What factor explains elevated ember exposure risk for structures at forest edges?

• A. Ember exposure is lower at forest edges due to shielding.
• B. Ember exposure varies with wind and fuels but is generally lower.
• C. Wind-driven embers and higher probability of firebrands contacting roofs and vents.
• D. Ember exposure only matters during droughts.

Answer: (C)

Ember exposure at forest edges is driven by wind-driven embers (firebrands) that can travel ahead of the main fire and land on roofs and vents. At the edge, structures sit in the path of those embers, which are likely to land on exposed roof surfaces, attic vents, soffits, and other openings. Once a firebrand contacts a roof or vent, it can ignite materials and start a structure fire even if the flames are not directly nearby. This makes embers a primary mechanism of risk for edge structures. Shielding alone doesn’t prevent embers from landing on and entering through openings, and the idea that exposure is generally lower at edges isn’t accurate—winds and the presence of nearby fuels actually increase ember flux. Ember risk isn’t limited to droughts; it occurs under a range of conditions as embers are produced and transported by wind.