Process of extinguishing fire by the use of an agent that interrupts the chemical reactions in the combustion process.

A geographical area which is administratively defined and for which organized fire suppression activities are formally planned.

Any agent which retards a chemical reaction.

Aircraft that is generally used for cargo, retardant dropping, agricultural operations, survey work and other specific projects, and may not transport passengers.

A device installed in a chimney, flue, or exhaust pipe to stop the emission of sparks and burning fragments.

A fireline trench on the downhill side of fire burning on steep slopes that is supposed to be built deep enough to catch rolling firebrands that could otherwise start fire below the fireline. A high berm on the outermost downhill side of the trench helps the cup trench catch material.

A fireline below a fire on a slope. Should be trenched to catch rolling material.

Highest monthly average of human-caused fires calculated for a protection unit.

The boundary between two fairly distinct fuel types.

Geographic areas designed by the Clean Air Act subject to the most stringent restrictions on allowable increment of air quality deterioration. Class I areas include Forest Service wildernesses and nation memorial parks over 5,000 acres, National Parks exceeding 6,000 acres, international parks, as well as other designated lands.