A fire broke out around 9 pm at the level of an idle electrolysis tank within a facility dedicated to recovering 2,700 m² of waste with high zinc content. Once the alarm went off inside the control room, a technician visited the workshop and noticed the onset of fire with yellow flames over the lower part of the tank. The containment resource at hand (i.e. extinguishers) was not sufficient to control the blaze and fire spread to the other facilities via pipes, tanks, ducts and cable paths. The emergency services were notified. The personnel and nearby residences were evacuated. A 4,000-litre soda tank exploded due to heat and the ensuing projections injured 2 fire-fighters; another person sustained an ankle injury. Several 13-kg LPG bottles used to supply the forklifts also exploded. Responders encountered water shortages and the building’s steel frame further complicated fire-fighters’ efforts. The extinction water was confined to the retention basins. The response team had the blaze under control by 3 am using 8 nozzles, including 1 foam nozzle, sand and powder; they removed the roof of the administrative part and cleared the premises. Fire-fighters measured airborne pollutants but could not detect any anomalies. An elected official and the Deputy Prefect visited the site. The roof of the building had collapsed and production machinery was destroyed. Traffic was stopped for a 5-hour period.
The classified facilities inspectorate, alerted four days after the incident, visited the site and requested rapid treatment of all liquid and solid wastes. The used hydroxide sludge and bath solutions were discarded at a dumpsite; fire water was pumped and eliminated at a specially-adapted installation or else discharged into the natural environment following treatment by a mobile unit. The operator also had to remove the three 4-m3 tanks of propane and gas bottles onsite, in addition to ensuring the good condition of the fence to prevent against intrusion. A groundwater analysis campaign was required to determine the eventual impact due to infiltration caused by defects in the retention seal.
The investigation conducted by the operator indicated that the fire was due to heating of the zinc powder by means of an oxidation phenomenon, produced by a combination of the following malfunctions:
- Faulty electrolysis tank pump, preventing the pumping of tank contents, giving rise to the zinc accumulation at the low point;
- Clogging of the lower tank evacuation outlet by zinc powder impregnated with soda, due to the pipe elbows and narrowing, making it impossible to proceed with a mechanical sweep of the plug;
- Forced circulation of air inside the plug, due to suction at the top of the receiving tank, positioned at the lower level.
This heating could not be controlled since the water injection system inside the tank had been turned off as a preventive step prior to an intervention step and then could not be placed back into service by workshop technicians, who escaped the premises at the outbreak of fire. It caused ignition of the clogged polypropylene pipe, with flames spreading (due to the absence of fire protection devices) to the entire site via other polypropylene pipes of the various workshops.
The operator adopted the following measures: vertical rectilinear flow of the electrolysis tank towards the discharge tank; isolation of the electrolysis room and zinc powder storage with 1-hour or 2-hour fire resistance walls; fire barrier system for transitioning from electrolysis tanks to lower discharge tanks (motorised valve with stainless steel sleeve); systems limiting the spread of fire in the site’s pipelines (motorised valves in the closed default position); storage of inflammable products (pallets, tanks and gas bottles) outside the main building.
