S290 Unit 3
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This document covers wildland fuel characteristics and their impact on fire behavior. It discusses the components of fuels, including ground, surface and aerial fuels. It describes seven key fuel characteristics - loading, size/shape, compactness, horizontal/vertical continuity, moisture content and chemical content. It also defines the four dead fuel timelag categories and explains how fuel models are used to predict fire behavior based on typical fuel characteristics.
S290 Unit 3
- 2. 3-2-S290-EPUnit 3 Fuels Unit 3 Objectives 1. Identify and describe basic wildland fuel characteristics. 2. Identify and describe seven characteristics of fuels that affect wildland fire behavior. 3. Identify and define by size class the four dead fuel timelag categories used to classify fuels. 4. Describe how fuel availability is essential to predicting wildland fire behavior. 5. Describe the fuel model concept and its utility for predicting wildland fire behavior.
- 3. 3-3-S290-EPUnit 3 Fuels Fuel Make-up • Fuel characteristics • Fuel moisture • Fuel temperature
- 4. 3-4-S290-EPUnit 3 Fuels Fuels Any combustible material that: – Is living or dead – Is in or on the ground – Is in the air – Can ignite and burn 3-4-S290-EP
- 5. 3-5-S290-EPUnit 3 Fuels Fuel Combinations • Kind • Amount • Size • Shape • Position • Arrangement
- 6. 3-6-S290-EPUnit 3 Fuels Fuel Levels and Components • Ground • Surface • Aerial fuels
- 7. 3-7-S290-EPUnit 3 Fuels Ground Fuels All combustible materials lying beneath the surface: • Deep duff • Tree roots • Rotten buried logs • Other organic material
- 8. 3-8-S290-EPUnit 3 Fuels Ground Fuels • Important in terms of line construction and mop-up • Typical fire spread: –smoldering –creeping
- 9. 3-9-S290-EPUnit 3 Fuels Surface Fuels All combustible materials lying on or immediately above the ground: • Needles or leaves • Duff • Grass • Small dead wood • Downed logs • Stumps • Large limbs • Shrubs to about six feet in height • Litter
- 10. 3-10-S290-EPUnit 3 Fuels Surface Fuels • Less compact than ground fuels • Have other characteristics more favorable for faster rates of spread • Fires often have higher rates of spread • Most wildfires ignite in and are carried by the surface fuels
- 11. 3-11-S290-EPUnit 3 Fuels Surface Fuels Important in terms of line construction and mop-up, most important regarding fire spread and fire behavior
- 12. 3-12-S290-EPUnit 3 Fuels Aerial Fuels All green and dead materials located in the upper canopy: • Tree branches and crowns • Snags • Hanging moss • Tall shrubs
- 13. 3-13-S290-EPUnit 3 Fuels Aerial Fuels Open canopy: Faster spreading surface fire than closed canopy stands. –Torching of individual trees –Crowning is unlikely
- 14. 3-14-S290-EPUnit 3 Fuels Aerial Fuels Closed canopy: • Greater than 6 feet in height. • Best opportunity for a running crown fire. • Canopy closure is usually given in percent. – 25 percent of the ground is visible, there is 75 percent canopy closure.
- 15. 3-15-S290-EPUnit 3 Fuels Aerial Fuels Important in terms of fire spread and fire behavior due to torching, crowning, and spotting.
- 17. 3-17-S290-EPUnit 3 Fuels Seven Characteristics of Fuels that Affect Wildland Fire Behavior Seven principal characteristics: • Fuel loading • Size and shape • Compactness • Horizontal continuity • Vertical arrangement • Moisture content • Chemical content Two main categories: • Physical and chemical characteristics • Moisture content
- 18. 3-18-S290-EPUnit 3 Fuels Fuel Loading The amount of fuel present expressed quantitatively in terms of weight of fuel per unit area. Measured in: tons/acre (tons/acre) OR pounds/acre (lbs/acre)
- 19. 3-19-S290-EPUnit 3 Fuels Loading Varies by Fuel Group Grass <1-5 Tons/Acre Shrub 2-80 Tons/Acre Slash 10-200 Tons/Acre Timber Litter 4-12 Tons/Acre
- 20. 3-20-S290-EPUnit 3 Fuels Size and Shape Surface area to volume ratio
- 21. 3-21-S290-EPUnit 3 Fuels Size and Shape Small fuels ignite and sustain combustion easier than large pieces of fuel.
- 22. 3-22-S290-EPUnit 3 Fuels Size and Shape • Higher ratios burn more readily • Lower ratios do not burn as readily
- 23. 3-23-S290-EPUnit 3 Fuels Size and Shape Firebrands • Small embers – Ordinarily produce short-range spotting – Cannot sustain combustion • Flatness and greater surface-area-to-volume ratios have increased the aerodynamic qualities • Examples: – Cedar fronds – Bark plates – Pine needles
- 24. 3-24-S290-EPUnit 3 Fuels Size and Shape Rolling firebrands • Important to spotting downslope • Examples: – Pine cones – Round logs – Round yucca plants
- 25. 3-25-S290-EPUnit 3 Fuels Compactness = Spacing Between Fuel Particles Closely compacted –Less surface area exposed –Restrict oxygen –Inhibit convective and radiant heat transfer –In most cases, slower rate of spread is expected Loosely compacted –Normally react faster to moisture changes –Have more oxygen available for combustion –Rate of spread is usually greater
- 26. 3-26-S290-EPUnit 3 Fuels Fuel Bed Depth and Orientation • Fuel Bed The average height of surface fuel that is contained in the combustion zone of a spreading fire front. • Orientation The horizontal or vertical orientation of the fuel array that carries the fire.
- 27. 3-27-S290-EPUnit 3 Fuels Vertically Oriented Fuels Fuelloadincrease Fuelbeddepthincreasesrapidly Average depth of fuels 1.5 1 .5 4 3 2 1 FEET TONS/AC Grass group Shrub group
- 28. 3-28-S290-EPUnit 3 Fuels Horizontally Oriented Fuels Fuelloadincrease Fuelbeddepthincreasesslowly Average depth of fuels Timber litter group Slash group 3 2 FEET TONS/AC 2 1 1.50 22 1.25 Average depth of fuels Slash Litter
- 29. 3-29-S290-EPUnit 3 Fuels Horizontal Continuity • Horizontal distribution of fuels at various levels or planes. • Characteristics influence: – Where a fire will spread – How fast fire will spread – Whether fire travels through • Surface fuels • Aerial fuels • Both
- 30. 3-30-S290-EPUnit 3 Fuels Continuous vs. Patchy Fuels 3-30-S290-EP
- 31. 3-31-S290-EPUnit 3 Fuels Aerial Fuels Closed Open 20 mph 2 mph 5 mph 3-31-S290-EP
- 32. 3-32-S290-EPUnit 3 Fuels Vertical Arrangement Fuels above ground and their vertical continuity, which influences fire reaching various levels or vegetation strata. 3-32-S290-EP
- 33. 3-33-S290-EPUnit 3 Fuels Ladder Fuels
- 35. 3-35-S290-EPUnit 3 Fuels Precipitation Dew Ground moisture Fuel Moisture Content Humidity Evaporation Evaporation 3-35-S290-EP
- 36. 3-36-S290-EPUnit 3 Fuels Live and Dead Fuel Moisture • Dead Fuel Moistures – rarely below 3-4%, fluctuate often due to environmental conditions. • Live Fuel Moistures – range much higher, with moisture contents of perhaps as high as 300% or more, fluctuate much more slowly, relate to growing season.
- 37. 3-37-S290-EPUnit 3 Fuels Fine Dead Fuels • Are considered the primary carrier of a surface fire. • Consist of needle/leaf litter, cured out grass.
- 38. 3-38-S290-EPUnit 3 Fuels Live to Dead Ratio
- 39. 3-39-S290-EPUnit 3 Fuels Chemical Contents All fuels, living or dead, contain fiber that is known as cellulose. Include, but are not limited to certain volatile substances such as: • oils • resins • wax • pitch
- 40. 3-40-S290-EPUnit 3 Fuels Chemical Contents Volatile fuels: • Chaparral in the southwest • Palmetto in the southeast • Greasewood in the Pacific northwest • Fountaingrass in Hawaii • Pitchy stumps from some conifers • Jack Pine in the Lake States • Pitch Pine in the northeast • Black Spruce in Alaska
- 41. 3-41-S290-EPUnit 3 Fuels Fuel Characteristics/Fire Behavior Compactness Loading Horizontal Continuity Vertical Arrangement Chemical Content Moisture Content Size and Shape 3-41-S290-EP
- 42. 3-42-S290-EPUnit 3 Fuels Fuel Characteristics Five fuel characteristics that most effect ignition: • Compactness • Loading • Chemical content • Size and shape • Moisture content
- 43. 3-43-S290-EPUnit 3 Fuels Fuel Characteristics • Ignition • Spread • Intensity • Spotting • Torching • Crowning Six primary fire behavior characteristics involved with the rate of spread:
- 44. 3-44-S290-EPUnit 3 Fuels Timelag Time needed under specified conditions for a fuel particle to lose about 63 percent of the difference between its initial moisture content and its equilibrium moisture content.
- 45. 3-45-S290-EPUnit 3 Fuels Dead Fuel Timelag Categories • 1-hour • 10-hour • 100-hour • 1000-hour Which category gains/loses moisture the fastest?
- 46. 3-46-S290-EPUnit 3 Fuels Available Fuels Grass Up to 100% Shrub 5-95% Slash 10-70% Timber litter 5-25% Fuels that will ignite and support combustion at the flaming front under specific conditions.
- 47. 3-47-S290-EPUnit 3 Fuels Consumption of Various Fuels by Fires The following play an important part in a fuel's availability to burn: • Size • Arrangement • Moisture content • Duration and intensity of the fire
- 48. 3-48-S290-EPUnit 3 Fuels Fuel Characteristics and the Fuel Model FUEL MODEL Vertical arrangement Moisture contentSize and Shape Loading Chemical content Compactness Horizontal continuity
- 49. 3-49-S290-EPUnit 3 Fuels Fuel Models 13 models: • Grass (3 fuel models) • Shrub (4 fuel models) • Timber Litter (3 fuel models) • Slash (3 fuel models)
- 50. 3-50-S290-EPUnit 3 Fuels Fuel Models Anderson’s Aids to Determining Fuel Models for Estimating Fire Behavior
- 51. 3-51-S290-EPUnit 3 Fuels Major Fuel Groups The four major fuel groups are: • Grass • Shrub • Timber Litter • Slash
- 52. 3-52-S290-EPUnit 3 Fuels Grass Group Grass is primary carrier of fire Fuel bed: 1’ to 2.5’ deep Fuel Characteristics: – 300 lbs/acre to several tons/acre – Usually < 0.25” in diameter – Compactness – Moisture content changes rapidly due to changes in RH Fire Behavior: rapid burnout, low intensity, wind strong influence, ROS 35 to 100+ ch/hr, FL 0 to 12 ft
- 53. 3-53-S290-EPUnit 3 Fuels Shrub Group Shrub is primary carrier of fire Fuel bed: 2’ to 6’ deep Fuel Characteristics: – 1 to 80 tons/acre – Usually < 1” in diameter, dead + live fuels – Compactness: loosely layered to very deep – Some volatiles may be present Fire Behavior: very low to extreme intensities, wind strong influence, ROS 18 to 75 ch/hr, FL 4 to 19 ft
- 54. 3-54-S290-EPUnit 3 Fuels Timber Litter Group Surface litter is primary carrier of fire Fuel bed: 0.2’ to 1’ deep Fuel Characteristics: – Size and shape mixed: litter, leaves, needles to large branchwood – Compactness: loosely layered to compact – Vertical arrangement < 1’, typically < 3” – Moisture content retained when litter is compact Fire Behavior: slow burning to running surface fires, torching, crowing possible, ROS 2 to 8 ch/hr, FL 1 to 5 ft.
- 55. 3-55-S290-EPUnit 3 Fuels Slash Group Slash is primary carrier of fire Fuel bed: 1’ to 3’ deep Fuel Characteristics: – Size and shape all sizes – Fuel loading between 12 and 58 tons/acre Fire Behavior: moderate to rapid spread rates, moderate to high intensities dependent on fuel arrangement, ROS 6 to 14 ch/hr, FL 4 to 11 ft, firebrands often produced and lifted into convection column, rolling materials may start spot fires
- 56. 3-56-S290-EPUnit 3 Fuels Group vs. Model Grass Group: Fuel Model 1 Short Grass (<1 foot high) Fuel Model 2 Timber (grass and understory) Fuel Model 3 Tall Grass (2 feet high) Shrub Group: Fuel Model 4 Chaparral (6 feet) Fuel Model 5 Short Brush (2 feet) Fuel Model 6 Intermediate Brush Fuel Model 7 Southern Rough
- 57. 3-57-S290-EPUnit 3 Fuels Timber Litter Group: Fuel Model 8 Closed Timber Litter Fuel Model 9 Hardwood Litter Fuel Model 10 Timber (litter and understory) Slash Group: Fuel Model 11 Light slash Fuel Model 12 Moderate slash Fuel Model 13 Heavy slash Group vs. Model
- 58. 3-58-S290-EPUnit 3 Fuels Introduction to the Standard Fire Behavior Fuel Models The new Standard Fire Behavior Fuel Models, sometimes referred to as “the 40 fuel models.”
- 59. 3-59-S290-EPUnit 3 Fuels New Model Parameters • Load by class and component • Surface-area-to-volume (SAV) ratio by class and component • Fuel model type (static or dynamic) • Fuelbed depth • Extinction moisture content • Fuel particle heat content
- 60. 3-60-S290-EPUnit 3 Fuels Need for the New Models Original 13: • For the severe period of the fire season. • Have worked well for predicting spread rate and intensity at peak of fire season. • Have limitations for other purposes: – Prescribed fire – Wildland fire use – Simulating the effects of fuel treatments on potential fire behavior – Simulating transition to crown fire using crown fire initiation
- 61. 3-61-S290-EPUnit 3 Fuels Need for the New Models New Models: • Improve the accuracy of fire behavior predictions outside of the severe period of the fire season. • Increase the number of fuel models: – Applicable in high-humidity areas. – For forest litter – For litter with grass – For shrub understory • Increase the ability to simulate changes in fire behavior
- 62. 3-62-S290-EPUnit 3 Fuels Grass New Fuel Groups Grass - Shrub
- 63. 3-63-S290-EPUnit 3 Fuels New Fuel Groups Shrub Timber - Understory
- 64. 3-64-S290-EPUnit 3 Fuels New Fuel Groups Slash - Blowdown Timber - Litter
- 65. 3-65-S290-EPUnit 3 Fuels Unit 3 Objectives 1. Identify and describe basic wildland fuel characteristics. 2. Identify and describe seven characteristics of fuels that affect wildland fire behavior. 3. Identify and define by size class the four dead fuel timelag categories used to classify fuels. 4. Describe how fuel availability is essential to predicting wildland fire behavior. 5. Describe the fuel model concept and its utility for predicting wildland fire behavior.