Fire broke out in the crusher hopper of the ‘organic solids’ workshop at a plant dedicated to processing special industrial wastes. Flames exiting the crusher were detected by camera after introducing a 220-litre metal barrel identified as ‘oven washing sludge’. The control room technician immediately activated the emergency shutdown procedure: the crusher and ventilation were turned off, and carbon dioxide (CO2) injection into the crusher hopper was initiated. The fire in the debris recovery bin was extinguished, but small flames were still falling from the crusher knives. Manually injecting inert gas (CO2) into the crushing chamber helped gradually reduce the intensity and number of these flames. The barrel causing the fire could only be extracted from the crusher once all safeguards had been verified. Each time the automatic extinction system stopped, new flashes dropping from the crusher were noticed. Ultimately, 5 hours later, once the wastes had been conveyed by extinction water and with all fire safety protections on the crusher duct system reset, the hydraulic unit could be restarted. Barrel residue was removed from the crushing chamber and poured into a retention basin filled with water plus an emulsifier additive. Both the residue analysis and information provided by the producer made it possible to determine the exact residue composition: an anthracite sludge containing yellow phosphorus crystals, i.e. pyrophoric crystals. This incident had multiple causes, including: a barrel identification error committed by the producer; and inefficiencies in testing conducted at the acceptance workshop to detect the presence of pyrophoric substances, especially given the predominance of anthracite sludge. Several corrective measures were implemented to modify: the programmable controller safety chain for reactivation once the alarms had been tripped and waste designation in the preliminary acceptance certifications so as to avoid confusion.