Explosion at a chlorine electrolyser

In a chlorine electrolysis facility, a mixture of oxygen and hydrogen in one of the electrolyser cells a short-circuit ignited causing a deflagration. The cover of the cell was a thin plastic film which broke as planned. The production was stopped.

According to the investigation, the inlet line of the electrolyte in the cell was blocked, which lead to an increase of the temperature in the cell and to the increase of oxygen production. On top of that, the alarm related to temperature control did not function.

The INITIATING cause was a malfunction in the cell of a chlorine electrolyser.
Contributing cause was the malfunctioning of the alarm system related to the temperature monitoring of the process.

The root cause was probably an underestimation of this hazard in the safety design of the process. Nevertheless, a correct mitigating measure (weak enclosure to reduce the risk of a e deflagration) operated as designed and limited damage,

electrolyser cells

A short circuit ignite a mixture of oxygen and hydrogen in an electrolyser cell.

14:30 Leak detected from a pipe at 17 bar. The operator evacuates a hundred employees, stops production and puts the establishment in the safe mode. The emergency plan is initiated.
Water curtains are put into action and measurements of toxicity and explosimetry are carried out.
15:30 The pressure in the pipe at 0.5 bar. The measurements of toxicity and explosimetry in the ambient air being satisfactory,
15:45 Emergency plan is terminated
Public firefighters are on site but will not intervene.

After the accident, the plant operator put in place a system of monitoring and control of the process performed by on-site teams.
This measure was completed later by the installation of an automatic alarm system. Finally, a study was performed to increase the reliability of the whole monitoring system of the installation.