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Prescribed Burning Guidelines
in the Northern Great Plains

Methods of spreading fire in grasslands

Kinds of fires

There are three basic kinds of prescribed fires: (1) backing, (2) head, and (3) flank fires.

Backing fires. Backing fires (Fig 12) burn into the wind. Fire is started along a prepared base line, such as a road, plowed line, stream, wetland, or other barrier, and allowed to burn into the wind.

Backing fires are generally the easiest way to burn. Flame lengths are shorter, rate of fire spread is slow, and smoke density is generally less than in head or flank fires. Backing fires burn hotter at the ground surface and do a better job of total fuel consumption than head or flank fires. Overall burn costs per acre will be higher, however, because of the longer time to complete the burn.

Backing fires work best with wind velocities of 6-19 km/h (4-12 mph) from a constant direction. Some disadvantages are the time required and the need for interior firelines at frequent intervals (usually every 150 to 300 meters) to speed up the burning of a large or long area.

Burning downward on slopes has an effect similar to backfires in flat country.

Head fires. Head fires (Fig 13) burn with the wind. They have greater flame lengths, faster rates of spread, greater smoke volumes, and burn cooler at the ground surface than backing fires or flank fires.

Because head fires burn faster than other kinds of fires, lower overall burn costs can be expected per acre of burn. Containment becomes more critical, however, as wind speed and fuel quantity increase.

You must be absolutely sure the fire will not escape. Burn out a strip downwind with a backfire wide enough to control the head fire.

Flank fires. Flank fires (Fig 14) burn at oblique angles to the wind direction. They are a modification of backing fires in that lines of fires are set to burn into the wind but at angles to the wind direction.

Flank fires are often used to secure the flanks of a head fire as the head fire progresses. This method of firing can stand little variation in wind direction and needs expert crew coordination and timing.

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