A Comparison of the Correlation Between ESI and Other Thermal Indices (WBGT, WBDT, TWL, HI, SET, PET, PSI, and PSIHR): A Field Study

Heat is one of the harmful physical factors in the workplace. Occupational heat stress refers to the net load that the
workers should put up with as a result of the combined impact of metabolic heat, environmental factors, and clothing causing heat
storage in the body.
Objectives: This study aimed to compare the correlation between environmental stress index (ESI) and other thermal indices including
wet-bulb globe temperature (WBGT), wet-bulb dry temperature (WBDT), thermal work limit (TWL), heat index (HI), standard
effective temperature (SET), and physiological equivalent temperature (PET).
Methods: Data were collected from 30 workers in one pelletizing factory located in southeastern Iran. The measurement of environmental
variables and workers’ physiological responses at the workplace was implemented in 10 conditions. Pearson productmoment
correlation coefficient and linear regression were utilized to determine the relationship between ESI and environmental/
physiological variables.
Results: The results showed that the strongest correlation was recorded between ESI and dry temperature (r = 0.96), natural wet
temperature (r = 0.96), and heart rate in the working condition (r = 0.94). ESI was strongly correlated withWBDT(r = 0.99) andWBGT
(r = 0.98).
Conclusions: It is concluded that ESI is strongly related to heat indices(WBGT,WBDT, TWL, HI, SET, PET, PSI,andPSIHR)andheat stress
was higher than the legitimate range in some of the working stations. The highest coefficient was recorded for the relationship
between ESI and WBDT.