Effects of high heat flux exposures on tensile strength of firefighters' protective clothing

Abstract

SummaryThe effects of thermal aging on tensile strength of three Kevlar/PBI blends used in the outer shell layer of firefighters' protective clothing were examined using cone calorimeter exposures of 10‐70 kW/m2 for 30‐300 seconds. Lower heat flux exposures of 10‐15 kW/m2 did not result in significant change in the tensile strength of the fabrics, but significant losses of tensile strength were first observed as the heat fluxes increased to 20‐30 kW/m2 for two ripstop fabrics, and 45 kW/m2 for the third fabric. Further decreases in tensile strength were observed with increasing heat flux until there was almost a total loss of original tensile strength following exposure to 70 kW/m2. Decreases in tensile strength were explained by comparing fabric temperature measurements made using an infrared thermometer, key temperatures in thermal gravimetric analysis test results, and the appearance of the three fabrics after the exposures. While duration of exposure had little effect on tensile strength after exposures to 10 kW/m2, tensile strength decreased with duration of exposure for heat fluxes of 20‐40 kW/m2. The effect of duration was greatest for a heat flux of 20 kW/m2. These results indicate that one must consider not only the maximum temperature that the fabric reaches, but the complete temperature‐time trace, including the time at which the fabric remains at the maximum temperature, when examining the effects of thermal aging on tensile strength.