Validation of heat strain risk assessment (HSRA) indices compared to wet bulb globe temperature (WBGT) and predicted heat strain (PHS) indices

Heat strain risk assessment (HSRA) indices have recently been developed for more precise prediction of heat strain. This study aimed to evaluate the validity of these indices compared to the wet bulb globe temperature (WBGT) and predicted heat strain (PHS) indices under different thermal and occupational conditions. This cross-sectional study was performed in environemntal settings of warm-dry and warm-humid in 2024. In the study, 200 Iranian male workers from two warm industries participated. Initially, their demographic data were gathered. Subsequently, they were instructed to perform their usual tasks after a 30-minute rest period. After 90 min of working, physiological and environmental parameters were measured. Additionally, the metabolic rate and clothing thermal insulation of participants were assessed, and they filled out the observational-perceptual heat stress risk assessment (OPHSRA) questionnaire. After that, indices were calculated. The Spearman correlation coefficient was employed to analyze the relationships among them. Additionally, a linear regression analysis was conducted to plot the curve and compute the regression coefficients. Receiver operating characteristic (ROC) analysis was also used to determine the accuracy of these indices. The highest regression coefficients were observed between tympanic temperature and PHSRA (R2 = 0.77), EHSRA (R2 = 0.75), and PHS (R2 = 0.72) indices. Similarly, the greatest regression coefficients were found between heart rate and PHSRA (R2 = 0.71), EHSRA (R2 = 0.68), and PHS (R2 = 0.65) indices. The OPHSRA and WBGT indices had the lower regression coefficients with tympanic temperature (R2 = 0.69 and R2 = 0.67) and heart rate (R2 = 0.61 and R2 = 0.42) compared to the aforementioned indices, respectively. Moreover, EHSRA (AUC = 0.950 and AUC = 0.907) and PHSRA (AUC = 0.947 and AUC = 0.900) indices had the highest diagnostic accuracies of ROC curves related to tympanic temperature and heart rate, respectively. The results showed that the HSRA indices have acceptable validity in predicting thermal strain.