Bushfire Attack Level

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What does Bushfire Attack Level (BAL) refer to?

The NSW Rural Fire Service (NSWRFS) refers to the BAL as a: "means of measuring the severity of a building's potential exposure to ember attack, radiant heat and direct flame contact, using increments of radiant heat expressed in kilowatts per metre squared, which is the basis for establishing the requirements for construction to improve protection of building elements from attack by bush fire.

The BAL constitutes the combination of the bushfire elements radiant heat, embers and flame length merging to differing extents from a combination of:

  1. combustible vegetation
  2. the slope upon which the fire is most likely to travel
  3. the distance from the dominant hazard, and
  4. a Fire Danger Index of 100 80 or 50.

The table below summarises the NSWRFS information on the differing categories of attack and the associated explanations.

Bushfire Attack Level Description of Bushfire attack and exposure level
BAL-LOW There is insufficient threat to warrant specific construction requirements, but residents should still do basic property preparation.
BAL-12.5 Attack by burning debris is significant with low levels of radiant heat. Specific construction requirements for ember protection and accumulation of debris are warranted (Level 1 construction standards).
BAL-19 Attack by burning debris is significant with an increased radiant heat levels threatening some building elements. Specific construction requirements for protection against embers and radiant heat are warranted (Level 2 construction standards).
BAL-29 Attack by burning debris is significant and radiant heat levels can threaten building integrity. Specific construction requirements for protection against embers and higher radiant heat are warranted. Some flame contact is possible.
BAL-40 Increased attack from burning debris with significant radiant heat and the potential for flame contact. The extreme radiant heat and potential flame contact could threaten building integrity. Buildings must be designed and constructed in a manner that can withstand the extreme heat and potential flame contact.
FLAME ZONE Radiant heat levels and flame contact are likely to significantly threaten building integrity and result in significant risk to residents who are unlikely to be adequately protected. The flame zone is outside the scope of the BCA and the NSW Rural Fire Service may recommend protection measures where the applicant does not provide an adequate performance solution.

Information in the table sourced from the New South Wales Rural Fire Service.

Additional: Where a facade is "shielded" totally from the dominant facade the "shielded" facade may be reduced by one level of BAL/Construction Level. The NSW Rural Fire Service does not support any external building elements at BAL 40 or BAL FZ that will flame and/or combust.

What is involved in a Bushfire Attack Level (BAL) assessment?

The typical BAL calculation procedure involves:

(a) Inspect the Local Government Area Bushfire Prone Land map (b) Identify the Fire Danger Index for the Local Government Area (c) Classify the dominant vegetation type within 140 metres of the closest point of the construction site (d) Measure the dominant slope under the dominant vegetation (e) Match the Fire Danger Index with the dominant vegetation, the dominant slope and the distance from the dominant vegetation to the closest point of the construction site.(f) Identify the Bushfire Attack Level.

A site specific BAL assessment is required as part of the complying development process. It provides a rating based on the expected level of bush fire attack in accordance with AS3959-2009 and Addendum Appendix 3 of Planning for Bush Fire Protection 2006.

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