Fire at a electrolyser in a chemical plant

A fire broke out on the hydrogen tank of an electrolysis cell at a chemical plant. Hydrogen leaked trough the hydraulic safeguard of the tank, due to an overpressure in the hydrogen line. The ignition source remained unidentified.
An alarm alerted the operators. The emergency shutdown was triggered, and the fire was extinguished using fire extinguishers and a damp mop to cool the top of the electrolytic cells.

The INITIATING CAUSE was the failure of the hydraulic safeguards, unable to counter-act the increase in pressure in the hydrogen line.
The malfunction was due to a low-level of water, caused on its turn by the failure of the operators to perform a refill.
The ARIA report is unclear regarding the cause of the hydrogen over-pressure, explaining it with the activation of the chlorine burner because of the detection of a drop in hydrogen pressure, likely due to pressure losses caused by blockages related to freezing.

The operators did not refill the safeguards due to the imminent shutdown of the electrolysis unit. They were also occupied with managing smokes from several electrolytic cells. No clear instructions were in place to prioritise checking the hydrogen tank levels.

The ROOT CAUSE is related to shortcoming in operative instructions, possibly triggering an overload of the personnel in charge during an emergency.

electrolyer, hydrogen guards

The ARIA report does not directly lesson learnt elements.
Nevertheless, it should be investigated if it is possible to provide efficient passive barriers in case of active barriers deactivation. Also procedures (control) and their priority should be reviewed.