BAL is an acronym for Bushfire Attack Level. This is the accepted method of quantifying the level of exposure that a development may experience during the passage of an extreme bushfire. Determining the BAL ensures that development is undertaken in such a way that risk to people and property is minimised. It is used to determine the appropriate level of construction required, relative to the potential bush fire attack. Australian Standard 3959-2009 Construction of buildings in bush fire prone areas sets out the minimum construction requirements for each of the categories of bush fire attack.
BAL-LOW: Minimal attack from radiant heat and flame, although some attack by burning debris is possible. There is insufficient threat to warrant fire resistant products, however basic property preparation is still advised.
BAL-12.5: Low levels of radiant heat but attack by burning debris is significant. The radiant heat is less likely to threaten building elements. However fire and debris protection products are warranted (Level 1 construction standards).
BAL-19: Significant attack from burning debris, radiant heat levels can threaten buildings. Specific fire protection construction methods and products are warranted.
BAL-29: Significant attack from burning debris, radiant heat levels can threaten buildings and some flame contact is possible. Specific fire protection construction products are warranted.
BAL-40: Extreme radiant heat, increased attack from burning debris and potential flame contact, which can all threaten building integrity. All buildings must be designed and constructed with specific fire protection materials that can withstand extreme radiant heat and potential flame contact.
Flame Zone: Radiant heat levels will exceed 40kW/m2 and will significantly threaten building integrity and residential safety. Flame Zone areas exceed the scope of the Building Code of Australia. Applicants are recommended to take protection measures in order to make bushfire prone lands safer and comply with BAL criteria. Protection measures that would be required include drenching systems and radiant heat barriers.