THE FIRE TRIANGLE

[Music] [Music] uh [Music] [Applause] fire can be one of the most destructive forces on earth uncontrolled it may spread quickly destroying anything that will burn how do men control fires can all fires be controlled in the same way to find out let's visit the headquarters of a big city fire department here in the fire department laboratory we can learn the principles of fair control before a fire can start three things must be present first there must be something that will burn anything that will burn is called a fuel second there must be enough heat one fire often supplies the heat needed to start another and finally there must be a gas called oxygen there is oxygen in the air if we keep air from a fire the fire goes out so the three ingredients of a fire are fuel enough heat and oxygen which is present in the air put them together fire results we call this the fire triangle let's examine each side of this triangle separately what kinds of material will burn the fuel can be solid like a match or a piece of wood it can be liquid like oil or it may be a gas like the gas used in the stove to start these materials burning we need the second ingredient heat we will heat these fuels with an electric coil this instrument shows the temperature of the coil in hundreds of degrees fahrenheit the little pointer is just passing 200 degrees fahrenheit the block of wood will not burn until it is much hotter than the match different fuels require different amounts of heat to ignite them 600 degrees fahrenheit and the wood begins to burn to ignite the oil will require still more heat when the temperature of the oil rises above 900 degrees fahrenheit the oil will begin to burn an even higher temperature as from an open flame is required to ignite the gas so fuel and heat are necessary for a fire fuel and heat and one thing more oxygen there can be no fire without oxygen air supplies the fire with oxygen oxygen heat and fuel these are the three ingredients of fire and uncontrolled fire may be very destructive to control fires the men who fight them remove one of the sides of the fire triangle they remove either the fuel or the heat or the oxygen which can they remove to control a forest or brush fire they can remove the fuel they cut away the grass and brush in the path of the fire they chop down the trees sometimes bulldozers can be used to remove brush and grass when the fire reaches the cleared area it will die out for lack of fuel firemen also control fire by removing the heat they do so by drenching fires with huge quantities of water water cools the hot fuel firemen may soak fuel with water before fire reaches wet fuels will not heat as quickly as dry ones water cools the burning fuel the fire goes out removing oxygen is the third way in which a fire may be controlled many fire extinguishers work by keeping oxygen from a fire this type of extinguisher contains a chemical called carbon dioxide to see how carbon dioxide keeps oxygen from a fire let's go to the laboratory carbon dioxide comes out of the extinguisher as a white spray like frost it quickly becomes a gas which is clear and colorless like the air but carbon dioxide is heavier than air so we can pour it over the fire let's see that again the heavy carbon dioxide gas settles over the burning material keeping oxygen away from the fire methods of removing oxygen are important to firefighters because oxygen removal is usually the only safe way to control two special kinds of fires one of these special fires is an oil or gasoline fire water cannot be used to remove the heat from such a fire oil and gasoline are lighter than water they float on top of it water simply spreads an oil or gasoline fire firemen put out such fires by removing the oxygen carbon dioxide gas works very well if the fire is not too large a burning airplane may contain much gasoline airport firemen will try to shut off oxygen from the fire this tank truck contains a chemical foam the foam will not burn and it is so light that it will float on oil or gasoline it smothers the fire by keeping oxygen from reaching the burning fuel without oxygen the fire will die out the other kind of fire that requires special handling is an electrical fire to put water on an electrical fire can be extremely dangerous to the firemen in the laboratory we can see why electricity must pass through these wires to light the bow if we place the wires in a glass beaker and pour in water we can see that electricity will pass through water to light the bulb electricity could pass through water to injure the firemen in an electrical fire the first thing firemen do is shut off the electricity if they cannot be sure that all the electricity is disconnected they use a chemical to remove the oxygen this chemical is a fine powder which will not carry electricity it covers the burning materials and prevents oxygen from reaching [Applause] when fuel heat and oxygen are brought together a fire occurs these ingredients make up the fire triangle firemen control fires by removing one of these ingredients they may remove the burnable material the fuel they may remove heat by drenching the fire with water they may also control fires by removing the oxygen oil and gasoline fires are usually controlled by removing the oxygen in an electrical fire firemen first shut off the electricity controlling fire can be dangerous it requires scientific knowledge fire experiments should never be attempted without expert supervision if you discover a fire call your fire department immediately firemen are experts in the science of fire control you