The drill and damage between old street and essex road stations. Courtesy of RAIB

Construction drilling breaks tunnel roof and shuts railway for two days in London

Published 19th April 2013

Construction error leads to potentially fatal railway accident

The Rail Accident Investigation Board (RAIB) is investigating what they call a “Dangerous occurrence” which took place in a tunnel between Essex Road and Old Street station in London.

The RAIB is investigating the incident that occurred on the morning of March 8, 2013 when a drill broke through the tunnel wall in a single bore tunnel inside which First Capital Connect runs a 10 minute interval service between Finsbury Park and Moorgate. These trains carry millions of passengers from Hertford and Welwyn Garden City and intermediate stations, to the City in class 313 electric commuter trains.

Passing water

At 10:09 hrs the driver of train with a reporting number of 2V16, the 10:02 hrs service from Moorgate to Welwyn Garden City, reported that water was gushing from the roof of the tunnel. As is normal with these things, any unusual potentially unsafe occurrence is followed up usually with the driver of the following train who proceeds slowly and examines the line.

The following service which was running without passengers onboard, carried out the examination at slow speed and when it was about 420 metres north of Old Street station, the driver and a Network Rail Mobile Operations Manager who was with him, saw two large metallic objects that had apparently fallen from a hole in the roof of the tunnel.

Had this drill fallen on a passenger train in the rush hour, there probably would have been a derailment causing many injuries and even possibly fatalities given the fact that the tunnels are very narrow. Other trains would have stopped in the tunnels without electric power so a major rescue operation (which is rehearsed) would have had to take place.

Electric shock for the drill driver?

The line is electrified using the third rail system and one of the objects that came thgrough the tunnel wall was in contact with the live conductor rail which carries 650 volts DC current. These objects were later identified as sections of an auger (drill) that had penetrated the tunnel lining before falling onto the track. Each section measured approximately two metres in length and was 0.35 metres in diameter.

Immediate checks carried out revealed that the augering operation was being made in conjunction with construction activity on land about 13 metres above the top of the tunnel.

Risks out of sight?

The RAIB’s investigation is independent of any investigation by the Health and Safety Executive or the Office of Rail Regulation. The RAIB will publish its final report with its conclusions and recommendations how to improve safety following the conclusion of its investigation. This may take up to 12 months but as this case seems to be a clear cut incident, it may be produced earlier.

Written by Phil Marsh

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