Topography & Fuels : Wildland Firefighting

_________ is the direction a slope is facing.

Aspect

_______ refers to the spacing between fuel particles. If the fuels are very compact, there is less surface area exposed to the flames and the oxygen necessary to support combustion. You can expect a slower rate of spread. Fuels that are looser in their arrangement are drier, easier to ignite, and burn with a higher rate of spread

Compactness

_________ heat travels by contact through one object to another, and the material directly determines how well the heat will be insulated or conducted.

Conductive

Don't ever underestimate a fire in light fuels. It can ignite easily, move extremely fast, and burn with great intensity. A very high percentage of fire fatalities are the result of underestimating fire in light fuels. Light fuels are also referred to as "_____ fuels" or "______ fuels."

Fine, flashy

_______ heat moves as a heated air mass.

Convective

_________ fuels are those that will allow a surface fire to "climb" or move into the crowns of trees.

Ladder

______ ern Aspect - On slopes facing _____ you normally find heavier fuels with high moisture content. These sites also have the lowest average temperatures, lowest rate of spread, latest curing dates, and last areas of snow melt. _____ ern aspects usually have heavier fuels.

North

______ is removed by covering with dirt, retardant or foam. _____ is removed by cooling with water, foam, retardant or dirt. ______ is removed by cutting a fireline between the fuel that is burning and unburned fuel

Oxygen, Heat, Fuel

________ and _________ aspects are the most vulnerable to fire. This is due to the fact that the fuels are usually lighter (easier to ignite), flashy (contributing to a faster burn rate), and warmer (again, easier to ignite). Winds from the southwest are usually hot and dry, with lower relative humidities. These slopes are the warmest during the primary burning hours.

South, southwest

__________ fuels : Grass, forest litter, and brush up to about six feet in height are considered surface fuels. Surface fuels are where fires usually start. They are responsible for most fire spread and for "carrying fire" to the aerial fuels

Surface

_________ is the time it takes for the moisture content of fuels and the surrounding air to equalize.

Time lag

_______ is a steep, narrow chute canyon. This is one of the places where the combination of topography, weather and fuel can really create havoc.

chimney

The movement of heat transferring from burning to unburned fuels is what causes a fire to spread. Heat moves in three very different ways:

conduction, convection and radiation

Ridge lines provide a break between slopes. Considering terrain and weather conditions, ridge lines are often one of the best places to construct _______ in steep country.

fireline

Fuels can be divided into three groups or levels:

ground fuels, surface fuels, and aerial fuels

The __________ or distribution of fuels has an impact on how a fire spreads; the rate of spread; and whether the fire will move along the surface or through the crowns; or both. A fuel bed may either be continuous or patchy.

horizontal continuity

The vertical arrangement and continuity of the fuels are very important characteristics. They determine whether a fire will be able to move into the aerial fuels with ease or not. When there are fuels available for combustion throughout the vertical fuel bed, it is said that there are _______

ladder fuels

Fuels at ______ elevations dry out earlier in the year

lower

The three factors of fuel that affect the start and spread of wildland fire are: (3)

moisture content the size and shape of the fuel fuel loading.

The steeper the slope, the closer the fuels are to the flame (on the uphill side), and therefore, the faster the rate of spread and the _______ the flame front. Another problem associated with slope is that burning materials can roll downhill, thus contributing to the spread of the fire and endangering firefighters below.

narrower

Time lag is expressed as a rate (usually in hours) ■ Dead grass is considered a __ hour fuel. It takes about __ hour of exposure to change the dead fuel moisture in grass up or down ■ Logs are considered a ______ hour fuel. It takes about ____ hours of exposure to a (higher/lower) air moisture content to change the dead fuel moisture in logs

one one 1,000 1,000

The three elements of the fire triangle are: heat, fuel and oxygen. Fire is a chemical reaction called _____

rapid oxidation

Aerial fuels -Aerial fuels are those fuels that are ___ feet or more in height

six

Eastern aspect -The fuels on slopes facing east are usually ________, between those found on northern slopes and those found on southern slopes. Surface heating occurs earlier in the day because these slopes are the first to receive solar radiation. They are also the first to cool in the afternoon. Eastern slopes are normally on the ___, or facing away from the general wind direction.

transitional lee

The three principal environmental elements affecting wildland fires are: _______, ______, and _____

weather, topography and fuels.

Western aspect -The fuels on a west facing slope are transitional between the light fuels of southern slopes and the heavier fuels on northern slopes. Surface heating occurs in the afternoon and cooling begins later in the day. Westerly slopes are generally on the _____ side of a mountain

windward

There are several environmental factors that directly influence dead fuel moisture (4)

■ Relative humidity ■ Precipitation ■ Temperature ■ Wind

On slight slopes (to 5%) rate of spread is not increased; on moderate slopes (30%) rate of spread is increased by a factor of ____ ; on steep slopes (over ___ %) rate of spread will again double.

2, 55

Be on the alert for extreme burning conditions when fuel moistures reach these levels: - 1 hour fuels when the relative humidity is at ____ percent or below - 10 hour fuels are at ___ percent or below - 1000 hour fuels are at 13 percent or below

25 7

Three factors control how "well" grass will bum: ■ level of curing ■ amount of fuel ■ dead fuel moisture (grasses with fuel moistures above ___ % will not normally bum).

30

For every __ degree increase in temperature, the chemical reaction, that is fire, doubles in speed.

18

Fuel loading can be separated into four size classifications. The size of the fuel affects how it will respond to various forms of moisture (rain, dew and relative humidity). Size also impacts how quickly a dead fuel will lose moisture. The four size classifications are: ■ Grasses and litter - _______ inch in diameter ■ Twigs and small stems - ______ inch in diameter ■ Branches -_______ inches in diameter ■ Large stems and branches - ________ inches in diameter

0 to 1/4-inch 1/4-to 1 1 to 3 more than 3

Fuel loading is the amount (volume) of fuel available for a fire to burn. It is usually measured in tons per acre. Grassy fuels can range from _____ tons per acre; brush ranges from ______ tons per acre; slash can range from ______ tons per acre; and timber can range from ______ tons per acre.

1 to 5 20 to 40 30 to 200 100 to 600

Wildland fuel loads range from 1 to 3 tons per acre in ____ to over 200 tons per acre in _____

Grass, timber

__________ : Deep duff, roots, and rotten buried logs are considered ground fuels.

Ground Fuels

________ moves as "rays or waves". Radiation can pre-heat fuels or ignite unbumed fuels across a fireline or though a window

Radiation

South and west-facing slopes will normally bum hotter in the ______

afternoon

A ______ is a break in the fuel, or change in fuel type or condition (fuel moisture and/or density), that can slow or stop the spread of a wildland fire.

barrier