Effect of moisture content on thermal protective performance of fabric assemblies by a stored energy approach under flash exposure

Firefighters wearing protective clothing perspire profusely in the process of performing their duties, and sweat increases moisture in the inner layers of multilayer protective clothing. Also, the outer shell fabrics inevitably become wet. In this study, two kinds of outer shell fabrics (aramid IIIA fabric and aramid 1313 and flame-retardant viscose-blended fabric) and three kinds of thermal liner fabrics with different thicknesses were selected. Two wetness conditions were investigated to simulate the sweating in thermal liner fabric with or without the wet outer shell fabric. A modified thermal protective performance (TPP) tester was employed to explore the effects of moisture and its distribution on stored thermal energy developed in six fabric systems and on TPP under flash exposure. Pearson correlations were established to analyze the relationships of the fabric systems' thickness and second-degree burn time, and of absorbed energy and second-degree burn time in different configurations. The statistical analysis from these obtained data indicated that the thickness of fabric systems had no significant correlation for second-degree burn time (p>0.05), but the absorbed energy exhibited a strong relation (the lowest R-2 value could reach 0.8070 and p-values were all much less than 0.05). Performance results for the wet thermal liner indicated that the negative impact on thermal protection reached the greatest degree in 15% wetness, but in some extreme situations (100% wetness), the performance was improved (the maximum increase can achieve 116.2% over performance in dry condition). However, the existing moisture in the outer shell showed a positive effect. These findings will enable the engineering of textile materials that achieve high performance protection from thermal hazards and give some guidance to firefighters during operations.