How Fire Extinguisher Work

Fire extinguishers parts consist of tube, pressure gauge, nozle, safety pin, handle and high pressure gas canister at the top inside the tube. The tube filled with water or a smothering material, such as CO2.
When you pull the safety pin and squeeze the handle, the handle pushes on an actuating rod which presses the valve down to open a passage to the nozzle. The compressed gas inside a canister is released, applying a downward pressure on the fire-extinguishing material (water or smothering material). This pushes the material out the nozzle with high amounts of pressure.

Water Extinguishers
Water extinguishers are filled with regular tap water and pressurized with oxygen. The best way to remove heat is to dump water on the fire but, depending on the type of fire, this is not always the best option.

Dry Chemical Extinguishers
Dry chemical extinguishers are filled with either foam or powder, usually sodium bicarbonate (baking soda) or potassium bicarbonate, and pressurized with nitrogen. Baking soda is effective because it decomposes at 158 degrees Fahrenheit and releases carbon dioxide (which smothers oxygen) once it decomposes. Dry chemical extinguishers interrupt the chemical reaction of the fire by coating the fuel with a thin layer of powder or foam, separating the fuel from the surrounding oxygen.
Warning: when used indoors, powder can obscure vision or damage goods and machinery. It is also very messy.

Carbon Dioxide (CO2) extinguishers
CO2 extinguishers contain carbon dioxide, a non-flammable gas, and are highly pressurized. The pressure is so great that it is not uncommon for bits of dry ice to shoot out. CO2 is heavier than oxygen so these extinguishers work by displacing or taking away oxygen from the surrounding area. CO2 is also very cold so it also works by cooling the fuel.
Carbon Dioxide is ideal for fires involving electrical apparatus, and will also extinguish class B liquid fires, but has NO POST FIRE SECURITY and the fire could re-ignite.