Release from a LH2 tanker

A truck carrying 6,000 gallons of liquid hydrogen (1,600 kg) experienced an accidental loss of confinement while travelling.
The truck driver noticed a white vapour cloud coming from the rear of his trailer and an increase in the internal vapour pressure gauge. he decided to stop the vehicle in an area he considered safe. The hydrogen did not ignited, only a plume of condensing water vapour was visible.
The firefighters were alarmed 10 minutes later. They decided to let the hydrogen to be released and to dissipate into the atmosphere. They closed the motorway and evacuated the neighbourhood. During the emergency, it became clear that the tank's inner lining had started failing and that the external shell was in direct contact with the liquid or cryogenic hydrogen.
This natural release process took 14 hours. The firefighters decided to call off the evacuation and reopened the motorway when the truck company experts communicated that they had released as much hydrogen as possible, and declared the situation safe.
Since the remaining liquid hydrogen in the tank had started building pressure in the tank, the tank was moved to an area considered safe, far away from power lines, which represent a fire risk, because of the increased possibility of ignition. The area was cleared and the truck was left there for the time required to declare the situation definitively safe.
[Note of the event validator: although the source does not say it, it can be assumed that before moving away the truck the relief valve was closed again, and that this caused the increase of internal pressure noticed. It is further logic to assume that after the tank was moved to the area considered safe, the valve was opened again to allow for further release and diffusion of the hydrogen still inside. However, it could exist an alternative explanation for the increase in pressure: the firefighters used water to warm up the tank and accelerate the venting of the residual hydrogen. This could have caused the freezing of the relief valve and blocked the venting].

INITIATING CAUSE was the unexplained loss of vacuum between the inner vessel and outer vessel of the LH2 tank on the trailer, due probably to a weld failure.

ROOT CAUSE: it is impossible to inderify a root cause different than a material degradation. This could be induced by a design fault or a damage occurred during operation.

cryogenic tank

The truck was transporting hydrogen from the place of production to the place of use, along a approximately 1600 km long route. The incident happened at a location at 65 km from destination.

The voluntary evacuation of a neighbourhood, including closure of the school, and closure of roads, which caused a gigantic traffic jam.

Critical technical information is missing in the event description, hindering the extraction of specific lessons. For example, the pressure relief system of the cryogenic tank is not provided, and therefore it is not possible to assess the decision by the driver to open a relief valve to mitigate the consequence of pressure oscillation in the tank.

The following general lesson can be attempted:
Despite the correct handling of the emergency by the first responders, they deployed a large amount of precaution measures, with the evacuation of the neighbourhood, an extensive closure of the local road transport and the intervention of the transport company engineers and governmental experts.
1. This is a sign that formalised procedures on how to handle massive transport of hydrogen were missing or were not enough specific. The knowledge on how to handle these cases should not remain inside the company perimeters, but broadly shared and agreed with local authorities and the first responders.
2. As in the case of transport of hazardous substances, these procedures should also consider the specific routes used by drivers, and minimise the need to drive through densely populated areas.