Backing Fires

Backing Fire Technique

A backing fire is started along a baseline (anchor point), such as a road, plow line, stream or other barrier, and allowed to back into the wind. Variations in wind speed have little effect on the rate of spread of a fire burning into the wind. Such fires proceed at a speed of 1 to 3 chains per hour. Backing fires are the easiest and safest type of prescribed fire to use, provided wind speed and direction are steady. They produce minimum scorch and are especially useful in heavy fuels and young pine stands.

Major disadvantages of backing fires are the slow progress of the fire and the increased potential for feeder-root damage with increased exposure to heat if the lower litter is not moist enough. When a large area is to be burned, it often must be divided into smaller blocks with interior plow lines (usually every 5 to 15 chains). All blocks must be ignited at about the same time to complete the burn in a timely manner. In-stand winds of 1 to 3 mph at eye level are desirable with backing fires. These conditions dissipate the smoke and prevent heat from rising directly into tree crowns.

When the relative humidity is low, a steady wind is blowing, and fuels are continuous, an excellent burn can be anticipated once the fire backs away from the downwind control line. Under such conditions, however, extra care must be taken to make sure the initial fire doesnt spot across the line.

Factors Associated with Backing Fires:

• Must be ignited along the downwind control line.
• Use in heavy roughs.
• Use in young stands (minimum basal diameter of 3 inches) when air temperature is below 45^oF
• Normally result in little crown scorch.
• Costs are relatively high because of additional interior plow lines and extended burning period resulting from slower movement of the fire.
• Not flexible to changes in wind direction once interior lines are plowed.
• Requires steady in-stand winds (optimum: 1 to 3 mph).
• Will not burn well if actual fine-fuel moisture is above 20 percent.
• Requires good fuel continuity to carry well.
• A single torch person can progressively ignite lines.