Author(s): Marty Ahrens. Published on September 1, 2011.


A 16,000-acre brush fire meets a freeway in Southern California. Brush, grass, and smaller forest fires are common occurrences for many local fire departments across the country.(Photograph: AP Wide World/Mike Meadows)

Brush, Grass, and Forest Fires
Wildfire in the United States is much more than the dramatic fires that grab headlines—it’s also the smaller brush, grass, and forest fires, nearly 1,000 every day, that are mostly fought by local fire departments. 

NFPA Journal®, October 2011 

By Marty Ahrens

Editor’s note: The following is an excerpted version of NFPA’s 
Brush, Grass, and Forest Fires report from August, 2010.

Huge fires in the wildland-urban interface have made headlines in recent years, with stories about the federal and state agencies that battle to contain them. But local fire departments around the country are also engaged in fighting wildfire, responding to a range of smaller, but numerous, brush, grass, and forest fires.

During the five-year period of 2004–2008, local U.S. fire departments responded to an estimated average of 356,800 brush, grass, and forest fires per year. On average, 976 brush, grass, or forest fires were reported per day. These incidents accounted for one-quarter (23 percent) of all fires reported to local fire departments. During this period, 4,800 buildings, on average, were involved annually in brush, grass, and forest fires handled by local departments.



Mulch + Fire
Why mulch can pose a fire problem — and why it can be especially hazardous in areas prone to wildfires.

The 356,800 natural vegetation fires reported per year include an average of:

  • 145,400 (41 percent) brush or brush and grass mixture fires;
  • 132,000 (37 percent) grass fires;
  • 36,700 (10 percent) forest, woods, or wildland fires; and
  • 42,700 (12 percent) natural vegetation fires that were not classified further.

[Most of the statistics in this report are national estimates derived from the details provided by the U.S. Fire Administration’s National Fire Incident Reporting system (NFIRS) and NFPA’s annual fire department experience survey. Only fires reported to local fire departments are included in these estimates. Information from the National Interagency Fire Center’s website about wildland fires handled by state and federal wildland agencies is discussed below.]

Local responses to these fires peaked in March and April. However, 4,700 such fires were reported on July 4, almost five times the daily average. These incidents were also more common on Saturday and Sunday than other days of the week. The peak time of day for these fires is between noon and 6 p.m.

Roughly four of every ten brush, grass, or forest fires occurred on properties described as open land or fields. Nine percent of these fires occurred at one- or two-family homes. During this period, heavy or light vegetation was the item first ignited in an average of 4,800 reported home structure fires per year.

The leading causes of brush, grass, and forest fires were summarized with data from several NFIRS fields. These causes were pulled from different NFIRS fields and are not mutually exclusive. The leading causes were: intentional (20 percent), hot embers or ashes (17 percent), outside fires for debris or waste disposal (15 percent), high wind (13 percent), smoking materials (12 percent), playing with heat source (6 percent), fireworks (5 percent), electrical power or utility lines (4 percent), and lightning (4 percent). The cause profile varies by type of fire and type of material first ignited. Lightning caused 15 percent of the forest fires but only 4 percent of these fires overall. While high wind is not a heat source, wind can cause non-hostile fires, such as campfires or fires for open burning, to spread out of control.

In almost two-thirds of these fires, the item first ignited was some type of light vegetation, including grass, leaves, needles, chaff, mulch, and compost. A separate field asks about the composition of the item first ignited. An unclassified natural product was first ignited in a quarter of these fires. Hay or straw was first ignited in one of every five (19 percent) grass fires and 8–12 percent of the remaining categories. Wood chips, sawdust, or shavings were first ignited in 8 percent of total forest, brush, or grass fires.

Unlike the giant wildland fires that make the news, three-quarters of brush, grass, and forest fires handled by local fire departments burned less than an acre. Three out of five (57 percent) forest, woods, or wildland fires, and three-quarters (72–77 percent) of the remaining types of fires, consumed less than one acre. Nine percent of the forest, wildland, or wood fires consumed more than 10 acres (4 hectares), compared to 3–4 percent of the remaining types of fires.

One reason that forest, woods, or wildland fires were likely to grow larger than other vegetation fires is that the response time tended to be longer. It took local fire departments 15 minutes or more to reach one-fifth (21 percent) of the forest, woods, or wildland fires. For the other categories of natural vegetation fires, only 11–12 percent of the responses took that long. Also, only one-quarter (28 percent) of forest, woods, or wildland fires were reached within five minutes, compared to 38–40 percent of other categories of natural vegetation fires.

Regional breakdown
Wildland fires in the West may get the headlines, but the busiest region is the South, where 54 percent of all local fire department responses are to some kind of wildfire incident. The Midwest ranked second. Local fire departments in the Northeast had the smallest percentages of all types of reported brush, grass, or forest fires.

The distribution of fires in the Northeast was also different. Fires involving brush or brush and grass mixtures accounted for almost two-thirds (64 percent) of the brush, grass, or forest fire responses in the region, compared to a little more than one-third (38 percent) in the South, Midwest, and West. Fires involving grass accounted for only 12 percent of these fires in the Northeast compared to 33–41 percent in the other three regions.

The table at right shows that the South also had the highest rate of total brush, grass, and forest fires per 1,000 square miles (2,590 square kilometers) overall, as well as the highest rate for grass and forest fires specifically. The Northeast ranked second overall but led the country in the rate of brush or brush and grass mixture fires. Local fire departments in the West had the lowest rate for all the fire categories studied. This may seem counterintuitive, but large parts of the West are not protected by local fire departments.

According to the National Atlas, the federal government owns almost a third of the land in the U.S. Most federally owned lands are in the West. In their 2007 report, Forest Resources of the United States, Smith, Miles, Perry, and Pugh noted that 80 percent of the forested federal or state land owned is in the West. Almost half (46 percent) of the private, municipal, or county forested lands were in the South. The Northeast had the smallest amount of forested land in all categories of ownership.

Wildland Fire Statistics from the National Interagency Fire Center
State and federal agencies handle some vegetation or wildland fires independently and assist local departments with others. Information on federal and state wildland firefighting activities is available at the National Interagency Fire Center’s website at An unknown number of fires included in their statistics were also handled by local fire departments and included in NFPA’s estimates.

The total number of wildland fires handled by federal or state wildland fire agencies since 1985 ranged from a low of 48,900 in 1989 to highs of 96,400 in 1996 and 2006. In 2009, these agencies responded to 78,972 wildland fires that burned 5.9 million acres (2.4 million hectares) with an average of 75 acres (30 hectares) burned per fire. 

Because of normal fluctuation, five year rolling averages can better identify trends. The acreage burned in wildland fires handled by wildland fire agencies was higher in 2004–2007 than at any point since 1985. The rolling averages show a fairly steady increase in burned acreage beginning in the late 1990s, while the average number of fires handled in recent years was actually lower than a decade ago. The data suggest that it is the severity, rather than the frequency, of these fires that is the major change.

The 13 percent of wildland fires handled by wildland fire agencies that were started by lightning in 2005–2009 consumed almost two-thirds (62 percent) of the total burned wildland acres.

Firefighter Fatalities
On average, 18 firefighters per year were fatally injured by wildland or prescribed fires.

In her report on the subject, NFPA’s Rita Fahy reported that from 1999 through 2008, 180 (18 percent) of the 1,007 firefighter fatalities (excluding firefighters killed on September 11, 2001) died as a result of wildland fires, defined here as forest, brush, or grass fires, and prescribed fires. Fire ground injuries caused more than half (57 percent) of these fatalities. Almost half of the victims were associated with local fire departments, including 40 percent who were volunteers and 6 percent career firefighters; 54 percent were associated with federal or state agencies. More than one-quarter (28 percent) of all fire ground firefighter fatalities resulted from wildland or prescribed fires.

Marty Ahrens is manager of NFPA’s Fire Analysis Services.

Mulch + Fire
Why mulch can pose a fire problem — and why it can be especially hazardous in areas prone to wildfires 

Mulch fires are attracting increased attention. As more homes and businesses ban indoor smoking, a larger share of smoking is done outside. Too often, discarded cigarettes end up in the landscaping mulch, leaves, or vegetation. In a March 2008 Fire Engineering article, Mark Finucane wrote that the Johnston City, Tennessee Fire Department responds to an average of 100 mulch fires per year. Burning mulch was sometimes right next to a building and could ignite the underside of the structure’s siding and spread into the structure. Large piles of mulch can spontaneously ignite.

In 2010, the Massachusetts Department of Fire Services issued a press release reminding people to keep smoking materials out of bark mulch. Massachusetts had 184 fires in the past five years that began with mulch and spread to buildings. A 2008 Massachusetts mulch fire caused $5 million in damage to a sprinklered apartment building and permanently displaced 36 residents.

Heat sources were analyzed in brush, grass, and forest fires beginning with two types of material that could be mulch: a) wood chips, sawdust, and shavings; and b) hay or straw. Smoking materials started half (48 percent) the fires that began with wood chips, sawdust, or shavings, compared to 14 percent that began with hay or straw. Hot embers or ashes were common heat sources for both hay or straw and wood chips.

In general, fires starting with hay or straw were more likely than wood chips, sawdust or shavings to have had a flaming ignition source such as matches (16 percent vs. 3 percent), lighters, (6 percent vs. 3 percent), and fireworks (6 percent vs. 1 percent). Arcing was also a more frequent heat source in hay or straw fires (5 percent vs. 1 percent). An unclassified hot or smoldering object was the heat source in only 5 percent of the hay or straw fires compared to 13 percent of the wood chips, sawdust, or shavings fires.
In a 2003 Journal of Arboriculture article, Steward, Sydnor, and Bishop described how 13 landscape mulches were ignited by cigarettes, matches, and a propane torch. Ground recycled pallets, composted yard waste, and shredded pine bark were the most easily ignited by cigarettes. Decorative ground rubber, pine straw, and oat straw were the most easily ignited by the propane torch. Weathering increased the ignitability of some mulches and decreased others.

In their 2007 paper on mulch flammability, Zipperer, Long, Hinton, Maranghides, and Mell studied four mulches: pine straw, shredded cypress wood and bark, small pine bark chunks, and large pine bark chunks under laboratory and field conditions. Pine straw was easiest to ignite. The large pine bark and pine straw produced large amounts of heat and had high rates of consumption. However, the pine straw burned for the shortest length of time. The authors noted that “each one of the tested mulches burned and none are 100 percent safe. Mulch should not be used next to flammable material or vinyl surfaces on buildings… Only decorative gravel or stones or some other non-flammable material should be used immediately adjacent to the home.”

— Marty Ahrens