Thermal Hazards from Electric Vehicle Fires: Experimental Data and Predictive Model
摘要
Fire incidents involving battery electric vehicles (BEVs) are becoming increasingly prevalent. There is presently a dearth of data encompassing heat release rates and the resulting thermal hazards from BEV fires; consequently, there is a need to investigate the severity of those hazards, and to provide guidance on safe separation distances from burning BEVs. A series of experiments were conducted on six different BEVs, having battery capacities ranging from 28 kW h to 91 kW h. Heat release rate (HRR) was measured by mass loss calorimetry, fire size was measured from video recordings, and the spatially varying heat flux to the surroundings of the vehicles was measured using plate sensors and infrared thermography. A solid flame cylinder source model (CSM) was developed to simulate heat transfer from the burning BEVs to their surroundings. Peak HRR was found to range from 4.4 MW to 12.1 MW, and the corresponding flame volumes from 4.7 m3 to 11.1 m3; these measurements were found to be proportional, resulting in an Orloff-DeRis constant of 1054 kW m−3. From this finding, expressions were developed to represent the fire size in terms of the peak HRR, based on Froude scaling. The CSM predictions of heat flux were optimized to the field measurements, and the radiative fraction was calculated to be 0.21. From these results, heat flux to the surroundings of a burning BEV can be predicted given knowledge of only a single parameter: the peak heat release rate of the fire. A quasi-mechanistic model was developed for the minimum safe separation distance to a vertical surface in the proximity of a burning BEV based on safety thresholds corresponding to unprotected individuals, firefighters under emergency operating conditions, and ignition risk to combustible materials. The findings of this study will support future fire hazard analyses and performance-based designs around electric vehicle fire safety.