Full emptying of a LH2 tank

A liquid hydrogen tank vented its entire contents, due to the premature activation (rupture) of the burst disc. The hydrogen was discharged to atmosphere via the vent stack of the tank.
Venting was very loud and formed a condensed moisture cloud visible from the top of the stack. It lasted approximately 5 minutes. Liquid air was also visible coming off the stack.

The fire brigade evacuated the area and checked its safety. No injuries.

The INITIATING CAUSE was an unexplained failure of the pressure release device below its pressure activation setting.
The mitigating safety system in place functioned as designed. Nothing is known on the possible cause of the disc failure.

burst disc,
tank

On-site staff called the fire department, which arrived promptly and evacuated the area. Normal operations resumed after the fire department was able to determine there were no unsafe conditions.

In this event the safety systems functioned as designed.
It also showed that liquid air can form during a cryogenic gas release. It can then fall off the vent stack, carried by the high flow of cold gas produced by the rupture of the disc.
Liquid air may also splash off flanges or other pieces and will cause a small vapor cloud as it falls from the stack. During the event, falling liquid air was mistaken for liquid hydrogen.

The tank had a second (redundant) safety system, which was put into service and the tank was returned to normal operation. Both rupture discs were replaced and the tank was inspected.