A dust explosion occurred in the handling facilities (elevators and conveyor belts) of a port terminal (grain silo) during an operation to load corn onto a ship. The explosion led to two more explosions just a few seconds later that were more powerful than the first:
- an explosion in the dust collector filter due to the intake of incandescent particles,
- another explosion in the handling tower’s elevators, including those not of service.
The opening of the vents on the dust collector system limited the overpressure effect, estimated to be between 100 and 150 mbar at the filter level. The dust check valve, located upstream from the dust collector’s bag filter, was severely damaged. The flap’s spindle was ripped off, and the flap itself was pushed inward. Property damage in the handling tower was distributed according to the amount of dust accumulation throughout the zones: deformation of the elevators, partial collapse of the brick wall and glass breakage in the control room and in other tower installations, and traces of combustion up to the 9th floor of the tower. The operator in the control room, on the first floor of the handing tower, was slightly injured by broken glass. The firefighters checked for hot spots with thermal imaging cameras and conducted explosimeter measurements. According to the emergency responders, 750 tonnes of corn had already been loaded onto the ship when the explosion occurred. No damage to the ship or the silo structure was reported. The environment and third parties were not affected, and the internal emergency plan was not initiated. Following the accident, the operator issued a press release via the website of the Permanent Secretary for Industrial Pollution Prevention.
According to the inquiry that followed, the first explosion was due to excessive dust accumulation inside the handling equipment and frictional heating of particles that had accumulated in the elevator’s legs without any defect being detected by the systems in place. These particles likely became attached due to the handling of the wet corn during the drying operation. The dust concentration in the elevators of the handling facilities was estimated at 200 g/m³, which is three times the lower flammability limit for corn. This concentration, abnormally high for an elevator’s vertical portion equipped with a suction system, generated the second explosion in this installation.
It should be noted that the site had numerous preventive and protective measures as set out in the guide for state of the art silos, including anti-static straps, belt offset and rotation monitoring controls on the elevators. The storage cells were separate from the handling tower, and the tops and bottoms of the elevators were equipped with reliable openings to release possible overpressure.