Manual venting from a LH2 tanker in transit

A liquid hydrogen tanker was returning empty to the base, when a pressure build-up forced the drivers to perform a manual venting.

[Zalosh and Short, 1978]

The INITIATING CAUSE was the over-pressurisation of the tank when returning empty of liquid hydrogen after delivery.

The ROOT CAUSE was probably a small shortcoming in the execution of the procedure for stabilisation of the tank pressure after delivery.

manual vent

Police stopped the highway traffic in one direction for several hours, causing a queue up to 7 km. A special company 'pumped out' the hydrogen from trailers (it is unclear how this operation was performed. Considering the lack of details of the sources, it could have as well consisted in simple controlled release in the environment).

This event could be considered almost a near miss. The safety procedure (manual venting) preventing the pressure to increase beyond the allowed value functioned as planned, avoiding uncontrolled hydrogen release.

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 to transport , transfer and store hydrogen outdoors away from occupied areas."