In a parquet factory, a fire broke out in the wood chip silo extraction area designed to feed a biomass boiler. The firefighters checked the silo with a thermal camera but were unable to detect anything abnormal and left. One week later (20/05), smoke appeared in the hopper indicating that hot spots still remained.

The silo was inerted with nitrogen from below to lower the oxygen level. At the same time, foam was injected from above to cool down the contents and avoid a dust explosion. Finally, a plate was installed at the extraction chute at the bottom of the silo to prevent all influx of oxygen and to better smother the hot spots. The technique of spraying water drown from the top of the silo was not chosen because of the risk of explosion and collapse of the structure. Emergency personnel conducted reconnaissance in the upper part of the silo and then monitored the site throughout the night. The silo was then emptied and the extinguishing water confined. Production was shut down for an estimated 2 hours.

Metal-to-metal contact

Mechanical heating (steel against bronze alloy contact) in the silo’s extraction screw is thought to have caused the fire. The part responsible for the increase in temperature (the key) was replaced on the incriminated silo as well as on another silo on the site.

Operator’s action plan following the event

In order to better detect smouldering fires inside the silo, the manufacturer decided to invest in a thermal camera and in gas and spark detectors. A wider access road to the silo is to be created so that Manitou-type machinery can be used. Finally, a procedure to be followed in the event of a silo fire is drafted.