Leak from a LH2 tanker

A liquid hydrogen tanker-tractor was travelling on a highway, when the drivers noticed vapour coming from the tank. They pulled the vehicle safely off the road and discovered that the vapour was coming out of the tanker cabinet doors. They opened the cabinet doors and let the vapour dissipated immediately. A vapour recovery valve had opened 1/4 of a turn and the dust cap had vibrated off the vapour recovery line. The drivers tightened the valve and put the dust cap bank on. The leak stopped immediately.
Since the drivers confirmed that the valve and the cap were tightened at the beginning of the trip, road vibration must have caused the valve to open slightly and the dust cap to come off.
The drivers resumed the journey without any further incidents.
Vibrations associated with the piping and cabinet area of this tanker model are being reviewed by company engineers in an effort to eliminate the risk induced by vibrations.

The INITIATING was the slight opening of a valve due to road vibrations.
The ROOT CAUSE can only be assumed, related to design and perhaps material shortcoming.

valve, dust cap, vibrations

The drivers tightened the valve and put the dust cap bank on. The leak stopped immediately.

Vibrations as cause of releases due to partial opening of valves are a recurrent problem reported in the PHMSA dataset during a period between 1990 and 2000. It is probable that later on a better design, better choice of materials and more accurate operative procedures contributed to reduce the frequency of the occurrence.

The PHMSA report states that "Vibrations associated with the piping and cabinet area of this model trailer are being reviewed by company engineers in an effort to eliminate the risk induced by vibrations."