A significant hydrogen leak occurred during refueling of the onboard hydrogen storage tank of a fuel cell-powered lift truck while it was completely depowered. The in-tank shutoff solenoid valve had recently been replaced, and this was the initial refueling event after the replacement. The fuel zone access panel was removed to allow constant visual leak checking with Snoop leak-detection fluid. The event occurred during the final pressure testing of the repaired system when an O-ring failed at approximately 4500 psi, releasing the entire contents of the hydrogen tank in about 10 minutes. The dispenser hose/nozzle was immediately disconnected, and the leak location was quickly isolated to the tank/valve interface. A 30-foot boundary around the lift truck was cleared of personnel and equipment. The combustible gas detector mounted on the wall above the hydrogen dispenser did not alarm because a large overhead facility fan was providing ventilation throughout the event. The leaking hydrogen did not ignite, no one was injured, and there was no property damage as a result of this event.

The fuel cell systems for the lift trucks were originally built by Company A and placed into service in 2009. Company B assumed the service and support responsibilities in 2011, and then subcontracted the service labor to Company C. The only instructions given to Company C regarding the tank valve and the O-ring were to follow the tank valve manufacturer’s torque specification for ensuring a seal.

Shortly after this event occurred, an investigation was undertaken by Company B. Company C reported that the O-ring was clean, lubricated, and tight when installed. However, after removing the failed tank and valve from the lift truck for investigation, it was noted that there was insufficient insertion depth of the in-tank solenoid valve, and the O-ring was not able to provide a sufficient seal due to inadequate compression at the tank/valve interface. This situation was caused by the internal thread of the tank that did not allow full engagement at the specified tank manufacturer’s torque requirement, and this geometric discrepancy was confirmed by comparison with a new tank that had been purchased as a spare. The investigation revealed that the tank threads were modified on other tanks of this same model, but not on the specific tank involved in this event. Thus, the tank would have required substantially more torque than provided to fully compress the O-ring as intended (i.e., much more than the manufacturer’s recommended torque specification).

Information regarding the difficulties in original manufacturing and the later modification of tank threads to attain a proper seal was not transferred from Company A to Company B, and the Company A fuel cell team had since been disbanded. The tank supplier has begun modifying its tanks to accommodate the valve, so newer batches are in compliance, while the earlier systems require the higher torque to ensure a good seal.

Incident Date
Jul 21, 2011
  • Vehicle & Fueling Systems
  • Fueling Dispenser
  • Hydrogen Production/Use Systems
  • Fuel Cell
  • Piping/Fittings/Valves
  • Gasket
  • Vehicle & Fueling Systems
  • Fuel Cell Vehicle
  • Vehicle & Fueling Systems
  • Fueling Hose
  • Hydrogen Storage Equipment
  • Gas cylinder
Damage and Injuries
When Incident Discovered
Lessons Learned

A hydrogen release of this type is a significant event. The event highlighted a number of procedural contributing factors that will influence the manner in which these fuel cell systems will be serviced in the future. A complicating factor in this event was that multiple companies were involved, and communications among them were inadequate. It is likely that the condition existed from the original manufacture of the fuel cell systems, and may even have been understood by the Company A fuel cell team, but the history is not fully known since that team no longer exists. Company B’s investigation also discovered that a similar leak had been experienced at the same facility and a similar replacement had been required, but there was no corporate memory of the repair or the underlying failure mode.

If a situation arises as a result of consolidation or equipment transfer wherein another entity takes ownership or service and support responsibility for fuel cell systems, the full design history and operating records of the systems must be fully documented and accessible. This will allow for proper knowledge transfer of underlying design considerations or problematic reliability or safety-related issues, and potentially prevent this type of avoidable incident from occurring again.

Another lesson relates to how high-pressure components within the hydrogen fuel storage system are qualified following a repair. It is envisioned that in the near future, there will likely be regional service centers equipped with re-manufacturing capabilities to support commercial fuel cell deployments. These repair shops would be equipped with the infrastructure to properly purge and pressurize equipment with small-molecule gas to test for leaks.