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3 December 1998 |
Ref 98/283 |
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There will be bushfires in Western Australia this summer.
Researchers will be lighting 'hot' fires in two areas of jarrah
forest in the State's south-west. Recent fatalities to firefighters
in Victoria emphasise the danger of bushfires and the need for
accurate information on fire behaviour.
The fires of Project Vesta will provide much information on the
speed of spread and the behaviour of fire. The two areas chosen
for the experimental burns are near Margaret River, with relatively
high rainfall, and in drier country east of Harvey.
According to Phil Cheney, leader of the CSIRO Forestry and Forest
Products fire research group, all burning was planned to be completed
last summer, but early and severe fire weather conditions made
this impossible.
The experiment is being undertaken jointly by CSIRO and the Western
Australian Department of Conservation and Land Management (CALM).
"Important findings have emerged already," says Phil
Cheney. "Current prediction systems need to be reassessed.
In moderate to medium-intensity wildfires, some things are happening
that we are not predicting at all well."
The rule-of-thumb that doubling the amount of fuel will double
the rate of fire spread turns out to be dangerously unreliable.
"In some experimental fires, doubling the fuel load increased
the rate of spread by five or six times," Mr Cheney says.
"Another set of fires showed no consistent relationship
at all."
In some cases heavy fuel appears to actually reduce the rate
of spread.
"We suspect that, at low wind speeds, strong convection
from these fires draws the flames inward, tending to make a fire's
progress slower and more erratic," says Mr Cheney. "But
when a threshold wind speed is exceeded, which varies with the
fuel load, the situation changes dramatically and the fire rapidly
achieves its potential rate of spread."
Mr Cheney thinks that under some conditions this may be as much
as 10 times greater than the rate that would be predicted using
current methods.
An important finding from wind measurements during last summer's
research is that gusts tend not to travel far in a forest, with
the result that readings taken more than about 40 metres downwind
from a fire may have little predictive value. "It appears
that a gust flows a small distance, dissipates, and is replaced
by another gust."
"Quite big changes of wind speed in a forest may have a
relatively localised effect. The danger is that if a gust exceeds
a fire's threshold wind speed the fire might suddenly take off
at a rate 3-5 times faster than before," he says. "This
is particularly dangerous for firefighters."
According to CALM Senior Research Scientist Dr Lachie McCaw,
information gained from Project Vesta will be critical to the
development of systems used to predict fire behaviour and assess
the threats posed by uncontrolled fires.
"Land management agencies and rural fire authorities use
these types of decision support systems on a daily basis during
the fire season and need the best available information,"
says McCaw. "It is imperative that the full program of experimental
fires scheduled for Project Vesta this summer be completed."
Financial support for Project Vesta is being provided by the
members of the Australasian Fire Authorities Council (AFAC),
the Hermon Slade Foundation, Isuzu-General Motors and the shires
of Harvey, Nannup, Bridgetown-Greenbushes, Mundaring and Swan,
however, further funding is needed.
More information :
Mr Phil Cheney (02) 6281 8379
Dr Lachie McCaw (08) 9771 7998
Mr Mick Crowe (02) 6281 8357
0419 696 184
E-mail: Mick.Crowe@ffp.csiro.au
For more information on Project Vesta visit the web site at:
http://www.ffp.csiro.au/vesta/index.html
(Australia's largest scientific research organisation)
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