The malfunctioning of the non-return valve of the hydrogen compressor caused the pressure between the hydrogen bottle and the compressor to rise up to the maximum allowed pressure of 275 barg. As a consequence, as foreseen by the safety system, the rupture disk of the safety valve broke and the hydrogen content of the gas bottle and the pipe section involved was released on top of the building. The flame was seen for a very short period by a guard, and could have been caused by the following series of events:

Expansion of hydrogen at the end of the exhaust pipe.
Consequent mixing of hydrogen and air up to a near-stoichiometric mixture and increase of gas temperature.
Mixture ignition due to sparks from static electricity generated by gas molecule friction against suspended dust particles. The safety system properly reacted to a malfunctioning component of the gas distribution system and avoided any risk to personnel or property.

Incident Date
Apr 05, 2006
  • Motive Power Systems
  • Compressor
  • Safety Systems
  • Measurement / Sensing Device
  • Piping/Fittings/Valves
  • Piping
  • Piping/Fittings/Valves
  • Valve
  • Pressure Relief Devices
  • Pressure Transducer
  • Safety Systems
  • Fire-Extinguishing Equipment
  • Pressure Relief Devices
  • Burst Disk
  • Piping/Fittings/Valves
  • Gasket
  • Piping/Fittings/Valves
  • Flange
  • Hydrogen Storage Equipment
  • Gas cylinder
  • Hydrogen Storage Equipment
  • Hydrogen tubes
  • Safety Systems
  • emergency shut down procedures and disconnects
  • Hydrogen Storage Equipment
  • Vent line
Damage and Injuries
Probable Cause
When Incident Discovered
Lessons Learned

The following corrective actions have been taken:

The non-return valve was dismantled, cleaned, and tested. Following positive testing, the system was restarted and pressurized without any further malfunctioning.
The hydrogen discharge pipe was extended from the low roof of the compressor building (2.5 m) to the higher roof of a neighboring building (6 m). With this modification, any potential hydrogen ignition would occur at approximately 6 meters from ground, farther from personnel than the 2.5 meters of the previous situation.
The compressor was sent to the manufacturer for preventive maintenance in order to lower the frequency of component malfunctioning.
Plans for regular maintenance of the non-return valve will be recorded in the next revision of the Design and Safety Report.
A flame arrestor was purchased and mounted at the end of the exhaust pipe on top of the building.