On the heels of Oregon’s most expensive wildfire season ever, in 2018 researchers at Oregon State University are increasing efforts to better predict how the blazes behave, including how they generate fire-spreading embers.

Our team has been chosen by the U.S. Department of Defense to spearhead a new $2.1 million effort to study the burning of live fuels. Oregon State University will partner with the U.S. Forest Service on a four-year grant awarded through the Department of Defense’s Strategic Environmental Research Development Program.

The Department of Defense is interested in the research because they have a lot of land and the land burns. Live fuels are basically trees that are green and living. Those trees are often what torches. But dead fuels have primarily been studied historically.

The work will be built around the theory that there are likely just a handful of factors – such as pyrolysis, the decomposition that results from high temperatures, and the products of that decomposition – that cause differences in burning behavior when live fuels burn.

Most live-fuel studies tend to be fuel-specific, controlling for variation in burning behavior based on time of year and moisture content. But with those results it’s difficult to know how new fuels will burn or even how the same fuel will burn outside the conditions that have been studied. So it’s better to understand what’s driving the sensitivity when there are different fuels.

Our theory is that it’s just a few processes that cause the differences when different live fuels are burned. If we can understand what they are we can better predict how new species would burn.

The research will provide Department of Defense managers with fire models that can predict ignition, burning rate and fuel consumption for mixtures of live and dead fuels. That will allow them to more effectively plan prescribed burning as well as wildfire responses. It will involve a mix of lab work, modeling and field studies.

In recent months the research group has examined the burning behavior of more than 100 trees representing four different species – Douglas fir, grand fir, western juniper and ponderosa pine – in the range of 10 to 15 feet tall.

Most wildfire research involves either prescribed burns or work in a laboratory on samples as big as 1 meter or 3.2 feet. In the lab all the parameters can be controlled, like temperature, size and moisture content. But the question remains if the results can be scaled.

With a prescribed burn researchers are working in actual conditions. But it’s difficult to understand cause and effect. There’s so much out of researcher control that it’s difficult to know what’s driving the various phenomena.

With trees that are about 10 feet tall researchers can bridge the scales between laboratory and prescribed burns. They can look at many species and start to vary the parameters they think are important. The experiments are on an intermediate scale but have a replicate size that’s not rivaled by any study I’ve ever found.

This past December researchers studied the effect of fire retardant on ember generation. They found that under some conditions, trees coated in the retardant sent off fewer embers that contained enough energy to start a new fire. That effort was in partnership with an industry sponsor, P N Solutions.

Embers are wildfires’ most unpredictable modes of causing spread. By understanding how embers form and travel through the air, we can more accurately predict how fire will spread. Techniques for studying embers include infrared videography, collecting embers in trays of water, and measuring scorch marks on squares of fire-resistant fabric placed on the ground at varying distances from the fire.

“By using fire-resistant fabric to collect embers, in conjunction with trays filled with water, the fraction of ‘hot’ embers can be determined and used to help predict spotting,” said Tyler Hudson, a graduate student in Oregon State University’s College of Engineering.

The char marks on the fabric are used to estimate how much energy an ember has when it lands. Trees coated in fire retardant tended to produce bigger embers but generally with less energy.

This past year in Oregon the cost of fire suppression for the first time exceeded half a billion dollars, according to the Northwest Interagency Coordination Center, which provides logistical support and intelligence for federal and state wild-land fire-suppression agencies. The state in 2018 saw 1,880 fires burn 1,322 square miles — more land area than the state of Rhode Island.

David Blunck is an assistant professor of mechanical engineering at Oregon State University.