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FIRE BEHAVIOR
State of GeorgiaBASIC FIRE FIGHTER TRAINING COURSE
Fire Behavior2
FIRE
Fire is the self-sustaining process
of rapid oxidation of a fuel,
which produces heat and light
Fire Behavior3
Oxygen
Fuel
Heat
FIRE TRIANGLE
Fire Behavior4
Oxygen
FIRE TRIANGLE
Oxygen (O2 ) supports combustion and life
21% O2 in air
14-16% O2 necessary to support flame• serious impairment of personnel
Below 10% O2 combustion will slow then stop• unconsciousness will occur in personnel
Some fuels contain oxygen
Fire Behavior5
Fuel
FIRE TRIANGLE
Physical States• Solid
– wood, paper, plastics
– converted to gas by pyrolysis
– size and shape of fuel effects ease of ignition and rate of burning
• Liquid– gasoline, kerosene, paint thinner
– vaporization produces gas
• Gases– natural gas, LP gas, acetylene
Fire Behavior6
Heat
FIRE TRIANGLE
Sources of heat energy• Chemical
– heat of combustion
– spontaneous heating
• Electrical– arcing
– resistance
– static discharge
• Mechanical– friction
– compression
• Solar– sun
• Nuclear
Fire Behavior7
FIRE TRIANGLE
Oxygen
Fuel
Heat
Fire Behavior8
A 3-dimensional representation used to explain the concept of fire as it produces flaming combustion
FIRE TETRAHEDRON
Chemical Chain Reaction
Oxygen
HeatFuel
Fire Behavior9
CHEMICAL CHAIN REACTION
In the burning process fuel elements are released by heat produced by the fire. These elements join
in the fire to produce more heat which releases more fuel elements
FIRE TETRAHEDRON
Fire Behavior10
PRODUCTS OF COMBUSTION
HeatSmokeLightFire Gases
Fire Behavior11
THE BURNING PROCESSStages or Phases of Burning Within a Structure
Oxygen content: 20% - 21%
Temperature: slightly elevated
Once ignited, the fire is small and confined to material first ignited
Incipient, Ignition, Growth
Fire Behavior12
Oxygen Content: 15% - 19%
Temperature: may exceed 10000 F
Rollover is possible
Fire spreads rapidly
Flashover is possible
THE BURNING PROCESSStages or Phases of Burning Within a Structure
Steady State / Free Burning Fully Developed
Fire Behavior13
A point at which the rate of heat release begins to decline as the fire consumes the fuel
THE BURNING PROCESSStages or Phases of Burning Within a Structure
Decay
Fire Behavior14
THE BURNING PROCESS Stages or Phases of Burning Within a Structure
Time
Temperture
Ignition
Backdraft Potential
DecayGrowth
FullyDevelopedFire
Post-Flashover
Incipient21-20% oxygen
Free Burning19-15% oxygen
Smoldering14% and below oxygen
Flashover Potential
Fire Behavior15
THERMAL LAYERING
The tendency of heated air and gases to form into layers in a confined room or building according to
temperatures of the gases.
Coolest Gases
Hottest Gases
Fire Behavior16
Use straight stream or very narrow fog pattern
Apply water to burning material (direct attack)
Do not flow water too long
THERMAL LAYERING
To avoid upsetting the Thermal Layering:
Fire Behavior17
An explosion or very fast burning of heated gases resulting from the introduction of oxygen when air is admitted to an overheated room or building that
is heavily charged with smoke and fire gases, depleted of oxygen, and with extremely high
temperatures
BACKDRAFT
Fire Behavior18
CONDITIONS NEEDED FOR A BACKDRAFT
Heavy concentration of gases (Dense Smoke)
Unventilated confined space
Extreme heat build-up
Fire Behavior19
Little or no visible flame (Smoldering)
Building may appear to “breath” as smoke leaves building in “puffs” (intervals)
Black smoke becoming dense gray-yellow
Windows turn extremely black and cracked
Muffled sound
BACKDRAFT INDICATORS
Fire Behavior20
A fire condition that takes place when unburned combustible gases released during the incipient stage, which have collected at the ceiling, ignite and a fire front develops that expands very rapidly across the ceiling
ROLLOVER
Fire Behavior21
A condition that occurs when a room or other area becomes heated to a point that ALL contents of the room reach their ignition temperature and ignite simultaneously
FLASHOVER
Fire Behavior22
METHODS of HEAT TRANSFER Conduction
• heat travels through intervening medium
• metals are good conductors– pipes
– steel beams
Convection• heat travels through air currents
• hot air rises
Radiation• heat waves are similar to rays of the sun
• travel in all directions until they strike an object
• unaffected by wind
Fire Behavior23
METHODS of EXTINGUISHMENT
Reduce Temperature• cool with water
Remove Fuel • turn off the valve (liquids & gases)
• remove solid fuel from path of fire
Exclude Oxygen• smother with dirt or foam blanket
• flood area with inert gas (CO2)
Break Chemical Chain Reaction• some fire extinguisher agents (dry chemical)