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Fire scientist Jack Cohen: make homes less ignitable; embers—not just nearby flames—drive structure loss
Summary
Jack Cohen, a longtime fire-lab scientist, told an audience that structure ignitions during wildland-urban fires often come from windborne embers and that homeowner measures—nonflammable roofs, defensible space and prescribed burns—can make ignitions manageable when suppression is overwhelmed.
Jack Cohen, a fire scientist associated with a fire laboratory, told a public presentation that reducing a home’s ignitability is the most effective way to prevent structure loss during severe wildland-urban interface fires.
Why it matters: Cohen argued that suppression can be effectively zero when many structures are exposed simultaneously under high-wind conditions. Therefore, homeowner actions and structural measures that reduce ignition potential are critical to increasing the chance a structure survives when suppression resources are strained.
Key points Cohen made: He said embers (firebrands) can ignite structures well ahead of a flame front and that “if it had a flammable roof, it was history,” based on his analysis of past fires. He pointed to a nearly completed house that survived Patty Canyon because it had a nonflammable roof and lacked combustible landscaping and a wood pile. Cohen said, “What you can do is you can reduce the ignitability of your structure so that ignitions are manageable.”
Cohen reviewed historical incidents to illustrate his claims: he cited large-loss events such as Laguna Beach (where he quoted published tallies of acres and homes lost), the Oakland loss of roughly 2,200 structures in a single event, and the 1871 Peshtigo fire to show the variety and scale of major conflagrations. He contrasted vegetation types—Ponderosa pine, Douglas fir, lodgepole and spruce-fir—and explained how natural fire regimes differ by ecosystem and affect fire behavior and mitigation options.
Practical measures discussed: Cohen emphasized defensible space, roof and siding materials, thinning and pruning understory trees, and prescribed burning under controlled conditions to restore a landscape’s historical fire mosaic. He described how some homeowners have created defensible property by pruning crowns 10 to 15 feet above the ground, removing ladder fuels and providing gravel drives and perimeter clearings to give firefighters a chance to work safely.
Limitations and homeowner responsibility: Cohen stressed that no measure can guarantee a home will never ignite but said reducing ignitability makes fires “manageable” rather than catastrophic. He highlighted that homeowners live in the house and federal/state/local fire services cannot mandate every private action; therefore, homeowner choices are central to survival in high-consequence events.
Follow-up: Cohen said additional speakers would examine construction and property-level measures in more detail; his presentation framed structure-level interventions as complementary to broader vegetation management and suppression planning.
