What is fire?

Fire is a Chemical reaction involving rapid oxidation or burning of a fuel. It needs four components to occur.

Tetrahedron of Fire

If we want to understand how fire extinguishers work, we first need to know a little about combustion.

I will try to explain fundamental theories of fire and explosion, chemical and physical reactions that take place during a fire.

 

Triangle of Combustion (fuel, heat, and oxygen) was explained and represented, for many years the. Further fire research discovered that a fourth element, a chemical chain reaction, was an important component of fire. The fire triangle was changed to a fire tetrahedron to reflect this fourth element. A tetrahedron can be described as a pyramid which a solid is having four plane faces explained as below

 

FUEL - Fuel can be any combustible material – whether it can be solid, liquid or gas. Most solids and liquids become a vapor or gas before they will burn.

 

OXYGEN - The air we breathe contains about 21% oxygen. Fire only needs an atmosphere with at least 16% oxygen which is below than normal condition.

 

HEAT - Heat is the energy necessary to increase the temperature of the fuel to a point where sufficient vapors are given off for ignition to occur.

 

CHEMICAL CHAIN REACTION - A chain reaction can occur when the three elements of fire are present in the proper conditions and proportions. Fire occurs when this rapid oxidation or burning takes place. 

Removal of any element explained above will be result in the fire being extinguished.

Therefore, theoretically, the fire extinguishers or whatever the firefighting method take away one or more elements of the fire tetrahedron.

 Although the symbol explain simply, it is similar way, how to theoretically extinguish a fire, by creating a barrier using foam and prevent oxygen interfacing to the fire. By applying water you can lower the temperature below the ignition temperature (may varied depend on fuel) or in a flammable liquid fire by separating or diverting the fuel. Finally interfering with the chemical chain reaction by mopping up the free radicals in the chemical reaction using, BCF and other halon extinguishers, it also creates an inert gas barrier. 

A Definition of Fire

The accepted definition of combustion or fire, is a process involving rapid oxidation at elevated temperatures accompanied by the evolution of heated gaseous products of combustion, and the emission of visible and invisible radiation.

Classes of fire

Combustible and flammable fuels involved in fires have been broken down into five categories:

• Class A fires – are fires involving organic solids like paper, wood, Etc
• Class B fires – are fires involving flammable Liquids
• Class C fires – are fires involving flammable Gasses
• Class D fires – are fires involving Metals
• Class F fires – are fires involving Cooking oils.