In the foundry workshop of an aluminium production plant, 10 g of chlorine (Cl2) were emitted at 8:45 am during an argon purge of the gaseous Cl2 circuit in the ‘valve’ room. This purge had been decided in order to allow for intervention of the maintenance unit on a defective expansion valve. Concentrations of 7 to 8 ppm Cl2 were measured. The workshop was evacuated; the internal emergency plan was triggered and external first responders alerted. No injuries were reported. This discharge was due to the saturation, despite monthly titration, of soda solution in the tank designated for Cl2 neutralisation during a purge. The operator installed a 2nd treatment tank, as the soda supplier was incapable of quickly delivering the company if a need arose. Inspectors requested a soda titration after each purge. On the same day at the end of the afternoon, a fire without any correlation to this incident occurred in the site’s ‘paste’ workshop (ARIA no. 30187).