Influence of the Air Gap in Firefighter Personal Protective Equipment on Skin Temperature in Pre-Flashover Thermal Exposures

Abstract

Exposure to pre-flashover thermal conditions is typically considered as routine for many structural firefighters, and these low level thermal exposures pose a threat of burn injury. Skin burns occur as a result of prolonged exposure within these environments, and this hazard must be addressed to reduce the number of firefighters that fall victim to thermal injury. The incorporation of an air gap within firefighter personal protective equipment (PPE) was explored in this work to gain an understanding of the influence of the air gap on skin temperature in pre-flashover thermal exposures. The relationship between the air gap size and skin temperature was investigated both through experimental and numerical means. Experimental testing was conducted to measure the temperatures at a representative skin layer positioned underneath firefighter PPE with an incorporated air gap subject to thermal exposures consistent with pre-flashover conditions. Material property testing was conducted for the same PPE-air gap assembly and the effective thermal properties for the bulk assembly were input into a computational model constructed with Fire Dynamics Simulator (FDS) to predict the temperatures at the equivalent skin position. The results show that the presence of an air gap within firefighter PPE prolongs the time to critical skin temperatures, and reduces the maximum temperatures reached at the skin surface. As the air gap thickness increases, the time to burn injury increases and the maximum temperatures at the skin decrease for both thermal exposures. These findings fundamentally suggest that the larger the air gap, the more thermal insulation is provided for the firefighter. Based on comparisons of the conduction-driven model with the experimental temperature data, the model was demonstrated to be accurate to within 15% of the experiments in the prediction of burn injury times for low heat flux exposures and small air gap sizes. The agreement of the model also confirms that the heat transfer is conduction-dominated for air gap sizes leading up to 6.35 mm, and transitions to alternative modes of heat transfer among larger air gap sizes.