At a pyrotechnic plant, a violent explosion erupted inside a production unit due to compression in the triggering delay on recreational fireworks (delay referred to as “espolette”). The explosion took place at the level of the loading machine housing, during a black powder compression phase, and was followed by 2 less intense bursts. The spread of debris and shattered material were noticeable. The technician sustained multiple injuries (thorax, forearm, face, including an eye and neck). Property loss was considerable: the machine was damaged (broken protection screens, inoperable black powder flow system, a portion of which had been projected through the back partition on the box embedded within the aluminium frame on the blast-proof wall, a compression piston split into several pieces strewn over a 6-m radius), deterioration as well to the adjacent workstation (broken side screen, ruptured piston, burned hopper contents).

The accumulation of explosive product, combined with poor positioning of the socket and trajectory of the piston through the delay mechanism, would have caused this accident (punching, thus causing a friction-rubbing contact). The violence of the explosion, along with an analysis of the projection paths, suggests that the black powder had gradually accumulated inside a cavity at the level of the clearance hole on the power feed system inside the machine housing (with a free air volume of 67.2 cm³). This cavity had not been identified as a dust trap and, as such, no guideline was issued calling for its periodic disassembly for cleaning. The disassembly of devices on other workstations led to observing a case where powder was effectively present.

Before restarting the unit, the operator eliminated tube confinement and pyrotechnic powder trapping in the openings; moreover, the operator established a general machine cleaning instruction sheet and revised the screen protection procedure by avoiding the use of metal elements as much as possible. It was also proposed to modify the pneumatic casings (through the use of programmable automatons?). Experts have emphasised the risks of dust accumulation and underscored the importance of implementing appropriate cleaning guidelines.