Release from a LH2 tanker in transit

Due to a loss of confinement of the inner shell of the liquid hydrogen tank, the vacuum of the external shell was destroyed. The reduced thermal insulation capacity of the shell caused evaporation of the liquid hydrogen resulting in pressure build-up and venting of hydrogen gaseous through the pressure relief valve.

[Zalosh and Short, 1978]

The INITIATING CAUSE was the leak of liquid hydrogen into the thermal insulation shell of the tank, due probably to a crack.
The ROOT CAUSE is unknown.

vacuum thermal insulation

During the fire-fighters' response, water from the plant's collector pipe was diverted to the site's emergency basin until official observation of the absence of amine (i.e. a pollutant characteristic of shop operations).

Zalosh et al (see references), concluded their analysis of hydrogen transportation accidents till 1978 with the following conclusions:
"Finally, an encouraging aspect of the transportation incident compilation is that 71% of the hydrogen releases did not lead to an ignition. ... The relatively few ignitions may be due to either to lack of ignition sources or to the rapid dispersal of hydrogen into the atmosphere. In any event, the accident data provide further incentive t o transport , transfer and store hydrogen outdoors away from occupied areas."