Intro to Wildland Fire Behavior S-190

Under normal conditions, a north facing aspect will have more fire activity than a south facing aspect. T/F

False (less)

Ridges

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

Creeping Fire

Fire burning with a low flame and spreading slowly.

Elevation plays a large role in determining the conditions and amount of ---.

Fuel

The fire triangle consists of oxygen, heat and ---.

Fuel

Fire Triangle

Fuel, air/oxygen, heat

A fire on ground level is primarily influenced by what 2 things?

Fuels and wind

Conduction

Heat is conducted from one fuel particle to another in the same way, through direct contact. Wood is a poor conductor (heat doesn't travel through it easily). Least important of the 3 heat transfer method to fire behavior.

Radiation

Heat transfer method that can dry surrounding fuels and sometimes ignite them.

Why do fuels at lower elevations dry out earlier in the year than those at higher elevations?

Higher temperatures

What is a concern with fires on steep slopes?

Possibility of burning material rolling down the hill and igniting fuel below the main fire

Wide Canyons

Prevailing wind direction can be altered by the direction of the canyon. Cross-canyon spotting of fires is not common except in high winds. Strong differences in fire behavior will occur on north and south aspects.

How is heat transferred? (3)

Radiation, convection and conduction

What are the 3 methods of heat transfer?

Radiation, convection and conduction

Natural Barriers

Rivers, lakes, rock, slides

Man-Made Barriers

Roads, highways, reservoirs, fireline constructed by fire resources

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.

Topography

The configuration of the earth's surface including its relief and the position of its natural and man-made features.

It is much easier to predict the influences which --- will have on a wildfire than the influences of fuel and weather.

Topography

Pockets of a Fire

Unburned indentations in the fire edge formed by fingers or slowly burning areas.

Fires burn more rapidly ---.

Uphill

A fire that starts near the bottom of the slope during normal daytime wind conditions will normally spread --- and has more area to spread upslope than a fire that starts near the top of the slope.

Faster

The steeper the slope, the --- the fire burns. Why?

Faster, because the fuels above the fire are brought into closer contact with the upward moving flames.

Smoldering

Fire burning without flame and barely spreading.

Spot Fire

Fire ignited outside the perimeter of the main fire by a firebrand.

Narrow Canyons

Fire in a steep narrow canyon can easily spread to fuels on the opposite side by radiation and spotting. Wind eddies and strong upslope air movement may be expected at sharp bends in the canyon.

Convection

Smoke column above a fire that occurs when lighter warm air moves upward and the hot gases and embers which compose the column can dry and ignite other fuels.

Fire Perimeter

The entire outer edge or boundary of a fire.

Barriers

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

Flare Up

Any sudden acceleration in the rate of spread or intensification of the fire. Unlike blowup, a flareup is of relatively short duration and does not change existing control plans.

Island

Area of unburned fuel inside the fire perimeter.

Spotting

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.

Running Fire

Behavior of a fire spreading rapidly with a well defined head.

What helps the fuel catch fire more easily? (2)

Convection and radiant heat

--- affects fire behavior in several other ways like the amount of precipitation received, wind exposure, and its relationship to the surrounding terrain.

Elevation

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.

In --- there may be no fuel.

Extremely high elevations

How can heat be supplied to a fuel to start a fire? (3)

Matches, lightning and cigarettes

Fuels with a high --- content do not burn as well as others in the same area.

Moisture

South and Southwest Slopes

More exposed to sunlight, lighter/sparser fuels, higher temperatures, lower humidity and lower fuel moisture. These slopes are the most critical in terms of start and spread of wildland fires.

North Facing Slopes

More shade, heavier fuels, lower temperatures, higher humidity and higher fuel moistures. These slopes will have less fire activity than the others.

Should you fight fire without an anchor point?

No, an anchor point minimizes the chance of being flanked by the fire while the line is being constructed.

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 ft in diameter. Large fire whirls have the intensity of a small tornado.

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.

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 a 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 in in diameter). Light fuels typically have a shallow one , whereas heavy fuels have a deeper one.

Slope

The amount or degree of incline of a hillside.

Elevation

The height of the terrain above mean sea level, usually expressed in feet. (ASL = Above Sea Level)

Fingers of a Fire

The long narrow extensions of a fire projecting from the main body.

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's roughly parallel to the main direction of spread.

What is a major factor in the resulting fire behavior?

The position of the fire in relation to the topography

Point of Origin

The precise location where a competent ignition source came into contact with the material first ignited and sustained combustion occurred.

Head of a Fire

The side of the fire having the fastest rate of spread.

Contained

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.

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.

Certain topographic features can influence --- and --- for small areas, independent of general weather conditions for an area.

Wind speed and direction

Crown Fire

A fire that advances from top to top of the trees of 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.

Box Canyons

Air will be drawn in from the canyon bottom creating very strong upslope drafts. These drafts create rapid fire spread up the canyon (chimney effect). This affect can result in extreme fire behavior and can be very dangerous.

Anchor Point

An advantageous location, usually a barrier to fire spread, from which to start constructing a fireline. It's used to minimize the chance of being flanked by the fire while the line is being constructed.

Control Line

An inclusive term for all constructed or natural barriers and treated fire edges used to contain a fire.

Torching

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

When is a fire 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.

Aspect

The direction a slope is facing (its exposure in relation of the sun). The --- of a slope determines the amount, condition and type of fuels present.

What can 'shape of country' (terrain) influence?

The direction of fire spread, rate of spread and the intensity.

Chain

Unit of measure in land survey, equal to 66 ft (20 m) (80 of these = 1 mile). Commonly used to report fire perimeters and other fireline distances. Popular in fire management because of its convenience in calculating acreage (ex 10 square of these = 1 acre).