Pollution
Humain
Environnement
Economique

At 00:40 am., an explosion followed by a fire occurred in a chemical company closed since the 05/08 for summer stop during which maintenance works was carried out on the installations. All installations were stopped but the clarification process of 14 t of an organic peroxide containing diisopropylbenzene in a tank. This operation was supervised by one technician which supervises the system from the control room, inspects the plants regularly and actuates the necessary operation on the tank process.

The tank is a 50 m³ vertical cylinder of 6 mm- stainless steel with a plane bottom and an upper rounded cap (height 5.5 m / diameter 3.50 m). The bottom, lateral and upper cap are welded. The tank has a man path with a diameter of 60 cm with a clapet valve. The bottom of the tank is fitted with an internal cracking coil carrying vapour at 4 bars. In the past, water at 60°C was used as heating fluid, it was changed to vapour to reduce process time. The temperature control is actuated with a thermocouple inserted at around 0.70 meters over the coil: the temperature is reported in the control room with 2 visual/acoustic high temperatures alarms respectively at 55°C and 60°C.

The process consists in eliminating water and soda in a cycle of several 2-steps phases :

  1. introduction of gaseous carbon dioxide (CO2) and heating at a temperature between 35°C and 45°C, through a liquid circulating in the internal tank coil; the continuous recirculation of the product is obtained with an external pump.
  2. once the temperature of 45°C is reached, both heating and recirculation of the product are stopped for 6 hours to allow for product decantation ; water is drained from the tank bottom.

However during the plant stop, the control systems were under retrofitting works to transfer to a distributed control system (DCS). In the control room, the thermometer of the tank was deactivated, the temperature could only be read on the tank with a visual thermometer fixed with bails on the external piping. The reading scale went only to 120°C, without any alarm system.

The fifth cycle of clarification started on the 15/08 at 12.30. Due to a shift change at 2 pm, the technician forgot to stop the heating and recirculation (normally around 3 pm) and did it only at 8.30 pm. After the 10 pm. shift change, the technician checked the temperature in the control room (not reported anymore) and started a visual inspection of the plant. At 23.20 pm., the technician, during his control tour, saw a steam leak from the upper valve of the tank and the temperature had topped 120°C. He closed the steam valves of the heating and switched on the external cooling system of the tank, but the thermal decomposition process of the peroxyde had begun and the tank exploded 80 min later, creating a 100 m high fireball. The tank lid was thrown on the roof of an electric cabin about 50 meters away.

The technician, back by fireman from a chemical company in the vicinity, used both fixed and mobile water systems to fight the fire. All the cooling systems of the tanks of the LPG and benzene storage nearby were activated due to the temperature rise detected by proper sensors.

The material damage were evaluated at 150,000 euros. After measures in the environment, no environmental impact was recorded.

The operator changed process and adopted proper managerial measures in its SMS.