The Fire Triangle vs  Fire Extinguishers

12/15/2020 (Permalink)

Fire is rapid oxidation (combustion) involving three components; fuel, oxygen and heat.  Once started, for a fire to continue to burn all three elements must be present.  These components form what is called the Fire Triangle.  Eliminate one leg of the triangle and the fire goes out.  Different types of fire extinguishers work by eliminating one or more of the legs of the fire triangle.

There are four main types of fire extinguishers, water, dry powder, foam and CO₂.  The most common fire extinguisher is water. These are tanks filled with water and a propellant such as nitrogen or carbon dioxide. They work by mainly removing heat; additionally they also help by restricting the oxygen supply. Water extinguishers attack two legs of the fire triangle.

The second type, dry powder extinguishers, are tanks filled with a dry chemical and pressurized with nitrogen. The dry chemical is designed to absorb heat, melt and coat the fuel.  This reduces flammable vapors and cuts off the oxygen supply to the fuel.  Monoammonium phosphate is the most common dry powder.  Others include sodium bicarbonate and potassium bicarbonate.

The third type of extinguisher is carbon dioxide.  This consists of a tank filled with liquid and gaseous carbon dioxide.  When the liquid is released from the tank it rapidly expands and turns into gas.  When turning into a gas a great amount of heat is absorbed taking out one leg of the triangle.  The carbon dioxide also envelopes the fuel cutting off the oxygen thereby taking out a second leg of the triangle.

The fourth type is the foam extinguisher also known as AFFF (aqueous film-forming foam).  This consists of a tank of water and a foaming agent pressurized with nitrogen.  The water and foaming agent are mixed as they exit the nozzle forming foam that coats the fire preventing oxygen from reaching the fuel.  It also absorbs heat since the foam is mainly water. Foam attacks two legs of the triangle.