How do controlled burns work? Prescribed Fire is sometimes exactly what nature ordered; learn how to do it the safe and legal way so you can take control of your land.
Prescribed fire is a difficult topic to address because in most places there are few easy options for getting your prairie burned. There are enough safety concerns with fire that if you don’t have considerable experience it’s not a good idea to try to burn your own site. Check with local conservation organizations to see if there are training courses offered in your area and volunteer yourself to help with other burns to gain experience. Other options can include experienced neighbors, contractors, local rural fire departments, or local conservation organizations. In all cases, the first step is to learn what your local laws concerning prescribed fire are. Talk to your local fire department, and find out what the protocol is for obtaining permission to burn. If you don’t feel comfortable with burning your prairie yourself, check with your fire chief and/
or other landowners in the area for other options. In some places, there are local contractors who can burn your prairie for you. Even local volunteer fire departments can sometimes help out, for a fee or just for experience.
There are three main steps to conducting a safe and effective burn on your prairie: planning, site preparation, and implementation.
Planning
The first step in planning a burn is to have a clear objective. Are you trying simply to remove the litter and standing dead grass? Are you trying to kill trees? If so, do you have large trees you want to save or do you want every- thing dead? Are you trying to suppress cool-season grasses or facilitate their growth? All of these questions should be answered before you start thinking about how and when the burn will be conducted.
Once you have an objective, there are at least five critical components to a fire plan. These are presented to give you an idea of the kind of planning that has to occur. Much more thought and information will be required to put together an actual plan.
Firebreaks. Decide where you will stop the fire on all sides of the unit and what preparation you will need to make that happen. Roads, disked cropfields, and other bare areas can be helpful, but often you will want to use mowed lines or other kinds of breaks as well. If you mow a firebreak, make sure that you also rake the dead grass out before lighting the fire. If you’re going to burn in the spring, mowing in the late fall can allow any cut grass that isn’t raked out to settle down to the ground during the winter, where it will be much less likely to catch fire during your burn.
Fuel. Consider the kinds of fuels available within the unit to be burned and in the adjacent areas. Is the grass tall and continuous or short and patchy? Are there living trees or piles of dead trees that will shoot embers into the air when they’re burned? What are the fuels outside the unit? Would you be able to easily catch a fire that hops over your line?
Potential hazards. Are there buildings, fields, hay bales, or anything else inside the unit or downwind that could be vulnerable to fire? What kinds of concerns might there be with smoke from your fire? Are there homes or roads that would be affected by large amounts of smoke? Is your entire unit accessible by the equipment you plan to use for your fire? What about accessibility to adjacent sites?
Desired weather conditions. A good weather forecast is essential. There are great websites (the National Weather Service and Weather Underground provide two of them) that give detailed forecasts of multiple conditions. In addition, you may be able to call your local National Weather Service office and talk to the public forecaster on the day of the fire to double-check conditions. Try to get forecasts that break down the day into hourly segments if possible, so you can get a feel for how the day will likely progress.
The air temperature, relative humidity, and wind speed will be the three biggest factors controlling your fire, but others are important too, like the atmospheric mixing height that helps determine how your smoke lifts. Generally speaking, you’ll want your air temperature to be between about 40 and 70 degrees Fahrenheit. When it’s colder than that you can have trouble getting the fire to burn well, and you may experience problems with the functioning of both people and equipment. Higher temperatures will mean hotter fires, which can be both good and bad, and you don’t want to burn in temperatures so hot that you risk heat exhaustion for crew members. The relative humidity is very important and should be between 30 and 60 percent for most fires. Lower than 30 percent can be dangerous in tallgrass vegetation, and higher than 60 percent can make it difficult for the fire to carry. Wind speeds of 10-15 mph are ideal, but a little higher wind speed can be acceptable in some circumstances. Lower wind speeds can actually be dangerous because the fire takes longer (more time for things to go wrong) and the wind is more likely to switch directions. Higher wind speeds are obviously trouble too, especially when you have a lot of fuel (tall, dense grass) and/or low humidity. Of equal importance to the wind speed is the wind direction. Be sure the wind is blowing in the direction you want and not toward any hazard areas.
Double-check the forecast before lighting to make sure there is no potential for the wind to shift during the next 6-8 hours.
Finally, it is important to remember that the temperature, humidity, and wind must be considered as a group, not individually. A higher wind speed might be acceptable when relative humidity is high, for example, but not when it’s already near the low end of the acceptable range. Don’t burn near the low point of the relative-humidity range and the high point of the temperature and/or wind speed range.
Contingency plans. This is the most important but often least considered part of a good burn plan. Consider the worst-case scenario, and be ready for it. Do you have the equipment you need to catch a fire that escapes? Can you get that equipment where it needs to go? Do you know whom to call for help if the fire escapes? Who will watch the fire inside the unit while others are chasing the part that is escaping? What will you do if someone is injured during the fire? What happens if the water truck breaks down? Experienced prescribed-fire leaders commonly say, “If you haven’t lost a fire, you will.” Be sure that an escape is manageable and won’t become a disaster.
A final, important component of planning is adequate equipment and crew to carry out the fire. The number of people you need will depend greatly on the size of the fire, the amount of fuel, the topography, the equipment you have, and the experience of the crew. It is difficult to conduct even a simple fire safely with fewer than 5 people, and 6 to 8 or more is often much better.
Some of the basic equipment needs for a fire include radios for communication, drip torches for lighting, portable water pumps, and safety equipment. Be sure to have a backup for each piece of equipment that you rely on. There are a number of water pump options, including backpack sprayers, ATV- mounted sprayers, and larger units that fit in the back of a truck or tractor or on a trailer. It is a good idea to have at least one or two larger units that have a high-pressure, low-volume pump. For the safety of your crew, it’s important to have everyone wear leather boots and clothing without any nylon or other materials that could melt. Nomex, or some other kind of flame-retardant outerwear, is important as well. The specific equipment needs for your fire should be discussed with someone with lots of local experience burning your kind of site.
Site Preparation
Site preparation starts months before you light a fire because the first component of that preparation is determining that there is adequate fuel. If you graze or hay your prairie, make sure that there is enough regrowth available to carry a fire next season. In general you should plan for at least half a season of rest to build up sufficient thatch and dead material. If you plan to burn in the growing season (late spring or summer) you’ll want even more fuel to carry the fire through the green, juicy vegetation.
Besides preparing your fuel, be sure your firebreaks are ready. If you are mowing breaks through tall fuel, they should be plenty wide and raked clean, with no tree piles, tall weedy areas, or cedar trees near the edge of the fire unit that could send embers across the firebreak in a strong gust. You may want to till or disk a line along the edge of a firebreak to expose mineral soil and make the fire easier to control. However, this kind of soil disturbance can have other serious consequences so consider your options carefully. Disked breaks can be an easy place for invasive plant species to gain a foothold. They can also affect many wildlife species, particularly turtles that like to nest in previously disked breaks and then are killed when the break is disked again.
Implementation
There are several ways to conduct a safe and effective prescribed fire. I will describe the most commonly used technique here, the ring fire approach, because it works well in many situations. It should definitely not be seen as the best or only method to burn a prairie, but it includes many of the important elements of a safely conducted fire.
With a ring fire, the ignition begins at the furthest downwind point of the burn unit. The first step is to light the backing fire along the entire downwind edge of the firebreak, allowing the fire to back into the unit (against the wind) but not across the firebreak. The backing fire leaves behind a large swath of black burned area along that whole side. Then both flanks of the fire are lit (walking into the wind) simultaneously, and that fire is allowed to burn into the unit (sideways to the wind) but not across the firebreak. Once the flanks are sufficiently blackened, the head fire is lit across the upwind side of the fire and allowed to roar with the wind until it puts itself out when it hits the blackened border you created with the backing and flank fires.
Insurance and Liability
Every state deals differently with liability for prescribed fire. Check with an attorney or your insurance company to clarify your situation before you burn.
In many cases prescribed fire is covered by the insurance held by agricultural landowners, but you should double-check your own situation. If you hire a contractor or someone else to burn your prairie, be sure you know who would be liable if something went wrong. Liability has to be taken very seriously these days. It should not necessarily stop you from burning, but it should definitely factor into your decision-making process.
From The Ecology and Management of Prairies in the Central United States, by Chris Helzer © 2010 The Nature Conservancy. Used with permission of the University of Iowa Press, 2010.
