Wildland Fire S-190, Introduction to Wildland Fire Behavior

topography

the configuration of the earth's surface including its relief and the position of its natural and man-made features; easier to predict influences topography will have on wildfire than fuel and weather

aspect

the direction a slope is facing. (its exposure in relation of the sun)

fire perimeter

the entire outer edge or boundary of a fire

the steeper the slope

the faster the fire burns

elevation

the height of terrain above mean sea level, usually expressed in feet ASL

fingers of a fire

the long narrow extensions of a fire projecting from the main body from shifting of winds

air temperature varies with

time location height above the earth's surface

1000-hour fuels

3-8 inch in diameter

barriers

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

flare up

any sudden acceleration in the rate of spread or intensification of the fire. unlike blowup, a flare-up is of relativity short duration and does not change existing control plans

parts of a fire

point of origin, head, flank, rear, perimeter, fingers, pockets, island, spot fire

3 methods of heat transfer

radiation, convection, conduction

the amount of moisture that fuels can absorb from or release to the air depends largely on

relative humiditiy

spotting fire

behavior of a fire producing sparks or embers that are carried by the wind and which start new fires beyond the zone of direct ignition by the main fire; snags produce column of air

changes in air temperature near the surface of the earth are caused by

changing seasons alternations of night and day migrating weather systems

ladder fuels

combustible materials that aid the spread of fire from the surface to the upper canopy. Include: -surface litter -shrubs linked to torch fire-spot fires

wide canyons

may alter wind direction; cross canyon spotting of fires is not common except in high winds; strong differences in fire behavior will occur on north and south aspects

natural barriers

rivers lakes rocks slides fuels with higher moisture content do not burn as well as others in the same area

man-made barriers

roads highways reservoirs fireline constructed by fire resources

weather

short-term variations in the atmosphere

fire behavior terms

smoldering, creeping, running, spotting, torching, crown, flare up, firewhirl, backing, flaming front,

firewhirl

spinning vortex column of ascending hot air and gases rising from a fire and carrying aloft smoke, debris, and flame. fire whirls range in size from less than one foot to over 500 feet in diameter. large fire whirls have the intensity of a small tornado

a fire which starts near the bottom of a slope during normal upslope daytime wind conditions will normally ___________ and has ____________ upslope than a fire that starts near the top of the slope.

spread faster, more area to spread

box canyons

start near base of box canyon; provide for rapid rates of fire spread due to the channeling of wind and heat in upslope drafts chimney affect

narrow canyons

steep narrow canyon fire can easily spread to fuels on the opposite side by radiation and spotting; strong upslope drafts may be expected

Surface, Ground, Crown

surface- most of fires- burning litter and grass ground-burning organic soil into root systems crown- burning crowns of trees

As the sun rises

temperature increases, relatively humidity decreases

backing fire

that portion of the fire with slower rates of fire spread and lower intensity, normally moving into the wind and/or down slope. also called heel fire

flaming front

that zone of a moving fire where the combustion is primarily flaming. behind this flaming zone combustion is primarily glowing or involves the burning out of larger fuels (greater than about 3 inches in diameter). light fuels typically have a shallow flaming front, whereas heavy fuels have a deeper front.

fuel loading

the amount of fuel present expressed quantitatively in terms of weight of fuel per unit area.

relative humidity

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

fuel moisture

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

slope

the amount or degree of incline of a hillside

torching fire

the burning of the foliage of a single tree or a small group of trees, from the bottom up

controlled

the completion of control line around a fire, any spot fires, and any interior islands to be saved. burn out any unburned area adjacent to the fire side of the control lines. cool down all hot spots that are immediate threats to the control line, until the lines can reasonably be expected to hold under the foreseeable conditions

fuel arrangement

the manner in which fuels are spread over a certain area; horizontal continuity and vertical arrangment

before a wet fuel can burn

the moisture it contains must evaporate, smaller fuel will take on and lose moisture faster than heavier fuels

timelag

the rate at which dead fuel gains or loses moisture time needed under specific conditions for a fuel particle to lose about 63 percent of the difference between its initial moisture content and its equilibrium moisture content categories: 1 hour = 0-1/4" diameter 10 hour = 1/4-1" d 100 hour = 1-3" d 1000 hour = 3-8" d

the most common field instrument used to measure temperature and relative humidity is

the sling psychrometer

point of origin

the start the precise location where a competent ignition source came into contact with the material first ignited and sustained combustion occurred usually rear & upwind

shape of country - terrain

topographic condition influence wind speed and direction; influence direction of fire, speed, rate of spread, and intensity

pockets of a fire

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

______ is the primary weather element that affects fuel moisture content and the resulting flammability of wildland fuels

moisture

timber litter

most dominant in mountainous topography, especially in the northwest provides fuel for ground fire

heat transfer

movement of heat from one burning piece to another so that the fire triangle can continue 3 processes

contained

no longer spreading the status of a wildfire suppression action signifying that a control line has been completed around the fire, and any associated spot fires, which can reasonably be expected to stop the fire's spread

Fuels at lower elevations dry out ____ in the year than those at higher elevations

earlier

smoldering fire

fire burning without flame and barely spreading

low relative humidity is an indicator of

high fire danger

the more surface exposure to volume ratio fuel has

the more easily the fuel will dry and burn

fireline

the part of a containment or control line that is scraped or dug to mineral soil

flank of a fire

the part of a fire's perimeter that is roughly parallel to the main direction of spread lower flame, greatest variability where most fire is fought

head of a fire

the side of fire having the fastest rate of speed most intensity downwind

radiation

warming heat wave; can dry surrounding fuels and ignite them

grass shrub

found in the plains regions and high deserts a significant contributor to fire spread due to the fine fuels mixed with the aerial/shrub fuel

timber-understory

found thoughout most areas provide ladder to aerial crown fuels

shrub

found thoughout most areas some examples: -palmetto/gallberry in the southeast sagebrush in the great basin chaparral in the southwest and california

3 elements that must be present and combined before combustion can occur (fire triangle)

fuel to burn, air to supply oxygen to the flame, and heat to start and continue the combustion process remove any single one and there can be no fire

fire behavior depends of these fuel characteristics

fuel type fuel loading fuel availability

ground level fire is influenced by

fuels and winds primarily

wet fuels

fuels that have a high moisture content because of exposure to precipitation or high relative humidity

dry fuels

fuels that have low moisture content because of prolonged exposure to sunshine, dry winds, drought, or low relative humidity

six major fuel types in wildland fires

grass grass-shrub shrub timber-understory timber litter slash-blowdown

north facing slopes

have more shape which causes: -heavier fuels -lower temperatures -higher humidity -higher fuel moistures

the majority of large fire outbreaks occur when air temperature is

high and relatively humidity is low

smaller fuels have a ______ surface area to volume ratio than larger fuels

higher

Uniform fuels

include all fuels distributed continuously over the area (horizontal) areas containing a network of fuels which connect with each other to provide a continuous path for a fire to spread are included in this category

patchy fuels

include all fuels distributed unevenly over the area, or areas of fuel with definite breaks or barriers present (horizontal) patches of bare ground or rock

slash-blowdown

includes: logs, chunks of wood, bark, branches, stumps, broken understory trees, shrubs

seasonal and diurnal temperature changes can be larger or small, depending on

latitude elevation topography proximity to the moderating influences of nearby oceans or lakes

a north facing aspect will have ____________ than a south facing slope

less fire activity

convection

lighter, warm air moves upward. the hot gases and embers that compose the smoke column can dry and ignite other fuels; wind driven; most important in wild fire

in the early morning hours, temperature typically reaches its _____________ point and relative humidity reaches its ________ point

lowest, highest

island

or long ribbons safety hazard area of unburned fuel or just got a surface burn inside the fire perimeter

100-hour fuels

1-3 inch in diameter

1-hour fuels

0-1/4 inch in diameter

10-hour fuels

1/4-1 inch in diameter

crown fire

a fire that advances from top to top of trees or shrubs more or less independent of a surface fire. crown fires are sometimes classed as running or dependent to distinguish the degree of independence from the surface fire; mostly in pine, spruce, gamble oak

ground fuels

all combustible materials lying beneath the surface: -deep duff -tree roots -rotten buried logs -other organic materials

surface fuels

all combustible materials lying on or immediately above the ground: -needles or leaves -grass -stumps -downed logs

aerial fuels

all green and dead materials located in the upper canopy include: -tree branches and crowns -snags -hanging moss

anchor point

an advantageous location, usually a barrier to fire spread, from which to start constructing a fireline. the anchor point is used to minimize the chance of being flanked by the fire while the line is being constructed near something that won't burn ex. road side mowed field if no good anchor point, use a J hook

control line

an inclusive term for all constructed or natural barriers and treated fire edges used to contain a fire mineral soil break

fuel

any burnable material; source of energy that drives the fire

When temperature increases, relatively humidity _____________

decreases

when temperature reaches its maximum for the day, the relative humidity

decreases to a minimum

elevation affects fire behavior in ways such as

determining conditions and amount of fuel in an area, amount of precipitation received, wind exposure, and its relationship to the surrounding terrain.

conduction

direct contact causes fuels to heat up. wood does not conduct heat easily, so this is the least important of the 3

mop-up

extinguishing or removing burning material near control lines, felling snags, and trenching logs to prevent rolling after an area has burned, to make a fire safe, or to reduce residual smoke switch from containing to putting out

fuel availability

factors (size and shape) involved when talking about the availability of a fuel for combustion

ridges

fire burning along lateral ridges may change direction when they reach a point where the ridge drops off into a canyon. change in direction is caused by the flow of air in the canyon.

creeping fire

fire burning with a low flame and spreading slowly; timber litter or short grass

spot fire

fire ignited outside the perimeter of the main fire by a firebrand raining embers

running fire

fire spreading rapidly with a well defined head

grass

found in most areas more dominant as a fuel in desert and range areas can become prevalent after a fire in timber areas burns hottest and fastest

chain

unit of measure in land survey, equal to 66 feet (20 M) (80 chains equal 1 mile). commonly used to report fire perimeters and other fireline distances. popular in fire management because of its convenience in calculating acreage (example: 10 square chains equal one acre)

fire burns faster

uphill, convection and radiation help fuel catch more easily; concern of burning material rolling downhill

saddle

wind blowing through a saddle or pass in a mountain range can increase in speed as it passes through the constricted area and spreads out on the downwind side with possible eddy action.

south and southwest slopes

worst for fire are normally exposed to sunlight and generally have: -lighter and sparser fuels -higher temperatures -lower humidity -lower fuel moisture

rear of a fire

• that portion of a fire spreading directly into the wind or down slope • that portion of a fire edge opposite the head • slowest spreading portion of a fire edge. Also called heel of a fire