Thermal protective performance of turnout gear at high heat flux intensity

Abstract

The safety offered by the firefighters’ protective garment has been evaluated by a Thermal Protective Performance (TPP) Test. Current national and international standards recommend a maximum flux of 84 kW m2 ⁄ to be used as an assessment of the fabric, for extreme cases, which is based on a study conducted by Behnke in 1984.

Recently, fire tests, conducted on the modern compartments interior furnishing and construction layout, reported to record an average flux of 200 kW m2 ⁄ , after flashover or during backdraft. To evaluate the risk at this intensity, it is proposed to carry out the fabric test under a higher level of heat flux of 126 kW m2 ⁄ , which represents a typical heat flux at an initial phase of a fully developed fire. The proposed value of 126 kW m2 ⁄ is a step increment from 84 kW m2 ⁄ , beyond that, it is unrealistic to simulate the risk to firefighters.

A custom-built bench-scale setup is designed to vertically test a multi-layered firefighter garment (meta/para-aramid), comprised of the outer shell, moisture barrier and thermal liner. A subjective concept of “critical time” is introduced to examine the safety level with increasing heat flux. A firefighter educated with “critical time” can better evaluate the escape period to a changing fire incident during duty. The critical time subjected to incident flux levels of 40, 84 and 126 kW m2 ⁄ is estimated as 180, 25 and 15 seconds, respectively. The garment performance at 126 kW m2 ⁄ is improved by 32% with the utilization of auxiliary layers of meta-aramid.

The comprehensive analytical analysis showed that; (1) air gap in multiple layered assembly is optically thin; (2) for ∆T = 0 − 1500 ℃, enclosed cavity ranging from 1 – 7 mm is conduction dominant; (3) radiative attenuation in a smoke layer is 4.5 - 8.5%; (4) fabric-skin air gap should be treated as a convective media for the thermal manikin tests and (5) the fabric temporal-thermal properties reflect material decomposition and is essential for the numerical formulation.

At the thermal environment of 84 kW m2 ⁄ and above, moisture effects are insignificant in superficial burn estimates. It is observed that the numerical formulation for the benchtop test lacks spatial burn information. Therefore, a multi-physics numerical model is developed utilizing Gauss-Seidel serial coupling to approximate spatial temperature distribution analogous to thermal manikin experiments and is recommended for the firefighter’s protective garment numerical evaluation.

Date of Award	Feb 2022
Original language	English
Sponsors	Korean Ministry of Public Safety and Security & Korean Conformity Laboratories
Supervisor	Seng-Kwan Choi (Supervisor) & Jianping Zhang (Supervisor)