Fire on a hydrogen bus fleet

A fire started in the night on one of the fuel cells and hydrogen bus of a garage of a public transport company. There were seven buses parked on a parking lot outside. 6 buses were destroyed by the fire and the 7th, the last in the row, was severely damaged.
The fire brigades extinguished the fire 6 hours later. There was nobody on the location at the start of the event and nobody was injured. A nearby hydrogen refuelling station, located 150 meters from the incident, was not affected.

The thermally activated pressure relief valves worked as expected and the hydrogen tanks did not failed by overpressure. The noises heard by residents during the night were due to the release of the tanks and the bursting of tires due to the heat of the fire.

The cause of the fire is unknown and under judicial investigation. From preliminary observations, the authorities tended to exclude the possibility of arson.
The evidences provided by the surveillance video indicated a probable electrical origin of the fire, originated at the front of the bus, in the cabin. The electrical battery is also located at the front, on the roof. There is no presence of hydrogen there. The battery may have had a role in the start of the first propagation of the fire. In any case, the battery also caught fire, which propagated then to the rest of the bus. None of the high-pressure tanks of the hydrogen storage system failed due to overpressure, indicating that all the pressure relief valves activated as expected.

batteries, bus

DESCRIPTION OF THE BUS
All seven buses were of the same brad. Their power system consisted of:
(i) A Li battery of 36 kWh, installed on the roof, at the front.
(ii) A hydrogen storage system with a of about 40 kg at 350 bar, installed on the roof, at the rear.

Total loss of the vehicles, which costed of 4.9 million euros.
280 kg of hydrogen was lost.
Atmospheric checks carried out within a 500-meter radius were negative for air pollution. Additionally, the fire had no impact on the drinking water supply.

In this incident, 6 buses were destroyed by a fire originated on one of them. A 7th bust was heavily damaged. Additional protective measures could be used to prevent this domino effect.
To avoid that the fire propagates from one bust to another, the prescribed minimal parking distance between buses should be increased. For conventional (diesel) buses, 5 meters distance between buses is it is recommended to prevent domino effects in case of fires. In case of hydrogen buses, a fire could thermally activate the pressure relief devices (PRD) of the hydrogen storage system, with possible ignition and jet flame. Although the venting direction of the PRD is vertically upwards, thus not directly affecting neighbouring buses, additional effect, such as delayed ignition or secondary fires should be considered when assessing the parking distances.
Moreover, it should be explored the improvement of the buss design, bus to prevent the propagation of an electrical or battery fire to the rest of the bus structure.