This document defines key terms related to fire chemistry and behavior. It explains that the three necessary elements for a fire are heat, fuel, and an oxidizing agent (usually oxygen from air). Fires start when these elements come together in the proper proportions. Fuels must be in gaseous form to burn, requiring solids and liquids to undergo pyrolysis or vaporization first when heated. Heat is then transferred between objects via conduction, convection or radiation to allow the fire to spread.

1. CHEMISTRY AND BEHAVIOR OF FIRE

2. DEFINITION OF TERMS
• Fire (Various definitions):
1. Rapid oxidation of matter accompanied
by heat or flame;
2. A rapid chemical reaction that gives off
energy and products of combustion that are
very different in composition from the fuel
and oxygen that combine to produce them;
3. A chemical reaction that occurs, when
fuel, air and a source of ignition are brought
together at the same time and in proper
proportions.

3. • Oxidation – A complex chemical reaction of
organic materials with oxygen in air or other
oxidizing agents resulting in the formation of a
more stable compound.
• Organic materials – Substances containing
carbon, such as plant and animal materials.
More stable compounds are simply those with
less bound up chemical energy.
• Combustion – A self sustaining process of
rapid oxidation.

4. • Fuel – Any form of matter capable of burning.
• Heat – A form of energy that raises
temperature.
• British thermal unit (BTU) – The amount of
heat needed to raise the temperature of one
pound of water to one degree Fahrenheit.
• Calorie – The amount of heat needed to raise
the temperature of one gram of water to one
degree Celsius.

5. • Fahrenheit – English unit of temperature with
32⁰ as freezing point of water and 212⁰ as
boiling point.
• Celsius – Metric unit of temperature with 0⁰
as freezing point of water and 100⁰ as boiling
point.
• Vapor pressure – A measure of the tendency
of a substance to evaporate.
• Boiling point – When vapor pressure exceeds
atmospheric pressure. Also when rate of
evaporation exceeds rate of condensation.

6. • Flash point – The minimum temperature at
which a liquid fuel gives off vapors to form an
ignitable mixture with oxygen in air.
• Fire point – The temperature at which a liquid
fuel will produce vapors sufficient to support
continuous combustion when heated.
• Vaporization – Process by which gases
(vapors) are evolved from liquid when heated.
• Pyrolysis – Process by which gases (vapors)
are evolved from solid when heated.

7. • Flammable limits (range) – The limits within
the percentage of a substance in vapor state in
air will burn once it is ignited. This is where
the fuel vapor in air mixture is in proper
proportions to support combustion.
• Specific gravity – Density of a liquid in relation
to water. This is the weight of the liquid
compared to the weight of an equal volume of
water.
• Vapor density – Density of gas or vapor in
relation to air. This is the weight of the gas or
vapor compared to the weight of an equal
volume of air.

8. THREE (3) ELEMENTS OF FIRE
• Heat
• Fuel
• Oxygen
For a fire to occur, three (3) things must be
present at the same time and in proper
proportions; a fuel, a source of ignition (heat),
and a source of oxygen (air or any oxidizing
agent).

9. FUEL
• Fuel is the material or substance being
oxidized or burned in the combustion process.
In scientific terms, the fuel in a combustion
reaction is known as reducing agent. Most
common fuels contain carbon along with
combinations of hydrogen and oxygen. These
fuels can broken down further into
hydrocarbon-based fuels (such as gasoline, oil,
and plastics) and cellulose-based materials
(such as wood an paper).

10. • There are also other based fuels that are less
complex in their chemical makeup, including
hydrogen gas and combustible metals such as
magnesium and sodium. In the combustion
process there are two (2) fuel-related factors:
1. the physical state of the fuel; and
2. its distribution.
• These factors are discussed as follows:

11. • A fuel may be found in any of the three states
of matter: solid, liquid or gas.
• Only gases burn; to burn fuels must normally
be in its gaseous state.
• For solids and liquids, energy must be
expended to cause these physical changes.
• The initiation of combustion of a liquid or
solid fuel require their conversion into
gaseous state by heating.

12. SOLID FUELS
• Fuel gases are evolved from solid fuels by
pyrolysis. Pyrolysis is the chemical
decomposition of a substance through the
action of heat.
• Simply stated, as solid fuels are heated,
combustible materials are driven from the
substance. If there is sufficient fuel and heat,
the process of pyrolysis generates sufficient
quantities of burnable gases to ignite.

13. • Because of their nature, solid fuels have a
definite shape and size. This property
significantly affects the ignition of the fuel.
• Of primary importance is the surface-to-mass
ratio of the fuel. The surface-to-mass ratio is
the surface area of the fuel in relation to the
mass.
• Wood is one of the best examples of the
surface-to-mass ratio. To produce usable
materials, a tree must cut into a log.

14. • The mass of the log is very high, but the
surface area is relatively low, thus the surface-to-
mass ratio is low.
• The log is then milled into boards. The result
of this process is to reduce the mass of the
individual boards as compared to the log, but
the resulting surface area is increased, thus
increasing the surface to mass ratio.
• As the surface area increases, more of the
material is exposed to heat and thus
generates more burnable gases by pyrolysis.

15. • The physical position of the solid fuel is also of
great importance.
• If the solid fuel is in a vertical position, fire will
spread will be more rapid than if it is in
horizontal position.
• The rapidity of fire spread is due to the
increased heat transfer through the three (3)
ways of heat transfer, which will be explained
later.

16. LIQUID FUELS
• Fuels gases are evolved from liquid fuels
through a process known as vaporization.
• Vaporization, in scientific terms, is the
transformation of a liquid to its vapor or
gaseous state. There must be some energy
input in order to cause this transformation.
• In most cases, this energy is provided in the
form of heat.

17. • A liquid assumes the shape of its container.
• The surface-to-volume ratio of liquids is an
important factor.
• When contained in a container, the specific
volume of a liquid has relatively low surface-to-
volume ratio.
• When it is released, this ratio increases
significantly as does the amount of the fuel
vaporized from the surface.

18. • The specific gravity fuel liquid is an important
factor in the degree of hazard of a liquid.
• A liquid fuel with a specific gravity of less than
one (1) is more hazardous that a fuel liquid
with a specific gravity of more that one (1).
• Solubility of a fuel liquid is also an important
factor.
• Polar Solvents, such as alcohol, dissolves or
mix with water.
• Hydrocarbons, such as oils or gasoline, do not
mix with water

19. HEAT
• Heat is the energy element of fire. It is a form
of energy which may be described as a
condition caused by “molecules in motion”
• When heat, through a source of ignition,
comes in contact with a fuel, the heat (as a
form of energy) supports the combustion
process.

20. SOURCES OF HEAT
• Heat can be derived from other forms of
energies that results in the ignition of a fuel.
• The five (5) general categories of heat energy
are:
1. Chemical Heat Energy
2. Electrical Heat Energy
3. Mechanical Heat Energy
4. Nuclear Heat Energy
5. Solar Heat Energy

21. CHEMICAL HEAT ENERGY
• Common types of heat generated as a result
of chemical reaction are:
1. Heat of Combustion – Heat generated by
the process of oxidation of matter. Ex: Flame
of a candle.
2. Spontaneous heating – Heating of an
organic substance without the addition of an
external heat. Ex: Oil soaked rag.

22. • Heat of decomposition – Release of heat from
decomposing compounds, usually due to
bacterial action. Ex: Compost pile
• Heat of solution – Heat released by the
solution of matter in a liquid. Some acids
when dissolved in water, can produce violent
reactions, spewing heat with explosive force.

23. ELECTRICAL HEAT ENERGY
• Electrical heat energy has the ability to
generate high temperature that are capable of
igniting any combustible material near the
heated area.
• Heat generated by electricity can occur in a
variety of ways, such as:

24. • Resistance heating – Generated by an
electrical current passing through a conductor
with a small resistance: Ex: Overloaded
circuits.
• Dielectric heating – Action of pulsating a DC or
AC at high frequency on a non conductive
material. Ex: Defective micro-oven.

25. • Leakage current heating – Generated by
current leaks to surrounding combustible
materials. Ex: Wires which are not well
insulated.
• Static electricity – Build up of a positive charge
on one surface and a negative charge on the
another surface. Ex: Lightning.

26. MECHANICAL HEAT ENERGY
• Mechanical Heat Energy is generated in two
(2) ways; by friction and by compression.
1. Heat by friction is created by the
movement of two surfaces against its other.
2. Heat by compression is generated when a
gas is compressed. Diesel engines ignite fuel
vapor without a spark plug by the use of this
principle.

27. NUCLEAR HEAT ENERGY
• Nuclear heat energy is generated when atoms
are either split apart or combined.
1. Fission is the splitting of atoms.
2. Fusion is the combining of atoms.

28. SOLAR HEAT ENERGY
• Solar heat energy is heat transmitted from the
sun in the from of electromagnetic radiation.
• Typically, solar energy is transmitted fairly and
evenly over the surface of the earth and in
itself is not capable of starting a fire. However,
when it is concentrated on a particular point,
as through the use of a lens, it may ignite
combustible materials.

29. TRANSMISSION OF HEAT
• The transfer of heat from one point or object
to another is a basic concept in the study of
fire. Heat is the energy transferred from one
body to another when the temperature of the
two bodies are different. Temperature is an
indicator of heat and is the measure of the
warmth or coldness of an object based on an
standard.

30. • The transfer of heat from the initial fuel to
other fuels in and beyond the area of the fire
origin controls the growth of the fire.
Investigators use this knowledge of heat
transfer as they analyze the fire scene and
determine the method of heat transfer from
the fuels involved in the ignition to other fuels
in the area of origin.
• Heat moves from warmer objects to those
that are cooler.

31. • The rate that heat is transferred is related to
the temperature differential of the two
bodies. The greater the temperature
difference is between the bodies, the greater
is the transfer rate.
• Heat can be transferred from one body to
another in three (3) ways; conduction,
convection, and radiation.

32. CONDUCTION
• Conduction is the transfer of heat from one
body to another by direct contact or by an
intervening heat conducting medium.
• It is the point-to-point transmission of heat
energy.
• Conduction occurs when a body is heated as a
result of direct contact with a heat source.

33. CONVECTION
• Convection is the transfer of heat by the
movement of heated liquids or gases.
• When heat is transferred by convection, there
is a movement or circulation of a fluid (any
substance, liquid or gas, that will flow) from
one place to another.
• As with all heat transfer, the flow of heat is
from the warmer area to the cooler area.

34. RADIATION
• Radiation is the transfer of heat through the
medium of space or atmosphere.
• It is the transformation of energy as an
electromagnetic wave, without an intervening
medium.
• The best example of heat transfer by radiation
is the sun’s heat. The energy travels from the
sun through space and warms the earth
surface.

35. HEAT MEASUREMENTS
• The temperature of a material is the
measurement of heat condition of a material
which indicates whether it can take up heat
from its surroundings or give it out to its
surroundings.
• It is a purely relative measurement and has
been standardized in terms of the freezing
point and the boiling point of pure water

36. • Fahrenheit denote the freezing point of water
as 32⁰ and the boiling point as 212⁰. The
difference between these points is divided
equally into 180 divisions (or degrees).
• Celsius denote the freezing point of water as
0⁰ and the boiling point as 100⁰. The
difference between these points are divided
equally into 100 divisions.

37. • To convert Fahrenheit degrees to Celsius,
subtract 32 from ⁰F and divide the result by
1.8.
• To convert Celsius degrees to Fahrenheit,
multiply the ⁰C by 1.8 and add 32.
• Remember the above additions and
subtractions must be done algebraically.
• It is also convenient to note that -40⁰C is equal
to -40⁰F.

38. HEAT CAPACITY
• The heat capacity of a substance, or its
thermal capacity, is that property of a
material for absorbing heat with a consequent
temperature rise per unit weight.
• It is measured in terms of heat units necessary
to raise the temperature of the substance to
one degree; i.e. BTU or Calorie.

39. SPECIFIC HEAT
• The specific heat a substance is the ratio of
the heat capacity of the substance to the heat
capacity of water.
• This value is 1.00 Btu per pound or 1.00
calorie per gram.
• It can be seen that specific heat, heat capacity,
and thermal capacity are synonymous terms.

40. • The specific heat of various substances vary
over a considerable range.
• This can be seen by the following table:
Substance Specific Heat Substance Specific Heat
Water 1.00 Zinc 0.093
Paraffin 0.694 Iron 0.109
Copper 0.093 Mercury 0.033

41. • The above table shows that if it takes 1000 Btu
of heat from a fire to raise the temperature of
1000 lbs. of water to 1⁰F, it only requires a
heat input of 109 Btu from a fire to raise the
temperature of 1000 ponds of iron to 1⁰F.
• Conversely, the same relationship holds in
lowering substances 1⁰F by removing heat or
subtracting Btu’s in order to cool them to safe
temperatures.

42. OXIDIZING AGENTS
• The oxygen in air around us is considered as
the primary oxidizing agent.
• Normally, air consists of about 21% oxygen.
• Aside from air there are other oxidizing
agents. These are those materials that yield
oxygen or other oxidizing gases during the
course of a chemical reaction.
• Oxidizers themselves are not combustible, but
they support combustion when combined
with fuel.

43. COMMON OXIDIZERS
• While oxygen is the most common oxidizer,
there are other substances that fall into the
category, such as the following:
1. Bromates 7. Nitrates
2. Bromine 8. Nitric Acid
3. Chlorates 9. Nitrites
4. Chlorine 10. Perchlorates
5. Fluorine 11. Permanganates
6. Iodine 12. Peroxides

44. HOW A FIRE WILL START
• For a fire to start, all the three elements, fuel,
heat, and oxygen must come together at the
same time and in proper proportions.
• When a source of ignition (heat) comes in
contact with fuel in air, the heat energy
supports the combustion reaction through
pyrolysis or vaporization of solid or liquid
fuels.

45. • The heat energy from the source of ignition is
also necessary for ignition to occur and for the
continuous production and ignition of fuel
vapors or gases.
• The time it takes for a combustion reaction to
occur is the determining factor in the type of
reaction that is observed.

46. • If the fuel is in liquid state, the temperature of
the heat absorbed from the source of ignition
must reach flash point the fuel, at which
vapors will start to be evolved from the fuel
but not sufficient enough to support
combustion.

47. • If the liquid fuel continue to absorb more heat
energy from the source of ignition,
temperature increases until it reaches fire
point at which vapors produced are already
sufficient enough to support continuous
combustion.

48. • However, for combustion to occur after a fuel
has been converted into vapor or gaseous
state, it must be mixed with air (oxidizer) in
proper ratio.
• The range of concentration of the fuel vapor
and air is called flammable limits (range).

49. FLASH POINTS AND IGNITION TEMPERATURES
OF SELECTED FUEL LIQUIDS
Substance Flash Point Ignition Temp.
Asphalt 400⁰F 905⁰F
Fuel Oil 105⁰F 490⁰F
Turpentine 95⁰F 464⁰F
Alcohol 55⁰F 700⁰F
Gasoline -45⁰F 495⁰F

50. IGNITION TEMPERATURES OF SELECTED FUELS
Substance Ignition Temp.
Hydrogen 1085⁰F
Carbon 925⁰F
Sulphur 450⁰F
Coal 750⁰F
Wood 450⁰F
Kerosene 490⁰F

51. FLAMMABLE LIMITS (RANGES)
FOR SELECTED MATERIALS
Material Lower Flammable Upper Flammable
Limit (LFL) Limit (UFL)
Acetylene 2.5% 100%
Carbon Monoxide 12.5% 74.0%
Ethyl Alcohol 3.3% 19.0%
Fuel Oil 0.7% 5.0%
Gasoline 1.4% 7.6%
Methane 5.0% 15.0%
Propane 2.1% 9.5%

52. THE FIRE TRIANGLE AND
THE FIRE TETRAHEDORN
• The fire triangle is a graphical representation
of fire in the smoldering mode and incipient
free burning mode.
• The fire tetrahedron is a graphical
representation of fire in the flaming mode.

53. • For many years the fire triangle was used to
teach the elements of fire. While this simple
example is useful, it is not technically
complete.
• When a fire becomes free burning,
combustion occurs and the fire is in flaming
mode.
• Once the fire is in flaming mode, it can
continue when enough heat energy produced
causes the continuous development of the
fire.

54. • In the flaming mode, there are four (4)
components of fire necessary to continuous
combustion process. These components are:
1. Oxygen (oxidizing agent)
2. Fuel (reducing agent)
3. Heat
4. Self-sustained chemical reaction.

55. FIRE DEVELOPMENT
• When the four components of the fire
tetrahedron come together, combustion
occurs.
• For a fire to grow beyond the first material
ignited, heat must be transmitted beyond the
first material to additional fuel available.
• In the early development of the fire, heat rises
and forms a plume of hot gas.

56. • If the fire is in the open (outside or in large
building), the fire plume rises unobstructed
and air is drawn into it as it rises. The spread
of the fire in an open area is primarily due to
heat energy that is transmitted from the
plume to nearby fuels.
• Fire spread in outside fires can be increased
by wind and sloping terrain that allow
exposed fuels to be preheated.

57. • The development of a fire in a compartment is
more complex than a fire in the open.
• A compartment is an enclosed room or space
within the building. The term compartment
fire is defined as a fire that occurs within such
space.
• The growth and development of a
compartment fire is usually controlled by the
availability of fuel and oxygen.

58. • When the amount of fuel to burn is limited,
the fire is said to be fuel controlled.
• When the amount of available oxygen is
limited, the condition is called ventilation
controlled.
• Recently, researchers have attempted to
describe compartment fires in terms of stages
or phases that occur as fire develops.

59. STAGES OF COMPARTMENT FIRES
• The stages of compartment fires are:
1. Ignition
2. Growth
3. Flashover
4. Fully Developed
5. Decay

60. IGNITION STAGE
• Ignition stage describes the period when the
four components of fire come together and
combustion begins.
• The physical act of ignition can be piloted
(caused by spark or flame) or non-piloted
(caused when a material reaches its ignition
temperature as a result of self heating) such
as spontaneous ignition.
• At this point, the fire is small and generally
confined in the material (fuel) first ignited.

61. GROWTH STAGE
• Shortly after ignition, a fire plume begins to
form above the burning fuel. As the plume
develops, it begins to draw air from the
surrounding space.
• Unlike an unconfined fire, the plume in a
compartment is rapidly affected by the ceiling
and walls of the space. The first impact is the
amount of air that is drawn into the plume.

62. • Because the air is cooler than the hot gases
generated by the fire, the air has a cooling
effect on the plume temperatures. The
location of the fuel package in relation to the
compartment walls determines the amount of
air that is drawn and thus the amount of
cooling that takes place.
• Fuel packages that are located near walls will
draw less air and will have higher plume
temperature.

63. • Fuel packages located in corners draw even
less air and will have the highest plume
temperature.
• This factor significantly impacts the
temperature that are developed in the hot gas
layer above the fire. As the hot gas rise, they
begin to spread outward when they hit the
ceiling. This spread continues until the walls
that make up the compartment are reached.
• The depth of the gas layer then begins to
increase.

64. • The temperatures in the compartment during
this period are dependent on the amount of
heat conducted into the compartment ceiling
and walls as the gases flow over them, the
location of the initial fuel package, and the
resulting air drawn into the plume.
• Research shows that the gas temperatures
decrease as the distance from the centerline
of the plume increases.

65. • The growth stage continues if enough fuel and
oxygen are available.
• Compartment fires in the growth stage are
generally fuel controlled.
• As the fire grows, the overall temperature in
the compartment increases as does the
temperature of the gas layer at the at the
ceiling level.

66. FLASHOVER STAGE
• Flashover is the transition between the
growth and fully developed fire stages and is
not a specific event such as ignition.
• During flashover, conditions in the
compartment change very rapidly as the fire
changes from one that is dominated by the
burning of the materials first ignited to one
that involves all of the combustibles within
the compartment.

67. • The hot gas layer that develops at the ceiling
level during the growth stage causes radiant
heating of combustible materials remote from
the origin of the fire.
• Typically, this radiant heating causes pyrolysis
to take place in the combustible materials in
the compartment.
• The gases generated during this time are
heated to their ignition temperatures by the
radiant heat energy from the gas layer at the
ceiling.

68. • Just prior to flashover, several things are
happening within the burning compartment.
The temperatures are rapidly increasing,
additional fuel packages are becoming
involved, and the fuel packages in the
compartment are giving off combustible gases
as a result of pyrolysis.
• As flashover occurs, the combustible materials
in the compartment and the pyrolysis gases
ignite. The result is a full-room involvement.

69. FULLY DEVELOPED STAGE
• The fully developed stage occurs when all
combustible materials in the compartment are
involved in the fire.
• During this period of time, the burning fuels in
the compartment are releasing maximum
amount of heat possible and producing large
volumes of fire gases.

70. • The heat released and the volume of fire gases
produced depend on the number and size of
the ventilation openings in the compartment.
• The fire frequently becomes ventilation
controlled; and therefore, large volumes of
unburned gases are produced.
• During this stage, hot unburned fire gases are
likely to begin flowing from the compartment
of origin into adjacent spaces or
compartments. These hot gases ignite as they
enter a space where air is more abundant.

71. DECAY STAGE
• As the available fuel in the compartment is
consumed by the fire, the rate of heat release
begins to decline. Once again the fire becomes
fuel controlled, the amount of fire diminishes,
and the temperatures within the
compartment begin to decline.
• The remaining mass of glowing embers can,
however, result in moderately high
temperatures in the compartment for some
time.

72. FACTORS THAT IMPACT FIRE DEVELOPMENT
• As the compartment fire progresses from
ignition to decay, several factors impact the
behavior of a fire and its development within
a compartment. These factors are:
1. Size, number, and arrangement of
ventilation openings;
2. Volume of the compartment;

73. 3. Thermal properties of the compartment
enclosures;
4. Ceiling height of the compartment;
5. Size, composition, and location of the fuel
package that is first ignited; and
6. Availability and locations of additional
fuel packages.

74. • For a fire to develop, there must be sufficient
air available to support burning beyond
ignition stage.
• The size and number of ventilation openings
in a compartment determine how the fire
develops within the space.
• The compartment size and shape and the
ceiling height determine whether a significant
hot gas will form or not.

75. • The location of the initial fuel package is also
very important in the development of the hot
gas layer.
• The plumes of burning fuel packages in the
center of a compartment draw more air and
are cooler than those against the walls or in
the corners of the compartment.

76. SPECIAL CONSIDERATIONS
• Several conditions or situations occur during
the course of a fire’s development that should
be discussed. These conditions can occur as a
fire proceeds through the stages of growth
and development. These conditions or
situations are:
1. Flameover/Rollover
2. Thermal Layering of Gases
3. Backdraft

77. FLAMEOVER/ROLLOVER
• The terms flameover and rollover are used to
describe a condition where flames move
through or across the unburned gases during a
fire’s progression. Flameover is distinguished
from flashover involvement of only the fire
gases and not the surfaces of other fuel
packages within a compartment. This
condition may occur during the growth stage
as the hot gas layer forms at the ceiling of the
compartment.

78. • Flames may be observed in the layer when the
combustible gases reach their ignition
temperature. While the flames add to the
total heat generated in the compartment, this
condition is not flashover. Flameover may also
be observed when unburned fire gases vent
from a compartment during the growth and
fully-developed stages. As these hot gases
vent from the burning compartment into the
adjacent space, they mix with oxygen; if they
are at their ignition temperature, flames often
become visible in the layer.

79. • A flameover will not result in the ignition of
target fuels within the compartment but may
result in burn patterns on walls and other
combustible building elements with which the
gases are in direct contact

80. THERMAL LAYERING OF GASES
• The thermal layering of gases is the tendency
of gases to form into layers according to
temperature. Other terms used to describe
this layering of gases by heat are heat
stratification and thermal balance. The hottest
gases tend to be in the top layer, while the
cooler gases form the lower layers. Smoke, a
heated mixture of air, gases, and particles,
rises. If a hole is made in a roof, smoke will
rise from the building or room to the outside.

81. • Thermal layering is critical in fire fighting
activities. As long as the hottest air and gases
are allowed to rise, the lower levels will be
safer for firefighters. This normal layering of
the hottest gases to the top and out the
ventilation opening can be disrupted if water
is applied directly into the layer.

82. • When water is applied to the upper level of
the layer, where the temperature is hottest,
the rapid conversion to steam can cause the
gases to mix rapidly. This swirling mixture of
smoke and steam disrupts normal thermal
layering, and hot gases mix throughout the
compartment. This process is sometimes
referred to as disrupting the thermal balance
or creating a thermal imbalance.

83. • Many firefighters have been burned when
thermal layering was disrupted. Should this
condition occur during fire fighting operations,
the investigator could observe
uncharacteristic patterns in the compartment
during scene examination.

84. BACKDRAFT
• As the fire grows in a compartment, large
volume of hot, unburned fire gases can collect
in unventilated spaces. These gases may be at
or above their ignition temperatures but have
insufficient oxygen available for actual ignition
to take place. Any action during fire fighting
operations that allows air to mix with these
hot gases can result in an explosive ignition
called backdraft.

85. • Many firefighters have been killed or injured
as a result of a backdraft. The potential for
backdraft can be reduced with proper vertical
ventilation (opening at highest point). Because
the unburned gases rise, the building or space
should be opened at the highest possible
point to allow them to escape before entry is
made.

86. • The following conditions may indicate the
potential for a backdraft to occur:
1. Pressured smoke exiting small openings.
2. Black smoke becoming dense gray-yellow.
3. Confined and excessive heat.
4. Little or no visible flame.
5. Smoke leaving the building in puffs or at
intervals.
6. Smoke-stained windows.

87. • Should a backdraft occur, the fire investigator
will observe blastlike damage in the building.
Homes have been known to be moved from
their foundations, and walls of multiple-storey
buildings have been blown off.

88. PRODUCTS OF COMBUSTION
• Heat
1. Responsible for the spread of fire.
2. Causes burn, dehydration, exhaustion
and/or injury to respiratory tract.
• Flame
1. The visible luminous body of burning gas.
2. When burning gas is mixed with proper
amounts of oxygen, becomes hotter and less
luminous.

89. • Smoke
1. Unburned, finely divided particles of soot.
2. Contents vary depending of the exact
material that is burning.
3. Causes suffocation.
• Fire gases
1. Evolved from fuel during process of
combustion.
2.Most gases evolved are toxic to humans.