Scenarios of fire behavior using physical models of tunnels with different inclinations

Critical velocity remains one of the most important design parameters in the theory and practice of emergency ventilation of road tunnels. It should be noted that basing practice only on this value can lead to serious error. Therefore, it is necessary to take into account other important parameters of a particular tunnel and to develop in advance a clear algorithm of actions to manage emergencies. In this paper, numerical and physical models are used to investigate the scenarios of fire development of different strengths. The nature of the expected aerodynamic resistance in the tunnel caused by fire is analyzed. In particular, the reduction of ventilation velocity caused by the throttle effect and the algebraic summation of flows are distinguished from each other. Fires are simulated in a stainless metal sheet tunnel model in a laboratory setting, taking into account the critical Froude number, and the nature of the backlayering length variation depending on the tunnel slope is illustrated. The paper shows that the fire not only practically “reduces” the tunnel cross-section, but also causes additional traction due to the change in the density of the air mixture, which acts against the fan in the case of downward ventilation. It is also demonstrated that in inclined tunnels, in case of deactivated ventilation, when only natural traction acts during the fire, it is possible to reliably determine the numerical value of the critical ventilation velocity.