This document discusses extreme wildland fire behavior. It describes the four common denominators of tragedy fires as occurring in light fuels, during shifts in wind, and when fires respond to topography. Extreme fire behavior results from a combination of dry fuels, windy conditions, low humidity, and unstable atmosphere. Three stages of crown fire development are discussed: passive, active, and independent. Spotting can occur over long distances and is influenced by firebrand sources, transport mechanisms, and receptive fuels. Probability of ignition tables are provided to assess the chance of a firebrand igniting a fire based on temperature and fuel moisture levels.

1. 11-1-S290-EPUnit 11 Extreme Wildland Fire Behavior
Unit 11

2. 11-2-S290-EPUnit 11 Extreme Wildland Fire Behavior
Unit 11 Objectives
1. Describe the four common
denominators of fire behavior on
tragedy wildland fires.
2. Describe extreme fire behavior
characteristics and recognize fire
environment influences that
contribute to extreme fire behavior.

3. 11-3-S290-EPUnit 11 Extreme Wildland Fire Behavior
Unit 11 Objectives
3. Describe the three stages of crown
fire development and identify the
key factors and indicators leading
to crown fire development.
4. Identify the three factors that
contribute to the spotting problem
and describe the conditions
associated with each factor.

4. 11-4-S290-EPUnit 11 Extreme Wildland Fire Behavior
Unit 11 Objectives
5. Define the probability of ignition,
describe its use, and determine it
using tables.
6. Define firewhirls (vortices), the
conditions under which they are
likely to develop and their
implications to wildland fire behavior.
7. Explain the difference between wind-
driven and plume-dominated fires.

5. 11-5-S290-EPUnit 11 Extreme Wildland Fire Behavior
The Four Common
Denominators of Fire
Behavior on Tragedy Fires

6. 11-6-S290-EPUnit 11 Extreme Wildland Fire Behavior
Common Denominators
• On relatively small fires or deceptively
quiet areas of large fires.
• In relatively light fuels, such as grass,
herbs, and light brush.
• When there is an unexpected shift in
wind direction or in wind speed.
• When fire responds to topographic

7. 11-7-S290-EPUnit 11 Extreme Wildland Fire Behavior
Why are firefighters dying
on these types of fires?
• Sudden alignment of key elements in
the fire environment.
• Recent examples:
– South Canyon:
brush fuel type
– Cramer:
brush fuel type
– Tuolumne:
light flashy fuels
(grass, leaves,
light brush)

8. 11-8-S290-EPUnit 11 Extreme Wildland Fire Behavior
Extreme Fire Behavior
Characteristics and Fire
Environment Influences That
Contribute to Extreme Fire
Behavior

9. 11-9-S290-EPUnit 11 Extreme Wildland Fire Behavior

10. 11-10-S290-EPUnit 11 Extreme Wildland Fire Behavior
Extreme Fire Behavior
• Precludes suppression actions
• High rate of spread and frontal fire
intensity
• Crowning
• Prolific spotting
• Presence of large fire whirls
• Well established convection column
• Erratic manner

11. 11-11-S290-EPUnit 11 Extreme Wildland Fire Behavior
Contributing Factors
Extreme fire behavior results from a
combination of environmental factors:
– Available fuels
– Wind
– Low fuel moisture
– Unstable
atmosphere

12. 11-12-S290-EPUnit 11 Extreme Wildland Fire Behavior
Available Fuels
• The micro-climate and soil conditions
• Vegetative stage of development
• Seasonal and diurnal changes

13. 11-13-S290-EPUnit 11 Extreme Wildland Fire Behavior
Fuels Characteristics
• Continuous fine
fuels
• Heavy loading
• Ladder fuels
• Tight crown
spacing (<20 ft)

14. 11-14-S290-EPUnit 11 Extreme Wildland Fire Behavior
Wind
Extreme fire behavior has been
associated with strong winds including:
– Frontal
– Thunderstorm
– Foehn winds

15. 11-15-S290-EPUnit 11 Extreme Wildland Fire Behavior
Wind
• Surface winds above 10 mph
• Lenticular clouds
• High, fast moving clouds
• Approaching cold
front
• Cumulonimbus
development
• Sudden calm
• Battling or shifting winds

16. 11-16-S290-EPUnit 11 Extreme Wildland Fire Behavior
Low Fuel Moistures and
Relative Humidities
• Fine fuel moistures
• 1000-hr fuel moistures
• Live fuel moistures
• Daily RH’s and
nighttime recovery

17. 11-17-S290-EPUnit 11 Extreme Wildland Fire Behavior
Unstable Atmosphere
An unstable atmosphere
contributes to the vertical
motion of the air.

18. 11-18-S290-EPUnit 11 Extreme Wildland Fire Behavior
Primary Unstable
Atmosphere Indicators
• Good visibility
• Gusty winds and
dust devils
• Cumulus clouds
• Castellanus
clouds in the
morning
• Smoke rising
straight up
• Inversion
beginning to lift

19. 11-19-S290-EPUnit 11 Extreme Wildland Fire Behavior
Combining Influences
• Fuels are dry and plentiful (drought).
• Atmosphere unstable or was unstable for
hours, possibly days prior to the fire.
• Free air wind speeds
at or slightly above
the elevation of the
fire is 18mph
or greater.

20. 11-20-S290-EPUnit 11 Extreme Wildland Fire Behavior
The Three Stages of Crown
Fire Development and
Identify the Key Factors
and Indicators Leading to
Crown Fire Development

21. 11-21-S290-EPUnit 11 Extreme Wildland Fire Behavior
Types of Crown Fire
(wind driven)
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22. 11-22-S290-EPUnit 11 Extreme Wildland Fire Behavior
Passive
• One to a few trees
• Commonly called
“torching”
• Dependent on surface fire
11-22-S290-EP

23. 11-23-S290-EPUnit 11 Extreme Wildland Fire Behavior
Active
• Spread through aerial fuels
• Dependent on surface fire
• Surface fire can precede and vice-
versa
• Pulsating spread rate
11-23-S290-EP

24. 11-24-S290-EPUnit 11 Extreme Wildland Fire Behavior
Independent
• Will outrun the reinforcing surface fire.
• Combustion process and heat transfer
mechanisms take place in the aerial fuels.
• Surface fire spread results from crown fire
spread.
11-24-S290-EP

25. 11-25-S290-EPUnit 11 Extreme Wildland Fire Behavior
Conditions Contributing
to Crown Fires
• Crown flammability
• Surface to crown
heat transfer
• Crown to crown
heat transfer

26. 11-26-S290-EPUnit 11 Extreme Wildland Fire Behavior
Crown Flammability
• Fine dead fuel moisture
• Live foliar moisture
• Foliage flammability
• Crown closure (“compactness”)
– >75% will improve heat transfer
mechanisms of convection and radiation
– less closure allows heat to be lost
11-26-S290-EP

27. 11-27-S290-EPUnit 11 Extreme Wildland Fire Behavior
Surface to Crown
Heat Transfer
• Surface fire intensity
• Vertical
arrangement
• Steepness of
slope
11-27-S290-EP

28. 11-28-S290-EPUnit 11 Extreme Wildland Fire Behavior
Crown to Crown
Heat Transfer
• Crown spacing (20’ or less)
• Crown level winds (20 mph
or greater 20 ft. above
the surrounding
vegetation)
• Steepness of slope
(similar in crown
fuels to its effect
on surface fuels)
11-28-S290-EP

29. 11-29-S290-EPUnit 11 Extreme Wildland Fire Behavior

30. 11-30-S290-EPUnit 11 Extreme Wildland Fire Behavior
Does this stand have the
potential to crown?

31. 11-31-S290-EPUnit 11 Extreme Wildland Fire Behavior
Factors That Contribute to
the Spotting Problem and
the Conditions Associated
With Each Factor

32. 11-32-S290-EPUnit 11 Extreme Wildland Fire Behavior
The eight contributing
factors fall into the following
three areas:
• Firebrand source
• Transportation
• Receiving fuels
and environment

33. 11-33-S290-EPUnit 11 Extreme Wildland Fire Behavior
Firebrand Source
• Probability of production
• Number of firebrands
• Type of firebrands
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34. 11-34-S290-EPUnit 11 Extreme Wildland Fire Behavior
Transportation
• Convective lifting
• Wind field
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35. 11-35-S290-EPUnit 11 Extreme Wildland Fire Behavior
Receiving Fuels
and Environment
• Receptive fuel
• Probability of ignition
• Environmental conditions
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36. 11-36-S290-EPUnit 11 Extreme Wildland Fire Behavior
Short-Range vs.
Long-Range Spotting
• Wind field and convective lifting dictate the
maximum spotting distance.
• Spotting
distances
recorded in
excess of
15 miles!

37. 11-37-S290-EPUnit 11 Extreme Wildland Fire Behavior
Short-Range Spotting
Strong surface winds and limited
convective lifting.
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38. 11-38-S290-EPUnit 11 Extreme Wildland Fire Behavior
Long-Range Spotting
• Large, aerodynamic firebrands
• Strong convective lifting
• Wind field enabling
maximum height
and transportation
(running crown
fires, large fire
whirls)
11-38-S290-EP

39. 11-39-S290-EPUnit 11 Extreme Wildland Fire Behavior
Determining Potential
Spot Fire Locations
• Observe convective column or ash
“fallout”
• “Where there is one, there are
probably more.”
11-39-S290-EP

40. 11-40-S290-EPUnit 11 Extreme Wildland Fire Behavior
Numerous Spots
• Getting frequent spot fires across the line
is one of the 18 Watchouts.
• What is “frequent”?
– Generally faster than you can pick them up

41. 11-41-S290-EPUnit 11 Extreme Wildland Fire Behavior
The Probability
of Ignition
(PGI)

42. 11-42-S290-EPUnit 11 Extreme Wildland Fire Behavior
Probability of Ignition
Rating of the probability that a glowing
firebrand will cause a fire, providing it
lands on receptive fuels.

43. 11-43-S290-EPUnit 11 Extreme Wildland Fire Behavior
Probability of Ignition Table
Dry-Bulb
Shading Temp 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
(Percent) (oF)
100+ 100 100 80 70 60 60 50 40 40 30 30 20 20 20 20 10
100-109 100 90 80 70 60 60 50 40 40 30 30 20 20 20 10 10
90-99 100 90 80 70 60 50 40 40 30 30 30 20 20 20 10 10
80-89 100 90 80 70 60 50 40 40 30 30 30 20 20 10 10 10
Unshaded 70-79 100 80 70 60 60 50 40 40 30 30 30 20 20 10 10 10
<50% 60-69 90 80 70 60 50 50 40 30 30 20 20 20 20 10 10 10
50-59 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10 10
40-49 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10 10
30-39 80 70 60 50 50 40 30 30 20 20 20 10 10 10 10 10
100+ 100 90 80 70 60 50 50 40 40 30 30 20 20 20 10 10
100-109 100 90 80 70 60 50 50 40 30 30 30 20 20 20 10 10
90-99 100 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10
80-89 100 80 70 60 60 50 40 40 30 30 20 20 20 10 10 10
Shaded 70-79 90 80 70 60 50 50 40 30 30 30 20 20 20 10 10 10
>50% 60-69 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10 10
50-59 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10 10
40-49 90 80 60 50 50 40 30 30 30 20 20 20 10 10 10 10
30-39 80 80 60 50 50 40 30 30 20 20 20 10 10 10 10 10
FINE DEAD FUEL MOISTURE (PERCENT)

44. 11-44-S290-EPUnit 11 Extreme Wildland Fire Behavior
Dry-Bulb
Shading Temp 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
(Percent) (oF)
100+ 100 100 80 70 60 60 50 40 40 30 30 20 20 20 20 10
100-109 100 90 80 70 60 60 50 40 40 30 30 20 20 20 10 10
90-99 100 90 80 70 60 50 40 40 30 30 30 20 20 20 10 10
80-89 100 90 80 70 60 50 40 40 30 30 30 20 20 10 10 10
Unshaded 70-79 100 80 70 60 60 50 40 40 30 30 30 20 20 10 10 10
<50% 60-69 90 80 70 60 50 50 40 30 30 20 20 20 20 10 10 10
50-59 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10 10
40-49 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10 10
30-39 80 70 60 50 50 40 30 30 20 20 20 10 10 10 10 10
100+ 100 90 80 70 60 50 50 40 40 30 30 20 20 20 10 10
100-109 100 90 80 70 60 50 50 40 30 30 30 20 20 20 10 10
90-99 100 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10
80-89 100 80 70 60 60 50 40 40 30 30 20 20 20 10 10 10
Shaded 70-79 90 80 70 60 50 50 40 30 30 30 20 20 20 10 10 10
>50% 60-69 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10 10
50-59 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10 10
40-49 90 80 60 50 50 40 30 30 30 20 20 20 10 10 10 10
30-39 80 80 60 50 50 40 30 30 20 20 20 10 10 10 10 10
FINE DEAD FUEL MOISTURE (PERCENT)
Exercise1
11-44-S290-EP

45. 11-45-S290-EPUnit 11 Extreme Wildland Fire Behavior
Dry-Bulb
Shading Temp 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
(Percent) (oF)
100+ 100 100 80 70 60 60 50 40 40 30 30 20 20 20 20 10
100-109 100 90 80 70 60 60 50 40 40 30 30 20 20 20 10 10
90-99 100 90 80 70 60 50 40 40 30 30 30 20 20 20 10 10
80-89 100 90 80 70 60 50 40 40 30 30 30 20 20 10 10 10
Unshaded 70-79 100 80 70 60 60 50 40 40 30 30 30 20 20 10 10 10
<50% 60-69 90 80 70 60 50 50 40 30 30 20 20 20 20 10 10 10
50-59 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10 10
40-49 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10 10
30-39 80 70 60 50 50 40 30 30 20 20 20 10 10 10 10 10
100+ 100 90 80 70 60 50 50 40 40 30 30 20 20 20 10 10
100-109 100 90 80 70 60 50 50 40 30 30 30 20 20 20 10 10
90-99 100 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10
80-89 100 80 70 60 60 50 40 40 30 30 20 20 20 10 10 10
Shaded 70-79 90 80 70 60 50 50 40 30 30 30 20 20 20 10 10 10
>50% 60-69 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10 10
50-59 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10 10
40-49 90 80 60 50 50 40 30 30 30 20 20 20 10 10 10 10
30-39 80 80 60 50 50 40 30 30 20 20 20 10 10 10 10 10
FINE DEAD FUEL MOISTURE (PERCENT)
11-45-S290-EP

46. 11-46-S290-EPUnit 11 Extreme Wildland Fire Behavior
Firewhirls (Vortices), the
Conditions Under Which
They are Likely to Develop
and Their Implications to
Wildland Fire Behavior

47. 11-47-S290-EPUnit 11 Extreme Wildland Fire Behavior
Fire Vortices
A firewhirl/vortex is
defined as a spinning,
moving column of
ascending air rising from a
vortex and carrying aloft
smoke, debris and fire.
Firewhirls belong to the
same family as tornadoes
and dust devils.

48. 11-48-S290-EPUnit 11 Extreme Wildland Fire Behavior
Two Types of Vortices
Vertical Vortices
or Firewhirls
Horizontal
or Roll Vortices
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49. 11-49-S290-EPUnit 11 Extreme Wildland Fire Behavior
Horizontal Vortices
• Rare, exemplifies
extreme fire
behavior
• Note “finger” (FOD)
moves 100m at
100mph and
retreats within 3
seconds
• Not well
understood
*Looking down

50. 11-50-S290-EPUnit 11 Extreme Wildland Fire Behavior
3 Types of Vertical Vortices
Thermally driven
– Similar to the dust devil which results from
some form of horizontal wind shear
associated with convective activity in an
unstable atmosphere.
Convection column
– This form of firewhirl originates high in the
convection column.
Wake type
– Occur on lee sides of physical obstructions

51. 11-51-S290-EPUnit 11 Extreme Wildland Fire Behavior
When and Where to Expect
Firewhirls
• Are the result of local events or
processes.
• Occur more frequently when the air
mass is unstable to a considerable
height.
• Assess the potential for firewhirls by
watching for evidence of dust devils and
light winds.

52. 11-52-S290-EPUnit 11 Extreme Wildland Fire Behavior
Factors Contributing to
Firewhirl Formation
• Sun perpendicular to slope
• Minimum cloudiness
• Low RH
• Dry exposed soil or
burned area
• Light winds
• Unstable atmosphere
• Smoke rising to great
heights
• Clouds growing vertically

53. 11-53-S290-EPUnit 11 Extreme Wildland Fire Behavior
Other Considerations
These conditions can increase the
chance of firewhirls:
• The start of upslope
winds
• Wind blowing across
ridges
• Up and down canyon
winds at corners and
spurs
• Hot spots in fire area
• Changing air mass

54. 11-54-S290-EPUnit 11 Extreme Wildland Fire Behavior
Implications to Wildland Fire
Behavior
• Can increase or alter wind flows.
• Carry firebrands up into transport winds
(long range spotting).
• Can wander over fire lines and collapse
(short range spotting).
• Can cause severe damage and threaten
life and property.

55. 11-55-S290-EPUnit 11 Extreme Wildland Fire Behavior
The Difference Between
Wind-Driven
and
Plume-Dominated Fires

56. 11-56-S290-EPUnit 11 Extreme Wildland Fire Behavior
Wind-Driven Fire
Power of wind >Power of fire

57. 11-57-S290-EPUnit 11 Extreme Wildland Fire Behavior
Plume-
Dominated
Fire
Power of fire >
Power of wind

58. 11-58-S290-EPUnit 11 Extreme Wildland Fire Behavior
Wind-Driven Fires
• Often those that escape initial attack
and become the largest
• Easier to predict direction of spread
• Wind shift poses a problem
• Smoke column bent over by wind
• Spotting downwind
• Flanks and heel generally safe

59. 11-59-S290-EPUnit 11 Extreme Wildland Fire Behavior
Plume-Dominated Fire
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60. 11-60-S290-EPUnit 11 Extreme Wildland Fire Behavior
Plume-Dominated Fire
• Fire activity result of convective activity
of the plume
• Spread rate and direction very
unpredictable
• Spotting can be in all directions
• Generally low windspeeds
• Generally pulses – can build, collapse,
build, etc.

61. 11-61-S290-EPUnit 11 Extreme Wildland Fire Behavior
Functions Like a
Thunderstorm
• Indrafts
– Can be from all directions
– Provides oxygen, increases preheating
• Downbursts
– Rising air is cooled and can rush forcefully
to the ground
– Downburst winds spread out in all
directions
– Sudden calm, presence of virga or rain

62. 11-62-S290-EPUnit 11 Extreme Wildland Fire Behavior
Virga/Downburst

63. 11-63-S290-EPUnit 11 Extreme Wildland Fire Behavior
Review Unit 11 Objectives
1. Describe the four common
denominators of fire behavior on
tragedy wildland fires.
2. Describe extreme fire behavior
characteristics and recognize fire
environment influences that
contribute to extreme fire behavior.

64. 11-64-S290-EPUnit 11 Extreme Wildland Fire Behavior
Review Unit 11 Objectives
3. Describe the three stages of crown
fire development and identify the
key factors and indicators leading
to crown fire development.
4. Identify the three factors that
contribute to the spotting problem
and describe the conditions
associated with each factor.

65. 11-65-S290-EPUnit 11 Extreme Wildland Fire Behavior
Review Unit 11 Objectives
5. Define the probability of ignition,
describe its use, and determine it
using tables.
6. Define firewhirls (vortices), the
conditions under which they are
likely to develop and their
implications to wildland fire behavior.
7. Explain the difference between wind-
driven and plume-dominated fires.