the wildland/urban interface
DESCRIPTION
The Wildland/Urban Interface. Part A: The Fire Behavior and the Wildland-Fire Environment. (Rev. 01/31/2006). Objectives. Students will learn: About California’s wildland fire problem To understand the wildland fire environment Factors influencing wildfire behavior - PowerPoint PPT PresentationTRANSCRIPT
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(Rev. 01/31/2006)
Part A:The Fire Behavior and the
Wildland-Fire Environment
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Students will learn:
• About California’s wildland fire problem
• To understand the wildland fire environment
• Factors influencing wildfire behavior
• How to prepare homes for wildfire
• About special considerations for evacuation
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California has one of the most severe wildland fire problems in the world because of:
• Population
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California has one of the most severe wildland fire problems in the world because of:
• Population
• Vegetation
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California has one of the most severe wildland fire problems in the world because of:
• Population
• Vegetation
• Topography
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California has one of the most severe wildland fire problems in the world because of:
• Population,
• Vegetation,
• Topography, and
• Climate
In wildland/urban interface areas, wildfire isn’t a matter of “IF,” it’s a matter of “WHEN.”
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In California, thousands of people choose to build homes within or near wildland areas.
These areas are covered with flammable, native vegetation.
This environment may be desirable for some, but it comes with consequences.
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California’s native plants and shrubs are among the most flammable in the world.
Chamise, buckwheat and sage are referred to as chaparral.
Local hillsides and canyons are covered with these flammable plant materials.
VEGETATION = FUEL
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In mountain areas, forests with large meadows are predominant.
Fire danger exists in this environment, as well.
VEGETATION = FUEL
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The act of burning is COMBUSTION
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Combustion is supported when fuel, heat and oxygen (air) combine in the just the right amounts.
Oxygen Heat
Fuel
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– Removing the fuel, or– Removing the oxygen, or– Cooling the temperature of
the fuel
Combustion is interrupted by…
Oxygen Heat
Fuel
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Slowest
Fastest
Transfer of heat by contact
Transfer of heat by contact, air and direction (rising)
Transfer of heat by contact & through the air
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Factors that influence ignition and fire spread:
Fuels
Fuel moisture
Fuel size
Fuel continuity
Vertical spacing
Horizontal spacing
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Spacing & Ladder Fuels
Fire will use tightly-spaced vegetation as a “ladder” to climb from surface plants and shrubs into aerial vegetation, like tree canopies.
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Three fundamental parts of weather have a significant impact on wildfire:
• Temperature
• Relative Humidity
• Wind
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Temperature:• Preheats fuels
• Preheats the ground
• Affects air currents
• Reduces firefighter endurance
• Reduces moisture in the air:
– The higher the temperature, the lower the relative humidity
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Relative Humidity:• Water vapor in the air
• Expressed in a percentage
• Hot temperature = reduced humidity
• Cool temperature = increased humidity
• Higher humidity = higher fuel moisture
• Fires usually burn more rapidly during the day due to lower humidity
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Wind:• Has the greatest influence on rate and direction of fire spread
• “Bends” flames close to fuel
• Generally: blows up-slope during day blows down-slope at
night
• Unpredictable
• Hazardous to firefighters
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Topography = the configuration of the land
• Topography has significant affect on RATE and DIRECTION of fire spread.
• Three fundamental parts of topography:
SLOPE
ASPECT
TERRAIN
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• The steeper the slope, the faster
the fire will move
• Slope influences fire by preheating fuels
• Wind currents usually flow uphill
• Convected heat causes a draft
• Burning material can roll downhill
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• The direction a slope faces (N, S, E, W) affects the spread of fire
• Southern aspect:
• receives more direct radiation
• fuels are usually drier, but less dense
• receives a stronger slope wind
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• The “lay of the land”
• Obstructions include ridges & canyons
• Cause wind turbulence & erratic fire behavior
• Fires in canyons or steep drainages are DANGER ZONES!Wi
nd
Wind
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CONVECTION:
Pieces of burning material are lifted into a convection column.
Embers settle on homes and vegetation far ahead of the fire-front.
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WIND:
Causes short-range spot fires ahead of fire-front.
The combination of convection & wind can carry brands considerable distances, causing long-range spotting.
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• The Elements of Fire: - Fuel, Heat, and Oxygen
• Fire Spread: - Convection, Radiation, Conduction
• Weather and Wildfire: - Temperature, Humidity, and Wind
• Topography: - Slope, Aspect, and Terrain
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Defensible Space & Zones
The “Small Things”
Access & Egress
Special Considerations
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An area surrounding structures that allows firefighters and equipment the space to defend against an approaching wildfire.
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• Driveways and other access roads must meet or exceed your fire department’s needs.
• Display address with 4” high numerals (Min) on a contrasting background.
Fire department access is extremely important & often overlooked
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• Keep roadways free from overhanging vegetation, fence posts or signage.
• “Vertical Clearance”
• Driveway/road surface and weight requirements.
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• Minimum 16-foot wide driveway/access road is needed.
• May need a wider road if a number of homes are served – allowing for two way traffic (access & egress).
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• Evacuation routes
Home
Scenic
Drive
Pine Way
Lone Quail Pass
Red Fox R
un
TWO WAYS OUT!
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Home
Scenic
Drive
Pine Way
Lone Quail Pass
Red Fox R
un
TWO WAYS OUT!
• Evacuation routes
• Special-needs evacuations: Plan ahead!
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• Evacuation routes
• Special-needs evacuations: Plan Ahead!
• Livestock & pet evacuations
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• Evacuation routes
• Special-needs evacuations Plan Ahead!
• Livestock & pet evacuations
• “Safe” areas
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Wildfires are a year-round threat to communities throughout California
To prepare for the impacts of wildfires, continue to:
• Identify your local wildland fire problem,
• Monitor your local wildland environment,
• Make your home defendable against wildfire, and
• Plan for any special considerations for evacuation in your neighborhood