phases of wildfires

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Phases of wildfires. Preignition (energy absorbing) Preheating – drying out Pyrolysis – chemical degradation Combustion (energy liberating) Fire triangle in place. Fire triangle. All components must be present for fire to occur. Why wood burns. - PowerPoint PPT Presentation

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Chapter 14 - Fires

Phases of wildfiresPreignition (energy absorbing)Preheating drying outPyrolysis chemical degradation Combustion (energy liberating)Fire triangle in place

Fire triangleAll components must be present for fire to occur

Why wood burnsWet wood high heat capacity of water absorbs heat making the wood difficult to igniteOnce dry it ignites at 572F, its flash pointFlammable gases given offConditions for wildfirePlant material + oxygen + heat

Combustion equation

How to fight fireRemove or reduce one componentWater reduces heatSlurry blocks oxygenRemove fuelCut or clear areaLight backfire

Ladder fuel effect

What spreads fire?Fuel types

Weather and wind

Topography

Its own behaviorTypes of fuel and resultsGrass, trees, shrubs, slash piles, homesRapid advanceGrass fires: about 4 mph with 6-8 ft flamesShrub fires: oily material 8 mph, 50 ft flamesUnderstory fuel source importantNo litter little damage, fast movingLots of litter hot, damaging fireLadder fuels crown fires

Flat topography; no windFlat topography; windHillslope and wind

Smoke plume these can produce the fires own weatherWhat is the primary heat moving process here?Types of firesGround fireCreep along, mainly smolders, few flames

Surface firesVariable intensityBurns low vegetation and lower parts of trees

Crown firesBurns upper parts of treesCan produce firestormMove rapidlyImpossible to stop

Results of crown fireCoconino National Forest

Causes of wildfiresHuman caused (85%)Arson 26%Equipment 10%Juveniles - 4%Campfires 3%Railroads 3%Other/unknown 50%Naturally caused (15%)

One day two BIG firesOct 8, 1871Extremely windy conditions affect both areasPeshtigo, WI15 mile wide fire frontTraveled 40 miles northward1,152 diedChicago, ILOLeary barn caught fire300 died3.3 sq mi destroyedWeather that produced winds

Extent of Peshtigo fires

Central Chicago following fire

CaliforniaChaparral shrubland plant community; contains a lot of oily, dried vegetationFires occur every yearMajor fires in 1991Oakland and Berkeley Hills25 died, 2,449 homes destroyed; 437 aptsonly 1,600 acres but $1.5 billion damageCaused by cooking fires in a camp set up by homeless peopleOakland fires in 1991

California firesSanta Ana windsCommon October to MarchHigh pressure over NevadaCool, dry air descends over mtnsAir heats up, generating winds

Major fires due to Santa Ana windsOctober/November 1993Santa Ana winds15 major fires in southern California3 dead, 1,150 homes, $1 billion damage215,000 acres [300 sq mi]October/November 2007Mexico border to Santa Barbara350,000 homes evacuated>500,000 acres burned> 2,100 homes destroyed

October/November 2008Santa Ana windsFires in Montecito, SylmarMontecito fire due to bonfireInterstates closedMore than 1,200 homes destroyedAlmost 50,000 acresAugust 2009Station Fire, 161,000 acres NE of PasadenaArson caused

Fire suppression20th century approach put fires out!!Trees per acre increased dramaticallyIn 1970s decision was to let fires started naturally burn; human-caused extinguishedPrescribed burnsFormerly controlled burnsLos Alamos, NM, burned in May 2000; 280 homes destroyedYellowstone National ParkBurn areas shadedDry winter in 1987-88Low moisture content and many beetle ridden treesFires began in June and July 1988By mid-August very dry and fire lasted until Nov1.4 million acres burned, about half of the parkNatural-burn policy in place since 1976

Rodeo-Chediski Fire of June 2002

Two separate fires grew together;5,000 firefightersMore than 500 homes burned;732 sq mi destroyedWallow FireMay and June 2011Largest fire in AZ history burned 538,000 acres, including 15,000 acres in New MexicoCaused by campfire lit by two cousins

Aftermath of firesRejuvenation of land naturally due to released nutrients and opening of seeds replantingErosion and landslidesFormation of hydrophobic layer caused by oils and organic compounds vaporizing and recondensing in cooler layers under the surfaceExpense to fight firesFiscal costLoss of lifeReduced air quality

Schultz Fire north of Flagstaff June 20, 2010 burned 15,000 acres

Extremely high winds rapidly spread fire caused by a campfireArea north of Flagstaff following 1996 fire

SummaryGood:Increase in soil nutrients and regeneration of vegetation (aspen, conifers)Reduction of potentially larger firesBad:More erosion, runoff, mass wasting, loss of life (human and animal)What is there to learn?Restrict development in heavily forested areasDecrease fuel sources with prescribed burnsUndertake preventative measures through educationA healthy forest

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