During a delivery around 11:15 am at a drinking water purification plant, 400 litres of aluminium polychlorosulphate were transferred by error from a bulk container into a plastic tank containing 400 litres of bleach (NaClO). A chemical reaction ensued, with the release of chlorine (Cl2) into the atmosphere and crystallisation of the liquid mix in the tank.
The response team set up a safety perimeter. The toxic Cl2 cloud that formed caused illness to the lorry driver, who would miss 11 days of work, the plant employee, 2 neighbours and a fire-fighter wearing a self-breathing apparatus. The first 4 victims were hospitalised for observation. The tank and premises were ventilated. The cleaning effluent and waste (2 m3) were recovered in the container.
The 30 or so fire-fighters mobilised were onsite the entire afternoon in an attempt to restore service at the plant. During the evening, the network was shut down as a precaution, and local health services performed sampling; 1,400 households spread over 10 municipalities were concerned by these measures. The facility informed both the public and the press, then distributed bottles of drinking water. According to the press, the public information campaign took a long time, as the automatic call service neglected those without a land line.
On 16th August, the analyses performed by the regional health agency indicated that the pollution had been absorbed. Water supply was determined to be fit once again for consumption as of 2 pm that day. The highly-corrosive Cl2 especially damaged the installations, automated mechanisms and air compressor; total property damage was estimated at over 50,000.
According to the delivery service, several organisation-related causes led to this accident: a delivery form that went unchecked by the receiving agent, bulk container labelling not verified by the driver, labels concealed by the lorry rod, reciprocal controls of connections not performed, a client’s bleach tank without proper tags. Remedial actions were introduced: a new driver awareness campaign specific to material transfer procedures; prohibition to proceed with a transfer in the absence of the receiving agent; mandatory two-stage reciprocal controls of all connections before any transfer, as formalised by implementation of lorry/tank buffer controls and a double signature requirement; inspection and information transmission regarding client installations via use of a specific document (driver contact sheet); labelling on the upper part of the valve for compressible containers; and obligation to always carry a mask with a filtering cartridge.