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At the time of a vehicle fire, high pressure hydrogen gas in a tank (a high pressure hydrogen gas cylinder) of a fuel cell vehicle (FCV), which is a passenger vehicle, must exhaust through a pressure relief device (PRD) as quickly as possible in order to prevent any accidental bursts by a temperature rise of hydrogen gas in the cylinder. The high temperature region surrounding a vehicle develops when the hydrogen gas is released through a small nozzle to the air directly. Therefore, to suppress the high temperature region, the effectiveness of a diffusion box is considered further. A pressure relief device (PRD) detects differences in temperature of the environment surrounding an FCV on fire and releases hydrogen gas in a tank to the air by which the valve opens when the temperature in the environment becomes high. The PRD also releases hydrogen gas through a nozzle, e.g. installed upward or downward, to the outside of the vehicle. The PRD is required to be installed in an FCV.

Recently, vehicles with high capacity traction batteries for driving such as Ni-MH, lithium-ion have come to be produced in the world. However, the damage has not been clarified in the case of these vehicles fire by a traffic accident or arson. In particular, lithium-ion cells in high temperature environment may cause a thermal runaway which emits smoke or flare. Therefore, it is necessary to examine what kinds of phenomena occur when a vehicle with a lithium-ion battery catches fire. In this paper, the authors studied the situation and temperature characteristics of a hybrid electric vehicle fire to investigate the temperature input to a lithium-ion battery on a vehicle. We assumed an accident that gasoline leaking from other vehicle would be spread under a vehicle and ignited. In a vehicle fire test, gasoline was spread under a hybrid electric vehicle without the traction battery instead of a vehicle with lithium-ion battery, and ignited.