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Chapter 4
Products of combustion

Flame

Flame is refers to:

- Luminous body of burning gas;

- Product of incomplete combustion;
- The matter produced by fire;
- It is composed of burning incandescent gasses; and,
- It is the manifestation of fire, when fire is in gas phased
combustion.

A flame is a mixture of reacting gases and solids emitting

visible, infrared, and sometimes ultraviolet light, the frequency spectrum of
which depends on the chemical composition of the burning material and
intermediate reaction products. In many cases, such as the burning
of organic matter, for example wood, or the incomplete combustion of
gas, incandescent solid particles called soot produce the familiar red-
orange glow of 'fire'. This light has a continuous spectrum. Complete
combustion of gas has a dim blue color due to the emission of single-
wavelength radiation from various electron transitions in the excited
molecules formed in the flame. Usually oxygen is involved,
but hydrogen burning in chlorine also produces a flame,
producing hydrogen chloride (HCl). Other possible combinations producing
flames, amongst many, are fluorine and hydrogen,
and hydrazine and nitrogen tetroxide. Hydrogen and
hydrazine/UDMH flames are similarly pale blue, while burning boron and its
compounds, evaluated in mid-20th century as a high energy
fuel for jet and rocket engines, emits intense green flame, leading to its
informal nickname of "Green Dragon".
The glow of a flame is complex. Black-body radiation is emitted from
soot, gas, and fuel particles, though the soot particles are too small to
behave like perfect blackbodies. There is also photon emission by de-
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excited atoms and molecules in the gases. Much of the radiation is emitted
in the visible and infrared bands. The color depends on temperature for the
black-body radiation, and on chemical makeup for the emission spectra.
The dominant color in a flame changes with temperature. The photo of the
forest fire in Canada is an excellent example of this variation. Near the
ground, where most burning is occurring, the fire is white, the hottest color
possible for organic material in general, or yellow. Above the yellow region,
the color changes to orange, which is cooler, then red, which is cooler still.
Above the red region, combustion no longer occurs, and the uncombusted
carbon particles are visible as black smoke.

The common distribution of a flame under normal gravity conditions

depends on convection, as soot tends to rise to the top of a general flame,
as in a candle in normal gravity conditions, making it yellow. In micro
gravity or zero gravity,[8] such as an environment in outer space, convection
no longer occurs, and the flame becomes spherical, with a tendency to
become more blue and more efficient (although it may go out if not moved
steadily, as the CO2from combustion does not disperse as readily in micro
gravity, and tends to smother the flame). There are several possible
explanations for this difference, of which the most likely is that the
temperature is sufficiently evenly distributed that soot is not formed and
complete combustion occurs.[9] Experiments by NASA reveal that diffusion
flames in micro gravity allow more soot to be completely oxidized after they
are produced than diffusion flames on Earth, because of a series of
mechanisms that behave differently in micro gravity when compared to
normal gravity conditions.[10] These discoveries have potential applications
in applied science and industry, especially concerning fuel efficiency.
In combustion engines, various steps are taken to eliminate a flame. The
method depends mainly on whether the fuel is oil, wood, or a high-energy
fuel such as jet fuel.
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Flame temperatures

Temperatures of flames by appearance

It is true that objects at specific temperatures do radiate visible light.

Objects whose surface is at a temperature above approximately 400 °C
(752 °F) will glow, emitting light at a color that indicates the temperature of
that surface. See the section on red heat for more about this effect. It is a
misconception that one can judge the temperature of a fire by the color of
its flames or the sparks in the flames. For many reasons, chemically and
optically, these colors may not match the red/orange/yellow/white heat
temperatures on the chart. Barium nitrate burns a bright green, for
instance, and this is not present on the heat chart.

Typical temperatures of flames

Main article: adiabatic flame temperature

The "adiabatic flame temperature" of a given fuel and oxidizer pair
indicates the temperature at which the gases achieve stable combustion.

 Oxy-dicyanoacetylene 4,990 °C (9,000 °F)

 Oxy-acetylene 3,480 °C (6,300 °F)
 Oxyhydrogen 2,800 °C (5,100 °F)
 Air-acetylene 2,534 °C (4,600 °F)
 Blowtorch (air-mapp gas) 2,200 °C (4,000 °F)
 Bunsen burner (air-natural gas) 1,300 to 1,600 °C (2,400 to 2,900 °F)[11]
 Candle (air-paraffin) 1,000 °C (1,800 °F)
 Smoldering cigarette:
 Temperature without drawing: side of the lit portion; 400 °C (750 °F);
middle of the lit portion: 585 °C (1,100 °F)
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 Temperature during drawing: middle of the lit portion: 700 °C

(1,300 °F)
 Always hotter in the middle.

Fire ecology

Every natural ecosystem has its own fire regime, and the organisms in
those ecosystems are adapted to or dependent upon that fire regime. Fire
creates a mosaic of different habitat patches, each at a different stage
of succession.[12] Different species of plants, animals, and microbes
specialize in exploiting a particular stage, and by creating these different
types of patches, fire allows a greater number of species to exist within a
landscape.

TYPES OF FLAME according to color and completeness of combustion

a Luminous Flame – a reddish orange in color, it deposits soot because it

is a product of incomplete combustion, it has lower temperature.

b Non luminous flame – bluish in color, it does not deposit soot because it
is a product of complete combustion, it has higher temperature than
luminous flame.

c Laminar- particles follow a smooth path.

d Turbulent- un steady flame

 What are the TYPES OF FLAME according to burning fuel and air
mixture

a Premixed Flame – e.g. flame of Bunsen burner.

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b Diffusion Flame – e.g. flame of oxyacetylene torch (diffused – dispersed;

widely spread)

 What are the TYPES OF FLAME based on smoothness

a Laminar Flame – (Smooth Flame) flame is laminar when a particle

follows a smooth path through a gaseous flame.

b Turbulent Flame – (Rough Flame) those having unsteady, irregular and

eddies.

PYROLYSIS refers to the chemical process whereby fire consumes

the most solid part of the fuel. It is the thermal decomposition of
combustible matter. The process involves the following:

1.The fuel is heated until its temperature reaches its fire point.

2.Decomposition takes _place - moisture in the fuel is converted to

vapor. 3_ Decomposition produces combustible vapors that rise to
the surface of the fuel. Combustible vapors are technically termed
as free radicals.

Smoke

Smoke is a visible product of incomplete combustion.

Highly combustible vapors

- Hydrogen gas (H)

- Carbon Monoxide (CO)
- Carbon dioxide (CO2)
- Nitrogen (N)
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Chapter 5
Causes of Fire

Natural causes

1.Spontaneous heating, automatic chemical reaction that results to

spontaneous combustion due to auto-ignition of organic materials;
the gradual rising of heat in a confined space until ignition
temperature is reached.

2.Lightning, a form of static electricity; a natural electric current with

great magnitude, producing tremendous amperage and voltage.
Lightning can cause fire directly or indirectly. Indirectly when it strikes
telephone and other transmission lines, causing an induced line
surge. It can cause a flashfire or dust explosion. When lightning
strikes a steel or metal rod covered with dust, the dust would
suddenly burn thus resulting to an explosion.

A lightning may be in the form of:

- Hot bolt - longer in duration; capable only of igniting combustible

materials.

- Cold bolt - shorter in duration; capable of splintering a property or

literally blowing apart an entire structure; produces electrical
current with tremendous amperage and very high temperature.

3.Radiation of sunlight - when a light hits a concave mirror,

concentrating the light on a combustible material thereby ignites it.

Accidental causes of fire

1.Short-circuit- unusual or accidental connection between points at

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different potentials (charge) in an electrical circuit of relatively

low resistance.

2.Arcing - production of sustained luminous electrical discharge between

separated electrodes when electrical current crosses the gap
between 2 electrical conductors.

3.Sparking - production of incandescent particles when two different

potentials come in contact; occurs during short-circuits or welding
operations.

4.Induced current - induced line surge-- increase of electrical energy flow or

power voltage; sudden increase of electrical current resulting to the
burning of insulating materials, exploding of the fuse-box, or burning
of active electrical appliances.

5.Overheating of electric a l appliances increase or rising of

amperage while electric current is flowing in a transmission line
resulting to the damage or destruction of insulating materials; maybe
gradual or rapid; internal or external.

Intentional causes

Incendiary - preparations or traces of accelerant and plants and

trailer then the cause of fire is intentional.
a)Accelerant – highly flammable chemicals that are used to
facilitate flame propagation.
b)Plant - the preparation or gathering of combustible materials
needed to start a fire.
c)Trailer – the preparation of flammable substances in order to
spread the fire.

Common causes of accidental fires

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1. Electrical Short Circuit

2. Electrical Grounded Circuit
3. Electrical Overloading
4. Loose Connection or Improper Splicing
5. LPG – Liquefied Petroleum Gas

Characteristics of LPG:

1.it is liquid inside the container but automatically transformed into

gaseous state when release so that it can be transported easily and
stored economically (1:270);

2.It is 1.5 heavier than air; and

3.It is colorless, tasteless and odorless, but an oxidizing agent called

“Ethyl Mercaptan” is introduced to determine leakage.

-oOo-

Chapter 6
Fire Behavior

Thermal balance and thermal imbalance:

Thermal balance refers to the rising movement or pattern of the fire; the
normal behavior when the fire is undisturbed.

Thermal imbalance is the abnormal movement of fire due to

interference of foreign matter.

Dangerous/fatal behavior of fire

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Backdraft

Backdraft is the sudden and rapid (violent) burning of heated glasses in

a confined area that occurs in the form of explosion because of improper
ventilation. If not properly ventilated, highly flammable vapors maybe
accumulated such that when a door or window is suddenly opened, the
room violently sucks the oxygen and simultaneously, a sudden combustion
may occur which may happen as an explosion.

Characteristics of Backdraft:

A. Fire gases are under pressure

B. Existence of black smoke that is becoming dense gray yellow
C. Confinement of excessive heat
D. There is little flame or no visible flame
E. Smoke leaves the building in puffs or by intervals
F. Windows are smoke stained
G. Muffled sounds are heard inside the building
H. Violent rushing of air inside when opening is made

Flashover

Flashover is the sudden ignition of accumulated radical gases produced

when there is incomplete combustion of fuels. There will be a very intense
fire that is capable of travel to a hundred yards within a few seconds.

Biteback

A fatal condition that takes place when the fire resists extinguishment
operation and becomes stronger and bigger instead.

Flash fire
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Flash fire a.k.a. as dust explosion; when a metal post that is completely
covered with dust is hit by a lightning creating a violent chemical reaction
that produces a very bright flash followed by an explosion.
Flash point

The minimum temperature at which a liquid fuel gives off sufficient

vapor to form an ignitable mixture with a near surface. At this temperature,
the ignited vapor will flash but will not continue to burn.

Fire point

The temperature at which a liquid fuel will produce vapors sufficient to

support combustion once ignited.

Ignition temperature

The minimum temperature to start self-sustained combustion

independent of the heating source.

Physical Properties Of Fire

a Specific Gravity – the ratio of the weight of a solid or liquid substance to

the weight of an equal volume of water

b Vapor density – the weight of a volume of pure gas composed to the

volume of water.

c Vapor Pressure – the force exerted by the molecules on the surface of

the liquid at equilibrium.
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d Temperature – the measure of thermal degree of the agitation of

molecules of a given substances the measure of the molecular activity of
the substance.

e Boiling point – the constant temperature at which the vapor pressure of

the liquid is equal to the atmospheric pressure.

f Ignition temperature or Kindling temperature – the minimum temperature

to which the substance is the air must be heated in order to initiate on
cause self-contained combustion without the addition of heat from
outside sources.

g Fire point – the temperature at which the material will give off enough
vapors to keep burning.

h Flash point – the temperature at which a material is not hot enough to

keep burning but still give off enough vapors to cause a flame to “flash”
across the surface.

Chemical properties of fire

a Endothermic Reaction – are changes whereby energy is absorbed or is

added before the reaction takes place. *Absorbed / added energy

b Exothermic Reaction – reactions or changes that release of give off

energy (heat) thus they produce substances with less energy that the
reactants. Give off / Release energy

c Oxidation – a chemical changes in which combustible material (fuel) and

an oxidizing agent part.

d Combustion Flame – the manifestation of fire when the fire in gas-

phased combustion. A matter that is produced by fire.(result of fire)