the february 2009 fires - 2009 Victorian Bushfires Royal Commission

The February 2009 Fires
Fire Behaviour
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Fire behaviour results from the interaction of fuel, weather, topography and the fire itself. Overlaying this
basic framework is a direct link between drought, increased fire activity and more intense fire behaviour. 49
This summary of the fire behaviour on 7 February is drawn largely from the evidence of Dr Kevin Tolhurst,
senior lecturer and researcher at the University of Melbourne.
The weather conditions leading up to 7 February, and the combination of the drought and the heatwave,
led to increased combustibility and volatile fire behaviour because many of Victoria’s normally moist forests
were dry. 50 These forest fuels carried the fire more easily than ordinarily expected. In turn, this led to fires of
exceptional severity. So the conditions leading up to 7 February not only dried out Mountain Ash forests,
which ordinarily would have been too moist to burn, but also added additional fuel loads to these forests. 51
Areas of bush had also died due to the cumulative effects of the drought over preceding years. Mr David
McGahy, the Arthurs Creek-Strathewen CFA Brigade Captain who has lived in the area for 40 years,
observed:
… [the bush] was dying because of the cumulative effect of all the dry years. It was in a lot of trouble,
the bush. I remember talking to one of the DSE chaps and he said, ‘If we cop a fire through here, it’s had
it, this bush. It’s not going to regenerate because it is under too much stress now.’ So it was extreme.
The week before we had had two or three days of 45 and it was just extreme. We knew if it came, it was
going to be something special. 52
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The fine fuels were desiccated by the conditions and they added again to the fuel load. Fine fuels respond
much more to the short-term conditions such as the temperature, relative humidity and local wind
conditions. Woody fuels — twigs, branches and fallen leaves — add to the heat coming off the burnt
area. They also add considerably to the heat in the main convection column which, in turn, drives the fire.
Normally those woody fuels burn behind the firefront and do not contribute much to the nature of the fire.
However, when there is a large fire, under these dry conditions, they can add considerably to the convection
column, which influences the whole firefront. 53
The fires of 7 February did not progress in a single, easily distinguishable line — there was a ‘fire zone’
that extended kilometres ahead of the firefront. 54 As described in the paragraphs below, this zone
contained spotting that started further fires, which in turn burnt some areas well ahead of the main
firefront. Subsequently, the main firefront passed over the same areas, further burning any remaining
fuel. This process expedited the progress of the fires.
The fires varied in description and behaviour:
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classic grass and scrub fires in western Victoria
conventional bushfires progressing from ground fires to flame heights of 30(+) metres
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extensive spotting directly sighted 13–14 kilometres ahead of firefronts and estimated up to 35 kilometres
ahead of firefronts, with greater spotting over shorter distances, causing additional fires to ignite 57
spot fires further from the firefront, burning in the direction of the prevailing wind, while spot fires closer
to the main firefront burnt back towards the fire. 58
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