Fire at a Chlorine Electrolyzer Plant
Chlorine was released in the liquefaction unit of a chlorine electrolysis plant, due to the rupture of a pipe. During the re-start phase of an electrolysis workshop in a chemical plant, chlorine (Cl2) gas leaked from a pipeline in a confined chlorine liquefaction unit, specifically at the pipeline carrying residual chlorine from the gas/liquid separator to a liquid bleach manufacturing plant. The leak took place when few tens of cm of this pipeline failed, due to the combustion of the pipeline steel by chlorine, which in turn was caused by the presence of hydrogen in the pipeline due to lack of monitoring. According to the rules, hydrogen concentration in the residual chlorine must remain below the 4.6 %vol value (the hydrogen low explosion limit, LEL). It is manually controlled by the rate of evaporation of chlorine in the gas/liquid separator and monitored through analysis. During the accident, the technician failed to reduce the increasing hydrogen concentration in the pipeline that reached 6.7%, crossing the LEL. To bring down the concentration, the evaporation rate of chlorine was increased causing thus a rise in the residual chlorine flow rate. This probably provided the low energy needed to start combustion. The flame stabilized near a valve and a flow meter and caused the combustion of iron / chlorine when the temperature reached 130 C.
Event Date
January 13, 2004
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
The immediate cause of the accident was the ignition of the chlorine in the pipeline due to a hydrogen content above the allowed maximum. Nothing is said on the reason of this hydrogen increase. An intermediate cause was the attempt to reduce the probability of hydrogen-chorine combustion by increasing the chlorine flow. is present within residual chlorine in the pipe. The concentration is monitored and should not go over LIE (4.6%). During the incident, this concentration went to 6.7% without reaction of the operator. To lower this value, the evaporation rate of chlorine is increased by increasing the flow which probably gave the small energy needed to ignite the H2/Cl2 melt. This ignition results in the burning of the steel pipe : tens centimeters of pipe disappeared resulting in the detected Cl2 leak.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
liquefaction of chlorine, pipeline
Storage/Process Medium
Location Type
Location description
Industrial Area
Operational Condition
Pre-event Summary
The chlorine leak occurred at the start up phase of the electrolyzer
Consequences
Number of Injured Persons
4
Number of Fatalities
1
Lessons Learned
Lessons Learned
To reduce the chances of reoccurrence of such an accident, the operator decided to improve monitoring of the hydrogen concentration and shutdown the electrolysis workshop when the H2 concentration crosses 3.5 % in residual chlorine. Furthermore this concentration was guaranteed by continuously performing the material balance of pure chlorine.Further elements of the lesson learned from this event are contained in the full ARIA investigation report provided under references.
Event Nature
Emergency Action
The operators shutdown the facilities and evacuated the premises. The internal emergency plan of the site was triggered and lifted after 1 hour and 30 minutes.
Release Type
Release Substance
Hydrogen Release Concentration (%)
100.00
Release Amount (kg)
3.00
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
Full investigation repot (with pictures), event no. 26208 of the French database ARIA (accessed December 2020)