An overflow of slag occurred around 11 am in a ferromanganese manufacturing plant due to a hole drilled at mid-height of an electric furnace (rated capacity: 1,000 t / H: 11 m), above the upper level of the molten metal. The flow was collected in the retention basin, but some was projected onto the casting floor by the jet due to hydrostatic pressure, ignited the electrical cables, a pallet of “taphole clay” (a mixture of refractory materials and organic binders), and then the building cladding. The IOP was activated; power and fluid supplies in the affected area were interrupted. Fearing an explosion, the emergency services evacuated 70 employees and set up a safety perimeter of 500 m. The fire department extinguished the fire, which emitted considerable smoke, and the security staff of the facility re-established the cooling of the damaged furnace caused by the molten slag. At the beginning of the afternoon, after stopping the leak, the ferromanganese alloy was drained using casting equipment. The intervention of emergency services ended at 2:30 pm. After cooling, the slag was removed with a loader. No one was injured; property damage was estimated at 1.59 million and operating losses at 25 million.
The Classified Facilities Inspectorate conducted an investigation. Since complete renewal of the furnace lining, from April to June 2004, abnormal temperature rises at the surface had required a number of interventions by a specialised refractory subcontractor, who performed these works. After this type of intervention, the furnace normally has a lifespan of 10 to 15 years without any significant maintenance. In August 2007, with the temperature becoming critical and the furnace only operating at reduced power, a new intervention was planned in the presence of the service provider. In order to diagnose the condition of the refractory material, two sections were cut from the furnace; it was during cutting of the second section that molten slag spewed out a few minutes after the intervention. The first observations showed that the refractory wall was heavily damaged in the sprue area, in particular the partial destruction of carbon blocks (stamping mass) provided to ensure the thermal insulation and sealing of the furnace. The investigations carried out subsequently with refractory specialists failed to ascertain with certainty the causes of the premature wear; problems with material quality or the installation were suggested.
Following the accident, the operator was to undertake the following measures: temporary repair of the furnace and reinforcement of furnace temperature monitoring, with new threshold limits to activate the alarms and fire extinction system; rehabilitation of the retention tank; reorganisation of nearby storage; and a review of procedures and specific preventive actions to be taken in the event of an incident.