A leaking liquid hydrogen cryogenic pump shaft during the process of filling a gaseous tube delivery trailer to 2400 psi at a liquid hydrogen transfilling location caused a series of explosions and a fire. After approximately 30 minutes of filling, the operator heard a single loud explosion and then saw flames and ripples from heat generation near the ground in the hydrogen fill area. The operator quickly actuated the emergency alarm system that shut down the cryogenic pump and closed the air-actuated valves on the cryogenic pump supply line. After this shutdown, three smaller explosions were heard as well as the sound of gas releasing from a safety relief valve. The fire department was called to the scene and participated in the final shutdown of the hydrogen system as the fire was extinguished prior to their arrival. The partially filled tube trailer (~ 1800 psi) was disconnected and moved away from the incident area to a safe location. There were no injuries from this incident and only a small amount of equipment damage with some floor charring.
A leak at the cold end packing of the liquid hydrogen pump was determined to be the source of the hydrogen that exploded and burned. The ignition source was most likely static electricity or frictional energy on the cryogenic pump shaft. A Notice of Violation was issued by the fire department that prevents the start-up of the liquid hydrogen system until all necessary safeguards are in place to re-start the system. A thorough investigation followed this incident and a summary is provided in Attachment 1. Highlights in Attachment 1 include findings of the cryogenic pump disassembly, operation of the shutdown pressure switch, speculation that the nitrogen purge system was inoperative, as well as more incident details.
- Upgrade the liquid hydrogen pump control system to shut down operation of the pump and protect the system when malfunctions like leaks, pump cavitation, or loss of purge gas occur.
- Verify that maintenance procedures used for liquid hydrogen systems meet the requirements of the manufacturer. Ensure that personnel performing maintenance have the necessary training to work on liquid hydrogen pumps. Ensure that liquid hydrogen pump maintenance procedures are in the training system and that work performed is documented in the maintenance system.
- Install an hour meter in pump systems to ensure that maintenance can be performed based on hours of service instead of on a fixed schedule. Program the recommended maintenance interval into the maintenance system.
- Communicate the incident to all company team members through the safety bulletin and discussions at safety meetings/conference calls.
- Share best practices with other company entities that have liquid hydrogen pumping installations. Send this report to other company entities operating or installing this type of equipment.
- Make changes required by the fire department to resume operation and have drawings approved by state PE.
- The operator’s quick response and training of emergency shutdown procedures at this facility prevented this from developing into a much larger and more serious incident.
- Remember that gaseous hydrogen typically propagates much faster in air than cold liquid hydrogen. Cold liquid hydrogen has a density near air and instead of dissipating up quickly, it may propagate more slowly from the source of the leak. In this incident, the cold liquid hydrogen remained near ground level until it was warmed by the surrounding conditions.