Experimental study on thermal and toxic hazards connected to different accident scenarios in road tunnels

Tunnels have long been used for speeding up road and rail connections between places separated by natural barriers and for reducing traffic congestion in urban areas. Not surprisingly, Italy with its particular orography and geographic position, has the largest tunnel length in Europe (more than 1900 km, not including city metro tunnels), and equal to 27% of the European total. However, in parallel with an always increasing interest for underground transportation structures, there is also an increasing concern for possible fire emergencies occurring inside tunnels and critical underground infrastructures, taking into account the peculiar geometry of infrastructures. In recent years serious accidents such as the fires in the Mont Blanc, Gotthard and Tauern tunnels have led to increasing attention to safety in tunnels. The transport of dangerous substances (inflammable and toxic) by road and rail is widespread in Italy and incidents involving this type of transport present an additional serious problem. Even if the last two decades have often seen drops in road accidents and a consistently high level of safety, recent accidents have shown that some types of commercial products, depending on their chemical composition, can cause large fires with severe evolving scenarios. If vehicles carrying hazardous substances (inflammable or toxic) were to be involved the accident scenarios could assume catastrophic proportions. The distribution of areas with high concentrations of plants at major risk in Italy generates a large flux of vehicles in the ADR category on the national road network. Although the rail network has different characteristics it is also subject to the risk of tunnel accidents, in particular because of the presence of very long tunnels. Finally, the case of fires in urban subway systems cannot be neglected. In this context, the major problem is due to the high density of passengers and the possibility of large concentrations of toxic combustion products in the underground stations. Notwithstanding extensive studies on fire simulation in tunnel, reported in scientific literature, there is still a substantial lack of information on the different toxic products from combustion of light or heavy vehicles. In particular, there is a need for reliable test methods suitable to provide toxic products yields connected to defined accidental fire scenarios. The objectives of the present paper are the experimental determination of thermal profiles inside and outside the gallery, under different thermal power emission and the qualitative and quantitative determination of toxic compounds of smoke from burning vehicles in a tunnel. Experimental techniques used to measure compounds from fire range in size from bench-top apparatus for testing small specimens, up to full scale tests. Regardless of the scale, it is important that fire reaction runs are carried out in conditions that closely replicate the type of fire to which the vehicle could be exposed. In particular, one of the main results of this work lies in providing an effective and reliable analytical methodology to optimize the analysis of toxic compounds of interest in tunnel fire scenarios.