Extinguishing fire - class-VIII

Sodium bicarbonate can be used for fire extinguishers purpose as it releases carbon dioxide. 

For fires involving electrical equipment and inflammable material like petrol, carbon dioxide is the best extinguisher. Carbon dioxide being heavier than oxygen, covers the fire like a blanket. Since, the contact between the duel and oxygen is cut off, the fire is extinguished.

Carbon dioxide is being a gas can be store in cylinder's under high pressure like L.P.G.When released from the cylinder, carbon dioxide expands enormously in volume and cools down. So, it not only forms blanket around the fire, it also brings down the temperature of the fuel.

Water conducts electricity with electrical equipment's. Hence the area under water is developed with electricity. Therefore water is not used to the extinguished fire caused by electrical equipment.

We cannot use petrol as a fire extinguisher, because petrol is a combustible liquid which on combustion produces a lot of heat energy. So petrol is not used to stop the fire.

Soda-acid fire extinguishers work by reacting sulfuric acid with sodium bicarbonate (NaHCO3) to produce carbon dioxide gas, which displaces oxygen and puts out the fire. Option A is the standard chemical composition for this type of extinguisher.

In general, the stability of bromine in a typical flame retardant molecule means that the molecule can offer the highest activity as a flame active retardant, while also being cost effective.  The choice of flame retardant systems for any particular application depends on how the material decomposes in a fire, as well as the materials’ physical property. Brominated flame retardants, because they act in the flame, can be used in just about every application.

Carbon dioxide is heavier than oxygen. Due to this, carbon dioxide forms a blanket around the burning material and makes a barrier between the burning material and oxygen. As oxygen supply is cutoff, it helps in extinguishing the fire.

Water, when poured over fire absorbs large amount of heat and hence the temperature of wood falls below the ignition temperature. Thus the fire goes off.

Fire is extinguished by  :
(A) Removing all combustible substance. Fuel is one of the requirements for producing fire. In the absence of fuel, combustion will not occur.
(B) Cutting off a supply of air. Air (oxygen) is essential for combustion. In the absence of air, combustion will not occur.
(C) Cooling the burning substance. This reduces the temperature below its ignition temperature. The fire will not spread.

Fire can be extinguished by spraying, carbon dioxide, carbon tetrachloride or water.
Note:
Fire is extinguished by
(A) removing all combustible substance. Fuel is one of the requirements for producing fire. In the absence of fuel, combustion will not occur.
(B) cutting off the supply of air. Air (oxygen) is essential for combustion. In the absence of air, combustion will not occur.
(C) cooling the burning substance. This reduces the temperature below its ignition temperature. The fire will not spread.

Both options A and B describe the difference between fire extinguishing action of water and $CO _2$.

• Water helps to extinguish a fire in two ways: it cools the substance that undergoes combustion and brings the temperature of the combustible material below its ignition temperature. The water vapor formed due to the heat of fire surrounds the substance that undergoes combustion and cuts the supply of oxygen. 
  
• Carbon dioxide is highly volatile and it is heavier than oxygen. So, it immediately vaporizes to cut off the supply of air. In the absence of supporter of combustion, fire is extinguished. Also, it does not damage electrical equipment.
  

Some Class-B fires (hydrocarbons, petroleums, and fuels on fire) cannot be efficiently controlled with water. $CO _2$ being heavier than oxygen covers the fire like a blanket. Hence, one of the important factor for fire is cut off and the fire is controlled.

The ignition temperature of paper is lower compared to that of aluminium. When paper is wrapped around an aluminium pipe; the ignition temperature increases. That is why paper itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.

The foam type of fire extinguisher is also called as soda acid fire extinguisher. It consists of dilute sulphuric acid and sodium bicarbonate (soda). When it is released under high pressure in the form of foam, it covers the surface of fire and controls it by cutting off oxygen.

Ignition temperature is the lowest temperature at which a combustible substance when heated (as in a bath of molten metal) takes fire in air and continues to burn. It is also called also autogenous ignition temperature.

The substances which has a very low ignition temperature and can catch fire easily with a flame are called as inflammable substances. It is the ability of a substance to burn or ignite, causing fire or combustion. For eg; LPG, petrol etc. 

The three essential things required to control fire are fuel, heat and air. 

The cheapest and most widely used fire extinguisher is water because it is easily available. But it is preferably used for class A fires. like fire in solids, wood, paper etc. Not suitable for Class B (Liquid) fires, or where electricity is involved. 

Forest fires are usually due to campfires, burning of debris, littering of cigarettes or intentional acts of arson.