A leak on a tank containing a concentrated hydrochloric acid (HCl) solution occurred at night, at a chemical products wholesaling site. Upon contact with the rainwater present in the retention basin, the concentrated solution released gas in forming a white cloud that wound up intoxicating 5 employees of the neighbouring cheese factory; these individuals would be hospitalised for 5 hours of exams. Firefighters notified the operator, who stopped the leak by closing the reservoir foot valve and dissipated the cloud with a cleaning hose. The premises of the cheese factory were ventilated, and the acid solution contained in the retention basin was drained into the onsite treatment plant; nonetheless, 100 litres were discharged into the courtyard of the cheese-making facility due to a leak on the transfer line.

Lime was then spread in the retention structure and on the polluted ground in order to neutralise the acid. The soiled earth would later be excavated over a depth of 50 to 70 cm for treatment by a specialised centre; water samples taken on 2 piezometers downstream from the site did not reveal the presence of pollution.

A short circuit on the hydrochloric acid processing installation caused activation of the acid pump and triggered the associated solenoid valve, thereby drawing the HCl discharge through the packing gun conveniently placed in the retention basin. The inability of the storage valve to close at the end of the shift during the evening of the previous day was also considered as a reason.

Moreover, the lack of a seal on the retention drainage line was an undetected outcome of the sulphuric acid leak that had occurred a month earlier (ARIA 32913).

In terms of feedback, a verification procedure for tank foot valve closure was adopted, in addition to installing polyethylene storage reservoirs with integrated retention and rainfall protection, emergency shutdowns of the storage and packing unit electric systems.