Welcome to CalcTree's Bushfire Attack Level (BAL) calculation tool! On this page, you'll be able to quickly find the BAL for a given location in Australia based on AS 3959-2018.


The BAL is a way of assessing how much danger a building is in from ember attack, radiant heat, and direct flame contact. The severity is determined by kilowatts/m2, which is a measure of the radiant heat that is present due to fire.
According to the Australian Standard AS 3959-2009 Construction of Buildings in Bushfire Prone Areas, the BAL is a fundamental factor in determining the specifications necessary to enhance the protection of building components from bushfire damage.

Simplified Calculation

The drop-down toggles above show the various BAL ratings and the heat flux for each rating. Essentially, the greater the distance from the fire, the lower the heat flux, and therefore the construction standard in regard to bushfire protection is lower.
This simplified calculation to AS 3959:2018, Cl 2. CFA offices more readily accept it, and it provides a table of minimum distances from vegetation that must be adhered to for each attack level. An alternative detailed calculation method can be found in AS 3959:2018 Appendix B.

Simplified process to determine BAL


→ Fire Danger index



What is it?

→ BAL Low Threat Exclusion

BAL Low Threat Exclusion
:(a) Vegetation more than 100m from site

What is it?

→ Predominant Vegetation Classification

Vegetation Classification
:A. Forest

What is it?

→ Distance to Classified Vegetation

Distance between site and classified vegetation

What is it?

→ Effective Slope Under Classified Vegetation

Effective slope under classified vegetation
:Downslope >10 to 15 degrees

What is it?


Bushfire Attack Level

:BAL - Low

Bushfire Danger
:There is insufficient risk to warrant specific construction requirements

Upper distance limits for BALs






Construction requirements for determined BAL
Based on the bushfire attack level determined, construction requirements should meet the following provisions from AS3959:2018.

Construction Requirements
:Section 4

💬 We'd love your feedback on this template! It takes 1min

Rating system


BAL - 12.5 🔥

BAL - 19 🔥🔥

BAL - 29 🔥🔥🔥

BAL - 40 🔥🔥🔥🔥

BAL - FZ 🔥🔥🔥🔥🔥