Fire at a Flare Stack of a Chemical Plant
Fire in chemical plant (Seveso-classified)The fire developed at the top of the flare stack of a during a violent thunderstorm.The flare stack is used to discharge hydrogen produced by the restarting of chlorine electrolysis cells. The fire was ignited despite steam and nitrogen had specifically were injected to prevent it from occurring. The sites firefighters cooled the flare stack while the technicians turned off the electrolysis cells to cut off the hydrogen feeding the flames. The electrolysis cells had been restarted following a power outage that had occurred earlier, at the start of the storm. The fire was extinguished after approximately 3 hours, and the electrolysis unit was restarted. According to the ARIA report (see references) steam and nitrogen are injected to dilute the hydrogen stream and raise the minimum ignition energy of the hydrogen-oxygen mixture. However, this does not altogether eliminate the risk of ignition, because the hydrogen remains above the minimum ignition concentration. A bolt of lightning to the flare stack was sufficient to start a fire.
Event Date
July 29, 2013
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
Immediate cause was the lightning bolt which released enough energy to ignite the hydrogen reach mixture out of the flare stack.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
flare stack, electrolyzer cells
Storage/Process Medium
Location Type
Location description
Industrial Area
Pre-event Summary
A thunderstorm had caused a power outage and the stopping of the electrolysis cells one hour before the incident.
Consequences
Number of Injured Persons
4
Number of Fatalities
1
Currency
Lessons Learned
Lessons Learned
The ARIA report (see references) The same event occurred already five years earlier. At that time, the corrective actions had been:1) Installation of a velocity-seal on the stack to avoid the possibility of a backfire in case of de-pressurisation of the stack; 2) Reduction of the diameter at the exit of the flare stack to increase flow velocity;3) Improvement on the second flare stack to limit possible heat flow on the neighbouring cooling system of the chlorine. The report does not mention the lesson learned in the second event. One obvious follow-up action would be the assessment of the hydrogen concentrations in and at the exit of the flare stack, and consequently performing a risk assessment to ascertain the need for modification of the venting conditions, including the steam/nitrogen dilution process.
Event Nature
Emergency Action
1:20 Power outage and restart of the electrolyzer2:45 Lightning bolt ignited the hydrogen at the top of he flare stack3:10 The sites firefighters started cooling the flare stack.4:57 The fire was extinguished 5:10 the electrolyzer was restarted
Release Type
Release Substance
Ignition Source
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Flame Type
Source Category
References
References
Event description in the French database ARIA
https://www.aria.developpement-durable.gouv.fr/accident/44133/
(accessed September 2020)
News of the 29 July 2013 on the site of the the Platform Chimique du Pont de Claix
http://www.plateformechimiquedupontdeclaix.com/feu-sur-une-cheminee-de-…