In a 3500-m² industrial building housing 3 companies, a fire on the premises of a warehouse containing electrical insulation products spread to the other 2 firms. One distributes electrical devices, the other treats urban and industrial sludge. A large plume of smoke was released as the fire was fed by PVC or polyamide ducts, silicone fixtures, polyurethane and epoxy finishes, solvents and oils. Notified by a neighbouring industry, over 110 fire-fighters arrived at the scene with extensive hydraulic equipment and blocked the sewer network. A chemical emergency unit performed air quality analyses that revealed 10 ppm of chlorine and 32 ppm of hydrocyanic acid adjacent to the fire source. The thickness of this smoke, some of which could be toxic, led authorities to confine residents of the nearby subdivision inside their homes, in addition to closing traffic on the A33 and A31 motorways and other roads in the vicinity. Traffic slowdowns caused several minor collisions. More than an hour after the outbreak, an explosion in the back of the building produced a fireball, ejecting debris as far as the neighbouring subdivision. The Prefecture set up a crisis response unit. Water and soil analyses were carried out. Air analyses conducted by the AIRLOR network indicated values below the toxic thresholds for both Cl2 and CN, in the presence of wind helping disperse the smoke. The fire was brought under control in 2 hours. The building was completely destroyed by flames, while dilatation of the frame prompted collapse of the walls and metal roof. The employees of all 3 companies were placed on leave for a few days.