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Fire Protection Handbook
Fire Protection Handbook
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Fire Protection HandbookPage 1: Fundamentals of FireA Definition of FireOne generally accepted definition of combustion or fire is a process involving rapid oxidation at elevated temperatures accompanied by the evolution of heated gaseous products of combustion, and the emission of visible and invisible radiation. Oxidation occurs all around us in the form of rust on metal surfaces, and in our bodies by metabolising the food we eat. However, the key word that sets combustion apart from other forms of oxidation is the word “rapid”. The combustion process is usually associated with the oxidation of a fuel in the presence of oxygen with the emission of heat and light. Oxidation, in the strict chemical sense, means the loss of electrons. For an oxidation reaction to occur, a reducing agent, the fuel, and an oxidizing agent, usually oxygen, must be present. As heat is added, the ignition source, the fuel molecules and oxygen molecules gain energy and become active. This molecular energy is transferred to other fuel and oxygen molecules which creates a chain reaction. A reaction takes place where the fuel loses electrons and the oxygen gains electrons. This exothermic electron transfer emits heat and/or light. If the fire is in a fire grate or furnace we refer to this process as a controlled fire, and in a building it is an uncontrolled fire. The Fire Tetrahedron
A tetrahedron can be described as a solid pyramid which is a solid having four plane faces. These four face represent the four elements that must be present for fire to occur: fuel, heat, oxygen, and a chemical chain reaction. Removal of any one of these essential elements will result in the fire being extinguished. The four elements are: oxygen to sustain combustion, sufficient heat to raise the material to its ignition temperature, fuel or combustible material and subsequently an exothermic chemical chain reaction in the material. Theoretically, fire extinguishers put out fire by taking away one or more elements of the fire tetrahedron. The symbol is a good analogy of how to theoretically extinguish a fire, by creating a barrier using foam for instance and prevent oxygen getting to the fire. By applying water you can lower the temperature below the ignition point, or in a flammable liquid fire by removing or diverting the fuel. Finally, interfering with the chemical chain reaction by mopping up the free radicals in the chemical reaction by using halon extinguishers creates an inert gas barrier. Stages of a FireThere are three generally recognized stages to a fire: the incipient stage, smoldering stage, and flaming stage. The incipient stage is a region where preheating, distillation and slow pyrolysis are in progress. Gas and sub-micron particles are generated and transported away from the source by diffusion, air movement, and weak convection movement, produced by the buoyancy of the products of pyrolysis. The smoldering stage is a region of fully developed pyrolysis that begins with ignition and includes the initial stage of combustion. Invisible aerosol and visible smoke particles are generated and transported away from the source by moderate convection patterns and background air movement. The flaming stage is a region of rapid reaction that covers the period of initial occurrence of flame to a fully developed fire. Heat transfer from the fire occurs predominantly from radiation and convection from the flame. Classes of Fire
SummaryA fire begins by an external ignition source in the form of a flame, spark, or hot ember. This external ignition source heats the fuel in the presence of oxygen. As the fuel and oxygen are heated, molecular activity increases. If sufficiently heated, a self-sustaining chemical chain reaction or molecular activity occurs between the fuel and oxygen. This will continue the heating process and the resulting chain reaction will escalate without the need for an external ignition source. Once ignition has occurred, it will continue until one of the following occurs:
FIRE SAFETY, AT ITS MOST BASIC, IS BASED UPON THE PRINCIPLE OF KEEPING FUEL SOURCES AND IGNITION SOURCES SEPARATE.![]()
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