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Bushfire Attack Level (BAL)

What is a BAL?

A Bushfire Attack Level (BAL) is a means of measuring the severity of a building’s potential exposure to ember attack, radiant heat and direct flame contact. It’s measured in increments of radiant heat (expressed in kilowatts/m2).  In plain english, 1 kilowatt is equal to 1000 x 1 bar heaters / 1meter square.  

A BAL is the basis for establishing the requirements for construction (under Building Code of Australia as setout in the Australian Standard AS 3959-2018 Construction of Buildings in Bushfire Prone Areas), to improve protection of building elements from bushfire attack.

BAL ratings are the radiant heat flux divided into five classes (BAL 12.5, 19, 29, 40 & FZ-Flame Zone).  The greater the distance from the fire the lower the heat flux and therefore the construction standard is lower.

To put all of this into some sort of context, A BAL 12.5 = (12500 x 1 bar electric heaters / 1m2).

BAL Ratings

BAL—LOW is based on insufficient risk to warrant specific bushfire construction requirements. It is predicated on low threat vegetation and non vegetated areas

BAL—12.5 is primarily concerned with protection from ember attack and radiant heat up to and including 12.5 kW/m2 where the site is less than 100 m from the source of bushfire attack.

BAL—19 is primarily concerned with protection from ember attack and radiant heat greater than 12.5 kW/m2 up to and including 19 kW/m2.

BAL—29 is primarily concerned with protection from ember attack and radiant heat greater than 19 kW/m2 up to and including 29 kW/m2.

BAL—40 is primarily concerned with protection from ember attack, increased likelihood of flame contact and radiant heat greater than 29 kW/m2 and up to and including 40 kW/m2.

BAL—FZ is primarily concerned with protection from flame contact together with ember attack and radiant heat of more than 40 kW/m2.

Construction in BAL—FZ may require reliance on measures other than construction. The requirements for construction of a building BAL—FZ may be regulated by the building authorities having jurisdiction in the States and Territories of Australia.