During a casting run on one of the blast furnaces (BF) at a steel mill, a reaction occurred in a slag (molten residue) overflow ditch causing 1 to 3-kg blocks of hot material to be blasted over a radius of some 100 metres. A series of small fires, quickly brought under control by in-house responders, broke out on roughly 100 above-ground cables, along a telecommunication network rack and in waste containers placed 25 m away. A dozen cars parked 100 m from the BF were damaged (broken windows and body dents); also, the hoses on a hydraulic excavator needed to be changed. Impacts were recorded on the metal cladding and roofs of adjoining installations. The production of 2 furnaces was turned off for 2 hours; one of these closures was due to destruction of the belts conveying crushed coal, while the other furnace was slowed by a down oxygen feed line. While waiting for communications to be restored between the various units, production continued for several hours under difficult conditions.

According to the mill operator, two anomalies simultaneously arose in the slag pit: the presence of cast iron, along with water or a foreign substance. A number of preventive measures were adopted to reinforce monitoring of the BF slag pits, subsequent to 2 similar incidents in 1998 and 2002. The Inspection Authorities for Classified Facilities advised that the local government authority mandate the operator to implement systems limiting the consequences of any recurrence and moreover issue specifications governing the layout (water disposal, notification of the ban on dumping foreign substances), operations (guidelines) and regular inspection of slag pits.