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 1 A Guide to Managing Heat Stress: Developed for Use in the Australian Environment Developed for the Australian Institute of Occupational Hygienists Ross Di Corleto, Ian Firth & Joseph Maté November 2013 November 2013 2 Contents CONTENTS 3 PREFACE 6 A GUIDE TO MANAGING HEAT STRESS 7 Section 1: Risk assessment (the three step approach). 8 Section 2: Screening for clothing that does not allow air and water vapour movement. 12 Section 3: Level 2 assessment using detailed analysis. 13 Section 4: Level 3 assessment of heat strain. 15 Section 5: Occupational Exposure Limits 17 Section 6: Heat stress management and controls 18 BIBLIOGRAPHY 21 Appendix 1 - Basic Thermal Risk Assessment – Apparent Temperature 23 Appendix 2 – Table 5: Apparent Temperature Dry Bulb/Humidity scale. 25 3 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 4 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 5 PREFACE In 2001 the Australian Institute of Occupational Hygienists (AIOH) established the Heat Stress Working Group to develop a standard and relevant documentation in relation to risks associated with hot environments. This group produced “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. 6 A Guide to Managing Heat Stress The human body must regulate its internal temperature within a very narrow range to maintain a state of well-being. To achieve this, the temperature must be balanced between heat exchanges with the external thermal environment and the generation of heat internally by the metabolic processes associated with life and activity. The effects of excessive external heat exposures can upset this balance and result in a compromise of health, safety, efficiency and productivity, which precede the possibly more serious heat related illnesses. These illnesses can range from prickly heat, heat cramps, heat syncope, heat exhaustion, heat stroke and in severe cases, death. The prime objective of heat stress management is the elimination of any injury or risk of illness as a result of exposure to excessive heat. Assessment of both heat stress and heat strain can be used for evaluating the risk to worker health and safety. A decision-making process such as that shown in Figure 1 can be used. Figure 1 and the associated Documentation for this Guide provides means for determining conditions under which it is believed that an acceptable percentage of adequately hydrated, unmedicated, healthy workers may be repeatedly exposed without adverse health effects. Such conditions are not a fine line between safe and dangerous levels. Professional judgement and a program of heat stress management, with worker education and training as core elements are required to ensure adequate protection for each situation. This Heat Stress Guide provides guidance based on current scientific research (as presented in the Documentation), which enables individuals to decide and apply appropriate strategies. It must be recognised that whichever strategy is selected, an individual may still suffer annoyance, aggravation of a pre-existing condition, or even physiological injury. Responses to heat in a workforce are individual and will vary between personnel. Because of these characteristics and susceptibilities, a wider range of protection may be warranted. Note that this Guide should not be used without also referencing the accompanying Documentation. This Guide is concerned only with health considerations and not those associated with comfort. For additional information related to comfort, readers are directed to more specific references such as International Standards Organization (ISO) 7730 – 2005: Ergonomics of the thermal environment - Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria. 7 HEAT STRESS is the net heat load to which a worker may be exposed from the combined contributions of metabolism associated with work and environmental factors such as: • 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 8 environment follows. Making sure to consider factors such as air velocity, humidity, clothing, metabolic load, posture and acclimatisation 3. Where the allowable exposure time is less than 30 minutes or there is a high involvement level of personal protective equipment (PPE), then some form of physiological monitoring should be employed (Di Corleto, 1998a) The first level, or the basic thermal risk assessment, is primarily designed as a qualitative risk assessment that does not require specific technical skills in its administration, application or interpretation.