Shortly before 10 a.m., a fire broke out on a bar of solid rocket propellant during a machining operation in a weapons and ammunition factory. The technician alerted his co-worker and asked the technicians in the adjacent workshop to alert the emergency services. The burning bar ignited and severed the flammable cord, triggering the automatic flooding system. The flooding was able to douse the flames and prevent the fire from spreading.

The fire destroyed the 0.82 kg bar of propellant which was on the lathe, 9 bars in closed crates and some propellant chips in closed bins. The work had to be completed in the evening so cleaning could be performed before the plant shut down for the annual leave period.

The operator recharged the flooding installation, cleaned and inspected the lathe.

The accident occurred during the machining operations (straightening, turning in 2 passes and threading) of 10 hollow bars on a lathe. During the operation, the hollow bar is held between the lathe-centre and the tailstock. After having made adjustments and initiated the finishing pass of the cylindrical section (rotation at 1,000 rpm), which lasts 4 minutes, the technician went to the adjacent cell to switch on the vacuum machine in order to prepare the inhibition resin. There he met with the methods technician and validated the operating process with him. Upon his return, the bar was on fire on the lathe, and the flooding system suppressed the flames.

The experienced technician was trained and authorised to machine propellant. Since he had left his workstation, he was unable to stop the operation at the end of the machining run. The stop could not be disengaged as the 4 machining passes were performed with different tools, and therefore had different stop settings. At the end of the run, the tool holder blocked the knob, and the motor twisted the knob stop and continued its rotation. The impact or the friction of the metal parts must have caused sparks or overheating which caused the fire to ignite.

The safety documents were compiled; the flooding system operated correctly. The technician should not have left his workstation, particularly when “prototype” work is being performed. This reminder was issued in the presence of the production foreman on September 5 and clarifications were made to the operating procedures. The automatic end stop is now activated, even in the case of single machining operations on pyrotechnic products.