Back to School - How Fire Works

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Back to School - How Fire Works

Back to School - How Fire Works

That's right folks... its back to school time with a bit of basic chemistry! We are going to talk about fire, how it 'works', what types of fire extinguishers or fire safety equipment are available to fight different types of fires and how these various methods of extinguishing fires work. Its very simple, it should be easy to remember, it should help you if you ever try and fight a fire and lastly it may stop you from being severely injured if you use the wrong fire extinguisher for the type of fire.


Fire is simple really

For something so simple, fire can be catastrophic as the whole of the Austrailan nation knows. Fire can be hard to stop, it can be fast, it can be unpredicatable it causes massive damage every year and unfortunately people lose their lives to it.

In simple terms, fire only needs 3 things:-

  • Heat
  • Fuel
  • Oxygen (or air)

fire_triangle

When sufficient quanities of these elements are present then fire happens. The 3 elements of fire are represented in something called the Fire Triangle as shown.

As with any triangle if you take one of the sides away the triangle collapses. The same thing happens with fire. Remove any of the 3 elements and the fire cannot continue burning.

Remove air / oxygen - The fire can't breathe

Remove heat - The fire can't ignite or continue to combust

Remove Fuel - The fire has nothing to eat.

This fire triangle is very important in understanding how fire extinguishers and fire blankets work. Both methods of extinguishing fires rely on removing one of the elements of this fire triangle.

How different Fire Extinguishers Extinguish

There are a variety of fire extinguishers available to buy. They all have certain applications and some are only suitable for use on very specific fires.

  • Dry powder fire extinguisher - The most common fire extinguisher available. Used for Class A fires (combustible materials such as paper and wood), Class B fires (Flammable and combustible liquids - NOT OILS) and Class E fires (electrical) - These fire extinguishers emit a very fine powder under pressure and cover the burning 'fuel' therefore starving the fire of oxygen and fuel. Dry powder is a very effective method of extinguishing fires, however it can create a mess, visibility problems in enclosed areas and should also be avoided where sensitive electronic equipment such as computers exist.
  • Carbon Dioxide fire extinguisher - Commonly used in offices and server rooms. Carbon dioxide (CO2) fire extinguishers are suitable for Class B fires (Flammable and combustible liquids - NOT OILS) and Class E fires (electrical). CO2 fire extinguishers are not highly rated for Class B fires and should be used with caution on these fires due to very high pressure gas being emitted. CO2 fire extinguishers remove the oxygen in the air by replacing it with large volumes of carbon dioxide, therefore extinguishing the fire. CO2 fire extinguishers are very clean, suitable for use in sensitive electronics areas and can be partially discharged. When operating they are very noisey, can create breathing problems within small enclosed areas and the nozzles can get cold enough to cause frostbite!
  • Water fire extinguisher - Water fire extinguishers are becoming less and less common as we now have more electrical and electronic devices that ever before. Water fire extinguishers are suitable only for Class A fires (combustible materials such as paper and wood) and should NEVER be used in the vicinity of electrical devices or on flammable liquid / cooking oil fires. Water fire extinguishers are unusual in that they extinguish fires by removing the heat by cooling the burning fuel down. As water evaporates it removes heat, therefore the heat in the fire causes the water to evaporate, creating cooling.
  • Foam fire extinguishers - Foam fire extinguisher are used for Class A fires (combustible materials such as paper and wood) and Class B fires (Flammable and combustible liquids - NOT OILS) and like water should NEVER be used in the vicinity of electrical devices. The foam works in a very similar way to powder. With flammable liquid fires the fuel is the vapour from the liquid (in simple terms - like a gas) the foam lays on the flammable liquid surface and seals the surface preventing any vapour from escaping and burning. With Class A fires the foam works in a similar way to water by removing heat, and also similarly to powder by smothering the fuel, preventing oxygen and fuel mixing.
  • Wet chemical fire extinguishers -Wet chemical fire extinguishers are used for Class A fires (combustible materials such as paper and wood) and Class F fires (Cooking oils and Fats) and like water should NEVER be used in the vicinity of electrical devices. Wet chemical fire extinguishers work in a similar way to foam but the chemical is able to withstand the heat of the oil without breaking down and without vaporising violently. The wet chemical seals the surface of the oil and prevents vapours escaping from the oil (which is what is burning) and also stops oxygen from coming into contact with the oil. The fuel and the oxygen are removed from the fire triangle.
  • Fire Blankets - Fire blankets perform the same job as a wet chemical fire extinguisher but are only rated for Class F fires. By placing a fire blanket over a pan that has oil on fire in it, the fire blanket suffocates the oxygen from the fire, extinguishing the fire.

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