In a shotgun cartridge loading shop, welding work was being conducted on the railing of the distribution platform, on the side of the wall adjacent to a shooting tunnel. The connecting door between the shop and the tunnel was definitively shut and locked from inside the tunnel; it had not been opened in 2 years. The threshold of the door was positioned below the loading shop ground level, increasing the accumulation of dust, which subsequently ignited with the sparks generated by the weld. A flame must have been lit on the other side of the door (i.e. on the tunnel side), causing combustion of the soundproof lining covering the tunnel walls and ceiling. The fire outbreak was contained by fire-fighters before spreading to the neighbouring production workshops. The welder was not injured. The measurement equipment (speed sensors) and suction device located in the tunnel were damaged and had to be replaced; the soundproof lining was completely destroyed. On the other hand, the building structure remained intact and both the computer and electronic equipment in the control room adjoining the tunnel were submitted for verification.