A fire broke out in a polyurethane dust storage silo at about 9:50 a.m. in a plant specialising in the manufacture of polyurethane foam insulation panels. At the time of the accident, the 120 m³ silo, measuring 15 m tall, was filled to one-third of its capacity. Following a blockage at the compactor outlet, the maintenance department was alerted by smoke after opening the compactor hatch under the silo. Briquette compacting operations had stopped.
Operation of the silo:
It is located outside. it is intended for the storage of two types of waste:
- fine machining dusts which are filtered through a bag filter;
- coarser grinds from a grinder of discarded polyurethane panels.
The silo has a flat bottom. The waste is guided by two worm screws; one planetary rotating around the entire circumference of the silo and the other vertical feeding the compactor located under the silo. The compactor turns the waste into briquettes.
At that point, the internal contingency plan was initiated. After
attempting to contain the fire internally with 4 hoses, the director called the emergency services for assistance and evacuated the 120 employees from the site. The inspection authorities for classified facilities were asked to provide support during the intervention. The fire brigade was able to bring the fire under control with 2 fire hoses. A trapdoor at the base of the unit was opened to empty the tank when a detonation occurred with a flame front shooting out the access hatches. A quarter of an hour later, no more smoke was noted. HCN and CO analyses were conducted while the unloading process was underway; the gas measurements in the silo indicated 500 ppm of CO and 70 ppm of HCN. The values are zero at a distance of just 3 m from the silo. Some of the staff returned to work at around 12:00 p.m.
The hot spot in the silo was noted that was related to heating caused by a jam in the silo’s vertical auger. The jam had been caused by an excessive amount of edge strip paper and facing strips wrapped up in the auger, which prevented the compactor from being supplied. The presence of polyurethane dust in the silo, coupled with overheating, eventually led to the fire.
The operator set up a program in which the silo is completely emptied every 15 days, and the silo is opened and the auger visually inspected. Cleaning is performed as required. This operation is recorded. A control system was installed to shut down the two feed augers if the compactor is no longer supplied. Other measures are being studied, such as the installation of HCN and CO detectors in the silo or temperature detectors in the auger bell. The silo’s quick emptying system could be improved by a “suction type” system and a second opening. A pre-shredding of the paper is also being studied. A fire of different origin had already occurred on this silo in 2012 (ARIA 43035).
