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

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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

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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

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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)