While refilling the hydrogen system after an outage caused by a power failure, the excess flow valve located at the hydrogen tank tripped, but did not go fully shut.

The large valve is equipped with a small bypass valve so that the valve can be pressurized on both sides as is required before the valve can be reset. The O-ring which makes this small valve gas tight was deformed and improperly seated, thus allowing gas to flow to each side of the large valve. This permitted the valve to trip normally, but not to seat properly. The following is the manufacturer's evaluation after disassembly and inspection of the valve.

This valve was recently installed to provide excess flow protection to the underground portion of the hydrogen system piping and to provide redundant protection to the entire system. To have this valve out of service means that the protection remains the same as it has for many years, with the distribution system from the building's hydrogen control point onward being protected by an excess flow valve. This building's valve has always tested properly on the annual test and tested properly on a recent test.

Follow up: The valve has been returned to the manufacturer, rebuilt, tested and re-installed in our system. Testing on re- installation indicates that the valve is working properly.

Incident Date
Jul 27, 1991
  • Hydrogen Storage Equipment
  • Vessel
  • Piping/Fittings/Valves
  • Valve
Damage and Injuries
Probable Cause
When Incident Discovered
Lessons Learned

Equipment that is designed to provide a safety barrier must be stringently tested upon installation.
A procedure requiring annual testing of both excess flow valves, which includes proper seating for closure and proper flow, has been developed.