Optimization of the Size and Distribution of Phase Change Material (PCM) in Firefighters’ Turnout Gear
Authors: Xu Susan , Pollard Jonisha , Zhao Weihuan 
Published: November 2024

In 2022, approximately 65,650 firefighter injuries were recorded on duty, marking an 8% rise from the 2021 tally of 60,750 injuries [1]. The majority of these injuries took place during fireground operations, with burns and thermal stress accounting for about 15% of such incidents [1]. Given this problem,a pressing need exists to advance turnout gear technology for better thermal protection for firefighters. Our proposal involves integrating phase change material (PCM) into firefighters' turnout gear to enhance its protective capabilities through utilizing the large amounts of latent heat of fusion. Our study involves numerical simulations, serving as a guide for future experimental designs and testing protocols to streamline efforts and time investment. Notably, existing numerical investigations on fire protective clothing predominantly employ one-dimensional (1D) models [2], lacking a comprehensive three-dimensional (3D) turnout gear-equipped human thermal model to assess the overall thermal performance of turnout gear on the body. Therefore, our study represents a pioneering effort, being the first 3D numerical analysis aimed at determining the optimal dimensions of PCM and strategically placing PCM segments within the turnout gear to maximize thermal protection coverage while minimizing the PCM quantity required. MethodsWe 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 divided into multiple segments covering the main body while avoiding joints to maintain firefighter body movement and activities. The bioheat transfer module in COMSOL 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 [3], 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 [4]. These heat fluxes represented the radiant/convective heat sources in fire scenarios. Utilizing 3.0-mm-thick PCM segments with a melting temperature of 60°C, as established in prior research by our team [5], we investigated three different sizes of PCM segments and their corresponding distributions within the turnout gear. These sizes included small (1"-2") segments ranging from 4 to 12 pieces, medium (2"-4") segments with 2 to 6 pieces, and large (4"-6") segments with 1 to 2 pieces distributed in each thermal zone of the human body. Using a larger number of small PCM segments can maintain the same latent heat capacity as the large PCM segments but have more efficient heat absorption.ResultsThe size of PCM segments did not significantly affect the thermal protection time as long as there were enough PCM segments to cover the area. These segments proved effective in reducing temperature increases in areas not directly shielded by PCM segments during periods of intense heat.ConclusionThis computational study has demonstrated that the segment size of PCM has minimal impact on the overall thermal protection efficacy of PCM-integrated firefighters’ turnout gear, provided there is sufficient coverage of PCM pieces within the gear. However, smaller PCM segments are recommended for enhanced flexibility and comfort in firefighters’ turnout gear. The findings from 3D modeling can serve as a foundation for the advancement of next-generation firefighter turnout gear.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). Mention of any company or product does not constitute endorsement by the NIOSH, CDC