During the dismantling of a non-radioactive sodium storage installation in a non-nuclear facility at an atomic energy research centre, 400 kg of sodium residue ignited at 10:30 am in emitting white sodium oxide (NaO) smoke as a tank bottom was being cleaned. The smoke permeated the building’s utility rooms and fumarole discharges escaped from the building. Some 20 individuals had to be evacuated, with no injuries reported. The operator inerted the tank under nitrogen and increased the ventilation speed. The tank temperature was closely monitored (10°C drop every half-hour), as was the hydrogen concentration. The fire was extinguished at the beginning of the afternoon, and the emergency services remained onsite until the slow residue combustion had ended. The installation as placed under surveillance until the residues had solidified. The incident was classified a Level I on the INES scale of nuclear events.