At 7:20 a.m., at a chemical manufacturing plant, a tank car containing butadiene (a liquefied, highly flammable gas) derailed and collided with another railcar loaded with butadiene. The tank that was struck tipped over onto its side although no leakage was detected. The other tank remained upright but was derailed. Firefighters secured the area and began monitoring the railcars continuously. The railway used jacks and lift tables to put the railcar back on the rails after checking their integrity. It was directed to the unloading station where its contents were emptied, and then removed from service.

Concerning the railcar that had tipped over, the operator contacted the TRANSSAID network and specialised companies to implement the protocols to partially drain the contents and then lift the railcar. A safety perimeter was established and drainage operations began 5 days after the accident. During this operation, a leak occurred on a gas side seal on the tank. A flare was established to channel the leak, then it was stopped by tightening the system where the joint was located. The leak was limited to less than 20 litres of butadiene. When the railcar reached the halfway point, it was sealed and then lifted by a specialised company using slings and four cranes. To perform this operation, the operator evacuated the area and implemented protective measures (mobile gas detectors and fire-fighting equipment). After verifying its integrity, the railcar was transferred to the unloading station and then to a maintenance area for repair.

The impact between the two butadiene railcars resulted from a shunting operation of a four-car train within the site. Upon passing a switch that could be manoeuvred without chocking, the rear axle of the last tanker moved the switch, opening the wrong track. This displacement was made possible by the combination of several factors:

• the curvature of the track was unsuitable for long railcars such as the one involved,
• the rigidity of the train due to the tight coupling between the cars,
• the forcing open of the bogies (rotational movement).

Although the train crew managed to stop the manoeuvre, the tanker, which had gone in the wrong direction, struck the first car of the train parked on the track. The impact, combined with the ballast movement of the liquid and the rigidity of the coupling, was enough to overturn the railcar.

To avoid this type of event, the operator:

• requires low-speed operation and the presence of an operator when passing this type of switch,
• conducts a complete audit of the network switches,
• controls the coupling of railcars to reduce the rigidity of the trains,
• limits the speed of the trains to 6 km/h,
• prohibits parking on track after a switch that can be operated without chocking.