A Guide to Managing Heat Stress: Developed for Use in the Australian Environment

A GUIDE TO MANAGING HEAT STRESS: DEVELOPED FOR USE IN THE AUSTRALIAN ENVIRONMENT

AUSTRALIAN INSTITUTE OF OCCUPATIONAL HYGIENISTS INC (Incorporated in Victoria) Registered Office Unit 2, 8-12 Butler Way Tullamarine VIC 3043 Tel: +61 3 9338 1635 Email: [email protected] Postal Address PO Box 1205 TULLAMARINE VIC 3043

“We all rejoiced at the opportunity of being convinced, by our own experience, of the wonderful power with which the animal body is endued, of resisting heat vastly greater than its own temperature”

Dr Charles Blagden, M. D. F. R. S. (1775)

Cover image “Sampling molten copper stream” used with the permission of Rio Tinto

A Guide to Managing Heat Stress: Developed for Use in the Australian Environment

Developed for the Australian Institute of Occupational Hygienists

Ross Di Corleto, Ian Firth & Joseph Maté

November 2013

Contents

CONTENTS 3

PREFACE 6

A GUIDE TO MANAGING HEAT STRESS 7

Section 1: Risk assessment (the three step approach). 8

Section 2: Screening for clothing that does not allow air and water vapour movement. 12

Section 3: Level 2 assessment using detailed analysis. 13

Section 4: Level 3 assessment of heat strain. 15

Section 5: Occupational Exposure Limits 17

Section 6: Heat stress management and controls 18

BIBLIOGRAPHY 21

Appendix 1 - Basic Thermal Risk Assessment – Apparent Temperature 23

Appendix 2 – Table 5: Apparent Temperature Dry Bulb/Humidity scale. 25

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

1.0 INTRODUCTION 27

1.1 Heat Illness – A Problem Throughout the Ages. 27

1.2 Heat and the Human Body 28

2.0 HEAT RELATED ILLNESSES 29

2.1 Acute Illnesses 30

2.1.1 Heat Stroke 30 2.1.2 Heat Exhaustion 31 2.1.3 Heat Syncope (Fainting) 31 2.1.4 Heat Cramps 32 2.1.5 Prickly Heat (Heat Rash) 32

2.2 Chronic Illness 32

2.3 Related Hazards 33

3.0 CONTACT INJURIES 34

4.0 KEY PHYSIOLOGICAL FACTORS CONTRIBUTING TO HEAT ILLNESS 36

4.1 Fluid Intake 36

4.2 Urine Specific Gravity 43

4.3 Heat Acclimatisation 45

4.4 Physical Fitness 47

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

5.0 ASSESSMENT PROTOCOL 48

6.0 WORK ENVIRONMENT MONITORING AND ASSESSMENT 50

6.1 Risk Assessment 50

6.2 The Three Stage Approach 51 6.2.1 Level 1 Assessment: A Basic Thermal Risk Assessment 53

6.3 Stage 2 of Assessment Protocol: Use of Rational Indices 54

6.3.1 Predicted Heat Strain (PHS) 55 6.3.2 Thermal Work Limit (TWL) 58 6.3.3 Other Indices 60

7.0 PHYSIOLOGICAL MONITORING - STAGE 3 OF ASSESSMENT PROTOCOL 62

7.1 Core Temperature 65

7.2 Heart Rate Measurements 67

8.0 CONTROLS 70

8.1. Ventilation 72

8.2 Radiant Heat 73

8.3 Administrative Controls 76 8.3.1 Training 76 8.3.2 Self-Assessment 77 8.3.3 Fluid Replacement 77 8.3.4 Rescheduling of Work 77 8.3.5 Work/Rest Regimes 77 8.3.6 Clothing 78 8.3.7 Pre-placement Health Assessment 80

8.4 Personal Protective Equipment 81 8.4.1 Air Cooling System 81 8.4.2 Liquid Circulating Systems 82 8.4.3 Ice Cooling Systems 83 8.4.4 Reflective Clothing 84

9.0 BIBLIOGRAPHY 85

Appendix A: Heat Stress Risk Assessment Checklist 103

Appendix B: Preliminary Plant Heat Stress Risk Assessment Sheet 104

Appendix C: Thermal Measurement 105

Appendix D: Encapsulating Suits 108

PREFACE In 2001 the Australian Institute of Occupational Hygienists (AIOH) established the Heat Stress Working Group to develop a standard and relevant documentation in relation to risks associated with hot environments. This group produced “The heat stress standard and documentation developed for use in the Australian environment (2003).” Since that time there have been a number of developments in the field and it was identified that the standard and documentation were in need of review. As a result “A guide to managing heat stress: developed for use in the Australian environment (2013)” and associated documentation have been produced and now replace the previous standard and documentation publications. There has been a slight shift in the approach such that the emphasis of these documents is on guidance rather than an attempt to establish a formal standard. They provide information and a number of recommended approaches to the management of thermal stress, with associated references. The guidance is in two parts:

• the first, a brief summary of the approach written for interested parties with a non- technical background, and

• the second, a more comprehensive set of documentation for the occupational health practitioner.

These are not intended to be definitive documents on the subject of heat stress in Australia. They will hopefully provide enough information and further references to assist employees and employers (persons conducting a business or undertaking) as well as the occupational health and safety practitioner, to manage heat stress in the Australian workplace.

The authors wish to acknowledge the contribution of Gerald V Coles to the original manuscript, which provided the foundation for this document.

A Guide to Managing Heat Stress The human body must regulate its internal temperature within a very narrow range to maintain a state of well-being. To achieve this, the temperature must be balanced between heat exchanges with the external thermal environment and the generation of heat internally by the metabolic processes associated with life and activity. The effects of excessive external heat exposures can upset this balance and result in a compromise of health, safety, efficiency and productivity, which precede the possibly more serious heat related illnesses. These illnesses can range from prickly heat, heat cramps, heat syncope, heat exhaustion, heat stroke and in severe cases, death. The prime objective of heat stress management is the elimination of any injury or risk of illness as a result of exposure to excessive heat.

Assessment of both heat stress and heat strain can be used for evaluating the risk to worker health and safety. A decision-making process such as that shown in Figure 1 can be used. Figure 1 and the associated Documentation for this Guide provides means for determining conditions under which it is believed that an acceptable percentage of adequately hydrated, unmedicated, healthy workers may be repeatedly exposed without adverse health effects. Such conditions are not a fine line between safe and dangerous levels. Professional judgement and a program of heat stress management, with worker education and training as core elements are required to ensure adequate protection for each situation.

This Heat Stress Guide provides guidance based on current scientific research (as presented in the Documentation), which enables individuals to decide and apply appropriate strategies. It must be recognised that whichever strategy is selected, an individual may still suffer annoyance, aggravation of a pre-existing condition, or even physiological injury. Responses to heat in a workforce are individual and will vary between personnel. Because of these characteristics and susceptibilities, a wider range of protection may be warranted. Note that this Guide should not be used without also referencing the accompanying Documentation.

This Guide is concerned only with health considerations and not those associated with comfort. For additional information related to comfort, readers are directed to more specific references such as International Standards Organization (ISO) 7730 – 2005: Ergonomics of the thermal environment - Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria.

HEAT STRESS is the net heat load to which a worker may be exposed from the combined contributions of metabolism associated with work and environmental factors such as: • air temperature, • humidity, • air movement • radiant heat exchange and • clothing requirements

The effects of exposure to heat may range from a level of discomfort through to a life threatening condition such as heat stroke. A mild or moderate heat stress may adversely affect performance and safety. As the heat stress approaches human tolerance limits, the risk of heat-related disorders increases.

HEAT STRAIN is the body’s overall response resulting from heat stress. These responses are focussed on removing excess heat from the body.

Section 1: Risk assessment (the three step approach). The decision process should be started if there are reports of discomfort due to heat stress. These include but are not limited to: • prickly heat, • headaches, • nausea, • fatigue, or when professional judgement indicates the need to assess the level of risk. Note: any one of the symptoms can occur and may not be sequential as described above.

A structured assessment protocol is the best approach, as it provides the flexibility to meet the requirements for the individual circumstance. The three tiered approach for the assessment of exposure to heat has been designed in such a manner that it can be applied to a number of varying scenarios where there is a potential risk of heat stress. The suggested approach involves a three-stage process which is dependent on the severity and complexity of the situation. It allows for the application of an appropriate intervention for a specific task utilising a variation of risk assessment approaches. The recommended method would be as follows:

1. A basic heat stress risk assessment questionnaire incorporating a simple index

2. If a potential problem is indicated from the initial step, then the progression to a second level index to enable a more comprehensive investigation of the situation and general

environment follows. Making sure to consider factors such as air velocity, humidity, clothing, metabolic load, posture and acclimatisation

3. Where the allowable exposure time is less than 30 minutes or there is a high involvement level of personal protective equipment (PPE), then some form of physiological monitoring should be employed (Di Corleto, 1998a)

The first level, or the basic thermal risk assessment, is primarily designed as a qualitative risk assessment that does not require specific technical skills in its administration, application or interpretation. The second step of the process begins to look more towards a quantitative risk approach and requires the measurement of a number of environmental and personal parameters such as dry bulb and globe temperatures, relative humidity, air velocity, metabolic work load and clothing insulation. The third step requires physiological monitoring of the individual, which is a more quantitative risk approach. It utilises measurements based on an individual’s strain and reactions to the thermal stress to which they are being exposed. This concept is illustrated in Figure 1.

It should be noted that the differing levels of risk assessment require increasing levels of technical expertise. While a level 1 assessment could be undertaken by a variety of personnel requiring limited technical skills, the use of a level 3 assessment should be restricted to someone with specialist knowledge and skills. It is important that the appropriate tool is selected and applied to the appropriate scenario and skill level of the assessor.

Figure 1: Heat Stress Management Schematic (adapted from ACGIH 2013) Level 1. Perform Basic Risk Assessment

Does task involve use of impermeable clothing? (i.e. PVC)

Continue work, Unacceptable risk? No monitor conditions

Yes

Are data available for Monitor task to ensure No detailed analysis conditions & collect data

Level 2 Analyse data with rational heat stress index (i.e. PHS, TWL) No Yes

Unacceptable heat stress risk based on analysis?

Yes

Job specific controls practical Yes Maintain job specific controls and successful?

Level 3 Undertake physiological monitoring

No Excessive heat strain based on monitoring?

Yes

Cease work

Level 1 Assessment: a basic thermal risk assessment A suggested protocol for the level 1 assessment is termed the “Basic Thermal Risk Assessment”. 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 individual's 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 7243:1989 and ISO 8996:2004 standards.

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

Class Examples Resting Resting, sitting at ease Low / Light Sitting at ease; light manual work; hand and arm work; car driving; Work standing; casual walking; sitting or standing to control machines.

Moderate / Sustained hand and arm work (e.g. hammering); arm and trunk Moderate Work work; moving light wheelbarrow; walking around 4.5 km/h.

High / Heavy Intense arm and trunk work; carrying heavy material; shovelling; Work sawing hard wood; moving heavily loaded wheelbarrows; carrying loads upstairs. Source: (ISO 8996:2004).

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.

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 ‘No’ 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 (i.e. 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

ambient conditions are considered cool and the risk assessment determines “Low Risk”. If workers are required to wear additional clothing that does not allow air and water vapour movement, then the ‘Yes’ 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: • clothing type, • air speed, • air temperature, • water vapour content of the air (e.g. humidity), • posture, • length of exposure, and • 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 ‘No’ 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

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 (i.e. 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 ‘required wettedness’. 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:

• fit for the activity being considered, and • in good health, and • screened for intolerance to heat, and • properly instructed, and • able to self-pace their work, and • under some degree of supervision (minimally a buddy system).

In work situations which:

• either the maximum evaporation rate is negative, leading to condensation of water vapour on the skin; • 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 (<38.2°C) and sweat rate (<1.2 kg/hr) (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.

If the exposure does not exceed the criteria for the detailed analysis, then the ‘No’ 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 ‘Yes’ 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 ‘No’ 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 individual’s working environment cannot be accurately assessed. A common example is work involving the use of encapsulating “hazmat” 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 and/or 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.

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: • Sustained (several minutes) heart rate in excess of 180 beats per minute minus the individuals age in years (eg,180 – age), for individuals with assessed normal cardiac performance; OR • Body core temperature greater than 38.5°C (101.3°C) for medically selected and acclimatised personnel; or greater than 38°C (100.4°C) in unselected, unacclimatised workers; OR • When there are complaints of sudden and severe fatigue, nausea, dizziness, or light-headedness; OR • A worker's 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 • A worker experiences profuse and prolonged sweating over hours and may not be able to adequately replenish fluids; OR • Greater than 1.5% weight loss over a shift: OR • 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: • ‘Heart Rate Limit = 185 - 0.65A’, where A = Age in years; • 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: • HRL, sustained = 180 – age. • 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

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 ‘No’ 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 ‘Yes’ 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 and/or 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 safe/unsafe limits and should only be used as guides.

Use of Urinary Specific Gravity testing

Water intake at one’s 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

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 1.000. Studies (Sawka et al, 2007; Ganio et al, 2007; Cheuvront & Sawka, 2005; Casa et al, 2000) recommend that a USG of greater than 1.020 would reflect dehydration. While not regarded as fool proof or the “gold standard” 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 Urine Specific Loss (%) Gravity Well Hydrated <1 1.010 Minimal dehydration 1 - 3 1.010 – 1.020 Significant 3 - 5 1.021 – 1.030 dehydration Severe dehydration > 5 > 1.030 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, work/rest 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.

Table 4: Examples of control methods

Elimination/substitution • Hot tasks should be scheduled to avoid the hottest part of the day or where practical undertaken during night shifts. • Walls and roof structures should utilize light coloured or reflective materials • Structures should be designed to incorporate good air flow. This can be done via the positioning of windows, shutters and roof design to encourage ‘chimney effects’. This will help remove the heat from the structure. • Walls and roofs should be insulated.

Engineering • Pipework and vessels associated with hot processes should be insulated and clad to minimize the introduction of heat into the work environment. • 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 ‘chiller’ units can be used. • 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. • Relocating hot processes away from high access areas. • Dehumidifying air to increase the evaporative cooling effect. Often steam leaks, open process vessels or standing water can artificially increase humidity within a building. • Utilize mechanical aids that can reduce the metabolic workload on the individual.

Administrative • Ready access to cool palatable drinking water is a basic necessity. • Where applicable, suitable electrolyte replacements should also be available. • 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

teams with high mobility, even a simple shade structure readily available from hardware stores or large umbrellas can provide relief from solar radiation. • Where work-rest regimes are necessary heat stress indices, such as WBGT, PHS or TWL assist in determining duration of work and rest periods. • Training workers to identify symptoms and the potential onset of heat-related illness as part of the ‘buddy system’. • Encouraging “self-determination” or pacing of the work to meet the conditions and reporting of heat related symptoms. • Consider pre-placement medical screening for work in hot areas (ISO 12894).

Personal protective equipment • PPE such as cooling vests with either ‘phase change’ 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. • Vortex tube air cooling may be used in some situations, particularly when a cooling source is required when supplied air respirators are used. • 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.

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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 < 30 min  30 min – 1hour  1 hour - 2 hours  > 2 hrs  Confined space No  Yes  Task complexity Simple  Moderate  Complex  Climbing, up/down stairs or ladders None  One level  Two levels  > Two levels  Distance from cool rest area <10 Metres  10 - 50 Metres  50-100 Metres  >100 Metres  Distance from drinking water <10 Metres  10 - 30 Metres  30-50 Metres  >50 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 < 27°C  >27°C ≤ 33°C  >33°C ≤ 41°C  > 41°C  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 • Mark each box according to the appropriate conditions. • When complete add up using the value at the top of the appropriate column for each mark. • Add the sub totals of Table A & Table B and multiply with the sub-total of Table C for the final result. • If the total is less than 28 then the risk due to thermal conditions are low to moderate. • 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. • 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.

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 30°C, and the relative humidity at 70%. This equates to an apparent temperature of 35°C (see Table 5 in appendix 2).

Using the above information in the risk assessment we have: Assessment Point Value HAZARD TYPE 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 < 30 min  30 min – 1hour  1 hour - 2 hours  > 2 hrs  Confined space No  Yes  Task complexity Simple  Moderate  Complex  Climbing, up/down stairs or ladders None  One level  Two levels  > Two levels  Distance from cool rest area <10 Metres  <50 Metres  50-100 Metres  >100 Metres  Distance from drinking water <10 Metres  <30 Metres  30-50 Metres  >50 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 < 27°C  >27°C ≤ 33°C  >33°C ≤ 41°C  > 41°C  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.

Appendix 2 – Table 5: Apparent Temperature Dry Bulb/Humidity 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 (%) (°C) 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)

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 & Joseph Maté

November 2013

1.0 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.

1.1 Heat Illness – 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 Judith’s husband, Manasseh from exposure in the fields supervising workers where it says “He had suffered a sunstroke while in the fields supervising the farm workers and later died in bed at home in Bethulia” (Judith 8:3).

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 “thirst and sun”. 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 11,000 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 “the wonderful power with which the animal body is endued, of resisting heat vastly greater than its own temperature” (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).

1.2 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 body’s 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 injury/illness*. 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 & Passmore, 1967; ISO 8996, 2004). It is sometimes practicable

* Safe Work Australia (2011) refers to heat related illnesses and OSHA (https://www.osha.gov/SLTC/heatstress/) considers heat exhaustion and heat stroke cases to be heat-related illness due to the number of human factors that contribute to a worker's susceptibility to heat stress (refer to Section 4.0), while ACGIH (2013) refers to heat stress and heat strain cases as being heat-related disorders. They are not usually considered injuries.

to assess such loads by direct observation of the component movements of the worker’s activities (Lehmann et al, 1950); such as upper or lower body movements.

Apart from individual variations such as obesity and height, the rate of transfer of heat from working tissues to the skin surface depends on the existence of a temperature gradient between the working tissues and the skin. In short, as an individual becomes larger, the surface area reduces as a ratio of volume. Thus, a smaller person can dissipate heat more effectively than a larger person as the smaller individual has a larger surface area to body mass ratio than a large individual (Anderson, 1999; Dennis & Noakes, 1999).

Circumstances exist where the body’s metabolic heat production exceeds normal physiological functioning. This is typical when performing any physical activity for prolonged periods. Under such a scenario, the surrounding environment must have the capacity to remove excess heat from the skin surface. Failure to remove the excess heat can result in failure to safely continue working in the particular environment.

However, it is essential to recognise that the level of exposure to be permitted by the management of any work situation, or by regulatory requirements, necessitates a socio-economic decision on the proportion of the exposed population for whom safeguarding is to be assured. The Heat Stress Guide provides only guidance, based on the available scientific data (as presented in this Documentation), by which such a decision is reached and applied.

It must be recognised that whatever standard or guidance is chosen, an individual may suffer annoyance, aggravation of a pre-existing condition, or occasionally even physiological damage. The considerable variations in personal characteristics and susceptibilities in a workforce may lead to such possibilities at a wide range of levels of exposure. Moreover, some individuals may also be unusually responsive to heat because of a variety of factors such as genetic predisposition, age, personal habits (eg. alcohol or other drugs), disease, or medication. An occupational physician should evaluate the extent to which such workers require additional protection when they are liable to heat exposure, because of the multifactorial nature of the risk.

2.0 Heat Related Illnesses

This section briefly describes some of the common heat related illnesses that are possible to experience when working in hot environments. Although these illnesses

appear sequentially in this text, this may not be the order of appearance by an individual experiencing a heat related illness.

2.1 Acute Illnesses

Incorrect management of exposure to elevated thermal environments can lead to a number of acute illnesses which range from:

• prickly heat, • heat cramps, • heat syncope (fainting), • heat exhaustion, to • heat stroke.

The most serious of the heat-induced illnesses requiring treatment is heat stroke, because of its potential to be life threatening or result in irreversible tissue damage. Of the other heat-induced illnesses, heat exhaustion in its most serious form can lead to prostration and can cause serious illnesses as well as heat syncope. Heat cramps, while debilitating and often extremely painful, are easily reversible if properly and promptly treated. These are discussed in more detail below.

The physiologically related illnesses resulting from the body’s inability to cope with an excess heat load are usually considered to fall into three or four distinct categories. It has been suggested (Hales & Richards, 1987) that heat illnesses actually form a continuum from initial symptoms such as lethargy through to heat-related stroke. It is important to note that the accepted usual symptoms of such heat illness may show considerable variability in the diagnosis of the individual sufferer, in some cases requiring appropriate skilled medical assessment. The broad classification of such illnesses is as follows.

2.1.1 Heat Stroke Heat stroke, which is a state of thermoregulatory failure, is the most serious of the heat illnesses. Heat stroke is usually considered to be characterised by hot, dry skin; rapidly rising body temperature; collapse; loss of consciousness; and convulsions. If deep body temperature exceeds 40°C (104°F), there is a potential for irreversible tissue damage. Without initial, prompt and appropriate medical attention, including removal of the victim to a cool area and applying a suitable method for reduction of the rapidly increasing body temperature, heat stroke can be fatal. Whole body immersion in a cold / ice water bath has been shown to remove heat from the body the quickest (Casa et al, 2007). If such equipment is not available, immediate

cooling to reduce body temperature below 39°C is necessary. Other methods of cooling may include spraying with cool water and/or fanning to promote evaporation. Irrespective of the cooling method, a heat stroke victim needs immediate, experienced medical attention.

2.1.2 Heat Exhaustion Heat exhaustion, while serious, is initially a less severe illness than heat stroke, although it can become a preliminary to heat stroke. Heat exhaustion is generally characterised by clammy, moist skin; weakness or extreme fatigue; nausea; headache; no excessive increase in body temperature; and low blood pressure with a weak pulse. Without prompt treatment, collapse is inevitable.

Heat exhaustion most often occurs in persons whose total blood volume has been reduced due to dehydration (i.e. depletion of total body water as a consequence of deficient water intake). Individuals who have a low level of cardiovascular fitness and/or are not acclimatised to heat have a greater potential to become heat exhaustion victims, particularly where self-pacing of work is not practised. Note that where self-pacing is practised, both fit and unfit workers tend to have a similar frequency of heat exhaustion. Self-paced workers reduce their work rate as workplace temperatures increase, hence hyperthermia in a self-paced setting is generally due to exposure to extreme thermal environments (external heat) rather than high metabolic loads (internal heat) (Brake & Bates, 2002c).

Depending on the extent of the exhaustion, resting in a cool place and drinking cool slightly saline solution (Clapp et al, 2002) or an electrolyte supplement will assist recovery, but in more serious cases a physician should be consulted prior to resumption of work. Salt-depletion heat exhaustion may require further medical treatment under supervision.

2.1.3 Heat Syncope (Fainting) Exposure of fluid-deficient persons to hot environmental conditions can cause a major shift in the body’s remaining blood supply to the skin vessels in an attempt to dissipate the heat load. This ultimately results in an insufficient supply of blood being delivered to the brain (lower blood pressure) and consequently fainting. The latter condition may also occur even without significant reduction in blood volume in conditions such as wearing impermeable encapsulating clothing assemblies, or with postural restrictions (Leithead & Lind, 1964).

2.1.4 Heat Cramps Heat cramps are characterised by painful spasms in one or more skeletal muscles. Heat cramps may occur in persons who sweat profusely in heat without replacing salt losses, or unacclimatised personnel with higher levels of salt in their sweat. Resting in a cool place and drinking cool slightly saline solution (Clapp et al, 2002), or an electrolyte supplement, may alleviate the cramps rapidly. Use of salt tablets is undesirable and should be discouraged. Thereafter, such individuals should be counselled to maintain a balanced electrolyte intake, with meals if possible. Note that when heat cramps occur, they occur most commonly during the heat exposure, but can occur sometime after heat exposure.

2.1.5 Prickly Heat (Heat Rash) Heat rashes usually occur as a result of continued exposure to humid heat with the skin remaining continuously wet from unevaporated sweat. This can often result in blocked glands, itchy skin and reduced sweating. In some cases, depending on its location on the body, prickly heat can lead to lengthy periods of disablement (Donoghue & Sinclair, 2000). When working in conditions that are favourable for prickly heat to develop (eg. exposure to damp situations in tropical or deep underground mines), control measures to reduce exposure may be important to prevent periods of disablement. Keeping the skin clean, cool and as dry as possible to allow the skin to recover is generally the most successful approach to avoid prickly heat.

2.2 Chronic Illness

While the foregoing acute and other shorter term effects of high levels of heat stress are well documented, less data are available on chronic, long-term effects and appear generally less conclusive. Psychological effects in subjects from temperate climates, following long-term exposure to tropical conditions, have been reported (Leithead & Lind, 1964). Following years of daily work exposures at high levels of heat stress, chronic lowering of full-shift urinary volumes appears to result in a higher incidence of kidney stones despite greatly increased work shift fluid intake (Borghi et al, 1993).

In a review of chronic illnesses associated with heat exposure (Dukes-Dobos, 1981) it was proposed that they can be grouped into three types: • Type 1 - The after effects of an acute heat illness; i.e. reduced heat tolerance, reduced sweating capacity.

• Type 2 - Occur after working in hot conditions for weeks, months or a few years (similar to general stress reactions); i.e. headache, nausea, hypertension, reduced libido. • Type 3 – Tend to occur more frequently among people living in climatically hot regions of the world; i.e. kidney stones, heat exhaustion from suppressed sweating (anhidrotic) (NIOSH, 1997).

A study of heat waves in Adelaide indicated that men aged between 35 to 64 years of age had an increased hospital admission rate for kidney disease (Hansen et al, 2008).

Some studies have indicated that long-term heat exposure can also contribute to issues relating to liver, heart, digestive system, central nervous system, skin illnesses and gestation length (Porter et al, 1999; Wild et al, 1995). Evidence to support these findings are inconclusive.

Consideration may be required of the possible effects on human reproduction. This is in relation to temporary infertility in both females and males [where core temperatures are above 38°C (100.4°F)] (NIOSH, 1997). There may also be an increased risk of malformation of the unborn foetus when during the first trimester of pregnancy a female’s core temperature exceeds 39°C (102.2°F) for extended periods (AMA, 1984; Edwards et al, 1995; Milunsky et al, 1992;). Note that no published cases of the latter effect have been reported in an industrial setting.

In addition to the illnesses, previous occurrences of significant heat induced illnesses can predispose an individual to subsequent incidents and impact on their ability to cope with heat stress (Shibolet et al, 1976; NIOSH, 1997). In some cases, workers may develop intolerance to heat following recovery from a severe heat illness (Shapiro et al, 1979). Irreparable damage to the body’s heat-dissipating mechanisms has been noted in many of these cases.

2.3 Related Hazards

While the direct health effects of heat exposure are of concern there are also some secondary characteristics of exposure that are noteworthy. These range from reduced physical and cognitive performance (Hunt, 2011) and increased injury incidence among physically active individuals (Knapik et al, 2002), as well as increased rates of trauma, crime, and domestic violence (McMichael et al, 2003). A relationship has also been shown between an increase in helicopter pilot errors and

ambient heat stress (Froom, et al 1993) and an increased incidence of errors by US army recruits during basic combat training (Knapik et al, 2002).

The effects of excessive heat exposures and dehydration can result in a compromise of safety, efficiency and productivity losses. In fact, higher summer temperatures may be partially responsible for increased injury incidence among physically active individuals (Knapik et al, 2002). Workers under thermal stress have been shown to also experience increased fatigue (Brake & Bates, 2001; Cian et al, 2000; Ganio et al, 2011). Studies have shown that dehydration can result in the reduction in performance of a number of cognitive functions including visual vigilance and working memory and an increase in tension and anxiety has also been noted (Ganio et al, 2011). Further studies have demonstrated impairment in perceptive discrimination, short term memory and psycho–motor skills (Cian et al, 2000). These typically precede more serious heat related illnesses (Leithead & Lind, 1964; Ramsey et al, 1983; Hancock, 1986).

3.0 Contact Injuries

Within the occupational environment, there are numerous thermal sources that can result in discomfort or burns to the skin. These injuries may range from burns to the outer layer of skin (epidermis) but do not penetrate to the deeper layers, partial thickness burns that penetrate the epidermis but not the dermis, and full thickness burns that penetrate the epidermis and dermis, and damage the underlying tissue below.

Figure 1: The structure of human skin (adapted from Parsons, 2003)

In recent times there have been a number of developments in information relating to burns caused by hot surfaces. In particular ISO 13732 Part 1 (2006) provides information concerning exposures of less than 1 second. Additional information relating to skin contact with surfaces at moderate temperatures can be found in ISO/TS 13732 Part 2 (2001).

A number of curves have been developed identifying temperatures and contact times that result in discomfort, partial skin thickness burns and full skin thickness burns. An example developed by Lawrence and Bull (1976) is illustrated in Figure 2. Burns and scalds can occur at temperatures as low as 45°C given a long contact time. In most cases, an individual’s natural reflex or reaction results in a break of contact within 0.25 seconds, but this may not always be possible in situations where a hot material such as molten metal or liquid has been splashed onto someone. During such a scenario, the molten material remains in contact with the skin or alternatively, they become immersed in the liquid. To minimise the risk of scalding burns from hot water services used for washing or showering, particularly the elderly or vulnerable populations, a temperature of 43°C should not be exceeded (PHAA, 2012).

Figure 2: The relation of time and temperature to cause discomfort and thermal injury to skin (adapted from Lawrence & Bull, 1976).

An example of a risk assessment methodology for potential contact burns when working with hot machinery is outlined below:

1. Establish by task analysis and observation, worker behaviour under normal and extreme use of the machine. Consultation should take place with the operator/s to review the use of the equipment and identify contact points, touchable surfaces and length of contact periods.

2. Establish conditions that would produce maximum temperatures of touchable parts of the equipment (not normally heated as an integral part of the functioning of the machine).

3. Operate the equipment and undertake surface temperature measurements.

4. Dependent on the equipment and materials identified in step 1, determine which is the most applicable burn threshold value. Multiple thresholds may need to be utilised where different materials are involved.

5. Compare the measured results with the burn thresholds.

ISO 13732 Part 1 (2006) Section 6.1 provides a more comprehensive example of a risk assessment.

4.0 Key Physiological Factors Contributing to Heat Illness

4.1 Fluid Intake

The importance of adequate hydration (euhydration) and the maintenance of correct bodily electrolyte balance, as essential prerequisites to the prevention of injurious heat strain, cannot be overemphasised. The most effective means of regulating temperature is via the evaporation of sweat, which may account for up to 98% of the cooling process (Gisolfi et al, 1993). At a minimum, thermoregulation in hot conditions requires the production and evaporation of sweat at a rate equivalent to heat absorbed from the environment and gained from metabolism. While in a dehydrated state, an individual’s capacity to perform physical work is reduced, fatigue is increased and there are also psychological changes. It has also been shown to increase the perceived rate of exertion as well as impairing mental and cognitive function (Montain & Coyle, 1992). “Rational” heat stress indices (Belding & Hatch, 1955, ISO 7933, 2004) can be used to calculate sweat requirements, although their precision may be limited by uncertainty of the actual metabolic rate and personal factors such as physical fitness and health of the exposed individuals.

The long-term (full day) rate of sweat production is limited by the upper limit of fluid absorption from the digestive tract and the acceptable degree of dehydration, after maximum possible fluid intake has been achieved. The latter is often considered to be 1.2 L/hr (Nielsen, 1987), a rate that can be exceeded by sweating losses, at least over shorter periods. However, Brake et al (1998) have found that the limit of the stomach and gut to absorb water is in excess of 1 L/hr over many hours (about 1.6 to 1.8 L/hr, providing the individual is not dehydrated). Never the less, fluid intake is often found to be less than 1 L/hr in hot work situations, with resultant dehydration (Hanson et al, 2000; Donoghue et al, 2000).

A study of fit, acclimatised, self-paced workers (Gunn & Budd, 1995) appears to show that mean full-day dehydration (replaced after work) of about 2.5% of body mass has been tolerated. However, it has been suggested that long-term effects of such dehydration are not adequately studied and that physiological effects occur at 1.5% to 2.0% dehydration (NIOSH, 1997). The predicted maximum water loss (in one shift or less) limiting value of 5% of body mass, proposed by the International Organisation for Standardisation (ISO 7933, 2004), is not a net fluid loss of 5%, but of 3% due to re-hydration during exposure. This is consistent with actual situations identified in studies in European mines under stressful conditions (Hanson et al, 2000). A net fluid loss of 5% in an occupational setting would be considered severe dehydration.

Even if actual sweat rate is less than the possible rate of fluid absorption, early literature has indicated that thirst is an inadequate stimulus for meeting the total replacement requirement during work and often results in ‘involuntary dehydration’ (Greenleaf, 1982; Sawka, 1988). Although thirst sensation is not easy to define, likely because it evolves through a graded continuum, thirst has been characterized by a dry, sticky, and thick sensation in the mouth, tongue, and pharynx, which quickly vanishes when an adequate volume of fluid is consumed (Goulet, 2007). Potable water should be made available to workers in such a way that they are encouraged to drink small amounts frequently that is about 250 mL every 15 minutes. However, these recommendations may suggest too much or too little fluid depending on the environment, the individual and the work intensity, and should be used as a guide only (Kenefick & Sawka, 2007). A supply of reasonably cool water (10° - 15°C or 50°- 60°F) (Krake et al, 2003; Nevola et al, 2005) should be available close to the workplace so that the worker can reach it without leaving the work area. It may be desirable to improve palatability by suitable flavouring.

In selecting drinks for fluid replacement, it should be noted that solutions with high solute levels reduce the rate of gastrointestinal fluid absorption (Nielsen, 1987) and materials such as caffeine and alcohol can increase non-sweat body fluid losses by diuresis (increased urine production) in some individuals. Carbonated beverages may prematurely induce a sensation of satiety (feeling satisfied). Another consideration is the carbohydrate content of the fluid, which can reduce absorption and in some cases result in gastro-intestinal discomfort. A study of marathon runners (Tsintzas et al,1995) observed that athletes using a 6.9% carbohydrate content solution experienced double the amount of stomach discomfort than those who drank a 5.5% solution or plain water. In fact, water has been found to be one of the quickest fluids absorbed (Nielsen, 1987). Table 1 lists a number of fluid replacement drinks with some of their advantages and disadvantages.

The more dehydrated the worker, the more dangerous the impact of heat strain. Supplementary sodium chloride at the worksite should not normally be necessary if the worker is acclimatised to the task and environment, and maintains a normal balanced diet. Research has shown that fluid requirements during work in the heat lasting less than 90 minutes in duration can be met by drinking adequate amounts of plain water (Nevola et al, 2005). However water will not replace salts/electrolytes or provide energy as in the case of carbohydrates. It has been suggested that there might be benefit from adding salt or electrolytes to the fluid replacement drink at the concentration at which it is lost in sweat (Donoghue et al, 2000). Where dietary salt restriction has been recommended to individuals, consultation with their physician should first take place. Salt tablets should not be employed for salt replacement. An unacclimatised worker maintaining a high fluid intake at high levels of heat stress can be at serious risk of salt-depletion heat exhaustion and should be provided with a suitably saline fluid intake until acclimatised (Leithead & Lind, 1964).

For high output work periods greater than 60 minutes, consideration should be given to the inclusion of fluid that contains some form of carbohydrate additive of less than 7% concentration (to maximise absorption). For periods that exceed 240 minutes, fluids should also be supplemented with an electrolyte, which includes sodium (~20- 30 mmol/L) and trace potassium (~5 mmol/L) to replace those lost in sweat. A small amount of sodium in beverages appears to improve palatability (ACSM, 1996; O’Connor, 1996), which in turn encourages the consumption of more fluid, enhances the rate of stomach emptying and assists the body in retaining the fluid once it has been consumed. While not common, potassium depletion (hypokalemia) can result in serious symptoms such as disorientation and muscle weakness (Holmes, n.d.).

Tea, coffee and drinks such as colas and energy drinks containing caffeine are not generally recommended as a source for rehydration and currently there is differing opinion on the effect. A review (Clapp et al, 2002) of replacement fluids lists the composition of a number of commercially available preparations and soft drinks with reference to electrolyte and carbohydrate content (Table 2) and the reported effects on gastric emptying (i.e. fluid absorption rates). It notes that drinks containing diuretics such as caffeine should be avoided. This is apparent from the report of the inability of large volumes (6 or more litres per day) of a caffeine-containing soft drink to replace the fluid losses from previous shifts in very heat-stressful conditions, (AMA, 1984), with resulting repeat occurrences of heat illness.

Caffeine is present in a range of beverages (Table 3) and is readily absorbed by the body, with blood levels peaking within 20 minutes of ingestion. One of the effects of caffeinated beverages is that they may have a diuretic effect in some individuals (Pearce, 1996); particularly when ingested at rest. Thus, increased fluid loss resulting from the consumption of caffeinated products could possibly lead to dehydration and hinder rehydration before and after work (Armstrong et al, 1985; Graham et al, 1998; Armstrong, 2002). There have been a number of recent studies (Roti et al, 2006; Armstrong et al, 2007; Hoffman, 2010, Kenefick & Sawka, 2007) that suggest this may not always be the circumstance when exercising. In these studies, moderate chronic caffeine intake did not alter fluid-electrolyte parameters during exercise or negatively impact on the ability to perform exercise in the heat (Roti, 2006; Armstrong et al, 2007) and in fact added to the overall fluid uptake of the individual. There may also be inter-individual variability depending on physiology and concentrations consumed. As well as the effect on fluid levels, it should also be noted that excessive caffeine intake can result in nervousness, insomnia, gastrointestinal upset, tremors and tachycardia (Reissig et al, 2009) in some individuals.

Table 1: Analysis of fluid replacement (adapted from Pearce, 1996)

Beverage type Uses Advantages Disadvantages Sports drinks Before, during • Provide energy • May not be correct mix and after work • Aid electrolyte • Unnecessary excessive replacement use may negatively • Palatable affect weight control. • Excessive use may exceed salt replacement requirement levels • Low pH levels may affect teeth Fruit juices Recovery • Provide energy • Not absorbed as rapidly • Palatable as water. Dilution with • Good source of vitamins water will increase and minerals (including absorption rate. potassium) Carbonated drinks Recovery • Provide energy (“Diet” • Belching versions are low calorie) • ‘Diet’ drinks have no • Palatable energy • Variety in flavours • Risk of dental cavities • Provides potassium • Some may contain caffeine • Quick “fillingness” • Low pH levels may affect teeth

Water and mineral Before, during • Palatable • Not as good for high water and after • Most obvious fluid output events of 60-90 exercise • Readily available mins + • Low cost • No energy • Less effect in retaining hydration compared to sports drinks Milk Before and • Good source of energy, • Has fat if skim milk is recovery protein vitamins and not selected minerals • Not ideal during an high • Common food choice at output period of work breakfast events • Chocolate milk or plain • Not absorbed as rapidly milk combined with fruit as water. improve muscle recuperation (especially if ingested within 30 minutes of high output period of work)

Table 2: Approximate composition of electrolyte replacement and other drinks (compositions are subject to change) Adapted from Sports Dietician 2013

Carbohydrate Protein Sodium Potassium Additional (g/100mL) (g/L) (mmol/L) (mg/L) Ingredients

Aim for (4-7) (10 - 25) Gatorade 6 0 21 230 Gatorade 6 0 36 150 Endurance Accelerade 6 15 21 66 Calcium, Iron, Vitamin E Powerade No n/a 0.5 23 230 Sugar Powerade Isotonic 7.6 0 12 141 Powerade Energy 7.5 0 22 141 100mg caffeine per Edge 450ml serve

Powerade 7.3 17 13 140 Recovery Staminade 7.2 0 12 160 Magnesium PB Sports 6.8 0 20 180 Electrolyte Drink Mizone Rapid 3.9 0 10 0 B Vitamins, Vitamin C Powerbar 7 0 33 Endurance Formula Aqualyte 3.7 0 12 120 Propel Fitness 3.8 0 0.8 5 Vitamin E, Niacin, Water Panthothenic Acid, Vitamin B6, Vitamin B12, Folic Acid

Mizone Water 2.5 0 2 0 B Vitamins, Vitamin C Lucozade Sport 6.4 Trace 20.5 90 Niacin, Vitamin B6, Body Fuel Drink Vitamin B12, Pantothenic Acid Endura 6.4 34.7 160 Red Bull 11 37.5 Caffeine 32 mg/100mL Coca Cola 11 5.98 Caffeine (Regular) 9.6 mg/100mL

Table 3: Approximate caffeine content of beverages (source: energyfiend.com)

Beverage mg caffeine per 100mL Coca Cola 9.6 Coca Cola Zero 9.5 Diet Pepsi 10.1 Pepsi Max 19.4 Pepsi 10.7 Mountain Dew 15.2

Black Tea 17.8 Green Tea 10.6 Instant Coffee 24.1 Percolated Coffee 45.4 Drip Coffee 61.3 Decaffeinated 2.4 Espresso 173 Chocolate Drink 2.1 Milk Chocolate (50g 10.7 bar)

Alcohol also has a diuretic effect and will influence total body water content of an individual.

Due to their protein and fat content, milk, liquid meal replacements, low fat fruit “smoothies”, commercial liquid sports meals (eg. Sustagen) will take longer to leave the stomach (Pearce, 1996), giving a feeling of fullness that could limit the consumption of other fluids to replace losses during physical activities in the heat. They should be reserved for recuperation periods after shift or as part of a well- balanced breakfast.

Dehydration does not occur instantaneously; rather, it is a gradual process that occurs over several hours to days. Hence, fluid consumption / replacement should also occur in a progressive manner. Due to the variability of individuals and different types of exposures it is difficult to prescribe a detailed fluid consumption regime. However, below is one adapted from the American College of Sports Medicine- Exercise and Fluid Replacement (Sawka et al, 2007)

“Before

Pre-hydrating with beverages, if needed, should be initiated at least several hours before the task to enable fluid absorption and allow urine output to return toward normal levels. Consuming beverages with sodium and/or salted snacks or small meals with beverages can help stimulate thirst and retain needed fluids.

During

Individuals should develop customized fluid replacement programs that prevent excessive (<2% body weight reductions from baseline body weight) dehydration. Where necessary, the consumption of beverages containing electrolytes and carbohydrates can help sustain fluid electrolyte balance and performance.

After

If time permits, consumption of normal meals and beverages will restore the normal state of body water content. Individuals needing rapid and complete recovery from excessive dehydration can drink ~1.5 L of fluid for each kilogram of body weight lost. Consuming beverages and snacks with sodium will help expedite rapid and complete recovery by stimulating thirst and fluid retention. Intravenous fluid replacement is generally not advantageous, unless medically merited.”

The consumption of a high protein meal can place additional demands on the body’s water reserves, as some water will be lost in excreting nitrogenous waste. High fat foods take longer to digest, diverting blood supply from the skin to the gut, thus reducing cooling potential.

However, an education and hydration program at work should stress the importance of consuming meals. It has been observed in a study of 36 adults over 7 consecutive days (de Castro, 1988) that fluid ingestion was primarily related to the amount of food ingested and that fluid intake independent of eating was relatively rare. In addition, other studies have reported that meals seem to play an important role in helping to stimulate the thirst response, causing the intake of additional fluids and restoration of fluid balance.

Thus, using established meal breaks in a workplace setting, especially during longer work shifts (10 to 12 hours), may help replenish fluids and can be important in replacing sodium and other electrolytes (Kenefick & Sawka, 2007).

4.2 Urine Specific Gravity The US National Athletic Trainers Association (NATA) has indicated that “fluid replacement should approximate sweat and urine losses, and at least maintain hydration at less than 2% body weight reduction (Casa et al, 2000). NATA also state that a urine specific gravity (USG) of greater than 1.020 would reflect dehydration as indicated in Table 4 below.

Table 4: National Athletic Trainers Association index of hydration status (adapted from Casa et al (2000))

Body Weight Urine Specific Loss (%) Gravity Well Hydrated <1 1.010 Minimal dehydration 1 - 3 1.010 – 1.020 Significant 3 - 5 1.021 – 1.030 dehydration Severe dehydration > 5 > 1.030

Current research indicates that a USG of 1.020 is the most appropriate limit value for the demarcation of dehydration (Sawka et al, 2007; Cheuvront & Sawka 2005). At this value, a body weight loss of approximately 3% fluid or more would be expected. A 2 to 3% loss in body fluid is generally regarded as the level at which there is an increased perceived effort, increased risk of heat illness and reduced physical and cognitive performance (Hunt et al, 2009). There are a number of methods available for the monitoring of USG but the most practical and widespread is via the use of a refractometer, either electronic or hand held. More recently some organisations have also been utilising urine dip sticks (litmus test) for self-testing by employees.

While proving to be an effective tool, the approach needs to be used keeping in mind that it is not without potential error. It has been suggested that where diuresis occurs, the use of USG as a direct indicator of body water loss may not be appropriate (Brake, 2001). It has also been noted that if dehydrated individuals drink a large volume of water rapidly (eg. 1.2 L in 5 minutes), this water enters the blood and the kidneys produce a large volume of dilute urine (eg. urine specific gravity of 1.005), before normal body water levels have been achieved (Armstrong, 2007). In addition, the urine will be light in colour and have USG values comparable to well-hydrated individuals (Kenefick & Sawka, 2007).

Generally, for individuals working in ongoing hot conditions the use of USG may be an adequate method to assess their hydration status (fluid intake). Alternatively the use of a qualitative test such as urine colour (Armstrong et al, 1998) may be an adequate method.

Urine colour as a measure of dehydration has been investigated in a number of studies (Armstrong et al, 1998; Shirreffs, 2000) and found to be a useful tool to track levels of hydration. The level of urine production will decrease as dehydration

increases and levels of less than approximately 250mL produced twice daily for men and 150mL for women, would indicate dehydration (Armstrong et al, 1998). Colour also intensifies as the urine concentrates, with a dark yellow colour indicating severe dehydration through to a pale straw colour when hydrated. It should be noted that colour may be affected by illness, medications, vitamin supplements (eg. Berocca®) and food colouring.

Shirreffs (2000) noted that no "gold standard" hydration status marker exists, although urinary measures of colour, specific gravity and osmolality were more sensitive at indicating moderate levels of hypohydration than were blood measurements of haematocrit and serum osmolality and sodium concentration.

In a later publication the opinion was that “the current evidence and opinion tend to favour urine indices, and in particular urine osmolality, as the most promising marker available” (Shirreffs, 2003).

4.3 Heat Acclimatisation

Acclimatisation is an important factor for a worker to withstand episodes of heat stress while experiencing minimised heat strain. However, in the many studies made of it, there is such complexity and uncertainty as to make definitive statements about its gain, retention and loss in individuals, and in particular situations, unreliable. This demands that caution be exercised in applying generalisations from the reported observations. Wherever the state of acclimatisation bears on the action to be taken, physiological or behavioural (eg. in the matter of self-pacing) responses must over ride assumptions as to the level and effects of acclimation on exposed individuals.

Heat acclimatisation is a complex process involving a series of physiological modifications, which occur in an individual after multiple exposures to a stressful environment (NIOH, 1996b; Wyndham et al, 1954; Prosser & Brown, 1961). Each of the functional mechanisms (eg. cardiovascular stability, fluid and electrolyte balances, sweat rates, osmotic shifts and temperature responses) has its own rate of change during the heat acclimatisation process.

Acquisition of heat acclimatisation is referred to on a continuum as not all functional body changes occur at the same rate (ACGIH 2013). Thus, internal body temperatures, skin temperatures, heart rate and blood pressures, sweat rate, internal body fluid shifts and renal conservation of fluid, each progress to the new compensatory level at different rates.

Mere exposure to heat does not confer acclimatisation. Increased metabolic activity for approximately 2 hours per day is required (Bass, 1963). Acclimatisation is specific to the level of heat stress and metabolic load. Acclimatisation to one heat- stress level does not confer adequate acclimatisation to a higher level of heat stress and metabolic heat production (Laddell, 1964).

The basic benefits of heat acclimatisation are summarised in Table 5, and there continues to be well-documented evidence of the value of these (Bricknell, 1996).

Table 5: Heat acclimatisation benefits

Someone with heat acclimatisation exposed to environmental and activity related heat stress has:

• More finely tuned sweating reflexes, with increased sweat production rate at lower electrolyte concentrations;

• Lower rectal and skin temperatures than at the beginning of exposure (Shvartz et al, 1974);

• More stable and better regulated blood pressure with lower pulse rates;

• Improved productivity and safety

• Reduction in resting heart rate in the heat (Yamazaki & Hamasaki, 2003);

• Decreased resting core temperature (Buono et al, 1998);

• Increase in plasma volume (Senay et al, 1976);

• Change in sweat composition (Taylor, 2006);

• Reduction in the sweating threshold (Nadel et al, 1974); and

• Increase in sweating efficiency (Shvartz et al, 1974).

Heat acclimatisation is acquired slowly over several days (or weeks) of continued activity in the heat. While the general consensus is that heat acclimatisation is gained faster than it is lost, less is known about the time required to lose acclimatisation. Caplan (1944) concluded that, in the majority of cases he was studying, “there was sufficient evidence to support the contention that loss of acclimatization predisposed to collapse when the individual had absented himself for … two to seven days”, although it was “conceivable that the diminished tolerance to hot atmospheres after a short period of absence from work may have been due to

the manner in which the leave was spent, rather than loss of acclimatization.” Brake et al (1998) suggest that 7 to 21 days is a consensus period for loss of acclimatisation. The weekend loss is transitory and is quickly made up, such that by Tuesday or Wednesday an individual is as well acclimatised as they were on the preceding Friday. If, however, there is a week or more of no exposure, loss is such that the regain of acclimatisation requires the usual 4 to 7 days (Bass, 1963). Some limited level of acclimatisation has been reported with short exposures of only 100 minutes per day such as reduced rectal (core) temperatures, reduced pulse rate and increased sweating (Hanson & Graveling, 1997).

4.4 Physical Fitness

This parameter per se does not appear to contribute to the physiological benefits solely due to acclimatisation, nor necessarily to the prediction of heat tolerance. Nevertheless, the latter has been suggested to be determinable by a simple exercise test (Kenney et al, 1986). Clearly the additional cardiovascular strain that is imposed by heat stress, over-and-above that which is tolerable in the doing of a task in the absence of that stress, is likely to be of less relative significance in those with a greater than average level of cardiovascular fitness. It is well established that aerobic capacity is a primary indicator of such fitness and is fundamentally determined by oxygen consumption methods (ISO 8996, 1990), but has long been considered adequately indicated by heart-rate methods (ISO 8996, 1990; Astrand & Ryhming, 1954; Nielsen & Meyer, 1987).

Selection of workers for hot jobs with consideration to good general health and physical condition is practised in a deep underground metalliferous mine located in the tropics of Australia with high levels of local climatic heat stress. This practice has assisted in the significant reduction of heat illness cases reported from this site (AMA, 1984). The risk of heat exhaustion at this mine was found to increase significantly in relation to increasing body-mass index (BMI), and with decreasing

predicted maximal oxygen uptake (VO2max) of miners (although not significantly) (Donoghue & Bates, 2000).

Where it is expected that personnel undertaking work in specific areas will be subject to high environmental temperatures, they should be physically fit and healthy (see Section 8.3.7). Further information in this regard may be found in ISO 12894 (2001) “Ergonomics of the Thermal Environment – Medical Supervision of Individuals Exposed to Extreme Hot or Cold Environments.”

4.5 Other Considerations in Reducing Exposure in Heat-Stress Conditions

Demonstration to the workforce of organisational commitment to the most appropriate program of heat-stress management is an essential component of a heat stress management plan. It is also important that the necessary education and training be utilised for full effect. Without a full understanding of the nature and effects of heat stress by those exposed, the application of the data from assessment and the implementation of many of the control strategies evolving from these assessments will be of limited value.

Where exposure to hazardous radiofrequency / microwave radiation may occur, it is important to consider any contribution that this might add to other components of a heat stress load. Studies of work situations in sub-tropical conditions have shown that, without appropriate management, heat exposures can exceed acceptable limits in light of standards for such radiation (Wright & Bell, 1999).

5.0 Assessment Protocol

Over the years numerous methods have been employed in the attempt to quantify the effect of heat stress or to forewarn of its impending approach. One of the traditional methods employed is the utilisation of a heat stress index. Thermal indices have been used historically in the assessment of potential heat stress situations. “A heat stress index is a single number which integrates the effects of the basic parameters in any human thermal environment such that its value will vary with the thermal strain experienced by the person exposed to a hot environment” (Parsons, 2003).

There are numerous (greater than 30; Goldman, 1988) heat stress indices that are currently available and in use by various organizations. Discussion over which index is best suited for industrial application is ongoing. Some suggestions for the heat stress index of choice are Effective Temperature (eg. BET), Wet Bulb Globe Temperature (WBGT), or Belding and Hatch’s Heat Stress Index (his). Alternatively, a rational index such as the Thermal Work Limit (TWL) or Predicted Heat Strain (PHS) has been recommended. For example, within the mining industry, there has been a wide spectrum of acceptable limits : • Queensland mines and quarrying regulations required “a system for managing the risk” (Qld Government 2001) where the wet bulb exceeds 27oC but allowed temperatures up to 34oC wet bulb (WB);

• Queensland coal mines temperatures also refer to where a wet bulb exceeds 27oC but limits exposure to an effective temperature (ET) of 29.4oC; • West Australian Mines Safety and Inspection Regulations (1995) require an air velocity of not less than 0.5 m/s where the wet bulb is greater than 25°C:

In the past there have also been limits in place at mines in other global regions: • German coal mines have had no work restrictions at less than 28oC dry bulb (DB) and 25oC ET, but allow no work at greater than 32oC DB; • UK mines no longer have formal limits, but suggest that substantial extra control measures should be implemented for temperatures above 32oC WB or 30oC ET; • South Africa under its mining Code of Practice required a heat stress management program for hot environments, defined as being “any environment where DB < 37.0 ºC and a WB range of 27.5 – 32.5ºC inclusive“.

In an Australian deep underground metalliferous mine, a significant relationship was found for increasing risk of heat exhaustion and increasing surface temperatures, such that surface temperatures could be used to warn miners about the risk of heat exhaustion (Donoghue et al, 2000).

The correct selection of a heat stress index is one aspect of the answer to a complex situation as each location and environment differs in its requirements. Thus, the solution needs to address the specific needs of the demands.

A structured assessment protocol, similar to that proposed by Malchaire et al (1999) and detailed in Section 6.2, is the suggested approach, as it has the flexibility to meet the occasion.

For work in encapsulating suits, there is evidence that convergence of skin temperatures with core temperature may precede appearance of other physiological measures at the levels usually indicative of unacceptable conditions (Pandolf & Goldman, 1978; Dessureault et al, 1995). Hence, observations of subjective behavioural indices (eg. dizziness, clumsiness, mental confusion; see Section 2 for detail on symptoms) are also important in predicting the onset of heat illnesses. While sweating is an essential heat-regulating response and may be required to be considerable (not necessarily with ill effect if fluid and electrolyte intakes are adequate), visible, heavy sweating with run-off of unevaporated sweat is indicative of a level of strain with a possibility of consequent heat-related illnesses.

It follows from the foregoing that anyone who shows signs and symptoms of undue heat strain must be assumed to be in danger. Appropriate steps must be taken so

that such persons are rendered less heat stressed and are not allowed to return to the hot work site until all adverse heat-strain signs and symptoms have disappeared. Such assessment of heat stress from its behavioural and physiological effects is extremely important to indicate the likelihood of injurious heat strain, because it is now clear that the safety of workers in an elevated heat exposure cannot be predicted solely by environmental measurements. It is thus very important that all workers and supervisors involved in tasks where there is a potential for heat induced illnesses should be involved in some form of training to assist in the recognition of the indicative symptoms of heat strain (see Section 8.3.1).

6.0 Work Environment Monitoring and Assessment

6.1 Risk Assessment “Monitoring” does not always necessitate physiological measures, but requires an informed discussion with and observation of workers and work practices. Such precautions may be regarded as a further factor in the elimination of cases of work- related heat stroke, where they are applied to limit the development of such other less serious cases of heat illness (eg. heat rash) as are thereby initially detected and treated. They are likewise included in the surveillance, control measures and work practices in the recommended standards for heat exposure in India.

Risk assessments are an invaluable tool utilised in many facets of occupational health and safety management. The evaluation of potentially hazardous situations involving heat stress also lends itself to this approach. It is important that the initial assessment must involve a review of the work conditions, the task and the personnel involved. Risk assessments may be carried out using checklists or proformas designed to prompt the assessor to identify potential problem areas. The method may range in its simplest form from a short checklist through to a more comprehensive calculation matrix, which will produce a numerical result for comparative or priority listing.

Environmental data are part of the necessary means of ensuring, in the majority of routine work situations, that thermal conditions are unlikely to have become elevated sufficiently to raise concern for worker well-being. When concern is so raised, or signs of heat strain have been observed, such data can also provide guidance as to the most appropriate controls to be introduced. An assurance of probable acceptability and some of the necessary data are provided by use of an index, such

as the ISO Predicted Heat Strain (PHS) or Thermal Work Limit (TWL), as recommended in this document.

When used appropriately, empirical or direct methods have been considered to be effective in many situations in safeguarding nearly all workers exposed to heat stress conditions. Of these, the Wet Bulb Globe Temperature (WBGT) index, developed from the earlier Effective Temperature indices (Yaglou & Minard, 1957), was both simple to apply and became widely adopted in several closely related forms (NIOSH, 1997; ISO 7243:1989; NIOH, 1996a) as a useful first order indicator of environmental heat stress. The development of the WBGT index from the Effective Temperature indices was driven by the need to simplify the nomograms and to avoid the need to measure air velocity.

Although a number of increasingly sophisticated computations of the heat balance have been developed over time as rational methods of assessment, the presently most effective has been regarded by many as the PHS, as adopted by the ISO from the concepts of the Belding and Hatch (1955) HSI. In addition, the TWL (Brake & Bates, 2002a) developed in Australia, is another rational index that is finding favour amongst health and safety practitioners.

The following sections provide detail essential to application of the first two levels in the proposed structured assessment protocol. There is an emphasis on work environment monitoring, but it must be remembered that physiological monitoring of individuals may be necessary if any environmental criteria may not or cannot be met.

The use solely of a heat stress index for the determination of heat stress and the resultant heat strain is not recommended. Each situation requires an assessment that will incorporate the many parameters that may impact on an individual in undertaking work in elevated thermal conditions. In effect, a risk assessment must be carried out in which additional observations such as workload, worker characteristics, personal protective equipment, as well as measurement and calculation of the thermal environment, must be utilised.

6.2 The Three Stage Approach

A structured assessment protocol is the best approach, with the flexibility to meet the occasion. A recommended method would be as follows:

1. 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. It can be conducted as a walk-

through survey carrying out a basic heat stress risk assessment (ask workers what the hottest jobs are), and possibly incorporating a simple index (eg. AP, WBGT, BET, etc). The use of a check sheet to identify factors that impact on the heat stress scenario is often useful at this level. It is also an opportunity to provide some information and insight to the worker. Note that work / rest regimes should not be considered at this point – the aim is simply to determine if there is a potential problem. If there is, implement general heat stress exposure controls.

2. If a potential problem is indicated from the initial step, then progress to a second level of assessment to enable a more comprehensive investigation of the situation and general environment. This 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 (expressed as a “clo” value). Ensure to take into account factors such as air velocity, humidity, clothing, metabolic load, posture and acclimatisation. A rational index (eg. PHS, TWL) is recommended. The aim is to determine the practicability of job-specific heat stress exposure controls.

3. Where the allowable exposure time is less than 30 minutes or there is high usage of personal protective equipment (PPE), then some form of physiological monitoring should be employed (Di Corleto, 1998a). The third step requires physiological monitoring of the individual, which is a more quantitative risk approach. It utilises measurements based on an individual’s strain and reactions to the thermal stress to which they are being exposed. Rational indices may also be used on an iterative basis to evaluate the most appropriate control method. The indices should be used as a ‘comparative’ tool only, particularly in situations involving high levels of PPE usage.

6.2.1 Level 1 Assessment: A Basic Thermal Risk Assessment A suggested protocol for the level 1 assessment is termed the “Basic Thermal Risk Assessment”. 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 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.

Metabolic work rate is of equal importance to environmental assessment in evaluating heat stress. Table 6 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 7243 (1989) and ISO 8996 (2004) standards.

Table 6: Examples of activities within metabolic rate classes

Class Examples Resting Resting, sitting at ease

Low / Light Sitting at ease; light manual work; hand and arm work; car driving; Work standing; casual walking; sitting or standing to control machines.

Moderate / Sustained hand and arm work (eg. hammering); arm and trunk Moderate Work work; moving light wheelbarrow; walking around 4.5 km/h.

High / Heavy Intense arm and trunk work; carrying heavy material; shovelling; Work sawing hard wood; moving heavily loaded wheelbarrows; carrying loads upstairs. Source: (ISO 8996:2004).

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 or off-the-shelf weather units. Its simplicity is one of the advantages in its use as it requires very little

technical knowledge and measurements can be taken using a simple sling psychrometer.

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.

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

A “Basic Thermal Risk Assessment” utilising the apparent temperature, with worked example, and “Heat Stress Risk Assessment Checklist” are described in Appendix 1 of the guide.

6.3 Stage 2 of Assessment Protocol: Use of Rational Indices

When the “Basic Thermal Risk Assessment” indicates that the conditions are, or may be, unacceptable, relatively simple and practical control measures should be considered. Where these are unavailable, a more detailed assessment is required. Of the “rational” indices, the studies made employing the ‘Required Sweat Rate’

(SW Req) (ISO 7933, 1989) and the revisions suggested for its improvement (Mairiaux & Malchaire, 1995; Malchaire et al, 2000; Malchaire et al, 2001), indicate that the version known as Predicted Heat Strain (ISO 7933, 2004) will be well suited to the prevention of excessive heat strain at most typical Australian industrial workplaces

(Peters, 1991). This is not to say that other indices with extensive supporting physiological documentation would not be appropriate.

It is extremely important to recognise that metabolic heat loads that are imposed by work activities are shown by heat balance calculations in the ‘rational’ heat stress indices (Belding & Hatch, 1955; Brake & Bates, 2002a; ISO 7933, 2004) to be such major components of heat stress. At the same time, very wide variations are found in the levels of those loads between workers carrying out a common task (Malchaire et al, 1984, Maté et al, 2007; Kenny et al, 2012). This shows that even climatic chamber experiments are unlikely to provide any heat-stress index and associated limits in which the environmental data can provide more than a conservative guide for ensuring acceptable physiological responses, in nearly all those exposed. Metabolic workload was demonstrated in a climate chamber by Ferres et al, (1954) and later analysed in specific reference to variability when using WBGT (Ramsey & Chai, 1983) as a index.

6.3.1 Predicted Heat Strain (PHS)

The Heat Stress Index (HSI) was developed at the University of Pittsburgh by Belding and Hatch (1955) and is based on the analysis of heat exchange originally developed by Machle and Hatch in 1947. It was a major improvement in the analysis of the thermal condition as it began looking at the physics of the heat exchange. It considered what was required to maintain heat equilibrium, whether it was possible to be achieved and what effect the metabolic load had on the situation as well as the potential to allow for additional components such as clothing effects.

The Required Sweat Rate (SW Req) was a further development of the HSI and hence was also based on the heat balance equation. Vogt et al (1982) originally proposed it for the assessment of climatic conditions in the industrial workplace. The major improvement on the HSI is the facility to compare the evaporative requirements of the person to maintain a heat balance with what is actually physiologically achievable.

One important aspect of the index is that it takes into account the fact that not all sweat produced is evaporated from the skin. Some may soak into the clothing or some may drip off. Hence the evaporative efficiency of sweating (r) is sometimes less than 1, in contrast to the HSI where it is always taken as 1. Knowing the evaporative efficiency corresponding to the required skin wetness, it is possible to

determine the amount of sweat required to maintain the thermal equilibrium of the body (Malchaire, 1990).

If heat balance is impossible, duration limits of exposure are either to limit core temperature rise or to prevent dehydration. The required sweat rate cannot exceed the maximum sweat rate achievable by the subject. The required skin wetness cannot exceed the maximum skin wetness achievable by the subject. These two maximum values are a function of the acclimatisation status of the subject (ISO 7933, 1989; ISO 7933, 2004). As such limits are also given for acclimatised and unacclimatised persons; those individuals who remain below the two limits of strain (assuming a normal state of health and fitness) will be exposed to a relatively small risk to health.

The thermal limits are appropriate for a workforce selected by fitness for the task in the absence of heat stress and assume workers are:

• Fit for the activity being considered, and • In good health; and • Screened for intolerance to heat; and • Properly instructed; and • Able to self pace their work; and • Under some degree of supervision (minimally a buddy system).

In 1983, European laboratories from Belgium, Italy, Germany, the Netherlands, Sweden and the UK carried out research (BIOMED) that aimed to design a practical strategy to assess heat stress based on the thermal balance equation. Malchaire et al (2000) undertook a major review of the methodology based on 1113 files of responses to people in hot conditions. Additional studies (Bethea et al, 2000;

Kampmann et al, 2000) also tested the SW Req method and identified limitations in a number of different industrial environments in the field. From this, a number of major modifications were made to take into account the increase in core temperature associated with activity in neutral environments. These included:

• Convective and evaporative exchanges; • Skin temperature; • The skin–core heat distribution; • Rectal temperature; • Evaporation efficiency; • Maximum sweat rate; and suggested limits to • Dehydration; and

• Increase in core temperature (Malchaire et al, 2001).

The prediction of maximum wetness and maximum sweat rates was also revised, as well as the limits for maximum water loss and core temperature. The revised model was renamed the “Predicted Heat Strain” (PHS) model, derived from the Required

Sweat Rate (SWReq).

The inputs to the method are the six basic parameters; dry bulb temperature, radiant temperature, air velocity, humidity, metabolic work load and clothing. The required evaporation for the thermal balance is then calculated using a number of algorithms from:

Ereq = M – W – Cres – Eres – C – R - Seq,

This equation expresses that the internal heat production of the body, which corresponds to the metabolic rate (M) minus the effective mechanical power (W), is

balanced by the heat exchanges in the respiratory tract by convection (Cres) and evaporation (Eres), as well as by the heat exchanges on the skin by conduction (K), convection (C), radiation (R) and evaporation (E), and by the eventual balance, heat storage (S), accumulating in the body (ISO 7933, 2004).

The maximum allowable exposure duration is reached when either the rectal temperature or the accumulated water loss reaches the corresponding limits (Parsons, 2003). Applying the PHS model is somewhat complicated and involves the utilisation of numerous equations. In order to make the method more user friendly a computer programme adapted from the ISO 7933 standard has been developed by users.

To fully utilise the index, a number of measurements must be carried out. These include:

• Dry bulb temperature; • Globe temperature; • Humidity; • Air velocity; • Along with some additional data in relation to clothing, metabolic load and posture.

The measurements should be carried out as per the methods detailed in ISO 7726 (1998). Information in regard to clothing insulation (clo) may be found in Annex D of ISO 7933 (2004) and more extensively in ISO 9920 (2007) .

In practice it is possible to calculate the impact of the different measured parameters in order to maintain thermal equilibrium by using a number of equations as set out in

ISO 7933. They can be readily used to show the changes to environmental conditions that will be of greatest and most practicable effect in causing any necessary improvements (Parsons, 1995). This can be achieved by selecting whichever is thought to be the more appropriate control for the situation in question and then varying its application, such as:

• Increasing ventilation; • Introducing reflective screening of radiant heat sources; • Reducing the metabolic load by introducing mechanisation of tasks; • Introduction of air-conditioned air; and / or • Control of heat and water vapour input to the air from processes.

This is where the true benefit of the rational indices lies, in the identification and assessment of the most effective controls. To use these indices only to determine whether the environment gives rise to work limitations is a waste of the versatility of these tools.

6.3.2 Thermal Work Limit (TWL) Brake and Bates (2002a) have likewise developed a rational heat stress index, the TWL, based on underground mining conditions and more recently in the Pilbara region of north-west Australia (Miller & 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 (<38.2oC) and sweat rate (<1.2 kg/hr). The index has been developed using published experimental studies of human heat transfer, and established heat and moisture transfer equations through clothing. Clothing parameters can be varied and the protocol can be extended to unacclimatised workers. The index is designed specifically for self-paced workers and does not rely on estimation of actual metabolic rates. Work areas are measured and categorised based on a metabolic heat balance equation, using dry bulb, wet bulb and air movement to measure air-cooling power (W.m-2).

The TWL uses five environmental parameters • Dry bulb, • Wet bulb, • Globe temperatures, • Wind speed, and • Atmospheric pressure.

With the inclusion of clothing factors (clo) it can predict a safe maximum continuously sustainable metabolic rate (W.m-2) for the conditions being assessed. At high values of TWL (>220 W.m-2), the thermal conditions impose no limits on work. As the values increase above 115 W.m-2, adequately hydrated self-paced workers will be able to manage the thermal stress with varying levels of controls, including adjustment of work rate. As the TWL value gets progressively lower, heat storage is likely to occur and the TWL can be used to predict safe work rest-cycle schedules. At very low values (<115 W · m-2), no useful work rate may be sustained and hence work should cease (Miller & Bates, 2007b). These limits are provided in more detail in Table 7 below.

Table 7: Recommended TWL limits and interventions for self-paced work (Bates et al 2008)

Risk TWL Comments & Controls Unrestricted self-paced work Low >220 • Fluid replacement to be adequate Acclimatisation Zone Well hydrated self-paced workers will be able to accommodate 181- Moderate to the heat stress by regulating the rate at which they work. Low 220 • No unacclimatised worker to work alone • Fluid replacement to be adequate Acclimatisation Zone Moderate 141- • No worker to work alone High 180 • Fluid replacement to be adequate Buffer Zone The workload exceeds the TWL and even with adequate fluid replacement, heat storage will limit work time. TWL can be used to predict safe work rest cycling schedules. • No un-acclimatised* worker to work. • No worker to work alone 116- • Air flow should be increased to greater than 0.5m/s High 140 • Redeploy persons where ever practicable • Fluid replacement to be adequate • Workers to be tested for hydration, withdraw if dehydrated • Work rest cycling must be applied • Work should only continue with authorisation and appropriate management controls Withdrawal Zone Persons cannot continuously work in this environment without increasing their core body temperature. The work load will determine the time to achieve an increase in body temperature, Critical <116 i.e. higher work loads mean shorter work times before increased body temperature.

As the workload exceeds the TWL and even with adequate fluid replacement heat storage will limit work time.

• Essential maintenance and rescue work only. • No worker to work alone. • No un-acclimatised worker to work • Fluid replacement to be adequate • Work-rest cycling must be applied • Physiological monitoring should be considered. *Unacclimatised workers are defined as new workers or those who have been off work for more than 14 days due to illness or leave (outside the tropics).

A thermal strain meter is available for determining aspects of this index (see website at www.calor.com.au). When utilised with this instrument, the TWL is an easy to use rational index that can be readily applied to determine work limitations as a result of the hot working environment. As mentioned earlier, as it is a rational index that assesses a wide range of influencing factors it can also be used in the identification of controls and their effectiveness.

6.3.3 Other Indices 6.3.3.1 WBGT The development of WBGT concepts as the basis for a workplace heat index has resulted in the use of two equations. The WBGT values are calculated by the following equations, where solar radiant heat load is present (Equation 1) or absent (Equation 2) from the heat stress environment:

For a solar radiant heat load (i.e. outdoors in sunlight):

WBGT = 0.7NWB + 0.2GT + 0.1DB (1) or

Without a solar radiant heat load, but taking account of all other workplace sources of radiant heat gains or losses:

WBGT = 0.7NWB + 0.3GT (2)

Where: WBGT = Wet Bulb Globe Temperature NWB = Natural Wet-Bulb Temperature DB = Dry-Bulb Temperature GT = Globe Temperature

All determined as described in the section “Thermal Measurement” (Appendix C).

It is considered that the two conditions (i.e. with and without solar radiant heat contribution) are important to distinguish because the black globe thermometer (GT) reacts to all radiant energy in the visible and infrared spectrum. Human skin and clothing of any colour are essentially “black bodies” to the longer wavelength infrared

radiation from all terrestrial temperature sources. At the shorter infrared wavelengths of solar radiation, dark-coloured clothing or dark skins absorb such radiation more readily than light-coloured fabrics or fair skin (Yaglou & Minard, 1957; Kerslake, 1972). Accordingly, the contribution of solar radiation to heat stress for most work situations outdoors has been reduced in relation to that from the ambient air.

Application of the findings should be approached with due caution, for there are many factors in the practical working situation that are quite different from these laboratory conditions and can adversely affect heat exchanges or physiological responses. These factors include the effect of:

• Exposure for 8 to 12 hours instead of the much shorter experiment time periods; • Variations in the pattern of work and rest; • The effect of acclimatisation; • The age of the individual • The effect of working in different postures; and • That of any other factor that appears in the environment and may affect the heat exchanges of the individual.

It is not usually practicable to modify the simple application of any first-stage screening evaluation of a work environment to take direct account of all such factors.

It should be noted that while this document provides details for the calculation of the WBGT associated with the ISO 7243 (1989) and ACGIH (2013) procedures, it does not endorse the notion that a WBGT work/rest method is always directly applicable to work conditions encountered in Australia.

Some studies in India (Parikh et al, 1976; Rastogi et al, 1992), Australia (Donoghue et al, 2000; Boyle, 1995; Tranter, 1998; Brake & Bates, 2002b, Di Corleto, 1998b) and United Arab Emirates (Bates & Schneider, 2008) suggest that the ISO and ACGIH limit criteria may be unnecessarily restrictive. For example, the WBGT criteria suggested for India (NIOH, 1996a) appear to be higher than those recommended in the ACGIH TLV. However, one study in Africa (Kahkonen et al, 1992) suggests that the WBGT screening criteria are more permissive than the “Rational” ISO criterion (ISO 7933, 1989). Other studies (Budd et al, 1991; Gunn & Budd, 1995) suggest that at levels appearing unacceptable by the ACGIH screening criteria, the individual behaviour reactions of those exposed can sufficiently modify physiological responses to avoid ill-effect. Additional studies (Budd, 2008; Parsons, 1995) have indicated that there are a number of issues with the use of the WBGT

and caution should be exercised when applying the index to ensure it is applied correctly utilising adjustments as indicated.

It is recommended that caution be exercised when applying the WBGT index in the Australian context and remember that there are a number of additional criteria to consider when utilising this index. More detail is available in the ACGIH documentation (ACGIH, 2013).

Optionally, the WBGT may be used in its simplest form such that where the value exceeds that allowable for continuous work at the applicable workload, then the second level assessment should be undertaken.

6.3.3.2 Basic Effective Temperature

Another index still in use with supporting documentation for use in underground mine situations is the Basic Effective Temperature (BET), as described by Hanson and Graveling (1997) and Hanson et al (2000). BET is a subjective empirically based index, combining dry bulb temperature, aspirated (psychometric) wet bulb temperature and air velocity, which is then read from specially constructed nomograms. Empirical indices tend to be designed to meet the requirements of a specific environment and may not be particularly valid when used elsewhere.

A study measuring the physiological response (heat strain) of miners working in a UK coal mine during high temperature, humidity and metabolic rates, was used to produce a Code of Practice on reducing the risk of heat strain, which was based on the BET (Hanson & Graveling, 1997). Miners at three hot and humid UK coal mines were subsequently studied to confirm that the Code of Practice guidance limits were at appropriate levels, with action to reduce the risk of heat strain being particularly required where BET’s are over 27oC (Hanson et al, 2000).

7.0 Physiological Monitoring - Stage 3 of Assessment Protocol

At the present time, it is believed that it will be feasible to utilise the proposed PHS or TWL assessment methodology in most typical day-to-day industrial situations where a basic assessment indicates the need. It is thought that the criteria limits that can thereby be applied can be set to ensure the safeguarding of whatever proportion of those exposed is considered acceptable. This is provided that the workforce is one that is fit to carry on its activities in the absence of heat stress.

There are however, circumstances where rational indices cannot assure the safety of the exposed workgroup. This might be because the usual PHS (or alternative indices) assessment methodology is impracticable to use, or cannot be appropriately interpreted for the circumstances, or cannot be used to guide any feasible or practicable environmental changes.

Such circumstances may sometimes require an appropriate modified assessment methodology and interpretation of data, better suited to the overall situation, while in some other such cases personal cooling devices (making detailed assessment of environmental conditions unnecessary) may be applicable. However, there will remain situations set by the particular characteristics of the workforce and, notably, those of emergency situations, where only the direct monitoring of the strain imposed on the individuals can be used to ensure that their personal tolerance to that strain is not placed at unacceptable risk. These will include, in particular, work in encapsulating suits (see also Appendix D).

Special precautionary measures need to be taken with physiological surveillance of the workers, being particularly necessary during work situations where:

• either the maximum evaporation rate is negative, leading to condensation of water vapour on the skin;

• 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.

Sweat rate, heart rate, blood pressure and skin temperature measurements associated with deep-body temperatures are physiological parameters strongly correlated with heat strain. Recommendations for standardised measures of some of these responses have been made (ISO 9886, 2004). However, they are often inaccessible for routine monitoring of workers in industrial environments, and there is evidence that interpretation of heart rate and blood pressure data will require specialist evaluation (McConnell et al, 1924). While methods of monitoring both heart rate and (surrogates for) deep body temperature in working personnel are now available, further agreement on the consensus of the applicability of the latter appears to be required (Decker et al, 1992; Reneau & Bishop, 1996).

There has been increase of use in a direct measure of core temperature during work by a miniature radio transmitter (telemetry) pill that is ingested by the worker. In this application, an external receiver records the internal body temperature throughout an exposure during its passage through the digestive tract and it has been shown to be

feasible in the development of guidelines for acceptable exposure conditions and for appropriate control measures (NASA, 1973; O’Brien et al, 1998; Yokota et al, 2012). No interference with work activities or the work situation is caused by its use, which has been validated by two Australian studies (Brake & Bates, 2002c; Soler-Pittman, 2012).

The objectives of a heat stress index are twofold:

• to give an indication as to whether certain conditions will result in a potentially unacceptable high risk of heat illness to personnel; and • to provide a basis for control recommendations (NIOSH, 1997).

There are however situations where guidance from an index is not readily applicable to the situation. Indices integrating: • the ambient environment data • assessments of metabolic loads • clothing effects, and • judgements of acclimatisation status do not readily apply where a worker is in their own micro-environment. Hence job or site-specific guidelines must be applied or developed which may require physiological monitoring.

One group in this category includes encapsulated environments / garments. In these situations metabolic heat, sweat and incident radiant heat result in an uncompensable microclimate. These conditions create a near zero ability to exchange heat away from the body, as the encapsulation acts as a barrier between the worker and environment. Data has been collected on external environments that mimic encapsulating garments with the resultant calculations of WBGT and PHS being irrelevant (Coles, 1997).

Additional information in relation to exposure in encapsulated suits can be found in Appendix D.

The role of physiological measurements is one of assessing the total effects on the subject of all the influencing criteria (environmental and personal) resulting in the strain.

The important physiological changes that occur during hot conditions and/or high workloads are increases in:

• core temperatures; • sweat rate; and

• heart rate.

7.1 Core Temperature

Body core temperature measurement has long been the most common form of research tool in the area of heat stress. NIOSH (1997) and WHO (1969) recommend a maximum temperature of 38oC for repeated periods of exposure. WHO suggest that “in closely controlled conditions the deep body temperature may be allowed to rise to 39°C.”

For individuals, there is a core temperature range (with diurnal variation of approximately ±1oC) (Brake & Bates, 2002c) while at rest. This is true during conditions of steady state environmental conditions and no appreciable physical activity. If such an individual carries out work in the same environment, such as a series of successively increased steady-state workloads, within their long-term work capacity, an increase in steady-state body temperature will be reached at each of these increased workloads. If sets of increasingly warm external environmental conditions are then imposed on each of those levels of workload, each such steady- state body temperature level previously noted will initially continue to remain relatively constant over a limited range of more stressful environmental conditions (Nielsen. 1938).

Nevertheless, with successively increasing external thermal stress, a point is reached at each workload where a set of external conditions is found to raise the steady-state body temperature. The increase in environmental thermal stress that causes this rise will be smaller as the steady-state workload becomes greater. This range of climates for each workload in which the steady-state body temperature has been essentially constant has been designated the “prescriptive zone” by Leithead and Lind (1964), for that workload.

To remain in the prescriptive zone and thus avoid risk of heat illness, there must be a balance between the creation of metabolic heat and the heat exchange between the body and the environment. This exchange is dependent on numerous factors. These include the rate at which heat is generated in functioning tissues, the rate of its transfer to the body surface, and the net rates of conductive, convective, radiative and evaporative heat exchanges with the surroundings.

This balance can be defined in the form of an equation: S = M - W - R - C - E - K

where S = rate of increase in stored energy M = rate of metabolic heat production W = external work rate performed by the body K, C, R and E are the rates of heat losses by conduction, convection, radiation, and evaporation from the skin and respiratory tract.

As previously mentioned, telemetry pills are the most direct form of core temperature measurement. Means are now available for internal temperature values to be telemetered to a control unit from which a signal can be transferred to a computer or radioed to the user (Yokota et al, 2012; Soler-Pittman, 2012).

Oesophageal temperature also closely reflects temperature variations in the blood leaving the heart (Shiraki et al, 1986) and hence, the temperature of the blood irrigating the thermoregulation centres in the hypothalamus (ISO 9886, 2004). This method is invasive, as it requires the insertion of a probe via the nasal fossae and hence would be an unacceptable method of core temperature measurement in the industrial environment.

Rectal temperature, while most often quoted in research, is regarded as an unacceptable method by the workforce in industrial situations for temperature monitoring. This is unfortunate as deep body temperature limits are often quoted in literature via this method. There is also the added problem associated with the lag time involved in observing a change in temperature (Gass & Gass, 1998).

Oral temperatures are easy to obtain but may show discrepancies if the subject is a mouth breather (particularly in high stress situations), or has taken a hot or cold drink (Moore & Newbower, 1978), and due to location and duration of measurement.

Tympanic thermometers and external auditory canal systems have also been in use for a number of years. Tympanic membrane measurements are commonly utilised in medical facilities and have been found to be non-invasive and more reliable than the oral method in relation to core body temperatures (Beaird et al, 1996).

The ear canal method has had greater acceptance than rectal measurements by the workforce but may not be as accurate as was first thought. Greenleaf & Castle (1972) demonstrated some variations in comparison to rectal temperatures of between 0.4 to 1.1ºC. The arteries supplying blood to the auditory canal originate from the posterior auricular, the maxillary and the temporal areas (Gray, 1977) and general skin temperature changes are likely to be reflected within the ear canal. This could lead to discrepancies in situations of directional high radiant heat.

Skin temperature monitoring has been utilised in the assessment of heat strain in the early studies by Pandolf and Goldman (1978). These studies showed that convergence of mean skin with core temperature was likely to have resulted in the other serious symptoms noted, notwithstanding modest heart rate increases and minimal rises in core temperature. Studies carried out by Bernard and Kenney utilised the skin temperature but “the concept does not directly measure core temperature at the skin, but rather is a substitute measure used to predict excessive rectal temperature” (Bernard & Kenney, 1994). In general, the measurement of skin temperature does not correlate well with the body core temperature.

7.2 Heart Rate Measurements

These measurements extend from the recovery heart-rate approach of Brouha (1967) to some of the range of assessments suggested by WHO (1969), ISO 9886 (2004) and the ACGIH (2013) in Table 8.

Heart rate has long been accepted as an effective measure of strain on the body and features in numerous studies of heat stress (Dessureault et al, 1995; Wenzel et al, 1989; Shvartz et al, 1977). This is due to the way in which the body responds to increased heat loads. Blood circulation is shifted towards the skin in an effort to dissipate heat. To counteract the reduced venous blood return and maintain blood pressure as a result of an increased peripheral blood flow, heat rate is increased, which is then reflected as an increased pulse rate. One benefit of measuring heart rate compared to core body temperature is the response time. This makes it a very useful tool as an early indication of heat stress.

WHO (1969) set guidelines in which the average heart rate should not exceed 110 beats per minute with an upper limit of 120 beats per minute. “This was predominantly based on the work of Brouha at Alcan in the 1950’s on heart rate and recovery rate. Subsequent work by Brouha and Brent have shown that 110 beats per minute is often exceeded and regarded as quite satisfactory” (Fuller & Smith, 1982). The studies undertaken by Fuller and Smith (1982) have supported the feasibility of using the measurement of body temperature and recovery heart rate of the individual worker based on the technique developed by Brouha (1967), as described below. Their work illustrated that 95% of the times that one finds a P1 (heart rate in the first 30 – 60 seconds of assessment) value of less than 125, the oral temperature will be at or below 37.6°C (99.6 °F). It is important to note that heart rate is a function of metabolic load and posture.

The very simple Brouha’s recovery rate method involved a specific procedure as follows:

• At the end of a cycle of work, a worker is seated and temperature and heart rate are measured. The heart rate (beats per minute; bpm) is measured from 30 to 60 seconds (P1), 90 to 120 seconds (P2), and 150 to 180 seconds (P3). At 180 seconds, the oral temperature is recorded for later reference. This information can be compared with the accepted heart rate recovery criteria, for example: P3<90 or

P3≥ 90, P1 - P3 ≥ 10 are considered satisfactory. High recovery patterns indicate work at a high metabolic level with little or no accumulated body heat.

• Individual jobs showing the following condition require further study.

P3 ≥ 90, P1 - P3 < 10. Insufficient recovery patterns would indicate too much personal stress (Fuller & Smith, 1982).

At the present time, the use of a sustained heart rate (eg. that maintained over a 5- minute period) in subjects with normal cardiac performance, of “180-age” beats per minute (ACGIH, 2013) is proposed as an upper boundary for heat-stress work situations where monitoring of heart rate during activities is practicable. Moreover, such monitoring, even when the screening criteria appear not to have been overstepped, may detect individuals who should be examined for their continued fitness for their task, or may show that control measures are functioning inadequately.

Table 8: 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: • Sustained (several minutes) heart rate in excess of 180 bpm minus the individuals age in years (eg.180 – age), for individuals with assessed normal cardiac performance; OR • Body core temperature greater than 38.5°C (101.3°C) for medically selected and acclimatised personnel; or greater than 38°C (100.4°C) in unselected, unacclimatised workers; OR • There are symptoms of sudden and severe fatigue, nausea, dizziness, or

light-headedness; OR • Recovery heart rate at one minute after a peak work effort is greater than 120 bpm (124 bpm was suggested by Fuller and Smith (1982)); OR • A worker experiences profuse and prolonged sweating over hours and may not be able to adequately replenish fluids; OR • Greater than 1.5% weight loss over a shift: OR • 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:

• ‘Heart Rate Limit (HRL) = 185 - 0.65A’, where A = Age in years; • 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: • HRL, sustained = 180 – age. • 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 irritability, discomfort or flu-like symptoms, the worker should be removed for rest under observation in a cool location. Symptoms of heat stroke (Section 2.1.1) 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.

Physiological monitoring is complex and where assessment indicates the necessity of such monitoring, it must be undertaken by a competent person with proven technical skills and experience in relation to the study of heat stress and/or human physiology. This is particularly critical where there are additional medical complications arising from medical conditions or medications being administered.

8.0 Controls

Where a problem area has been identified, controls should be assessed and implemented in a staged manner, such that the hierarchy of controls is appropriate to the risk:

• Elimination or substitution of the hazard - the permanent solution. For example, use a lower temperature process, relocate to a cooler area or reschedule work to cooler times.

• Engineering controls such as rest areas with a provision of cool drinking water and cool conditions (eg. air conditioning and shade); equipment for air movement (eg. use of fans) and/or chilled air (eg. use of an air conditioner); insulation or shielding for items of plant causing radiant heat; mechanical aids to reduce manual handling requirements.

• Administrative controls such as documented procedures for inspection, assessment and maintenance of the engineering controls to ensure that this equipment continues to operate to its design specifications; work / rest regimes based on the interpretation of measurements conducted; and job rotation.

• Personal protective equipment (PPE) should only be used in situations where the use of higher level controls is not commensurate with the degree of risk for short times, while higher level controls are being designed, or for short duration tasks.

Table 9: Examples of control methods

Elimination/substitution • Hot tasks should be scheduled to avoid the hottest part of the day or where practical undertaken during night shifts. • Walls and roof structures should utilize light coloured or reflective materials. • Structures should be designed to incorporate good air flow. This can be done via the positioning of windows, shutters and roof design to encourage ‘chimney effects’. This will help remove the heat from the structure. • Walls and roofs should be insulated.

moved, hence fans to increase air flow or in extreme cases, cooled air from ‘chiller’ units can also be utilised. • 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. • Relocating hot processes away from high access areas. • Dehumidifying air to increase the evaporative cooling effect. Often steam leaks, open process vessels or standing water can artificially increase humidity within a building. • Utilize mechanical aids that can reduce the metabolic workload on the individual.

Administrative • Ready access to cool palatable drinking water is a basic necessity. • Where applicable, suitable electrolyte replacements should also be available (refer to Section 4.1). • 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 teams with high mobility, even a simple shade structure readily available from hardware stores or large umbrellas can provide relief from solar radiation. • Where work-rest regimes are necessary, heat stress indices such as WBGT, PHS or TWL, assist in determining duration of work and rest periods (refer to Section 6.3). • Training workers to identify symptoms and the potential onset of heat-related illness as part of the ‘buddy system’. • Encouraging “self-determination” or self pacing of the work to meet the conditions and reporting of heat related symptoms. • Consider pre-placement medical screening for work in hot areas (ISO 12894).

Personal protective equipment • PPE such as cooling vests with either ‘phase change’ 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. • Vortex tube air cooling may be used in some situations, particularly when a cooling source is required when supplied air respirators are used. • Choose light coloured materials for clothing and ensure they allow good air flow across the skin to promote evaporative cooling.

8.1. Ventilation Appropriate ventilation systems can have a very valuable and often very cost effective role in heat stress control. It may have one or all of three possible roles therein. Ventilation can remove process-heated air that could reduce convective cooling or even cause an added convective heat load on those exposed. By an increased rate of airflow over sweat wetted skin, it can increase the rate of evaporative cooling and it can remove air containing process-added moisture content which would otherwise reduce the level of evaporative cooling from sweating.

It should also be noted that, although the feasibility and cost of fully air-conditioning a workplace might appear unacceptable, product quality considerations in fixed work situations may in fact justify this approach. Small-scale “spot” air-conditioning of individual work stations has been found to be an acceptable alternative in large- volume, low-occupancy situations, particularly when extreme weather conditions are periodic but occurrences are short-term.

Generally, the ventilation is used to remove or dilute the existing hot air at a worksite with cooler air, either by natural or forced mechanical ventilation. It will also play a major role where the relative humidity is high, allowing for the more effective evaporation of sweat in such circumstances.

Three types of systems are utilised: a) Forced Draft – air is blown into a space forcing exhaust air out. b) Exhaust – air is drawn out of a space or vessel allowing for air to enter passively through another opening. c) Push-pull – is a combination of both of the above methods where one fan is used to exhaust air through one opening while another forces fresh air in through an alternative opening.

Where practical, using natural air movement via open doors, windows and other side openings can be beneficial. It is less frequently recognised that a structure induced “stack” ventilation system from the release of process-created or solar heated air by high level (eg. roof ridge) openings, and its replacement by cooler air drawn in at the worker level, may be valuable (Coles, 1968).

For any of these methods to work effectively, the ingress air should be cooler than the air present in the work area. Otherwise, in some situations the use of ambient air will provide little relief apart from perhaps increasing evaporative cooling. The solution in these situations will require the use of artificially cooled air. An example of such a system would be a push-pull set-up utilising a cooling air device on the inlet. Cooling can be provided using chillers, evaporative coolers or vortex tubes.

Large capacity mechanical air chillers or air conditioning units are also an option and are capable of providing large quantities of cooled air to a location. They are based on either evaporative or refrigerated systems to reduce air temperature by actively removing heat from the air. While very effective, they can prove to be quite expensive.

In all cases it may be important to evaluate the relative value of the three possible roles of increased air movement. Although convective cooling will cease when air dry-bulb temperature exceeds skin temperature, the increased convective heating above that point may still be exceeded by the increased rate of evaporative cooling created by the removal of saturated air at the skin surface until a considerably higher air temperature is reached.

Use of the calculation methodology of one of the “rational” heat stress indices will indicate whether the temperature and moisture content of air moving at some particular velocity in fact provides heating or cooling.

The increased evaporative cooling that can be due to high rates of air movement, even at high dry bulb air temperature, may result in rates of dehydration that might exceed the possible amount of fluid replacement into the body over the period of exposure experienced (see Section 4.1). This can be to an extent that may affect the allowable exposure time.

8.2 Radiant Heat Radiant heat from various sources can be controlled in a number of ways. Some involve the use of barriers between the individual and the source, while others

change the nature of the source. The three most commonly used methods involve insulation, shielding and changing surface emissivity.

Insulation of a surface is a common method and large reductions in radiation can be achieved utilising this procedure. Many different forms of synthetic mineral fibre† combined with metal cladding are used to decrease radiant heat flow. Added benefits to insulation in some situations are the reduction of potential sites capable of resulting in contact burns (see Section 3.0) and reducing heat losses of the process.

Reduction of emissivity of a particular surface can also result in the reduction of heat sent from it. A flat black surface (emissivity (e) = 1.0) emits the most heat while a perfectly smooth polished surface (i.e. e = 0) emits the least. Hence if it is possible to reduce the emissivity, then the radiant heat can also be reduced. Common examples of emissivity are steel (e=0.85), painted surfaces (e=0.95) and polished aluminium or tin having a rating of 0.08. Hence the use of shiny metal cladding over ‘hot’ pipe lagging.

Shielding is an effective and simple form of protection from radiant heat. These can be either permanent installations or mobile. Figure 3 illustrates a number of methods for the control of radiant heat by various arrangements of shielding. While solid shields such as polished aluminium or stainless steel are effective and popular as permanent structures, other more lightweight mobile systems are becoming available. Aluminised tarpaulins made of a heavy-duty fibreglass cloth with aluminium foil laminated to one side are now readily available from most industrial insulation suppliers. These may be made up with eyelets to allow tying to frames or handrails to act as a temporary barrier during maintenance activities.

The use of large umbrellas and portable shade structures, when undertaking work in the sun, have also been proven to be relatively cheap and effective controls.

† Note that the use of synthetic mineral fibres requires health precautions also.

Figure 3: The control of radiant heat by various arrangements of shielding. (Hertig & Belding, 1963) Source 171°C Wall @ 35°C No shield: radiant 80.6 heat load (R) on worker

R= 1524 W kcal/hr

47.5

Shield “black” e=1.0 both sides R = 454 W

37.2 Shield black facing source, and aluminium e=0.1 facing man. R=58 W

36.7 Shield aluminium facing source, “black” facing man. R= 44 W

Shield aluminium both 35.8 sides R=15 W

8.3 Administrative Controls

These controls may be utilised in conjunction with environmental controls where the latter cannot achieve the remediation levels necessary to reduce risk to an acceptable level.

Self-assessment should be used as the highest priority system during exposures to heat stress. This allows adequately trained individuals to exercise their discretion in order to reduce the likelihood of over exposure to heat stress. No matter how effectively a monitoring system is used, it must be recognised that an individual’s physical condition can vary from day to day. This can be due to such factors as illnesses, acclimatisation, alcohol consumption, individual heat tolerance and hydration status.

Any exposure must be terminated upon the recognition or onset of symptoms of heat illness.

8.3.1 Training

Training is a key component necessary in any health management program. In relation to heat stress it should be conducted for all personnel likely to be involved with:

• Hot environments; • Physically demanding work at elevated temperatures; or • The use of impermeable protective clothing.

Any combination of the above situations will further increase the risk.

The training should encompass the following:

1. Mechanisms of heat exposure; 2. Potential heat exposure situations; 3. Recognition of predisposing factors; 4. The importance of fluid intake; 5. The nature of acclimatisation; 6. Effects of using alcohol and drugs in hot environments; 7. Early recognition of symptoms of heat illness; 8. Prevention of heat illness; 9. First aid treatment of heat related illnesses; 10. Self-assessment;

11. Management and control; and 12. Medical surveillance programs and the advantages of employee participation in programs.

Training of all personnel in the area of heat stress management should be recorded on their personal training record.

8.3.2 Self-Assessment

Self-assessment is a key element in the training of individuals potentially exposed to heat stress. With the correct knowledge in relation to signs and symptoms, individuals will be in a position to identify the onset of a heat illness in the very early stages and take the appropriate actions. This may simply involve having to take a short break and a drink of water. In most cases this should only take a matter of minutes. This brief intervention can dramatically help to prevent the onset of the more serious heat related illnesses. It does require an element of trust from all parties, but such a system administered correctly, will prove to be an invaluable asset in the control of heat stress, particularly when associated with the acceptance of self- pacing of work activities.

8.3.3 Fluid Replacement

Fluid replacement is of primary importance when working in hot environments, particularly where there is also a work (metabolic) load. Moderate dehydration is usually accompanied by a sensation of thirst which if ignored can result in dangerous levels of dehydration (>5% of body weight) within 24 hours. Even in situations where water is readily available, most individuals almost never completely replace their sweat loss, so they are usually in mild negative total body water balance (BOHS, 1996). As the issue of fluid replacement has already been dealt with in earlier discussion (see Section 4.1), it will not be elaborated further.

8.3.4 Rescheduling of Work

In some situations, it may be possible to reschedule hot work to a cooler part of the day. This is particularly applicable for planned maintenance or routine process changes. While this is not always practical, particularly during maintenance or unscheduled outages, some jobs may incorporate this approach.

8.3.5 Work/Rest Regimes

The issue of allowable exposure times (AET) or stay times is a complex one. It is dependent on a number of factors, such as metabolism, clothing, acclimatisation and general health, not just the environmental conditions. One of the more familiar

systems in use is the Wet Bulb Globe Temperature (WBGT). Details of operation of the WBGT have already been discussed (see Section 6.3.3) and hence will not be elaborated in this section. Similarly, the ISO 7933 method using the required sweat rate gives an estimated AET for specific conditions.

It must be strongly emphasised that these limits should only be used as guidelines and not definitive safe/unsafe limits. Also they are not applicable for personnel wearing impermeable clothing.

8.3.6 Clothing

An important factor in the personal environment is that of the type of clothing being worn during the task, as this can impede the body’s capacity to exchange heat. Such effects may occur whether the heat input to the body is from physical activity or from the environment. The responsible factors are those that alter the convective and evaporative cooling mechanisms (Belding & Hatch, 1955; ISO 7933, 2004) between the body surface and the ambient air (i.e. clothing).

In Stage 1 of the proposed structured assessment protocol (section 6.2.1), the criteria have been set for the degree of cooling provided to workers fully clothed in summer work garments (lightweight pants and shirt). Modifications to that cooling rate include other clothing acting either as an additional insulating layer, or further reducing ambient air from flowing freely over the skin. Where there is significant variation in the type of clothing from that mentioned above, a more comprehensive rational index should be utilised; for example ISO 7933. Convective heating or cooling depends on the difference between skin and air temperature, as well as the rate of air movement. In essentially all practical situations, air movement leads to cooling by evaporation of sweat. Removal of moisture from the skin surface may be restricted, because air above it is saturated and not being exchanged, hence evaporative cooling is constrained.

Study of the effect of clothing (acting primarily as an insulator) (Givoni & Goldman, 1972) on body temperature increase has resulted in suggestions (Ramsey, 1978) for modifications to the measure of some indices based on the “clo” value of the garments. “Clo” values (Gagge et al, 1941), from which other correcting values could be deduced, are available in an International Standard (ISO 9920, 2007), both for individual garments and for clothing assemblies. These corrective values should not be used for clothing that significantly reduces air movement over the skin. As one moves towards full encapsulation, which increasingly renders the use of heat stress index criteria irrelevant, the use of more comprehensive assessment methods such

as physiological monitoring becomes necessary. The possible importance of this, even in less restrictive clothing, in higher stress situations must be recognised. It has been shown that, as with the allocation of workloads in practical situations, the inherent range of variability in the allocation of the levels of insulation by clothing must be recognised (Bouskill et al, 2002). The level of uncertainty that these variations can introduce, even in the calculation of a comfort index for thermal environments, has been shown to be considerable (Parsons, 2001).

The effect of sunlight on thermal load is dependent on both direct and the reflected forms. It can be assumed that the amount of transmitted radiation will be absorbed either by the clothing or the skin and contribute to the heat load (Blum, 1945). Table 10 illustrates the reflection of total sunlight by various fabrics and their contribution to the heat load.

Table 10: Reflection of total sunlight by various fabrics

Item Fabric Contribution to Reflected the heat load (%) (%) Data from Aldrich (Wulsin, 1943) 1 Shirt, open weave, (Mock 55.9 44.1 Leno), Slightly permeable 2 Cotton, khaki – (230 g) 43.7 56.3 3 Cotton, percale (close 33.2 66.8 weave), white 4 Cotton, percale, OD 51.5 48.5 5 Cotton, tubular balbriggan 37.6 62.4 6 Cotton, twill, khaki 48.3 51.7 7 Cotton, shirting worsted, OD 61.1 38.9 8 Cotton, denim, blue 67.4 32.6 9 Cotton, herringbone twill 73.7 26.3 10 Cotton, duck No.746 92.8 7.2 Data from Martin (1930) 11 Cotton shirt, white 29.0 71.0 unstarched, 2 thicknesses 12 Cotton shirt khaki 57.0 43.0 13 Flannel suiting, dark grey 88.0 12.0 14 Dress suit 95.0 5.0

The colour of clothing can be irrelevant with respect to the effect of air temperature or humidity, unless when worn in open sunlight. Light or dark clothing can be worn indoors with no effect on heat strain, as long as the clothing is of the same weight, thickness and fit. Even in the sunlight the impact of colour can be rendered relatively insignificant if the design of the clothing is such that it can minimise the total heat gain by dissipating the heat.

The answer to "why do Bedouins wear black robes in hot deserts?" is consistent with these observations. Shkolnik et al. (1980) showed that in the sun at ambient air temperatures of between 35 and 46oC, the rate of net heat gain by radiation within black robes of Bedouins in the desert was more than 2.5 times as great as in white. Given the use of an undergarment between a loose-fitting outer black robe, there is a chimney effect created by the solar heating of the air in contact with the inside of the black garment. This increases air movement to generate increased convective and evaporative cooling of the wearer, hence negating the impact of the colour.

8.3.7 Pre-placement Health Assessment

Pre-placement health assessment screening should be considered to identify those susceptible to systemic heat illness, or in tasks with high heat stress exposures. ISO 12894 provides guidance for medical supervision of individuals exposed to extreme heat. Health assessment screening should consider the worker's physiological and biomedical aspects, and provide an interpretation of job fitness for the jobs to be performed. Specific indicators of heat intolerance should only be targeted.

Some workers may be more susceptible to heat stress than others. These workers include: • those who are dehydrated (see Section 4.1); • unacclimatised to workplace heat levels (see Section 4.3); • physically unfit, • having low aerobic capacity, as measured by maximal oxygen consumption, and • being overweight (BMI should preferably be below 24-27 - see Section 4.4); • elderly (>50 years); • or, suffering from: • diabetes; • hypertension; • heart, circulatory or skin disorders;

• thyroid disease; • anaemia; or • using medications that impair temperature regulation or perspiration.

Workers with a past history of renal, neuromuscular, respiratory disorder, previous head injury, fainting spells, or previous susceptibility to heat illness may also be at risk (Brake et al, 1998; Hanson & Graveling, 1997). Those more at risk might be excluded from certain work conditions or be medically assessed more frequently.

Short-term disorders and minor illnesses such as colds or flu, diarrhoea, vomiting, lack of sleep and hangover should also be considered. These afflictions will inhibit the individual’s ability to cope with heat stress and hence make them more susceptible to an onset of heat illness.

8.4 Personal Protective Equipment

Where the use of environmental or administrative controls have proven to be inadequate, it is sometimes necessary to resort to personal protective equipment (PPE) as an adjunct to the previous methods.

The possibility remains of using personal cooling devices, with or without other protective clothing, both by coolant delivered from auxiliary plant (Quigley, 1987) or by cooled air from an external supply (Coles, 1984). When the restrictions imposed by external supply lines become unacceptable, commercially available cool vests with appropriate coolants (Coleman, 1989) remain a possible alternative, as do suit- incorporated cooling mechanisms when the additional workloads imposed by their weight are acceptable. The evaporative cooling provided by wetted over-suits has been investigated (Smith, 1980).

There are a number of different systems and devices currently available and they tend to fit into one of the following categories:

a) Air Circulating Systems b) Liquid Circulating Systems c) Ice Cooling Systems d) Reflective Systems

8.4.1 Air Cooling System

Air circulating systems usually incorporate the use of a vortex tube cooling system. A vortex tube converts ordinary compressed air into two air streams, one hot and one cold. There are no moving parts or requirement of electricity and cooling capacities

of up to 1,760 W are achievable by commercially available units using factory compressed air at 690 kPa. Depending on the size of the vortex tube, they may be used on either a large volume such as a vessel or the smaller units may be utilised as a personal system attached to an individual on a belt and feeding a helmet or vest.

The cooled air may be utilised via a breathing helmet similar to those used by abrasive blasters or spray painters, or alternatively through a cooling vest. As long as suitable air is available between 0.3 and 0.6 m3.min-1 at 520 to 690 kPa, this should deliver at least 0.17 m3.min-1of cooled air to the individual. Breathing air quality should be used for the circulating air systems.

Cooling air systems do have some disadvantages, the most obvious being the need to be connected to an airline. Where work involves climbing or movement inside areas that contain protrusions or “furniture”, the hoses may become caught or entangled. If long lengths of hose are required, they can also become restrictive and quite heavy to work with. In some cases, caution must also be exercised if the hoses can come in contact with hot surfaces or otherwise become damaged.

Not all plants have ready access to breathable air at the worksite and specialised oil- less compressors may need to be purchased or hired during maintenance periods.

Circulating air systems can be quite effective and are considerably less expensive than water circulating systems.

8.4.2 Liquid Circulating Systems

These systems rely on the principle of heat dissipation by transferring the heat from the body to the liquid and then the heat sink (which is usually an ice water pack). They are required to be worn in close contact with the skin. The garment ensemble can comprise a shirt, pants, and hood that are laced with fine capillary tubing, which the chilled liquid is pumped through. The pump systems are operated via either a battery pack worn on the hip or back, or alternatively through an “umbilical cord” to a remote cooling unit. The modular system without the tether allows for more mobility.

These systems are very effective and have been used with success in areas such as furnaces in copper smelters. Service times of 15 to 20 minutes have been achieved in high radiant heat conditions. This time is dependent on the capacity of the heat sink and the metabolism of the worker.

Maintenance of the units is required, hence a selection of spare parts would need to be stocked, as they are not readily available in Australia. Due to the requirement of a

close fit, suits would need to be sized correctly to wearers. This could limit their usage, otherwise more than one size will need to be stocked (i.e. small, medium, large, extra large) and this may not be possible due to cost.

A further system is known as a SCAMP – Super Critical Air Mobility Pack, which utilises a liquid cooling suit and chills via a heat exchanger “evaporating” the super critical air. The units are however, very expensive.

8.4.3 Ice Cooling Systems

Traditional ice cooling garments involved the placement of ice in an insulating garment close to the skin such that heat is conducted away. This in turn cools the blood in the vessels close to the skin surface, which then helps to lower the core temperature.

One of the principal benefits of the ice system is the increased mobility afforded the wearer. It is also far less costly than the air or liquid circulating systems.

A common complaint of users of the ice garments has been the contact temperature. Some have also hypothesised that the coldness of the ice may in fact lead to some vasoconstriction of blood vessels and hence reduce effectiveness.

Also available are products which utilise an organic n-tetradecane liquid or similar. One of the advantages of this substitute for water is that they freezes at temperatures between 10 - 15oC, resulting in a couple of benefits. Firstly it is not as cold on the skin and hence more acceptable to wearers. Secondly, to freeze the solution only requires a standard refrigerator or an insulated container full of ice water. Due to its recent appearance, there is limited data available other than commercial literature on their performance. Anecdotal information has indicated that they do afford a level of relief in hot environments, particularly under protective equipment, but their effectiveness will need to be investigated further. They are generally intended for use to maintain body temperature during work rather than lowering an elevated one. This product may be suitable under a reflective suit or similar equipment.

To achieve the most from cooling vests, the ice or other cooling pack should be inserted and the vest donned just before use. Depending on the metabolic activity of the worker and the insulation factor from the hot environment, a vest should last for a moderate to low workload for between half an hour up to two hours. This method may not be as effective as a liquid circulating system; however, it is cost effective.

Whole-body pre-chilling has been found to be beneficial and may be practical in some work settings (Weiner & Khogali, 1980).

The use of ice slushies in industry has gained some momentum with literature indicating a lower core temperature when ingesting ice slurry versus tepid fluid of equal volumes (Siegel et al, 2012) in the laboratory setting. Performance in the heat was prolonged with ice slurry ingested prior to exercise (Siegel et al, 2010). The benefits of ingesting ice slurry may therefore be twofold, the cooling capacity of the slurry and also the hydrating component of its ingestion.

8.4.4 Reflective Clothing

Reflective clothing is utilised to help reduce the radiant heat load on an individual. It acts as a barrier between the person’s skin and the hot surface, reflecting away the infrared radiation. The most common configuration for reflective clothing is an aluminised surface bonded to a base fabric. In early days this was often asbestos, but materials such as Kevlar®, rayon, leather or wool have now replaced it. The selection of base material is also dependent on the requirements of the particular environment (i.e. thermal insulation, weight, strength etc).

The clothing configuration is also dependent on the job. In some situations only the front of the body is exposed to the radiant heat, such as in a furnace inspection, hence an apron would be suitable. In other jobs, the radiant heat may come from a number of directions, as in a furnace entry scenario; hence a full protective suit may be more suitable. Caution must be exercised when using a full suit, as it will affect the evaporative cooling of the individual. For this reason the benefit gained from the reduction of radiant heat should outweigh the benefits lost from restricting evaporative cooling. In contrast to other forms of cooling PPE, the reflective ensemble should be worn as loose as possible with minimal other clothing to facilitate air circulation to aid evaporative cooling. Reflective garments can become quite hot hence caution should be exercised to avoid contact heat injuries.

It may also be possible to combine the use of a cooling vest under a jacket to help improve the stay times. However, once combinations of PPE are used, they may become too cumbersome to use. It would be sensible to try on such a combination prior to purchase to ascertain the mobility limitations.

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Appendix A: Heat Stress Risk Assessment Checklist As has been pointed out, there are numerous factors associated with heat stress. Listed below are a number of those elements that may be checked for during an assessment.

Hazard Type Impact

1 Dry Bulb Temperature Elevated temperatures will add to the overall heat burden. 2 Globe Temperature Will give some indication as to the radiant heat load. 3 Air Movement – Wind Speed Poor air movement will reduce the effectiveness of sweat evaporation. High air movements at high temps (>42oC) will add to the heat load 4 Humidity High humidity is also detrimental to sweat evaporation 5 Hot Surfaces Can produce radiant heat as well as result in contact burns 6 Metabolic work rate Elevated work rates increase can potentially increase internal core body temperatures. 7 Exposure Period Extended periods of exposure can increase heat stress. 8 Confined Space Normally result in poor air movement and increased temperatures. 9 Task Complexity Will require more concentration and manipulation. 10 Climbing, ascending, descending – Can increase metabolic load on the body. work rate change 11 Distance from cool rest area Long distances may be dis-incentive to leave hot work area or seen as time wasting. 12 Distance from Drinking Water Prevents adequate re-hydration.

Employee Condition

13 Medications Diuretics, some antidepressants and anticholinergics may affect the body’s ability to manage heat. 14 Chronic conditions i.e. heart or May result in poor blood circulation and reduced body circulatory cooling. 15 Acute Infections, i.e. colds, flu, fevers Will impact on how the body handles heat stress. i.e. thermoregulation 16 Acclimatised Poor acclimatisation will result in poorer tolerance of the heat. i.e. less sweating, more salt loss. 17 Obesity Excessive weight will increase the risk of a heat illness. 18 Age Older individuals (>50) may cope less well with the heat. Fitness A low level of fitness reduces cardiovascular and aerobic capacity. 19 Alcohol in last 24 hrs Will increase the likelihood of dehydration. Chemical Agents 23 Gases, vapours & dusts soluble in May result in chemical irritation/burns and dermatitis. sweat 24 PPE 25 Impermeable clothing Significantly affect the body’s ability to cool. 26 Respiratory protection (negative Will affect the breathing rate and add an additional stress pressure) on the worker. 27 Increased work load due to PPE Items such as SCBA will add weight and increase metabolic load. 28 Restricted mobility Will affect posture and positioning of employee.

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Appendix B: Preliminary Plant Heat Stress Risk Assessment Sheet

Plant Area:

General Description: i.e. Process and/or Photo.

Localised Heat: Yes No Description:

Local Ambient Temperature Relative Humidity °C % (approx): (approx): Exposed Hot Surfaces: Yes No Description:

Poor <0.5 m/s Mod 0.5-3.0 m/s Good >3.0 m/s Air Movement:

Confined Space Yes No Expected Work Rate High Medium Low Personal Protective Equipment Yes No If Yes Type:

Comments: ______

Carried out by: ______Date: _____/_____/______

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Appendix C: Thermal Measurement Wet Bulb Measurements

If a sling or screened-bulb-aspirated psychrometer has been used for measurement of the dry-bulb temperature, the (thermodynamic) wet-bulb temperature then obtained also provides data for determination of the absolute water vapour content of the air. That temperature also provides, together with the globe thermometer measurement, an alternative indirect, but often more practicable and precise, means of finding a reliable figure for the natural wet-bulb temperature. While to do so requires knowledge of the integrated air movement at the site, the determined value of such air movement at the worker position is itself also an essential parameter for decision on the optimum choice of engineering controls when existing working conditions have been found unacceptable.

Furthermore, that value of air velocity va provides for the determination of the mean radiant temperature of the surroundings (MRTS) from the globe thermometer temperature where this information is also required (Kerslake, 1972; Ellis et al, 1972). Importantly, using published data (Romero Blanco, 1971) for the computation, the approach of using the true thermodynamic wet-bulb figure provides results for the natural wet-bulb temperature (tnwb) which in some circumstances can be more convenient than a practicable application of a stationary, unscreened, natural wet-bulb thermometer.

Certain practical observations or checks can be utilised prior to commencement and during measurement of the tw, such as:

• When the wick is not wetted the two temperatures tw and ta should be equivalent.

• Where the relative humidity of the environment is less than 100% then tw should be less

than ta.

Globe Thermometers Where smaller globes are used on instruments there should be some assurance that such substitute hollow copper devices yield values equivalent to the standardised 15 cm (6 inch) copper sphere. The difference between the standard and smaller globes is small in indoor measurements related to thermal comfort rather than heat stress (Humphreys, 1977). The relevance of black-body devices to the radiant heat exchanges between man and the environment were analysed by Hatch (1973). That study indicates that, in cases where heat-stress indices have been devised to use a standard globe thermometer as the measure of the mean radiant temperature of the surroundings, and that globe temperature is used as input to an index calculation, the use of other devices may be inappropriate. The difference between smaller and standard globes becomes considerable at high air velocities and large differences between dry bulb air and globe temperatures (eg. outdoor work in the

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sun, and in some metal industries), and necessitate corrections being applied. While smaller globes have shorter response times, that of the standard globe has also been suggested to be better related to the response time of the deep-body temperature (Oleson, 1985).

Measurement of the environmental parameters. The fundamental instruments required to perform this first-stage assessment of an environment are dry-bulb, globe thermometers, an anemometer and depending on the index to be used, a natural wet-bulb thermometer. The measurement of the environmental parameters has been summarised below. For a more comprehensive discussion of the methodology, readers are directed to ISO 7726 “Ergonomics of the thermal environment - Instruments for measuring physical quantities.”

1. The range of the dry and the natural wet-bulb thermometers should be -5°C to + 50°C (23° - 122°F), with an accuracy of ± 0.5°C.

a. The dry-bulb thermometer must be shielded from the sun and the other radiant surfaces of the environment without restricting the air flow around the bulb. Note that use of the dry-bulb reading of a sling or aspirated psychrometer may prove to be more convenient and reliable.

b. The wick of the natural wet-bulb thermometer should be kept wet with distilled water for at least 0.5 hour before the temperature reading is made. It is not enough to immerse the other end of the wick into a reservoir of distilled water and wait until the whole wick becomes wet by capillarity. The wick should be wetted by direct application of water from a syringe 0.5 hour before each reading. The wick should extend over the bulb of the thermometer, covering the stem about one additional bulb length. The wick should always be clean, and new wicks should be washed and rinsed in distilled water before using.

c. A globe thermometer, consisting of a 15 cm (6 inch) diameter, hollow copper sphere, painted on the outside with a matte black finish or equivalent, should be used. The bulb or sensor of a thermometer [range -5°C to +100°C (23° - 212°F) with an accuracy of ± 0.5°C (± 0.9°F)] must be fixed in the centre of the sphere. The globe thermometer should be exposed at least 25 minutes before it is read. Smaller and faster responding spheres are commercially available today and may be more practical, but their accuracy in all situations cannot be guaranteed.

d. Air velocity is generally measured using an anemometer. These come in many different types and configurations and as such care should be taken to ensure that the appropriate anemometer is used. Vane, cup and hot wire anemometers are particularly sensitive to the direction of flow of the air and quite erroneous

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values can result if they are not carefully aligned. Omni-directional anemometers such as those with a hot sphere sensor type are far less susceptible to directional variation.

2. A stand, or similar object, should be used to suspend the three thermometers so that it does not restrict free air flow around the bulbs, and the wet-bulb and globe thermometer are not shaded. Caution must be taken to prevent too close proximity of the thermometers to any nearby equipment or structures, yet the measurements must represent where or how personnel actually perform their work.

3. It is permissible to use any other type of temperature sensor that gives a reading identical to that of a mercury thermometer under the same conditions.

4. The thermometers must be placed so that the readings are representative of the conditions where the employees work or rest, respectively.

5. There are now many commercially available devices providing, usually from electronic sensors, direct read-out of dry-bulb, natural wet-bulb, and globe temperatures according to one or more of the equations that have been recommended for integration of the individual instrument outputs. In some cases, the individual readings can also be output, together with a measure of the local air movement. The majority employ small globe thermometers, providing more rapid equilibration times than the standard globe, but care must then be taken that valid natural wet-bulb temperatures (point 1b.) are also then assessed. In such cases, the caution in regard to the globe at point 1c must also be observed, and mounting of the devices must ensure compliance with point 2. The possibility of distortion of the radiant heat field that would otherwise be assessed by the standard globe should be considered and may therefore require adequate separation of the sensors and integrator, and their supports. Adequate calibration procedures are mandatory.

6. While a single location of the sensors at thorax or abdomen level is commonly acceptable, it has been suggested that in some circumstances (eg. if the exposures vary appreciably at different levels) more than one set of instrumental readings may be required particularly in regard to radiation (eg, at head, abdomen, and foot levels) and combined by weighting (ISO 7726, 1998) thus:

Tr = Trhead +2 x Trabdomen + Trfoot 4

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Appendix D: Encapsulating Suits

Pandolf and Goldman (1978) showed that in encapsulating clothing the usual physiological responses to which WBGT criteria can be related are no longer valid determinants of safety. Conditions became intolerable when deep body temperature and heart rate were well below the levels at which subjects were normally able to continue activity, the determinant being the approaching convergence of skin and rectal temperatures. A contribution to this by radiant heat, above that implied by the environmental WBGT, has been suggested by a climatic chamber study (Dessureault et al, 1995), and the importance of this in out-door activities in sunlight in cool weather has been indicated (Coles, 1997). Appropriate personal monitoring then becomes imperative. Independent treadmill studies in encapsulated suits by NIOSH (Belard & Stonevich, 1995) showed that even in milder indoor environments (70°F [21.1°C] and 80°F [26.7°C] – i.e. without solar radiant heat – most subjects in similar PPE had to stop exercising in less than 1 hour. It is clear, however, that the influence of any radiant heat is great, and when it is present the ambient air temperature alone is an inadequate indication of strain in encapsulating PPE. This has been reported especially to be the case when work is carried out outdoors with high solar radiant heat levels, again with mild dry bulb temperatures. Dessureault et al (1995) using multi-site skin temperature sensors, in climatic chamber experiments including radiant heat sources, suggested that Goldman’s proposal (Goldman, 1985) of a single selected skin temperature site was likely to be adequate for monitoring purposes. This suggests that already available personal monitoring devices for heat strain (Bernard & Kenney, 1994) could readily be calibrated to furnish the most suitable in-suit warnings to users. Either one of Goldman’s proposed values – of 36°C skin temperature for difficulty in maintenance of heat balance and 37°C as a stop-work value – together with the subject’s own selected, age-adjusted, moving time average, limiting heart rate, could be utilised.

They showed moreover, that conditions of globe temperature approximately 8°C above an external dry bulb of 32.9°C resulted in the medial thigh skin temperature reaching Goldman’s suggested value for difficulty of working, in little over 20 minutes. (The WBGT calculated for the ambient conditions was 27.4°C and at the 255 W metabolic workload would have permitted continuous work for an acclimatised subject in a non-suit situation). In another subject in that same study, the mean skin temperature (of six sites) reached 36°C in less than 15 minutes at a heart rate of 120 BPM at dry bulb 32.5°C, wet bulb 22.4°C, globe temperature 39.5°C – i.e. WBGT of 26.8°C – when rectal temperature was 37°C. The study concluded that for these reasons, and because no equilibrium rectal temperature was reached when the exercise was continued, “the adaptation of empirical indices like WBGT … is not viable.” Nevertheless the use of skin temperature as a guide 108

parameter does not seem to have been considered. However, with the development of the telemetry pill technology this approach has not been progressed much further.

Definitive findings are yet to be observed regarding continuous work while fully encapsulated. The ACGIH (2013) concluded that skin temperature should not exceed 36°C and stoppage of work at 37°C is the criterion to be adopted for such thermally stressful conditions. This is provided that a heart rate greater than 180-age BPM is not sustained for a period greater than 5 minutes.

Field studies among workers wearing encapsulating suits and SCBA have confirmed that the sweat-drenched physical condition commonly observed among such outdoor workers, following short periods of work, suggests the probable complete saturation of the internal atmosphere, with dry and wet bulb temperatures therein being identical (Paull & Rosenthal, 1987).

In recent studies (Epstein et al, 2013), it was shown that personal protective equipment clothing materials with higher air permeability result in lower physiological strain on the individual. When selecting material barrier clothing for scenarios that require full encapsulation such as in hazardous materials management, it is advisable that the air permeability of the clothing material should be reviewed. There are a number of proprietary materials now available such as Gore-Tex® and Nomex which are being utilised to develop hazardous materials suits with improved breathability. The material with the highest air permeability that still meets the protective requirements in relation to the hazard should be selected.

Where practical, in situations where encapsulation are required to provide a protective barrier or low permeability, physiological monitoring is the preferred approach to establish work-rest protocols.

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