Comparison of Outdoor Environmental Heat Index (OEHI) and Other Environmental and Physiological Heat Indices: A Case of Outdoor Workers in Low Thermal Stress Conditions

This study aims to assess the consistency of the newly developed Outdoor Environmental Heat Index (OEHI) with existing environmental and physiological heat indices in low thermal stressconditions. This comparison is necessary due to potential variations in the performance of a heat stress index when applied in conditions different from those for which it was developed. Two current and valid outdoor heat indices, including Wet Bulb Globe Temperature (WBGT) and Humidex (HD), were used in a descriptive-analytical study to compare the results obtained by OEHI and other indices in evaluating the same condition. Furthermore, the authors considered tympanic temperature as a physiological response to heat and assessed the work environment of 63 outdoor workers at three-hour intervals during the workday. The highest coefficient of determination was assigned to OEHI and Humidex index (R2>0.99, P<0.0001). Regarding the correlation between the OEHI and the WBGT index, this correlation with and without considering the time of the measurement was higher than 0.98. Comparisons for the correlations of thermal indices with tympanic temperature showed poor and significant relations between thermal indices and tympanic temperature (R2<0.19, P<0.0001). OEHI can evaluate the thermal condition in low heat stress conditions, similar to other current and valid thermal stress indices, including WBGT and Humidex. The OEHI shows a better correlation with the Humidex than the WBGT index. However, due to the poor correlation observed between OEHI and tympanic temperature in low-stress conditions, it is recommended to use this index just as a screening index to estimate thermal environmental conditions.