Soy flakes combusted inside a dryer at a factory, operating under Classified Facilities authorisation, manufacturing soy protein concentrates. The site’s installations included a soybean meal fat extraction unit using hexane, and a sugar extraction unit running on ethanol. Following a series of 4 or 5 malfunctions within a 24-hour period, the plant experienced a succession of shutdowns/restarts, hindering the circulation of operating instructions from one shift to the next. During the last shutdown at 11 pm on 22nd January, technicians emptied the installation; however, since one of the dryers’ outlets was obstructed, soy flakes remained inside. The heated air flow was not turned off until 1 am on 23rd January, causing these flakes to become dehydrated. When repaired at 2 pm that day, the installation was started back up and the injection of hot air activated combustion of products remaining inside the dryer. Temperature rose in the air exhaust duct. Drops of mineral oil stemming from a casing leak on the floor above ignited when they fell onto a segment of the hot duct where a piece of insulation was missing. At 2:10 pm, the technician witnessed a fire outbreak on the duct and proceeded by extinguishing it, placing the installation in safety mode and notifying emergency fire services and management. Fire-fighters opened the dryer to extinguish the combustible. The plant was shut down for 5 days, without any layoffs, in order to determine the exact causes of the incident. The operator believed that an incandescent particle originating in the heat exchanger (heated with indirect steam at 8 bar, yet without any protective filter) triggered the combustion.

Subsequent to this incident, the operator introduced a list of controls to be performed during shutdown/restart phases, including dryer emptying, deactivation of air heating and the injection of cold air for a specific period, in addition to ensuring relevant personnel training. The heat exchanger pressure was lowered from 8 to 2.5 bar, the leaking casing was repaired and all equipment prone to oil leaks was inspected. The operator also planned on installing an automated servo-control on both the dryer emptying and heater shutdown in the event of production interruptions, assessing the feasibility of a rotor change on the fan diffusing hot air, inserting a protective filter on the heat exchanger air inlet and a fire water intake connection in the dryer, repairing defective insulation, and studying the installation of a spark detector in the hot air pipeline.