s-190 Wildland Fire Behavior

precise location where ignition source became in contact with material first ignited and sustained combustion

side of fire having fastest rate of spread

part of fire's perimeter that is roughly parallel to main direction of spread

• portion of fire opposite of head
• slowest spreading portion of fire edge
• aka heel

entire outer edge or boundary of fire

long narrow extensions of fire projecting from the main body

unburned indentations in fire edge formed by slow burning areas or fingers

area of unburned fuel inside the fire perimeter

fire ignited outside perimeter by firebrands

• Fuel to burn
• air to provide oxygen for combustion
• heat to start and continue combustion process

remove any single one and there can be no fire

• radiation- heat ray or wave
• convection- heat transfer thru air. hot air rises
• conduction- direct contact of heat thru a medium

control line is completed around the fire and any spot fires. confident that spread and forward progress has stopped

hotspots are out, line will hold, burn out any unburned areas inside line

• six major fuel types
• grass- burns hottest and fastest
• grass:shrub- significant contributor to spread, fine fuels mixed with aerial/shrub fuel
• shrub- some highly flammable
• timber:understory- ladder to aerial crown fuels
• timber: litter- dominant in mountainous topo. provides fuel for ground fires
• slash: blowdown- debris left after natural or human events. fuel for fire spread

affects rate of spread

• uniform fuels- fuels distributed evenly over the area. network of connected fuels providing continuous spread
• patchy fuels- fuels distributed unevenly across an area. fuel with definite breaks or barriers

• ground fuel-all combustible materials beneath the surface: duff, roots, buried logs
• surface fuel- all combustible materials lying on or immediately above ground: needles, duff, grass, logs, shrubs, stumps
• ladder fuel- combustible materials that aid the spread of fire from surface to canopy: shrubs, moderate height vegitation, tree trunks
• aerial fuels- all green/dead fuels in uper canopy: tall shrubs, tree branches and crowns, snags

• weather
• fuel
• topography

• surface winds above 10 mph
• lenticular clouds- indicate high winds aloft with potential to surface
• high fast moving clouds- indicate wind shifts
• approaching cold front- wind will increase in speed and and change direction
• cumulonimbus development- possible wind speed/direction indicators and potential for erratic winds
• sudden calm- wind change coming
• battling or shifting winds
• columns-  leaning, sheared, well developed, changing

• unstable atmosphere:
•    -gusty winds cumulus clouds
•    -castellatus clouds in a.m.
•    -smoke rising straight up
•    -inversion lifting
• RH below 25%
• temp. above 85 degrees

• continuous fine fuels
• heavy loading of fuels
• ladder fuels and tight crown spacing and numerous snags
• firebrand sources
• bug kill/ dead trees preheated canopy
• steep slopes greater than 50%
• chutes/chimneys
• firewhirls
• frequent spotting

• strong upslope drafts creating rapid spread
• one way in/one way out

• easily spreads fuel to opposite side with radiation and spotting
• strong upslope air movement at sharp bends in canyon

burning with low flame and slow spread

behavior of fire spread rapidly with well defined head

burning of the foliage of single tree or small group from bottom up. little or no lateral spread

• aka heel of fire
• part of fire with slower spread and lower intensity, usually moving into wind or downhill

zone of moving fire where combustion is primarily flaming

• location usually a barrier to spread from which to start constructing line
• minimizes chance of being flanked

• part of conrol line that is scraped to mineral soil
• all constructted or natural barriers used to contain fire

• unit of measure = 66 ft.
• one mile is 80 chains
• 10 chains is one acre

• more exposed to sunlight
• lighter sparser fuels, higher temp, lower RH, lower fuel moisture

• have more shade
• heavier fuels, lower temp, higher RH, higher fuel moisture
• less fire activity than south facing slope

• degree of incline on hillside
• fire burns more rapidly uphill, steeper the slope the faster it burns
• fire on level ground is influenced by wind and fuels

 wind blowing through saddle can increase speed as it passes through constricted area and spreads out on downwind side

any obstruction to the spread of fire, an area or strip lacking any flammable fuel

• amount of fuel present
• expressed in tons per acre

• 1 hr fuels: 0-1/4 inch diameter
• 10 hr fuels: 1/4-1 inch
• 100 hr fuels: 1-3 inch
• 1000 hr fuels: 3-8 inches

degree of hottnes/coldness in the air

amount of moisture in the air divided by the amount the air could hold when saturated

• temp increase- RH decreases
• temp decrease- RH increases

fine fuels react rapidly while heavy fuels are not drastically effected

duration has more effect then amount of precipitation

• resists upward motion
• clouds in layers
• columns drift apart after limited rise
• poor visibility
• fog layers
• steady winds

the direction from which the wind is blowing, not where its blowing towards