In a workshop manufacturing resins for adhesives used in a chemical plant, a flash and explosion occurred on a big bag bulk container being filled with resin pellets, followed by a second explosion on a conveyor belt and then the outbreak of fire on 2 dust removal machines. The facility’s internal emergency plan was activated. One person sustained slight burns on his hands and 2 others were in a state of shock. Workshop equipment was no longer operable and the building’s plastic cladding was heavily damaged. At least 3 weeks of repairs would be necessary prior to restart. An electrostatic discharge caused a dust cloud to ignite inside the big bag container. The formation of an explosive atmosphere within the container’s vapour space reduced ventilation system efficiency due to a dust leak in the suction duct on the feed chute that, detected the day before, had gone unaddressed.

The electrostatic discharge was initiated due to big bag incompatibility: given the product’s extreme sensitivity to electrostatic ignition sources (minimum ignition energy = 1.16 mJ; lower flammable limit = 15 g/m³), the big bags used for the operation should have been of type C, which was not the case, in violation of manufacturer’s specifications. A sliding electrostatic surface discharge between the inner body surfaces (insulation) and head (conductor) of the big bag ignited the cloud and led to the explosion on the upper part of the soft packaging. The phenomenon then spread to the suction ducts and bagging circuits. At the same time, the suction of incandescent particles into the dust removal machinery triggered explosions during declogging phases. The prevention measures adopted were intended to limit dust quantity in the installations and eventual dust suspension by imposing a duct intake suction speed of at least 18 m/s, daily cleaning of equipment (or even twice a day), and installation of an overflow cone on a conveyor belt to limit dust dispersion. Moreover, the equipotentiality of workshop facilities received special attention: the use of type C big-bag containers, grounding, and the introduction of conductive braids fastened to the equipment that could only be removed with special tools.