A rupture disc blew on a 20,000-gallon liquid hydrogen tank, causing the vent stack to exhaust cold gaseous hydrogen. Emergency responders were called to the scene. To stabilize the tank, the remaining hydrogen was removed from the tank except for a small volume in the heel of the tank that could not be removed manually. The tank vacuum was lost. Firemen sprayed the tank with water and directed a stream onto the fire exiting the vent stack. The water was channeled directly into the open vent stack, and the exiting residual hydrogen gas (between -423 F and -402 F) caused the water in the vent stack to freeze. The water freezing caused the vent stack to be sealed off, disabling the only exit for the cold hydrogen gas. After a time, the residual hydrogen gas in the tank warmed up, causing view more

Incident Synopsis
While a hot air dryer was being used to free a coupling in a hydrogen cryostat (an apparatus used to maintain constant low temperatures), a flash fire occurred. The H2 cryostat was being dismantled.

Causes
The temperature at the center of the cryostat was sufficiently low to liquefy air. The prescribed requirements for purging and bringing the cryostat to room temperature were circumvented. The H2 - air mixture was formed and ignition was assumed to be a spark from an open filament of the dryer.