A discharge of coke dusts and zinc oxide took place around 10 pm in a non-ferrous metal plant following shutdown of the ventilation system on a furnace filled with coke in order to ‘clean’ it of zinc oxide residues (i.e. the WAELTZ oxide product). This shutdown ‘interrupted’ the pressure drop in the installation and occurred after detecting a temperature rise in the hopper of an activated charcoal filter. Alerted by a sound alarm, the personnel restarted the unit; however, the probe was triggered several times at night, causing dust emissions. The next morning, the furnace was turned off for further investigation and the operator informed the Environmental authority of the night-time incidents. At 11 am, fire broke out on the activated charcoal filters after a hatch was opened and a hotspot ignited due to the ensuing draught. The filters were sprinkled by the site’s fixed installations and external first responders were notified; the fire was extinguished in 45 min. The authority inspectors conducted a same-day investigation. When inspectors arrived, the furnace was still hot yet no longer being fuelled with coke; gases were being drawn by the series of 140 filters left undamaged by the fire; however, they still contained trace amounts of activated charcoal. The release of white smoke clouds observed around 2 pm by inspectors stopped that afternoon, at which time the operator was authorised to restart the furnace at low pressure. To avoid solidification of its contents, which would have necessitated 5 weeks of production downtime, the furnace damaged by backfiring during the fire outbreak had to be quickly repaired to complete its cleaning process. The inspectorate permitted restart with the use of line another filters provided that the source of the hotspot was identified and moreover that the temperature probe threshold was lowered; in the event of another incident, the damaged line would be used as a bypass. No injuries were reported. The extinction water, held in a stormwater basin, was discharged as part of the process. Sampling and analyses of neighbouring ponds were scheduled for the month of September. The operator also planned on informing the town halls of Harnes, Fouquières-les-Lens and Noyelles-sous-Lens regarding these site incidents.