English summary
On Wednesday 19 August 2020, at 5.07 am, freight train no. 50 233, comprising a locomotive and 31 wagons, coming from Dourges and bound for Vénissieux, came to a halt in the middle of the track between the towns of Villeneuve-sur-Yonne and Saint‑Julien-du-Sault (89). The stoppage was caused by a leak in the brake pipe. The train had derailed 8 km and caused major damage to the infrastructure. Once at the stop, the train driver carried out an inspection of the train and noted the derailment of the front bogie of the 29ᵉ wagon. This wagon was loaded with two tank containers carrying ethyl acetate, a flammable hazardous material.
The direct cause of the derailment was the breakage of the right-hand spindle of the 125th axle of the train following a blockage of the axle-box, itself the result of a forging defect in the wheel which generated a defect in the circularity of its running surface.
The lack of circularity of the right-hand front wheel of the incident wagon caused the axle-box to deteriorate. The hot box detection systems measured the progressive heating of the axle-box as the train moved forward. The abnormal heating of this box could not be identified by the driver despite two visits to the train following two simple "hot box" alarms generated by the Bobigny and Moret systems. Continuing to run the train led to excessive heating of the box until the axle spindle broke. After the spindle broke and the corresponding axle derailed, the train continued for about 8 km before coming to a halt at Pk 131.5 near Saint-Julien-du-Sault.
As a result of this investigation, the BEA-TT has issued four recommendations and one invitation relating to :
• Maintenance of rolling stock running gear : during all wagon maintenance operations in the workshop, generalise the examination of wheel circularity defect indices defined in the CEN standards and the Uniform Contract of Use for Wagons. Standard EN 15 313 and the related VPI guide need to be amended accordingly to cover this risk, given that this defect has been developing since the wheel was put into service (in particular in May 2019 when the company in charge of maintenance (ECE) received the wagon without detecting it) ;
• Tools and assistance for Freight drivers operating on the RFN to deal with hot box detection (HBD) alarms :
- equip drivers with tools to help them visit the train and recognise hot boxes ;
- update freight train drivers’ knowledge of HBD procedures ;
- revisit the driving guidelines in order to better deal with the case of a second Simple Alarm occurring on the same box and the case of an Unconfirmed Simple Alarm.
• Centralising temperature informations and alarms from hot box and brake application detection systems in order to optimise operation and support for operators, traffic agents, drivers and infrastructure maintainers ;
• The frequency of installation of HBDs depending on the type of current freight traffic (speed, axle load, etc.) and the acceptable level of residual risk ;
• Raising awareness of the impact of HBDs on the system’s level of safety among the infrastructure manager’s staff, traffic agents and infrastructure maintainers.