Characterization of Air Gaps and Their Impact on the Thermal Insulation Performance of Multi-layer Firefighter Clothing

Quantitative evaluation of the thickness of the air gap that forms at every location of the human body when wearing firefighter clothing is important for understanding the thermal insulation due to the air gaps, thermal comfort, and mobility of firefighter clothing. The current thermal protection performance of firefighter clothing is mainly determined by bench-scale tests, which are highly repeatable and reliable, but they do not reproduce the wearing conditions such as air gaps. Therefore, it is important to evaluate the thermal insulation performance of garments to correlate the performance of garments with the results of bench-scale tests. Currently, the protective performance against heat and flame of garments can be evaluated for flame with a heat flux of 84 kW/m(2) using a thermal manikin. However, this heat flux is much higher than the typical heat that firefighters are exposed to during firefighting inside a building. Therefore, the purpose of this study was to develop a method to assess the performance of garments based on the results of bench-scale tests for low heat fluxes, which has not been adopted as a performance standard for firefighter clothing. First, the thickness and distribution of the air gaps that form in all locations of a male standard-body manikin when wearing firefighter clothing were quantitatively evaluated by a 3-D body scanner using firefighter clothing of the same size and the same patterning with different thermal liners. Next, bench-scale tests were conducted to reproduce the total thickness and distribution of the air gaps, to evaluate the relationship between the characteristics of the air gaps and the thermal insulation performance against the heat of the firefighter clothing, and the effect of fabric structure of thermal liner on the thermal insulation performance. In addition, a normalization equation for air gap thickness and thermal insulation performance was proposed for universal use of these evaluations, and a method was developed to investigate the details of the thermal insulation effect caused by the air gap and fabric structure of firefighter clothing. This study is very important because it enables firefighters and manufacturers of firefighter clothing to assess the risk of skin burns at low heat fluxes in various locations of the human body based on the results of bench-scale tests and to optimize the thermal insulation design of firefighter clothing effectively at low cost.