S-190: Module 2 - Principles of Wildland fire Behavior

When air holds the maximum amount of moisture, the air is saturated, and its RH is, (Blank), percent.

100 percent

Most fuels must reach between, (blank), &, (blank) degrees, in order to ignite.

400 to 700 degrees Fahrenheit

What is a "chute"?

A chute is a steep v-shaped drainage on a slope which can easily channel smoke and fire upward at a rapid rate.

What is a "saddle"?

A saddle is a common name for a depression between two adjacent hilltops.

(Blank), fuels burn rapidly once they ignite because air circulates easily between these fuels and the ground.

Arial fuels

A slopes, (BLANK), is the compass direction the slope faces.

Aspect

The, (blank), of a slope determines the effect of the sun's heat on the slope's plants & trees, air temperature, & moisture retention of the soil.

Aspect

What is "atmospheric stability"?

Atmospheric stability is the degree that vertical motion is the atmosphere is enhanced or suppressed.

What are the three different types of canyons?

1. Box canyons 2. Narrow canyons, & 3. Wide canyons

What are the three types of clouds that you should be on the lookout for?

1. Cumulus 2. Cumulonimbus, & 3. Stratus cloud sheets

What are the 4 elements of Weather?

1. Temperature 2. RH 3. Precipitation, & 4. Wind

(Blank), affects the amount of moisture air can hold.

Air temperature.

Local microclimates can, (blank), fire activity.

Alter

Fuel moisture is affected by the, (blank), & the, (blank), or percipitation

Amount & Duration

What is an "inversion layer"?

An inversion layer is when the temperature actually increases with height. In such situations, the air is said to be stable as along as the inversion is present.

What is a "barrier" defined as?

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

Why is the rate of spread (ROS) increased for upslope fires?

Because: 1. The flames are closer to fuel sources. 2. Wind currents typically move uphill during the day, pushing heat to new fuel sources. 3. Upslope fires create a draft, increasing the ROS.

(Blank), kits include a sling psychrometer that measures local temperature & humidity.

Belt Weather Kits

Upslope fires can cause, (blank), to roll downhill.

Burning Debris

(Blank), air holds less moisture than hot air.

Cold Air

What is a Wide Canyon's specific effect on fire?

Cross-canyon spotting of fires is not common except in high winds.

(Blank), clouds, often called thunderheads often indicate strong, gust winds that shift erratically as a storm passes.

Cumulonimbus Clouds

(Blank), clouds are generally easy to spot as they are slightly "fluffy" and have rounded tops with a flat base. These clouds have vertical air currents indicating unstable conditions with possibly gust or strong winds.

Cumulus Clouds

What are examples of slash and blow-down fuels?

Dead fall, logging residuals.

Subsurface fuels, (blank) burn rapidly.

Don't

What are two things that effect fuel types?

Elevation and moisture content

What are medium fuels?

Examples of medium fuels include shrubs or brush up to 6 feet in height & the grass under-story. Medium fuels generally produce a Medium ROS.

In the absence of winds, fire usually moves, (blank), uphill than downhill.

Faster. So the steeper the slope, the faster a fire moves.

In general, (blank), fuels have a higher surface area to volume ratio then, (blank), fuels.

Fine fuels; Heavy fuels

What is a Narrow Canyon's specific effect on fire?

Fire can easily spread fuels on the opposite side by radiation and spotting.

When you have a fire at the top of a slope, building a, (blank), just beyond a ridge will help you contain the advancing fire.

Fireline

Fuel, (blank), is a characteristic used to describe the horizontal & vertical spacing of fuels is a given area.

Fuel continuity. Fuel continuity influences the spread of fire.

(Blank), refers to the amount of both live & dead fuel in a specific area.

Fuel load (sometimes called fuel volume)

Fuel, (blank), is the amount of water in a fuel, expressed as a percentage of the total oven-dry weight of that fuel.

Fuel moisture

Fuel, (Blank), &, (Blank), affect the rate of heat transfer and the change in moisture content.

Fuel size & shape

(Blank), winds are the result from air being forced over mountain ridges by convection or high barometric pressure.

Gravity Winds

Fuel size affects the rate of, (blank), and the change in, (blank), content.

Heat Transfer; & Moisture Content

Air cools as it rises and expands and, (blank), as it descends and compresses.

Heats

What are heavy fuels?

Heavy fuels consist of heavy continuous shrubs or brush more than 6 feet in height & timber slash. Combustion of these fuels includes high--intensity burning but generally a low ROS.

The, (blank), of cumulus clouds indicate the depth and intensity of the instability.

Height

The majority of large fire outbreaks occur when air temperature is, (blank), and the RH is, (blank).

High; Low

Under an inversion, fuel moisture content is usually, (blank), decreasing ROS & fire intensity.

Higher

With all other factors affecting fire behavior being equal, areas of, (blank), fuel loading will generate more heat than those with, (blank), fuel loads.

Higher, Lesser

More moisture in the air reduces the, (blank), point of fuels.

Ignition Point

As air drops in elevation the atmospheric pressure, (blank).

Increases. This causes the air to compress and heat. The resulting winds can create poor conditions for wildland fire control.

Local topography effects a fire's, (blank), & (blank).

Intensity, and, Rate/Direction of Spread.

Temperature and Relative Humidity have a, (blank) relationship.

Inverse relationship.

Wind channeling is, (blank).

Is a direct result of natural features like chutes & saddles.

What is "Equilibrium moisture content"?

It refers to the time it takes for the moisture in fuels to equalize with the moisture in the surrounding air.

Inversions can often be spotted because you see a, (blank), of clouds or smoke hanging over a surface.

Layer

What are "light fuels"?

Light Fuels (also called fine or flashy fuels), are surface fuels, such as short grasses & light shrubs or brush which burn rapidly & with high intensity. Light fuels take on & give up moisture faster than heavier fuels. Generally, light fuels produce a relatively High ROS.

(Blank), fuels take on and lose moisture faster than, (blank), fuels.

Light; Heavy

What are some examples of man-made fuel sources?

Log decks at saw mills, dump sites, & above-ground oil and natural gas pipelines.

Fires generally burn at, (blank), intensity and spreads slowly in highly compact fuels.

Low

Fire in highly compact fuels generally burn with, (blank), intensity.

Low Intensity

Generally, (blank), humidity increases fire activity, creates a greater fire intensity, higher rate of spread, & more spot fires.

Low humidity

What are examples of shrub fuels?

Mesquite, chaparrel, & Alaska black spruce

Cool air can help you control wildfires by increasing the level of, (blank), in the fuels.

Moisture

Relative Humidity can add or remove, (blank), to fuels.

Moisture

A, (blank), facing slope tends to have heavier fuels, lower temperatures, higher humidity, & higher fuel moisture, than a, (blank), facing slope.

North, South

What are examples of timber fuels?

Oaks, hickory, cypress, & cedar.

(Blank), or, (blank), plants, usually have a lower moisture content than young or live plants.

Old or dead

Wildland fires tend to burn much faster upslope than on level ground because of, (BLANK).

Preheated fuels

Solar, (blank), heating can influence fire behavior by influencing fuel moisture and ignition points.

Radiant Heating

When fuels are separated by natural or man-made barriers, (blank), may not be sufficient to preheat or ignite the surrounding fuels.

Radiant heat

Moisture in the air is known as, (Blank).

Relative Humidity

When the, (blank), is low (less than 30 percent), air absorbs moisture from fuels, dehydrates them, and makes them more susceptible to ignition.

Relative Humidity

Slope is measure in, (blank over blank), which is expressed as a percentage.

Rise over Run Example: A rise of 25 feet divided by a horizontal distance of 100 feet & then multiplied by 100 represents a 25 percent slope.

What are some natural barriers?

Rivers, lakes, burned areas, swamps, & rock outcroppings.

What are some man-made barriers?

Roads, highways, reservoirs, & firelines constructed by fire resources.

Fires starting near the base of box canyons & narrow canyons may react similar to, (blank).

Similar to a fire in a wood burning stove or fireplace. Air will be drawn in from the canyon bottom creating very strong upslope drafts.These upslope drafts create what is called the "chimney effect".

(Blank), is the primary culprit for fuel, ground, & air temperature,

Solar radiation

In the Northern Hemisphere, the slopes facing, (blank), receive direct sun rays & become hotter than the slopes facing any other direction.

South

Steady winds or smoke rising up and spreading out in a horizontal fashion indicate, (blank), air.

Stable

(Blank), clouds indicate stable layers in the atmosphere with little or no winds.

Stratus Clouds

Once ignited, (blank), fuels are often difficult to find and extinguish.

Subsurface fuels

(Blank), is variable due to the time of day, the weather, the seasons, latitude, elevation, topography, & the type of surface it's near.

Temperature

Measurements of, (blank), &, (blank), can indicate the strength of a night inversion.

Temperature & Humidity

Atmospheric stability can be determined by measuring the rate of, (blank), change with differences in elevation.

Temperature change

In the absence of a visible smoke or cloud layer, the top of the inversion can be found by measuring, (blank), at various points up and down the slope.

Temperatures

What is a Box Canyon's specific effect on fire?

The creation of strong upslope drafts results in extreme fire behavior.

What are uniform or continuous fuels?

They are fuels that are close together & spread evenly over an area.

What do warm & hot winds do?

They usually accelerate the loss of moisture by lowering relative humidity and increasing evaporation.

Night inversions are not only affected by the cool air moving in during nighttime hours, but also by:

Topography, Temperature, & Humidity.

What are the three "fire environment components"?

Topography, fuel, & weather.

Smoke rises more in a column in, (blank), conditions.

Unstable

(Blank), is the most variable of the three fire environment components.

Weather

What are examples of grass fuels?

Wild oats, & tundra species. Note: Grasses burn the hottest and fastest of all the fuel types.

When fuels are close together, a fire spreads, (blank), because of radiant heat transfer and produces a relatively uniform and predictable ROS.

faster

The, (blank), the distance between aerial fuels, the slower they ignite.

further

There are typically less fuel loads at, (blank), elevations.

higher elevations

Because of high temperatures, fuels as, (blank), elevations, dry out earlier in the year than those at, (blank), elevations.

lower elevations, higher elevations

What is one fuel that you might find no matter where you're fighting fires?

man-made structures

Stability is directly related to the, (blank), distribution of the atmosphere.

temperature distribution

unstable air encourages the, (blank), movement of air and tends to increase fire activity.

vertical movement

What are 7 fuel characteristics that fire behavior is dependent on?

1. Fuel Loads 2. Size & shape 3. Continuity 4. Vertical arrangement 5. Moisture 6. Temperature, & 7. Compaction.

What are three indicators when an inversion breaks?

1. Increase in temperature 2. Decrease in RH; & 3. Increase or shift in wind

What are 3 types of inversion?

1. Night inversions 2. Subsidence inversions; & 3. Marine inversions

Why are "chutes" & "saddles" so dangerous?

1. They drastically accelerate fires. 2. They alter the flow of winds causing erratic fire behavior. 3. They change the rate and direction of spread by acting like chimneys & literally propel the fire up as if through a stove pipe.

Moisture in live fuels depends primarily on the moisture in the soil, whereas the moisture in dead fuels depends on, (blank), (blank), & (blank).

Atmospheric temperature, humidity, & solar radiation.