Study on the key parameters of vehicle fires for the growth stage in road tunnels

As the golden period for evacuation and rescue in road tunnel fires, the fire growth stage is indispensable for security. The key parameters of this stage must be clearly defined, including the maximum heat release rate (HRR), growth time, and growth coefficient. Based on the squared model, the correlations between the key parameters are investigated according to the existing fire tests of vehicle-related materials and actual vehicles or mock-ups. The maximum HRR and the growth coefficient of different types of vehicles are obtained. The results show that the maximum HRR is linearly related to the growth coefficient in the fire tests of vehicle-related materials. And it is logarithmically related in the fire tests of actual vehicles or mock-ups. The growth coefficient and growth time represent the possibility of a disaster. The larger the growth coefficient is or the shorter the growth time is, the greater the possibility is. The maximum HRR in a fire is 2 ~ 10 MW for a car, 10 ~ 50 MW for a bus, and 50 ~ 200 MW for a heavy goods vehicle. The growth coefficient in a fire is 0.003 ~ 0.013 kW/s² for a car, 0.05 ~ 0.15 kW/s² for a bus, and 0.2 ~ 0.3 kW/s² for a heavy goods vehicle. The corresponding fire growth types are slow and medium, fast, fast, and ultra-fast, respectively. This study is beneficial for the establishment of the fire growth model and the setting of emergency response time.