Heat Stress Kills Workers

Exposure to heat and hot environments puts workers at risk for heat stress, which can result in heat illnesses and death. Guidance for prevention exists, but heat illness prevention programs are not formally implemented by most employers.


A new report published by the CDC describes findings from a review of 2012?2013 Occupational Safety and Health Administration (OSHA) federal enforcement cases resulting in citations under paragraph 5(a)(1), the "general duty clause" of the Occupational Safety and Health Act of 1970. That clause requires that each employer "furnish to each of his employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to [his or her] employees."


Because OSHA has not issued a heat standard, it must use 5(a)(1) citations in cases of heat illness or death to enforce the employers' obligations to provide a safe and healthy workplace. During the two-year period reviewed, 20 cases of heat illness or death were cited for federal enforcement under paragraph 5(a)(1) among 18 private employers and two federal agencies. Thirteen worksites were outdoors.


Seven cases occurred in indoor facilities with a local heat source, such as laundry equipment or combustion engines. The cases occurred in various workplaces, including two in solid waste collection, two in mail delivery, nine in outdoor worksites (e.g., ship repair, landscaping, roofing, and oil servicing), two in laundries, and five in indoor worksites with machinery or other heat sources


In 13 cases, a worker died from heat exposure, and in seven cases, two or more employees experienced symptoms of heat illness. Most of the affected employees worked outdoors, and all performed heavy or moderate work, as defined by the American Conference of Governmental Industrial Hygienists. Nine of the deaths occurred in the first three days of working on the job, four of them occurring on the worker's first day. In the cases that involved heat illness but not a death, the number of days on the job did not appear to contribute to any of the heat-related incidents.


Heat illness prevention programs at these workplaces were found to be incomplete or absent, and no provision was made for the acclimatization of new workers. Acclimatization is the result of beneficial physiologic adaptations (e.g., increased sweating efficiency and stabilization of circulation) that occur after gradually increased exposure to heat or a hot environment. Whenever a potential exists for workers to be exposed to heat or hot environments, employers should implement heat illness prevention programs (including acclimatization requirements) at their workplaces.


To understand the effectiveness of existing heat illness prevention campaigns and tools, OSHA convened the Heat Illness Workgroup to conduct a systematic review of cases of occupational heat illness or death cited for federal enforcement under paragraph 5(a)(1) during 2012–2013. Cases were identified by OSHA's Directorate of Enforcement Programs.


For all cases reviewed, the workgroup established a list of program elements it considered important based on published literature and members' professional experience. These included information on local weather conditions, work processes and workload, employer heat illness prevention program elements, health outcomes, numbers of persons affected, and individual risk factors. When needed, OSHA Compliance Safety and Health Officers were consulted for case clarification.


All heat illnesses and deaths occurred on days with a heat index in the range of 84.0°F–105.7°F (29.0°C–41.0°C), although those working in direct sunlight might have experienced a heat index that was up to 15.0°F (8.3°C) higher than reported.


None of the employer heat illness prevention programs were complete. Twelve had no program at all, seven provided inadequate water management, and 13 failed to provide shaded rest areas. Only one of the employers used work-rest cycles (i.e., scheduled periods of rest between periods of work based on temperature, humidity, and the intensity of the work activity), and none had an acclimatization program.


Heat-related deaths often occur in occupations in which workers are performing tasks in hot environments, causing them to build metabolic heat faster than their bodies can release heat and cool down. In North Carolina, during 2008–2010, work-related heat illnesses resulting in emergency department visits were more common than work-related emergency department visits with any other cause among persons aged 19–45 years. In Maricopa County, Arizona, during 2002–2009, outdoor work in construction and agriculture accounted for 35% of heat-related deaths in men. A total of 68 crop production worker deaths were reported in the United States during 1992–2006, resulting in an annual average death rate of 0.39 deaths per 100,000 crop workers. Particularly in agriculture, estimates of heat illness cases are likely to be undercounted because some surveys exclude workers on small farms.


Although OSHA's Heat Illness Prevention Campaign's core message, "Water, Rest, Shade," has been widely disseminated and reflects many similar public health messages, this review shows that some employers have not developed complete heat illness prevention programs. Strikingly, in the cases reviewed, the failure to support acclimatization appears to be the most common deficiency and the factor most clearly associated with death.


Employers need to provide time to acclimatize for workers absent from the job for more than a few days, new employees, and those working outdoors during an extreme heat event or heat wave. Employers must ensure that all workers acclimatize to hot environments by gradually increasing duration of work in the hot environment. In addition, health care providers should be aware of the loss of acclimatization in their patients who have been out of work for a week or more and counsel them that they will need time to regain acclimatization once they return to their job.


New workers and all workers returning from an absence of more than a week should begin with 20% of the usual duration of work in the hot environment on the first day, increasing incrementally by no more than 20% each subsequent day. During a rapid change leading to excessively hot weather or conditions such as a heat wave, even experienced workers should begin on the first day of work in excessive heat with 50% of the usual duration of work, 60% on the second day, 80% on the third, and 100% on the fourth day. Full acclimatization might take up to 14 days or longer to attain, depending on individual or environmental factors.


Employers should be aware of the importance of all elements, including acclimatization, in their heat illness prevention programs. They should be diligent about the following:


  • designating a person to develop, implement, and manage the program
  • monitoring the temperature (e.g., heat index and wet bulb globe temperature) of their worksite
  • providing water and rest breaks in a shaded, cool area
  • acclimatizing workers by gradually increasing the exposure to heat or a hot environment
  • modifying work schedules as necessary to reduce workers' exposure to heat
  • training workers on the signs and symptoms of heat illness
  • monitoring workers for signs of heat stress
  • planning for emergencies and response.


Guidance provided by the CDC's National Institute for Occupational Safety and Health includes information on acclimatization, work-rest schedules, adequate hydration, indices for monitoring environmental heat stress (including wet bulb globe temperature), and other recommendations that can be used for developing a heat illness prevention program.


See the CDC Report


Also see the CDC’s Heat Stress Workplace Safety & Health Topics


Also see OSHA’s Heat Illness Resources