Fire Extinguishers How they work and the different purposes
History of the Fire Extinguisher <ul><li>The first version of a modern fire extinguisher was invented in the United Kingdom by George Manby in 1816. This model was a 3 gallon copper vessel that contained potassium carbonate under compressed air.
At the end of the 19 th century there was the invention of the Soda-Acid extinguisher. This cylinder contained 2 gallons of water that had sodium bicarbonate mixed with it. Inside the cylinder was a container that had concentrated sulphuric acid. Once the handle was pulled it would break the container causing a reaction that would make carbon dioxide that forces the water out of the cylinder under high pressure. </li></ul>
Classification of Fires <ul><li>Fires are classified into five different categories in the United states by the Nation Fire Protection Association.
Fire extinguishers are designed specially for these different classes of fires. Often times because of chemical reactions within the fire more then one type of extinguisher is effective. </li></ul>
Classification of Fires <ul><li>Class A – Used for putting out fires fueled by general materials such as wood and paper, and are usually a mixture of water and carbon dioxide. The symbol used to identify this is a triangle around the letter A.
Class B – Used for putting out fires fueled by liquids or grease. The symbol used to identify is a square around the letter B.
Class C – Used for putting out electric fires, the mixture inside the cylinder is non conducting so that the user is not electrocuted.
Class D – Used to put out fires on flammable metals or other toxic chemicals. The symbol is a star around the letter D. These extinguishers are much more expensive then the other extinguishers and require special training to operate.
Class K – Used to put out kitchen fires or areas that have a high probability of a grease fire. This class has only been around since 1998 so there are fewer of them. </li></ul>
Fire Extinguishers <ul><li>A fire extinguisher can emit a solid, liquid, or a gas, depending on the class of the fire. </li></ul>
Water Fire Extinguishers <ul><li>Water is the most common chemical used as a defense on a class A fire. Most water based extinguishers also have a chemical to prevent the inside of it from rusting.
Wetting agents are also added so that the water sticks to the surface.
Water extinguishes fires because the water cools the fire below its ignition point, and large amounts of water can also deprive the fire of oxygen.
Water will not work on all types of fires, if water is sprayed onto burning liquid petroleum will just spread the flames around more. And water sprayed on an electric fire will cause the user to get shocked. </li></ul>
Foam Fire Extinguishers <ul><li>Foam fire extinguishers are usually used to fight class B fires, but can be affective on class A fires also. These extinguishers are mainly water based but have a foaming agent so that the foam will sit on top of the liquid depriving it from the needed oxygen.
Common foams are meant to only work on nonpolar flammable liquids such as petrol, but break down too fast to work on polar liquids like alcohol. Polar liquids have another foam called “alcohol foam”. </li></ul>
Dry Powder <ul><li>Dry powder extinguishers are used for class B and C fires.
This powder is a mixture of sodium bicarbonate and calcium carbonate made into a fine powder. It is propelled by carbon dioxide or nitrogen.
When this is sprayed onto a fire it interfere with the chemical process of fire. Along with some cooling and exclusion of oxygen.
These extinguishers are good for knocking down big class B flames but will not keep the fire suppressed.
Many times dry powder will be used with foam extinguishers for attacking large class B fires. </li></ul>
Wet Chemical Extinguishers <ul><li>These extinguishers are used for class K fires. Mainly containing potassium acetate, sprayed out in a fine mist. The mist cools the flame front, and the potassium salts saponify the burning oils making a layer of foam over the surface. This chemical is only used for animal fats or vegetable oils so it is not affective on a class B fire. </li></ul>
Saponification <ul><li>This is the hydrolysis of an ester under basic conditions to form an alcohol and the salt of the acid.
Commonly used to refer to the reaction of a metallic alkali (base) with a fat or oil to form soap.
Once the extinguisher is sprayed it converts the burning substance to a non-combustible soap. This also has a cooling affect and suppresses the flames with the mist, </li></ul>
Carbon Dioxide Extinguishers <ul><li>Co ₂ Works on class B and C fires by displacing less dense oxygen. This can cause a problem when you are in a confined area when you also need oxygen. This is a very toxic chemical when in a high concentration.
It is very commonly used on electrical fires because it being a gas does not leave any residue harming the equipment. </li></ul>
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