Cooling Action

• Fires extinguishers are designed to remove one or all of the three properties involved in fire--extreme heat, fuel and oxygen. To put out a fire, you need to cool the thing that is fueling it, thus removing the heat. You can also smother the oxygen that is fanning the flames by covering the fire. The other way to put out a fire is to remove the fuel source, but that is difficult to do without accomplishing the first two steps. A fire extinguisher should help cool the fuel source to the point where it will no longer burn.
  
  

Inner Works

• Fire extinguishers are made by packing liquid or coolant inside of a sturdy metal canister under pressure. There is a lever at the top of the cylinder that, when pressed, will release the pressurized coolant inside of the tube. Liquid carbon dioxide is the most commonly used gas inside a separate canister just inside the tube opening. This gas is controlled by a release valve at the top of the tube. When a person pulls the trigger to this valve, the gas propels the liquid out of the cylinder.
  
  

• Dry chemical fire extinguishers depend on pressure to work. You should have the pressure in your extinguisher checked every 6 years by your local fire department. Use these types of extinguishers by pulling out the safety pin and pressing down on the activating lever. This causes a chain reaction, where the lever pushes a rod that has a sharp end. The end punctures the tube of gas inside of the cylinder, which pressurizes the contents of the extinguisher and allows it to escape.