Wildfire resilience field guide
Embers vs Radiant Heat vs Direct Flame: how homes are exposed to wildfire.
CAL FIRE identifies three major wildfire exposure pathways for homes. They act differently, which is why home hardening and defensible space need more than one type of mitigation.
Three pathways
Ignition can arrive through the air, through heat, or through flames.
CAL FIRE’s wildfire action guidance identifies flying embers, direct flame contact and radiant heat as three ways a home can be exposed during wildfire.
Burning particles can travel ahead of the main flame front and ignite receptive material on, in or near a structure.
Heat transferred across space from nearby burning fuels can raise combustible materials toward ignition temperature without flame touching them.
Flames from vegetation, attachments or nearby combustibles physically contact the building.
One pathway can create another: embers can ignite a fence or shrub, which then creates direct flame and radiant heat exposure.
Why embers matter
Structure ignition can occur ahead of the flame front.
CAL FIRE states that embers are a major cause of home ignition and can be carried well ahead of a wildfire. Vulnerable vents, gutters, roofs, decks and combustible material near the building can provide ignition pathways.
Engineering view
Different pathways need different tools.
Source
CAL FIRE wildfire action guidance.
CAL FIRE — Ready, Set, Go! Wildfire Action Plan ↗
Published 21 September 2026.