In a chemical plant, 33 % hydrochloric acid solution leaked out of a transfer pipe connecting a production unit to a waste water treatment pit. The fire-fighters on site neutralised the acidic vapours with a deluge gun, two water shield nozzles in the immediate vicinity of the leak and one adjacent to the site. Water curtains in a neighbouring production unit were deployed to protect a nearby motorway. The leak was stopped after an hour and thirty minutes (after isolating the pipe) and had resulted in a loss of 20 m³ of hydrochloric acid, mainly recovered along with the fire water in the site’s neutralisation pit. Heavy corrosion was seen at the sides of the pit. The facility was repaired overnight and re-commissioned. According to the operator, the acidic cloud did not interfere with the neighbouring motorway traffic. The accident was due to a rapidly corroding flange joint on the vent supplying hydrochloric acid to the neutralisation pit. The bolting that was rapidly corroded by the acid gave in and led to the leak. The pipeline was made of surface-treated PVC, the joint used was in expanded PTFE with a zinc-plated/bichromate bolting. The operator sought a feedback on adapting the type of joint used in presence of HCl and studied the possible impact of vibrations on the tightening of the joint. Moreover, an instruction to isolate the acid pipe had been put in place.