080623 BlueCare Bushfire Assessment Report_Iss B_screen version.pdf [As Published] · 132008.1128

                                                                                                                                   Bushfire Protection Assessment
                                                                                                                                                         BlueCare
                                                                                                                                  Grass Tree Court, Sunrise Beach




APPENDIX 1:                             DESIGN FIRE’S
Bushfire Design Fire’s for the portion of the surrounding bushland most influencing bushfire behaviour have been
evaluated as part of the bushfire engineering process. The design fire is determined to enable matching of the building
design and material science to the resultant exposure. This included determination of:


•       Flame length;

•       Rate of spread;

•       Fire intensity;

•       Radiant heat flux as a function of distance; and

•       Radiant heat time profile.

A design fire for the heathlands has been determined. Sensitivity studies were not undertaken for this project. Sensitivity
studies could be undertaken for wind speed and fuel loads. However were not considered warranted as the proposed
Master Plan enables the provision of appropriate bushfire mitigation responses.



Calculations


The following equations were used in determining the following fire behaviour characteristics.

Fire Intensity:                                     McArthur’s Equation                      I = HWR/36

Rate of Spread:                                     Noble’s Equation                         R = 0.049*V1.21*VH0.54

Flame Length:                                       Alexander’s Equation                     Lf = 0.0775*I0.46 (heath)
                                                                                                                  4
                                                                                                                      T
Radiant Heat Flux:                                  View Factor Model                        Qd = φσΤ
                                                                                                              e


Where
                                        2                        2                       2                2                   2               2                 2
                φ = 1/π{ (X /√ 1 + X ) tan-1[Y /√1+ X ] + (Y /√ 1 + Y ) tan-1[X1/√1+ X ] + (X /√ 1 + X ) tan-1[Y /√1+ X ] + (Y /√ 1 + X )
                           1            1              1        1           1        1                1                   2   2        1      2     2       2
                                                2
                       tan-1[Y √1+ X ]}
                               1/           1

                                                       -11          2   4
σ = Stefan-Boltzman constant (5.67 x 10                      kW/m K )
                                    0
Τ = Temperature of flame ( K).
    e
X , Y , X , Y are intermediate variables, which are defined by:
    1   1   2     2
                X = [Lf (sin α + θ- 0.5cos(α+θ) tan θ) – d sinθ - h]/d cosθ - 0.5 Lf cos (α+θ)]
                 1
                Y = Y = (0.5Wf)/[d cosθ - 0.5Lfcos(α+θ)]
                 1    2
                X = {h+[d cosθ - 0.5Lf cos(α+θ)] tan θ}/{d cosθ - 0.5Lf cos (α + θ)]
                 2


Where Wf = flame width (m)
α = flame angle (degrees)
d= distance between vegetation and receiver
h= height of radiation receiving point (m) from the ground.
T= transmittance factor




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                                                                                © 23 June 2008
                                                                                Reference: 1285