Tag: fire

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Weather Conditions for Controlled Burns

Although controlled burns can be conducted under pre-determined weather conditions, burns can be unsafe if the experience of the burn boss and crew is inadequate.

People new to burning should consider using the 60:40 rule. The 60:40 rule refers to restricting burn conditions to air temperatures less than 60 degrees Fahrenheit and relative humidity (Rh) greater than 40% with a wind speeds of 5-15 mph measured at 6 feet above the surface of the ground.

Rule of Halves

The rule of halves is an easy way to remember how to predict changes in fire behavior when the weather changes. When the air temperature increases by 20 degrees Fahrenheit, the relative humidity decreases by 50%. For example, if the air temperature changes from 60 degrees Fahrenheit with 40% relative humidity to 80 degrees Fahrenheit, the relative humidity will change from 40% to 20%, making the spotfire risk increase dramatically. In most cases, do not burn if there is a forecasted frontal passage or wind shift within 12 hours.

Weather Tools

There are many weather tools available. Make sure and check the wind direction, speed, temperature and relative humidity a few days before the burn, and right before the burn. It is very helpful to take notes of weather conditions during the burn. This can help people learn how to predict fire behavior in the future. On-site weather meters can be very helpful in taking up-to-date weather.

If conditions are not correct, including all parts of the prescription, do not start the fire. If the fire is not going well, put it out. Do not leave the fire until it is completely out, which means no smoke detected for at least one hour.

View this fact sheet for more detailed weather information regarding spotfires: http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2704/NREM-2878web.pdf

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FEIS (Fire Effects Information System) is easy to use

When planning a prescribed fire or understanding the results of a wildfire, it is important to define the desired fire effects.  Fire effects are defined as: The physical, biological, and ecological impacts of fire on the environment.  We categorize effects in to groups first order and second order.  First order effects are related to the burn itself (effects of combustion) while second order effects are usually seen later and relate to the stress caused by the fire interacting with the environment.  Examples of some fire effects might be reduction of undesirable species, increase in species diversity, reduction in canopy cover or number of trees, and increases in cattle weight gains. 

Fire effects living things differently and researchers have been working to understand fire effects.  You can access this information through a website that provides summaries of fire effects by species, regions, and even ecosystems.  The Fire Effects Information System is a clearinghouse of summarized easy to use fire effects information.  There are links to regional summaries as well as species specific information.  They cover fire effects on a wide range of flora (including a special section on invasive species), fauna, soils, and air. The species descriptions include basic biology, distributions, as well as information on how the species will respond to fire.  Citations are also available resources.  There is even a tutuorial to get you started!  The website is easy to use and researchers work to update species summaries as often as possible.

Go to: http://www.feis-crs.org/beta/

 

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Reduce Smoke Through Ignition Techniques

Reducing the impacts of smoke should be considered when planning a prescribed fire. Smoke management is not really about the reduction of emissions, but the redistribution of emissions, which is done by choosing wind direction, atmospheric conditions (such as mixing height), and ignition techniques to manage the convection. Perhaps less discussed are ignition techniques themselves. Following are some basic guidelines when planning ignition techniques to reduce smoke emissions. We must be aware, however, of potential tradeoffs between reduced smoke emissions and achieving ecological goals with fire.

How to influence smoke

Smoke includes a mix of chemicals including bits of the unconsumed fuel. Unconsumed fuel on the ground leads to smoldering phase burning. Smoldering produces more smoke than burning in the flaming stage of ignition. Ignition techniques that lead to more complete combustion should produce less smoke than other techniques. Here are some examples.

Parts of a fire.

1. Backing fire. Backing fires (fires that burn against the wind) consume fuels more completely than head or flanking fires; thus, backing fires generally produce less smoke. Tradeoffs include increased time to complete burns because backing fires move more slowly, and flame lengths are relatively short so may not provide sufficient heat to kill some plants.

2. Headfire. Headfires (burn with the wind) move more quickly, produce more heat, generally consume fuel less completely, and produce taller flame lengths. Incomplete fuel combustion results in greater smoke production than backfires. Although headfires may produce more smoke, they may be used to complete a fire more quickly, thereby reducing the overall burn time. Furthermore, the speed and intensity of headfires releases more heat that can help the smoke to rise in a column, facilitating dispersal at higher levels in the atmosphere. Headfires can also be more challenging to conduct safely if used exclusively.

3. Ring headfire. This technique uses a combination of back, flank, and head fires. Backfires and flanking fires are used around the perimeter to create a safe black zone to send the headfire towards. This technique is often used because of its safety and compromise in completion time. The backfire portion of the fireline may be less smoky, but generates steady amounts of heat so when the headfire begins, smoke forms a column and is dispersed aloft. The placement of the head and backfire zones can be adjusted to avoid smoke in sensitive areas and apply the right flame length/residence time combination to treat fuels in different parts of the burn unit. Ring headfires are generally not recommended when wildlife is a consideration because animals may be entrapped.

4. Additional techniques, such as chevron, single point ignition, and strip head-firing, are often used to speed the development of a safe zone around a burn unit perimeter. These techniques can also be applied to create pulses of heat to lift smoke aloft. Keep in mind that head fires typically produce more smoke through incomplete ignition and subsequent smoldering, but generate high levels of heat. Size of the strips used with these techniques can make a huge difference. Large strips may produce more smoke, but because of increased heat production, the smoke is lofted higher more quickly than with smaller strips. A quick completion of a burn can reduce the time of potential exposure to smoke though generating more smoke in the short period.

When choosing an ignition technique, consider many factors, including smoke, and prioritize them with respect to objectives and risks.

Read more:

Resources: NWCG Fire Use Working Team. 2001. Smoke management guide for prescribed and wildland fire. NFES 1279, PMS 420-2 or an older version from Feb. 1985.

NWCG. 2012. Glossary of wildland fire terminology. PMS 205. http://www.nwcg.gov/pms/pubs/glossary/pms205.pdf

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Prescribed Fire Associations

Land managers across the country often have four primary reasons why they do not use prescribed fire which are: liability, limited training or experience with fire, the need for labor, and lack of equipment. All of these reasons can be addressed by forming or joining a prescribed burning association.

A prescribed burn association is where a group of landowners form a partnership in an area to pool their labor and equipment to conduct prescribed burns on each other’s land. If there is not a burn association nearby, the best way to form one is to call a meeting of interested people and involve key members of the community (landowners, lessees, cooperative extension, state and federal land management agencies, and local fire departments). Next, pick a leader.  This should be a local land owner/manager because this should be a locally led grass roots organization. Then determine the area of operation of the association, which can be an entire county, multiple counties or just focused around a community. Next, set some goals and work to achieve them. Many burn associations have been able to receive grants to purchase equipment and pay for training opportunities.

Currently there are 53 prescribed burn associations across the nation in eight states. These locally-led associations are safely and effectively using prescribed fire to manage their lands, not only for their benefit, but for the benefit of all the people around them. For more information about forming prescribed burn associations’ check out the following publications:

Prescribed Fire Associations http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2819/NREM-2880web.pdf

Prescribed Burning Associations in Texas http://www.tpwd.state.tx.us/publications/pwdpubs/media/pwd_br_w7000_1019.pdf

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When is the Best Time of Year to Conduct Prescribed Burns?

One of the main questions many land owners and fire managers often ask about prescribed burning is when is the best time of year to burn? This will vary depending upon specific land management goals. Timing will also depend upon when the burn can be accomplished safely and under favorable weather conditions. When planning prescribed burns it is important for fire managers to know and understand how many days are actually available during a specific season or over the entire year. Knowing this will allow fire managers to plan for and execute a predetermined number of burns during a given year. It can also aid in determining in which season or seasons it may be best to conduct their burns.

Limited Number of Burn Days

Most fire managers have several prescribed fires to conduct during a specific burn season, and if an adequate number of days are not available, some burns will not be conducted that year. Burns not conducted are usually postponed until the next year, adding more burns and needed burn days to an already limited schedule the following year. It can also drastically change management plans on that par­ticular burn unit. More often than not, many burn units are not burned regularly or at all because of a limited number of burn days due to restricting burning during a traditional burn season. This can negatively impact resources in numerous ways, along with creating an increased work load and cost on fire managers trying to implement prescribed burns.

Because of the limited number of burn days, a fire manger may try to burn when conditions are marginal. This can result in a prescribed fire that is not as effective as it should be causing manage­ment goals to not be met. On the other hand, safety may be compromised when prescribed burns are performed under marginal or less than desired conditions because of the need to complete all of the planned burns during that traditional time frame. If prescribed fires were conducted year-round, then more days would be available for burning, and the most optimum days for achieving goals and safety could be used.

Weather Variables

Weather has a major impact on prescribed fires and associated fire behavior. Therefore, the number of days available to burn each year is constrained by weather variables such as: temperature, wind speed, and relative humidity. Achieving the prescribed set of weather conditions during a particular time of the year has always been a dilemma faced by fire managers. If the goals of the prescribed burn are not extremely specific and safety concerns are maintained, then a wide range of conditions can be used for temperature, relative humidity, and wind speed. Often, a narrow window of weather parameters is required due to safety issues, policy, and regulation, which will reduce the number of available burn days.

Even if weather conditions can be met, timing of the prescribed burn is often limited to a single season by policy, tradition, or a lack of understanding of fire effects. Again, this limits the number of available days left to conduct prescribed burns. Remember that historically, fires occur throughout North America at any time of the year. Records show that fires set by Native Americans occurred in nearly all months, with a majority in the late summer. Also a majority of the lightning-caused fires in many regions of the United States occur during the growing season. In many areas burn season is late winter to early spring to correspond with green-up for livestock production, which also coincides with highly variable and changing weather conditions. However,  conditions during the later winter can be favorable for wildfires which will further limit to the number of available burn days.

Limiting burning to a single season will continue to severely limit the application of prescribed fire in many areas. Also the lack understanding fire affects on native plant communities will also reduce the seasonal opportunities for conducting prescribed burns.

There are several publications and videos available that can assist fire managers to better understand fire prescriptions, fire effects and the best time to burn.

The Best Time of Year to Conduct Prescribed Burns http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-7504/NREM-2885web.pdf

Fire Effects in Native Plant Communities http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2703/NREM-2877web.pdf

Fire Prescriptions for Native Plant Communities http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2704/NREM-2878web.pdf

The Impact of Fire on the Landscape SunupTV http://www.youtube.com/watch?v=xh7_onVw8PQ&feature=plcp

Prescribed Burning for Pasture Management SunupTV http://www.youtube.com/watch?v=jq0XAsWq8Ok&feature=plcp

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How does fire impact grazing?

Recently burned areas attract grazing animals because of increased forage quality and palatability. Recently burned areas also have fewer external parasites such as flies and ticks which influence habitat use. Grazing animals follow fires; thus, fire can be used to rotate animals across the landscape. However, animals tend to concentrate on these areas until a more recent burned area is available; thus, when a manager wishes to move livestock, fire is a good tool to achieve this.

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Historically, was fire important?

Yes. Fire shaped the plant and animal communities that we see presently on the landscape. The important factor is scale, both temporal (time) and spatial (size). Managers should attempt to mimic historic scale of fire to meet the needs of all native species. Even in areas that require very infrequent fire (e.g., 200 years) fire is still important to these systems.

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Are fire and grazing interrelated?

Yes, grazing animals preferentially forage on recently burned areas due to the increased palatability of new and re-sprouting vegetation. As a result, fine fuel loads at these sites are reduced, subsequently lowering their near-term burn potential. Conversely and simultaneously, fine fuels on adjacent unburned areas buildup in the absence of concentrated grazing resulting in an increased burn potential over time. The result is an ever-changing mosaic of burned and unburned patches across the landscape driven by the interaction between fire and grazing.

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