Explosion in a gas containers company

The event took place in centre for assembly and maintenance of empty gas cylinders. Three workers were dismantling a rack of eight hydrogen cylinders for maintenance. When woeking at the when they felt a bang and heard a gas leak. The alarm 15 minutes later, the site was evacuated after approximately an hour, the power shut off and the area was ventilated. Safety barriers were put in place to prevent traffic and firefighters intervened.
Hydrogen concentrations around 10% to 15% of the Low Flammability Level. The operator closed the cylinder's maintenance valve. 3 hours later, the hydrogen concentration was below the detector's detection limit. Firefighters left the site the emergency plan was terminated.

The operators who were present at the scene of the bang were taken to the hospital for examination. Three neighbouring businesses were evacuated for a day.

The INITIATING CAUSE was an accidental release of hydrogen from a 57-litre cylinder which was still containing pressurised hydrogen.
The company using these cylinders had found the rack defective and had returned it to the centre, believing the cylinders had been emptied. The maintenance valve on one cylinder was likely left closed, preventing it from being emptied. The user company did not perform a double check before reshipping back the cylinders. The operator at the centre where the incident occurred did not perform any checks upon receipt of the rack.

When starting the maintenance work on the rack, the workers began by loosening the caps to reposition the cylinders on a new rack. When loosening the cap of the one cylinder identified, they encountered abnormal resistance but kept loosening it, resulting in a detonation accompanied by a loud gas leak.

The ROOT CAUSE was lack of risk assessment considering the possibility that cylinders received from customers could still be full. This inadequate risk assessment had as consequence the unavailability of effective checks and procedures. Moreover, the management of the centre-customers responsibilities was inadequate.

valve, cylinder,rack

The 3 workers were hospitalised for medical controls, but were only lightly injured.

The company where the hydrogen release occurred was assembling and maintaining containers for compressed gases. Although not explicitly said by the source, it is probable that standard activities were not covering handling of various species of compressed gases and that the related working instructions were not designed for this. This would explain the lack of a check on the content of cylinders received back from customers, even though this check is easy to execute.
Moreover, an important contribution to the incident was caused by the customer company, which also did not perform any check on the successful accomplishment of the operation of emptying before shipping the cylinders. This case highlights the importance of agreement between parties, when the responsibility on safety is shared among them.

Following this incident, the operator:

(1) Modified certain maintenance valve models to make their position easier to read.
(2) Distributed a cylinder pressure monitoring procedure to all user companies.
(3) Added a measure to verify the purging of storage racks upon return by user companies or during interventions carried out by the operator at third-party sites.
(4) Implemented drills with a specialized company to prepare for similar incidents
(5) Raised staff awareness of the risk of gas being present in cylinders returned by user companies.