Appendix D - Bushfire Risk Assessment and Management Plan

                          2000

                          1800

                          1600
  Fire Run Distance (m)



                          1400

                          1200

                          1000

                          800                                                        Fas t
                          600                                                        Medium Fas t
                                                                                     Slow
                          400

                          200

                            0
                                 0    5    10   15    20     25    30    35     40   45      50     55   60

                                                           Elapsed Time (min)


                                 Figure 2. Graphic Formats of Equations (4), (6) and (8)
In addition, one can predict the relative rate of spread for a given fire run distance by
utilizing the flowing two step approach:
(1) Estimate the elapsed time corresponding to a given fire run distance by performing
    iterative calculations with Equation (2) or its graphic format (Figure 2);
(2) Determine the relative rate of spread corresponding to the estimated time by using
    the Equation (1) or its graphic format (Figure 1).
For instance, the times corresponding to fire run distances of 100m, 200m, 300m,
400m and 500m are determined to be 4.6 minutes, 7.6 minutes, 10.4 minutes, 13.2
minutes and 15.8 minutes for a fast growth fire in accordance with Figure 2. The
relative rate of spread corresponding to these fire run distances are then be determined
being 0.795, 0.871, 0.904, 0.923 and 0.935 for the same type of fire in accordance
with Figure 1.
By applying the approach described above, the direct relationship between fire run
distance and relative rate of spread can then be established. The curves shown in
Figure 3 is the graphic representation of the relationship between fire run distance and
relative rate of spread under the three different fire growth scenarios. With this graph,
the relative rate of spread can be directly determined for a given fire run distance under
a given fire scenario. For instance, for a block of bushfire prone land with a maximum
fire run distance of 300m the maximum relative rates of fire spread for a fire within this
block of land are determined to be 0.90, 0.80 and 0.70 respectively for fast, medium
and slow growth fires.