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Wednesday, December 20, 2017 The Nugget Newspaper, Sisters, Oregon
Smaller branches pack the biggest fire-spreading punch
By Steve Lundeberg
AP Writer
CORVALLIS — As the
West tallies the damages
from the 2017 wildfire sea-
son, researchers at Oregon
State University are trying
to learn more about how
embers form and about the
blaze-starting potential they
carry.
Pr eliminar y findings
indicate the diameter of the
branches that are burning
is the biggest single factor
behind which ones will form
embers the most quickly and
how much energy they’ll
pack.
“Increased population in
the wildland-urban interface
means increased risk to life
and property from wildland
fires,” said Tyler Hudson,
a graduate student in the
College of Engineering.
“Spot fires started by embers
lofted ahead of the main fire
front are difficult to predict
and can jump defensible
space around structures.”
Research shows smaller-
diameter branches are better
at producing embers, also
known as firebrands.
“Embers are wildfires’
most challenging mode of
causing spread,” said David
Blunck, assistant professor of
mechanical engineering. “By
understanding how embers
form and travel through the
air, scientists can more accu-
rately predict how fire will
spread. We have a multiscale
approach that involves burn-
ing samples in a laboratory
setting, larger burns – burn-
ing 10-foot-tall trees – and
then working with the U.S.
Forest Service to participate
in prescribed burns.”
In his lab, Blunck’s
research group controls mul-
tiple parameters which can
influence generation rates:
fire intensity, crosswind
velocity, species of tree,
diameter of the sample, fuel
condition (natural vs. pro-
cessed), and moisture con-
tent of the fuel.
“Fire intensity had little
effect on the time needed for
ember generation,” Hudson
said. “And natural samples
and dowels with similar
diameters can have quite
different ember generation
times.”
Using samples of Douglas
fir, western juniper, pon-
derosa pine and white oak
with diameters of 2 and 6
millimeters, the researchers
determined that 2-millimeter
samples generated embers
roughly five times as fast as
6-millimeter samples.
This trend can be
explained by the observa-
tion that the bending stress
is proportional to 1 divided
by the cube of the diameter
– thus, the larger the diam-
eter, the smaller amount of
bending stress and a lesser
likelihood of breakage, and
ember creation. Moreover,
smaller diameters have
less fuel that needs to be
burned.
In the field, researchers
can track embers’ energy
“from the time they leave
the tree until they get to their
destination,” Hudson said,
using techniques ranging
from infrared videography
to measuring scorch marks
on squares of fire-resistant
fabric placed on the ground
at varying distances from the
fire.
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Blunck, Hudson and fel-
low mechanical engineering
graduate student Mick Carter
presented their prelimi-
nary findings in April at the
10th edition of the biennial
U.S. National Combustion
Meeting in College Park,
Maryland.
In August, Blunck was
among a group of collabo-
rators receiving a $500,000
grant from the National
Institute of Standards and
Technology “for the devel-
opment of a computer model
that will define patterns for
firebrand distribution dur-
ing wildland-urban interface
fires and their likelihood of
igniting nearby structures.”
This past fire season in
Oregon, roughly 2,000 fires
combined to burn more than
a half-million acres – that’s
about 1,000 square miles,
an area the size of Rhode
Island.
One of the most devas-
tating of those blazes was
the Eagle Creek fire in the
Columbia River Gorge,
which scorched nearly
50,000 acres and threatened
the historic Multnomah Falls
Lodge – and provided a ter-
rifying illustration of what
embers can do.
“The fire jumped the
river and started burning
in Washington because of
embers,” Blunck said. “We
estimate that the fire jumped
2 miles across the river.”
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