Fire Classification — Know How to Handle It
We have all seen a building or a plant burning in flames. We all understand what fire is? We know that fire is another name given for combustion. Combustion, or “fire,” is a process that occurs when oxygen and heat combine in a reaction in the presence of fuels. When this reaction occurs very quickly, combustion takes place, and in it, the fuel begins to dry out and burns producing flames.
Class of Fire, Fuel & extinguishing agent
Class A
Ordinary combustible material such as wood, cloth, paper etc. extinguishing agent — Water type, CO2, DCP
Class B
Flammable liquid and gas such as grease, gasoline, hydrocarbon etc. extinguishing agent — Foam, CO2, DCP
Class C
Electrical fire — extinguishing agent — CO2, DCP
Class D
Combustible metal such as sodium, magnesium, pyrophoric substances etc. extinguishing agent — Sodium chloride (MET-L-X)
What is the Fire Tetrahedron?
Four elements must be present, and besides, in the proper proportion. These four elements are:
Tetrahedron
- HEAT,
2. OXYGEN
3. FUEL and
4. CHEMICAL CHAIN REACTION
Three elements (fuel, heat and oxygen) are called the fire triangle. If these three elements, or any of them, are not in the proper quantity, there will be no combustion. For example where you visit this page, but there is no combustion or fire. Why? Because the fire triangle is not in the proper balance, or because although some of these elements have been combined, the third is not present. But, of course, when all three are present, and in the correct proportion then start chain chemical reaction and fire appears, and this fire can burn rapidly with great flames,
Heat
What is heat? Heat is a form of energy and energy is molecules in motion. This molecular activity is measured by the temperature that is expressed in degrees centigrade. When the fuel reaches a certain temperature, it begins to “break down”, releasing molecules in the form of gases, first water vapour and then others, which are highly flammable. This temperature is called the “vaporization point” of the fuel. The “ignition temperature” of a fuel is the temperature at which these gases will ignite and cause combustion to continue even after the source of external heat, such as a match or lighter, is removed.
Oxygen
Oxygen is one of the elements that are part of our atmosphere, in a volume of 21%
Fuel
A fire does not exist if there is no material to burn, for now, we must remember that the fuel does not burn without the presence of heat and oxygen in the correct proportion.
Chemical Chain Reaction
There is no longer fire if the fire triangle (fuel, heat and oxygen) fail to maintain the Chemical Chain Reaction. Simple no reaction no fire, we use a DCP fire extinguisher to stop the chemical chain reaction
What are the three heat transfer (spread) phenomenon
Sometimes oxygen is consumed so rapidly at the base of the fire that its proportion decreases, and the fire is soon out of balance, although there is still enough heat and steam left. As the hot gases rise into the air, they become saturated with oxygen again, and flames may appear in the plume of smoke far above the fire. The oxygen supply for combustion depends on the ability of the air to circulate freely between the fuels. But heat must also be able to reach the fuel, to raise its temperature to that of ignition. How does this process happen? There are 3 forms of heat transmission: -
RADIATION — CONDUCTION — CONVECTION
Radiation
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