Conducting Prescribed Fires: A Comprehensive Manual

chapter 10. Firebreaks

Firebreaks, also known as fireguards or firelines, are one of the most important elements of a properly conducted prescribed fire. Firebreaks serve several purposes, but the most crucial is to contain the fire within the boundary of the burn unit. Well-constructed firebreaks make burning safer and reduce the amount of work you have to do when conducting prescribed burns. Firebreaks should be constructed by removing any vegetation and exposing the bare ground or mineral soil so the fire cannot creep across the line and escape from the burn unit. Bare-ground firebreaks are by far the safest type. One essential use for a firebreak is to delineate the boundary of the burn unit. This is vital so that members of the fire crew can see the boundaries and not light fires outside the burn unit. For example, we conducted a burn where the boundary around the unit had been plowed, except one area with quite a few trees. In that area, we blew a line down to bare ground with a leaf blower. We had an experienced person running the torch and stripping out the leaf litter, but the line was not well defined and the person was not informed where our firebreaks were. The person went about the assigned task and ended up lighting fires along what he thought was the firebreak. Fortunately, he was stopped about 50 yards (45.7 m) outside the burn unit, and we were able to get the fire contained quickly before any major problems developed. Another important use for firebreaks is to allow vehicle and equipment access to the entire unit. Typically, vehicles constitute your main holding and suppression equipment. It is a great deal safer and easier on crew members if you can access the entire unit and not have to use hand tools to contain or suppress a spotfire. Firebreaks also allow vehicles to quickly and safely patrol the line while you watch for spotfires and problem areas. Having vehicle access is also extremely important for assisting with mop-up activities after the fire has died down. While consulting on a prescribed fire at a ranch in the San Bois Mountains of southeastern Oklahoma, we encountered a situation that demonstrated the need for firebreaks around the entire unit. This ranch was just starting to use prescribed fire; the first unit they burned was about 800 acres (323.7 ha) and had very steep slopes. The manager claimed that there were about 300 yards (274.3 m) of fireline out of the 6 miles (9.7 km) total with a slope too steep for the dozer. The 300 yards actually turned out to be closer to 0.5 mile chapter 10 Firebreaks Even so the tongue is a little member, and boasteth great things. Behold, how great a matter a little fire kindleth! —James 3:5 Firebreaks 89 (0.8 km). We had planned on making a firebreak by using rakes and leaf blowers . I told the manager that before the day was over, the ranch hands would figure out how to get a dozer down the mountain and make a firebreak because they would not like the hard work of hand lines. We started burning, and after three hours and two spotfires (with only leaf blowers and rakes to fight them), we had only 300 yards of fireline in. The manager and crew then understood how important it was to get a firebreak around the entire unit. When we finished eight hours later, the ranch hands knew that next time they could get a dozer down the slope. Good firebreaks assist with containing the fire, allowing access for equipment, and reducing the workload on the crew, which make setting fires a great deal safer and easier. Firebreaks can also be used to reduce fuel along the edge of a prescribed fire area to make ignition easier and safer. For example, tallgrass prairies contain large quantities of fuel that are over 3 feet tall (0.91 m). This fine fuel can have flame lengths of over 6 feet (1.8 m) on a backfire, which can reach across a narrow firebreak. These flame lengths also create a tremendous amount of heat, which can put crew members at risk and damage equipment. In these instances you may need to mow or shred a desired width inside the burn unit and then cut your fireline to bare ground around the outside of the mowed area. This combination will help reduce flame length and...