Vapor Breakthrough from Liquid Drops Impacting Air-Permeable Chemical Protective Fabric

Abstract

The interaction between drop impact and vapor breakthrough for several kinds of air-permeable fabric composites (an outer shell with an adsorbent liner) is determined under convective flow conditions. Vapor breakthrough is measured using methyl sali cylate, a chemical agent simulant, for static and dynamic liquid drop placement on either the shell fabric alone or in combination with an activated carbon-loaded foam liner backing. Vapor concentration, detected by means of a photo-ionizer, is used to determine breakthrough curves, while image analysis provides a quantitative charac terization of the impact behavior of the liquid drops by measuring liquid spreading. splashing, and breakthrough. Drop impact velocities up to 6 m/s are measured on cotton/Kevlar®/nylon and cotton/nylon twill weave outer shell fabrics. For static drops, fabric composites with an outer wicking fabric give much lower total vapor breakthrough than do nonwicking fabrics, whereas for dynamic drops at subterminal impact velocities, the difference between nonwicking and wicking shell fabrics is re duced because of surface spreading and splashing. There is an inverse correlation be tween wetted area and vapor breakthrough due to localized vapor saturation of the adsorbent liner fabric. Below a critical drop velocity of 4.5 m/s, there is no direct liquid penetration through the shell fabric.