Leak from a LH2 storage tank

The event occurred at a high-intensity lamp manufacturing facility. Hydrogen leaked from a gland nut installed on a 9,000-gallon horizontal liquid hydrogen tank located at the rear of the facility. A large white plume consisting of condensed moisture from air in contact with the cold hydrogen was visible 200 feet (60 m) above the tank.
The manager noticed the leak during his normal morning rounds and initiated the plant's emergency response procedure, which implied calling the local fire department and the hydrogen supply company.

The fire department requested that the facility was not shut down but rather to continue operations, to reduce the hydrogen inventory in the tank. The emergency strategy consisted, among other measure, in a personnel evacuation and the creation of a 500-foot safety area.

The technician of the hydrogen supply company arrived on site, thawed out the ice buildup around the leaking gland nut using warm water, and tightened the nut. This stopped the hydrogen leak. The technician found out that that the leak originated from packing material around the valve, that had come loose because of the recent extreme cold weather.

The INTIATING CAUSE was a leaking gland nut in combination with increased boil-off. This abnormal venting of hydrogen from the tank due to lower facility consumption, in combination with extreme temperature conditions, placed thermal stress on the gland nut, causing a leak.
The ROOT CAUSE could be reasonably attributed to a combination of harsh environmental conditions and material degradation.

gland nut, LH2 tank

The fire department requested that the facility was not shut down but rather to continue operations, to reduce the hydrogen inventory in the tank.
(1) A checkpoint was established near the tank side of the building where hydrogen level readings were taken and reported every 5 minutes. Employees of the plant were notified to exit the front of the building in the event of an evacuation signal.
(2) As hoses were turned on by the fire department, a drop in water pressure tripped the internal alarm, causing an evacuation of the plant. All employees were accounted for and were asked to return to work, as this was a false alarm condition.
(3) Two local streets were closed, radios, cell phones, and other electronic devices were shut down within a 500-foot safety zone to eliminate any static electricity that could ignite the hydrogen gas,
(4) Airplanes were diverted from their normal flight path to the local airport.
(5) Firefighters set up combustible gas monitors inside the building, but no gas was detected.
The incident lasted approximately two hours.

This event consisted in a small incident and a large emergency intervention. This is often the case when first responders cannot assess with the required certainty the escalation potential of the event. More in-depth knowledge of the involved technology and its hazards would help in such situation, by the plant operation as well as by the responders.

The reason for the low consumption of hydrogen was the shutdown of some production equipment and from the delay of additional production equipment to start operation. Therefore, the tank size resulted too large for the facility's hydrogen demand. It is unknown if the facility could have foreseen the low demand and adapted the hydrogen inventory onsite. Probably, liquid hydrogen delivery occurred always by a completely fill of the tank. In any case, liquid hydrogen storage tank should be able to deal safety with large boil-off flows. The release was a combination of different factors, improbable to be known in advance.

On the wake of this event, the following measures were adopted:
(1) The hydrogen supplier exchanged the 9,000-gallon tank for a smaller 4,500-gallon tank to significantly reduce pressure build up from lower usage.
(2) the hydrogen supplier will conduct annual training on handling all types of gases used by the facility and will include the local fire department in this training.
(3) The facility will continue daily rounds to look for visual evidence of leaks.