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S290 Unit 11

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University of Alaska, Fairbanks
University of Alaska, Fairbanks

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.

Educación
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11-1-S290-EPUnit 11 Extreme Wildland Fire Behavior Unit 11
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.
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.
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.
11-5-S290-EPUnit 11 Extreme Wildland Fire Behavior The Four Common Denominators of Fire Behavior on Tragedy Fires
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
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)
11-8-S290-EPUnit 11 Extreme Wildland Fire Behavior Extreme Fire Behavior Characteristics and Fire Environment Influences That Contribute to Extreme Fire Behavior
11-9-S290-EPUnit 11 Extreme Wildland Fire Behavior
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-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
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
11-13-S290-EPUnit 11 Extreme Wildland Fire Behavior Fuels Characteristics • Continuous fine fuels • Heavy loading • Ladder fuels • Tight crown spacing (<20 ft)
11-14-S290-EPUnit 11 Extreme Wildland Fire Behavior Wind Extreme fire behavior has been associated with strong winds including: – Frontal – Thunderstorm – Foehn winds
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
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
11-17-S290-EPUnit 11 Extreme Wildland Fire Behavior Unstable Atmosphere An unstable atmosphere contributes to the vertical motion of the air.
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
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.
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
11-21-S290-EPUnit 11 Extreme Wildland Fire Behavior Types of Crown Fire (wind driven) 11-21-S290-EP
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
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
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
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
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
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
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
11-29-S290-EPUnit 11 Extreme Wildland Fire Behavior
11-30-S290-EPUnit 11 Extreme Wildland Fire Behavior Does this stand have the potential to crown?
11-31-S290-EPUnit 11 Extreme Wildland Fire Behavior Factors That Contribute to the Spotting Problem and the Conditions Associated With Each Factor
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
11-33-S290-EPUnit 11 Extreme Wildland Fire Behavior Firebrand Source • Probability of production • Number of firebrands • Type of firebrands 11-33-S290-EP
11-34-S290-EPUnit 11 Extreme Wildland Fire Behavior Transportation • Convective lifting • Wind field 11-34-S290-EP
11-35-S290-EPUnit 11 Extreme Wildland Fire Behavior Receiving Fuels and Environment • Receptive fuel • Probability of ignition • Environmental conditions 11-35-S290-EP
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!
11-37-S290-EPUnit 11 Extreme Wildland Fire Behavior Short-Range Spotting Strong surface winds and limited convective lifting. 11-37-S290-EP
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
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
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
11-41-S290-EPUnit 11 Extreme Wildland Fire Behavior The Probability of Ignition (PGI)
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.
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)
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
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
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
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.
11-48-S290-EPUnit 11 Extreme Wildland Fire Behavior Two Types of Vortices Vertical Vortices or Firewhirls Horizontal or Roll Vortices 11-48-S290-EP
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
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
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.
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
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
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.
11-55-S290-EPUnit 11 Extreme Wildland Fire Behavior The Difference Between Wind-Driven and Plume-Dominated Fires
11-56-S290-EPUnit 11 Extreme Wildland Fire Behavior Wind-Driven Fire Power of wind >Power of fire
11-57-S290-EPUnit 11 Extreme Wildland Fire Behavior Plume- Dominated Fire Power of fire > Power of wind
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
11-59-S290-EPUnit 11 Extreme Wildland Fire Behavior Plume-Dominated Fire 11-59-S290-EP
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.
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
11-62-S290-EPUnit 11 Extreme Wildland Fire Behavior Virga/Downburst
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.
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.
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.

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S290 Unit 11

  • 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) 11-21-S290-EP
  • 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 11-33-S290-EP
  • 34. 11-34-S290-EPUnit 11 Extreme Wildland Fire Behavior Transportation • Convective lifting • Wind field 11-34-S290-EP
  • 35. 11-35-S290-EPUnit 11 Extreme Wildland Fire Behavior Receiving Fuels and Environment • Receptive fuel • Probability of ignition • Environmental conditions 11-35-S290-EP
  • 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. 11-37-S290-EP
  • 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 11-48-S290-EP
  • 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 11-59-S290-EP
  • 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.