In 2010 Dr Tony Boyle was asked to prepare an expert witness report on the safety management system aspects of the train derailment at Potters Bar in 2002* and he subsequently gave evidence at the Inquest. This evidence is available on the Potters Bar Inquest website.

The Potters Bar rail crash occurred because nuts that were supposed to hold a set of points together had worked loose, allowing the points to fail as a train passed over them. Seven people were killed in the subsequent derailment and crash. The nuts on the type of points involved in the derailment had a history of coming loose and because of this they were inspected weekly and the nuts tightened as necessary. Dr Boyle pointed out that had an effective safety management system based on BS OHSAS 18001 been in place there would have been various processes that might have prevented the accident. The table below shows the sub-elements of the BS OHSAS 18001 safety management system that, had they been effective, would have prevented the derailment.


Sub-element Effects
Operational control This sub-element should have ensured that there were written instructions for the maintenance of points and thus prevented inadequate work.  There were in fact written instructions but, as was discovered during the investigation into the derailment, these had been ‘lost’.  When found, they showed that the nuts had been being tightened in an inappropriate way.  Had they been tightened appropriately they would not have come loose – they had been designed not to come loose.
Nonconformity and corrective action Nuts coming loose on points is a nonconformity and the nonconformity procedure should have ensured that the causes of the loose nuts on points were investigated and remedied.  Simply tightening the nuts is correction – dealing with the symptoms – not corrective action – dealing with the causes.
Records There should have been records of nonconformities (such as loose nuts on points) so that they were available for measuring purposes (see below).
Measuring This sub-element should have ensured that nonconformities were subject to trend analyses (to determine whether things were getting better or worse) and pattern analyses (to determine whether, for example, particular types of points had higher rates of nonconformities).
Risk assessment This should have ensured that the risks associated with poor maintenance and inspection were identified and controlled effectively.
Internal audit A proper management system audit would have identified the absence of instructions for tightening the nuts on the points and the audit would have been halted until the instructions had been found.  This sub-element should also have ensured that that the weaknesses in the other sub-elements were identified and rectified.

It is Hastam’s experience that few organisations have

  • an operational control procedure,
  • a Nonconformity and corrective action procedure,
  • a Measuring procedure that includes measurement of nonconformities, or
  • an Internal audit procedure that includes management system auditing.

* Dr Boyle was also asked to comment on the safety management system aspects of a similar train derailment at Grayrigg in 2007. However, for clarity, we have only referred to the Potters Bar derailment in this case study.