Channel Tunnel Safety Case: development of the risk criteria

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 Channel Tunnel is a novel project with many unique features. Even so, the general principles of risk analysis, which have been developed in other industries, are equally applicable. The process involves identifying a comprehensive set of accidents that could occur during system operation, and estimating the likelihood and severity of each scenario. One of the main purposes and benefits of adopting a quantitative approach within the Safety Case is that it provides a framework within which all risks can be evaluated on a common (quantified) basis, thereby allowing the significance of individual hazards to be assessed in the context of the system as a whole. In addition to enabling the acceptability of the risks to be assessed against pre-defined risk criteria, the QRA model can be used to evaluate the benefit of measures intended to improve safety, so that expenditure can be prioritised on the basis of cost effectiveness, whilst enabling operators to demonstrate that risks are reduced to levels which are as low as reasonably practicable as required by UK legislation