Effects of various protective clothing and thermal environments on heat strain of unacclimated men: The PHS (Predicted Heat strain) model revisited

Five protective garments (light summer clothing L, high visibility clothing HV, military clothing MIL, climber coverall CLM and firefighting clothing FIRE) were assessed on eight unacclimated male subjects at two environments: moderate warm environment with high humidity (MWH, 20.0°C, 86% relative humidity) and warm environment with moderate humidity (WMH, 30.0°C, 47% relative humidity). The thermophysiological responses and subjective sensations were reported. The PHS model (ISO7933) was used for predicting thermophysiological responses for each testing scenario. It was found that there were significant differences between clothing FIRE and other clothing on thermal sensation (p<0.05). Significant differences were found on skin humidity sensation between FIRE and L, HV or MIL (p<0.001). The RPE value in FIRE is significantly different with L and HV (p<0.05). In MWH, the post-exercise mean skin temperatures increased by 0.59 and 1.29°C in MIL and CLM. In contrast, mean skin temperatures in L, HV, MIL, CLM and FIRE in WMH increased by 1.7, 2.1, 2.1, 2.8 and 3.3°C, respectively. The PHS model presented good performance on predicted mean skin temperatures in MIL and CLM at the two studied environments. However, the skin temperature prediction with light clothing in WMH was weak. For thick protective clothing, the prediction on rectal temperature was protective. It is thus concluded that the results generated by the PHS model for high insulating clothing and measurements performed in high humidity environments should be explained with caution.