Operation Limits of Firefighter Protective Ensembles in Non-Flaming, Pre-Flashover Exposures

High heat flux tests at short exposure times are beneficial in estimating thermal protection when exposed to direct flame impingement, but evidence from the field has shown that firefighters are experiencing thermal burn injuries in fire environments that are thought to be ordinary exposures over a longer time period. The current study uses a novel approach to measure the thermal response of two different, three-layer structural firefighting protective ensembles exposed to a predominantly convective, low-level heat flux over a longer period of time in a controlled environment. In a series of experiments, representative personal protective clothing assemblies were exposed to ambient temperatures ranging from 100°C to 300°C, corresponding to the ambient temperatures a firefighter may be exposed to during a structure fire. The temperature rise up to 55°C, measured by a copper slug calorimeter and protected by the PPE samples, was chosen as an upper bound and compared to currently accepted thermal operating classes for firefighters. Results show that the time for reaching the 55°C benchmark was approximately 1000s at 100°C to approximately 100s at 300°C. Using the Heat Transfer Index (HTI) method, loss of insulation performance of the samples was indicated at exposures above 100°C. An exponential decay relationship was observed between the time for the copper calorimeter to reach 55°C and the exposure temperature which can provide insight into firefighter safe operational times at exposure temperatures not included in this study.