Copyright© 2000. Delmar is a division of Thomson Learning.

Objectives
1 of 3
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Describe the chemistry and physics of fire.
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Identify the sources of heat.
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Describe the characteristics of fire.
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Describe the effect of oxygen on fire.
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Define combustion.

Objectives
2 of 3
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Describe vapor pressure and vapor density.
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Describe the meaning of flammable and explosive limits.
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Describe the three types of heat transfer.
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Describe the significance of the thermal conductivity of materials.

Objectives
3 of 3
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Describe fuel types and their effects on combustion.
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Describe the basis for the theory of fire extinguishment.
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Identify the classes of fire and methods of extinguishment.
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Describe the effects of thermal balance.

Introduction
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Fire has played a major role in the development of society.
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Fire has been a friend and enemy.
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Burning, known as combustion, is a chemical reaction.
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It is important to understand the behavior of fire and what causes it to begin, grow, and spread.

Fire Triangle, Tetrahedron, and Pyramid

Measurements
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Measurement is an important part of firefighting.
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Need to know common terms for heat, electricity, volume, length, energy output, concentrations, and weight.
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Understanding measurements and limits for each on the fire ground is important.

Measurements

Chemistry and Physics of Fire
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Universe made of matter.
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Matter is never destroyed.
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Matter may change form.
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All living things are made of cells .
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Cells are made up of compounds.
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Compounds are made up of molecules .
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Molecules are made up of two or more elements .

Chemistry and Physics of Fire
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Chemistry and Physics of Fire
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Substances that are or were living are referred to as organic.
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Organic substances contain carbon, hydrogen, and oxygen.
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A non-living substance can be considered organic if it’s made of chemicals that were once alive.

Chemistry and Physics of Fire
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Organic compounds are made of various chemicals.
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Chemicals are made up of a combination of molecules.
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Molecules are joined and separated by bonding actions.
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Combination and separation of molecules and atoms causes oxidation and combustion.

Chemistry and Physics of Fire
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Atoms are made up of electrons, neutrons, & protons.
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Neutrons and protons make up the center of the atom.
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Electrons rotate around the nucleus.

Chemistry and Physics of Fire
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Atoms that lack electron will be quick to link-up and form molecules.
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Substances that are non-living, such as minerals, are referred to as inorganic substances.
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For the most part, only organic materials burn.
• A “bond” holds molecules together.

Endothermic Reaction
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When molecules are joined heat is absorbed.
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Known as endothermic reaction.

Exothermic Reaction
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When bonds break, heat is released.
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Known as an exothermic reaction.

Oxidizer
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Oxidizer acts as a catalyst in the breakdown of otherwise stable molecules.
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An oxidizer can pull apart a molecule and break the bond that existed.
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The oxidation process is evident during combustion.

Sources of Heat
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Heat
• is an energy source that powers the universe.
• can neither be created nor destroyed.
• is a physical manifestation of energy as it changes from one form to another.
• comes from four basic sources.
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Chemical
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Electrical
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Mechanical
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Nuclear

Chemical Heat
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Most common source of heat.
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Anything that burns does so through an exothermic reaction.
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Pyrolysis is decomposition or transformation of a compound caused by heat.

Mechanical Heat
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Friction causes heat that can reach levels hot enough to ignite other combustibles.
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Build up of heat from friction often causes machinery fires.
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The source of heat has to be stopped when extinguishing a fire.

Electrical Heat
1 of 2
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Most recognized source of heat.
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An electrical current can generate heat.
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Electricity is a flow of electrons from an area of greater concentration to lesser.
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Places with large quantities of electrons are negatively charged.
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Places that lack electrons are positively charged.

Electrical heat
2 of 2
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Conductors allow flow of electrons.
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One electron jumps onto an atom which releases another move to the next atom.
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Heat generated by conductors varies greatly.
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Electrical energy is a heat source.

Flow of Electrons

Nuclear Heat
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Generated the same way as other forms.
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Radioactive material is very unstable.
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Not much can be done to safely fight a nuclear fire.

Nuclear Energy and Heat

Combustion
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Term often confused with fire.
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Fire is a self-sustaining process that emits light and heat as byproducts of chemical reaction.
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In combustion the released heat energy is reinvested in the process, causing continued reaction.
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If there is continuous access to fuel, oxygen, and heat, the growth will accelerate.

Oxygen and its Effect on Combustion
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Air contains about 21 % oxygen.
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Oxygen acts as catalyst to combustion.
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This chemical reaction is called oxidation.
• Oxygen can affect a material’s combustibility.
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High concentrations of oxygen can cause some material to ignite spontaneously.

Vapor Pressure and Vapor Density
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Pressure is a continuous application of force by one body on another body that it is touching.
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Vapor pressure is the amount of pressure exerted by a liquid as it converts to gas and exerts pressure against a confined container.

Vapor Pressure and Vapor Density
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Molecules in a closed container are constantly moving and colliding.
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Some molecules escape into the air and fill the area
(diffusion.)
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If the weight of the gas is lighter than air, molecules escape (evaporation.)
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Equilibrium is reached when the amount molecules freed equal those reabsorbed.

Vapor Pressure and Vapor Density
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Air pressure changes at different altitudes.
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At sea level, air pressure is 14.7 psi.
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Gases that weigh less than the same volume of air will be lighter and tend to rise.
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Gases that weigh greater than air will be heavier and tend to drop to low lying areas.
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Vapor pressure is the force exerted on the sides of a closed container.

Vapor Density

BLEVE
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A BLEVE occurs when a vessel holding liquid ruptures from pressure being exerted on its sides when the liquid inside boils and the pressure exceeds the container’s ability to hold it.

BLEVE
2 of 3

BLEVE
3 of 3
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Even a non-flammable liquid container can rupture.
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A flammable liquid can create a great fireball.

Ignition
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When a substance heats up, burning gases are liberated.
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When all ingredients of a self-sustaining chemical reaction are present, ignition occurs.
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Ignition is the point when a material is able to sustain combustion from the heat generated by the material itself.

Boiling Point
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All materials exist as a solid, liquid, or gas.
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Pressure and temperature affect the state of matter.
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A change in temperature or pressure may change the form of the substance.

Flammable and Explosive Limits
1 of 2
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Combustible materials need certain requirements to oxidize.
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Different concentrations of oxygen may be required.
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Combustion can only take place when a substance is a gas.
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Gases can only ignite when certain concentrations are present.

Flammable and Explosive Limits
2 of 2
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When a gas concentration falls into a range that it can ignite, it is within its flammable or explosive limit.
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Flammable limits can change with temperature and surrounding conditions.

The Burning Process -
Characteristics Of Fire Behavior
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Burning process occurs in defined stages.
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Various stages must be recognized and firefighting tactics adjusted.

Growth Stage
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Speed, growth, and size of fire depends on several factors:
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Oxygen supply.
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Fuel.
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Container size.
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Insulation.

Fully Developed Stage
• All contents within the perimeter of the fire’s boundaries are burning.
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The speed and extent of a fully developed stage fire depends on amount of air.
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In an outside fire, the amount of fuel available will determine the size of the fire.

Decay Stage
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When all fuel is consumed, fire will begin to diminish.
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The fire will begin to extinguish itself when fuel exhausted.
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These factors will dictate attack strategies.

Four Stages of Fire

Fully Developed Phase - Flashover

Decay Stage of Fire

Modes Of Heat Transfer
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Heat is a by-product of combustion.
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Heat transfers its energy through:
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Conduction
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Convection
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Radiation

Conduction
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Transfer of heat from a hot object.
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Transfer can be to another object or another part of the same object.
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Molecules and atoms are excited resulting in the spread of heat.
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Heat is conducted through different materials at different rates.
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Density, time, and application of heat will affect rate of conduction.

Conduction

Convection
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Air that is hotter than its surroundings rises.
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Air that is cooler than its surroundings sinks.
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As air is heated molecules push onto one another seeking space to expand.

Convection

Radiation
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When combustion occurs, light traveling in light waves is produced.
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Light waves range from ultraviolet to infrared.
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Electromagnetic forces in lightwaves travel across vacuums and land on remote objects.
Example: Sun heats earth through radiation.

Radiation
2 of 2
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Radiation is a major contributor to flashover.
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Objects in the room reach their ignition temperature through this process.
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Heat has to be kept from developing in order to prevent the fire from extending.

Radiation

Heat Transfer in Fire

Thermal Conductivity Of Materials
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All matter will conduct heat.
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The ability to conduct thermal energy depends on its density.
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The less dense the object is, the more difficult it is for heat to transfer through it.

Physical State Of Fuels And Effect On
Combustion
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Matter is found in one of three states.
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Most fuels combust in gaseous state
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The physical state of matter can affect combustion.

States of Matter

Solid
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Molecules in a solid material are packed closely together.
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When heat is applied, molecules become agitated and collide with each other.
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This causes molecules to break apart.
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Heat produced causes additional molecules to break away, become a gas, and combust.

Liquid
• Burning is dependent on the substance’s ability to place its molecules into suspension.
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Can not burn unless it is in suspension.
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Acts as a heat sink and dissipate the introduced heat into cooler areas.
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A rise in temperature leads to a boiling or flashpoint.

Gas
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Primed for combustion.
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A ready state that will permit a chemical reaction.

Thermal Balance And Imbalance
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During combustion, heat is liberated.
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Thermal balance and imbalance causes smoke to column and mushroom.
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Heated air and smoke rise.
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Ascent stops when thermal balance is reached establishing an equilibrium.
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This causes a mushroom effect.

Theory Of Fire Extinguishment
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To stop a fire, remove one of its essential ingredients.
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Fire will collapse if missing one ingredient.
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A fire will be extinguished, if:
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Temperature is lowered.
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Fuel is eliminated.
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Oxygen is eliminated.
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Chemical flame is repressed.

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Class A
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Class B
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Class C
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Class D
Classes Of Fire

Wrap-Up
1 of 2
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Combustion results from the actual chemical reaction of heat, fuel, and oxygen.
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For the most part organic material will burn.
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Heat sources are chemical, mechanical, electrical, and nuclear.

Wrap-Up
2 of 2
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Burning process occurs in three stages: growth, fully developed, and decay.
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Heat is transferred through conduction, convection, and radiation.
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Fires are classified into different types and are extinguished differently.