Manual venting from a LH2 tanker in transit

The pressure building valve opened due to vibration from the road, causing the build-up of the internal pressure. The drivers performed a hydrogen venting and re-sealed the valve.

[Zalosh and Short, 1978]

The INITIATING CAUSE was the loosening of a valve due to vibration while travelling.
The ROOT CAUSE could be attributed to a shortcoming in the design of the connections or to the failing to tighten correctly the valve.

pressure building valve

Since the leak could not be stopped locally, The fire brigade decided to drain the whole content of the pallet (246 m3) by gradually opening the valves and by keeping the rack cool.

The rack of the bottles was empty after four hours and the rescue operation ends at noon after the cylinder rack has been checked by an expert from the gas supply company. The residents returned to their homes and the plant's activity restarted one hour later.

A specialized expert emergency support cell estimated the leakage rate at 0.48 kg/s. They also estimated the distance to the Low flammability limit (LFL) about 30 m and the effects of an explosion in the event of delayed ignition of the cloud in the open air at 50 and 20 mbar over-pressure, for respectively 80 and 130 m.

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."