Western wildfire preparedness fundamentals — the complete US household reference for fire-adjacent communities

Why this is the reference document

Most Western US wildfire preparedness guidance is scattered across CAL FIRE pages, US Forest Service technical documents, county emergency management sites, and Red Cross publications. This briefing consolidates the household-actionable subset.

If you live in California, Oregon, Washington, Idaho, Montana, Wyoming, Colorado, Utah, Arizona, New Mexico, or Nevada AND within 1 mile of natural vegetation, this is the briefing to bookmark and refer to throughout fire season.

The Defensible Space Concept

CAL FIRE specifies two zones around any home in fire-prone area:

### Zone 1: Ember-Resistant Zone (0-5 feet from house) - No combustible material against the house - No mulch, no shrubs, no firewood stacks, no fences directly attached - Composite or metal roof — wood shingles are unacceptable - Vent screens 1/8" mesh (1/4" allows embers through) - Gutters cleared of needles and leaves - No combustible decorations

### Zone 2: Lean-Clean-Green (5-30 feet) - Grass trimmed below 4 inches - Shrubs and trees pruned so canopies don't touch (or form ladder fuel) - Dead leaves and pine needles removed - Tree limbs trimmed 6+ feet above ground - No woodpiles within 30 feet of house

### Zone 3: Extended (30-100 feet, if applicable) - Reduce dense vegetation - Pruning maintained - Defensive priorities

Fire Behavior — Why Wildfires Spread So Fast

Wildfires spread through three mechanisms:

1. Direct flame: the fire front itself moves through fuel (vegetation) 2. Radiant heat: hot surfaces ignite combustible material nearby (within 100-200 feet of intense fire) 3. Embers (the dominant cause): glowing material lofted into the air by fire convection. Embers can travel 1-2 miles in moderate wind, up to 5 miles in extreme conditions, igniting structures far from any visible fire.

Most wildfire structure losses are from embers, not direct flame. This is why Defensible Space focuses on preventing ember ignition.

Red Flag Warning System

National Weather Service issues Red Flag Warnings when conditions create elevated wildfire danger:

• Relative humidity below 15-20%
• Sustained wind 15+ mph
• Air temperature high relative to seasonal normal

These three combine to make any fire that starts uncontrollable. Red Flag Warnings are issued 12-24 hours in advance. The 24-hour window is the household decision window.

Pre-Season Annual Preparation

Each spring (before May), households in fire-prone areas should:

• Re-do Defensible Space (each year, not once)
• Clean every gutter and downspout
• Inspect roof for missing or damaged shingles
• Trim trees within reach of roof
• Maintain pruning standards in Zones 1-3
• Test outdoor faucets and hose connections

This is a 1-2 weekend commitment. ~$50-200 in supplies (mulch removal, replacement vegetation, gutter guards). Pays off for decades.

Daily Awareness During Fire Season (June-October)

When Red Flag Warning is active:

• Avoid spark-producing activities: no mowing, no power tools, no welding, no chainsaws
• No outdoor burning (yard waste, BBQ, fireworks)
• Don't park in tall dry grass (catalytic converters reach 800°F+)
• Avoid driving through tall grass with hot exhaust
• Sleep with windows closed (smoke from nearby fires can fill bedrooms within 30 minutes)
• Have evacuation bag pre-packed in car (not on shelf)

Evacuation Triggers

Evacuation orders escalate through:

• Voluntary evacuation: consider leaving; prepare actively
• Advisory: prepare to leave; pack vehicles
• Mandatory evacuation: must leave; failing to leave puts you at significant risk

If you receive a mandatory evacuation order, you have approximately 15-30 minutes to depart. Pre-packing your bag (next section) is essential.

The 15-Minute Evacuation Bag

This is the bag you grab when leaving on 15 minutes notice. Should be in your car or by the door from May through October.

### Documents (in waterproof folder) - Driver's license, passport, insurance card, deed - Medical records summary - Pet records (rabies certificate, microchip info) - Photo of all valuable possessions for insurance

### Supplies (1 week minimum) - Medications for everyone - Phone charger + battery pack - Cash $300-500 in small bills - Change of clothes per person - Sturdy shoes - Water and snacks - N95 masks (smoke filtration)

### Critical items - Family photos (irreplaceable) - Sentimental items if practical - Pet leashes, food, water - Backup keys to vehicles and house

Sheltering In Place if Unable to Evacuate

If wildfire cuts off evacuation routes, sheltering inside may be the only option:

• Interior room — interior bathroom or small windowless room
• Wet towels at door seals
• Bathtub full of water (emergency supply + heat sink)
• Hose ready for spot fires after fire passes
• All windows and doors closed
• Stay low — heat and smoke rise
• Wait until fire front passes before opening any door
• Plan for embers landing on roof and walls — be prepared to combat small fires

Post-Fire Return

If you evacuated:

• Wait for official "all clear" before returning
• Check structural integrity before entering damaged homes
• Beware power lines — treat all as energized
• Document damage with photos for insurance
• Check water supply for safety before drinking
• Watch for embers that may have ignited inside walls during fire
• Smoke and ash health risks persist for days
• Mental health support — wildfire trauma is real; family conversation matters

What this is not

This is not a guarantee of safety. The vast majority of fire-adjacent Western US households will not face direct wildfire impact in any specific year. The point of this reference is that the household with proper Defensible Space and pre-packed evacuation bag handles a fire-adjacent year as inconvenience, while the household without these handles it with chaos.

The single most-leveraged action for fire-prone households is maintaining Zone 1 (0-5 feet) Defensible Space year-round. Cal Fire and NIST research on defensible space consistently finds that Zone 1 maintenance substantially reduces structure loss probability in a fire event.

One thing this week: if you live in a fire-prone region, walk around your home. Look at Zone 1 (0-5 feet). What is there that could ignite from an ember? Pine needles in gutters? Wood mulch against siding? Dry shrubs touching the house? Schedule one Saturday this autumn to clear it.

— Systems Fail Lab