Brush, grass and forest fires

This analysis examines the circumstances, causal patterns of brush, grass and forest fires reported to local fire departments. Regional differences are also noted. A brief summary of statistics from the National Interagency Fire Center is also included.

Executive Summary

Fires in the wildland/urban interface have often been in the news in recent years. Nine of the 25 costliest fires in the U.S. were described as either wildland or wildland/urban interface fires. The eight costliest fires were in the last two decades. Federal or state agencies are typically involved in these massive fires. The term wildland/urban interface (WUI) is typically used to describe areas where extensive vegetation mixes with numerous structures and their inhabitants. WUI fires of note often begin and grow large in the vegetated areas before spreading to structures. 

What many people don’t realize is how often local fire departments around the country are called to much smaller brush, grass and forest fires.

During 2004-2008, local fire departments responded to an estimated average of 356,800 brush, grass, and forest fires per year. This translates to 976 such fires every day. 

• Only 10% of these fires were coded as forest, woods, or wildland fires. 
• Two of every five (41%) were brush or brush and grass mixtures;
• more than one-third (37%) were grass fires; and
• 12% were unclassified forest, brush or grass fires. 

In three-quarters (74%) of the brush, grass, and forest fires handled by local fire departments, less than an acre burned. Only 4% burned more than ten acres. Fires in forests tended to be larger than other vegetation fires. Only three-fifths (57%) of the forest fires were less than an acre while 9% consumed more than ten acres.

Regional differences are seen in the overall frequency of these fires and in rates per 1,000 square miles. The rate is based on total area without regard for ownership. 

• More than half (54%) of total brush, grass, and forest fires handled by local fire departments were in the South, as were 51-63% of the specific types of vegetation fires. The South also had the highest rate of total brush, grass, and forest fires per 1,000 square miles overall as well as the highest rate for grass and forest fires specifically. It ranked second in brush or brush and grass mixture fires. 
• One of every five brush, grass or forest fire responses handled by local fire departments occurred in the Midwest. The Midwest ranked second in all four of the specific types of vegetation and third on all measures of brush, grass or forest fires per 1,000 square miles.   
• The Northeast had the smallest percentages of all types of reported brush, grass, or forest fires. However, the Northeast also covers the smallest area of the four census regions.  It led the country in the rate of fires involving brush or brush and grass mixtures per 1,000 square miles. The Northeast had the second highest rate for total brush, grass, and forest fires and forest woods or wildland fires specifically. It ranked third in the rate for grass fires.
• Local fire departments in the West ranked third in the percentage of U.S. brush, grass, and forest fires handled, but they had the lowest rate of fires per 1,000 square miles for all the fire categories studied. Although most of the largest wildland fires were in the West, many of these were on lands owned by the federal government and are not protected by local fire departments. 

Brush, grass and forest fires endanger much more than other brush, grass and forest land. One indication can be seen in the property use codes recorded for these fires. In many cases, the property use codes describe places where people, buildings, and vehicles would be expected to be nearby. Roughly one-third of (36%) these fires occurred in open lands or fields. One in six occurred on highways, streets or parking areas. Nine percent, or an average of 31,700 fires per year, occurred at one- or two-family homes.                                                                                              

The important point is that these fires often occur on properties where people live, work, or travel. A brush, grass, or forest fire can spread to buildings or vehicles on the property.  A fire that starts outside a building can get into the concealed spaces between the exterior and interior. A fire inside the wall or attic space may not activate smoke alarms or sprinklers until it gets into the living space.  

Prevention and Mitigation Strategies
Many of the same wildfire safety strategies employed by property owners and residents in the wildland/urban interface can reduce the likelihood of structural ignition or fire spread from brush, grass or forest fires throughout the country. Vegetation, landscaping, and garden materials can be fuel sources for fires in a wide variety of settings. NFPA’s Firewise program helps people who live in wildland-urban interfaces protect their homes from wildfire. Much of the Firewise advice makes sense for anyone who has a yard even if they do not live or work in a wildland-urban interface. There are two important goals in fire prevention and fire protection. The first is to prevent unwanted fires from starting in the first place. The second goal is to minimize the probability that a fire, once started, will cause serious harm. 

To prevent fires, it is necessary to know how they typically start. The leading causes of brush, grass and forest fires were intentional (20%), hot embers or ashes (17%), outside fires for debris or waste disposal (15%), high wind (13%), smoking materials (12%), playing with heat source (6%), fireworks (5%), electrical power or utility lines (4%), and lightning (4%). The cause profile varies by type of fire and type of material first ignited. Lightning caused 15% of the forest fires but only 4% of these fires overall.  Because the causes are pulled from different NFIRS fields, they are not mutually exclusive. 

Prevention strategies are relatively easy to identify for some of the causes. Be sure that smoking materials are disposed of properly in fire-resistant containers. Provide metal containers for cigarette disposal to prevent them from being tossed on the ground. If you have a campfire or bonfire, be sure it is completely out. Avoid outside fires on windy days.  Leave fireworks to the professionals. Keep matches and lighters away from children. Preventing deliberate, malicious fires is far more challenging. When dealing with human beings, it is easier to say what should be done than to ensure that the procedures are always followed. 

To protect your home or property from potential fire spread from a brush, grass or forest fire, reduce the available fuel on and around the home. In particular, keep plants that burn fast and hot away from the structure. Get rid of dead branches, leaves, brush and tree limbs that hang over your home. Use gravel or some other non-combustible material next to the building instead of an organic mulch. Ensure the home itself is as ignition-resistant as possible by choosing non-flammable roofing, fire-resistant siding, screened or ember-resistant vents, and attachments (fences, decks, porches) that are fire-resistant or modified to keep from carrying fire to the main structure.

Most people have a long list of things to do around home and yard and not enough time to do them in.  It may help to know that landscaping to reduce the threat of fire can pay off in additional ways.  Some of these techniques also increase the security of your home. In their information on crime prevention through environmental design, the Seattle Police Department recommends a maximum height of three feet for hedges and a minimum height of eight feet for tree canopies, particularly in areas close to doors and windows. This approach provides fewer hiding places. Higher tree canopies make it less likely that a fire that starts on the ground will reach the branches. Keeping tree branches, vegetation, and mulch away from siding or roof can not only limit fire spread, it can help keep carpenter ants out of the home.

Many of us would like to have a more natural yard to make our lands more attractive to birds and pollinators.  It is important to remember fire safety in the process.