Severity
Incident
Leak
Yes
Ignition
Yes
Ignition Source
Friction on the vent stack wall at the stack outlet

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 the tank to over-pressurize and rupture with an explosion known as a BLEVE (boiling liquid expanding vapor explosion).

Incident Date
Jan 01, 1974
Setting
Equipment
  • Hydrogen Storage Equipment
  • Vessel
  • Pressure Relief Devices
  • Burst Disk
  • Ventilation System
  • Venting System
  • Hydrogen Storage Equipment
  • Vent line
Characteristics
When Incident Discovered
Lessons Learned

Place signs on all liquid hydrogen tanks indicating that no water is to be put on the vent stack.
An additional secondary backup vent stack was added to liquid hydrogen tanks. This secondary stack is designed to be used only if needed in the event the main vent stack becomes plugged with ice, such as what occurred in this incident. The main vent stack is still the primary means of venting all relief devices, rupture discs, and any normal venting of hydrogen. The secondary vent stack would only be used if the main vent stack failed.