Pollution
Humain
Environnement
Economique

On the ground floor of a 5,000-m² rubber manufacturing building, fire broke out at 6:21 am in an internal mixer at the beginning of a mixing cycle involving various substances in the preparation of gum rubber. The injection of plasticizers and other operations planned for the mixture were not carried out due to an incident affecting the process. The temperature rose well above the planned 140°C to reach 250°C. Noting this deviation, the operator at 6:27 am removed the rubber compound from the conveyor feeding an external mixer. As the conveyor belt was advancing towards this mixer, the mixture suddenly ignited before being cooled by employees. The flames and smoke were drawn into the exhaust duct mounted on the external mixer. The procedure for warning and evacuating site employees was launched at 6:38 am. The sprinkler system was activated one minute later by the five sprinkler heads overhanging the installation. At 6:53 am, the fire-fighters arrived at the site and sprayed the mixer with a foam solution. The main fire was extinguished at 7:15 am. The intervention by fire-fighters ended at 9 am and the employees returned to the premises. The facility was placed back into service three days later at around 10 am. According to the operator, this process incident was caused by a malfunction of the automatic control system, which did not control the injection of plasticizer and subsequent operations. The rise in temperature during production of the mixture was mainly due to the mechanical action of the mixer and the absence of plasticizer and other ingredients, thus increasing friction and consequently the temperature of the mixture. A sensor measured the mixture’s temperature, but no alarm warned of any abnormal rise. The operator decided to couple the internal temperature measurement with alarm activation in order to attract the technician’s attention. In addition, the operator studied the possibility of automatically controlling the opening of the drainage trap door to the mixer whenever the internal temperature set point was exceeded. These changes were to be introduced on the two internal mixers in service.