Incident Synopsis
A H2 air explosion occurred near a H2 compressor, located outside. Gaseous H2 had been released from a vent stack when a relief valve was actuated. The source of ignition was not known, but considerable damage was inflicted onto the system by the ensuing fire and explosion. Following the explosion, the shut-off valves were closed and the system was vented.

Two relief valves were located in the 3,000 psig system downstream of a 5,000/3,000 regulator. The relief valves were sized to handle substantially different flows. (One was designed for another program.) The relief valve was believed to have opened when the pressure setting was being increased from 2,700 to 2,900 psig. The accuracy of the 5,000 psig gauge used to control the dome of the 5,000/3,000 regulator control combined with the tolerance of the relief valve settings (+-3 percent) was sufficient to open the valve. Large flows were vented due to the large relief valve. In addition, the vent stack cap was designed so that the vented gases were released in a horizontal rather than vertical direction.

Incident Date
Dec 31, 1969
  • Motive Power Systems
  • Compressor
  • Piping/Fittings/Valves
  • Valve
  • Ventilation System
  • Vent Stack Cap
Damage and Injuries
Probable Cause
When Incident Discovered
Lessons Learned

First, it appears that the system may not have been vented properly. CGA G-5.5 should be used for determining safe locations based on the variables of the specific setup. Also, if the compressor was tied to a storage system, a backflow prevention device may have limited the amount of gas that was released. Finally, it appears that equipment was left in place from previous activities. Such equipment should be evaluated to make sure that it is appropriate and safe for use in new processes.