Hydrogen release from a LH2 tanker

A liquid hydrogen tanker was en route on the highway when the driver noticed a vapour plume in the rear-view mirror. The driver exited the highway and stopped at the first available safe location.
Upon inspection of the cargo, the driver noticed that the pressure in the inner vessel of the double-walled tank had risen above 3.45 barg (50 psig), causing the opening of the safety relief valve.
Later, a thorough inspection revealed a leak in the annular space vacuum relief plate, leading to a loss of vacuum. That failure increased the heat transfer to the cryogenic hydrogen, consequently increasing vaporisation.

The INITIATING CAUSE was a loss of vacuum of he insulation shell of the liquid hydrogen tank. The Pressure Relief Device (PRD) worked as expected.

PRD

This is a near miss. The PRD functioned as expected, releasing the hydrogen vapour in overpressure

No emergency action was necessary: the pressure in the inner vessel of the double-walled tank had risen above 3.45 barg (50 psig), and the safety relief valve opened to release excess hydrogen vapour.

This is an example of a successful mitigation of a mechanical failure. On a liquid hydrogen tank, the function of the Pressure Relief Device (PRD) is to release hydrogen vapour, when the tank internal pressure increase due to the evaporation of liquid hydrogen. The reduction of the insulation capacity of the tank accelerated the evaporation rate and the PRD released more vapour. In this way, the internal pressure of the tank remained below the maximal allowed value.