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Anatomy of Fire and Fire Triangle

Anatomy of Fire & Definition of Combustion:-

Anatomy of Fire:

Fires occur naturally ignited by lightning strikes or by volcanic products. Fire was the first controlled chemical reaction discovered by humans in the form of campfires and bonfires and continues to be the main method to produce energy for humanity. Usually the fuel is carbon, hydrocarbons or more complicated mixtures such as wood that contains partially oxidized hydrocarbons. The thermal energy produced from combustion of either fossil fuels such as coal or oil, or from renewable fuels such as firewood, is harvested for diverse uses such as cooking, production of electricity or industrial or domestic heating.

Definition of Combustion:-

Combustion is a high-temperature exothermic redox chemical reaction between a fuel and an oxidant, usually atmospheric oxygen that produces oxidized, often gaseous products, in mixture termed as smoke. Combustion in a fire produces a flame and the heat produced can make combustion self-sustaining. It is often a complicated sequence of elementary radical. Solid fuels, such as wood, first undergo endothermic pyrolysis to produce gaseous fuels whose combustion then supplies the heat required to produce more of them. Combustion is often hot enough that light in the form of either glowing or a flame is produced.

Fire triangle:-

Fire is an external sign of chemical reaction, usually the combination of carbon and or hydrogen with oxygen, resulting in the release of energy in the form of
heat, light and sound. Hence, there are three basic elements required for Fire.
These are:-

  • A source of Ignition (Heat)
  • The presence of Oxygen (Air)
  • Combustible Substance (Fuel)

These three elements can be represented by a triangle popularly known as “FIRETRIANGLE“.

Steps of combustion of fuel in Chemistry:-

STEP I:

The chemical reaction of hydrogen combustion occurs because certain atoms are very reactive; being unstable they quickly combine with other atoms. Adding the single hydrogen atom to the mixture of hydrogen gas and oxygen lead to a series of chemical reactions.

STEP II:

The single hydrogen atom (H) reacted with a molecule of oxygen (02) ‘producing molecule of hydroxyl I radical (OH) and an atom of oxygen (0).
Both OH & 0 are highly reactive.

H+02     –>   OH+ 0

STEP III:

The OH radical reacts rapidly with a hydrogen molecule producing water H20, and another hydrogen atom (H).
The oxygen atom liberated in step 11 reacts with hydrogen molecule (H2) producing new OH and H Radicals.

OH + H2  –>  H20 + H

O+H2  –>  OH + H

STEP IV:

The new OH molecule reactswithH2 molecule producing another molecule of water (H20) and another Hydrogen atom (H)

OH + H2  –>  H20 + H

STEP V:

The hydrogen atoms liberated by this reaction quickly react with 02 molecules to produce several H atoms and the process repeats in cyclic order.

This is known as Chain Reaction. Hence Fire now can be represented as a Tetrahedron the four faces of which indicate Fuel

  • Heat
  • Oxygen (Air)
  • Chain reaction.

It can also be represented as four sides of a square to indicate
1. Fuel.
2. Heat.
3. Oxygen (Air).
4. Chain reaction.

Fuels:

A matter which can readily burn is called ‘Fuel’ types:

  • Solid fuels.
  • Liquid fuels.
  • Gaseous fuels.

Solid Fuels:

Wood, paper textiles are the examples of solid fuel. Solid fuels are categorize as follows:

Tinder fuels:

All such solid more then 20 sq. centimeter area per gram are known as tinder fuels, dry grass, kite paper, newspaper, saw dust, etc. are tinder fuels. Tinder fuels catch fire most easily. That is why they are helpful instating fire.

Kindling fuels:

All such solid fuels which occupy an area between 2 and 20 sq. centimeter per gram are caned kindling fuels. Twigs used for cleaning teeth tiny pieces of wood. Wood scraps. Thick card boards are the examples of kindling fuels. Tinder fuels will help to ignite the kindling fuels.
Bulk fuels:
All such solid fuels which occupy an area of 0. 04 up to bulk fuels. Thick logs of wood, wooden furniture, cots, and wooden planks are examples of bulk fuel, kindling fuel will help the bulk fuel to ignite.

Liquid fuels:

Kerosene oil, petrol, diesel oil are the examples of liquid fuels. Liquid fuels are categorized as follows:

Lighter than water:

All liquid fuels which have density of less than one gramper cubic centimeter are lighter than water. Kerosene oil, petrol is lighter than water.

Miscible in water:

All such liquid fuels which will readily mix in water are miscible in water. Alcohol, acetone are the examples. In order to facilitate use of proper fire fighting techniques flammable or combustible liquids are further classified as follows:

 

Anatomy Of Fire

ClassCriteriaNature
IALIQUID HAVE A FLASH POINT BELOW 73 OF AND A BOILING POINT BELOW 100 FEXTREMELY FLAMMABLE
IBLIQUID HAVE A FLASH POINT BELOW 73 OF AND A BOILING POINT GREATER 100 FHIGHLY
FLAMMABLE
ICLIQUID HAVE A FLASH POINT GREATER THAN EQUAL TO 73 OF AND A BOILING POINT GREATER 100 FFLAMMABLE
IIALIQUID HAVE A FLASH POINT GREATER THAN EQUAL TO 100 OF AND A BOILING POINT GREATER 140 FEXTREMELY COMBUSTIBLE
IIBLIQUID HAVE A FLASH POINT GREATER THAN EQUAL TO 140 OF AND A BOILING POINT GREATER 200 FHIGHLY
COMBUSTIBLE
IICLIQUID HAVE A FLASH POINT GREATER THAN EQUAL TO 200 OFFCOMBUSTIBLE