Attachment C - Bushfire Management Plan · 132008.1128.04

                                                                 Retirement Living & Aged Care Facility
                                                                        Grasstree Court, Sunrise Beach

4.1.1       Direct Flame Contact
Direct flame attack refers to flame contact from the main fire front, where the flame which engulfs
burning vegetation is one and the same as that which assumes contact with the building. It is
estimated that only 10 to 20 per cent of buildings lost to bushfire occur as a direct result of flame
attack.

4.1.2       Ember and Firebrand Attack
The convective forces of bushfire raise burning embers into the atmosphere on prevailing winds and
deposit them to the ground ahead of the fire front. Typically, ember attack occurs approximately
30 minutes prior to the arrival of the fire front and continues during the impact of the fire front and
for several hours afterwards, thus it is the longest lasting impact of bushfire attack. Firebrands occur
in a very similar manner but relate to larger items of debris that may still be carried by the wind when
alight, such as candle and ribbon barks.

In essence, building loss via ember attack relates largely to the vulnerabilities and peculiarities of
each building, its distance from the classifiable vegetation and whether an occupant (or the like) is
present to actively defend it. It is estimated by the CSIRO that approximately 80 to 90 per cent of
buildings lost by bushfire are lost as a result of ember attack either in isolation or in combination with
radiant heat impact.

4.1.3       Radiant Heat Flux
Exposure to radiant heat remains one of the leading causes of fatalities associated with bushfire
events. Measured in kilowatts per m2, radiant heat is the heat energy released from the fire front
which radiates to the surrounding environment, deteriorating rapidly over distance. In terms of
impacts on buildings, radiant heat can pre-heat materials making them more susceptible to ignition,
or can cause non-piloted ignition of certain materials if the energy transmitted reaches a threshold
level. Radiant heat can also damage building materials such as window glazing, allowing openings
into a building through which embers may enter. Radiant heat impact is an especially important
factor in building-to-building ignition.

In terms of radiant heat exposure for humans, it can cause pain to unprotected skin in milder
situations or life threatening and fatal injury in higher exposure thresholds.




              Figure 4 - The effects of radiant heat (NSWRFS, 2006; Drysdale, 1999, CFA, 2012)


Status: Final                                                                                      July 2020
Project No.: 18-030                                                                                 Page 16