Do Heat Standards Reduce Heat-Related Illness? Evidence from California

• In Event: Extreme Heat, Health, and Urban Adaptation

Abstract

Background:Extreme heat is a growing health challenge in the United States, contributing to rising heat-related illness (HRI) rates, emergency care utilization, and lost productivity. Outdoor workers are particularly vulnerable due to prolonged exposure to high temperatures and physically demanding labor. In 2005, California became one of the first states to implement a Heat Illness Prevention in Outdoor Places of Employment standard, requiring employers to provide water, shade, training, and emergency response measures. In the absence of a federal occupational heat standard, evidence on whether such regulations reduce heat-related morbidity remains limited. As climate change intensifies extreme heat events and the Occupational Safety and Health Administration (OSHA) considers a national heat standard, understanding health effects of early-adopting state policies is increasingly important.Purpose:To evaluate the causal impact of California’s heat standard on HRI emergency department (ED) visits among working-age adults.Data:This retrospective observational study used 2005-2008 California Healthcare Cost and Utilization Project (HCUP) State Emergency Department Databases (SEDD) data, capturing all-payer ED encounters not resulting in admission. HRI cases were identified using ICD-9-CM diagnosis codes (992.0-992.9; E900.0-E900.1). The unit of analysis was county-month across all 58 California counties. The outcome was the monthly HRI ED visit rate per 100,000 working-age adults aged 16-64.Research Design and Methods:The intervention was the permanent enactment of the standard in late July 2006. I employed an interrupted time series (ITS) design using a balanced county-level panel. The model included a linear time trend, a post-policy level-change indicator, and an interaction term capturing changes in the post-policy trend. To account for temporal persistence, a one-month lag of the dependent variable was included. Models adjusted for time-varying county-level covariates, including monthly maximum temperature, relative humidity, precipitation, poverty rates, and outdoor workforce size. Month indicators controlled for seasonality, and county fixed effects accounted for time-invariant differences. Population-weighted generalized estimating equations with robust standard errors clustered at the county level were used to estimate policy effects.Results:Findings indicate that the mean monthly HRI ED visit rates declined from 1.41 per 100,000 population pre-policy to 1.07 per 100,000 population post-policy. Population-weighted dynamic ITS confirmed these patterns after adjusting for weather, socioeconomic factors, and seasonality. Before implementation, rates exhibited a significant upward trend of 0.055 visits per 100,000 monthly (p<0.001). Policy implementation was associated with an immediate reduction of 0.95 visits per 100,000 (β=-0.952, p<0.001). The post-policy trend declined by 0.047 visits per 100,000 monthly relative to the pre-policy trend (β=-0.047, p<0.001), indicating sustained attenuation of morbidity. Additionally, higher maximum temperatures (β=0.103 per °F, p<0.001) and higher poverty rates were associated with increased HRI rates, while outdoor workforce size was not meaningfully associated with increased HRI rates.Conclusion:California’s heat illness prevention standard was associated with both immediate and sustained reductions in HRI ED utilization among working-age adults.Implications:As federal policymakers consider national heat protections, evidence from early-adopting states such as California suggests that occupational heat regulations may reduce acute healthcare utilization and yield meaningful health and economic benefits.

Author

• Gogoal Falia, Texas A&M University
  Presenting Author