A leak of hot raw bitumen was observed at 5:00 p.m. at the base of a tank in a bitumen and road surface emulsion plant. The tank contained 30 t of a bitumen and polyphosphoric acid mixture. The hot product, 160 °C, flowed into the retention tank. The tank was then drained to another storage vessel by means of a straight body truck. The transfer operation was completed at 6:20 p.m. A certain quantity (1 tonne) of product remained in the tank as it could not be drained. The emergency services left the premises at around 6:30 p.m., but a subcontractor on site detected smoke and flames at the base of the tank at 9 p.m.

The emergency services and the facility operator were alerted. Upon their arrival, they noticed that the leak had resumed and product had flowed into the retention basin, and electrical cables had caught fire. The installation was secured. The sewerage system’s isolation valves were closed. The fire brigade sprayed down the tank and was able to bring the fire under control. A specialised company recovered and treated 1 t of bitumen and 1 m³ of firefighting water collected from the retaining basin. The damage was estimated at 120,000 €.

The operator had an expert assessment conducted on the tank at the origin of the leak. A significant amount of corrosion was discovered: craters and under thicknesses were detected on the bottom of the tank. The initial hypothesis was that this degradation was caused by an incompatibility between the steel of the tank and the polyphosphoric acid, introduced before the bitumen in accordance with the operating procedures. Furthermore, after the tank had been drained, the electrical supply to the heating elements in the tank were not switched off. This may have caused the mixture and the bitumen-impregnated insulation to ignite.

The operator suspended production of the mixture in question and initiated works for the development of a new manufacturing process. The electrical lockout procedure was modified so that the tanks are no longer supplied with electricity when they are shut down. The bottom of the tank was replaced.