Fire safety design of road tunnels

Abstract: This thesis can be described as a journey in performance-based fire safety design. Along the way questions such as what fire safety is, how it can be measured, whether we are posing the right questions, or engineer the best solutions, have arisen. The safety journey naturally started out with the traditional view, with fire safety engineering based on limit-based design. Using this paradigm the safety problem is limited to fire safety issues, and safety levels are defined for each fire safety objective in isolation. This contradicts the basic rationale of decision-making where the best trade-off is sought between all objectives, most often by use of Cost-Benefit Analysis (CBA). This naturally led to the second stop of the safety journey called CBA-based design where risk is exchanged as a cost factor in a cost-benefit framework. In this paradigm safety is a relative concept depending also on a few other measurable objectives. Throughout this work, the focus of the journey has been on road tunnels. Tunnels are hard physical and technical systems. However, they exist in a social reality and a complex society. During the design process many social and soft issues surface that can conflict with technical fire safety measures. The journey thus went on to acknowledge both the scientific or technical aspects of risk and social structures; the ethical and democratic aspects of risk, in a decision-making framework. This emphasizes how the problem is framed, what our objectives are, and how creative alternatives are generated and assessed. It may not even be relevant to talk about "how safe should the tunnel be" because it is subordinate to the overall decision condition, all aspects considered. In the end a design alternative is chosen that exhibit the highest utility on all objectives together, i.e. safety in balance with other objectives. For any tentative design, safety can develop in two directions; Firstly, it may be that some safety measures are too conservative or in conflict with other objectives such as cost or the environment, i.e. resources are better used elsewhere. Secondly, it may also be possible to achieve more safety; it is argued that a Vision Zero design philosophy with its emphasis on inherently safer or fail-safe systems highlight important safety qualities which are not highlighted in limit-based or CBA-based design. Along the way (a) road tunnel fire safety and risk literature were studied, (b) interviews were made with tunnel fire safety professionals (c) performance based requirements for road tunnel fire safety were derived, (d) the accuracy of tunnel fire dynamics models applied in road tunnel fire risk analysis was compared with experimental data, and (e) the design framework of fire safety engineering was critically analyzed and an alternative fire safety design framework was proposed.