An abnormal amount of acidic water droplets was released from a stack on an iron and steel site between 10:00 a.m. and 4:00 p.m. The stack collects scrubbed gaseous effluents emitted from a facility where hot-rolled coils are pickled with hydrochloric acid, and another where spent hydrochloric acid baths are regenerated. The incident was detected at around 8:00 p.m. by workers who noticed spots on their vehicles in the plant’s car park. The droplets were carried by the wind and deposited along a 300 m distance on the site. No odd smells, colours or fumes were reported. The site operator closed the car park from 9:00 p.m. until the following day. No local residents were affected. Property damage was estimated at €100,000.

The incident was caused by the spent hydrochloric acid bath facility. Built in 1984, this 850 °C fluidised-bed pyrohydrolysis treatment unit consists of two lines that alternately operate according to an average cycle of 14 weeks. The line that was not in operation was undergoing maintenance. On the day of the incident, regeneration line 1 had been restarted (gradual preheat) following extensive work. Line 2 had been kept running. This uncommon operation was because of the longer-than-expected heating time of line 1 due to the maintenance performed (the refractory materials had been extensively repaired) and because the maximum temporary storage capacity of the spent baths had been reached. This operating mode had been approved by the facility’s builder in 2008 following extensive work, but had never been used before. It was during this time, which led to an increase in the flow rate of the discharged gases, that the acidic water droplets were released.

The site operator modified the start-up procedure. One line cannot be preheated while the other line is operating. It also conducted a study to improve gas scrubbing and thereby reduce the amount of acids discharged from the stack.