In a chemical plant, a fire broke out at about 1.30 pm under the roof of a liquid sulphur storage tank filled to 10% of its capacity (14 m high and 15 m radius – 15,000 t cylinder) and had to be shut down within 2 months. The steam fire-extinguishing systems (6.8 t/h) was automatically activated by the temperature sensor located below the roof (threshold = 160 °C). In-house firefighters installed 2 small nozzles to cool the tank. The external emergency services were alerted and the internal emergency plan was activated at 2.45 pm. The emergency response system was then reinforced using a deluge gun (3,500 l/min) for cooling the tank’s shell and using a large nozzle on a ladder for diluting the sulphur vapours that were escaping from the roof and vents. Nevertheless, a cloud of sulphur dioxide and trioxide (respectively SO2 and SO3) formed above the town. The SO2 concentration measured by the local air pollution control network reached a peak of 350 µg/m³ over 15 min. At 5 pm, the SO2 concentration was only 70 µg/m³. At 9 pm, the tank’s temperature had stabilised and SO2 emissions had stopped. Finally, the internal emergency plan was lifted at 10 pm. The fire had only affected the roof of the tank. The temperature probes located in the middle and at the bottom of the tank showed no rise in temperature. The sulphur flower deposited below the roof and on the tank’s frame had fuelled the fire, with the air circulating under the roof via the vent and the holes of the damaged roof acting as the oxidant. Various hypotheses were put forward with regard to ignition of the fire, such as, self-ignition of pyrophoric iron sulphide (FeS), self-ignition of the sulphur flower, and an electrostatic phenomenon caused by the stormy weather that preceded the accident. Finally, the tank was replaced by a tank with a volume 8 times smaller but having a double steam injection capacity. This tank was equipped with a self-supporting temperature-controlled roof and a central tracked vent thus preventing sulphur flower deposition. Other measures taken after the accident included improvement of the communication with the Autonomous Port of Le Havre and revision of the internal emergency plan integrating the data for this fire.