Abstract: With the continuous increase in the proportion of electric buses in public transportation, the demand for charging and overnight parking of electric buses in indoor parking lots or garages is growing. However, there is little research on the fire hazards of electric buses and their influence to the surrounding buses and the garages. In this paper, a test platform was established, and a full-size burning test of an electric bus with lithium iron phosphate batteries was carried out by inducing fire through overcharging the battery packs. The test results indicate that approximately 3 minutes after the thermal runaway of the lithium batteries and the appearance of an open flame, the flame emerging from the battery compartment caused the upper window glass to break, and the flame immediately entered the cabin of the bus and quickly ignited the interior materials and seats. In the subsequent approximately 10 minutes, the fire spread rapidly from the rear of the bus to the front, resulting in a fierce combustion of the entire vehicle. The temperature and radiant heat flux intensity at a distance of 1 meter around the burning bus could reach approximately 500~685 °C and 55~84 kW/m2, respectively. The high temperature and radiant heat flux intensity might lead to the ignition of the surrounding buses. During the test, the maximum measured temperatures below the garage ceiling were mostly below 1 000 °C, but instantaneous high temperatures at a few locations could reach approximately 1 225 °C. The research results provide beneficial technical parameters for understanding the fire development patterns of electric buses and determining the fire prevention measures for electric bus stations.

Key words: electric bus, lithium iron phosphate battery, overcharging, fire test, fire spread