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 1 OBJECTIVES 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 1 OBJECTIVES (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 Continuity and Vertical Arrangement
Uniform
Patchy
Vertical Arrangement:
Ground
Surface
Aerial

14. Uniform Fuels

15. Patchy Fuels

16. Vertical Arrangement of Fuels

17. Group 2 -- Weather Temperature Wind Relative Humidity Precipitation
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. Steep Slopes Cause Rapid Fire Spread
Convection and Radiant Heat
Flame is closer to fuel

21. Position of Fire on Slope
FIRE NEAR TOP OF SLOPE
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 1 OBJECTIVES 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 1 OBJECTIVES (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.

31. UNIT 2 OBJECTIVES
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.

32. UNIT 2 OBJECTIVES (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.

33. 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.

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

35. Cold Front Winds

36. 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.

37. 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.

38. Fire Before Cold Front Passage

39. Fire After Cold Front Passage

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

41. Examples of Foehn Winds

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

43. 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.

44. Thunderstorm

45. 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.

46. Sea Breeze Land Breeze

47. Slope Winds

48. Valley Winds

49. Temperature/Relative Humidity Chart
Noon
Midnight
Noon

50. 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

51. Visual Indicators of Stable Air
Cloud in layers, no vertical motion
Stratus type clouds
Smoke column drifts apart after limited rise
Poor visibility in lower levels due to accumulation of haze
Fog layers
Steady winds

52. Inversion

53. Thermal Belt

54. Subsidence

55. Dust Devils

56. Firewhirls
Generated by intense fires. Can pick up large burning embers and toss them far across the fireline causing spot fires.

57. Indicators of Problem and Extreme Fire Behavior
Fuel Indicators
Unusually dry fuels.
Large amount of light fuel (shrubs, grass, needles).
Fuels exposed to direct sunlight.
Fuels dried by prolonged drought.
Ladder fuels that allow a surface fire to move into the crowns of shrubs or trees.
Crown foliage dried by surface fire.
Concentration of snags.

58. Indicators of Problem and Extreme Fire Behavior
Topography Indicators
Steep slopes.
Chutes, saddles, and box canyons which provide conditions for “chimney effect.”
Narrow canyons may increase fire spread by radiant heat and spotting.

59. Indicators of Problem and Extreme Fire Behavior
Weather Indicators
Strong Wind.
Sudden changes in wind direction and velocity due to weather fronts.
High, fast-moving clouds may indicate unusual surface winds.
Unexpected calm may indicate wind shift.
Thunderstorms above or close to the fire.
Unusually high temperatures and low relative humidity.
Dust devils and whirlwinds developing.
Bent smoke column.

60. Indicators of Problem and Extreme Fire Behavior
Fire Behavior Indicators
Keep an eye on the smoke column. Indicates direction of fire spread, location of spot fires, and changes in fire intensity.
Many simultaneous fires starting or smoldering fires beginning to pick up in intensity.
Fire begins to torch small groups of trees or shrubs.
Frequent spot fires occurring.
Firewhirls beginning to develop inside the main fire.
Crown fires.

61. UNIT 2 OBJECTIVES
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.

62. UNIT 2 OBJECTIVES (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.