Firebreaks

Prescribed Fire January 29, 2016 Print Friendly and PDF

Firebreaks, also called fireguards or fuel breaks, usually define the perimeter of a prescribed fire or controlled burn and help contain the fire. Firebreaks are areas that lack combustible fuels along the perimeter of a burn area. Firebreaks are important considerations during planning, preparation, and implementation of prescribed fires.

Appropriate firebreak width varies depending upon several factors such as fuel loads, fuel heights, fuel types, and fire-fighting equipment available. For the most part, firebreaks are commonly 10-60 feet wide. However, firebreaks can be as narrow as a walking trail when burning in tree leaves with light winds or as wide as 3,000 feet when burning high volume volatile fuels, such as large junipers.

Although many firebreaks are capable of stopping back fires or other low intensity fires, most firebreaks are not designed to stop head fires by themselves. Ignition techniques such as back fires, flank fires, and strip fires typically are utilized to widen blackened areas along firebreaks and increase the effectiveness of firebreaks.

When preparing any firebreak it is important to minimize coarse (greater than 2 inches in diameter) and volatile fuels near firebreaks in the burn unit. Coarse fuels can burn for relatively long times and volatile fuels contain oils that cause them to burn intensely. These considerations are addressed in the article “Move Coarse, Volatile Fuels Away from Firebreaks” at www.noble.org/ag/wildlife/move-fuels-away.

Several types of firebreaks exist, each having specific advantages and disadvantages. Most prescribed fires utilize more than one type of firebreak.

Types of firebreaks

Disturbed bare-soil firebreaks are common and effective firebreaks. They usually are prepared with equipment such as disks, plows, rototillers, bulldozers, graders or hand tools. Any vegetation and soil moved off a firebreak should be moved to the outside of the firebreak away from the burn unit. Clumps of vegetation with or without soil on the burn side of a firebreak can smolder for extended time periods and cause spot fires if not extinguished. Well-prepared bare soil firebreaks minimize water use during a burn. Disturbed bare-soil firebreaks should be prepared prior to a burn, but when prepared too early, vegetation can grow or leaves can accumulate on them, decreasing their effectiveness for stopping a fire. Bare-soil firebreaks work best on relatively level terrain without many rocks or stumps. Erosion is more likely on bare-soil firebreaks where slopes exceed 3%. Preparation often becomes impractical where rocks or stumps are excessive. When soil moisture is high, disturbed bare-soil firebreaks can impede movement of fire-fighting equipment.

Bare soil firebreak created with rototiller

Photo 1: Bare-soil firebreak created with rototiller (by Steven Smith).

Roads, whether paved, gravel or dirt, can be effective firebreaks. Roads usually require little or no prior preparation and minimize water needs during a burn. They also provide a good base for moving fire-fighting equipment. However, smoke across or on public roads can create traffic problems, which may limit usable wind directions for burns or may require additional labor for traffic management. Burning along the edge of pavement on Federal and state highways may be illegal, so check with state and local laws before doing this. A disadvantage of burning along public roads is many roads have fences and utility lines along them with wooden components that require extra labor and water to prevent fire damage.

Gravel road as a firebreak

Photo 2: Gravel road as a firebreak (by Mary Howard).

Water features, such as lakes, ponds, wetlands, creeks or rivers also can be used as effective firebreaks. They usually require little or no prior preparation and reduce water needs during a burn. However, contingency plans need to be in place in case a spot-fire develops across a water feature, because access may be difficult to extinguish the spot-fire. 

Water feature, a lake as a firebreak

Photo 3: Water feature, a lake as a firebreak (by Chris Cowlbeck).

Abrupt elevation changes, such cliffs, quarries, spoil piles, canyons, gulches or gullies, can serve as firebreaks. They usually require little or no prior preparation and minimize water needs during a burn. However, like water features, contingency plans need to be in place in case a spot-fire develops across an abrupt elevation change because access may be difficult to extinguish the spot-fire.

Abrupt elevation change, such as a gully as a firebreak

Photo 4: Abrupt elevation change, such as a gully as a firebreak (by Samuel Roberts Noble Foundation staff).

Cleared paths through leaf litter in timber or woodlands can be prepared using leaf blowers, mowers or hand tools. Leaves should be moved to the outside edge of the firebreak away from the burn because piles of leaves on the burn side can smolder for extended time periods and cause escapes if not extinguished. Since cleared paths through leaf litter are bare-soil firebreaks, they reduce water needs during a burn. A disadvantage is significant labor may be required to remove briers, logs and other debris from the path prior to clearing leaves. Another disadvantage is leaves usually can be cleared only a few days or hours prior to a burn to avoid wind or additional leaf fall putting more leaves on the firebreak. Planning ahead allows spraying existing vegetation with a backpack sprayer months in advance to limit vegetation, such as briers or brambles, along the firebreak.

Cleared path through leaf litter as a firebreak in Cross Timbers

Photo 5: Cleared path through leaf litter as a firebreak in Cross Timbers (by Mike Porter).

Green vegetation also can be effective firebreaks. This can be cool-season pasture or cultivated crops, and even growing warm-season plant communities with limited amounts of old residue. For late dormant-season burns, planted cool-season crops or naturalized cool-season plants can be maintained annually as firebreaks (for more information go to www.noble.org/ag/wildlife/greenfireguards). Caution should be exercised when using green vegetation as firebreaks because green vegetation can burn when vegetation is dry during drought, or when low humidity, high temperature, or strong winds exist. Sometimes green vegetation firebreaks may require the use of water to help stop fire at the firebreak because dormant growth may be mixed with green vegetation allowing fire to creep across a firebreak.

Green vegetation as a firebreak during winter

Photo 6: Green vegetation as a firebreak during winter (by Mike Porter).

Blackened areas or preburned areas can be used as firebreaks. These areas can be burned several days or weeks prior to the primary burn. More commonly, back fire, flank fire and or strip fire are used, but not extinguished, to create blackened areas along other types of firebreaks to widen firebreaks as part of the prescribed burning process. Blackened areas commonly provide safe areas for moving personnel and fire-fighting equipment. When using preburned blackened areas as firebreaks, caution should be exercised to make sure the thatch or mulch layer is fully burned. Sometimes the thatch layer does not burn well because of high moisture content, but if the main fire is ignited under drier conditions, the partially burned thatch layer can re-ignite.

Burned plot at NF CR

Photo 7: Blackened area as a firebreak (by Samuel Roberts Noble Foundation staff).

Wet lines can serve as temporary firebreaks. Wet-line firebreaks involve spraying water on vegetation along the perimeter of the burn unit and then igniting fire along the edge of the wet vegetation. Ignition, spraying and mop-up must be coordinated well to avoid escapes. Usually, sprayed vegetation is effective for stopping or slowing fire only for a short period of time. Monitoring and mop-up are essential because the wet line will dry and the fire can escape out of the burn unit. Wet lines are commonly used over mowed, hayed, or grazed vegetation to decrease flame lengths, fire intensity, and water needs. Wet lines can be used without mowing, but this should be done only by experienced, well-equipped crews. Wet lines require lots of water and are labor intensive and time-consuming, which often limit the amount of area that can be burned.

Wet line over mowed vegetation as a firebreak

Photo 8: Wet line over mowed vegetation as a firebreak (by Samuel Roberts Noble Foundation staff).

More information about firebreaks is available in the fact sheet “Firebreaks for Prescribed Burning” at http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-8542/NREM-2890web.pdf.

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This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.