Wildland Fires

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Instructor: Professor Stanley Williams Email: [email protected] Course Website: http://glg110.asu.edu TA: Carol Butler Email: [email protected] Today: Wildland Fires GLG110 Geologic Disasters & Environment


Outline Definitions Need for Fire Causes Controls on Fire Behavior Stages & Types of Fire Fighting the Fire Post-Fire Reducing the Risk & Fire Safety Much of today’s lecture comes from “Chapter 13: Fire” from Geologic Disasters by Patrick Abbot, (McGraw-Hill, 2002)

Disaster of the Day: 

Southern California & Mexico 660,000 acres in densely pop. suburbs (this is 150,000 more since Tuesday) 2,600 homes destroyed; 300,000 at risk at least 20 deaths (worst since 1991) Disaster of the Day

Disaster of the Day: 

Disaster of the Day Strong Santa Ana winds from mountains have stopped Temperatures dropping Winds now from ocean Moist air helps Winds too strong, push flames other way now and ground firefighting aircraft Salton Sea MX San Diego Los Angeles

Disaster of the Day: 

Disaster of the Day 1 Firefighter killed others wounded when flames overcame crew near San Diego yesterday Reports of men throwing flaming items out windows of truck to start a couple of the fires

Disaster of the Day: 

Disaster of the Day Trees vulnerable due to bark beetle destruction = many dead trees = easy tinder Bush declared region a disaster area View from the International Space Station San Diego covered by smoke

Disaster of the Day: 

Disaster of the Day Nearly 13,000 firefighters, some from neighboring states May be costliest disaster in California’s history $9 M/day

Disaster of the Day 2: 

Disaster of the Day 2 Colorado 2 new fires, downed powerlines? Many area firefighters are in California Strong winds fueling fire ~600 acres burned so far near Boulder and Denver


Definition Fire = extremely hot release of energy from chemical reaction between oxygen and woody material Fire is photosynthesis in reverse Photosynthesis: Carbon Dioxide + Water + heat from Sun = wood + Oxygen Fire: wood + Oxygen = carbon dioxide + water + released heat

Wildland Fire: 

Wildland Fire Wildfire = out of control fire Wildland Fire = fire that is occuring in the natural environment Most days, in the U.S., a wildland fire is burning

Need for Fire: 

Need for Fire Fire is often an essential part of the ecosystem Grasslands, seasonal tropical forests, some temperate-climate forests, Mediterranean-climate shrub lands Cleans up fire fuel, promotes seed growth


Causes Natural Lightning (especially when associated with drought) Lightning strikes >100,000 times/day 10-20% of these strikes cause a fire Human Activity (9-10 wildland fires) 1 out of 5 human-caused wildfires started by a camp or warming fire that got away 1 out of 10 wildland fires is caused by a careless smoker


Causes Combination Santa Ana winds downed power lines in 1983 started fire that burned 9 days in California

Controls on Fire Behavior: 

Controls on Fire Behavior Fuel supply and type Landscape and topography Wind Moisture Time of Day Human Activity Image: www.wildlandfire.com


Fuel Any combustible material is fuel Grasses = fast spreading fires Shrubs = easy burning, hot fires from high natural oil content Slash = debris left on ground after logging or windstorms Trees and forests Houses and other structures Some materials are more flammable than others

Fire & Time of Day: 

Fire & Time of Day Nightfall – warm air traps cooler air against mountains Winds calm Humidity rises Dampens fire spread Daylight – trapping layer breaks up allows accumulated smoke and combustible gases to rise Spurs the fire

Fire & Topography: 

Fire & Topography Hot gases rise in column creating a torch A slope, brings gases into contact with vegetation above Winds can create blowup

Fire & Topography: 

Fire & Topography Storm King Mountain, Colorado 1994 Fire started by lightning in drought-dry area on mountain top Spread generally downslope with a few upslope bursts of short duration Consistent spread rate 14 firefighters were killed on 4th day of the fire in a “blowup”

Fire & Topography: 

Fire & Topography Contributing Factors Fire at bottom of narrow canyon Dry, cold front moved into area Steep upslope winds resulted Flames crowned in unburned area at 6 to 9 ft/second Communications breakdown, firefighters unaware of wind shift Origin of blowup

Stages of Wildland Fire: 

Stages of Wildland Fire Any wildland fire transitions through 4 stages in its active “life” Preheating: water is expelled Pyrolysis: thermal degradation of wood and release of flammable gases (above 480°F) Flaming Combustion Glowing Combustion

Stages of Fire: 

Stages of Fire I. Preheating & Pyrolysis II. Flaming Combustion III. Glowing Combustion

Types of Wildland Fires: 

Types of Wildland Fires Ground Fires = burn unnoticeably underground in bogs and forests (coal fires) spread is slow they may pop out of the ground anywhere and cause damage in unlikely areas Surface Fires = burn in grass, shrubs, plant matter (leaves, fallen bark) easy to control

Types of Wildland Fires: 

Types of Wildland Fires Crown Fires: Dependant = heat and embers from surface fires ignite tops of trees tends to occur in low winds are low with trees spaced far apart

Types of Wildland Fires: 

Types of Wildland Fires Crown Fires: Running = burn extremely hot, travel rapidly, can change direction quickly most dangerous aspect = convection currents produce massive firestorms and tornados send embers ahead of the main fire front creating new fires in another direction firefighters worst nightmare

June 2002: Rodeo Chediski Fire: 

June 2002: Rodeo Chediski Fire


Over 2 weeks, the Rodeo and Chedeski fires merged into the largest and most expensive fire in Arizona’s known history, costing more than $30 million http://earthobservatory.nasa.gov/NaturalHazards

Rodeo Chediski Fire: 

Rodeo Chediski Fire Chediski fire started by woman lost in woods for 3 days Not charged Rodeo fire started maliciously by contract firefighter Claimed ½ million acres, 400 homes


Oakland Firestorm, 1991 http://geo.arc.nasa.gov/sge/jskiles/top-down/gif_folder/oakland-fire1.gif Worst fire involving loss of life and property since the Great San Francisco Earthquake and Fire of 1906 25 deaths, 3,000 homes destroyed http://graphics.stanford.edu/~lucasp/pictures/fire/fire.html


5 pm 11:30 am Oakland Firestorm Rapid spread in many different directions

Oakland Firestorm: 

Oakland Firestorm Origin = steep hillside in box canyon; wooded area with heavy underbrush, narrow streets and steep terrain 5 year long drought in area Weather conditions = unusual east wind, at speeds >65 mph, record high temperatures Radio communications were often difficult or impossible because: 1.Overload (too many units on the same channel) 2.Too few mutual aid channels available 3.Steep, hilly terrain interfered with signals

Oakland Firestorm: 

Oakland Firestorm Fire units lost water, forcing retreat Cause: 1.Fire suppression efforts 2.Citizens wetting roofs and vegetation 3.Water flowing freely in destroyed homes 4.Tanks and reservoirs could not be refilled because of fire-caused electrical failure 5.Many mutual aid fire engine companies could not connect to hydrants because of hose coupling size differences

Fighting Wildland Fires: 

Fighting Wildland Fires Planes and helicopters dump water on it Firefighters dig ditch around fire front Major highways are similar firebreak Spray trees (And buildings) Burnout

Fighting Wildland Fires: 

Fighting Wildland Fires Control Line Set smaller fires with helicopter drops to draw burnout uphill Fuel moved from Burnout zone Burnout Wind Direction Burnout Move fuel from region Set small fires downhill and downwind from wildfire Fire Front


Post-Fire Erosion Landslides Water Contamination Erosion Mitigation Recovery


Post-Fire: Erosion Fire increases the susceptibility for erosion and mass movement Emplace rain gauges on slopes to give warning of possible overload

Post-Fire: Landslides: 

Post-Fire: Landslides Debris Flow on I-70 following Storm King Mountain (Colorado) fire, 1994

Post-Fire: Erosion & Pollution: 

Post-Fire: Erosion & Pollution Airborne pollutants during fire reach downstream supplies Erosion washes pollutants into streams and rivers Debris Ash Phosphorous Mercury Pollutes water and can kill fish

Post-Fire: Erosion Mitigation: 

Post-Fire: Erosion Mitigation Straw spread on ground to absorb moisture Log barriers to retard downslope soil movement Seeding vegetation which grows quickly to stabilize slope Note sediment piled up against log

Post-Fire: Slope Recovery: 

Post-Fire: Slope Recovery Recovery time depends on: severity of burn soil & rock type vegetation type Climate severity of erosion human activity On the slopes of the Storm King Mountain fire

Reducing the Risk of Fire: 

Reducing the Risk of Fire Controlled burn (defensive) Gets rid of brush fuel Fire Breaks Clear buffer areas Roads, Cuts (bulldozers & chainsaws) Structure Protection Spray with water Preparedness Protection

House Placement: 

House Placement Buildings at the top of a slope need setback to help avoid increased heat flow by convection and radiation Defensive space includes a 30 ft wide zone around the building with no tall trees

How to sacrifice your home to the fire gods: 

How to sacrifice your home to the fire gods

How to sacrifice your home to the fire gods: 

Built on slope Wood Construction Wood desk overhangs slope Firewood next to house Wooden roof shingles Tree limbs overhang house Shrubs against house Large windows face slope Unprotected louvers face slope No spark arrester on chimney top Narrow driveway prevents fire truck access Wooden eaves extend beyond walls How to sacrifice your home to the fire gods


Image: US Forest Service Image: US Forest Service

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