Release from a hydrogen refuelling station

The release occurred in the hydrogen storage unit of a refuelling station.
In the night a leakage occurred at one of the 120 high pressure bottles (800 bar). The leakage occurred at a screwed fitting at the bottle-to-pipe connection. All three sensors installed at nearby control panels detected the hydrogen (signal threshold 0. 40 % LEL) and lead to an immediate shutdown of the station.
The affected high pressure bank was separated from the other banks so that a maximum of only 60 kg had to be released, corresponding to the total inventory of one bank. No ignition took place.
A pedestrian heard the alarm and called the police, who called the station manufacturer. In parallel, the operation team received the alarm at their remote monitor. Police called the fire brigade and installed a safer perimeters of 200 m, closing all the roads.
The station manufacturer technicians were called on-site and arrived 2 hours later. They started a controlled additional de-pressurisation through a vent line bypass which brought the hydrogen to the bus dispenser vent line. After approximately 5 hours, the pressure in the affected hydrogen container was at around 1-2 bar and could be sealed again.

The INITIATING CAUSE was a leakage from a connection.
It was known that the screwed connection at the high-pressure bottle could fail with a higher probability during start-up of operation and during the first 200 cycles with a higher probability than after it. System design of the screwed fitting was not allowing more than 7 kg/h of flow from such a leakage.
The safety measures in place worked as designed and the emergency was managed successfully, avoiding escalation.
The incident highlighted nevertheless some shortcoming in mitigating measures for worse-case scenario (was a possible ignition of hydrogen considered? Was there an interlocked fire-suppression system? Was the alarm communication system optimal?).

storage bottle

DESCRIPTION OF THE FACILITY
The storage system of the HRS consisted in 4 high pressure banks. Each bank consisted of 30 bottles at 800 bar, with a total of 60 kg/bank and a total ivnentory of 240 kg.

No damage.

An official systematic investigation into the failure cause was expected to be started, subject to appointment of a consultant by the civil court .

A pedestrian heard the alarm and called the police, who called the station manufacturer. In parallel, the operation team received the alarm at their remote monitor. Police called the fire brigade and installed a safer perimeters of 200 m, closing all the roads.
The station manufacturer technicians were called on-site and arrived 2 hours later. They started a controlled additional de-pressurisation through a vent line bypass which brought the hydrogen to the bus dispenser vent line. After approximately 5 hours, the pressure in the affected hydrogen container was at around 1-2 bar and could be sealed again.

The automatic alarm systems and safeguards worked as planned, and effectively minimised the amount of hydrogen released.
However, the consequences would have been different in case of (delayed) ignition in a confined space.
On top of the lessons learnt which brought to the corrective measures adopted, a general lesson learnt regarded the need to organise training for worst-case scenarios, including drill exercises .

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(1) A long plan firewall has been installed 2 days after the incident, to protect other cylinders from jet flame coming for one of them. This had already been planned before the accidental release.
(2) As a further cylinders protection against overheating, a dry sprinkler system was installed above the high-pressure storage banks.
(3) The alarm system was modified. The audible alarms will continue only for 1 minute (sirens in outside areas were audible from far away) while the visible alarms will continue. An additional alarm notification via SMS and on audible basis was installed at operators control room, to allow an immediate notification to the operator.
(4) The storage pressure was reduced in 3 of 4 banks to 600 bar until additional measures have been implemented.
(5) Emergency plans and procedures were reviewed, improved and documented.