Fire requires an oxidizing agent (usually oxygen), fuel, and heat in a chemical chain reaction known as the fire tetrahedron. There are four main ways to extinguish fire: reducing temperature, removing fuel, excluding oxygen, or inhibiting the chemical reaction. Fires are classified into A, B, C, or D depending on the type of fuel. Heat transfers between objects via conduction, convection, or radiation. A fire progresses through incipient, free-burning, and smoldering phases as oxygen is consumed.

1. Fire Behavior

2. Fire Behavior
• Introduction
• Physical Science
– Definition
– Basic Components
– Fire Tetrahedron
– Fire Extinguishment Theory
– Classification of Fires
• Other References

3. Introduction
• Fire has been both a help and hindrance to
mankind
– heated homes, cooked our food, helped us to
become technologically advanced
• Firefighters should have a basic
understanding of the science of fire and the
factors that affect its ignition, growth, and
spread to perform safely and effectively in
any firefighting function

4. Physical Science
• Definition
– Fire is a rapid oxidation of combustible materials
accompanied by the released of heat and light at
various intensities.
– Pyrolysis is the chemical change brought about by heat.
• Basic Components:
– Oxidizing Agent (Oxygen)
• those materials that yield oxygen or other oxidizing gases
during the course of a chemical reaction
• bromates, bromine, chlorates, chlorine, fluorine, iodine, nitrates,
nitric acid, nitrites, perchlorates, permanganates, peroxides

5. Physical Science (Cont…)
– Heat
• a form of energy; energy in transit
• sources
– chemical – chemical reactions generate heat
– electrical – current flow generates heat; ex. overloading, static,
lightning
– mechanical – friction and compression
– nuclear – fission or fusion of atoms
• ways on how heat supports the combustion reaction
– causes the pyrolysis or vaporization of solid and liquid fuels and
the production of ignitable vapors or gases
– provides the energy necessary for ignition
– causes the continuous production and ignition of fuel vapors or
gases so that the combustion reaction can continue

6. Physical Science (Cont…)
– Fuel
• the material or substance being oxidized or burned in the
combustion process
• also known as the reducing agent
• forms
– Solid – coal, wood, plastic, paper, cloth, wax, grease, leather, cork,
etc
– Liquid – gasoline, kerosene, turpentine, alcohol, paint, varnish, oil,
etc
– Gas – natural gas, propane, butane, hydrogen, acetylene, carbon
monoxide, etc
– Chemical Chain Reaction
• a series of reactions that occur in sequence with the results of
each individual reaction being added to the rest

7. Physical Science (Cont…)
The Fire Tetrahedron

8. Physical Science (Cont…)
• Fire Extinguishment Theory
– Temperature Reduction
– Fuel Removal
– Exclusion of Oxygen
– Chemical Flame Inhibition

9. Physical Science (Cont…)
• Classification of Fire
– Class A – Ordinary combustible materials
• wood, paper, cloth, paper, rubber, and many plastics
• can be extinguished by temperature reduction
– Class B – Flammable/combustible liquids
• gasoline, kerosene, alcohol, paint, varnish, etc
• oxygen exclusion is the most effective extinguishing method
• removal of fuel and temperature reduction can also be applied,
as well as interruption of the chain reaction by dry chemical
agents

10. Physical Science (Cont…)
• Classification of Fire (Cont…)
– Class C – Energized electrical fires
• household appliances, computers, transformers, and
overhead transmission lines
• can sometimes be controlled by a non-conducting
extinguishing agent such as halon, dry chemical, or
CO2
• safest procedure is to de-energize high voltage
circuits and fight the fire appropriately depending
upon the fuel involved

11. Physical Science (Cont…)
• Classification of Fire (Cont…)
– Class D – Combustible metal fires
• aluminum, magnesium, titanium, zirconium, sodium.,
potassium, etc
• hazardous in powdered form
• water and other common extinguishing agents are
ineffective due to extremely high temperature
• special extinguishing agents are available for control
of fire in each of the metals

12. Physical Science (Cont…)
• Mechanism of Heat
Transfer
– Conduction
• the point-to-point
transmission of heat
energy
• result of direct contact
with a heat source

13. Physical Science (Cont…)
• Mechanism of Heat
Transfer (Cont…)
– Convection
• the transfer of heat
energy by the
movement of heated
liquids or gases
• there is movement or
circulation of a fluid

14. Physical Science (Cont…)
– Radiation
• the transmission of
energy as an
electromagnetic
wave without an
intervening medium

15. Physical Science (Cont…)
• Phases of Fire
– Incipient
• the oxygen content in the air has not been significantly reduced
• fire maybe producing a flame temperature well above 1000OF
(537OC), but the room temperature may be only slightly
increased
– Free-Burning
• oxygen-rich air is drawn into the flame as convection carries the
heat to the uppermost regions of the confined area
• temperature in the upper regions can exceed 1300OF (700OC)
• it continues to consume the free oxygen until it reaches the
point where there is insufficient oxygen to react with the fuel

16. Physical Science (Cont…)
• Phases of Fire (Cont…)
– Smoldering
• flame may cease to exist if the area of confinement is
sufficiently airtight
• burning is reduced to glowing embers
• fire will continue to smolder, and the room will
completely fill with dense smoke and gases of
combustion at a temperature of well over 1000OF
(537OC)
• creates the possibility of a backdraft (an explosive
ignition resulting from the combination of air with hot
gases)