Investigating the Association between Heat Stress and its Psychological Response to Determine the Optimal Index of Heat Strain

Exposure to high temperatures is common among workers in warm environments leading to some undesirable effects. The aim of this study was to examine physiological responses to heat stress to determine the optimal index for direct measurement of physiological strain in workers of hot environments. In this study, 40 workers of melting and casting process were evaluated. Thermal stress was evaluated based on the WBGT index and physiological strain by measuring oral and tympanic temperature, urine temperature, heart rate, and recovery heart rate. Data was analyzed using SPSS v.16 software. Heat stress exceeded the national and international recommended limits based on the WBGT index in 80% of cases of workstations. The correlations between heat strains including tympanic temperature, oral temperature, urine temperature, heart rate and heart rate recovery to heat stress index were significant, while tympanic temperature had a stronger association according to simple linear regression (P<0.01, R2=0.78). Tympanic temperature had a stronger correlation with the WBGT index among the investigated indices. Accordingly, tympanic temperature could be a useful indicator compared to other parameters for measuring physiological strain in warm workplaces due to the ease of measurement, noninvasive nature, acceptance by workers, and fast and non- interference in the measurement process.