An experimental study on the burning rates of interacting fires in tunnels

Multiple fires may occur in close proximity in process industries, power generation and fuel storage facilities and confinement conditions such as tunnels, which can lead to a considerable alteration in fire characteristics and safety design. The topic is of significant importance to the fire safety research because there is little work in the literature that investigates the case of interacting fires, which have a destructive potential. In this work, we study the effects of an adjacent fire source on the burning rate and heat release rate characteristics of tunnel fires. Square ethanol pools of 10 and 15 cm in size and 0.22-1 cm in depth were used as fire sources in a reduced scale tunnel model. Ventilation to the tunnel was varied between 0 and 1.5 m/s. Pool fires were configured in single and dual pool orientations. Variations in the pool fire burning rates were discussed as being functions of pool size and depth, and a result of the interaction with the secondary fire. The maximum burning rate enhancement factor, defined as the ratio of the parameter for interacting fires to non-interacting ones, was shown to be 2.3. This was due to the enhancing effect of the secondary fire on the heat feedback to the fuel, and the increased combustion mass transfer. Tests with relatively larger pool sizes burned faster, with an advanced onset of the transition to a bulk boiling phase, which was attributed to the controlling heat feedback mechanism associated with the pool size.