Understanding when spotfires are likely to occur
Spotting – the ignition and development of spotfires – is a feature of bushfire behaviour in Australia. It is a major contributor to the loss of control of fires, the hazard faced by firefighters, and damage to the built environment.
There are a range of factors that contribute to spotting, including how easily a firebrand can be lofted and transported, how far it travels, how long it flames and smoulders and the fuel that it lands on. Environmental conditions, such as wind speed and the moisture content of the fuel are also important considerations.
Due to its complexity spotting is a poorly understood phenomenon; however, understanding when spotfires are likely to occur is essential for suppression planning and determining the potential impact on fire behaviour and firefighter safety.
Investigating spotfire ignition conditions
We examined the probability of successful spotfire ignition on fuel beds of different moisture contents in varying wind conditions.
Our research, carried out under controlled conditions in a small wind tunnel, replicated the type of conditions found in the dry eucalypt forests of southern Australia.
We found that for flaming firebrands, ignition probability depends on the presence of wind at the fuel level and on the moisture content of the fuel.
For glowing firebrands, ignition probability depends on the moisture content of the fuel and on wind speed.
Better spotfire occurrence prediction
The key triggers for spotfire potential that we identified will enable fire managers to better determine when spotting will be a hazard and provide a basis for prediction of its occurrence.
Further research is needed to build robust models for the full range of possible firebrand characteristics and environmental conditions, including wind gusts.