Prescribed burning

This section gives the principles of prescribed burning, the equipment needed, and how burns are set up.

Weather Considerations

Those carrying out prescribed burns become intense weather watchers. The weather is the most critical factor in the success of any burn.

Burn seasons

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 burn

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 speeds.

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 burns

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 objectives.

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 coals visible.

Sign 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.

Burn unit

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.

Fire breaks

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 burns.

A 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 feet.

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.

Preparing 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.

A 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.

Clearing 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 dead trees.

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.

Fire 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

Suppression equipment
Pumping system
Backpack tanks

Ignition equipment
Drip torch
Propane torch not recommended

Mobility equipment
Utility vehicles

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 containers.

Backpack 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.

Pumper 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.

Pumper 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 recommended.

Drip 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 gasoline.