Chapter 4
Fire Behavior
Introduction
•
Since ancient times, fires has been
one of the most important life
-
sustaining components
•
Fire has played a major role as a tool
in the development of society
•
Sometimes an ally, sometimes an
enemy
•
Much has been learned about fire in
the last thirty years
4.
2
Fire Defined
•
Fire
is burning
–
Burning is
combustion
–
Combustion is a chemical reaction
•
Deflagration
is combustion at a rate
below the speed of sound
•
Detonation
is combustion above the
speed of sound
•
Fire tetrahedron
is the assembly of
heat, fuel, oxygen, and a self
-
sustaining chemical reaction
4.
3
4.
4
Figure 4
-
2 The old and new ways of visualizing the
combustion process: the fire triangle and the fire tetrahedron.
4.
5
Figure 4
-
3 An exothermic reaction.
Heat
•
For a fire to begin, fuels need to be
heated
•
Chemical heat: various chemicals
react with each other
•
Mechanical heat: friction of two
materials rubbing against each other
•
Electricity most recognized source of
heat
•
Nuclear heat comes from unstable
radioactive materials
4.
6
4.
7
Figure 4
-
5 Heat from friction can be produced whenever
any rubbing or compression occurs.
4.
8
Figure 4
-
6 Electricity is simply a flow of electrons from a
place where there are many to a place where they are
lacking.
4.
9
Figure 4
-
7 The process of creating nuclear energy and heat.
Fuel
•
Material consumed by the combustion
process
•
Molecules in a solid are packed closely
together
•
Liquid’s ability to burn depends on
substance's ability to place its molecules
into suspension
•
Gaseous fuels are in a state of suspension
–
Primed for combustion
•
Fuel must be at a certain temperature
before combustion can take place
4.
10
4.
11
Figure 4
-
8 States of matter. Solid materials have dense
arrangements of molecules whereas gaseous molecules are
more free
-
flowing.
Oxygen
•
Acts as a catalyst for the combustion
process
•
Oxidation is the process of oxygen
bonding to other elements and
compounds
•
Oxidation affects the process of
combustion
•
Chemical reaction accelerated with
an abundance of oxygen
4.
12
4.
13
Figure 4
-
11 The speed of combustion is affected by the amount
of oxygen present.
Chemical Chain Reaction
•
When heat, fuel, and oxygen combine
to start combustion, a chemical chain
reaction forms
•
Scientists discovered certain
chemicals introduced into burning
process can stop flaming
•
Foundation for understanding how
fires begin is grounded in the fire
tetrahedron
4.
14
Fire Growth
•
Once a fire begins, it will grow in a
self
-
sustaining manner
•
The heat being released will be
transferred to other fuels
•
The firefighter who understands fire
growth can better predict fire behavior
4.
15
Modes of Heat Transfer
•
Heat is a by
-
product of combustion
•
Conduction is the transfer of heat
through a solid object
•
Convection is the transfer of heat
through air and liquid currents
•
Radiation is the transfer of heat
through invisible lightwaves
4.
16
4.
17
Figure 4
-
12 Examples of heat transfer in fire.
4.
18
Figure 4
-
14 A natural fire plume in an unrestricted space.
4.
19
Figure 4
-
16 (A) Radiation, single heat source. (B) Radiation,
multiple heat sources.
(A)
(B)
Fire Phases
•
Burning occurs in clearly defined
phases
•
Ignition phase: substance begins to
heat up, liberates gases that can burn
•
Growth phase: fire begins to grow
from the point of ignition
•
Fully developed phase: all contents
within perimeter of fire's boundaries
are burning
•
Decay stage: all fuel consumed and
the fire diminishes in size
4.
20
4.
21
Figure 4
-
17 The four phases of fire.
4.
22
Figure 4
-
19 Full involvement of a structure is an example of a
fully
-
developed
-
phase fire.
Products of Combustion
•
Matter is neither lost nor gained; it
changes form
•
By
-
products of burning process are
heat, light, and smoke
•
Heat causes dehydration, heat
exhaustion, and burns
•
Light can cause damage to eyesight
•
Smoke is the most dangerous
product of combustion
4.
23
4.
24
Figure 4
-
21 The products of combustion are deadly
and include light, heat, and smoke.
Specific Fire Characteristics
and Events
•
Liquid, electrical, and metal fires
have certain characteristics
•
Several unique fire events can occur
within a compartment or structure
•
Learning to “read smoke” can help
predict fire behavior
4.
25
Liquid Fires
•
Liquid fuels must vaporize
•
Vaporization
is the process in which
liquids are converted to gas or vapor
•
Most liquid fires do not mix well with
water
–
Typically extinguished by coating the
liquid with an agent such as foam
•
Liquid heated to a high pressure in a
closed vessel can explode
–
BLEVE (boiling liquid expanding vapor
explosion)
4.
26
4.
27
Figure 4
-
23 A boiling liquid vapor explosion (BLEVE).
Electrical Fires
•
Class C fire: electrical energy is
creating heat
•
Control of a Class C fires begins with
control of electricity
•
Fire control efforts are aimed toward
Class A or B materials
•
Use of water can present extreme
shock hazards while fire is still
electrically energized
4.
28
Metal Fires
•
Class D metal fire is a chemical
reaction fire
•
In some cases, the presence of
water will cause a violent reaction
•
Control of Class D fires can be quite
difficult or amazingly simple
•
Shape, size, amount, and type of
metal burning will dictate the best
extinguishment method
4.
29
Hostile Fire Events
•
Any uncontrolled fire in a building is
a hostile fire event
•
Hostile fire event
: unique fire
phenomenon
–
Flashover
–
Backdraft
–
Rapid fire spread
4.
30
Reading Smoke at
Structural Fires
•
Firefighter applies understanding of basic
fire behavior by reading smoke
–
Helps discover clues about the location of the
fire
•
Smoke volume is an indicator of the
amount of fuels that are “off
-
gassing”
•
Smoke velocity is an indicator of pressure
that has built up within the building
•
Smoke density is indicative of the amount
of fuel that is laden within the smoke
4.
31
4.
32
Figure 4
-
24 Smoke leaving a building has four attributes:
volume, velocity, density, and color.
(Photo by Keith
Muratori from FIREGROUNDIMAGES.com)
4.
33
Figure 4
-
25 Turbulent smoke flow is a warning sign of
impending flashover. The brown smoke issuing from the eves
indicates that the roof trusses have been heated
—
a collapse
warning sign.
(Photo by Keith Muratori from
FIREGROUNDIMAGES .com)
4.
34
Table 4
-
3 Reading Smoke Shortcuts
Lessons Learned
•
Firefighter survival and fire attack
effectiveness is dependent on the
understanding of fire dynamics
–
Ingredients needed for combustion
–
Heat sources
–
Fuels
–
Fire phases
–
Special considerations
–
Reading smoke
4.
35
Enter the password to open this PDF file:
File name:
-
File size:
-
Title:
-
Author:
-
Subject:
-
Keywords:
-
Creation Date:
-
Modification Date:
-
Creator:
-
PDF Producer:
-
PDF Version:
-
Page Count:
-
Preparing document for printing…
0%
Commentaires 0
Connectez-vous pour poster un commentaire