Compiled Plans & Documents OPW18-0342 02

                                                               Retirement Living & Aged Care Facility
                                                                      Grasstree Court, Sunrise Beach

4.1.4       Fire Driven Wind
The convective forces of bushfire typically result in strong to gale force fire-driven winds which in
itself, can lead to building damage. The typical effects of fire driven wind include the conveyance
of embers, damage from branches and debris hitting the building, as well as direct damage to
vulnerable building components such as lifting roofs or roof materials and the damage / breakage
of windows.

4.1.5       Smoke
Smoke emission remains a secondary effect of bushfire and is one which is typically not addressed
by bushfire hazard assessment. Irrespective, it is important to note the potentially severe impact of
smoke emission on the human respiratory system. It can lead to difficulties in breathing, severe
coughing, blurred or otherwise compromised vision, and can prove fatal. It is also important to note
that toxic smoke can occur during bushfire, particularly where buildings or materials are ignited.
With regard to evacuation, it can reduce visibility and create difficulties for particularly vulnerable
persons.

4.2         Vegetation Communities
Fuel load and arrangement represents a considerable component in dictating to a large degree
the behaviour of fire in terms of intensity, rate of spread and flame height, and typically relates to
dead plant material less than 6mm thick, and live plant material thinner than 3mm. On this basis, it
stands to reason that different vegetation groups yield very different fire behaviour and intensity by
virtue of their characteristics and fuel load output. The characteristics are not necessarily related to
ecological values but remain a function of the propensity for certain groups of vegetation to ignite
and sustain fire due to fuel load and arrangement, it can guide estimates on how quickly fire might
spread and the likely fire behaviour and intensity which may occur.

Vegetation type, density and arrangement can further influence fire behaviour and intensity.
Vertical and horizontal continuity is also a significant element. Thus, vegetation forms a critical
element of analysis throughout this report.

4.3         Topography
Topography (effective slope) and to a lesser degree, aspect, are also factors which influence fire
behaviour and intensity. Topography can have a drastic affect, with the rate of speed doubling for
every 10 degrees of upslope and slowing by half for every 10 degrees of downslope, as a general
rule. Aspect can also affect bushfire behaviour where areas with northerly and / or westerly aspects
experience a higher level of solar access than those areas with a southern or eastern aspect.
Notwithstanding, in times of drought and below average rainfall moisture levels in soil and
vegetation in more sheltered areas with southerly and easterly aspects can also decrease
substantially giving rise to significantly higher fuel abundance where the preceding fire regime has
been less frequent or intense. Thus, aspect can be of less consequence.

4.4         Landscape and Localised Fire Hazard
Two types of risk are relevant in terms of bushfire hazard including:

     •    landscape risk – where large expanses of bushland over tens to hundreds of hectares are
          located in immediate proximity to, and may traverse, urban periphery suburbs/townships

     •    localised risk – which is most commonly presented by fragmented areas of vegetation larger
          than 1 hectare in size.

These two types of hazard present different types of fire behaviour, fire intensity and potential rate
of spread characteristics.




Status: Final                                                                                  March 2019
Project No.: 18-030                                                                               Page 17