At a research centre devoted to non-ferrous metals, steels and special alloys that performs pyrometallurgical activities in order to devise or improve metal production processes, a furnace was punctured upon completing a pilot operation as part of a research project.

The technician was familiar with the metal casting process (with partial or total furnace drain) following a “furnace-penetration” melting phase using an oxygen lance around the casting hole. The accident occurred during one of these casting runs and entailed the overflow of a molten ferronickel alloy into a recovery pit located beneath the furnace. The pit’s sheet metal bottom was in turn punctured, with the molten metal flowing into the pit’s second bottom where it came into contact with humidity present in the pit, notably in the sand contents; this abnormal humidity was due to both water infiltration after heavy rainfall (spattering on the ground) and the quality of sand that had not been replenished. Hydrogen (H2) formed and violently exploded, with incandescent projections subsequently triggering several fire outbreaks by igniting combustible substances (e.g. pallets, cardboard) stored in various spots throughout the workshop.

A primary fire source at the mezzanine level required the intervention of external fire-fighters. Centre employees however succeeded in controlling the secondary outbreaks, despite difficulties encountered with onsite extinguishers: pins removed on some, pin removal constraints for others, limited usage duration. Since the accident zone had been isolated from the main building, the site was not evacuated. The affected zone was cordoned off and rendered inaccessible. The 5 employees present in the workshop at the time noticed the furnace puncture and left the area prior to the explosion; only 4 slight injuries were reported. The furnace was destroyed; property damage costs were estimated at €700,000, with operating losses reaching €300,000. Rebuilding the new experimental device would delay future studies.

Several measures were adopted: improving the current return to minimise penetration risks (DC furnace technique) and temperature monitoring of these returns (thermocouples); avoiding water in the pit (enhanced runoff system to reduce splatter); venting the pit (no shutoff with interrupted energy supply) to prevent H2 build-up; placing emergency exits for control room personnel; facilitating smoke exhaust in the building and installing outlets; introducing a sound alarm should the building require evacuation; redesigning the energy shutoff switch; displaying a control room table with a list of individuals present in the lobby area; controlling access during tests (flashing lights?). These measures were to be implemented as well on the 2 new furnaces scheduled for installation.