Upload
don-sur
View
227
Download
0
Embed Size (px)
Citation preview
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 2/39
• It is the condition of being safe from risk or
danger of fire.
• The quality or state of not presenting or
involving risk or danger of fire.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 4/39
Fire has been both a help and a
hindrance to mankind throughout history.
Fire has heated our homes, cooked our food,and helped us to become technologically
advanced. Fire, in its hostile mode, has also
endangered us for as long as we have usedit.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 5/39
FIRE
• Is a chemical reaction. It is the rapid oxidation of a fuel producing heat and light.
• It is an oxidation taking place with a rate rapid enoughto produce heat and light.
Is a rapid, self-sustaining oxidation processaccompanied by the evolution of heat and light of varying intensity.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 6/39
Triangle of Fire
For many years, the fire triangle
(oxygen, fuel and heat) was used to teachthe components of fire. While this simple
example is useful, it is NOT technically
correct.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 8/39
Fire Tetrahedron
Each component of the tetrahedron must
be in place for combustion to occur.Remove one of the four components and
combustion will not occur. If ignition has
already occurred, the fire is extinguished
when one of the components is removed
from the reaction.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 9/39
OXYGEN (Oxidizing Agent)
Oxidizing agents are those materials
that yield oxygen or other oxidizing gases
during the course of a chemical reaction.Oxidizers are not themselves combustible,
but they support combustion when
combined with a fuel.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 10/39
FUEL
Fuel is the material or substance being
oxidized or burned in the combustion process.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 11/39
HEAT
Heat is the energy component of the fire
tetrahedron. When heat comes into contact
with a fuel, the energy supports the
combustion reaction.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 12/39
SELF-SUSTAINED CHEMICAL
REACTIONCombustion is a complex reaction
that requires a fuel (in the gaseous or
vapor state), an oxidizer, and a heat
energy to come together in a very
specific way. Once flaming combustionor fire occurs, it can only continue when
enough heat energy is produced to cause
the continued development of fuel vapors
or gases. Scientists call this type of reaction a “chain reaction”. A chain
reaction is a series of reactions that occur
in sequence with the result of each
individual reaction being added to the
rest.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 13/39
Fire Development
When the four components of the fire
tetrahedron come together, ignition occurs.
For a fire to grow beyond the first materialignited, heat must be transmitted beyond the
first material to additional fuel packages.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 14/39
Stages of Fire
• Ignition
• Growth
• Flashover
• Fully developed
• Decay
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 16/39
IGNITION
Ignition describes the period when the
four elements of the fire tetrahedron come
together and combustion begins
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 17/39
GROWTH
Shortly after ignition, a fire plume
begins to form above the burning fuel. As
the plume develops, it begins to draw or entrain air from the surrounding space into
the column.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 18/39
FLASHOVER
Flashover is the transition between thegrowth and the fully developed fire stages
and is not a specific event such as ignition.During flashover, conditions in thecompartment change very rapidly as the firechanges from one that is dominated by the
burning of the materials first ignited to onethat involves all of the exposed combustible surfaces within the compartment.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 19/39
FULLY DEVELOPED
The fully developed fire stage occurs
when all combustible materials in thecompartment are involved in the fire.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 20/39
DECAY
As the fire consumes the available fuel
in the compartment, the rate of heat released begins to decline.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 21/39
MODES OF HEAT TRANSFER
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 22/39
Heat is by-product of combustion that is
of significant importance to the firefighter.It is heat that causes fire to sustain its
combustion and, more important, to extend.
When heat given off as a product of
combustion is exposed to an unheated
substance, certain changes occur that can
make the new substance a contributing
factor in extending a fire.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 23/39
CONDUCTION
When a hot object transfers its heat,conduction has taken place. The transfer could beto another object or to another portion of the sameobject. As we have discovered and will beconstantly reinforced about, combustion occurs onthe molecular level. When an object heats up, theatoms become agitated and begin to collide with
one another. A chain reaction of molecules andatoms, like a wave energy, occurs and causes theagitated molecules to pass the heat energy to areasof non-heat.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 24/39
CONVECTION
Air that is hotter than its surroundings rises.
Air that is cooler than its surroundings sinks. Air
is made up of many molecules floating aboutfreely. Even so, it still has weight. Some
molecules are made up of the same element. For
example, oxygen in its natural state will combine
with another oxygen atom to form a stable oxygenmolecule. In a given volume, air at a given
temperature will have the same density.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 25/39
When heated, as in conduction theory,the molecules become agitated and begin to
collide with one another. In the process, themolecules are demanding more space toaccommodate the vibrations and they push
into one another as they seek that space.When that happens, the density of a givenvolume is reduced and it weighs less.Because it weighs less, it rises until it
reaches equilibrium-the level at which theweight is the same as the surroundingatmosphere.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 26/39
RADIATION
The last form of heat transfer occurs by
radiation. As we have already seen, heatenergy can be transmitted directly when
molecules collide with one another and
cause the waves of heat energy to travel.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 27/39
Conduction
Convection
Radiation
Flame Plume
Examples of heat transfer in fire
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 28/39
SPECIAL CONSIDERATIONS
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 29/39
Flameover / Rollover
The terms flameover and rollover describe a
condition where flames move through or across
the unburned gases during a fires’ progression.Flameover is distinguished from flashover by its
involvement of only the fire gases and not the
surfaces of other fuel packages within a
compartment. This condition may occur during thegrowth stage as the hot-gas layer forms at the
ceiling of the compartment.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 31/39
Thermal Layering of Gases
The thermal layering of gases is the
tendency of gases to form into layers
according to temperature. Other termssometimes used to describe this tendency
are heat stratification and thermal balance.
The hot gases tend to be in the top layer,while the cooler gases form the lower
layers.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 33/39
Backdraft
Firefighters operating at fires in the buildingmust use care when opening a building to gainentry or to provide horizontal ventilation (openingdoors or windows). As the fire grows in a
compartment, large volumes of hot, unburned firegases can collect in unventilated spaces. Thesegases may be at or above their ignitiontemperature but have insufficient oxygen available
to actually ignite. Any action during thefirefighting operations that allows air to mix thesehot gases can result in an explosive ignition called
backdraft.
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 35/39
PRODUCTS OF COMBUSTION
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 36/39
Products of Combustion
1. Heat
2. Light3. Smoke
4. Toxic gases
7/28/2019 b Fire Behavior
http://slidepdf.com/reader/full/b-fire-behavior 38/39
FIRE EXTINGUISHMENT
THEORYFire is extinguished by limiting or interrupting
one or more of the essential elements in the
combustion process (fire tetrahedron). A fire may be extinguished by:
a.) Reducing its Temperature
b.) Removal of available Fuel
c.) Exclusion of Oxygen
d.) Inhibition of Self-Sustained Chemical
Chain Reaction.