:

. Physiological basis

• Predisposing factors e Recognition

. Treatment 1.5.4 Section 4: Current Standards and Practices Audience. Heat Stress Advisor Purpose. To summarize the general approach to heat stress management espoused by different organizations as they form the basis of the HSM Program.

Content. Information relating to government or industry standards and descriptions of the approaches used by general industry and the military.

1-10 l

r. _. ~ . _ , - ~ _ . _ . _ . . _ . . - _ _

1.5.5 Section 5: Evaluation of Heat Stress Audience. Heat Stress Advisor Purpose. To present a methodology for evaluating the heat stress associated with a job, and to recommend the most effective countermeasures.

Content. Information necessary to evaluate the heat stress and develop recommend-ations:

. Environcental assessment

. Estimation of metabolism

= Decision tree to define the conditions

• Recommendations for countermeasures 1.5.6 Section 6: Engineering Controls Audience. Heat Stress Advisor and those who are involved in developing engineering controls (e.g., engineering deparment).

Purpose. To present the different engineering controls that can be effectively used to control heat stress.

Content. Discussion of engineering controls in terms of the sources to be controlled:

• Metabolism

. Air temperature and humidity

. Air velocity

. Radiant heat Additional topics: maintenance of engineering controls and a method for estimat.ing the effects of engineering controls on the environmental measures.

1.5.7 Section 7: Work Practices Audience. Heat Stress Advisor and those who want to know the rationale for work practices, including line supervisors of maintenance, operations, and health physics.

Purpose. To present the work practices commonly used as countermeasures to heat stress.

Content. Work practices are methods of adjusting the way work is done to limit 1-11

the exposure and the effects of heat stress. Combinations of work practices are frequently used. Tne work practices described are:

• Self-determination

• Stay and recovery times

. Fluid replacement

• Clothing requirements e Acclimation a Buddy system

. Scheduling . . Personal monitoring 1.5.8 Section 3: Personal Protection Audience. Heat Stress Advisor, as well as anyone involved-in the selection of personal protection for heat stress.

Purcose. To show the advantages and limitations of different categories of personal protection.

Content. Categories of personal protection:

• Circulating air systems

. Ice cooling garments

. Liquid cooling systems

. Reflective clothing Discussion of each category in terms of:

• Operation

• Types available

• Methods of use 1.5.9 Section 9: Medical Evaluation for Heat Stress Audience. Corporate medical director and plant physician. The HSA should also be familiar with this section.

Purpose. To summarize the important considerations for judging a person's level t

of tolerance to heat exposures, and to suggest a follow-up exercise test for individuals who may have a reduced tolerance for heat stress.

Content.

• Background on medical evaluation

• Physician's guide and checklist

. Exercise test and interpretation

• Recommendations for heat intolerant workers 1.5.10 Section 10: Training 1

Audience. Heat Stress Advisor and the person responsible for health and safety l training.

1-12  !

l Purpose. To suggest a training program and course content.

Content. Description of the training program, including:

• Heat stress causes and effects

• Heat stress hygiene

• - Heat illnesses

• Countermeasures in use

• Costs of training program l

Schedule and format e

d 1-13

..r_ , _ _ . . - - . _ . , _ . _ . , . _ _ _ _ , _ . - - - . . . ~ , - _ _ . _ . , , . , _ , . . . , , . - , . . . , . . . . - . , . _

Section 2 NEAT EXCHANGE AND THERM 0 PHYSIOLOGY Under conditions of heat stress, the body experiences a heat gain from environmental and internal sources. To maintain body temperature in a narrow and safe range of 37 to 38'C (98 to 100'F), the heat gain must be balanced by heat loss. The heat loss is controlled through physiological adaptations. This section explains the basic principles of heat exchange and the physiological responses to control it. The information will aid the reader in understanding the causes of heat illnesses, the basis for evaluation, and the rationale for countermeasures. It also provides technical information to support the training program (see Section 10).

The first part of this section elaborates on the exchange of heat (or heat transfer) between a person and his environment. The second part explains the physiological responses of the body to heat stress, referred to as thermophysiology.

2.1 HEAT TRANSFER During the course of a day, the body dissipates as much heat as it obtains so that body temperature stays about the same. This balance is expressed in a simple equation:

M+C+R=E in which M = Metabolism C = Convection R = Radiant Heat E = Evaporative Cooling of Sweat The above equation is frequently presented with a i sign before C and R. The purpose is to emphasize that C and R can represent heat gains or losses (as explained below). This notation is mathematically redundant and is not used here. When the valbe for C or R from the equations that follow is positive, it 2-1

f means a heat gain; and a negative value means a loss from the body. The equations presented in this section are intended to be qualitative and, for this reason, the coefficients and units are not provided. These can be found in several references, such as (9).

2.1.1 Metabolism M (metabolism) is a sequence of chemical reactions that occur as muscles perform work. These chemical reactions allow muscles to contract (work) and produce heat as a by-product. The harder the work, the more heat is generated.

The heat generated by the muscles is taken to the skin by blood circulation. As the blood goes through the muscles, it takes up the heat. The hot blood is then pumped to the cooler skin, where the heat leaves the bicod and is stored in the skin. The skin serves as the principal site for heat exchange with the environment. That is, the heat gain from the environment and the heat loss to the environment occur at the skin.

In the nuclear power industry, the heat generated in a worker by metabolism is a significant portion Jf the heat stress. The amount of heat generated by the muscles can be estimated from tables of typical activities. Such a table is provided as Table 5-3.

2.1.i <ection C (convection) represents the heat transfer from the air. Convection is related to environmental factors by the following relationship:

C = 0V .6 (Tg-Tg )/I c Three factors influence how much heat is transferred. One factor is the insulating effect of the clothing (Ic ). Clothing adds insulation so that the more skin that is covered and/or the thicker the cover, the greater the value of I 0"d

' c the lower the rate of heat transfer.

The second factor is air velocity (V). The higher the air velocity, the greater the rate of heat transfer. Because the air velocity is a power function, the velocity must increase by a facter of 3 to double the rate'of heat transfer.

2-2 I-__-______._-________-_____________---_-_---_-_____-__-___-_______.__________________

1 The third factor is the temperature difference between the air (Tatr) and the skin (Tskin). The larger the difference, the greater the hea't transfer rate will be.

The one important aspect of this factor is the direction of the heat transfer.

Frequently the air temperature is greater than the skin temperature (about 36'C or 96'F) and the equation is positive, meaning that the heat goes from the air to the person. When the air temperature is less than 36'C (96*F), the equation becomes negative and there is a heat loss from the body to the air. In this case, the body is cooled by convection.

2.1.3 Radiant Heat R is the radiant heat transfer. It can be described by the equation R = (Tw-Tskin)/IR Radiant heat transfer is a subtle heat exchange because the heat is from infrared energy. Radiant heat exchange occurs between two solid bodies. The best example is the warmth a person feels as he stands near a hot surface, such as a steam line

, or a fire. It is the same type of heat that is received from the sun.

Two factors affect the amount of radiant heat transfer. The first is clothing insulation (IR ). As with convection (C), the more the skin is covered or the thicker the clothing, the less the transfer of heat. This is similar to insulation on a pipe. In addition, if the clothing has a shiny surface, the infrared Ndiation is reflected away. (The values of IR andcI are different because clothing affects C and R differently.)

The second factor is the temperature difference. If the average temperature of the surrounding walls'and equipment (T w ).is greater than skin temperature, there is a heat gain. On the other hand, if the difference is negative (the surroundings have a lower temperature)t the body will lose heat by radiation.

2.1.4 Evaporation E represents the cooling of the skin by the evaporation of sweat. This is the primary mechanism for cooling the body. As the sweat is secreted onto the skin, it evaporates into the air. Since the heat necessary to evaporate the sweat is taken from the skin, the skin temperature is reduced. In this way, the heat broughttotheskinfromthe(musclesbythebloodaswellastheheatgained i

1 4

1 s 2-3 4

W

s. . . - .,__ . _ . . _.. , - _ .- _ - __.- - _. ,,

i from the environment (convection and radiation) is dissipated or removed from the body.

The recuired rate of sweat evaporation, and therefore the rate of evaporative cooling (E), is adjusted to balance the heat gain from the sum of M (metabolism),

C (convection), and R (radiant heat). It is possible that no saeating is required because the heat gain from M and the environment (either C, R, or neither) is balanced by losses (either C, R, or both). That is, the heat balance equation looks like M+R+C=0 (Remember that negative values for R and C are possible and mean that there is a loss of heat from the body.)

On the other hand, there is a maximum sweat rate. The maximum can be due to one of two facto s. The first is a physiological maximum. A person has a limit to the amount of sweat he can produce and evaporate, and therefore the amount of cooling the sweat can provide is limited. This limit is about one liter or quart of saeat per hour.

The second limit to evaporative cooling is the environment. This limit can be expressed by E,,, V0 .6 (p skin ' H0 IN E

=

2 This equation Indicates three factors that can limit maximum evaporation (E,,x)*

clothing insulation (IE ), air velocity (V), and humidity (Pg 0). As clothing 2

insulation increases, the maximum loss due to sweat decreases. This occurs because the clothing blocks at least some of the sweat from' evaporating off the skin. Obviously, when impermeable clothing is worn, there can be litte or no evaporation. As air velocity (V) increases, the maximum evaporation rate (Emax) becomes higher. Air humidity (Pg 0) is the amount of water in the air. Most df 2

the time, the humidity is considerably less than Pskin (the measure of humidity of the sweat on the skin), but as Pg2 0 (air humidity) increases, E,,x decreases until it reaches zero.

In summary, sweating will increase from zero to a maximum level to maintain a

~

balance between the heat gained from metabolism and from the environment. The 2-4

. - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ~ _ _ _ _

maximum can be either the most sweat a person can produce or the most that can be evaporated to the air. If the required sweat is greater than the maximum, the body temperature will increase because the excess heat will be stored in the body.

This situation can be tolerated only for limited periods of time without excessive increases in body temperature. This is the principle that governs the amount of time a person can work under heat stress.

2.2 PHYSIOLOGICAL RESPONSES TO HEAT STRESS (THERM 0 PHYSIOLOGY)

The human body's responses to heat stress are centrolled by an area of the brain known as the hypothalamus. This group of specialized nerve cells is connected to the skin (where temperature-sensitive nerve cells are located), the central nervous system (the brain and spinal cord), and other parts of the body. The hypothalamus acts in many ways like a thermostat in that it has a "setpoint" temperature. When heat stress raises body temperature above this fixed setpoint, a signal is created that turns on the body's cooling systems.

When heat stress occurs, the body must do two things: (1)' increase blood flow to take heat from the muscles to the skin (the cardiovascular response), and (2) increase sweat rate to dissipate heat by evaporative cooling. The result of the heat stress exposure is a change in body temperature, which becomes most pronounced when sweating is insufficient. The body also makes some adaptations (called acclimation) as it becomes accustomed to heat exposures. These responses are discussed in the following sections.

2.2.1 Cardiovascular Responses

• The cardiovascular system is composed of the heart and all the blood vessels.

During work, the heart must pump blood to the working muscles and the skin. The amount of blood sent to the muscles.is in direct proportion to the amount of work being performed. For light work, the blood flow is low and increases as the amount of work increases.

With muscular work and heat stress, the blood vessels in the skin dilate and blood flow to the skin increases. An increase in the heat that must be dissipated requires a proportionate increase in blood flow to the skin. Because the blood to the muscles and the blood to the skin follow parallel pathways, the total amount of blood pumped from the heart is the sum of the demands for the muscles and the skin (plus a little more for other parts of the body).

2-5 i

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l l

i With so much extra blood flow going to the skin for heat dissipation, the heart has to beat faster, which explains why heart rates are higher in heat stress conditions than during the same work in cooler conditions. The increasing demand for output from the heart is seen by the increasing heart rate.

2.2.2 Sweating Responses

• When there is a heat stress on the body, sweating is activated. The sweat glands produce a dilute salt solution (sweat) directly onto the skin surface. The average body has about 2 million of these glands, making them the most numerous cegans in the body. Provided that the environment is not too humid, the skin is cooled as sweat evaporates. The sweating rate increases to meet greater demands (up to a maximum level of 1 liter or quart per hour). Sweating is a powerful mechanism to cool the body, but it must evaporate to do the cooling. Therefore, saeat that drips off the body or is absorbed by clothing is not effective for cooling.

While sweating represents a powerful Comper3atory mechanism to heat stress, it also represents the price that must be paid. The sweat is composed mostly of water taken frcm the body and placed on the skin for evaporation. The loss in water through sweating can be up to 1 liter /hr. If the body dehydrates more than 1.5% of body weight (about 1.2 liters or 1.2 kg -- 2-1/2 pounds), the ability to work diminishes rapidly. This occurs because the blood volume decreases and there is not enough to support the required blood flow. It is most important to replace the lost fluids.

2.2.3 Body Temperature Another normal response to heat stress is an increase in body temperature.

Generally, body temperature will go up by 0.5'C (l'F) with work in a cool environ-ment. An increase beyond this point is a major concern because it has been asso-ciated wit'h heat illnesses, accidents, and other undesirable effects.

, Therefore, the ideal is to minimize the increase in body temperature by making sure that the required sweat loss from the heat balance equation (pg 2-1) is less than either the environmental or physiological maximum. In practice, however, this does not work. There are periods when the body temperature.goes above 38'C

(100*F), and a recovery time must be allowed to let the body temperature return to normal. Figure 2-1 illustrates'this point by showing a cycle of increasing and l

decreasing body temperature. The recovery period can involve either a minimum

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2-6 1 l

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Danger Safe E

u E

a E

iS 1 _______ _._____ ____

Work Work Work Figure 2-1. Time course of body temperature for cycles of work and rest where the recovery is adequate, activity in a cool area or less demanding work. There is a trade-off between the level of activity and the time allowance. Figure 2-2 illustrates the results of not allowing sufficient recovery, showing an accumulative build up of heat and a rise in body temperature to unsafe levels.

2.2.4 Acclimation Continuous exposure to heat causes a gradual adjustment (called acclimation) in the body systems, which leads to improved heat tolerance. These adaptations include the following:

• Lower body temperature Reduced heart rate

= Increased sweat production Production of a more dilute (less salty) sweat As can be seen in Ffgure 2-3, daily exposures to heat stress can cause a person's sweating rate to increase, with a resulting decrease in heart rate and body 2-7

Danger Safe 2

m I E

R E

3 g -

= _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _

Work Work Work Figure 2-2. Time course of body temperature for cycles of work and recovery where the recovery is ng sufficient.

39 5 , , , , .

,, , ,0 Seed Rae 3t o -

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\ k N Heart Rate lek -1.)

• 10 -

s_

8ody Tempermure

=

120

' - 1. 2

31. $ f ' I i I 3 1 1 9 ConsacWive Days of Egosure Figure 2-3. Adjustments of body temperature, heart rate, and sweat rate during acclimation by daily exposures to heat stress.

temperature. When these conditions are maintained at low levels, the physiological demands are lower and the person can work better and more safely.

Most of these changes occur within 4 to 7 days, with complete acclimation taking 12 to 14 days of exposure. But because the sweat rate is increased, fluid replacement becomes a high priority.

2-8

The ideal acclimation procedure calls for work in a hot environment for about 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> a day over a period of 8 to 10 days. The acclimation can occur whether the air is dry or humid, and is independent of work intensity. Light work for longer

periods of time'is just as good as heavier work for shorter periods.

In work situations, it is possible to acclimate safely by working under progressive heat exposures. For the unacclimated person, heat stress exposures can start at 50% of that expected of a fully acclimated worker and then increase by 10% per day. This is accomplished by adjusting either the amount of time or the amount of

, work.

The beneficial effects of heat acclimation usually persist for several weeks.

However, if the worker leaves the job, measurable losses can be detected in less than one week. It is therefore recommended that an employee's work demand be reduced when he has been away from heat stress exposures for a period of time. A schedule for reacclimation is given in Table 7-1.

i Illness, fatigue, and alcohol consumption enhance the deacclimation process, and impaired heat tolerance can be detected after as little time as a weekend.

2.2.5 Hydration Preventing dehydration is crucial in coping with heat stress. High sweat rates cause excessive loss of body fluids and hence a deficit of body water or denydration. Since body temperature is more important than body water, the brain maintains sweating, and the resultant body water deficit can be, therefore, driven to extremes. Work efficiency will be decreased even with fluid deficits as low as 1.5% of body weight, a loss frequently observed during work under heat stress.

The body combats this dehydration by several mechanisms. The hypothalamus senses the dehydration and turns on the thirst mechanism. However, even when water is plentiful, fluid losses are usually not completely replenished by immediate drink-ing. Satiety, or the feeling that one's thirst has been satisfied, comes about before body fluid levels have been adequately replenished. Therefore, even though drinking causes a temporary relief of thirst, normal body fluid levels are not generally re-established until meal times.

Prior to heat stress exposure, workers are urged to drink as much as possible without causing gastric discomfort. If drinking is possible during work, drinking 2-9

about 250 ml (8 oz) of fluid at 15-30 minute intervals is strongly encouraged.

Where ingestion of fluids is restricted (e.g., in controlled areas) work times may.

have to be shortened. Post-work' rehydration should be stressed in tr.aining.

Of interest to workers is the effect of dehydration on increasing dizziness and fainting. Sudden standing after work in a lying or sitting position during heat exposure often causes dizziness or fainting in the dehydrated worker.

The commercial market offers a wealth of so-called " replacement drinks." purported to replace electrolytes and other substances lost in the sweat. No evidence was found in this study to indicate that these commercial replacement-drinks rehydrate the body better than cool water. However, providing workers with a brand name drink frequently encourages them to drink more than if only water is provided.- If this is the case. there is nothing wrong with providing, replacement drinks, but dilute iced tea or lemonade will work just as well if the sugar content is kept low. The small amounts of salts lost in the sweat are best (and easily) replaced by eating moderately salted foods before and after heat stress exposures.

2-10.

Section 3 RECOGNITION AND TREATMENT OF HEAT ILLNESS Over exposure to heat stress can cause heat illness. Heat illnesses can be divided broadly into 5 classes in order of increasing severity: heat rash, heat cramps, heat syncope, heat exhaustion, and heat stroke. Every plant employee should be trained in the recognition and first step treatment (first aid) of these pathological states. Table 3-1 sumarizes the heat illnesses, and each is discussed below. (The descriptions in the table under Physiological Malfunctions are provided for medically trained personnel.) Unfamiliar terms can be found in a medical dictionary.

3.1 HEAT RASH Heat rash, also called " prickly heat," is a comon skin irritation caused by the skin being continuously wet with sweat. Heat rash is prevalent in any industrial environment that gives the worker unrelieved exposure to humid heat. In the nuclear power industry, the use of vapor-barrier clothing creates a humid micro-environment under the clothing. Since the skin remains wet during work, heat rash may become a problem for those workers with sensitive skin. There is a wide range of individual susceptibility.

Clinically, the sweat glands become obstructed and an inflamatory reaction ensues. The results are pinpoint red spots on the affected skin areas, a bothersome and often painful itching, and a " prickling" sensation upon further exposure to heat. Heat rash also reduces the effectiveness of the inflamed sweat gland to produce sweat and therefore cool the body.

Heat rash can often be prevented by intermittent relief from the humid environment and by maintaining dry skin as much as possible between exposures. Between expo-sures, a talcum powder or corn starch powder may be helpful for those individuals whose condition is not further aggravated by its use. While heat rash is not generally a health-threatening condition, it is important to prevent secondary infection, and if the condition persists, a physician should be consulted.

3-1

_..m . _ _ . _ . _ _ _ _ _

Table 3-1 Sumary Table of Hec' Olsorders Disorder Cause Physiological Halfunction Cilnical Manifestations Treatment

! Heat Acute obstruction of Inflanunatory reaction Punctate erythematous Intermittent relief Rash sweat glands around cbstructed glarwis vesicles on affected from humid heat unrelieved exposure to Itchy skin skin areas Maintain dry skin huald heat with skin Prickling sensations on Prevent secondary continuously wetted heat esposure infection by sweat t

Heat Profuse sweating Low serum sodium and Painful cramps in mJscles Oral administration Cramps Hard work chloride Nscle twitching in legs, of water Dehydration arms and abdomen use salted food Heat Standing ismobile Loss of vasomotor tone Weakness or fatigue Rest in recumbant Syncope Blood pooling Pooling of blood in depen- Blurred vision position Cerebral hyposta dent parts of body Pallor Oral aestnistration of l w Elevated temperatures . Syncope water

! A>

, Heat Dehydration from water Low Na* & C1 in sweat Dry mouth, excessive Bed rest in cool

! Exhaustion depletion (and/or High hematocrit, serum thirst, concentrated environment l salt depletion) protein and sodium urine Restore water (and salt)

Heavy prolonged Hypertonic contraction of Uncoordinated actions balance sweating cellular fluid (water Headache, dizziness, Provide small quantitles High urine output, depletion) fatigue of semi-liquid food

diarrhea or vomiting Hypotonic contraction of Nscle weakness may contribute to cellular fluid (salt l the dehydration depletion) l Elevated Tcore and T skin

, Heat Sudden onset of thereo- Inadequate circulatory Estremely high body. Immediate and effective l Stroke regulatory failure transfer of heat from temperatures cooling; to 38.9*C -:

l Abnormal tolerance for core to skin (>40.5*C or 105*f) (102*f) within I hr hyperthernia, and failure of central drive Absence of sweating, Use alcohol rinse, cool '

sustained exertion for sweating dry skin and chills air fans, or ice water i in young adults Irrational behavior bath

! Circulatory imparments Seizure and cosa I in older workers l Drugs f

l

[

+ _ __ _ , _ _ , . . _ . - _ _ __ _.

3.2 HEAT CRAMPS Heat cramps are characterized by muscle twitching or painful cramping, usually following heavy work with profuse sweating. The legs, arms, and abdominal muscles are the most commonly affected muscle groups. While often painful, muscle cramps are a relatively innocuous condition, and relief from cramping follows soon after the worker rests in a cooler environment. Heat cramps are more likely to occur when workers are not acclimated (e.g., early in the summer, following a lengthy illness, or upon first exposure to heat stress) since sweat is less dilute (contains more salt) in the unacclimated state.

Heat cramps are associated with large losses of sodium and chloride in the sweat. Normally, acc11mation and salting of foods are sufficient for the prevention of cramps. If cramps persist, a physician may order an oral administration of low concentration saline solution, or in extreme cases, an IV (intravenousdrip).

Workers undertaking hard physical tasks as part of the heat stress exposure should be urged to add a little extra salt to their meals. Workers on salt-restricted diets should consult their physician. Salt tablets should g be used, since they tend to cause retention of both salt and water in the digestive system (stomach and small intestine), and thus make less water and electrolytes available to the rest of the body.

3.3 HEAT SYNCOPE When a person is exposed to heat stress for prolonged periods of time, a large percentage of blood is sent to the skin for heat dissipation to the environment.

In the standing posture, gravity aggravates this situation by causing additional blood to pool in the legs. The body has a unique way of fighting this pooling: it contracts the leg muscles, and the muscle contractions force blood backi.toward the heart. However, if the individual is standing, squatting, kneeling or sitting immobile for long periods, this so-called " muscle pump" does not operate. Since each person has a limited volume of blood, the pooling of blood in skin and lower body limits the amount of blood the heart can pump to other regions of the body.

If the situation is severe enough, brain blood flow may decrease to the point

, where the individual passes out momentarily. This situation is known as heat syncope. (Syncope is synonomous with fainting.)

3-3

Heat syncope can also result from long periods of work where the person is lying on nis back. In work situations it is often necessary to assume this posture to reach out-of-the-way valves or pipes within confined spaces. After such work, the worker can prevent syncope or dizziness by standing slowly and breathing normally.

Heat syncope, in itself, is seldom life-threatening since the person regains consciousness almost immediately. Because he is no longer standing, enough blood flows to the brain. If the work area is so confining as to prevent the worker from assuming a horizontal position, he may have to be removed from the imediate area by other workers. In constrained spaces or other critical job situations, a momentary loss of consciousness may be critical. In some power plant situations, a loss of consciousness may result in a serious fall. Workers should be taught t%4 such occurrences may be prevented by a simple action, such as flexing and ur. flexing leg muscles or shuffling their feet at various times during work in constrained areas.

The initial 5)mptoms of heat syncope at0 aimilar to other prefainting conditions

-- .eakness or fatigue, blurred vision, lightheadedness, or chills. Rest in a reclining or lying position will prevent syncope. If this is impossible, the person should lower his head between his knees. When a fainting victim regains consciousness, he should be urged to drink water. Recurrent episodes suggest consultation with a physician.

3.4 HEAT EXHAUSTION Heat exhaustion is caused by dehydration from either water depletion or salt depletion. Salt depletion is rare. The cause of heat exhaustion is most often long periods af heavy sweating, although other factors may predispose a worker to dehydration (e.g., vomiting, diarrhea, excessive alcohol intake). Table 3-2 highlights the differences between water-depletion and salt-depletion heat exhau tion. Unless salt depletion is obvious, heat exhaustion should be treated as a water-depleted dehydration state.

Common symptoms are a dry mouth, excessive thirst, loss of cocrdination, dizziness, and headache. The victim often appears pale and shaky, and feels cool and clammy to the touch. While this observation is generally used to delineate heat exhaustion from the more serious heat stroke, it does not represent an absolute diagnostic criterion. Body core temperatures are usually in the 38-39'C (100-102'F) range, although they may go higher.

34

4 Table 3-2 Distinguishing Features of the Two Types of Heat Exhaustion i

Feature Water-depletion Salt-depletion Occurrence Common Less common Duration of symptoms Hours to days 3-5 days Thirst Prominent Absent Cramps Absent Present Sweating Decreased Unchanged Vomiting Rare Usual Giddiness Rare Common Urine concentration High Moderate There is a wide range of individual tolerances, with some individuals able to withstand temperatures over 39'C with seemingly no ill effects, while others become functionally debilitated at core temperatures-below 39'C. Over 90% of 1 serious heat illnesses can be classified as heat exhaustion.

1

! Treatment for heat exhaustion entails getting the victim to rest in a cool environment as quickly as possible. As long as the victim is conscious, he should

, be urged to drink as much fluids ar possible. Small quantities of semi-liquid food often help.

Although heat exhaustion caser outnumber heat stroke cases (see below). every heat exhaustion case should be treated at. having the potential to develop into heat stroke. Each documented case of hest exhaustion should be checked by a physician, nurse, or EMT before the person re-enters a heat stress situation.

3.5 HEAT STROKE Heat stroke is defined as a sudden failure of the thermoregulatory system (the body's systems that respond to heat stress). When this occurs, less blood flow is sent to the skin and sweating decreases or stops altogether. Heat stroke is a life-threatening illness and should be treated as such. Prompt attention is necessary. All employees should therefore be trained to recognize the signs and symptoms of both heat exhaustion and beat stroke.

3-5

1 When thermoregulation falls, body tarperatures may rise to over 40*C (104*F), a level that is harmful to the body's tissues, including the sensitive nervous tissue that makes up the brain. There is frequently a cessation of sweating, causing the skin to appear dry, red, and warm to the touch. The victim experiences chills, often accompanied by nausea and dizziness. He may become confused or irrational. Seizures and coma follow quickly if the body is not rapidly cooled (to <39'C or 102*F within the first hour).

While emergency medical personnel at the site can take'a rectal temperature, suspicion of heat stroke from other symptoms is sufficient reason to begin treatment. An alconol rinse, cool air fans, and cool water baths are effective in lowerirg body temperature, as are frozen water' garments, which are available in many power plants. Followup care by a physician is essential due to secondary disorders (shock, kidney disorders, etc.),

1 It is interesting that the majority of documented heat stroke cases involve 4 sustained physical exertion in healthy young adults. Most cases can be linked to (1) forced exertion, as in the military, or (2) voluntary overexertion precipitated by a refusal to recognize the warning signs of impending illness (often a result of the so-called " macho attitude"). Again, lack of adequate

acclimation may contribute. However, there are other recognized contributing factors. Primary among these are age (circulatory insufficiencies and other disease processes), obesity, and acute or chronic alcohol ingestion or drug abuse.

Lack of training may be a contributing factor. While few reported cases have invot<ed women, there are no sex differences in either susceptibility or course of the disease.

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Section 4 CURRENT STANDARDS AND PRACTICES The Heat Stress Management (HSM) Program has a foundation in proven methods of controlling heat stress in industry and the military. This section of the report sumarizes those methods that provide the framework for the HSM Program. The section is divided into:

• Evaluation Methods

=

Current Practices to Manage Heat Stress 4.1 EVALUATION METH005 The first step in any program of heat stress management is to provide an evaluation scheme against which job requirements and environment can be compared.

The discussion of evaluation will first cover regulatory activities and recomendations from professional societies, and then military and other industrial approaches.

4.1.1 Standards for Heat Stress Evaluation Heat stress in industrial environments has received regulatory attention because worker health and safety can be compromised by lack of control. While there is no promulgated standard in the U.S., the goal of proposed standards is to prevent the internal body (core) temperature from exceeding 38'C (100*F), a level that an international panel of experts considers to be safe (3). Two key provisions of a standard are (1) a method for measuring and assessing the work environment and metabolism, and (2) an action level to mark the point above which countermeasures against heat stress are implemented.

An important regulatory concern is establishment of a measurement method that is simple, rugged, reliable, and predictive. Most of the past standards work has gravitated to the wet bulb gicbe temperature (WBGT) (see Section 5.1.1 for a description). The principal advantage of W8GT is the ease of measurement and suitability to harsh industrial environments._ It has been used successfully to 4-1

limit activities of military recruits during hot weather training (4) and was also used to develop an experimental base for investigation of heat stress.

For industrial purposes in both the United States and abroad, the WBGT is used to establish an action level (AL), which is a trigger' point rather than a maximum or permissible limit. This means that if the environment has a WBGT value greater than the AL, some action should be taken to reduce the effects on the workers. It does not mean that work should not be performed.

4.1.1.1 Rationale for Action Levels. The purpose of the AL is to prevent workers from storing enough heat to raise their body temperatures by 1*C (2*F) to 38'C (100'F). Proposed standards and recommendations based on WBGT derive their approach from a classic study by A. Lind (5). He examined the effect of heat stress, expressed as Effective Temperature (which under his conditions is very i

similar to WBGT), on body core or rectal temperature (Tre) at three levels of work. Typical data are shown in Figure 4-1.

As can be seen, for each level of work, T re stays relatively constant even with increasing heat stress until a certain point, at which T increases rapidly.

re Selow this point is the safe or prescriptive zone. Above this point, small changes in heat stress mean a large change in T re. Therefore, to ensure that body te' perature is not subjected to large variations, the environment for a given metabolism should be controlled so that Tre does not leave the prescriptive zone.

This upper level of preferable heat stress exposure is the upper limit of the prescriptive zone (ULPZ). The ULPZ has been determined for a large population of young men at different work rates. To be protective, the population ULPZ was selected so that 95% of the group would have an individual upper limit above the ULPZ. Figure 4-1 shows the ULPZ for the 5th percentile (95% protected).

4.1.1.2 Proposed U.S. Standards. Although there is no promulgated standard for heat Stress in the United States, fnur documented approacnes have been published by government or professional organizattors. One was recommended by the National Institute for Occupational Safety and HetIth (NIOSH) (6) to the Occupational Safety and Health Administration (OSHA). The recommended work practices of NIOSH use the WBGT (wet bulb globe temperature) as the environmental measure with a specified action level.

l 1

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An OSHA review committee reviewed the proposal and modified it by lowering the l

range of metabolisms and adding a second action level for conditions of high air l

1 4-2 '

- -. {

EFFECTIVE TEMPERATURE 'C 15 20 25 30 35 8 ' '

u.10l.5 .u 38.5 E - E g 101.0 g i a

$ loas - ULPZ y 42o Kcai / hr. ,

33.0w[

a N a 510a0 - soo xcal / hr. g O

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2 99.5 18o Kcal / hr. -

37,3 2 2

= s

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w S 98.5 ' ' ' ' w 37.0 60 70 80 90 EFFECTIVE TEMPERATURE *F Figure 4-1. Body core temperature as a function of metabolism and environmental heat stress with the 5th percentile ULPZ.

mcvement(7). In 1974, the constittee reconsiended the work practices standard to 4

OSHA, but it was divided as to the clear need for a standard. For this reason, OSHA asked for supplementary material, which is expected by tne end of 1985.

Recommendations for work in hot environments were also made by the Physical Agents Constittee of the American Conference of Governmental Irt!ustrial Hygienists (ACGIH)

(8). These reconsnendations are commonly referred to as the TLV Threshold Limit Value. The recommendations followed the NIOSH publication closely.

The fourth recommendation for an AL was published by the American Industrial

)

Hygiene Association (AIHA) in Heating and Cooling for Man in Industry (9), written '

by a group of practicing industrial hygienists. The book discusses various techniques of evaluating heat stress and some methods of controlling it. The WBGT index was presented by the A!HA group as a means to easily assess the environment on a day-to-day basis. The action level was one developed by Exxon Research and l Engineering Co. Experience indicates that most acclimatized workers are protected I by this limit.

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The four recommendations for heat stress action limits based on W8GT are depicted in Figure 4-2. The NIOSH and TLV recommendations are identical. The AIHA tends to cover the low range of metabolism. The OSHA (Low Wind) recomendation covers a mid-range of metabolisms; the NIOSH and TLV cover a high range of metabolisms.

The OSHA (High Wind) recommendation has a higher action level because of the assumption that enhanced cooling at higher air velocities was not reflected in the WBGT. A subsequent study on the effect of air velocity on cooling and WBGT concluded that the WBGT adequately reflects the added cooling effects of increased air velocity (10). Therefore, the distinction that OSHA made is not necessary.

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c 3 NIOSH T1.V s,

- a---6 OSHA ( Low Wind) h -

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I e i i i . f 0 100 200 300 400 500 Metabolism ( kcal/hr)

Figure 4-2. Heat stress action levels as proposed by different organizations.

4.1.1.3 International Standards. The International Standards Organization (150) published a draft standard in 1982 using the WBGT as an index of heat stress (11).

In terms of measurement method and action level the ISO draft is identical to the TLV recomended by the ACGIH. Some form of this draft standard has been adopted by Norway, Sweden, and Belgium (,l_2). As a draft standard, it must be available for coments for five years before the ISO will recomend it as a final standard.

The Swedish standard uses the psychometric wet bulb rather than the natural wet bulb to make the computation of WBGT. The psychometric wet bulb temperature (Tpwb) is a measure of the amount of water vapor in the air. To measure Tpwb, a thermometer similar in design to the natural wet bulb thermometer (see Section 5.1.1.2) is used, but the air is rapidly forced over the bulb by a fan or 4-4

other device. T pwb is usually lower than the natural wet bulb temperature, but will be the same with high ambient air velocities. In fact, there is no difference between the two if the air velocity is above i m/sec. (200 fpm). The greatest deviation will be about 1.5'C (3*F) in still air, in which case the Swedish calculation for WBGT would be lower. In practice, the Swedish standard is a little less protective.

The Belgian standard uses the WBGT values but calculates the Corrected Effective Temperature (CET) (a close correlate to WBGT). The more complicated procedure needed to determine CET is used because much of the physiological database is

based on CET. Basically, the levels of heat stress for the AL are the same as in recommended levels in the United States.

Although the Europeans have made some changes in the way the index is calculated, there is a high degree of similarity between the international WBGT standards and the U.S. reconmendations.

4.1.2 Arred Forces The armed forces have active research programs in heat stress at the Army Research i

Institute for Environmental Medicine, the Air Force School of Aerospace Medicine, and the Naval Medical Research Institute. These research programs have led to a Triservices Bulletin that addresses heat stress and is entitled " Prevention, Treatment and Control of Heat Injury" (13). It is directed to medical department personnel to help them establish a program to control heat stress and to aid in 4

the diagnosis and treatment of heat illnesses.

The WBGT index was developed to control heat stress casualties in military training camps and has been supported by field and laboratory research programs..

Using five ranges of WBGT described in the Triservices Bulletin, activities are increasingly curtailed with increasing WBGT as described below. The interesting feature of this approach is that the action levels are progressive rather than dichotomous (either there is or is not heat. stress). The progressive ranges of W8GT and the associated actions are:

=

26-28'C (79-82*F): Caution should be taken because heat illnesses 4

may occur.

28-29'C (82-84*F): Discretion should be used for heavy exercise with unacclimated personnel.

, 4-5

• 29-31*C (84-88'F): No strenuous work for personnel with le'ss than three weeks of heat exposure, and reduced levels for those with at least two weeks of exposure.

31-32'C (88-90*F): Reduced work rates for all but very fit personnel (and they should be limited to six hours / day).

Above 32*C (90'F): Reduced work for everyone.

It is noted in the document that these ranges should be reduced by 6*C (11*F) if heavy clothing or vapor barrier clathing is worn.

The U.S. Army also recommends the use of the WGT (wet globe temperature, commonly called the Botsball) because of its simplicity, as described in Circular 40-82-3 (14). In the circular, the W8GT ranges are adjusted for equivalent WGT readings. A warning was later issued, however, against using the Botsball when the relative humidity is below 30%.

For industrial-type, military work situations, the bulletin recommends instituting het weather practices at WBGT action levels that are the same as those presented in Figure 4-2.

4.1.3 Evaluation Methods Used in Industry While the WBGT is most often used in industry because of its simplicity and use in proposed standards, three other approaches are also used to evaluate heat stress:

• Rational Indices

• Simplified Tables

• Heart Rate Recovery 4.1.3.1 Rational Indices. Rational indices are based on a calculation of the worker's heat balance. Estimates of the contributions of the different components of heat stress are needed for this heat balance calculation.- The WBGT and the effective temperature scales, in contrast, are empirical indices. To calculate a heat balance, the dry bulb (air), psychometric wet bulb and globe temperatures are measured along with air. velocity and metabolism. These data are used to calculate first the heat gain or loss by convection and radiation, then the heat gain due to metabolism, and finally the amount of heat loss by sweat evaporation required to maintain thermal balance. The required sweat loss can be compared with the 4-6

maximum rate possible to determine if the heat stress conditions will allow a balance to occur.

If the calculation results in an imbalance, this method allows identification of the largest sources of heat gain, which are the likely targets for countermeasures.

Different countermeasures can be evaluated in terms of their impact on the thermal balance. In addition, a method of calculating an Allowable Exposure Time and a Minimum Recovery Time is possible to help plan work cycles (9).

4.1.3.2 Simplified Tables. The Human Factors group at Eastman Kodak has prepared a book entitled Ergonomic Design for People at Work (15). In the approach described, the environment is divided inta.three zones: comfort, discomfort, and health risk. The comfort zone involves no heat stress. The discomfort zone represents conditions that stress the worker to the highest tolerable levels. The health risk zone represents heat strest conditions that are time limiting. The metabolisms associated with work are grouped as light, moderate, heavy and very heavy, and the environments are defined by air (dry ' bulb) temperature and relative humidity. For a given category of metabolism and environment (air temperature and relative humidity), it is possible to determine quickly from tables in which zone the required work occurs. For the health risk zone, suggested stay times are provided.

4.1.3.3 Heart Rate Recovery. Investigators at DuPont have reported the successful use of recovery heart rates as an assessment of physiological strain (16) due to heat stress. The procedure requires three estimates of heart rate measured in beats per minute (bpm). This is accomplished by stopping the worker and having him sit down, and then by counting the number of heart beats from 30 to 60 sec.,

from 90 to 120 sec., and from 150 to 180 sec. af ter sitting. The three sets of counts are then doubled to provide heart rates (bpm), which can be referred to as P1, P2, and P3, respectively. The following logic table is used to determine the quality of recovery:

P3 < 90 bpm: full recovery P3 > 90 bpm and PI-P3 > 10 bpm: marginal recovery P3 > 90 bpm and P1-P3 < 10 bpm: no recovery.

If there is full recovery, the individual has not been overexposed to the heat stress and he can continue to work. If the recovery is marginal, the worker is not yet overexposed but he is working very close to his tolerance level and small 1 4-7

.--. ,- , , -l

increases in heat stress can lead to an overexposure. No recovery means that the individual is overstressed by the work and the heat stress must be reduced.

This physiological approach is most effective for evaluating an individual's response to heat stress. It can be used collectively across individuals as a guide to assessing the level of heat stress. Because this technique involves disruption of work and is more cumbersome than measuring W8GT, it is not viewed as a possible standard.

4.1.4 Comments on Evaluation Methods It is clear that the most accepted method of assessing the environment is the WBGT. It is an empirical index that has analogs for the principal avenues of heat exchange and predicts heat stress well enough to be considered for standards. For this reason, it is used to assess the environment in the HSM Program.

While the concept of an action level is acceptable, the emphasis must be placed on the fact that heat stress has a progressive impact with increases above the AL.

Also different workers will respond differently for a given value of W8GT. In fact, two action levels are used in this document. They define a range of moderate stress and the conditions for high stress so that some distinction can be made on expected degree of stress.

The application of rational indices to the work environment requires more effort than WBGT and more expertise than may be found at most nuclear sites. For this reason, it is not advocated as an alternative method. This document, however, recommends countermeasures based on the heat balance approach for possible environmental scenarios. In this way, the underlying advantage of-the rational indices is contained within the recommendations.

Finally, most of the WBGT action levels assume that ordinary work clothes (light cotton shirt and pants) are worn. Adjustments must be made for different clothing ensembles, and these adjustments have been included in the evaluation process presented in this document (see Section 5).

4.2 CURRENT PRACTICES TO MANAGE HEAT STRESS It is important not only to evaluate heat stress but to implement c:antermeasures.

The comprehensive documents on evaluation discussed in the preceding section (Section 4.1) also recommend countermeasures. Just as there is'a general l

4-8 i

l J

consensus on WBGT as an evaluation tool, there is general agreement on the types of countermeasures available. The authors of the documents discussed in Section 4.1 recomended countermeasures when the AL was exceeded. The countermeasures can be grouped into the following categories:

. Engineering Controls

. Work Practices

. Personal Protection The three major categories of heat stress countermeasures, with types of applications under eacn category, are shown in the first column of Table 4-1. The top row identifies the six publications dealing with heat stress evaluation discussed in Section 4.1 that also recommend countermeasures. For each counterme&sure, a bullet under the publication indicates that that publication recomends the countermeasure. NIOSH (6) and OSHA Review Comittee (Z) recomend engineering controls and personal protection by category. The emphasis of these two publications and the Triservices (Armed Forces) recomendations is on work practices. The TLVs from the ACGIH (8) recommend only a couple of work practices.

The A!HA (9) and Kodak (l_5), the two written by industrial practitioners, contain the most comphrehensive recommendations. Based'on information obtained during the site visits and from the mail-out questionnaire, nuclear power stations as a whole make use of all the countermeasures in Table 4-1.

4.2.1 Engineering Controls Engineering controls change the environment or the job so that the magnitude of the heat stress is reduced. It is a comon philosophy among health and safety professionals to examine the use of engineering controls as the first choice because they impose the least burden on the worker. Work practices and personal protection are considered only after the technical and economic feasibility of engineering controls have been evaluated.

In the references listed in Table 4-1, no distinction is made between permanent or temporary controls. The goal is a reduction in heat stress, and the actual implementation is left to the discretion of the individual facility.

^

4.2.1.1 Types of controls. Engineering controls discussed in tne literature can be grouped into several types of applications:  !

4-9

Table 4-1 Tabulation of Countermeasures Recommended in Six Heat Stress Evaluation Documents EVALUATION DOCUMENTATION OSHA NIOSH Armed Kadek Rev ACGlH AlHA (6) Com (8) (9)

COUNTERMEASURES (13) (15)

(7)

Engineering Controls G $

Metecolism G g 9 Air temperature e G Hum 10t ty g $

Air velocity 9 9 l

Recient neat G f $

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work Prectices Training e e e G water & seit G 9 9 9 9 e Acclimation 9 9 9 9 worx/ rest cycles 9 e G 9 9 9 Seneculing work e e e e Self-ceterminetton 9 9

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Personal Protection G $

Air systems e- e Ice germents e Reflective clothing e e i

4-10 1

I

e Mechanical assists to reduce metabolism

. Ventilation to reduce air temperature and/or humidity e Air conditioning to reduce air temperature (and possibly humidity)

• Fans (or other air movers) to increase air velocity to enhance evaporative cooling.and/or convective cooling

• Shields, insulation, and surface emissivity to reduce radiant heat The types of engineering controls that are appropriate depend on the nature of the heat stress. Deciding which controls may be most beneficial requires knowledge of the relative contributions of convection, radiation, metabolism, and sweat evaporation (see Section 2) to the overall haat exchange. The greatest contributors to the stress are addressed first. This, in turn, requires knowledge of the biophysics of heat exchange. Using heat exchange to evaluate engineering controls is described in several sources (for instance see 6 and 9).

4.2.1.2 Treatment in the HSM Program. ~As indicated above, the best approach to treating engineering controls is to determine the greatest contributors to the overall heat stress and attack those sources. Information contained in a heat balance analysis provides important insights into relative contributions of each source. To avoid requiring the HSA to perform this heat balance analysis, the HSM Program considers the possible heat stress scenarios and divides them into 24 conditions described by a simple measurement scheme (see Section 5). There is a description of each condition in the Appendix, which lists the engineering Controls that are most beneficial.

The engineering controls for a particular condition in the Appendix are selected by evaluating the different possibilities for heat stress under that condition.

The evaluation uses heat balance equations similar to those described by Kamon and Ryan*(H). Some of the conditions have special cases that are described by environmental qualifiers. For these situations, additional engineering controls are also appropriate and are indicated.

Detailed descriptions of each engineering control are prov.ided in Section 6.

- *The equations that were used are from a confidential source.

4-11 l

4.2.2 Work Practices While engineering controls are recommended to lower the level of heat stress,'it is recognized that, at times, work must be performed above the action level. When this occurs, work practices should be implemented to reduce the risks of suffering

. heat illnesses. To this end, five work practices are endorsed by the publications dealing with heat stress management in Table 4-1. These are:

,

• Training in the recognition and treatment of heat illnesses

• Water and salt replacement

. Acclimation

. Work / rest cycles (Stay times)

• Scheduling work In addition, self-determination, clothing adjustments, buddy system, and personal monitoring are now used'in the nuclear power industry, and these are supported by the project Technical Advisory Group (TAG). Each of these work practices are described in Section 7.

4.2.2.1 Training. There is a general agreement that all workers should be aware of the heat illnesses including the causes, recognition and first aid treatment.

The OSHA Review Committee (7) further recommends training in heat stress hygiene, which includes actions an individual can take to preserve his tolerance for heat stress. There are no recommendations in the reviewed documents for how often the training should be given. In fact, in some, training appears to be discretionary, as any other work practice.

It is recommended in this program that training be expanded to include heat exchange and basic physiological responses. The purpose is to give the workers the rationale for the countermeasures and an understanding of how they can perscnally reduce the risk of heat illness. Training is considered an essential part of the program. If there is any exposure to heat stress, the workers should have basic training, as described in Section 10. The reconnended period is approximately annual as part of the general employee training (or RWP training).

In addition, a heat stress alert program and workplace meetings are adjuncts to the formal training.

4-12

. ~ . . -- - -

4.2.2.2 Water and salt replacement. There is uniform agreement that the water and salt lost by sweating must be replaced. The basis for this work practice is discussed in Section 2.2.5. The HSM Program also considers water replacement as essential and recossendations are made in Section 7.

4.2.2.3 Acclimation. Acclimation (also called acclimatizaticn) is the set _of physiological a'djustments that allows improved heat stress tolerance. It is explained in Section 2.2.4. The heat stress action levels discussed in Section ,

4.1 assume an acclimated workforce. For this reason, acclimation is important, and NIOSH and the OSHA Review Committee-suggest schedules for acclimation. 4 In the HSM Program acclimation is identified as a work practice and a schedule is provided, not as a formal recommendation, but as advisory information. Implemen-tation of acclimation as a work practice is discussed in Section 7.

4.2.2.4 Work / rest cycles and stay times. Work / rest cycles assume that heat buildup during work is dissipated during the rest or recovery part of the cycle.

The heat buildup may not be the maximum that can be tolerated. On the other hand, stay times are based on the highest, safe accumulation of heat in the body. After this maximum exposure, sufficient recovery must be allowed. Rest time as the rest part'of a work cycle and recovery time serve the same purpose. It can be spent in actual rest or doing light work in cool areas. In essence, work / rest cycles and stay and recovery times convey similar information to manage heat stress.

Both the TLV (@) and the A!HA (9) documentation describe fixed work / rest cycles and corresponding WBGT action levels. The TLV literature (g) also presents a method to estimate work / rest cycles for task specific situations, based on a Time Weighted Average (TWA). The AIHA (9) describes a method to calculate stay times and minimum recovery times based on heat balance calculations. In addition, the Navy has charts of stay times for which a summary is contained in the Triservices Bulletin (13). In all cases .the clothing is' assumed to be ordinary work clothes and does not account for the clothing ensembles that may be used in the nuclear industry (see Section 5.1.2). The Navy approach also assumes young, fit males.

Several utilities provided the project with their guidelines for stay times for heat stress. They are generally based on the information found in the AIHA and Triservices documents. Inaddition,theKodakbook(11)providesguidancefor stay times.

4-13 i

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I Kamon and Ryan (17) published a method to calculate stay times that can be implemented on a programable calculator. (If the reader plans to use Kamon's i

1 article, there is an imprortant errata reference given with the citation.) It uses a heat balance approach that is more sophisticated than the approaches published in the NIOSH and AIHA documents. One nuclear station uses.this approach to specify stay times.

As a first step in synthesizing information on stay times for the HSM Program, median stay times based on the utility and Kodak data were compiled for four clothing ensembles (see Section 5.1) as they were available. For each ensemble, the stay time data were adjusted to three levels of metabolism (125, 250, and 375 Kcal/hr). If the environmental conditions were not described by WBGT, an estimate of WBGT was made.

The second step was to use heat balance equations to estimate stay times for the same clothing ensembles and metabolisms across different environmental conditions that yield the same WBGTs. This was done with a computer simulation of the different enviornmental conditions.

Figure 4-3 is a schematic curve showing the relationship between stay time and WBGT. There are t.vo important features. First, for. stay times less than 30 minutes, the curve is very steep, which means small changes in stay time represent large changes in the WBGT. Second,. for stay times greater than one hour, there are large changes in stay time for small changes in the W8GT. This means that small changes in the environmental sources of heat stress can have a large effect on the ability to work.

For each combination of metabolism and clothing ensemble, the range of stay times for values of WBGT in increments of 2'C were examined across the available sources. Based on the examination of the data, the ranges of stay time in Table 7-2 were selected. There was close agreement for short stay times (less than 30 minutes) and long stay times (8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />), but wide variations in intermediate values. As expected for the intermediate values, where different combinations of environmental conditions give similar values of,W8GT but represent a large range in the heat balance and the physiological response, there were wide variations in the stay times. Therefore, a conservative (more protective) range of stay times for a given WBGT is given in Table 7-2. This also means that higher stay times may be reasonable.

4-14

4 I

I I

WBGT f f i f f I  ! t

( l I I I & I I O.5 1 2 3 4 STAY Til1E (hr)

Figure 4-3. Schematic Lurve illustrating the relationship between stay time and WBGT.

Table 7-3 provides the same information as 7-2 except that a range of WBGTs is given for a fixed stay time and combination of clothing ensemble and metabolism.

4.2.2.5 Scheduling. One means of controlling heat stress is to schedule a job when the heat stress from the environment is low. This practice is recommended by most of the documents cited in Table 4-1, and is also recommended in the HSH Program.

I 4.2.2.6 Other work practices. Self-determination was reported frequently in the mati-out questionnaire as a work practice in use at nuclear power stations, and the project TAG highly recommends it as a work practice.

Clothing adjustments and the buddy system are also recommended by the TAG.

4-15 i

Personal monitoring is developing as a work practice. OuPont (16) uses it as tool to evaluate heat stress. % recommendation of a NIOSH workshop on heat stress (M ,

pg 169, #6) is that personal monitoring can be used to demonstrate effective heat stress management in lieu of environmental standards. EPRI is currently (1984-1986) investigating methods of personal monitoring at the Pennsylvania State University (RP2166-3) and is considering future work in this area.

4.2.2.7 Coments on work oractices. Work practices are frequently presented as a list of actions that can be taken to reduce the risks of heat illnesses during heat stress exposures. In fact, some work practices can be discretionary, but others should be a central part of the work. In the HSM Program, the important work practices are called Universal Work Practices-(see Section 5.4.1). These include self-determination, fluid replacement, acclimation, buddy system, and work scheduling. The other work practices can be used as additional countermeasures as indicated by the evaluation process in Section 5. Detailed descriptions of work practices are provided in Section 7.

4.2.3 Personal Protection Personal protection is generally recognized as an important means to reduce heat stress by providing a more hospitable micreenvironment for the user. The methods of personal protection are grouped as

. Circulating air systems

. Ice cooling garments

. Liquid cooling systems

. Reflective clothing NIOSH (6) and the OSHA Review Committee (7) recommend personal protection as a category for alleviation of heat stress. Their principal advice is to be sure

that it is appropriate, but they do not provide any guidance. The AIHA (9) and Kodak (15) documents suggest circulating air systems (especially with a vortex tube) and reflective clothing for radiant heat. The Kodak book also mentions ice garments. In addition, nuclear power stations have reported the use of liquid cooling systems. l l

An EPRI report (2) describes tests of three commercial systems for personal cooling used in the nuclear industry. One is an ice garment and the other two are l liquid cooling systems. )

4-16 l I

i

s Section 8 of this document describes the four methods of personal protection against heat stress. The discussion is based on information collected from laboratory experiments and field experience.

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1 l

Section 5 EVALUATION OF HEAT SfRESS The purpose of this section is to describe a procedure that can be used to evaluate the level of heat stress associated with a particular task or work location, and to identify countermeasures for reducing the risks of heat illnesses while also maximizing worker performance on these tasks.

This.section presents the information necessary for evaluation of heat stress:

• Description of required data

• Methods of collecting the data e Evaluation using a decision tree

• Recommended countermeasures 5.1~ DESCRIPTION OF REQUIRED DATA The data required to perform tne evaluation and to develop recommendations is collected for the three major causes of heat stress:

• Environment

• Metabolism

. Clothing 5.1.1 Environment The following environmental data are required for_the evaluation:

Tair: -Air temperature (also known as dry bulb temperature)

Tnwb: Natural wet bulb temperature

• T:g Globe temperature Vair: Air velocity (estimated)

-

• WBGT: Wet bulb globe temperature 5-1

The following sections describe the individual measures. All temperatures should be accurate to 0.5'C (l'F). A further discussion on measuring equipment is presented in Section 5.1.1.6.

5.1.1.1 Air ~.'emperature. T is the most familiar temperature because it is air easily measured and is referred to most often in discussions of weather.

T air can be measured by glass thermometer (either mercury or alcohol) or by an electronic sensor (e.g., thermocouple or thermistor). The thermometer or electronic sensor is placed in the open air so that the air can move freely about the bulb or sensor.

Air temperature has only limited value in assessing the degree of heat stress when used alone. In the HSM Program, it is used for comparisons with Tnwb and Tg in order to gain insight into the level of humidity and radiant heat.

5.1.1.2 Natural Wet Bulb Tempertture. Tnwb provides information on the humidity-of the air and therefore on how well sweat can evaporate.

T nwb is measured by placing a wetted wick around the bulb of a glass thermometer or the sensor of an electronic device. Typically, the other end of the wick is placed in a water reservoir so that the wick always remains wet. The bulb or senser with wick is placed in the air in such a way that there is no disruption of normal air movement.

As water evaporates from the wick, the temperature will drop. This wet bulb depression or difference from Tair is an indication of how well the environment will evaporate sweat. The magnitude of the depression depends on the air humidity and the air velocity around the wick. If the humidity is low (dry air), the Tnwb will be lower and hence the depression higher. If the humidity is very high (near 100%), there will be no depression. It is not possible for i nwb to be greater than T air-Air velocity will also enhance the depressinn or lower the natural wet bulb temperature. For the same air humidity, greater air velocities will cause more evaporation and therefore a lower temperature. In a similar fashion air velocity enhances the evaporation of sweat.

5-2

In sumary, low inwb values with respect to Tair represent the best environmental conditions (low humidity and/or high air velocity) for sweat evaporation.

5.1.1.3 Globe Temperature. T reflects g ~ heat exchange due to convection (C) and radiaticr.(R). .

Measurement ofgT is accomplished with a 15 cm (6 inch) copper globe painted flat black on the outside. A thermometer bulb or sensor placed in the middle of the globe indicates Tg.

The globe readily absorbs radiant heat (infrared energy) from any hot surfaces.

In the same way, it will lose radiant heat to cool surfaces. If there are radiant heat sources, then the temperatu're inside the globe will tand to increase. If the surrounding surfaces are generally cooler than the globe (representing heat losses by radiation), the globe temcerature will drop.

Tg also reflects convective heat exchange. That is, as air temperature increases so does globe temperature. Likewise, lower air temperatures will tend to lower T.g The effect of air temperature on the globe is modified by air velocity just as convective heat exchange is modified.

If T gis greater than Tair, a source of radiant heat exists that adds to the heat stress. If they are the same, radiant heat does not have a significant role.

To summarize,gT reflects the combined effects of convective and radiant heat exchange.

5.1.1.4 Air Velocity. Vair has effects on evaporation and convection that are adequately accounted for in inwb and g T . It also affects the insulating qualities of clothing, and, for this reason, an estimate of Vair is necessary. This can be done by assigning one of three categories to the air velocity, as described in Table 5-1. Although air speed can be measured directly, an estimate based on the descriptions in the table is adequate.

5.1.1.5 Wet Bulb Globe Temperature (WBGT). The WBGT is a comonly used index for heat stress. It is calculated for indoor conditions as WBGT = 0.7 . Tnwb + 0.3 . T g i

5-3

Table 5-1 Categories of Air Velocity Low: . <0.1 m/sec (<20 fpm)

. no perceivable air motion Moderate:

• Between 0.1 and 1.0 m/sec (20 and 200 fpm)

= Some air motion (such as might be felt while walking slowly)

High: . >l m/sec (>200 fpm)

= Easily noticed air motion such as found near fans, blowers, and ventilation ducts The index accounts for evaporative cooling (embodied in inwb) and for convective and radiant heat exchange (via T g

), which are major factors in determining the contributions of environmental causes to the heat stress. The relative weights for the two temperatures were empirically developed to be related to the physiological response to heat stress.

5.1.1.6 Measurement Devices. The necessary temperatures for environmental assessment can be obtained from homemade devices or from connercially available devices. If a site is interested in building its own, sufficient information is available in a NIOSH document (6) or the ACGIH TLV book (8).

Because of the time and costs involved in making a device, utilities and other industries that use W8GT usually purchase a commercial device. The commercial devices generally use thermistor technology to measure the temperature. If a commercial device is purchased, it should provide independent readouts for Tair*

Tnwb, and T g . As an added convenience, the device will also calculate the W8GT (indoor).

One commercial device measuresg T with a small globe. When used with proper correction factors (built into the device), this device provides a Tg reading that is a substitute for a large globe reading.

The project team is not aware of a commercial device designed to measure inwb alone. This measurement is included in those devices for assessing W8GT.

5-4

e 5.1.2 Clothine i Clothing is an important factor in the evaluation of heat stress because it reduces the effectiveness of sweating as a means to cool the body. Generally the effects are dependent on the surface area covered and the fabrics. While every I clothing ensemble used in the nuclear industry has its own insulating character-istics, approximations over a range of insulation values will be sufficient for the evaluation described below.. Four clothing ensembles were selected to cover

the range of clothing used in the nuclear industry. They are described in Table

] 5-2. There are three selections that represent significant changes in clothing l insulation value (WC, CC, and DC). The fourth ensemble includes all uses of vapor i barrier clothing.

i  !

Table 5-2 Typical Clothing Ensembles (with reference abbrettations)

I i

I WC: Work clothes that would be freely worn in a radiologically clean but hot environment (e.g., cotton pants and shirt with open neck) i CC: Cotton coveralls with gloves and hood, or regular work clothes with lab coat and gloves that would be worn in lightly radiologically l contaminated areas I

j OC: Double cotton coveralls with gloves and hood that would be worn in

areas with heavy but dry radiological contaminants 1 CP

Cotton coveralls and vapor barrier suit with gloves and hood that j would be worn around wet radiological contaminants or when working j with strong chemicals

• I, 1

l Work clotnes (WC) include any type of ordinary work clothes such as a single layer

} of light-weight clothing like jeans and T-shirt. When allowed, the workers will '

{ select a low insulating ensemble for hot environments. The insulating value of i this ensemble is about 0.5 - 0.7 clo. (Note: clo is a measure of insulation or j resistance to heat flow. It is given here for information, but is not needed for the further use of this document.)

Cotton coveralls (CC) include any clothing configuration with a single heavy layer or two layers of light clothing over much of the body. The typical insulating 5-5 l

L -- -

value is 0.7 - 1.0 clo. Sevaral clothing configurations are included in this category:

. Cotton anticantamination coveralls with gloves and hood but no street clothes underneath

• Work (street) clothes, lab coat, and gloves e Heavy-weight coveralls Couble cotton coveralls (DC) include any clothing configuration that uses two layers of heavy clothing, such as cotton anti-Cs, or one set of cotten and a layer of cacer (permeable) coveralls. The insulating value is between 1.0 and 1.3 clo.

! Co_tton coveralls with plastics (CP) include any clothing configuration that has a coverall or street clothes and an outer layer of clothing that can be called

" plastics" or rubber gear. Basically, the outer layer forms a vapor barrier. The clothing insulation is again between 1.0 and 1.3 clo, but the vapor barrier adds further to the heat stress.

The CP ensemble represents the greatest barrier 'o evaporation of sweat. OC also represents a significant barrier to evaporation. Both of these ensemble's, therefore, contribute to heat stress and should be used only when required for worker protection.

5.1.3 Metabolism A major contributor to heat Stress is the heat generated internally as the body j performs work. For this reason, it is necessary to estimate the metabolism l associated with the different work activities. Tables can be used that give typical values for different activities. Such a table is shown as Table 5-3.

This table contains values from standard sources (e.g., 6, 8, 9,, 16).

Table 5-3 divides the metabolisms into four categories: Low, Moderate. High and Very High. & metabolisms are associated with sedentary to very light activities. These can range from sitting or standing still while monitoring a gage to a slow walk on a level surface. Operating powered equipment such as a crane and calibrating instruments also require a low metabolism.

Moderate metabolisms result from work that is generally easily accomplished if it is done in a comfortable environment. An average walking speed or moderate arm motion usually has a moderate metabolism. The types of tasks include pump and 5-6

l Table 5-3 Table of Metabolisms for Different Activities Metabolism '

Activity L sit / monitor insDection siow waik 2.1 kcal/ min ceiieration 125 kcal/hr '*'D*'"' D""

(e g., cranes, reings) .

M sort materiais (e g., ciatning)

Moderate - cescena stairs or inocers 4.2 kcal/ min "nti

',' ",',nsuietion "8

250 kcal/hr manuei volve eingnment - easy H manuai vaive eiignment - airricuit High metenais nanaiing - iignt 6.2 kcal/ min *"*""

manuai decontamination 375 kcal/hr manuai noisting VH cismo stairs or inaaers Very High scrum/erusn/screDe nono saw 8.3 kcal/ min metenais nanaiing - neevy 500 kcal/hr Shov'i f

5-7

. _ . _ _ _ _ _m_._.__._ . _ _ _- ._ _ . _ _ . . _ _ _ _ _ . _ _ _

i T

1 i

i valve rebuilding and sorting materials. If the person is working with no heat stress, he should be physically able to do the task for most of the day. Heat stress will limit a worker with a moderate metabolism to a shorter .vork time.

H_i,g!! metabolism involves demanding work, like lifting and_ moving most objects and l performing manual decontamination activities. If a job requires high metabolism ,

j with temperatures around 18'C (65'F), the worker can perform for about an hour or less before he requires a rest. So, even without heat stress, he has a limit to the length of time he can work without stopping.

l  ;

1

Very High metabolism reflects activities that are very demanding and that under j the best of conditions can be done only;for a short time (much less than one  ;

hour). Very high metabolism would be present for ladder Climbing, shoveling, and i heavy materials handling. These types of activities are usually performed in t conjunction with other activities so that the average demand on the worker is. I i less. ,

j  !

5.1 DATA GATHERING ,

l The data gathering process has two steps: ,

i.

J

• Identify jobs and locations I

{

• Record environmental data I i i I

i The Environmental Assessment form shown in Figure 5-1, or a similar form, is used

, in the data gathering phase. The discussion below follows the order in the form.

i I 5.2.1 Job / Location Identification I

i 5.2.1.1 First Time Identification. There are two ways that the Heat Stress I Advisor (HSA) can begin to identify heat stress situations. One approach is to survey the entire plant using the Environmental Assessment form. This requires assessing all locations and all the jobs in a location under all conditions of plant status (operating, hot shutdown, cold shutdown, extended outage, etc.), and

! then determining the category of heat stress for these conditions. This detailed

! assessment is a tedious and time consuming approach and is g,t t required.

l In the recomended approach, the HSA talks with supervisors and workers about l certain plant areas and jobs. The HSA's own experience in the plant will suggest i plant areas and jobs that may pose problems of heat stress. He'can review records i

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1 i Figure 5-1. Environmental Assessment Form 5-9

of heat illnesses reported to the medical department or first aid station. A list of these jobs and areas can be made on the Environmental Assessment form.

For each job, an estimate of the metabolism is made by referring to Table 5-3. If the HSA estimates that a job requires as little physical effort as those listed under low in the table, an "L" is placed in the Metabolism column on the form. If any job requires a typical physical effort similar to the ones listed under Moderate, an "M" is indicated in the Metabolism column. If the work is very strenuous, like the activities under the High heading, enter an "H".' It is unlikely that a job would be Composed solely of activities under the Very High category. If the HSA is uncertain of an estimate for metabolism, he can ask the opinion of one or more of those who perform the activity after they have reviewed the metabolism table (Table 5-3).

Next, the clothing ensemble for each job is entered on the form. The abbreviations given in Table 5-2 are adequate entries. The environmental data gathering is described below.

5.2.1.2 Subsequent identification. After the HSM Program has been in place for a while and the first time evaluations have been completed, questions will arise about heat stress for other jobs and locations. The Environment Assessment form (Figure 5-1) is used as described to assess these jobs and locations.

5.2.2 Environmental Data Collection Whether the evaluation is for the initial list of possible heat stress situations or for situations identified subsequently, environmental data is gathered. These include Tair. I nwb, Tg , and Vair as indicated on the assessment form.

5.2.2.1 Actual Measurements. The temperature measurements are made as near as possible to the spot where the work is performed. At the same time, an approximation of the air velocity (Vair) is made based on Table 5-1.

The ideal time for the measurements is when the conditions for the job are present. If the Jeb is performed during normal operations, the measurements are made then. On the other hand, if the job is performed during a refueling outage, that is the time to make the measurements. If the HSA has reason to believe that there is a variation in any of the temperatures, he makes repeated measurements.

5-10

. - . . - . - .- _ - . _ - - - . - - . ~ . - ~. -. .. .- ,

i I

i l i f If a direct reading instrument for W8GT is not used, the W8GT is calculated for l 3

each job (see Section 5.1.1.5). If multiple measurements were made for one job i

{ because the HSA thought there was a variation, the highest W8GT is selected for I the purpose of evaluation. If the HSA suspects that the highest value is invalid i due to measurement error or highly unlikely conditions, the next higher W8GT is selected to represent the environment for that location.

! 5.2.2.2 Estimated Measurements. Occasionally, estimates of the environmental 4

f measures are required in order to calculate a W8GT. Estimations are very j ur, reliable, however, and should be made only when actual measurements are not

possible.  ;

f i

j Estimates may be required for air temperature, level of humidity, and sources of I

{ radiant heat. Using any available information (e.g., the control room readings),  ;

{ the HSA first estimates T air. The estimate is entered on the Environmental  !

Assessment form, i Estimate of natural wet bulb I

l The method of calculating an estimate of Tnwb depends on whether the level of i

humidity is high or moderate. High humidity should be considered present if the job is located in a confined space (where there is little or no '

ventilation) and if water or steam is present. In this case, the estimate is given by i

inwb = Ta ge - 3*C (5'F) i If the location has ventilation or no sources of water such as puddles on the

{ floor or escaping steam, humidity will not be high. In this case, the j estimation of i nwb 15 i

4

( inwb = 0.7 . Tair i j The HSA calculates the estimate of inwb from Tair and enters the value on the i

{

Environmental Assessment form. ,

' Estimate of alobe temperature 3

I The globe temperature estimate deals with radiant heat sources. Two cases are

! considered, one in which actual data are available from past experience and a 5-11 i

i

.- _ =_ - _

second where no data are avaliable with which to make an estimate. In the first case, the HSA has actual data on T air and Tg and is interested in knowing what would happen if only the air temperature is changed. In this

case, he calculates a AT from the known values of Tg and Tair as ai = Tg-Tale (known values) the new T g is then calculated from the estimated value of T air as

Tg.T397 + AT (new values)

J i

for example, if the measured values for T air and Tgare 30 and 35'C i resrectively, and the estimated value for the new T is 40*C, the estimated air value for the new Tg would be 45'C.

In the second case, where there are no previous data on which to base an estimate of Tg , assumptions must be made on the effects of radiant heat. If

, there are no surfaces in the work location that are higher than air j temperature, the HSA can assume that i

Tg=Tair i

This means that the work is performed in an area where there are no high temperature (greater than 50*C or 120*F) fluid or steam lines, no large operating motors, no structures dissipating latent heat, or no other specific sources of radiant heat.

If the HSA knows that there are sources of radiant heat while the plant is at temperature and he does not have an idea from past experience on how much the Tg may be above Tair, he must make an estimate for Tg . For planning purposes, t

the highest likely value, based on data gathered at two nuclear plants, would be i

Tg=Tair+7'C(13'F).

It should be noted that larger increases have been found close to steam lines.

Whenever estimates for the environmental temperatures are used for planning exposures, it is important to verify those estimates as soon as possible so that

, 5-12 f

i I

l

any differences between planned and actual values can be used to adjust the selection and implementation of countermeasures.

During situations when an exposure based on estimates occurs at the same time the measurements first become possible, the HSA must make the measurements and be prepared to adjust the countermeasures accordingly. The most treediate adjustment is to stay times (see Section 7.5); another possibility is to make recomendations for personal protection (see Section 8).

5.3 EVALUATION OF HEAT STRESS A decision tree is shown in Figure 5-2 for use in evaluating the heat stress associated with a particular job and location. The decision tree provides a basis for selecting countermeasures based on the data contained in the Environmental Assessment form.

5.3.1 Use of Decision Tree The three levels of the decision tree are based on the data contained in the Environmental Assessment (Figure 5-1). The entry level is clothing. The four branches represent the four clothing ensembles described earlier in this section (Table 5-2). The second decision tree level is metabolism, which is estimated on the Environmental Assessment form and is used to determine the next branch in the decision tree. The third decision tree level is the environment based on W8GT.

For a given level of clothing and metabolism, the environmental conditions may ,

allow sufficient heat loss so that there is no appreciable heat stress. This condition is indicated by a specific WBGT, below which no countermeasures are necessary. This is Indicated on the decision tree as no heat stress. Under conditions of no heat stress, it is reasonable to expect virtually all workers to be able to work an 8-hour day.

For each combination of clothing and metabolism, there are two other branches on the third level based on the W8GT index. Each of these branches leads to a condition number. For each condition number, the Appendix has recomended countermeasures. The highest branch on the decision tree for each clothing /

metabolism combination is the hiqh heat stress (labeled as HIGH) condition for that clothing / metabolism combination. The high heat stress conditions are marked by the point at which at least some workers are not be expected to work for more 5-13 I

Decision Tree

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Figure 5-2. Decision tree for evaluation of hot environments with condition numbers that are keyed to further information in the Appendix. (Thedecisiontree is also included in the Appendix along with a version for *f.)

5-14

than 30 minutes. As the WBGT increases beyond the indicated threshold, the probability that a worker can tolerate the heat for 30 minutes decreases.

Themiddlebranchisthemoderateheatstress(labeledasM00) condition, marked by a range of W8GTs that fall between the no heat stress condition and the high heat stress. The moderate heat stress condition represents a range of environmental conditions for which increasing levels of W8GT mean that the expected stay time to protect virtually all workers decreases from 8 nours to 30 minutes.

i Note that the moderate heat stress conditions are odd-numbered and the high stress conditions are even-numbered. Enter the condition number or "N/S" (for no stress) on the Environmental Assessment form. If the condition number is an even number, it should be circled or otherwise highlighted.

There are some special cases in which the decision tree indicates a moderate level of heat stress where, in fact, there is no heat stress. The special cases are clearly indicated in the condition description in the Appendix.

5.3.2 Order of Priority After the HSA obtains the condition numbers for all activities for which he has data or good estimates, he then notes all conditions that are even-numoered or highlighted. Because these represent high heat stress, they deserve immediate attention.

Any situation in which workers are currently exposed to hest stress deserve imediate attention. The next priority are those situations in which workers may

, be exposed in the near future. Finally, the remaining situations are addressed.

Within each of these three categories, the HSA exercises his judgment. Two factors that he should consider are the W8GT and number of workers exposed.

Higher W8GTs usually mean that the heat stress is higher and therefore deserves more attention. This is suojectively balanced by the HSA against the number of workers exposed. If the difference in W8GT is 2*C (4'F) or less, it is best to concentrate on the larger number of workers first.

There is no absolute rule for prioritization of the moderate heat stress condi-tions(odd-numberedconditionnumbers). The judgment of the HSA is sufficient.

Again, he should consider imediacy of the situation and potential number of 5-15

.~ .- . . . _ - - _ - - .. -

exposed personnel. Remember that situations involving W8GTs nearer the high end l

, of the range pose a greater threat than those near the low end.

I 5.4 RECOMMENOATIONS FOR COUNTERMEASURES After the Environmental Assessment form is completed, there is enough information l

to recomend countermeasures for the heat stress associated with the different ,

jobs. For conditions of moderate or high heat stress, general recomendations are presented below. In addition, more specifics on countermeasures that are appropriate for the 24 different heat stress conditions on the decision tree are i

given in the Appendix. '

t 4  !

For detailed discussions of the countermeasures, the HSA is referred to other sections of this document. Specifically: '

. Section 6: Engineering Controls Section 7: Work Practices 1

)

i

=

Section 8: Personal Protection 1

. Section 10: Training ,

l 5.4.1 General Recomendations l The general recommendations are appitcable to all conditions that can be described as moderate or high heat stress from the decision tree. That is, the following i recomendations are considered any time there are exposures to heat stress, i

5.4.1.1 Training. All personnel who may be exposed to moderate or high heat

{ stress should receive heat stress training. Training should ngt be considered as an option.

I 1

5.4.1.2 Engineering Controls. Engineering controls are considered first because they L

-! lower the heat stress directly rather than modify the way the work is performed.  !

) Among engineering controls, reducing the air temperature is effective for most '

q conditions of heat stress. Specific recomendations for engineering controls are contained in the Appendix.

f I

l 1 5.4.1.3 Universal Work Practices. Five work practices are universally i

recommended for work in moderate or high stress conditions

1 e

Self-determination (Section1.11 1

i.

j 5-16  :

j  !

a

1 I

• Emphasis on fluid replacement (Section 7.2]

. Acclimation [Section 7.3]

. Scheduling [Section 7.4)

• Suddy system [Section 7.7) 5.4.2 Specific Recomunendations Each of the 24 heat stress conditions identified in the decision tree has additional, appropriate countermeasures. For each condition, there is a page in j the Appendix that is identified by condition number, clothing ensemble, metabolism

~

l and heat stress level. The page contains the specifications for the condition, a description.of the causes of heat stress, and the list of appropriate countermeasures.

The list of countermeasures for each condition description is the list of specific

! recosamendations. The countermeasures in the list should be considered in addition M the general recomunendations. Countermeasures that are not mentioned in either the general or specific recomunendations are less effective in controlling the heat stress.

The list of specific countermeasures includes at least engineering controls and work practices; and personal protection is recomunended for high heat stress conditions. Within each category of countermeasure there is not priorite unless specific conditions are indicated. Af ter each specific recommendation, a reference in brackets is made to the section number in this document that describes the countermeasure.

, Engineering controls are examined first. If any are practical, the effect on the decision analysis must be determined as discussed in Section 6.

l 8eyond the Universal Work Practices, the work practices are discretionary. Again, j there is no priority. If personal protection is used, the Universal Work l Practices are still applicable, but stay times in particular must be adjusted as i described in Section 8.

I i

d 5 17

i Section 6 ENGINEERING CONTROLS Engineering controls reduce heat stress directly by changing the conditions of the job. The purpose is to reduce the heat gain from metabolism and the environment I

and/or to increase the heat loss from the body to the environment. Tnere are four broad areas to examine:

• Metabolism

• Air temperature and humidity

. Air velocity

• Radiant heat Within each of these areas, engineering controls are developed as temporary or x

portable solutions and as permanent installations. The decision on the selected approach is left to the discretion of the plant, based on the particular situation.

1 j 6.1 EFFECTS OF ENGINEERING CONTROLS ON EVALUATION In investigating the possibilities of the different engineering controls, it is important to give primary emphasis to.those suggested in the Appendix through the decision tree evaluation in Section 5. These are the controls that are most effective for the particular Condition. As with any countermeasure, the solution for one problem may not be appropriate for another. For instance, reducing metabolism is most appropriate when vapor barrier clothing is worn or metabolism is high, but it is not the first course of action when clothing requirements are light and metabolism is moderate. In this case, controlling air temperature may be the better approach.

The effective use of engineering controls will reduce heat stress because controls enange the environment or the metabolic demands of the work. Two aspects of engineering controls must be considered: the goals to be achieved and the results as they affect the heat stress evaluation process.

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6.1.1 Goals of Engineering Controls The condition descriptions in the Appendix list a set of general engineering controls that are appropriate to the heat stress situation being considered.

These controls should be considered of equal importance unless otherwise indicated. Within the set of available choices, the HSA, in consultation with other departments that the HSA thinks should be involved, will select one or more of the controls for consideration.

The ideal goal for engineering controls is to change the environmental and metabolic conditions to a level of no stress on the decision tree (Figure 5-2).

This is accomplished by lowering the W8GT and/or metabolic demands. For high heat stress conditions, if the ideal goal cannot be achieved, then the goal is to change the conditions to moderate heat stress. To the extent that WBGT is selected as the target, the engineering controls are designed to reach that target. This effort will most likely involve the engineering department or someone who is familiar with the basic design principles for the engineering controls. Methods for estimating W8GT for changes in the environmental conditions are given in Section 6.7.

Of course, engineering controls may reduce the heat stress without changing the overall category of the stress in the decision tree. For instance, work in the water boxes may represent a moderate level of stress; boosting the ventilation may lower the WBGT but not enough to drop to the no stress level. The abfif ty to work longer, with lower chances for heat illness, is achieved and the added ventilation is therefore an advantage. Again, estimates are made on the impact of the engineering control (s) on the environment or metabolism. Guidelines for-estimating the environmental effects are given in the last part of this section (see Section 6.7), and the advice of the engineering department may be necessary.

Generally speaking, the engineering controls should reduce the W8GT by 2*C (4'F) to obtain appreciable gains. Another way to assess the gains in engineering controls is to note the changes in stay times (see Section 7.5) that will occur for changes in W8GT and metabolism. If the stay time changes are small, the effects of the control are small. This assessment can be used regardless of whether or not stay times are an accepted site work practice.

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6.1.2 Reevaluation of Heat Stress Once a set of engineering controls is selected and their effects are estimated or known, the heat stress conditions have changed and a reevaluation is necessary. A new Environmental Assessment form (figure 5-1) is completed to reflect the new conditions (either measured or estimated). The new information is used to reenter the decision tree and the new condition number found.

The new condition number may or may not be the same as the previous number. In either case, the engineering controls are examined first to decide whether further controls are desirable. For instance, increasing the ventilation rate may be a'n additional improvement.

In most cases, however, no additional engineering controls are expected. The next step is to select the work practices, and personal protection if appropriate.

6.2 METAB01.!SM i

A major source of heat gain for nuclear station workers is the heat produced internally by the working muscles. The only method for controlling the internal heat generation is to reduce metabolism. To select the parts of s job that are '

the best targets for reduction, a task analysis will indicate activities with a high metabolism. The objective is to lower the average metabolism.

The ideal goal is to drop the average metabolism by one (.ategory (e.g., from high to moderate). But a reduction of even 20 kcal/hr can significantly increase the ability to work by lowering the internal source of heat stress.

If the category of metabolism has been changed, a reevaluation of the heat stress should be made by reentering the information on the decision tree. This was discussed above (Section 6.1.2) in terms of environmental changes.

6.2.1 Evaluation of Metabolism by Task Analysis Once a job is identified as a target for reduced metabolism, a task analysis is performed.

On the Environmental Assessment form,'a job's metabolism is estimated as an intuitive average of all the tasks that make up the job. The estimate is based on typical' activities given in Table 5-3. To determine which tasks in a job contribute most to the heat stress, perform a task analysis using the form in Figure 6-1.

The tasks tha't contribute the most to heat stress should be examined so that methods can be sought to reduce the metabolism.

6-3

Sheet of TASK ANALYSIS Job Date / /

Location 1 2 3 4 5 Task Task Time Metabolism Total Number Description (min) (kcal/ min) Metabolism 1

Figure 6-1. Task analysis form for listing the individual tasks that are performed in completing a job described in the Environmental Assessment (Figure 5-1).

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The task analysis is designed to identify each task in a job. To do this, the HSA works with someone farsiliar with the job. The first step is to list in order of performance each task required, starting at the point that special clothes are donned or when the work location is entered, whichever occurs first. The tasks are described by the type of action, such as donning protective clothing, movement to work location, standing-by, torquing bolts, lifting components, etc. More than one sheet may be necessary to include all the tasks.

An estimate of Task Time in minutes required to perform each task in the job is entered in Column 3. At the sama time, an estimate of the metabolism required to perform the task is made by referring to Table 5-3. If the task falls clearly into one of the four categories of Low, Moderate, High, or Very High, the typical metabolism for that category (2.1, 4.2, 6.3, or 8.5 kcal/ min, respectively) is entered under Metabolism (Column 4). If the task appears to be more demanding than the activities listed under Low, but less demanding than Moderate, a value of 3.1 kcal/ min is placed under Metabolism. In a similar fashion, a judgment that a task metabolism falls between Moderate and High means that 5.2 kcal/ min is entered; or between High and Very High, use 7.4 kcal/ min.

Any task or sequence of tasks under any condition that has a metabolism greater than 7 kcal/ min for more than 15 continuous minutes, or any that have a rate greater than 4 kcal/ min for 30 continuous minutes is a consideration for reduced metabolism. They represent a metabolism sufficient to place an excessive demand on the cardiovascular system, especially when coupled with moderate or high heat stress.

In the analysis of the tasks, another factor not reflected in the metabolisms is the isometric work that may be required. Large forces may be exerted, such as torquing down on a bolt or holding something in one position, that do not appear as a high metabolic demand. Isometric work .however, restricts blood flow and may cause fainting or light headedness. For this reason, alternatives for this work are a consideration when it is performed under heat stress conditiens.

For the next step in the analysis, combine repetitions of the same task for the same job into one entry (one row in Figure 6-1). This is done by drawing a line through the entry line(s) that contain the second or later entries for the same task, and adding together the Task Times for each entry. Add this total to the Task Time in the first entry to represent a total for that task. For example, if

! 6-5

J walking to different areas is part of the job that represents several tasks, these tasks are combined into one entry for walking.

The next step is to multiply the Task Time (Column 3) times the Metabolism (Column

4) to determine the Total Metabolism (Column 5) for each task. Enter this value in Column 5.

The list of tasks are rank ordered in decreasing value of Total Metabolism. Thus, the task with the greatest Total Metabolism is ranked first, the second laroest next, and so on.

This is the order in which the tasks are reviewed for changes to reduce metabolism. Remember that the goal is to reduce the average metabolism to a lower category. Most attention is given to the tcp half of the list.. If a task represents less than 10% of the total, it is going to have a small effect on the total or average metabolism.

6.2.2 Reduction of the Metabolism Reductions in metabolism can be acccmplished by providing a powered assist or otherwise limiting manual demands (e.g., sharing the work). To see a net reduction in the metabolism for the entire workforce, however, the total manual effort must be reduced, and this is done by reducing the work that is required by using a powered assist. The powered assist Can take different forms, depending on the job. ExamplesofdevicescanbefoundinEPRIreports(for. instance 18and B) . Air and electric powered tools are frequently used to reduce the manual effort. Another type of powered assist is a crane to move materials that.would otherwise be carried. A specific example of how a utility reduced metabolism was seen for a job that required adding bags of boric acid to the system. A ground level hopper was built to avoid having the worker carry the bag up stairs to the tank top and pour the boric acid. Another example is the construction of scaffolding to make it easier to reach critical areas, thus reducing the metabolism.

To illustrate the principle of reducing work, if opening a valve requires a torque of 10 kg.m for 50 revolutions, the metabolism remains the same whether the valve handle is short (requiring a large force) or long (requiring a smaller force but more. motion). A powered assist, such as an air driver, reduces the metabolism required because some or all of the energy comes from an external source rather than the muscles.

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As another example, if a worker must carry a device to the work area, the metabolism is reduced if the device is redesigned into a lighter item, or if it is lifted to the work area by a powered lift, such as a jib crane. Manually lifting it with block and tackle does not reduce the metabolism required to move the item.

The trade-off with a powered assist is that the metabolism required to put it into use must be less than the metabolism it will save.

6.2.3 Evaluation of Reduced Metabolism The average metabolism for the job is calculated by adding all the entries in Column 3 (Task Time) and all the entries in Column 5 (Total Metabolism), and then dividing the Column 5 total by the Column 3 total. As different alternatives are examined for the tasks, their effects on the average are determined by (1) estimating the Metabolism (Column 4) and Task Time (Column 3), (2) recalculating a Total Metabolism (Column 5), and (3) recalculating the average metabolism as'Just described.

6.3 AIR TEMPERATURE AND HUMIDITY One goal in controlling air temperature and humidity is to make the heat exchange with the environment more favorable to the worker. This means reducing the heat gain by convection if the air temperature is greater than 35'C (95'F) or enhancing heat loss by lowering air temperature below 35'C (95'F). Lowering the humidity enhances evaporative cooling by sweat. Basically .the more the ambient temperature and/or humidity can be reduced in conditions of heat stress, the better the heat balance for the worker. The overall effects can be judged by changes in WBGT as discussed in Section 6.1.2.

Three approaches are effective in reducing air temperature and humidity in the working environment:

• Ventilation

. Central Air Conditioning

. Local Air Conditioning Two informative sources for designing engineering controls for heat stress are Heating and Cooling for Man in Industry (9) and Industrial Ventilation (20).

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6.3.1 ventilation ,

Ventilation is used to exhaust hot air from a closed space and to bring in cooler outside air, to exhaust hot air and water vapor at its source, and to redistribute air in a closed area. The enclosed space can be as large as a building or the smallest work space in the plant. The ventilation systems used to acccmplish the air movement can be either permanent or temporary, depending on plant design constraints, the nature of the job, and the required air movement.

6.3.1.1 General Ventilation. General ventilation is used to dilute the hot air with cooler air (typically, outside air). This is accomplished by removing air from the work space and replacing it with outside air. This can be accomplished using either natural or mechanical air movement.

Mechanical systems can be a " push" type that brings in cooler air and forces

~

exhaust air out through openings in the building or work space, or a " pull" system that exhausts air and allows the make-up air to enter passively. " Push-Pull" systems are also used, and they have the best control over distribution of air with less total air movement.

The WBGT reduction that can be achieved depends on:

• Outside air temperature

• Heat sources a Volume of air flow

• Humidity Under typical circumstances, the inside air temperature will be slightly higher than the outside air temperature. "Outside" refers to the air spaces that are the source of the make-up air, which may be either inside or outside of a building.

For instance, when ventilating the water boxes, the outside air generally Comes from the turbine or auxiliary building. As the outside air enters the space, it will cool the existing air (dilution) and be warmed by any heat sources. The heat sources include steam lines, motors (and other electrical sources), latent heat (decay heat), and solar load, depending on the volume or space being considered.

The volume of air flow ultimately determines the amount of heat that can be removed from the work space and therefore the air temperature in the work. space.

6-8

It is best to rely on the engineering department to develop an estimate of the j temperature drop for different configurations.

I i

For large volumes, such as an entire building or large rooms, a permanent l ventilation system may be the most practical approach. The permanent system can be aided by modifying flow paths within regulatory constraints. This can mean opening / closing doors or other barriers within the area or to the outside. An example from one plant is shown in Figure 6-2, where the floor plugs were removed to allow more air flow between floors. (Note the safety rail that was installed.)

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, Figure 6-2. Floor plugs removed in turbine building to aid general ventilation.

1 For smaller volumes, portable ventilation systems may be the best approach. This is especially true when the main access is a manway. For instance, steam generators can be ventilated by attaching a portable air mover at one side and drawing air out. In this way, make-up air can flow into the other end where work is being performed. This approach is also used for condenser repair work.

Where work is being performed in an enclosed space with only one access point, flexible ductwork can be used to bring in outside air or to exhaust inside air.

l l

l 6-9 l

No matter what size or type of general ventilation is used, three obvious principles must be observed:

• Allow the make-up air to sweep over the work areas. That is, the primary flow patterns should encompass the work area.

• Avoid short circuiting the air patterns. That is, the make-up air inlets should not be physically near the exhaust points.

• Consider the possibility that the level of airborne contaminants may be increased due to air movement.

6.3.1.2 Redistribution. Ventilation can also be used to mix air from hot and cool areas. While there is a disadvantage to this for work.in the cooler areas, the gains for the workers in the hot areas can be appreciable. (One utility that used a redistribution system in the containment building during operation reported improvements in equipment performance, which also meant less maintenance time.)

6.3.2 Central Air Conditioning unlike general ventilation, which lowers the air temperature in large spaces by diluting the hot air with cooler air, central air conditioning actively reduces air temperature by removing heat from the air.

6.3.2.1 Mechanical Systems. One utility has achieved a great deal of success in reducing heat stress by reducing air temperatures by means of chillers in the ventilation systems, and several are planning them. Chillers circulate cool water through heat exchangers over which air from the ventilation system is passed. In this way, the air temperature is reduced. There can also be some reduction in humidity. The primary justification for this method has been the protection or life extension of equipment in the plant, but advantages to workers have been reported.

Chillers usually use a body of water (e.g., river or lake) as' a heat sink. During the summer months, when the demands on the chiller would be high, the water temperature is higher and its effectiveness therefore reduced. Planning for heat loads and sizing must account for higher water temperatures during the summer.

One site reported a virtual loss of cooling capacity during sunumer outages when -

using the available water source in its chillers.

Mechanical refrigeration can also be used to air condition large spaces, but this approach may be very expensive to install and operate. The sizing and cost 6-10

estimates can be made by the engineering department or contractors with ventilation experience.

6.3.2.2 Evaporative Cooling. Evaporative cooling of the air is accomplished by passing hot, dry air through sprays of water. As the water evaporates, heat is taken from the air and therefore the air temperature drops. The disadvantage of this technique is that it adds moisture to the air that results in a higher humidity. For this reason, it is most effective when the air is dry so that the benefits of the reduced air temperature are greater than the impact of higher humidity.

6.3.3 Local Air Conditioning Local air conditioning actively reduces air temperature by using mechanical '

refrigeration at the work site. Two methods have been used successfully at nuclear stations: (1) cool rooms and (2) portable cooled-air blowers.

6.3.3.1 Cool Rooms. Cool rooms are relatively small enclosures that have an air conditioner (A/C) to cool the air within them. The air conditioners are the size typically used as room A/Cs in houses, and are capable of reducing the temperature by about 10*C (20*F).

Cool rooms can be purchased from vendors or constructed by the plant facilities department. During an outage, one plant site reported covering an existing tool cage and installing the A/C, and then dismantling it before the plant went back into operation. The walls and roof do not need to be tightly sealed or well insulated.

Nuclear sites report'using cool rooms in two different ways. One is to enclose the work space so that the workers perform their jobs in the cool environment.

These cool rooms also serve the purpose of containing contamination. With this method, a tent is constructed to enclose the area and a portable A/C is installed.

It should be noted that if surface contaminants are present, the A/C blower ray cause them to become airborne requiring the use of a respirator.

Another use of the cool room is as a recovery room located near hot jobs. The room is used as..a staging area for workers to wait for the time they are needed, to prepare for the work by donning protective equipment, and to cool down after i

6-11' l i

exposure to heat stress. The degree to which recovery rooms can be kept clean depends on the procedures and practices employed.

The use of cool rooms is a reasonable approach to providing a cool environment at minimal cost on a transient, temporary basis.

6.3.3.2 Portable Cooled-Air Blowers. Portable blowers with a built-in air conditioner or a vortex tube have enjoyed success at nuclear stations. The principal advantage is that the set-up time is minimal. The cooled air is directed toward the worker, and as long as he is near the outlet, he will be in the envelope of cool air.

The portable cooled-air blower can function like a portable, push-type ventilation system for closed areas. This is especially valuable when the source air is warmer than desired.

6.3.4 Selection of Air Cooling Method The selection of a method to reduce air temperature and humidity.is based on both effectiveness of the method and costs. Reducing the temperature by ventilation is the least expensive method for large volumes and most small volumes. The principal disadvantage is that the dilution technique cannot reduce the air temperature and humidity lower than those in the scurce of air for the ventilation.

If teateratures and humidities lower than the source air are needed, air conditioning must be considered. Local air conditioning is less expensive in the short term, and if the needs are sporatic and confined to small areas, it may be less expensive than central air conditioning. On the other hand, if many jobs and workers as well as equipment can be served by a central system, a permanent one can be cos.t-effective. In many cases, the cost of any large, permanent engineering control may be too great to justify solely by enhanced employee performance. It will be necessary to consider equipment performance as well.

6.4 AIR VELOCITY Changes in air velocity have two effects: (1) modification of the magnitude of the convective heat exchange, and (2) enhancement of evaporative cooling. If the air velocity is less than 0.1 m/sec (20 fpm), the air is essentially still and it has no effects on convection and evaporation. As the air velocity increases from 0.1 m/sec (20 fpm) to 2 m/sec (400 fpm), there are increases in the amount of 6 l l

I convention and evaporation. Increases in air velocity above 2 m/sec (400 fpm) do not cause any c' anges in the heat exchange by convection and evaporation.

4 It is also worth noting that air velocity is a two-edged sword. If the air temperature es greater than 35'C (95'F), there 'is an increase in the convective heat gain with increasing air velocity; at the same time, evaporative cooling increases. For cotton clothing requirements (no vapor barrier suits) with low convective heat gain (air temperatures _less than 38'C (100'F)), there can be an advantage to increasing the air velocity. However, if the air temperature is high (greater than 43*C or 110*F), the increase in convective heat gain can surpass the gains in evaporative cooling. It is important to note that air velocity has no effect on evaporative cooling for vapor barrier clothing, but it changes convective heat flow because there is heat transfer through the clothing.

For air temperatures less than 35'C (95'F), increasing air velocity up to 2 m/sec (400 fpm) can help reduce the heat stress. There is also an upper comfort limit to the air velocity over the person if he is wearing traditional work clothes or a single set of cotton coveralls. In Table 6-1, the maximum comfortable air velocity is given for different activities. ,

Table 6-1 Maximum air velocities for comfort around a working person (9)

1. Air temperature less than 21*C (70'F): 0.3 m/sec (60 fpm)

2. Air temperature greater than 21*C (70*F) and 2.1 continuous exposure: 0.8 m/sec (150 fpm) 2.2 intermittent exposure (atworker'sdiscretion): 4 m/sec (800 fpm)

(Note: Regardless of comfort 2 m/sec is the maximum for useful cooling)

Air velocity over a person can be accomplished using permanent or temporary ventilation systems, portable fans, or portable cooled-air blowers. A typical portable fan is shown in Figure 6-3.

i 6.5 RADIANT' HEAT Radiant heat comes frca hot surfaces that are in the line of sight of the exposed person. To reduce the heat gain by controlling radiant heat, several simple engineering approaches can be taken:

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. Insulating hot surfaces

• Changing surface emissivity

) e Shielding i l

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, f In essence, controlling radiant sources means reducing the heat flow from the ,

i source or breaking the line of sight between the workers and the source with a  !

shield.

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6.5.1 Insulating Hot Surfaces Insulating those surfaces likely to be sources of radiant heat reduces the temperature of the outermost surface (the one that is responsible for radiating to the workers). Because the rate of radiant heat flow is very sensitive to the surface temperature, large reductions in radiation can be obtained by lowering the surface temperature. For example, the radiant heat flow from a hot pipe can be

! decreased by 1/3 by reducing the surface temperature by 50'C (120*F). An added benefit to insulation is a reduction in the surrounding air temperature due to lower heat losses from the source.

6.5.2 Changing Surface Emissivity j The rate of heat sent from a hot surface at a given temperature is determined by the emissivity (e) of the surface. A flat black surface (e=1.0) sends away the 6-14'

most heat, while a perfectly smooth, polished surface (e=0) sends off no radiant heat. Therefore, radiant heat can be reduced by decreasing the emissivity of the surface. Polished aluminum or tin has an emissivity of 0.08 as opposed to steel (e=0.85) or painted surfaces (e=0.95). That is why the outer covering of many insulated steam lines has a shiny metal sheath. In fact, steam lines are a good example of the use of both insulation and lowered emissivity to reduce heat losses from the system and thereby reduce heat stress in the work environment.

6.5.3 Shielding The purpose of shieluing is to interrupt the radiant heat pathway between the worker and the hat surfaces. Shields can be either temporary or permanent, at the discretion of the site.

For nuclear stations, the most useful, cost-effective approach is aluminum sheets (except in corrosive areas or otherwise restricted). Stainless steel or other polished surface (reflective) material is also good.. Aluminum foil with a rigid backing has been effective wnen installed with the aluminum side facing the hot surface. With such shielding, as much as 95% of the radiant heat is reflected away.

Transparent shielding is possible by using special glass or metal mesh screens.

It is important to place shielding so that it does not disrupt airflow patterns.

6.6 MAINTENANCE Maintenance of engineering controls is paramount to their success. For ventilation and air conditioning systems, filters and heat exchanges must be kept clean. This warning was repeated by several plant sites during the project-surveys and visits. Maintenance schedules and procedures should be provided by the vendor or engineering department.

For systems that do not meet design goals, the reasons must be investigated and simple solutions may become obvious.

In the case of shielding, the shields must be kept clean. Otherwise, the emissivity will increase with accumulation of dirt.

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6.7 ESTIMATING THE CHANGES IN W8GT DUE TO ENGINEERING CONTROLS The overall goal of engineering controls is to change the environment or metabolism to reduce the heat stress. While planning for engineering controls, it is necessary to estimate the effects of the controls on WBGT so that these effects can be evaluated as described in Section 6.1. This section describes a method for estimating WBGT, but to understand how the engineering controls affect the environment, the HSA should consult with the engineering department. The engineering department manager can best match skills with the need. Once an estimate of the WBGT is made, the HSA can reenter the decision tree (Figure 5-2) to determine if the level of heat stress has changed, or consult the stay time table (Table 7-2) to estimate improvements in heat stress exposure times, j

The following paragraphs are recommendations on how to estimate the changes in all

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the environmental measurements. It must be remembered that they are only estimates and, due to the possible errors, the new conditions with the controls in place can differ from the estimate toward either lesser or greater WBGT.

6.7.1 Air Temperature The air temperature, Tair, is affected by ventilation, air conditioning, and most other engineering controls except simple changes in air velocity (i.e., using a fan).

For ventilation, the lowest possible T air is that of the source of the intake (fresh) air. This might be outdoor air or air from nearby areas of the plant.

Therefore, Tair will be between the value without ventilation and the source. A first approximation would be an average of the two values; but if the change-over is high (maybe 20 changes / hour) with good mixing, T air should be close to the source air temperature. The best estimate will come from an engineering analysis.

For air conditioning, the designer of the system can provide the best estimate or the engineering department can be consulted. Knowledge of the volume of the space, the sources of heat, and the capacity of the air conditioning system are essential.

For radiant heat, shielding may have little effect on T air. Insulation should j j have a large effect, but once again an expert in thermal analysis from the '

engineering department must be consulted.

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6.7.2 Air Velocity The air movement can be assumed to be M if there is no ventilation or general ventilation (purging) with no local inlets or exhausts. If there is local ventilation, the air velocity can be assumed as Moderate. The air velocity near cooling fans or other large air movers can be taken as High. Refer to Table 5-1 for descriptions of these ranges.

6.7.3 Natural Wet Bulb T

nwb depends on the humidity of the air and the air velocity. Humidity of the air, in turn, depends on the source of air when ventilation is used, on sources of water vapor in the work area (e.g., wet floors and walls, or steam leaks), and water removal (dehumidification) by chillers or air conditioners. A thermal analysis of the proposed countermeasure which should be performed by the engineering department, is used to estimate a psychometric wet bulb (Tpwb). A basic textbook on engineering analysis or handbook of mechanical engineering or heating / air conditioning would describe the methodology. Table 6-2 is then used to estimate T nwb from Tpwb and air velocity.

Table 6-2 Estimation of T mb from T pwb for different air velocities.

Low: T = T pwb + 1.5'C (3*F) nwb Velocity Moderate: +

T nwb

= T owb 1.0'C (2*F) ,

High: T nwb

= T pwb 6.7.4 Globe Temperature The globe temperature, T g , depends on Tair' Vair, and the average temperature of the solid surroundings. This means that T will g change because some engineering controls will change Tair and/or Vair only. T galso changes if some action is taken to decrease the sources of radiant heat; that is, the average temperature of the solid surroundings is changed.

The estimation of Tg is made sequentially, following the order presented here.

First compute the effects due to changes in air temperature, then in temperatures of the solid surroundings, and finally in the air velocity. Before this process starts, the HSA must know the Tair, Tg and V air for the job before the engineering 6-17

_ _ _ _ _ .._ . ___ _ _ . _ . _ . . _ _ , , . ~ . .

controls are installed as well as estimates of air temperature (est-Tage) and air velocity (est-Vair) under the new conditions.

6.7.4.1 Air Temperature Change. The first effect on globe temperature is due to a. change in air temperature. The air temperature change is calculated-as ,

aTair = est-Tair - Tair Then the first intermediate value of the estimated globe temperature is T

gg =Tg + aTair 6.7.4.2 Temperature Changes of Radiant Sources. A second effect.on globe temperature is a change in the surface temperatures of radiant sources. To estimate the effect, two factors must be considered: (1) the fraction of the surrounding area that changes temperature (fA) and (2) the temperature change (aT3 ). The fraction of the surrounding area that changes temperature due to controls on the radiant heat sources must be estimated. The first. step in estimating fg is illustrated in Figure 6-4. An approximation of the area that receives treatment for radiant heat (e.g., shielding or insulation) is made by assuming a flat rectangular surface that covers the treatment. The second step is to estimate the angles in degrees that represent two adjoining sides of the rectangle from the globe thermometer (called a and b in the figure). Then I "

axb A 80000 The next step is to estimate the change in surface temperature due to one of the following three treatments. If a shield has clean polished surfaces (front and back), the effective surface temperature (eff-T 3)-can be taken as est-T air- If the shield is dirty or has a painted surface, eff-T3is the average of the surface temperature of the radiant source (TS ) and est-Tair-If insulation is used to reduce the surface temperature, the effective surface temperature (eff-T3 ) is the estimate of the surface temperature on the outside of the added insulation. The engineering department can supply this estimate based on the insulation parameters.

l I

6-18 l l

14  : I3 I I & 1 t 2 3 4

ql b s J location of the globe thermometer rectangular surf ace that approximates the size and location of the radiant heat treatment (e.g., shield)

Figure 6-4. Illustration of method to approximate angles for radiant heat treatments in order to estimate fA*

Changes in emissivity are more difficult to estimate reliably. While the surface temperature does change, the primary effect is the amount of heat given off. The effective surface temperature (eff-T 3) then depends on the change in emissivity.

In the following equation, e3 is the previous emissivity and est-c3 is the emissivity of the new surface control. For emissivity changes:

eff-T 3 =[T est-c 3 s

Once eff-T3 has been estimated, the effective change in surface temperature is calculated as aT3=T3 - eff-73 The globe temperature (Tg2) due to engineering controls for radiant heat is given by 6-19

T g2 = Tg g - (fA aTg )o where a is the factor given below based on air velocity before any new engineering controls are added.

For different air velocity categories, Low: a= 1 Moderate: s = 0.6 High: 2 = 0.4 6.7.4.3 Air Velocity Changes. Finally, if air velocity is changed, the effect of air on Tg changes. In this case, it is the transition condition that determines T

the adjustment. The est-T is calculated from:

g est-Tg=Tg2 + s [Tair - Tg2I Values for a est-Vair Air Velocity L M H L 0 -0.2 -0.4 V

air M 0.2 0 -0.2 H 0.4 0.2 0 6.7.5 Recalculation of W8GT The estimated value of W8GT is calculated from est-Tnwb and est-T g . This value is used to estimate the effect of the engineering control.

W8GT = 0.7 est-Tnwb + 0.3 est-T g 6-20' L.

Section 7 WORK PRACTICES i'

Work practices reduce the effects of heat stress by changing the way the work is  ;

performed. These changes can be fairly subtle but have an important effect. Work practices include the following:

• Training t

Self-determination

. Fluid replacement Acclimation

• Scheduling hot work 4

. Stay times and recovery

. Clothing

. Buddy system Personal monitoring Training is very important for all workers who may be exposed to heat stress and for their supervisors. For this reason, it is discussed in a separate section (Section10). The other work practices are discussed below.

. 7.1 SELF-DETERMINATION l

Self-determination means allowing the worker to use his discretion in setting the pace of the work and the exposure time. Self-determination requires adequate training so that a worker can best understand how he responds to heat exposures.

As a rule, self-determination should be used as the overridino practice durine exposures to heat stress.

7.1.1 Self-pacing Metabolism and heat exposures are largely determined by external factors, but the i j

worker can exercise some control over these factors by controlling his rate of  !

work (and therefore metabolism) and exposure to peak heat sources. In laboratory 7-1 l .

experiments as well as in reports of industrial experience, workers in a self-paced work situation can and do adjust the pattern of work to avoid overexposure.

The total amount of work that is accomplished with self-pacing can exceed the total for externally paced work, that is the worker optimizes his performance.

The important effect of self-pacing is the avoidance of high, sustained demands on the cardiovascular system. This, in turn, reduces the chances that the worker will' experience a heat illness.

There may be situations for which external pacing of the work is required. As one example, work in a high radiation area must be accomplished as quickly as possible to reduce the radiation exposure.

7.1.2 Self-limitation The worker should be given the discretion to terminate his exposure to heat in order to reduce the chances of overexposure. Any exposure must be terminated with the onset of symptoms of heat illness.

The primary purpose of self-limitation is to avoid overexposures, which may occur even with the best planning. Problems can arise from

• Large differences among individuals in their tolerance to heat

= Day-to-day differences for a given individual

• State of acclimation

= Illness and other health factors 7.2 FLUID REPLACEMENT When a worker is exposed to heat stress, a normal body response is sweating for evaporative cooling. The sweating results in a fluid loss that must be replaced.

Thirst is an insufficient drive to ensure that fluid losses are balanced. For this reason, the worker must be encouraged to drink water or other acceptable -

drinks, and barriers to these drinks should be minimized.

i l

l 7-2

7.2.1 Replacement Schedule The highest likely need for an individual's fluid replacement is one liter or  !

quart per hour of heat exposure. It is best, therefore, to plan to have as many I liters of replacement fluids as there are person-hours of heat exposure.

Under ideal conditicins, the worker should drink at 15 to 20 minute intervals. By spreading the volume over the hour, more fluids can be comfortably ingested.

Because water intake is prohibited in some areas, this ideal cannot be achieved.

In such cases, workers should be encouraged, but not forced, to drink a half liter (1 pint) per hour of scheduled work before entering the restricted area, and then j to drink as much as possible afterwards to help maintain the fluid balance.

J 7.2.2 Barriers Water should be easily accessible in all parts of the plant, especially in areas where hot jobs are performed. In this way, workers are more likely to drink.

Besides water fountains'placed in unrestricted areas in the plant, many stations provide flavored drinks in the change rooms and eating areas. This further enhances the availability of fluids and encourages workers to drink frequently.

Schemes can be developed to provide drink to workers in uncontaminated parts of the restricted areas. This can be achieved under current NRC regulations, and several sites have reported site procedures for providing drinks in restricted areas.

One power station (a PWR) reported setting up a drinking station in an uncontaminated area near the personnel hatch during an ounge. Workers could doff their respirator and outer gloves, frisk their hands and face, and then take a drink. In this way, they avoided having to completely change out each time they required a drink. This was reported as an efficient way to provide fluid replacement, but it requires careful planning.

In the case of BWRs, much more of.the plant area is under radiological restrictions and therefore providing for fluid replacement is more difficult. One BWR reports the use of prcpacked drinks in clean arstas of the RCA. For instance, a maintenance worker can carry a prepackaged drink into the RCA if he will be working in an area approved by Radiation Protection.

7'-3

7.2.3 Replacement Fluids The replacement of lost water is the primary concern. Several comercial salt replacement fluids have been reported as being widely used in the nuclear industry. These commercial fluids are physiologically effective, but, based on the evidence reviewed, they are no more so than ordinary water.

An important aspect of encouraging fluid replacement is making the drink palatable so that workers are more inclined to drink it beyond satisfying immediate thirst. As the first consideration, fluid' temperature should be between 10 and 15*C (50 and 60*F). Secondly, flavoring the drink helps. Besides the comercial replacement drinks (with the added salts), lemonade or dilute iced tea are good alternatives. Using citrus flavors or extracts in water also works well.

Salt (Nacl) replacement need g be part of the fluids. The typical American diet has sufficient salt for most needs. The only concern would be during periods of acclimation, when the workers should be advised to use more salt than usual. (A worker on a salt restricted diet should consult his physician.)

7.3 ACCLIMATION Acclimation (frequently called acclimatization) is a physiological adaptation to heat stress. After it has been achieved, the body sweats more (better evaporative l cooling) while losing less salt and maintaining lower body temperatures and cardiovascular demands.

A person acclimates to a given level of heat stress with repeated exposures.

After five days he is 90% acclimated. While formal acclimation procedures are not necessary, supervisors should recognize the worker adaptations that occur. As a reference for performance expectations, an acclimation program includes progressive exoosure times to heat stress, beginning on the first day with 50% of what can be expected of a fully adapted worker, and increasing the exposure time about 10% per day for the next 5 days.

Because a person loses some of his adaptation to heat stress when he is not routinely exposed, a period'of reacclimation should also be considered. Table 7-1 gives a schedule for reacclimation of workers who have been away from heat stress for routine reasons (e.g., vacation, reassignment, etc.) or illness. For the appropriate type and period of absence from heat exposures, the progressive exposure times should start with the first percentage and increase to the next fce successive days (see Table 7-1). For instance, if a worker is ill for one week, 74'

Table 7-1 Schedule of reacclimation after different periods away from heat stress exposures Routine Absence Illness  % Exposure Time by Day

• 3- 5 days 1 - 3 days 90 6 - 12 days 4 - 5 days 50 90 12 - 20 days 6 - 8 days 50 75 90 2 21 days a 9 days 50 60 70 80 90

• % exposure time for a fully acclimated person on successive days for reacclimation then he chould start at 50% of the full day's exposure, and increase to 75% on the second day and 90% on the third.

7.4 SCHEDULING HOT WORK To the. extent possible, work should be performed when the thermal stress from the environment is at a minimum or a no stress level. An effective means of controlling heat stress is to allow an area to cool before anyone works in it.

This can be accomplished in three ways:

• Working at cooler times of day

• Allowing latent heat to dissipate

• Allowing heat waves to pass The above methods provide guidance, but must be balanced against the need to accomplish the work. They are most suitable for jobs where large fianges (>3'C or 5'F WBGT) can be expected, and for jobs that are not on the critica; path.

The target temperature for cool-down depends on the work that must be ,

accomplished. Ideally, the environment should reach a no heat stress level in the decision tree (Figure 5-2) for the metabolism and clothing ensemble. On the other hand, if a job requires a certain time to perform, the stay time tables (next section) indicate the target W8GT for a given clothing ensemble and metabolism.

7.5 STAY TIMES AND RECOVERY l Many jobs in a nuclear station require work under conditions in which a thermal balance cannot be maintained. In these cases, the body temperature steadily increases and it is important to limit the increase to a safe level. A prescribed 7-5

stay time on the job can be used to ensure this margin of safety. It is also important that the person recover from this increase in body temperature.

7.5.1 Stay Times The stay time is dependent on metabolism, clothing ensemble, and environmental conditions. Stay time categories are given in Table 7-2 as a function of W8GT, metabolism, and clothing. Each category represents a range of work times for which workers can reasonably be expected to tolerate the heat stress. In this table, the environmental condition is represented by the measured or anticipated WBGT. For a given clothing ensemble (WC, CC, DC, PC), a group of columns 1s-selected and'then a metabolism column within the clothing group. The user then moves down the column to the row defined by the W8GT. A range of stay times in minutes (or hours) is found for that combination.

The range of stay times reflects two factors. The first is the inherent variability among workers. The stay times could be longer for workers in good health and physical condition, fully recovered from previous exposures, and acclimated to the heat. A few workers, however, may not be able to stay the j entire time if they are til, intolerant to heat, or not recovered from prior j exposures. The lower value should protect most workers under most conditions.

The higher value for stay time is less protective, and workers should be informed that they may experience the symptoms of heat illnesses. The second factor is the nature of WBGT as an approximation of the environmental stress. Under some conditions (e.g., very humid conditions), the lower stay times for a W8GT are more appropriate. On the other hand, if the radiant heat is high, long stay times in the range for a given W8GT are protective of most workers. Because of the inexact nature of stay times, it is igortant to use them for planning and as an advisory for work times, but not to use them as an abulute as for radiation exposure.

A second use of Table 7-2 is to determine the effects of changing the environment (WBGT), clothing requirements (e.g., changing from DC to CC), and metabolism

. (lowering the amount of work performed by the inoividual). The effect is reflected in the change of stay times.

Table 7-3 is a similar table except that W8GT values for the work areas are given for the different categories of stay time, metabolism and clothing ensemble. This table is most useful when a stay time is specified by the nature or plan of the job, and a target W8GT is sought. The lower WBGT is the most protective and is i

1.s

• t

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l Table 7-2 Ranges of Stay Times in Minutes (or "h" for Hours) for Different WBCTs (and Botaball Readings) in *C and *F by Combinations of Clothing Ensemble and Metabolism Work Clothee Cotton Coveralle Double Cottone Cottone plus Plastice see abeliem Hetabeltem Metabol8em seetabeliem WILT (notaball) im Ned Nigh tow peod Nish Low seud Nigh 1.ow Mod Nash

• C *W 50 (47) 122 (116) 15 30 0-10 5-15 0-5 5-15 48 (45)  !!$ (112) 20-45 5-15 15-30 5-10 10-20 5-15 7 46 (43) 115 (109) 20-45 5-20 20-45 5-15 15-30 0-10 15-20 44 (41) 111 (105) 30-60 10-25 20-45 5-20 20-45 5-15 15-30 0-10 42 (39) 108 (102) 45-90 15-30 5-10 30-60 10-25 20-45 5-20 20-45 5-15 y 40 (37) 104 ( 99) 60-90 15-45 10-20 45-90 15-40 5-10 30-60 10-25 20-45 5-20 6 e

N 38 (35) 100 ( 95)90-120 20-45 15-30 60-90 15-45 10-25 45-90 15-30 5-10 30-60 10-25 '

M (33) 97 ( 92) 2h-4h 30-60 15-40 90-120 25-45 15-30 60-90 15-45 10-20 45-90 15-30 5-10 34 (31) 93 ( 88) h-th 45-90 20-45 "a-4h 30-60 15-45 90-120 20-45 15-30 60-90 15-45 10-20 32 (29) 90 ( 85) ut.90-120 3040 3h-Sh 60-100 25-50 2h-4h 3040 15-40 90-120 20-45 15-30 30 (27) +6 ( SI) E 2h-4h 60-120 E th-2h 30-90 h-Sh 45-90 20-45 2h-4h 30-60 15-40  ;

28 (26) 42 ( 78) Nt. E 2h-4h E lb-4h th-h ut.90-120 '30-60 h-Sh 45-90 20-45 l

26 (24) 79 ( 75) ut. NI. 4h-Sh E NE. h-Sh Nt. 2h-4h 60-120 K 90 820 3040 24 (22) 75 ( 71) ut. E E E E E Nt. K 2h-4h E 2h-4h 60-120 22 (20) 72 ( 68) E E E MI. E NE. E E 4h-th NI. K 2h-4h 20 (18) 68 ( 64) E E Nt. ut. NI. E E E E NL Ns. 4h-Sh

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more preferable for humid environments. On the other hand, the higher W8GTs can be used if there is radiant heat and moderate humidity.

I Figure 7-1 illustrates the method used by one site to use stay times as input to

! job planning. A survey of the plant is taken during the late afternoon (a time f when the highest temperatures are found) and posted in an area where most l employees will see it as they enter the plant buildings. At the bottom of the l

survey, the curve for minimum likely stay times for three different metabolisms is j given. Next to the curves is a table that gives the highest' stay time that should l be considered for a given W8GT and metabolism.

3 7.5.2 Estimation of W8GT for Stay Times

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i

} The environment can be assessed quickly using the Botsball (wet globe temperature)

} thermometer. The Botsball thermometer (available from Howard Engineering) was j developed as a simple replacement for W8GT. It uses a small black globe that is covered by a wet, wicking material. The following equation can be used to relate Botsball to W8GT: -

W8GT = 1.05 Botsball + 1.1'C (W8GT = 1.05 80tsball + 0.6*F) 1 i

Because it is simple and relatively inexpensive, several can be made available to e

! maintenance and operations departments for'on-the-job evaluation for stay times.

f It is important to note that the Botsball should not be used as a substitute for j W8GT elsewhere in the program. Also, the Botsball should not be used if the

relative humidity is below 30% (dry environments).

r Air temperature (Tair) in a work location can correlate closely with W8GT. If this is the case, T air can be used to predict stay times. If the HSA wants to investigate this possibility, he must develop a database that relates measured q values of each. The HSA, however, must involve someone who is competent in I statistical analysis to devise a measurement plan and assess the results.

i

! 7.5.3 Recovery Times i Recovery from heat exposure is completed when the person's physiological state has

! returned to its preexposure condition. Practically, this means recovery is

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complete when any stored heat has been dissipated and lost water replaced. Water i .

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i 7-10

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1 replacement is difficult to assess, but one indicator is no large decrease in body l weight (no more than 1 kg or 2 pounds) during the course of the day.

When the stay times are limited as indicated by Table 7-2 and 7-3, the body stores  !

heat and increases in temperature. To permit dissipation of stored heat, recovery

time of up to one hour may be needed if the actual work time equals the maximum i stay time indicated in Table 7-2. The recovery area should be cool, between 20

,and 23*C (68 and 73*F), and the person should be dressed in light clothing.

When a heat exposure is less than the maximum stay time, a recovery time estimate is:

Recovery time = actual exposure time x 60 minutes.

maximum stay time 7.6 CLOTHING i Reducing clothing requirements improves the heat balance because it will reduce j the resistance to evaporative cooling. Clothing. requirements are examined in two ways, both in consultation with radiation control. The first is to reduce the need for extra clothing by decontaminating the work area. This has been successful at several plants as a method to reduce radiation exposures and -

respirator use as well as heat exposures. Most important is removing wet sources so that cottons provide sufficient protection, and plastics (or other liquid barrier protection) are not required.

The second way to reduce clothing requirmeents is to consider the likely sites of contamination and design the protection accordingly. One nuclear station reported reductions in protective clothing to reduce the heat stress by adapting the extent of impermeable clothing to the work. For instance, if wet contamination is confined to the floor, only rubber boots and impermeable pants are used.

Other possibilities exist for reduction of heat stress by changes in protective -

clothing. An example being considered is the use of Gortex (TM) as a water barrier. Because this material allows water vapor,' and therefore sweat, to escape, it should be " cooler." There is not sufficient experience, however, to recommend its use on the basis of reduced heat stress.

l l

7-11 l

1

7.7 BUD 0Y SYSTEM A buddy system allows two workers to observe each other. In this way, one can provide help to the other if needed. While the buddy system is recommended for work at moderate heat stress exposures, it should definitely be in effect during high heat stress exposures. An additional advantage of the buddy system is that it permits workers to share work and therefore reduce metabolism and hence the heat stress.

7.8 PERSONAL MONITORING Personal monitoring is a method to' assess the worker's response to a heat exposure while he works. Once a predetermined set cf conditions is reached, the worker is advised by visual or aural alerts to reduce the heat stress by reducing his metabolism or by leaving the work area. Two physiological responses to heat stress that are generally regarded as important candidates for assessing a worker's tolerance:

• Body temperature

. Heart rate While personal monitoring is not recommended for every worker under all conditions, it would be helpful to a worker planning to extend himself as far as possible. Two general conditions may require this approach. The first is when a person who may be heat intolerant (see Section 9) tries to perform at a level with other workers. The second condition is when the worker maximizes the amount of time he works. Under these conditions, normal stay time recommendations are exceeded and the chances of incurring a heat illness increase. .The advantage is that the individual is not limited by a conservative estimate of tolerance based on a wide variation of tolerances.

The personal monitor is primarily a tool to aid in the self-determination of the exposure. It can provide a warning when'a worker approaches his tolerance limit. This information would be used by the wearer to determine when his exposure should end.

7.8.1 Body Temperature The important objective in controlling heat stress is to prevent an excessive body temperature increase (greater than 1*C or 2*F). Another objective is to prevent l

i 7-12

i j l

skin temperature from exceeding body temperature, a condition that can occur while a person is wearing vapor barrier clothing.

It is difficult to measure body temperature in a work environment. Oral temperature, the most familiar technique, is reliable only for the resting state.

During work, it becomes progressively lower than body temperature due to increased breathing through the mouth. The ingestion of hot or cold drinks can also have a

, drastic effect on oral temperature. While it is possible oto use oral tenperature as an indicator, the threshold would have to be very conservative to be protective.

The most reliable method is rectal temperature, but the process of obtaining it is unacceptable to workers. Other measures of body temperature (e.g., ear canal) are unreliable as well as difficult and uncomfortable. There is a consercial device worn on the chest or back that uses heat flux to measure deep body temperature.

It also is unreliable in most work situations.

As part of the EPRI heat stress research, the Pennsylvania State University has designed a prototype sensor that is taped to the skin that correlates well with body temperature. This device is being tested for possible applications in the nuclear industry. The results of this research will be included in an update of this document.

7.8.2 Heart Rate Heart rate is an indication of the cardiovascular strain that a person experiences when exposed to heat stress. It can be measured by palpation (feeling an artery expand with each heart beat) or by surface electrodes (usually placed on the chest).

Heart r4te threshold and recovery heart rate can be used for the purpose of monitoring heat exposure. -

, 7.8.2.1 Heart Rate Threshold. A number of commercial devices are available to monitor the heart rate. They usually have a maximum setting so that an aural alarm will sound when the heart rate crosses over the threshold. If this type of device is used, the threshold should be set according to the person's age in years. The threshold is selected using the following equation:

HR (threshold) = [200 - 0.67 (Age - 25)] x 0.8 l 7-13

_ _ __ ,__ ~ _ _. -. _ __ _ . _

A problem with a fixed setting, however, is that the heart rate may temporarily jump above the threshold with some types of work. Most often the transient jump occurs with the exertion of large forces, such as required for torquing dcwn on a bolt. For momentary alarm thresholds, the user should consider only sustained (more than 30 seconds) alarms. Another way to avoid transient excursions above the threshold is to select a device that averages the heart rate over pcriods of about 30 seconds.

A further advantage of personal monitoring of heart rate is that it helps pace the work. As mentioned in the discussion of self-determination, a self-paced task allows the worker to optimize his performance. This is achieved by keeping the heart rate below threshold and thus reducing periods of high exertion that can cause early termination of work. Devices to monitor heart rate are commercially available.

7.8.2.2 Recovery Heart Rate. If it is suspected that an exposure to heat stress may be excessive, the recovery heart rate pattern can be examined via a method developedatDuPont(M). To use this technique, the worker must stop working for four minutes. From 30 to 60 seconds after the work, the heart beats are counted and multiplied by 2 (call this rate P t). From 150 to 180 seconds (2-1/2 to 3 minutes) after work stops, count the heart beats and multiply by 2 (call this rate P3 ). A simple logic table in Table 7-4 indicates the relative stress the individual is under. If no stress is indicated, he can continue. If marginal stress is indicated, work can proceed with caution (reduce metabolism and perform further checks). If high stress is indicated, the work should be terminated.

Table 7-4 Heart rate recovery patterns to indicate level of stress (see M).

P3 < 90: no excessive stress P3 > 90 and Pg-P3 > 10: marginal stress P3 > 90 and Pt-P3 < 10: high stress l

4 7-14

Section 8 PERSONAL PROTECTION Personal protection from heat stress is usually accomplished by using some form of personal' cooling. Several types of devices are available:

. Circulating air systems

!

• Ice cooling garments

. Circulating liquid systems The principle of operation is to provide a microenvironment under the clothing that can better take up the heat from metabolism and block heat exchange with the outer environment, thereby controlling heat stress.

In addition, reflective clothing reduces radiant heat gain if hot surfaces are present.

8.1 CIRCULATING AIR SYSTEMS 8.1.1 Principle of Operation Circulating air systems direct compressed air from a house-supplied air system around the trunk of the body. The greatest advantage is seen for use under impermeable garments or double cotton coveralls, but there are also advantages for other clothing ensembles. The air provides cooling in two ways. The most important is that it enhances the evaporative cooling of sweat. Clothing lowers the effect of sweating on cooling because it restricts the evaporation and provides an insulation layer between the skin and the environment. By passing the air under most of the clothing, the insulation barrier is virtually eliminated.

Under humid conditions, the circulating air has a lower humidity and thus further enhances the evaporative cooling. l Circulating air also enhances convective cooling as long as the air entering the  !

clothing ensemble is less than 36'C (97'F). The lower the air temperature, the more convective cooling is. achieved.

8-1

8.1.2 Types of Circulating Air Systems Circulating air systems are described by method of air entry under the clothing and by whether or not a vortex cooling system is used. One method of entry involves a supplied air hood (" bubble hood") provided for respiratory protection.

The exhaust air from the hood is forced around the neck and under the clothing.

The air then escapes through openings in the suit. The second method of entry is directly under the clothing without any circulation around the head.

A vortex tube can be used for reducing the temperature of the circulating air (see Figure 8-1). The cooled air from this tube is used for either method of entry (bubble hood or directly to the clothes). Compressed air enters the tube so as to create a cyclone effect. A portion of this air expands rapidly and cools, and then is directed to a low pressure outlet. The remaining air takes up the heat lost from the cooled air, and the hot air is exhausted from another port to the environment.

There are several manufacturers of supplied air hoods that force the air into the clothing from around the neck. This is accomplished with a " bib" around the neck that ttcks under the clothes. A second layer of the bib stays on the outside of the gara nt to reduce the potential for any contamination reaching under the clothing.

For direct entry under the clothes, there are three possibilities: (1) a single inlet to the suit, (2) a distribution tree, and (3) a perforated vest. In the single inlet system, the air is delivered to one spot around the trunk.

Distribution of the air is assumed to occur with normal motions of the body, with air flow paths to divergent exits. A distribution tree delivers the air to different locations on the body. An example is shown in Figure 8-2. The distribution is accomplished using fabric channels, plastic tubes, or any other appropriate method. The tree frequently delivers air to the arms and legs as well as around the trunk of the worker. A perforated vest for air distribution is also available, as shown in Figure 8-3. This ensures a good distribution of the air around the torso. The arms and legs get the air through openings at the wrists and ankles.

8-2

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8.1.3 Use of Circulating Air While circulating air systems offer a powerful means of cooling, their efficient use requires careful attention to:

. Embodiment

. Source of supplied air

. Applications for vortex cooling

. Logistics

. Estimation of effects 8.1.3.1 Embodiment. There must be good circulation of air around the torso and, to a lesser extent, the extremities. Embodiment must be considered whether a vortex tube is selected or not. Separate recommendations are based on whether the supplied air hood or the direct feed method is used.

Supplied air hood. With the bubble hood, at least two-thirds of the air should vent through the legs at the ankles to ensure good circulation about 8-4

the torso. This means that rain wear with vents on the back should be used only with the vents restricted by tape. Also, the wrist openings should be taped to reduce, but not eliminate, air losses.

Direct feed. With direct feed systems, the air line enters at the waist from the back or side. The use of a distribution system is recomended. While there may be advantages in directing the air along the extremities, it is most important to achieve good distribution around the torso. .

8.1.3.2 Source of Supplied Air. Supplied air hoods require about 0.17 -

0.42 m3 / min (6 - 15 cfm) to meet the mandated air flow requirements for breathing air. This is usually supplied at 60 to 80 psi. (All supplied air respirators must be operated at the manufacturer's stated pressures in accordance with its NIOSH approval and the air must meet the ANSI breathing air standard.)

It is assumed that the. exhaust air from direct feed systems.will not raise airborne contaminants. Direct feed systems should also use at least 0.17 m /3 min (6 cfm) of air flow for cooling purposes. While there are no regulations that govern the air quality for direct feed air cooling systems, it is best to use breathing air (CGA - Grade D or meet ANSI 29.2 1960) because the user may inhale the exhaust air containing contaminants for which he is not protected.

If a vortex tube is used to cool the air supplied to the person, the demand on the supplied air system changes. A vortex tube requires between 0.3 and 0.6 m 3/ min (10 and 20 cfs) of air at 75-100 psi in order to deliver at least 0.17 m /3 min (6 cfm) of cooled air to the person.

~

In conclusion, house air of breathing quality (Grade 0) should be used for all types of circulating air systems. Portable filtration, breathing air panels can be used to convert instrument air into Grade 0 breathing air. The volume rate requirements differ according to whether or not a vortex tube is used. Without 3

the tube, 0.17 m / min (6 cfm) is the typical requirement. With a vortex, it depends on the manufacturer and model, but to supply 0.17 m3 / min (6 cfm) to the worker, a flow rate of 0.3 to 0.6 m 3/ min (about 10 to 20 cfm)'is required.

8.1.3.3 Applications for Vortex Cooling. The purpose of supplying air inside protective clothing is to enhance convective cooling and the evaporative cooling of sweat. To achieve this, the air should be dry and less than skin temper-ature. Generally, the air from a compressed air source is dry enough, but the 8-5

i l

temperature may be high because as the air travels through fixed lines and air hoses, it can gain heat from the environment. Table 8-1 is a table of maximum desirable air temperatures at the inlet to the bubble hood or under the i

clothing. If the supplied air temperature is above the indicated temperature, vortex cooling should be considered to extend the usage time. (Note: Any other system that reduces the temperature of the supplied air can be used. No alternative was found in use, but a custom-built unit could use mechanical refrigeration, for instance, to cool the air. It is important that NIOSH approvals not be voided; therefore consultation with an industrial hygenist is i recomended.)

J Table 8-1 Recommended maximum air temperatures for supplied air entering circulating air cooling systems for indefinite stay times at different metabolisms Maximum Supplied Metabolism Air Temperature Low 40*C (104*F)

Moderate 33*C (91*F)

High 28'C ( 82*F) l Note: The air temperature for low metabolism can be higher than skin temperature because of the enhanced evaporative cooling out weighs gains due to convection.

It is r.ecessary to evaluate the flow rate and temperature reduction of a particular model before it is used. A vortex tube is capable of reducing the air temperature by 15 to 25*C (27 to 50*F).

i Any vortex tube used with a supplied air respirator must be supplied by the

manufacturer of the breathing air system (respirator) and be NISOH approved for

that combination of vortex and respirator.

A vortex tube should not be used to supply air to either a fitted full face or half mask. First, it will not contribute to lowering the level of heat stress and i is therefore a waste of air. In addition, there were wide spread reports that 8-6 '

I supplied air respirators using fitted masks and pro ..eng cool air gave a false sense of cooling and the users would sometimes overextend themselves.

8.1.3.4 Logistics. There are two common logistics problems associated with circulating air cooling systems: (1) getting the supplied air to the desired location, and (2) working while attached to the air hose. A third set of problems arise with the use of vortex tubes.

Most plants have permanent air lines distributed to the general 3reas of the plant. While this air is intended for other purposes, ports are often installed in areas in which air cooling is desirable. It may be necessary, however, to prepare the areas for use by bringing in a temporary air line from the closest permanent port to a filter and manifold near the work location. This problem is similar to establishing ports for supplied air respirators and is dealt with in a similar fashion.

Being attached to an air hose is a common complaint of workers using either an airline respirator or a circulating air cooling system. It is therefore important to minimize the amount of hose that is carried. To achieve this, the distance that the worker moves while attached to the airline should be kept as small as possible. This leads to three considerations:

1. Circulating air systems should be used in locations where there is not much traveling and climbing is less than 1.5 m (4 to 5 feet).

The work area should require less than 16 m (50 ft) of hose (although more may be tolerated by the workers). The need to climb or to move over and through tight spaces discourages workers from using circulating air systems and create safety hazards.

I

2. It is not necessary for a worker to be continuously attached to the system. The remote port can be near the primary work area, and the workers can detach themselves to leave the area for such reasons as getting tools. This will work if the changes are not frequent or the disconnect / reconnect is not cumbersome. There is less need to have active cooling going to and from the job location.

3. The air cooling system can be used effectively if there are long pauses between shorter bursts of activity. In this case, a worker can be cooled while waiting to perform the next phase. The system is also useful for a worker who is "on deck." For instance, if a worker stationed in containment is wearing a vapor barrier clothing ensemble, he can be kept cool while waiting to perform his task.

Without the cooling, any of these stand-by conditions may allow heat accumulation while the worker is not accomplishing useful work, t

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8-7

Another set of problems arises with the use of the vortex tube. One problem is contamination. To prevent contamination, it is possible to wrap the vortex tube before entry into a radiologically controlled environment. Care must be exercised not to cover the exhaust port. There were also reports that the hot exhaust air causes discomfort to the wearer. To reduce this problem, leather holders are available, but the best alternative is to extend the input line so that the vortex tube is away from the body, as shown in Figure 8-4.

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Figure 8-4. Vortex tube hanging from inlet air hose away from the user, 8.1.3.5 Estimation of Effects. It is difficult to propose what an equivalent environment and clothing ensemble would be for air cooling systems. Because the person exposed to the heat stress does not receive the full impact of the clothing or the ambient environment, these factors must be adjusted for workers wearing I circulating air systems. If circulating air systems have a good air flow and distribution with low air temperatures (less than 28'C or 82*F), they should allow unlimited stay times. If this is not the case, the clothing level is equivalent to ordinary work clothes (or a single set of cotton coveralls if the cooling system distributes air over a layer of work clothes or cotton coveralls). The equivalent WBGT used for evaluation is taken as the inlet air temperature minus 3'C (5'F). Thus, if the inlet air temperature is 30'C, the WBGT is about 27'C.

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This WBGT and equivale.nt clothing ensemble is then used in the decision tree (Figure 5-2) or in the stay time tables (Tables 7-2 and 7-3).

8.2 ICE COOLING GARMENTS 8.2.1 Principle of Operation The purpose of ice cool.ing garments is to place a heat sink inside the insulating layers of clothing to absorb the heat gain due to metabolism. A typical ice cooling garment is shown in Figure 8-5. When the ice packs are in contact with the user, heat is conducted away from the skin to the ice. In this way, the skin is cooled, which, in turn, cools the blood that returns to the body core. For practical purposes, the ice cooling replaces sweat as the major mechanism to dissipate heat. An insulating layer is placed over the ice garment and serves two functions: (1) it prevents environmental heat from reaching the ice and melting it before it can aid the user and (2) it further isolates the user from the environment.

l The principal advantage of ice garments over circulating air systems is the

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greatly increased mobility. Among self-contained systems (ice garments and the liquid cooling systems discussed in the next section), the ice garments are much less expensive. Because the effects of convection and radiation are reduced, the major source of heat gain is metabolism. Therefore, the cooling requirements are based on the work that must be performed.

8.2.2 Types of Ice Coolinq Garments An ice cooling garment relies on a heat-absorbing material placed on or near the skin. The material undergoes a phase change (e.g., solid to liquid) as it acts as a heat sink. Ice made from frozen water is the best example of an ice cooling

) garment material. Frozen water systems have been designed and refined over the

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past 20 years. EPRI sponsored the development for one design (2) that has spawned l commercial versions. A number of commercial garments of varying designs.are i

available.

While water ice is the most common heat sink in ice cooling systems, another is dry ice (frozen CO2), which has about the same cooling capacity per kilogram as water ice. The main advantage of CO 2 ice is the phase change from solid to gas, which reduces the weight of the cooling garment as the heat is taken up. The

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principal problems are (1) the low temperature of CO2 fce makes handling it a 8-9

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safety problem; (2) CO2 ice is more expensive to produce or procure; and (3) the j user may be exposed to high levels of CO2 gas. For these reasons, it has not been  ;

comonly accepted as an alternative to water ice. j There are other alternatives, such as frozen lithium nitrate. The principal E advantage is a higher temperature for the phase change, which gives less of a cold i

feeling. The heat absorbing capacity is similar to that of dry or water ice.

Such an alternative, however, is not commercially available.

l 8.2.3 Recomended Methods

The ice cooling system can be a very effective method of personal orotection for periods of an hour or more, but it must be used correctly. During the investiga-tions, several cases of improper use vere found.that compromised the ice cooling system. The proper use must include correct procedures in four areas

. Freezing and storage of the ice

. Donning procedures l

i 8-10

l I

. Maintenance 1

! . Service time i

j 8.2.3.1 Freezing and Storage. Thc water packets must be completely frozen to ensure full heat absorbing capacity. The temperature of the packets should be about -6*C (20*F). Usually a commercially available freezer can freeze enough packets for several garments in 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. It is very important that the freezer air be free to circulate around the individual packets. If the packets are bunched together

or layered, they will insulate each other and take much longer to freeze.

A rapid freezing technique developed by one power station is shown in

Figure 8-6. The exhat st gas from a dewar of liquid nitrogen is

:irculated through the chest to drop the temperature rapidly, and the ice packets are usually frozen

in 20 minutes. Once frozen, the ice packets are placed in the garment. The l garment is then stored in the freezer until it is needed. (The ice packets can be frozen in the garment using nitrogen, but this takes considerably longer.)

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8-11

8.2.3.2 Donning Procedures. Once the ice garment is removed from the freezer, it begins to absorb heat. For this reason, the removal of the garment from the freezer should be delayed to the last moment. If a person dons the garment and then remains in a standby position, he uses the cooling capacity of the garment without performing useful work. The best approach is for the worker to suit up as

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much as possible without donning the garment (leaving it in the freezer or in an ice chest), and then complete the procedure just before he performs his job.

Just before the garment is donned, the user should feel several of the packets to assure himself that they are completely frozen. If any of the packets have started to melt, the garment (or at least the suspect packets) should be exchanged.

Typically, the garment is worn over a thin insulating material like a T-shirt or net shirt. Too much insulation, however, prevents proper functioning. The recommendations of the manufacturer in this matter should be observed. The purpose of the thin layer is to prevent excessive cooling of the skin. Experience of the users helps determine the best approach.

The garment should fit closely. This is necessary to get the most contact with the cooling surfaces, and to avoid the " pumping" of warm air from outside the garment around the ice as the user moves.

An outer insulating jacket is an integral part of the ice cooling garment. Some failures of ice cooling garments can be traced to the absence of the insulating jacket in environments with air temperatures above 35'C (95'F). The jacket reduces the amount of heat from the environment that will melt the ice, and therefore deprives the user of the full cooling capacity of the ice. It is important that the insulating jacket provide a flexible seal around the ice garment to minimize the infiltration of air from outside the garment.

8.2.3.3 Maintenance. The key maintenance concerns with the ice garments are e Integrity of the ice packets

. Cleaning of the garment The ice packets must be checked for leakage after use. If water loss is evident, they should be discarded. Replacements are available from the vendors; one power station makes its own.

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'1 8-12

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l Since the ice garments used in nuclear stations have generally not been radiologi-cally contaminated, they can be sanitized in a clean laundry facility. In the event of radiological contamination, however, it may be difficult to decontaminate

' some parts of the ice cooling garments. It may be convenient to treat all ice vests used in radiological areas as contaminated, and then launder them with contaminated laundry.

8.2.3.4 Service Time. The cooling capacity of the ice cooling garments is determined by the amount of ice or other medium, such as dry ice or lithium nitrate. The major component of the heat sink capacity is the latent heat associated with the phase change. In the case of ice (frozen, solid water), the latent heat is 80 kcal/kg. This means that one kilogram (2.2 pounds) of ice will absorb 80 kcal (320 BTU) of heat as it goes from a solid to a liquid. Under ideal conditions, the total heat absorbing capacity of ice that starts at -6'C (20*F) is about 90 kcal/kg. Ideal conditions, however, are not usually met, and for planning purposes an efficiency of 60% can be expected. This means that the practical cooling capacity of ice cooling garments is 54 kcal/kg.

l The service time of an ict cooling garment is dependent on the amount of ice contained in the garment and the metabolism. Table 8-2 gives the approximate service time increments for different levels of metabolism per kilogram (and pound) of ice that starts at -6*C (20'F). The service times are estimated by l multiplying the service time increment by the weight of ice and adding about 10 I

minutes. A typ cal garment has 5 kg of ice and therefore a service time of about

one hour for moderate metabolisms (9 x 5 + 10).

Table 8-2 Approximate service time increments (STI) in r..nutes for ice garments

that start at -6'C (20'F) per kilogram (or pound) of ice.

I Metabolism min /kg min /lb Low 15 7 ,

j Moderate 9 4 High 6 3 l Garment Service Time (min) = STI . (wt of ice) + 10 min.

8-11

Longer service times for ice cooling garments have been measured by Pennsylvania State University (PSU) (RP1705) (Z) and reported to the authors by utilities.

Users can therefore expect them, but the expectations should be based on experience at the specific power station. PSU also compared the service times of ice garments to liqui _d cooling systems under controlled conditions (!).

Ultimately, the user defines the actual service time. Once the cooling capacity of the ice has been expended, the garment increases the heat stress due to insulation effects. When the user notices that the ice has melted and he does not perceive any further benefit, he should start to terminate the heat exposure, including an allowance for egress.

8.3 LIQUID COOLING SYSTEMS 8.3.1 Principle of Operation The liquid cooling systems, like the ice cooling garments, attempt to supplant sweat evaporation as the principal mode of heat dissipation. They are worn in close contact with the trunk of the body (and possibly on the head and other extremities). The difference from other cooling systems is that an intervening fluid transfers the heat from the skin to the heat sink.

The working fluid is basically water, which may contain some additives. The liquid is circulated around the body through narrow tubes to provide favorable heat transfer. The flow patterns include larger supply and return plenues and narrower parallel channels to provide even distribution of the 11guld. After taking up the body heat, the liquid travels to the heat sink, where the temperature is reduced.

The heat sink is composed of ice. As the heat taken from the body is delivered to the ice, the ice takes up the heat in a fashion similar to the ice cooling garments. The major portion of the heat absorbing capacity is in the latent hes,t associated with the phase change from solid to liquid.

The liquid is moved through the system via a pump powered by a rechargeable battery pack. In most cases, the heat sir.k, pump, and battery pack are carried on the person by a belt or as an integral part of the cooling system. One vendor supplies a configuration with a tether between the heat sink / pump and the user.

8-14

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i 8.3.2 Types of Liquid C)oling Garments Two different types of 11guid cooling garments were found at nuclear stations.

One is a modular liquid cooling system. The heat exchange with the person occurs in the garment worn around the trunk of the body, and can include a head piece.

It uses a refreezable ice canister with a pump and battery built into one package, and includes a second package for a second ice canister. The two packages can be worn on a belt, providing close access to the cooling garment, or they can be connected to the user through a tether composed of the hot and cold liquid lines wrapped in insulation.

l The second type, pictured in Figure 8-8, is an integral liquid cooling system. In

] this device, the heat sink, pump, and battery are inseparable parts of the cooling l system. The heat sink is a reservoir for the circulating liquid (water), in which ice is placed. As the ice melts, it becomes part of the working liquid.

l 8-15

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The chilled water is circulated around heat exchangers on both the front and back

) surfaces of the cooling system. The system is designed so that the reservoir and i

I other equipment can be worn on either the back or the front, depending on the l constraints of the work area, job, or other protective equipment.

8.3.3 Recommended Method of Use j The design of the liquid cooling systems allows the user more mobility than the

! air cooling systems. Even with the modular system using a tether, the worker is not dependent on an airline port, and the entire system as easily transported to the work site.

i Three usage aspects of liquid cooling garments are discussed further:

i i

e Limitation l

e Service time e Maintenance 8-16.

8.3.3.1 Limitation. From a study comparing ice cooling garments to liquid cooling systems, evidence suggests that the heat :ransfer rate in the liquid cooling systems cannot match moderate or high metabolisms (2_). For this reason, the I liquid cooling garments should be used only for low metabolism (see Table 5-3).

i 8.3.3.2 Service Time. The service time is dependent on the capacity of the heat sink and the metabolism. For low metabolism, the heat generation should be less

! than 1.7 kcal/ min. If the liquid cooling systems are 80% efficient (possibly a high estimate), they should absorb about 70 kcal of heat per kilogram of ice at

-6'C (20*F). This means the service time for low metabolism is about 40 minutes

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per kilogram (20 minutes per pound) of ice in the heat sink.

j Pennsylvania State University compared the service time of ice garments and liquid i

cooling systems at moderate metabolises (200 and 300 kcal/hr) under conditions of l high heat stress (2). Without replenishing the heat sink, the ice garments provided longer service times. The service time for moderate and high metabolises may be improved (especially for the modular system) if the heat sink is frequently replenished (as often as every 15 minutes). In this way, a larger temperature gradient to the heat sink can be maintained and the rate enhanced.

The service time of the liquid cooling systems is lengthened by replenishing the j heat sinks when the user finds the heat loss is not sufficient. This has been done in radiologically clean areas for the modular system and is relatively simple

the ice canister in the package is replaced with a fresh one. For the integral system, water is removed from the reservoir before the same volume of ice is added. In both systems, if the heat sink is under anticontamination clothing, it will be more difficult to replenish.

8.3.3.3 Maintenance. The garments can be washed along with radiologically clean

garments in a clean plant laundry to sanitize them for subsequent use. In the

event that they become contaminated, decontamination is possible.

The batteries must be recharged and the pump operation checked before use. The system can be checked for leaks when it is recharged after laundering.

)

e 8-17

8.4 REFLECTIVE CLOTHING 8.4.1 Principle of Operation The purpose of reflective clothing is to lower the radiant heat load on the

, person. It works because the clothing reflects away the infrared radiation from j hat surfaces in the surroundings instead of allowing the skin to absorb the heat.

8.4.2 Types of Reflective Clothing The most common reflective clothing is an aluminized coating bonded to different kinds of fabric. The fabric types that might be used are dictated by the other job and clothing requirements (e.g., tensile strength, thermal insulation, etc).

Reflective clothing ensembles can range from aprons to jackets to completely

, enclosing suits.

8.4.3 Recommended Methods of Use

, Reflective clothing is very effective in reducing the effects of radiant heat sources, but it must be used appropriately. Since it reduces the capacity for evaporative cooling by sweat, the reduction of radiant heat gain must be at least as much as the reduction in evaporative cooling to realize an advantage.

Three recommendations must be considered in the use of reflective clothing:

• Ensemble

• Fit / personal cooling

• Effects on heat stress 8.4.3.1 Ensemble. The type of reflective clothing should be chosen with regard to the source and the work to be performed. The goal is to shield (or shade) only the exposed parts of the body. For example, if the job requires monitoring a hot j source where most of the exposure is to the front of the person, an apron is more appropriate than a whole suit. On the other hand, if the worker is completely surrounded by radiant sources, a jacket or an encapsulating suit may be best.

8-18 4

8.4.3.2 Fit / Personal Cooling. To get as much natural cooling as possible, it is important to keep the reflective clothing as loose as possible and to minimize clothing under the reflective clothing so that air will naturally circulate with i body motion. This vill help the evaporative cooling of s'weat.

It may still be necessary to use personal cooling if a jacket or encapsulating suit is required. If this is the case, a personal cooling system can be chosen from those described earlier in this section.

l 8.4.3.3 Effects on Heat Stress. The effects on heat stress of the reflective clothing must be evaluated. There are two concerns: clothing and WBGT. For clothing, if an apron (or equivalent) or a loose fitting jacket is worn over work clothes or a single cotton coverall, the equivalent clothing ensemble is double cotton coveralls (OC). If a whole body suit is considered over work clothes or cotton coveralls, the equivalent ensemble is cotton coveralls with vapor barrier clothing (CP). Both of these considerations tend to increase the level of equivalent heat stress.

The reduction in heat stress comes from an apparent reduction in WBGT under the clothing. For a reflective jacket or apron, the equivalent globe temperature (Tg ')can be taken as Tg=Tair+0.25(Tg-Tair)

For an encapsulating reflective suit 1

Tg=Tair The new W8GT is then calculated. This value is used in conjunction with the category of clothing ensemble determined above to reenter the decision tree (Figure 5 2) and to use the stay time tables (Tables 1-2 and 7 3).

I 8-19

Section 9 ME0! CAL EVALUATION FOR HEAT STRESS Medical evaluation of workers is an important component within a comprehensive i

heat stress management program because heat stress management is designed to

! protect most, but not all, workers.

While there are no figures available for the extent of heat intolerance in the worker population, some indication of the extent of heat intolerance can be gained :

I from data reported in other industries (20, 2_1,). For example, among workers in j the gold mines of South Africa, approximately 25% are heat intolerant in the j unacclimated state. After rigorous acclimation, 2% of the working population

)

remainheatintolerant(H). Similar percentages have been shown for Israeli workers (H). The extent of worker intolerance is sufficient to warrant some type of medical evaluation process.

There is no standard definition of " heat intolerance" since physiological adaptations to heat stress span a continuum of resporises. In this study, it is defined as a relatively lesser physiological ability to withstand heat stress.

While medical evaluation of workers for respirator use is commonplace in the nuclear power industry, no such evaluation process for heat stress has been 4 devised. The medical evaluation recommended here for heat stress exposure is a two-stage process. First, those workers whose characteristics suggest a risk of heat intolerance are identified. Second, for those who may be at risk, a sPart exercise test predicts relative heat tolerance. A percentile approach in the exercise test indicates relative' tolerance, that is, individual tolerance with respect to others who have been tested. The exercise test is recomunended as 4n

! adjunct evaluation tool at the examining physician's discretion.

The information presented in this section is intended to provide guidance and is used at the discretion of the utility. Ultimate medical evaluation rests with the examining physician. The section begins with a " Physician's Guide" that describes l the major risk factors associated with heat stress. Based on the risk factors, a 1

9-1

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checklist (Section 9.1.2) is suggested for initial evaluation. If the initf41 evaluation indicates the possibility of heat intolerance, further evaluation j employing an exercise test is possible (Section 9.2).

9.1 PHYSICIAN'S GUIDE FOR EVALUATING WORKERS FOR HOT J005

)

9.1.1 Background '

Based on the premise that some workers are relatively heat intolerant, the problem f of how to predict individual heat tolerance becomes important. Medical evaluation is advised for all workers who are exposed to moderate or high heat stress. The Heat Stress Advisor can identify these workers as those working on jobs associated with heat stress from the evaluation described in Section 5.

Wide variation exists among people with respect to heat stress tolerance, making it difficult to predict individual responses. However, several general physical [

and physiological characteristics are associated with some intolerance. Included .

among these correlates of heat intolerance are a medical history of heat illness,  !

acclimation state, age, body composition and size, aerobic fitness level, hypertension, and drug and alcohol abuse.

Routine medical exams, while necessary to assess physiological integrity, tell little about a healthy worker's potential inability to tolerate heat stress.

Special emphasis should be placed on the circulatory system, where physiological  :

strain from heat stress is largely manifested. This is especially true in the nuclear power industry where protective clothing is worn that Ilmits evaporation i of sweet. Therefore, the primary importance is placed on the functional capacities of the cardiovascular system. A thorough review of the respiratory system and skin is also important for detection of potential difficulties in adapting to heat stress.

The following physical characteristics are associated with heat intolerance.

9.1.1.1 Medical History of Heat 111 ness. In_lury. or intolerance. A history of ,

heatintolerance(eitheroccupationalornon-occupational),non-acclimatability, "

or incidence of heat stroke is a strong indicator of intolerance. Available 1 literature (id)suggeststhatworkersaremoresusceptiabletoheatstroke subsequent to a previous episode. Among the questions to consider asking are the fonowin, l 1

9-2

. Are you aware of any personal difficulty in toleratirig hot conditions?

. Are you prone to heat rash or prickly heat?

. Have you ever suffered from heat exhaustion or heat stroke?

. Have you ever passed out during hot weather or intense exercise?

. Do you have difficulty with muscle cramps in hot weather?

9.1.1.2 Acci1mationState. When a worker is exposed to hot environments over a period of 8 to 10 days, a series of physiological adaptations take place (see Section 2 and 7) which allow the worker to better withstand the heat. The examiner should strive to ascertain information about relative acclimation state (e.g., "Do you exercise outdoors in warm weather on a regualr basis?"). Worker acclimation is recommended as a work practice, as outlined in Section 7.3. Any history of difficulties in acclimating should be ascertained.

Because loss of acc11mation is fairly rapid, a worker should undergo re-accIl-mation if he is away from heat exposures for several days (see Table 7-1). Loss of acclimation state is even greater in those workers who are away from the job due to illness. Fatigue and alcohol consumption also contribute to the early loss of acclimation effects.

9.1.1.3 Le_x e . Sex differences in responses to heat stress are best examined by research that matches groups of women and men with respect to fitness level and/or surface area-to-mass ratto (for instance see Q). From these studies it appears that true sex differences in thermoregulation are minimalt therefore, there is no basis for disqualification of an individual from a hot job based solely on sex.

9.1.1.4 A_ge. Sunuier heat waves in large American cities have provided ample evidence of the relatively greater heat intolerance of the middle-aged (50-65) and elderly (65andolder). With few exceptions, laboratory studies have concurred that adults past the fifth decade seem to be a greater risk in hot environments than younger individuals. However, it is not clear whether this reduced tolerance is a consequence of the aging process or a consequence of scos conconstitant functional change, such as a reduction ,in cardiovascular fitness.

From the available literature, it appears that for moderate heat stress, age does not appear to be a factor in relative thermal tolerance. However, for high heat stress, tolerance appears to decrease in older individuals as a population.

'9-3

Several investigators have implied that if the older worker stays fit, no age differences are evident. Older workers who have always worked on hot jobs should be educated with respect to the relationship betweeen heat tolerance and physical fitness, and should be urged to maintain a good fitness level.

Age should not be a sole criterion for disqualifying workers from work on hot jots because wide variation exists with respect to individual responses. Increasing l

I age does, however, represent added risk while working under heat stress.

j 9.1.1.5 Obesity. Obese individuals have a lower heat tolerance than lean individuals. Obesity is marked by body fat in excess of 30% total weight. It may j

affect a person's at'llity to tolerate heat stress through various mechanisms, as

}

j reviewed by Buskirk ( H). These mechanisms include

• Compromise in cardiac function (higher pulse rate, cardiac

! enlargement, lower skin blood flow) i

• Altered body surface contour that may limit heat exchange with the environment 3

i

• Higher heat load per kilogram of bodyweight (lower specific heat values)

• Alteration in sweating and sweat gland distribution j Many simple methods are available to estimate percent of body fatness. The least i expensive of these is' skinfold measurement, which can be done in a minute or less i

in some instances. Many models of skinfold calipers are available. The best models have parallel jaw surfaces and a constant " squeezing" tension. Inexpensive plastic calipers have become available recently, but they should be avoided l

I because of inaccuracy and lack of reproducibility. The simplest skinfold technique (U)involvesmeasurementoftheskinfoldthicknessoveronesite,the relaxed tricep muscle. A thickness greater than 23 mm (0.9 in) for men or 30 mm (1.2 in) for women constitutes obesity.

j Those unfamiliar with the use of skinfold calipers or without access to such ,

equipment should still attempt to decide whether the worker's obesity is great enough to present an added risk in the heat. An alternate method is to examine l

3 the body mass index (BMI) (2_6). 6 BMI is equal to the worker's weight in kilograms divided by the square of his height in meters. Using this calculation, the criterion for obesity is BMI >30 kg/m2 (for men and women). (Using pounds and I inches, BMI >0.043 lb/in2 .)

94

The obese worker should be provided with information and counselling with respect to weight loss and the coronary problems of obesity, e.g., diabetes, hypertension, coronary artery disease (CAD), etc.

9.1.1.6 Oy gs and Alcohol. Prescription medications and drug abuse including alcoholism may predispose workers to excessive heat strain by physiologicsily or behaviorally altering thermoregulatory function. Such drugs may limit workers in exposure to heat stress. The drugs listed by Minard (27) as being potentially limiting include:

e diuretics e antihistamines e vasodilators e muscle relaxants e central nervous system

• tranquilizers and sedatives inhibitors e beta-blocking agents e amphetamines e anticholinergic medications e atropine 9.1.1.7 Hypertension. An estimated 19.2 million Americans have definite hypertension, as defined by a systolic blood pressure greater than 160 mmHg or a diastolic pressure greater than 95 mmHg. This represents 20% of working age Americans. Although much data exists concerning hypertensives' responses to exercise and work, little data deels specifically with the heat stress question.

Recently, Kenney and Kamon (28) studied a group of untreated hypertensives working inheat(38'C,48%RH). Although heart rate and core temperature responses were similar, the hypertensive group responded with a lower cardiac output and a markedly decreased skin blood flow response. These results imply a lower heat tolerance as a result of even mild hypertension (e.g., 150/100 mmHg).

Furthermore, the vast majority of diagnosed hypertensives take some form of antihypertensive medication. These medications, primarily diuretics, vasodi-lators, and sympathetic inhibitors, may decrease heat tolerance, although more research in required to demonstrate this with certainty. Untreated hypertensives with sustained elevated pressures as well as treated hypertensives should be considered potentially heat intolerant.

9.1.1.8 Cardiovascular System. Physiological adjustments to heat stress are manifested largely in the cardiovascular system. Therefore, medical evaluation of applicants for jobs involving heat stress requires the examiner to place primary 9-5

emphasis on functional capacities of the heart and circulatory system. This applies both in taking a medical and occupational history as weil as in the examiner's physical examination and in the evaluation of laboratory findings.

Laboratory tests include the 12 lead EKG, the 14 x 17 inch chest x-ray, and other components, such as routine blood counts and urinalysis, i Organic diseases of the heart or vascular system of significant degree represent serious limitations for heat stress exposures. Valvular heart disease, myocardial disease, coronary artery disease, renal vascular disease, cerebral vascular disease, or disease of other peripheral arteries are examples of disorders that may be considered as serious.

In case of a minor functional disorder (e.g., benign arrhythmias), the examiner must decide whether or not heat stress exposure will constitute a significant added risk to the employee.

Minor organic vascular disorders (e.g., varicose veins) that can be treated are not considered as serious limitations.

It is important to emphasize that these recomendations are all for new employment. If the worker has successfully performed under heat stress, he is likely to continue to do so.

9.1.1.9 Skin. The presence or history of skin disease of a recurrent and generalized nature that would be aggravated by heat exposure or that would impair the secretory function of the sweat glands has the potential to limit the worker's tolerance to heat stress on a temporary basis. As an example, recent acute injury to the skin and sweat gland.s (e.g., extensive and severe sunburn) temporarily limits sweat production. Not until normal sweat gland function has returned or the examiner is satisfied that chronic impairment of sweat gland function is not a possibility should the applicant be considered free of risk for exposure to heat stress.

9.1.1.10 Respiratory System. Chronic obstructive pulmonary disease of more than minor degree may limit tolerance. Restrictive disorders (e.g., pulmonary fibrgsis) require careful evaluation with regard to etiology and. degree of pulmonary impairment, as well as the disease status (stable or progressive). Both restrictive and obstructive diseases result in impaired pulmonary circulation, which can lead eventually to cor pulmonale.

9-6.

i

i l

An active lung disease (e.g., tuberculosis) is serious, and findings should be reported to the applicant's primary care physician. Following treatment, the worker may be reconsidered for heat stress exposures. Other chronic or recurrent acute respiratory diseases require the examining physician to determine on clinical grounds whether the worker is acceptable for assignment to a job requiring heat stress exposure.

9.1.1.11 Other Systems. The physical examination usually includes other physiogical systems, such as liver and biliary, renal and urinary, endocrine and metabolic, and digestive. In taking the medical history and in performing the physical examination, the examiner should inquire into and examine the above systems, with particular attention to possible chronic impairments. Disease of these systems are considered as a serious limit only if the worker is not under treatment by a personal physician. Clinical judgment of the examining physician, however, must be used in deciding whether the worker could tolerate heat stress.

If, in the examiner's judgment, the impairment would jeopardize safe performance of the job, or if heat stress would aggravate the impairment, the worker should be considered for restriction.

9.1.1.12 Physical Fitness. An important criterion for successful job performance under heat stress is the employee's level of physical fitness. For any work level, the upper limit of heat tolerance is lower for the physically unfit.

It has been reconmiended (2J.), therefore, that the preplacement examination include a simple submaximal exercise test of some kind for estimation of physical fitness.

An exercise test specific to heat tolerance but incorporating a " fitness component," was developed as part of EPRI RP2166-3. By having a worker perform a submaximal exercise test at a fixed intensity (see Section 9.2), the worker's aerobic capacity becomes a factor in test performance; by adding vapor barrier clothing, the test becomes specific for heat tolerance. As indicated below, the use of such a test is reconsiended in the HSM Program on a selective basis, following completion of the medical checklist (Figure 9-1).

l 9.1.2 Medical Evaluation Checklist Following a medical exam, an exercise test can be used to predict relat.tve heat tolerances. For example, an obese worker with no history of work in the heat would be a good candidate for this follow-up procedure. To select those candidates who exhibit sufficient risk to warrant a followup exercise examination, 9-7 l . . - -, - .- - - - - - . .- - . . - . ~ . . .

MEDICAL CHECKLIST Patient Date YES NO 1 1 History of heat intolerance (e g., heet stroke, heat exhaustion)

2. 2. History of non-acclimetability 3 3 More than 50 years old with no history of workin hot environments 4 4 Obese (body f at greater then 305) 5 5. Prescription medications 6 6 Skin disease symptomology over large areas 7 7. History of alcohol or drug abuse 8 8 Hypertension (greater then 160/95 mmhg) 9 9 Work history of overextending stay times,

~mocho~ herotcs, etc Action- ,

Figure 9-1. Candidate checklist that can be used as an initial evaluation for heat stress intolerance.

9-8 '

the checklist in Figure 9-1 can be used. A "Yes" answer to any of the items is a likely indicator; and a "Yes" to two or more items it a very strong indicator of potential risk.

Remember that the best indicator for successful performance in the heat is a past history of heat tolerance. On the other hand, tolerance to heat stress can be slowly lost as the risk factors develop in an individual. Therefore, new .

employees should be evaluated for ris:* factors before their exposure to' heat stress. Current employees can be evaluated on a periodic basis (e.g., during respirator physicals). The period can be every two years for those under 40 and yearly for those over 40. The periodic evaluation need not be rigidly scheduled; that is, a delay of six months on current employees is reasonable.

The initial evaluation using the checklist or the method selected by the utility can be administered by a physician, nurse, or contract medical service. The actual implementation is at the discretion of the medical director.

9.2 HEAT TOLERANCE EXERCISE TEST 9.2.1 Background A heat tolerance exercise te.st was developed and evaluated by Pennsylvania State University (PSU) under EPRI contract (RP2166-3).* Based'on survey data gathered as part of this project and literature data, the following goals were adopted for a heat-specific exercise test suitable for use in the nuclear power industry:

1. To make the test a reliable, scientifically based predictor of physiological performance in a high heat stress environment

2. To minimize test duration, preferably less than 30 minutes total test time

3. To be able to administer the test in a neutral ambient environment (normal room temperature), so as to preclude the need to provide hot conditions

4. To minimize (a) equipment and (b) expertise and sophistication necessary to perform the test

5. To minimize variables measured during the test (reducing them to one, if possible) and to make such measurement as simple and noninvasive as possible

• A supplementary detailed report of the MS development and validation is available from EPRI. .

9-9

6. To standardize test modality to an ergometer, which is inexpensive and reliable (i.e., reproducible workload settings). Ideally the workload should be reproducible on several optional modalities (e.g.,

exercise bike, step-test, treadmill)

While the exercise test is not proposed as an across-the-board screening exam, it has utility for (1) those individuals whose history or medical exam results identify them as potentially heat intolerant individuals, or (2) those individuals selected to perform critical tasks that require above average tolerance to extend the. stay time.

9.2.2 Exercise Test The exercise test protocol accomplishes two objectives: (1) it creates a heat stress condition without the need for raising ambient temperatures, and (2) it establishes a heat Stress that is effectively represented by heart rate alone.

The exercise test is built on simple physiological principles. The physiological effectors of thermoregulation are cutaneous vasodilation and the production and evaporation of sweat. The skin blood flow transfers deep heat to the skin for dissipation via convection, radiation and sweat evaporation. To increase cardiac output to support the working muscles and the cutaneous circulation, heart rate increases. If sweating is eliminated as a viable avenue of heat dissipation, heat strain should increase and be reflected by heart rate increase alone.

To take advantage of this, a vapor barrier suit (VBS) made from Tyvek (TM) was used to eliminate evaporation of sweat.

In addition to the VBS, the test requires the worker to exercise at a workload of 850 Kg.m/ min. 'The experiments at PSU used a bicycle ergometer, which is a device that controls the amount of work that is performed. While.an exercise bike can be relatively inexpensive, a stool-stepping test can also be used. In this case, the patient steps onto the stool, one foot at a time, and then steps back off, one foot at a time. The stepping rate for different step heights is given in Table 9-1.

The duration of the exercise is 20 minutes or until volitional fatigue (whichever occurs first). At the end of the test, the subject should continue to move his

leg muscles to avoid pooling of the venous blood in the legs. This can be done by' an easy walk or by zero-load cycling on a cycle ergometer.

9-10' l -

l Table 9-1 Step height and stepping frequency for a stool stepping exercise.

Step Height, em (in) Step rate, steps / min 20 (8") 30 30 (12") 24 40 (16") 20 Five minutes after the exercise test with continued leg movements, the heart rate is measured.' This can be done using an EKG recording or by palpating a pulse for 10 seconds and multiplying by 6. ,

9.2.3 Intepretation The HRR5 (heart rate after five minutes of recovery) as described above is the important seasurement. Referring to Table 9-2 (based _on PSU data from EPRI RP2166-3), the range into which the HRR5 falls describes the population percentile in terms of heat tolerance. Anyone who falls into the St% percentile should be regarded with concern. If he is to be exposed to heat stress, he should be carefully monitored to determine how well he tolerates the exposure after two weeks, a period that allows for some acclimation to the heat.

Table 9-2 Test sample percentiles from EPRI RP2166-3 associated with the HRR5 score.

Distribution of HRR5 Scores

• Percentile HR R5 95th 80 beats / min 75th 100 50th 110 25th 120 5th 140

• Suggested interpretation , ,

80-105: Above average tolerance 105-115: Average tolerance 115-140: Below average tolerance

> 140: Diminished tolerance possible (may be at risk) .

4 9-11

= . - .--

9.3 RECOMMENDATIONS Ultimate responsibility for the medical qualification of a worker for heat stress exposures lies with the examining physician Any medical evaluation in a heat stress management program should include the following:

. A periodic medical evaluation that delineates those wo'rkers whose d

physical or physiological characteristics and/or health habits add the potential risk for heat stress intolerance e An exercise test specific to heat tolerance for those who may have the potential risk for heat stress intolerance

= A worker education program that outlines basic aspects of heat stress and strain as well as recognition and prevention of heat illness and injury The medical evaluation of risk and exercise test results are not intended to be

. used for work restriction but to indicate a risk of intolerance. Identified workers may be advised that their tolerance to heat may be much less than average and that self-determination is the key method to avoid an overexposure. These workers may also be encouraged to use person'al protection at their discretion. If the plant uses personal monitoring, workers with a potential risk of intolerance may also be encouraged to use the monitor.

4 All workers who demonstrate a potential intolerance based on the exercise test may be given the opportunity to attempt jobs under heat stress with careful supervision and after heat stress training. After allowing sufficient exposure for acclimation, if the individual demonstrates an intolerance to heat stress, then the worker, plant management, and the mecical director can determine which jobs the worker can safely perfom.

9.4 HYPOTHETICAL APPLICATION Worker X, a 50 year-old power plant maintenance foreman, has been moved into a position that frequently requires exposure to extremely hot areas of the plant.

In his previous job, no exposure to heat was required. A yearly physical exam reveals that he has high blood pressure, a condition often associated with an inability to tolerate heat stress (2_8).

As a followup procedure, Worker X is asked to step up and down for 20 minutes (24 times / min) on a one foot stool while wearing vapor barrier clothing. Five minutes after completing this task, his pulse rate is measured by the site nurse.

~ 9-12 f

.,------.n ..-n , , ,,_. . -.-. - ...-r- , . . . . . , , . ,.-a n.,c.., , _ , , ,--.,n.7.- ..,~.~mv.. ,e .-

A HR of 140 bps (5th percentile) indicates that, indeed, Worker X has a relatively poor ability to tolerate work in a hot environment. While this does not disqualify him from working under heat stress, it signals site health and safety personnel that he may be at risk. On the other hand, a HR score of 80 (95th

~

percentile) indicates that Worker X is relatively more heat-tolerant that fellow workers with higher HR responses to the test. There is not an absolute cut-off criterion for assignment to hot work because the degree of heat stress varies widely.

1 n

9-13

Section 10 TRAINING

10.1 BACKGROUND

Heat stress training gives workers and supervisors information to compliment the countermeasures to heat stress, including engineering controls, work practices, and personal protection. The specific objectives of heat stress training.are:

• To explain personal responses to heat exposures

• To encourage good hygiene practices

• To minimize effects of heat illnesses

• To describe countermeasures and their limitations Individuals differ greatly in t'neir ability to tolerate heat stress. In addition, c.ny one individual responds differently to heat stress depending on his state of acclimation, state of health, type of heat stress, other stressors in the workplace, and other factors not understood. Workers and supervisors must, therefore, exercise good judgment in dealing with heat stress. Good judgments can be made with a correct understanding of heat stress.

Another faccor is the worker's physiological state, which defines his ability to tolerate heat stress. It is greatly influenced by what he does on and off the job. If he practices good heat stress hygiene, he will minimize risks for overexposure and be able to tolerate higher and longer exposures to heat stress.

Because heat stress in an integral part of some jobs, it is important to have those workers as physiologically prepared as possible; and this can only be accomplished with their knowledge of proper hygiene.

Heat stress training must also provide some guidam:e to the workers and supervisors in the use of countermeasures. They must be familiar with the correct procedures to follow when implementing countermeasures. With this in mind, a key goal.of training is to provide a worker with the information to make reasonable determinations of his ability to work under heat stress without compromising himself, others, or the plant. Moreover, when established countermeasures fail, l'0-1 i

i the individual must recognize that a problem exists and take action to prevent an unnecesse , overexposure.

As with any procedure or equipment, providing the employee with the framework to-understand how and why it works encourages him to use it properly. The same is true of the heat stress countermeasures. If the worker understands the functions and limitations, he is less likely to misuse the countermeasure and cause an overexposure or limit his ability to work.

While the Heat Stress Advisor (HSA) has the responsibility to recommend and imple-ment countermeasures to heat stress, he cannot be available every time a decision must be made on some element of the program, not to mention the loss of productivity if a crew is waiting for him. With adequate training, supervisors and workers have enough information to safely adapt the countermeasures to unique situations.

Heat stress training is part of the general employee training at some nuclear power stations. At present, however, it is not common at most stations. The reports of heat exhaustion mentioned to the project personnel suggest that employees and contractors would benefit from a training program. Furthermore, it is clear that the nuclear power industry believes that training is a crucial element in its operations. All personnel spend many hours each year in training. Within the area of health and safety alone, most plant employees receive at least four hours training per year dealing with nonradiological hazards like confined space entry and falling hazards. It is within the industrial health and safety program that heat stress training should be provided.

10.2 OVERVIEW OF TRAINING PROGRAM The training program recommended as part of the Heat Stress Management (HSM)

Program has three components:

• Formal training

• Workplace meetings

• Heat stress alert 10-2

The formal training can be part of the annual General Employee Training program given to plant employees who work in the restricted areas of the plant.

Responsibility for the formal program is shared between the HSA and the training department.

The workplace meetings are used to reinforce the lessons presented during formal training. This type of meeting is frequently used to review other health and safety issues and is a natural forum for heat stress discussions. The responsibility for preparing the material rests with the HSA. Department managers 4

frequently request such meetings.

)

' The heat stress alert is a one page memo to remind employees about heat stress.

It is an opportunity to sunnarize the major poin'ts of the heat stress prcgram.

The HSA is responsible for writing and distributing this alert.

It is the responsibility of the nuclear station to develop its own training program for heat stress. In this way, the program can best match plant needs and style. The HSA is responsible for specifying content and approving the final product. He may also provide the formal training or leave this responsibility to the training department.

This document provides the information necessary to develop and evaluate the content of a~ training program.

10.3 FORMAL TRAINING 10.3.1 Objectives The goal is to give the workers and supervisors the fundamentals of heat stress, l which include:

• Heat exchange and thermophysiology

= Heat stress hygiene

. Heat illnesses

. Countermeasures With the training, workers should be able to:

• Self-determine heat stress exposures I

10-3

• Take preventive actions to lower their risks of overexposure l (hygiene practices) {

• Understand the avenues of heat exchange to take full advantage of methods to reduce heat stress

• Recognize heat stress illnesses in themselves and others, and initiate, or call for, first aid

• Use site specific countermeasures correctly Supervisors have the same formal training with the following objectives:

• Understanding worker limits and the physiological basis

• Understanding the rationale for and accepting the countermeasures

• Applying knowledge to unique heat stress situations

• Taking proper actions in the event of heat stress illness For the nurse, first aid team, radiation protection personnel, and others responsible for the health and safety of the workforce, the formal training provides:

• Knowledge about recognition and treatment of heat illnesses

• Ability to discern the proper use of countermeasures 10.3.2 Content The suggested content for the formal heat stress training is presented here in a detailed outline. The outline suggests the points that should be included in the training, but the topics can be presented in a different order.

The outline can be used in one of two ways. First,"it can provide the content for an internally developed program. As an alternative, it can be used as a checklist to evaluate the content of prepackaged programs; and for missing 'itens, a supplemental lecture can be prepared.

Background for material in the outline is contained in other sections of this document. This material is referenced by page number inside the brackets ([ 1) at the end of the outline items.

4 10-4'

1. Interactions with Hot Jobs A. Heat Transfer

1. Metabolism (M): Heat gained in relation to the amount of work performed [2-2]

2. Convection (C): Heat gain from the air (if T

>97*F)orlosstotheair(ifTair<36'Cor,N'>)36*Cor F [2-2)

3. Radiation (R) [2-3]:

a. Heat gain from hot sources (e.g., steam' lines)

b. Heat loss to walls, floors, etc. that are less than 36'C (97'F)

, 4 Heat Balance

a. Sum up the sources: M+C+R [2-4]

b. If the sum is greater than zero, sweating is required

c. Sweating evaporates on the skin to cool the person [2-3l

d. Effects of clothing [2-2, 2-3, 2-41

8. Physiologiccl Responses

1. Heart rate increases to pump hot blood to skin to dissipate heat [2-5l

2. Body temperature increases [2-6]

j 3. Sweating increases to meet cooling requirements [2-5]

a. Limited to 1 liter per ho.r and by humid environments

b. The body loses the water, which must be replaced

4. Acclimation [2-8]

a. Adaptation to a level of heat stress

b. Ability to sweat increased and therefore more evaporative cooling C. Lower heart rates and body temperature innd therefore better ability to work

5. Work Patterns

a. Steady, evenly paced work less stressful than th6 same work done in intensive spurts with rest pauses [7-1)

b. Effects of heat stress accumulate if there is not enot;;b recovery time [2-6]

II. Heat Stress Hygiene A. Fluid Replacement [2-9, 7-21

1. Water must be replaced l

. l 10-5

2. Replacement with up to 1 liter (1 quart) per hour

a. Thirst is not an adequate indicator

b. Drinking every 15 to 20 minutes is best (250 ml or 8 oz)

c. Prehydration for work in radiation control areas (about 1/2 liter or 1 pint per hour of work)

3. No evidence was found that commercial replacement fluids improve performance or tolerance to heat if person has a proper diet and replaces lost water B. Self-determination (7-1]

1. Cessation of work with the appearance of symptoms of heat illness

a. Inform fellow worker (s) before leaving

b. Inform supervisor

c. Recover in cool area and drink fluids

2. Adjustment of work pattern (when possible) (2-6, 7-11

a. Work effort should be even and steady rather than in spurts of high activity

b. Slowing effort if heart is beating quickly (> 150 bpm)

C. Diet and Salt

1. Avoiding fad diets for weight reduction

2. Balanced diet (Diet supplements for heat stress are not necessary)

3. Salt replacement [2-9, 7-4)

a. Ordinary intake is usually sufficient

b. Increasing salt use with food during periods of acclimation

c. Following instructions of physician if on a salt-restricted diet D. Acclimation [2-8, 7-41

1. Increasing exposure cver 5 days to adjust to higher levels of heat stress

2. During acclimation period, salt food more

3. Loss of acclimation (7-4]

a. Without exposure

b. Illness 10-6'

, ,, , .--- - s .. ,, - -r- e - -

l I

E. Life Style

1. Alcohol [3-6, 9-5l

a. Dehydrates the body and lessens ability to sweat

~

b. Inhibits the thermoregulatory system and reduces tolerance

c. Increases chances of heat stroke (a very serious condition)

2. Drugs of abuse [9-5, 3-6)

a. Affects on the thermoregulatory system and reduce heat tolerance 3

b. Increasing the risk of neat stroke j 3. Extramural jobs or activities (accumulative effects) [2-61

a. Avoiding work, hobbies, etc. that may require. effort in hot environments before work

b. Activities before work may cause you to start work with increased body temperature

c. Following work, activities should be started only after

full recovery from work has been achieved 4 Adequate sleep i

F. Health Status

a. Chronic illnesses. Follow physician's recomendations once he has been fully informed of your occupation and heat exposure requirements. Diseases of special concern j are those in:

e cardiovascular system j e kidneys (renal function) e lungs e skin

. liver / pancreas l b. Acute illnesses: Report illnesses accompanied by a J

fever, such as viral and bacterial infections; illnesses

! that caused diarrhea, vomiting, or other losses of water; and skin rashes or sunburn that covers more than 10% of the skin surface

! III. Heat Illnesses and First Aid (Section 3l A. Cramps [3-3l

1. Cause: Hard work and profuse sweating

2. Symptoms: Painful cramps in active muscles, and muscle l twitches in legs, arms, and/or abdomen l 10-7 l

3. First aid: Drink fluids and use more salt at meal times B. Faintness [3-3, Syncope]

1. Cause: Staying in one position or posture under conditions of heat stress, especially standing quickly af ter sitting or lying down.

2. Symptoms: Weakness, blurred vision, pallor, and/or f ainting

3. First aid: Resting with legs up (recumbent position) and drinking fluids C. Heat Exhaustion [3-4]

1. Cause: Primarily a net loss of water but could be a loss of salt (Nacl) due to sweating or an illness (e.g., vomiting, diarrhea, alcohol ingestion)

2. Symptoms:

a. Dry mouth and excessive thirst

b. Concentrated urine (darker, more yellow than normal)

c. Headache and/or dizziness

d. Fatigue and weakness

e. Uncoordinated actions and slow reflexes

3. First Aid: Move to cool environment, stay in recumbent position, and drir.k fluids. Refer to Medical Department D. Heat Stroke: MEDICAL EMERGENCY [3-5]

1. Causes: Central nervous system (CNS) failure and/or sustained overexposure to heat stress. CMS failure can be caused by disease or drug (including alcohol) abuse.

2. Symptoms

a. Dry skin and/or chills

b. Irrational etd/or other atypical behavior

c. Sudden onset of pain or convulsions

d. Unconsciousness

3. First Aid

a. Call control room to notify medical personnel and to call an ambulance

b. Cool person immediately with very cold water or ice, or

• an alcohol rinse and fans 10-8'

l

)

i IV. Countermeasures (Note: This portion of the training is tailored to the specific site policies, procedures, and countermeasures)

A. List engineering controls, work practices, and personal protection in use B. Describe each countermeasure in use

1. Explain why it works

2. Explain how to use it i

3. Emphasize proper use, benefits, and limitations (Note: This is important because misuse of ice vests and other personal protection was found to severely limit protection.) -

Those responsible for first aid at the plant (e.g., nurse, EMTs, emergency response team) should read Section 3, Recognition and Treatment of Heat Illnesses, in addition to taking the formal training.

10.3.3 Delivery The formal heat stress training is given annually as part of other health and safety training. The most likely candidate time is during General Employee Training (also referred to as RWP training) or during other required annual training, but the discretion of the HSA, the training department, and plant management is followed. The important factor is annual attendance. In addition, the training is given to Contractor personnel who may be exposed to heat stress.

A minimum of 20 minutes is required to present the information contained in the outline, and generally no more than 30 minutes can be allocated to heat stress during the formal training programs. Thirty minutes is the' amount of time currently allocated for heat stress at some nuclear stations.

The medium for presentation can be lecture, slide / tape..or videotape. Most training departments, however, are employing videotapes and slide / tape presentations as the principal media. There is no clear advantage of one medium over the other; rather the plant must select the one or combination that best suits its style or training facilities.

l 10-9

10.3.4 Program Development The development of a training program can be directed toward an entirely original program or toward a prepackaged program with locally produced supporting material.

If an original program is going to be developed from the content outline, it is important to have the script and supporting visuals reviewed by an expert in heat stress. The' costs for an original videotape program developed solely inhouse would be about $7000. This includes the following costs (based on labor and overhead charges of $35/hr):

• Script development (40 hrs) $1400

• Review of script by consultant 1000

• Producing visual aids (40 hrs)- 1400

• Slide / videotaping (30 hrs). 1050

. Editing / dubbing (60 hrs) 2100 3

Total $6950 i These are minimal efforts. The result will be a program of just adequate content, without a presentation that uses professional actors / voices and high, quality visuals. If an outside vendor is used to produce an original program, the site personnel still assist in writing the script (40 hrs), shooting the scenes (25 hrs), and reviewing the product (15 hrs). These activities require about 80 work hours or $2800 plus $12,000 for a' slide / tape program or $25,000 for a videotape I program. This means professional assistance moves the price to develop a program to the range of $15,000 to 30,000.

On the other hand, a prepackaged program (either videotape or slide / tape) may be purchased for less then $500. In this case, the site personnel must:

• Review alternatives (40 hrs) $1400

• Develop supporting material (20 hrs) 700.

• Prepare lecture notes (20 hrs) 700 Total $2800 The total cost of the program is about $3300 -- much less than developing an original program.

10-10

10.3.5 Activities The responsibility for program development is pri:.iarily with the HSA. He must

• Review and select the prepackaged program

. Prepare the supporting material

• Give or train someone to give the supporting lecture The training department should assist the HSA in

• Identifying vendors of prepackaged material

• Selecting the program

• Reviewing the supporting material 10.3.6 Training Costs The training costs are based on the assumption that there will be 500 site employees ($35/hr) and 500 contractor employees ($50/hr) taking the training. If

! the training requires 30 minutes, the total labor costs are estimated as

• Site: 500 0.5 hr $35/hr = $ 8750

• Contractor: 500 0.5 hr = $50/hr = $12500 Total $21250 The' added cost for the instructor (HSA or other) depends on the number of presentations that are made. If the average class size is 25, there will be 40 one-half hour sessions (40 0.5 hr a $35/hr), at an additional cost of $700.

10.3.7 Other Considerations The above information provides basic background on program content and the minimal costs to present the information. The primary goal of any health and safety training program is to instill in the workers a pattern of behavior that j compliments other plant activities for employee protection. Other training activities include practice and application of key topics similar to the training in protective clothing that some nuclear stations now employ. In addition, novel training methods are emerging that may prove better than the traditional audiovisual approach that is frequently used. To implement a sound training program, the involvement of the training department is essential.

Ensuring training effectiveness, in general, includes the following considerations:

10-11

l l

. Positive reinforcement and incentives for correct behavior

. Retraining if indicated by incorrect behavior or repeated heat stress overexposures-(as is done for radiation protection)

• Performance and written tests on content

• Correct role modeling by supervisors and management if the training department cannot support these considerations, the HSA may consider an outside training agency with experience in health and safety programs.

It is also important to integrate heat stress management into other health and safety monitoring activities, such as the STOP program employed by several nuclear sites and many other industrial sites.

10.4 WORKPLACE MEETINGS 10.4.1 Objective The objective of workplace or " tool box" meetings is to reinforce the concepts taught in the formal training. The benefit accrues both to workers and supervisors.

10.4.2 Content The following three areas should be reinforced:

. Heat stress hygiene

. Proper use of countermeasures

. Heat stress illnesses ,

Within these areas, the leader (ideally the HSA) emphasizes topics that he thinks deser.'e special attention based on the audience or current activities in the j plant. For example, if workers are misusing personal prot'ection, the correct use can be emphasized. Or, if a new countermeasure is being introduced, he can discuss its application.

10.4.3 Format The workplace meeting is an informal opportunity to meet with department personnel to discuss a topic for about 15 minutes. Most department managers hold a tool box or workplace meeting on a monthly or more frequent basis. The HSA should ask the manager to invite him to make a presentation on heat stress at an appropriate 10-12

time. The best time is about six months after the formal training and just prior to a time when the employees have an increase in heat exposures. This could be prior to an outage or in the early spring.

Videotapes or slide / tape presentations are frequently used at workplace meetings, l c and the same prepackaged program as in the formal session may be used. Alterna-tives are a lecture or other prepackaged materials. If a prepackaged program is used for the workplace meetings, the basic material can be covered and there is less of a burden on the HSA to prepare the material. The HSA can take enough time (about 5 minutes) to emphasize a few special topics, especially those that are site specific.

10.4.4 Program Development Program development has two parts: (1) selection of prepackaged programs and (2) presentation of specific topics.

i If a second prepackaged program is used to provide variety of presentation, it can be selected as part of the selection process for the formal training. In this way, the added cost is only the purchase of the second program for about $500.

The specific topics are those topics that the HSA chooses to emphasize in his followup lecture. The lecture should take about an hour to prepare for each workplace meeting. Therefore, this preparation becomes a recurring cost of presentation.

i 10.4.5 Training Costs Two factors determine the training costs: the time of the department personnel I and the time of the HSA. For a department of 25 and a meeting time of 30 minutes

(an overestimate of the time that is needed), the cost is

~

25 0.5 hr . $35/hr = $437.50 In addition, the HSA needs one hour to prepare, one hour to bring and return 1

audiovisual equipment to the workplace meeting, and one-half hour for the meeting,

'for a cost of

! 2.5 hr $35/hr = $87.50 Therefore, one session would have a total presentation cost of $525. Because each department may have special topics, the cost of preparation and delivery should be the same for each workplace meeting.

l0-13 l

10.5 HEAT STRESS ALERT 10.5.1 Objective i

The objective of the Heat Stress Alert is to reinforce the lessons of the formal training.

10.5.2 Content The alert is a one page memo circulated to plant personnel. It highlights the following topics:

• Heat stress hygiene

• Heat illnesses

• Heat stress countermeasures The HSA covers all of the topics but olaces special emphasis on areas that he thinks require attention. For instance, if workers are not drinking fluids before a containment entry, he can remind them that this is important in order to reduce the risk of heat illness.

10.5.3 Format j The Heat Stress Alert is a memo intended to reinforce basic ideas. For a Heat Stress Alert, one utility uses their distinctive format for Safety Alerts, which has a readily identifiable logo and paper color. The Alert should be brief (about 1 page) and highlight only important items, using the same key terms that were used in the formal training.

In addition to being circulated by mail to all site employees and contractors, it should be posted on bulletin boards where other health and safety notices might be placed.

The timing of the alert is such that it precedes a time when heat stress exposures are likely to occur. This may be an outage or the summer months. In either case, it should occur between 4 and 7 months af ter the formal -training. Only one Heat Stress Alert is issued in a year. A second one could be issued if the HSA, in consultation with department managers, thinks it is desirable, such as prior to work that is likely to have high heat stress demands for many workers.

4 10-r4 l l

w. - w-,.-.w- em- ? --

g -- w, -- w-- --y, eg.-.+_a y-+. - - * -

4 10.5.4 Costs The costs of the Heat Stress Alert are in

. Writing the alert

. Distributing it

. Reading it The HSA can write the alert with one hour of effort. It is assumed that 3 work hours are required to prin't and distribute it and 60 work hours (700 x 5 min) to read it. The labor costs, then, are about $f.500. Material costs should be under

$100. The total costs are about $2600.

I

}

i e

l l

l a

10-15

e Section 11 REFERENCES

1. J. L. Seminara and S. O. Parsons. Human Factors Review of Power Plant Maintainability. EPRI NP-1567, 1981.

2. E. Kamon. Personal Cooling in Nuclear Power Stations. EPRI NP-2686, 1983.

3. World Health Organization. Health Factors Involved in Working under Conditions of Heat Stress. WHO Technical Report Series No. 412, 1969.

4 D. Minard. Effective Temperature Scale and its Modifications. Naval Medical Research Institute Research Report MR005.01-0001.01, 1964.

5. A. Lind. A physiological criterion for setting thermal environmental limits for everyday work. J. Appl. Physiol. 18: 51-56, 1963.

6. National Institute for Occupational Safety and Health (NIOSH). Criteria for a Recomended Standard for Occupational Exposure to Hot Environments. USDHEW, 1972.

7. J. D. Ramsey. Heat stress standard: OSHA's Advisory Comittee recomendations. National Safety News (June) pp 89-95, 1975.

8. American Conference of Governmental Industrial Hygienists (ACGIH). Threshold Limit Values for Chemical Substances and Physical Agents in the Workroom Environment with Intended Changes. Cincinnati: ACGIH, 1979.

9. American Industrial Hygiene Association (AIHA). . Heating and Cooling for Man in Industry. 2nd ed. Akron: AIHA, 1975.

10. E. Kamon and B. Avellini. Wind speed limits to work under hot environments for clothed men. J. Appl. Physiol. 46: 340-345, 1979.

11. International Standards Organization. Hot environments - Estimation of the heat stress on working man, based on the W8GT-index (wet bulb clobe temperature). ISO 7243-1982(E), 1982.

12. F. N. Dukes-Dobos and A. Henschel (eds). Proceedings of a NIOSH Workshop on Recommended Heat Stress Standards. Washington, D.C.: GPO, pp 4-13, 1980.

13. Triservices Document. Prevention. Treatment and Control of Heat Injury. US Army TB Med 507, 1980.

14. US Army. Prevention of Heat Injury. Circ. No 4C.82-3, 1982.

15. Eastman Kodak Company. Ergonomic Design for Peo,le at Work. Belmont CA:

Lifetime Learning Publications, 1983. ,

11-1 l

w

16. F. A. Fuller and P. E. Smith. Evaluation of heat stress in a hot workshop by physiological measurements. Am. Ind. Hyq. Assoc. J. 42: 32-37, 1981.

17. E. Kamon and C. Ryan. Effective heat strain inder using pocket computer. Am.

Ind. Hyg. J. 42: 611-615, 1981. (Errata: Am. Ind. Hyq. J. 43: A-43,1982T- '

18. Proceedings of the EPRI Technology Transfer Session on Bolting and Bolted Connections. EPRI NDE Center, Charlotte, NC, November, 1985 (in press).

19. A Study of Bolting Problems. Tools and Practices in the Nuclear Industry.

Final Report. EPRI NP-2174, 1981.

20. American Conference of Governmental Industrial Hygienists (ACGIH). Industrial Ventilation. 18th ed. Cincinnati: ACGIH, 1984.

21. C. H. Wynd' ham, N. 8. Strydom, A. J. S. Benade. A. J. van Rensberg. Heat stroke risk in unacclimatized and acclimatized men of different maximum oxygen intakes working under hot and humid conditions. Chamber of Mines Research Report No. 12/72 Johannesburg, South Africa: Chamber of Mines of South Africa, 1972.

22. E. Shvartz. Heat stress tolerance testin9 In F. N. Dukes-Dobos and A. Henschel (eds)., Proceedings of a NIOSH Workshop on Reconunended Heat Stress Standards. Washington. 0.C.: GPO, 1980.

23. W. L. Kenney. A review of comparative responses of men and women to heat stress. Environmental Research 37: 1-11, 1985.

24 E. R. Buskirk. Physiological effects of heat and cold. In: Wilson (ed.)

Obesity, pp. 119-139, Philadelphia: Davis, 1969.

25. C. C. Seltzer and J. Mayer. A simple criterion of obesity. Postgrad. Med.

38: 101-102, 1965.

26. A. Keys, F. Fidanza, M. J. Karvonen, N. Kimgra, and H. L. Taylor, Indices of relative weight and obesity. J. Chronic. Dis. 23:93, 1970.

27. D. Minard. Pre-employment and periodic medical examinations for workers on hot jobs. In F. N. Dukes-Dobos and A. Henschel (eds)., Proceedings of a NIOSH Workshop on Recommended Heat Stress Standards. Washington, D.C.: GPO, 1980.

28. W. L. Kenney and E. Kamon. Comparative physiological responses of normotensive and essentially hypertensive men to exercise in the heat. Euro.

J. Appl. Physiol. 52: 196-201, 1984.

11-2

Appendix HEAT STRESS CONDITION DESCRIPTIONS AND COUNTERMEASURES l

A-1

The appendix contains a copy of the Environmental Assessment form (Figure 5-1),

versions of the decision tree (Figure 5-2) in *C and 'F, and the 24 condition descriptions.

The condition descriptions are based on a clothing ensemble, a metabolism, and range of WBGTs, as specified in the decision tree. For each condition, heat balance analyses were performed to determine the principal sources of heat gain and loss. These analyses were used to recommend the countermeasures for that condition. For each countermeasure that is' recommended, a reference is made to the section number that describes those countermeasures in more detail. The reference is made in brackets at the end of each recommendation.

Within the condition descriptions, there are special cases. These are indicated by qualifications on one or more environmental factors. For radiant heat, special cases may be indicated as a difference between globe and air temperatures or as a simple value of globe temperature. The method of indication depends on the environments that are likely for that condition.

Before using the Appendix, read the document, especially Section 5.

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A-5

,,-,e . . -

Condition 1: WC/L/ Moderate Clothing: Work clothes Metabolism: Low WBGT: 32-44*C (90-111*F)

Level: Moderate Stress

~

If Tnwb < 32*C-(90*F), this is a special case. The heat stress is 1ow and no further action is necessary.

If Tnwb > 32*C, high humidity limits cooling by sweat evaportion. Under such

+ conditions, increasing air velocity will not enhance evaporation.

Engineering Controls .

• Reduce air temperature [6.3l

= Use ventilation or air conditioning to reduce humidity (6.31 l

Work Practices f

• Universal practices [5.4.1]

. Stay times [7.51 i

i i

i

' A-6 I

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1 Condition 2: WC/L/High Clothing: Work clothes 1 Metabolism: Low WBGT: > 44*C (> 111*F)

Level: High i

If inwb > 32*C (90*F), humidity limits sweat evaporation. Under these conditions increasing air velocity will not improve evaporation.

If T g> 45'C (115'F), radiant heat is an important contributor to the heat stress.

Engineering Controls

• Reduce air temperature [6.31

• If T h > 32*C, use ventilation or air conditioning to reduce hJai$ty[6.31 If Tg > 45'C, isolate radi mt sources of-heat [6.4]

Work Practices

• Universal practices [5.4.11

• Buddy system [7.7]

• Stay times for short durations [7.51 Personal Protection a Circulating air systems [8.11

= Ice garments [8.21

= Liquid cooling systems [8.31

• If T > 45'C with diffuse sources of radiant heat, use reflective clotEing[8.41 A-7 1

l

Condition 3: WC/M/ Moderate Clothing: Work clothes Metabolism: Moderate WBGT: 28-36*C (82-97'F)

Level: Moderate if Tnwb < 32*C (90*F). this is a special case. The conditions represent low heat stress and no-further actions are necessary.

If inwb > 32*C, high humidity limits cooling by sweat evaporation. Under such -

conditions. Increasing air velocity will not improve evaporation.

1 Engineering Controls

• Reduce air temperature [6.3l

• Use ventilation or air conditioning to reduce humidity [6.31 Work Practices c

• Universal practices [5.4.11

• Stay times 17.51 i

A-8,

. . _ . . _ . . . _ ~ . - _ _ _ . - _ _ - . . . _ . . . _. . _ . _ - . . . _ . _ _ _ . - . .. __ _ .

1 l

I l

i Ccndition 4: WC/M/High Clothing: Work Clothes Metabolism: Moderate WBGT: > 36*C (> 97'F)

Level: High If Tnwb > 32*C, high humidity limits sweat evaporation and increasing air velocity will not improve evaporation.

If (Tg-Tair) < 10*C (18'F), convection and metabolism are the main sources of heat gain. If the difference is greater 10*C, then radiant heat and metabolism are the main sources.

If Tg > 60*C (140*F), radiant heat is a main source of heat.

Engineering Co.itrols

. Reduce air temperature [6.31

. If T b > 32*C, use ventilation or air conditioning to reduce hum 1$ty[6.3]

If Tg > 60*C, isolate radiant heat sources [6.51 Work Practices

. Universal practices (5.4.11

. Buddy system [7.7]

. Stay times for short durations [7.51 Personal Protection-

. Circulating air systems [8.11

. Ice garments [8.2]

If Ta > 60*C with diffuse sources of radiant heat, use reflective clotning [8.4l

.A-9

Cor.dition 5: WC/H/ Moderate Clothing: Work clothes Metabolism: High W8GT: 24-32*C (75-90*F)

Level: Moderate Metabolic _ heat is the primary source of heat stress.

If inwb > 26*C (79'F), high humidity limits sweat evaporation. Increasing low or Moderate air velocity to High will enhance the evaporation.

If Tair > 50'C (120*F) and air velocity is High, convective heat gain is also a l main source of heat.

If (Tg-Tair) > 10*C (18'F), radiant heat is a main source of heat.

Engineering Controls Reduce metabolism (6.2l

• Reduce air temperature (6.11

• If inwb > 26'C, increase air velocity [6.4)

If Tm b > 26*C, use ventilation or air conditioning to reduce humidity [6.31

=

If Tair > 50'C, reduce air velocity [6.41

=

If (Tg-Tair) > 10'C, isolate radiant heat sources [6.51 Work Practices

• Universal practices [5.4.11~

• Stay times [7.51

= Emphasis on self-determination of work pace [7.1.11 A-10,

l l

Condition 6: WC/H/High Clothing: Work clothes Metabolism: High W8GT: > 32*C (> 90*F)

Level: High Metabolic heat is the dominate source of heat.

If Tnwb > 26*C (79'F), high humidity limits sweat evaporation.

If Tair > 50*C (120*F), convection is an important source of heat.

If (Tg-Tair) > 10'C (18'F), radiant heat is a main source of heat.

Engineering Controls

. Reduce metabolism [6.21

. Reduce air temperature [6.3]

. If Tnwb > 26*C, use ventilation or air conditioning to reduce humidity [6.3]

If (Tg-Tair) > 10*C, isolate radiant heat sources [6.51 Work Practices

. Universal practices [5.4.11

. Self-determination (emphasizedundertheseconditions)[7.1]

. Buddy system [7.7)

. Stay times for short durations [7.5]

Personal Protection

• Circulating air systems [8.11

. Ice garments [8.21

. If (To-Tj > 10'C with diffuse sources of radiant heat, use a

' reflectivecio) thing [8.4]

A-11

Condition 7: CC/L/ Moderate Clothing: Cotton enveralls Metabolism: Low W8GT: 30-42*C (86-108'F)

, Level: Moderate If inwb < 33*C (91*F), this is a special case. The heat stress is low and no j further action is necessary.

If Tnwb > 33*C, humidity limits sweat evaporation.

l Enginee' ring Controls f a Reduce air temperature [6.31 I .

• If T 33'C, use ventilation or air conditioning to reduce i humiEYIy>[6.3]

Work Practices

• Universal practices [5.4.1]

• Stay times [7.51 t

a -

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I Condition 8: CC/L/High Clothing: Cotton coveralls Metabolism: Low W8GT: > 42*C (> 108'F)

Level: High If inwb > 33*C (91*F), high humidity limits sweat evaporation.

If Tg > 60*C (140*F), radiant heat is a main source of heat.

Engineering Controls

• Reduce air temperature [6.3]

• If T 33*C, use ventilation or air conditioning to reduce hum 1NIy>(6.3]

If Tg > 60*C, isolate radiant sources of heat [6.51 Work Practices

• Universal practices (5.4.1l

• Buddy System [7.7)

• Staytimesforshortdurabfans(7.5l Personal Protection

• Circulating air systems (8.11

• Ice garments [8.2]

• Liquid cooling systems [8.3)

• If T > 60*C with diffuse sources of radiant heat, use reflective clot $1ng[8.41 6

'A-13

1 i

j Condition 9: CC/M/ Moderate Clothing: Cotton coveralls Metabolism: Moderate W8GT: 26-34'C(79-93'F)

Level: Moderate If inwb < 29'C (84*F), this is a special case. The heat stress is low and no further action is necessary.

Metabolism is the major source of heat gain.

If inwb > 29'C, high humidity limits sweat evaporation.

Engineering controls u

l

• Reduce metabolism (6.21 i

• Reduce air temperature [6.3l

• If T 29'C, use ventilation or air conditioning to reduce humihIIy>[6.31 i

Work Practices

!

• Universal practices (5.4.11 f

a Stay times (7.51 +

1 l

1 i

1 e

l 2

A-14,

Condition 10: CC/M/High Clothing: Cotton coveralls Metabolism: Moderate WBGT: > 34*C (> 93*F)

Level

High Metabolism is the largest source of heat.

If inwb > 29'C (84*F), high humidity limits sweat evaporation.

If Tair > 60*C (140*F), convective heat gain is an important source of heat.

If Tg > 60'C (140'F), radiant heat is an important source of heat.

Engineering Controls '

!

• Reduce air temperature [6.3l Reduce metabolism [6.2]

!

• If T j hum 1NIy>[29'C,useventilationorairconditioningtoreduce 6.31 If Tg > 60*C, isolate radiant sources of heat.

Work Practices

• Universalpractices[5.4.11 ,

• Buddy system [7.7l

• Stay times for short durations (7.51 1

l Personal Protection

• Circulating air systems 18.1)

• Ice garments [8.21

• If T > 60'C with diffuse sources of radiant heat, use reflective clot $1ng[8.4) i i

I

A-15 i

,. _ . _ . . _ _ _ . .- -- _ _ . = _ _ _ - _ - _ _ -

4 t

Condition 11: CC/H/ Moderate Clothing: Cotton coveralls Metabolism: High -

WBGT: 24-30*C (75-86*F)

Level: Moderate If inwb < 25'C (77'F) and the air velocity is High, this is a special case. The heat stress is low and no further action is necessary.

Metabolism is the largest source of heat gain.

If inwb > 25'C (77*), high humidity limits sweat evaporation.

Evaporative and convective cooling can be enhanced by increased air velocity.

Engineering Controls

• Reduce metabolism [6.2l

• Reduce air temperature [6.3l a

i

• Increase air velocity to High range [6.4l "

4

• If T humidTIy>[25'C, 6.31 use ventilation or air conditioning to reduce Work Practices

• Universal practices [5.4.11

• Stay times [7.5l l

i W

G A-16

Condition 12: CC/H/High Clothing: Cotton coveralls Metabolism: High I

W8GT: > 30*C (> 86*F)

Level: High

~

Setabolism is the largest contributor to heat stress.

If inwb > 25'C (77'F), high humidity limits sweat evaporation.

If Tair < 36*C (97'F), increasing air velocities increase heat losses due to convection and evaporation of sweat.

If Tg > 60'C (140'F), radiant heat is an important source of heat.

Engineering Controls

. Reduce metabolism [6.2]

. Reduce air temperature [6.3]

I . If Tair < 36*C, increase air velocity [6.4) i . If T husiNIy>[25'C,useventilationorairconditioningtoreduce 6.31 If Tg > 60*C, isolate radiant heat sources [6.51 Work Practices

. Universal practices [5.4.11

. Emphasis on self determination [7.11 4

. Buddy system [7.7) ,

. Stay times for short durations [7.51 Personal Protection e , Circulating air systems [8.11

. Ice garments [8.21

. If T 60*C with diffuse sources of radiant heat, use ref1Ec>tiveclothing[8.41

( -

i i

A-17 l

l ', - -- - - _ .

Condition 13: OC/L/ Moderate Clothing: Double cotton coveralls Metabolism: Low

~

W8GT: 28-40*C(82-104*F)

Level: Moderate If inwb < 32*C (90*F), this is a special case. The heat stress is' low and no further action is necessary.

If inwb > 32*C, high humidity and clothing limit sweat evaporation.

Increasing air velocity improves sweat evaporation under all conditions.

Engineering Controls

• Reduce air temperature [G.3l

• Increase air velocity [6.4)

• If T 32*C, use ventilation or air conditioning to reduce humiETIy>[6.31 i

Work Practices

!

• Universal practices [5.4.11 1

• Stay times [7.51 i .*

1 4

A-18

Condition 14: OC/L/High Clothing: Double cotton coveralls Metabolism: Low WBGT: > 40*C (> 104*F)

Level: High The heat stress is due to a combination of environmental heat load and reduced sweat evaporation.

If Tmb > 32*C (90*F), high humidity and clothing limits sweat evaporation.

If T g > 60*C (140*F), radiant heat is an important source of heat.

Engineering Controls

• Reduce air temperature [6.31

• Increase air velocity [6.4)

• If T 32*C, use ventilation or air conditioning to reduce humiNIy>[6.31 If Tg > 60*C, isolate radiate heat sources (6.51 Work Practices

• Universal practices [5.4.11

• Buddy system [7.7)

• Reduce clothing requirements (7.61

• Stay times for short durations [7.51 Personal Protection

• Circulating air systems 18.11

.* tcegarments[8.21

• Liquid cooling systems (8.31

• If Ta > 60*C with diffuse sources of radiant heat, use reflective clothing [8.4l l

4 A-19

i Condition 15: OC/M/ Moderate Clothing: Double cotton coveralls Metabolism: Moderate WBGT: 24-32'C (75-90*F) .

Level: Moderate If i nwb < 28'C (82'F), this is a special case. The heat stress is low and further action is not necessary.

Metabolism is the principal source of heat gain.

If Tnwb > 28 C, high humidity and clothing limit sweat evaporation.

i Engineering Controls

• Reduce metabolism (6.2]

• Reduce air temperature (6.31

• Use ventilation and air conditioning to reduce humidity [6.3)

Work Practices

• Universal practices [5.4.11 1

• Stay times [7.51 4

I 4

i A-20

, , . _ . - _ - . _ _ , . . _ . _ - _ _ . _ _ . _ ._ _ _ . - , . , , , ,-,,y. . -. , , ,, , . , , .

=_ .. - . -

Condition 16: OC/M/High Clothing: Double cotton coveralls I

Metabolism: Moderate I W8GT: > 32' C (> 90'F)

Level: High Metabolism is the largest source of heat gain and the insulation effects of clothing reduce sweat evaporation.

If Tnwb > 28'C (72'F), high humidity also reduces sweat evaporation.

If Tg > 50*C (120*F), radiant heat is an important source of heat.

Engineering Controls e Reduce metabolism [6.21

• Reduce air temperature [6.3]

If Tg > 50*C, isolate radiant heat sources [6.51

• If T humiNky>[28'C,useventilationorairconditioningtoreduce 6.31 Work Practices

• Universal practices [5.4.1]

• Buddy system [7.7)

• Reduce clothing requirements [7.6]

. Stay times for short durations [7.51

• Self-paced work [7.1.11 Personal Protection

• Circulating air systems [8.11

• Ice garments [8.21

. If T > 50*C with diffuse sources of radiant heat, use reflective clotEing[8.4]

~

I l 4

l

< l

? - I

! A-21 l

. - - - - , , + - . - - - , - - - - - . . . _ _ - . - - - , - - - ,

A l

Condition 17: OC/H/ Moderate Clothing: Double cotton coveralls Metabolism: High j WBGT: 20-28'C (68-82*F)

Level: Moderate Metabolism is the primary source of heat. Clothing inhibits sweat evaporation.

Engineering Controls

. Reduce metabolism [6.21

. Reduce air temperature [6.31

= Increase air velocity [6.41 I

Work Practices

. Universal practices [5.4.1

• Reduce clothing requirements [7.61

. Stay times [7.51

)

= Self paced work [7.1.1]

l

' A-22

- , . - _ - , - - . - . . _- ,_ ,_,,~. ,_ . . , _ . . . _ _ . _ , - - .

l Condition 18: OC/H/High-Clothing: Double cotton coveralls Metabolism: High W8GT: > 28'C (> 82'F)

Level: High High metabolism is the main source of heat and the clothing reduces sweat evaporation.

If Tg > 60*C (140*F), radiant heat is an important source of heat.

Engineering Controls

• Reduce metabolism [6.21

• Reduce air temperature [6.31

• Increase air velocity [6.41 If Tg > 60*C, isolate radiant heat sources [6.51 Work Practices

• Universal practices [5.4.11

• Reduce clothing requirements [7.6l

!

• Buddy system [7.7l

• Self-paced work [7.1.11

• Stay times for short durations [7.51 Personal Protection

• Circulating air systems [8.11

!cegarment,[8.2]

• If T > 60'C with diffuse sources of radiant heat, use reflective clotEing[8.4]

1 i

i k-23

. ... _ - _ - _ - .. - -- _ - . _ = . . . - - . ~. .. _

l 1

i Condition 19: CP/L/ Moderate ,

i Clothing: Impermeable suit over cotton coveralls Metabolism: Low j W8GT: 26-38'C (79-100*F)

Level: Moderate i

Metabolism is the primary source of heat gain, and clothing severely ilmits sweat evaporation.

High air velocities aid heat loss through convection. .

Engineering Controls

. Reduce air temperature [6.31

. Increase air' velocity [6.41 i Work Practices i

e Universal practices (5.4.11

. Reduce clothing requirements [7.6l l

l . Stay times [7.51 I

r 8

1 4

4 i

1 l

1 i

i A-24

Condition 20: CP/l/High Clothing: Impermeable suit with cotton coveralls Metabolism: Low W8GT: > 38'C (> 100*F) .

Level: High Metabolism is the primary source of heat gain, and clothing severely limits sweat evaporation.

j Engineering Controls j

e Reduce air temperature [6.31 Work Practices

. Universal practices [5.4.1]

j . Reduceclothing[7.6]

• Buddy system [7.7]

• Stay times for short durations [7.5]

Personal Protection ,

l

. Circulating air systems [8.11 I e Ice garments [8.21

• Liquid cooling systems [8.31 M

e i

i I A-25 i

Condition 21: CP/M/ Moderate Clothing: Impermeable suit with cotton coveralls Metabolism: Moderate I WBGT: 22-30*C(72-86'F)

Level: Moderate Metabolism is the greatest source of heat and clothing severely limits sweat evaporation.

If (Tg-Tair) > 20*C (36*F), radiant heat is an inportant source of heat.

. Engineering Controls

• Reduce metabolism [6.2l

• Reduce air temperature [6.3l 1

• If(Tg-Tatr) > 20*C, isolate radiant heat sources [6.51 Work Practices

e i Universal practices [5.4.1l

• Reduce clothing requirements [7.6l l

• Stay times [7.5]

I

• Self-paced work [7.1.11  :

e i

e i

?

l 1

v J

J A-26 ,

i.

i

Condition 22: CP/M/High Clothing: Impermeable suit with cotton coveralls Metabolisa: Moderate W8GT: > 30*C (> 86*F)

Level: High

Metabolic heat gain is the major source of heat load, and clothing severely limits sweat evaporation.

Engineering Controls

• Reduce metabolism [6.21

= Reduce air temperature [6.31 l Work Practices

• Universal practices [5.4.11

• Reduce clothing requirements [7.61  ;

e Buddy system [7.7)

• Self-paced work [7.1.11

= Stay times for short durations (7.51 Personal Protection

• Circulating air systems [8.1l

! = Icegarments(8.21 1

i l

s A-21

{ Condition 23: CP/H/ Moderate 1

l Clothing: Impermeable suit over cotton coveralls i Metabolism: High W8GT: 18-26*C (64-79'F)

Level: Moderate I Metabolism is the only source of heat gain, and clothing severely limits sweat evaporation.

} Engineering Controls i

1 e Reduce metabclism (very effective) [6.2l e Reduce air temperature [6.3]

Work Practices

!

• Universal practices [5.4.1) e Reduce clothing requirements [7.61

. Self-paced work [7.1.11

, a Stay times [7.5) ,

1

'}

l 4

I

)

i i

I

.i i

)

i A-2P 1

np - - , . . - - , ,. . _ . - , - - . .-_,..,,yn----.- - - - ,w

_ . - - - - -n, . , -, , . . - n y .w-- .

Condition 24: CP/H/High Clothing: Impermeable suit over cotton coveralls Metabolism: High W8GT: > 26*C (> 79'F)

Level: High Metabolism is the major source of the heat load, and clothing severely limits sweat evaporation.

Engineering Controls e Reduce metabolism (very effective) [6.21

• Reduce air temperature (6.3]

Work Practices

• Universalpractices[5.4.11

>-

• Reduce clothing requirements (7.61

. Emphasis on hydration [7.31 ~

. Self-paced work [7.1.11

• Buddy system [7.7)

• Stay times for short durations [7.5)

Personal Protection

. Circulating air systems [8.1]

• Ice garments [8.21 O

A-29

- . . _ - _ . - . . - _ -