Wildfires

Wildfires, also called forest fires and grass fires, are large fires that spread quickly and can cause much destruction. They can consume entire forests and destroy houses and buildings. While weather conditions, climate change, and other factors affect wildfires, people cause about 90 percent of wildfires.

A wildfire requires heat, fuel, and oxygen. Heat starts a fire and helps it spread by drying out nearby fuel. Fires usually need a minimum of 16 percent of oxygen content to burn. Air is about 21 percent oxygen. Burning fuel reacts with oxygen (oxidation) and releases heat; it also produces gases, smoke, and other combustion products.

Most wildfires are started by humans, either accidentally or intentionally. Some begin by accident such as when campfires are left unattended or not doused properly, a lit cigarette is tossed, or a person burning garbage cannot control the fire. In the United States in 2022, according to the National Interagency Fire Center, 61,429 wildfires were caused by humans and burned more than 3.3 million acres. Nature, such as in the form of lightning, causes about 10 percent of wildfires. Lava from volcanoes also can start fires. Other factors, such as droughts and insect infestations, can increase the likelihood and spread of wildfires.

Although wildfires can damage property and cause deaths of humans and animals, these blazes play an important part in many ecosystems. Fires remove dead and dying vegetation and make resources available to other organisms. Seeds of some plants, such as the lodgepole pine, cannot sprout without fire. Their seeds are sealed into cones or fruits covered with resin, which must be melted before the casing can open. Seeds of some plants only sprout when certain chemicals from smoke and scorched plants are present.

Wildfires also affect animal populations; they not only kill animals but also destroy their habitat. Areas that have burned can develop erosion problems if trees and other plants are gone. Erosion and runoff from charred areas can also affect streams and rivers. The smoke from fire may bring health risks. Wildfires can create a toxic haze, and the poor air quality can cause schools to close and airlines to ground flights. The toxic air also may cause respiratory infections and in extreme cases, death.

The US National Park Service uses a variety of methods to prevent wildfires. If a fire occurs in an area full of fuel—such as deep litter or fallen logs—it will burn hot and become very destructive. Some forested areas are managed through controlled burning, also known as prescribed burning. Thinning and mowing in areas with too much dead matter eliminates the fuel needed by fire. These mechanical methods reduce the chances of wildfires and prevent any fires from burning hot enough to severely damage plants.

Fire prevention specialists may create fuel breaks, which are strips or blocks of land in which the fuel has been reduced. They may cut down trees to increase gaps, which allows heat to escape, and remove vegetation that is close to trees to prevent fires from spreading tree to tree. Some communities create fuel breaks around homes to allow fires that engulf nearby trees to creep through lawns and around houses without burning them. Flames flare up again when they reach the next tree-covered area.

Prevention also involves paying attention to and eliminating ladder fuels, fuels that allow fire to progress from low to medium to high vegetation. Grasses are examples of low vegetation, shrubs are medium-tier vegetation, and trees are high vegetation. A single tree comprises ladder fuels—low-hanging branches, mid-level branches, and the treetop or crown of the tree.

Firebreaks can prevent, control, and stop wildfires. Unlike fuel breaks, which remove some of the vegetation, firebreaks are strips of ground without any fuel. Firebreaks may be bare soil or vegetation that is fire retardant (resistant to burning). These areas may be manmade, such as roads, or natural barriers, including ponds and streams. A fire driven by high winds, however, may cross a narrow firebreak.

The goal of firefighters when fighting wildfires is to protect lives and property. Fighting fire may involve a number of methods and equipment. Handcrews and bulldozer/tractor plow crews may be sent to use axes and other hand tools to create firebreaks. Firefighters who directly attack fires usually include engine crews, hotshot crews, helitack crews, and smokejumpers. Engine crews use fire engines with water tanks to reach and fight fires. Hotshot crews attack the most difficult fires and often work in remote areas. Helitack crews use helicopters to fight fire and may rappel directly into hard-to-reach areas to attack it on the ground. Smokejumpers parachute into remote areas.

Helicopters and airplanes are used to drop water and fire retardants. Dropped water cools the areas where ground crews are working and helps to make the dangerous work safer. The ground crews fight the fires, while the aircraft drop water on hot spots or directly on flames to slow the spread of fire. An indirect attack involves dropping water or retardant away from a fire to create a firebreak. A parallel attack is made closer to a fire and curbs the spread of flames. A direct attack focuses on hot spots or the very edge of a fire.