Embers
Embers are the most important cause of home ignition in wildfires. NIST's investigation of the 2007 Witch Creek Fire in San Diego County found that about two out of three destroyed homes were ignited directly or indirectly by wind-blown embers, not by the flames of the fire itself (Maranghides and Mell 2009). Every major fire since has confirmed the pattern.
Wind-driven embers travel a mile or more ahead of a fire front. That means ember exposure is close to inevitable for any San Mateo County home near wildland fuels during a wind-driven fire, whether or not flames ever reach the property. Embers ignite homes several ways: they collect against combustible material next to the house, land in gutter and roof debris, lodge in deck gaps and fence joints, and blow through vents into attics and crawl spaces.
You cannot stop the embers. You can remove what they ignite. An ember-safe home combines two equally important measures: building materials and design that resist ignition (home hardening), and well-chosen, well-placed, well-maintained near-home vegetation (defensible space), starting with a noncombustible Zone 0 in the first 5 feet. Prepare now, before a fire starts.
Ember Video Resources
Be Ember Aware (Part 1 of 2)
Be Ember Aware (Part 2 of 2)
Radiant Heat vs. Embers: Jack Cohen Interview
Jack Cohen, research physical scientist at the U.S. Forest Service Missoula Fire Sciences Laboratory, explains why home ignition is determined by the home and its immediate surroundings, not the wall of flame.
IBHS Ember Storm Test
The Insurance Institute for Business & Home Safety recreates a wind-driven ember storm against a full-scale test home in its research facility.