The effects of junction fire development on thermal behaviour at the field scale

Abstract

Junction fires, a type of dynamic fire behaviour, involve the merging of two active fire fronts. They have been known to result in extreme increases in rates of fire spread and intensity over short periods of time. When these phenomena occur during wildfires, they pose significant risks to emergency management and communities. Few studies have investigated rates of spread and fireline intensity of junction fires using field scale experiments. This study captured data from 16 junction fires in mallee-heathlands utilising a drone-mounted thermal camera. Mean rates of spread and fireline intensity were found to increase toward the 75 % stage of merging before decreasing, similar to those found in other studies. Although, normalised temperature areas increased continuously for the whole duration of merging. Additionally, a custom-built radiative heat flux device was used to measure temperature and radiant heat at the fireline within the junction fires. Peak radiative heat flux was also found to be highest at the 75 % stage of merging, following a gradual decrease as propagation progressed. Heat flux measurements were found to be similar to those of previous studies conducted in similar vegetation. Due to the many complex interactions between weather, fuel and fire behaviour, further studies need to be conducted to appropriately determine the effects of merging on rates of spread and fire intensity.