The second interim report into the Hatfield derailment on October 17 2000, issued by Britain’s Health & Safety Executive on January 23, includes an astonishing reconstruction of the first 35m of the high rail curving north at 1462m radius from the initial transverse fracture. As the 6m section reproduced below indicates, the way this rail shattered into fragments no more than 1m long is quite extraordinary, even allowing for the damage caused by derailed coaches travelling at 185 km/h. It may well be unique.
The 56 kg/m rail was rolled by British Steel (now Corus) and laid in 1995. It was mill heat treated to improve wear resistance, and was only slightly worn. The microstructure of the rail steel was examined in HSE’s laboratory where tests confirmed that it conformed to relevant standards.
The report says that some 300 fragments of rail were recovered in all. However, many were flakes that had spalled from the running surface of the high rail through this curve due to rolling fatigue cracks that had propagated at shallow depth. One such flake was 100mm long, 30mm wide and 3mm deep. Extensive spalling was present before the accident as some pits were rusty; others were clearly fresh.
However, it was brittle fracture, associated in about 50 cases with fatigue cracks that had turned down from the running surface into the rail head at 20í to 35í to the vertical, that caused the rail to break into so many pieces.
The rail was inspected in January 2000, and on several occasions subsequently, when its surface condition indicated the need for an immediate speed restriction and early replacement. The report is silent on these matters, pending a decision on the prosecution of individuals and the two companies mainly involved: Railtrack and its track maintenance contractor, Balfour Beatty.
HThe closing speed in the head-on collision at Ladbroke Grove in west London on October 5 1999 has been revised downwards by the HSE to 210 km/h in its final technical report. Previously said by HSE to be as high as 233 km/h, it is still believed to be the highest collision speed in railway history. n