Fire Prevention: Nature Of Fire (1958)

well to begin with cereals that we use daily must be considered a source of fuel it isn't the material itself but vapors given off by the material that burn for example wood shavings in a flask and heated will evolve vapors which can be ignited this is true of nearly all materials whether in a solid or a liquid state when heated these materials produce papers and the vapors can be ignited many solids first go through a liquid state before vaporization takes place with a candle for instance the ignited wick melson into a liquid the liquid is drawn into the wick and gives off a vapor which feeds the flame even when this candle is snuffed out vapors are still given off in sufficient quantity to be ignited at some distance from the wing these two liquids have been heated to a temperature at which they begin to give off vapors that can be ignited this temperature is known as the flashpoint for instance number one fuel oil has to be at approximately a hundred and six degrees Fahrenheit to reach its flashpoint diesel oil reaches its flashpoint at approximately 145 degrees Fahrenheit at these temperatures these liquids give off vapors that can be ignited readily some liquids have very high flash points while some have flash points so low that even at room temperature they are constantly giving off highly flammable vapors gasoline produces vapors at temperatures as low as 45 degrees below zero although not visible to the human eye these vapors may be revealed by means of a shadow image the vapors being heavier than air overflow the beaker even when the beaker is only partly filled with liquid gasoline that's why liquids such as these which vaporize at low temperatures always present a fire hazard and must be handled with great care nevertheless even the most highly flammable vapors will not burn without the presence of oxygen on the other hand with enough oxygen even steel can be made to burn first a beaker is filled with pure oxygen a wad of steel wool held over a flame will only glow but in contact with sufficient oxygen it burns readily ordinarily the oxygen required for combustion comes from the air for example the air surrounding this candle but when the candle is burned inside a glass beaker the supply of oxygen is gradually consumed the flame will diminish and go out to further illustrate this point we'll fill this beaker with carbon dioxide a wooden splint immersed in the gas will go out when the splint while still hot is once again surrounded by air the oxygen in the air reignites the splint another demonstration using this electric arcing device a sparked below the surface of the gasoline will create vapors but it will not M since there is no oxygen present but above the surface where the vapors mix with air the vapors again illustrating the importance of oxygen in supporters tchen now the third element ignition temperature this number one fuel oil has been heated to its flashpoint 106 degrees Fahrenheit and as we know this means combustible vapors are given off which combine readily with oxygen however combustion will not occur until the ignition temperature of the vapor oxygen mixture has been reached common sources of heat to produce ignition temperature are a flame an electric spark and this heating coil ignition temperatures vary for different materials this hot soldering iron demonstrates this gasoline requires a higher ignition temperature than is normally produced by a soldering iron but paper having a lower ignition temperature than gasoline ignites and the heat of the flames in turn is hot enough to ignite the gasoline vapors on the other hand a vapor oxygen mixture can also be heated to such a high temperature that it will ignite spontaneously this temperature of a fuel is called its self ignition temperature another example of self ignition with Stoddard solvent a common solvent used for cleaning purposes a welding torch is used to heat the steel plate although not in direct contact with the flammable liquid in the beaker the steel plate will finally get so hot that it will bring about self ignition of the vapors since the heat of its flame is greater than the ignition temperature of a fuel a fire will spread rapidly once it has gained headway however a flame applied directly to this heavy fuel oil goes out because the temperature of the fuel oil is still below its flashpoint by pouring a small amount of gasoline on the surface of the oil and igniting it the heat of the flame is sufficient to raise the temperature of the heavy oil to a point where vapors are produced these vapors then are readily ignited by the flaming gasoline so far this film has shown you the parts that fuel oxygen and ignition temperature play anytime these three elements are brought together you can expect a fire you can prevent a fire simply by removing or eliminating any one of these three elements we shall first consider the control of a fire by the removal of fuel in a tank or vessel filled with gasoline a fire such as this will be extinguished by draining the gasoline out of the bottom just as turning off the supply of gas to a Bunsen burner will cause the flame to go out so ignited vapors coming from a vent can be put out by shutting off the flow of fuel which stops the flow of vapors to the vent now observe that the elimination of oxygen will also stop a fire by covering this beaker of burning gasoline oxygen will be eliminated and the fire goes out oxygen can also be eliminated by displacing it with carbon dioxide an invisible gas widely used in fire extinguishers a fire can also be stopped by the removal of the third element ignition temperature this wood fire is extinguished by a fine spray of water which cools the burning wood below its ignition temperature the flame of a Bunsen burner can be made to go out with a fine wire mesh screen the screen conducts the heat away at such a high rate that the temperature of the burning gas and air mixture falls below its ignition temperature and the flame goes out you have seen how the presence of these three elements will cause a fire you have also seen how you can put out a fire by removing any one of these elements your understanding of the nature and control of fire plus constant vigilance are essential if we are to prevent the loss of lives and property [Music]