Fire from a LH2 tanker

A tanker was travelling on a highway, when a passing motorist notified a problem with the tanker to the drivers. They pulled the unit safely off the highway, went to rear of the tanker and opened the cabinet doors. They found the vapour recovery valve leaking slightly and the dust cap laying on the cabinet floor. One driver closed that valve and the leak stopped.
When the driver reached for the dust cap, the hydrogen ignited causing a flash fire. Both drivers received first and second degree burns.

A company investigation determined that the vapour recovery valve opened due to vibration. The road conditions on that stretch of highway were not particularly good and contributed to the opening of the valve.
This type of leaks had already occurred previously on similar trailers. Therefore the valve was removed from the tanker for analysis and to determine if a different type of valve could prevent accidental opening by vibrations.

The INITIATING cause was the slightly opening of a valve due to road vibration.

The ROOT CAUSE was a design which did not took into account the whole range of mechanical solicitations which the pressure control system of the trailer could experiment when travelling.

vapour recovery valve, dust cap

PHMSA record provides a value for the total damage of only 19 US$. If true, it may only refer to the cost of the valve.

The actions taken by the drivers were enough to stop the leak, but the flash fire shows that they did not take enough precautions

Clearly, the design of the pressure control system did not took into account the whole range of mechanical solicitations which the pressure control system of the trailer could experiment when travelling.

Since this type of leaks had already occurred previously on similar trailers, it would have been better to act preventively, instead of waiting for an escalation, which in this case consisted in the formation of a flammable and explosive mixture.

Moreover, inside a trailer cabinet, small leakages can already cause explosion, if the passive ventilation is not properly designed. This has been explained for example by J. Song et al., Hydrogen leakage and diffusion in the operational cabin of hydrogen tube bundle containers: A CFD study, International Journal of Hydrogen Energy 88 (2024) 986–1002

Finally, the actions taken by the drivers were enough to stop the leak, but the flash fire shows that they did not take enough precautions. Better guidelines or emergency procedures should be able to avoid this case.

The valve was removed from the trailer for analysis and to determine if a different type of valve could prevent accidental opening by vibrations.