Fire at the storage of a hydrogen refuelling station

This incident occurred at the storage system of a hydrogen refuelling station during an inspection. The inspection consisted in the visual inspection of individual pressure vessels of the storage system. The report is unclear on this point, but it seems that the inspection was an unplanned operation, due to the suspect of spurious materials in one of the vessel.
Before the inspection, the hydrogen inside the pressure vessel was replaced with nitrogen. The procedure consisted in the following steps:
(i) Install a temporary valve between the vent line connected to the pressure vessel,
(ii) Install a temporary gas line from the pressure vessel to temporary valve to supply nitrogen to the storage,
(iii) Releasing hydrogen from the vessel to the vent line
(iv) Injecting nitrogen into the vessel.
The operation of vessel emptying and refilling with nitrogen was repeated 5 times, when a hydrogen detector confirmed that hydrogen had been successfully replaced with nitrogen.
The visual inspection was executed by opening the rear of a pressure gauge and inserting a fiberscope into the connection. The inspection confirmed the presence of a foreign object in the vessel.
To suck it away, the suction hose of a vacuum cleaner was inserted through the same connection. Approximately 10 minutes later, a fire broke out from the vacuum cleaner being used for the suction work, causing one worker to suffer minor injuries (the team was made of three workers).

It must be noted that the hydrogen production equipment was in operation on the day of the incident and its vent line was connected to the vent line for hydrogen coming out of the pressure storage vessel. The temporary valve installed to separate the pressure vessel from the vent line was not closed, causing hydrogen that had been flowing from the hydrogen production device to the vent line to flow back into the pressure accumulator. This caused hydrogen to flow into a vacuum cleaner and to ignite due to the motor sparks.

INITIATING CAUSE
The operation of vessel purge was not successful, because the temporary valve installed to separate the pressure accumulator from the vent line was not closed. Hydrogen which was leaving the hydrogen production device toward the vent line could then flow back into the pressure vessel.

ROOT CAUSE
The closure of the isolation valve had been declared before the start of the activity. However, the valve was not close. In absence of detailed and effective procedures and checklists, this deviation could not be detected.

valve, tank

The incident occurred during a visual inspection of the storage vessels

DESCRIPTION OF THE FACILITY
The hydrogen filling station had been installed in 2001 as part of a demonstration project. Hydrogen was produced from natural gas in a reformer, then separated and purified. A compressor was used to store pure hydrogen in eight pressure vessels.

the fire must have been of limited dimension. Only the nearest worker was affected by it. The pressure in the vessel was very near ambient pressure, and the gas consisted of a mixture of hydrogen and nitrogen, two conditions contributing to the mitigating the consequences.

This incident has its origin in failing to check that all the actions foreseen have really taken place. Its cause lies on one side in the absence of a detailed, clear and understood procedures, and on the other side in shortcoming in the actions foreseen, which were not enough to guarantee the required safety. The following two specific lessons learnt can be drawn
1. When it is necessary to isolate a part of an equipment dealing with gases for inspection, repair or maintenance purposes, all possible gas connections between that part and the rest of the equipment must be blocked and kept blocked for the whole duration of the operation, to avoid unwanted gas flows. The components used for blocking the flow should be effective and fail-proof. Especially in operation which occur rarely, physical (visible) disconnections are preferable to simple operation of a valve the position of which may be difficult to be immediately checked.
2. When inspecting, cleaning, etc. high-pressure gas equipment, workers should use checklists and a four-eyes approach to confirm and ensure that all preparatory steps foreseen by the operating procedures have been executed before starting work.

1. The vent line of the hydrogen production equipment and hat of the storage system, which were connected before the incident, were completely separated.
2. A procedure manual was created for the specific operations to be performed during the work. A checklist for the procedure manual was also created in advance and required approval by a supervisor.
3. All workers were required to review the procedure manual and checklist before starting work.