Physics-based modelling of junction fires: parametric study

Background. Junction fires occur when two fire fronts merge. The rate of spread (ROS) and heat release rate (HRR) of the junction increase more quickly than that of each fire front, this effect exacerbated by slopes. Aims. Numerical modelling of junction fires and an interpretation of their behaviour are given examining the key influencing factors. Methods. Twenty physics-based simulations of laboratory-scale junction fires were performed for a shrub fuel bed using FIRESTAR3D, varying slope (0 degrees-40 degrees) and junction angles (15 degrees-90 degrees). Key results. Accelerative and decelerative behaviours were observed for junction angles lower than 45 degrees, but above this, deceleration was absent. The behaviour was firmly related to junction angle evolution, which controlled the flame and interactions between fire fronts. HRR followed similar trends; maximum HRR increased with increasing junction angle. Convection was the primary heat transfer mode in the initial propagation phase. In no-slope cases, radiation was the dominant method of heat transfer, but convection dominated fires on slopes. Conclusions. The physics-based model provided great insight into junction fire behaviour. The junction angle was critical for determining ROS and fire behaviour. Implications. The research helped to assess the effects of some topographical parameters in extreme fires. Situational awareness, operational predictions and firefighter safety will consequently improve.

Automated summary

This study investigated the behavior and influencing factors of junction fires through numerical modeling and interpretation. The results showed that the junction angle has a significant impact on the spread rate and behavior of the fires, and an increasing slope can exacerbate the acceleration effect. The research findings can be utilized to assess the effects of topographical parameters in extreme fires, which will enhance situational awareness, operational predictions, and firefighter safety.