Fire broke out in a dilution tank inside a paint factory. Maintenance personnel were completing a welding job on a structural frame installation, under which the motors on a 24,000-litre oil-based paint tank needed to be set. The tank lids were closed. When the welding job was finished, staff wetted the welds, in order to cool them, when they smelled a suspicious and increasingly strong odour before noticing a red glow at the tank bottom through a small orifice, and observed a temperature rise. Once fire-fighters arrived on the scene, the fire was extinguished, most likely by lack of oxygen. The temperature in the workshop topped 35°C, which favoured the slow combustion of paint residues in the tank. Moreover, since the tank lids were closed below the work zone, it was not considered necessary to install a tarp while the hot work permit was being prepared. The most likely hypothesis was a droplet of incandescent weld falling into the tank.