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. 

A hose connection with two outlets permitting two connections of the same coupling diameter to be taken from a single supply line.

Hose fitting that performs the functions of a Siamese or a wye (i.e., to combine the flow from two lines into a single line or to permit two lines to be taken from a single line).

Hose fitting (preferably gated) for combining flow from two or more lines of hose into a single stream; one male coupling to two female couplings.

In a discussion of fire retardant slurries, deterioration of viscosity.

Cleared path wide enough to permit single-lane vehicular access in a remote area.