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

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

4. 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

5. Conditions for wildfire
Plant material + oxygen + heat
Combustion equation

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

7. Ladder fuel effect

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

9. 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

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

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

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

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

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

16. Results of crown fire Coconino National Forest

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

19. One day – two BIG fires Oct 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

20. Weather that produced winds

21. Extent of Peshtigo fires

22. Central Chicago following fire

23. 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

24. Oakland fires in 1991

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

26. 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

27. October/November 2008 August 2009 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

28. 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

29. Yellowstone National Park
Burn areas shaded
Dry winter in
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

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

31. Wallow Fire May 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

32. 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

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

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

35. Area north of Flagstaff following 1996 fire

36. 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)

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

38. A healthy forest