Wildfire preparedness

Wildfires don't kill people who are already gone. The 2018 Camp Fire destroyed the town of Paradise, California in under four hours — 85 people died, more than 18,000 structures burned, and 50,000 people were displaced. Post-event analysis found that embers traveled up to 1 mile (1.6 km) ahead of the fire front, igniting homes that were not in the direct path of flames. Most of those structures could have been made significantly more resistant. Most of those deaths involved people who waited too long to leave.

Wildfire preparedness is two separate problems: reducing the probability your home ignites, and knowing exactly when to leave so you are not on the road when conditions make escape dangerous. Both require decisions made before fire season, not during it.

How wildfires spread: what the models miss

Wildfires spread by three mechanisms: direct flame contact, radiant heat, and embers (firebrands). Research from the Insurance Institute for Business & Home Safety (IBHS) and the 2018 Camp Fire investigation found that up to 90% of homes lost in wildfires are ignited by wind-blown embers — not the advancing fire front. Embers can be carried 1 mile (1.6 km) or more ahead of an active fire, landing on combustible roofing material, in gutters, against wood fences, or in dry vegetation immediately adjacent to the structure.

This changes the planning model. A home half a mile from the fire line is not automatically safe — it can be ignited by embers from the fire front long before flames arrive. The fire line moves toward you; the embers arrive first.

Grassland fires spread at speeds of up to 14 mph (23 km/h). Crown fires in forests move slower through the canopy but generate enormous ember loads. Urban interface fires — like the Camp Fire — can move faster through suburban neighborhoods than through open land because the homes themselves become fuel.

Red flag conditions are declared by the National Weather Service when fire weather reaches critical thresholds: sustained winds of 25 mph (40 km/h) or more, relative humidity below 15%, and dry fuel moisture conditions. During the Camp Fire, sustained winds were 25–30 mph (40–48 km/h) with gusts to 50 mph (80 km/h) — conditions that turned a spot fire into a town-destroying catastrophe within hours. Red flag warnings are your pre-evacuation signal: be ready to leave before you get an evacuation order.

Defensible space: the three zones

Defensible space is the buffer between your home and the surrounding vegetation. It does not guarantee survival, but it reduces ember ignition risk, gives firefighters a chance to defend the structure, and slows radiant heat exposure. California regulations (and similar frameworks in other western states) define three zones measured from the exterior walls of the structure.

Zone 0 — the 0 to 5-foot (1.5-meter) zone

Zone 0 is the most critical area and was formalized in California regulations based on Camp Fire research. The goal is non-combustible immediately adjacent to the structure: no wood mulch, no ornamental grasses, no stored wood, no combustible welcome mats, no wood trellises against the wall.

Replace wood mulch with gravel, decomposed granite, or bare soil. Move potted plants away from the foundation. Clear debris from the gap between the foundation and siding. This is the area where ember deposition directly against the structure creates the ignition pathway.

Zone 1 — 5 to 30 feet (1.5 to 9 meters)

Reduce vegetation density and remove combustible material:

Remove dead plants, dry grass, and leaves regularly
Space plants in "islands" rather than continuous beds — fire cannot travel as easily across gaps
Prune trees so the lowest branches are at least 10 feet (3 meters) above the ground
Remove vegetation within 10 feet (3 meters) of any structure
Clear roof gutters of leaves and debris — this is where embers pool and ignite

Zone 2 — 30 to 100 feet (9 to 30 meters)

Reduce fuel continuity — the goal is to slow fire spread and interrupt pathways:

Mow grass to a maximum of 4 inches (10 cm) height during fire season
Space trees at least 18 feet (5.5 meters) apart (crown to crown)
Remove ladder fuels — shrubs and low branches that allow ground fire to climb into the tree canopy
Store firewood and lumber piles at least 30 feet (9 meters) from any structure

Regional note

California requires homeowners in State Responsibility Areas and Very High Fire Hazard Severity Zones to maintain this defensible space and submit to inspection. Other western states have similar requirements under state and local codes. Check your county's fire hazard severity zone designation — it affects both your legal obligations and your insurance coverage.

Home hardening: reducing ember entry

Even perfect defensible space doesn't prevent embers from landing on the roof or entering through vents. Home hardening addresses the ignition pathways that embers exploit:

Roof: Composition shingles (Class A fire rating) significantly outperform wood shakes. The roof is the most common point of ember ignition. Homes with metal, tile, or Class A composition roofing survive wildfires at substantially higher rates than homes with wood-shake roofs.

Gutters: Screen gutters with metal mesh or replace with enclosed gutter systems. Ember-filled gutters ignite with almost no other fuel needed.

Vents: Standard attic vents with openings larger than 1/8 inch (3 mm) allow ember intrusion. Replace with California State Fire Marshal-approved ember-resistant vents, or cover openings with 1/16 to 1/8 inch (1.5 to 3 mm) corrosion-resistant metal mesh. This is often the cheapest single hardening upgrade per unit of protection — vents are an affordable to moderate investment.

Windows: Single-pane windows crack and fail from radiant heat before direct flame contact. Dual-pane or tempered glass provides more time. Ember-resistant window screening reduces direct ember entry.

Decks: Combustible decks directly connected to the structure give fire a pathway to exterior walls. Composite decking, metal framing, and screening the underside of decks with metal mesh reduces this pathway.

Fences: Wood fences attached to the house create a direct ember transport path from fire to structure. Replace the last 5 feet (1.5 meters) of fence adjacent to the home with non-combustible material.

The wildland-urban interface

The wildland-urban interface (WUI) is where developed land meets or mixes with undeveloped vegetation. The Camp Fire happened in the WUI. The 2018 Carr Fire in Redding, the 2020 Almaden Complex, and the 2021 Caldor Fire all involved WUI communities. More than 32 million homes in the US are in WUI zones.

WUI communities face a specific evacuation problem: a single road leading out, often through the same direction the fire is approaching. WUI evacuation planning requires knowing your community's single points of failure before fire season begins:

How many roads exit your neighborhood?
Which of those roads crosses the anticipated fire spread direction?
What is the estimated evacuation time for all residents using only the roads that remain open?

The Camp Fire's evacuation failure was partly structural — Paradise had one primary evacuation corridor that quickly gridlocked. Residents who left early survived; residents who waited for the evacuation order often spent hours in traffic with fire burning on both sides of the road.

Evacuation triggers: leave before the order

The most important wildfire decision is evacuation timing. Post-event data consistently shows that people who leave when a Watch or Warning is issued, rather than waiting for a mandatory Evacuation Order, fare better — less traffic, more intact roads, more time.

Establish your household trigger now, in writing:

Red flag warning = load the vehicle, know where you are going, have gas
Evacuation warning (voluntary) = leave now if you have pets, mobility limitations, livestock, or live on a single-access road
Evacuation order (mandatory) = leave immediately, no exceptions

"Watching to see what happens" has a documented body count. Fire behavior during red flag conditions is unpredictable, and the difference between a managed evacuation and gridlocked chaos is measured in tens of minutes.

Field note

Pre-load your vehicle during red flag warnings — don't wait for an evacuation order to start gathering things. Box up irreplaceable items (documents, hard drives, medications, family photos) and keep that box near the door during fire season. The decision to grab or not grab should be made in October, not at 2 a.m. with orange sky outside.

After the fire

Post-fire landscapes are hazardous. Slopes that lost ground cover are at high risk of debris flows in the first rain after a fire — a "post-fire debris flow" or "post-fire lahar" can travel faster than the original fire and affect areas that weren't burned. The 2018 Montecito debris flows killed 23 people five weeks after the Thomas Fire burned the slopes above town.

Burned structures may contain heavy metals, asbestos, and other hazardous materials in the ash. Do not handle debris or ash without an N95 respirator and gloves. Do not let children play in ash.

Water infrastructure in burned areas is commonly compromised — both from physical damage and from benzene and other volatile organic compounds that can migrate into distribution systems through damaged pipes. Treat tap water in fire-affected areas as potentially unsafe until the water utility issues specific clearance.

Wildfire preparedness checklist

Wildfire preparation connects to both shelter hardening for structural improvements and mobility planning for route selection and vehicle readiness. The medical foundation covers smoke inhalation first aid and respiratory gear for the post-fire re-entry period.