Fire in a chlorine electrolysis plant

First an explosion and then a fire occurred on the condensate piping of an chlorine electrolysis plant (SEVESO upper tiers). Flames escape from the end of the pipe and spill into a 75 m³ open sky tank, containing the electrolysis products (water, HCL, NaOH, Na).

According to the ARIA report, (see References) a maintenance operation was ongoing on the HCl furnace located nearby. Investigations conducted by the operator identified a design defect as the cause of the incident. The overflow of the guard hydrogen hydraulic system was wrongly connected to the condensate piping.
Due to the fact that the HCl furnace was in maintenance, an excess of hydrogen under overpressure developed and escaped through the condensate piping. The presence of hydrogen at the outlet of this pipe, combined with a spark related to the work on the furnace, caused a detonation and then the fire.
This ATEX zone was not identified during work on the furnace because hydrogen was not expected to be present in the area.

INITIATING cause was the ignition of the flammable hydrogen mixture present on the line of the condensate.
The root cause was a wrong design, which connected the hydrogen discharge pipe to the condensate pipe.

condensate piping

The electrolysis plant was normally function, maintenance works started nearby

The storage of epoxy is destroyed et three plastic pipelines are burned. The electrolysis unit is stopped for 24 ore.

According to the ARIA report, to be able to restart the production, the operator implemented the following actions:

1. modifications to allow the independent discharge to the atmosphere of the surplus of hydrogen.
2. assessment of the electrical equipment of the area.
3. Verification of the installation modifications history
4. Review of the HAZOP (Hazard and Operation Procedures) of the circuits of hydrogen, chlorine and hydrochloric acid .
5. Control of the hydrogen detection system of the electrolytic unit