Amended Bushfire Management Overlay requirements

On 31 July 2014, VC 109 amended bushfire protection arrangements applying to land covered by a Bushfire Management Overlay (BMO) in a planning scheme, notably Clause 44.06 Bushfire Management Overlay (click here) and Clause 52.47 Planning for Bushfire (click here).

A new Planning Practice Note 65 (click here) was issued in September to “provide advice on preparing and assessing an application under Clause 44.06 Bushfire Management Overlay.

The CFA has also issued revised “Standard Planning Permit Conditions (Bushfire Management Overlay)” (click here).

Anyone wanting advice on such planning scheme requirements should contact the municipal council administering the planning scheme involved and the CFA. However, a disturbing feature of an application for a permit is that some council planners seem to ‘drip-feed’ requirements, which add time, cost and frustration to borne by applicants.

As time permits I will continue with this blog to the extent I consider necessary to increase knowledge of bushfire behaviour and related matters.

Bushfire explained – Part 3: What burns and what does not burn as bushfire moves across the landscape

To properly address bushfire risk it’s important to understand what actually burns as fire moves across the landscape, especially as the Victorian Fire Risk Register – Bushfire (VFRR-B) is being raised by the CFA and certain municipal councils to ‘influence’ planning permit application decisions. I’ll come back to this later as not properly understood the Risk Register has the potential to unnecessarily frighten people and lead to poor decision-making.

Extending on from my 15 June posting “Bushfire explained – Part 2” (click here) following are some examples of unburnt vegetation in the path of bushfire, beginning with trees in the vicinity of the Lancefield–Kilmore Road, mid-way between Lancefield and Kilmore, as the 9 February Mickleham fire (click here) travelled north.  

Roadside eucalypts on the sides of the Lancefield–Kilmore Road showing predominantly only canopy or “crown” scorch. It would have been a ‘hot’ fire that passed beneath those trees, but not hot enough to ignite the canopies. Remember, this is the fire that took several days to control.

Below are trees in open fields south of the Lancefield–Kilmore Road showing only “crown” scorch.

Below are trees and shrubs in the path of the 9 February 2014 Gisborne fire as it travelled northeast towards Riddells Creek after the wind change. The fire weather conditions this day were described as being the worst since 7 February 2009 (Black Saturday).

Above, trees and low vegetation "scorched" as the fire continued its rush towards Riddells Creek having crossed the Sunbury-Riddells Creek Road just visible at right.

In the photographs immediately above and below this text observe how the fire only "scorched" the base of these tree trunks, except for where it took hold on an open section of the trunk in a tree in the lower photograph. This burning section of trunk would not have been part of the fire front.

Finally, some well established Pines near Gisborne (courtesy Haydn Bishop Electrics, Gisborne) that did not succumb to crown fire. Insufficient fine fuel around the base of these trees and lack of trunk fine fuel (needles) kept the fire at ground level. Relevant to earlier photographs of "scorched" Pines.

I’m hoping by now that it’s becoming apparent that trees don’t automatically burn and thus don’t contribute significantly to the intensity of bushfire; indeed in some circumstances trees can actually help shield a building from radiant heat and reduce ember attack. I’ll continue this theme in my next posting as it’s important, particularly in understanding how the Victorian Fire Risk Register – Bushfire (VFRR-B) seems to deal with bushfire and how that Risk Register is being applied.

Bushfire explained - Part 2: How bushfire moves across the landscape

From continuing observation of how bushfire protection issues are dealt with in Victoria, it seems the broad community is largely unaware of how bushfire moves across the landscape, with one of the great fallacies being that trees always burn as part of a bushfire.

I regularly encounter people addressing bushfire risk on their land who believe that large scale tree removal is required, which is unnecessary in the majority of situations.

Towards the end of my 21 April 2014 posting “Bushfires explained – Part 1” (click here) are two media photographs of unburnt vegetation around houses lost in the Blue Mountains, NSW, fires earlier this year. In my 17 March 2014 posting “Grassfires, a simple truth” (click here) there is a link to a video clip available at The Age website (click here) showing the effect of the Mickleham fire travelling north towards Darraweit Guim on 8 February 2014 after the wind change. The unburnt vegetation around buildings lost or damaged can readily be seen.

The following three photographs concern a dwelling at Humevale that succumbed to the headlong rush of the Kilmore East fire on 7 February 2009.

Situated on predominantly grassland that slopes down towards the north and northwest at 10 degrees, the nearest significant group of trees was a relatively narrow band of eucalypts along a natural drainage line aligned northeast–southwest approximately 230 metres north of northwest from the dwelling. The nearest forest was approximately 450 metres northwest of the dwelling.

Approximately 25 metres east of the dwelling was a treed fenceline approximately 15 metres wide that can be seen behind the dwelling. Beyond that fenceline the vegetation is predominantly grassland that burning under the effect of the strong north to north to north-westerly wind at the time would not have contributed to fire behaviour affecting the dwelling.

Note the proximity of the shrubs and trees around the dwelling.

Grassland immediately north to northwest of the dwelling, with the tree line mentioned above visible in the centre of the photograph and grassland beyond also visible.

The preceding two photographs were taken on 31 January 2008.

As can be seen in the above photograph taken on 11 March 2009, it was a brick veneer building with short lawn and well maintained and separated trees and shrubs around it.

Compare the effect of the fire on the leaves on the trees and shrubs in this photograph with the same vegetation in the first photograph — much of the leaf damage is scorching rather than total incineration. At the extreme left of the dwelling is scorched thick creeper that would not have contributed to a fire involving the dwellings. The scorching of the Pine tree behind the dwelling is also significant; it would not have contributed to loss of the dwelling.

Also significant is the obviously undamaged condition — even at ground level — of the blue steel shed to the right of the dwelling and a large steel garage that can just be seen at left background of the dwelling. This lockup garage, with door opening facing the south, and its contents were not affected by the fire.

Why was this dwelling lost? Probably because it was unattended at the time the fire went through and not been constructed to withstand ember attack — BAL-12.5 according to AS 3959 Construction of buildings in bushfire-prone areas.

A major contributor to ignition of this dwelling would have the failure of a timber door over the underfloor entrance.

Located just right of centre in the close up of the northern end of the dwelling this door went to ground level and had gaps around it that would have allowed ember penetration into the underfloor area. The timber door and its timber frame were largely destroyed, the combustion of which would have been assisted by ‘convection heating’ prior to the arrival of the fire front and fire burning up to it through dry grass at its base.

No doubt in my mind that the dwelling could have been used to safely shelter from the passing fire front, then a well-prepared person able to safely go outside and look for and extinguish ignitions — the dwelling would have taken time to reach total involvement.

In my next posting I will give more examples of what does not necessarily burn when a bushfire travels across the landscape and hopefully further counter some of the 'mythology' of bushfire in Australia.

Bushfire explained - Part 1

In my 16 February (click here) and 17 March 2014 (click here) postings I explained some of the basics of grass fires: how they spread across the landscape, how they impact on a building and surviving the passage of a grass fire using the family home as a bushfire shelter.

Considering how BMO bushfire management statements are received by some decision makers in Victoria, there appears to be a serious lack of understanding of the characteristics of bushfire as they move across the landscape and affect a dwelling, with a seemingly automatic assumption of a catastrophic result leading to inappropriate decisions in several of the cases in which I’ve been involved or observed from a distance. Consequently, it’s reasonable to assume that this is an indicator of bushfire knowledge, or lack of it, in the broader community.  

Bushfire spreads across the land in one or more forms:

Sparks, ember or firebrand attack

Fresh ignitions ahead of the main fire front due to “spotting” activity, being wind-borne embers or larger firebrands starting new fires in unburnt fuel (vegetation), sometimes out to many kilometres ahead of the main fire front depending on the type fuel available to be picked up by the wind or carried up in the convection column.*

The types of fuel that can “spot” ahead of a fire range from leaves and small pieces of tree bark on the ground within relatively close proximity of a “receiver” such as the family home; the bark of a stringybark species eucalypt tree for example Messmate that when burning is liberated by strong wind and blown horizontally at the “receiver” at distances possibly out to 100 metres; and the bark of certain of the gum species eucalypts such as Manna Gum the bark of which is sufficiently light to be carried up in a convection column and continue to burn before it returns to earth and lights a new fire, sometimes many kilometres ahead of the main fire.

This photograph is of eucalypt leaves and other dead material at the base of a stringybark on land at Toolern Vale on 12 September 2012. Leaves and twigs up to pencil size carry the fire front and are susceptible to being carried forward by wind close to the ground. The vegetation has reached "steady state" the land not having been burnt for greater than 30 years.

The following two photographs are of stringybark eucalypts on land at Buttermans Track, Christmas Hills that slopes up from the north towards the south. Taken on 4 July 2013 the trees show little sign of fire. The second of the two shows scattered small black spots on bark that is becoming deeply furrowed and exposing fine fibres of bark that will readily ignite if exposed to fire. Clearly the vegetation on this land has reached "steady state", an issue I'll return to in a future posting dealing with fire behaviour.

The following three photographs are of stringybark species eucalypts on land at Hobbs Road, Bullengarook. Photographed on 26 April 2013 the trees show diminishing signs of being involved in the Ash Wednesday 1983 fire as it approached Gisborne after the wind changed to the southwest. Given the small burn scars on the Buttermans Track trees their involvement in fire would have been pre-1983. The third photograph shows no sign of fire with the bark becoming deeply furrowed. In the 30 years since the Ash Wednesday fire the vegetation on this land has returned to "steady state".

Stringybarks photographed on 21 December 2009 on land at Aubrey Cuzens Drive, Marysville and showing signs of recovering from the Black Saturday fire 10 months earlier. Note how the bark is completely black with the fine fuel gone leaving the dense bark that ceased burning after the fire front had passed. Over time the burnt bark will be replaced as shown in the above photos.

The following two photographs are of gum eucalypts to illustrate the bark form mentioned above. The first photograph is of a gum in a Sunbury park on 14 February 2014 and the second on unmanaged land adjoining the Yarra River at Wonga Park on 3 September 2013. The pile of bark around the base of the tree will burn vigorously when dry with the resulting convection heating aiding the ignition of the bark suspended above and if the heating is sufficient send some of the suspended bark on a journey to possibly light a fire elsewhere in unburnt vegetation. It is this long range form of "spotting" that is responsible for the sometimes dramatic spread of forest fire in the summer months.

Radiant heat

Ignition due to high level radiant heat from the fire — the closer the fire front the greater the heat level to which the “receiver” is exposed. The less dense building materials such as Western Red Cedar weather boards can be expected to ignite and continue to burn if the radiant heat level is sufficiently high. Unprotected ‘ordinary’ window glass can be expected to fail early thereby allowing sparks and embers to penetrate the interior of the building. Table 1 on page 8 in the CFA's "Planning for Bushfire Victoria" provides information on the effect of radiant heat.

Flame contact

Concerning direct flame contact, the flammable nature of the “receiver” and the intensity and duration of the flame contact on the receiver influences its susceptibility to ignition. For example Western Red Cedar will readily ignite and likely continue to burn after the igniting (pilot) flame ceases as the fuel sustaining that flame is consumed whereas a much denser hardwood will likely cease to burn when the pilot flame is removed. In a direct flame contact situation unprotected windows are vulnerable to breaching, thereby allowing flames to penetrate into the interior of the building.

On 17 March 2014 (click here) I posted photographs of buildings vulnerable to ignition through flame contact, particularly the first two showing grass up to the edge of unprotected timber at ground level and shrubs against a window or timber.

Convection heating

While not a direct source of ignition, preheating of the “receiver” occurs when vulnerable surfaces are exposed to several hours of hot wind consistent with a north wind during a period of Total Fire Ban or are subjected to hot air generated by a fire. Simplistically, this preheating serves to reduce the temperature at which a pilot flame will ignite the “receiver”.

In the second paragraph (above) I’ve commented on what seems to be automatic assumptions by some decision makers that a proposed building would be subjected to fire of such intensity that it would not survive. The experience of severe bushfire events in Australia prove that’s largely not the situation.

Overwhelming evidence gathered in Victoria since the Beaumaris fire of 14 January 1944 (click here) proves that the vast majority of dwellings lost or damaged in a bushfire are ignited by ember attack. This was certainly the situation in the Ash Wednesday 1983 fires and the 2009 Black Saturday Bushfires in Victoria. Media photographs of the 2013 Sydney, NSW and Dunalley, Tasmania fires show dwellings that succumbed to ember attack and/or flammable vegetation too close and not being constructed to resist bushfire.

Below is an ABC News photograph of buildings that have succumbed to ember attack from the Blue Mountains, NSW fires earlier this year. The unburnt condition of the vegetation around the buildings is evidence of ember attack on unprotected and probably undefended buildings.

Below is a News Limited photograph of buildings in Winmalee, NSW that have succumbed to ember attack from the Blue Mountains, NSW fires earlier this year. Again, the unburnt condition of the vegetation around the buildings is evidence of ember attack on unprotected and probably undefended buildings.

The condition of the vegetation in both the above photographs are important indicators of how bushfire travels across the landscape that I will address in greater detail in "Bushfires explained - Part 2".

Australian Standard AS 3959 construction of buildings in bushfire-prone areas, first published in the aftermath of the Ash Wednesday 1983 fires in Victoria and South Australia, recommends design and construction measures to protect dwellings from bushfires at increasing levels of radiant heat exposure and ultimately flame contact.

All levels of design and construction in the current version of AS 3959 published in 2009 include measures to protect against ember attack. Of course AS 3959 is not the sole solution, with corresponding vegetation management (fuel reduction), no flammable rubbish, fire wood or similar in a position that if ignited will threaten the dwelling, and the occupants having a bushfire survival plan individualised to suit their situation while allowing for their physical and emotional strengths or limitations.

* Ahern, A. and Chladil, M. 1999, How far do bushfires penetrate urban areas? Disaster Prevention for the 21st Century. Proceedings of the Australian Disaster Conference, Canberra.