Characteristics of multiple pool fires in a tunnel with natural ventilation

Tunnel fires are usually accompanied with major casualties and properties losses, and multiple fires in a tunnel may cause intense burning behavior like fire merging, which could be more destructive and hazardous. Therefore, the characteristics and hazards of multiple pool fires in a tunnel were investigated under natural ventilation in this study through a series of experiments. Experimental results showed that the characteristics of one-dimensional fire arrays were different from those of square fire arrays in open space. Due to the extra heat feedbacks (e.g. from adjacent fire sources, tunnel wall and hot smoke), the burning rate was found being enhanced. When there is more than one fire source, it was observed that the flames deflect towards the center of one-dimensional fire arrays, leading to flame merging when fire spacing decrease to some extent, which would result in the increased hazards of the heptane fires. An empirical model was developed to predict the global dimensionless average burning rates based on modified fire area ratio, which characterizes the fuel load and incorporated fire spacing, fire number and the fuel pan size. The research results in this paper provide a theoretical guide on understanding the behaviors of multiple fire resources in tunnels.