Analyzing stored thermal energy and thermal protective performance of clothing

Protective clothing can store large amounts of energy when exposed to thermal (heat, flame) hazards. After exposure, the stored thermal energy discharges naturally—or may be forced if the clothing is compressed suddenly—and contributes to human skin burn injuries. In this study, the stored thermal energy that develops in thermal protective clothing materials was analyzed under different conditions. A stored energy approach that accounts for the thermal energy contained in the exposed test specimen is developed. The stored energy approach measures the total energy delivered to the sensor from a combination of the energy directly transmitted during exposure and the energy stored in the fabric system that is subsequently discharged after the thermal exposure. The study examines the effects of moisture on protective performance and the influence of air gaps between the fabrics and the sensor in terms of a stored energy approach and TPP/RPP (thermal protective performance/radiant protective performance) approach. A minimum exposure time that caused a prediction of a second degree burn was introduced and its contribution to burn injury was examined. These analyses demonstrate that the stored thermal energy obtained during thermal exposure is significant for multilayer protective clothing. Stored thermal energy contributes a large part of the total energy required to cause a second degree skin burn injury. The results indicate that, in cases of thermal exposure, stored thermal energy can reduce significantly the level of protection expected from wearing protective clothing.