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At last count, Thomas Fletcher has burned 4,000 leaves and branches from arid-landscape shrub species in a decadelong effort to improve the computer models that predict wildfire hazard and behavior.
This work at Brigham Young University is shedding new light on how brush fires ignite, propagate inside a bush and spread across a landscape.
"This interaction of temperature and flow and chemistry has a real application that can help save lives and property," said Fletcher, a professor of chemical engineering. "Every time we run more experiments, we learn new things that we hadn't known before, things that nobody has ever seen."
His research, funded by the U.S. Forest Service and the National Science Foundation, has so far yielded seven peer-reviewed papers, with an eighth in the works on "coalescence" — what happens when flames merge. His most recent article revealed the discovery that the presence of moisture in fuels may not inhibit the propagation of wildfire to the extent commonly believed.
To simulate the heat from a wildfire, Fletcher uses a flat burner with the flame contained under a porous material so it emanates a steady 1,800-degree heat. The burner is moved by pulleys toward the test foliage suspended in a transparent combustion chamber.
In this recent study, published in the International Journal of Wildland Fire, Fletcher and his students ignited the material, then quickly extinguished it by spraying it with nitrogen. The gas deprived it of heat and oxygen without damaging the material so it could be analyzed.
"Fifty to 60 percent of the moisture content is still in the leaf," Fletcher said. "Once a fire gets going, it doesn't matter if you have wet leaves or bone-dry plants. A big enough fire can ignite the leaves even though there still may be some moisture in the vegetation."
The Utah species he studies are sagebrush, gambol oak, juniper and sawtooth maple, some of the very plants that burned last week in the foothills around Herriman. He also tests shrubs from fire-prone landscapes in Florida and California.
The BYU researcher secured federal funding to advance the National Fire Plan Research Program, an interdepartmental effort to improve wildfire management. A key question explores how live green fuels behave differently from dead fuels in fire scenarios, according to BYU's Forest Service collaborator, David Weise, based in Riverside, Calif. At what temperatures, for example, does living foliage ignite and how long does it take for ignition to occur?
"All our operating models to make fire-spread predictions, for the most part, were developed using dead fuels, pine needles and wood. But there are lots of places where live fuels — shrubs, sage brush and chaparral, and pine forests — burn," Weise said. "Tom's work is doing very fundamental characterization of the burning properties of live fuels. That information needs to be synthesized and put into operational models."
The models fire managers use now were developed in the 1960s and 1970s and made simplifying assumptions. Computing power is now available to test the validity of these assumptions.
"We're adding fine-scale detail and incorporating things that those modelers had to set aside," Weise said.
Fletcher also said the models fire crew chiefs now run on their laptops are not well-grounded in physics.
"It runs fast and predicts something, but it's not as good as it can be," he said. "We're trying to improve that model so [the crew leader] can better understand where the fire is, where it's going, which houses can be saved and where he can safely place firefighters."