A five-pound CO2 cylinder being stored in a compressed gas storage cage at a power plant failed catastrophically and became a missile. The cylinder destroyed the storage cage, then struck one of six stationary hydrogen storage cylinders used as emergency make-up for the hydrogen supply system. One of the hydrogen cylinders was broken away from its mounts and moved 10 feet from its original location. The loss of this cylinder severed the manifold tubing, creating a leak path to the atmosphere for the remaining five hydrogen cylinders. The leaking hydrogen gas apparently self-ignited, engulfing the immediate area. The site fire brigade responded and used hose lines from a distance to provide cooling until the hydrogen supply was consumed. The fire was out within seven minutes, and no off-site fire assistance was needed. All normal supplies of hydrogen were isolated and a re-flash watch was established until all damaged hydrogen cylinders were removed to an isolated "safe zone." Damage was restricted to the CO2 cylinder, the six hydrogen cylinders, associated piping (which showed flame impingement), and the compressed gas storage cage.
Preliminary results indicated that the CO2 cylinder rupture was caused by tensile strength overload caused by overpressurization. The safety disc assembly was dissembled and it was found to contain three safety discs where there should have only been one. Installation of multiple safety discs probably resulted in failure to relieve the overpressure condition prior to cylinder rupture.
- Pressure Relief Devices
- Burst Disk
- Hydrogen Storage Equipment
- Gas cylinder
Revise fire protection operations surveillance tests to include a maximum of 110% of the agent net weight to prevent over-filled cylinders from being placed in service.
Identify cylinders currently in service that exceed the 110% maximum allowable limit, remove them from service, have them inspected and refilled to the new criteria, and then return them to service.
Purchase new compressed gas pilot control cylinders.
Revise the plant industrial safety program to enhance cylinder storage requirements by eliminating the use of ropes as restraints.
Purge the gas storage shed of all non-related storage, secure all cylinders with chain, fabricate cylinder racks for small cylinders, and eliminate storage of items next to the hydrogen system emergency manifold.
Conduct a probabilistic safety assessment of the possibility of missile hazards from compressed gas cylinders.
Change from the current CO2 vendor to another qualified service vendor.
Investigate whether a breakdown of the fire protection QA program occurred.