A Bushfire Attack Level (BAL) is a measurement of risk of a building’s exposure to ember attack, radiant heat and direct flame contact contained in Australian Standard AS 3959-2018 Construction of Buildings in Bushfire Prone Areas. The BAL rating determines the construction and building requirements necessary to protect homes in bushfire prone areas (BPA).
BAL Rating Levels
There are six levels of BAL ratings, each expressed as kilowatts/m2. Each level takes into consideration the Fire Danger Index, the slope of the land, types of surrounding vegetation and the proximity to other buildings.
| Bushfire Attack Level | Radiant Heat Exposure and Levels of Exposure | Description of Predicted Bushfire Attack and Levels of Exposure |
| Low | Insignificant | Very low risk. Radiant heat on the building is not significant enough to require specific construction requirements, however ember attack may still occur. |
| BAL – 12.5 | 0 – 12.5 kW/m2 | Low risk. There is a small risk of wind-ignited embers and burning debris causing ember attack. |
| BAL 19 | 12.5 – 19 kW/m2 | Moderate risk but with increasing levels of risk by wind-ignited embers and burning debris causing ember attack which could increase the likelihood of radiant heat exposure. |
| BAL – 29 | 19 – 29 kW/m2 | High risk with increasing levels of ember attack and burning debris ignited by wind borne embers which increases the likelihood of exposure to radiant heat. |
| BAL – 40 | 29 to 40 kW/m2 | Very high risk with increasing levels of ember attack and burning debris ignited by wind borne embers which increases the likelihood of exposure to radiant heat. Some direct exposure to flames possible. |
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BAL – FZ |
40 kW/m2 and flame contact | Risk is considered extreme. Direct exposure to flames from the fire front is likely in addition to high levels of radiant heat exposure and ember attack. |
Why BAL Ratings Are Important When Building Your Home
All new homes, extensions, and some outbuildings built in a bushfire prone area must be constructed to a minimum BAL 12.5 to help withstand an ember attack. As BAL ratings increase, the use of non-flammable materials and methods of construction become more important.
Prior to obtaining a building permit, a BAL assessment will need to be conducted by a Bushfire Planning & Design (BPAD) assessor who is accredited by Fire Protection Association Australia.
To learn more about Bushfire Attack Levels and how they may affect your building project, contact the team at Lateral Building Design.
