California’s 2005 heat standard was an important first step to protect workers. Yet critics argued that the standard contained ambiguous wording that enabled employers to avoid improving working conditions, relied on vulnerable workers to demand breaks, and was not actively enforced by the California Division of Occupational Safety and Health.

In 2010, California responded by launching a statewide initiative aimed at educating workers about their rights, improving compliance among employers, and increasing inspections and enforcement. Labor unions and worker advocates continued to argue for changes, and in 2015, California revised the standard to close loopholes related to rest, water, shade, and enforcement.

Several US states have followed California’s example. Since 2022, Colorado, Maryland, Nevada, Oregon, and Washington have passed new laws that mandate water, shade, and regular rest breaks for all outdoor workers on hot days. In August 2024, the Occupational Safety and Health Administration (OSHA) proposed a new standard that would require similar protections for workers throughout the United States.

A new study just published by Health Affairs compared heat-related deaths among outdoor workers in California with those in neighboring states without standards during the period 1999–20. Researchers obtained data for all 126 counties in Arizona, California, Nevada, and Oregon for the period 1999–20. They identified 6,145 heat-related deaths among outdoor workers during the study period.

Arizona had the highest cumulative number of deaths (2,546), followed by California (2,207), Nevada (1,124), and Oregon (268). The county-year with the highest number of heat-related deaths among outdoor workers was Maricopa County, Arizona, with 233 deaths in 2020. Among counties that reported heat-related deaths among outdoor workers, the mean annual death rate was 0.91 deaths per 100,000 residents. All fifty-eight counties in California were covered by a heat standard starting in 2005, whereas none of the sixty-eight counties in the neighboring states was covered by a heat standard during the study.

Results suggest that the effectiveness of California’s heat standard increased substantially over time. Researchers found no decrease associated with the policy during the initial implementation period (2005–09), but point estimates suggested a 33 percent decrease in heat-related deaths among outdoor workers after increased enforcement (2010–14) and a 51 percent decrease after California’s heat standard revisions went into effect (2015–20). Although these individual period estimates were not statistically significant, a Wald test confirmed that California’s enhanced approach from 2010 onward was associated with a statistically significant decrease in worker deaths.

“Our findings offer important lessons for other states regarding the potential promise and pitfalls of heat standards meant to protect outdoor workers. On the one hand, California’s experience suggests that heat standards can reduce heat-related deaths among outdoor workers. On the other hand, it highlights that such policies may have little impact unless they are carefully designed and effectively enforced. A review of recently implemented heat standards suggests that variation in effectiveness is likely: Although Maryland’s 2024 law closely mirrors California’s revised standard, for example, Nevada’s 2024 version lacks a trigger temperature for enforcement”