Pile and Windrow Burning

Windrows

The objective of piling logging debris before burning it is to prolong fire residence time on a restricted area so that larger materials have time to be consumed. Some areas will contain an unacceptable amount of large, scattered debris that must be concentrated to ensure consumption. This material should be piled and not windrowed. Windrowing can reduce site quality by removing topsoil. Piedmont soils are also susceptible to compaction from the heavy equipment used, especially during wet weather. Full exposure of the soil to the sun and rain bakes the top layer. Furthermore, the direct force of raindrops will clog soil pores and often results in erosion on steep slopes. The area beneath the windrows is lost to production because the debris is rarely consumed completely and what remains makes planting difficult or impossible. Even when windrows contain breaks spaced every couple of chains, they still present a barrier to firefighting equipment and wildlife.

Smoldering Windrows

The biggest deterrent to windrow burning, however, is that it causes a high percentage of all smoke incidents. Large volumes of fuel, including larger pieces that contain a lot of moisture, are consumed. However, oxygen for good combustion is lacking, especially in large piles and wide windrows. Large amounts of soil are often mixed in, further compounding the problem. The result is a fire that continues to smolder for days or weeks, creating air quality problems because the smoke produced by smoldering combustion is not hot enough to rise into the atmosphere. The smoke stays near the ground where it cools even more, drifting and concentrating in low areas because of cool air drainage. To make matters worse, the smoke often mixes with humid air to produce fog which further reduces visibility. Coupled with these problems is the fact that the weather changes from day to day making it impossible to predict, and thus manage, the smoke for more than a day or two. For these reasons, air quality regulations prohibit pile and windrow burning in some areas.

Piles

Although it generally costs more to pile than to windrow, piles are preferable to windrows because access within the area is no problem, planting is easier, burning is safer and, most important, smoke problems are significantly reduced since piles burn out much quicker! Generally, piles contain less dirt and dry faster. Burning piles can easily be "bumped" to remove any dirt and pushed in to increase consumption. The whole area can then be utilized.

Here are several guidelines that can help create piles that will burn effectively and minimize smoke production and soil impacts.

• Keep piles small and minimize the amount of soil in them so surface water can pass through, and the debris can dry quickly.
• Always pile when the ground surface is dry; less soil compaction will take place, and considerably less soil will end up in the piles.
• Allow fresh logging debris to cure first and to dry after rain. Then "shake" the debris while piling to remove as much soil as possible. If material is piled while green or wet, the centers of the piles take an exceedingly long time to dry.
• Construct piles with little soil and allow some air movement; this will result in a burn that consumes significantly more of the debris and produces less smoke. More efficient burning and greater heat output will lift smoke higher, reducing smoke concentrations near the ground.
• Burn when the atmosphere is neutral to slightly unstable, but not unstable enough to create control problems.

Pile Burning

Forest managers can take many steps to minimize these debris problems. Much of the larger material left after harvest is cull hardwood, and periodic use of underburns during the rotation will reduce the number of large hardwoods at harvest. Some of the cull material can often be sold or given away as firewood. Sites often can be prepared for seeding or planting by a broadcast burn without piling the debris. Trees should be cut close to the ground, leaving low stumps.

Advances in harvesting equipment and methods have also helped. Large mobile harvesters chip the whole tree, increasing utilization and reducing the need for site preparation. Tree-length logging and gate delimbing (backing a drag-load of trees through a metal grid) tend to concentrate much of the debris at the logging deck. Piles created in this manner are generally free of soil (providing logging was suspended in wet weather) and can be burned as is.

Techniques used to burn piled debris are somewhat fixed because of the character and placement of fuel. Traditionally, each pile is ignited along its perimeter, but burnout can be speeded up considerably by igniting the pile center. A helitorch is often used because burning globs of gelled gas penetrate deep into piled fuels and provide a "large" heat source. Tractor-mounted ignition devices that help burning fuel penetrate down toward the center of a pile have also been fabricated.

Factors associated with pile and windrow burning

• A large majority of all smoke related incidents are caused by this type of burning.
• Produces the most smoke of all firing techniques.
• Burns can continue to smolder for many weeks.
• Smoke produced at night tends to stay near the ground.
• Cannot be readily extinguished after ignition. If extinguished, even more effort is required to reignite them the next day.
• Can burn in light or variable winds.
• Usually safe and easy to control, provided piles are not next to the edge of the area and are not left unattended, particularly when burning during periods of high fire danger.
• Piles should be as free of soil as possible.
• Fuel should be dry.
• Burn area should be as small as economically practical.
• Need neutral to unstable conditions for good smoke dispersion -which generally do not occur after sunset.
• Need good mixing.