Slash Piles

by Nick Gromicko, CMI®
Slash (used as a noun) is the accumulation of limbs, leaves, pine needles and miscellaneous fuel left by natural debris and forest management activities, such as thinning, pruning, and timber harvesting. Slash piles are created by gathering these materials into manageable, isolated piles that can later be burned in safe manner.Slash piles are constructed and burned as a form of wildfire mitigation
Slash-burning is a form of fire mitigation designed to keep forests healthy and prevent dangerous wildfires by safely burning leaves, pine needles, downed trees, standing small trees, and thick vegetation. It is the responsibility of homeowners in forested, fire-prone areas to maintain the health and safety of surrounding forest through slash-burning on their property. Of equal importance, however, is that homeowners who burn slash must do so safely and follow the regulations required by their jurisdiction. Inspectors who visit properties in forested, fire-prone areas can advise their clients about the safety recommendations contained in this guide.
Composition and Construction
  • Pile slash at least six months prior to burning to allow it to dry. Dry slash burns more efficiently and with less smoke than green slash.
  • Remove all flammable debris, such as firewood, from the area prior to piling.
  • Piles should be wider than they are tall. Some jurisdictions restrict piles to less than 6 feet wide and 4 feet high.
  • Use a mixture of sizes and fuels throughout the pile. This prevents snow from filtering into the pile and extinguishing the fire while it is starting.
  • Pile branches with their butt-ends toward the outside of the pile, and overlap them so as to form a series of dense layers piled upon each other.Well-constructed slash pile
  • Do not burn wood that is especially thick, as it will take a long time to burn.
  • Do not burn any of the following materials in slash piles:
    • routine yard and garden waste;
    • rubber;
    • plastic;
    • structures;
    • construction debris;
    • household garbage;
    • materials that produce excessive smoke;
    • commercial/business waste; or
    • stumps 
  • Larger-diameter wood should be placed on the top of the pile, while smaller fuels should rest at the base.

Ignition and Dousing
If the needles and fine fuels within the pile have dried out throughout the summer, then the fire can be started with a large ball of newspaper placed at the bottom of the pile. If fuels are still partially green or if the pile is wet from rain or melting snow, then a hotter and longer burning source, such as sawdust saturated with diesel fuel, may be necessary. Grand County, Colorado, states that fuses and propane burners also provide relatively safe ignition. Gasoline, however, should never be used to ignite or fuel a slash fire! Follow these additional precautions regarding the ignition and dousing of a slash fire:
  • If multiple fires are to be burned, one pile should be burned first to test its burn rate. If suitable burning conditions exist, then additional piles may be ignited.
  • Ignite only those piles that can be watched with available manpower until the piles have burned down. As a general rule, three to six piles per person is a manageable rate if the piles are closely situated.
  • After the piles have burned down, re-pile any unburned slash and large wood chunks into the beds of coals before starting any new groups of piles.
  • Do not start any new piles after 2:00 p.m. as they may continue to burn into the evening. All burning must be extinguished by nightfall.
  • Test-burn one representative pile and visually monitor smoke dispersal from a distance prior to igniting all piles.
  • To extinguish the fire, use shovels, rakes or other hand tools to mix the coals and move unburned fuel toward the center. This final check of the burned slash is to identify and extinguish still-burning coals or materials. Dousing is usually accomplished by covering and mixing snow, water and/or soil with the burning fuels.
  • The fire is out only when the area is cold to the touch. A burn area covered with snow is not necessarily extinguished. 
  • Check the fire 24 hours after it has gone out to make sure it has not re-ignited.
LocationSlash piles should not be built beneath utility lines
  • Locate piles in large, open areas to provide for vehicle access and monitoring.
  • Do not pile slash over stumps, as these will burn in place and may take longer to extinguish.  If desired, remove the stumps first, and then add them to the slash pile. 
  • Maintain ample clearance from overhead and underground utility lines.
  • Locate piles far from the nearest vegetation, property boundaries and structures.
  • Locate piles in meadows, rock outcrops, or openings in forest stands.
  • Keep piles away from your residence and your neighbor's residence, including away from propane tanks and exposed decks.

Weather and Snow Cover 
  • The more snow around the piles, the better. Some jurisdictions require at least 3 inches of snow.
  • Don’t burn if substantial warming or drying is expected within three days after the fire.
  • Check the weather forecast to avoid burning during high winds or extremely dry conditions.       
  • Do not burn on calm, clear, cold days, since smoke may not disperse properly. Moderate winds and unstable air masses provide for optimum smoke dispersal. Experience has shown that burning during heavy snowfall results in good smoke dispersal (per Grand County, Colorado).
Additional Advice and Precautions
  • Pile slash immediately after cutting (while still green), and before winter snowfall.
  • If the fire is expanding too quickly or it escapes your burn area, call 911 immediately.
  • Only burn in winter.
  • Always have water, a rake and a shovel handy.
  • Attend the fire. If firefighters are called to the fire and you are not present, they will douse the fire and the police will issue you a fine.
  • Obtain a burning permit, if one is required in your jurisdiction. Always have the permit with you during the burn.
  • Notify the fire dispatch on the day of the burn. They will probably inquire about who you are, where the burn will take place, and the time you expect to start and finish the burn. Failure to notify dispatch, even if you possess a valid permit and follow all burning rules, may result in a fine.
  • On certain days, known as "red-flag warning days," slash piles may not be burned. Burning on these days will result in a large fine and the fire will be extinguished. You can inquire about these days at your local fire department.
In summary, slash-burning is a form of fire mitigation that must be performed safely and in compliance with local ordinances.