ESD No. 1 North Lake Travis Fire & Rescue

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ESD No. 1 North Lake Travis Fire Rescue
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• Fire Behavior /
• Fire Science

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Main Topics

• Types of Energy
• Types of Heat Transfer
• Fire Triangle
• Fire Tetrahedron
• Phases of Fire

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Introduction
Firefighters encounter a variety of conditions
when responding to a fire.
Wildland Fires may endanger a
structure Structural Fires may expose another
structure Flames may expel gases causing a life
hazard Fire in room of origin potential for
flashover Fire explosion caused by
non-ventilated building (backdraft)
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Introduction
A basic understanding of the science of fire will
help the firefighter to perform his/her duties
safely and effectively.
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Fire is a rapid chemical reaction that produces
energy.
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There are various types of energy found in
nature, such as Chemical energy released as a
result of a chemical reaction (ie.,
combustion) Mechanical energy an object in
motion has (ie., snow in an avalanche) Electrical
energy as a result of current flowing (ie.,
through a wire) Heat energy transferred between
two mediums with different temperatures (ie., sun
and earth) Light energy as visible wavelengths
produced by chemical reaction (ie.,
flashlight) Nuclear energy released as a result
of fission (ie., split atoms) or fusion (ie.,
compressed atoms)
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Two Stages of Energy
Kinetic energy possessed by a moving
object Potential energy stored in an object
that can be released at a later time
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• Heat is the tendency of energy transferred from
  one body to another when the temperatures are
  different usually from hot to cold.
• Heat transfers by three ways
• Conduction
• Convection
• Radiation

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Conduction
If you place a pot on a hot stove, the pot
heats. This is a transfer of excited atoms (the
heat source), moving to slower atoms (the pot),
causing them to accelerate. This is a
point-to-point contact method of heat transfer.
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Convection
When you hold your hand over the stove, you can
feel the energy (heat) from the flame even though
the flame isnt touching your hand. Convection
is the transfer of energy by the movement of
heated gases (air in this case) or liquids.
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Radiation
Go outside during a clear day and you feel the
warmth of the sun. The electromagnetic waves
that hit you result in heating your body. The
suns energy travels through a vacuum and we feel
it affects. Radiation is the cause of most
exposure fires.
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Combustion
Defined as the process of rapid oxidation,
resulting in fire. Oxidation can also be slow,
as in rusting, or instantaneous, as in an
explosion.
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Oxidation

• Rapid oxidation can occur in two forms
• Smoldering fires
• Steady state fire (also called free-burning
  fires)

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Fire Triangle
The Fire Triangle is an illustration that shows
that oxygen, fuel, and heat in certain
proportions create fire. If any one of the three
elements are removed, a fire cannot exist.
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Fire Triangle
As research methods of combustion improved over
the years, It was found that the fire triangle
only accurately portrayed The smoldering mode of
combustion.
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Fire Tetrahedron
Modern fire science recognized that in order to
support flaming combustion a fourth element
needed to be added to the Fire Triangle.
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Fire Tetrahedron
A chemical chain reaction is required to
continue flaming combustion. As with the fire
triangle, if any of the four elements of the Fire
Tetrahedron is removed, the fire is extinguished.
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PHASES OF FIRE
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Incipient Phase Steady-state Phase Hot-smoldering
Phase
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Incipient Phase

• The earliest phase of a fire, beginning with the
  actual ignition.
• Limited to the original materials of ignition
• Flame temperature may be over 1000F, yet the
  room temperature may be only slightly increased.

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Incipient Phase
Rollover Sometimes called flameover, rollover
occurs when unburned gases released during the
incipient phase accumulate at the ceiling level.
The superheated gases are pushed, under pressure,
away from the fire area where they mix with
oxygen. When their flammable range is reached
they ignite.
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Steady-state Phase

• Also called the free-burning phase, is generally
  when sufficient oxygen and fuel are available for
  fire growth and open burning to a point where
  total involvement is possible.
• Flame-spread is early part around 1300F
• Clear burning is accompanied by high
  temperatures with little or no smoke (ie.,
  propane fire)

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Steady-state Phase
Flashover Occurs when flames flash over the
entire surface of a room or area. It is caused
by the buildup of heat from the fire. When
unburned combustibles simultaneously reach their
ignition points, simultaneous ignition occurs and
the area becomes fully involved.
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Hot-smoldering Phase
After steady-state phase, flames may stop if
the area of confinement is sufficiently airtight.
The fire is reduced to embers. The area becomes
filled with dense smoke and gases. Superheated
gases may accumulate.
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Hot-smoldering Phase
Backdraft Also known as smoke explosion, the
superheated gases in the hot-smoldering (or
steady-state) phase(s) are rapidly ignited by
introduction of oxygen. As oxygen is introduced,
the stalled combustion resumes, sometimes as an
explosion.
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Conclusion

• An essential part of firefighting is for us
  (as firefighters) to continuously study and
  comprehend fire science and fire behavior. The
  days or Squirt the wet on the red, are over.

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Questions or Comments?