Emberometer could gauge threat of wildfire-spreading embers

Date:
August 18, 2021
Source:
National Institute of Standards and Technology (NIST)
Summary:
As wildfire fronts advance through landscapes or communities on the
ground, they also attack from above, launching volleys of glowing
embers into the air. Also known as firebrands, these specks of
burning debris can glide for up to 40 kilometers (approximately 24
miles) before landing and can cause up to 90% of home and business
fires during wildfires.



FULL STORY ==========================================================================
As wildfire fronts advance through landscapes or communities on the
ground, they also attack from above, launching volleys of glowing embers
into the air.

Also known as firebrands, these specks of burning debris can glide for
up to 40 kilometers (approximately 24 miles) before landing and can
cause up to 90% of home and business fires during wildfires.


========================================================================== Guidance on fending off ember attacks is sparse, largely because
so little is known about embers' behavior. But a new instrument,
dubbed an emberometer, could offer a glimpse at their true nature. In
a paper published in Experiments in Fluids, researchers at the National Institute of Standards and Technology (NIST) showcase the tool's ability
to characterize the size and trajectory of embers, which may provide
insights into their level of threat. With NIST's new tool, fire engineers
may be better equipped to protect buildings from embers and could produce
data to support cost-effective guidance in building codes.

The dangerous conditions in which embers arise and their seemingly random nature have made measuring them an uphill battle. One go-to approach has
been to collect embers from water-filled pans, which allows researchers
to count and size up embers after a fire has gone out, but it paints
far from a complete picture of what happens during ember exposures,
where structures are swarmed by flaming debris.

Because embers act so erratically, measuring how their behavior changes
from one second to the next while they are still airborne is crucial. NIST combustion specialist Nicolas Bouvet and his colleagues built the new instrument to do just that.

The emberometer is composed of a metal stand, shaped like a capital H
on its side, with point-and-shoot digital cameras attached to the end
of each of its four arms. The researchers designed it to be operated
from more than a kilometer away and embedded its electronic components
in fireproof materials to make the system deployable in fiery conditions.

Through a method known as particle tracking velocimetry, the emberometer
uses data from its four perspectives to trace the path of brightly lit
objects (such as embers) as they pass through a 2-cubic-meter (more than 70-cubic-foot) box- shaped space in front of the device. The system also captures the silhouettes of each ember from four different angles and
merges the perspectives to digitally reconstruct their 3D shapes.



==========================================================================
The emberometer made short work of the initial experiments, some of
which tested the device's ability to track burning wooden sticks fastened
to the end of a rotating metal arm, and to estimate the sizes of small
plastic spheres the researchers dropped in front of the cameras, Bouvet
said. With the simple tests behind them, the researchers' next move was
to find out if the device could put numbers to real embers.

In NIST's National Fire Research Laboratory -- a space where experiments involving intense flames can be carried out safely -- the authors set up
the emberometer downwind of a firebrand generator capable of producing
showers of embers at a larger scale.

In less than a minute, the emberometer observed hundreds of embers zip by
at speeds varying from tens to hundreds of centimeters per second. The
tool tracked the moving particles and reproduced their forms in 3D,
as before. The researchers checked the emberometer's sizing work by
collecting embers that had fallen into water-filled pans during the
experiment and comparing the doused pieces of wood to their digital counterparts.

"The emberometer compares very well to what is directly being collected
in the water pans," said Bouvet. "I'm very confident for the tracking,
and for the sizing we're satisfied." Because of the amount and complexity
of data captured by the emberometer, comparing different ember exposures
could be a challenge, even if the data is accurate. The researchers'
solution is a visual aid called a firebrand rose, which summarizes
the traits of an exposure by packaging information on the number and orientation of embers through space and time into one graph.



==========================================================================
The potential benefits of the emberometer are multifold. Engineers could
add depth to the shallow pool of data on real ember exposures by taking
the tool outdoors and also use it to ensure that embers produced in the
lab match field measurements.

Ultimately, ember exposures more true to life could lead to better
research into ember-proof materials, potentially leading to better
protection for structures during wildfires.

More outdoor research could make mitigation efforts more cost-effective
as well, if researchers using emberometers tie ember threat levels to environmental conditions, such as the intensity of drought or wind. That
data could inform new building codes and standards that offer fire safety professionals guidance on selecting a degree of protection appropriate
for the surrounding conditions.

"We want to be able to look at the fuel type, topography and weather, and
have an idea of how serious an ember exposure might be for a structure,"
Bouvet said. "Building codes can use that information to advise you on
how to harden your structure. If you're somewhere in the middle of a
grass field, it's not going to be the same as if you're surrounded by
tall trees." The NIST team's next step is to give its system a touch
of artificial intelligence. Because the device only has four eyes,
it cannot always make out every detail of an object's shape. But with
machine learning, the emberometer could fill in blind spots, improving
its size reconstruction measurements.

Soon after, the researchers plan to test-drive the emberometer in the
great outdoors, where it can face embers born out of real -- albeit
controlled - - wildland fires. By learning lessons in the field, the
team could further tighten its design, readying the emberometer for
widespread use.

========================================================================== Story Source: Materials provided by National_Institute_of_Standards_and_Technology_(NIST).

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Nicolas Bouvet, Eric D. Link, Stephen A. Fink. A new approach to
characterize firebrand showers using advanced 3D imaging techniques.

Experiments in Fluids, 2021; 62 (9) DOI: 10.1007/s00348-021-03277-6 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210818153218.htm

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