Fire extinguishing agents work basically in two ways — either by cooling the burning materials or by blanketing them with an inert coating that cuts off the supply of oxygen. There are different types of fire extinguishers. One of the most common ones uses water which has a high heat capacity. Water is released out of such extinguishers at high pressure so it acts like a powerful cooling agent. However, water type fire extinguishers cannot be used on electrical fires or where the burning substance involves oil. Foam type fire extinguishers use foaming agents that have a smothering and cooling effect on the fire. A dry chemical extinguisher sprays a very fine power of sodium bicarbonate or potassium bicarbonate or monoammonium phosphate. These solids coat the fuel and smother the fire. A safe and effective extinguisher for all confined fires uses carbon dioxide ( ) which acts as an inert blanket.
Based on the nature of the burning substance, different kinds of fire extinguishers are used, each having a specific design and mode of functioning.