In a polymerised rock wool factory, a process jam occurred around 4:30 pm on a polymerisation line oven. Production was shut down and the line emptied. During installation restart at 6:15 pm, fire broke out at the oven exhaust, triggering the response of personnel equipped with 2 fire hoses as well as shutdown of the extrusion process. The fire was extinguished within a few minutes at the oven exhaust, but immediately thereafter suction ducts were set ablaze and an explosion ensued in the factory chimney 100 m away. A 20-m² metal plate that had not been completely bolted onto the chimney base was blasted in the air and fell nearby without causing any damage. At the same time, natural gas and oxygen intakes were closed and the cupola furnace drained. Temperature quickly rose inside the oven, and the fire kept raging in the ducts. Factory staff continued to cool ducts and oven until fire-fighters arrived around 6:30 pm.
These responders ordered all non-essential personnel to evacuate and proceeded with cooling until complete extinction around 9:30 pm. Besides tearing out the chimney meter plug, this fire caused:
- destruction of the lining, heat insulation and coupling sleeves of a substantial part of the gas exhaust ducts along the production line;
- shutdown of the oven and fan belt drive units and motors plus their electrical cabling;
- partial destruction of a control station and the electrical cabling of another production line.
Employees on both damaged lines were reassigned to either the finishing workshop or the refurbishment shop. The inspection authority proposed an additional order to the Prefect requesting the operator update the facility’s safety report.
A root cause analysis indicated that the deposits of binders remaining in the oven at high temperature (280°C) after emptying underwent a slow decomposition that restored the basic organic compounds. Upon restarting the installation, air intake initiated the fire at the oven exhaust, thus facilitating spreading into the ducts along with the incomplete combustion of organic deposits. The decomposition of these deposits into VOC and CO combined with the other hot gases led to the formation of an explosive atmosphere at the chimney base.
