A pneumatic explosion occurred at about 4 p.m. in a pyrotechnic factory specialising in the manufacture of nitrocellulose-based hunting and sport shooting gunpowder. The event took place when an intake pipe was being sawn (vertical, 80 mm diameter stainless steel tube) in the extraction room of a production building. At the time of the accident, the site had been shut down for its annual technical inspection, a period used to conduct maintenance work after the workshops and installations have been cleaned. A scheduled technical intervention consisting of the removal of a dye tank (used for colouring the powder) that had been replaced by 3 new tanks, had just been completed by an external company. When this old tank was taken out of service, the air intake pipes, located directly below it, were no longer required. The explosion occurred on this portion of the pipe while a technician was cutting it manually with a hacksaw, while another technician was flooding it from the outside.
The high overpressure associated with the explosion resulted in the projection of numerous metal debris into the room and the rupture of several fragile elements of the intake system (ripping open flange-mounted metal foils and several of the system’s flexible components). The 3 technicians present in the room (2 employees, 1 temporary employee), 2 of whom were working at height on ladders placed on either side of the pipe, were seriously injured and transferred to the hospital. Two of them received flash burns to the face from the pneumatic rupture of the pipe. The arm of the 3rd individual was struck by metal fragments and had to be amputated.
The building was cooled down using the company’s water resources. The explosion was not followed by a fire and did not result in a secondary explosion. Following the accident, all work and interventions by external companies were suspended, and the premises were cleaned and decontaminated. The site’s activity resumed a few weeks later.
Pyrotechnic dust residues (a yellowish substance with a powdery texture) were found on the metal fragments of the torn pipe, on the floor of the workshop and outside the workshop, in the axis of the foil that had been ripped open. These findings indicate that the pipe had not been adequately washed during the preliminary rinsing operations. Nor had there been any verification of the effectiveness of this cleaning. The explosion could have been caused by the ignition of pyrotechnic dust residues which had accumulated inside the pipe. The technicians had used an unsuitable method for removing the piping by using manual sawing with a hacksaw, which generated a hot spot, rather than a pipe cutter. The accident was thus associated with the heating generated by the friction of the hacksaw blade on the stainless steel intake pipe.
The cutting operation was not scheduled. The plant operators had simply decided to remove it, for an unknown reason, in breach of the procedures in place (in particular, the procedure regarding interventions on hollow bodies containing pyrotechnic products and the procedure on prior measures to be taken before intervention on contaminated equipment). It had not been the subject of an intervention permit, a fire permit or validation by a manager. On the day of the accident, the site manager, his assistant, the head of the safety department and the industrial manager were on holiday.
Before restarting, all personnel were informed of the importance of complying with the intervention procedures and prior cleaning. The operator is currently considering modifying procedures to guarantee the safety of the installations and strengthening management procedures during critical periods. They will be integrated into the plant’s safety management system (SGS). Training for staff will now include a module on human behaviour and ways to avoid mistakes. In addition, the operator has now included in its risk analyses the dangerous phenomena resulting from the potential presence of dust in hollow bodies.
In December 2004, an accident (28707) involving a similar pipe cutting operation led the operator to revise the format of its intervention permit by adding an article entitled “hollow body cutting” and by making it mandatory to apply for a fire permit for any intervention involving a hot spot/suspicion of hot spot or heating in a contaminated environment.