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The paper presents the pattern of variation of critical velocity during longitudinal downward ventilation in an inclined road tunnel with its slope varying within 0-8 degrees. The results of both full-scale numerical modelling and laboratory experiments for a 1:10 scale tunnel models are presented. The effect of fire on the critical velocity and gradient factor was studied on the models. During the numerical modelling, the seat of fire, fans and tunnel portals were modelled with 0.1*0.1*0.1 m cells, while the cell...

Fires in road tunnels pollute the ventilation air of the underground space and create unfavorable conditions for life. International recommendations for the design of emergency ventilation share the statement that the critical velocity (specifically its numerical value of 3.0 m/s) can be used to predict the spread of toxic substances in underground space and to exclude backflow for the majority of tunnels. Nowadays, it is advisable to supplement this point of view with the results of new studies, which notes that ...