Full-Scale Fire Testing to Assess the Risk of Battery Electric Vehicle Fires in Underground Car Parks

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Abstract Battery-only electric vehicle (BEV) fires have recently emerged as a significant safety concern in modern society, particularly when they occur in car parking spaces, where the consequences can be severe. While relatively few fatalities and injuries are reported, the associated economic losses are substantial. Car park structures present several challenges from a fire safety perspective, including high energy content, confined geometry, and difficulties in detecting and accessing to the fire’s origin due to smoke accumulation in spaces with limited ventilation and exits. This study investigates this fire hazard by conducting a full-scale fire test on a modern BEV in an instrumented test rig that simulates a segment of an underground car park. The data obtained were compared with standard fire curves to assess the hazard’s characteristics and with the data from a companion study to identify differences between BEV fires in underground and surface car parks. The primary difference observed was deflagration venting, which occurred shortly after the initial ignition of combustible gases accumulated beneath the ceiling, lasting until 13 min and 5 s. This phenomenon led to a rapid initial growth of the BEV fire, which burned more intensely for a shorter duration in the semi-enclosed configuration comparted to the open configuration. The enclosed fire recorded an average ceiling-jet temperature of approximately 1100°C and a peak incident heat flux exceeding 225 kW/m2. Additionally, thermal runaway within the lithium-ion battery cells was analysed to understand the adverse effects of the enclosed environment on thermal runaway propagation. This fire testing provides critical insights for developing firefighting strategies including the proper preparation of equipment and the design of fire protection systems. The principal findings could inform tactics for mitigating unforeseen fire risks and contribute to revisions of fire safety regulations.