Kinds of running fires

Fire behavior is dependent on the wind direction, and several different kinds of fires exist.

The head fire is one that is running with the wind. Depending on the wind speed and other weather factors, the flames of a head fire can be from a few feet to 20-30 feet high. The latter is definitely not advisable. A head fire is potentially dangerous and should only be allowed when it is running towards an area that has already been completely fire proofed. Because head fires move rapidly, less of the fuel is consumed. With tall grass prairies, a head fire is virtually impossible to put out, whereas it is relatively easy with a savanna burn where the fuel is oak leaves.

Headfire

The backfire is one that is running against the wind. Because the wind is tending to push the fire back, toward the area already burned, the backfire is a low-intensity fire, hugging the ground, and moving slowly in the direction from which the wind is coming. Since the flames are being pushed behind the fire, in a direction where there is no fuel (it has already burned up), flame lengths are low. Depending on the nature of the fuel, the backfire may burn to greater or lesser intensity. Because they move more slowly, backing fires consume more of the fuel. A complete burn can be done as a backing fire but because of its slowness, this is usually not done.

Fire backburning through bur oak savanna

The flanking fire is one that is sideways with the wind. Depending on constancy of the wind direction, a flanking fire may burn slowly or more rapidly, but usually not as rapidly as a head fire.

Flanking fire burning through an Indian grass patch on a hill savanna.

The strip head fire is probably the most suitable for oak savannas. It burns a bit faster than a backfire, and is adaptable to burn units of various shapes. A series of strips are lighted, starting at the downwind side of the unit, burning only one strip at a time. Because the strips are fairly narrow, the fire is under good control. The strip-head fire can also be expanded, if conditions permit and enough personnel and equipment are available, so that several strips are lighted in sequence proceeding toward the upwind side of the unit. A strip head fire burns slightly faster than a backfire, is relatively safe, and works well for burning rectangular or odd shaped parcels. It is also cost-effective.

The perimeter fire is one that starts as a backfire, proceeds as two flanking fires, and then finishes once the unit is circled as a “head” fire. This can be the fastest sort of fire, because once the unit is “tied off”, the head fire quickly finishes the job. Most prairie burns are managed as perimeter fires.

Remember: When choosing a burn technique, the level of experience of the burn crew should be a major factor.

Slope and running fires

If the burn unit is on the side of a hill, the flame characteristics are mostly determined by the slope rather than the wind. A slope lighted from the bottom will burn as a head fire, irrespective of wind direction. This is because the rising flames burn the fuel on the uphill side of the burning front, and this phenomenon propagates up the hill. In addition, convection and radiant heat move upward, resulting in more preheating of the fuel and faster ignition.

A fire burning uphill is equivalent to a head fire.

On the other hand, when the fire is lighted from the top, the rising flames encounter fuel that has already been burned, so that the flaming front burns down the hill like a backfire.

If the wind is also blowing upslope, it adds to the effect of the slope. Thus, lower wind speeds are needed when burning upslope than when burning on the level. If the wind is too strong, an upslope burn may not be possible whereas the same wind on a level burn might not be a problem.

Getting the burn done

Weather and other conditions needed for the prescribed burn are monitored, and when conditions are suitable, and needed personnel are available, the burn is scheduled. The decision to perform the burn is made by the person who is to be in charge of the burn, the burn boss. Due to changing weather, the decision to burn can only be done one or two days before the burn. Sudden changes in weather or other factors may require that a scheduled burn be cancelled at the last minute. The acceptable weather conditions for the burn are laid out in the prescription.

On the day of the burn

On the day of the burn, all personnel assemble at the site well in advance of the time of lighting. Burn crew members should have fire-resistant outer clothing, leather shoes, and leather gloves. An orientation meeting is conducted at which the details of the prescribed burn are reviewed by the burn boss. The weather is reviewed, and weather variables that might change (such as wind speed or direction) are identified. If necessary, crew members will familiarize themselves with the burn unit by walking the whole periphery. At this time, the burn boss will point out items that might need particular attention.

The burn crew assembled before the burn. The burn boss describes the burn in detail and assigns tasks. The locations of fire breaks are reviewed on the burn map. Smoke management issues are discussed.

Conducting the burn

For most burns, two fire lines are used, operating in opposite directions. Each burn line has a line boss, who supervises the fire on that particular line. Each line has at least one crew member responsible for lighting, and other crew members with water. The line boss directs the crew members, and maintains communication with the burn boss. Usually the two burn teams start at a single point and move in opposite directions around the burn unit. Communication between crew members during the burn is vital. For burn units of any substantial size, two-way radios are essential. Before the burn begins, all radios should be tuned to the same channel and checked.
Cell phones can also be used, although they are not as convenient as two-way radios (see Safety, below).

Before the burn is started, a weather check is made to determine wind speed and direction, temperature, and relative humidity. Assuming conditions are favorable, a small test fire is first done to determine how the fuel burns. The test fire is done at an upwind corner of the burn unit and is essentially a small backing fire. The burn boss observes the behavior of the test burn. If conditions do not appear satisfactory, the test fire is put out and the burn crew moves to a different location, or the burn is cancelled. Assuming the test burn is satisfactory, a short strip of fuel is burned and observations continue. Once the burn boss is satisfied with the behavior of the fire, the two burn lines begin to proceed in opposite directions around the burn unit.

The test burn. The burn boss and burn crew observe the behavior of the fire and make any modifications in the burn plan.

Each fire line has at least one drip torch. The fire is always started at a good fire break on the downwind side of the burn unit, and allowed to burn as a backfire along the inner edge in order to create a substantial black line. Water is used to ensure that the backfire does not jump the break and burn outside the burn unit. Spotters should be positioned downwind of and outside the area of the backfire. (See Spot Fires, below)

The burn boss is in communication with each line boss, who report about the behavior and progress of their lines.

As the burn progresses, crew members with water cans spread out along the burn line, looking for spot fires or other problems, reporting frequently to the line bosses, and putting out any fires that start to “creep” out of the burn unit.

Careful attention must be taken to ensure that the blackline along the downwind side of the burn unit is wide and thoroughly black. Crew members with water packs monitor to make sure that the fire remains within the burn unit.

Spot fires

A spot fire is a fire that has started outside the intended burn unit. Spot fires usually arise from wind-blown embers that pass out of the burn unit and land upon nearby flammable material. Since these embers are igniting a fuel outside and upwind of the burn unit, the result will be the start of an unwanted head fire. This a serious situation and one that should be avoided at all costs. If a spot fire develops in dry fine fuel and the wind is strong, such a fire can rapidly turn into a roaring head fire which can be very difficult to extinguish.

To avoid a spot fire, personnel with water backcans called “spotters” must be stationed upwind of the burn unit, and if any “spots”arise they must move quickly to them and extinguish them. Although the position of spotter is generally a boring position on a burn crew, if a spot really does occur, the spotters role is vital.

Wetlining

If a pumper unit is available, a wet line can be used to help create a good black line on the downwind side of a burn unit, when laying down a blackline. This is very useful in grass, especially if the area outside the burn unit is also grassy. Although a semblance of wetlining can be done with backpack water cans, in most cases this technique will only be used if a high-pressure pumper unit is available (on a truck or ATV).

Use of wetlining to control the edge of a fire break. The unit to the right is not being burned. A pumper unit is needed for this task. The water moves ahead of the drip torch and wets the edge of the mowed fire break.

In this procedure, two (or more) people operate the pumper unit and manipulate the hose, and the person with the drip torch lights the fire behind the wetline. The wetline should be laid down on the side of the break nearest to the burn unit. The fire then backburns away from the wetline. Personnel with backpack water cans can follow further back to make sure that the burn does not cross the mowed fire break.

Wetlining can also be done in woods, but is less likely needed.

Chevrons

To quickly widen the blackline, strips of fire at right angles to the backfire (called chevrons) can be made. These are useful in savanna burns where oak leaves are the main fuel, because oak leaves burn much slower than prairie grass and chevrons speed up the burn process.

Use of "chevrons" to speed up the burn. These strips at right angles to the fire line quickly burn together and create the desired "blackline."

Completing the burn

Once the downwind black line and corners have been secured, the burn lines move in opposite directions around the flanks of the burn unit. It is important that wide blacklines are present on both the downwind side and the flanks of the unit, before the upwind side is lighted. Lighting the upwind side initiates the head fire and should greatly speed up the burn.

In some cases, interior lighting (sometimes called stripping) may be necessary to widen out the blackline or to ensure that all burnable material inside the unit have been burned. For stripping, a second drip torch is sent into the interior to light as directed by the line boss. Before any personnel are permitted into the interior of the burn unit the burn boss must make sure that the whole unit has been burned. Because savannas burn less completely than prairies, stripping is often necessary to achieve the desired degree of burn coverage.

Interior lighting (stripping) is often needed in oak savanna burns, especially in the early years of a restoration.

Mop-up

A rather bad "chimney" that has to be dealt with in mop-up. If the savanna unit had been fireproofed before the burn, this probably would not have happened. If this tree is near the edge of the burn unit it will have to be cut down to extinguish it.

Living trees and savanna burns

Although oak trees are relatively fire resistant, smoldering wood that lies next to trees can cause minor fire damage. Due to the manner in which the fire moves, the backside (upwind) side of a tree will be hotter than the downwind side, due to the manner in which the fire burns. Thus, after a burn is completed, the whole burn unit should be examined and any hot or burning debris should be kicked away from the tree bases.

Standing dead trees are especially prone to ignite at the base. There is a hazard that such trees might topple over if the base is burned too much. This presents a personnel hazard as well as a problem with mop-up. Especially after the burn has been completed, personnel should be cautioned to be on the alert for trees that might topple.

Comparison of different kinds of burns

A brief summary of the differences between three kinds of burns, prairie, savanna, and woodland, is given in the table below.

Safety

The prescribed burn is one of the most useful tools in ecological restoration, and if carried out properly should be incident-free. However, it must be carried out by trained personnel, and based on a precisely written burn plan. Fire should not be used casually or without proper thought and direction.

A burn should never be started until the burn boss has verified that conditions are safe. Personnel on the burn must be totally informed of the burn and their particular part in it. Each line boss must at all times keep track of all personnel on that line. It is especially important to keep all personnel away from the front of the flaming front of a head fire. Most important is to never attempt to out-run a head fire.

Although good 2-way radios are expensive, they are very important for the conduct of a burn, and for ensuring the safety of personnel. If there are insufficient radios for all personnel, then each person without a radio should be paired with someone who has a radio. Topography, trees, and smoke can reduce the visibility of personnel.

Cell phones can also be used, although communicating by them is slower and less efficient. Although cell phones are less subject to interference than two-way radios, and have wider coverage, reception in remote areas is often spotty. If cell phones are to be used, ensure that they will work well in the burn area before relying on them and program the phone numbers of all the cell phones being used. Ideally, the burn boss and line bosses should have a cell phone as well as a two-way radio.

The burn boss is responsible for keeping in touch with each line boss, and ensuring that all personnel on that line are accounted for. Frequent radio contact informing all participants of the progress of the burn is very important.

A first aid kit and plenty of drinking water should always be available. Proper clothing is important. Leather boots and gloves, eye protection, and fire-resistant clothing (Nomex) are essential. Clothing of synthetic fibers like nylon should not be worn, as they melt at relatively low temperatures. Long sleeve shirts and long pants should be worn, as well as hard hats. For visibility, bright colored-clothing should be worn.

Most members of the public will consider any fire to be a wildfire and dangerous. It is vital that the public be informed of the nature of the burn, and protected from the burn. Casual observers should not be permitted. Dangerous situations can create liability concerns and should be avoided.

• Have all fire breaks made before the day of the burn.
• Start early enough in the day
• Always have plenty of drip torch fuel, usually twice the amount you think you might need.
• Always have plenty of water, and place water bottles or tanks at various locations along the burn unit but outside the fire break.
• Always keep vehicles well outside outside the burn unit.
• Keep all personnel accounted for. Especially before lighting a head fire, make sure that all personnel are outside the burn unit.
• If the burn is going well, expand it to other units if time permits. You may not have favorable weather again for a while.
• Try to do larger burns. Finding the right conditions and obtaining a competent burn crew is difficult, so the golden opportunity should not be lost by doing small burns. Try to do the largest burn consistent with facilities and personnel.