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Phases of wildfires

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.

audrey-noel
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Phases of wildfires

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  1. Phases of wildfires • Preignition (energy absorbing) • Preheating – drying out • Pyrolysis – chemical degradation • Combustion (energy liberating) • Fire triangle in place

  2. Fire triangle All components must be present for fire to occur

  3. Why wood burns • Wet wood – high heat capacity of water absorbs heat making the wood difficult to ignite • Once dry it ignites at 572°F, its flash point • Flammable gases given off

  4. Conditions for wildfire • Plant material + oxygen + heat • Combustion equation

  5. How to fight fire • Remove or reduce one component • Water – reduces heat • Slurry – blocks oxygen • Remove fuel • Cut or clear area • Light backfire

  6. Ladder fuel effect

  7. What spreads fire? • Fuel types • Weather and wind • Topography • Its own behavior

  8. Types of fuel and results • Grass, trees, shrubs, slash piles, homes • Rapid advance • Grass fires: about 4 mph with 6-8 ft flames • Shrub fires: oily material 8 mph, 50 ft flames • Understory fuel source important • No litter  little damage, fast moving • Lots of litter  hot, damaging fire • Ladder fuels  crown fires

  9. Flat topography; no wind Flat topography; wind Hillslope and wind

  10. Smoke plume – these can produce the fire’s own weather What is the primary heat moving process here?

  11. Types of fires Ground fire Creep along, mainly smolders, few flames

  12. Surface fires Variable intensity Burns low vegetation and lower parts of trees

  13. Crown fires Burns upper parts of trees Can produce firestorm Move rapidly Impossible to stop

  14. Results of crown fireCoconino National Forest

  15. Causes of wildfires • Human caused (85%) • Arson – 26% • Equipment – 10% • Juveniles - 4% • Campfires – 3% • Railroads – 3% • Other/unknown – 50% • Naturally caused (15%)

  16. One day – two BIG firesOct 8, 1871 • Extremely windy conditions affect both areas • Peshtigo, WI • 15 mile wide fire front • Traveled 40 miles northward • 1,152 died • Chicago, IL • O’Leary barn caught fire • 300 died • 3.3 sq mi destroyed

  17. Weather that produced winds

  18. Extent of Peshtigo fires

  19. Central Chicago following fire

  20. California • Chaparral – shrubland plant community; contains a lot of oily, dried vegetation • Fires occur every year • Major fires in 1991 • Oakland and Berkeley Hills • 25 died, 2,449 homes destroyed; 437 apts • “only” 1,600 acres but $1.5 billion damage • Caused by cooking fires in a camp set up by homeless people

  21. Oakland fires in 1991

  22. California fires • Santa Ana winds • Common October to March • High pressure over Nevada • Cool, dry air descends over mtns • Air heats up, generating winds

  23. Major fires due to Santa Ana winds • October/November 1993 • Santa Ana winds • 15 major fires in southern California • 3 dead, 1,150 homes, $1 billion damage • 215,000 acres [300 sq mi] • October/November 2007 • Mexico border to Santa Barbara • 350,000 homes evacuated • >500,000 acres burned • > 2,100 homes destroyed

  24. October/November 2008 • Santa Ana winds • Fires in Montecito, Sylmar • Montecito fire due to bonfire • Interstates closed • More than 1,200 homes destroyed • Almost 50,000 acres • August 2009 • Station Fire, 161,000 acres NE of Pasadena • Arson caused

  25. Fire suppression • 20th century approach – put fires out!! • Trees per acre increased dramatically • In 1970s decision was to let fires started naturally burn; human-caused extinguished • Prescribed burns • Formerly “controlled burns” • Los Alamos, NM, burned in May 2000; 280 homes destroyed

  26. Yellowstone National Park • Burn areas shaded Dry winter in 1987-88 Low moisture content and many beetle ridden trees Fires began in June and July 1988 By mid-August very dry and fire lasted until Nov 1.4 million acres burned, about half of the park Natural-burn policy in place since 1976

  27. Rodeo-Chediski Fire of June 2002 Two separate fires grew together; 5,000 firefighters More than 500 homes burned; 732 sq mi destroyed

  28. Wallow FireMay and June 2011 Largest fire in AZ history burned 538,000 acres, including 15,000 acres in New Mexico Caused by campfire lit by two cousins

  29. Aftermath of fires • Rejuvenation of land • naturally due to released nutrients and opening of seeds • replanting • Erosion and landslides • Formation of hydrophobic layer caused by oils and organic compounds vaporizing and recondensing in cooler layers under the surface • Expense to fight fires • Fiscal cost • Loss of life • Reduced air quality

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

  31. Extremely high winds rapidly spread fire caused by a campfire

  32. Area north of Flagstaff following 1996 fire

  33. Summary • Good: • Increase in soil nutrients and regeneration of vegetation (aspen, conifers) • Reduction of potentially larger fires • Bad: • More erosion, runoff, mass wasting, loss of life (human and animal)

  34. What is there to learn? • Restrict development in heavily forested areas • Decrease fuel sources with prescribed burns • Undertake preventative measures through education

  35. A healthy forest

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