Key words: Tunnel fire, CO concentration, aspect ratio, CFD.

Abstract: In a tunnel fire, the production of smoke and toxic gases remains the principal factors prejudicial to users. More than 80 % of deaths are in direct relation to the toxicity and the opacity of smoke. In this paper, the smoke propagation and CO production in a longitudinally ventilated tunnel fires for different aspect ratio is analyzed numerically with large eddy simulation (LES) by Fire dynamic simulator (FDS). The evolution of the CO concentration longitudinally along the tunnel will be studied in this work. The tunnel slope’s effect on the CO concentration will also be studied. The FDS Numerical results are firstly verified by comparison with the experimental measurements of Li et al. [15-16], in terms of the critical velocity and the maximum smoke temperature under the ceiling. A relatively good agreement has been obtained. Results show that the CO concentration increases with the aspect ratio while this latter remains lower than 1 and then decreases as the aspect ratio increases for an aspect ratio greater than 1.