Civil and environmental engineering experts have undertaken distinctive live fire experiments to investigate the movement of firebrands—burning embers ejected from wildfires—that can ignite spot fires and accelerate the spread of devastating blazes.
In the turmoil of a wildfire, elements such as heat, wind, flames, and available fuel combine to generate embers that are lifted into nearby areas, igniting new spot fires and causing destruction and property damage, particularly in California’s wildland-urban interface. Researchers from the University of California, Irvine have conducted pioneering field tests to enhance our understanding of the physics behind these firebrands, providing insights that could aid authorities in modeling the effects of disasters that are increasingly common due to climate change.
In a recent article published in the journal Physics of Fluids, the UC Irvine team details their experimental setup at the UC Berkeley Blodgett Forest Research Station located in California’s Sierra Nevada mountains. They created a burning pile using wood from ponderosa pine and Douglas fir trees, incorporating branches and needles—key fuel sources in wildfires across Sierra.
During night experiments, the researchers employed high-speed imaging technology to observe the development and behavior of flames over approximately 20 minutes. They tracked the embers produced by the fire using a particle tracking velocimetry method, which offers essential insights into particle movement and allows for the examination of flow dynamics and turbulence with high precision.
To capture the firebrands expelled from the flames, the scientists placed a series of sheet pans filled with water around the fire. This approach enabled them to gather and subsequently analyze the size, shape, and density of the firebrands in a laboratory setting.
“With climate change leading to larger and more complex wildfires, and our construction patterns within the wildland-urban interface, these fires inflict damage directly affecting those living in these regions, both financially and in terms of safety,” explained co-author Tirtha Banerjee, an associate professor of civil and environmental engineering at UC Irvine. “Researchers have long sought to comprehend the role of embers in fire spread. Our team has made significant strides in understanding the physics and movement of firebrand propagation using cutting-edge instruments and methods.”
The researchers also analyzed the frequency at which embers were produced within the high-temperature air currents. While existing computer models suggest that firebrand movement is linked to fire intensity, Banerjee’s research group discovered that ember production is highly unpredictable, occurring in sporadic bursts that can project fire-starting debris far from the original blaze, making it challenging to forecast.
“Current models may minimize the risk of large firebrands being lifted and scattered over longer distances due to oversimplified views on fire plumes and ember shapes,” said lead author Alec Petersen, a postdoctoral researcher in civil and environmental engineering at UC Irvine. “We aim for our research to furnish vital experimental data from a real-world context to reassess these assumptions and parameterizations in forthcoming modeling endeavors.”
Petersen noted that the variability in fire plume and ember production rates is frequently overlooked in models predicting how far a particular size ember will travel.
“What is often ignored are instances where significant bursts of larger embers are released along with vigorous, turbulent updrafts from the plume. These statistically rare occurrences could be responsible for elevating embers with the greatest potential to cause spot fires farther than one might anticipate,” Petersen stated. “Given enough opportunities, these unusual events become likely, and wildfires release billions of embers. It only takes one ember to spark a new fire, so factoring in these intermittent effects could enhance risk assessments for potential new fire breakout locations.”
The field tests conducted at the Blodgett Forest Research Station received support from UC Berkeley professor Rob York. Funding for the research was provided by the National Science Foundation, NASA, and the U.S. Department of Agriculture.
