Tag: combustion

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.