Occupational heat exposure incidence and sociodemographic disparities for outdoor workers in the United States, 2010-2019.

backgroundOutdoor workers are at high risk of hazardous heat exposures and associated adverse health outcomes. Questions remain as to how many workers are exposed.

objectivesTo estimate the yearly incidence of outdoor workers in the United States (US) exposed to hazardous heat from 2010 to 2019 and assess whether marginalized populations of workers are disproportionately exposed.

methodsWe simulated the census tract-level, daily proportion of workers exposed to hazardous heat using multiple datasets containing (i) employment counts, (ii) work characteristics that influence susceptibility to heat exposure (e.g., metabolic rate), and (iii) county-level data on daily-average wet bulb globe temperature. Occupations were classified according to the US SOC structure. Overexposure was determined using ACGIH screening criteria for unacclimatized workers. Daily exposure proportions were summarized as annual, average exposure rates per 100 workers. At the census tract level, annual exposure rates and sociodemographic estimates were merged together to ecologically assess exposure disparities using generalized additive models. Estimates are publicly available alongside an interactive map ( https://sph-umich.shinyapps.io/work-heat-2010-2019/ ).

resultsEstimated daily incidence ranged from 0 to 7.3% of workers. Nationwide, there were an estimated 1.46 daily exposures per 100 workers from 2010 to 2019, equivalent to 5.44 billion worker-days. Nationwide exposure rates did not vary substantially year-to-year. Construction and Extraction (9.77 per 100 workers), Installation, Maintenance, and Repair (8.05 per 100 workers), and Farming, Fishing, and Forestry occupations (7.51 per 100 workers) had the highest estimated exposure rates. Regionally, estimated rates were highest in the South (3.26 per 100 workers), particularly in Florida and Texas. Low-income individuals, individuals without a high school diploma, foreign-born populations, and racial and ethnic minority individuals (particularly Hispanic) were disproportionately exposed. SIGNIFICANCE: The frequency of occupational heat exposure, its disproportionate burden on marginalized workers, and the increasing impact of climate change suggests a critical and urgent need for occupational regulation and surveillance of heat exposure. IMPACT: This study characterizes potentially hazardous heat exposures among outdoor workers for every census tract in the contiguous United States during 2010-2019. Current epidemiological and health impact studies of heat-related disease and mortality do not typically consider how occupational heat exposure may exacerbate adverse heat-related health outcomes in communities experiencing high heat. Our approach could reduce exposure misclassification bias in these studies. Policy-wise, these spatiotemporal estimates can support regulatory enforcement and consultation of occupational heat exposure by better targeting particular communities with high heat exposure. These estimates can also inform surveillance efforts and healthcare resources of state and local health departments.