The expansion or spreading out of a horizontal wind field. Generally associated with high pressure and light winds.

Chemical powders that will, in very small quantities, tend to prevent other powders from caking and flocculating. Imparts free-flowing qualities to powder. Used with fire retardant chemicals.

A narrow finger or band of fuel that connects two or more patches or areas of wildland fuel.

The distance between the flame tip and the midpoint of the flame depth at the base of the flame (generally the ground surface), an indicator of fire intensity.

The layer of decomposing organic materials lying below the litter layer of freshly fallen twigs, needles, and leaves and immediately above the mineral soil.

The top layer of forest floor, composed of loose debris of dead sticks, branches, twigs, and recently fallen leaves or needles; little altered in structure by decomposition.

Layer of decomposed organic matter on the forest floor beneath the fermentation layer and directly above the soil. It is that part of the duff in which decomposition has rendered vegetation unrecognizable and mixing of soil and organic matter is underway.

Two or more firefighters stationed at a strategic location for initial action on fires. Duties are essentially the same as those of individual firefighters.

Readily vaporized organic materials which, when mixed with oxygen, are easily ignited.

A title for subordinates of principal Command Staff and EOC director’s staff positions. The title indicates a level of technical capability, qualification, and responsibility subordinate to the primary positions. Assistants may also be assigned to unit leaders.