Wildland Fire Behavior

torching

Fire burning on the surface, but periodically igniting the crown of a single or small group of trees or shrubs before returning to the surface. Not as serious as a crown fire.

creeping

Fire burning with a low flame and spreading slowly

narrow canyons

Fire can spread easily (in steep narrow canyon) to fuels on the opposite site by radiation and spotting. Wind eddies and strong upslope air movement may be expected at sharp bends

spotting

Sparks or embers produced by the main fire are carried by winds or convection column.

fuel moisture content

The amount of water in fuel expressed as a percent of the oven dry weight of that fuel

1000 to 1800

Time of day all factors of fire intensity are at their highest; air and fuels are dry, temperature is high, winds may be strong

1800 to 0400

Time of day factors favorable for fire control; winds usually moderate, air is cooler, humidity increases, fuel moisture may increase

0600 to 1000

Time of day fire intensity begins to increase, making fire control more difficult

0400 to 0600

Time of day when fire can most easily be controlled; burning usually remains slow until dawn

box canyons or chutes

can act like a chimney, channeling both wind and fire

weather effects

causes a change in rate of spread, direction of spread, and fire intensity

topography effects

changes the direction and rate of spread

loose/open

compactness of fuels that are easier to ignite

smouldering

fire burning without flame and spreading very slowly

fuel effects

fire intensity will increase as more fuel becomes available to burn

backing

fire moving away from the head, downhill, or against the wind

running

fire spreading rapidly with a well defined head

crowning

fire that advances across tops of trees independent of surface fire. High fire intensity and high forward rate of spread. Very serious.

skunking around

fire that's not doing much

slope and wind speed

fires burn more intensely moving upslope or downwind because convective heating is more efficient

warmer

fuel temperature that takes less heat to ignite

well developed smoke column

high and capped with white cloud; intense burning conditions and unpredictable fire spread

compactness of fuels

if fuels are tightly arranged with little space for air or convection to move, the fire will be less intense

leaning smoke column

indicative of wind-driven fire, one with rapid rate of spread and short-range spotting

1000 hour fuels

large, dead fuels

firebrands

lifted by convective heating and dropped some distance ahead of main fire

saddles

low spots on ridgeline that fire can easily cut across

fuel moisture, temperature

most important fuel components

steepness of slope, aspect

most important topographic components

wind, temperature, relative humidity

most important weather components

spread

movement of the fire, usually measured by the rate per hour

downdraft

occur below the convective column

firebrand forces

popping, convection, winds, gravity

foehn winds

result of high-pressure systems moving over mountains. Air heated and dried by compression. When winds die down, can result in direction reversal

barriers that slow spread

rocks, streams, lakes, rock outcroppings

smaller/finer

size and shape of fuels that are easier to ignite

collapsing smoke column

smoke; downdraft winds can cause the fire to run in all directions

sheared smoke column

straight up and flattened off at top; indicative of strong upper-level winds, potential for long-range spotting and strong surface winds

winds aloft

strong upper-level winds tend to limit the vertical development of a fire. They cut off the vertical movement of the convective heat column.

trees torching

trees catching each other indicates dropping humidity

fuel loading

type and amount of fuel available to burn

plume driven fire

when fuels and/or topography allow a fire to develop great energy in a vertical sense. Direction of spread hard to predict.

indraft

winds that move in to replace heated air that is lifted by the convective action of the fire.

blowup

A sudden increase in fire intensity or rate of spread sufficient to preclude direct control or to upset existing control plans

firewhirls

Burn intensely, can create spot fires, occur on protected side of elevated terrain features, more dangerous than dust devils.

chain

66 feet