Bushfire Hazard Assessment and Management Plan

                                                           Bushfire Hazard Assessment and Management Plan



150 m of the development site is not classified as bushfire-prone and therefore, calculation of radiant
heat flux/bushfire attack level (BAL) is not applicable.

Section 5 outlines the requirements for management and mitigation of bushfire hazard for the bushfire-
prone vegetation within the site.

3.2 Radiant Heat Exposure and Bushfire Attack Levels

Bushfire attack levels (BALs) are used to quantify the levels of attack (radiant heat exposures/flux) that
built structures may experience during a fire event. The BAL is defined 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, and the basis for establishing the
requirements for construction to improve protection of building elements from attack by bushfire’
(Standards Australia, 2018).

AS3959:2018 adopts six BAL categories, which are based on the level of radiant heat flux to which
buildings may be exposed to during a bushfire event. This level of heat flux generally relates to the type
of vegetation, effective slope and how far a building is from hazardous vegetation. BALs apply to
buildings and any attached or adjacent structure within 6 m of the building.

The BRC Technical Guide requires that radiant heat exposure/bushfire attack levels (BALs) are
calculated using either the SPP Bushfire APZ calculator (QFES, 2019b), which is the preferred method
or Method 2 of AS3959:2018. Where Method 2 is used, the following inputs are to be used:

    •   site-specific values for FFDI (Step 1)

    •   ground-truthed VHCs (Step 2) and their associated fuel loads (provided in Figure 14 of the BRC
        Technical Guide); and

    •   site and effective slopes (Step 3).

When calculating minimum separation distances based on radiant heat exposure (Bushfire attack level)
in accordance with Method 2 of the Australian Standard AS3959:2018, the Standard requires that
understorey fuel load be used to determine the rate of spread and total fuel load (understorey +
overstorey) be used to determine flame height. AS3959:2018 defines understorey as ‘the vegetation
beneath the overstorey’ and the overstorey as ‘the canopy, being the tallest stratum of the vegetation
profile’. Where a continuous fire run is >150m, a nominal 10 t/ha is added to the ‘understorey’ fuel load
to give a ‘total fuel load’ to account for canopy fuels, except where it can be demonstrated that canopy
fuels will not be involved in the fire front (e.g. where there is an absence of ladder fuels and substantial
separation of canopy trees).

The site is located within a large patch of remnant open forest with a substantial density of a ladder
fuels. Given the extent of this patch, a potential continuous fire run greater than 150m is highly likely.
Accordingly, the following fuel loads shall be used in the Method 2 assessment –

    •   Understorey - potential fuel load of 24.2 t/ha;

    •   Total fuel load – potential fuel load of 34.2 t/ha (i.e. 24.2 + 10 t/ha).




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