The physiologic determination of the vapor permeation efficiency of clothing

Abstract

Two calculations of the coefficient for vapor permeation efficiency ( F pcl ) have been proposed for use in the rational (heat balance) approach to heat stress problems caused by wearing protective clothing—one proposed by Candas et al. (1987) and a second (derived from K e η′ ) proposed by Kenney et al. (1987). Both of these coefficients are based on the concept of sweating efficiency and each is used in the calculation of E max , the maximal evaporative capacity of the environment. This paper compares these 2 approaches based on data collected across several clothing ensembles common to industry. In general, the lighter and more permeable the ensemble, the closer the agreement between the two coefficients. However, as clothing becomes impermeable (e.g., vapor-barrier clothing made of plastic, coated Tyvek®, etc.), use of the former F pcl significantly overestimates E max . It is suggested that either calculation can be used for lightweight clothing (although Candas F pcl is simpler to calculate) but that the F pcl calculated by Kenney and co-workers is preferable for heavier ensembles.