Channel Tunnel Safety Case: Quantitative Risk Assessment Methodology. T.A.W. Geyer and M.I. Morris, Four Elements Limited, 8 Cavendish Square, London, UK; and R. M. Morris, Eurotunnel, PO Box 2000, Folkestone, Kent, UK
Four Elements was engaged by Eurotunnel to
carry out the Quantitative Risk Assessment (QRA) of the Channel
Tunnel Fixed Link. This formed a major and pivotal component
of the Safety Case required by the Intergovernmental Commission/Channel
Tunnel Safety Authority as an essential part of the evidence needed
for the granting of an Operating Certificate.
The paper would address the major elements
of the work, emphasising how traditional risk assessment techniques
were adapted for application to the railway system, in particular,
the development of various novel computational models and simulation
techniques to enable the risks of this complex and sophisticated
system to be quantified with adequate realism.
Four Elements also assisted Eurotunnel in defining
the risk criteria, consistent with government policies and industrial
precedents, which were agreed with the Safety Authority. The
structure of the criteria follows the UK Health and Safety Executive's
(HSE) approach of ensuring risks are reduced "As Low As Reasonably
Practicable". The approach to the derivation of the criteria
would be summarised.
The QRA work required the identification and
assessment of all risks to which passengers and Eurotunnel staff
may be exposed, especially those associated with fire, collision
and derailment. The paper would give examples of how the techniques
of fault tree and event tree analysis were used, and also describe
how Monte Carlo simulation techniques were used in the scenario
development assessment.
Besides demonstrating the overall level of
safety, the QRA has contributed to several design and operational decisions, notably in the specification
of emergency procedures and has helped Eurotunnel resist pressure
to implement excessively expensive design changes that were not,
in fact, effective in reducing risk The benefits of adopting a
quantified approach to the assessment of system hazards will be
addressed.