Abstract: In order to obtain a method of predicting time of the vehicle on fire to ignite its adjacent vehicles in the urban highway tunnel under a blocking scenario, the ignition time was studied based on the law of fire spreading in the tunnel. A calculation method of the radiation heat flux received by the adjacent vehicle in the tunnel was worked out by theoretical analysis. A method of predicting the ignition time of vehicles under fire was developed by linear fitting. The effectiveness of the prediction was verified by field test. The results show that the predicted value of ignition time is basically consistent with the experimental value which indicates the method has higher precision, and when the initial vehicle on fire is a small vehicle and the surrounding vehicles are randomly distributed, the small vehicles in the adjacent lanes will not be ignited, that the ignition times of the medium and large vehicles are about 30 min and 9 min respectively, that when the initial vehicle on fire is a large vehicle, the ignition time is about 5min when the adjacent vehicle is a small car, and that preliminary firefighting measures should be taken and personnel evacuation should be organized within 5 min when a fire breaks out.

Key words: urban highway tunnel, ignition time, flux-time product (FTP), blocking scenario, fire spreading, critical heat flux