Bushfire Behaviour

Fire Intensity
Vegetation
Weather
Topography

Some basic facts about bushfire behaviour may help you understand how fire can damage property and how to protect against it.

Fire Intensity 

The intensity of a fire refers to the amount of heat being generated. The higher the intensity the harder the fire is to control and the more damage it is likely to cause. Fire intensity depends on three major factors: vegetation, weather and topography.

Vegetation  

The type and amount of vegetation determines fuel load, which in turn determines fire intensity. The intensity of a fire increases in proportion to the amount of available fuel (flammable material less than 6mm in diameter). The more available fuel, the greater the fire intensity experienced. Forest and scrub fires are more intense and generate significantly more heat than grass fires. As a result the impact and potential damage of a forest or scrub fire on a home will be much greater. Reduction of fuels by clearing undergrowth provides the best method of reducing fire intensity and thus is an essential part of any fire protection strategy.

Weather  

Increasing temperature and wind velocity and decreasing relative humidity directly contribute to an increase in the rate of spread of fire and the resultant fire intensity. As fuels dry out ignition is easier and the rate of spread increases. In South Australia the prevailing fire winds are from the North. However, history has shown that a South Westerly wind change, although cooler, can increase the danger by swinging the fire in a different direction catching people unaware. It is therefore important, when developing a fire protection strategy for your home to take into consideration that the majority of fires are most likely to come from the Northern and Western sides.

Topography  

Fires burn more quickly and with greater intensity up slopes than on flat ground or downhill. Ridgetops and steep slopes therefore are the most dangerous sites to build on. North facing slopes are also dangerous as they receive more direct sunlight than South facing slopes, which dries out vegetation causing more intense fires.

Further information is available in the fact sheet - Bushfire Behaviour in Detail.