Hydrogen venting from LH2 tanker due to overpressure

While travelling to deliver liquid hydrogen to a customer, a tanker experienced an increase of the internal pressure of the cargo tank. The drivers pulled off the road and at that moment the pressure relief system activated. They operated a diverter valve, transferring the cargo tank to the second redundant pressure relief system. About 150 lbs. (68 kg) of product was lost. The delivery was then continued without further incident.

The INITIAL CAUSE was probably due to over-pressurisation of the LH2 tank, which triggered a hydrogen venting.
The PHMSA does no report if the over-pressurisation was due to degradation of the vacuum shell. From the fact that the journey continued without further incidents, it could be concluded that the over-pressurisation had been caused during loading of the tanker, so that the ROOT CAUSE could be failure to execute the procedure properly.

PRD

The PHMSA reports a loss of 150 lbs, i.e. 68 kg. On the contrary, the PHMSA corresponding column report a loss of only 18.8 LGA, i.e. 5 kg. Also the transport capacity is doubtful, 1437.5 LGA, corresponding to only 385 kg, which is ten time less than the usually transported values.

Less than 100 kg of hydrogen was lost.

The dirvers swithed the tank safety system to the an alternative, redundant one