Effects of Air Gaps on Heat Transfer and Energy Distribution in Protective Fabrics for Firefighting

ABSTRACT This research investigates the influence of air gap (AG) thickness and boundary conditions on the thermal storage and release characteristics of firefighter turnout gear. The study focuses on how AGs modify heat transfer mechanisms and affect energy distribution within fabric systems. By simulating a low‐radiation environment, the effects of varying AG thicknesses on stored energy, heat absorption, and cooling rates of fabric layers are systematically analyzed. The findings suggest that a closed AG with a thickness of 6.4 mm enables the fabric system to store 24% more energy at its center in comparison to fabric systems devoid of an AG, with the total stored energy reaching 138.5 kJ/m 2 . Furthermore, AGs exceeding 6.4 mm have been shown to significantly enhance lateral energy transfer, thereby improving energy uniformity across layers. Additionally, an increase in AG thickness from 6.4 to 12 mm has been observed to slow the cooling rate at the thermal liner (TL) surface by 18.7%. In open AG conditions, convective effects dominate, enhancing heat dissipation and storing energy more evenly. Furthermore, a transition from a closed to an open AG (≥ 6.4 mm) results in a 14.2% decrease in energy retention and a reduction in temperature gradients ( p < 0.01). These findings offer critical insights into the optimization of the thermal protective performance of firefighter turnout gear, emphasizing the importance of AG thickness and boundary conditions in thermal regulation strategies.