Fire on a hydrogen vehicle

This incident happened during a test of a hydrogen engine prototype vehicle, equipped with on-board liquefied hydrogen storage. The hydrogen gas leaked from a hose joint of a flexible pipe in the engine compartment. The leaked hydrogen ignited and a fire developed, involving also brake oil.
The engine test, which consisted in a real run of the vehicle, had started 6 hours before the incident. The driver left the vehicle when he saw smoke coming out of the engine compartment. Nobody was injured. The fires was extinguished with water and dry chemicals extinguishers.

INITIATING CAUSE: the fastening part of the flexible pipe connected to the engine loosened due to engine vibration, causing hydrogen gas to leak .

IGNITION CAUSE: The leaked hydrogen ignited because it came in contact with high-temperature objects, such as the exhaust manifold and turbocharger of the 700 and 900 engines. Nearby flammable materials (brake oil) also burned, causing smoke.

ROOT CAUSE: they could be related to error during installation (incorrect fixing of the hose) and/or to a design problem (underestimating the intensity of vibrations).

hose, pipe, engine

6 hours before the incident occurred, a test run had started.

DESCRIPTION OF THE VEHICLE
The vehicle was had an internal combustion engine, fed by an on-board liquefied hydrogen fuel storage.
The vehicle fuel supply system pressurised the liquefied hydrogen by means of a pump and vaporized it in an evaporator. The hydrogen gas was then directly injected into the engine via a pressure chamber.
The pressure chamber is designed to store a fixed amount of hydrogen gas in order to accommodate fluctuations in fuel consumption.

No injury. No damage.

Dismountable joints and connections represent components which are particular prone to leak hydrogen. When they are unavoidable part of a hydrogen supply systems, specific design measures have to be taken to minimise leakages and to mitigate the effect of them. Therefore:
(i) The piping should be designed to facilitate the tightness of joints.
(ii) Hot surface should be avoided in the surrounding of joints.
(iii) Vehicles vibrations should be characterised and appropriate measures must be taken to prevent fatigue damage of piping and loosening of fastening parts. When using flexible tubes for piping, it is more effective to use bellows tubes, which have better vibration resistance than spiral tubes. Regarding measures to prevent loosening of fastening parts, the selection and fastening management of joints around compressors in liquefied petroleum gas vehicles, natural gas vehicles, fuel cell vehicles, and stations that supply each fuel can be used as a reference.

(1) Change in piping layout
1.1 Hydrogen piping should not be placed near high-temperature objects.
1.2 Fastening parts of hydrogen piping should not be placed near high-temperature objects.
(2) Installation of exhaust route (duct)
2.1 Since it is unavoidable that flexible tube and the engine are connected by means of a fastening part, in the unlikely event that hydrogen gas leaks from the fastening part, a vent duct will be installed to exhaust the gas in a safe direction.
(3) Improved fastening management
3.1 The type of hose fitting was changed from a cone and thread type to a metal gasket type. The effectiveness of the change in fitting type was confirmed by vibration testing (the metal gasket type showed no loosening or leakage even after more than 1 million rotations. The cone and thread type showed loosening and leakage after 60,000 rotations).
3.2 A safety cover was created and installed to prevent loosening and improve leak detection capabilities.