Venting due to overpressure of a LH2 tanker

A liquid hydrogen tanker was travelling back to the base terminal after having delivered at a customer site. Almost arrived to the end of the journey, the tanker started to vent. The drivers pulled over and checked pressure gauges, reading a 55 lbs value (probably 3.8 barg). The hydrogen vapour vented for about 1 minute and stopped when the pressure was at 38 lbs (probably 2.6 barg). The drivers proceeded to the base terminal. Once there, the inspection determined that the tanker had lost insulation capacity to vacuum deterioration.
The tanker was warmed up with warm gas and purged with inert nitrogen and sent to another company site for testing. There they found that the external shell of the tank was not able to maintain the required vacuum quality. The tanker was then transported to company headquarter for further diagnosis and repair before returning to service.

INITIAL CAUSE was the deterioration of the vacuum between the inner vessel and outer vessel of the LH2 tank on the trailer, wit consequence loss of thermal isolation ability and over-pressurisation of the tank.

ROOT CAUSE: additional information of the reasons for the loss of vacuum is not provided.

vacuum thermal insulation

The tank was almost empty after delivery. The capacity is given in GCF, which probably does not refer to the max load (capacity) ,
The capacity is given in GCF, which probably does not refer to the max load (capacity) , but to the hydrogen gas left in the tank before venting. .

A loss of 1130 GCF is reportd, which probably corresponds to 2.9 kg

The fire brigade cooled the cylinders with by nebulized water. At the same time, they evacuated two persons that were working in the vicinity and closed the road to the traffic.
A thermal camera allowed to assess the temperature of the cylinders, therefore assisting the cooling of the hot spots.
The last operation was the emptying of the of the cylinders under jets of nebulized water.

This incident is very similar to other, such as the HIAD_070, which attributed to road vibrations the opening of the vapour return valve.