Generally if homes, shops and factories caught in fire then water is used to control fire. Water brings down the temperature of the combustible substance below its ignition temperature. The water vapour surrounds the combustible material, thus helping in cutting off the supply of air. So, that the fire is extinguished.
Fire produced by the burning of oil or petrol cannot be controlled by throwing water on it because water being heavier than oil, settles down the oil and oil continues to bum? So, now a day we can use different types of Fire Extinguisher for each type.
We know that there are 3 conditions necessary for producing and sustaining combustion.
- Presence of a combustible substance.
- Presence of a supporter of combustion.
- Attainment of ignition or kindling temperature.
Thus, fire can be controlled by removing one or more of these requirements of fire control. The fire extinguishers also try to cut off the supply of air or bring down the temperature of the fuel or both, to control the fire. The combustible substance as such cannot be eliminated in most of the cases from the place of fire.
There are various types of fire extinguishers used for controlling a fire.
For Example:- Soda – acid fire extinguisher : Carbon dioxide liberated by the reaction of sulphuric acid with sodium bicarbonate solution comes out with a stream of liquid water at high pressure. Water puts off the fire by lowering the temperature of the combustible material below its ignition temperature and carbon dioxide cut off the supply of air to the combustible substance
Types of combustion
Combustion is mainly of three types
- (1)Rapid combustion (2) Spontaneous combustion (3) Explosion
1.Rapid combustion: The combustion in which the gas burns rapidly produces heat and light is called rapid combustion. For example: When a burning matchstick is brought near a gas burner and the gas tap is opened, the gas immediately starts burning with the production of heat and light. Eg. Petrol, LPG, spirit, etc.
2. Spontaneous combustion: The combustion in which no external heat is given is known as spontaneous combustion. For example: Burning of white phosphorus in air.
3. Explosion: The combustion in which large amount of gases are evolved with the production of a tremendous amount of heat, light and sound is called explosion. For example: When a cracker is ignited, a sudden reaction, oxidation process takes place, and in which at high speed large amount of gas is evolved with the production of tremendous amount of heat, light and sound.
Structure of a flame
In order to understand the structure of a flame, light a wax candle and watch its flame. Carefully note the different coloured zones in the flame. Starting from the base of the flame, a flame has four zones.
(1) Blue zone: It is near the base of the flame. Vaporised wax gets oxidised to carbon monoxide and carbon monoxide bums completely with a blue flame in this zone.
(2) Dark inner zone: Surrounding the wick is the dark zone. There is no burning in this zone. If we pass a wooden splinter through the dark zone of the flame, it comes out unscratched (unburnt) showing that there is no ‘burning’ in this zone. However, some =burnt wax vapours are present in this zone.
(3) Luminous zone: In this region of the flame hydrogen burns with a brilliant yellow luminous flame. Burning hydrogen combines with oxygen to form water vapour. Carbon also burns in this zone giving some luminosity to the flame and producing carbon dioxide. Some unblunt carbon particles are left which give rise to soot.
(4) Outermost non-luminous zone: This zone is poorly visible and is slightly blue. It is the hottest part of the flame where complete oxidation (burning) of the fuel is taking place.