Characterizing the thermal protective performance of textiles under flame exposure

Annually, thousands of firefighters suffer injuries, with burn injuries making up 7%–8% of these cases. Despite wearing protective clothing, burn injuries still occur, which underscores its limitations. The effectiveness of protective clothing is heavily influenced by the unpredictable and variable conditions firefighters face during hazardous incidents. This study compared the effects of heat flux, air gaps, and fabric attributes on TPP in multilayer systems. Results revealed a negative correlation between heat flux and TPP, with higher flux intensities increasing energy transfer through conduction and radiation, diminishing protection. Flame exposure highlighted differences in heat transfer mechanisms, with conduction and radiation dominating at high flux, whereas at low heat flux, convection, even though minimal, significantly impacts TPP. Air gaps improved TPP up to 6-mm, providing maximum insulation. However, performance plateaued or declined at 12-mm due to the transition of a stagnant air gap into a convective medium. Under prolonged, low-flux exposure, the protective benefits of 6-mm gaps diminished, revealing possible interactions between air gap size and exposure conditions. This challenges the established thresholds for air gap effectiveness for different exposure conditions. Fabric attributes further influenced TPP, with air permeability showing a positive correlation in multilayer systems due to entrapped air-enhancing insulation, which contrasts traditional findings for single-layer fabrics. Additionally, fabric weight demonstrated dual effects, improving TPP in short, high-flux exposures but reducing it under low-flux, prolonged conditions due to stored heat and thermal diffusivity. These findings underscore the interplay between the study parameters, offering critical insights into the evaluation and design of thermal protective clothing.