Thought #38
September 2009
Author: Bill Thurston
Forest Fires in the United States
More than 100,000 forest fires clear 4 million to 5 million acres of land in the
United States every year.
Forest Fire Management
Forest Fire Management falls under the jurisdiction of these agencies:
The
U.S. Forest Service
which manages 191 million acres of national forests and grasslands.
The
National Park Service
which administers 80 million acres of national parks, monuments, historic sites,
natural areas, and other federal lands.
The
Bureau of Land Management
which manages 264 million acres of public lands, provides fire protection for
388 million acres.
The
U.S. Fish and Wildlife Service
which manages more than 92 million acres of national wildlife refuges and
wetland areas.
The
Bureau of Indian Affairs
which provides forest fire protection for 60 million acres of Indian
reservations and other trust lands.
Who are the American Fire Fighters?
America's firefighters have earned a reputation for being among the best in the
world. Their jobs are divided into these crews:
Fire Managers
When a forest fire starts, fire managers analyze the situation carefully to
determine the best course of action. Once fire managers have weighed these
elements and developed a suppression strategy, they decide what kind of
firefighters and equipment they will need to implement it.
These crews, usually consisting of 20 men and women, serve as the infantry of
forest fire forces. Their main responsibility is to construct a fireline or a
strip of land cleared of flammable materials around forest fires to contain
them.
These highly skilled firefighters specially trained in suppression tactics, are
usually used to attack forest
fires when they first start, and to suppress big fires in the most critical and
high risk areas.
Helitack crews are specially trained in the use of helicopters during fire
suppression. Some of the crew are trained to rappel from the helicopter to reach
fire in remote locations quickly. Because they can be rapidly deployed, they are
often the first to respond to a forest fire.
These airborne firefighters parachute from planes to attack forest fires in
remote and inaccessible areas when the fire first begins. They are often
supported by airplanes dropping personal gear, food, water, and specialized
equipment to help suppress fires.
Engine crews, which range in size from 3 to 10 firefighters, use 250 to 750
gallons of water and several hundred feet of hose to directly attack forest
fires. Some
engines carry special equipment to spray foam and chemicals on
vegetation, homes, and other structures to help them resist fire.
Incident Management Teams
These teams consist of fire experts whose primary responsibility is to develop
and implement strategies to suppress forest fires. Members of the team are in
charge of providing the food, equipment, transportation, and other goods and
services that firefighters need.
Cooperators outside the Forest Service
Crews such as aviation and firefighting contractors, and our very important
Federal, State, rural and
volunteer fire department partners.
How do the fire fighters fight the fire?
Some of the equipment used in fire suppression today has changed over the years,
while others have not. High tech equipment and new computer technologies allow
fire teams to have better and quicker information on fire mapping, satellite
imagery, accurate weather forecasts, and fire behavior modeling. Improvements in
aircraft systems for cargo, fire-retardant chemicals, water delivery systems,
and firefighter clothing have likewise evolved with the safety of the
firefighter and the public in mind. However, the main tool is still the
firefighter with hand tools such as pulaskis, shovels, and adze hoes.
Bulldozers and Tractor Plows
Tracked vehicles with plows for clearing vegetation and mechanized equipment can
build firelines or firebreak faster and more efficiently than human firefighters
in terrain that allows equipment use. Some vehicles also carry water to douse
forest fires and equipment to burn out.
Air Tankers
These large planes, fitted with tanks, provide direct support to firefighters on
the ground by dropping up to several thousand gallons of water or chemical
retardant
ahead of an advancing forest fire. As the fire hits the wet area or
retardant, it goes out. Even the Air National Guard helps out with the
Modular Airborne Fire Fighting Systems.
Helicopters fitted with fixed tanks or suspended buckets that range in size from
100 to 2,000 gallons support firefighters on the ground by dropping water, foam,
or retardant on or near the flaming trees, brush, and structures to cool hot
spots and prevent a fire from spreading and give firefighters time to contain
the fire.
Bambi Bucket
A bambi bucket is a collapsible bucket slung below a helicopter, used to dip
water from a variety of sources for fire suppression.
Pulaski
A combination chopping and trenching tool, a Pulaski combines a single-bitted
axe blade with a narrow adze like trenching blade fitted to a straight handle.
Useful for grubbing or trenching in duff and matted roots, it is also
well-balanced for chopping.
Fire Resistant Pants/Shirt
All forest firefighters wear flame resistant clothing made of a special high
strengthen, synthetic material known as Nomex.
Drip Torch
This device for dripping a stream of flaming liquid is used to facilitate rapid
ignition during burn out operations
on a forest fire.
Fire Shelter
An aluminized tent offering protection by means of reflecting radiant heat and
providing a volume of breathable air if the firefighter gets trapped by the
fire.
Fire Line
A linear fire barrier that is scraped or dug in mineral soil to prevent or deter
the advancement of a forest fire.
There are three conditions that need to be present in order for a forest fire to
burn, which firefighters refer to as the fire triangle: fuel, oxygen, and a heat
source. Fuel is any flammable material surrounding a fire, including trees,
grasses, brush, and manmade structures. The greater an area's fuel load, the
more intense the fire. Air supplies the oxygen a fire needs to burn. Heat
sources help spark the forest fire and bring fuel to temperatures hot enough to
ignite. Lightning, burning campfires or cigarettes, hot winds, and even the sun
can all provide sufficient heat to spark a forest fire.
Firefighters fight forest fires by depriving them of one or more of the fire
triangle fundamentals. Traditional methods include water dousing and spraying
fire retardants to extinguish existing fires. Clearing vegetation to create
firebreaks starves a fire of fuel and can help slow or contain it. Firefighters
also fight forest fires by deliberately starting fires in a process called
controlled burning. These prescribed fires remove undergrowth, brush, and ground
litter from a forest, depriving a forest fire of fuel.
The three primary classes of forest fires are surface, crown, and ground.
Surface fires
typically burn rapidly at a low intensity and consume light fuels while
presenting little danger to mature trees and root systems.
Crown fires
generally result from ground fires and occur in the upper sections of
trees, which can cause embers and
branches to fall and spread the fire.
Ground fires
are the most infrequent type of fire and are very intense blazes that destroy
all vegetation and organic manner, leaving only bare earth. These largest fires
actually create their own winds and weather, increasing the flow of oxygen and
feeding the fire.
The Forest Fire Burning Process
We can divide the stages of a forest fire into four phases.
1. Pre-ignition Phase
In this phase, the fuels (trees, brush, structures, etc.) ahead of the fire are
heated. Flammable materials move to the surface of the fuel and are released
into the surrounding air. Initially, these materials contain large amounts of
water vapor and don't ignite. As
temperatures increase, the fuel begins to decompose and release a stream of
combustible gases and vapors. Because these gases and vapors are hot they rise,
mix with the oxygen in the air, form combustible mixtures, and ignite usually
between 570 degrees Fahrenheit and 1110 degrees Fahrenheit producing the Flaming
Phase. Above 518 degrees Fahrenheit, the
fuel flames up even without a spark.
2. Flaming Phase
In this phase, the temperature rises rapidly. The heat creates for flammable
fuel gases which makes it even hotter.
Temperatures in this phase range between about 570 degrees F and 2550
degrees F. As the fuel is burnt the
temperature drops. The gases and soot in the air
no longer burn and become smoke that accompanies all forest fires. During
this phase, a sufficient number of sooty particles are generated to color the
visible smoke plume from black to gray.
3. Smoldering Phase
In this phase, the overall reaction rate of the fire has diminished to a point
where the temperature and concentration of combustible gases and vapors above
the fuel cannot sustain a persistent flame envelope. Consequently, the vapors
condense and are released as visible smoke to the atmosphere.
Smoldering often occurs after the flame front moves through a fuel bed in a
spreading fire The heat
release rate from smoldering fires is usually not sufficient to lift the smoke
into a well defined convective column. As a result, the smoke stays near the
ground in high concentrations. The smoke evolved during this phase is virtually
soot free and consists of sub-micron tar droplets. When the evolution
vapors ceases, the fuel particle is reduced to a black char and the final
phase of combustion can begin.
4. Glowing Phase
In this final phase of combustion, all the volatile components of the fuel have
been released and oxygen can now migrate to the fuel surface resulting in solid
or surface oxidation with its characteristic yellow glow.
Visible smoke is not present during this final phase
This phase continues, as long as temperatures remain high
enough, until only a small amount of noncombustible minerals remain as gray ash.
In a forest fire, the four phases just described are difficult to discern
because they occur both sequentially and simultaneously.
Forest fires move in two basic directions
Heading Fires.
A heading fire moves with the wind. The flame front moves rapidly from fuel
element to fuel element. Under these conditions most fuels are not consumed
completely before the main combustion zone moves ahead. A rather large zone of
smoldering fuel is left behind when fuel was substantial.
Backing Fires.
A backing fire moves into the wind. The advance of the flaming zone is not
nearly as rapid as in the
heading fire. Since the flames do not move as rapidly, more of the individual
fuel elements are consumed in the flaming zone. Thus, the smoldering time for
the fuels is reduced and total combustion efficiency of the fire is increased.
http://www.srs.fs.usda.gov/pubs/ja/uncaptured/ja_mcmahon014.pdf
Final Thought
Do you know how to act around a forest fire? Most of us are familiar with fires
of some kind. Maybe a camp fire or a fire pit in the back yard or maybe a
burning structure. To be safe, you just stand back from the fire so the flames
don't get you.
A forest fire is much different. First of all, it can be moving up to 14 miles
per hour. You can't outrun a forest fire. Second, the fire front moves at
different speeds at different places. This can create areas surrounded by fire.
Some of these areas in big forest fires came be large areas. You can think you
are watching a fire to the north and then realize you are surrounded. You can't
walk or drive down a road through the fireline. Remember it's temperature is 500
to 2550 degree Fahrenheit. And finally, a forest fire consumes massive amounts
of oxygen. You don't want to compete with a forest fire for oxygen which you
need to live.
Don't mess with forest fires.
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