Unwanted and unintended fire can cause a lot of damages and dead. This is why unwanted and unintended fires must be extinguished as fast as possible. This will be covered in this topic “Methods Of Fire Extinguishing”.
We will be considering the methods of fire extinguishing using the different fire extinguishers. Fires of any type are always extinguished through three (3) methods:
- Cooling
- Starvation and
- Smothering
Each of the above methods works by eliminating one component of the fire triangle.
Lets refer back to the fire triangle:
The three components listed on the fire triangle must be available in good proportion before there can be fire. At any point where one of the component is eliminated, fire cannot be sustained, it dies out naturally.
This is the concept that is used for extinguishing any form of fire.
Read Also: What is fire alarm system: How it works & Types
Types Of Extinguishing Agents
Different types of extinguishing agents have different modes of action, and certain ones are only appropriate for specific fire classes.
Dry chemical:
This is a powder-based agent that extinguishes by separating the three parts of the fire triangle. It prevents the chemical reactions involving heat, fuel, and oxygen, thus extinguishing the fire. During combustion, the fuel breaks down into free radicals, which are highly reactive fragments of molecules that react with oxygen. The substances in dry chemical extinguishers can stop this process.
Foams:
Applied to fuel fires as either an aspirated (mixed and expanded with air in a branch pipe) or non-aspirated form to create a frothy blanket or seal over the fuel, preventing oxygen reaching it. Unlike powder, foam can be used to progressively extinguish fires without flashback.
Water types:
Water cools burning material and is very effective against fires in furniture, fabrics, etc. (including deep-seated fires). Water-based extinguishers cannot be used safely on energized electrical fires or flammable liquid fires.
Wet chemical and water additives:
Wet chemical (potassium acetate, potassium carbonate, or potassium citrate) extinguishes the fire by forming an air-excluding soapy foam blanket over the burning oil through the chemical process of saponification (a base reacting with a fat to form a soap) and by the water content cooling the oil below its ignition temperature. Generally, class A and K (F in Europe) only, although older models also achieved class B and C fire-fighting capability in the past, current models are rated A:K (Amerex, Ansul, Buckeye and Strike First) or K only (Badger/Kidde).
Halons, Halon-replacement clean agents and carbon dioxide:
Clean agents extinguish fire by displacing oxygen (CO2 or inert gases), removing heat from the combustion zone (Halotron I, FE-36, Novec 1230) or inhibiting the chemical chain reaction (Halons, Halotron BrX). They are referred to as clean agents because they do not leave any residue after discharge, which is ideal for protecting sensitive electronics, aircraft, armored vehicles and archival storage, museums, and valuable documents.
Class D dry powder and other agents for metal fires:
There are several class D fire extinguisher agents available; some will handle multiple types of metals, others will not.
Lets get to explain the different methods of fire extinguishing:
Methods Of Fire Extinguishing
Cooling:
Cooling takes off heat from the fire triangle. This heat takes the position of an ignition source, sometimes the ignition source may be naked flame, sparks, etc. However, anytime the ignition source of a fire is removed, the fire will die out naturally.
Starvation:
Starvation robs the fire of burning fuel. The fuel can be solid, liquid or gaseous. When there is no more fuel for the fire to burn, the fire dies out automatically.
Smothering:
Here, oxygen supply is cut off from the fire. This is mostly done by covering the fire to prevent or reduce influx of oxygen into it.
Interrupting the Chemical Chain Reaction of Fire
The chemical reaction can be interrupted by combating and modifying the chemical composition of the free radicals besides reducing their emission. This can be achieved by:
- Cooling the material reduces the number of free radicals being emitted and slows down the chemical reaction
- BCF and other halon extinguishers can interrupt the chain reaction by eliminating free radicals. They form an inert gas barrier that prevents further combustion
These methods highlighted above can be used both at the incipient state of the fire and also at a more advanced stage by different fire safety professionals. Some can tackle fire at the infant stage, while others are trained to tackle fire at a more advanced stage.
Read Also: Fire extinguisher regulations: OSHA & General Regulation
In conclusion, these methods of fire extinguishing also forms what is called “The chemistry of fire extinction“. You need to understand this and each fire extinguisher agent to know which fire extinguisher is best for the different kinds of fire.
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