Exposure to heat at work: development of a quantitative European job exposure matrix (heat JEM).

Objective: With climate change exacerbating occupational heat stress, objective and systematic exposure assessment is essential for epidemiological studies. We developed a job exposure matrix (JEM) to assign occupational heat stress exposure across Europe.

Methods: Aligned with the International Organization for Standardization (ISO: 7243, 8996 and 9920), the heat JEM provides region- and year-specific estimates of annual heat stress hours by job title, using the International Standard Classification of Occupations 1988 for Europe [ISCO-88(COM)]. Heat stress was defined as wet bulb globe temperature effective (WBGT_eff) exceeding WBGT reference (WBGT_ref). Outdoor and indoor WBGT were determined using historical, region-specific hourly meteorological data (temperature, radiation, humidity, wind speed) across Europe, between 1970 and 2024. WBGT values were adjusted for job-specific clothing to obtain WBGT_eff. WBGT_ref was based on metabolic rate, calculated using body surface area and job-specific physical activity, and adjusted for acclimatization status. Further adjustments were made for the job title-specific presence of local heat and cooling sources, time spent indoors versus outdoors, and working schedules.

Results: The number of annual hours workers experience heat stress is highest among jobs involving local heat sources and physical demanding tasks, especially when work clothing is mandatory. Southern Europe has a higher annual heat stress burden compared to other regions. Exposure varies across calendar years and is substantially higher among unacclimatized versus acclimatized workers.

Conclusions: Incorporating job-, region-, and year-specific factors, the heat JEM provides a harmonized tool for studying occupational heat stress. Its transparent framework allows for updates with new data and extensions to other years and regions.