Numerical investigation of the effects of heterogeneous air gaps during high heat exposure for application in firefighter clothing

•Modeling of heat transfer in firefighter clothing considering heterogeneous air gap.•Systematic investigation of various air gap configuration that mimic realistic one.•Considering heterogeneous air gap enable a more realistic assessment of performance. For accurate prediction of thermal protective performance of firefighter clothing, a realistic assumption about the heterogeneous distribution of air gaps underneath the clothing is necessary. In this study, a numerical model of heat transfer through realistic heterogeneous air gaps under flash fire exposure was developed. First, the models of heat transfer and fluid motion were validated with data from scientific literature. The verified model was further developed and then used in a subsequent parametric study to quantify effects of heterogeneous air gap distributions. The results revealed that the difference in terms of heat transfer and skin burn injuries between heterogeneous air gaps with contact folds and equivalent homogeneous air gaps was greater than that between heterogeneous air gaps with non-contact folds and equivalent homogeneous air gaps. Fold aspect ratios showed a more prominent impact on heat transfer and skin burn times in the case of contact folds compared to non-contact folds. Exposure times to skin burn were continuously prolonged with increasing air gap thickness from 6.4 to 19.1 mm for homogeneous air gaps and heterogeneous air gaps with non-contact folds, while for heterogeneous air gaps with contact folds, there was an optimum air gap thickness around 12.7–15.9 mm.