Determining Bushfire Risk

The section gives an overview over Bushfire Attack Levels (BAL) that are used to determine construction requirements for buildings on bushfire zoned land.

The Bushfire Attack Level measures the severity of a building’s potential exposure to ember attack, radiant heat and direct flame contact and applies to buildings sited in designated bushfire-prone areas. Most Councils maintain online mapping tools that help to determine if a particular site falls within this category.

BAL ratings dictate both the construction methods and materials used in bushfire prone areas. The purpose of BAL ratings is to help prevent bushfires from destroying buildings and spreading to other areas. Each BAL rating is assumed to carry the same risks as the previous rating, as well as additional risks.

There are a number of factors that influence the applicable BAL.

• The locations general Fire Danger Index (FDI) ranging from low (0) to catastrophic (100)

• The hazards classified vegetation type(s)

• The distance of the site from the hazard

• The effective slope(s) under the classified vegetation type(s)

We recommend to engage a qualified bushfire consultant to determine the BAL according to the Australian Standard AS 3959–2009. A bushfire consultant can then prepare a bushfire risk assessment that advises on asset protection zones, well maintained areas between the building and the bushfire hazard, and other elements influencing bushfire safety.

Previously it was possible to go through a self- assessment process, however this has been phased out by most Councils. However, the following guidelines will allow an estimate of what level to expect.

BAL Level Overview

• BAL Low - Very Low Risk. There is insufficient risk to warrant specific construction requirements.

• BAL 12.5 - Low Risk. Ember Attack with heat flux of up to 12.5 kW/m2. Some construction requirements relating to the external surfaces of the building.

• BAL 19 - Moderate Risk. Increasing levels of ember attack and burning debris ignited by windborne embers, together with increasing heat flux of up to 19 kW/m2. Construction requirements relating to external materials, glazing and detailing.

• BAL 29 - High Risk. Increasing levels of ember attack and burning debris ignited by windborne embers, together with increasing heat flux of up to 29 kW/m2. Construction requirements relating to external materials, glazing, detailing and additionally to subfloors and floor construction.

• BAL 40 - Very High Risk. Increasing levels of ember attack and burning debris, together with increasing heat flux of up to 40 kW/m2 and increased likelihood of exposure to flames. Significant construction requirements for all parts of the building.

• BAL FZ - Flame Zone - Extreme Risk. Direct exposure to flames from fire, in addition to heat flux greater than 40 kW/m2 and ember attack. Significant protection is required to reduce the threat, such as radiant heat barriers and modifications to the building and surrounding property. Significant construction requirements for all parts of the building and specific requirements to protect all openings. Active protection measures such as sprinkler systems may be considered.