Bushfire Attack Level with a Radiant Heat Barrier — AS 3959 Method 2

Determine the Bushfire Attack Level (BAL) using the detailed Method 2 procedure of AS 3959, and optionally the reduced radiant heat flux at the site when an opaque, non-combustible barrier stands between the building and the classified vegetation.

Leave the barrier fields blank for a standard Method 2 assessment. The barrier calculation is an extension beyond AS 3959 Appendix B: the Bushfire Attack Level reported remains the unshielded result, and relying on the shielded figure requires the barrier to satisfy the relevant authority on non-combustibility, continuity, length and durability.

Site
For grassland classifications this is converted to the grassland FDI via Table B2, so it must be one of 40, 50, 70, 80 or 100.
Downslope means the land under the vegetation falls away from the site, so the fire runs uphill toward it.
°
Upslopes are capped at 15° by Equation B1. Downslopes steeper than 30° are outside Method 2.
°
Slope of the land between the site and the vegetation, positive when it falls from the site toward the vegetation. Method 2 does not apply beyond 20° either way.
m
Advanced options
km/h
kJ/kg
m
Paragraph B8 allows 100 m, or a justified lesser value.
K
°C
%
%
years
Radiant heat barrier (optional)
m
Height above the ground at the barrier itself. Leave blank for a standard Method 2 assessment.
m
Horizontal distance from the building to the barrier, measured toward the vegetation. Required when a barrier height is given — the shielding depends strongly on where the barrier stands.
m
Width centred on the line between the building and the fire. Leave blank only if the barrier is at least as wide as the flame.

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