3D Numerical Simulation for Thermal Protection of Phase Change Material-Integrated Firefighters’ Turnout Gear
Authors: Xu Susan , Pollard Jonisha , Zhao Weihuan 
Published: June 2024

Firefighters often work under dangerous and harmful conditions, which could cause unexpected accidents, injuries, and deaths. There were 19,200 injuries that occurred on the fireground in the United States in the year 2021, and more than 10% of these injuries were caused by burns and thermal stress [1]. The current NFPA 1971 (Standard on Protective Ensembles for Structural Fire Fighting and Proximity Fire Fighting) requests that firefighters’ turnout gear textiles meet the minimum requirement of a thermal protective performance (TPP) rating of 35, equating to 17.5 seconds until second-degree burns occur in a flashover situation [2]. Notably, exposure to a high-temperature environment could be much longer than a few seconds when firefighters conduct rescue tasks at a fire scene. Hence, research is needed to explore novel turnout gear technology that can significantly enhance thermal protection for firefighters. Phase change materials (PCMs) can absorb large amounts of latent heat while maintaining a constant melting temperature. We use this phenomenon to incorporate PCM into turnout gear to enhance the TPP. Numerical simulations were performed in this work which can guide future experimental design and testing to save time and effort. Currently, a three-dimensional (3D) turnout gear-equipped human thermal model is unavailable. Therefore, this work is the first 3D numerical study to explore (1) the thermal protection improvements of firefighters’ turnout gear by using PCM segments under flashover/explosive and hazardous conditions, and (2) the minimum amount of PCM required to enhance the thermal protection without significantly increasing the weight of firefighters’ turnout gear. Methods3D heat transfer simulations were performed through COMSOL Multiphysics (COMSOL, Inc., Burlington, MA 01803, USA). To maintain firefighters’ activities and movements in the fire scene, PCM was broken down into several segments to cover the main body but avoid joints. The blood circulation effect in the body was considered as a bioheat source in the model. The equivalent heat capacity method was used to simulate the phase-changing process. The heat flux applied at the outer surface of turnout gear (mimicking combined radiant and convective heat sources at the fire scene) was 83 kW/m2 for flashover/explosive conditions and 8.3 kW/m2 for typical hazardous conditions according to the current NFPA 1971 standard [2,3]. Various PCM segment thicknesses were studied to determine the minimum amount of PCM required to achieve sufficient thermal protection.ResultsThis study found that the 3.0-mm-thick PCM segments with a melting temperature of 60°C can extend the time for the skin surface to reach second-degree burn injury (60°C [3]) by 18 seconds and 52 seconds under flashover/explosive and hazardous conditions, respectively. Moreover, thinner PCM segments, i.e., 1.0-3.0 mm thickness, could also remarkably mitigate the temperature increase on the skin surface while reducing the added weight of turnout gear.ConclusionThe PCM segments could increase the time for the skin surface to reach second-degree burn injury by around 2.0 times compared to conventional firefighters’ turnout gear with no PCM. The 3D modeling results can be used to develop a next-generation firefighter turnout gear technology. DisclaimerThe findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the National Institute for Occupational Safety and Health (NIOSH), Centers for Disease Control and Prevention (CDC). References[1] Campbell, R., Hall, S., United States firefighter injuries in 2021, NFPA Res. December 2022. [2] NFPA 1971, Standard on Protective Ensembles for Structural Fire Fighting and Proximity Fire Fighting, 2018.[3] Coletta, G.C., Arons, I.J., Ashley, L.E., Drennan, A.P., 1976. The Development of Criteria for Firefighters' Gloves Volume II: Glove Criteria and Test Methods, Contract No. CDC-99-74-59, February 1976.