Overloading of a LH2 tanker in transit

A liquid hydrogen tanker had been slightly overloaded. This forced the drivers to performed a manually venting releasing 5000 cu. ft. of hydrogen (approximately 12 kg).

[Zalosh and Short, 1978]

The INITIATING CAUSE was the overpressure developed Iin the tank while en route.
The ROOT CAUSE was that the filling procedure had caused an overfilling of the tank.

manual vent

11:00 The tanker leaves a SEVESO-rated industrial gas production plant and tips over into a ditch. First responders set up a 200-m safety perimeter and evacuate the neighbours
11:30 to 14:00, the explosimeter measurements conducted at the degassing chimney outlet, at a height of 3-4 m, remain positive
During the emergency intervention, power and phone lines were cut, and the plant had to stop all production and evacuate its personnel.
At 14:30, fire-fighters extend the safety perimeter to 600 m and lift the cistern, allowing technicians with the transport company to access the cistern control box. The hydrogen degassing valve is closed.
17:30 The tanker is placed back on the road and escorted into the industrial gas production plant, which was equipped with a degassing unit

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."