Book excerpt: Occupational exposure to heat can result in injuries, disease, reduced productivity, and death. To address this hazard, the National Institute for Occupational Safety and Health (NIOSH) has evaluated the scientific data on heat stress and hot environments and has updated the Criteria for a Recommended Standard: Occupational Exposure to Hot Environments [NIOSH 1986a]. This updated guidance includes information about physiological changes that result from heat stress, and relevant studies such as those on caffeine use, evidence to redefine heat stroke, and more. Related products: Weather & Climate collection is available here: https://bookstore.gpo.gov/catalog/weather-climate Emergency Management & First Responders can be found here: https://bookstore.gpo.gov/catalog/emergency-management-first-responders Fire Management collection is available here: https://bookstore.gpo.gov/catalog/fire-management