Incident Investigation - Potters Bar Rail Crash
Health and Safety Executive (HSE) (now Office of Rail Regulation
British Transport Police (BTP).
A major accident occurred on 10 May 2002 when a Networker
Express train travelling from Kings Cross to Kings Lynn derailed
approximately 160m south of Potters Bar station. The rear (fourth)
vehicle of the train became detached from the rest of the train,
slid up the platform slopes and eventually came to rest transverse
to the tracks and under the station canopy. Seven people were
killed and many others were injured during the incident.
What We Did
HSL was contacted about 2 hours
after the accident and a team of engineering investigators was sent
immediately to the scene where they began an investigation under
the joint control of HMRI and BTP. Attention quickly focussed on
point 2182A south of the station which was clearly in a fault
condition and it was evident that the malfunction of this points
had led to the derailment. Nine other points in the vicinity of
Potters Bar were also examined and were found to exhibit similar,
although less serious, defects.
With the assistance and advice from rail industry personnel,
point 2182A, weighing approximately 15 tonnes, was detached from
the rails by thermal cutting and transported to HSL where it
underwent detailed metallurgical examination and series of
mechanical tests to assess its performance.
In addition, the performance of the four rail vehicles leading
up to and during the incident was studied. Their external condition
and crashworthiness was assessed and vehicle dynamics studies were
carried out to explain the behaviour of the vehicles during the
incident. A limited programme of vibration testing was performed to
assist in understanding the loosening of the nuts on the point.
It was concluded that four main factors contributed to the
failure of the point, these were: the poor condition of the
backdrive; the loss of nuts from the right-hand end of the rear
stretcher bar; the loss of nuts from the left-hand end of the front
stretcher bar and the fracture and disengagement of the lock
stretcher bar. The point failed in such a manner that the train was
being pulled into a reducing gap between the switch rails,
resulting in some of the wheels climbing over the rails and
eventual derailment of the rear end of the train.
HSL's findings were reported in the various reports issued by
the Major Incident Inquiry Board and a number of presentations were
made to interested parties. A possible generic problem with the
set-up of the points was identified at an early stage of the
investigation and this was communicated immediately to the
industry. As a result of this work, the industry introduced a Good
Practice Guide with the aim of preventing other accidents
being caused by the failure of this type of point.
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