A comparison of the correlation between heat stress indices (UTCI, WBGT, WBDT, TSI) and physiological parameters of workers in Iran

Heat is one of the harmful agents in many workplaces. The current study aimed at investigating the correlation between heat stress indices (Universal Thermal Climate Index (UTCI), wet-bulb globe temperature (WBGT), wet-bulb dry temperature (WBDT), Tropical Summer Index (TSI)) and Physiological parameters among mine workers. This cross-sectional study was conducted among workers of one of the mines located in southeast Iran in July–August 2017. Workplace environmental parameters and workers' physiological parameters were measured in thirty different ways from 10 a.m. to 2 p.m. The collected data were fed into SPSS 20 followed by conducting Pearson product moment correlation to detect the relationship between heat stress indices and workers' physiological parameters. Attempts were also made to examine the associations among heat stress indices themselves. The results of data analysis indicated that the mean scores of UTCI, WBGT, WBDT, and TSI were 34.59 ± 1.51 °C, 24.59 ± 0.62 °C, 28.37 ± 0.82 °C, and 31.51 ± 0.7 °C, respectively. On the other hand, the results of Pearson correlation revealed that UTCI and WBDT had the strongest association (r = 0.93, p < 0.0001). A significant correlation was also observed between UTCI and WBGT (r = 0.44, p < 0.0001). Conversely, no measurable correlation was detected between heat stress indices and workers’ physiological parameters (p > 0.05). The only statistically significant correlation coefficients were recorded between skin temperature and the two indices of WBGT and TSI. According to the value obtained for UTCI, the workers were exposed to severe heat stress. However, based on WBGT value and ISO 7243 standards for an adapted person, workers were not exposed to heat stress.