A difficult intervention

During the summer holiday period, a fire broke out around 2:30 p.m. in a sawdust silo at a company specialising in wood processing and transformation. The silo, standing 13.5 m high, consisted of a metal structure with a concrete casing and wooden floor. It had a capacity of 200 m³ but contained only 4 to 5 m³ of dust on the day of the accident. The firefighters had to deal with several difficulties during the intervention. A 25-metre safety perimeter was set up around the silo, which showed signs of damage. The upper access door to the silo was blocked shut, and firefighters had to use a gas-powered chainsaw to open it. The fire was eventually extinguished at around 7:00 p.m. The extinguishing water was confined to the site by blocking off the networks.

Lack of risk awareness despite the request for a fire permit

The fire had been caused by torch work on the feeder mechanism located on the silo’s roof. Maintenance personnel were in the process of dismantling the feeder, but the screws were embedded in concrete. A torch was used to remedy the situation. The silo had not been emptied prior to the hot-spot work. A fire permit had been issued. However, the existence of metal elements passing from the roof to the inside of the silo, and having contact with wood dust, had not been identified at that stage. While the torch was being used, the heat propagated through the heated metal to the inside of the silo. The wood dust, in contact with this metal element, then ignited. The combustion was then fuelled by the inrush of air caused when the door was opened by the technicians who had been alerted by the smell of smoke.

Measures taken

An assessment of the silo’s structural soundness was conducted before operations resumed. The report did not bring the strength of the silo’s superstructure into question. The vertical separations observed were related to the installation’s age. However, the accident worsened the situation. The expert recommended that tie rods be installed to strengthen the structure. A reminder was issued with regard to job site preparation guidelines, and the incident was featured in an “accident news flash” which was distributed to all the company’s sites.