section gives the principles of prescribed burning, the equipment
needed, and how burns are set up.
Those carrying out prescribed burns become intense weather
watchers. The weather is the most critical factor in the success
of any burn.
Although burns can be conducted at any time of year, in the
Midwest there are two main burn seasons, spring and fall.
However, what is spring in southern Illinois may still be
winter in the upper Midwest. A lot will depend upon the previous
winter, especially how much snow cover there had been. Also, the kinds of fuel
present in the burn unit are an important factor in determining
the best time to burn.
With fall burns snow melt is not an issue, although if the
burn is not done early enough in the season, it may be prevented
by an early snowfall. However, for savanna burns one has to
wait for the leaves to fall, and for the vegetation to senesce.
Spring burns may be delayed in a heavy snow year, but at least
all of the fuel has been well cured.
Weather conditions needed for the
Relative humidity and dew point are the
most important factors, since they will have a controlling
influence on fuel moisture. Even if the fuel was dry yesterday,
a strong dewfall on the morning of the burn may delay things.
Weather conditions that are best for savanna burns are often
different than for prairie burns. Whereas a wind speed of
5 mph and a relative humidity of 50% may be fine for a prairie
burn, the conditions for a savanna burn should include a stronger
wind speed and a lower relative humidity (for instance; 10-15
mph wind and 25-30% relative humidity). Oak leaves take longer
to dry out than vertically standing grass, and flame heights
are much lower, so the fire does not carry as well with lower
Wind direction is another important factor and the
required direction will depend upon the location of the burn
unit in relation to surrounding areas. Certain types of burn
units can only be burned when the wind is from particular
directions. Also, wind direction must be considered with different
slopes and aspects of the site. A wind shift during a burn
can have major effects, making it perhaps necessary to put
out a burn that is already in progress (often difficult to
accomplish). A north wind is generally associated with a cold
front and a south wind with a warm front.
The ideal wind is one that is steady from the same direction
throughout the duration of the burn. A very light wind, or
none at all, may make the burn more difficult to accomplish.
A steady 5 mph wind is preferable to no wind at all. For savanna
burns, with their low flame heights and thin fuels, the wind
should be at least 5 mph, preferably 8-10 mph, or on flat
topography up to 15 mph. A steady wind of 10mph is better
than a gusty wind of 5 mph.
Another consideration for wind direction is smoke management.
If the burn is in an urban or suburban area, a wind direction
must be selected that will blow the smoke away from the built-up
area. Also, the wind cannot be allowed to blow smoke across
a major highway.
Temperature is another important factor, because
hot fuels ignite better than cold ones. Also, temperature
affects relative humidity. A temperature of 75 degrees F may
be too hot for a prairie burn but could be just right for
a savanna burn. An ideal temperature for a spring savanna
burn is 70 F, but successful burns can be accomplished at
temperatures as low as 50 F when the R.H. is low and there
is a good strong wind from the right direction.
It is not just the weather on the day of the burn, but the
weather for the previous days, which may influence fuel moisture
content. Thus, if the fuel has been saturated with moisture
(from snow melt or rains), at least two days of warm, dry
air may be needed to bring the fuel to a burnable state.
The National Oceanographic and
Atmospheric Administration web site provides the most
detailed weather information. From the home page, one can
access various forecasts by keying in the state and the city
closest to where the burn is to take place. The page that
opens up offers a number of prediction tools, many of which
complement each other. The detailed weather analysis titled
“Forecast Discussion” is useful.
NOAA also operates a
weather radio system that provides round-the-clock reports
on the weather in various parts of the country. An interactive
map permits location of the transmitter closest to the burn
site. NOAA operates over 1000 transmitters so that detailed
weather reports for any burn area should be obtainable. A
radio capable of receiving these broadcasts should be carried
on the day of the burn.
Prescribed burning is defined as fire applied in a knowledgeable
manner to natural fuels on specific land areas under approved
conditions to accomplish predetermined, well-defined management
A prescribed burn is one that is under the complete control
of the burn crew. The fire is lighted where desired, burns
where and when intended, and is extinguished at the chosen
location. It is based on a written burn plan, called the prescription.
The prescription is
generally a multi-page document which has been carefully
reviewed and approved by the relevant agency, either governmental
or nongovernmental. Burns conducted by government agencies
such as the U.S. Forest Service, the Fish and Wildlife Service,
National Park Service, and by state departments of natural
resources are prescribed burns. All fire is potentially dangerous,
and those conducting prescribed burns have the responsibility
for insuring that the fire is under control at all times.
The Written Burn Plan
The prescribed burn
plan describes the objectives of the burn and the expected
results. The burn plan specifies, either in words or by a
map, the parcel of land to be burned, the landowner(s), and
owners of adjacent land not included in the burn. The history
of previous burns (if any) should be presented. Any considerations
of smoke management are identified. The burn plan specifies
the required governmental permits, and lists those who must
be notified on the day the burn is to take place. The locations
and characteristics of all fire breaks (fire control lines)
are given, as well as strategies for containment of fire within
the burn unit. Any preparations of the burn unit needed before
the burn can take place should be indicated, including a list
of fire sensitive elements within or near the burn unit that
must be protected. The burn plan should state the personnel
needed, as well as their qualifications and duties. The burn
plan also lists the equipment needed to conduct the burn.
The expected progress of the burn should be stated, and a
contingency plan identified for a burn not proceeding as expected.
Requirements for containment of the site after the burn is
completed (mop-up) should be listed. After the burn is completed,
a written evaluation of the burn should be made and included
as part of the final documentation for each prescribed burn.
The burn plan must outline the weather conditions which must
be met if the burn is to take place. It is vital to have the
best available weather reports. Local radio and television
stations are too general to be of much use. A detailed report
giving predicted wind speed and direction, relative humidity
or dew point, cloud cover, and temperature is necessary.
The neighbors and the local fire department should always
be notified of an upcoming burn.
Approval of a prescribed burn
Regulation of prescribed burns varies with the state and location
within the state. The land manager is responsible for obtaining
permits (if required). In the Upper Midwest, fire permits
are usually managed by the Department of Forestry of the state.
In addition to state requirements, there may be local requirements.
For any burn, the fire department responsible for that area
should be notified in advance of the fire. This notification
will forestall any possible problems if a member of the public
reports the fire to the emergency service agency.
Signs should be used to notify passersby of a burn in progress.
At a minimum, two signs are needed, at opposite ends of the
road or highway adjacent to the burn unit. The signs should
be left in place until there is no longer any smoke or glowing
used to announce that a prescribed (controlled) burn
is in progress. A variety of sign types are possible,
depending on the sign shop and the budget. Some groups
prefer collapsible cloth signs mounted on metal frames
that can be buried in the soil.
The burn prescription specifies the precise area to be burned,
which is called the burn unit. Depending on the circumstances,
burn units vary widely in size, from an acre to hundreds of
acres. In the Midwest, and especially for savanna burns, burn
units are relatively small, less than 100 acres. Although
larger burn units are desirable from an efficiency perspective,
the size of the unit will depend upon the site. If small burn
units must be established because of topography or other factors,
conditions may permit burning several independent burn units
in a single day. Once the weather is good and the burn crew
has been assembled, as much area as possible should be burned.
Before the burn can be carried out, adequate fire breaks (fire
control lines) must be created that completely surround the
burn area. Roads and waterways often serve as breaks, but
in many areas, fire breaks must be constructed. In grassy
areas, fire breaks are generally wide mowed areas, usually
broad enough for passage of a truck or all-terrain vehicle.
In wooded areas, fire breaks are created by removing all litter
in a wide zone down to the mineral soil. Any fire break should
ideally be wide enough to permit a vehicle to pass.
The width of the fire break depends upon the predicted length
of the flames. Since flame length depends upon the character
of the burn unit and the weather conditions on the day of
the burn, it is not possible to give specific fire break widths.
A “rule of thumb” is the break should be 1.5 times the flame
length. The NRCS often species 10-15 foot fire breaks for
burns of Conservation Reserve Program lands, but since the
fuel is grass, these widths are not applicable for savanna
town or county road makes an excellent fire break and
also serves as a means for transporting burn crews and
equipment. The principal problem is smoke management.
A spotter may be needed to control traffic.
Although the flame length of savanna burns is often just a
few inches, for most purposes the fire break for a savanna
fire in which the fuel is oak leaves should be at least two
It should be emphasized that although they are called fire
breaks, mowed strips are NOT safe lines across which
the fire will not cross. What does provide safety is a wide
burned area (called a “black line”) adjacent to and inside
the fire break. Because the black area has already burned,
there is no fuel available to carry a fire.
The first step in conducting a prescribed burn is to create
this essential black line.
a black line at the edge of the burn unit (which is to
the left). The unit of prairie on the right is not being
burned. The smoke pattern shows that the wind is from the left. This is therefore a BACK BURN, and the fire front is moving to the left.
Preparing the fire breaks
If fire breaks make use of paved county or town roads, little
or any preparation may be needed ahead of time. Service roads
through the savanna itself may also serve as fire breaks, although
their usefulness will depend upon their surfaces. A gravel
road is fairly satisfactory and a dirt road less so. If there
are a lot of leaves on the service road, they should be removed by
raking or with a leaf blower. Breaks that must be constructed
through grassland or woods and will require some preparation.
All fire breaks should be constructed ahead of time. On the
day of the burn, the fire breaks should require no preparation
except perhaps a pass with a leaf blower.
Fire break through grass If a fire break
is to be constructed through the middle of a grassland, then
it must be mowed with a tractor or walk-behind mower. After
the break has been mowed, a leaf blower should be used to
clear the loose grass and leaves. If a leaf blower is not
available, then the line should be carefully raked. The best
arrangement for raking a fire break is to have three or four people advance in a
line down the break with substantial metal rakes. The loose
material should be raked OUT of the burn unit. A 10-15 foot
fire break is ideal, although the exact width will depend
upon the site and how the burn is to be conducted.
mowed fire break through the middle of a two-unit prairie.
Because the wind was from the right, there was little
danger of the fire carrying to the unit on that side.
A pumper unit is standing by in case of a spot fire.
Fire break through woods If a fire break
is to be constructed in a woods, then personnel should first
walk the line and throw all woody materials outside the burn
unit. Then the line should be cleared with a brush cutter
followed by a leaf blower. The goal is to have a litter and
brush free zone, with bare soil showing. Since the flame lengths
in woods are lower than in grass, the break need not be so
wide. A four-foot wide fire break is probably acceptable for
a Midwest savanna burn.
a fire break through a wooded area. It is important to
clear all the way down to mineral soil. This is a two-person
job. The first person uses a powerful leaf blower to remove
the leaves and the second person "polishes"
the break with a rake. Ideally, a fire break should not
be established in the middle of a woods, but certain conditions
made this essential here.
Fire proofing a savanna burn unit
In addition to preparing adequate fire breaks, the burn unit
should be “fireproofed” so that mop-up problems can be minimized.
This means creating burn piles in the open, away from overhanging
branches. It also means clearing a wide fuel-free zone around
any trees that might be potential problems, such as standing
Clearing around problem trees is best done as a two-person
operation. One person operates a brush cutter with plastic
flail blades and the other person follows with a powerful
leaf blower and blows away all the cut debris, leaving a zone
of mineral soil around the base of the tree. The plastic blade
is preferable on the brush cutter because it does not damage
the bark of the tree. A string or weed whip is usually not
powerful enough for this task. If power equipment is not available,
rakes can be used. This work should be done only a few days
(at the most) before the burn, since new material will gradually
accumulate again and render the work useless.
Also, any living fire-sensitive trees that are to be left
should be fireproofed in the same manner.
proofing a savanna area before a burn. The brush cutter
mows the vegetation around the tree and the leaf blower
then clears it away. A ring of mineral soil is created
around the tree. This procedure is only done for dead
trees and for fire-sensitive species (such as this handsome
birch) which are being protected.
|Oak woods burn: cleared area around the birch did not burn and the tree was thus protected.
Equipment for prescribed burns
Propane torch not recommended
Prescribed burns should not be carried out without adequate
equipment for the job.
A reliable supply of water is essential, with proper equipment
for spraying water on fires. The simplest tool is the backpack
sprayer with hand pump, which can be used to spray water directly
on a fire. The minimum number of backpack sprayers for any
prescribed burn is four, but more are often used. Since each
backpack water can only holds about 5 gallons of water, extra
water should be available in plastic jugs or large truck-mounted
watercan used in prescribed burns. Capacity, 5 gallons.
The slide operated brass pump can squirt water 20-30 feet.
These units are sometimes called Indian fire pumps.
For larger burns, a high-pressure pumper unit is very desirable.
A pumper unit consists of a water tank of 50-100 gallons,
a high-pressure water pump driven by a gasoline motor, 100-300
feet of hose on a hose reel, and a lever operated adjustable
nozzle. Such a pumper unit can be mounted on a four-wheel
drive pickup truck or all-terrain utility vehicle. For very
large fires, a fire truck may be needed.
unit useful for prescribed burns. This unit was custom
built to fit in the back of a full-sized four-wheel drive
pickup truck. The unit has a 100 gallon tank, a high-pressure
pump capable of generating over 100 psi pressure, and
a high-pressure 300 foot hose on a reel. This sort of
unit works best with a 3-person team. One person drives
the truck, one operates the hose reel, and the third operates
the hose nozzle.
unit custom-built into the back of a Kawaski Mule utility
vehicle. This unit has a 65 gallon tank and 100 feet of
hose. The Mule is four-wheel drive and can go almost anywhere
on the site, both on and off road.
Rakes, shovels, and flappers can also be used to put out small
fires. Even a foot can be used to stamp out a tiny fire, but
for a fire of any significant size, water is essential.
Lighting is done with a drip torch. This is a hand-held device
consisting of a fuel reservoir, a burner arm, and an igniter,
and is used for dripping burning liquid fuel onto materials
to be burned. At least two drip torches are needed, and more
will be very useful. Propane torches are sometimes used for
ignition but lack the control of a drip torch and are not
torch used to ignite the fuel. This type of unit is almost universal
in the prescribed burn and wildland fire community. The canister
is constructed of heavy-duty aluminum. The torch has a fuel
trap to prevent flashback into the tank. There is an air valve
with tube inside that reaches the bottom of the tank so that
when the torch is in burning position the air is introduced
at the top of the fuel and does not bubble up through it. Attached
to the torch is the burning wand which has a pad that becomes
saturated with fuel. When lit the fuel mixture passes across
the pad and fire drips onto the grass or other burnable material.
The fuel is a mixture of 2-3 parts diesel and 1 part regular