Abstract: Abstract: A 1:8 scaled test bench was built to study the critical ventilation velocity in the case of transverse double fire sources in the longitudinal ventilation tunnel. The relationship between the critical ventilation velocity and heat release rate and the distance between fire sources was studied, when two fire sources were placed symmetrically in the tunnel. The results show that the critical ventilation velocity will gradually decrease with the increasing distance between fire sources while keeping the heat release rate unchanged. In cases considered, the greater the heat release rate, the greater the critical ventilation velocity, while keeping the distance between the ignition sources unchanged; When the heat release rate increases to a certain extent, the critical ventilation velocity will not change with the increasing heat release rate, but reach a constant. The influence factor is introduced to characterize the influence of the distance between two fire sources on the critical ventilation velocity, and the critical ventilation velocity model for the transverse tunnel fire with two fire sources is established.

Key words: tunnel fire, critical velocity, double fire sources, dimensional analysis