In an electrical motor and transformer plant, a chemical reaction with gaseous emissions occurred around 3 am on a 200-litre barrel of waste housed in a room open on one side. Personnel noticed a strong smell of varnish and notified first responders. Fire-fighters evacuated out of precaution 4 employees from the adjoining workshop. Seven barrels containing manufacturing residue, 4 of which deformed, were moved outside the room; the punctured barrel was immersed in a water tank to be cooled. A specialised subcontractor disposed of the wastes during the evening. According to the site operator, excessive barrel filling with a waste composed of 50% varnish / 50% diacetone-alcohol, combined with plug closing, caused this incident. The waste disposal instruction was completed and improved barrel identification introduced to avoid ambiguities regarding their contents. Operating losses were estimated at €3,000.