A large amount of smoke was seen exiting the facade of an incinerator in a hazardous waste treatment plant. The operating personnel set up a deluge sprayer to cool down the smoke fumes and protect themselves from the radiating heat. They activated the fire extinguishing system on the facade of the incinerator but were unable to open the explosion hatch on the post-combustion unit either automatically or manually. The abundant smoke was coming through the gaps in the incinerator’s panels. The internal intervention team arrived to assist and was finally able to open the explosion hatch, thereby releasing the fumes and hot gases.

The release of smoke from the incinerator resulted from an unexpected increase in pressure inside the installation. The smoke extractor had been blocked by the release of a large clump of dust which had accumulated in the cooling tower (owing to a high concentration of dust in the gases and insufficient water flow in the tower). The separation of the clump of dust resulted in the complete blockage of the usual circuit of gases and caused a backflow on the incinerator’s facade.

The problems encountered when opening the explosion hatch, which contributed to the pressure build-up in the installation, are related to the fact that this hatch was not regularly operated in a preventative manner. Agglomerates had accumulated around the hatch, leading to blockage of the opening system. Manual operation was difficult as the actuator was undersized.

Following the event, the operator decided to undertake the following measures:

• add an opening release system on the explosion hatch;
• operate the explosion hatch at each shutdown or on a monthly basis;
• work on improvements to reduce the speed at which the cooling tower becomes fouled;
• clean the cooling tower on a regular basis.