At 09:01 hrs on 5 July 2007 westbound train 117 struck a roll of fire resistant material lying on the track between Mile End and Bethnal Green tube stations on the Central Line of the London Underground Network.
The material had been used to secure bags of fast-setting concrete stored in the cross passages between the eastbound and westbound lines. While the concrete was not a fire hazard, the bags containing it were, and regulations required any such materials to be protected with fire resistant material.
The night before the accident, a Balfour Beatty gang assisted specialist contractors to replace contaminated ballast on the line. The works gang lacked a knife able to cut through the large roll of fire resistant material, so once the fast-setting concrete bags had been covered, the end of the fabric was still attached to the roll.
Between leaving the works gangs leaving the roll of material and the accident, 74 westbound and 59 eastbound trains should have passed through the section.
The action of wind from these trains enabled the heavy roll (which could have been up to 40kg) to move from the cross-passage and onto the westbound section and lie on the track.
According to the report, the damage could sustained could have been much worse, as "The bogie frames displaced the conductor rail to the left which then assisted in constraining the trajectory of the train so that the leading gear cases on the leading ends of the first and second cars remained on the rail head. This prevented the car bodies from further displacement and collision with the tunnel wall"
The RAIB made five recommendations:
- London Underground should change the training requirements for the Site Person in Charge (SPC), to ensure that it contains adequate information on the storage of materials including the effect of wind in cross passages.
- Metronet [or any successor organisation] should review risk assessments of materials in cross passages. If risk assessments mandated or inherited from LUL are found to be deficient then LUL should be made aware of the shortcoming.
- London Underground should address any deficiencies in risk assessments for stored materials.
- Metronet should review and if necessary amend the instructions for the use of fire-resistant blankets.
- Metronet should be aware of the wind effects that can occur in the deep level tube system.