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Introduction to Wildland Fire Behavior (S-190)

Introduction to Wildland Fire Behavior (S-190). Bureau of Land Management Salt Lake Field Office June 8-11, 1999. COURSE OBJECTIVES. Identify and discuss the three sides of the fire triangle.

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Introduction to Wildland Fire Behavior (S-190)

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  1. Introduction to Wildland Fire Behavior (S-190) Bureau of Land Management Salt Lake Field Office June 8-11, 1999

  2. COURSE OBJECTIVES • Identify and discuss the three sides of the fire triangle. • Identify the environmental factors of wildland fire behavior that affect the start and spread of wildland fire. • Recognize situations that indicate problem or extreme wildland fire behavior.

  3. UNIT 1OBJECTIVES • Describe the fire triangle. • Identify three methods of heat transfer. • List the three principle environmental elements affecting wildland fire behavior. • List three factors of fuel that affect the start and spread of wildland fire. • List three factors of weather that affect fuel moisture.

  4. UNIT 1OBJECTIVES (cont’d) • Describe how wind affects wildland fire spread. • Describe how slope affects wildland fire spread. • List four factors of topography that affect wildland fire behavior. • Describe the dangerous conditions that can develop in a box canyon and steep narrow canyons.

  5. Fire Triangle

  6. Heat Transfer • Radiation • Convection • Conduction

  7. Group 1 -- Fuels • Fuel Moisture • Size and Shape (light fuels vs. heavy fuels) • Fuel Loading • Horizontal Continuity (uniform and patchy) • Vertical Arrangement (ground, surface, aerial)

  8. Fuel Types • Grass • Shrub • Timber Litter • Logging Slash

  9. Fuel Characteristics • Fuel Moisture • Size and Shape • Fuel Loading • Horizontal Continuity • Vertical Arrangement

  10. Fuel Moisture The amount of water in a fuel expressed as a percentage of the oven-dry weight of that fuel.

  11. Categories of Fuel • Light Fuels: • Leaves • Grass • Shrubs • Heavy Fuels: • Limbs • Logs • Stumps

  12. Fuel Loading The quantity of fuels in an area.

  13. Horizontal ContinuityandVertical Arrangement • Horizontal Continuity: • Uniform • Patchy • Vertical Arrangement: • Ground • Surface • Aerial

  14. Uniform Fuels

  15. Patchy Fuels

  16. Vertical Arrangement of Fuels

  17. Group 2 -- Weather • Temperature • Wind • Increases supply of oxygen. • Drives convective heat into adjacent fuels. • Influences direction of spread and spotting. • Carries away moist air replacing it with drier air. • Dries fuels. • Raises fuel moisture if the air contains moisture. • Relative Humidity • As RH increases, fuel moisture increases. • Precipitation • Increases fuel moisture

  18. Group 3 -- Topography • Aspect • Slope • Steepness • Position of Fire • Top, middle, or bottom of slope • Shape of Country • Narrow canyons and box canyons • Elevation • Relates to curing of fuels, precipitation, length of fire season, etc.

  19. Aspect NORTH Heavy fuels Shade Moist SOUTH Light fuels Sunny Dry

  20. Flame is closer to fuel Steep Slopes Cause Rapid Fire Spread Convection and Radiant Heat

  21. SLOPE Position of Fire on Slope FIRE NEAR TOP OF SLOPE FIRE NEAR BOTTOM OF SLOPE HAS RAPID SPREAD UPSLOPE

  22. Box Canyon & Chimney Effect

  23. Radiant Heat Across Narrow Canyon

  24. Spotting Across Narrow Canyon

  25. Lateral Ridge to Canyon

  26. Mountains Cause Channelling of Wind

  27. Elevation TREES SHRUBS GRASS SEA LEVEL

  28. UNIT 1OBJECTIVES • Describe the fire triangle. • Identify three methods of heat transfer. • List the three principle environmental elements affecting wildland fire behavior. • List three factors of fuel that affect the start and spread of wildland fire. • List three factors of weather that affect fuel moisture.

  29. UNIT 1OBJECTIVES (cont’d) • Describe how wind affects wildland fire spread. • Describe how slope affects wildland fire spread. • List four factors of topography that affect wildland fire behavior. • Describe the dangerous conditions that can develop in a box canyon and steep narrow canyons.

  30. UNIT 2OBJECTIVES • List the indicators of an approaching cold front and describe what wind changes to expect. • List three common foehn wind conditions and the areas in which they occur. • Identify a thunderstorm and describe how and when it is dangerous.

  31. UNIT 2OBJECTIVES (cont’d) • Describe the daily cycle of slope and valley winds. • Describe the effect relative humidity has on wildland fire behavior. • Identify the wildland fire environment indicators that can produce problem and extreme fire behavior.

  32. General or Gradient Winds Large scale winds caused by high and low pressure systems, but generally influenced and modified in the lower atmosphere by terrain.

  33. Cold Front A cold front is the boundary line between a cooler air mass which is replacing a warmer air mass.

  34. Cold Front Winds

  35. Indicators of a Cold Front Passage • Line of cumulus clouds approaching from the west or northwest. • Large clouds of dust can precede the arrival of a cold front. • Shift in winds from the southeast, south, to the southwest, and increase in velocity. • Winds will be strongest, erratic, and gusty as the front reaches you. • Winds will continue to shift as the front passes, generally resulting in strong, gusty, cool winds out of the west and northwest.

  36. Cold Fronts are Potentially Dangerous • Wind direction will abruptly change. • Strong southerly winds ahead of front will drive the fire head to the north or northeast. • Winds shifting to west or northwest after front passes will drive fire head to the east or southeast. • Rapid drop in relative humidity within 24 hours of front passage.

  37. Fire Before Cold Front Passage

  38. Fire After Cold Front Passage

  39. Foehn Wind A dry wind with strong downward components, characteristic of mountainous regions.

  40. Examples of Foehn Winds

  41. Thunderstorm A storm produced by a cumulonimbus cloud and always accompanied by lightning, thunder, and strong gusty wind.

  42. Visual Indicators of Thunderstorm • Tall building cumulus cloud. • Cauliflower appearance of cloud. • Dark flat base. • Virga or rain falling from bottom of cloud. • Ice crystal top usually in anvil shape with fuzzy appearance.

  43. Thunderstorm

  44. Why a Thunderstorm is Dangerous • Produces strong, gusty surface winds affecting direction of fire spread. • Downdraft winds will be erratic but always away from the thunderstorm. • Thunderstorms also produce lightning which can be dangerous.

  45. Sea Breeze Land Breeze

  46. Slope Winds

  47. Valley Winds

  48. Noon Midnight Noon Temperature/Relative Humidity Chart

  49. Visual Indicators of Unstable Air Clouds grow vertically and smoke rises to great heights Cumulus type clouds Gusty winds Good visibility Dust devils and firewhirls

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