Effect of Phase Change Material Melting Points on Thermal Protection Behavior of Firefighters’ Turnout Gear

Abstract: Between 2018 and 2022, an average of 21,955 fireground injuries occurred annually in the United States [1]. Among these, thermal burns were one of the most common injuries, accounting for approximately 10% of fireground incidents [1]. This underscores the urgent need to improve turnout gear technology to provide better thermal protection for firefighters. Phase change materials (PCMs) can absorb substantial amounts of latent heat during the melting process while maintaining a constant temperature, which makes them ideal for enhancing thermal protection. Our proposal aims to leverage this protective property integrating PCM segments into turnout gear to improve its thermal protective performance (TPP). This study involves numerical simulations, which will serve as a foundation for future experimental designs and testing protocols. While existing numerical studies on fire protective clothing typically utilize one-dimensional (1D) models [2], there is a lack of comprehensive three-dimensional (3D) models that are capable of assessing the overall thermal performance of turnout gear on the human body. The goal is to determine the optimal PCM melting temperature range for turnout gear, maximizing thermal protection for firefighters. MethodWe conducted 3D heat transfer simulations using COMSOL Multiphysics (COMSOL, Inc., Burlington, MA 01803, USA). To accommodate firefighters' movements and activities in fire scenes, PCM was broken into multiple segments covering the main body while avoiding joints. The bioheat transfer module was utilized to model the human body's thermal regulation. The equivalent heat capacity method was employed to simulate the phase change process. Adhering to the guidelines of the National Fire Protection Association (NFPA 1971, Standard on Protective Ensembles for Structural Fire Fighting and Proximity Fire Fighting), heat fluxes of 83 kW/m2 and 8.3 kW/m2 were applied to the outer surface of turnout gear to replicate flashover and hazardous conditions, respectively [3,4]. These heat fluxes represented the radiant/convective heat sources in fire scenes. The 3.0-mm-thick PCM segments were utilized based on the prior research by our team [5]. We investigated the effects of different melting points of PCMs at various locations in clothing fabrics on the thermal protection behavior of PCM-integrated turnout gear. PCM melting points in the range of 40°C-200°C were evaluated. Three PCM locations-1 mm, 2 mm, and 3 mm beneath the outer shell surface-were investigated to explore the effect of PCM location on the optimum melting temperaturesResultsResults show that a PCM melting temperature range of 50°C-70°C provides optimal protection for the human body, extending the time it takes to reach second-degree burns from 18 seconds to approximately 45 seconds. This range is particularly effective because it aligns with the threshold for second-degree burns (approximately 60°C), helping to maintain skin temperature at or below 60°C for extended periods during fire exposure, thereby reducing the risk of severe burn injuries. Additionally, positioning the PCM closer to the inner surface of the clothing enhances its thermal protective performance.ConclusionIncorporating PCM segments with melting point of 50°C-70°C into firefighter turnout gear could increase the time it takes for skin to reach the threshold for second-degree burns by around 1.5 to 3 times, compared to traditional gear without PCM technology. The insights gained from 3D modeling provide a valuable foundation for developing next-generation turnout gear for firefighters.DisclaimerThe findings and conclusions in this abstract 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). Mention of any company or product does not constitute endorsement by NIOSH, CDC.References[1] Campbell, R. Firefighter Injuries on the Fireground. NFPA Research, July 2024. Available from: https://www.nfpa.org/education-and-research/research/nfpa-research/fire-statistical-reports/patterns-of-firefighter-fireground-injuries[2] Fonseca, A., Neves, S.F., Campos, J.B.L.M., 2021. Thermal performance of a PCM firefighting suit considering transient periods of fire exposure, post-fire exposure and resting phases. Applied Thermal Engineering 182, 115769.[3] NFPA 1971, Standard on Protective Ensembles for Structural Fire Fighting and Proximity Fire Fighting, 2018.[4] 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.

Keywords: firefighters' turnout gear design, phase change material, occupational safety

DOI: 10.54941/ahfe1006270

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