The employees in an industrial and commercial area noted a pungent and unpleasant smell at around 4 p.m. The chemical plants in the area have a portable radio communication protocol in the event of unusual occurrences. This made it possible to detect the source of the odour in a fine organic chemistry plant. A leak of quinoline steam – an irritating and highly odorous organic product (with an odour threshold at 71 ppm) – was detected on the connection between a deposition tower and a manufacturing reactor that was in the process of cooling down. The neighbouring plants confined some of their staff due to the odours carried by strong winds blowing in their direction.

The operator continued to cool down the reactor, and the deposition tower was stopped and cleaned with water once the tank had been emptied. This eliminated the last sources of odour caused by the 70 litres of hot quinoline trapped in the column. The contents of the tank (water, soda, bleach and quinoline) were stored in containers before disposal in an approved centre. The confinement at the neighbouring plants was lifted around 6 p.m.

Production begins with a 200 °C reflux phase of the 600 l of quinoline in the reactor. This step eliminates the residual water to purify the product. The hot vapours are trapped in the reactor’s condenser to be neutralised by the deposition tower. This double-jacketed condenser receives water preheated to 100°C by a water bath system.

On the day of the accident, the recirculation pump in the double boiler switched off due to a lack of feed water. Hot vapours were no longer trapped by condensation before reaching the column. They melted the polypropylene fitting and escaped into the atmosphere. The operator installed a pressure compensator on the water bath. The device ensures that water is permanently present in the double boiler, which thus reduces the risk of switching off.