Characteristics of the silo:
Height: 20 m with technical space
Material stored: 170 m³ of polyurethane dust (recycling)
In a factory manufacturing insulating panels, an abnormal temperature increase was detected at around 2:30 p.m. in a polyurethane dust silo used for recycling purposes. The temperature of the material had reached 180 °C. The operator evacuated the personal at 7 p.m. The internal emergency plan was initiated and the rescue services were alerted at 7:40 p.m.
After contacting a silo fire specialist, the firefighters attempted to suppress the smouldering fire with high-expansion foam injected from above and from below. This method of intervention was motivated by the fact that the foam would stick to the dust, thus preventing it from being suspended in the air and the formation of an explosive atmosphere. However, the operation was stopped because it led to the release of hydrogen cyanide.
At approximately 11 p.m., the operator, in consultation with the emergency services, used its extinguishing water system. The system consists of fire hoses designed to drive the diffuser head directly into the heart of the fire. At the same time, two specialised companies drained the tank. The fire was considered extinguished the following day around 12:30 p.m. The internal emergency plan was lifted at 1:30 p.m. The draining operation ended in the afternoon. Production was stopped for two days, and 15 employees were laid off temporarily over this period.
The combustion was attributed to strips of Kraft paper and facing around the silo’s central mast and this mast’s continuous operation. The wrapping of the strips around the mast caused the material to accumulate and heat up. The continuous rotation of the mast constantly generated heat. At minimum, this allows the temperature of the material to be maintained; at worst, it causes an increase in the temperature of the material. Furthermore, the lack of temperature control at the dust extraction level and the high amount of dust (more than 70%) in the silo does not allow for early detection of the heating phenomenon. The accumulation of strips was attributed to the following:
- wear of the teeth of the blades used to cut the upstream panels;
- the panels were offset as they were cut;
- insufficient cutting depth.
Following the accident, the operator undertook measures to improve its inspection and maintenance procedures for the filter and saw blades. He also undertook measures to optimise the parameters regarding the cutting and operating of the silo and installed temperature detection system at the base of the silo.