Table Of ContentA GUIDE TO MANAGING HEAT STRESS:
DEVELOPED FOR USE IN THE
AUSTRALIAN ENVIRONMENT
AUSTRALIAN INSTITUTE OF
OCCUPATIONAL HYGIENISTS INC
(Incorporated in Victoria)
Registered Office
Unit 2, 8-12 Butler Way
Tullamarine VIC 3043
Tel: +61 3 9338 1635
Email: [email protected]
Postal Address
PO Box 1205
TULLAMARINE VIC 3043
“We all rejoiced at the opportunity of being convinced, by our own experience, of
the wonderful power with which the animal body is endued, of resisting heat vastly
greater than its own temperature”
Dr Charles Blagden, M. D. F. R. S. (1775)
Cover image “Sampling molten copper stream” used with the permission of Rio Tinto
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A Guide to Managing Heat Stress: Developed for Use in the
Australian Environment
Developed for the Australian Institute of Occupational Hygienists
Ross Di Corleto, Ian Firth & Joseph Maté
November 2013
November 2013
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Contents
CONTENTS 3
PREFACE 6
A GUIDE TO MANAGING HEAT STRESS 7
Section 1: Risk assessment (the three step approach). 8
Section 2: Screening for clothing that does not allow air and water vapour movement. 12
Section 3: Level 2 assessment using detailed analysis. 13
Section 4: Level 3 assessment of heat strain. 15
Section 5: Occupational Exposure Limits 17
Section 6: Heat stress management and controls 18
BIBLIOGRAPHY 21
Appendix 1 - Basic Thermal Risk Assessment – Apparent Temperature 23
Appendix 2 – Table 5: Apparent Temperature Dry Bulb/Humidity scale. 25
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DOCUMENTATION OF THE HEAT STRESS GUIDE DEVELOPED FOR
USE IN THE AUSTRALIAN ENVIRONMENT 26
1.0 INTRODUCTION 27
1.1 Heat Illness – A Problem Throughout the Ages. 27
1.2 Heat and the Human Body 28
2.0 HEAT RELATED ILLNESSES 29
2.1 Acute Illnesses 30
2.1.1 Heat Stroke 30
2.1.2 Heat Exhaustion 31
2.1.3 Heat Syncope (Fainting) 31
2.1.4 Heat Cramps 32
2.1.5 Prickly Heat (Heat Rash) 32
2.2 Chronic Illness 32
2.3 Related Hazards 33
3.0 CONTACT INJURIES 34
4.0 KEY PHYSIOLOGICAL FACTORS CONTRIBUTING TO HEAT ILLNESS 36
4.1 Fluid Intake 36
4.2 Urine Specific Gravity 43
4.3 Heat Acclimatisation 45
4.4 Physical Fitness 47
4.5 Other Considerations in Reducing Exposure in Heat-Stress Conditions 48
5.0 ASSESSMENT PROTOCOL 48
6.0 WORK ENVIRONMENT MONITORING AND ASSESSMENT 50
6.1 Risk Assessment 50
6.2 The Three Stage Approach 51
6.2.1 Level 1 Assessment: A Basic Thermal Risk Assessment 53
6.3 Stage 2 of Assessment Protocol: Use of Rational Indices 54
6.3.1 Predicted Heat Strain (PHS) 55
6.3.2 Thermal Work Limit (TWL) 58
6.3.3 Other Indices 60
7.0 PHYSIOLOGICAL MONITORING - STAGE 3 OF ASSESSMENT
PROTOCOL 62
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7.1 Core Temperature 65
7.2 Heart Rate Measurements 67
8.0 CONTROLS 70
8.1. Ventilation 72
8.2 Radiant Heat 73
8.3 Administrative Controls 76
8.3.1 Training 76
8.3.2 Self-Assessment 77
8.3.3 Fluid Replacement 77
8.3.4 Rescheduling of Work 77
8.3.5 Work/Rest Regimes 77
8.3.6 Clothing 78
8.3.7 Pre-placement Health Assessment 80
8.4 Personal Protective Equipment 81
8.4.1 Air Cooling System 81
8.4.2 Liquid Circulating Systems 82
8.4.3 Ice Cooling Systems 83
8.4.4 Reflective Clothing 84
9.0 BIBLIOGRAPHY 85
Appendix A: Heat Stress Risk Assessment Checklist 103
Appendix B: Preliminary Plant Heat Stress Risk Assessment Sheet 104
Appendix C: Thermal Measurement 105
Appendix D: Encapsulating Suits 108
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PREFACE
In 2001 the Australian Institute of Occupational Hygienists (AIOH) established the Heat
Stress Working Group to develop a standard and relevant documentation in relation to
risks associated with hot environments. This group produced “The heat stress standard
and documentation developed for use in the Australian environment (2003).” Since that
time there have been a number of developments in the field and it was identified that the
standard and documentation were in need of review. As a result “A guide to managing
heat stress: developed for use in the Australian environment (2013)” and associated
documentation have been produced and now replace the previous standard and
documentation publications. There has been a slight shift in the approach such that the
emphasis of these documents is on guidance rather than an attempt to establish a formal
standard. They provide information and a number of recommended approaches to the
management of thermal stress, with associated references. The guidance is in two parts:
• the first, a brief summary of the approach written for interested parties with a non-
technical background, and
• the second, a more comprehensive set of documentation for the occupational
health practitioner.
These are not intended to be definitive documents on the subject of heat stress in
Australia. They will hopefully provide enough information and further references to assist
employees and employers (persons conducting a business or undertaking) as well as the
occupational health and safety practitioner, to manage heat stress in the Australian
workplace.
The authors wish to acknowledge the contribution of Gerald V Coles to the original
manuscript, which provided the foundation for this document.
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A Guide to Managing Heat Stress
The human body must regulate its internal temperature within a very narrow range to
maintain a state of well-being. To achieve this, the temperature must be balanced
between heat exchanges with the external thermal environment and the generation of heat
internally by the metabolic processes associated with life and activity. The effects of
excessive external heat exposures can upset this balance and result in a compromise of
health, safety, efficiency and productivity, which precede the possibly more serious heat
related illnesses. These illnesses can range from prickly heat, heat cramps, heat syncope,
heat exhaustion, heat stroke and in severe cases, death. The prime objective of heat
stress management is the elimination of any injury or risk of illness as a result of exposure
to excessive heat.
Assessment of both heat stress and heat strain can be used for evaluating the risk to
worker health and safety. A decision-making process such as that shown in Figure 1 can
be used. Figure 1 and the associated Documentation for this Guide provides means for
determining conditions under which it is believed that an acceptable percentage of
adequately hydrated, unmedicated, healthy workers may be repeatedly exposed without
adverse health effects. Such conditions are not a fine line between safe and dangerous
levels. Professional judgement and a program of heat stress management, with worker
education and training as core elements are required to ensure adequate protection for
each situation.
This Heat Stress Guide provides guidance based on current scientific research (as
presented in the Documentation), which enables individuals to decide and apply
appropriate strategies. It must be recognised that whichever strategy is selected, an
individual may still suffer annoyance, aggravation of a pre-existing condition, or even
physiological injury. Responses to heat in a workforce are individual and will vary between
personnel. Because of these characteristics and susceptibilities, a wider range of
protection may be warranted. Note that this Guide should not be used without also
referencing the accompanying Documentation.
This Guide is concerned only with health considerations and not those associated with
comfort. For additional information related to comfort, readers are directed to more
specific references such as International Standards Organization (ISO) 7730 – 2005:
Ergonomics of the thermal environment - Analytical determination and interpretation of
thermal comfort using calculation of the PMV and PPD indices and local thermal comfort
criteria.
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HEAT STRESS is the net heat load to which a worker may be exposed from the combined
contributions of metabolism associated with work and environmental factors such as:
• air temperature,
• humidity,
• air movement
• radiant heat exchange and
• clothing requirements
The effects of exposure to heat may range from a level of discomfort through to a life
threatening condition such as heat stroke. A mild or moderate heat stress may adversely
affect performance and safety. As the heat stress approaches human tolerance limits, the
risk of heat-related disorders increases.
HEAT STRAIN is the body’s overall response resulting from heat stress. These
responses are focussed on removing excess heat from the body.
Section 1: Risk assessment (the three step approach).
The decision process should be started if there are reports of discomfort due to heat
stress. These include but are not limited to:
• prickly heat,
• headaches,
• nausea,
• fatigue,
or when professional judgement indicates the need to assess the level of risk. Note: any
one of the symptoms can occur and may not be sequential as described above.
A structured assessment protocol is the best approach, as it provides the flexibility to meet
the requirements for the individual circumstance. The three tiered approach for the
assessment of exposure to heat has been designed in such a manner that it can be
applied to a number of varying scenarios where there is a potential risk of heat stress. The
suggested approach involves a three-stage process which is dependent on the severity
and complexity of the situation. It allows for the application of an appropriate intervention
for a specific task utilising a variation of risk assessment approaches. The recommended
method would be as follows:
1. A basic heat stress risk assessment questionnaire incorporating a simple index
2. If a potential problem is indicated from the initial step, then the progression to a second
level index to enable a more comprehensive investigation of the situation and general
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environment follows. Making sure to consider factors such as air velocity, humidity,
clothing, metabolic load, posture and acclimatisation
3. Where the allowable exposure time is less than 30 minutes or there is a high
involvement level of personal protective equipment (PPE), then some form of
physiological monitoring should be employed (Di Corleto, 1998a)
The first level, or the basic thermal risk assessment, is primarily designed as a qualitative
risk assessment that does not require specific technical skills in its administration,
application or interpretation. The second step of the process begins to look more towards
a quantitative risk approach and requires the measurement of a number of environmental
and personal parameters such as dry bulb and globe temperatures, relative humidity, air
velocity, metabolic work load and clothing insulation. The third step requires physiological
monitoring of the individual, which is a more quantitative risk approach. It utilises
measurements based on an individual’s strain and reactions to the thermal stress to which
they are being exposed. This concept is illustrated in Figure 1.
It should be noted that the differing levels of risk assessment require increasing levels of
technical expertise. While a level 1 assessment could be undertaken by a variety of
personnel requiring limited technical skills, the use of a level 3 assessment should be
restricted to someone with specialist knowledge and skills. It is important that the
appropriate tool is selected and applied to the appropriate scenario and skill level of the
assessor.
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