Understanding Fire
The Fire Triangle is a simple model developed to illustrate the ingredients necessary for most fires to burn. In order for a fire to ignite a fire requires three critical elements: heat, fuel, and an oxidizing agent (usually oxygen).
A fire can be extinguished by removing any one of the elements from the fire. For Example without sufficient heat, a fire cannot begin, and it cannot continue. Heat can be removed by dousing some types of fire with water; the water turns to steam, taking the heat with it. Keep in mind though water will actually increase or spread some other types of fires (such as combustible metal fires, or oil and gasoline. This is why Pressurized Water Extinguishers are rated only for CLASS A burning fires.
The Fire Triangle is a useful tool in explaining the basic make-up of most fires however it does not account for the make-up of all. There are certain chemical fires where knowing only the ?fire triangle? is not good enough...
This leads to the development of the Fire Tetrahedron.
The Tetrahedron is a triangular pyramid having four sides (including the bottom). Some fire suppression agents do not remove or reduce any of the three necessary components, but rather interfere with their chemical combination, such as Halon (no longer acceptable to be used in Commercial settings as it was later found to be an ozone depleting agent).
When the fire involves burning metals (known as a class-D fire) like lithium, magnesium, etc.), it is useful to consider the chemistry of combustion. Putting water on such a fire could result in the fire getting hotter (or even exploding) because such metals can react with water in an exothermic reaction to produce flammable hydrogen gas. In a case involving a fire as such, you must use a Class D rated Fire Extinguisher to interfere and break the chain reaction of metallic combustion to stop the fire.