Fire at a chlorine electrolyser

Two successive fires broke out in an interval of few minutes in four cells in the electrolysis room of a chlorine production plant.
The technicians brought the fire under control using the fire-fighting equipment located nearby. In both cases presence of hydrogen, ignited by a short circuit spark, was responsible for the two accidents.

Case (1): the hydrogen leaked when a rubber-plastic pipe was manually disconnected from a hydrogen collector. This operation is covered by a specific procedure, and it must be performed when hydrogen contained too much chlorine and was not good enough to be collected.

Case (2): the hydrogen leaked when a sleeve failed locally by corrosion.

The two sub-events are characterised by the same outcome, hydrogen fires during operation.

However, these two fires have different INITIATING and ROOT CAUSES.
In case (1) it was a mishap during the execution of a specific operation covered by a formal procedure. It could have been caused by an operation mistake and/or lack of supervision.
In case (2) it was probably due to the failure of a component due to corrosion.

In both cases, ther e was a shortcoming in the design of the electrical insulation of the electrolytic cells. the IGNITION SOURCE of the released hydrogen was an electrical spark caused by a short-circuit. Different potential causes of the short-circuit were identified:
- the compatibility of insulating material has not been checked
- lack of wet-proofing between anode and cathode
- not enough distance between anode and hydrogen pipe due to a modification of the connection and a miss-alignment of the cells.

Electrolyser's cells, sleeve, pipe

In both cases, the fire must have been of a very low itnensinty, and rhe technicians brought it under control using the fire-fighting equipment located nearby.

The two release of hydrogen ignited within a couple of minutes. The fire was extinguished by the operators.

The corrective actions required included:
(a) choice of a better suited insulating material,
(b) improving cell diaphragms to reduce the presence of chlorine in the hydrogen and avoid disconnection of the pipe from the trap,
(c) improving quality control and supervision by team leader,
(d) re-designing hydrogen flanges to space them out from the anode,
(e) communicating the accident to the staff,
(f) improving procedures and guidelines,
(g) taking stock of all insulation malfunctions of all cells.