Backing fire spread in dry eucalypt litter in a combustion wind tunnel

Background Understanding the factors that influence the behaviour of fire backing into the prevailing wind is critical to accurately simulating the propagation of an entire fire perimeter, particularly if a wind change turns backing fire into heading fire. Aims To identify the critical variables influencing backing fire behaviour in dry eucalypt litter by developing a statistical model of backing fire spread based on laboratory experiments. Methods Forty-eight experimental fires were conducted in dry eucalypt litter in a combustion wind tunnel utilising wind speed and fuel load as the primary independent variables. Linear models were developed to predict cumulative rate of spread. Key results Fuel load had a significant positive effect on backing spread rate while wind speed and fuel moisture content (FMC) both had significant negative effects, with no significant interaction effects. Conclusions Backing fire is slow but persistent. While the spread model remains to be validated against independent field-scale data, it may be of restricted general use in wildfires due to low spread rates in the dataset. Implications A more robust backing fire spread model derived from a better designed, more specific study of backing fire spread will enable improved prediction and simulation of fire perimeters across the landscape.