A study on risk assessment of road tunnel fires by full-scale testing

Heavy good traffic by road has continually increased over many years and owing to population or environmental impact reasons, the actual number of road tunnels has grown in many countries. It must be remarked that, due to the sharp reduction of vehicle pollutant emissions, the ventilation of road tunnel is more and more determined by the need of controlling smoke in case of fire. The first step of this study focused on full scale test program development. This included an assessment of the tunnel’s condition, identification of possible modifications, design of the ventilation system to be tested during fires and set-up of the test planning. Full-scale experimental runs were carried out utilizing a two-lane tunnel of the Highway A7 Genoa-Milan, in order to simulate the evolving scenarios following an accident with fire development. Firstly, experiments were performed with simulated smoke, so to obtain a complete fluid dynamic characterization of the tunnel, under different atmospheric conditions. The following testing was carried out with several fire loads characterized by different calorific value. Following aspects were deeply analyzed: longitudinal and transversal temperature gradients in presence and in absence of fire-extinguishing automatic systems; effects of different ventilation conditions; evolution of the heuristic pollutants during the fire. The second step was addressed laboratory-scale experimental runs: design and construction of the laboratory test facilities; experimental runs, data evaluation and preliminary modelling. Combining the results of full testing and theoretical modelling, practical recommendations are drawn concerning, from one side, general measures relating to the tunnel and the traffic (e.g. ventilation design and operation), on the other side specific measures to reduce the consequence of accidents and implement emergency response management.