When a wooden structure burns in a wildfire, it does more than collapse—it launches thousands of burning embers into the air, and researchers at Oregon State University have discovered that the taller the building, the more of these dangerous firebrands it produces.
In test burns of 21 wooden shed-like structures ranging from 1 to 3.6 meters tall, research associate Deepak Sharma and professor David Blunck's team found that taller buildings generated significantly more wind-carried firebrands that scatter across the landscape. This matters urgently: firebrands are responsible for up to 90% of structure losses in community wildfires, a finding that takes on tragic weight when you consider that last year, wildfires in greater Los Angeles destroyed approximately 18,000 structures in just two days.
The researchers burned each structure in lightly breezy conditions—winds of 2.25 to 4.5 mph—and measured both the total number of embers produced and the yield per kilogram of burned material. The results ranged from about 2,000 to 24,000 firebrands per structure, with mass-specific yield ranging from around 50 to 135 firebrands per kilogram. This was the first study to measure firebrand yield from single structures and to quantify it relative to the amount of material that actually burned, a methodological breakthrough in understanding wildfire behavior.
The study also revealed that exterior building materials matter enormously. Structures with highly flammable siding, such as cedar, produced both more embers overall and more embers per kilogram of combusted material than buildings with less combustible roofing and siding. As Sharma explains, when the same mass of material burns in two buildings, the one clad in highly flammable materials doesn't just produce more embers—those embers are more likely to keep burning after they land.
According to Blunck, understanding how these embers form and travel is foundational to fire science itself. "Embers are wildfires' most challenging mode of causing spread," he said. "By understanding how embers form and travel through the air, scientists can more accurately predict how fire will move from location to location." The research, published in Applications in Energy and Combustion Science, suggests that both building height and exterior materials affect firebrand production through their influence on fire intensity, wind-plume dynamics, and how materials fragment and maintain heat during transport.
The implications extend beyond pure science. These findings are designed to inform future empirical models and physics-based fire spread simulations—tools that communities in the wildland-urban interface desperately need. Sharma and his colleagues are already planning to broaden their investigation, looking at firebrand mass distributions, ignition potential, and a wider range of building assemblies and wind conditions. The goal is nothing less than helping communities design buildings that can be more resilient to wildfire and better predict how fires will actually spread, one dangerous ember at a time.