A hazard assessment will determine the severity of the potential bushfire hazards at your location.
This assessment will reveal the severity of the bushfire hazards on your property. This information will help you to site new buildings and will identify any specific bushfire hazards that need mitigating during your design and construction process. If you need a formal assessment for a building and planning proposal, please refer to the resources on planning for bushfire protection (from Planning Victoria).
You should complete the Hazard identification tutorial before attempting this assessment.
Draw a map of your property, showing the radiant heat contours around any nearby Classified vegetation. This will show which parts of your property have the greatest potential exposure to bushfire (and which areas have the least exposure!). This will help you to site your new home (or other structure) in order to minimise its exposure and decrease your risk. For existing homes, this information can reveal which parts of your house or garden have the greatest exposure – and which features may need to be protected (e.g., by installing a barrier or retrofitting the house to withstand the risk).
The radiant heat from a bushfire is typically described using BAL (Bushfire Attack Level) ratings. These ratings show the level of potential exposure at your site -based on its distance to vegetation, dominant vegetation type, and terrain. The higher the BAL, the greater the risk.
To draw BAL-based radiant heat contours:
- Take the property map and hazard checklist that you created in your Hazard identification.
- Using the information in your checklist (Print or download our checklist), calculate BAL for the Classified vegetation nearest to your home (or the vegetation that presents the most risk) or proposed building site, using our BAL assessment tool. For guidance, follow our step-by-step tutorials.
- Use the calculated distances to draw contours around the Classified vegetation on your map, as shown in the example below. Radiant heat is commonly expressed in Kw/m2 (kilowatts per meters squared). This value describes the intensity of the heat emanating from the fire. Radiant heat is a good indicator of how severe a bushfire might be under the given circumstances.
BAL can also be calculated using Method 1 in AS 3959:2018.
BAL-based contours show the potential bushfire hazard at different distances from the classified vegetation
In addition to the heat contours from step 1, it’s important to consider your level of exposure to any artificial or managed elements. Objects such as combustible fences, vehicles, and ornamental trees can ignite and spread fire.
These secondary fires (also called consequential fires) are a major cause of property damage during bushfires. For new builds, it is best to site your house in an area where it will not be affected by other combustible objects.
- On your map from Step 1, draw radiant heat contours around the combustible elements that you listed during your Hazard identification (e.g., neighbouring houses, sheds, fences, etc). See the drawing below for an example – for large combustible features (such as sheds and houses), draw a 6m buffer around the object to indicate the primary danger zone.
Radiant heat contours around neighbouring homes