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

Meng Deng,Agnes Psikuta,Yunyi Wang,Simon Annaheim,René M Rossi

doi:10.1016/j.ijheatmasstransfer.2021.121813

Abstract

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.

Highlights

Firefighters and other industry operators who work in high temperature environments are at risk of receiving skin burn injuries [1]
The previous studies by Udayraj et al and Talukdar et al were suited for comparison with the present study, as these three studies considered the coupling simulation of computational fluid dynamic (CFD) and radiation through the air gap
The effect of a heterogeneous air gap was analyzed in both contact and non-contact fold cases

Summary

Introduction

Firefighters and other industry operators who work in high temperature environments are at risk of receiving skin burn injuries [1]. According to NFPA 1971 [3], firefighters protective clothing are arranged as multilayer systems that include an outer shell, moisture barrier, and a thermal liner. The thermal protection provided by the clothing is given by the fabrics used and the air gaps between clothing and human body, as well as air gaps between fabric layers. These air gaps contribute to the protective performance of clothing, as stagnant air is a good thermal insulator due to low thermal conductivity [4]. In order to evaluate thermal protective performance, both standard benchtop tests and full-scaled manikin test systems were developed, for small-size fabric samples and full-size garments, respectively. Evaluation of thermal protective performance using purely experimental methods is time and cost intensive, as such experiments are de-

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Conclusion