Wildland fire behavior chapter 4
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
Smoldering
Fire burning without flame and spreading very slowly
Three factors that control the development of the vertical dimension are
Fire intensity, stability of the air, and wind aloft ( strong upper-level wind tend to limit the vertical development of a fire)
Backing
Fire moving away from the head down hill or against the wind
Running
Fire spreading rapidly with a well-defined head
Crowning
Fire that advances across tops of trees or shrubs more or less independent of surface fire. High fire intensity and high for rate of speed
Flames of 4 to 8 feet mean what
Fire too intense . The use of bulldozers, engines and retardant drops can be used
Fine fuels are usually the carrier of what
Fire, even in timber
Flame length less than 4 feet means what
Fires can't be attacked at the head or flanks using hand tools Handlines should hold fire
The larger attend our fields are less reactive to what
Relative humidity, but they can be tested by bending them
What are crown fires
They begin as an individual torching tree or bush if conditions are right the torching fuels will cause other trees a torch
Blowup
Sudden increase in fire intensity our rate of speed significant to preclude direct control or to upset existing suppression plans.
The weather related factors that influence fire behavior are
Temperature, relative humidity, atmospheric stability, wind speed and direction, and precipitation
Fuel moisture and temperature
The most important fuel components
The intensity of a fire increases what else will Increase
The rate at which the fuel is preheated
The probability of spotting is directly related to the intensity of what
The surface fire, burning conditions, overstory species, and crown spacing
Active crown fire
This fire is dependent on the surface fire, but there is much more transfer of heat from one bringing crown to the unburned grounds of other trees.
Flames of 8 to 11 feet mean what
Torching, crowning and spotting major fire runs. Control efforts at the head will probably be ineffective
When does a wind fire become a plume fire
When the energy released by the fire takes the convective column to such Heights that it's force becomes greater then the wind.
What three factors influence direction of fire
Wind, slope, condition of fuel
A relative humidity of 25% or less will allow fine feels to burn what
With considerable intensity
Crown level winds
of 20 miles per hour or more will permit and sustain convective and radiant heat transfer
Spotting occurs when
Burning material is carried ahead of the fire and deposited and unburned material.
The windspeed at 15 mph will
Have considerable movement in the brush and timber, and dust will be stirred up
Spotting
Sparks or embers produced by the main fire and carried by when our conviction columns across the control line
Short range spoting
Spotting that can be over ran by the existing fire
The windspeed at 10 mph will cause trees to
Standing single trees to sway from side to side
Plume driven fires
Sudden increase in Intensity Spotting occurs in all areas, The direction of spread is difficult to determine Downdraft should be a concern
Spotting in wind driven fires is
Downwind, and is a major contributer to its spread
Crown fires
Fastest spreading of all fires. Moves about 5mph or more
Creeping
Fire burning was low flame and spreading slowly
Indrafts winds
Are winds that move in to replace heated air that is lifted by the convective action of the fire. Provide oxygen to fire. It's a circle, increase in wind, increases the intensity of the fire, which in turn increases the wind
A vertical fire with the fire intensity being hot what happens
As the hot air rises cooler air from the surrounding areas will be drawn inward toward the fire to fill the void. These in drafts can actually found the fire increasing the intensity even more. Which in turn can cause it's own environment i.e. thunderclouds with lightning and strong winds.
0400 to 0800 hrs is that time of day when a fire can be when
Be easily controlled
Fine fuels moisture changes
Constantly and quickly,
What factors cause firebrands to be lifted and ignite a spot fire.
Convective lifting(the hotter the fire the higher the lift) Wind Fuel bed (where they land, High fuel) environmental conditions(moisture, slope, wind)
Flames Over 11 feet mean
Crowning, spotting and major fire runs are probable, Control at head ineffective
The Topographic factors that contribute to fire behavior are
Elevation, position on the slope, aspect, shape of the terrain, most important is steepness of slope
At 1800 to 0400 hrs factors are
Favorable
Fire intensity is affected by what four factors
Feel loading, compactness our arrangement of fuels, fuel moisture content, slope and wind speed
The fuel components that affect fire behavior are
Feel loading, size and shape of the fuel, compactness, horizontal and vertical continuity,chemical content, fuel moisture, Fuel temperature
What six factors influence the fire rate of spread and burn pattern
Fire intensity, wind speed, slope, feel type changes, natural or man-made barriers that stop or slow spread, and spotting
In the Beauford scale to estimate the windspeed a 5 mph wind will cause what
The leaves of a tree to flutter and move
Indrafts winds usually drop off just before what
The downdraft hits
Continuous fine fuels provide the potential for what
Rapid rates of spread
Long range spotting
Causes it's own fire
The vertical dimension should be considered when
When I fire develops and size or intensity
Wind driven fires
usually large and know what direction they are. The wind drives the heat to the unburned areas. A crown fire is very likely. Fast, long range spotting, direction is predictable, attack fire from flank, wind shifts are a concern
What are large dead fuels usually called
1000 hour fuels
What percentage will 1000 hour fuels burn
20%
Ten-hour feels with a few moisture content below what percentage are indicators of dry conditions
7%
What are the seven factors that constitute the fire environment
Fuel characteristics, fuel moisture, fuel temperature, topography, atmospheric stability, wind, fire behavior.
Where do crown fires occurs
Heavy timber fuels, canopies of tall shrubs, brush, plantations
At 1000 to 1800 hrs fire intensity is at its
Highest
Fast-moving clouds indicate what
Highwinds and may be signaling a Windshift. Be alert if the clouds are moving in a direction different from the surface winds.
Spot fires my hide and smolder for
Hours or days
Fuel moisture determines
If fuels Will be available to burn
Wind and convection are a problem. In the northern hemisphere what happens
In the northern hemisphere there is normally a counterclockwise movement of air as it rises. This means that there will be a higher percentage of spot fires on the left side of the fires head
1000 hour fuels are usually where there is considerable snowfall these feels big into influenced by her behavior when
In the summer after they have had time to dry out, if there's a drought, or there was an early spring
Oh 600 to 1000 hours fire in Intensity begins to
Increase making fire control more difficult
What four ways can spotting occur
Popping, convection, winds, gravity. Convective heating is the biggest problem dropping some distance
Crown spacing
Is 20 feet or less will permit convection and radiant heat transfer to occur at a level of intensity they can maintain a fire spread.
Passive crown fire
Is usually confined to one tree or a small group of trees
Independent crown fire
It is not dependent on the surface fire for its energy. This fire is developed in the crowns as the fire moves from one ground to another
For a crown fire to sustain its run it needs 6 factors
Low fuel moisture, relatively close crown spacing, intense surface fire, strong winds and steep slopes, ability to spot ahead
Downdraft occure
Occurs below the convective column. When heated air is lifted, cooled in the upper atmosphere, then back to the surface. Wind is spread everywhere.
Area ignition
Occurs when hundred of spot fires start influencing each other, and an area explodes in fire
What are the three progressive stages that crown fires developing
Passive, active, and independent