At around 2:10 pm in a marshalling yard, a 4-railcar convoy carrying coal collided with and damaged a group of 4 railcars carrying chlorine (Cl2), which were nearly empty, not yet degassed and at a full stop. Under this shock, 2 tanker cars overlapped one another. A bogie from the first was torn off while the second derailed.
The station’s internal emergency plan was activated. A safety perimeter encompassing the split siding was cordoned off. Notified at 2:15 pm, the first responders arrived at the scene at 2:35 pm. After visual confirmation that no leak was present, the car lifting operation was authorised. The station operator informed the prefecture at 8:45 pm upon the advice of an expert with the freight shipping company, who considered that the risk may have been underestimated by the fire-fighters. Called back to the site, the fire-fighting team confirmed their initial conclusions. The safety perimeter was reduced to 4 tracks.
On the morning of 23 December, the quantity of Cl2 contained in each railcar was evaluated at 1.6 t (1.5 t liquid and 53 m³ of gas). Since the safety report of the yard had not accounted for the dispersion of several tonnes of Cl2, a modelling request was submitted to the emergency situation support unit of a public agency. The distances of both irreversible effects and lethal effects were estimated at either 1,000 m and 350 m under normal situations (neutral weather conditions and a 5 m/s wind speed) or 3,000 m and 500 m under unfavourable conditions (very stable and a 3 m/s wind speed). A shopping centre was located just 1.2 km from the overlapping cars.
On 23 December at 3 pm, the prefecture assembled the fire-fighters, rail operator, shipping company and classified facilities inspectorate in order to specify the intervention conditions. With the option of onsite drainage rejected, it was decided to secure the overlapping tanker car with a crane at the time of evacuating the undamaged cars via the track. The overlapping tanker car could then be placed on the ground prior to cutting out the bogies with a blowtorch and removing the tank via a flatbed car to a degassing facility. Thermocouples used during the cutting operation would serve to monitor the temperature, given that the steel was capable of combusting when placed in contact with the Cl2 in the neighbourhood of 120°C. These sensitive operations were held at night.
The accident was caused by the mistaken order to send the 4 coal cars; the automatic braking system failed. Regulations regarding the rail transport of hazardous substances had been modified shortly beforehand in the aim of preventing this very type of accident. The damaged cars had still not been fitted with anti-overlapping devices to protect the back of the cars (temporary period).
The safety report produced for this yard in 2009 had been followed in April 2010 by a compliance request pursuant to the Ministerial decree issued on 18 February, 2010 that had yet to be implemented. The following month, 2 other accidents occurred at this same vital station (ARIA 39508 and 39703) due to the volume of rail traffic into and out of Germany.
