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).
A BAL is the basis for establishing the requirements for construction (under the Australian Standard AS 3959-2009 Construction of Buildings in Bushfire Prone Areas), to improve protection of building elements from bushfire attack.
The image below shows the various BAL ratings and the radiant heat flux for each rating. The greater the distance from the fire the lower the heat flux and therefore the construction standard is lower.
Once assessed, your site/property/asset will be defined one of six BAL ratings:
BAL Low: There is insufficient risk to warrant specific construction requirements
BAL 12.5: Ember attack. (BAL 12.5 Construction Requirements)
BAL 19: Increasing levels of ember attack and burning debris ignited by windborne embers, together with increasing heat flux. (BAL 19 Construction Requirements)
BAL 29: Increasing levels of ember attack and burning debris ignited by windborne embers, together with increasing heat flux. (BAL 29 Construction Requirements)
BAL 40: Increasing levels of ember attack and burning debris ignited by windborne embers, together with increasing heat flux and with the increased likelihood of exposure to flames. (BAL 40 Construction Requirements)
BAL FZ: Direct exposure to flames from fire, in addition to heat flux and ember attack. (BAL FZ Construction Requirements)
Where your building is greater than 100m from any classified vegetation the BAL rating will more than likely be BAL–LOW and will not require any special construction requirements. Where there is a risk or potential that ember attack could affect your home we recommend that BAL – 12.5 is applied.