In a plant manufacturing insulation boards made of polyisocyanurate (improved polyurethane), a fire broke out in a silo containing 500 m³ of polyurethane dust. At 8:30 a.m., when the brick production unit (fed by the silo) was being started up, the production of brown-coloured briquettes alerted the technicians. A burnt smell was then detected. Smoke began coming from the silo’s lower doors. The plant’s internal contingency plan was initiated, and the personnel were evacuated. The power supplies were shut off, and production was stopped. The silo’s automatic sprinkler system, spraying water from above and from below, was triggered. The emergency rescue services intervened with a special chemical hazards team. A bin was provided, equipped with a sprinkler system, into which the silo was unloaded. Tests were performed during the operation to detect hydrocyanic acid, and the exposure limit was never exceeded. The silo was completely emptied (150 m³) in about ten hours. At the end of the unloading process, the burnt material that had agglomerated around the central shaft of the silo was visible. The amount of dust burnt was estimated at 1 m³. The extinguishing water was contained on site. An external company was able to process the 1,500 kg of waste (dust and water).

The incident did not result in technical unemployment. A survey was conducted to determine what caused the hot spot in the silo. A similar accident, two years earlier (ARIA 44866), had led to the installation of an emergency device on this silo.

The operator had told the inspection authorities for classified facilities that the silo had not been used to full capacity since the January 2014 incident (loaded to 50 m³). However, during the week of 25 January, the brick producing unit had been shut down since the brick storage facility had lost its integrity. Dust had accumulated to 150 m³, the same level as in the previous incident. It, therefore, seemed that the heating problem was repeating itself as the dust was reaching critical thickness. The weight of the material was clogging the hopper and causing the system to overheat.

An emergency prefectural order signed the following day, provided for the drafting of an accident report and the verification of safety all devices before production could be resumed.

The operation of the silo was suspended until the causes of the damage had been identified, and the technical and organisational means were implemented to prevent such an accident from happening again. An audit of the silo and safety devices had to be conducted before being put back into service. In particular, level and temperature probes are required to be water and heat resistant. When production resumed, the dust from the dust collector was transferred to sealed containers, equipped with a temperature sensor that is regularly inspected.