Total evaporative resistance of selected clothing ensembles

With regard to heat stress, the limiting factor inherent in clothing ensembles is the total evaporative resistance. Clothing with higher evaporative resistance impedes the ability to cool by sweat evaporation. Knowing the evaporative resistance provides a means to compare candidate ensembles. Further, a value for evaporative resistance means that a rational method can be used to assess the heat stress exposure. Evaporative resistance of five clothing ensembles (cotton work clothes, cotton coveralls, and three coveralls of particle barrier, liquid barrier and vapor barrier properties) was determined empirically from wear tests during two study phases. For Phase 1, the metabolic rate was held constant at 160 W/m², and three levels of humidity (20, 50, 70% rh) were explored. Fourteen heat-acclimated participants (9 men and 5 women) completed trials for all combinations of clothing ensemble and environment. In the Phase 2 study, the humidity was held constant at 50% rh, and three levels of metabolic rate (114, 176, 250 W/m²) were explored. Fifteen heat-acclimated participants (11 men and 4 women) completed trials for all combinations of clothing ensemble and environment. The data from both phases were analyzed separately using ANOVA. Significant differences were found among ensembles (p\u3c0.0001). The vapor barrier ensemble had the highest resistance at 0.026 kPa m²/W. The liquid barrier was next at 0.018; followed by the particle barrier and cotton coveralls at 0.016. Work clothes was 0.014 kPa m²/W. Vapor and liquid barrier ensembles were found to be significantly different from other ensembles. From the Phase 2 study, evaporative resistances decreased with increased activity and ranged from 0.0024 (cotton coveralls) to 0.0094 (vapor barrier) kPa m²/W. The higher differences were associated with higher total evaporative resistance. The decreased evaporative resistances in Phase 2 can be explained by the pumping action associated with increased work. The relationship of Re,T to the difference of Pair -- Pskin was explored and found Re,T does not remain constant. Environment appeared to influence this relationship