Fire Behavior and Prescribed Fire. Heat Fuel Oxygen Fire Triangle.

Fire Behavior and Prescribed Fire

HeatFuelOxygenFire Triangle

Three Principal Environmental Elements Affecting Wildland Fire Behavior

FuelsFuel TypeFuel MoistureSize and ShapeFuel LoadingHorizontal ContinuityVertical Arrangement

Fuel MoistureThe amount of water in a fuel expressed as a percentage of the oven-dry weight of that fuel

Fuel TypesNonburnable Fuel Type Models (NB)Grass Fuel Type Models (GR)Grass-Shrub Fuel Type Models (GS)Shrub Fuel Type Models (SH)Timber-Understory Fuel Type Models (TU)Timber Litter Fuel Type Models (TL)Slash-Blowdown Fuel Type Models (SB)

Fuel moisture time lags: (Time it takes for a fuel to lose 63% of its moisture)Time lagFuel diameter 1-hour (fine fuels) 3 inch (large branches, tops, logs)Fuel Size

Fuel LoadingThe quantity of fuels in an area

Generally expressed in tons per acre

Horizontal Continuity:Uniform vs Patchy

Vertical Arrangement Ground Surface Aerial

All combustible materials lying beneath the surface including deep duff, roots, rotten buried logs, and other organic material

Usually called a PEAT FIRE

Ground Fuels

All materials lying on or immediately above the ground including needles or leaves, grass, downed logs, stumps, large limbs and low shrubs.Surface Fuels

All green and dead materials located in the upper forest canopy including tree branches and crowns, snags, moss, and high shrubs.Aerial Fuels

WeatherTemperature

Wind Speed and DirectionIncreases supply of oxygen Influences spread direction and spotting Dries fuels

WeatherRelative Humidity (RH)

Precipitation

TopographyAspect SlopePosition of FireShape of CountryElevationRelates to curing of fuels, precipitation, length of fire season, etc.

Aspect

Steep Slopes Cause Rapid Fire Spread

Slope Affects Fire BehaviorPreheatingDraftFaster Ignition and SpreadBurning Material Rolling Downslope

Position of Fire on Slope

Box Canyon & Chimney Effect

Radiant Heat AcrossNarrow Canyon

Spotting Across Narrow Canyon

Mountains Cause Channeling of Wind

Elevation

Characteristics of Fire BehaviorFire Intensity: Heat release per unit time (BTUs)

Fire intensity affected by

Flame Length: The distance measured from the average flame tip to the middle of the flaming zone at the base of the flame

Rate of Spread (ROS): The distance a fire travels during a given period of time

Increased fire intensityWindspeedSteepness of slopePrimary factors affecting rate of spread?

Slope Reversal

RunningTypes of Fire Behavior spreading quicklyCreeping spreading slowly with low flamesSmoldering burns without flames; barely spreadingSpotting sparks/embers carried by wind or combustion column or moved by gravitySpot fires new ignition pointsFire brand a piece of burning material

TorchingTypes of Extreme Fire Behavior surface fire moves into crowns of individual trees

Crowning

spreads from tree crown to tree crown (dependent, active, or independent)

Flareup sudden acceleration of fire spread or intensity (short duration, for portion of fire)

Blowup dramatic change in the behavior of the whole fire (rapid transition to a severe fire)Fire Whirls vortex (gas mass with rotational motion)

Fire Effects

Prescribed Fire

Prescribe Fire PlanBurn prescription writtenPre-burn site treatments completedEquipment designated & readyPersonnel identified & trainedApprovals & permits in handAuthorities & interested parties identified & notified*Latest forecasts checked** Day before & day of burn

Ignition DevicesHand-held/ground-based Drip torch Propane torch Fire fuse (flare) Flame thrower

Drip torch fuel:

3:1 or 3:2Diesel/gasoline

Ignition DevicesAerial

Helitorch

Delayed aerial ignition device

Ignition DevicesLightning

Ignition TechniquesBackfire (backing fire) Narrow burning zone Low smoke output

Backing Fire

Headfire (heading fire) Long flame lengths Fast rate of spread

Strip-heading FireDistance between strips controls intensity

Spotfire Useful in shifting winds What you get using a DAID

SpotfireDistance between spots controls intensity

Flankfire (flanking fire) Fire spreads at right angle to wind Requires careful crew coordination

Flanking Fire

HeadfireFlankfireBackfireWind

Smoke Management

Principles of smoke managementHave clear, defensible objectivesComply with local pollution regulationsNotify local fire & law enforcement officials, nearby residents, & adjacent landownersObtain the best available weather forecastsDont burn under highly stable conditionsBurn during midday; avoid night burnsUse caution near, upwind, or up-drainage of smoke sensitive areas

Principles of smoke management(continued)Use test fire to estimate smoke output & behaviorUse backing fires if feasibleBurn in small blocks if dispersion marginalDo not burn when fuel moisture highDont burn organic soilsMop-up along roads firstHave an emergency plan!

Prescribed Fire in the Central Hardwood Region

Prescribed Fire in the Central Hardwood RegionThe historic fire regime was thought to play a role in the maintenance of oak dominated forest prior to European settlement

Prescribed fire has been suggested as a tool for regenerating oak

Potential benefits included

Prescribed fires in late spring and summer are most lethal to oak competitors.

Prescribed Fire in the Central Hardwood Region

Generally, prescribed fire is best used in combination with reductions in overstory stocking (e.g. shelterwood, midstory removal) to release advance oak reproduction

Repeated burning most effective at increase oak competitivenessPrescribed Fire in the Central Hardwood Region

The use of prescribed fire in oak forests has increased over the last four decadesResults on oak regeneration has been highly variable

Prescribe Fire in the Central Hardwood RegionSite Preparation BurnFire can create conditions suitable for oak establishment by reducing litter layers and understory competition

Do not burn if acorn crop has just fallen or if new oak seedlings from recent crop are needed to regenerate the stand

Prescribe Fire in the Central Hardwood RegionSite Preparation BurnBurning can be done in dormant or growing seasons

High-intensity fires (flame lengths > 2 ft) in late spring decreases dense understory shaded more quickly

Multiple fires over several years are commonly necessary to reduce dense understories to a level that improves oak seedling survival and growth

Prescribed Fire in the Central Hardwood RegionRelease BurnBurn used to free competitive oak reproduction from competition

Burning done after midstory removal, first removal cut of shelterwood or after final removal cutFire should occur after released oaks develop a more robust root systemTypically,

Prescribed Fire in the Central Hardwood RegionRelease BurnModerate to high-intensity fires (flame lengths > 2 ft) to ensure topkill of understory layer

Done in mid to late spring (April to May)

Fire needs all three to sustain combustion.What are we removing when we construct a fire line?What are we removing when we put water on a fire?Both dirt and foam also help remove the oxygen as well as heat from a fireRadiation: heat generated from burning object affecting adjacient object.

Convection: Hot gases rising from fire. Dries out fuels and also can carry hot embers to start spot fires.

Conduction: Heat energy transferred within an object; metal rod in a camp fire. Wildland fuels are NOT a good conductor of heat Radiation: heat generated from burning object affecting adjacient object.

Convection: Hot gases rising from fire. Dries out fuels and also can carry hot embers to start spot fires.

Conduction: Heat energy transferred within an object; metal rod in a camp fire. Wildland fuels are NOT a good conductor of heat Radiation: heat generated from burning object affecting adjacient object.

Convection: Hot gases rising from fire. Dries out fuels and also can carry hot embers to start spot fires.

Conduction: Heat energy transferred within an object; metal rod in a camp fire. Wildland fuels are NOT a good conductor of heat Radiation: heat generated from burning object affecting adjacient object.

Convection: Hot gases rising from fire. Dries out fuels and also can carry hot embers to start spot fires.

Conduction: Heat energy transferred within an object; metal rod in a camp fire. Wildland fuels are NOT a good conductor of heat Horizontal - self explanatory

Vertical arrangement on following slidesBest called underground fire.Ground fires usually only a problem in drought situatuions99% of all fires.

Namely a crown fire!

Most difficult and dangerous to contain.Can burn independent of surface fire. Radiation: heat generated from burning object affecting adjacient object.

Convection: Hot gases rising from fire. Dries out fuels and also can carry hot embers to start spot fires.

Conduction: Heat energy transferred within an object; metal rod in a camp fire. Wildland fuels are NOT a good conductor of heat Radiation: heat generated from burning object affecting adjacient object.

Convection: Hot gases rising from fire. Dries out fuels and also can carry hot embers to start spot fires.

Conduction: Heat energy transferred within an object; metal rod in a camp fire. Wildland fuels are NOT a good conductor of heat ****BTUs, KJs***