The Rail Accident Investigation Branch (RAIB) today released its report into last year's freight train derailment just outside of Stewarton.

You can download a full copy of the report here

The sole purpose of RAIB investigations is to prevent future accidents and incidents and improve railway safety. The RAIB does not establish blame, liability or carry out prosecutions.

The RIAB has published the following summary of its investigation.

At 06:12 hrs on 27 January 2009 the last six tank wagons of a ten-wagon freight train, carrying a mixed consignment of gas oil, diesel and kerosene to a fuel depot south of Kilmarnock, derailed as the train crossed a metal underbridge south of Stewarton. The bridge, which takes the railway over the A735, collapsed under the train and the derailed wagons overturned.

There were no casualties from the derailment, but fuel from four of the derailed wagons leaked into watercourses, causing severe environmental damage, and there were localised fires.

The immediate cause of the derailment was the collapse of the bridge following a catastrophic failure of its east and centre main girders. Heavy corrosion had so significantly weakened these main girders that they were no longer able to carry the loading from the heaviest trains that were permitted over the bridge. This was because of:

* the form of construction of the bridge, leading to a hidden corrosion trap that affected the inner surfaces of the main girders, and hence to holes forming in the girders;
* the use of incorrectly assumed dimensions for the thickness of the main girder web plates, and not taking allowance for material loss due to corrosion, in the routine assessments of the bridge;
* no arrangements being made to inspect the hidden parts of the bridge girders where the heavy corrosion was occurring;
* neither fully repairing, nor painting, the bridge during waterproofing in 1987, when the heavy corrosion would have been revealed;
* the lack of any action in response to the main girder web corrosion issues that were identified during the last routine detailed examination of the bridge in October 2003;
* the lack of any response to the continued reporting of corrosion defects in the routine annual visual examinations since 2003;
* the lack of a formal means of alerting Network Rail of urgent issues findings arising from a special assessment of the bridge, which was undertaken when Network Rail verified the live load capacity of all its underbridges; and
* the decision to replace the bridge as part of an upgrade scheme, which resulted in information that was potentially relevant to the condition of the bridge, while it remained in service, not being considered.

Network Rail has commenced an exercise to assess all similar bridges to that at Stewarton, and to address other issues that have arisen from this derailment.

Recommendations

As a consequence of this accident, the RAIB has targeted eleven recommendations at Network Rail (one of which is also targeted at the owners of tank wagons outside the Private Wagons Registration Agreement (PWRA)). These cover:

* checks and remedial action with regard to other Network Rail bridges that may be at risk because of similar hidden corrosion issues or erroneous assessment findings;
* improvements to Network Rail's methods and processes for the examination of hidden critical parts of structures;
* improvements to the management of the information used for making decisions about the structural safety of Network Rail's bridges;
* improvements to Network Rail's bridge assessment procedures;
* evaluation of the use of track geometry recordings as a means of identifying structural issues with railway underbridges; and
* improvements to the construction of existing UK tank wagons.

The RAIB has also targeted one recommendation at the Department for Transport, concerning possible changes to international regulations concerning tank wagon design.