David W. DeGroot and Laura A. Pacha**

Exposure to high ambient temperatures while working in hot indoor environments or while working outdoors in hot weather is a common and potentially fatal occupational hazard. Unlike cold exposure (Chapter 7), which can be almost completely mitigated with proper clothing and equipment, it is impossible to fully mitigate the effects of a hot environment. Normally, body core temperature is maintained within a very narrow range. In the occupational setting, heat stress from the combined effects of environmental heat, metabolic heat, and often the use of impervious clothing can strain the ability to maintain heat balance, and core temperature may begin to rise, potentially leading to an exertional heat illness. Workplace heat exposure, in addition to causing heat-related illness, has been found to decrease productivity and to increase job-related accidents.1


No recent estimate of the number of workers exposed to hot environments has been published. In 1986, the National Institute for Occupational Safety and Health (NIOSH) estimated that 5–10 million Americans worked in jobs where heat stress was an occupational health hazard, and this range is probably still a reasonable estimate.2 Table 6.1 lists some common work sites where workers may be expected to experience heat stress.3 Heat-related deaths are common in the United States. From 1999 to 2009, there was an average of 658 heat-related deaths ...

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