Analyzing the Transient Thermophysical Properties of Heat-Resistant Fabrics in TPP Exposures

The effect of high intensity heat on the transient thermophysical properties has been investigated for eight protective fabrics made with polybenzimidazole (PBI), Kevlar®, Nomex®, and blends of PBI with Kevlar® or rayon fibers. Exposure conditions used for this study were 2.0 cal/cm ² .s, 50/50 radiant/convective, and a 2.0 cal/cm ² .s, 100% radiant heat. An interrupted exposure approach was used to obtain a series of test fabrics exposed for incrementally increasing durations. These samples were ana lyzed offline to determine the effect of timed exposures on properties affecting heat transfer. An analysis of momentary fluctuation reveals that two factors critically de termine the response of heat stable materials in TPP tests: one is the moisture in the fabric and its effect on fabric heating and transmission, and the other is the retention of effective thermal thickness.