Heat strain in chemical protective ensembles: Effects of fabric thermal properties

An ongoing challenge in material science has been to reduce heat strain experienced by individuals wearing chemical protective ensembles. The objective of this study is to analyze the relationship between the thermal properties of eight chemical protective fabrics and heat strain in ten chemical protective ensembles constructed with those fabrics. The fabric samples were tested on a sweating guarded hot plate to measure fabric thermal and evaporative resistance. The ensembles were then tested on thermal manikins to measure ensemble thermal and evaporative resistance. An empirical thermoregulatory model, the Heat Strain Decision Aid (HSDA), was used to predict thermal responses of core temperature and endurance times. Model inputs included ensemble thermal and evaporative resistances, four environmental conditions and a metabolic rate of 400 W. The fabric intrinsic thermal and evaporative resistances ranged from 0.01 to 0.05 m² °C·W^-1 and from 5.9 to 12.82 m² Pa·W^-1, respectively. Ensemble intrinsic thermal and evaporative resistances ranged from 0.23 to 0.31 m² °C·W^-1 and 51.7-67.8 m² Pa·W^-1, respectively. Predicted endurance times varied from 170 to 300 min at 20 °C/50% RH/2 m s^-1 and 26 °C/55% RH/9 m s^-1 conditions, and varied from 91 to 98 min at 30 °C/75% RH/2 m s^-1 and 40 °C/20% RH/2 m s^-1 conditions. Improved fabric thermal properties reduced heat strain and extended endurance times, but the magnitude of the extended times is dependent on the environmental conditions. Consequently, the benefits of improved fabric thermal properties may only be observed under certain environmental conditions.