Fire is a chemical reaction between the fuel and the comburent and is produced by an activation energy. The fuels can be very varied but the comburent is always oxygen, present in the atmospheric air in a proportion of 21%. For fire to occur, the fuel must be at the right temperature to start combustion. We could say then that fire is composed of the three elements that compose it, the fuel, the comburent and the activation energy, since if any of these three elements is not present in the combustion reaction, the fire does not occur.
These three elements have always been considered a necessary part of the combustion reaction, although today we must speak of a fourth component, the chain reaction. This implies that fire is composed of these four elements and therefore, that the elimination of any one of them will eventually extinguish the fire. Although only three of the four elements (fuel, oxidizer, and activation energy) are necessary for a fire to start, the fourth component, the chain reaction, is indispensable for the fire to continue. If we understand the effect of each of these components on the fire, we will also understand how to extinguish it:
– Extinguishing by suffocation: we must prevent the comburent from coming into contact with the fire, i.e. prevent the entry of new oxygen into the reaction.
– Modification of the fire atmosphere: it consists of exchanging the air surrounding the fire for an inert atmosphere, this is what is achieved by emptying a CO2 extinguisher on a fire, displacing the oxygen.
– Eliminate the fuel: the objective of this method is clear, by suppressing the fuel the fire is left without raw material to continue burning.
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