Experimental study on thermal and toxic hazards connected to fire scenarios in road tunnels.

The problem of toxic smoke in case of an accident with fire scenario is particularly severe in long tunnels and immediate effects from combustion product exposure often include fatalities. Notwithstanding extensive studies on fire simulation in tunnel, 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. In this paper, experimental runs in a laboratory scaled tunnel, simulating accidental fires of different heat release rates allowed firstly to characterize the thermal profiles in pool and car fires and to compare results by an analytical pool fire model. Results were compared as well with those obtained in a real scale tunnel, so as to quantitatively assess the scaling effect. A series of experiments was performed simulating an accidental scenario including pool fire from collision between a light vehicle and a HazMat heavy vehicle. An extensive set of experimental data allowed performing with good accuracy and reproducibility a complete characterization of toxic gases from car model fires, together with carbon monoxide and oxygen trends. The results obtained under different heat release rates allowed evidencing the dependence of the yields of toxic gases upon the considered scenario. Based on the intrinsic toxicity data of identified compounds, it is possible to draw practical conclusions, useful to assess the potential hazard associated to exposure to toxic smoke in road tunnel.