At approx. 2.15 p.m., during a COVID-19 pandemic lockdown period, in the “acid” room of a specialist baby food manufacturing plant, 400l of 96%-concentration sulphuric acid was accidentally transferred into a 30% nitric acid storage tank containing 1,250l. A yellowish then reddish cloud, resulting from the formation of nitrogen dioxide, formed as a result of the sulphuric acid reacting with the diluted nitric acid. 70 employees were evacuated. Firefighters were alerted. A 300m security perimeter was set up. Traffic was stopped on the nearby road from 3 p.m. to 6 p.m. the next day. As a precaution, a shopping centre was evacuated and inhabitants asked to lock down. Firefighters set up an open head system and a hose was aimed at the tank to cool it down. One firefighter sustained minor injuries. Staff returned to the plant at approx. 7 p.m., but the operation continued. Production was shut down for 7 hrs.

In conjunction with the plant manager, the plan was to arrange for draining of the tank by a specialist business after stabilisation by adding chromic acid. The operations begun on 10/04 were completed on 15/04 with the removal of the tank, which was disassembled. All the waste, including the uncontaminated water used to externally cool the tank, was disposed of by businesses authorised to process hazardous waste.

The accident was due to several human failures. The acid was ordered by a maintenance technician who was replacing the storekeeper while they were away on sick leave. Having difficulty finding the right item, the maintenance technician made a mistake and ordered sulphuric acid instead of nitric acid. Plus, the acid was usually transferred by the storekeeper, but this time it was transferred by a work-study trainee who was replacing them. The trainee had attended chemical risk training but was unexperienced (only one acid transfer to their credit). The procedure did not specify the type of acid to transfer. No poster was displayed in the room and the tank only indicated that it contained acid. They were accompanied by a full-time colleague from the maintenance department who was providing support outside the room but had not been specifically trained for this type of operation.

The operator took the following measures:

• set-up of posters in the room, on the retention system, and by the external tank;
• addition of checking of the item in the procedure as well as initial actions to be taken in case of emergency;
• automatic checking of the item before transfer;
• identification of the storekeeper’s tasks, responsibilities, and training necessary for each task connected with this position;
• increased technician transfer and chemicals training, and updating of the procedure;
• appointment of acid transfer managers: the storekeeper and 2 technicians, displaying on the door of the room of the list of authorised people.