A large release of acid vapours occurred around 1:45 pm while supplying reagents to the treatment plant at an electrical appliance factory. All 512 employees were evacuated and fire-fighters were alerted. This accident was caused by the pouring of 150 litres of hydrochloric acid into a tank still containing 200 litres of sulphuric acid. 15 employees bothered by fumes were taken to hospital ; 2 of them were kept for observation until the next day as a precautionary measure. Fire-fighters disconnected the 400-litre HCl delivery container and neutralised the mix. The Classified Facilities Inspectorate’s investigation indicated that the HCl should have replaced the sulphuric acid during the summer once the tank’s contents had been depleted. The mention of a low-level H2SO4 alert on a block diagram was incorrectly interpreted, since the filling team had considered that the tank was empty and therefore filled it with HCl. Following this accident, the use of H2SO4 was discontinued and the operator installed a new tank along with a lorry transfer zone.