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THE Rail Accident Investigation Branch has issued urgent safety advice on maintenance arrangements for wagons which primarily carry dangerous goods, following the derailment of an oil train near Llangennech in South Wales on August 26.

Ten wagons derailed, spilling around 330,000 litres of fuel and causing a fire which led to the evacuation of local residents ( RAIL

913). The route remains closed.

RAIB’s preliminary examination found that during the journey from Robeston, the brakes on all wheels of the third wagon became applied, with the leading axle ceasing to rotate.

This locking created ‘false flanges’ on the outer side of the wheel treads. When the train reached the crossover at Morlais Junction, the false flange on the right-hand wheel caught on the converging stock rail and distorted the track, leading to the derailment of both wheels.

Around 100 metres further on, the partly derailed wagon encountered facing points set to route the train to the right. The locomotive and first two wagons went to the right and the derailed third wagon went straight ahead. It turned onto its right-hand side and detached from the wagon in front, causing the points and track beyond them to be destroyed. The derailment of another nine wagons followed.

Detailed examination of the brake group on the third wagon found that the relay valve was loose on the pipe bracket. A sealing ring from the ports in the mating face had migrated to a position where it lodged between two other ports, distorting their sealing rings and potentially creating a route for air to pass from the auxiliary reservoir to the wagon brake cylinder, applying the brakes on the wagon.

RAIB’s urgent advice says that Entities in Charge of Maintenance (ECMs) should review their system of inspection and maintenance for wagons which primarily carry dangerous goods, to ensure they have suitable arrangements in place to manage the safety risk associated with malfunctioning brake systems.

This review should include an assessment of the adequacy of facilities, tools and equipment at all maintenance locations, and of the systems for ensuring the competence of those involved and the management systems and instructions for assuring the quality of work undertaken.

It should also assess the adequacy of methods for initial and ongoing assurance of the security of fastenings, and processes for the identification and tracking of safety-critical components.

The investigation found that the ECM for the wagon which initially derailed was unable to identify where and when the fastenings of the relay valve had last been disturbed.

There was no record of any check on the tightness of the fastenings ever having been made, and no process requiring such checks of provision of measures which would have indicated that fastenings were becoming loose.