Time-series analysis of the incidence trend of heat stress-related disorders in a hot and humid climate in a process industry.

Global warming is escalating occupational health risks worldwide, with outdoor workers in hot and humid regions facing disproportionate exposure to extreme heat. In such climates, the synergistic effects of high temperature and humidity critically impair thermoregulation, increasing susceptibility to heat stress-related disorders (HSRDs) a growing concern in low- and middle-income countries where adaptive capacity is limited. This study analyzed the six-year trend (2018-2023) in the HSRDs among outdoor workers in a hot, humid petrochemical industry in southern Iran. This retrospective longitudinal study collected health data on HSRDs alongside concurrent Wet-Bulb Globe Temperature (WBGT) index values. Additive time-series decomposition was used to analyze trends. Analyses were conducted using R and SPSS (p < 0.05). The mean WBGT index showed a significant, consistent increasing trend over the 6-year period (from 27.73 to 29.75 °C, p < 0.001). Exposure for site workers was highest, and summer critical (Sweltering) heat stress levels increased markedly from near zero to approximately 55% of the recorded time. General heat-related disorders showed the strongest association with elevated WBGT. A major challenge was identified in predictive modeling: only the model for general heat-related disorders showed relative accuracy (R2 = 0.692). Other specific disorders (e.g., headache, cramp, rash) exhibited unpredictable patterns with high error rates (44% to 147% MAPE). Heat stress exposure is intensifying continuously in these work environments. While the WBGT index trend is predictable, the incidence of specific HSRDs follows complex, unpredictable patterns, making prediction based solely on WBGT challenging. The results underscore the necessity for robust, continuous preventive interventions considering all individual and environmental factors.