A fire broke out in one of the 6 naphtha cracking furnaces of a petrochemical plant. The smoke emitted by the installation’s chimney generated a plume of black smoke that could be seen several kilometres away which drifted towards the sea given the South/South-westerly wind direction. The fire that remained contained in the furnace was brought under control after 1 hour of fire fighting by technicians and in-house emergency response teams. The installation was then cooled in order to be inspected by the operator.

The steam cracking furnaces comprised a refractory lining and tube bundles in which the naphtha was circulating, with the internal temperature varying between 600 and 1,000 °C. The accident was caused by the instantaneous ignition of gaseous naphtha that had escaped through one or more broken tubes. An operating error and the combined failure of a check valve caused a very large flow of cold naphtha to pass through the bundle; the sudden cooling caused a heat shock weakening the tubes which ruptured.

The consequences were limited to significant material damage rendering the furnace unusable for 6 weeks. In the lower section of the furnace (radiation), a large proportion of the tubes fell following their weakening due to the heat shock, and under the action of excessive heating related to the fire. The inspection of the upper section (convection) did not highlight any major damage.

Repairs were carried out within 6 weeks for a cost assessed at 0.8 million euros. Operating losses following shutdown of the ethylene production were between 1.3 and 1.5 million euros.