At a chemical industry site, the propylene foot valve (80 mm) on a tank containing 200 tonnes of hydrochloric acid in 33% solution broke and 140 tonnes of acid overflowed into the retention basin. A hydrochloric gas cloud formed due to acid evaporation. Site employees activated a water curtain around the basin, sprayed foam into the discharge ditch and sealed the leak. The internal response plan (POI) was triggered and the pumped acid neutralised. Measurements taken along the wind path outside the site turned out negative. A firefighter was slightly affected during the emergency effort. The damaged retention ditch was repaired and all facilities potentially in contact with the acid were listed, verified or altered.