A CRACKED RAIL which was 'almost impossible to detect' with current inspection techniques has been blamed for the near derailment of a 130km/h Virgin train and looks set to spark a nationwide investigation, NCE learned this week.
The five-year old rail shattered in five places on 29 April as an early morning train passed over it at Hemel Hempstead on the West Coast Main Line.
But only hours before the incident, the section of rail had been thoroughly checked and tamped by maintenance contractor GTRM. No cracks were spotted by its ultrasonic testing equipment and the rail was given a clean bill of health.
Health and Safety Executive inspectors said it was 'very fortunate' that no-one was killed in the incident. A full investigation to find the cause of what it believes is a new type of crack was launched immediately and is expected to be concluded in the next two to three weeks.
The results are likely to prompt urgent checks on other parts of the rail network and the development of a more reliable technique for detecting faults.
HM Principal Inspector of Railways for the Midlands Chris Hall said the hairline crack responsible for the break had not been detected by GTRM because of the way it had propagated inside the rail.
'The established ultrasonic technique requires cracks to be perpendicular or at least at an angle to the beam of ultrasound. This crack was at such an angle that it wasn't picked up,' he said.
Tests by specialist consultant Serco Railtest ruled out early suspicions that the British Steel manufactured rail failed due to a metallurgical fault. Hall said the crack was more likely to have been caused by contact fatigue due to a combination of heavy loading and poor track geometry.
'There is no getting away from the fact that a rail of that age should not have failed,' he said.
The revelation comes just days after the publication of rail safety statistics which show a 21% jump in rail breaks since last year. Speaking at the launch of the figures, HM Chief Inspector of Railways Vic Coleman criticised Railtrack's inspection regime and accused it of operating 'half blind' without full knowledge of the network.
A Railtrack spokesman said initial conclusions from the HSE investigation into the Hemel Hempstead incident had already prompted it to take action to check for the new type of cracks.
'A track engineer has reported the parameters of the rail break to other zone engineers and we are locating sites with similar parameters where we will carry out further checks,' he said.
So far only two locations at Tring and Rugby on the WCML have been checked as it takes four hours to test a 3m long section of track. But 'a dozen or so' locations around the country have been highlighted as potential danger spots, Railtrack confirmed.
Virgin Trains chief executive Chris Green said the incident in April had caused him 'serious concern'. He added: 'Everyone has reacted in the right way to this, but it must be a worry that these cracks can happen on a high speed rail line'.
GTRM said it was co-operating fully with Railtrack.