Thermal–fluid analysis of air gaps beneath thermal protective clothing through integrated CFD–thermophysiology modeling

This study presents a novel thermal–fluid analysis framework that fully integrates computational fluid dynamics with human thermophysiology to evaluate the influence of air gaps beneath thermal protective clothing on burn risk during flash fire exposure. The proposed fabric–air gap–human body model incorporates metabolic heat production and blood perfusion across multi-layered human tissues, effectively capturing the interactions among airflow, heat transfer, and thermal injury mechanisms. Validation against experimental data demonstrated high predictive accuracy for both skin temperature and heat flux. Simulations were conducted for various air gap configurations, varying in thickness (6.4 mm–12.5 mm), orientation (horizontal or vertical), and fabric wrinkle severity to represent realistic wear conditions. The results indicate that incorporating thermophysiological features accelerates skin burn onset by 15 %. Increasing air gap thickness improves thermal protection; for example, thicker air gaps reduced skin temperature by over 10 °C within 10 s of exposure. Vertical air gaps consistently provide superior protection by promoting buoyancy-driven displacement of heated air and mitigating convective heat transfer to the skin. In contrast, fabric wrinkles significantly compromise protective performance by increasing both radiative and convective heat fluxes. Overall, these findings provide practical guidance for enhancing the design of thermal protective clothing by ensuring sufficient air gap thickness, minimizing fabric wrinkling, and facilitating vertical ventilation to mitigate burn risk.