Wildland Fire Behavior and Topography

Questions and Answers

Topography can directly and indirectly affect fuels and their availability for combustion.

True

Of the three primary environmental factors that influence fire behavior, which is the least variable?

Topography

The least critical form of heat transfer that influences the rate of spread in a running wild land fire is:

Conduction

The point to which a combustible material must be heated to produce self-sustaining combustion is known as the:

Ignition temperature Signup and view all the answers

Fireline intensity is dependent upon:

Fuel moisture Signup and view all the answers

Two requirements for long range spotting are wind and a well developed convection column.

True Signup and view all the answers

A fire that advances through canopies of brush and trees is known as a:

Crown fire Signup and view all the answers

Fire is burning in litter on top of the ground, but occasionally carries into the crowns of individual trees, which produces burning embers that start new fires outside the fire perimeter.

Surface fire with torching and spotting Signup and view all the answers

What happens when a fire begins burning into the crowns and spreads through the canopy?

Ground fire with smoldering and flare ups Signup and view all the answers

Upward moving air contracts and warms.

False Signup and view all the answers

As air sinks, it:

Increases in pressure, warms and compresses Signup and view all the answers

Why do dry climates usually have lower nighttime temperatures than humid climates?

Because there is less water vapor in the air to absorb and reflect heat back to the surface at night Signup and view all the answers

On average the RH doubles with each 20F decrease of temperature, or halves with each 20F increase in temperature.

True Signup and view all the answers

The lowest RH occurs with the highest temperature.

True Signup and view all the answers

RH is usually lower on north aspects.

False Signup and view all the answers

Cloudiness has little effect on relative humidity and temperature.

False Signup and view all the answers

The type of vegetation has little effect on temperature and humidity.

False Signup and view all the answers

RH measures the amount of moisture in the air.

True Signup and view all the answers

Clouds form in layers.

Stable Signup and view all the answers

Gusty winds are categorized as:

Unstable Signup and view all the answers

Smoke column spreads out after limited rise.

Stable Signup and view all the answers

Clouds grow vertically.

Unstable Signup and view all the answers

Firebrands are lifted into the convection column.

Unstable Signup and view all the answers

Temperature decreases with an increase in elevation when an inversion is present.

False Signup and view all the answers

What is the general effect of stable air on wild land fires?

Fire activity decreases Signup and view all the answers

What conditions will occur under a surface inversion during the morning hours?

All of the above Signup and view all the answers

What are the different lighting processes that can lead to thunderstorm development?

Frontal, orographic, thermal, convergence Signup and view all the answers

Unstable air can often be found in low pressure systems and on the leading edge of cold fronts.

True Signup and view all the answers

Unstable air can be formed by either heating the air near the ground or by cooling the air aloft.

True Signup and view all the answers

Wind direction is:

The direction the wind is blowing from Signup and view all the answers

A wind is caused by:

The direction the wind is blowing from Signup and view all the answers

A slope wind is caused by:

Warm air rising and cold air settling Signup and view all the answers

Foehn winds can adversely affect wild land fires because they can produce:

Strong winds, warmer temperatures, and very low RH Signup and view all the answers

When stable air is forced over a mountain range, and then descends the leeward slopes as dry, warmed air, it is called:

A foehn wind Signup and view all the answers

Bends in canyons are likely places for wind eddies to form.

True Signup and view all the answers

Local winds are best defined as:

Small scale convective winds of local origin caused by differences in heating and cooling Signup and view all the answers

East, Mono, Santa Ana, and Chinook are all examples of:

Foehn winds Signup and view all the answers

Air flows clockwise around low pressure systems and counterclockwise around high pressure systems.

False Signup and view all the answers

Slope affects fuel availability to burn because:

Fuels are preheated upslope through radiation and convection. Rolling firebrands ignite new fuels below. Signup and view all the answers

Select the correct statement regarding the shape of the country and its effect on wild land fire behavior.

The shape of the country can influence the curing of fuels as well as the intensity and spread of wild land fires. Signup and view all the answers

Aspect affects fuels and their availability to burn because:

All of the above are correct Signup and view all the answers

Select the statement that best describes the effect of slope steepness on fuel availability.

A fire starting at the base of a slope has more fuel available for spread. Signup and view all the answers

A fuel model is defined as:

A set of tubers that define fuel input for use in the surface fire spread model. Signup and view all the answers

The 4 fuel groups as defined in the Fire Behavior Prediction System are:

Grass, shrub, timber litter, and logging slash. Signup and view all the answers

Available fuels are:

All dead and live fuels that will ignite and continue to burn. Signup and view all the answers

Fuel loading definition:

The oven dry weight of fuel in a given area, expressed in tons/acre or pounds/acre. Signup and view all the answers

Fuel moisture content definition:

The amount of water in a fuel expressed as a percent of the oven dry weight of that fuel. Signup and view all the answers

Fuel size and shape definition:

The surface-area-to-volume ratio. Signup and view all the answers

Fuel chemical content definition:

The presence of volatile substances in a fuel. Signup and view all the answers

Which of the following fuel characteristics affect all 6 wild land fire behavior concerns; i.e. ignition, spread, intensity, spotting, torching, and crowning?

Moisture content Signup and view all the answers

Which fuel has a higher surface-area-to-volume ratio?

Grass Signup and view all the answers

The 1 hour timelag fuel category is:

0.0 to 1/4 inch in diameter Signup and view all the answers

Fuel moisture timelag can best be described as:

The rate at which dead fuel gains or loses moisture. Signup and view all the answers

1 hour timelag fuel moisture is used in fire behavior calculations to determine:

Whether fine dead fuels are available for ignition and fire spread. Signup and view all the answers

The five stages of vegetative development for live fuel moisture are:

300%, 200%, 100%, 50%, less than 30% Signup and view all the answers

The following statement best describes timelag fuel categories:

1 hour timelag fuels react to changes in RH much faster than 100 hour fuels. Signup and view all the answers

Foehn winds always cause fuels to gain in moisture content.

False Signup and view all the answers

Dead grass reacts like a 1 hour timelag fuel.

True Signup and view all the answers

The fuel moisture at which fire will not spread is the:

Moisture of extinction Signup and view all the answers

Inputs used to determine fine dead fuel moisture content are:

Time of day, month of year, dry bulb temperature, RH, aspect, percent slope, shading of surface fuels. Signup and view all the answers

Select the fuel complex that would reach its moisture of extinction first during nighttime humidity recovery.

Cured cheatgrass Signup and view all the answers

If the wet bulb is not read at its lowest point, what will happen?

The calculated RH will be too high. Signup and view all the answers

What weather processes can and should be monitored visually?

All of the above Signup and view all the answers

When a cold front or thunderstorms are forecast in the vicinity of a fire, what is the most important information a security weather watch can provide?

Strong shifting winds Signup and view all the answers

The criteria for determining a Red Flag Warning is a combination of high to extreme fire danger and a critical fire weather pattern such as:

All of the above Signup and view all the answers

Spot weather forecasts are:

Forecasts that are issued to fit the time, topography, and weather of a specific location. Signup and view all the answers

Initiate action based on ____ fire behavior.

Current and expected Signup and view all the answers

Fire which can generally be attacked at the head or flanks by persons using hand tools have flame lengths that are:

Less than 4 feet Signup and view all the answers

Effective windspeed is the mid-flame windspeed increased for the effect of slope on fire spread.

True Signup and view all the answers

The surface fire characteristics chart relates:

Rate of spread and flame length. Signup and view all the answers

Regardless of fine dead fuel moisture percentage, rate of spread is determined by the live fuel moisture.

False Signup and view all the answers

En route to a fire you notice that smoke from a burning haystack rises straight up. What could this indicate on a wild land fire?

An unstable atmosphere may increase fire activity. Signup and view all the answers

A ground fire has burned under a thick stand of pine reproduction. What potential problems could occur?

A return possibly involving the canopies. Signup and view all the answers

You are on a fire in the coast range of Southern California. The fire is burning above you on the slope. At 1800, you experience a sudden calm in the sea breeze. What might you expect to occur next?

Wind may shift to downslope with possible foehn wind surfacing. Signup and view all the answers

The convection column from your fire has developed to several thousand feet as a result of intense burning. You notice the top of the column has been sheared off. What could happen next?

Expect moderate to long range spotting downwind. Strong winds aloft could surface on the fire. Signup and view all the answers

Wild land fire behavior in the third dimension:

All of the above Signup and view all the answers

4 factors that are responsible for the occurrence of fire behavior in the third dimension are:

Available fuels, wind, low atmospheric moisture, and instability. Signup and view all the answers

Three stages of crown fire development are:

Passive, active, and independent. Signup and view all the answers

Crown fire development depends on crown flammability along with adequate surface-to-crown and crown-to-crown heat transfer.

True Signup and view all the answers

The factors that contribute to the spotting problem can be classified into three general areas:

Firebrand source, transportation, and the receiving fuel. Signup and view all the answers

Probability of ignition is determined by:

Fuel shading, fine dead fuel moisture percent, and dry bulb temperature. Signup and view all the answers

Vortices are grouped as vertical or horizontal depending on their axis of rotation.

True Signup and view all the answers

When the wild land fire environment is dominated by a ______ fire, the convection column overpowers the wind field.

Plume-dominated Signup and view all the answers

Continuous fine fuels, heavy fuel loadings, ladder fuels, crown spacing, and special fuel situations are fuel characteristics that should NOT be monitored.

False Signup and view all the answers

Low RH and a high 1000 hour timelag fuel moisture are both critical fuel moisture indicators that should be monitored.

False Signup and view all the answers

Steep slopes, chutes, saddles, and narrow canyons are terrain indicators that should be monitored.

True Signup and view all the answers

Strong surface winds, lenticular clouds, high fast moving clouds, approaching cold front, cumulonimbus development, and sudden calm or battling winds are all indicators of wind that are not of great concern to wild land firefighters.

False Signup and view all the answers

Which of the following is an indicator of stable air?

Inversion Signup and view all the answers

Which is an indicator of possible fire behavior problems?

All of the above Signup and view all the answers

Study Notes

Topography and Fire Behavior

Topography directly and indirectly influences combustible fuels and their availability for combustion.
Among environmental factors affecting fire behavior, topography is the least variable.

Heat Transfer

The least critical heat transfer method influencing wildland fire spread is conduction.

Fire Characteristics

Ignition temperature is the heat required for self-sustaining combustion.
Fireline intensity depends on fuel size, moisture, temperature, and compactness/arrangement.

Spotting and Crown Fires

Long-range spotting requires wind and a developed convection column.
Crown fires advance through tree canopies, while surface fires may produce torching and spotting.

Air Movement

Upward moving air does not contract and warm; it expands and cools.
As air sinks, it warms through increased pressure and compression.

Relative Humidity (RH) Dynamics

In dry climates, lower nighttime temperatures result from reduced water vapor, which fails to retain heat.
RH generally doubles with a 20°F decrease in temperature and halves with a 20°F increase.
Lowest RH occurs at the highest temperatures.

Stability Indicators

Stable air manifests in layers with clouds, while unstable air is characterized by gusty winds and vertically growing clouds.

Fire Behavior and Atmospheric Conditions

Temperature generally decreases with elevation unless an inversion is present.
Under stable air, fire activity generally decreases, and pollutants can accumulate under inversions.
Unstable air often exists in low-pressure systems and can form through surface heating or upper air cooling.

Wind Effects

Winds are named based on their originating direction, influencing fire spread.
Foehn winds contribute to strong winds, warmer temperatures, and low humidity levels during wildland fires.

Fuel Characteristics

Slope affects fuel availability; fuels are preheated during upslope movement.
Aspect impacts moisture levels and vegetation types, influencing fire behavior.
Fuel moisture content and size directly affect ignition, spread, intensity, and other fire behavior dynamics.

Timelag Fuel Categories

Timelag categories (1-hour, 10-hour, etc.) denote the reaction time of dead fuels to moisture content changes.
Fine dead fuel moisture is critical in determining ignition availability and fire spread, particularly in grass fuels.

Vegetation Development

Vegetative stages are measured in percentages of moisture: 300%, 200%, 100%, 50%, and less than 30%.
Cured cheatgrass reaches moisture of extinction faster during nighttime humidity recovery.

Monitoring Fire Indicators

Key visual monitoring includes thunderstorm buildups, cloud types, and thermal air movement.
Red Flag Warnings indicate combinations of fire danger factors like dry lightning, low RH, and unstable air patterns.

Wildfire Management Insights

Effective firefighting involves recognizing fire behavior in three dimensions, including vertical movement and crowning phenomena.
Factors for spotting problems include firebrand generation and transportation.
Monitoring terrain and atmospheric conditions is crucial for effective fire response, with attention to features like steep slopes and wind patterns.

Fire Behavior Problems

Indicators of fire behavior issues encompass phenomena such as well-formed smoke columns, crowning trees, and frequent spot fires.
Continual observation of fuel hydration, meteorological conditions, and topography enhances firefighting efficacy.

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Description

Explore the critical factors influencing wildland fire behavior, including the role of topography, heat transfer methods, and fire characteristics. This quiz covers topics from spotting fires to air movement and relative humidity dynamics in the context of fire management.