Abstract:  In order to determine the dynamic fire scale and personnel evacuation scheme of urban road tunnel under fire spreading, the vehicle ignition time is calculated based on critical radiant heat flux theory.In addition, a full scale model built by FDS is applied to determine the dynamic fire scale under obstruction and to compare the distribution laws of temperature and visibility under two cases, namely, opening both two side cross passages at the same time and opening only one side cross passage. Furthermore, the evacuation time under two cases are compared through Pathfinder. Results show that, initial ignition needs 250 s, and the secondary ignition needs 615 s and 650 s, respectively. The maximal heat release rate of the fire reaches up to 39.1 MW, and a total of 11 vehicles were involved in the combustion. The laws of temperature and visibility distribution are basically the same under two cases but the evacuation time of opening both two side cross passages is only 390 s, which reduces by 320 s compared with the latter. It is suggested that in case of fire in four-hole road tunnel, the cross passages on both sides should be opened at the same time. It is suggested to take timely fire protection measures within 10 min to prevent the secondary ignition of the vehicles.

Key words: urban road tunnel, fire spread, ignition time, dynamic fire scale, personnel evacuation