chapter 08

Wildland Fires

Chapter 8

Objectives

• Explain the basic fire combustion principles and be able to apply them to wildland fires, and differentiate wildland fire behavior from structural fire behavior

• Examine how weather conditions impact wildland fuels and the behavior of wildland fires

Objectives (cont’d.)

• Describe the various parts of a wildland fire and identify how fire behavior impacts the methods of fire fighting wildland fires– Include some of the special techniques needed to

extinguish and control these fires

• Describe the method used to classify resources used on wildland fires and how fire behavior impacts the type and amount of resources needed to suppress wildland fires

Objectives (cont’d.)

• Describe the various resources and tools used in extinguishment of wildland fires

Introduction

• Vast difference between wildland fire fighting and structural fire fighting

• This chapter centers on differences and similarities between both types of fire fighting and differing extinguishment methods

• Triangle model still used by most wildland agencies

The Fire Triangle for Wildland Fires

• In wildland fire fighting, the heat is cooled, the fuel is removed, or the oxygen is excluded from the fuel– Water directed by hose lines, hand tools, or machines– Dirt or foam to smother, cool, and exclude oxygen

The Fire Triangle for Wildland Fires(cont’d.)

Figure 8-1 The fire triangle shows the wildland fire combustion process

Heat Removal

• Represents removal or reduction of the ignition temperature of the fuel

• Water is most effective, but other materials used• Yellowstone has used CAFS• Foam and fire retardants can be applied by

aircraft and special foam application-equipped vehicles such as the CAFS

Heat Removal (cont’d.)

Table 8-1 Foam expansion rate and drain time

Fuel Removal

• Most common method of extinguishment• Accomplished by:

– Cutting or scraping– Using bulldozers and/or hand crews– Backfiring operations

• Fuel is burned in front of the main fire

Oxygen Removal

• Accomplished by:– Throwing dirt at base of the flames or area of

combustion to cool down/exclude oxygen

• Aircrafts drop either water or flame retardant solutions– Must degenerate or be biodegradable generally within

thirty days

Wildland Heat Movement

• Heat moves in four ways:– Conduction: transfer of heat within material itself– Convection: transfer of heat by liquid or gas– Radiation: radiates energy ahead of fire– Direct flame impingement: flame front is moving

upslope where the flames lay down or move at an angle to the slope

Wildland Heat Movement (cont’d.)

Figure 8-4 Awildland fire canmove uphill quicklywhen the flameslean to an angle andheat the fuel byconvection currentsand direct flame

Wildland Fire Size-Up

• Five-step decision-making process:– Factors impacting life safety– Factors impacting property safety– Factors that may harm the environment– Factors that will harm wild life– The availability of needed fire fighting resources

Behavior of Wildland Fires

• Fire behavior triangle– Affected by weather, topography, and fuels

• Burning index: – A number in an arithmetic scale determined from fuel

moisture content, wind speed, and other selected factors that affect burning conditions

– Index from which the ease of fire ignition and their probable behavior may be estimated

Weather

• Temperature: fuel temperature is necessary to initiate and continue fire combustion process

• Stable and unstable air masses: vertical temperature distribution within air mass and vertically moving parcel of air

• Temperature inversion: cooler air close to ground surface and warmer air above cooler air

• Relative humidity: ratio or amount of water vapor in air to maximum amount air can hold

Weather (cont’d.)

• Wind velocity and direction: movement of warm to cooler air setting a circulation pattern of rising and descending air currents

• Foehn winds: when air is pushed over high elevations and flows downhill

• Fuel moisture: cooling effect from moisture in air• Dust devils and fire whirls: indicators of unstable

surface conditions and will cause erratic fire behavior

Topography

• Slope: fuel preheated by direct flame impingement and convective air currents; draft effect is created

• Aspect: direction a slope faces to the sun• Elevation: influences how air moves from the

valleys that are warming to the cooler ridges, positioning of warm/cool air masses in thermal belts, and length and type of fuel

Topography (cont’d.)

• Canyons: wideness or narrowness determines effect

• Saddles: low topography between two high points

• Ridges: elements that divide the terrain• Chimneys: steep, narrow draws in canyons

Figure 8-5 Elevation changes fuel types

• Fuel loading: the amount of fuel available to burn in a given area

• Light fuels: Grass and other small plants occur on the floor of all forests

• Medium fuels: Medium fuels consist of brush that is six feet in height or lower

• Heavy fuels: brush taller than six feet; timber, slash, and standing conifer and hardwood trees

Fuels (cont’d.)

• Fuel shape and arrangement: may determine how the fuel can affect the ignition and spread of a fire

• Aerial fuels: include all green and dead materials located in the upper forest canopy– Crown fires: advance along tree tops and shrubs

independently of the surface fire

Fuels (cont’d.)

• Amount of moisture in the fuel will affect how easily it will ignite and how intensely it will burn– Dead fuel moisture– Living fuel moisture

• Time lag: time it takes for the moisture content of fuel and the surrounding air to equalize

• The warmer the fuel, the less heat is required to ignite it

Fire Behavior- Identifying Parts of a Wildland Fire

Figure 8-7 Parts ofa wildland fire

Spotting

• Occurs when wind and convection columns broadcast hot fire brands into the unburned fuel (green area) ahead of the main fire

• Convection columns: thermally produced column of gases, smoke, and debris produced by a fire

Large Fires

• Can become so large that the combustion process creates its own indraft of oxygen– Backfire or burn out the fuel near the fire edge in an

effort to separate the fire from the fuel– Works well when the backfire is ignited to be

entrained into the main fire

Area Ignition

• Occurs when:– Spot fires take place in an area with unburned

vegetation– Spot fires are burning in a bowl or canyon or an area

where the heat from the spot fires is trapped

• Pre-heated vegetation in the area can explode into combustion

Fire Resources

• Include engine companies, water tenders or trucks that carry water, hand crews, aircraft (both fixed wing and rotary wing), and bulldozers

• Field operations guide: a small notebook designed to be carried in the shirt pocket, containing complete data on the ICS, including job titles, descriptions, and equipment classification systems

Engine Types

• Both air and ground are used and very versatile• Can fight fire both day and night• Not restricted by visibility• Can deliver water at various capacities • Can transport a crew to fire with their equipment• Crew can construct hand line

Hand Crew Types

• Biggest portion of suppression personnel• Use hand and power tools to reduce the fuel

side of the triangle• Type I: These persons are highly trained to work

on all fires directly on the fire line• Type II: These persons have some training with

fire line work restrictions

Bulldozer Types

• Provide a tactically balanced and integrated fire suppression force

• Attack the fuel side of the triangle• Type I: Heavy D-7, D-8, D-9

– Heavy, thick brush, timber or road construction

• Type II: Medium D-6 and HD-11– Heavy to medium brush

• Type III: Light D-4 and HD-6– Light fuels, grass, fast-moving fire

Fixed-Wing Aircraft Types

• Attack the heat leg of the fire triangle• Cool with water or retardants• Type I: capacity of 3,000 gallons• Type II: capacity of 1,800 to 2,999 gallons• Type III: capacity of 600 to 1,799 gallons• Type IV: capacity of 100 to 599 gallons

Rotary-Wing Helicopters

• Principle advantage of a helicopter is its ability to operate from locations close to and on fire line

• Cannot carry as much as the fixed-wing aircraft,• Work closer to houses and pinpoint application

of the retardant more precisely• Use for application water or retardant chemicals, • Carry injured firefighters

Rotary-Wing Helicopters (cont’d.)

Figure 8-10 Rotary-wing aircraft

Wildland Fire Tactics - Direct Method of Attack

• Attack itself is directed to edge of burning fire• Firing out: to “burn out” fuel between the main

fire line and the line being constructed for fire control

• May not be effective against intensely hot or fast-moving fire

• Requires close coordination of all crews

Wildland Fire Tactics - Indirect Method of Attack

• Construct control lines or backfire the fuel ahead of hot, intense fires, and large fires– Constructed control lines located using favorable

topography

• Work away from large amounts of heat and smoke and thus reduce fatigue

• Fire is not being extinguished when control lines are being put into place

• Unburned fuel may be left inside control line

Wildland Fire Tactics - Combination Attack

• Advantages of direct attack and indirect methods

• Work directly on fire line in areas that are safe and can be reached quickly in an effort to contain as much of the fire as possible

• Crews begin to work indirectly in areas where the fire line cannot be attacked directly to put in and burn out a clean line

Application of Attack Methods

• Tandem action: direct attack method with the attacking forces working in tandem (one unit following the other)

• Pincer action: moving crews along both flanks of the fire to a point where the flanking forces move closer together in a pinching action near the head of the fire

Application of Attack Methods (cont’d.)

• Envelopment action: taking suppression action on a fire at many points and in many directions simultaneously

• Parallel method: method of suppression in which the fire line is constructed approximately parallel to and just far enough from the fire edge to enable personnel and equipment to work effectively

Summary

• Original fire triangle model is often applied rather than the newer fire tetrahedron model

• Weather, fuel, topography and the combination thereof affect the fire behavior

• Three methods of attack:– Direct– Indirect– Combination attack

chapter 08

behavior of wildland

fighting wildland fires

wildland fires chapter

wildland agencies

fuel temperature

fuel removal

wildland heat movement

fuel water

Technology

chapter 08

08 chapter 08