Total Evaporative Resistance of Selected Clothing Ensembles

With regard to heat stress, the limiting factor inherent in clothing ensembles is the total evaporative resistance. For the same work demands, 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/sq m, 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/sq m) 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<0.0001). The vapor barrier ensemble had the highest resistance at 0.026 kPa sq m/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 sq m/W. Pair-wise comparisons adjusted for multiple comparisons were used to locate the differences among ensembles. Vapor and liquid barrier ensembles were found to be significantly different from other ensembles. Data from both studies support the conclusion that there are differences in evaporative resistances among selected ensembles tested.Air Force Inst of Tech Wright-Patterson AFB OH is the author of 'Total Evaporative Resistance of Selected Clothing Ensembles', published 2004 under ISBN 9781423520610 and ISBN 1423520610.