Towards Design Options and Trade-offs for Road Tunnels Incorporating Suppression Systems

The possibility of trade-offs in road tunnel design incorporating suppression has been evaluated. Different tunnel configurations and ventilation conditions is considered to identify potential trade-offs, offering options of design alternatives for future substantial cost-benefit savings. Suppression systems are regularly used in Australia and Japan, and the interest regarding suppression systems in tunnels are growing in the rest of the world and slowly getting implemented in tunnels in Europe and other continents. Due to changes for instance in research regarding the acceptable design fire size and the growing focus on the fire safety in tunnels in general around the world, there is an opportunity of introducing trade-offs in tunnel design incorporating suppression systems. Possible trade-offs has been identified and outlined using risk based comparison approach as part of an evaluative process considering relevant safety objectives. Reliability of suppression systems is shown to be an important aspect, as well as the behavior of tunnel users. One may argue that suppression systems should always be considered as a primary option in tunnel design to achieve a desirable level of safety, enable fire brigade intervention and limit any costs associated with a tunnel fire. As an additional benefit to suppression systems offer the opportunity of potential trade-offs, opening a window of more innovative solutions and cost-benefit approaches compared to traditional prescriptive tunnel safety design. Residual value of this evaluative work and its conclusions shows that, when incorporating trade-offs, aspects like ‘point of no return’, visibility and consequences of trade-offs in the event of suppression system failure must be addressed from a fire engineering and risk management point of view.