Event
- Event ID
- 439
- Quality
- Description
A common vent system was used to connect vent lines from liquid hydrogen storage vessels to the vent stack (which was lit flaring the gas). Low order detonations were observed around the vent stack which continued when the vent valves were closed. Oxygen concentrations measured in the vent system peaked at about 6% at which time an explosion would occur. The oxygen concentration would then drop to zero. These events continued until the hand valves in series with the rupture discs were closed. On subsequent inspection it was found that the rupture discs had blown in backwards probably by the initial explosion.
- Event Initiating system
- Classification of the physical effects
- Hydrogen Release and Ignition
- Nature of the consequences
- Macro-region
- North America
- Country
- United States
- Date
- -
- Component involved
- venting system (stack)
- Failure mode
- internal explosion
- Initiating cause
- accidental hydrogen entrance
- Root CAUSE analysis
A flange covering a part of the vent system was removed which resulted in air into the stack. A chimney effect was in existence when the vent was filled with low density hydrogen. Air mixed with the hydrogen and was ignited by the flare. Although the vent valves were closed, hydrogen continued to be supplied to the vent system due to the failure of the rupture discs in the first explosion.
Why the flange was removed is not told, but it suggests a ROOT CAUSE related to lack of management of change, and/or possible installation mishap.- Root causes
- Date entry in HIAD
- 01/11/2025
Facility
- Application
- Non-road vehicles
- Sub-application
- Aerospace
- Hydrogen supply chain stage
- All components affected
vent stack
- Process temperature range [C]
- cryogenic temperature (below -50°C)
- Location type
- Open
- Location
- industrial area
- Operational condition
- UNKNOWN
Emergency & Consequences
- Number of fatalities
- 0
- Number of injured persons
- 0
- Post-event summary
Possibley only some damage to stack vent exit
Lesson Learnt
- Lesson Learnt
The 'chimney effect' in venting stacks is a phenomenon allowing air to access the stack when low density hydrogen is vented. It was known to NASA engineers, but they did not have yet all the knowledge required to avoid it under all operative conditions (see Rhodes, R., Explosive lessons in hydrogen safety, Ask Magazine (2013).https://appel.nasa.gov/we-content/uploads/2013/04/513855main_ASK_41s_explosive.pdf).
Due to the rupture of the burst disk caused by the first explosion in the vent stack, there was a continuous hydrogen flow to the stack. it stopped when the valves connecting the liquid hydrogen tank to the stack via the disk were closed. This operation required an in-depth knowledge of the storage system, because closing those valves could allow the pressure in the tank to increase beyond the safety value.
In-depth data
- Release type
- gas
- Involved substances (% vol)
- H2 100%
- Probable IGNITION SOURCE
- Explosion type
References
- Sources categories
- ORDIN
- Reference & weblink
Mishap no 82 in
P. L. Ordin, Review of hydrogen accidents and incidents in NASA operations, 1974, NASA TM X-71565
https://ntrs.nasa.gov/citations/19740020344Hankinson and Lowesmith, Qualitative Risk Assessment of Hydrogen Liquefaction, Storage and Transportation, FCH JU project IDEALHY, Deliverable 3.10 (2013)
confidential
(accessed October 2025)Lowesmith et al., Safety issues of the liquefaction, storage and transportation of liquid hydrogen: An analysis of incidents and HAZIDS, Int. J. Hydrogen energy (2014) https://doi.org/10.1016/j.ijhydene.2014.08.002
