Experimental and theoretical investigation on road tunnel fire

Road traffic and especially heavy goods traffic has continually increased over many years and, correspondingly, due to population or environmental impact reasons, the actual number of road tunnels has grown in many countries. Notwithstanding the existence of broad national and international regulations, recent accidents involving tunnels (the most severe being Mont Blanc tunnel fire causing 38 fatalities) show that further research is still needed on the topic. In particular, while in the last few years extensive studies were performed in the field of road tunnel ventilation and most techniques concerning construction and safety have been steadily improving, the problems raised by dangerous goods have not yet been dealt satisfactorily. On the other side, 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 research was carried out on a real scale, utilizing a highway tunnel to simulate the evolving scenarios following an accident with fire development. A first series of experiments was performed with simulated smoke, so to obtain a complete fluodynamic characterization of the tunnel, under different atmospheric conditions. The following experimental runs were carried out with real fire development, utilizing alternatively different combustion materials and cars. In particular, following aspects were studied in depth: longitudinal and transverse temperature gradients in presence and in absence of fire-extinguishing automatic systems; evolution of the heuristic pollutant during the fire. In the second phase of the research, a laboratory scale tunnel was designed and realized “ad hoc”, on the basis of Froude similarity. Several experiments were carried out, considering three ventilation techniques and realizing fires characterized by different heat/smoke flow rates. This part of the research was focused on preliminar modelling of the phenomenon and the verification of the effectiveness of preventive and protective measures, both technical and managerial. Combining the results of full scale and laboratory tests, 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.