AUSTRALIAN INSTITUTE OF OCCUPATIONAL HYGIENISTS INC

(Incorporated in Victoria)

Registered OfficeUnit 2 8-12 Butler Way

Tullamarine VIC 3043 Tel +61 3 9338 1635

Email adminaiohorgau

Postal AddressPO Box 1205

TULLAMARINE VIC 3043

A GUIDE TO MANAGING HEAT STRESSDEVELOPED FOR USE IN THE

AUSTRALIAN ENVIRONMENT

ldquoWe 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 temperaturerdquo

Dr Charles Blagden M D F R S (1775)

Cover image ldquoSampling molten copper streamrdquo used with the permission of Rio Tinto

1

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 amp Joseph Mateacute

November 2013

November 2013

2

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 ndash Apparent Temperature 23

Appendix 2 ndash Table 5 Apparent Temperature Dry BulbHumidity scale 25

3

DOCUMENTATION OF THE HEAT STRESS GUIDE DEVELOPED FOR USE IN THE AUSTRALIAN ENVIRONMENT 26

10 INTRODUCTION 27

11 Heat Illness ndash A Problem Throughout the Ages 27

12 Heat and the Human Body 28

20 HEAT RELATED ILLNESSES 29

21 Acute Illnesses 30 211 Heat Stroke 30 212 Heat Exhaustion 31 213 Heat Syncope (Fainting) 31 214 Heat Cramps 32 215 Prickly Heat (Heat Rash) 32

22 Chronic Illness 32

23 Related Hazards 33

30 CONTACT INJURIES 34

40 KEY PHYSIOLOGICAL FACTORS CONTRIBUTING TO HEAT ILLNESS 36

41 Fluid Intake 36

42 Urine Specific Gravity 43

43 Heat Acclimatisation 45

44 Physical Fitness 47

45 Other Considerations in Reducing Exposure in Heat-Stress Conditions 48

50 ASSESSMENT PROTOCOL 48

60 WORK ENVIRONMENT MONITORING AND ASSESSMENT 50

61 Risk Assessment 50

62 The Three Stage Approach 51 621 Level 1 Assessment A Basic Thermal Risk Assessment 53

63 Stage 2 of Assessment Protocol Use of Rational Indices 54 631 Predicted Heat Strain (PHS) 55 632 Thermal Work Limit (TWL) 58 633 Other Indices 60

70 PHYSIOLOGICAL MONITORING - STAGE 3 OF ASSESSMENT PROTOCOL 62

4

71 Core Temperature 65

72 Heart Rate Measurements 67

80 CONTROLS 70

81 Ventilation 72

82 Radiant Heat 73

83 Administrative Controls 76 831 Training 76 832 Self-Assessment 77 833 Fluid Replacement 77 834 Rescheduling of Work 77 835 WorkRest Regimes 77 836 Clothing 78 837 Pre-placement Health Assessment 80

84 Personal Protective Equipment 81 841 Air Cooling System 81 842 Liquid Circulating Systems 82 843 Ice Cooling Systems 83 844 Reflective Clothing 84

90 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

5

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 ldquoThe heat stress standard

and documentation developed for use in the Australian environment (2003)rdquo 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 ldquoA guide to managing

heat stress developed for use in the Australian environment (2013)rdquo 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

bull the first a brief summary of the approach written for interested parties with a non-

technical background and

bull 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

6

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 ndash 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

7

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

bull air temperature

bull humidity

bull air movement

bull radiant heat exchange and

bull 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 bodyrsquos 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

bull prickly heat

bull headaches

bull nausea

bull 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

8

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 individualrsquos 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

9

Figure 1 Heat Stress Management Schematic (adapted from ACGIH 2013)

Level 1Perform Basic Risk

Assessment

Unacceptable risk

No

Does task involve use of impermeable clothing (ie PVC)

Continue work monitor conditionsNo

Are data available for detailed analysis

Level 2Analyse data with rational heat stress index (ie PHS

TWL)

Yes

Unacceptable heat stress risk based on analysis

Job specific controls practical and successful

Level 3Undertake physiological

monitoring

Cease work

Yes

Yes

No

Monitor task to ensure conditions amp collect dataNo

No

Maintain job specific controlsYes

Excessive heat strain based on monitoring

Yes

No

10

Level 1 Assessment a basic thermal risk assessment A suggested protocol for the level 1 assessment is termed the ldquoBasic Thermal Risk

Assessmentrdquo It has been designed as a simple tool which can be used by employees or

technicians to provide guidance and also as a training tool to illustrate the many factors

that impact on heat stress This risk assessment incorporates the contributions of a

number of factors that can impact on heat stress such as the state of acclimatisation work

demands location clothing and other physiological factors It can also incorporate the use

of a first level heat stress index such as Apparent Temperature or WBGT It is designed to

be an initial qualitative review of a potential heat stress situation for the purposes of

prioritising further measurements and controls It is not intended as a definitive

assessment tool Some of its key aspects are described below

Acclimatisation plays a part as it is a set of gradual physiological adjustments that improve

an individuals ability to tolerate heat stress the development and loss of which is

described in the Documentation

Metabolic work rate is of equal importance to environmental assessment in evaluating heat

stress Table 1 provides broad guidance for selecting the work rate category to be used in

the Risk Assessment There are a number of sources for this data including ISO

72431989 and ISO 89962004 standards

Table 1 Examples of Activities within Metabolic Rate (M) Classes

Class Examples

Resting Resting sitting at ease Low Light

Work Sitting at ease light manual work hand and arm work car driving

standing casual walking sitting or standing to control machines

Moderate

Moderate Work Sustained hand and arm work (eg hammering) arm and trunk

work moving light wheelbarrow walking around 45 kmh

High Heavy

Work

Intense arm and trunk work carrying heavy material shovelling

sawing hard wood moving heavily loaded wheelbarrows carrying

loads upstairs

Source (ISO 89962004)

Apparent temperature (Steadman 1979) can be used as part of the basic thermal risk

assessment The information required air temperature and humidity can be readily

obtained from most local weather bureau websites off-the-shelf weather units or

measured directly with a sling psychrometer Its simplicity is one of the advantages in its

use as it requires very little technical knowledge

11

The WBGT index also offers a useful first-order index of the environmental contribution to

heat stress It is influenced by air temperature radiant heat and humidity (ACGIH 2013)

In its simplest form it does not fully account for all of the interactions between a person

and the environment but is useful in this type of assessment The only disadvantage is

that it requires some specialised monitoring equipment such as a WBGT monitor or wet

bulb and globe thermometers

Both indices are described in more detail in the Documentation associated with this

standard

These environmental parameters are combined on a single check sheet in three sections

Each aspect is allocated a numerical value A task may be assessed by checking off

questions in the table and including some additional data for metabolic work load and

environmental conditions From this information a weighted calculation is used to

determine a numerical value which can be compared to pre-set criteria to provide

guidance as to the potential risk of heat stress and the course of action for controls

For example if the Assessment Point Total is less than 28 then the thermal condition risk

is low The lsquoNorsquo branch in Figure 1 can be taken Nevertheless if there are reports of the

symptoms of heat-related disorders such as prickly heat fatigue nausea dizziness and

light-headedness then the analysis should be reconsidered or proceed to detailed

analysis if appropriate If the Assessment Point Total is 28 or more further analysis is

required An Assessment Point Total greater than 60 indicates the need for immediate

action and implementation of controls (see Section 6)

Examples of a basic thermal risk assessment tool and their application are provided in

Appendix 1

Section 2 Screening for clothing that does not allow air and water vapour movement

The decision about clothing and how it might affect heat loss can also play an important

role in the initial assessment This is of particular importance if the clothing interferes with

the evaporation of sweat from the skin surface of an individual (ie heavy water barrier

clothing such as PVC) As this is the major heat loss mechanism disruption of this

process will significantly impact on the heat stress experienced Most heat exposure

assessment indices were developed for a traditional work uniform which consisted of a

long-sleeved shirt and pants Screening that is based on this attire is not suitable for

clothing ensembles that are more extensive and less permeable unless a detailed analysis

method appropriate for permeable clothing requirements is available With heat removal

hampered by clothing metabolic heat may produce life-threatening heat strain even when

12

ambient conditions are considered cool and the risk assessment determines ldquoLow Riskrdquo If

workers are required to wear additional clothing that does not allow air and water vapour

movement then the lsquoYesrsquo branch in the first question of Figure 1 should be taken

Physiological and behavioural monitoring described in Section 4 should be followed to

assess the potential for harm resulting from heat stress

Section 3 Level 2 assessment using detailed analysis

It is possible that a condition may be above the criteria provided in the initial risk

assessment and still not represent an unacceptable exposure To make this

determination a detailed analysis is required as in the Documentation

Note as discussed briefly above (see Section 2) no numerical screening criteria or limiting

values are applicable where clothing does not allow air or water vapour movement In this

case reliance must be placed on physiological monitoring

The screening criteria require a minimum set of data in order to make an assessment A

detailed analyses requires more data about the exposures including

bull clothing type

bull air speed

bull air temperature

bull water vapour content of the air (eg humidity)

bull posture

bull length of exposure and

bull globe temperature

Following Figure 1 the next question asks about the availability of such exposure data for

a detailed analysis If exposure data are not available the lsquoNorsquo branch takes the

evaluation to the monitoring of the tasks to collect this data before moving on to the use of

a rational heat stress index These types of indices are based on the human heat balance

equation and utilise a number of formulae to predict responses of the body such as

sweating and elevation of core temperature From this information the likelihood of

developing a heat stress related disorder may be determined In situations where this

data cannot be collected or made available then physiological monitoring to assess the

degree of heat strain should be undertaken

Detailed rational analysis should follow ISO 7933 - Predicted Heat Strain or Thermal Work

Limit (TWL) although other indices with extensive supporting physiological documentation

may also be acceptable (see Documentation for details) While such a rational method

(versus the empirically derived WBGT or Basic Effective Temperature (BET) thresholds) is

13

computationally more difficult it permits a better understanding of the source of the heat

stress and can be a means to assess the benefits of proposed control modifications on the

exposure

Predicted heat strain (PHS) is a rational index (ie it is an index based on the heat balance

equation) It estimates the required sweat rate and the maximal evaporation rate utilising

the ratio of the two as an initial measure of lsquorequired wettednessrsquo This required

wettedness is the fraction of the skin surface that would have to be covered by sweat in

order for the required evaporation rate to occur The evaporation rate required to maintain

a heat balance is then calculated (Di Corleto et al 2003)

In the event that the suggested values might be exceeded ISO 7933 calculates an

allowable exposure time

The suggested limiting values assume workers are

bull fit for the activity being considered and

bull in good health and

bull screened for intolerance to heat and

bull properly instructed and

bull able to self-pace their work and

bull under some degree of supervision (minimally a buddy system)

In work situations which

bull either the maximum evaporation rate is negative leading to condensation of

water vapour on the skin

bull or the estimated allowable exposure time is less than 30 minutes so that the

phenomenon of sweating onset plays a major role in the estimation of the

evaporation loss of the subject Special precautionary measures need to be

taken and direct and individual physiological surveillance of the workers is

particularly necessary

The thermal work limit (TWL) was developed in Australia initially in the underground

mining industry by Brake and Bates (2002a) and later trialled in open cut mines in the

Pilbara region of Western Australia (Miller and Bates 2007a) TWL is defined as the

limiting (or maximum) sustainable metabolic rate that hydrated acclimatised individuals

can maintain in a specific thermal environment within a safe deep body core temperature

(lt382degC) and sweat rate (lt12 kghr) (Tillman 2007)

Due to this complexity these calculations are carried out with the use of computer

software or in the case of TWL pre-programmed monitoring equipment

14

If the exposure does not exceed the criteria for the detailed analysis then the lsquoNorsquo branch

can be taken Because the criteria in the risk assessment have been exceeded

monitoring general heat stress controls are appropriate General controls include training

for workers and supervisors and heat stress hygiene practices If the exposure exceeds

the suggested limits from the detailed analysis or set by the appropriate authority the

lsquoYesrsquo branch leads to the iterative assessment of job-specific control options using the

detailed analysis and then implementation and assessment of control(s) If these are not

available or it cannot be demonstrated that they are successful then the lsquoNorsquo branch

leads to physiological monitoring as the only alternative to demonstrate that adequate

protection is provided

Section 4 Level 3 assessment of heat strain

There are circumstances where the assessment using the rational indices cannot assure

the safety of the exposed workgroup In these cases the use of individual physiological

monitoring may be required These may include situations of high heat stress risk or

where the individualrsquos working environment cannot be accurately assessed A common

example is work involving the use of encapsulating ldquohazmatrdquo suits

The risk and severity of excessive heat strain will vary widely among people even under

identical heat stress conditions By monitoring the physiological responses to working in a

hot environment this allows the workers to use the feedback to assess the level of heat

strain present in the workforce to guide the design of exposure controls and to assess the

effectiveness of implemented controls Instrumentation is available for personal heat

stress monitoring These instruments do not measure the environmental conditions

leading to heat stress but rather they monitor the physiological indicators of heat strain -

usually elevated body temperature andor heart rate Modern instruments utilise an

ingestible core temperature capsule which transmits physiological parameters

telemetrically to an external data logging sensor or laptop computer This information can

then be monitored in real time or assessed post task by a qualified professional

Monitoring the signs and symptoms of heat-stressed workers is sound occupational

hygiene practice especially when clothing may significantly reduce heat loss For

surveillance purposes a pattern of workers exceeding the limits below is considered

indicative of the need to control the exposures On an individual basis these limits are

believed to represent a time to cease an exposure until recovery is complete

Table 2 provides guidance for acceptable limits of heat strain Such physiological

monitoring (see ISO 12894 2001) should be conducted by a physician nurse or

equivalent as allowed by local law

15

Table 2 Physiological Guidelines for Limiting Heat Strain The American Conference of Industrial Hygienists (ACGIH 2013) has published

physiological limits for a number of years and states that exposure to

environmentally or activity-induced heat stress must be discontinued at any time

when

bull Sustained (several minutes) heart rate in excess of 180 beats per minute

minus the individuals age in years (eg180 ndash age) for individuals with

assessed normal cardiac performance OR

bull Body core temperature greater than 385degC (1013degC) for medically

selected and acclimatised personnel or greater than 38degC (1004degC) in

unselected unacclimatised workers OR

bull When there are complaints of sudden and severe fatigue nausea

dizziness or light-headedness OR

bull A workers recovery heart rate at one minute after a peak work effort is

greater than 120 beats per minute 124 bpm was suggested by Fuller and

Smith (1982) OR

bull A worker experiences profuse and prolonged sweating over hours and

may not be able to adequately replenish fluids OR

bull Greater than 15 weight loss over a shift OR

bull In conditions of regular daily exposure to the stress 24-hour urinary

sodium excretion is less than 50 mmoles

ISO 9886 (2004) suggests that exposure to environmentally or activity-induced heat

stress must also be discontinued at any time when

bull lsquoHeart Rate Limit = 185 - 065Arsquo where A = Age in years

bull Individual variability can range up to 20 bpm from this average so this

level could present a risk for some individuals Where there is

uncertainty the sustained heart rate over a work period should not

exceed the previously mentioned

bull HRL sustained = 180 ndash age

bull No matter which limiting values are used interpretation requires

discussion with the workers affected and may require the services of a

specialist such as an occupational hygienist or occupational physician

If a worker appears to be disoriented or confused or demonstrates uncharacteristic

16

irritability discomfort or flu-like symptoms the worker should be removed for rest

under observation in a cool location Symptoms of heat stroke need to be monitored

closely and if sweating stops and the skin becomes hot and dry immediate

emergency care is essential

The prompt treatment of other heat-related disorders generally results in full

recovery but medical advice should be sought for treatment and return-to-work

protocols

Following good occupational hygiene sampling practice which considers likely extremes

and the less tolerant workers the absence of any of these limiting observations indicates

acceptable management of the heat stress exposures With acceptable levels of heat

strain the lsquoNorsquo branch in the level 3 section of Figure 1 is taken Nevertheless even if the

heat strain among workers is considered acceptable at the time the general controls are

necessary In addition periodic physiological monitoring should be continued to ensure

that acceptable levels of heat strain are being maintained

If excessive heat strain is found during the physiological assessments then the lsquoYesrsquo

branch is taken This means that the work activities must cease until suitable job-specific

controls can be considered and implemented to a sufficient extent to control that strain

The job-specific controls may include engineering controls administrative controls and

personal protection

After implementation of the job-specific controls it is necessary to assess their

effectiveness and to adjust them as needed

Section 5 Occupational Exposure Limits

Currently there are fewer workplaces where formal exposure limits for heat stress still

apply however this practice is found mainly within the mining industry There are many

variables associated with the onset of heat stress and these can be a result of the task

environment andor the individual Trying to set a general limit which adequately covers

the many variations within industry has proven to be extremely complicated The attempts

have sometimes resulted in an exposure standard so conservative in a particular

environment that it would become impractical to apply It is important to note that heat

stress indices are not safeunsafe limits and should only be used as guides

Use of Urinary Specific Gravity testing

Water intake at onersquos own discretion results in incomplete fluid replacement for individuals

working in the heat and there is consistent evidence that relying solely on thirst as an

17

indicator of fluid requirement will not restore water balance (Sawka 1998) Urine specific

gravity (USG) can be used as a guide in relation to the level of hydration of an individual

(Shirreffs 2003) and this method of monitoring is becoming increasingly popular in

Australia as a physiological limit Specific gravity (SG) is defined as the ratio weight of a

substance compared to the weight of an equal volume of distilled water hence the SG of

distilled water is 1000 Studies (Sawka et al 2007 Ganio et al 2007 Cheuvront amp

Sawka 2005 Casa et al 2000) recommend that a USG of greater than 1020 would

reflect dehydration While not regarded as fool proof or the ldquogold standardrdquo for total body

water (Armstrong 2007) it is a good compromise between accuracy simplicity of testing

in the field and acceptability to workers of a physiological measure Table 3 shows the

relationship between SG of urine and hydration

Table 3 US National Athletic Trainers Association index of hydration status Body Weight

Loss ()

Urine Specific

Gravity

Well Hydrated lt1 1010

Minimal dehydration 1 - 3 1010 ndash 1020

Significant

dehydration

3 - 5 1021 ndash 1030

Severe dehydration gt 5 gt 1030 Source adapted from Casa et al 2000

Section 6 Heat stress management and controls

The requirement to initiate a heat stress management program is marked by

(1) heat stress levels that exceed the criteria in the Basic Thermal Risk Assessment or

level 2 heat index assessment or

(2) work in clothing ensembles that are air or water vapour impermeable

There are numerous controls across the hierarchy of controls that may be utilised to

address heat stress issues in the workplace Not all may be applicable to a particular task

or scenario and often may require some adjusting before a suitable combination is

achieved

In addition to general controls appropriate job-specific controls are often required to

provide adequate protection During the consideration of job-specific controls detailed

analysis provides a framework to appreciate the interactions among acclimatisation stage

metabolic rate workrest cycles and clothing Table 4 lists some examples of controls

available The list is by no means exhaustive but will provide some ideas for controls

18

Table 4 Examples of control methods

Eliminationsubstitution

bull Hot tasks should be scheduled to avoid the hottest part of the day or where

practical undertaken during night shifts

bull Walls and roof structures should utilize light coloured or reflective materials

bull Structures should be designed to incorporate good air flow This can be done via

the positioning of windows shutters and roof design to encourage lsquochimney

effectsrsquo This will help remove the heat from the structure

bull Walls and roofs should be insulated

Engineering

bull Pipework and vessels associated with hot processes should be insulated and clad

to minimize the introduction of heat into the work environment

bull In high humidity areas such as northern Australia more air needs to be moved

hence fans to increase air flow or in extreme cases cooled air from lsquochillerrsquo units

can be used

bull Where radiated heat from a process is a problem insulating barriers or reflective

barriers can be used to absorb or re-direct radiant heat These may be permanent

structures or movable screens

bull Relocating hot processes away from high access areas

bull Dehumidifying air to increase the evaporative cooling effect Often steam leaks

open process vessels or standing water can artificially increase humidity within a

building

bull Utilize mechanical aids that can reduce the metabolic workload on the individual

Administrative

bull Ready access to cool palatable drinking water is a basic necessity

bull Where applicable suitable electrolyte replacements should also be available

bull A clean cool area for employees to rest and recuperate can add significant

improvement to the cooling process Resting in the work environment can provide

some relief for the worker the level of recovery is much quicker and more efficient

in an air-conditioned environment These need not be elaborate structures basic

inexpensive portable enclosed structures with an air conditioner water supply and

seating have been found to be successful in a variety of environments For field

19

teams with high mobility even a simple shade structure readily available from

hardware stores or large umbrellas can provide relief from solar radiation

bull Where work-rest regimes are necessary heat stress indices such as WBGT PHS

or TWL assist in determining duration of work and rest periods

bull Training workers to identify symptoms and the potential onset of heat-related

illness as part of the lsquobuddy systemrsquo

bull Encouraging ldquoself-determinationrdquo or pacing of the work to meet the conditions and

reporting of heat related symptoms

bull Consider pre-placement medical screening for work in hot areas (ISO 12894)

Personal protective equipment

bull PPE such as cooling vests with either lsquophase changersquo cooling inserts (not ice) Ice

or chilled water cooled garments can result in contraction of the blood vessels

reducing the cooling effect of the garment

bull Vortex tube air cooling may be used in some situations particularly when a cooling

source is required when supplied air respirators are used

bull Choose light coloured materials for clothing and ensure they allow good air flow

across the skin to promote evaporative cooling

Heat stress hygiene practices are particularly important because they reduce the risk that

an individual may suffer a heat-related disorder The key elements are fluid replacement

self-assessment health status monitoring maintenance of a healthy life-style and

adjustment of work expectations based on acclimatisation state and ambient working

conditions The hygiene practices require the full cooperation of supervision and workers

20

Bibliography ACGIH (American Conference of Governmental Industrial Hygienists) (2013) Threshold

Limit Values for Chemical Substances and Physical Agents and Biological Exposure

Indices Cincinnati ACGIH Signature Publications

Armstrong LE (2007) Assessing hydration status The elusive gold standard Journal of

the American College of Nutrition 26(5) pp 575S-584S

Brake DJ amp Bates GP (2002) Limiting metabolic rate (thermal work limit) as an index of

thermal stress Applied Occupational and Environmental Hygiene 17 pp 176ndash86

Casa DJ Armstrong LE Hillman SK Montain SJ Reiff RV amp Rich BSE (2000)

National Athletic Trainers association Position Statement Fluid replacement for Athletes

Journal of Athletic Training 35(2) pp 212-224

Di Corleto R Coles G amp Firth I (2003) The development of a heat stress standard for

Australian conditions in Australian Institute of Occupational Hygienists Inc 20th Annual

Conference Proceedings Geelong Victoria December AIOH

Di Corleto R Firth I Mate J Coles G (2013) A Guide to Managing Heat Stress and

Documentation Developed For Use in the Australian Environment AIOH Melbourne

Ganio MS Casa DJ Armstrong LE amp Maresh CM (2007) Evidence based approach to

lingering hydration questions Clinics in Sports Medicine 26(1) pp 1ndash16

ISO 7243 (1989) Hot environments - Estimation of the heat stress on working man

based on the WBGT - index (wet bulb globe temperature)

ISO 7933 (2004) Ergonomics of the thermal environment Analytical determination and

interpretation of heat stress using calculation of the Predicted Heat Strain ISO 7933

ISO 8996 (2004) Ergonomics of the Thermal Environment ndash Determination of Metabolic

Rate Geneva ISO

ISO 9886 (1992) Evaluation of thermal strain by physiological measurements

ISO 12894 (2001) Ergonomics of the thermal environment ndash Medical supervision of

individuals exposed to extreme hot or cold environments

Miller V Bates G (2007) Hydration of outdoor workers in north-west Australia J

Occup Health Safety mdash Aust NZ 23(1) pp 79ndash87

21

Sawka MN (1998) Body fluid responses and hypohydration during exercise heat

stress in KB Pandolf MN Sawkaand amp RR Gonzalez (Eds) Human Performance

Physiology and Environmental Medicine at Terrestrial Extremes USA Brown amp

Benchmark pp 227 ndash 266

Shirreffs SM (2003) Markers of hydration status European Journal of Clinical Nutrition

57(2) pp s6-s9

Steadman RG (1979) The assessment of sultriness Part 1 A temperature humidity

index based on human physiology and clothing science Journal of applied meteorology

(July)

Tillman C (2007) (Ed) Principles of Occupational Health amp Hygiene - An Introduction

Allen amp Unwin Academic

22

Appendix 1 - Basic Thermal Risk Assessment using Apparent Temperature (Informative example only)

HAZARD TYPE Assessment Point Value 0 1 2 3 Sun Exposure Indoors Full Shade Part Shade No Shade Hot surfaces Neutral Warm on Contact Hot on contact Burn on contact Exposure period lt 30 min 30 min ndash 1hour 1 hour - 2 hours gt 2 hrs Confined space No Yes Task complexity Simple Moderate Complex Climbing updown stairs or ladders None One level Two levels gt Two levels Distance from cool rest area lt10 Metres 10 - 50 Metres 50-100 Metres gt100 Metres Distance from drinking water lt10 Metres 10 - 30 Metres 30-50 Metres gt50 Metres Clothing (permeable) Single layer (light) Single layer (mod) Multiple layer Understanding of heat strain risk Training given No training given Air movement Strong Wind Moderate Wind Light Wind No Wind Resp protection (-ve pressure) None Disposable Half Face Rubber Half Face Full Face Acclimatisation Acclimatised Unacclimatised

SUB-TOTAL A 2 4 6 Metabolic work rate Light Moderate Heavy SUB-TOTAL B 1 2 3 4 Apparent Temperature lt 27degC gt27degC le 33degC gt33degC le 41degC gt 41degC SUB-TOTAL C

TOTAL = A plus B Multiplied by C = Examples of Work Rate Light work Sitting or standing to control machines hand and arm work assembly or sorting of light materials Moderate work Sustained hand and arm work such as hammering handling of moderately heavy materials Heavy work Pick and shovel work continuous axe work carrying loads up stairs Instructions for use of the Basic Thermal Risk Assessment

bull Mark each box according to the appropriate conditions bull When complete add up using the value at the top of the appropriate column for each mark bull Add the sub totals of Table A amp Table B and multiply with the sub-total of Table C for the final result bull If the total is less than 28 then the risk due to thermal conditions are low to moderate bull If the total is 28 to 60 there is a potential of heat-induced illnesses occurring if the conditions are not

addressed Further analysis of heat stress risk is required bull If the total exceeds 60 then the onset of a heat-induced illness is very likely and action should be taken as

soon as possible to implement controls It is important to note that that this assessment is to be used as a guide only A number of factors are not included in this assessment such as employee health condition and the use of high levels of PPE (particularly impermeable suits) In these circumstances experienced personnel should carry out a more extensive assessment

23

Worked Example of Basic Thermal Risk Assessment An example of the application of the basic thermal risk assessment would be as follows A fitter is working on a pump out in the plant at ground level that has been taken out of service the previous day The task involves removing bolts and a casing to check the impellers for wear approximately 2 hours of work The pump is situated approximately 25 metres from the workshop The fitter is acclimatised has attended a training session and is wearing a standard single layer long shirt and trousers is carrying a water bottle and a respirator is not required The work rate is light there is a light breeze and the air temperature has been measured at 30degC and the relative humidity at 70 This equates to an apparent temperature of 35degC (see Table 5 in appendix 2) Using the above information in the risk assessment we have

HAZARD TYPE Assessment Point Value

0 1 2 3 Sun Exposure Indoors Shade Part Shade No Shade Hot surfaces Neutral Warm on Contact Hot on contact Burn on contact Exposure period lt 30 min 30 min ndash 1hour 1 hour - 2 hours gt 2 hrs Confined space No Yes Task complexity Simple Moderate Complex Climbing updown stairs or ladders None One level Two levels gt Two levels Distance from cool rest area lt10 Metres lt50 Metres 50-100 Metres gt100 Metres Distance from drinking water lt10 Metres lt30 Metres 30-50 Metres gt50 Metres Clothing (permeable) Single layer (light) Single layer (mod) Multiple layer Understanding of heat strain risk Training given No training given Air movement Strong Wind Moderate Wind Light Wind No Wind Resp protection (-ve pressure) None Disposable Half Face Rubber Half Face Full Face Acclimatisation Acclimatised Unacclimatised

3 6 0 SUB-TOTAL A 9 2 4 6 Metabolic work rate Light Moderate Heavy SUB-TOTAL B 2 1 2 3 4 Apparent Temperature lt 27degC gt27degC le 33degC gt33degC le 41degC gt 41degC SUB-TOTAL C 3

A = 9 B = 2 C = 3 therefore Total = (9+2) x 3 = 33 As the total lies between 28 and 60 there is a potential for heat induced illness occurring if the conditions are not addressed and further analysis of heat stress risk is required

24

Appendix 2 ndash Table 5 Apparent Temperature Dry BulbHumidity scale Align dry bulb temperature with corresponding relative humidity to determine apparent temperature in unshaded section of table Numbers in () refer to skin humidities above 90 and are only approximate

Dry Bulb Temperature Relative Humidity () (degC) 0 10 20 30 40 50 60 70 80 90 100 20 16 17 17 18 19 19 20 20 21 21 21 21 18 18 19 19 20 20 21 21 22 22 23 22 19 19 20 20 21 21 22 22 23 23 24 23 20 20 21 22 22 23 23 24 24 24 25 24 21 22 22 23 23 24 24 25 25 26 26 25 22 23 24 24 24 25 25 26 27 27 28 26 24 24 25 25 26 26 27 27 28 29 30 27 25 25 26 26 27 27 28 29 30 31 33 28 26 26 27 27 28 29 29 31 32 34 (36) 29 26 27 27 28 29 30 30 33 35 37 (40) 30 27 28 28 29 30 31 33 35 37 (40) (45) 31 28 29 29 30 31 33 35 37 40 (45) 32 29 29 30 31 33 35 37 40 44 (51) 33 29 30 31 33 34 36 39 43 (49)

34 30 31 32 34 36 38 42 (47)

35 31 32 33 35 37 40 (45) (51)

36 32 33 35 37 39 43 (49)

37 32 34 36 38 41 46

38 33 35 37 40 44 (49)

39 34 36 38 41 46

40 35 37 40 43 49

41 35 38 41 45

42 36 39 42 47

43 37 40 44 49

44 38 41 45 52

45 38 42 47

46 39 43 49

47 40 44 51

48 41 45 53

49 42 47

50 42 48

(Source Steadman 1979)

25

Documentation of the Heat Stress Guide Developed for Use in the Australian Environment

Developed for the Australian Institute of Occupational Hygienists

Ross Di Corleto Ian Firth amp Joseph Mateacute

November 2013

26

10 Introduction Heat-related illness has been a health hazard throughout the ages and is a function

of the imposition of environmental heat on the human body which itself generates

heat

11 Heat Illness ndash A Problem Throughout the Ages

The hot thermal environment has been a constant challenge to man for centuries and

its impact is referenced throughout history The bible tells of the death of Judithrsquos

husband Manasseh from exposure in the fields supervising workers where it says

ldquoHe had suffered a sunstroke while in the fields supervising the farm workers and

later died in bed at home in Bethuliardquo (Judith 83)

The impact of heat on the military in history is also well recorded the problems

confronted by the armies of King Sennacherib of Assyria (720BC) whilst attacking

Lashish Herodotus (400BC) reports of Spartan soldiers succumbing to ldquothirst and

sunrdquo Even Alexander the Great in 332BC was warned of the risks of a march across

the Libyan Desert And there is little doubt that heat stress played a major role in the

defeat of the Crusaders of King Edward in the Holy Land fighting the Saracens whilst

burdened down with heavy armour in the Middle Eastern heat (Goldman 2001)

It is not only the workers and armies that are impacted but also the general

population One of the worst cases occurred in Peking China in 1743 when during a

10 day heat wave 11000 people were reported to have perished (Levick 1859)

In 1774 Sir Charles Blagden of the Royal Society outlined a series of experiments

undertaken in a heated room in which he commented on ldquothe wonderful power with

which the animal body is endued of resisting heat vastly greater than its own

temperaturerdquo (Blagden 1775)

Despite this experience and knowledge over the ages we are still seeing deaths in

the 20th century as a result of heat stress Severe heat related illnesses and deaths

are not uncommon among pilgrims making the Makkah Hajj (Khogali 1987) and

closer to home a fatality in the Australian military (ABC 2004) and more recently

amongst the Australian workforce (Australian Mining 2013)

27

12 Heat and the Human Body

The human body in a state of wellbeing maintains its internal temperature within a

very narrow range This is a fundamental requirement for those internal chemical

reactions which are essential to life to proceed at the proper rates The actual level

of this temperature is a product of the balance between heat exchange with the

external thermal environment and the generation of heat internally by the metabolic

processes associated with life and activity

The temperature of blood circulating through the living and working tissues is

monitored by receptors throughout the body The role of these receptors is to induce

specific responses in functional body systems to ensure that the temperature

remains within the appropriate range

The combined effect of external thermal environment and internal metabolic heat

production constitutes the thermal stress on the body The levels of activity required

in response to the thermal stress by systems such as cardiovascular

thermoregulatory respiratory renal and endocrine constitute the thermal strain

Thus environmental conditions metabolic workload and clothing individually or

collectively create heat stress for the worker The bodyrsquos physiological response to

stressors for example sweating increased heart rate and elevated core

temperature is the heat strain

Such physiological changes are the initial responses to thermal stress but the extent

at which these responses are required will determine whether that strain will result in

thermal injuryillness It is important to appreciate that while preventing such illness

by satisfactorily regulating human body temperature in a heat-stress situation those

responses particularly the sweat response may not be compatible with comfort

(Gagge et al 1941)

The rate of heat generated by metabolic processes is dependent on the level of

physical activity To precisely quantify the metabolic cost associated with a particular

task without directly or indirectly measuring the individual is not possible This is due

to the individual differences associated with performing the task at hand As a

result broad categories of metabolic loads for typical work activities have been

established (Durnin amp Passmore 1967 ISO 8996 2004) It is sometimes practicable

Safe Work Australia (2011) refers to heat related illnesses and OSHA (httpswwwoshagovSLTCheatstress) considers heat exhaustion and heat stroke cases to be heat-related illness due to the number of human factors that contribute to a workers susceptibility to heat stress (refer to Section 40) while ACGIH (2013) refers to heat stress and heat strain cases as being heat-related disorders They are not usually considered injuries

28

ldquoWe 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 temperaturerdquo

Dr Charles Blagden M D F R S (1775)

Cover image ldquoSampling molten copper streamrdquo used with the permission of Rio Tinto

1

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 amp Joseph Mateacute

November 2013

November 2013

2

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 ndash Apparent Temperature 23

Appendix 2 ndash Table 5 Apparent Temperature Dry BulbHumidity scale 25

3

DOCUMENTATION OF THE HEAT STRESS GUIDE DEVELOPED FOR USE IN THE AUSTRALIAN ENVIRONMENT 26

10 INTRODUCTION 27

11 Heat Illness ndash A Problem Throughout the Ages 27

12 Heat and the Human Body 28

20 HEAT RELATED ILLNESSES 29

21 Acute Illnesses 30 211 Heat Stroke 30 212 Heat Exhaustion 31 213 Heat Syncope (Fainting) 31 214 Heat Cramps 32 215 Prickly Heat (Heat Rash) 32

22 Chronic Illness 32

23 Related Hazards 33

30 CONTACT INJURIES 34

40 KEY PHYSIOLOGICAL FACTORS CONTRIBUTING TO HEAT ILLNESS 36

41 Fluid Intake 36

42 Urine Specific Gravity 43

43 Heat Acclimatisation 45

44 Physical Fitness 47

45 Other Considerations in Reducing Exposure in Heat-Stress Conditions 48

50 ASSESSMENT PROTOCOL 48

60 WORK ENVIRONMENT MONITORING AND ASSESSMENT 50

61 Risk Assessment 50

62 The Three Stage Approach 51 621 Level 1 Assessment A Basic Thermal Risk Assessment 53

63 Stage 2 of Assessment Protocol Use of Rational Indices 54 631 Predicted Heat Strain (PHS) 55 632 Thermal Work Limit (TWL) 58 633 Other Indices 60

70 PHYSIOLOGICAL MONITORING - STAGE 3 OF ASSESSMENT PROTOCOL 62

4

71 Core Temperature 65

72 Heart Rate Measurements 67

80 CONTROLS 70

81 Ventilation 72

82 Radiant Heat 73

83 Administrative Controls 76 831 Training 76 832 Self-Assessment 77 833 Fluid Replacement 77 834 Rescheduling of Work 77 835 WorkRest Regimes 77 836 Clothing 78 837 Pre-placement Health Assessment 80

84 Personal Protective Equipment 81 841 Air Cooling System 81 842 Liquid Circulating Systems 82 843 Ice Cooling Systems 83 844 Reflective Clothing 84

90 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

5

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 ldquoThe heat stress standard

and documentation developed for use in the Australian environment (2003)rdquo 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 ldquoA guide to managing

heat stress developed for use in the Australian environment (2013)rdquo 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

bull the first a brief summary of the approach written for interested parties with a non-

technical background and

bull 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

6

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 ndash 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

7

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

bull air temperature

bull humidity

bull air movement

bull radiant heat exchange and

bull 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 bodyrsquos 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

bull prickly heat

bull headaches

bull nausea

bull 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

8

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 individualrsquos 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

9

Figure 1 Heat Stress Management Schematic (adapted from ACGIH 2013)

Level 1Perform Basic Risk

Assessment

Unacceptable risk

No

Does task involve use of impermeable clothing (ie PVC)

Continue work monitor conditionsNo

Are data available for detailed analysis

Level 2Analyse data with rational heat stress index (ie PHS

TWL)

Yes

Unacceptable heat stress risk based on analysis

Job specific controls practical and successful

Level 3Undertake physiological

monitoring

Cease work

Yes

Yes

No

Monitor task to ensure conditions amp collect dataNo

No

Maintain job specific controlsYes

Excessive heat strain based on monitoring

Yes

No

10

Level 1 Assessment a basic thermal risk assessment A suggested protocol for the level 1 assessment is termed the ldquoBasic Thermal Risk

Assessmentrdquo It has been designed as a simple tool which can be used by employees or

technicians to provide guidance and also as a training tool to illustrate the many factors

that impact on heat stress This risk assessment incorporates the contributions of a

number of factors that can impact on heat stress such as the state of acclimatisation work

demands location clothing and other physiological factors It can also incorporate the use

of a first level heat stress index such as Apparent Temperature or WBGT It is designed to

be an initial qualitative review of a potential heat stress situation for the purposes of

prioritising further measurements and controls It is not intended as a definitive

assessment tool Some of its key aspects are described below

Acclimatisation plays a part as it is a set of gradual physiological adjustments that improve

an individuals ability to tolerate heat stress the development and loss of which is

described in the Documentation

Metabolic work rate is of equal importance to environmental assessment in evaluating heat

stress Table 1 provides broad guidance for selecting the work rate category to be used in

the Risk Assessment There are a number of sources for this data including ISO

72431989 and ISO 89962004 standards

Table 1 Examples of Activities within Metabolic Rate (M) Classes

Class Examples

Resting Resting sitting at ease Low Light

Work Sitting at ease light manual work hand and arm work car driving

standing casual walking sitting or standing to control machines

Moderate

Moderate Work Sustained hand and arm work (eg hammering) arm and trunk

work moving light wheelbarrow walking around 45 kmh

High Heavy

Work

Intense arm and trunk work carrying heavy material shovelling

sawing hard wood moving heavily loaded wheelbarrows carrying

loads upstairs

Source (ISO 89962004)

Apparent temperature (Steadman 1979) can be used as part of the basic thermal risk

assessment The information required air temperature and humidity can be readily

obtained from most local weather bureau websites off-the-shelf weather units or

measured directly with a sling psychrometer Its simplicity is one of the advantages in its

use as it requires very little technical knowledge

11

The WBGT index also offers a useful first-order index of the environmental contribution to

heat stress It is influenced by air temperature radiant heat and humidity (ACGIH 2013)

In its simplest form it does not fully account for all of the interactions between a person

and the environment but is useful in this type of assessment The only disadvantage is

that it requires some specialised monitoring equipment such as a WBGT monitor or wet

bulb and globe thermometers

Both indices are described in more detail in the Documentation associated with this

standard

These environmental parameters are combined on a single check sheet in three sections

Each aspect is allocated a numerical value A task may be assessed by checking off

questions in the table and including some additional data for metabolic work load and

environmental conditions From this information a weighted calculation is used to

determine a numerical value which can be compared to pre-set criteria to provide

guidance as to the potential risk of heat stress and the course of action for controls

For example if the Assessment Point Total is less than 28 then the thermal condition risk

is low The lsquoNorsquo branch in Figure 1 can be taken Nevertheless if there are reports of the

symptoms of heat-related disorders such as prickly heat fatigue nausea dizziness and

light-headedness then the analysis should be reconsidered or proceed to detailed

analysis if appropriate If the Assessment Point Total is 28 or more further analysis is

required An Assessment Point Total greater than 60 indicates the need for immediate

action and implementation of controls (see Section 6)

Examples of a basic thermal risk assessment tool and their application are provided in

Appendix 1

Section 2 Screening for clothing that does not allow air and water vapour movement

The decision about clothing and how it might affect heat loss can also play an important

role in the initial assessment This is of particular importance if the clothing interferes with

the evaporation of sweat from the skin surface of an individual (ie heavy water barrier

clothing such as PVC) As this is the major heat loss mechanism disruption of this

process will significantly impact on the heat stress experienced Most heat exposure

assessment indices were developed for a traditional work uniform which consisted of a

long-sleeved shirt and pants Screening that is based on this attire is not suitable for

clothing ensembles that are more extensive and less permeable unless a detailed analysis

method appropriate for permeable clothing requirements is available With heat removal

hampered by clothing metabolic heat may produce life-threatening heat strain even when

12

ambient conditions are considered cool and the risk assessment determines ldquoLow Riskrdquo If

workers are required to wear additional clothing that does not allow air and water vapour

movement then the lsquoYesrsquo branch in the first question of Figure 1 should be taken

Physiological and behavioural monitoring described in Section 4 should be followed to

assess the potential for harm resulting from heat stress

Section 3 Level 2 assessment using detailed analysis

It is possible that a condition may be above the criteria provided in the initial risk

assessment and still not represent an unacceptable exposure To make this

determination a detailed analysis is required as in the Documentation

Note as discussed briefly above (see Section 2) no numerical screening criteria or limiting

values are applicable where clothing does not allow air or water vapour movement In this

case reliance must be placed on physiological monitoring

The screening criteria require a minimum set of data in order to make an assessment A

detailed analyses requires more data about the exposures including

bull clothing type

bull air speed

bull air temperature

bull water vapour content of the air (eg humidity)

bull posture

bull length of exposure and

bull globe temperature

Following Figure 1 the next question asks about the availability of such exposure data for

a detailed analysis If exposure data are not available the lsquoNorsquo branch takes the

evaluation to the monitoring of the tasks to collect this data before moving on to the use of

a rational heat stress index These types of indices are based on the human heat balance

equation and utilise a number of formulae to predict responses of the body such as

sweating and elevation of core temperature From this information the likelihood of

developing a heat stress related disorder may be determined In situations where this

data cannot be collected or made available then physiological monitoring to assess the

degree of heat strain should be undertaken

Detailed rational analysis should follow ISO 7933 - Predicted Heat Strain or Thermal Work

Limit (TWL) although other indices with extensive supporting physiological documentation

may also be acceptable (see Documentation for details) While such a rational method

(versus the empirically derived WBGT or Basic Effective Temperature (BET) thresholds) is

13

computationally more difficult it permits a better understanding of the source of the heat

stress and can be a means to assess the benefits of proposed control modifications on the

exposure

Predicted heat strain (PHS) is a rational index (ie it is an index based on the heat balance

equation) It estimates the required sweat rate and the maximal evaporation rate utilising

the ratio of the two as an initial measure of lsquorequired wettednessrsquo This required

wettedness is the fraction of the skin surface that would have to be covered by sweat in

order for the required evaporation rate to occur The evaporation rate required to maintain

a heat balance is then calculated (Di Corleto et al 2003)

In the event that the suggested values might be exceeded ISO 7933 calculates an

allowable exposure time

The suggested limiting values assume workers are

bull fit for the activity being considered and

bull in good health and

bull screened for intolerance to heat and

bull properly instructed and

bull able to self-pace their work and

bull under some degree of supervision (minimally a buddy system)

In work situations which

bull either the maximum evaporation rate is negative leading to condensation of

water vapour on the skin

bull or the estimated allowable exposure time is less than 30 minutes so that the

phenomenon of sweating onset plays a major role in the estimation of the

evaporation loss of the subject Special precautionary measures need to be

taken and direct and individual physiological surveillance of the workers is

particularly necessary

The thermal work limit (TWL) was developed in Australia initially in the underground

mining industry by Brake and Bates (2002a) and later trialled in open cut mines in the

Pilbara region of Western Australia (Miller and Bates 2007a) TWL is defined as the

limiting (or maximum) sustainable metabolic rate that hydrated acclimatised individuals

can maintain in a specific thermal environment within a safe deep body core temperature

(lt382degC) and sweat rate (lt12 kghr) (Tillman 2007)

Due to this complexity these calculations are carried out with the use of computer

software or in the case of TWL pre-programmed monitoring equipment

14

If the exposure does not exceed the criteria for the detailed analysis then the lsquoNorsquo branch

can be taken Because the criteria in the risk assessment have been exceeded

monitoring general heat stress controls are appropriate General controls include training

for workers and supervisors and heat stress hygiene practices If the exposure exceeds

the suggested limits from the detailed analysis or set by the appropriate authority the

lsquoYesrsquo branch leads to the iterative assessment of job-specific control options using the

detailed analysis and then implementation and assessment of control(s) If these are not

available or it cannot be demonstrated that they are successful then the lsquoNorsquo branch

leads to physiological monitoring as the only alternative to demonstrate that adequate

protection is provided

Section 4 Level 3 assessment of heat strain

There are circumstances where the assessment using the rational indices cannot assure

the safety of the exposed workgroup In these cases the use of individual physiological

monitoring may be required These may include situations of high heat stress risk or

where the individualrsquos working environment cannot be accurately assessed A common

example is work involving the use of encapsulating ldquohazmatrdquo suits

The risk and severity of excessive heat strain will vary widely among people even under

identical heat stress conditions By monitoring the physiological responses to working in a

hot environment this allows the workers to use the feedback to assess the level of heat

strain present in the workforce to guide the design of exposure controls and to assess the

effectiveness of implemented controls Instrumentation is available for personal heat

stress monitoring These instruments do not measure the environmental conditions

leading to heat stress but rather they monitor the physiological indicators of heat strain -

usually elevated body temperature andor heart rate Modern instruments utilise an

ingestible core temperature capsule which transmits physiological parameters

telemetrically to an external data logging sensor or laptop computer This information can

then be monitored in real time or assessed post task by a qualified professional

Monitoring the signs and symptoms of heat-stressed workers is sound occupational

hygiene practice especially when clothing may significantly reduce heat loss For

surveillance purposes a pattern of workers exceeding the limits below is considered

indicative of the need to control the exposures On an individual basis these limits are

believed to represent a time to cease an exposure until recovery is complete

Table 2 provides guidance for acceptable limits of heat strain Such physiological

monitoring (see ISO 12894 2001) should be conducted by a physician nurse or

equivalent as allowed by local law

15

Table 2 Physiological Guidelines for Limiting Heat Strain The American Conference of Industrial Hygienists (ACGIH 2013) has published

physiological limits for a number of years and states that exposure to

environmentally or activity-induced heat stress must be discontinued at any time

when

bull Sustained (several minutes) heart rate in excess of 180 beats per minute

minus the individuals age in years (eg180 ndash age) for individuals with

assessed normal cardiac performance OR

bull Body core temperature greater than 385degC (1013degC) for medically

selected and acclimatised personnel or greater than 38degC (1004degC) in

unselected unacclimatised workers OR

bull When there are complaints of sudden and severe fatigue nausea

dizziness or light-headedness OR

bull A workers recovery heart rate at one minute after a peak work effort is

greater than 120 beats per minute 124 bpm was suggested by Fuller and

Smith (1982) OR

bull A worker experiences profuse and prolonged sweating over hours and

may not be able to adequately replenish fluids OR

bull Greater than 15 weight loss over a shift OR

bull In conditions of regular daily exposure to the stress 24-hour urinary

sodium excretion is less than 50 mmoles

ISO 9886 (2004) suggests that exposure to environmentally or activity-induced heat

stress must also be discontinued at any time when

bull lsquoHeart Rate Limit = 185 - 065Arsquo where A = Age in years

bull Individual variability can range up to 20 bpm from this average so this

level could present a risk for some individuals Where there is

uncertainty the sustained heart rate over a work period should not

exceed the previously mentioned

bull HRL sustained = 180 ndash age

bull No matter which limiting values are used interpretation requires

discussion with the workers affected and may require the services of a

specialist such as an occupational hygienist or occupational physician

If a worker appears to be disoriented or confused or demonstrates uncharacteristic

16

irritability discomfort or flu-like symptoms the worker should be removed for rest

under observation in a cool location Symptoms of heat stroke need to be monitored

closely and if sweating stops and the skin becomes hot and dry immediate

emergency care is essential

The prompt treatment of other heat-related disorders generally results in full

recovery but medical advice should be sought for treatment and return-to-work

protocols

Following good occupational hygiene sampling practice which considers likely extremes

and the less tolerant workers the absence of any of these limiting observations indicates

acceptable management of the heat stress exposures With acceptable levels of heat

strain the lsquoNorsquo branch in the level 3 section of Figure 1 is taken Nevertheless even if the

heat strain among workers is considered acceptable at the time the general controls are

necessary In addition periodic physiological monitoring should be continued to ensure

that acceptable levels of heat strain are being maintained

If excessive heat strain is found during the physiological assessments then the lsquoYesrsquo

branch is taken This means that the work activities must cease until suitable job-specific

controls can be considered and implemented to a sufficient extent to control that strain

The job-specific controls may include engineering controls administrative controls and

personal protection

After implementation of the job-specific controls it is necessary to assess their

effectiveness and to adjust them as needed

Section 5 Occupational Exposure Limits

Currently there are fewer workplaces where formal exposure limits for heat stress still

apply however this practice is found mainly within the mining industry There are many

variables associated with the onset of heat stress and these can be a result of the task

environment andor the individual Trying to set a general limit which adequately covers

the many variations within industry has proven to be extremely complicated The attempts

have sometimes resulted in an exposure standard so conservative in a particular

environment that it would become impractical to apply It is important to note that heat

stress indices are not safeunsafe limits and should only be used as guides

Use of Urinary Specific Gravity testing

Water intake at onersquos own discretion results in incomplete fluid replacement for individuals

working in the heat and there is consistent evidence that relying solely on thirst as an

17

indicator of fluid requirement will not restore water balance (Sawka 1998) Urine specific

gravity (USG) can be used as a guide in relation to the level of hydration of an individual

(Shirreffs 2003) and this method of monitoring is becoming increasingly popular in

Australia as a physiological limit Specific gravity (SG) is defined as the ratio weight of a

substance compared to the weight of an equal volume of distilled water hence the SG of

distilled water is 1000 Studies (Sawka et al 2007 Ganio et al 2007 Cheuvront amp

Sawka 2005 Casa et al 2000) recommend that a USG of greater than 1020 would

reflect dehydration While not regarded as fool proof or the ldquogold standardrdquo for total body

water (Armstrong 2007) it is a good compromise between accuracy simplicity of testing

in the field and acceptability to workers of a physiological measure Table 3 shows the

relationship between SG of urine and hydration

Table 3 US National Athletic Trainers Association index of hydration status Body Weight

Loss ()

Urine Specific

Gravity

Well Hydrated lt1 1010

Minimal dehydration 1 - 3 1010 ndash 1020

Significant

dehydration

3 - 5 1021 ndash 1030

Severe dehydration gt 5 gt 1030 Source adapted from Casa et al 2000

Section 6 Heat stress management and controls

The requirement to initiate a heat stress management program is marked by

(1) heat stress levels that exceed the criteria in the Basic Thermal Risk Assessment or

level 2 heat index assessment or

(2) work in clothing ensembles that are air or water vapour impermeable

There are numerous controls across the hierarchy of controls that may be utilised to

address heat stress issues in the workplace Not all may be applicable to a particular task

or scenario and often may require some adjusting before a suitable combination is

achieved

In addition to general controls appropriate job-specific controls are often required to

provide adequate protection During the consideration of job-specific controls detailed

analysis provides a framework to appreciate the interactions among acclimatisation stage

metabolic rate workrest cycles and clothing Table 4 lists some examples of controls

available The list is by no means exhaustive but will provide some ideas for controls

18

Table 4 Examples of control methods

Eliminationsubstitution

bull Hot tasks should be scheduled to avoid the hottest part of the day or where

practical undertaken during night shifts

bull Walls and roof structures should utilize light coloured or reflective materials

bull Structures should be designed to incorporate good air flow This can be done via

the positioning of windows shutters and roof design to encourage lsquochimney

effectsrsquo This will help remove the heat from the structure

bull Walls and roofs should be insulated

Engineering

bull Pipework and vessels associated with hot processes should be insulated and clad

to minimize the introduction of heat into the work environment

bull In high humidity areas such as northern Australia more air needs to be moved

hence fans to increase air flow or in extreme cases cooled air from lsquochillerrsquo units

can be used

bull Where radiated heat from a process is a problem insulating barriers or reflective

barriers can be used to absorb or re-direct radiant heat These may be permanent

structures or movable screens

bull Relocating hot processes away from high access areas

bull Dehumidifying air to increase the evaporative cooling effect Often steam leaks

open process vessels or standing water can artificially increase humidity within a

building

bull Utilize mechanical aids that can reduce the metabolic workload on the individual

Administrative

bull Ready access to cool palatable drinking water is a basic necessity

bull Where applicable suitable electrolyte replacements should also be available

bull A clean cool area for employees to rest and recuperate can add significant

improvement to the cooling process Resting in the work environment can provide

some relief for the worker the level of recovery is much quicker and more efficient

in an air-conditioned environment These need not be elaborate structures basic

inexpensive portable enclosed structures with an air conditioner water supply and

seating have been found to be successful in a variety of environments For field

19

teams with high mobility even a simple shade structure readily available from

hardware stores or large umbrellas can provide relief from solar radiation

bull Where work-rest regimes are necessary heat stress indices such as WBGT PHS

or TWL assist in determining duration of work and rest periods

bull Training workers to identify symptoms and the potential onset of heat-related

illness as part of the lsquobuddy systemrsquo

bull Encouraging ldquoself-determinationrdquo or pacing of the work to meet the conditions and

reporting of heat related symptoms

bull Consider pre-placement medical screening for work in hot areas (ISO 12894)

Personal protective equipment

bull PPE such as cooling vests with either lsquophase changersquo cooling inserts (not ice) Ice

or chilled water cooled garments can result in contraction of the blood vessels

reducing the cooling effect of the garment

bull Vortex tube air cooling may be used in some situations particularly when a cooling

source is required when supplied air respirators are used

bull Choose light coloured materials for clothing and ensure they allow good air flow

across the skin to promote evaporative cooling

Heat stress hygiene practices are particularly important because they reduce the risk that

an individual may suffer a heat-related disorder The key elements are fluid replacement

self-assessment health status monitoring maintenance of a healthy life-style and

adjustment of work expectations based on acclimatisation state and ambient working

conditions The hygiene practices require the full cooperation of supervision and workers

20

Bibliography ACGIH (American Conference of Governmental Industrial Hygienists) (2013) Threshold

Limit Values for Chemical Substances and Physical Agents and Biological Exposure

Indices Cincinnati ACGIH Signature Publications

Armstrong LE (2007) Assessing hydration status The elusive gold standard Journal of

the American College of Nutrition 26(5) pp 575S-584S

Brake DJ amp Bates GP (2002) Limiting metabolic rate (thermal work limit) as an index of

thermal stress Applied Occupational and Environmental Hygiene 17 pp 176ndash86

Casa DJ Armstrong LE Hillman SK Montain SJ Reiff RV amp Rich BSE (2000)

National Athletic Trainers association Position Statement Fluid replacement for Athletes

Journal of Athletic Training 35(2) pp 212-224

Di Corleto R Coles G amp Firth I (2003) The development of a heat stress standard for

Australian conditions in Australian Institute of Occupational Hygienists Inc 20th Annual

Conference Proceedings Geelong Victoria December AIOH

Di Corleto R Firth I Mate J Coles G (2013) A Guide to Managing Heat Stress and

Documentation Developed For Use in the Australian Environment AIOH Melbourne

Ganio MS Casa DJ Armstrong LE amp Maresh CM (2007) Evidence based approach to

lingering hydration questions Clinics in Sports Medicine 26(1) pp 1ndash16

ISO 7243 (1989) Hot environments - Estimation of the heat stress on working man

based on the WBGT - index (wet bulb globe temperature)

ISO 7933 (2004) Ergonomics of the thermal environment Analytical determination and

interpretation of heat stress using calculation of the Predicted Heat Strain ISO 7933

ISO 8996 (2004) Ergonomics of the Thermal Environment ndash Determination of Metabolic

Rate Geneva ISO

ISO 9886 (1992) Evaluation of thermal strain by physiological measurements

ISO 12894 (2001) Ergonomics of the thermal environment ndash Medical supervision of

individuals exposed to extreme hot or cold environments

Miller V Bates G (2007) Hydration of outdoor workers in north-west Australia J

Occup Health Safety mdash Aust NZ 23(1) pp 79ndash87

21

Sawka MN (1998) Body fluid responses and hypohydration during exercise heat

stress in KB Pandolf MN Sawkaand amp RR Gonzalez (Eds) Human Performance

Physiology and Environmental Medicine at Terrestrial Extremes USA Brown amp

Benchmark pp 227 ndash 266

Shirreffs SM (2003) Markers of hydration status European Journal of Clinical Nutrition

57(2) pp s6-s9

Steadman RG (1979) The assessment of sultriness Part 1 A temperature humidity

index based on human physiology and clothing science Journal of applied meteorology

(July)

Tillman C (2007) (Ed) Principles of Occupational Health amp Hygiene - An Introduction

Allen amp Unwin Academic

22

Appendix 1 - Basic Thermal Risk Assessment using Apparent Temperature (Informative example only)

HAZARD TYPE Assessment Point Value 0 1 2 3 Sun Exposure Indoors Full Shade Part Shade No Shade Hot surfaces Neutral Warm on Contact Hot on contact Burn on contact Exposure period lt 30 min 30 min ndash 1hour 1 hour - 2 hours gt 2 hrs Confined space No Yes Task complexity Simple Moderate Complex Climbing updown stairs or ladders None One level Two levels gt Two levels Distance from cool rest area lt10 Metres 10 - 50 Metres 50-100 Metres gt100 Metres Distance from drinking water lt10 Metres 10 - 30 Metres 30-50 Metres gt50 Metres Clothing (permeable) Single layer (light) Single layer (mod) Multiple layer Understanding of heat strain risk Training given No training given Air movement Strong Wind Moderate Wind Light Wind No Wind Resp protection (-ve pressure) None Disposable Half Face Rubber Half Face Full Face Acclimatisation Acclimatised Unacclimatised

SUB-TOTAL A 2 4 6 Metabolic work rate Light Moderate Heavy SUB-TOTAL B 1 2 3 4 Apparent Temperature lt 27degC gt27degC le 33degC gt33degC le 41degC gt 41degC SUB-TOTAL C

TOTAL = A plus B Multiplied by C = Examples of Work Rate Light work Sitting or standing to control machines hand and arm work assembly or sorting of light materials Moderate work Sustained hand and arm work such as hammering handling of moderately heavy materials Heavy work Pick and shovel work continuous axe work carrying loads up stairs Instructions for use of the Basic Thermal Risk Assessment

bull Mark each box according to the appropriate conditions bull When complete add up using the value at the top of the appropriate column for each mark bull Add the sub totals of Table A amp Table B and multiply with the sub-total of Table C for the final result bull If the total is less than 28 then the risk due to thermal conditions are low to moderate bull If the total is 28 to 60 there is a potential of heat-induced illnesses occurring if the conditions are not

addressed Further analysis of heat stress risk is required bull If the total exceeds 60 then the onset of a heat-induced illness is very likely and action should be taken as

soon as possible to implement controls It is important to note that that this assessment is to be used as a guide only A number of factors are not included in this assessment such as employee health condition and the use of high levels of PPE (particularly impermeable suits) In these circumstances experienced personnel should carry out a more extensive assessment

23

Worked Example of Basic Thermal Risk Assessment An example of the application of the basic thermal risk assessment would be as follows A fitter is working on a pump out in the plant at ground level that has been taken out of service the previous day The task involves removing bolts and a casing to check the impellers for wear approximately 2 hours of work The pump is situated approximately 25 metres from the workshop The fitter is acclimatised has attended a training session and is wearing a standard single layer long shirt and trousers is carrying a water bottle and a respirator is not required The work rate is light there is a light breeze and the air temperature has been measured at 30degC and the relative humidity at 70 This equates to an apparent temperature of 35degC (see Table 5 in appendix 2) Using the above information in the risk assessment we have

HAZARD TYPE Assessment Point Value

0 1 2 3 Sun Exposure Indoors Shade Part Shade No Shade Hot surfaces Neutral Warm on Contact Hot on contact Burn on contact Exposure period lt 30 min 30 min ndash 1hour 1 hour - 2 hours gt 2 hrs Confined space No Yes Task complexity Simple Moderate Complex Climbing updown stairs or ladders None One level Two levels gt Two levels Distance from cool rest area lt10 Metres lt50 Metres 50-100 Metres gt100 Metres Distance from drinking water lt10 Metres lt30 Metres 30-50 Metres gt50 Metres Clothing (permeable) Single layer (light) Single layer (mod) Multiple layer Understanding of heat strain risk Training given No training given Air movement Strong Wind Moderate Wind Light Wind No Wind Resp protection (-ve pressure) None Disposable Half Face Rubber Half Face Full Face Acclimatisation Acclimatised Unacclimatised

3 6 0 SUB-TOTAL A 9 2 4 6 Metabolic work rate Light Moderate Heavy SUB-TOTAL B 2 1 2 3 4 Apparent Temperature lt 27degC gt27degC le 33degC gt33degC le 41degC gt 41degC SUB-TOTAL C 3

A = 9 B = 2 C = 3 therefore Total = (9+2) x 3 = 33 As the total lies between 28 and 60 there is a potential for heat induced illness occurring if the conditions are not addressed and further analysis of heat stress risk is required

24

Appendix 2 ndash Table 5 Apparent Temperature Dry BulbHumidity scale Align dry bulb temperature with corresponding relative humidity to determine apparent temperature in unshaded section of table Numbers in () refer to skin humidities above 90 and are only approximate

Dry Bulb Temperature Relative Humidity () (degC) 0 10 20 30 40 50 60 70 80 90 100 20 16 17 17 18 19 19 20 20 21 21 21 21 18 18 19 19 20 20 21 21 22 22 23 22 19 19 20 20 21 21 22 22 23 23 24 23 20 20 21 22 22 23 23 24 24 24 25 24 21 22 22 23 23 24 24 25 25 26 26 25 22 23 24 24 24 25 25 26 27 27 28 26 24 24 25 25 26 26 27 27 28 29 30 27 25 25 26 26 27 27 28 29 30 31 33 28 26 26 27 27 28 29 29 31 32 34 (36) 29 26 27 27 28 29 30 30 33 35 37 (40) 30 27 28 28 29 30 31 33 35 37 (40) (45) 31 28 29 29 30 31 33 35 37 40 (45) 32 29 29 30 31 33 35 37 40 44 (51) 33 29 30 31 33 34 36 39 43 (49)

34 30 31 32 34 36 38 42 (47)

35 31 32 33 35 37 40 (45) (51)

36 32 33 35 37 39 43 (49)

37 32 34 36 38 41 46

38 33 35 37 40 44 (49)

39 34 36 38 41 46

40 35 37 40 43 49

41 35 38 41 45

42 36 39 42 47

43 37 40 44 49

44 38 41 45 52

45 38 42 47

46 39 43 49

47 40 44 51

48 41 45 53

49 42 47

50 42 48

(Source Steadman 1979)

25

Documentation of the Heat Stress Guide Developed for Use in the Australian Environment

Developed for the Australian Institute of Occupational Hygienists

Ross Di Corleto Ian Firth amp Joseph Mateacute

November 2013

26

10 Introduction Heat-related illness has been a health hazard throughout the ages and is a function

of the imposition of environmental heat on the human body which itself generates

heat

11 Heat Illness ndash A Problem Throughout the Ages

The hot thermal environment has been a constant challenge to man for centuries and

its impact is referenced throughout history The bible tells of the death of Judithrsquos

husband Manasseh from exposure in the fields supervising workers where it says

ldquoHe had suffered a sunstroke while in the fields supervising the farm workers and

later died in bed at home in Bethuliardquo (Judith 83)

The impact of heat on the military in history is also well recorded the problems

confronted by the armies of King Sennacherib of Assyria (720BC) whilst attacking

Lashish Herodotus (400BC) reports of Spartan soldiers succumbing to ldquothirst and

sunrdquo Even Alexander the Great in 332BC was warned of the risks of a march across

the Libyan Desert And there is little doubt that heat stress played a major role in the

defeat of the Crusaders of King Edward in the Holy Land fighting the Saracens whilst

burdened down with heavy armour in the Middle Eastern heat (Goldman 2001)

It is not only the workers and armies that are impacted but also the general

population One of the worst cases occurred in Peking China in 1743 when during a

10 day heat wave 11000 people were reported to have perished (Levick 1859)

In 1774 Sir Charles Blagden of the Royal Society outlined a series of experiments

undertaken in a heated room in which he commented on ldquothe wonderful power with

which the animal body is endued of resisting heat vastly greater than its own

temperaturerdquo (Blagden 1775)

Despite this experience and knowledge over the ages we are still seeing deaths in

the 20th century as a result of heat stress Severe heat related illnesses and deaths

are not uncommon among pilgrims making the Makkah Hajj (Khogali 1987) and

closer to home a fatality in the Australian military (ABC 2004) and more recently

amongst the Australian workforce (Australian Mining 2013)

27

12 Heat and the Human Body

The human body in a state of wellbeing maintains its internal temperature within a

very narrow range This is a fundamental requirement for those internal chemical

reactions which are essential to life to proceed at the proper rates The actual level

of this temperature is a product of the balance between heat exchange with the

external thermal environment and the generation of heat internally by the metabolic

processes associated with life and activity

The temperature of blood circulating through the living and working tissues is

monitored by receptors throughout the body The role of these receptors is to induce

specific responses in functional body systems to ensure that the temperature

remains within the appropriate range

The combined effect of external thermal environment and internal metabolic heat

production constitutes the thermal stress on the body The levels of activity required

in response to the thermal stress by systems such as cardiovascular

thermoregulatory respiratory renal and endocrine constitute the thermal strain

Thus environmental conditions metabolic workload and clothing individually or

collectively create heat stress for the worker The bodyrsquos physiological response to

stressors for example sweating increased heart rate and elevated core

temperature is the heat strain

Such physiological changes are the initial responses to thermal stress but the extent

at which these responses are required will determine whether that strain will result in

thermal injuryillness It is important to appreciate that while preventing such illness

by satisfactorily regulating human body temperature in a heat-stress situation those

responses particularly the sweat response may not be compatible with comfort

(Gagge et al 1941)

The rate of heat generated by metabolic processes is dependent on the level of

physical activity To precisely quantify the metabolic cost associated with a particular

task without directly or indirectly measuring the individual is not possible This is due

to the individual differences associated with performing the task at hand As a

result broad categories of metabolic loads for typical work activities have been

established (Durnin amp Passmore 1967 ISO 8996 2004) It is sometimes practicable

Safe Work Australia (2011) refers to heat related illnesses and OSHA (httpswwwoshagovSLTCheatstress) considers heat exhaustion and heat stroke cases to be heat-related illness due to the number of human factors that contribute to a workers susceptibility to heat stress (refer to Section 40) while ACGIH (2013) refers to heat stress and heat strain cases as being heat-related disorders They are not usually considered injuries

28

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 amp Joseph Mateacute

November 2013

November 2013

2

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 ndash Apparent Temperature 23

Appendix 2 ndash Table 5 Apparent Temperature Dry BulbHumidity scale 25

3

DOCUMENTATION OF THE HEAT STRESS GUIDE DEVELOPED FOR USE IN THE AUSTRALIAN ENVIRONMENT 26

10 INTRODUCTION 27

11 Heat Illness ndash A Problem Throughout the Ages 27

12 Heat and the Human Body 28

20 HEAT RELATED ILLNESSES 29

21 Acute Illnesses 30 211 Heat Stroke 30 212 Heat Exhaustion 31 213 Heat Syncope (Fainting) 31 214 Heat Cramps 32 215 Prickly Heat (Heat Rash) 32

22 Chronic Illness 32

23 Related Hazards 33

30 CONTACT INJURIES 34

40 KEY PHYSIOLOGICAL FACTORS CONTRIBUTING TO HEAT ILLNESS 36

41 Fluid Intake 36

42 Urine Specific Gravity 43

43 Heat Acclimatisation 45

44 Physical Fitness 47

45 Other Considerations in Reducing Exposure in Heat-Stress Conditions 48

50 ASSESSMENT PROTOCOL 48

60 WORK ENVIRONMENT MONITORING AND ASSESSMENT 50

61 Risk Assessment 50

62 The Three Stage Approach 51 621 Level 1 Assessment A Basic Thermal Risk Assessment 53

63 Stage 2 of Assessment Protocol Use of Rational Indices 54 631 Predicted Heat Strain (PHS) 55 632 Thermal Work Limit (TWL) 58 633 Other Indices 60

70 PHYSIOLOGICAL MONITORING - STAGE 3 OF ASSESSMENT PROTOCOL 62

4

71 Core Temperature 65

72 Heart Rate Measurements 67

80 CONTROLS 70

81 Ventilation 72

82 Radiant Heat 73

83 Administrative Controls 76 831 Training 76 832 Self-Assessment 77 833 Fluid Replacement 77 834 Rescheduling of Work 77 835 WorkRest Regimes 77 836 Clothing 78 837 Pre-placement Health Assessment 80

84 Personal Protective Equipment 81 841 Air Cooling System 81 842 Liquid Circulating Systems 82 843 Ice Cooling Systems 83 844 Reflective Clothing 84

90 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

5

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 ldquoThe heat stress standard

and documentation developed for use in the Australian environment (2003)rdquo 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 ldquoA guide to managing

heat stress developed for use in the Australian environment (2013)rdquo 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

bull the first a brief summary of the approach written for interested parties with a non-

technical background and

bull 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

6

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 ndash 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

7

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

bull air temperature

bull humidity

bull air movement

bull radiant heat exchange and

bull 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 bodyrsquos 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

bull prickly heat

bull headaches

bull nausea

bull 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

8

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 individualrsquos 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

9

Figure 1 Heat Stress Management Schematic (adapted from ACGIH 2013)

Level 1Perform Basic Risk

Assessment

Unacceptable risk

No

Does task involve use of impermeable clothing (ie PVC)

Continue work monitor conditionsNo

Are data available for detailed analysis

Level 2Analyse data with rational heat stress index (ie PHS

TWL)

Yes

Unacceptable heat stress risk based on analysis

Job specific controls practical and successful

Level 3Undertake physiological

monitoring

Cease work

Yes

Yes

No

Monitor task to ensure conditions amp collect dataNo

No

Maintain job specific controlsYes

Excessive heat strain based on monitoring

Yes

No

10

Level 1 Assessment a basic thermal risk assessment A suggested protocol for the level 1 assessment is termed the ldquoBasic Thermal Risk

Assessmentrdquo It has been designed as a simple tool which can be used by employees or

technicians to provide guidance and also as a training tool to illustrate the many factors

that impact on heat stress This risk assessment incorporates the contributions of a

number of factors that can impact on heat stress such as the state of acclimatisation work

demands location clothing and other physiological factors It can also incorporate the use

of a first level heat stress index such as Apparent Temperature or WBGT It is designed to

be an initial qualitative review of a potential heat stress situation for the purposes of

prioritising further measurements and controls It is not intended as a definitive

assessment tool Some of its key aspects are described below

Acclimatisation plays a part as it is a set of gradual physiological adjustments that improve

an individuals ability to tolerate heat stress the development and loss of which is

described in the Documentation

Metabolic work rate is of equal importance to environmental assessment in evaluating heat

stress Table 1 provides broad guidance for selecting the work rate category to be used in

the Risk Assessment There are a number of sources for this data including ISO

72431989 and ISO 89962004 standards

Table 1 Examples of Activities within Metabolic Rate (M) Classes

Class Examples

Resting Resting sitting at ease Low Light

Work Sitting at ease light manual work hand and arm work car driving

standing casual walking sitting or standing to control machines

Moderate

Moderate Work Sustained hand and arm work (eg hammering) arm and trunk

work moving light wheelbarrow walking around 45 kmh

High Heavy

Work

Intense arm and trunk work carrying heavy material shovelling

sawing hard wood moving heavily loaded wheelbarrows carrying

loads upstairs

Source (ISO 89962004)

Apparent temperature (Steadman 1979) can be used as part of the basic thermal risk

assessment The information required air temperature and humidity can be readily

obtained from most local weather bureau websites off-the-shelf weather units or

measured directly with a sling psychrometer Its simplicity is one of the advantages in its

use as it requires very little technical knowledge

11

The WBGT index also offers a useful first-order index of the environmental contribution to

heat stress It is influenced by air temperature radiant heat and humidity (ACGIH 2013)

In its simplest form it does not fully account for all of the interactions between a person

and the environment but is useful in this type of assessment The only disadvantage is

that it requires some specialised monitoring equipment such as a WBGT monitor or wet

bulb and globe thermometers

Both indices are described in more detail in the Documentation associated with this

standard

These environmental parameters are combined on a single check sheet in three sections

Each aspect is allocated a numerical value A task may be assessed by checking off

questions in the table and including some additional data for metabolic work load and

environmental conditions From this information a weighted calculation is used to

determine a numerical value which can be compared to pre-set criteria to provide

guidance as to the potential risk of heat stress and the course of action for controls

For example if the Assessment Point Total is less than 28 then the thermal condition risk

is low The lsquoNorsquo branch in Figure 1 can be taken Nevertheless if there are reports of the

symptoms of heat-related disorders such as prickly heat fatigue nausea dizziness and

light-headedness then the analysis should be reconsidered or proceed to detailed

analysis if appropriate If the Assessment Point Total is 28 or more further analysis is

required An Assessment Point Total greater than 60 indicates the need for immediate

action and implementation of controls (see Section 6)

Examples of a basic thermal risk assessment tool and their application are provided in

Appendix 1

Section 2 Screening for clothing that does not allow air and water vapour movement

The decision about clothing and how it might affect heat loss can also play an important

role in the initial assessment This is of particular importance if the clothing interferes with

the evaporation of sweat from the skin surface of an individual (ie heavy water barrier

clothing such as PVC) As this is the major heat loss mechanism disruption of this

process will significantly impact on the heat stress experienced Most heat exposure

assessment indices were developed for a traditional work uniform which consisted of a

long-sleeved shirt and pants Screening that is based on this attire is not suitable for

clothing ensembles that are more extensive and less permeable unless a detailed analysis

method appropriate for permeable clothing requirements is available With heat removal

hampered by clothing metabolic heat may produce life-threatening heat strain even when

12

ambient conditions are considered cool and the risk assessment determines ldquoLow Riskrdquo If

workers are required to wear additional clothing that does not allow air and water vapour

movement then the lsquoYesrsquo branch in the first question of Figure 1 should be taken

Physiological and behavioural monitoring described in Section 4 should be followed to

assess the potential for harm resulting from heat stress

Section 3 Level 2 assessment using detailed analysis

It is possible that a condition may be above the criteria provided in the initial risk

assessment and still not represent an unacceptable exposure To make this

determination a detailed analysis is required as in the Documentation

Note as discussed briefly above (see Section 2) no numerical screening criteria or limiting

values are applicable where clothing does not allow air or water vapour movement In this

case reliance must be placed on physiological monitoring

The screening criteria require a minimum set of data in order to make an assessment A

detailed analyses requires more data about the exposures including

bull clothing type

bull air speed

bull air temperature

bull water vapour content of the air (eg humidity)

bull posture

bull length of exposure and

bull globe temperature

Following Figure 1 the next question asks about the availability of such exposure data for

a detailed analysis If exposure data are not available the lsquoNorsquo branch takes the

evaluation to the monitoring of the tasks to collect this data before moving on to the use of

a rational heat stress index These types of indices are based on the human heat balance

equation and utilise a number of formulae to predict responses of the body such as

sweating and elevation of core temperature From this information the likelihood of

developing a heat stress related disorder may be determined In situations where this

data cannot be collected or made available then physiological monitoring to assess the

degree of heat strain should be undertaken

Detailed rational analysis should follow ISO 7933 - Predicted Heat Strain or Thermal Work

Limit (TWL) although other indices with extensive supporting physiological documentation

may also be acceptable (see Documentation for details) While such a rational method

(versus the empirically derived WBGT or Basic Effective Temperature (BET) thresholds) is

13

computationally more difficult it permits a better understanding of the source of the heat

stress and can be a means to assess the benefits of proposed control modifications on the

exposure

Predicted heat strain (PHS) is a rational index (ie it is an index based on the heat balance

equation) It estimates the required sweat rate and the maximal evaporation rate utilising

the ratio of the two as an initial measure of lsquorequired wettednessrsquo This required

wettedness is the fraction of the skin surface that would have to be covered by sweat in

order for the required evaporation rate to occur The evaporation rate required to maintain

a heat balance is then calculated (Di Corleto et al 2003)

In the event that the suggested values might be exceeded ISO 7933 calculates an

allowable exposure time

The suggested limiting values assume workers are

bull fit for the activity being considered and

bull in good health and

bull screened for intolerance to heat and

bull properly instructed and

bull able to self-pace their work and

bull under some degree of supervision (minimally a buddy system)

In work situations which

bull either the maximum evaporation rate is negative leading to condensation of

water vapour on the skin

bull or the estimated allowable exposure time is less than 30 minutes so that the

phenomenon of sweating onset plays a major role in the estimation of the

evaporation loss of the subject Special precautionary measures need to be

taken and direct and individual physiological surveillance of the workers is

particularly necessary

The thermal work limit (TWL) was developed in Australia initially in the underground

mining industry by Brake and Bates (2002a) and later trialled in open cut mines in the

Pilbara region of Western Australia (Miller and Bates 2007a) TWL is defined as the

limiting (or maximum) sustainable metabolic rate that hydrated acclimatised individuals

can maintain in a specific thermal environment within a safe deep body core temperature

(lt382degC) and sweat rate (lt12 kghr) (Tillman 2007)

Due to this complexity these calculations are carried out with the use of computer

software or in the case of TWL pre-programmed monitoring equipment

14

If the exposure does not exceed the criteria for the detailed analysis then the lsquoNorsquo branch

can be taken Because the criteria in the risk assessment have been exceeded

monitoring general heat stress controls are appropriate General controls include training

for workers and supervisors and heat stress hygiene practices If the exposure exceeds

the suggested limits from the detailed analysis or set by the appropriate authority the

lsquoYesrsquo branch leads to the iterative assessment of job-specific control options using the

detailed analysis and then implementation and assessment of control(s) If these are not

available or it cannot be demonstrated that they are successful then the lsquoNorsquo branch

leads to physiological monitoring as the only alternative to demonstrate that adequate

protection is provided

Section 4 Level 3 assessment of heat strain

There are circumstances where the assessment using the rational indices cannot assure

the safety of the exposed workgroup In these cases the use of individual physiological

monitoring may be required These may include situations of high heat stress risk or

where the individualrsquos working environment cannot be accurately assessed A common

example is work involving the use of encapsulating ldquohazmatrdquo suits

The risk and severity of excessive heat strain will vary widely among people even under

identical heat stress conditions By monitoring the physiological responses to working in a

hot environment this allows the workers to use the feedback to assess the level of heat

strain present in the workforce to guide the design of exposure controls and to assess the

effectiveness of implemented controls Instrumentation is available for personal heat

stress monitoring These instruments do not measure the environmental conditions

leading to heat stress but rather they monitor the physiological indicators of heat strain -

usually elevated body temperature andor heart rate Modern instruments utilise an

ingestible core temperature capsule which transmits physiological parameters

telemetrically to an external data logging sensor or laptop computer This information can

then be monitored in real time or assessed post task by a qualified professional

Monitoring the signs and symptoms of heat-stressed workers is sound occupational

hygiene practice especially when clothing may significantly reduce heat loss For

surveillance purposes a pattern of workers exceeding the limits below is considered

indicative of the need to control the exposures On an individual basis these limits are

believed to represent a time to cease an exposure until recovery is complete

Table 2 provides guidance for acceptable limits of heat strain Such physiological

monitoring (see ISO 12894 2001) should be conducted by a physician nurse or

equivalent as allowed by local law

15

Table 2 Physiological Guidelines for Limiting Heat Strain The American Conference of Industrial Hygienists (ACGIH 2013) has published

physiological limits for a number of years and states that exposure to

environmentally or activity-induced heat stress must be discontinued at any time

when

bull Sustained (several minutes) heart rate in excess of 180 beats per minute

minus the individuals age in years (eg180 ndash age) for individuals with

assessed normal cardiac performance OR

bull Body core temperature greater than 385degC (1013degC) for medically

selected and acclimatised personnel or greater than 38degC (1004degC) in

unselected unacclimatised workers OR

bull When there are complaints of sudden and severe fatigue nausea

dizziness or light-headedness OR

bull A workers recovery heart rate at one minute after a peak work effort is

greater than 120 beats per minute 124 bpm was suggested by Fuller and

Smith (1982) OR

bull A worker experiences profuse and prolonged sweating over hours and

may not be able to adequately replenish fluids OR

bull Greater than 15 weight loss over a shift OR

bull In conditions of regular daily exposure to the stress 24-hour urinary

sodium excretion is less than 50 mmoles

ISO 9886 (2004) suggests that exposure to environmentally or activity-induced heat

stress must also be discontinued at any time when

bull lsquoHeart Rate Limit = 185 - 065Arsquo where A = Age in years

bull Individual variability can range up to 20 bpm from this average so this

level could present a risk for some individuals Where there is

uncertainty the sustained heart rate over a work period should not

exceed the previously mentioned

bull HRL sustained = 180 ndash age

bull No matter which limiting values are used interpretation requires

discussion with the workers affected and may require the services of a

specialist such as an occupational hygienist or occupational physician

If a worker appears to be disoriented or confused or demonstrates uncharacteristic

16

irritability discomfort or flu-like symptoms the worker should be removed for rest

under observation in a cool location Symptoms of heat stroke need to be monitored

closely and if sweating stops and the skin becomes hot and dry immediate

emergency care is essential

The prompt treatment of other heat-related disorders generally results in full

recovery but medical advice should be sought for treatment and return-to-work

protocols

Following good occupational hygiene sampling practice which considers likely extremes

and the less tolerant workers the absence of any of these limiting observations indicates

acceptable management of the heat stress exposures With acceptable levels of heat

strain the lsquoNorsquo branch in the level 3 section of Figure 1 is taken Nevertheless even if the

heat strain among workers is considered acceptable at the time the general controls are

necessary In addition periodic physiological monitoring should be continued to ensure

that acceptable levels of heat strain are being maintained

If excessive heat strain is found during the physiological assessments then the lsquoYesrsquo

branch is taken This means that the work activities must cease until suitable job-specific

controls can be considered and implemented to a sufficient extent to control that strain

The job-specific controls may include engineering controls administrative controls and

personal protection

After implementation of the job-specific controls it is necessary to assess their

effectiveness and to adjust them as needed

Section 5 Occupational Exposure Limits

Currently there are fewer workplaces where formal exposure limits for heat stress still

apply however this practice is found mainly within the mining industry There are many

variables associated with the onset of heat stress and these can be a result of the task

environment andor the individual Trying to set a general limit which adequately covers

the many variations within industry has proven to be extremely complicated The attempts

have sometimes resulted in an exposure standard so conservative in a particular

environment that it would become impractical to apply It is important to note that heat

stress indices are not safeunsafe limits and should only be used as guides

Use of Urinary Specific Gravity testing

Water intake at onersquos own discretion results in incomplete fluid replacement for individuals

working in the heat and there is consistent evidence that relying solely on thirst as an

17

indicator of fluid requirement will not restore water balance (Sawka 1998) Urine specific

gravity (USG) can be used as a guide in relation to the level of hydration of an individual

(Shirreffs 2003) and this method of monitoring is becoming increasingly popular in

Australia as a physiological limit Specific gravity (SG) is defined as the ratio weight of a

substance compared to the weight of an equal volume of distilled water hence the SG of

distilled water is 1000 Studies (Sawka et al 2007 Ganio et al 2007 Cheuvront amp

Sawka 2005 Casa et al 2000) recommend that a USG of greater than 1020 would

reflect dehydration While not regarded as fool proof or the ldquogold standardrdquo for total body

water (Armstrong 2007) it is a good compromise between accuracy simplicity of testing

in the field and acceptability to workers of a physiological measure Table 3 shows the

relationship between SG of urine and hydration

Table 3 US National Athletic Trainers Association index of hydration status Body Weight

Loss ()

Urine Specific

Gravity

Well Hydrated lt1 1010

Minimal dehydration 1 - 3 1010 ndash 1020

Significant

dehydration

3 - 5 1021 ndash 1030

Severe dehydration gt 5 gt 1030 Source adapted from Casa et al 2000

Section 6 Heat stress management and controls

The requirement to initiate a heat stress management program is marked by

(1) heat stress levels that exceed the criteria in the Basic Thermal Risk Assessment or

level 2 heat index assessment or

(2) work in clothing ensembles that are air or water vapour impermeable

There are numerous controls across the hierarchy of controls that may be utilised to

address heat stress issues in the workplace Not all may be applicable to a particular task

or scenario and often may require some adjusting before a suitable combination is

achieved

In addition to general controls appropriate job-specific controls are often required to

provide adequate protection During the consideration of job-specific controls detailed

analysis provides a framework to appreciate the interactions among acclimatisation stage

metabolic rate workrest cycles and clothing Table 4 lists some examples of controls

available The list is by no means exhaustive but will provide some ideas for controls

18

Table 4 Examples of control methods

Eliminationsubstitution

bull Hot tasks should be scheduled to avoid the hottest part of the day or where

practical undertaken during night shifts

bull Walls and roof structures should utilize light coloured or reflective materials

bull Structures should be designed to incorporate good air flow This can be done via

the positioning of windows shutters and roof design to encourage lsquochimney

effectsrsquo This will help remove the heat from the structure

bull Walls and roofs should be insulated

Engineering

bull Pipework and vessels associated with hot processes should be insulated and clad

to minimize the introduction of heat into the work environment

bull In high humidity areas such as northern Australia more air needs to be moved

hence fans to increase air flow or in extreme cases cooled air from lsquochillerrsquo units

can be used

bull Where radiated heat from a process is a problem insulating barriers or reflective

barriers can be used to absorb or re-direct radiant heat These may be permanent

structures or movable screens

bull Relocating hot processes away from high access areas

bull Dehumidifying air to increase the evaporative cooling effect Often steam leaks

open process vessels or standing water can artificially increase humidity within a

building

bull Utilize mechanical aids that can reduce the metabolic workload on the individual

Administrative

bull Ready access to cool palatable drinking water is a basic necessity

bull Where applicable suitable electrolyte replacements should also be available

bull A clean cool area for employees to rest and recuperate can add significant

improvement to the cooling process Resting in the work environment can provide

some relief for the worker the level of recovery is much quicker and more efficient

in an air-conditioned environment These need not be elaborate structures basic

inexpensive portable enclosed structures with an air conditioner water supply and

seating have been found to be successful in a variety of environments For field

19

teams with high mobility even a simple shade structure readily available from

hardware stores or large umbrellas can provide relief from solar radiation

bull Where work-rest regimes are necessary heat stress indices such as WBGT PHS

or TWL assist in determining duration of work and rest periods

bull Training workers to identify symptoms and the potential onset of heat-related

illness as part of the lsquobuddy systemrsquo

bull Encouraging ldquoself-determinationrdquo or pacing of the work to meet the conditions and

reporting of heat related symptoms

bull Consider pre-placement medical screening for work in hot areas (ISO 12894)

Personal protective equipment

bull PPE such as cooling vests with either lsquophase changersquo cooling inserts (not ice) Ice

or chilled water cooled garments can result in contraction of the blood vessels

reducing the cooling effect of the garment

bull Vortex tube air cooling may be used in some situations particularly when a cooling

source is required when supplied air respirators are used

bull Choose light coloured materials for clothing and ensure they allow good air flow

across the skin to promote evaporative cooling

Heat stress hygiene practices are particularly important because they reduce the risk that

an individual may suffer a heat-related disorder The key elements are fluid replacement

self-assessment health status monitoring maintenance of a healthy life-style and

adjustment of work expectations based on acclimatisation state and ambient working

conditions The hygiene practices require the full cooperation of supervision and workers

20

Bibliography ACGIH (American Conference of Governmental Industrial Hygienists) (2013) Threshold

Limit Values for Chemical Substances and Physical Agents and Biological Exposure

Indices Cincinnati ACGIH Signature Publications

Armstrong LE (2007) Assessing hydration status The elusive gold standard Journal of

the American College of Nutrition 26(5) pp 575S-584S

Brake DJ amp Bates GP (2002) Limiting metabolic rate (thermal work limit) as an index of

thermal stress Applied Occupational and Environmental Hygiene 17 pp 176ndash86

Casa DJ Armstrong LE Hillman SK Montain SJ Reiff RV amp Rich BSE (2000)

National Athletic Trainers association Position Statement Fluid replacement for Athletes

Journal of Athletic Training 35(2) pp 212-224

Di Corleto R Coles G amp Firth I (2003) The development of a heat stress standard for

Australian conditions in Australian Institute of Occupational Hygienists Inc 20th Annual

Conference Proceedings Geelong Victoria December AIOH

Di Corleto R Firth I Mate J Coles G (2013) A Guide to Managing Heat Stress and

Documentation Developed For Use in the Australian Environment AIOH Melbourne

Ganio MS Casa DJ Armstrong LE amp Maresh CM (2007) Evidence based approach to

lingering hydration questions Clinics in Sports Medicine 26(1) pp 1ndash16

ISO 7243 (1989) Hot environments - Estimation of the heat stress on working man

based on the WBGT - index (wet bulb globe temperature)

ISO 7933 (2004) Ergonomics of the thermal environment Analytical determination and

interpretation of heat stress using calculation of the Predicted Heat Strain ISO 7933

ISO 8996 (2004) Ergonomics of the Thermal Environment ndash Determination of Metabolic

Rate Geneva ISO

ISO 9886 (1992) Evaluation of thermal strain by physiological measurements

ISO 12894 (2001) Ergonomics of the thermal environment ndash Medical supervision of

individuals exposed to extreme hot or cold environments

Miller V Bates G (2007) Hydration of outdoor workers in north-west Australia J

Occup Health Safety mdash Aust NZ 23(1) pp 79ndash87

21

Sawka MN (1998) Body fluid responses and hypohydration during exercise heat

stress in KB Pandolf MN Sawkaand amp RR Gonzalez (Eds) Human Performance

Physiology and Environmental Medicine at Terrestrial Extremes USA Brown amp

Benchmark pp 227 ndash 266

Shirreffs SM (2003) Markers of hydration status European Journal of Clinical Nutrition

57(2) pp s6-s9

Steadman RG (1979) The assessment of sultriness Part 1 A temperature humidity

index based on human physiology and clothing science Journal of applied meteorology

(July)

Tillman C (2007) (Ed) Principles of Occupational Health amp Hygiene - An Introduction

Allen amp Unwin Academic

22

Appendix 1 - Basic Thermal Risk Assessment using Apparent Temperature (Informative example only)

HAZARD TYPE Assessment Point Value 0 1 2 3 Sun Exposure Indoors Full Shade Part Shade No Shade Hot surfaces Neutral Warm on Contact Hot on contact Burn on contact Exposure period lt 30 min 30 min ndash 1hour 1 hour - 2 hours gt 2 hrs Confined space No Yes Task complexity Simple Moderate Complex Climbing updown stairs or ladders None One level Two levels gt Two levels Distance from cool rest area lt10 Metres 10 - 50 Metres 50-100 Metres gt100 Metres Distance from drinking water lt10 Metres 10 - 30 Metres 30-50 Metres gt50 Metres Clothing (permeable) Single layer (light) Single layer (mod) Multiple layer Understanding of heat strain risk Training given No training given Air movement Strong Wind Moderate Wind Light Wind No Wind Resp protection (-ve pressure) None Disposable Half Face Rubber Half Face Full Face Acclimatisation Acclimatised Unacclimatised

SUB-TOTAL A 2 4 6 Metabolic work rate Light Moderate Heavy SUB-TOTAL B 1 2 3 4 Apparent Temperature lt 27degC gt27degC le 33degC gt33degC le 41degC gt 41degC SUB-TOTAL C

TOTAL = A plus B Multiplied by C = Examples of Work Rate Light work Sitting or standing to control machines hand and arm work assembly or sorting of light materials Moderate work Sustained hand and arm work such as hammering handling of moderately heavy materials Heavy work Pick and shovel work continuous axe work carrying loads up stairs Instructions for use of the Basic Thermal Risk Assessment

bull Mark each box according to the appropriate conditions bull When complete add up using the value at the top of the appropriate column for each mark bull Add the sub totals of Table A amp Table B and multiply with the sub-total of Table C for the final result bull If the total is less than 28 then the risk due to thermal conditions are low to moderate bull If the total is 28 to 60 there is a potential of heat-induced illnesses occurring if the conditions are not

addressed Further analysis of heat stress risk is required bull If the total exceeds 60 then the onset of a heat-induced illness is very likely and action should be taken as

soon as possible to implement controls It is important to note that that this assessment is to be used as a guide only A number of factors are not included in this assessment such as employee health condition and the use of high levels of PPE (particularly impermeable suits) In these circumstances experienced personnel should carry out a more extensive assessment

23

Worked Example of Basic Thermal Risk Assessment An example of the application of the basic thermal risk assessment would be as follows A fitter is working on a pump out in the plant at ground level that has been taken out of service the previous day The task involves removing bolts and a casing to check the impellers for wear approximately 2 hours of work The pump is situated approximately 25 metres from the workshop The fitter is acclimatised has attended a training session and is wearing a standard single layer long shirt and trousers is carrying a water bottle and a respirator is not required The work rate is light there is a light breeze and the air temperature has been measured at 30degC and the relative humidity at 70 This equates to an apparent temperature of 35degC (see Table 5 in appendix 2) Using the above information in the risk assessment we have

HAZARD TYPE Assessment Point Value

0 1 2 3 Sun Exposure Indoors Shade Part Shade No Shade Hot surfaces Neutral Warm on Contact Hot on contact Burn on contact Exposure period lt 30 min 30 min ndash 1hour 1 hour - 2 hours gt 2 hrs Confined space No Yes Task complexity Simple Moderate Complex Climbing updown stairs or ladders None One level Two levels gt Two levels Distance from cool rest area lt10 Metres lt50 Metres 50-100 Metres gt100 Metres Distance from drinking water lt10 Metres lt30 Metres 30-50 Metres gt50 Metres Clothing (permeable) Single layer (light) Single layer (mod) Multiple layer Understanding of heat strain risk Training given No training given Air movement Strong Wind Moderate Wind Light Wind No Wind Resp protection (-ve pressure) None Disposable Half Face Rubber Half Face Full Face Acclimatisation Acclimatised Unacclimatised

3 6 0 SUB-TOTAL A 9 2 4 6 Metabolic work rate Light Moderate Heavy SUB-TOTAL B 2 1 2 3 4 Apparent Temperature lt 27degC gt27degC le 33degC gt33degC le 41degC gt 41degC SUB-TOTAL C 3

A = 9 B = 2 C = 3 therefore Total = (9+2) x 3 = 33 As the total lies between 28 and 60 there is a potential for heat induced illness occurring if the conditions are not addressed and further analysis of heat stress risk is required

24

Appendix 2 ndash Table 5 Apparent Temperature Dry BulbHumidity scale Align dry bulb temperature with corresponding relative humidity to determine apparent temperature in unshaded section of table Numbers in () refer to skin humidities above 90 and are only approximate

Dry Bulb Temperature Relative Humidity () (degC) 0 10 20 30 40 50 60 70 80 90 100 20 16 17 17 18 19 19 20 20 21 21 21 21 18 18 19 19 20 20 21 21 22 22 23 22 19 19 20 20 21 21 22 22 23 23 24 23 20 20 21 22 22 23 23 24 24 24 25 24 21 22 22 23 23 24 24 25 25 26 26 25 22 23 24 24 24 25 25 26 27 27 28 26 24 24 25 25 26 26 27 27 28 29 30 27 25 25 26 26 27 27 28 29 30 31 33 28 26 26 27 27 28 29 29 31 32 34 (36) 29 26 27 27 28 29 30 30 33 35 37 (40) 30 27 28 28 29 30 31 33 35 37 (40) (45) 31 28 29 29 30 31 33 35 37 40 (45) 32 29 29 30 31 33 35 37 40 44 (51) 33 29 30 31 33 34 36 39 43 (49)

34 30 31 32 34 36 38 42 (47)

35 31 32 33 35 37 40 (45) (51)

36 32 33 35 37 39 43 (49)

37 32 34 36 38 41 46

38 33 35 37 40 44 (49)

39 34 36 38 41 46

40 35 37 40 43 49

41 35 38 41 45

42 36 39 42 47

43 37 40 44 49

44 38 41 45 52

45 38 42 47

46 39 43 49

47 40 44 51

48 41 45 53

49 42 47

50 42 48

(Source Steadman 1979)

25

Documentation of the Heat Stress Guide Developed for Use in the Australian Environment

Developed for the Australian Institute of Occupational Hygienists

Ross Di Corleto Ian Firth amp Joseph Mateacute

November 2013

26

10 Introduction Heat-related illness has been a health hazard throughout the ages and is a function

of the imposition of environmental heat on the human body which itself generates

heat

11 Heat Illness ndash A Problem Throughout the Ages

The hot thermal environment has been a constant challenge to man for centuries and

its impact is referenced throughout history The bible tells of the death of Judithrsquos

husband Manasseh from exposure in the fields supervising workers where it says

ldquoHe had suffered a sunstroke while in the fields supervising the farm workers and

later died in bed at home in Bethuliardquo (Judith 83)

The impact of heat on the military in history is also well recorded the problems

confronted by the armies of King Sennacherib of Assyria (720BC) whilst attacking

Lashish Herodotus (400BC) reports of Spartan soldiers succumbing to ldquothirst and

sunrdquo Even Alexander the Great in 332BC was warned of the risks of a march across

the Libyan Desert And there is little doubt that heat stress played a major role in the

defeat of the Crusaders of King Edward in the Holy Land fighting the Saracens whilst

burdened down with heavy armour in the Middle Eastern heat (Goldman 2001)

It is not only the workers and armies that are impacted but also the general

population One of the worst cases occurred in Peking China in 1743 when during a

10 day heat wave 11000 people were reported to have perished (Levick 1859)

In 1774 Sir Charles Blagden of the Royal Society outlined a series of experiments

undertaken in a heated room in which he commented on ldquothe wonderful power with

which the animal body is endued of resisting heat vastly greater than its own

temperaturerdquo (Blagden 1775)

Despite this experience and knowledge over the ages we are still seeing deaths in

the 20th century as a result of heat stress Severe heat related illnesses and deaths

are not uncommon among pilgrims making the Makkah Hajj (Khogali 1987) and

closer to home a fatality in the Australian military (ABC 2004) and more recently

amongst the Australian workforce (Australian Mining 2013)

27

12 Heat and the Human Body

The human body in a state of wellbeing maintains its internal temperature within a

very narrow range This is a fundamental requirement for those internal chemical

reactions which are essential to life to proceed at the proper rates The actual level

of this temperature is a product of the balance between heat exchange with the

external thermal environment and the generation of heat internally by the metabolic

processes associated with life and activity

The temperature of blood circulating through the living and working tissues is

monitored by receptors throughout the body The role of these receptors is to induce

specific responses in functional body systems to ensure that the temperature

remains within the appropriate range

The combined effect of external thermal environment and internal metabolic heat

production constitutes the thermal stress on the body The levels of activity required

in response to the thermal stress by systems such as cardiovascular

thermoregulatory respiratory renal and endocrine constitute the thermal strain

Thus environmental conditions metabolic workload and clothing individually or

collectively create heat stress for the worker The bodyrsquos physiological response to

stressors for example sweating increased heart rate and elevated core

temperature is the heat strain

Such physiological changes are the initial responses to thermal stress but the extent

at which these responses are required will determine whether that strain will result in

thermal injuryillness It is important to appreciate that while preventing such illness

by satisfactorily regulating human body temperature in a heat-stress situation those

responses particularly the sweat response may not be compatible with comfort

(Gagge et al 1941)

The rate of heat generated by metabolic processes is dependent on the level of

physical activity To precisely quantify the metabolic cost associated with a particular

task without directly or indirectly measuring the individual is not possible This is due

to the individual differences associated with performing the task at hand As a

result broad categories of metabolic loads for typical work activities have been

established (Durnin amp Passmore 1967 ISO 8996 2004) It is sometimes practicable

Safe Work Australia (2011) refers to heat related illnesses and OSHA (httpswwwoshagovSLTCheatstress) considers heat exhaustion and heat stroke cases to be heat-related illness due to the number of human factors that contribute to a workers susceptibility to heat stress (refer to Section 40) while ACGIH (2013) refers to heat stress and heat strain cases as being heat-related disorders They are not usually considered injuries

28

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 ndash Apparent Temperature 23

Appendix 2 ndash Table 5 Apparent Temperature Dry BulbHumidity scale 25

3

DOCUMENTATION OF THE HEAT STRESS GUIDE DEVELOPED FOR USE IN THE AUSTRALIAN ENVIRONMENT 26

10 INTRODUCTION 27

11 Heat Illness ndash A Problem Throughout the Ages 27

12 Heat and the Human Body 28

20 HEAT RELATED ILLNESSES 29

21 Acute Illnesses 30 211 Heat Stroke 30 212 Heat Exhaustion 31 213 Heat Syncope (Fainting) 31 214 Heat Cramps 32 215 Prickly Heat (Heat Rash) 32

22 Chronic Illness 32

23 Related Hazards 33

30 CONTACT INJURIES 34

40 KEY PHYSIOLOGICAL FACTORS CONTRIBUTING TO HEAT ILLNESS 36

41 Fluid Intake 36

42 Urine Specific Gravity 43

43 Heat Acclimatisation 45

44 Physical Fitness 47

45 Other Considerations in Reducing Exposure in Heat-Stress Conditions 48

50 ASSESSMENT PROTOCOL 48

60 WORK ENVIRONMENT MONITORING AND ASSESSMENT 50

61 Risk Assessment 50

62 The Three Stage Approach 51 621 Level 1 Assessment A Basic Thermal Risk Assessment 53

63 Stage 2 of Assessment Protocol Use of Rational Indices 54 631 Predicted Heat Strain (PHS) 55 632 Thermal Work Limit (TWL) 58 633 Other Indices 60

70 PHYSIOLOGICAL MONITORING - STAGE 3 OF ASSESSMENT PROTOCOL 62

4

71 Core Temperature 65

72 Heart Rate Measurements 67

80 CONTROLS 70

81 Ventilation 72

82 Radiant Heat 73

83 Administrative Controls 76 831 Training 76 832 Self-Assessment 77 833 Fluid Replacement 77 834 Rescheduling of Work 77 835 WorkRest Regimes 77 836 Clothing 78 837 Pre-placement Health Assessment 80

84 Personal Protective Equipment 81 841 Air Cooling System 81 842 Liquid Circulating Systems 82 843 Ice Cooling Systems 83 844 Reflective Clothing 84

90 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

5

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 ldquoThe heat stress standard

and documentation developed for use in the Australian environment (2003)rdquo 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 ldquoA guide to managing

heat stress developed for use in the Australian environment (2013)rdquo 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

bull the first a brief summary of the approach written for interested parties with a non-

technical background and

bull 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

6

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 ndash 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

7

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

bull air temperature

bull humidity

bull air movement

bull radiant heat exchange and

bull 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 bodyrsquos 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

bull prickly heat

bull headaches

bull nausea

bull 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

8

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 individualrsquos 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

9

Figure 1 Heat Stress Management Schematic (adapted from ACGIH 2013)

Level 1Perform Basic Risk

Assessment

Unacceptable risk

No

Does task involve use of impermeable clothing (ie PVC)

Continue work monitor conditionsNo

Are data available for detailed analysis

Level 2Analyse data with rational heat stress index (ie PHS

TWL)

Yes

Unacceptable heat stress risk based on analysis

Job specific controls practical and successful

Level 3Undertake physiological

monitoring

Cease work

Yes

Yes

No

Monitor task to ensure conditions amp collect dataNo

No

Maintain job specific controlsYes

Excessive heat strain based on monitoring

Yes

No

10

Level 1 Assessment a basic thermal risk assessment A suggested protocol for the level 1 assessment is termed the ldquoBasic Thermal Risk

Assessmentrdquo It has been designed as a simple tool which can be used by employees or

technicians to provide guidance and also as a training tool to illustrate the many factors

that impact on heat stress This risk assessment incorporates the contributions of a

number of factors that can impact on heat stress such as the state of acclimatisation work

demands location clothing and other physiological factors It can also incorporate the use

of a first level heat stress index such as Apparent Temperature or WBGT It is designed to

be an initial qualitative review of a potential heat stress situation for the purposes of

prioritising further measurements and controls It is not intended as a definitive

assessment tool Some of its key aspects are described below

Acclimatisation plays a part as it is a set of gradual physiological adjustments that improve

an individuals ability to tolerate heat stress the development and loss of which is

described in the Documentation

Metabolic work rate is of equal importance to environmental assessment in evaluating heat

stress Table 1 provides broad guidance for selecting the work rate category to be used in

the Risk Assessment There are a number of sources for this data including ISO

72431989 and ISO 89962004 standards

Table 1 Examples of Activities within Metabolic Rate (M) Classes

Class Examples

Resting Resting sitting at ease Low Light

Work Sitting at ease light manual work hand and arm work car driving

standing casual walking sitting or standing to control machines

Moderate

Moderate Work Sustained hand and arm work (eg hammering) arm and trunk

work moving light wheelbarrow walking around 45 kmh

High Heavy

Work

Intense arm and trunk work carrying heavy material shovelling

sawing hard wood moving heavily loaded wheelbarrows carrying

loads upstairs

Source (ISO 89962004)

Apparent temperature (Steadman 1979) can be used as part of the basic thermal risk

assessment The information required air temperature and humidity can be readily

obtained from most local weather bureau websites off-the-shelf weather units or

measured directly with a sling psychrometer Its simplicity is one of the advantages in its

use as it requires very little technical knowledge

11

The WBGT index also offers a useful first-order index of the environmental contribution to

heat stress It is influenced by air temperature radiant heat and humidity (ACGIH 2013)

In its simplest form it does not fully account for all of the interactions between a person

and the environment but is useful in this type of assessment The only disadvantage is

that it requires some specialised monitoring equipment such as a WBGT monitor or wet

bulb and globe thermometers

Both indices are described in more detail in the Documentation associated with this

standard

These environmental parameters are combined on a single check sheet in three sections

Each aspect is allocated a numerical value A task may be assessed by checking off

questions in the table and including some additional data for metabolic work load and

environmental conditions From this information a weighted calculation is used to

determine a numerical value which can be compared to pre-set criteria to provide

guidance as to the potential risk of heat stress and the course of action for controls

For example if the Assessment Point Total is less than 28 then the thermal condition risk

is low The lsquoNorsquo branch in Figure 1 can be taken Nevertheless if there are reports of the

symptoms of heat-related disorders such as prickly heat fatigue nausea dizziness and

light-headedness then the analysis should be reconsidered or proceed to detailed

analysis if appropriate If the Assessment Point Total is 28 or more further analysis is

required An Assessment Point Total greater than 60 indicates the need for immediate

action and implementation of controls (see Section 6)

Examples of a basic thermal risk assessment tool and their application are provided in

Appendix 1

Section 2 Screening for clothing that does not allow air and water vapour movement

The decision about clothing and how it might affect heat loss can also play an important

role in the initial assessment This is of particular importance if the clothing interferes with

the evaporation of sweat from the skin surface of an individual (ie heavy water barrier

clothing such as PVC) As this is the major heat loss mechanism disruption of this

process will significantly impact on the heat stress experienced Most heat exposure

assessment indices were developed for a traditional work uniform which consisted of a

long-sleeved shirt and pants Screening that is based on this attire is not suitable for

clothing ensembles that are more extensive and less permeable unless a detailed analysis

method appropriate for permeable clothing requirements is available With heat removal

hampered by clothing metabolic heat may produce life-threatening heat strain even when

12

ambient conditions are considered cool and the risk assessment determines ldquoLow Riskrdquo If

workers are required to wear additional clothing that does not allow air and water vapour

movement then the lsquoYesrsquo branch in the first question of Figure 1 should be taken

Physiological and behavioural monitoring described in Section 4 should be followed to

assess the potential for harm resulting from heat stress

Section 3 Level 2 assessment using detailed analysis

It is possible that a condition may be above the criteria provided in the initial risk

assessment and still not represent an unacceptable exposure To make this

determination a detailed analysis is required as in the Documentation

Note as discussed briefly above (see Section 2) no numerical screening criteria or limiting

values are applicable where clothing does not allow air or water vapour movement In this

case reliance must be placed on physiological monitoring

The screening criteria require a minimum set of data in order to make an assessment A

detailed analyses requires more data about the exposures including

bull clothing type

bull air speed

bull air temperature

bull water vapour content of the air (eg humidity)

bull posture

bull length of exposure and

bull globe temperature

Following Figure 1 the next question asks about the availability of such exposure data for

a detailed analysis If exposure data are not available the lsquoNorsquo branch takes the

evaluation to the monitoring of the tasks to collect this data before moving on to the use of

a rational heat stress index These types of indices are based on the human heat balance

equation and utilise a number of formulae to predict responses of the body such as

sweating and elevation of core temperature From this information the likelihood of

developing a heat stress related disorder may be determined In situations where this

data cannot be collected or made available then physiological monitoring to assess the

degree of heat strain should be undertaken

Detailed rational analysis should follow ISO 7933 - Predicted Heat Strain or Thermal Work

Limit (TWL) although other indices with extensive supporting physiological documentation

may also be acceptable (see Documentation for details) While such a rational method

(versus the empirically derived WBGT or Basic Effective Temperature (BET) thresholds) is

13

computationally more difficult it permits a better understanding of the source of the heat

stress and can be a means to assess the benefits of proposed control modifications on the

exposure

Predicted heat strain (PHS) is a rational index (ie it is an index based on the heat balance

equation) It estimates the required sweat rate and the maximal evaporation rate utilising

the ratio of the two as an initial measure of lsquorequired wettednessrsquo This required

wettedness is the fraction of the skin surface that would have to be covered by sweat in

order for the required evaporation rate to occur The evaporation rate required to maintain

a heat balance is then calculated (Di Corleto et al 2003)

In the event that the suggested values might be exceeded ISO 7933 calculates an

allowable exposure time

The suggested limiting values assume workers are

bull fit for the activity being considered and

bull in good health and

bull screened for intolerance to heat and

bull properly instructed and

bull able to self-pace their work and

bull under some degree of supervision (minimally a buddy system)

In work situations which

bull either the maximum evaporation rate is negative leading to condensation of

water vapour on the skin

bull or the estimated allowable exposure time is less than 30 minutes so that the

phenomenon of sweating onset plays a major role in the estimation of the

evaporation loss of the subject Special precautionary measures need to be

taken and direct and individual physiological surveillance of the workers is

particularly necessary

The thermal work limit (TWL) was developed in Australia initially in the underground

mining industry by Brake and Bates (2002a) and later trialled in open cut mines in the

Pilbara region of Western Australia (Miller and Bates 2007a) TWL is defined as the

limiting (or maximum) sustainable metabolic rate that hydrated acclimatised individuals

can maintain in a specific thermal environment within a safe deep body core temperature

(lt382degC) and sweat rate (lt12 kghr) (Tillman 2007)

Due to this complexity these calculations are carried out with the use of computer

software or in the case of TWL pre-programmed monitoring equipment

14

If the exposure does not exceed the criteria for the detailed analysis then the lsquoNorsquo branch

can be taken Because the criteria in the risk assessment have been exceeded

monitoring general heat stress controls are appropriate General controls include training

for workers and supervisors and heat stress hygiene practices If the exposure exceeds

the suggested limits from the detailed analysis or set by the appropriate authority the

lsquoYesrsquo branch leads to the iterative assessment of job-specific control options using the

detailed analysis and then implementation and assessment of control(s) If these are not

available or it cannot be demonstrated that they are successful then the lsquoNorsquo branch

leads to physiological monitoring as the only alternative to demonstrate that adequate

protection is provided

Section 4 Level 3 assessment of heat strain

There are circumstances where the assessment using the rational indices cannot assure

the safety of the exposed workgroup In these cases the use of individual physiological

monitoring may be required These may include situations of high heat stress risk or

where the individualrsquos working environment cannot be accurately assessed A common

example is work involving the use of encapsulating ldquohazmatrdquo suits

The risk and severity of excessive heat strain will vary widely among people even under

identical heat stress conditions By monitoring the physiological responses to working in a

hot environment this allows the workers to use the feedback to assess the level of heat

strain present in the workforce to guide the design of exposure controls and to assess the

effectiveness of implemented controls Instrumentation is available for personal heat

stress monitoring These instruments do not measure the environmental conditions

leading to heat stress but rather they monitor the physiological indicators of heat strain -

usually elevated body temperature andor heart rate Modern instruments utilise an

ingestible core temperature capsule which transmits physiological parameters

telemetrically to an external data logging sensor or laptop computer This information can

then be monitored in real time or assessed post task by a qualified professional

Monitoring the signs and symptoms of heat-stressed workers is sound occupational

hygiene practice especially when clothing may significantly reduce heat loss For

surveillance purposes a pattern of workers exceeding the limits below is considered

indicative of the need to control the exposures On an individual basis these limits are

believed to represent a time to cease an exposure until recovery is complete

Table 2 provides guidance for acceptable limits of heat strain Such physiological

monitoring (see ISO 12894 2001) should be conducted by a physician nurse or

equivalent as allowed by local law

15

Table 2 Physiological Guidelines for Limiting Heat Strain The American Conference of Industrial Hygienists (ACGIH 2013) has published

physiological limits for a number of years and states that exposure to

environmentally or activity-induced heat stress must be discontinued at any time

when

bull Sustained (several minutes) heart rate in excess of 180 beats per minute

minus the individuals age in years (eg180 ndash age) for individuals with

assessed normal cardiac performance OR

bull Body core temperature greater than 385degC (1013degC) for medically

selected and acclimatised personnel or greater than 38degC (1004degC) in

unselected unacclimatised workers OR

bull When there are complaints of sudden and severe fatigue nausea

dizziness or light-headedness OR

bull A workers recovery heart rate at one minute after a peak work effort is

greater than 120 beats per minute 124 bpm was suggested by Fuller and

Smith (1982) OR

bull A worker experiences profuse and prolonged sweating over hours and

may not be able to adequately replenish fluids OR

bull Greater than 15 weight loss over a shift OR

bull In conditions of regular daily exposure to the stress 24-hour urinary

sodium excretion is less than 50 mmoles

ISO 9886 (2004) suggests that exposure to environmentally or activity-induced heat

stress must also be discontinued at any time when

bull lsquoHeart Rate Limit = 185 - 065Arsquo where A = Age in years

bull Individual variability can range up to 20 bpm from this average so this

level could present a risk for some individuals Where there is

uncertainty the sustained heart rate over a work period should not

exceed the previously mentioned

bull HRL sustained = 180 ndash age

bull No matter which limiting values are used interpretation requires

discussion with the workers affected and may require the services of a

specialist such as an occupational hygienist or occupational physician

If a worker appears to be disoriented or confused or demonstrates uncharacteristic

16

irritability discomfort or flu-like symptoms the worker should be removed for rest

under observation in a cool location Symptoms of heat stroke need to be monitored

closely and if sweating stops and the skin becomes hot and dry immediate

emergency care is essential

The prompt treatment of other heat-related disorders generally results in full

recovery but medical advice should be sought for treatment and return-to-work

protocols

Following good occupational hygiene sampling practice which considers likely extremes

and the less tolerant workers the absence of any of these limiting observations indicates

acceptable management of the heat stress exposures With acceptable levels of heat

strain the lsquoNorsquo branch in the level 3 section of Figure 1 is taken Nevertheless even if the

heat strain among workers is considered acceptable at the time the general controls are

necessary In addition periodic physiological monitoring should be continued to ensure

that acceptable levels of heat strain are being maintained

If excessive heat strain is found during the physiological assessments then the lsquoYesrsquo

branch is taken This means that the work activities must cease until suitable job-specific

controls can be considered and implemented to a sufficient extent to control that strain

The job-specific controls may include engineering controls administrative controls and

personal protection

After implementation of the job-specific controls it is necessary to assess their

effectiveness and to adjust them as needed

Section 5 Occupational Exposure Limits

Currently there are fewer workplaces where formal exposure limits for heat stress still

apply however this practice is found mainly within the mining industry There are many

variables associated with the onset of heat stress and these can be a result of the task

environment andor the individual Trying to set a general limit which adequately covers

the many variations within industry has proven to be extremely complicated The attempts

have sometimes resulted in an exposure standard so conservative in a particular

environment that it would become impractical to apply It is important to note that heat

stress indices are not safeunsafe limits and should only be used as guides

Use of Urinary Specific Gravity testing

Water intake at onersquos own discretion results in incomplete fluid replacement for individuals

working in the heat and there is consistent evidence that relying solely on thirst as an

17

indicator of fluid requirement will not restore water balance (Sawka 1998) Urine specific

gravity (USG) can be used as a guide in relation to the level of hydration of an individual

(Shirreffs 2003) and this method of monitoring is becoming increasingly popular in

Australia as a physiological limit Specific gravity (SG) is defined as the ratio weight of a

substance compared to the weight of an equal volume of distilled water hence the SG of

distilled water is 1000 Studies (Sawka et al 2007 Ganio et al 2007 Cheuvront amp

Sawka 2005 Casa et al 2000) recommend that a USG of greater than 1020 would

reflect dehydration While not regarded as fool proof or the ldquogold standardrdquo for total body

water (Armstrong 2007) it is a good compromise between accuracy simplicity of testing

in the field and acceptability to workers of a physiological measure Table 3 shows the

relationship between SG of urine and hydration

Table 3 US National Athletic Trainers Association index of hydration status Body Weight

Loss ()

Urine Specific

Gravity

Well Hydrated lt1 1010

Minimal dehydration 1 - 3 1010 ndash 1020

Significant

dehydration

3 - 5 1021 ndash 1030

Severe dehydration gt 5 gt 1030 Source adapted from Casa et al 2000

Section 6 Heat stress management and controls

The requirement to initiate a heat stress management program is marked by

(1) heat stress levels that exceed the criteria in the Basic Thermal Risk Assessment or

level 2 heat index assessment or

(2) work in clothing ensembles that are air or water vapour impermeable

There are numerous controls across the hierarchy of controls that may be utilised to

address heat stress issues in the workplace Not all may be applicable to a particular task

or scenario and often may require some adjusting before a suitable combination is

achieved

In addition to general controls appropriate job-specific controls are often required to

provide adequate protection During the consideration of job-specific controls detailed

analysis provides a framework to appreciate the interactions among acclimatisation stage

metabolic rate workrest cycles and clothing Table 4 lists some examples of controls

available The list is by no means exhaustive but will provide some ideas for controls

18

Table 4 Examples of control methods

Eliminationsubstitution

bull Hot tasks should be scheduled to avoid the hottest part of the day or where

practical undertaken during night shifts

bull Walls and roof structures should utilize light coloured or reflective materials

bull Structures should be designed to incorporate good air flow This can be done via

the positioning of windows shutters and roof design to encourage lsquochimney

effectsrsquo This will help remove the heat from the structure

bull Walls and roofs should be insulated

Engineering

bull Pipework and vessels associated with hot processes should be insulated and clad

to minimize the introduction of heat into the work environment

bull In high humidity areas such as northern Australia more air needs to be moved

hence fans to increase air flow or in extreme cases cooled air from lsquochillerrsquo units

can be used

bull Where radiated heat from a process is a problem insulating barriers or reflective

barriers can be used to absorb or re-direct radiant heat These may be permanent

structures or movable screens

bull Relocating hot processes away from high access areas

bull Dehumidifying air to increase the evaporative cooling effect Often steam leaks

open process vessels or standing water can artificially increase humidity within a

building

bull Utilize mechanical aids that can reduce the metabolic workload on the individual

Administrative

bull Ready access to cool palatable drinking water is a basic necessity

bull Where applicable suitable electrolyte replacements should also be available

bull A clean cool area for employees to rest and recuperate can add significant

improvement to the cooling process Resting in the work environment can provide

some relief for the worker the level of recovery is much quicker and more efficient

in an air-conditioned environment These need not be elaborate structures basic

inexpensive portable enclosed structures with an air conditioner water supply and

seating have been found to be successful in a variety of environments For field

19

teams with high mobility even a simple shade structure readily available from

hardware stores or large umbrellas can provide relief from solar radiation

bull Where work-rest regimes are necessary heat stress indices such as WBGT PHS

or TWL assist in determining duration of work and rest periods

bull Training workers to identify symptoms and the potential onset of heat-related

illness as part of the lsquobuddy systemrsquo

bull Encouraging ldquoself-determinationrdquo or pacing of the work to meet the conditions and

reporting of heat related symptoms

bull Consider pre-placement medical screening for work in hot areas (ISO 12894)

Personal protective equipment

bull PPE such as cooling vests with either lsquophase changersquo cooling inserts (not ice) Ice

or chilled water cooled garments can result in contraction of the blood vessels

reducing the cooling effect of the garment

bull Vortex tube air cooling may be used in some situations particularly when a cooling

source is required when supplied air respirators are used

bull Choose light coloured materials for clothing and ensure they allow good air flow

across the skin to promote evaporative cooling

Heat stress hygiene practices are particularly important because they reduce the risk that

an individual may suffer a heat-related disorder The key elements are fluid replacement

self-assessment health status monitoring maintenance of a healthy life-style and

adjustment of work expectations based on acclimatisation state and ambient working

conditions The hygiene practices require the full cooperation of supervision and workers

20

Bibliography ACGIH (American Conference of Governmental Industrial Hygienists) (2013) Threshold

Limit Values for Chemical Substances and Physical Agents and Biological Exposure

Indices Cincinnati ACGIH Signature Publications

Armstrong LE (2007) Assessing hydration status The elusive gold standard Journal of

the American College of Nutrition 26(5) pp 575S-584S

Brake DJ amp Bates GP (2002) Limiting metabolic rate (thermal work limit) as an index of

thermal stress Applied Occupational and Environmental Hygiene 17 pp 176ndash86

Casa DJ Armstrong LE Hillman SK Montain SJ Reiff RV amp Rich BSE (2000)

National Athletic Trainers association Position Statement Fluid replacement for Athletes

Journal of Athletic Training 35(2) pp 212-224

Di Corleto R Coles G amp Firth I (2003) The development of a heat stress standard for

Australian conditions in Australian Institute of Occupational Hygienists Inc 20th Annual

Conference Proceedings Geelong Victoria December AIOH

Di Corleto R Firth I Mate J Coles G (2013) A Guide to Managing Heat Stress and

Documentation Developed For Use in the Australian Environment AIOH Melbourne

Ganio MS Casa DJ Armstrong LE amp Maresh CM (2007) Evidence based approach to

lingering hydration questions Clinics in Sports Medicine 26(1) pp 1ndash16

ISO 7243 (1989) Hot environments - Estimation of the heat stress on working man

based on the WBGT - index (wet bulb globe temperature)

ISO 7933 (2004) Ergonomics of the thermal environment Analytical determination and

interpretation of heat stress using calculation of the Predicted Heat Strain ISO 7933

ISO 8996 (2004) Ergonomics of the Thermal Environment ndash Determination of Metabolic

Rate Geneva ISO

ISO 9886 (1992) Evaluation of thermal strain by physiological measurements

ISO 12894 (2001) Ergonomics of the thermal environment ndash Medical supervision of

individuals exposed to extreme hot or cold environments

Miller V Bates G (2007) Hydration of outdoor workers in north-west Australia J

Occup Health Safety mdash Aust NZ 23(1) pp 79ndash87

21

Sawka MN (1998) Body fluid responses and hypohydration during exercise heat

stress in KB Pandolf MN Sawkaand amp RR Gonzalez (Eds) Human Performance

Physiology and Environmental Medicine at Terrestrial Extremes USA Brown amp

Benchmark pp 227 ndash 266

Shirreffs SM (2003) Markers of hydration status European Journal of Clinical Nutrition

57(2) pp s6-s9

Steadman RG (1979) The assessment of sultriness Part 1 A temperature humidity

index based on human physiology and clothing science Journal of applied meteorology

(July)

Tillman C (2007) (Ed) Principles of Occupational Health amp Hygiene - An Introduction

Allen amp Unwin Academic

22

Appendix 1 - Basic Thermal Risk Assessment using Apparent Temperature (Informative example only)

HAZARD TYPE Assessment Point Value 0 1 2 3 Sun Exposure Indoors Full Shade Part Shade No Shade Hot surfaces Neutral Warm on Contact Hot on contact Burn on contact Exposure period lt 30 min 30 min ndash 1hour 1 hour - 2 hours gt 2 hrs Confined space No Yes Task complexity Simple Moderate Complex Climbing updown stairs or ladders None One level Two levels gt Two levels Distance from cool rest area lt10 Metres 10 - 50 Metres 50-100 Metres gt100 Metres Distance from drinking water lt10 Metres 10 - 30 Metres 30-50 Metres gt50 Metres Clothing (permeable) Single layer (light) Single layer (mod) Multiple layer Understanding of heat strain risk Training given No training given Air movement Strong Wind Moderate Wind Light Wind No Wind Resp protection (-ve pressure) None Disposable Half Face Rubber Half Face Full Face Acclimatisation Acclimatised Unacclimatised

SUB-TOTAL A 2 4 6 Metabolic work rate Light Moderate Heavy SUB-TOTAL B 1 2 3 4 Apparent Temperature lt 27degC gt27degC le 33degC gt33degC le 41degC gt 41degC SUB-TOTAL C

TOTAL = A plus B Multiplied by C = Examples of Work Rate Light work Sitting or standing to control machines hand and arm work assembly or sorting of light materials Moderate work Sustained hand and arm work such as hammering handling of moderately heavy materials Heavy work Pick and shovel work continuous axe work carrying loads up stairs Instructions for use of the Basic Thermal Risk Assessment

bull Mark each box according to the appropriate conditions bull When complete add up using the value at the top of the appropriate column for each mark bull Add the sub totals of Table A amp Table B and multiply with the sub-total of Table C for the final result bull If the total is less than 28 then the risk due to thermal conditions are low to moderate bull If the total is 28 to 60 there is a potential of heat-induced illnesses occurring if the conditions are not

addressed Further analysis of heat stress risk is required bull If the total exceeds 60 then the onset of a heat-induced illness is very likely and action should be taken as

soon as possible to implement controls It is important to note that that this assessment is to be used as a guide only A number of factors are not included in this assessment such as employee health condition and the use of high levels of PPE (particularly impermeable suits) In these circumstances experienced personnel should carry out a more extensive assessment

23

Worked Example of Basic Thermal Risk Assessment An example of the application of the basic thermal risk assessment would be as follows A fitter is working on a pump out in the plant at ground level that has been taken out of service the previous day The task involves removing bolts and a casing to check the impellers for wear approximately 2 hours of work The pump is situated approximately 25 metres from the workshop The fitter is acclimatised has attended a training session and is wearing a standard single layer long shirt and trousers is carrying a water bottle and a respirator is not required The work rate is light there is a light breeze and the air temperature has been measured at 30degC and the relative humidity at 70 This equates to an apparent temperature of 35degC (see Table 5 in appendix 2) Using the above information in the risk assessment we have

HAZARD TYPE Assessment Point Value

0 1 2 3 Sun Exposure Indoors Shade Part Shade No Shade Hot surfaces Neutral Warm on Contact Hot on contact Burn on contact Exposure period lt 30 min 30 min ndash 1hour 1 hour - 2 hours gt 2 hrs Confined space No Yes Task complexity Simple Moderate Complex Climbing updown stairs or ladders None One level Two levels gt Two levels Distance from cool rest area lt10 Metres lt50 Metres 50-100 Metres gt100 Metres Distance from drinking water lt10 Metres lt30 Metres 30-50 Metres gt50 Metres Clothing (permeable) Single layer (light) Single layer (mod) Multiple layer Understanding of heat strain risk Training given No training given Air movement Strong Wind Moderate Wind Light Wind No Wind Resp protection (-ve pressure) None Disposable Half Face Rubber Half Face Full Face Acclimatisation Acclimatised Unacclimatised

3 6 0 SUB-TOTAL A 9 2 4 6 Metabolic work rate Light Moderate Heavy SUB-TOTAL B 2 1 2 3 4 Apparent Temperature lt 27degC gt27degC le 33degC gt33degC le 41degC gt 41degC SUB-TOTAL C 3

A = 9 B = 2 C = 3 therefore Total = (9+2) x 3 = 33 As the total lies between 28 and 60 there is a potential for heat induced illness occurring if the conditions are not addressed and further analysis of heat stress risk is required

24

Appendix 2 ndash Table 5 Apparent Temperature Dry BulbHumidity scale Align dry bulb temperature with corresponding relative humidity to determine apparent temperature in unshaded section of table Numbers in () refer to skin humidities above 90 and are only approximate

Dry Bulb Temperature Relative Humidity () (degC) 0 10 20 30 40 50 60 70 80 90 100 20 16 17 17 18 19 19 20 20 21 21 21 21 18 18 19 19 20 20 21 21 22 22 23 22 19 19 20 20 21 21 22 22 23 23 24 23 20 20 21 22 22 23 23 24 24 24 25 24 21 22 22 23 23 24 24 25 25 26 26 25 22 23 24 24 24 25 25 26 27 27 28 26 24 24 25 25 26 26 27 27 28 29 30 27 25 25 26 26 27 27 28 29 30 31 33 28 26 26 27 27 28 29 29 31 32 34 (36) 29 26 27 27 28 29 30 30 33 35 37 (40) 30 27 28 28 29 30 31 33 35 37 (40) (45) 31 28 29 29 30 31 33 35 37 40 (45) 32 29 29 30 31 33 35 37 40 44 (51) 33 29 30 31 33 34 36 39 43 (49)

34 30 31 32 34 36 38 42 (47)

35 31 32 33 35 37 40 (45) (51)

36 32 33 35 37 39 43 (49)

37 32 34 36 38 41 46

38 33 35 37 40 44 (49)

39 34 36 38 41 46

40 35 37 40 43 49

41 35 38 41 45

42 36 39 42 47

43 37 40 44 49

44 38 41 45 52

45 38 42 47

46 39 43 49

47 40 44 51

48 41 45 53

49 42 47

50 42 48

(Source Steadman 1979)

25

Documentation of the Heat Stress Guide Developed for Use in the Australian Environment

Developed for the Australian Institute of Occupational Hygienists

Ross Di Corleto Ian Firth amp Joseph Mateacute

November 2013

26

10 Introduction Heat-related illness has been a health hazard throughout the ages and is a function

of the imposition of environmental heat on the human body which itself generates

heat

11 Heat Illness ndash A Problem Throughout the Ages

The hot thermal environment has been a constant challenge to man for centuries and

its impact is referenced throughout history The bible tells of the death of Judithrsquos

husband Manasseh from exposure in the fields supervising workers where it says

ldquoHe had suffered a sunstroke while in the fields supervising the farm workers and

later died in bed at home in Bethuliardquo (Judith 83)

The impact of heat on the military in history is also well recorded the problems

confronted by the armies of King Sennacherib of Assyria (720BC) whilst attacking

Lashish Herodotus (400BC) reports of Spartan soldiers succumbing to ldquothirst and

sunrdquo Even Alexander the Great in 332BC was warned of the risks of a march across

the Libyan Desert And there is little doubt that heat stress played a major role in the

defeat of the Crusaders of King Edward in the Holy Land fighting the Saracens whilst

burdened down with heavy armour in the Middle Eastern heat (Goldman 2001)

It is not only the workers and armies that are impacted but also the general

population One of the worst cases occurred in Peking China in 1743 when during a

10 day heat wave 11000 people were reported to have perished (Levick 1859)

In 1774 Sir Charles Blagden of the Royal Society outlined a series of experiments

undertaken in a heated room in which he commented on ldquothe wonderful power with

which the animal body is endued of resisting heat vastly greater than its own

temperaturerdquo (Blagden 1775)

Despite this experience and knowledge over the ages we are still seeing deaths in

the 20th century as a result of heat stress Severe heat related illnesses and deaths

are not uncommon among pilgrims making the Makkah Hajj (Khogali 1987) and

closer to home a fatality in the Australian military (ABC 2004) and more recently

amongst the Australian workforce (Australian Mining 2013)

27

12 Heat and the Human Body

The human body in a state of wellbeing maintains its internal temperature within a

very narrow range This is a fundamental requirement for those internal chemical

reactions which are essential to life to proceed at the proper rates The actual level

of this temperature is a product of the balance between heat exchange with the

external thermal environment and the generation of heat internally by the metabolic

processes associated with life and activity

The temperature of blood circulating through the living and working tissues is

monitored by receptors throughout the body The role of these receptors is to induce

specific responses in functional body systems to ensure that the temperature

remains within the appropriate range

The combined effect of external thermal environment and internal metabolic heat

production constitutes the thermal stress on the body The levels of activity required

in response to the thermal stress by systems such as cardiovascular

thermoregulatory respiratory renal and endocrine constitute the thermal strain

Thus environmental conditions metabolic workload and clothing individually or

collectively create heat stress for the worker The bodyrsquos physiological response to

stressors for example sweating increased heart rate and elevated core

temperature is the heat strain

Such physiological changes are the initial responses to thermal stress but the extent

at which these responses are required will determine whether that strain will result in

thermal injuryillness It is important to appreciate that while preventing such illness

by satisfactorily regulating human body temperature in a heat-stress situation those

responses particularly the sweat response may not be compatible with comfort

(Gagge et al 1941)

The rate of heat generated by metabolic processes is dependent on the level of

physical activity To precisely quantify the metabolic cost associated with a particular

task without directly or indirectly measuring the individual is not possible This is due

to the individual differences associated with performing the task at hand As a

result broad categories of metabolic loads for typical work activities have been

established (Durnin amp Passmore 1967 ISO 8996 2004) It is sometimes practicable

Safe Work Australia (2011) refers to heat related illnesses and OSHA (httpswwwoshagovSLTCheatstress) considers heat exhaustion and heat stroke cases to be heat-related illness due to the number of human factors that contribute to a workers susceptibility to heat stress (refer to Section 40) while ACGIH (2013) refers to heat stress and heat strain cases as being heat-related disorders They are not usually considered injuries

28

DOCUMENTATION OF THE HEAT STRESS GUIDE DEVELOPED FOR USE IN THE AUSTRALIAN ENVIRONMENT 26

10 INTRODUCTION 27

11 Heat Illness ndash A Problem Throughout the Ages 27

12 Heat and the Human Body 28

20 HEAT RELATED ILLNESSES 29

21 Acute Illnesses 30 211 Heat Stroke 30 212 Heat Exhaustion 31 213 Heat Syncope (Fainting) 31 214 Heat Cramps 32 215 Prickly Heat (Heat Rash) 32

22 Chronic Illness 32

23 Related Hazards 33

30 CONTACT INJURIES 34

40 KEY PHYSIOLOGICAL FACTORS CONTRIBUTING TO HEAT ILLNESS 36

41 Fluid Intake 36

42 Urine Specific Gravity 43

43 Heat Acclimatisation 45

44 Physical Fitness 47

45 Other Considerations in Reducing Exposure in Heat-Stress Conditions 48

50 ASSESSMENT PROTOCOL 48

60 WORK ENVIRONMENT MONITORING AND ASSESSMENT 50

61 Risk Assessment 50

62 The Three Stage Approach 51 621 Level 1 Assessment A Basic Thermal Risk Assessment 53

63 Stage 2 of Assessment Protocol Use of Rational Indices 54 631 Predicted Heat Strain (PHS) 55 632 Thermal Work Limit (TWL) 58 633 Other Indices 60

70 PHYSIOLOGICAL MONITORING - STAGE 3 OF ASSESSMENT PROTOCOL 62

4

71 Core Temperature 65

72 Heart Rate Measurements 67

80 CONTROLS 70

81 Ventilation 72

82 Radiant Heat 73

83 Administrative Controls 76 831 Training 76 832 Self-Assessment 77 833 Fluid Replacement 77 834 Rescheduling of Work 77 835 WorkRest Regimes 77 836 Clothing 78 837 Pre-placement Health Assessment 80

84 Personal Protective Equipment 81 841 Air Cooling System 81 842 Liquid Circulating Systems 82 843 Ice Cooling Systems 83 844 Reflective Clothing 84

90 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

5

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 ldquoThe heat stress standard

and documentation developed for use in the Australian environment (2003)rdquo 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 ldquoA guide to managing

heat stress developed for use in the Australian environment (2013)rdquo 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

bull the first a brief summary of the approach written for interested parties with a non-

technical background and

bull 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

6

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 ndash 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

7

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

bull air temperature

bull humidity

bull air movement

bull radiant heat exchange and

bull 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 bodyrsquos 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

bull prickly heat

bull headaches

bull nausea

bull 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

8

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 individualrsquos 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

9

Figure 1 Heat Stress Management Schematic (adapted from ACGIH 2013)

Level 1Perform Basic Risk

Assessment

Unacceptable risk

No

Does task involve use of impermeable clothing (ie PVC)

Continue work monitor conditionsNo

Are data available for detailed analysis

Level 2Analyse data with rational heat stress index (ie PHS

TWL)

Yes

Unacceptable heat stress risk based on analysis

Job specific controls practical and successful

Level 3Undertake physiological

monitoring

Cease work

Yes

Yes

No

Monitor task to ensure conditions amp collect dataNo

No

Maintain job specific controlsYes

Excessive heat strain based on monitoring

Yes

No

10

Level 1 Assessment a basic thermal risk assessment A suggested protocol for the level 1 assessment is termed the ldquoBasic Thermal Risk

Assessmentrdquo It has been designed as a simple tool which can be used by employees or

technicians to provide guidance and also as a training tool to illustrate the many factors

that impact on heat stress This risk assessment incorporates the contributions of a

number of factors that can impact on heat stress such as the state of acclimatisation work

demands location clothing and other physiological factors It can also incorporate the use

of a first level heat stress index such as Apparent Temperature or WBGT It is designed to

be an initial qualitative review of a potential heat stress situation for the purposes of

prioritising further measurements and controls It is not intended as a definitive

assessment tool Some of its key aspects are described below

Acclimatisation plays a part as it is a set of gradual physiological adjustments that improve

an individuals ability to tolerate heat stress the development and loss of which is

described in the Documentation

Metabolic work rate is of equal importance to environmental assessment in evaluating heat

stress Table 1 provides broad guidance for selecting the work rate category to be used in

the Risk Assessment There are a number of sources for this data including ISO

72431989 and ISO 89962004 standards

Table 1 Examples of Activities within Metabolic Rate (M) Classes

Class Examples

Resting Resting sitting at ease Low Light

Work Sitting at ease light manual work hand and arm work car driving

standing casual walking sitting or standing to control machines

Moderate

Moderate Work Sustained hand and arm work (eg hammering) arm and trunk

work moving light wheelbarrow walking around 45 kmh

High Heavy

Work

Intense arm and trunk work carrying heavy material shovelling

sawing hard wood moving heavily loaded wheelbarrows carrying

loads upstairs

Source (ISO 89962004)

Apparent temperature (Steadman 1979) can be used as part of the basic thermal risk

assessment The information required air temperature and humidity can be readily

obtained from most local weather bureau websites off-the-shelf weather units or

measured directly with a sling psychrometer Its simplicity is one of the advantages in its

use as it requires very little technical knowledge

11

The WBGT index also offers a useful first-order index of the environmental contribution to

heat stress It is influenced by air temperature radiant heat and humidity (ACGIH 2013)

In its simplest form it does not fully account for all of the interactions between a person

and the environment but is useful in this type of assessment The only disadvantage is

that it requires some specialised monitoring equipment such as a WBGT monitor or wet

bulb and globe thermometers

Both indices are described in more detail in the Documentation associated with this

standard

These environmental parameters are combined on a single check sheet in three sections

Each aspect is allocated a numerical value A task may be assessed by checking off

questions in the table and including some additional data for metabolic work load and

environmental conditions From this information a weighted calculation is used to

determine a numerical value which can be compared to pre-set criteria to provide

guidance as to the potential risk of heat stress and the course of action for controls

For example if the Assessment Point Total is less than 28 then the thermal condition risk

is low The lsquoNorsquo branch in Figure 1 can be taken Nevertheless if there are reports of the

symptoms of heat-related disorders such as prickly heat fatigue nausea dizziness and

light-headedness then the analysis should be reconsidered or proceed to detailed

analysis if appropriate If the Assessment Point Total is 28 or more further analysis is

required An Assessment Point Total greater than 60 indicates the need for immediate

action and implementation of controls (see Section 6)

Examples of a basic thermal risk assessment tool and their application are provided in

Appendix 1

Section 2 Screening for clothing that does not allow air and water vapour movement

The decision about clothing and how it might affect heat loss can also play an important

role in the initial assessment This is of particular importance if the clothing interferes with

the evaporation of sweat from the skin surface of an individual (ie heavy water barrier

clothing such as PVC) As this is the major heat loss mechanism disruption of this

process will significantly impact on the heat stress experienced Most heat exposure

assessment indices were developed for a traditional work uniform which consisted of a

long-sleeved shirt and pants Screening that is based on this attire is not suitable for

clothing ensembles that are more extensive and less permeable unless a detailed analysis

method appropriate for permeable clothing requirements is available With heat removal

hampered by clothing metabolic heat may produce life-threatening heat strain even when

12

ambient conditions are considered cool and the risk assessment determines ldquoLow Riskrdquo If

workers are required to wear additional clothing that does not allow air and water vapour

movement then the lsquoYesrsquo branch in the first question of Figure 1 should be taken

Physiological and behavioural monitoring described in Section 4 should be followed to

assess the potential for harm resulting from heat stress

Section 3 Level 2 assessment using detailed analysis

It is possible that a condition may be above the criteria provided in the initial risk

assessment and still not represent an unacceptable exposure To make this

determination a detailed analysis is required as in the Documentation

Note as discussed briefly above (see Section 2) no numerical screening criteria or limiting

values are applicable where clothing does not allow air or water vapour movement In this

case reliance must be placed on physiological monitoring

The screening criteria require a minimum set of data in order to make an assessment A

detailed analyses requires more data about the exposures including

bull clothing type

bull air speed

bull air temperature

bull water vapour content of the air (eg humidity)

bull posture

bull length of exposure and

bull globe temperature

Following Figure 1 the next question asks about the availability of such exposure data for

a detailed analysis If exposure data are not available the lsquoNorsquo branch takes the

evaluation to the monitoring of the tasks to collect this data before moving on to the use of

a rational heat stress index These types of indices are based on the human heat balance

equation and utilise a number of formulae to predict responses of the body such as

sweating and elevation of core temperature From this information the likelihood of

developing a heat stress related disorder may be determined In situations where this

data cannot be collected or made available then physiological monitoring to assess the

degree of heat strain should be undertaken

Detailed rational analysis should follow ISO 7933 - Predicted Heat Strain or Thermal Work

Limit (TWL) although other indices with extensive supporting physiological documentation

may also be acceptable (see Documentation for details) While such a rational method

(versus the empirically derived WBGT or Basic Effective Temperature (BET) thresholds) is

13

computationally more difficult it permits a better understanding of the source of the heat

stress and can be a means to assess the benefits of proposed control modifications on the

exposure

Predicted heat strain (PHS) is a rational index (ie it is an index based on the heat balance

equation) It estimates the required sweat rate and the maximal evaporation rate utilising

the ratio of the two as an initial measure of lsquorequired wettednessrsquo This required

wettedness is the fraction of the skin surface that would have to be covered by sweat in

order for the required evaporation rate to occur The evaporation rate required to maintain

a heat balance is then calculated (Di Corleto et al 2003)

In the event that the suggested values might be exceeded ISO 7933 calculates an

allowable exposure time

The suggested limiting values assume workers are

bull fit for the activity being considered and

bull in good health and

bull screened for intolerance to heat and

bull properly instructed and

bull able to self-pace their work and

bull under some degree of supervision (minimally a buddy system)

In work situations which

bull either the maximum evaporation rate is negative leading to condensation of

water vapour on the skin

bull or the estimated allowable exposure time is less than 30 minutes so that the

phenomenon of sweating onset plays a major role in the estimation of the

evaporation loss of the subject Special precautionary measures need to be

taken and direct and individual physiological surveillance of the workers is

particularly necessary

The thermal work limit (TWL) was developed in Australia initially in the underground

mining industry by Brake and Bates (2002a) and later trialled in open cut mines in the

Pilbara region of Western Australia (Miller and Bates 2007a) TWL is defined as the

limiting (or maximum) sustainable metabolic rate that hydrated acclimatised individuals

can maintain in a specific thermal environment within a safe deep body core temperature

(lt382degC) and sweat rate (lt12 kghr) (Tillman 2007)

Due to this complexity these calculations are carried out with the use of computer

software or in the case of TWL pre-programmed monitoring equipment

14

If the exposure does not exceed the criteria for the detailed analysis then the lsquoNorsquo branch

can be taken Because the criteria in the risk assessment have been exceeded

monitoring general heat stress controls are appropriate General controls include training

for workers and supervisors and heat stress hygiene practices If the exposure exceeds

the suggested limits from the detailed analysis or set by the appropriate authority the

lsquoYesrsquo branch leads to the iterative assessment of job-specific control options using the

detailed analysis and then implementation and assessment of control(s) If these are not

available or it cannot be demonstrated that they are successful then the lsquoNorsquo branch

leads to physiological monitoring as the only alternative to demonstrate that adequate

protection is provided

Section 4 Level 3 assessment of heat strain

There are circumstances where the assessment using the rational indices cannot assure

the safety of the exposed workgroup In these cases the use of individual physiological

monitoring may be required These may include situations of high heat stress risk or

where the individualrsquos working environment cannot be accurately assessed A common

example is work involving the use of encapsulating ldquohazmatrdquo suits

The risk and severity of excessive heat strain will vary widely among people even under

identical heat stress conditions By monitoring the physiological responses to working in a

hot environment this allows the workers to use the feedback to assess the level of heat

strain present in the workforce to guide the design of exposure controls and to assess the

effectiveness of implemented controls Instrumentation is available for personal heat

stress monitoring These instruments do not measure the environmental conditions

leading to heat stress but rather they monitor the physiological indicators of heat strain -

usually elevated body temperature andor heart rate Modern instruments utilise an

ingestible core temperature capsule which transmits physiological parameters

telemetrically to an external data logging sensor or laptop computer This information can

then be monitored in real time or assessed post task by a qualified professional

Monitoring the signs and symptoms of heat-stressed workers is sound occupational

hygiene practice especially when clothing may significantly reduce heat loss For

surveillance purposes a pattern of workers exceeding the limits below is considered

indicative of the need to control the exposures On an individual basis these limits are

believed to represent a time to cease an exposure until recovery is complete

Table 2 provides guidance for acceptable limits of heat strain Such physiological

monitoring (see ISO 12894 2001) should be conducted by a physician nurse or

equivalent as allowed by local law

15

Table 2 Physiological Guidelines for Limiting Heat Strain The American Conference of Industrial Hygienists (ACGIH 2013) has published

physiological limits for a number of years and states that exposure to

environmentally or activity-induced heat stress must be discontinued at any time

when

bull Sustained (several minutes) heart rate in excess of 180 beats per minute

minus the individuals age in years (eg180 ndash age) for individuals with

assessed normal cardiac performance OR

bull Body core temperature greater than 385degC (1013degC) for medically

selected and acclimatised personnel or greater than 38degC (1004degC) in

unselected unacclimatised workers OR

bull When there are complaints of sudden and severe fatigue nausea

dizziness or light-headedness OR

bull A workers recovery heart rate at one minute after a peak work effort is

greater than 120 beats per minute 124 bpm was suggested by Fuller and

Smith (1982) OR

bull A worker experiences profuse and prolonged sweating over hours and

may not be able to adequately replenish fluids OR

bull Greater than 15 weight loss over a shift OR

bull In conditions of regular daily exposure to the stress 24-hour urinary

sodium excretion is less than 50 mmoles

ISO 9886 (2004) suggests that exposure to environmentally or activity-induced heat

stress must also be discontinued at any time when

bull lsquoHeart Rate Limit = 185 - 065Arsquo where A = Age in years

bull Individual variability can range up to 20 bpm from this average so this

level could present a risk for some individuals Where there is

uncertainty the sustained heart rate over a work period should not

exceed the previously mentioned

bull HRL sustained = 180 ndash age

bull No matter which limiting values are used interpretation requires

discussion with the workers affected and may require the services of a

specialist such as an occupational hygienist or occupational physician

If a worker appears to be disoriented or confused or demonstrates uncharacteristic

16

irritability discomfort or flu-like symptoms the worker should be removed for rest

under observation in a cool location Symptoms of heat stroke need to be monitored

closely and if sweating stops and the skin becomes hot and dry immediate

emergency care is essential

The prompt treatment of other heat-related disorders generally results in full

recovery but medical advice should be sought for treatment and return-to-work

protocols

Following good occupational hygiene sampling practice which considers likely extremes

and the less tolerant workers the absence of any of these limiting observations indicates

acceptable management of the heat stress exposures With acceptable levels of heat

strain the lsquoNorsquo branch in the level 3 section of Figure 1 is taken Nevertheless even if the

heat strain among workers is considered acceptable at the time the general controls are

necessary In addition periodic physiological monitoring should be continued to ensure

that acceptable levels of heat strain are being maintained

If excessive heat strain is found during the physiological assessments then the lsquoYesrsquo

branch is taken This means that the work activities must cease until suitable job-specific

controls can be considered and implemented to a sufficient extent to control that strain

The job-specific controls may include engineering controls administrative controls and

personal protection

After implementation of the job-specific controls it is necessary to assess their

effectiveness and to adjust them as needed

Section 5 Occupational Exposure Limits

Currently there are fewer workplaces where formal exposure limits for heat stress still

apply however this practice is found mainly within the mining industry There are many

variables associated with the onset of heat stress and these can be a result of the task

environment andor the individual Trying to set a general limit which adequately covers

the many variations within industry has proven to be extremely complicated The attempts

have sometimes resulted in an exposure standard so conservative in a particular

environment that it would become impractical to apply It is important to note that heat

stress indices are not safeunsafe limits and should only be used as guides

Use of Urinary Specific Gravity testing

Water intake at onersquos own discretion results in incomplete fluid replacement for individuals

working in the heat and there is consistent evidence that relying solely on thirst as an

17

indicator of fluid requirement will not restore water balance (Sawka 1998) Urine specific

gravity (USG) can be used as a guide in relation to the level of hydration of an individual

(Shirreffs 2003) and this method of monitoring is becoming increasingly popular in

Australia as a physiological limit Specific gravity (SG) is defined as the ratio weight of a

substance compared to the weight of an equal volume of distilled water hence the SG of

distilled water is 1000 Studies (Sawka et al 2007 Ganio et al 2007 Cheuvront amp

Sawka 2005 Casa et al 2000) recommend that a USG of greater than 1020 would

reflect dehydration While not regarded as fool proof or the ldquogold standardrdquo for total body

water (Armstrong 2007) it is a good compromise between accuracy simplicity of testing

in the field and acceptability to workers of a physiological measure Table 3 shows the

relationship between SG of urine and hydration

Table 3 US National Athletic Trainers Association index of hydration status Body Weight

Loss ()

Urine Specific

Gravity

Well Hydrated lt1 1010

Minimal dehydration 1 - 3 1010 ndash 1020

Significant

dehydration

3 - 5 1021 ndash 1030

Severe dehydration gt 5 gt 1030 Source adapted from Casa et al 2000

Section 6 Heat stress management and controls

The requirement to initiate a heat stress management program is marked by

(1) heat stress levels that exceed the criteria in the Basic Thermal Risk Assessment or

level 2 heat index assessment or

(2) work in clothing ensembles that are air or water vapour impermeable

There are numerous controls across the hierarchy of controls that may be utilised to

address heat stress issues in the workplace Not all may be applicable to a particular task

or scenario and often may require some adjusting before a suitable combination is

achieved

In addition to general controls appropriate job-specific controls are often required to

provide adequate protection During the consideration of job-specific controls detailed

analysis provides a framework to appreciate the interactions among acclimatisation stage

metabolic rate workrest cycles and clothing Table 4 lists some examples of controls

available The list is by no means exhaustive but will provide some ideas for controls

18

Table 4 Examples of control methods

Eliminationsubstitution

bull Hot tasks should be scheduled to avoid the hottest part of the day or where

practical undertaken during night shifts

bull Walls and roof structures should utilize light coloured or reflective materials

bull Structures should be designed to incorporate good air flow This can be done via

the positioning of windows shutters and roof design to encourage lsquochimney

effectsrsquo This will help remove the heat from the structure

bull Walls and roofs should be insulated

Engineering

bull Pipework and vessels associated with hot processes should be insulated and clad

to minimize the introduction of heat into the work environment

bull In high humidity areas such as northern Australia more air needs to be moved

hence fans to increase air flow or in extreme cases cooled air from lsquochillerrsquo units

can be used

bull Where radiated heat from a process is a problem insulating barriers or reflective

barriers can be used to absorb or re-direct radiant heat These may be permanent

structures or movable screens

bull Relocating hot processes away from high access areas

bull Dehumidifying air to increase the evaporative cooling effect Often steam leaks

open process vessels or standing water can artificially increase humidity within a

building

bull Utilize mechanical aids that can reduce the metabolic workload on the individual

Administrative

bull Ready access to cool palatable drinking water is a basic necessity

bull Where applicable suitable electrolyte replacements should also be available

bull A clean cool area for employees to rest and recuperate can add significant

improvement to the cooling process Resting in the work environment can provide

some relief for the worker the level of recovery is much quicker and more efficient

in an air-conditioned environment These need not be elaborate structures basic

inexpensive portable enclosed structures with an air conditioner water supply and

seating have been found to be successful in a variety of environments For field

19

teams with high mobility even a simple shade structure readily available from

hardware stores or large umbrellas can provide relief from solar radiation

bull Where work-rest regimes are necessary heat stress indices such as WBGT PHS

or TWL assist in determining duration of work and rest periods

bull Training workers to identify symptoms and the potential onset of heat-related

illness as part of the lsquobuddy systemrsquo

bull Encouraging ldquoself-determinationrdquo or pacing of the work to meet the conditions and

reporting of heat related symptoms

bull Consider pre-placement medical screening for work in hot areas (ISO 12894)

Personal protective equipment

bull PPE such as cooling vests with either lsquophase changersquo cooling inserts (not ice) Ice

or chilled water cooled garments can result in contraction of the blood vessels

reducing the cooling effect of the garment

bull Vortex tube air cooling may be used in some situations particularly when a cooling

source is required when supplied air respirators are used

bull Choose light coloured materials for clothing and ensure they allow good air flow

across the skin to promote evaporative cooling

Heat stress hygiene practices are particularly important because they reduce the risk that

an individual may suffer a heat-related disorder The key elements are fluid replacement

self-assessment health status monitoring maintenance of a healthy life-style and

adjustment of work expectations based on acclimatisation state and ambient working

conditions The hygiene practices require the full cooperation of supervision and workers

20

Bibliography ACGIH (American Conference of Governmental Industrial Hygienists) (2013) Threshold

Limit Values for Chemical Substances and Physical Agents and Biological Exposure

Indices Cincinnati ACGIH Signature Publications

Armstrong LE (2007) Assessing hydration status The elusive gold standard Journal of

the American College of Nutrition 26(5) pp 575S-584S

Brake DJ amp Bates GP (2002) Limiting metabolic rate (thermal work limit) as an index of

thermal stress Applied Occupational and Environmental Hygiene 17 pp 176ndash86

Casa DJ Armstrong LE Hillman SK Montain SJ Reiff RV amp Rich BSE (2000)

National Athletic Trainers association Position Statement Fluid replacement for Athletes

Journal of Athletic Training 35(2) pp 212-224

Di Corleto R Coles G amp Firth I (2003) The development of a heat stress standard for

Australian conditions in Australian Institute of Occupational Hygienists Inc 20th Annual

Conference Proceedings Geelong Victoria December AIOH

Di Corleto R Firth I Mate J Coles G (2013) A Guide to Managing Heat Stress and

Documentation Developed For Use in the Australian Environment AIOH Melbourne

Ganio MS Casa DJ Armstrong LE amp Maresh CM (2007) Evidence based approach to

lingering hydration questions Clinics in Sports Medicine 26(1) pp 1ndash16

ISO 7243 (1989) Hot environments - Estimation of the heat stress on working man

based on the WBGT - index (wet bulb globe temperature)

ISO 7933 (2004) Ergonomics of the thermal environment Analytical determination and

interpretation of heat stress using calculation of the Predicted Heat Strain ISO 7933

ISO 8996 (2004) Ergonomics of the Thermal Environment ndash Determination of Metabolic

Rate Geneva ISO

ISO 9886 (1992) Evaluation of thermal strain by physiological measurements

ISO 12894 (2001) Ergonomics of the thermal environment ndash Medical supervision of

individuals exposed to extreme hot or cold environments

Miller V Bates G (2007) Hydration of outdoor workers in north-west Australia J

Occup Health Safety mdash Aust NZ 23(1) pp 79ndash87

21

Sawka MN (1998) Body fluid responses and hypohydration during exercise heat

stress in KB Pandolf MN Sawkaand amp RR Gonzalez (Eds) Human Performance

Physiology and Environmental Medicine at Terrestrial Extremes USA Brown amp

Benchmark pp 227 ndash 266

Shirreffs SM (2003) Markers of hydration status European Journal of Clinical Nutrition

57(2) pp s6-s9

Steadman RG (1979) The assessment of sultriness Part 1 A temperature humidity

index based on human physiology and clothing science Journal of applied meteorology

(July)

Tillman C (2007) (Ed) Principles of Occupational Health amp Hygiene - An Introduction

Allen amp Unwin Academic

22

Appendix 1 - Basic Thermal Risk Assessment using Apparent Temperature (Informative example only)

HAZARD TYPE Assessment Point Value 0 1 2 3 Sun Exposure Indoors Full Shade Part Shade No Shade Hot surfaces Neutral Warm on Contact Hot on contact Burn on contact Exposure period lt 30 min 30 min ndash 1hour 1 hour - 2 hours gt 2 hrs Confined space No Yes Task complexity Simple Moderate Complex Climbing updown stairs or ladders None One level Two levels gt Two levels Distance from cool rest area lt10 Metres 10 - 50 Metres 50-100 Metres gt100 Metres Distance from drinking water lt10 Metres 10 - 30 Metres 30-50 Metres gt50 Metres Clothing (permeable) Single layer (light) Single layer (mod) Multiple layer Understanding of heat strain risk Training given No training given Air movement Strong Wind Moderate Wind Light Wind No Wind Resp protection (-ve pressure) None Disposable Half Face Rubber Half Face Full Face Acclimatisation Acclimatised Unacclimatised

SUB-TOTAL A 2 4 6 Metabolic work rate Light Moderate Heavy SUB-TOTAL B 1 2 3 4 Apparent Temperature lt 27degC gt27degC le 33degC gt33degC le 41degC gt 41degC SUB-TOTAL C

TOTAL = A plus B Multiplied by C = Examples of Work Rate Light work Sitting or standing to control machines hand and arm work assembly or sorting of light materials Moderate work Sustained hand and arm work such as hammering handling of moderately heavy materials Heavy work Pick and shovel work continuous axe work carrying loads up stairs Instructions for use of the Basic Thermal Risk Assessment

bull Mark each box according to the appropriate conditions bull When complete add up using the value at the top of the appropriate column for each mark bull Add the sub totals of Table A amp Table B and multiply with the sub-total of Table C for the final result bull If the total is less than 28 then the risk due to thermal conditions are low to moderate bull If the total is 28 to 60 there is a potential of heat-induced illnesses occurring if the conditions are not

addressed Further analysis of heat stress risk is required bull If the total exceeds 60 then the onset of a heat-induced illness is very likely and action should be taken as

soon as possible to implement controls It is important to note that that this assessment is to be used as a guide only A number of factors are not included in this assessment such as employee health condition and the use of high levels of PPE (particularly impermeable suits) In these circumstances experienced personnel should carry out a more extensive assessment

23

Worked Example of Basic Thermal Risk Assessment An example of the application of the basic thermal risk assessment would be as follows A fitter is working on a pump out in the plant at ground level that has been taken out of service the previous day The task involves removing bolts and a casing to check the impellers for wear approximately 2 hours of work The pump is situated approximately 25 metres from the workshop The fitter is acclimatised has attended a training session and is wearing a standard single layer long shirt and trousers is carrying a water bottle and a respirator is not required The work rate is light there is a light breeze and the air temperature has been measured at 30degC and the relative humidity at 70 This equates to an apparent temperature of 35degC (see Table 5 in appendix 2) Using the above information in the risk assessment we have

HAZARD TYPE Assessment Point Value

0 1 2 3 Sun Exposure Indoors Shade Part Shade No Shade Hot surfaces Neutral Warm on Contact Hot on contact Burn on contact Exposure period lt 30 min 30 min ndash 1hour 1 hour - 2 hours gt 2 hrs Confined space No Yes Task complexity Simple Moderate Complex Climbing updown stairs or ladders None One level Two levels gt Two levels Distance from cool rest area lt10 Metres lt50 Metres 50-100 Metres gt100 Metres Distance from drinking water lt10 Metres lt30 Metres 30-50 Metres gt50 Metres Clothing (permeable) Single layer (light) Single layer (mod) Multiple layer Understanding of heat strain risk Training given No training given Air movement Strong Wind Moderate Wind Light Wind No Wind Resp protection (-ve pressure) None Disposable Half Face Rubber Half Face Full Face Acclimatisation Acclimatised Unacclimatised

3 6 0 SUB-TOTAL A 9 2 4 6 Metabolic work rate Light Moderate Heavy SUB-TOTAL B 2 1 2 3 4 Apparent Temperature lt 27degC gt27degC le 33degC gt33degC le 41degC gt 41degC SUB-TOTAL C 3

A = 9 B = 2 C = 3 therefore Total = (9+2) x 3 = 33 As the total lies between 28 and 60 there is a potential for heat induced illness occurring if the conditions are not addressed and further analysis of heat stress risk is required

24

Appendix 2 ndash Table 5 Apparent Temperature Dry BulbHumidity scale Align dry bulb temperature with corresponding relative humidity to determine apparent temperature in unshaded section of table Numbers in () refer to skin humidities above 90 and are only approximate

Dry Bulb Temperature Relative Humidity () (degC) 0 10 20 30 40 50 60 70 80 90 100 20 16 17 17 18 19 19 20 20 21 21 21 21 18 18 19 19 20 20 21 21 22 22 23 22 19 19 20 20 21 21 22 22 23 23 24 23 20 20 21 22 22 23 23 24 24 24 25 24 21 22 22 23 23 24 24 25 25 26 26 25 22 23 24 24 24 25 25 26 27 27 28 26 24 24 25 25 26 26 27 27 28 29 30 27 25 25 26 26 27 27 28 29 30 31 33 28 26 26 27 27 28 29 29 31 32 34 (36) 29 26 27 27 28 29 30 30 33 35 37 (40) 30 27 28 28 29 30 31 33 35 37 (40) (45) 31 28 29 29 30 31 33 35 37 40 (45) 32 29 29 30 31 33 35 37 40 44 (51) 33 29 30 31 33 34 36 39 43 (49)

34 30 31 32 34 36 38 42 (47)

35 31 32 33 35 37 40 (45) (51)

36 32 33 35 37 39 43 (49)

37 32 34 36 38 41 46

38 33 35 37 40 44 (49)

39 34 36 38 41 46

40 35 37 40 43 49

41 35 38 41 45

42 36 39 42 47

43 37 40 44 49

44 38 41 45 52

45 38 42 47

46 39 43 49

47 40 44 51

48 41 45 53

49 42 47

50 42 48

(Source Steadman 1979)

25

Documentation of the Heat Stress Guide Developed for Use in the Australian Environment

Developed for the Australian Institute of Occupational Hygienists

Ross Di Corleto Ian Firth amp Joseph Mateacute

November 2013

26

10 Introduction Heat-related illness has been a health hazard throughout the ages and is a function

of the imposition of environmental heat on the human body which itself generates

heat

11 Heat Illness ndash A Problem Throughout the Ages

The hot thermal environment has been a constant challenge to man for centuries and

its impact is referenced throughout history The bible tells of the death of Judithrsquos

husband Manasseh from exposure in the fields supervising workers where it says

ldquoHe had suffered a sunstroke while in the fields supervising the farm workers and

later died in bed at home in Bethuliardquo (Judith 83)

The impact of heat on the military in history is also well recorded the problems

confronted by the armies of King Sennacherib of Assyria (720BC) whilst attacking

Lashish Herodotus (400BC) reports of Spartan soldiers succumbing to ldquothirst and

sunrdquo Even Alexander the Great in 332BC was warned of the risks of a march across

the Libyan Desert And there is little doubt that heat stress played a major role in the

defeat of the Crusaders of King Edward in the Holy Land fighting the Saracens whilst

burdened down with heavy armour in the Middle Eastern heat (Goldman 2001)

It is not only the workers and armies that are impacted but also the general

population One of the worst cases occurred in Peking China in 1743 when during a

10 day heat wave 11000 people were reported to have perished (Levick 1859)

In 1774 Sir Charles Blagden of the Royal Society outlined a series of experiments

undertaken in a heated room in which he commented on ldquothe wonderful power with

which the animal body is endued of resisting heat vastly greater than its own

temperaturerdquo (Blagden 1775)

Despite this experience and knowledge over the ages we are still seeing deaths in

the 20th century as a result of heat stress Severe heat related illnesses and deaths

are not uncommon among pilgrims making the Makkah Hajj (Khogali 1987) and

closer to home a fatality in the Australian military (ABC 2004) and more recently

amongst the Australian workforce (Australian Mining 2013)

27

12 Heat and the Human Body

The human body in a state of wellbeing maintains its internal temperature within a

very narrow range This is a fundamental requirement for those internal chemical

reactions which are essential to life to proceed at the proper rates The actual level

of this temperature is a product of the balance between heat exchange with the

external thermal environment and the generation of heat internally by the metabolic

processes associated with life and activity

The temperature of blood circulating through the living and working tissues is

monitored by receptors throughout the body The role of these receptors is to induce

specific responses in functional body systems to ensure that the temperature

remains within the appropriate range

The combined effect of external thermal environment and internal metabolic heat

production constitutes the thermal stress on the body The levels of activity required

in response to the thermal stress by systems such as cardiovascular

thermoregulatory respiratory renal and endocrine constitute the thermal strain

Thus environmental conditions metabolic workload and clothing individually or

collectively create heat stress for the worker The bodyrsquos physiological response to

stressors for example sweating increased heart rate and elevated core

temperature is the heat strain

Such physiological changes are the initial responses to thermal stress but the extent

at which these responses are required will determine whether that strain will result in

thermal injuryillness It is important to appreciate that while preventing such illness

by satisfactorily regulating human body temperature in a heat-stress situation those

responses particularly the sweat response may not be compatible with comfort

(Gagge et al 1941)

The rate of heat generated by metabolic processes is dependent on the level of

physical activity To precisely quantify the metabolic cost associated with a particular

task without directly or indirectly measuring the individual is not possible This is due

to the individual differences associated with performing the task at hand As a

result broad categories of metabolic loads for typical work activities have been

established (Durnin amp Passmore 1967 ISO 8996 2004) It is sometimes practicable

Safe Work Australia (2011) refers to heat related illnesses and OSHA (httpswwwoshagovSLTCheatstress) considers heat exhaustion and heat stroke cases to be heat-related illness due to the number of human factors that contribute to a workers susceptibility to heat stress (refer to Section 40) while ACGIH (2013) refers to heat stress and heat strain cases as being heat-related disorders They are not usually considered injuries

28

71 Core Temperature 65

72 Heart Rate Measurements 67

80 CONTROLS 70

81 Ventilation 72

82 Radiant Heat 73

83 Administrative Controls 76 831 Training 76 832 Self-Assessment 77 833 Fluid Replacement 77 834 Rescheduling of Work 77 835 WorkRest Regimes 77 836 Clothing 78 837 Pre-placement Health Assessment 80

84 Personal Protective Equipment 81 841 Air Cooling System 81 842 Liquid Circulating Systems 82 843 Ice Cooling Systems 83 844 Reflective Clothing 84

90 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

5

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 ldquoThe heat stress standard

and documentation developed for use in the Australian environment (2003)rdquo 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 ldquoA guide to managing

heat stress developed for use in the Australian environment (2013)rdquo 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

bull the first a brief summary of the approach written for interested parties with a non-

technical background and

bull 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

6

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 ndash 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

7

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

bull air temperature

bull humidity

bull air movement

bull radiant heat exchange and

bull 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 bodyrsquos 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

bull prickly heat

bull headaches

bull nausea

bull 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

8

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 individualrsquos 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

9

Figure 1 Heat Stress Management Schematic (adapted from ACGIH 2013)

Level 1Perform Basic Risk

Assessment

Unacceptable risk

No

Does task involve use of impermeable clothing (ie PVC)

Continue work monitor conditionsNo

Are data available for detailed analysis

Level 2Analyse data with rational heat stress index (ie PHS

TWL)

Yes

Unacceptable heat stress risk based on analysis

Job specific controls practical and successful

Level 3Undertake physiological

monitoring

Cease work

Yes

Yes

No

Monitor task to ensure conditions amp collect dataNo

No

Maintain job specific controlsYes

Excessive heat strain based on monitoring

Yes

No

10

Level 1 Assessment a basic thermal risk assessment A suggested protocol for the level 1 assessment is termed the ldquoBasic Thermal Risk

Assessmentrdquo It has been designed as a simple tool which can be used by employees or

technicians to provide guidance and also as a training tool to illustrate the many factors

that impact on heat stress This risk assessment incorporates the contributions of a

number of factors that can impact on heat stress such as the state of acclimatisation work

demands location clothing and other physiological factors It can also incorporate the use

of a first level heat stress index such as Apparent Temperature or WBGT It is designed to

be an initial qualitative review of a potential heat stress situation for the purposes of

prioritising further measurements and controls It is not intended as a definitive

assessment tool Some of its key aspects are described below

Acclimatisation plays a part as it is a set of gradual physiological adjustments that improve

an individuals ability to tolerate heat stress the development and loss of which is

described in the Documentation

Metabolic work rate is of equal importance to environmental assessment in evaluating heat

stress Table 1 provides broad guidance for selecting the work rate category to be used in

the Risk Assessment There are a number of sources for this data including ISO

72431989 and ISO 89962004 standards

Table 1 Examples of Activities within Metabolic Rate (M) Classes

Class Examples

Resting Resting sitting at ease Low Light

Work Sitting at ease light manual work hand and arm work car driving

standing casual walking sitting or standing to control machines

Moderate

Moderate Work Sustained hand and arm work (eg hammering) arm and trunk

work moving light wheelbarrow walking around 45 kmh

High Heavy

Work

Intense arm and trunk work carrying heavy material shovelling

sawing hard wood moving heavily loaded wheelbarrows carrying

loads upstairs

Source (ISO 89962004)

Apparent temperature (Steadman 1979) can be used as part of the basic thermal risk

assessment The information required air temperature and humidity can be readily

obtained from most local weather bureau websites off-the-shelf weather units or

measured directly with a sling psychrometer Its simplicity is one of the advantages in its

use as it requires very little technical knowledge

11

The WBGT index also offers a useful first-order index of the environmental contribution to

heat stress It is influenced by air temperature radiant heat and humidity (ACGIH 2013)

In its simplest form it does not fully account for all of the interactions between a person

and the environment but is useful in this type of assessment The only disadvantage is

that it requires some specialised monitoring equipment such as a WBGT monitor or wet

bulb and globe thermometers

Both indices are described in more detail in the Documentation associated with this

standard

These environmental parameters are combined on a single check sheet in three sections

Each aspect is allocated a numerical value A task may be assessed by checking off

questions in the table and including some additional data for metabolic work load and

environmental conditions From this information a weighted calculation is used to

determine a numerical value which can be compared to pre-set criteria to provide

guidance as to the potential risk of heat stress and the course of action for controls

For example if the Assessment Point Total is less than 28 then the thermal condition risk

is low The lsquoNorsquo branch in Figure 1 can be taken Nevertheless if there are reports of the

symptoms of heat-related disorders such as prickly heat fatigue nausea dizziness and

light-headedness then the analysis should be reconsidered or proceed to detailed

analysis if appropriate If the Assessment Point Total is 28 or more further analysis is

required An Assessment Point Total greater than 60 indicates the need for immediate

action and implementation of controls (see Section 6)

Examples of a basic thermal risk assessment tool and their application are provided in

Appendix 1

Section 2 Screening for clothing that does not allow air and water vapour movement

The decision about clothing and how it might affect heat loss can also play an important

role in the initial assessment This is of particular importance if the clothing interferes with

the evaporation of sweat from the skin surface of an individual (ie heavy water barrier

clothing such as PVC) As this is the major heat loss mechanism disruption of this

process will significantly impact on the heat stress experienced Most heat exposure

assessment indices were developed for a traditional work uniform which consisted of a

long-sleeved shirt and pants Screening that is based on this attire is not suitable for

clothing ensembles that are more extensive and less permeable unless a detailed analysis

method appropriate for permeable clothing requirements is available With heat removal

hampered by clothing metabolic heat may produce life-threatening heat strain even when

12

ambient conditions are considered cool and the risk assessment determines ldquoLow Riskrdquo If

workers are required to wear additional clothing that does not allow air and water vapour

movement then the lsquoYesrsquo branch in the first question of Figure 1 should be taken

Physiological and behavioural monitoring described in Section 4 should be followed to

assess the potential for harm resulting from heat stress

Section 3 Level 2 assessment using detailed analysis

It is possible that a condition may be above the criteria provided in the initial risk

assessment and still not represent an unacceptable exposure To make this

determination a detailed analysis is required as in the Documentation

Note as discussed briefly above (see Section 2) no numerical screening criteria or limiting

values are applicable where clothing does not allow air or water vapour movement In this

case reliance must be placed on physiological monitoring

The screening criteria require a minimum set of data in order to make an assessment A

detailed analyses requires more data about the exposures including

bull clothing type

bull air speed

bull air temperature

bull water vapour content of the air (eg humidity)

bull posture

bull length of exposure and

bull globe temperature

Following Figure 1 the next question asks about the availability of such exposure data for

a detailed analysis If exposure data are not available the lsquoNorsquo branch takes the

evaluation to the monitoring of the tasks to collect this data before moving on to the use of

a rational heat stress index These types of indices are based on the human heat balance

equation and utilise a number of formulae to predict responses of the body such as

sweating and elevation of core temperature From this information the likelihood of

developing a heat stress related disorder may be determined In situations where this

data cannot be collected or made available then physiological monitoring to assess the

degree of heat strain should be undertaken

Detailed rational analysis should follow ISO 7933 - Predicted Heat Strain or Thermal Work

Limit (TWL) although other indices with extensive supporting physiological documentation

may also be acceptable (see Documentation for details) While such a rational method

(versus the empirically derived WBGT or Basic Effective Temperature (BET) thresholds) is

13

computationally more difficult it permits a better understanding of the source of the heat

stress and can be a means to assess the benefits of proposed control modifications on the

exposure

Predicted heat strain (PHS) is a rational index (ie it is an index based on the heat balance

equation) It estimates the required sweat rate and the maximal evaporation rate utilising

the ratio of the two as an initial measure of lsquorequired wettednessrsquo This required

wettedness is the fraction of the skin surface that would have to be covered by sweat in

order for the required evaporation rate to occur The evaporation rate required to maintain

a heat balance is then calculated (Di Corleto et al 2003)

In the event that the suggested values might be exceeded ISO 7933 calculates an

allowable exposure time

The suggested limiting values assume workers are

bull fit for the activity being considered and

bull in good health and

bull screened for intolerance to heat and

bull properly instructed and

bull able to self-pace their work and

bull under some degree of supervision (minimally a buddy system)

In work situations which

bull either the maximum evaporation rate is negative leading to condensation of

water vapour on the skin

bull or the estimated allowable exposure time is less than 30 minutes so that the

phenomenon of sweating onset plays a major role in the estimation of the

evaporation loss of the subject Special precautionary measures need to be

taken and direct and individual physiological surveillance of the workers is

particularly necessary

The thermal work limit (TWL) was developed in Australia initially in the underground

mining industry by Brake and Bates (2002a) and later trialled in open cut mines in the

Pilbara region of Western Australia (Miller and Bates 2007a) TWL is defined as the

limiting (or maximum) sustainable metabolic rate that hydrated acclimatised individuals

can maintain in a specific thermal environment within a safe deep body core temperature

(lt382degC) and sweat rate (lt12 kghr) (Tillman 2007)

Due to this complexity these calculations are carried out with the use of computer

software or in the case of TWL pre-programmed monitoring equipment

14

If the exposure does not exceed the criteria for the detailed analysis then the lsquoNorsquo branch

can be taken Because the criteria in the risk assessment have been exceeded

monitoring general heat stress controls are appropriate General controls include training

for workers and supervisors and heat stress hygiene practices If the exposure exceeds

the suggested limits from the detailed analysis or set by the appropriate authority the

lsquoYesrsquo branch leads to the iterative assessment of job-specific control options using the

detailed analysis and then implementation and assessment of control(s) If these are not

available or it cannot be demonstrated that they are successful then the lsquoNorsquo branch

leads to physiological monitoring as the only alternative to demonstrate that adequate

protection is provided

Section 4 Level 3 assessment of heat strain

There are circumstances where the assessment using the rational indices cannot assure

the safety of the exposed workgroup In these cases the use of individual physiological

monitoring may be required These may include situations of high heat stress risk or

where the individualrsquos working environment cannot be accurately assessed A common

example is work involving the use of encapsulating ldquohazmatrdquo suits

The risk and severity of excessive heat strain will vary widely among people even under

identical heat stress conditions By monitoring the physiological responses to working in a

hot environment this allows the workers to use the feedback to assess the level of heat

strain present in the workforce to guide the design of exposure controls and to assess the

effectiveness of implemented controls Instrumentation is available for personal heat

stress monitoring These instruments do not measure the environmental conditions

leading to heat stress but rather they monitor the physiological indicators of heat strain -

usually elevated body temperature andor heart rate Modern instruments utilise an

ingestible core temperature capsule which transmits physiological parameters

telemetrically to an external data logging sensor or laptop computer This information can

then be monitored in real time or assessed post task by a qualified professional

Monitoring the signs and symptoms of heat-stressed workers is sound occupational

hygiene practice especially when clothing may significantly reduce heat loss For

surveillance purposes a pattern of workers exceeding the limits below is considered

indicative of the need to control the exposures On an individual basis these limits are

believed to represent a time to cease an exposure until recovery is complete

Table 2 provides guidance for acceptable limits of heat strain Such physiological

monitoring (see ISO 12894 2001) should be conducted by a physician nurse or

equivalent as allowed by local law

15

Table 2 Physiological Guidelines for Limiting Heat Strain The American Conference of Industrial Hygienists (ACGIH 2013) has published

physiological limits for a number of years and states that exposure to

environmentally or activity-induced heat stress must be discontinued at any time

when

bull Sustained (several minutes) heart rate in excess of 180 beats per minute

minus the individuals age in years (eg180 ndash age) for individuals with

assessed normal cardiac performance OR

bull Body core temperature greater than 385degC (1013degC) for medically

selected and acclimatised personnel or greater than 38degC (1004degC) in

unselected unacclimatised workers OR

bull When there are complaints of sudden and severe fatigue nausea

dizziness or light-headedness OR

bull A workers recovery heart rate at one minute after a peak work effort is

greater than 120 beats per minute 124 bpm was suggested by Fuller and

Smith (1982) OR

bull A worker experiences profuse and prolonged sweating over hours and

may not be able to adequately replenish fluids OR

bull Greater than 15 weight loss over a shift OR

bull In conditions of regular daily exposure to the stress 24-hour urinary

sodium excretion is less than 50 mmoles

ISO 9886 (2004) suggests that exposure to environmentally or activity-induced heat

stress must also be discontinued at any time when

bull lsquoHeart Rate Limit = 185 - 065Arsquo where A = Age in years

bull Individual variability can range up to 20 bpm from this average so this

level could present a risk for some individuals Where there is

uncertainty the sustained heart rate over a work period should not

exceed the previously mentioned

bull HRL sustained = 180 ndash age

bull No matter which limiting values are used interpretation requires

discussion with the workers affected and may require the services of a

specialist such as an occupational hygienist or occupational physician

If a worker appears to be disoriented or confused or demonstrates uncharacteristic

16

irritability discomfort or flu-like symptoms the worker should be removed for rest

under observation in a cool location Symptoms of heat stroke need to be monitored

closely and if sweating stops and the skin becomes hot and dry immediate

emergency care is essential

The prompt treatment of other heat-related disorders generally results in full

recovery but medical advice should be sought for treatment and return-to-work

protocols

Following good occupational hygiene sampling practice which considers likely extremes

and the less tolerant workers the absence of any of these limiting observations indicates

acceptable management of the heat stress exposures With acceptable levels of heat

strain the lsquoNorsquo branch in the level 3 section of Figure 1 is taken Nevertheless even if the

heat strain among workers is considered acceptable at the time the general controls are

necessary In addition periodic physiological monitoring should be continued to ensure

that acceptable levels of heat strain are being maintained

If excessive heat strain is found during the physiological assessments then the lsquoYesrsquo

branch is taken This means that the work activities must cease until suitable job-specific

controls can be considered and implemented to a sufficient extent to control that strain

The job-specific controls may include engineering controls administrative controls and

personal protection

After implementation of the job-specific controls it is necessary to assess their

effectiveness and to adjust them as needed

Section 5 Occupational Exposure Limits

Currently there are fewer workplaces where formal exposure limits for heat stress still

apply however this practice is found mainly within the mining industry There are many

variables associated with the onset of heat stress and these can be a result of the task

environment andor the individual Trying to set a general limit which adequately covers

the many variations within industry has proven to be extremely complicated The attempts

have sometimes resulted in an exposure standard so conservative in a particular

environment that it would become impractical to apply It is important to note that heat

stress indices are not safeunsafe limits and should only be used as guides

Use of Urinary Specific Gravity testing

Water intake at onersquos own discretion results in incomplete fluid replacement for individuals

working in the heat and there is consistent evidence that relying solely on thirst as an

17

indicator of fluid requirement will not restore water balance (Sawka 1998) Urine specific

gravity (USG) can be used as a guide in relation to the level of hydration of an individual

(Shirreffs 2003) and this method of monitoring is becoming increasingly popular in

Australia as a physiological limit Specific gravity (SG) is defined as the ratio weight of a

substance compared to the weight of an equal volume of distilled water hence the SG of

distilled water is 1000 Studies (Sawka et al 2007 Ganio et al 2007 Cheuvront amp

Sawka 2005 Casa et al 2000) recommend that a USG of greater than 1020 would

reflect dehydration While not regarded as fool proof or the ldquogold standardrdquo for total body

water (Armstrong 2007) it is a good compromise between accuracy simplicity of testing

in the field and acceptability to workers of a physiological measure Table 3 shows the

relationship between SG of urine and hydration

Table 3 US National Athletic Trainers Association index of hydration status Body Weight

Loss ()

Urine Specific

Gravity

Well Hydrated lt1 1010

Minimal dehydration 1 - 3 1010 ndash 1020

Significant

dehydration

3 - 5 1021 ndash 1030

Severe dehydration gt 5 gt 1030 Source adapted from Casa et al 2000

Section 6 Heat stress management and controls

The requirement to initiate a heat stress management program is marked by

(1) heat stress levels that exceed the criteria in the Basic Thermal Risk Assessment or

level 2 heat index assessment or

(2) work in clothing ensembles that are air or water vapour impermeable

There are numerous controls across the hierarchy of controls that may be utilised to

address heat stress issues in the workplace Not all may be applicable to a particular task

or scenario and often may require some adjusting before a suitable combination is

achieved

In addition to general controls appropriate job-specific controls are often required to

provide adequate protection During the consideration of job-specific controls detailed

analysis provides a framework to appreciate the interactions among acclimatisation stage

metabolic rate workrest cycles and clothing Table 4 lists some examples of controls

available The list is by no means exhaustive but will provide some ideas for controls

18

Table 4 Examples of control methods

Eliminationsubstitution

bull Hot tasks should be scheduled to avoid the hottest part of the day or where

practical undertaken during night shifts

bull Walls and roof structures should utilize light coloured or reflective materials

bull Structures should be designed to incorporate good air flow This can be done via

the positioning of windows shutters and roof design to encourage lsquochimney

effectsrsquo This will help remove the heat from the structure

bull Walls and roofs should be insulated

Engineering

bull Pipework and vessels associated with hot processes should be insulated and clad

to minimize the introduction of heat into the work environment

bull In high humidity areas such as northern Australia more air needs to be moved

hence fans to increase air flow or in extreme cases cooled air from lsquochillerrsquo units

can be used

bull Where radiated heat from a process is a problem insulating barriers or reflective

barriers can be used to absorb or re-direct radiant heat These may be permanent

structures or movable screens

bull Relocating hot processes away from high access areas

bull Dehumidifying air to increase the evaporative cooling effect Often steam leaks

open process vessels or standing water can artificially increase humidity within a

building

bull Utilize mechanical aids that can reduce the metabolic workload on the individual

Administrative

bull Ready access to cool palatable drinking water is a basic necessity

bull Where applicable suitable electrolyte replacements should also be available

bull A clean cool area for employees to rest and recuperate can add significant

improvement to the cooling process Resting in the work environment can provide

some relief for the worker the level of recovery is much quicker and more efficient

in an air-conditioned environment These need not be elaborate structures basic

inexpensive portable enclosed structures with an air conditioner water supply and

seating have been found to be successful in a variety of environments For field

19

teams with high mobility even a simple shade structure readily available from

hardware stores or large umbrellas can provide relief from solar radiation

bull Where work-rest regimes are necessary heat stress indices such as WBGT PHS

or TWL assist in determining duration of work and rest periods

bull Training workers to identify symptoms and the potential onset of heat-related

illness as part of the lsquobuddy systemrsquo

bull Encouraging ldquoself-determinationrdquo or pacing of the work to meet the conditions and

reporting of heat related symptoms

bull Consider pre-placement medical screening for work in hot areas (ISO 12894)

Personal protective equipment

bull PPE such as cooling vests with either lsquophase changersquo cooling inserts (not ice) Ice

or chilled water cooled garments can result in contraction of the blood vessels

reducing the cooling effect of the garment

bull Vortex tube air cooling may be used in some situations particularly when a cooling

source is required when supplied air respirators are used

bull Choose light coloured materials for clothing and ensure they allow good air flow

across the skin to promote evaporative cooling

Heat stress hygiene practices are particularly important because they reduce the risk that

an individual may suffer a heat-related disorder The key elements are fluid replacement

self-assessment health status monitoring maintenance of a healthy life-style and

adjustment of work expectations based on acclimatisation state and ambient working

conditions The hygiene practices require the full cooperation of supervision and workers

20

Bibliography ACGIH (American Conference of Governmental Industrial Hygienists) (2013) Threshold

Limit Values for Chemical Substances and Physical Agents and Biological Exposure

Indices Cincinnati ACGIH Signature Publications

Armstrong LE (2007) Assessing hydration status The elusive gold standard Journal of

the American College of Nutrition 26(5) pp 575S-584S

Brake DJ amp Bates GP (2002) Limiting metabolic rate (thermal work limit) as an index of

thermal stress Applied Occupational and Environmental Hygiene 17 pp 176ndash86

Casa DJ Armstrong LE Hillman SK Montain SJ Reiff RV amp Rich BSE (2000)

National Athletic Trainers association Position Statement Fluid replacement for Athletes

Journal of Athletic Training 35(2) pp 212-224

Di Corleto R Coles G amp Firth I (2003) The development of a heat stress standard for

Australian conditions in Australian Institute of Occupational Hygienists Inc 20th Annual

Conference Proceedings Geelong Victoria December AIOH

Di Corleto R Firth I Mate J Coles G (2013) A Guide to Managing Heat Stress and

Documentation Developed For Use in the Australian Environment AIOH Melbourne

Ganio MS Casa DJ Armstrong LE amp Maresh CM (2007) Evidence based approach to

lingering hydration questions Clinics in Sports Medicine 26(1) pp 1ndash16

ISO 7243 (1989) Hot environments - Estimation of the heat stress on working man

based on the WBGT - index (wet bulb globe temperature)

ISO 7933 (2004) Ergonomics of the thermal environment Analytical determination and

interpretation of heat stress using calculation of the Predicted Heat Strain ISO 7933

ISO 8996 (2004) Ergonomics of the Thermal Environment ndash Determination of Metabolic

Rate Geneva ISO

ISO 9886 (1992) Evaluation of thermal strain by physiological measurements

ISO 12894 (2001) Ergonomics of the thermal environment ndash Medical supervision of

individuals exposed to extreme hot or cold environments

Miller V Bates G (2007) Hydration of outdoor workers in north-west Australia J

Occup Health Safety mdash Aust NZ 23(1) pp 79ndash87

21

Sawka MN (1998) Body fluid responses and hypohydration during exercise heat

stress in KB Pandolf MN Sawkaand amp RR Gonzalez (Eds) Human Performance

Physiology and Environmental Medicine at Terrestrial Extremes USA Brown amp

Benchmark pp 227 ndash 266

Shirreffs SM (2003) Markers of hydration status European Journal of Clinical Nutrition

57(2) pp s6-s9

Steadman RG (1979) The assessment of sultriness Part 1 A temperature humidity

index based on human physiology and clothing science Journal of applied meteorology

(July)

Tillman C (2007) (Ed) Principles of Occupational Health amp Hygiene - An Introduction

Allen amp Unwin Academic

22

Appendix 1 - Basic Thermal Risk Assessment using Apparent Temperature (Informative example only)

HAZARD TYPE Assessment Point Value 0 1 2 3 Sun Exposure Indoors Full Shade Part Shade No Shade Hot surfaces Neutral Warm on Contact Hot on contact Burn on contact Exposure period lt 30 min 30 min ndash 1hour 1 hour - 2 hours gt 2 hrs Confined space No Yes Task complexity Simple Moderate Complex Climbing updown stairs or ladders None One level Two levels gt Two levels Distance from cool rest area lt10 Metres 10 - 50 Metres 50-100 Metres gt100 Metres Distance from drinking water lt10 Metres 10 - 30 Metres 30-50 Metres gt50 Metres Clothing (permeable) Single layer (light) Single layer (mod) Multiple layer Understanding of heat strain risk Training given No training given Air movement Strong Wind Moderate Wind Light Wind No Wind Resp protection (-ve pressure) None Disposable Half Face Rubber Half Face Full Face Acclimatisation Acclimatised Unacclimatised

SUB-TOTAL A 2 4 6 Metabolic work rate Light Moderate Heavy SUB-TOTAL B 1 2 3 4 Apparent Temperature lt 27degC gt27degC le 33degC gt33degC le 41degC gt 41degC SUB-TOTAL C

TOTAL = A plus B Multiplied by C = Examples of Work Rate Light work Sitting or standing to control machines hand and arm work assembly or sorting of light materials Moderate work Sustained hand and arm work such as hammering handling of moderately heavy materials Heavy work Pick and shovel work continuous axe work carrying loads up stairs Instructions for use of the Basic Thermal Risk Assessment

bull Mark each box according to the appropriate conditions bull When complete add up using the value at the top of the appropriate column for each mark bull Add the sub totals of Table A amp Table B and multiply with the sub-total of Table C for the final result bull If the total is less than 28 then the risk due to thermal conditions are low to moderate bull If the total is 28 to 60 there is a potential of heat-induced illnesses occurring if the conditions are not

addressed Further analysis of heat stress risk is required bull If the total exceeds 60 then the onset of a heat-induced illness is very likely and action should be taken as

soon as possible to implement controls It is important to note that that this assessment is to be used as a guide only A number of factors are not included in this assessment such as employee health condition and the use of high levels of PPE (particularly impermeable suits) In these circumstances experienced personnel should carry out a more extensive assessment

23

Worked Example of Basic Thermal Risk Assessment An example of the application of the basic thermal risk assessment would be as follows A fitter is working on a pump out in the plant at ground level that has been taken out of service the previous day The task involves removing bolts and a casing to check the impellers for wear approximately 2 hours of work The pump is situated approximately 25 metres from the workshop The fitter is acclimatised has attended a training session and is wearing a standard single layer long shirt and trousers is carrying a water bottle and a respirator is not required The work rate is light there is a light breeze and the air temperature has been measured at 30degC and the relative humidity at 70 This equates to an apparent temperature of 35degC (see Table 5 in appendix 2) Using the above information in the risk assessment we have

HAZARD TYPE Assessment Point Value

0 1 2 3 Sun Exposure Indoors Shade Part Shade No Shade Hot surfaces Neutral Warm on Contact Hot on contact Burn on contact Exposure period lt 30 min 30 min ndash 1hour 1 hour - 2 hours gt 2 hrs Confined space No Yes Task complexity Simple Moderate Complex Climbing updown stairs or ladders None One level Two levels gt Two levels Distance from cool rest area lt10 Metres lt50 Metres 50-100 Metres gt100 Metres Distance from drinking water lt10 Metres lt30 Metres 30-50 Metres gt50 Metres Clothing (permeable) Single layer (light) Single layer (mod) Multiple layer Understanding of heat strain risk Training given No training given Air movement Strong Wind Moderate Wind Light Wind No Wind Resp protection (-ve pressure) None Disposable Half Face Rubber Half Face Full Face Acclimatisation Acclimatised Unacclimatised

3 6 0 SUB-TOTAL A 9 2 4 6 Metabolic work rate Light Moderate Heavy SUB-TOTAL B 2 1 2 3 4 Apparent Temperature lt 27degC gt27degC le 33degC gt33degC le 41degC gt 41degC SUB-TOTAL C 3

A = 9 B = 2 C = 3 therefore Total = (9+2) x 3 = 33 As the total lies between 28 and 60 there is a potential for heat induced illness occurring if the conditions are not addressed and further analysis of heat stress risk is required

24

Appendix 2 ndash Table 5 Apparent Temperature Dry BulbHumidity scale Align dry bulb temperature with corresponding relative humidity to determine apparent temperature in unshaded section of table Numbers in () refer to skin humidities above 90 and are only approximate

Dry Bulb Temperature Relative Humidity () (degC) 0 10 20 30 40 50 60 70 80 90 100 20 16 17 17 18 19 19 20 20 21 21 21 21 18 18 19 19 20 20 21 21 22 22 23 22 19 19 20 20 21 21 22 22 23 23 24 23 20 20 21 22 22 23 23 24 24 24 25 24 21 22 22 23 23 24 24 25 25 26 26 25 22 23 24 24 24 25 25 26 27 27 28 26 24 24 25 25 26 26 27 27 28 29 30 27 25 25 26 26 27 27 28 29 30 31 33 28 26 26 27 27 28 29 29 31 32 34 (36) 29 26 27 27 28 29 30 30 33 35 37 (40) 30 27 28 28 29 30 31 33 35 37 (40) (45) 31 28 29 29 30 31 33 35 37 40 (45) 32 29 29 30 31 33 35 37 40 44 (51) 33 29 30 31 33 34 36 39 43 (49)

34 30 31 32 34 36 38 42 (47)

35 31 32 33 35 37 40 (45) (51)

36 32 33 35 37 39 43 (49)

37 32 34 36 38 41 46

38 33 35 37 40 44 (49)

39 34 36 38 41 46

40 35 37 40 43 49

41 35 38 41 45

42 36 39 42 47

43 37 40 44 49

44 38 41 45 52

45 38 42 47

46 39 43 49

47 40 44 51

48 41 45 53

49 42 47

50 42 48

(Source Steadman 1979)

25

Documentation of the Heat Stress Guide Developed for Use in the Australian Environment

Developed for the Australian Institute of Occupational Hygienists

Ross Di Corleto Ian Firth amp Joseph Mateacute

November 2013

26

10 Introduction Heat-related illness has been a health hazard throughout the ages and is a function

of the imposition of environmental heat on the human body which itself generates

heat

11 Heat Illness ndash A Problem Throughout the Ages

The hot thermal environment has been a constant challenge to man for centuries and

its impact is referenced throughout history The bible tells of the death of Judithrsquos

husband Manasseh from exposure in the fields supervising workers where it says

ldquoHe had suffered a sunstroke while in the fields supervising the farm workers and

later died in bed at home in Bethuliardquo (Judith 83)

The impact of heat on the military in history is also well recorded the problems

confronted by the armies of King Sennacherib of Assyria (720BC) whilst attacking

Lashish Herodotus (400BC) reports of Spartan soldiers succumbing to ldquothirst and

sunrdquo Even Alexander the Great in 332BC was warned of the risks of a march across

the Libyan Desert And there is little doubt that heat stress played a major role in the

defeat of the Crusaders of King Edward in the Holy Land fighting the Saracens whilst

burdened down with heavy armour in the Middle Eastern heat (Goldman 2001)

It is not only the workers and armies that are impacted but also the general

population One of the worst cases occurred in Peking China in 1743 when during a

10 day heat wave 11000 people were reported to have perished (Levick 1859)

In 1774 Sir Charles Blagden of the Royal Society outlined a series of experiments

undertaken in a heated room in which he commented on ldquothe wonderful power with

which the animal body is endued of resisting heat vastly greater than its own

temperaturerdquo (Blagden 1775)

Despite this experience and knowledge over the ages we are still seeing deaths in

the 20th century as a result of heat stress Severe heat related illnesses and deaths

are not uncommon among pilgrims making the Makkah Hajj (Khogali 1987) and

closer to home a fatality in the Australian military (ABC 2004) and more recently

amongst the Australian workforce (Australian Mining 2013)

27

12 Heat and the Human Body

The human body in a state of wellbeing maintains its internal temperature within a

very narrow range This is a fundamental requirement for those internal chemical

reactions which are essential to life to proceed at the proper rates The actual level

of this temperature is a product of the balance between heat exchange with the

external thermal environment and the generation of heat internally by the metabolic

processes associated with life and activity

The temperature of blood circulating through the living and working tissues is

monitored by receptors throughout the body The role of these receptors is to induce

specific responses in functional body systems to ensure that the temperature

remains within the appropriate range

The combined effect of external thermal environment and internal metabolic heat

production constitutes the thermal stress on the body The levels of activity required

in response to the thermal stress by systems such as cardiovascular

thermoregulatory respiratory renal and endocrine constitute the thermal strain

Thus environmental conditions metabolic workload and clothing individually or

collectively create heat stress for the worker The bodyrsquos physiological response to

stressors for example sweating increased heart rate and elevated core

temperature is the heat strain

Such physiological changes are the initial responses to thermal stress but the extent

at which these responses are required will determine whether that strain will result in

thermal injuryillness It is important to appreciate that while preventing such illness

by satisfactorily regulating human body temperature in a heat-stress situation those

responses particularly the sweat response may not be compatible with comfort

(Gagge et al 1941)

The rate of heat generated by metabolic processes is dependent on the level of

physical activity To precisely quantify the metabolic cost associated with a particular

task without directly or indirectly measuring the individual is not possible This is due

to the individual differences associated with performing the task at hand As a

result broad categories of metabolic loads for typical work activities have been

established (Durnin amp Passmore 1967 ISO 8996 2004) It is sometimes practicable

Safe Work Australia (2011) refers to heat related illnesses and OSHA (httpswwwoshagovSLTCheatstress) considers heat exhaustion and heat stroke cases to be heat-related illness due to the number of human factors that contribute to a workers susceptibility to heat stress (refer to Section 40) while ACGIH (2013) refers to heat stress and heat strain cases as being heat-related disorders They are not usually considered injuries

28

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 ldquoThe heat stress standard

and documentation developed for use in the Australian environment (2003)rdquo 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 ldquoA guide to managing

heat stress developed for use in the Australian environment (2013)rdquo 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

bull the first a brief summary of the approach written for interested parties with a non-

technical background and

bull 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

6

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 ndash 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

7

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

bull air temperature

bull humidity

bull air movement

bull radiant heat exchange and

bull 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 bodyrsquos 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

bull prickly heat

bull headaches

bull nausea

bull 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

8

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 individualrsquos 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

9

Figure 1 Heat Stress Management Schematic (adapted from ACGIH 2013)

Level 1Perform Basic Risk

Assessment

Unacceptable risk

No

Does task involve use of impermeable clothing (ie PVC)

Continue work monitor conditionsNo

Are data available for detailed analysis

Level 2Analyse data with rational heat stress index (ie PHS

TWL)

Yes

Unacceptable heat stress risk based on analysis

Job specific controls practical and successful

Level 3Undertake physiological

monitoring

Cease work

Yes

Yes

No

Monitor task to ensure conditions amp collect dataNo

No

Maintain job specific controlsYes

Excessive heat strain based on monitoring

Yes

No

10

Level 1 Assessment a basic thermal risk assessment A suggested protocol for the level 1 assessment is termed the ldquoBasic Thermal Risk

Assessmentrdquo It has been designed as a simple tool which can be used by employees or

technicians to provide guidance and also as a training tool to illustrate the many factors

that impact on heat stress This risk assessment incorporates the contributions of a

number of factors that can impact on heat stress such as the state of acclimatisation work

demands location clothing and other physiological factors It can also incorporate the use

of a first level heat stress index such as Apparent Temperature or WBGT It is designed to

be an initial qualitative review of a potential heat stress situation for the purposes of

prioritising further measurements and controls It is not intended as a definitive

assessment tool Some of its key aspects are described below

Acclimatisation plays a part as it is a set of gradual physiological adjustments that improve

an individuals ability to tolerate heat stress the development and loss of which is

described in the Documentation

Metabolic work rate is of equal importance to environmental assessment in evaluating heat

stress Table 1 provides broad guidance for selecting the work rate category to be used in

the Risk Assessment There are a number of sources for this data including ISO

72431989 and ISO 89962004 standards

Table 1 Examples of Activities within Metabolic Rate (M) Classes

Class Examples

Resting Resting sitting at ease Low Light

Work Sitting at ease light manual work hand and arm work car driving

standing casual walking sitting or standing to control machines

Moderate

Moderate Work Sustained hand and arm work (eg hammering) arm and trunk

work moving light wheelbarrow walking around 45 kmh

High Heavy

Work

Intense arm and trunk work carrying heavy material shovelling

sawing hard wood moving heavily loaded wheelbarrows carrying

loads upstairs

Source (ISO 89962004)

Apparent temperature (Steadman 1979) can be used as part of the basic thermal risk

assessment The information required air temperature and humidity can be readily

obtained from most local weather bureau websites off-the-shelf weather units or

measured directly with a sling psychrometer Its simplicity is one of the advantages in its

use as it requires very little technical knowledge

11

The WBGT index also offers a useful first-order index of the environmental contribution to

heat stress It is influenced by air temperature radiant heat and humidity (ACGIH 2013)

In its simplest form it does not fully account for all of the interactions between a person

and the environment but is useful in this type of assessment The only disadvantage is

that it requires some specialised monitoring equipment such as a WBGT monitor or wet

bulb and globe thermometers

Both indices are described in more detail in the Documentation associated with this

standard

These environmental parameters are combined on a single check sheet in three sections

Each aspect is allocated a numerical value A task may be assessed by checking off

questions in the table and including some additional data for metabolic work load and

environmental conditions From this information a weighted calculation is used to

determine a numerical value which can be compared to pre-set criteria to provide

guidance as to the potential risk of heat stress and the course of action for controls

For example if the Assessment Point Total is less than 28 then the thermal condition risk

is low The lsquoNorsquo branch in Figure 1 can be taken Nevertheless if there are reports of the

symptoms of heat-related disorders such as prickly heat fatigue nausea dizziness and

light-headedness then the analysis should be reconsidered or proceed to detailed

analysis if appropriate If the Assessment Point Total is 28 or more further analysis is

required An Assessment Point Total greater than 60 indicates the need for immediate

action and implementation of controls (see Section 6)

Examples of a basic thermal risk assessment tool and their application are provided in

Appendix 1

Section 2 Screening for clothing that does not allow air and water vapour movement

The decision about clothing and how it might affect heat loss can also play an important

role in the initial assessment This is of particular importance if the clothing interferes with

the evaporation of sweat from the skin surface of an individual (ie heavy water barrier

clothing such as PVC) As this is the major heat loss mechanism disruption of this

process will significantly impact on the heat stress experienced Most heat exposure

assessment indices were developed for a traditional work uniform which consisted of a

long-sleeved shirt and pants Screening that is based on this attire is not suitable for

clothing ensembles that are more extensive and less permeable unless a detailed analysis

method appropriate for permeable clothing requirements is available With heat removal

hampered by clothing metabolic heat may produce life-threatening heat strain even when

12

ambient conditions are considered cool and the risk assessment determines ldquoLow Riskrdquo If

workers are required to wear additional clothing that does not allow air and water vapour

movement then the lsquoYesrsquo branch in the first question of Figure 1 should be taken

Physiological and behavioural monitoring described in Section 4 should be followed to

assess the potential for harm resulting from heat stress

Section 3 Level 2 assessment using detailed analysis

It is possible that a condition may be above the criteria provided in the initial risk

assessment and still not represent an unacceptable exposure To make this

determination a detailed analysis is required as in the Documentation

Note as discussed briefly above (see Section 2) no numerical screening criteria or limiting

values are applicable where clothing does not allow air or water vapour movement In this

case reliance must be placed on physiological monitoring

The screening criteria require a minimum set of data in order to make an assessment A

detailed analyses requires more data about the exposures including

bull clothing type

bull air speed

bull air temperature

bull water vapour content of the air (eg humidity)

bull posture

bull length of exposure and

bull globe temperature

Following Figure 1 the next question asks about the availability of such exposure data for

a detailed analysis If exposure data are not available the lsquoNorsquo branch takes the

evaluation to the monitoring of the tasks to collect this data before moving on to the use of

a rational heat stress index These types of indices are based on the human heat balance

equation and utilise a number of formulae to predict responses of the body such as

sweating and elevation of core temperature From this information the likelihood of

developing a heat stress related disorder may be determined In situations where this

data cannot be collected or made available then physiological monitoring to assess the

degree of heat strain should be undertaken

Detailed rational analysis should follow ISO 7933 - Predicted Heat Strain or Thermal Work

Limit (TWL) although other indices with extensive supporting physiological documentation

may also be acceptable (see Documentation for details) While such a rational method

(versus the empirically derived WBGT or Basic Effective Temperature (BET) thresholds) is

13

computationally more difficult it permits a better understanding of the source of the heat

stress and can be a means to assess the benefits of proposed control modifications on the

exposure

Predicted heat strain (PHS) is a rational index (ie it is an index based on the heat balance

equation) It estimates the required sweat rate and the maximal evaporation rate utilising

the ratio of the two as an initial measure of lsquorequired wettednessrsquo This required

wettedness is the fraction of the skin surface that would have to be covered by sweat in

order for the required evaporation rate to occur The evaporation rate required to maintain

a heat balance is then calculated (Di Corleto et al 2003)

In the event that the suggested values might be exceeded ISO 7933 calculates an

allowable exposure time

The suggested limiting values assume workers are

bull fit for the activity being considered and

bull in good health and

bull screened for intolerance to heat and

bull properly instructed and

bull able to self-pace their work and

bull under some degree of supervision (minimally a buddy system)

In work situations which

bull either the maximum evaporation rate is negative leading to condensation of

water vapour on the skin

bull or the estimated allowable exposure time is less than 30 minutes so that the

phenomenon of sweating onset plays a major role in the estimation of the

evaporation loss of the subject Special precautionary measures need to be

taken and direct and individual physiological surveillance of the workers is

particularly necessary

The thermal work limit (TWL) was developed in Australia initially in the underground

mining industry by Brake and Bates (2002a) and later trialled in open cut mines in the

Pilbara region of Western Australia (Miller and Bates 2007a) TWL is defined as the

limiting (or maximum) sustainable metabolic rate that hydrated acclimatised individuals

can maintain in a specific thermal environment within a safe deep body core temperature

(lt382degC) and sweat rate (lt12 kghr) (Tillman 2007)

Due to this complexity these calculations are carried out with the use of computer

software or in the case of TWL pre-programmed monitoring equipment

14

If the exposure does not exceed the criteria for the detailed analysis then the lsquoNorsquo branch

can be taken Because the criteria in the risk assessment have been exceeded

monitoring general heat stress controls are appropriate General controls include training

for workers and supervisors and heat stress hygiene practices If the exposure exceeds

the suggested limits from the detailed analysis or set by the appropriate authority the

lsquoYesrsquo branch leads to the iterative assessment of job-specific control options using the

detailed analysis and then implementation and assessment of control(s) If these are not

available or it cannot be demonstrated that they are successful then the lsquoNorsquo branch

leads to physiological monitoring as the only alternative to demonstrate that adequate

protection is provided

Section 4 Level 3 assessment of heat strain

There are circumstances where the assessment using the rational indices cannot assure

the safety of the exposed workgroup In these cases the use of individual physiological

monitoring may be required These may include situations of high heat stress risk or

where the individualrsquos working environment cannot be accurately assessed A common

example is work involving the use of encapsulating ldquohazmatrdquo suits

The risk and severity of excessive heat strain will vary widely among people even under

identical heat stress conditions By monitoring the physiological responses to working in a

hot environment this allows the workers to use the feedback to assess the level of heat

strain present in the workforce to guide the design of exposure controls and to assess the

effectiveness of implemented controls Instrumentation is available for personal heat

stress monitoring These instruments do not measure the environmental conditions

leading to heat stress but rather they monitor the physiological indicators of heat strain -

usually elevated body temperature andor heart rate Modern instruments utilise an

ingestible core temperature capsule which transmits physiological parameters

telemetrically to an external data logging sensor or laptop computer This information can

then be monitored in real time or assessed post task by a qualified professional

Monitoring the signs and symptoms of heat-stressed workers is sound occupational

hygiene practice especially when clothing may significantly reduce heat loss For

surveillance purposes a pattern of workers exceeding the limits below is considered

indicative of the need to control the exposures On an individual basis these limits are

believed to represent a time to cease an exposure until recovery is complete

Table 2 provides guidance for acceptable limits of heat strain Such physiological

monitoring (see ISO 12894 2001) should be conducted by a physician nurse or

equivalent as allowed by local law

15

Table 2 Physiological Guidelines for Limiting Heat Strain The American Conference of Industrial Hygienists (ACGIH 2013) has published

physiological limits for a number of years and states that exposure to

environmentally or activity-induced heat stress must be discontinued at any time

when

bull Sustained (several minutes) heart rate in excess of 180 beats per minute

minus the individuals age in years (eg180 ndash age) for individuals with

assessed normal cardiac performance OR

bull Body core temperature greater than 385degC (1013degC) for medically

selected and acclimatised personnel or greater than 38degC (1004degC) in

unselected unacclimatised workers OR

bull When there are complaints of sudden and severe fatigue nausea

dizziness or light-headedness OR

bull A workers recovery heart rate at one minute after a peak work effort is

greater than 120 beats per minute 124 bpm was suggested by Fuller and

Smith (1982) OR

bull A worker experiences profuse and prolonged sweating over hours and

may not be able to adequately replenish fluids OR

bull Greater than 15 weight loss over a shift OR

bull In conditions of regular daily exposure to the stress 24-hour urinary

sodium excretion is less than 50 mmoles

ISO 9886 (2004) suggests that exposure to environmentally or activity-induced heat

stress must also be discontinued at any time when

bull lsquoHeart Rate Limit = 185 - 065Arsquo where A = Age in years

bull Individual variability can range up to 20 bpm from this average so this

level could present a risk for some individuals Where there is

uncertainty the sustained heart rate over a work period should not

exceed the previously mentioned

bull HRL sustained = 180 ndash age

bull No matter which limiting values are used interpretation requires

discussion with the workers affected and may require the services of a

specialist such as an occupational hygienist or occupational physician

If a worker appears to be disoriented or confused or demonstrates uncharacteristic

16

irritability discomfort or flu-like symptoms the worker should be removed for rest

under observation in a cool location Symptoms of heat stroke need to be monitored

closely and if sweating stops and the skin becomes hot and dry immediate

emergency care is essential

The prompt treatment of other heat-related disorders generally results in full

recovery but medical advice should be sought for treatment and return-to-work

protocols

Following good occupational hygiene sampling practice which considers likely extremes

and the less tolerant workers the absence of any of these limiting observations indicates

acceptable management of the heat stress exposures With acceptable levels of heat

strain the lsquoNorsquo branch in the level 3 section of Figure 1 is taken Nevertheless even if the

heat strain among workers is considered acceptable at the time the general controls are

necessary In addition periodic physiological monitoring should be continued to ensure

that acceptable levels of heat strain are being maintained

If excessive heat strain is found during the physiological assessments then the lsquoYesrsquo

branch is taken This means that the work activities must cease until suitable job-specific

controls can be considered and implemented to a sufficient extent to control that strain

The job-specific controls may include engineering controls administrative controls and

personal protection

After implementation of the job-specific controls it is necessary to assess their

effectiveness and to adjust them as needed

Section 5 Occupational Exposure Limits

Currently there are fewer workplaces where formal exposure limits for heat stress still

apply however this practice is found mainly within the mining industry There are many

variables associated with the onset of heat stress and these can be a result of the task

environment andor the individual Trying to set a general limit which adequately covers

the many variations within industry has proven to be extremely complicated The attempts

have sometimes resulted in an exposure standard so conservative in a particular

environment that it would become impractical to apply It is important to note that heat

stress indices are not safeunsafe limits and should only be used as guides

Use of Urinary Specific Gravity testing

Water intake at onersquos own discretion results in incomplete fluid replacement for individuals

working in the heat and there is consistent evidence that relying solely on thirst as an

17

indicator of fluid requirement will not restore water balance (Sawka 1998) Urine specific

gravity (USG) can be used as a guide in relation to the level of hydration of an individual

(Shirreffs 2003) and this method of monitoring is becoming increasingly popular in

Australia as a physiological limit Specific gravity (SG) is defined as the ratio weight of a

substance compared to the weight of an equal volume of distilled water hence the SG of

distilled water is 1000 Studies (Sawka et al 2007 Ganio et al 2007 Cheuvront amp

Sawka 2005 Casa et al 2000) recommend that a USG of greater than 1020 would

reflect dehydration While not regarded as fool proof or the ldquogold standardrdquo for total body

water (Armstrong 2007) it is a good compromise between accuracy simplicity of testing

in the field and acceptability to workers of a physiological measure Table 3 shows the

relationship between SG of urine and hydration

Table 3 US National Athletic Trainers Association index of hydration status Body Weight

Loss ()

Urine Specific

Gravity

Well Hydrated lt1 1010

Minimal dehydration 1 - 3 1010 ndash 1020

Significant

dehydration

3 - 5 1021 ndash 1030

Severe dehydration gt 5 gt 1030 Source adapted from Casa et al 2000

Section 6 Heat stress management and controls

The requirement to initiate a heat stress management program is marked by

(1) heat stress levels that exceed the criteria in the Basic Thermal Risk Assessment or

level 2 heat index assessment or

(2) work in clothing ensembles that are air or water vapour impermeable

There are numerous controls across the hierarchy of controls that may be utilised to

address heat stress issues in the workplace Not all may be applicable to a particular task

or scenario and often may require some adjusting before a suitable combination is

achieved

In addition to general controls appropriate job-specific controls are often required to

provide adequate protection During the consideration of job-specific controls detailed

analysis provides a framework to appreciate the interactions among acclimatisation stage

metabolic rate workrest cycles and clothing Table 4 lists some examples of controls

available The list is by no means exhaustive but will provide some ideas for controls

18

Table 4 Examples of control methods

Eliminationsubstitution

bull Hot tasks should be scheduled to avoid the hottest part of the day or where

practical undertaken during night shifts

bull Walls and roof structures should utilize light coloured or reflective materials

bull Structures should be designed to incorporate good air flow This can be done via

the positioning of windows shutters and roof design to encourage lsquochimney

effectsrsquo This will help remove the heat from the structure

bull Walls and roofs should be insulated

Engineering

bull Pipework and vessels associated with hot processes should be insulated and clad

to minimize the introduction of heat into the work environment

bull In high humidity areas such as northern Australia more air needs to be moved

hence fans to increase air flow or in extreme cases cooled air from lsquochillerrsquo units

can be used

bull Where radiated heat from a process is a problem insulating barriers or reflective

barriers can be used to absorb or re-direct radiant heat These may be permanent

structures or movable screens

bull Relocating hot processes away from high access areas

bull Dehumidifying air to increase the evaporative cooling effect Often steam leaks

open process vessels or standing water can artificially increase humidity within a

building

bull Utilize mechanical aids that can reduce the metabolic workload on the individual

Administrative

bull Ready access to cool palatable drinking water is a basic necessity

bull Where applicable suitable electrolyte replacements should also be available

bull A clean cool area for employees to rest and recuperate can add significant

improvement to the cooling process Resting in the work environment can provide

some relief for the worker the level of recovery is much quicker and more efficient

in an air-conditioned environment These need not be elaborate structures basic

inexpensive portable enclosed structures with an air conditioner water supply and

seating have been found to be successful in a variety of environments For field

19

teams with high mobility even a simple shade structure readily available from

hardware stores or large umbrellas can provide relief from solar radiation

bull Where work-rest regimes are necessary heat stress indices such as WBGT PHS

or TWL assist in determining duration of work and rest periods

bull Training workers to identify symptoms and the potential onset of heat-related

illness as part of the lsquobuddy systemrsquo

bull Encouraging ldquoself-determinationrdquo or pacing of the work to meet the conditions and

reporting of heat related symptoms

bull Consider pre-placement medical screening for work in hot areas (ISO 12894)

Personal protective equipment

bull PPE such as cooling vests with either lsquophase changersquo cooling inserts (not ice) Ice

or chilled water cooled garments can result in contraction of the blood vessels

reducing the cooling effect of the garment

bull Vortex tube air cooling may be used in some situations particularly when a cooling

source is required when supplied air respirators are used

bull Choose light coloured materials for clothing and ensure they allow good air flow

across the skin to promote evaporative cooling

Heat stress hygiene practices are particularly important because they reduce the risk that

an individual may suffer a heat-related disorder The key elements are fluid replacement

self-assessment health status monitoring maintenance of a healthy life-style and

adjustment of work expectations based on acclimatisation state and ambient working

conditions The hygiene practices require the full cooperation of supervision and workers

20

Bibliography ACGIH (American Conference of Governmental Industrial Hygienists) (2013) Threshold

Limit Values for Chemical Substances and Physical Agents and Biological Exposure

Indices Cincinnati ACGIH Signature Publications

Armstrong LE (2007) Assessing hydration status The elusive gold standard Journal of

the American College of Nutrition 26(5) pp 575S-584S

Brake DJ amp Bates GP (2002) Limiting metabolic rate (thermal work limit) as an index of

thermal stress Applied Occupational and Environmental Hygiene 17 pp 176ndash86

Casa DJ Armstrong LE Hillman SK Montain SJ Reiff RV amp Rich BSE (2000)

National Athletic Trainers association Position Statement Fluid replacement for Athletes

Journal of Athletic Training 35(2) pp 212-224

Di Corleto R Coles G amp Firth I (2003) The development of a heat stress standard for

Australian conditions in Australian Institute of Occupational Hygienists Inc 20th Annual

Conference Proceedings Geelong Victoria December AIOH

Di Corleto R Firth I Mate J Coles G (2013) A Guide to Managing Heat Stress and

Documentation Developed For Use in the Australian Environment AIOH Melbourne

Ganio MS Casa DJ Armstrong LE amp Maresh CM (2007) Evidence based approach to

lingering hydration questions Clinics in Sports Medicine 26(1) pp 1ndash16

ISO 7243 (1989) Hot environments - Estimation of the heat stress on working man

based on the WBGT - index (wet bulb globe temperature)

ISO 7933 (2004) Ergonomics of the thermal environment Analytical determination and

interpretation of heat stress using calculation of the Predicted Heat Strain ISO 7933

ISO 8996 (2004) Ergonomics of the Thermal Environment ndash Determination of Metabolic

Rate Geneva ISO

ISO 9886 (1992) Evaluation of thermal strain by physiological measurements

ISO 12894 (2001) Ergonomics of the thermal environment ndash Medical supervision of

individuals exposed to extreme hot or cold environments

Miller V Bates G (2007) Hydration of outdoor workers in north-west Australia J

Occup Health Safety mdash Aust NZ 23(1) pp 79ndash87

21

Sawka MN (1998) Body fluid responses and hypohydration during exercise heat

stress in KB Pandolf MN Sawkaand amp RR Gonzalez (Eds) Human Performance

Physiology and Environmental Medicine at Terrestrial Extremes USA Brown amp

Benchmark pp 227 ndash 266

Shirreffs SM (2003) Markers of hydration status European Journal of Clinical Nutrition

57(2) pp s6-s9

Steadman RG (1979) The assessment of sultriness Part 1 A temperature humidity

index based on human physiology and clothing science Journal of applied meteorology

(July)

Tillman C (2007) (Ed) Principles of Occupational Health amp Hygiene - An Introduction

Allen amp Unwin Academic

22

Appendix 1 - Basic Thermal Risk Assessment using Apparent Temperature (Informative example only)

HAZARD TYPE Assessment Point Value 0 1 2 3 Sun Exposure Indoors Full Shade Part Shade No Shade Hot surfaces Neutral Warm on Contact Hot on contact Burn on contact Exposure period lt 30 min 30 min ndash 1hour 1 hour - 2 hours gt 2 hrs Confined space No Yes Task complexity Simple Moderate Complex Climbing updown stairs or ladders None One level Two levels gt Two levels Distance from cool rest area lt10 Metres 10 - 50 Metres 50-100 Metres gt100 Metres Distance from drinking water lt10 Metres 10 - 30 Metres 30-50 Metres gt50 Metres Clothing (permeable) Single layer (light) Single layer (mod) Multiple layer Understanding of heat strain risk Training given No training given Air movement Strong Wind Moderate Wind Light Wind No Wind Resp protection (-ve pressure) None Disposable Half Face Rubber Half Face Full Face Acclimatisation Acclimatised Unacclimatised

SUB-TOTAL A 2 4 6 Metabolic work rate Light Moderate Heavy SUB-TOTAL B 1 2 3 4 Apparent Temperature lt 27degC gt27degC le 33degC gt33degC le 41degC gt 41degC SUB-TOTAL C

TOTAL = A plus B Multiplied by C = Examples of Work Rate Light work Sitting or standing to control machines hand and arm work assembly or sorting of light materials Moderate work Sustained hand and arm work such as hammering handling of moderately heavy materials Heavy work Pick and shovel work continuous axe work carrying loads up stairs Instructions for use of the Basic Thermal Risk Assessment

bull Mark each box according to the appropriate conditions bull When complete add up using the value at the top of the appropriate column for each mark bull Add the sub totals of Table A amp Table B and multiply with the sub-total of Table C for the final result bull If the total is less than 28 then the risk due to thermal conditions are low to moderate bull If the total is 28 to 60 there is a potential of heat-induced illnesses occurring if the conditions are not

addressed Further analysis of heat stress risk is required bull If the total exceeds 60 then the onset of a heat-induced illness is very likely and action should be taken as

soon as possible to implement controls It is important to note that that this assessment is to be used as a guide only A number of factors are not included in this assessment such as employee health condition and the use of high levels of PPE (particularly impermeable suits) In these circumstances experienced personnel should carry out a more extensive assessment

23

Worked Example of Basic Thermal Risk Assessment An example of the application of the basic thermal risk assessment would be as follows A fitter is working on a pump out in the plant at ground level that has been taken out of service the previous day The task involves removing bolts and a casing to check the impellers for wear approximately 2 hours of work The pump is situated approximately 25 metres from the workshop The fitter is acclimatised has attended a training session and is wearing a standard single layer long shirt and trousers is carrying a water bottle and a respirator is not required The work rate is light there is a light breeze and the air temperature has been measured at 30degC and the relative humidity at 70 This equates to an apparent temperature of 35degC (see Table 5 in appendix 2) Using the above information in the risk assessment we have

HAZARD TYPE Assessment Point Value

0 1 2 3 Sun Exposure Indoors Shade Part Shade No Shade Hot surfaces Neutral Warm on Contact Hot on contact Burn on contact Exposure period lt 30 min 30 min ndash 1hour 1 hour - 2 hours gt 2 hrs Confined space No Yes Task complexity Simple Moderate Complex Climbing updown stairs or ladders None One level Two levels gt Two levels Distance from cool rest area lt10 Metres lt50 Metres 50-100 Metres gt100 Metres Distance from drinking water lt10 Metres lt30 Metres 30-50 Metres gt50 Metres Clothing (permeable) Single layer (light) Single layer (mod) Multiple layer Understanding of heat strain risk Training given No training given Air movement Strong Wind Moderate Wind Light Wind No Wind Resp protection (-ve pressure) None Disposable Half Face Rubber Half Face Full Face Acclimatisation Acclimatised Unacclimatised

3 6 0 SUB-TOTAL A 9 2 4 6 Metabolic work rate Light Moderate Heavy SUB-TOTAL B 2 1 2 3 4 Apparent Temperature lt 27degC gt27degC le 33degC gt33degC le 41degC gt 41degC SUB-TOTAL C 3

A = 9 B = 2 C = 3 therefore Total = (9+2) x 3 = 33 As the total lies between 28 and 60 there is a potential for heat induced illness occurring if the conditions are not addressed and further analysis of heat stress risk is required

24

Appendix 2 ndash Table 5 Apparent Temperature Dry BulbHumidity scale Align dry bulb temperature with corresponding relative humidity to determine apparent temperature in unshaded section of table Numbers in () refer to skin humidities above 90 and are only approximate

Dry Bulb Temperature Relative Humidity () (degC) 0 10 20 30 40 50 60 70 80 90 100 20 16 17 17 18 19 19 20 20 21 21 21 21 18 18 19 19 20 20 21 21 22 22 23 22 19 19 20 20 21 21 22 22 23 23 24 23 20 20 21 22 22 23 23 24 24 24 25 24 21 22 22 23 23 24 24 25 25 26 26 25 22 23 24 24 24 25 25 26 27 27 28 26 24 24 25 25 26 26 27 27 28 29 30 27 25 25 26 26 27 27 28 29 30 31 33 28 26 26 27 27 28 29 29 31 32 34 (36) 29 26 27 27 28 29 30 30 33 35 37 (40) 30 27 28 28 29 30 31 33 35 37 (40) (45) 31 28 29 29 30 31 33 35 37 40 (45) 32 29 29 30 31 33 35 37 40 44 (51) 33 29 30 31 33 34 36 39 43 (49)

34 30 31 32 34 36 38 42 (47)

35 31 32 33 35 37 40 (45) (51)

36 32 33 35 37 39 43 (49)

37 32 34 36 38 41 46

38 33 35 37 40 44 (49)

39 34 36 38 41 46

40 35 37 40 43 49

41 35 38 41 45

42 36 39 42 47

43 37 40 44 49

44 38 41 45 52

45 38 42 47

46 39 43 49

47 40 44 51

48 41 45 53

49 42 47

50 42 48

(Source Steadman 1979)

25

Documentation of the Heat Stress Guide Developed for Use in the Australian Environment

Developed for the Australian Institute of Occupational Hygienists

Ross Di Corleto Ian Firth amp Joseph Mateacute

November 2013

26

10 Introduction Heat-related illness has been a health hazard throughout the ages and is a function

of the imposition of environmental heat on the human body which itself generates

heat

11 Heat Illness ndash A Problem Throughout the Ages

The hot thermal environment has been a constant challenge to man for centuries and

its impact is referenced throughout history The bible tells of the death of Judithrsquos

husband Manasseh from exposure in the fields supervising workers where it says

ldquoHe had suffered a sunstroke while in the fields supervising the farm workers and

later died in bed at home in Bethuliardquo (Judith 83)

The impact of heat on the military in history is also well recorded the problems

confronted by the armies of King Sennacherib of Assyria (720BC) whilst attacking

Lashish Herodotus (400BC) reports of Spartan soldiers succumbing to ldquothirst and

sunrdquo Even Alexander the Great in 332BC was warned of the risks of a march across

the Libyan Desert And there is little doubt that heat stress played a major role in the

defeat of the Crusaders of King Edward in the Holy Land fighting the Saracens whilst

burdened down with heavy armour in the Middle Eastern heat (Goldman 2001)

It is not only the workers and armies that are impacted but also the general

population One of the worst cases occurred in Peking China in 1743 when during a

10 day heat wave 11000 people were reported to have perished (Levick 1859)

In 1774 Sir Charles Blagden of the Royal Society outlined a series of experiments

undertaken in a heated room in which he commented on ldquothe wonderful power with

which the animal body is endued of resisting heat vastly greater than its own

temperaturerdquo (Blagden 1775)

Despite this experience and knowledge over the ages we are still seeing deaths in

the 20th century as a result of heat stress Severe heat related illnesses and deaths

are not uncommon among pilgrims making the Makkah Hajj (Khogali 1987) and

closer to home a fatality in the Australian military (ABC 2004) and more recently

amongst the Australian workforce (Australian Mining 2013)

27

12 Heat and the Human Body

The human body in a state of wellbeing maintains its internal temperature within a

very narrow range This is a fundamental requirement for those internal chemical

reactions which are essential to life to proceed at the proper rates The actual level

of this temperature is a product of the balance between heat exchange with the

external thermal environment and the generation of heat internally by the metabolic

processes associated with life and activity

The temperature of blood circulating through the living and working tissues is

monitored by receptors throughout the body The role of these receptors is to induce

specific responses in functional body systems to ensure that the temperature

remains within the appropriate range

The combined effect of external thermal environment and internal metabolic heat

production constitutes the thermal stress on the body The levels of activity required

in response to the thermal stress by systems such as cardiovascular

thermoregulatory respiratory renal and endocrine constitute the thermal strain

Thus environmental conditions metabolic workload and clothing individually or

collectively create heat stress for the worker The bodyrsquos physiological response to

stressors for example sweating increased heart rate and elevated core

temperature is the heat strain

Such physiological changes are the initial responses to thermal stress but the extent

at which these responses are required will determine whether that strain will result in

thermal injuryillness It is important to appreciate that while preventing such illness

by satisfactorily regulating human body temperature in a heat-stress situation those

responses particularly the sweat response may not be compatible with comfort

(Gagge et al 1941)

The rate of heat generated by metabolic processes is dependent on the level of

physical activity To precisely quantify the metabolic cost associated with a particular

task without directly or indirectly measuring the individual is not possible This is due

to the individual differences associated with performing the task at hand As a

result broad categories of metabolic loads for typical work activities have been

established (Durnin amp Passmore 1967 ISO 8996 2004) It is sometimes practicable

Safe Work Australia (2011) refers to heat related illnesses and OSHA (httpswwwoshagovSLTCheatstress) considers heat exhaustion and heat stroke cases to be heat-related illness due to the number of human factors that contribute to a workers susceptibility to heat stress (refer to Section 40) while ACGIH (2013) refers to heat stress and heat strain cases as being heat-related disorders They are not usually considered injuries

28

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 ndash 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

7

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

bull air temperature

bull humidity

bull air movement

bull radiant heat exchange and

bull 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 bodyrsquos 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

bull prickly heat

bull headaches

bull nausea

bull 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

8

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 individualrsquos 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

9

Figure 1 Heat Stress Management Schematic (adapted from ACGIH 2013)

Level 1Perform Basic Risk

Assessment

Unacceptable risk

No

Does task involve use of impermeable clothing (ie PVC)

Continue work monitor conditionsNo

Are data available for detailed analysis

Level 2Analyse data with rational heat stress index (ie PHS

TWL)

Yes

Unacceptable heat stress risk based on analysis

Job specific controls practical and successful

Level 3Undertake physiological

monitoring

Cease work

Yes

Yes

No

Monitor task to ensure conditions amp collect dataNo

No

Maintain job specific controlsYes

Excessive heat strain based on monitoring

Yes

No

10

Level 1 Assessment a basic thermal risk assessment A suggested protocol for the level 1 assessment is termed the ldquoBasic Thermal Risk

Assessmentrdquo It has been designed as a simple tool which can be used by employees or

technicians to provide guidance and also as a training tool to illustrate the many factors

that impact on heat stress This risk assessment incorporates the contributions of a

number of factors that can impact on heat stress such as the state of acclimatisation work

demands location clothing and other physiological factors It can also incorporate the use

of a first level heat stress index such as Apparent Temperature or WBGT It is designed to

be an initial qualitative review of a potential heat stress situation for the purposes of

prioritising further measurements and controls It is not intended as a definitive

assessment tool Some of its key aspects are described below

Acclimatisation plays a part as it is a set of gradual physiological adjustments that improve

an individuals ability to tolerate heat stress the development and loss of which is

described in the Documentation

Metabolic work rate is of equal importance to environmental assessment in evaluating heat

stress Table 1 provides broad guidance for selecting the work rate category to be used in

the Risk Assessment There are a number of sources for this data including ISO

72431989 and ISO 89962004 standards

Table 1 Examples of Activities within Metabolic Rate (M) Classes

Class Examples

Resting Resting sitting at ease Low Light

Work Sitting at ease light manual work hand and arm work car driving

standing casual walking sitting or standing to control machines

Moderate

Moderate Work Sustained hand and arm work (eg hammering) arm and trunk

work moving light wheelbarrow walking around 45 kmh

High Heavy

Work

Intense arm and trunk work carrying heavy material shovelling

sawing hard wood moving heavily loaded wheelbarrows carrying

loads upstairs

Source (ISO 89962004)

Apparent temperature (Steadman 1979) can be used as part of the basic thermal risk

assessment The information required air temperature and humidity can be readily

obtained from most local weather bureau websites off-the-shelf weather units or

measured directly with a sling psychrometer Its simplicity is one of the advantages in its

use as it requires very little technical knowledge

11

The WBGT index also offers a useful first-order index of the environmental contribution to

heat stress It is influenced by air temperature radiant heat and humidity (ACGIH 2013)

In its simplest form it does not fully account for all of the interactions between a person

and the environment but is useful in this type of assessment The only disadvantage is

that it requires some specialised monitoring equipment such as a WBGT monitor or wet

bulb and globe thermometers

Both indices are described in more detail in the Documentation associated with this

standard

These environmental parameters are combined on a single check sheet in three sections

Each aspect is allocated a numerical value A task may be assessed by checking off

questions in the table and including some additional data for metabolic work load and

environmental conditions From this information a weighted calculation is used to

determine a numerical value which can be compared to pre-set criteria to provide

guidance as to the potential risk of heat stress and the course of action for controls

For example if the Assessment Point Total is less than 28 then the thermal condition risk

is low The lsquoNorsquo branch in Figure 1 can be taken Nevertheless if there are reports of the

symptoms of heat-related disorders such as prickly heat fatigue nausea dizziness and

light-headedness then the analysis should be reconsidered or proceed to detailed

analysis if appropriate If the Assessment Point Total is 28 or more further analysis is

required An Assessment Point Total greater than 60 indicates the need for immediate

action and implementation of controls (see Section 6)

Examples of a basic thermal risk assessment tool and their application are provided in

Appendix 1

Section 2 Screening for clothing that does not allow air and water vapour movement

The decision about clothing and how it might affect heat loss can also play an important

role in the initial assessment This is of particular importance if the clothing interferes with

the evaporation of sweat from the skin surface of an individual (ie heavy water barrier

clothing such as PVC) As this is the major heat loss mechanism disruption of this

process will significantly impact on the heat stress experienced Most heat exposure

assessment indices were developed for a traditional work uniform which consisted of a

long-sleeved shirt and pants Screening that is based on this attire is not suitable for

clothing ensembles that are more extensive and less permeable unless a detailed analysis

method appropriate for permeable clothing requirements is available With heat removal

hampered by clothing metabolic heat may produce life-threatening heat strain even when

12

ambient conditions are considered cool and the risk assessment determines ldquoLow Riskrdquo If

workers are required to wear additional clothing that does not allow air and water vapour

movement then the lsquoYesrsquo branch in the first question of Figure 1 should be taken

Physiological and behavioural monitoring described in Section 4 should be followed to

assess the potential for harm resulting from heat stress

Section 3 Level 2 assessment using detailed analysis

It is possible that a condition may be above the criteria provided in the initial risk

assessment and still not represent an unacceptable exposure To make this

determination a detailed analysis is required as in the Documentation

Note as discussed briefly above (see Section 2) no numerical screening criteria or limiting

values are applicable where clothing does not allow air or water vapour movement In this

case reliance must be placed on physiological monitoring

The screening criteria require a minimum set of data in order to make an assessment A

detailed analyses requires more data about the exposures including

bull clothing type

bull air speed

bull air temperature

bull water vapour content of the air (eg humidity)

bull posture

bull length of exposure and

bull globe temperature

Following Figure 1 the next question asks about the availability of such exposure data for

a detailed analysis If exposure data are not available the lsquoNorsquo branch takes the

evaluation to the monitoring of the tasks to collect this data before moving on to the use of

a rational heat stress index These types of indices are based on the human heat balance

equation and utilise a number of formulae to predict responses of the body such as

sweating and elevation of core temperature From this information the likelihood of

developing a heat stress related disorder may be determined In situations where this

data cannot be collected or made available then physiological monitoring to assess the

degree of heat strain should be undertaken

Detailed rational analysis should follow ISO 7933 - Predicted Heat Strain or Thermal Work

Limit (TWL) although other indices with extensive supporting physiological documentation

may also be acceptable (see Documentation for details) While such a rational method

(versus the empirically derived WBGT or Basic Effective Temperature (BET) thresholds) is

13

computationally more difficult it permits a better understanding of the source of the heat

stress and can be a means to assess the benefits of proposed control modifications on the

exposure

Predicted heat strain (PHS) is a rational index (ie it is an index based on the heat balance

equation) It estimates the required sweat rate and the maximal evaporation rate utilising

the ratio of the two as an initial measure of lsquorequired wettednessrsquo This required

wettedness is the fraction of the skin surface that would have to be covered by sweat in

order for the required evaporation rate to occur The evaporation rate required to maintain

a heat balance is then calculated (Di Corleto et al 2003)

In the event that the suggested values might be exceeded ISO 7933 calculates an

allowable exposure time

The suggested limiting values assume workers are

bull fit for the activity being considered and

bull in good health and

bull screened for intolerance to heat and

bull properly instructed and

bull able to self-pace their work and

bull under some degree of supervision (minimally a buddy system)

In work situations which

bull either the maximum evaporation rate is negative leading to condensation of

water vapour on the skin

bull or the estimated allowable exposure time is less than 30 minutes so that the

phenomenon of sweating onset plays a major role in the estimation of the

evaporation loss of the subject Special precautionary measures need to be

taken and direct and individual physiological surveillance of the workers is

particularly necessary

The thermal work limit (TWL) was developed in Australia initially in the underground

mining industry by Brake and Bates (2002a) and later trialled in open cut mines in the

Pilbara region of Western Australia (Miller and Bates 2007a) TWL is defined as the

limiting (or maximum) sustainable metabolic rate that hydrated acclimatised individuals

can maintain in a specific thermal environment within a safe deep body core temperature

(lt382degC) and sweat rate (lt12 kghr) (Tillman 2007)

Due to this complexity these calculations are carried out with the use of computer

software or in the case of TWL pre-programmed monitoring equipment

14

If the exposure does not exceed the criteria for the detailed analysis then the lsquoNorsquo branch

can be taken Because the criteria in the risk assessment have been exceeded

monitoring general heat stress controls are appropriate General controls include training

for workers and supervisors and heat stress hygiene practices If the exposure exceeds

the suggested limits from the detailed analysis or set by the appropriate authority the

lsquoYesrsquo branch leads to the iterative assessment of job-specific control options using the

detailed analysis and then implementation and assessment of control(s) If these are not

available or it cannot be demonstrated that they are successful then the lsquoNorsquo branch

leads to physiological monitoring as the only alternative to demonstrate that adequate

protection is provided

Section 4 Level 3 assessment of heat strain

There are circumstances where the assessment using the rational indices cannot assure

the safety of the exposed workgroup In these cases the use of individual physiological

monitoring may be required These may include situations of high heat stress risk or

where the individualrsquos working environment cannot be accurately assessed A common

example is work involving the use of encapsulating ldquohazmatrdquo suits

The risk and severity of excessive heat strain will vary widely among people even under

identical heat stress conditions By monitoring the physiological responses to working in a

hot environment this allows the workers to use the feedback to assess the level of heat

strain present in the workforce to guide the design of exposure controls and to assess the

effectiveness of implemented controls Instrumentation is available for personal heat

stress monitoring These instruments do not measure the environmental conditions

leading to heat stress but rather they monitor the physiological indicators of heat strain -

usually elevated body temperature andor heart rate Modern instruments utilise an

ingestible core temperature capsule which transmits physiological parameters

telemetrically to an external data logging sensor or laptop computer This information can

then be monitored in real time or assessed post task by a qualified professional

Monitoring the signs and symptoms of heat-stressed workers is sound occupational

hygiene practice especially when clothing may significantly reduce heat loss For

surveillance purposes a pattern of workers exceeding the limits below is considered

indicative of the need to control the exposures On an individual basis these limits are

believed to represent a time to cease an exposure until recovery is complete

Table 2 provides guidance for acceptable limits of heat strain Such physiological

monitoring (see ISO 12894 2001) should be conducted by a physician nurse or

equivalent as allowed by local law

15

Table 2 Physiological Guidelines for Limiting Heat Strain The American Conference of Industrial Hygienists (ACGIH 2013) has published

physiological limits for a number of years and states that exposure to

environmentally or activity-induced heat stress must be discontinued at any time

when

bull Sustained (several minutes) heart rate in excess of 180 beats per minute

minus the individuals age in years (eg180 ndash age) for individuals with

assessed normal cardiac performance OR

bull Body core temperature greater than 385degC (1013degC) for medically

selected and acclimatised personnel or greater than 38degC (1004degC) in

unselected unacclimatised workers OR

bull When there are complaints of sudden and severe fatigue nausea

dizziness or light-headedness OR

bull A workers recovery heart rate at one minute after a peak work effort is

greater than 120 beats per minute 124 bpm was suggested by Fuller and

Smith (1982) OR

bull A worker experiences profuse and prolonged sweating over hours and

may not be able to adequately replenish fluids OR

bull Greater than 15 weight loss over a shift OR

bull In conditions of regular daily exposure to the stress 24-hour urinary

sodium excretion is less than 50 mmoles

ISO 9886 (2004) suggests that exposure to environmentally or activity-induced heat

stress must also be discontinued at any time when

bull lsquoHeart Rate Limit = 185 - 065Arsquo where A = Age in years

bull Individual variability can range up to 20 bpm from this average so this

level could present a risk for some individuals Where there is

uncertainty the sustained heart rate over a work period should not

exceed the previously mentioned

bull HRL sustained = 180 ndash age

bull No matter which limiting values are used interpretation requires

discussion with the workers affected and may require the services of a

specialist such as an occupational hygienist or occupational physician

If a worker appears to be disoriented or confused or demonstrates uncharacteristic

16

irritability discomfort or flu-like symptoms the worker should be removed for rest

under observation in a cool location Symptoms of heat stroke need to be monitored

closely and if sweating stops and the skin becomes hot and dry immediate

emergency care is essential

The prompt treatment of other heat-related disorders generally results in full

recovery but medical advice should be sought for treatment and return-to-work

protocols

Following good occupational hygiene sampling practice which considers likely extremes

and the less tolerant workers the absence of any of these limiting observations indicates

acceptable management of the heat stress exposures With acceptable levels of heat

strain the lsquoNorsquo branch in the level 3 section of Figure 1 is taken Nevertheless even if the

heat strain among workers is considered acceptable at the time the general controls are

necessary In addition periodic physiological monitoring should be continued to ensure

that acceptable levels of heat strain are being maintained

If excessive heat strain is found during the physiological assessments then the lsquoYesrsquo

branch is taken This means that the work activities must cease until suitable job-specific

controls can be considered and implemented to a sufficient extent to control that strain

The job-specific controls may include engineering controls administrative controls and

personal protection

After implementation of the job-specific controls it is necessary to assess their

effectiveness and to adjust them as needed

Section 5 Occupational Exposure Limits

Currently there are fewer workplaces where formal exposure limits for heat stress still

apply however this practice is found mainly within the mining industry There are many

variables associated with the onset of heat stress and these can be a result of the task

environment andor the individual Trying to set a general limit which adequately covers

the many variations within industry has proven to be extremely complicated The attempts

have sometimes resulted in an exposure standard so conservative in a particular

environment that it would become impractical to apply It is important to note that heat

stress indices are not safeunsafe limits and should only be used as guides

Use of Urinary Specific Gravity testing

Water intake at onersquos own discretion results in incomplete fluid replacement for individuals

working in the heat and there is consistent evidence that relying solely on thirst as an

17

indicator of fluid requirement will not restore water balance (Sawka 1998) Urine specific

gravity (USG) can be used as a guide in relation to the level of hydration of an individual

(Shirreffs 2003) and this method of monitoring is becoming increasingly popular in

Australia as a physiological limit Specific gravity (SG) is defined as the ratio weight of a

substance compared to the weight of an equal volume of distilled water hence the SG of

distilled water is 1000 Studies (Sawka et al 2007 Ganio et al 2007 Cheuvront amp

Sawka 2005 Casa et al 2000) recommend that a USG of greater than 1020 would

reflect dehydration While not regarded as fool proof or the ldquogold standardrdquo for total body

water (Armstrong 2007) it is a good compromise between accuracy simplicity of testing

in the field and acceptability to workers of a physiological measure Table 3 shows the

relationship between SG of urine and hydration

Table 3 US National Athletic Trainers Association index of hydration status Body Weight

Loss ()

Urine Specific

Gravity

Well Hydrated lt1 1010

Minimal dehydration 1 - 3 1010 ndash 1020

Significant

dehydration

3 - 5 1021 ndash 1030

Severe dehydration gt 5 gt 1030 Source adapted from Casa et al 2000

Section 6 Heat stress management and controls

The requirement to initiate a heat stress management program is marked by

(1) heat stress levels that exceed the criteria in the Basic Thermal Risk Assessment or

level 2 heat index assessment or

(2) work in clothing ensembles that are air or water vapour impermeable

There are numerous controls across the hierarchy of controls that may be utilised to

address heat stress issues in the workplace Not all may be applicable to a particular task

or scenario and often may require some adjusting before a suitable combination is

achieved

In addition to general controls appropriate job-specific controls are often required to

provide adequate protection During the consideration of job-specific controls detailed

analysis provides a framework to appreciate the interactions among acclimatisation stage

metabolic rate workrest cycles and clothing Table 4 lists some examples of controls

available The list is by no means exhaustive but will provide some ideas for controls

18

Table 4 Examples of control methods

Eliminationsubstitution

bull Hot tasks should be scheduled to avoid the hottest part of the day or where

practical undertaken during night shifts

bull Walls and roof structures should utilize light coloured or reflective materials

bull Structures should be designed to incorporate good air flow This can be done via

the positioning of windows shutters and roof design to encourage lsquochimney

effectsrsquo This will help remove the heat from the structure

bull Walls and roofs should be insulated

Engineering

bull Pipework and vessels associated with hot processes should be insulated and clad

to minimize the introduction of heat into the work environment

bull In high humidity areas such as northern Australia more air needs to be moved

hence fans to increase air flow or in extreme cases cooled air from lsquochillerrsquo units

can be used

bull Where radiated heat from a process is a problem insulating barriers or reflective

barriers can be used to absorb or re-direct radiant heat These may be permanent

structures or movable screens

bull Relocating hot processes away from high access areas

bull Dehumidifying air to increase the evaporative cooling effect Often steam leaks

open process vessels or standing water can artificially increase humidity within a

building

bull Utilize mechanical aids that can reduce the metabolic workload on the individual

Administrative

bull Ready access to cool palatable drinking water is a basic necessity

bull Where applicable suitable electrolyte replacements should also be available

bull A clean cool area for employees to rest and recuperate can add significant

improvement to the cooling process Resting in the work environment can provide

some relief for the worker the level of recovery is much quicker and more efficient

in an air-conditioned environment These need not be elaborate structures basic

inexpensive portable enclosed structures with an air conditioner water supply and

seating have been found to be successful in a variety of environments For field

19

teams with high mobility even a simple shade structure readily available from

hardware stores or large umbrellas can provide relief from solar radiation

bull Where work-rest regimes are necessary heat stress indices such as WBGT PHS

or TWL assist in determining duration of work and rest periods

bull Training workers to identify symptoms and the potential onset of heat-related

illness as part of the lsquobuddy systemrsquo

bull Encouraging ldquoself-determinationrdquo or pacing of the work to meet the conditions and

reporting of heat related symptoms

bull Consider pre-placement medical screening for work in hot areas (ISO 12894)

Personal protective equipment

bull PPE such as cooling vests with either lsquophase changersquo cooling inserts (not ice) Ice

or chilled water cooled garments can result in contraction of the blood vessels

reducing the cooling effect of the garment

bull Vortex tube air cooling may be used in some situations particularly when a cooling

source is required when supplied air respirators are used

bull Choose light coloured materials for clothing and ensure they allow good air flow

across the skin to promote evaporative cooling

Heat stress hygiene practices are particularly important because they reduce the risk that

an individual may suffer a heat-related disorder The key elements are fluid replacement

self-assessment health status monitoring maintenance of a healthy life-style and

adjustment of work expectations based on acclimatisation state and ambient working

conditions The hygiene practices require the full cooperation of supervision and workers

20

Bibliography ACGIH (American Conference of Governmental Industrial Hygienists) (2013) Threshold

Limit Values for Chemical Substances and Physical Agents and Biological Exposure

Indices Cincinnati ACGIH Signature Publications

Armstrong LE (2007) Assessing hydration status The elusive gold standard Journal of

the American College of Nutrition 26(5) pp 575S-584S

Brake DJ amp Bates GP (2002) Limiting metabolic rate (thermal work limit) as an index of

thermal stress Applied Occupational and Environmental Hygiene 17 pp 176ndash86

Casa DJ Armstrong LE Hillman SK Montain SJ Reiff RV amp Rich BSE (2000)

National Athletic Trainers association Position Statement Fluid replacement for Athletes

Journal of Athletic Training 35(2) pp 212-224

Di Corleto R Coles G amp Firth I (2003) The development of a heat stress standard for

Australian conditions in Australian Institute of Occupational Hygienists Inc 20th Annual

Conference Proceedings Geelong Victoria December AIOH

Di Corleto R Firth I Mate J Coles G (2013) A Guide to Managing Heat Stress and

Documentation Developed For Use in the Australian Environment AIOH Melbourne

Ganio MS Casa DJ Armstrong LE amp Maresh CM (2007) Evidence based approach to

lingering hydration questions Clinics in Sports Medicine 26(1) pp 1ndash16

ISO 7243 (1989) Hot environments - Estimation of the heat stress on working man

based on the WBGT - index (wet bulb globe temperature)

ISO 7933 (2004) Ergonomics of the thermal environment Analytical determination and

interpretation of heat stress using calculation of the Predicted Heat Strain ISO 7933

ISO 8996 (2004) Ergonomics of the Thermal Environment ndash Determination of Metabolic

Rate Geneva ISO

ISO 9886 (1992) Evaluation of thermal strain by physiological measurements

ISO 12894 (2001) Ergonomics of the thermal environment ndash Medical supervision of

individuals exposed to extreme hot or cold environments

Miller V Bates G (2007) Hydration of outdoor workers in north-west Australia J

Occup Health Safety mdash Aust NZ 23(1) pp 79ndash87

21

Sawka MN (1998) Body fluid responses and hypohydration during exercise heat

stress in KB Pandolf MN Sawkaand amp RR Gonzalez (Eds) Human Performance

Physiology and Environmental Medicine at Terrestrial Extremes USA Brown amp

Benchmark pp 227 ndash 266

Shirreffs SM (2003) Markers of hydration status European Journal of Clinical Nutrition

57(2) pp s6-s9

Steadman RG (1979) The assessment of sultriness Part 1 A temperature humidity

index based on human physiology and clothing science Journal of applied meteorology

(July)

Tillman C (2007) (Ed) Principles of Occupational Health amp Hygiene - An Introduction

Allen amp Unwin Academic

22

Appendix 1 - Basic Thermal Risk Assessment using Apparent Temperature (Informative example only)

HAZARD TYPE Assessment Point Value 0 1 2 3 Sun Exposure Indoors Full Shade Part Shade No Shade Hot surfaces Neutral Warm on Contact Hot on contact Burn on contact Exposure period lt 30 min 30 min ndash 1hour 1 hour - 2 hours gt 2 hrs Confined space No Yes Task complexity Simple Moderate Complex Climbing updown stairs or ladders None One level Two levels gt Two levels Distance from cool rest area lt10 Metres 10 - 50 Metres 50-100 Metres gt100 Metres Distance from drinking water lt10 Metres 10 - 30 Metres 30-50 Metres gt50 Metres Clothing (permeable) Single layer (light) Single layer (mod) Multiple layer Understanding of heat strain risk Training given No training given Air movement Strong Wind Moderate Wind Light Wind No Wind Resp protection (-ve pressure) None Disposable Half Face Rubber Half Face Full Face Acclimatisation Acclimatised Unacclimatised

SUB-TOTAL A 2 4 6 Metabolic work rate Light Moderate Heavy SUB-TOTAL B 1 2 3 4 Apparent Temperature lt 27degC gt27degC le 33degC gt33degC le 41degC gt 41degC SUB-TOTAL C

TOTAL = A plus B Multiplied by C = Examples of Work Rate Light work Sitting or standing to control machines hand and arm work assembly or sorting of light materials Moderate work Sustained hand and arm work such as hammering handling of moderately heavy materials Heavy work Pick and shovel work continuous axe work carrying loads up stairs Instructions for use of the Basic Thermal Risk Assessment

bull Mark each box according to the appropriate conditions bull When complete add up using the value at the top of the appropriate column for each mark bull Add the sub totals of Table A amp Table B and multiply with the sub-total of Table C for the final result bull If the total is less than 28 then the risk due to thermal conditions are low to moderate bull If the total is 28 to 60 there is a potential of heat-induced illnesses occurring if the conditions are not

addressed Further analysis of heat stress risk is required bull If the total exceeds 60 then the onset of a heat-induced illness is very likely and action should be taken as

soon as possible to implement controls It is important to note that that this assessment is to be used as a guide only A number of factors are not included in this assessment such as employee health condition and the use of high levels of PPE (particularly impermeable suits) In these circumstances experienced personnel should carry out a more extensive assessment

23

Worked Example of Basic Thermal Risk Assessment An example of the application of the basic thermal risk assessment would be as follows A fitter is working on a pump out in the plant at ground level that has been taken out of service the previous day The task involves removing bolts and a casing to check the impellers for wear approximately 2 hours of work The pump is situated approximately 25 metres from the workshop The fitter is acclimatised has attended a training session and is wearing a standard single layer long shirt and trousers is carrying a water bottle and a respirator is not required The work rate is light there is a light breeze and the air temperature has been measured at 30degC and the relative humidity at 70 This equates to an apparent temperature of 35degC (see Table 5 in appendix 2) Using the above information in the risk assessment we have

HAZARD TYPE Assessment Point Value

0 1 2 3 Sun Exposure Indoors Shade Part Shade No Shade Hot surfaces Neutral Warm on Contact Hot on contact Burn on contact Exposure period lt 30 min 30 min ndash 1hour 1 hour - 2 hours gt 2 hrs Confined space No Yes Task complexity Simple Moderate Complex Climbing updown stairs or ladders None One level Two levels gt Two levels Distance from cool rest area lt10 Metres lt50 Metres 50-100 Metres gt100 Metres Distance from drinking water lt10 Metres lt30 Metres 30-50 Metres gt50 Metres Clothing (permeable) Single layer (light) Single layer (mod) Multiple layer Understanding of heat strain risk Training given No training given Air movement Strong Wind Moderate Wind Light Wind No Wind Resp protection (-ve pressure) None Disposable Half Face Rubber Half Face Full Face Acclimatisation Acclimatised Unacclimatised

3 6 0 SUB-TOTAL A 9 2 4 6 Metabolic work rate Light Moderate Heavy SUB-TOTAL B 2 1 2 3 4 Apparent Temperature lt 27degC gt27degC le 33degC gt33degC le 41degC gt 41degC SUB-TOTAL C 3

A = 9 B = 2 C = 3 therefore Total = (9+2) x 3 = 33 As the total lies between 28 and 60 there is a potential for heat induced illness occurring if the conditions are not addressed and further analysis of heat stress risk is required

24

Appendix 2 ndash Table 5 Apparent Temperature Dry BulbHumidity scale Align dry bulb temperature with corresponding relative humidity to determine apparent temperature in unshaded section of table Numbers in () refer to skin humidities above 90 and are only approximate

Dry Bulb Temperature Relative Humidity () (degC) 0 10 20 30 40 50 60 70 80 90 100 20 16 17 17 18 19 19 20 20 21 21 21 21 18 18 19 19 20 20 21 21 22 22 23 22 19 19 20 20 21 21 22 22 23 23 24 23 20 20 21 22 22 23 23 24 24 24 25 24 21 22 22 23 23 24 24 25 25 26 26 25 22 23 24 24 24 25 25 26 27 27 28 26 24 24 25 25 26 26 27 27 28 29 30 27 25 25 26 26 27 27 28 29 30 31 33 28 26 26 27 27 28 29 29 31 32 34 (36) 29 26 27 27 28 29 30 30 33 35 37 (40) 30 27 28 28 29 30 31 33 35 37 (40) (45) 31 28 29 29 30 31 33 35 37 40 (45) 32 29 29 30 31 33 35 37 40 44 (51) 33 29 30 31 33 34 36 39 43 (49)

34 30 31 32 34 36 38 42 (47)

35 31 32 33 35 37 40 (45) (51)

36 32 33 35 37 39 43 (49)

37 32 34 36 38 41 46

38 33 35 37 40 44 (49)

39 34 36 38 41 46

40 35 37 40 43 49

41 35 38 41 45

42 36 39 42 47

43 37 40 44 49

44 38 41 45 52

45 38 42 47

46 39 43 49

47 40 44 51

48 41 45 53

49 42 47

50 42 48

(Source Steadman 1979)

25

Documentation of the Heat Stress Guide Developed for Use in the Australian Environment

Developed for the Australian Institute of Occupational Hygienists

Ross Di Corleto Ian Firth amp Joseph Mateacute

November 2013

26

10 Introduction Heat-related illness has been a health hazard throughout the ages and is a function

of the imposition of environmental heat on the human body which itself generates

heat

11 Heat Illness ndash A Problem Throughout the Ages

The hot thermal environment has been a constant challenge to man for centuries and

its impact is referenced throughout history The bible tells of the death of Judithrsquos

husband Manasseh from exposure in the fields supervising workers where it says

ldquoHe had suffered a sunstroke while in the fields supervising the farm workers and

later died in bed at home in Bethuliardquo (Judith 83)

The impact of heat on the military in history is also well recorded the problems

confronted by the armies of King Sennacherib of Assyria (720BC) whilst attacking

Lashish Herodotus (400BC) reports of Spartan soldiers succumbing to ldquothirst and

sunrdquo Even Alexander the Great in 332BC was warned of the risks of a march across

the Libyan Desert And there is little doubt that heat stress played a major role in the

defeat of the Crusaders of King Edward in the Holy Land fighting the Saracens whilst

burdened down with heavy armour in the Middle Eastern heat (Goldman 2001)

It is not only the workers and armies that are impacted but also the general

population One of the worst cases occurred in Peking China in 1743 when during a

10 day heat wave 11000 people were reported to have perished (Levick 1859)

In 1774 Sir Charles Blagden of the Royal Society outlined a series of experiments

undertaken in a heated room in which he commented on ldquothe wonderful power with

which the animal body is endued of resisting heat vastly greater than its own

temperaturerdquo (Blagden 1775)

Despite this experience and knowledge over the ages we are still seeing deaths in

the 20th century as a result of heat stress Severe heat related illnesses and deaths

are not uncommon among pilgrims making the Makkah Hajj (Khogali 1987) and

closer to home a fatality in the Australian military (ABC 2004) and more recently

amongst the Australian workforce (Australian Mining 2013)

27

12 Heat and the Human Body

The human body in a state of wellbeing maintains its internal temperature within a

very narrow range This is a fundamental requirement for those internal chemical

reactions which are essential to life to proceed at the proper rates The actual level

of this temperature is a product of the balance between heat exchange with the

external thermal environment and the generation of heat internally by the metabolic

processes associated with life and activity

The temperature of blood circulating through the living and working tissues is

monitored by receptors throughout the body The role of these receptors is to induce

specific responses in functional body systems to ensure that the temperature

remains within the appropriate range

The combined effect of external thermal environment and internal metabolic heat

production constitutes the thermal stress on the body The levels of activity required

in response to the thermal stress by systems such as cardiovascular

thermoregulatory respiratory renal and endocrine constitute the thermal strain

Thus environmental conditions metabolic workload and clothing individually or

collectively create heat stress for the worker The bodyrsquos physiological response to

stressors for example sweating increased heart rate and elevated core

temperature is the heat strain

Such physiological changes are the initial responses to thermal stress but the extent

at which these responses are required will determine whether that strain will result in

thermal injuryillness It is important to appreciate that while preventing such illness

by satisfactorily regulating human body temperature in a heat-stress situation those

responses particularly the sweat response may not be compatible with comfort

(Gagge et al 1941)

The rate of heat generated by metabolic processes is dependent on the level of

physical activity To precisely quantify the metabolic cost associated with a particular

task without directly or indirectly measuring the individual is not possible This is due

to the individual differences associated with performing the task at hand As a

result broad categories of metabolic loads for typical work activities have been

established (Durnin amp Passmore 1967 ISO 8996 2004) It is sometimes practicable

Safe Work Australia (2011) refers to heat related illnesses and OSHA (httpswwwoshagovSLTCheatstress) considers heat exhaustion and heat stroke cases to be heat-related illness due to the number of human factors that contribute to a workers susceptibility to heat stress (refer to Section 40) while ACGIH (2013) refers to heat stress and heat strain cases as being heat-related disorders They are not usually considered injuries

28

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

bull air temperature

bull humidity

bull air movement

bull radiant heat exchange and

bull 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 bodyrsquos 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

bull prickly heat

bull headaches

bull nausea

bull 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

8

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 individualrsquos 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

9

Figure 1 Heat Stress Management Schematic (adapted from ACGIH 2013)

Level 1Perform Basic Risk

Assessment

Unacceptable risk

No

Does task involve use of impermeable clothing (ie PVC)

Continue work monitor conditionsNo

Are data available for detailed analysis

Level 2Analyse data with rational heat stress index (ie PHS

TWL)

Yes

Unacceptable heat stress risk based on analysis

Job specific controls practical and successful

Level 3Undertake physiological

monitoring

Cease work

Yes

Yes

No

Monitor task to ensure conditions amp collect dataNo

No

Maintain job specific controlsYes

Excessive heat strain based on monitoring

Yes

No

10

Level 1 Assessment a basic thermal risk assessment A suggested protocol for the level 1 assessment is termed the ldquoBasic Thermal Risk

Assessmentrdquo It has been designed as a simple tool which can be used by employees or

technicians to provide guidance and also as a training tool to illustrate the many factors

that impact on heat stress This risk assessment incorporates the contributions of a

number of factors that can impact on heat stress such as the state of acclimatisation work

demands location clothing and other physiological factors It can also incorporate the use

of a first level heat stress index such as Apparent Temperature or WBGT It is designed to

be an initial qualitative review of a potential heat stress situation for the purposes of

prioritising further measurements and controls It is not intended as a definitive

assessment tool Some of its key aspects are described below

Acclimatisation plays a part as it is a set of gradual physiological adjustments that improve

an individuals ability to tolerate heat stress the development and loss of which is

described in the Documentation

Metabolic work rate is of equal importance to environmental assessment in evaluating heat

stress Table 1 provides broad guidance for selecting the work rate category to be used in

the Risk Assessment There are a number of sources for this data including ISO

72431989 and ISO 89962004 standards

Table 1 Examples of Activities within Metabolic Rate (M) Classes

Class Examples

Resting Resting sitting at ease Low Light

Work Sitting at ease light manual work hand and arm work car driving

standing casual walking sitting or standing to control machines

Moderate

Moderate Work Sustained hand and arm work (eg hammering) arm and trunk

work moving light wheelbarrow walking around 45 kmh

High Heavy

Work

Intense arm and trunk work carrying heavy material shovelling

sawing hard wood moving heavily loaded wheelbarrows carrying

loads upstairs

Source (ISO 89962004)

Apparent temperature (Steadman 1979) can be used as part of the basic thermal risk

assessment The information required air temperature and humidity can be readily

obtained from most local weather bureau websites off-the-shelf weather units or

measured directly with a sling psychrometer Its simplicity is one of the advantages in its

use as it requires very little technical knowledge

11

The WBGT index also offers a useful first-order index of the environmental contribution to

heat stress It is influenced by air temperature radiant heat and humidity (ACGIH 2013)

In its simplest form it does not fully account for all of the interactions between a person

and the environment but is useful in this type of assessment The only disadvantage is

that it requires some specialised monitoring equipment such as a WBGT monitor or wet

bulb and globe thermometers

Both indices are described in more detail in the Documentation associated with this

standard

These environmental parameters are combined on a single check sheet in three sections

Each aspect is allocated a numerical value A task may be assessed by checking off

questions in the table and including some additional data for metabolic work load and

environmental conditions From this information a weighted calculation is used to

determine a numerical value which can be compared to pre-set criteria to provide

guidance as to the potential risk of heat stress and the course of action for controls

For example if the Assessment Point Total is less than 28 then the thermal condition risk

is low The lsquoNorsquo branch in Figure 1 can be taken Nevertheless if there are reports of the

symptoms of heat-related disorders such as prickly heat fatigue nausea dizziness and

light-headedness then the analysis should be reconsidered or proceed to detailed

analysis if appropriate If the Assessment Point Total is 28 or more further analysis is

required An Assessment Point Total greater than 60 indicates the need for immediate

action and implementation of controls (see Section 6)

Examples of a basic thermal risk assessment tool and their application are provided in

Appendix 1

Section 2 Screening for clothing that does not allow air and water vapour movement

The decision about clothing and how it might affect heat loss can also play an important

role in the initial assessment This is of particular importance if the clothing interferes with

the evaporation of sweat from the skin surface of an individual (ie heavy water barrier

clothing such as PVC) As this is the major heat loss mechanism disruption of this

process will significantly impact on the heat stress experienced Most heat exposure

assessment indices were developed for a traditional work uniform which consisted of a

long-sleeved shirt and pants Screening that is based on this attire is not suitable for

clothing ensembles that are more extensive and less permeable unless a detailed analysis

method appropriate for permeable clothing requirements is available With heat removal

hampered by clothing metabolic heat may produce life-threatening heat strain even when

12

ambient conditions are considered cool and the risk assessment determines ldquoLow Riskrdquo If

workers are required to wear additional clothing that does not allow air and water vapour

movement then the lsquoYesrsquo branch in the first question of Figure 1 should be taken

Physiological and behavioural monitoring described in Section 4 should be followed to

assess the potential for harm resulting from heat stress

Section 3 Level 2 assessment using detailed analysis

It is possible that a condition may be above the criteria provided in the initial risk

assessment and still not represent an unacceptable exposure To make this

determination a detailed analysis is required as in the Documentation

Note as discussed briefly above (see Section 2) no numerical screening criteria or limiting

values are applicable where clothing does not allow air or water vapour movement In this

case reliance must be placed on physiological monitoring

The screening criteria require a minimum set of data in order to make an assessment A

detailed analyses requires more data about the exposures including

bull clothing type

bull air speed

bull air temperature

bull water vapour content of the air (eg humidity)

bull posture

bull length of exposure and

bull globe temperature

Following Figure 1 the next question asks about the availability of such exposure data for

a detailed analysis If exposure data are not available the lsquoNorsquo branch takes the

evaluation to the monitoring of the tasks to collect this data before moving on to the use of

a rational heat stress index These types of indices are based on the human heat balance

equation and utilise a number of formulae to predict responses of the body such as

sweating and elevation of core temperature From this information the likelihood of

developing a heat stress related disorder may be determined In situations where this

data cannot be collected or made available then physiological monitoring to assess the

degree of heat strain should be undertaken

Detailed rational analysis should follow ISO 7933 - Predicted Heat Strain or Thermal Work

Limit (TWL) although other indices with extensive supporting physiological documentation

may also be acceptable (see Documentation for details) While such a rational method

(versus the empirically derived WBGT or Basic Effective Temperature (BET) thresholds) is

13

computationally more difficult it permits a better understanding of the source of the heat

stress and can be a means to assess the benefits of proposed control modifications on the

exposure

Predicted heat strain (PHS) is a rational index (ie it is an index based on the heat balance

equation) It estimates the required sweat rate and the maximal evaporation rate utilising

the ratio of the two as an initial measure of lsquorequired wettednessrsquo This required

wettedness is the fraction of the skin surface that would have to be covered by sweat in

order for the required evaporation rate to occur The evaporation rate required to maintain

a heat balance is then calculated (Di Corleto et al 2003)

In the event that the suggested values might be exceeded ISO 7933 calculates an

allowable exposure time

The suggested limiting values assume workers are

bull fit for the activity being considered and

bull in good health and

bull screened for intolerance to heat and

bull properly instructed and

bull able to self-pace their work and

bull under some degree of supervision (minimally a buddy system)

In work situations which

bull either the maximum evaporation rate is negative leading to condensation of

water vapour on the skin

bull or the estimated allowable exposure time is less than 30 minutes so that the

phenomenon of sweating onset plays a major role in the estimation of the

evaporation loss of the subject Special precautionary measures need to be

taken and direct and individual physiological surveillance of the workers is

particularly necessary

The thermal work limit (TWL) was developed in Australia initially in the underground

mining industry by Brake and Bates (2002a) and later trialled in open cut mines in the

Pilbara region of Western Australia (Miller and Bates 2007a) TWL is defined as the

limiting (or maximum) sustainable metabolic rate that hydrated acclimatised individuals

can maintain in a specific thermal environment within a safe deep body core temperature

(lt382degC) and sweat rate (lt12 kghr) (Tillman 2007)

Due to this complexity these calculations are carried out with the use of computer

software or in the case of TWL pre-programmed monitoring equipment

14

If the exposure does not exceed the criteria for the detailed analysis then the lsquoNorsquo branch

can be taken Because the criteria in the risk assessment have been exceeded

monitoring general heat stress controls are appropriate General controls include training

for workers and supervisors and heat stress hygiene practices If the exposure exceeds

the suggested limits from the detailed analysis or set by the appropriate authority the

lsquoYesrsquo branch leads to the iterative assessment of job-specific control options using the

detailed analysis and then implementation and assessment of control(s) If these are not

available or it cannot be demonstrated that they are successful then the lsquoNorsquo branch

leads to physiological monitoring as the only alternative to demonstrate that adequate

protection is provided

Section 4 Level 3 assessment of heat strain

There are circumstances where the assessment using the rational indices cannot assure

the safety of the exposed workgroup In these cases the use of individual physiological

monitoring may be required These may include situations of high heat stress risk or

where the individualrsquos working environment cannot be accurately assessed A common

example is work involving the use of encapsulating ldquohazmatrdquo suits

The risk and severity of excessive heat strain will vary widely among people even under

identical heat stress conditions By monitoring the physiological responses to working in a

hot environment this allows the workers to use the feedback to assess the level of heat

strain present in the workforce to guide the design of exposure controls and to assess the

effectiveness of implemented controls Instrumentation is available for personal heat

stress monitoring These instruments do not measure the environmental conditions

leading to heat stress but rather they monitor the physiological indicators of heat strain -

usually elevated body temperature andor heart rate Modern instruments utilise an

ingestible core temperature capsule which transmits physiological parameters

telemetrically to an external data logging sensor or laptop computer This information can

then be monitored in real time or assessed post task by a qualified professional

Monitoring the signs and symptoms of heat-stressed workers is sound occupational

hygiene practice especially when clothing may significantly reduce heat loss For

surveillance purposes a pattern of workers exceeding the limits below is considered

indicative of the need to control the exposures On an individual basis these limits are

believed to represent a time to cease an exposure until recovery is complete

Table 2 provides guidance for acceptable limits of heat strain Such physiological

monitoring (see ISO 12894 2001) should be conducted by a physician nurse or

equivalent as allowed by local law

15

Table 2 Physiological Guidelines for Limiting Heat Strain The American Conference of Industrial Hygienists (ACGIH 2013) has published

physiological limits for a number of years and states that exposure to

environmentally or activity-induced heat stress must be discontinued at any time

when

bull Sustained (several minutes) heart rate in excess of 180 beats per minute

minus the individuals age in years (eg180 ndash age) for individuals with

assessed normal cardiac performance OR

bull Body core temperature greater than 385degC (1013degC) for medically

selected and acclimatised personnel or greater than 38degC (1004degC) in

unselected unacclimatised workers OR

bull When there are complaints of sudden and severe fatigue nausea

dizziness or light-headedness OR

bull A workers recovery heart rate at one minute after a peak work effort is

greater than 120 beats per minute 124 bpm was suggested by Fuller and

Smith (1982) OR

bull A worker experiences profuse and prolonged sweating over hours and

may not be able to adequately replenish fluids OR

bull Greater than 15 weight loss over a shift OR

bull In conditions of regular daily exposure to the stress 24-hour urinary

sodium excretion is less than 50 mmoles

ISO 9886 (2004) suggests that exposure to environmentally or activity-induced heat

stress must also be discontinued at any time when

bull lsquoHeart Rate Limit = 185 - 065Arsquo where A = Age in years

bull Individual variability can range up to 20 bpm from this average so this

level could present a risk for some individuals Where there is

uncertainty the sustained heart rate over a work period should not

exceed the previously mentioned

bull HRL sustained = 180 ndash age

bull No matter which limiting values are used interpretation requires

discussion with the workers affected and may require the services of a

specialist such as an occupational hygienist or occupational physician

If a worker appears to be disoriented or confused or demonstrates uncharacteristic

16

irritability discomfort or flu-like symptoms the worker should be removed for rest

under observation in a cool location Symptoms of heat stroke need to be monitored

closely and if sweating stops and the skin becomes hot and dry immediate

emergency care is essential

The prompt treatment of other heat-related disorders generally results in full

recovery but medical advice should be sought for treatment and return-to-work

protocols

Following good occupational hygiene sampling practice which considers likely extremes

and the less tolerant workers the absence of any of these limiting observations indicates

acceptable management of the heat stress exposures With acceptable levels of heat

strain the lsquoNorsquo branch in the level 3 section of Figure 1 is taken Nevertheless even if the

heat strain among workers is considered acceptable at the time the general controls are

necessary In addition periodic physiological monitoring should be continued to ensure

that acceptable levels of heat strain are being maintained

If excessive heat strain is found during the physiological assessments then the lsquoYesrsquo

branch is taken This means that the work activities must cease until suitable job-specific

controls can be considered and implemented to a sufficient extent to control that strain

The job-specific controls may include engineering controls administrative controls and

personal protection

After implementation of the job-specific controls it is necessary to assess their

effectiveness and to adjust them as needed

Section 5 Occupational Exposure Limits

Currently there are fewer workplaces where formal exposure limits for heat stress still

apply however this practice is found mainly within the mining industry There are many

variables associated with the onset of heat stress and these can be a result of the task

environment andor the individual Trying to set a general limit which adequately covers

the many variations within industry has proven to be extremely complicated The attempts

have sometimes resulted in an exposure standard so conservative in a particular

environment that it would become impractical to apply It is important to note that heat

stress indices are not safeunsafe limits and should only be used as guides

Use of Urinary Specific Gravity testing

Water intake at onersquos own discretion results in incomplete fluid replacement for individuals

working in the heat and there is consistent evidence that relying solely on thirst as an

17

indicator of fluid requirement will not restore water balance (Sawka 1998) Urine specific

gravity (USG) can be used as a guide in relation to the level of hydration of an individual

(Shirreffs 2003) and this method of monitoring is becoming increasingly popular in

Australia as a physiological limit Specific gravity (SG) is defined as the ratio weight of a

substance compared to the weight of an equal volume of distilled water hence the SG of

distilled water is 1000 Studies (Sawka et al 2007 Ganio et al 2007 Cheuvront amp

Sawka 2005 Casa et al 2000) recommend that a USG of greater than 1020 would

reflect dehydration While not regarded as fool proof or the ldquogold standardrdquo for total body

water (Armstrong 2007) it is a good compromise between accuracy simplicity of testing

in the field and acceptability to workers of a physiological measure Table 3 shows the

relationship between SG of urine and hydration

Table 3 US National Athletic Trainers Association index of hydration status Body Weight

Loss ()

Urine Specific

Gravity

Well Hydrated lt1 1010

Minimal dehydration 1 - 3 1010 ndash 1020

Significant

dehydration

3 - 5 1021 ndash 1030

Severe dehydration gt 5 gt 1030 Source adapted from Casa et al 2000

Section 6 Heat stress management and controls

The requirement to initiate a heat stress management program is marked by

(1) heat stress levels that exceed the criteria in the Basic Thermal Risk Assessment or

level 2 heat index assessment or

(2) work in clothing ensembles that are air or water vapour impermeable

There are numerous controls across the hierarchy of controls that may be utilised to

address heat stress issues in the workplace Not all may be applicable to a particular task

or scenario and often may require some adjusting before a suitable combination is

achieved

In addition to general controls appropriate job-specific controls are often required to

provide adequate protection During the consideration of job-specific controls detailed

analysis provides a framework to appreciate the interactions among acclimatisation stage

metabolic rate workrest cycles and clothing Table 4 lists some examples of controls

available The list is by no means exhaustive but will provide some ideas for controls

18

Table 4 Examples of control methods

Eliminationsubstitution

bull Hot tasks should be scheduled to avoid the hottest part of the day or where

practical undertaken during night shifts

bull Walls and roof structures should utilize light coloured or reflective materials

bull Structures should be designed to incorporate good air flow This can be done via

the positioning of windows shutters and roof design to encourage lsquochimney

effectsrsquo This will help remove the heat from the structure

bull Walls and roofs should be insulated

Engineering

bull Pipework and vessels associated with hot processes should be insulated and clad

to minimize the introduction of heat into the work environment

bull In high humidity areas such as northern Australia more air needs to be moved

hence fans to increase air flow or in extreme cases cooled air from lsquochillerrsquo units

can be used

bull Where radiated heat from a process is a problem insulating barriers or reflective

barriers can be used to absorb or re-direct radiant heat These may be permanent

structures or movable screens

bull Relocating hot processes away from high access areas

bull Dehumidifying air to increase the evaporative cooling effect Often steam leaks

open process vessels or standing water can artificially increase humidity within a

building

bull Utilize mechanical aids that can reduce the metabolic workload on the individual

Administrative

bull Ready access to cool palatable drinking water is a basic necessity

bull Where applicable suitable electrolyte replacements should also be available

bull A clean cool area for employees to rest and recuperate can add significant

improvement to the cooling process Resting in the work environment can provide

some relief for the worker the level of recovery is much quicker and more efficient

in an air-conditioned environment These need not be elaborate structures basic

inexpensive portable enclosed structures with an air conditioner water supply and

seating have been found to be successful in a variety of environments For field

19

teams with high mobility even a simple shade structure readily available from

hardware stores or large umbrellas can provide relief from solar radiation

bull Where work-rest regimes are necessary heat stress indices such as WBGT PHS

or TWL assist in determining duration of work and rest periods

bull Training workers to identify symptoms and the potential onset of heat-related

illness as part of the lsquobuddy systemrsquo

bull Encouraging ldquoself-determinationrdquo or pacing of the work to meet the conditions and

reporting of heat related symptoms

bull Consider pre-placement medical screening for work in hot areas (ISO 12894)

Personal protective equipment

bull PPE such as cooling vests with either lsquophase changersquo cooling inserts (not ice) Ice

or chilled water cooled garments can result in contraction of the blood vessels

reducing the cooling effect of the garment

bull Vortex tube air cooling may be used in some situations particularly when a cooling

source is required when supplied air respirators are used

bull Choose light coloured materials for clothing and ensure they allow good air flow

across the skin to promote evaporative cooling

Heat stress hygiene practices are particularly important because they reduce the risk that

an individual may suffer a heat-related disorder The key elements are fluid replacement

self-assessment health status monitoring maintenance of a healthy life-style and

adjustment of work expectations based on acclimatisation state and ambient working

conditions The hygiene practices require the full cooperation of supervision and workers

20

Bibliography ACGIH (American Conference of Governmental Industrial Hygienists) (2013) Threshold

Limit Values for Chemical Substances and Physical Agents and Biological Exposure

Indices Cincinnati ACGIH Signature Publications

Armstrong LE (2007) Assessing hydration status The elusive gold standard Journal of

the American College of Nutrition 26(5) pp 575S-584S

Brake DJ amp Bates GP (2002) Limiting metabolic rate (thermal work limit) as an index of

thermal stress Applied Occupational and Environmental Hygiene 17 pp 176ndash86

Casa DJ Armstrong LE Hillman SK Montain SJ Reiff RV amp Rich BSE (2000)

National Athletic Trainers association Position Statement Fluid replacement for Athletes

Journal of Athletic Training 35(2) pp 212-224

Di Corleto R Coles G amp Firth I (2003) The development of a heat stress standard for

Australian conditions in Australian Institute of Occupational Hygienists Inc 20th Annual

Conference Proceedings Geelong Victoria December AIOH

Di Corleto R Firth I Mate J Coles G (2013) A Guide to Managing Heat Stress and

Documentation Developed For Use in the Australian Environment AIOH Melbourne

Ganio MS Casa DJ Armstrong LE amp Maresh CM (2007) Evidence based approach to

lingering hydration questions Clinics in Sports Medicine 26(1) pp 1ndash16

ISO 7243 (1989) Hot environments - Estimation of the heat stress on working man

based on the WBGT - index (wet bulb globe temperature)

ISO 7933 (2004) Ergonomics of the thermal environment Analytical determination and

interpretation of heat stress using calculation of the Predicted Heat Strain ISO 7933

ISO 8996 (2004) Ergonomics of the Thermal Environment ndash Determination of Metabolic

Rate Geneva ISO

ISO 9886 (1992) Evaluation of thermal strain by physiological measurements

ISO 12894 (2001) Ergonomics of the thermal environment ndash Medical supervision of

individuals exposed to extreme hot or cold environments

Miller V Bates G (2007) Hydration of outdoor workers in north-west Australia J

Occup Health Safety mdash Aust NZ 23(1) pp 79ndash87

21

Sawka MN (1998) Body fluid responses and hypohydration during exercise heat

stress in KB Pandolf MN Sawkaand amp RR Gonzalez (Eds) Human Performance

Physiology and Environmental Medicine at Terrestrial Extremes USA Brown amp

Benchmark pp 227 ndash 266

Shirreffs SM (2003) Markers of hydration status European Journal of Clinical Nutrition

57(2) pp s6-s9

Steadman RG (1979) The assessment of sultriness Part 1 A temperature humidity

index based on human physiology and clothing science Journal of applied meteorology

(July)

Tillman C (2007) (Ed) Principles of Occupational Health amp Hygiene - An Introduction

Allen amp Unwin Academic

22

Appendix 1 - Basic Thermal Risk Assessment using Apparent Temperature (Informative example only)

HAZARD TYPE Assessment Point Value 0 1 2 3 Sun Exposure Indoors Full Shade Part Shade No Shade Hot surfaces Neutral Warm on Contact Hot on contact Burn on contact Exposure period lt 30 min 30 min ndash 1hour 1 hour - 2 hours gt 2 hrs Confined space No Yes Task complexity Simple Moderate Complex Climbing updown stairs or ladders None One level Two levels gt Two levels Distance from cool rest area lt10 Metres 10 - 50 Metres 50-100 Metres gt100 Metres Distance from drinking water lt10 Metres 10 - 30 Metres 30-50 Metres gt50 Metres Clothing (permeable) Single layer (light) Single layer (mod) Multiple layer Understanding of heat strain risk Training given No training given Air movement Strong Wind Moderate Wind Light Wind No Wind Resp protection (-ve pressure) None Disposable Half Face Rubber Half Face Full Face Acclimatisation Acclimatised Unacclimatised

SUB-TOTAL A 2 4 6 Metabolic work rate Light Moderate Heavy SUB-TOTAL B 1 2 3 4 Apparent Temperature lt 27degC gt27degC le 33degC gt33degC le 41degC gt 41degC SUB-TOTAL C

TOTAL = A plus B Multiplied by C = Examples of Work Rate Light work Sitting or standing to control machines hand and arm work assembly or sorting of light materials Moderate work Sustained hand and arm work such as hammering handling of moderately heavy materials Heavy work Pick and shovel work continuous axe work carrying loads up stairs Instructions for use of the Basic Thermal Risk Assessment

bull Mark each box according to the appropriate conditions bull When complete add up using the value at the top of the appropriate column for each mark bull Add the sub totals of Table A amp Table B and multiply with the sub-total of Table C for the final result bull If the total is less than 28 then the risk due to thermal conditions are low to moderate bull If the total is 28 to 60 there is a potential of heat-induced illnesses occurring if the conditions are not

addressed Further analysis of heat stress risk is required bull If the total exceeds 60 then the onset of a heat-induced illness is very likely and action should be taken as

soon as possible to implement controls It is important to note that that this assessment is to be used as a guide only A number of factors are not included in this assessment such as employee health condition and the use of high levels of PPE (particularly impermeable suits) In these circumstances experienced personnel should carry out a more extensive assessment

23

Worked Example of Basic Thermal Risk Assessment An example of the application of the basic thermal risk assessment would be as follows A fitter is working on a pump out in the plant at ground level that has been taken out of service the previous day The task involves removing bolts and a casing to check the impellers for wear approximately 2 hours of work The pump is situated approximately 25 metres from the workshop The fitter is acclimatised has attended a training session and is wearing a standard single layer long shirt and trousers is carrying a water bottle and a respirator is not required The work rate is light there is a light breeze and the air temperature has been measured at 30degC and the relative humidity at 70 This equates to an apparent temperature of 35degC (see Table 5 in appendix 2) Using the above information in the risk assessment we have

HAZARD TYPE Assessment Point Value

0 1 2 3 Sun Exposure Indoors Shade Part Shade No Shade Hot surfaces Neutral Warm on Contact Hot on contact Burn on contact Exposure period lt 30 min 30 min ndash 1hour 1 hour - 2 hours gt 2 hrs Confined space No Yes Task complexity Simple Moderate Complex Climbing updown stairs or ladders None One level Two levels gt Two levels Distance from cool rest area lt10 Metres lt50 Metres 50-100 Metres gt100 Metres Distance from drinking water lt10 Metres lt30 Metres 30-50 Metres gt50 Metres Clothing (permeable) Single layer (light) Single layer (mod) Multiple layer Understanding of heat strain risk Training given No training given Air movement Strong Wind Moderate Wind Light Wind No Wind Resp protection (-ve pressure) None Disposable Half Face Rubber Half Face Full Face Acclimatisation Acclimatised Unacclimatised

3 6 0 SUB-TOTAL A 9 2 4 6 Metabolic work rate Light Moderate Heavy SUB-TOTAL B 2 1 2 3 4 Apparent Temperature lt 27degC gt27degC le 33degC gt33degC le 41degC gt 41degC SUB-TOTAL C 3

A = 9 B = 2 C = 3 therefore Total = (9+2) x 3 = 33 As the total lies between 28 and 60 there is a potential for heat induced illness occurring if the conditions are not addressed and further analysis of heat stress risk is required

24

Appendix 2 ndash Table 5 Apparent Temperature Dry BulbHumidity scale Align dry bulb temperature with corresponding relative humidity to determine apparent temperature in unshaded section of table Numbers in () refer to skin humidities above 90 and are only approximate

Dry Bulb Temperature Relative Humidity () (degC) 0 10 20 30 40 50 60 70 80 90 100 20 16 17 17 18 19 19 20 20 21 21 21 21 18 18 19 19 20 20 21 21 22 22 23 22 19 19 20 20 21 21 22 22 23 23 24 23 20 20 21 22 22 23 23 24 24 24 25 24 21 22 22 23 23 24 24 25 25 26 26 25 22 23 24 24 24 25 25 26 27 27 28 26 24 24 25 25 26 26 27 27 28 29 30 27 25 25 26 26 27 27 28 29 30 31 33 28 26 26 27 27 28 29 29 31 32 34 (36) 29 26 27 27 28 29 30 30 33 35 37 (40) 30 27 28 28 29 30 31 33 35 37 (40) (45) 31 28 29 29 30 31 33 35 37 40 (45) 32 29 29 30 31 33 35 37 40 44 (51) 33 29 30 31 33 34 36 39 43 (49)

34 30 31 32 34 36 38 42 (47)

35 31 32 33 35 37 40 (45) (51)

36 32 33 35 37 39 43 (49)

37 32 34 36 38 41 46

38 33 35 37 40 44 (49)

39 34 36 38 41 46

40 35 37 40 43 49

41 35 38 41 45

42 36 39 42 47

43 37 40 44 49

44 38 41 45 52

45 38 42 47

46 39 43 49

47 40 44 51

48 41 45 53

49 42 47

50 42 48

(Source Steadman 1979)

25

Documentation of the Heat Stress Guide Developed for Use in the Australian Environment

Developed for the Australian Institute of Occupational Hygienists

Ross Di Corleto Ian Firth amp Joseph Mateacute

November 2013

26

10 Introduction Heat-related illness has been a health hazard throughout the ages and is a function

of the imposition of environmental heat on the human body which itself generates

heat

11 Heat Illness ndash A Problem Throughout the Ages

The hot thermal environment has been a constant challenge to man for centuries and

its impact is referenced throughout history The bible tells of the death of Judithrsquos

husband Manasseh from exposure in the fields supervising workers where it says

ldquoHe had suffered a sunstroke while in the fields supervising the farm workers and

later died in bed at home in Bethuliardquo (Judith 83)

The impact of heat on the military in history is also well recorded the problems

confronted by the armies of King Sennacherib of Assyria (720BC) whilst attacking

Lashish Herodotus (400BC) reports of Spartan soldiers succumbing to ldquothirst and

sunrdquo Even Alexander the Great in 332BC was warned of the risks of a march across

the Libyan Desert And there is little doubt that heat stress played a major role in the

defeat of the Crusaders of King Edward in the Holy Land fighting the Saracens whilst

burdened down with heavy armour in the Middle Eastern heat (Goldman 2001)

It is not only the workers and armies that are impacted but also the general

population One of the worst cases occurred in Peking China in 1743 when during a

10 day heat wave 11000 people were reported to have perished (Levick 1859)

In 1774 Sir Charles Blagden of the Royal Society outlined a series of experiments

undertaken in a heated room in which he commented on ldquothe wonderful power with

which the animal body is endued of resisting heat vastly greater than its own

temperaturerdquo (Blagden 1775)

Despite this experience and knowledge over the ages we are still seeing deaths in

the 20th century as a result of heat stress Severe heat related illnesses and deaths

are not uncommon among pilgrims making the Makkah Hajj (Khogali 1987) and

closer to home a fatality in the Australian military (ABC 2004) and more recently

amongst the Australian workforce (Australian Mining 2013)

27

12 Heat and the Human Body

The human body in a state of wellbeing maintains its internal temperature within a

very narrow range This is a fundamental requirement for those internal chemical

reactions which are essential to life to proceed at the proper rates The actual level

of this temperature is a product of the balance between heat exchange with the

external thermal environment and the generation of heat internally by the metabolic

processes associated with life and activity

The temperature of blood circulating through the living and working tissues is

monitored by receptors throughout the body The role of these receptors is to induce

specific responses in functional body systems to ensure that the temperature

remains within the appropriate range

The combined effect of external thermal environment and internal metabolic heat

production constitutes the thermal stress on the body The levels of activity required

in response to the thermal stress by systems such as cardiovascular

thermoregulatory respiratory renal and endocrine constitute the thermal strain

Thus environmental conditions metabolic workload and clothing individually or

collectively create heat stress for the worker The bodyrsquos physiological response to

stressors for example sweating increased heart rate and elevated core

temperature is the heat strain

Such physiological changes are the initial responses to thermal stress but the extent

at which these responses are required will determine whether that strain will result in

thermal injuryillness It is important to appreciate that while preventing such illness

by satisfactorily regulating human body temperature in a heat-stress situation those

responses particularly the sweat response may not be compatible with comfort

(Gagge et al 1941)

The rate of heat generated by metabolic processes is dependent on the level of

physical activity To precisely quantify the metabolic cost associated with a particular

task without directly or indirectly measuring the individual is not possible This is due

to the individual differences associated with performing the task at hand As a

result broad categories of metabolic loads for typical work activities have been

established (Durnin amp Passmore 1967 ISO 8996 2004) It is sometimes practicable

Safe Work Australia (2011) refers to heat related illnesses and OSHA (httpswwwoshagovSLTCheatstress) considers heat exhaustion and heat stroke cases to be heat-related illness due to the number of human factors that contribute to a workers susceptibility to heat stress (refer to Section 40) while ACGIH (2013) refers to heat stress and heat strain cases as being heat-related disorders They are not usually considered injuries

28