Pollution
Humain
Environnement
Economique

At around 2:15 p.m., mercaptan leaked out of an unvented tank container at a transport company after its valve had been incorrectly moved. A strong odour was detected in some 30 towns in the area. Emergency services set up a cordon and halted traffic. They evacuate or confine several schools. Emergency services receive 150 calls from local residents about the unpleasant odours. Trace amounts of mercaptan are added to a city’s gas supply to give it a distinctive odour. Gas measurements, and those made using colorimetric tubes to detect the presence of mercaptan on site, were negative. The plant operator issues a press release. The situation was considered to be under control three days later. During this period, the company’s sewer lines were cleaned as part of the efforts to locate the leak. These cleaning operations resulted in odours that raised local residents’ concerns.

The container in question was fitted with a dip tube for filling. Shortly before the event, an attempt to fill the container at a chemical plant had failed. It was assumed that mercaptan left inside the container had clogged the dip tube and the container was sent back to the transport company. Upon its arrival, two technicians decided to work on the container. While site procedures state that only empty and cleaned tanks may be serviced, the technicians removed the dip tube’s blind flange. One of them then opened/closed the butterfly valve upstream of the tube, causing some 10 litres of gas to be released.

The technicians were suspended.