Improvements in passenger rail vehicle fire performance have reduced the occurrence of fires on trains, and have reduced the frequency of serious train fires. This has been confirmed by recent test data and recent fire statistics. Recent papers, such as those by Bowman & Tooley (1), Van Weyenberge & Deckers (2) and Cunningham & Hebden (3), as well as earlier work by Scott (4), have argued the case for adoption of a risk-informed approach to the specification of design fires for tunnel ventilation systems (TVS) design. By balancing estimation of risk against the consequences, such an approach could result in TVS that are designed for a smaller fire than the largest potential fire derived from hazard analysis of the vehicle. Such an approach could lead to significant reductions in carbon usage and in both capital and operating costs, leading to more sustainable underground infrastructure, without compromising safety. The approach follows well-established risk management principles already utilised elsewhere in the transportation sector and within other industries. An obstacle to the widespread adoption of such an approach is the lack of guidance for agreeing risk acceptance criteria. Recent fire tests and actual fire occurrence data are reviewed, and the issue of sparse data for statistical usage is discussed. The risk-informed approach is recapitulated and proposals for risk acceptance criteria are proposed that could be used to specify TVS design fires, with due consideration of appetite for residual societal risk, and presence of any applicable mitigation measures, for example, vehicle fire performance design. Risk may be assessed either using qualitative or quantitative methods. A relevant example is presented from an active project, where the risk-informed approach has been adopted, allowing the tunnel ventilation system to be designed for a fire scenario that is less onerous than the largest fire size at the most disadvantageous location predicted by hazard analysis alone.
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