Effect Of Moisture Content On Heat Protection Performance Of Fire - Resistant Fabrics

Protective clothing and textile-based equipment are critical for firefighters to ensure their safety and health. Ineffective protection at a fire scenario with multiple hazards can cause injury and fatality among victims and firefighting personnel. Current firefighter protective clothing is composed of multilayer fabric system. The outer shell fabrics usually inevitably get wetted in the process of performing tasks, and at the same time, sweat from firefighters may increase moisture in the inner layer. In this study, two kinds of outer shell fabrics (aramid IIIA, aramidl313 and flame retardant viscose blended fabric), and three kinds of thermal liner fabrics with different thicknesses were selected. Three wet conditions were simulated which are outer shell fabric, thermal liner fabric and both. A modified thermal protective performance tester (TPP) was applied to evaluate the thermal protective performance provided by these wetted fabrics, the second degree skin burn time was predicted and absorbed energy indexes were also calculated. The effect of moisture contained in the different layers and distribution on heat and moisture transfer were explored, and the mechanism associated with heat and mass transfer was analyzed.Under the intensity of 15.4 kW/m2 heat source, single, doubled, multilayer fabrics’exposure time are tested with the exposure time of 40s,60s,80s. The results showed the outer shell fabrics were wetted, the predicted second degree skin burn time of single layer and double layer fabric with different moisture contents tends longer than dry, and the difference exhibits as high as 63.8%. Additionally the second degree burn time shows negatively linear correlation with absorbed total energy. The same trend was found in multilayer fabrics with aramid 1313 and flame retardant viscose blended outer shell layer, but a lower rate of 26.3% was revealed. For the case of wetted thermal liner fabric, the predicted second degree skin burn time for all samples are lower than dry, the minimum was reduced by 31.0%, and the tendency of second degree burn time changed from decrease to increase when moisture content increased. For the condition of outer and thermal liner fabric both wetted, the predicted second degree skin burn time decreases first and then increases with the increase of moisture, and when the actual moisture content is high, the second degree burn time can be higher than dry and it shows difference as high as 12.8%.Under the intensity of 84.3 kW/m2 heat source, the effect of stored thermal energy on the thermal protective performance in different moisture contents is explored in this study. The exposure time of single layer, double layer and multilayer fabric was 5s,8s and 10s respectively, and the recording time was 40s,70s and 70s respectively. When outer shell fabrics were wetted, the absorbed energy of single and double layer fabric with different moisture content tends shorter than dry, and decreased with the increase of moisture. For multilayer fabrics, the change of second degree skin burn time is more complicated, and the physical and surface properties of the fabric can be changed obviously. For the case of wetted thermal liner fabric, when same amount of water was added, the smaller of thermal liners’ thickness, the higher of the actual moisture content, the more positive effect on fabric. Performance in both wet conditions, the outer layer moisture has a positive effect on the thermal protective performance of the fabric.