Aerial
Fuels�All live and dead vegetation located in the forest canopy or above the surface
fuels, including tree branches and crowns, snags, moss, and high brush.
Anchor
Point�An advantageous location or point, usually a barrier to fire spread, from which
to start constructing fireline. It is
used to minimize the chance of being flanked by the fire while
the line is being constructed.
Aspect�The
direction a slope is facing, i.e., its exposure in relation to the sun.
Available
Fuels�Those fuels which will burn during a passage of a flaming front under
specific burning and fuel conditions.
Backfiring�When
attack is indirect, intentionally setting fire to fuels inside the control line to
contain a fire. Backfiring is a tactic which makes possible a strategy of locating control lines at
places advantageous to the firefighter.
Barrier�Any
obstruction to the spread of fire; typically an area or strip devoid of flammable
fuel.
Blackline
Concept�Fuels that remain between the main fire and a fireline are burned out to
insure safety of control forces and security of control lines.
Burning
Out�When attack is direct, or parallel and the control line touches points of the fire.
Burning out is intentionally setting fire to fuels inside the control line to strengthen the line.
Burning out is almost always done by the crew boss as a part of line construction. The control
line is considered incomplete unless there is no fuel between the fire and the control line.
Burning
Period�That part of each 24-hour period when fires will spread most rapidly.
Typically,
this is from about mid-morning to about sundown, or late afternoon.
Canopy�The
stratum containing the crowns of the tallest vegetation present, (living or dead)
usually above 20 feet.
Celsius�(Centigrade)
A temperature scale with 0 °C as the melting point of ice and 100 °C as
the boiling point of water.
Chain�A
measuring instrument consisting of 100 wire links each 7.92 inches long, or 792
inches, or 66 feet.
Chinook,
or Chinook Wind�A foehn wind blowing down the eastern slopes of the
Cascades, Rocky Mountains, and over the adjacent plains in the United States and Canada. In
winter, this warm, dry wind causes snow to disappear with remarkable rapidity, and hence it
has been nicknamed the �snoweater.� In hot dry weather, Chinook winds can quickly extend
fire weather conditions to the �extreme.�
Cirrus�A
form of high cloud, composed of ice crystals, which often does not obscure the sun.
Climate�The
prevalent or characteristic meteorological conditions of any place or region, and
their extremes.
Cloud�A
visible cluster of minute water and/or ice particles in the atmosphere above the
earth�s surface.
Cold
Front�The leading edge of a relatively cold air mass that displaces warmer air. The
heavier cold air may cause some of the warm air to be lifted. If the lifted air contains enough
moisture, cloudiness, precipitation, and even thunderstorms may result. In case both air masses
are dry, there may be no cloud formation. Following a cold front passage (in the Northern
Hemisphere), often westerly or northwesterly winds of 10 to 20 mi/h, or more, continue for 12
to 24 hours.
Combustion�The
rapid oxidation of combustible materials that produces heat energy.
Combustion
Period�Total time required for a specified fuel component to be completely
burned.
Compactness�The
spacing between fuel particles. This can be especially important in the
surface layer of fuels, where the amount of air circulation affects rate of drying, rate of
combustion, etc.
Condensation�The
process by which a vapor becomes a liquid.
Conduction�The
transfer of heat between molecules in contact with one another.
Conflagration�A
raging destructive fire. Often used to denote such a fire with a moving front
as distinguished from a fire storm.
Continuity
of Fuels�The proximity of fuels to each other that governs the fire�s capability to
sustain itself. This applies to aerial fuels as well as surface fuels.
Contour
Map�A map having lines of equal elevation that represent the land surface.
Control
Line�An inclusive term for all constructed or natural fire barriers and treated fire
edges used to control a fire.
Control
Line Standards�The depth and width to which fuels must be treated or removed to
control any portion of a wildfire perimeter.
Convection�Vertical
air movements resulting in the transport of atmospheric properties. In
meteorology, atmospheric motions that are predominantly vertical; i.e., usually upward.
Convection
Column�The thermally-produced ascending column of gases, smoke, and debris
produced by a fire.
Convective
Winds�All winds�up, down, or horizontal�that have their principal origins in
local temperature differences.
Creeping�Fire
burning with a low flame and spreading slowly.
Crown
Closure�The spacing between tree crowns; usually expressed as the percent of area
covered by tree crowns in the forest canopy region as viewed from above.
Crown
Fire�A fire that advances from top-to-top of trees or shrubs. Crown fires are classed
as passive, active, or dependent to distinguish the degree of dependence on the surface fire.
Cumulonimbus�The
ultimate growth of a cumulus cloud into an anvil shape, with considerable
vertical growth, usually fibrous ice crystal tops, and probably accompanied by lightning, thunder,
hail, and strong winds.
Cumulus�A
principal, low cloud-type in the form of individual cauliflower-like cells of sharp
nonfiberous outline and less vertical development than cumulonimbus.
Dew
Point�The temperature to which air must be cooled, at constant pressure and moisture
content, in order for saturation to occur.
Direct
Attack�A method of suppression that treats the fire as a whole, or all its burning edge,
by wetting, cooling, smothering, or by chemically quenching it or mechanically separating it from
unburned fuel.
Diurnal�Daily,
especially pertaining to cyclic actions which are completed with 24 hours, and
which recur every 24 hours.
Dry
Bulb�A name given to an ordinary thermometer used to determine the temperature of the
air (to distinguish it from the wet bulb).
Dry
Lightning Storm�A lightning storm with negligible precipitation reaching the ground.
Duff�A
mat of partially decomposed organic matter immediately above the mineral soil,
consisting primarily of fallen foliage, herbaceous vegetation and decaying wood (twigs and small
limbs).
Eddy�A
whirl or circling current of air or water, different and differentiated from the general
flow.
Elevation�The
height of the terrain above mean sea level, usually expressed in feet.
Equilibrium
Moisture Content (EMC)�The level at which dead fuels neither gain nor lose
moisture with time, under specific constant temperature and humidity. The water vapor pressure
in the air is equal to the vapor pressure in the fuel. A fuel particle, at EMC, will have no net
exchange of moisture with its environment.
Equilibrium
Vapor Pressure�Occurs when there is no net gain or loss of water molecules
between the air and a solid or liquid.
Evaporation�The
transformation of a liquid to the gaseous state. Heat is lost by the liquid
during this process.
Extreme
Fire Behavior�Implies a level of wildfire behavior characteristics that ordinarily
precludes methods of direct control action. One or more of the following is usually involved:
high rates of spread; prolific crowning and/or spotting; presence of firewhirls; a strong
convection column. Predictability is difficult because such fires often exercise some degree of
influence on their environment, behaving erratically and sometimes dangerously.
Fahrenheit�A
temperature scale on which 32 °F denotes the temperature of melting ice, and
212 °F the temperature of boiling water, both under standard atmospheric pressure.
Fine
Fuels�Fuels that are less than 1/4 inch in diameter such as grass, leaves, draped pine
needles, fern, tree moss, and some kinds of slash which, when dry, ignite readily and are
consumed rapidly. (Also called Flash Fuels.)
Fire
Perimeter�The entire outer edge or boundary of a fire.
Fire
Storm�Violent convection caused by a large continuous area of intense fire. It�s often
characterized by destructively violent surface indrafts near and beyond the perimeter, and
sometimes by tornado-like whirls.
Firebrand�Any
source of heat, natural or manmade, capable of igniting wildland fuels.
Flaming or glowing fuel particles that can be carried naturally by wind, convection currents, or
by gravity into unburned fuels.
Firebreak�A
natural or constructed barrier used to stop or check fires that may occur, or to
provide a control line from which to work.
Firing
Out�Also called Firing. The act of setting fire to fuels between the control line and the
main fire in either a backfiring or burning out operation.
Fireline�The
part of a control line that is scraped or dug to mineral soil. Sometimes called
Firetrail.
Firewhirl�A
spinning, moving column of ascending air which carries aloft smoke, debris and
flames. These range from a foot or two in diameter to small tornadoes in size and intensity.
Flanking�Attacking
a fire by working along the flanks either simultaneously or successively
from a less active or anchor point and endeavoring to connect the two lines at the head.
Flanks
of a Fire�The parts of a fire�s perimeter that are roughly parallel to the main direction
of spread.
Flare-up�Any
sudden acceleration of fire spread or intensification of the fire. Unlike blowup,
a flare-up is of relatively short duration and does not radically change existing control plans.
Flash
Fuels�Fuels such as grass, leaves, draped pine needles, fern, tree moss, and some
kinds of slash that ignite readily and are consumed rapidly when dry. (Also called Fine Fuels.)
Flashover�Rapid
combustion and/or explosion of unburned gases trapped at some distance
from the main fire front. Usually occurs only in poorly ventilated topography. More commonly
associated with structural fire behavior.
Foehn
(Pronounced �fern�)�A type of general wind that occurs when stable, high pressure
air is forced across and then down the lee slopes of a mountain range. The descending air is
warmed and dried due to adiabatic compression. Locally called by various names such as Santa
Ana, Mono, Chinook, etc.
Fog�A
cloud at or near the earth�s surface. Fog consists of numerous droplets of water which
individually are so small that they cannot readily be distinguished by the naked eye.
Front�The
transition zone between two different air masses.
Frost�Crystals
of ice formed and deposited like dew, but at a temperature below freezing.
Fuelbreak�A
wide strip or block of land on which the native or preexisting vegetation has
been permanently modified so that fires burning into it can be more readily extinguished. It may
or may not have fire lines constructed in it prior to fire occurrence.
Fuel
Moisture Content�The amount of water in a fuel, expressed as a percentage of the
ovendry weight of that fuel.
General
Winds�Large scale winds caused by high- and low-pressure systems but generally
influenced and modified in the lower atmosphere by terrain.
Gradient
Wind�A wind that flows parallel to the isobars or contours and has a velocity such
that the pressure gradient, Coriolis, and centrifugal forces acting in the area are in balance. It
does not occur at the earth�s surface due to fractional influence, but occurs at a height of roughly
1,500 feet above mean terrain height. Nearly synonymous with �Free Air� winds.
Ground
Fire�All combustible materials lying beneath the ground surface including deep duff,
roots, rotten buried logs, peat and other woody fuels.
Gust�A
sudden, brief increase in the speed of the wind.
Head
of a Fire�The most rapidly spreading portion of a fire�s perimeter, usually to the
leeward or upslope.
Heavy
Fuels�Fuels of large diameter such as snags, logs, and large limb wood that ignite and
are consumed much more slowly than flash fuels. (Also Called Coarse Fuels.)
High�An
area of relatively high atmospheric pressure that has a more or less closed
circulation; an anticyclone. Winds around a high move clockwise in the Northern Hemisphere,
while spiraling out from the high toward lower pressure.
Horizontal
Continuity�The horizontal distribution of fuels at various levels or planes.
Hotspotting�Checking
the spread of fire at points of more rapid spread, or special threat. It
is usually the initial step in prompt control with emphasis on first priorities.
Humidity�The
measure of water vapor content in the air.
Ignition�The
initiation of combustion.
Indirect
Attack�A method of suppression in which the control line is mostly located along
natural firebreaks, favorable breaks in topography, or at considerable distance from the fire, and
all intervening fuel is backfired or burned out. The strip to be backfired is wider than in the
parallel method and usually allows a choice of the time when burnout or backfiring will be done.
Insolation�Solar
radiation received at the earth�s surface.
Instability�A
state of the atmosphere in which the vertical distribution of temperature is such
that an air particle, if given either an upward or downward impulse, will tend to move vertically
away with increasing speed from its original level. (Unstable air.)
Inversion�A
layer in the atmosphere where the temperature increases with altitude.
Ladder
Fuels�Fuels which provide vertical continuity between strata. Fire is able to carry
from surface fuels by convection into the crowns with relative ease.
Land
Breeze�A light nighttime breeze which originates over the relatively cool land surface
and flows out over the warmer coastal waters.
Lightning�A
sudden visible flash of energy and light caused by electrical discharges from
thunderstorms.
Litter�The
uppermost layer of loose debris composed of freshly fallen or slightly decomposed
organic materials such as dead sticks, branches, twigs, and leaves or needles.
Local
Winds�Small-scale convective winds of local origin caused by temperature differences.
Long-Range
Spotting�Large glowing firebrands are carried high into the convection column
and then fall out downwind beyond the main fire starting new fires. Such spotting can easily
occur 1/4 mile or more from the firebrands� source.
Low�An
area of relatively low atmospheric pressure in which winds tend to move in a
counterclockwise direction, spiraling in toward the low�s center.
Precipitation�The
collective name for moisture in either liquid or solid form large enough to
fall from the atmosphere and reach the earth�s surface.
Pressure
Gradient�The change in atmospheric pressure per unit of horizontal distance.
Psychrometer�An
instrument for measuring atmospheric temperature and humidity, consisting
of a dry-bulb thermometer and a wet-bulb thermometer (bulb covered with a muslin wick);
used in the calculation of dew point and relative humidity.
Rainfall�A
term sometimes synonymous with rain, but most frequently used in reference to
amounts of precipitation (including snow, hail, etc.).
Rain
Gage�An instrument for measuring precipitation.
Rate
of Spread�The relative activity of a fire in extending its horizontal dimensions. It is
expressed as rate of increase of the total perimeter of the fire; or as rate of forward-spread of
the fire front; or as rate of increase in area, depending on the intended use of the information.
Usually its (forward) rate of spread is expressed in chains or acres per hour.
Reburn�1.
Subsequent burning of an area in which fire has previously burned but has left
flammable fuel that ignites when burning conditions are more favorable. 2. An area that has
reburned.
Relative
Humidity�The ratio of the amount of moisture in the air to the amount which the air
could hold at the same temperature and pressure if it were saturated; usually expressed in
percent.
Resistance
to Control�The relative difficulty of constructing and holding a control line as
affected by resistance to line construction and fire behavior. (Also called Difficulty of Control.)
Ridge�An
elongated area of relatively high pressure extending from the center of a high-pressure region.
Roll
Cloud�A turbulent altocumulus-type cloud formation found in the lee of some large
mountain barriers. The air in the cloud rotates around an axis parallel to the range. Also
sometimes refers to part of the cloud base along the leading edge of a cumulonimbus cloud; it is
formed by rolling action in the wind shear region between cool downdrafts within the cloud and
warm updrafts outside the cloud. (Sometimes called Rotor Cloud.)
Running�Behavior
of a fire that is spreading rapidly, usually with a well-defined head.
Safety
Island�An area for escape in the event the line is outflanked or in case a spot fire
causes fuels outside the control line to render the line unsafe. In firing operations, crews
progress so as to maintain a safety island close at hand, allowing the fuels inside the control line
to be consumed before going ahead.
Saturated
Air�Air that contains the maximum amount of water vapor it can hold at a given
pressure and temperature (relative humidity of 100 percent).
Scratch
Line�An unfinished preliminary control line hastily established or constructed as an
emergency measure to check or slow the spread of a fire.
Sea
Breeze�A daytime breeze in which cooler, higher pressure air from over coastal waters
moves on shore to replace heated air rising off the warmer land mass.
Short-Range
Spotting�Firebrands, flaming sparks, or embers are carried by surface winds,
starting new fires beyond the zone of direct ignition by the main fire. The range of such spotting
is usually less than 1/4 mile.
Size
and Shape�Fuel characteristics affecting the fuel moisture timelag, the amount of heat
required for ignition and to sustain combustion, and the burnout time of fuels. The surface-area-to-volume
ratio is a representation of size and shape.
Slash�Debris
left after logging, pruning, thinning, or brush cutting; also debris resulting from
thinning, wind, or fire. It may include logs, chunks, bark, branches, stumps, and broken
understory trees or brush.
Slope
Winds�Small scale convective winds that occur due to local heating and cooling of a
natural incline of the ground.
Slope
Percent�The ratio between the amount of vertical rise of a slope and horizontal
distance as expressed in a percent. One hundred feet of rise to 100 feet of horizontal distance
equals 100 percent.
Smoldering�Behavior
of a fire burning without flame and barely spreading.
Snag�A
standing dead tree or part of a dead tree from which at least the leaves and smaller
branches have fallen. (Often called Stub, if less than about 20 feet tall.)
Spot
Fire�Fire set outside the perimeter of the main fire by flying (or rolling) sparks or
embers.
Spotting�Behavior
of a fire producing sparks or embers that are carried by convection
columns and/or the wind and which start new fires beyond the zone of direct ignition by the main
fire.
Stability�A
state of the atmosphere in which the vertical distribution of temperature is such
that an air particle will resist vertical displacement from its level. (Stable Air.)
State
of Weather�A brief description of current weather that expresses the amount of cloud
cover, kind of precipitation, and/or restrictions to visibility being observed at a weather
observation site.
Subsidence�An
extensive sinking motion of air in the atmosphere, most frequently occurring
in polar highs. The subsiding air is warmed by compression and becomes more stable. Of
particular importance due to the heating and drying of the air. It is often the cause of very rapid
drying of fuels in the smaller size classes.
Suppress
a Fire�To extinguish a fire or confine the area it burns within fixed boundaries.
Surface-Area-to-Volume
Ratio�The ratio of the surface area of a fuel to its volume, using
the same linear unit for measuring volume; the higher the ratio, the finer the particle.
Surface
Fire�A fire that burns surface litter, debris, and small vegetation.
Surface
Fuels�All materials lying on, or immediately above, the ground, including needles or
leaves, duff, grass, small dead wood, downed logs, stumps, large limbs, low brush and
reproduction.
Surface
Wind�The wind measured 20 feet above the average top of the vegetation. It is often
a combination of local and general winds.
Temperature�A
measure of the degree of hotness or coldness of a substance.
Temperature
Lapse Rate�The amount of temperature change with altitude change,
expressed as degrees Fahrenheit per 1,000 feet of rise or fall.
Thermal
Belt�An area of a mountainous slope that typically experiences the least variation in
diurnal temperatures, has the highest average temperatures, and thus, the lowest average relative
humidity.
Thermometer�An
instrument for measuring temperature; in meteorology, generally the
temperature of the air.
Thunder�The
sound emitted by rapidly expanding gases along the channel of a lightning
discharge.
Thunderstorm�A
storm invariably produced only by a cumulonimbus cloud, and always
accompanied by lightning and thunder; usually attended by strong wind gusts, heavy rain, and
sometimes hail. It is usually of short duration, seldom over 2 to 3 hours for any one storm.
Topography�The
configuration of the earth�s surface, including its relief and the position of its
natural and manmade features.
Torching�Fire
burning principally as a surface fire that intermittently ignites the crowns of trees
or shrubs as it advances.
Vertical
Arrangement�The relative heights of fuels above the ground and their vertical
continuity, which influences fire reaching various levels or strata. (Surface fuels vs. aerial fuels,
and their relationships to one another.)
Vertical
Development of Column�Depending on fire intensity and atmospheric conditions,
the smoke or convection column might rise a hundred feet or many thousands of feet. A low
intensity fire with a low smoke column might be termed �two-dimensional,� whereas a high
intensity fire with a well-developed convection column rising thousands of feet into the
atmosphere can be termed a �threedimensional� fire. (See Convection Column.)
Virga�Wisps
or streaks of water or ice particles falling out of a cloud but evaporating before
reaching the earth�s surface.
Visibility�The
greatest distance that prominent objects can be seen and identified by unaided,
normal eyes. (Usually expressed in miles, or fractions of a mile.)
Warm
Front�The discontinuity at the forward edge of an advancing current (or mass) of
relatively warm air which is displacing a retreating colder air mass.
Weather�The
short-term variations of the atmosphere in terms of temperature, pressure,
wind, moisture, cloudiness, precipitation, and visibility.
Wet
Bulb Temperature�The lowest temperature to which air can be cooled by evaporating
water into it at a constant pressure when the heat required for evaporation is supplied by the
cooling of the air. It is measured by the wet bulb thermometer, which usually employs a wetted
wicking on the bulb as a cooling (through evaporation) device.
Wet
Line�A fire control line, usually temporary, prepared by treating the fuels with water
and/or chemicals which will halt the spread of the fire.
Wildfire�1.
An unplanned wildland fire requiring suppression action, or other action according
to agency policy, as contrasted with a prescribed fire burning within prepared lines enclosing a
designated area, under prescribed conditions. 2. A free burning wildfire unaffected by fire
suppression measures.
Wildland
Fuels�Any organic material, living or dead, in the ground, on the ground, or in the
air, that will ignite and burn.
Wind�The
horizontal movement of air relative to the surface of the earth.
Wind-driven
Wildfire�A wildland fire that is controlled by a strong consistent wind.
Windspeed
Meter�A handheld device which indicates wind speed, usually in miles per hour.
(See Anemometer.)
