As record-breaking heat waves become the norm, a new study from the Worker’s Compensation Research Institute (WCRI) finds that California’s heat standard has cut work-related injuries on hot days for industries with substantial exposure to outside heat. Since taking effect, the regulation has driven down injury rates in construction (15-17%), agriculture (24-27%), and transportation (19-25%).
California’s Heat Standard
California adopted the first U.S. outdoor heat standard in 2005 after several agricultural workers died during a summer heat wave, the study notes. “Substantial changes to the outdoor heat standards were made in 2010 and 2015, and in July 2024, California adopted heat standards for indoor workers.”
The six core components of the California heat standard are access to at least one quart of free, pure, cool water per worker per hour; access to shade—or alternative cooling methods that are at least as effective as shade—upon request; provisions for high heat (at or above 95°F) in specific industries, such as the ability to contact a supervisor if needed, pairing workers with buddies as a means of observation, or regular radio or cell phone communication with an employee working alone; emergency response procedures and heat illness prevention plan; acclimatization protocols; and training for workers and supervisors.
Other states, such as Washington, Colorado, Oregon, Maryland, Nevada, and Minnesota, have followed California’s occupational heat standards with similar regulations.
Impact of the Heat Standard
“At all temperature cutoffs and in all high-risk industries, there is a negative and statistically significant decline in the frequency of work-related injuries on hot days after the heat standard was adopted.” In the construction, agriculture, and transportation industries, the yearly effects are negative and statistically significant in most years after the heat standard was introduced, according to the report.
Furthermore, the study finds that “the likelihood of injury declines with each five-degree increase in temperature, indicating that in general the higher the maximum outside temperature, the more effective the heat standard in reducing work-related injuries in the industries with substantial exposure to outside heat.”
The heat standard’s effect increased with the outside temperature, with the strongest impact for temperatures above 95°F. The largest impact was seen on younger workers, with the largest decrease in frequency of work-related injuries on hot days for workers aged 35 and below being 18% in construction and 27% in agriculture, according to the study.
Prevalence of Heat-Related Injury
“Beyond heat-related illnesses (such as heat exhaustion, heat syncope, or rhabdomyolysis), excessive temperature can impair a worker’s perception and judgment, leading to accidents like being hit by moving machinery.” Meanwhile, heat-related illnesses become 11 to 18 times more frequent on days when outside temperature increase above 95°F relative to days with maximum temperatures of 75-80°F, the study finds.
Several states have adopted heat standards requiring employers to provide essentials like cool drinking water, shade, work breaks, and acclimatization-to-heat and emergency response plans when temperatures become excessive.
Impacts of Heat on Workers
“Working in excessive heat contributes to an increased prevalence of heat-related illnesses, such as heat exhaustion, syncope, and cramps,” the report explains. “Research has shown that heat-related injuries are more frequent when there is excessive heat. Additionally, a recent California Workers’ Compensation Institute (CWCI) report shows that the heat-related injuries in agriculture, construction, and landscaping represent about 0.65-0.67% of all work-related injuries and illnesses in each respective industry.”
Working in excessive heat can also indirectly contribute to an overall increase in workplace injuries by impairing perception, cognition, and motor skills, and increasing fatigue, according to the report, leading to accidents such as falling off a ladder or being hit by a moving machine. “Relative to cool days…working outdoors when the temperature is in the upper 80s leads to a 2 to 7% increase in injury risk, and working outdoors when temperatures are above 100 degrees leads to an even higher increase in injury risk—15% higher.”
Mitigating the Impacts of Heat
“Body cooling and acclimatization can lessen the effects of excessive heat,” according to the report. “Employers can support body cooling by providing air conditioning, shade, and water, and giving workers time to acclimate to the heat.” Furthermore, having the ability to rest in the shade reduces the body’s “heat gain,” and being repeatedly exposed to heat allows the body to acclimate to hot conditions and better tolerate them.
A 2021 study referenced in the report found that after California adopted heat regulations, workplace injuries on hot days declined by roughly 30%; “however, the authors noted that they could not rule out that their finding reflects either an improvement in cooling technology or a reduction in the likelihood of workplace injuries in response to the tight labor market during the Great Recession,” the report explains.
Workers and Settings at Highest Risk
“Overall, workers in job that are more exposed to heat—younger workers and men—are more likely to have an increased likelihood of experiencing a work-related injury on hot days,” notes the report. “Within occupation, however, the workers with the greatest sensitivity to working in the heat are older workers and women.”
When it comes to company size, workers at larger firms are less affected by temperature than those working at smaller or medium firms, and there is a greater increase in injuries on hot days in firms that historically have fewer injury claims.
As more states, including Arizona, Florida, Georgia, Illinois, Massachusetts, New Jersey, New York, Rhode Island, Virginia, and Texas, as well as the Occupational Safety and Health Administration (OSHA), consider the adoption of new heat standards, the study’s findings provide compelling evidence on how heat standards affect injury rates during extreme heat.