Determining the Bushfire Attack Level (BAL)
With referance to Australian Standard AS 3959

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Methodology:
The determination of classifiable vegetation and in-particular the edge of classifiable vegetation under
AS3959 is still somewhat subjective when just Method 1 under AS3559 is taken in isolation.
However when taking into account an understanding of AS3959 Appendix B, the complex Method 2, and other
industry publications we find that we can bring science into play, most notably with the measurement of the
surface fine fuel hazard.

In assessing classifiable vegetation and in-particular the edge of classifiable vegetation, account is taken of the
Overall Fuel Hazard = (the sum of the influences of) Bark Hazard + Elevated Fuel Hazard + Surface Fine Fuel Hazard
and the Fuel Continuity, both Horizontal and Vertical ie Density, Canopy, Understorey and Litter-Bed build up.

In some cases the edge of the classifiable vegetation can be some distance from the first vegetation (including trees)
encountered, when taking into account the Overall Fuel Hazard and Fuel Continuity.

There are a number of exclusions to classifiable vegetation (AS3959 clause 2.2.3.2), perhaps the most significant is
Low threat vegetation, including managed etc, maintained etc. This is taken to include areas of minimal surface
fine fuel hazard as assessed by litter-bed height.

As such areas of trees with low density, minimal understory and sparse litter-bed build up are often considered to
be low threat vegetation and may be excludable from the assessment.

Trees on managed residential blocks as well as isolated trees are also generally considered to be
low threat vegetation and may be excludable from the assessment.

Areas of Fire Damaged / Fire Killed vegetation are more difficult to assess. Fundamental questions are:
i) Is it likely this area will ever return to a steady state fuel load typical of its pre-fire vegetation classification
within say the next 10 years? (project Vesta demonstrated that the majority of fuel load had returned and a
significant leveling off occurs after 10 years)
ii) If not, why not?
iii) If not, what steady state fuel load is it likely to return to?

The majority of publicly available aerial photos including Google etc are greater than 5 years old and in a lot of
cases they bear little semblance to the current situation.
It should be noted that even our own photos taken at the site have a compressing effect and do not accurately show
the distance to and the density of the vegetation. This is where our Drone Surveys are invaluable.




Available 7 days a week, ring us on 0417 885 747

We would welcome the opportunity of expanding on any of the points mentioned above.

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BAL ASSESSMENTS
Mobile: 0417 885 747
email: [email protected]

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