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 m open sky tank, containing the electrolysis products (water, HCL, NaOH, Na). According to the ARIA report, (see source) 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.
Event Date
August 13, 2018
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
Immediate 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.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
condensate piping
Storage/Process Medium
Location Type
Location description
Industrial Area
Pre-event Summary
The electrolysis plant was normally function, maintenance works started nearby
Currency
Lessons Learned
Lessons Learned
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 history4. Review of the HAZOP (Zarard and Operation Procedures) of the circuits of hydrogen, chlorine and hydrochloric acid . 5. Control of the hydrogen detection system of the electrolytic unit
Event Nature
Emergency Action
14:25 Immediately after the explosion, the staff started the fighting of the fire by means of fire-hoses. 14:30 The fire brigade arrived and cooled the platform where the furnace was located. 15:00 Observing that the fire gains intensity when reducing the cooling effect of the water, the operator decided to stop the production and the fire stopped. Due tot possible presence of invisible flame, the fire brigade carries out a control by thermal camera on the various pipes overhanging the tank being exposed to thermal radiation, and leave at 16:00
Release Type
Release Substance
Ignition Source
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Flame Type
Source Category
References
References
Description of the event in the French database ARIA
https://www.aria.developpement-durable.gouv.fr/accident/52072/
(accessed September 2020)