Development and validation of modified predicted heat strain model for various metabolic rates in hot-humid...

As the hot and humid environments in deep underground spaces deteriorate with increasing mining depth, there is an increased demand to accurately assess worker heat stress levels in underground environments characterized by high relative humidity and air velocity. A modified predicted heat strain (mPHS) model was proposed through the correction factors of air velocity and relative humidity for the clothing thermal insulation and vapor resistance. The predictive performances of the mPHS model for mean skin temperature, sweat loss, and core temperature were validated in low, moderate, and high metabolic rates. The model's guidances for deep underground environments were discussed, and the maximum allowable exposure times (MAET) for 168 conditions were provided. The results demonstrated that the mPHS model exhibited superior predictive performance within 60-320 W/m² when compared with the original model, especially for mean skin temperature and core temperature, with a maximum reduction in the predictive difference of 1.60 °C and 0.61 °C. The acceptability of the predicted mean skin temperature elevated from 33.65% to 91.35% and 41.7% to 100% in the conditions of 60-120 W/m² and 140-200 W/m², respectively. In the hot environments, the influence of air velocity (0.3-0.8 m/s) on MAET was more pronounced than that of relative humidity (50%-80%). An increase in air velocity of 0.1 m/s, coupled with a 5% decrease in relative humidity, leads to an approximate extension of the MAET by 18 min. The results could contribute a theoretical insight for predicting thermal physiology in hot-humid underground environments.