Model of ventilation flows during large tunnel fires

In order to describe the reduction in the longitudinal airflow velocity due to the fire and hot gases resistances in a large tunnel fire, a theoretical model, taking into consideration the pressure losses over the fire source and obstructions, the thermal stack effects, and the hydraulic resistance induced by the tunnel walls, fire protection boards and a HGV trailer mock-up, is developed and validated using the large-scale tests data from the fire tests performed in the Runehamar tunnel with longitudinal ventilation in Norway 2003. Two large mobile fan units were used to create a longitudinal flow within the tunnel and prevent smoke backlayering upstream of the fire. One fan was located outside the entrance of the tunnel and the other inside the tunnel. The fire load consisted of a mock-up simulating a heavy goods vehicle (HGV) trailer creating a maximum heat release rates in the range of 66–202 MW. Two methods of calculating the mean temperature related to the thermal expansion and stack effect are proposed and compared.

► A theoretical model of ventilation flow during large tunnel fires is developed.
► Large-scale tests data from the Runehamar tunnel fire tests were used to validate the model.
► Two methods of calculating the mean temperature related to thermal expansion and stack effect are investigated.
► Average temperature at the middle point is considered as the mean temperature.