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CHEMISTRY OF FIRE

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 SEQUENCE
 Introduction
 Theory of Combustion
 Definition
 Products of Fire
 Their effects on human body
 Terms Used In Temperature( flash point, fire point,
auto ignition temperature)
 Transmission of Heat (Conduction, Convection
and Radiation)
 Classification of Fire
 Methods of Fire Extinction

CHEMISTRY OF FIRE 3
 INTRODUCTION
 Fire is Friend of Man /enemy.
 Fire as a Man made disaster.
 Fire loss, Human and Property.

CHEMISTRY OF FIRE 4
 THEORY OF COMBUSTION

CHEMISTRY OF FIRE 5
 DEFINITION
 Fire is a rapid oxidation process

OR

 Fire is a chemical reaction between fuel and oxygen at

suitable temperature
OR
 Fire is a chemical reaction or series of chemical
reactions in which fuel chemically combines with an oxidizing
agent and sufficient quantity of energy in the form of heat,
flame, light etc, is released

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CHEMISTRY OF FIRE
 PRODUCTS OF FIRE
 Products of fire & effects on life safety
 Light
 Heat
 Flame
 Toxic Gases

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CHEMISTRY OF FIRE
 TERMS USED IN TEMPRATURE
 Flash Point.
 Fire Point.
 Auto Ignition Temperature.

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CHEMISTRY OF FIRE
 TERMS USED IN TEMPRATURE
• Flash point The minimum temperature at sufficient vapors
from a fuel are available in which a momentary flash can be
produced when ignited by some external source.
• Fire point It is the lowest temp: at which sufficient vapors
from a fuel are available in which sustained combustion can be
started when some piloted ignition is applied.
• Auto-ignition temperature It is the minimum temp: at which
sufficient amount of flammable vapors are produced from the
substance in addition to rise off internal energy so that
combustion reaction takes place automatically with out
introduction of flame.
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CHEMISTRY OF FIRE
 TRANSMISSION OF HEAT
 Conduction.
 Convection.
 Radiation.

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CHEMISTRY OF FIRE
 Heat transfers within and between
buildings by convection, conduction and radiation
CONVECTION
Convection is heat transfer by air motion.
During a fire heated air expands and moves away
from the fire, exerting pressure against doors,
damper in air ducts and the like and penetrating
the openings

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CHEMISTRY OF FIRE
 CONDUCTION
Conduction is heat transfer through solid
materials. During a fire heat can be transferred through
steal beams, metal conduit, wire and ducts, and so on
which are good conductors of heat. Conversely, wood,
mineral wool, glass fiber, and similar materials are poor
conductors of heat

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CHEMISTRY OF FIRE
 RADIATION
Radiation is heat transfer by electromagnetic
waves. During a fire hot surfaces can radiate heat,
igniting combustibles distance away. For example,
fire can leapfrog across wide malls in shopping
center by radiation of heat energy. Radiant heat
energy increases rapidly as the source becomes
hostler. The radiant energy is proportional to the
fourth power of the absolute temperature (e.g., F
+ 460) of the source.
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CHEMISTRY OF FIRE
 CLASSIFICATION OF FIRE

 A – CLASS ( SOILDS) (WATER )

 B – CLASS (LIQUIDS)(FOAM)
 C – CLASS (GASES)(CO2)
 D – CLASS (METALS) (DCP)
 E – CLASS (ELECTRIC & ELECTRICAL
EQUIPMENT) (CO2)

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CHEMISTRY OF FIRE
 A-CLASS

 Wood,
 paper,
 cloth,
 etc.

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CHEMISTRY OF FIRE
 B-CLASS

Liquids
(oils, paints etc.)

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CHEMISTRY OF FIRE
 C-CLASS

Gases’ fire

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CHEMISTRY OF FIRE
 D-CLASS

Metals
like
magnesium,
aluminum
etc.

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CHEMISTRY OF FIRE
 METHODS OF FIRE EXTINCTION

STARVATION
SMOTHERING
COOLING

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CHEMISTRY OF FIRE
 STARVATION

By removing combustible material from near vicinity of the

fire.

a) The drainage of fuel from burning oil tanks.

b) Cutting the fuel supply in gas fires.

c) The working out of cargo at ship fire.

d) Cutting of trenches in peat, heath and moor in forest fires.

e) Demolition of building to create a fire stop.

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CHEMISTRY OF FIRE
 B) By removing the fire from neighborhood of
combustible materials as for instance:-.
a) Pulling apart a burning haystack.
b) Removing thatched roof.
c) By sub-dividing the burning material, when the
smaller fires produced may be left to burn out to
be extinguished more easily by other means:-.
i) Emulsification of the surface of burning oil.
ii) The beating out of a heath fire.

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CHEMISTRY OF FIRE
SMOTHERING
It is the technique by which the supply of
oxygen or any other oxidizing agent required for
combustion is checked. In the absence of an oxidizing
agent the combustion reaction cannot prolong hence
the fire is extinguished. For this technique the
following fire fighting media are used
1. Foam
2. CO2
3. DCP
4. Steam
5. Sand
6. Water (in form of spray or fog).
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CHEMISTRY OF FIRE
 COOLING
In order to produce and then sustain the combustion
process a continuous supply of heat energy is required. If
temperature is lowered, then fire can be extinguished.
This is achieved by using water which is considered, to be
the best fire fighting medium for cooling purpose due to
the following characteristic:-
I. Water is a cheapest source.
II. It is a good heat absorbent.
III. It has dual purpose simultaneously, i.e. cooling and
smothering.
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CHEMISTRY OF FIRE
 TRIANGLE OF FIRE

• Fuel
• Oxygen
• Heat (in form of temperature)

el
fu

ox
yg
Heat en
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CHEMISTRY OF FIRE
 TYPES OF FUEL:

 Carbon
 Hydrocarbons
 Combustible
Metals
 Non- Metals
 Cellulosic
Substances

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CHEMISTRY OF FIRE
 FLAMMABILITY LIMITS

Substances Lower Limit Upper limit

Hydrogen 04 75
Methane 05 15
Ethane 02 08
Petrol 1.4 7.9
Kerosene 0.7 5.0
Propane 2.1 9.5
Butane 1.8 8.4

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CHEMISTRY OF FIRE
 HEAT OF COMBUSTION OF FUEL

Amount of heat a fuel released during its complete

oxidation is called its heat of combustion ,which is
given as under

Wood 7000 BTU/Lbs

Liquid fuels 16000 to21000BTU/Lbs
Coal 12500 BTU/Lbs
Gases 20000to23000BTU/Lbs

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CHEMISTRY OF FIRE
 CLASSFICATION OF FIRE

• A – CLASS ( SOILDS) (WATER )

• B – CLASS (LIQUIDS)(FOAM)
• C – CLASS (GASES)(CO2)
• D – CLASS (METALS) (DCP)
• E – CLASS (ELECTRIC & ELECTRICAL
EQUIPMENT) (CO2)

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CHEMISTRY OF FIRE
 OXYGEN OR OXIDIZING AGENTS

A substance which permits substances to burn is called

oxidizing agent.

OR

Anything which provides oxygen for the process of

combustion is called oxidizing agent.

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CHEMISTRY OF FIRE
 NAME OF OXIDIZING AGENTS
Air

Halogens

Hydrogen Peroxide

Sodium Peroxide

Permanganates

Chlorates

Nitrates
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CHEMISTRY OF FIRE
 HEAT AND TEMPERATURE

Heat is a form of energy and is used in raising the

temperature of fuel at a point where sufficient vapors
are produced to take part in chemical reaction
( combustion ).

Temperature is the degree of hotness or coldness of a

body. The behavior of the substances varies at
different temperature as flash point, fire point, auto-
ignition and spontaneous combustion.

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CHEMISTRY OF FIRE
 TERMS USED IN TEMPRATURE

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CHEMISTRY OF FIRE
 PROPERTIES OF SOME COMMON LIQUID FUELS

Name F.PoC I.T C L/L U/L S.G V.D

Ethyl 13 423 4.3 19.0 0.8 1.6

Alcohol
Gasoline -43 2 80 to 1.4 7.4 0.8 3to4
456

Kerosene 38 229 0.7 5.0 1.0 -

Petroleum -46 22 8 1.1 5.9 0.6 2.5

Ether benzene

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CHEMISTRY OF FIRE
 PRODUCTS OF FIRE
&
EFFECTS ON LIFE SAFETY

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CHEMISTRY OF FIRE
 Generally there are two types of products liberated in
the process of combustion
 Thermal products (Heat & Flame)
 Non –thermal products ( Smoke & Toxic gases
Toxic Gases
CO2, CO,SO2,H2S,HCN ,NH3 ,HCL, NO2

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CHEMISTRY OF FIRE
 SMOKE
Visible smoke is composed of unburned
particles ,dust and liquid droplets

Effects

 Suffocation
 Visibility is affected.
 Creates irritation in the respiratory tract.

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CHEMISTRY OF FIRE
 EFFECTS OF TOXIC GASES
Carbon-Di-Oxide(CO2).The main effect of
CO2 is suffocation but at different concentration it has different
effects as shown in the table:-
Amount of CO2 in air Effects
0.5% No symptoms and no permanent danger.

2.0% Increase the breathing rate by 50%

3.0% Increase the breathing rate by 100%

5.0 Vomiting, dizziness, breathing difficulties

after 30 minutes.
8.10% Vomiting, headache, dizziness,
unconsciousness and death after some
time.
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CHEMISTRY OF FIRE
 CARBON-MONO-OXIDE (CO)
When (co) is inhaled, it combines with hemoglobin;
and car boxy hemoglobin is formed. Car boxy hemoglobin has
different effects as shown in the table:-
Amount of Car boxy
Hemoglobin in blood Effects
10 Possible shortness of breathe
20-30 Shortness of breathe, headache.
30-50 Severe headache, mental confusion,
dizziness, fatigue
50-70 Unconsciousness, death and
respiratory failure if exposure is
continued.
70 & above rapidly fatal.
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CHEMISTRY OF FIRE
 SULPHER-DI-OXIDE (SO2)

Its source materials are rubber ,wood , sulfuric

acid and pesticides etc. Its toxicological effects
are eyes and lungs irritation.

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CHEMISTRY OF FIRE
 HYDROGEN SUPHIDE (H2S)

Its source materials are leather , wood and other materials

containing Sulpher. Its lethal concentration is 20 PPM. It is a

nerve agent and creates paralysis.

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CHEMISTRY OF FIRE
 AMMONIA (NH3)

When wool, silk and melamine are involved

in fires then (NH3) is produced. It is soluble

in water and its main effect is irritation in eyes.

It is fatal if exposure is longer.

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CHEMISTRY OF FIRE
 HYDROGEN CHLORIDE (HCl)

Its source materials are plastics i.e.PVC and ploy

urethane. At low concentration causing coughing ,
choking and irritation in eyes.
At high concentration can damage the upper
respiratory tract, causing asphyxiation or death.

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CHEMISTRY OF FIRE
 NITROGEN DIOXIDE (NO2 )

Source materials are fabrics, cellulose acetate and all plastics containing Nitrogen.Its main

effect is Asphyxiation and longer exposure can prove fatal.

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CHEMISTRY OF FIRE
 HEAT
Effects of Heat

 It declines blood pressure.

 By inhalation of hot air fluid may build up in
lungs.
 It can cause burns & scalds
 It can cause hypothermia

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CHEMISTRY OF FIRE
 FLAME
The burning of most materials is an exothermic
process .The energy from the process is evolved as heat
which posses convective & radioactive components .
The radioactive components represent energy
released in the visible and infra-red portion of
spectrum and is seen as flame or luminosity .

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 THANKS

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CHEMISTRY OF FIRE