1 2 Criteria for a Recommended Standard: 3 Occupational Exposure to Heat and Hot 4 Environments 5 6 Revised Criteria 2013 7 8 9 10 11 12 13 14 15 16 17 18 19 DEPARTMENT OF HEALTH AND HUMAN SERVICES 20 Centers for Disease Control and Prevention 21 National Institute for Occupational Safety and Health 22 This information is distributed solely for the purpose of pre dissemination peer review under applicable information quality guidelines. It has not been formally disseminated by the National Institute for Occupational Safety and Health. It does not represent and should not be construed to represent any agency determination or policy. EXTERNAL REVIEW DRAFT 1 Foreword 2 [To be finalized.] 2 This information is distributed solely for the purpose of pre dissemination peer review under applicable information quality guidelines. It has not been formally disseminated by the National Institute for Occupational Safety and Health. It does not represent and should not be construed to represent any agency determination or policy. EXTERNAL REVIEW DRAFT 1 Executive Summary 2 The National Institute for Occupational Safety and Health (NIOSH) has evaluated the scientific 3 data on heat stress and hot environments, and updated the Criteria for a Recommended Standard: 4 Occupational Exposure to Hot Environments [NIOSH 1986a]. This document was last updated 5 in 1986, and in recent years, including during the Deepwater Horizon oil spill response of 2010, 6 questions were raised regarding the need for revision to reflect recent research and findings. This 7 revision includes additional information relating to the physiological changes that result from 8 heat stress; updated information from relevant studies, such as those on caffeine usage; evidence 9 to redefine heat stroke and associated symptoms; and updated information on physical 10 monitoring and personal protective equipment and clothing that can be used to control heat 11 stress. 12 Workers who are exposed to extreme heat or work in hot environments may be at risk for heat 13 stress. Exposure to extreme heat can result in occupational illnesses caused by heat stress, 14 including heat stroke, heat exhaustion, heat cramps, or heat rashes. Heat can also increase the 15 risk of injuries in workers as it may result in sweaty palms, fogged-up safety glasses, and 16 dizziness. Other heat injuries, such as burns, may occur as a result of accidental contact with hot 17 surfaces or steam. Workers at risk of heat stress include outdoor workers and workers in hot 18 environments, such as firefighters, bakery workers, farmers, construction workers, miners, boiler 19 room workers, factory workers, and others. 20 In 2011, NIOSH published with the Occupational Safety and Health Administration (OSHA) a 21 co-branded heat illness-related infosheet. Through this combined effort, many recommendations 22 were updated, including recommended water consumption. In addition, factors that increase risk 23 and symptoms of heat-related illnesses were more thoroughly defined. 24 Chapters on basic knowledge of heat balance and heat exchange largely remained unchanged, 25 although clothing insulation factors have been updated to reflect current International 26 Organization for Standardization (ISO) recommendations. Additional information on the 27 biological effects of heat has become available in recent studies, specifically increasing the 28 understanding of the central nervous system, circulatory regulation, the sweating mechanism, 29 water and electrolyte balance, and dietary factors. New knowledge has been established about 30 risk factors that can increase a worker’s risk of heat-related illness. Those over the age of 60 are 31 at additional risk for suffering from heat disorders [Kenny et al. 2010]. Additional studies have 32 examined sex-related differences regarding sweat-induced electrolyte loss and whole-body sweat 33 response, as well as how pregnancy affects heat stress tolerance [Meyer et al. 1992; Navy 34 Environmental Health Center 2007; Gagnon and Kenny 2011]. As obesity and the increasingly 35 overweight portions of the population in the United States continue to increase, this is now a 3 This information is distributed solely for the purpose of pre dissemination peer review under applicable information quality guidelines. It has not been formally disseminated by the National Institute for Occupational Safety and Health. It does not represent and should not be construed to represent any agency determination or policy. EXTERNAL REVIEW DRAFT 1 major health concern in workers. Heat disorders among the obese and overweight occur more 2 frequently than in lean individuals [Henschel 1967; Chung and Pin 1996; Kenny et al. 2010]. 3 Another factor affecting heat-related illness is drug usage, including alcohol, prescription drugs 4 and caffeine. Caffeine usage has long been argued against, as it has a diuretic effect and may 5 reduce fluid volume leading to cardiovascular strain during heat exposure [Serafin 1996]. 6 However, more recent studies have found that the effect of caffeine on heat tolerance may be far 7 less significant than previously suspected [Roti et al. 2006; Armstrong et al. 2007a; Ely et al. 8 2011]. 9 The definition of heat stroke has also changed in recent years. Heat stroke is now classified 10 either as classical heat stroke or, more commonly in industrial settings, exertional heat stroke. 11 Characteristics of the individual (e.g., age, health status), the type of activity in which they were 12 involved (e.g., sedentary versus strenuous exertion) and the symptoms (e.g., sweating versus dry 13 skin) vary between these two classifications [DOD 2003]. Re-education is needed in the 14 workplace; particularly, in regards to symptoms, as many workers have incorrectly been taught 15 that, as long as they were still sweating, they were not in danger of heat stroke. 16 Measurements of heat stress are largely the same, although additional information is added on 17 bimetallic thermometers and the psychrometric chart. The psychrometric chart is a useful 18 graphical representation of the relationships among dry bulb temperature, wet bulb temperature, 19 relative humidity, vapor pressure and dew point temperature. These charts are especially 20 valuable for assessing the indoor thermal environment. 21 Heat stress can be reduced by modifying one of more of the following factors: metabolic heat 22 production or heat exchange by convection, radiation or evaporation. In a controlled 23 environment, these last three can be modified through engineering controls, including increasing 24 ventilation, bringing in cooler outside air, reducing the hot temperature of a radiant heat source 25 or shielding the worker, and utilizing air conditioning equipment. Heat stress can also be 26 administratively controlled through limiting the exposure time or temperature (e.g., work/rest 27 schedules), reducing metabolic heat load and enhancing heat tolerance (e.g., acclimatization). 28 While most healthy workers will be able to acclimatize over a period of time, some workers may 29 be heat intolerant. Heat intolerance may be related to many factors; however, a heat tolerance 30 test may be used to evaluate an individual’s tolerance, especially after an episode of heat 31 exhaustion or exertional heat stroke [Moran et al. 2007]. 32 Health and safety training is important for employers to provide to workers before they begin 33 working in a hot environment. This training should include information about the recognition of 34 heat-related illness symptoms, proper hydration (e.g., drink 8 oz. of water or other fluids every 35 15-20 minutes), the care and use of heat-protective clothing and equipment, the effects of various 36 factors affecting heat tolerance (e.g., drugs, alcohol, obesity, etc.), the importance of 4 This information is distributed solely for the purpose of pre dissemination peer review under applicable information quality guidelines. It has not been formally disseminated by the National Institute for Occupational Safety and Health. It does not represent and should not be construed to represent any agency determination or policy. EXTERNAL REVIEW DRAFT 1 acclimatization, the importance of reporting symptoms and appropriate first aid. Supervisors also 2 should be provided with appropriate training about how to monitor weather reports and weather 3 advisories. Additional preventive strategies against heat stress include establishing a Heat-Alert 4 program and providing auxiliary body cooling and protective clothing (e.g., water-cooled 5 garments, air-cooled garments, cooling vests, and wetted overgarments). 6 The NIOSH Recommended Alert Limit (RAL) and Recommended Exposure Limit (REL) were 7 evaluated. It was determined that the current RAL for unacclimatized workers and REL for 8 acclimatized workers are still protective. No new data were identified to use as the basis for an 9 updated REL and RAL. The RAL and REL were developed with the intent to protect most 10 healthy workers exposed to environmental and metabolic heat below the appropriate NIOSH 11 RAL/REL from developing adverse health effects. In addition, no worker should be exposed to 12 environmental and metabolic heat loads exceeding the Ceiling Limits without adequate heat- 13 protective clothing and equipment. The WBGT-based threshold values for acclimatized workers 14 are similar to those of OSHA, the American Conference of Governmental Industrial Hygienists 15 (ACGIH), the American Industrial Hygiene Association (AIHA), and the International 16 Organization for Standardization (ISO). 17 While many new research developments have occurred since the last revision of this document, 18 the need for additional research continues. Two newer areas of research that will likely continue 19 to grow include the effects of climate change on outdoor workers and how heat stress affects 20 toxic response to chemicals. It is unclear whether and to what extent global climate change may 21 impact known hazards of heat exposures for outdoor workers with regard to increased severity, 22 prevalence and distribution [Schulte and Chun 2009]. In relation to toxicology, heat exposure 23 can affect the absorption of chemicals into the body.