The Fire Triangle

1 James C. Coco, ed., Large Property Damage Losses in the Hydrocarbon-Chemical Industry A Thirty Year Review (New York J. H. Marsh McLennan, 1997). 

or burning, is the rapid exothermic oxidation of an ignited fuel. The fuel can be in solid, liquid, or vapor form, but vapor and liquid fuels are generally easier to ignite. The combustion always occurs in the vapor phase liquids are volatized and solids are decomposed into vapor before combustion. 

When fuel, oxidizer, and an ignition source are present at the necessary levels, burning will occur. This means a fire will not occur if (1) fuel is not present or is not present in sufficient quantities, (2) an oxidizer is not present or is not present in sufficient quantities, and (3) the ignition source is not energetic enough to initiate the fire. 

Two common examples of the three components of the fire triangle are wood, air, and a match and gasoline, air, and a spark. However, other, less obvious combinations of chemicals can lead to fires and explosions. Various fuels, oxidizers, and ignition sources common in the chemical industry are 

Liquids gasoline, acetone, ether, pentane Solids plastics, wood dust, fibers, metal particles Gases acetylene, propane, carbon monoxide, hydrogen 

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The Fire Triangle The well-known/i/ g triangle (see Fig. 26-33) is used to represent the three conditions necessary for a fire (1) fuel, (2) oxygen or other oxidizer (a gaseous oxidizer such as chlorine, a liquid oxidizer such as bromine, or a solid oxidizer such as sodium bro-mate), and (3) heat (energy). 

If one of the conditions in the fire triangle is missing, fire does not occur, and if one is removed, fire is extinguished. Usually a fire occurs when a source of heat contacts a combustible material in air, and then the heat is supphed by the combustion process itself. 

The fire triangle indicates how fires may be fought or prevented ... 

Removal of one of the eorners of the fire triangle normally results in extinguishment of a fire. Propagation of a flame ean also be stopped by inhibition of the ehain reaetions, e.g. using dry powders or organo-halogen vaporizing liquids. 

Draw the fire triangle and explain the simple theory of combustion. 

Theoretically, if one corner of the fire triangle is eliminated a fire or explosion is impossible. However, in practice, if flammable gases or vapours are mixed with air in flammable concentrations, sooner or later the mixture is likely to catch fire or explode because of the difficulty of eliminating every source of ignition. For reliable control of flammable materials, including combustible dusts, the aim is to remove two corners from the fire triangle. This can include some combination of ... 

The investigation of an industrial fire or explosion invariably starts with an effort to identify each element in the fire triangle. Quite often, the fuel is known and so either the oxidizer or the ignition source becomes the focus of the investigation. For example, in a blender used to mix a... 

The essential elements for combustion are fuel, an oxidizer, and an ignition source. These elements are illustrated by the fire triangle, shown in Figure 6-1. 

For any fire or combustion explosion to occur, three conditions must be met (as shown in the fire triangle of Figure 6-1). First, a combustible or explosive material must be present. Second, oxygen must be present to support the combustion reaction. Finally, a source of ignition must be available to initiate the reaction. If any of the three conditions of the fire triangle is eliminated, the triangle is broken and it is impossible for a fire or combustion explosion to result. This is the basis for the first six design methods listed above. 

The Fire Triangle The fire triangle is shown in Fig. 23-2. It shows... 

The usual oxidizer in the fire triangle is oxygen in the air. However, gases such as fluorine and chlorine liquids such as peroxides and chlorates and solids such as ammonium nitrate and some metals can serve the role of an oxidizer. Exothermic decomposition, without oxygen, is also possible, e.g., with ethylene oxide or acetylene. 

If any one side of the fire triangle is removed, a fire will not result. In the past, the most common method for fire control was elimination of ignition sources. However, experience has shown that this is not robust enough. Current fire control prevention methods continue with elimination of ignition sources, while focusing efforts more strongly on preventing flammable mixtures. 

FIG. 23-2 The fire triangle showing the requirement for combustion of gases and vapors. [D. A. Crowl, Understanding Explosions, Center for Chemical Process Safety (CCPS) of the American Institute of Chemical Engineers (AIChE) copyright 2003 AIChE and reproduced with permission. ]... 

Fire can only occur when all three of the above elements are present and in the proper conditions and proportions. These three basic conditions are often represented as a fire triangle shown in Figure B-1. The combustion reaction itself is often included as a fourth central element of the fire triangle. 

If one of the sides of the fire triangle is missing, the fire will not start. If one side is removed, the fire will be extinguished. The fire triangle forms the foundation for all methods of fire prevention and firefighting (NFPA, 1997). 

There are three basic theories that are used to describe the reaction known as fire. They are the fire triangle, the tetrahedron of fire, and the life cycle of fire. Of the three, the first is the oldest and best known, the second is accepted as more fully explaining the chemistry of fire, while the third is a more detailed version of the fire triangle. Each is briefly described below. 

Water, of course, does not work with all materials. There is a special class of materials that are water reactive, and hence water becomes an unacceptable extinguishing agent. For these class of materials another approach to eliminating the fire is taken. Specifically, we must remove the oxidizer leg from the fire triangle i.e. cut off the supply of oxygen which fuels the air to fuel mixture. 

The Fire Triangle. The well-known fire triangle (see Fig. 3.1) is used to represent the three conditions necessary for a fire ... 

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