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