Sustainability WA

What Influences Bushfire

The term bushfire behaviour refers to how a bushfire will react to surrounding environmental conditions and landscape.

Why is this important? Because, if we understand the way a bushfire is likely to behave, it will allow us to predict the intensity, rate of travel and, direction of a bushfire, in a given set of circumstances or location.

Fire conditions, which a proposed development may be exposed to, can then be predicted and appropriate measures taken to ensure the best chance of survival of property and safety of occupants during a bushfire event.

Analysis of bushfire behaviour also allows for predictions to be made during a bushfire event. This analysis can help identify property and lives that are at risk, ensuring firefighting resources are allocated appropriately. Thus, the study of bushfire behaviour allows us to predict and help minimize the effects of a bushfire.

Bushfire behaviour is usually expressed in terms of flame heights, rate of spread, spotting behaviour (distance and rate of spot fires being lit by burning embers) and fire intensity. This behaviour can be influenced by three main factors as shown in the diagram below:

First, fuel or vegetation available to the fire, including how the fuel is structured, fuel type, moisture content and the amount of fuel.

Secondly, the weather conditions, including humidity, ground temperature, ambient temperature, wind speed, and wind direction.

Third, the topography, particularly the slope of the land under the vegetation. Fire running uphill will move faster, doubling with each increase of ten degrees when compared to one over flat ground.

Therefore, if the fuel, weather and slope, is known it will assist to predict a bushfire’s behaviour including flame height, rate of spread, and spotting behaviour.

We use these three factors to determine a Bushfire Attack Level(BAL). This BAL rating, can then be used to determine the appropriate construction requirements of your project to ensure that you meet the correct building standards and help reduce the effect of a bushfire on the builidng.

To learn more about how these items go together to create the BAL see our article here: How a BAL rating is calculated

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