Keywords: quantitative risk analysis, tunnel risk, fire risk, consequence analysis, fire evacuation, traffic statistics, accident evaluation, expected risk, scenario analysis.

This paper covers the topic of quantitative risk analysis as applied in the extended application of TuRisMo, the Austrian risk assessment methodology for road tunnels, published in guideline RVS 09.03.11 [1]. It shows that by application of appropriate statistical and numerical models it is not only possible to demonstrate that the required safety level can be reached but also to compare the risk level of different designs in a relative approach.

In the first section the background of tunnel risk assessment is presented to give a basic understanding of the issue followed by a description of the requirements and applicable methods for the calculation of the expected risk values for risk of mechanical accidents as well as for fire risk. At first the statistical approach for the assessment of mechanical risk is presented. Starting with the definition of different types of scenarios corresponding frequencies for these types of events are derived based on an evaluation of accidents in tunnels of the Austrian motorway network. The dependency of incident frequency of the traffic volume and correction functions for deviating traffic compositions are shown.

Then the possible approaches for the assessment of fire risk in tunnels are discussed concluding in the requirement of numerical simulations of smoke propagation and people evacuation. This is because of the low number of fire incidents in tunnels no statistical approach is possible. After presenting the relevant influencing factors that have to be taken into account, approaches for the impacts on system stability are discussed. In this context the need for systematic variation of parameters for the calculation of average risk values is explained. It is shown how the complexity can be reduced by the application of statistical methods focusing on the selection of representative scenarios. Furthermore efficient models for the simulation of smoke propagation and the evacuation of people are presented.

Finally the application of the methodology in the upgrading process for the Ucka tunnel is presented. Different ventilation systems are compared and additional measures of risk mitigation are assessed in order to provide assistance in the design selection process and to demonstrate that the required safety standard can be reached.

1

"RVS 09.03.11 Tunnel Safety - Tunnel Risk Model", FSV, Austria, 2008.

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