![]() Non-flaming, smouldering or glowing embers.įor the flaming mode it is necessary for solid and liquid fuels to be vaporised.The combustion process occurs in two modes: ![]() If the fire is in a fire grate or furnace we refer to this process as a controlled fire, and if it is a building on fire we refer to this process as an uncontrolled fire. This exothermic electron transfer emits heat and/or light. This molecular energy is transferred to other fuel and oxygen molecules which creates a chain reaction where the fuel loses electrons and the oxygen gains electrons. As heat is added, the ignition source, fuel molecules, and oxygen molecules gain energy and become active. For an oxidation reaction to occur, a reducing agent (the fuel) and an oxidising agent (usually oxygen) must be present. Oxidation, in the strict chemical sense, means the loss of electrons. The combustion process is usually associated with the oxidation of a fuel in the presence of oxygen with the emission of heat, light, and other exhaust products. However, the key word that sets combustion apart from other forms of oxidation is the word “rapid”. Oxidation occurs all around us in the form of rust on metal surfaces, and in our bodies by metabolising the food we eat. One generally accepted definition of combustion or fire, is a process involving rapid oxidation at elevated temperatures accompanied by the evolution of heated gaseous products, and the emission of visible and invisible radiation. The 2D figure opposite represents a 3D model of a tetrahedron. ![]() However, this type of extinguisher is being phased out and in the future other extinguishing agents may be found using this principle. Finally, interfering with the chemical chain reaction is possible by “mopping up” the free radicals in the chemical reaction using BCF and other halon extinguishers, which also create an inert gas barrier. By applying water you can lower the temperature below the ignition point, or for a flammable liquid fire it would remove or divert the fuel. For example, a foam extinguisher would create a barrier around the combustible materials and cut off the supply of oxygen as well as reducing heat. This model, although simplistic, is a good analogy as to the theory of how to extinguish a fire. Theoretically, fire extinguishers put out fire by taking away one or more elements of the fire tetrahedron. Each of the four sides of the fire tetrahedron symbolise the Fuel, Heat, Oxygen and Chemical Chain Reaction. 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. Removal of any one of these essential elements will result in the fire being extinguished. ![]() Essentially all four elements must be present for fire to occur, fuel, heat, oxygen, and a chemical chain reaction. A tetrahedron can be described as a pyramid which is a solid having four plane faces. The fire triangle was changed to a fire tetrahedron to reflect this fourth element. Further fire research determined that a fourth element, a chemical chain reaction, was a necessary component of fire. The Fire Tetrahedron (A pyramid)įor many years the concept of fire was symbolised by the Triangle of Combustion and represented, fuel, heat, and oxygen. However, this page will offer an introduction into the fundamental theories of fire and explosion. It is impossible in this short introduction to completely describe all the complex chemical and physical reactions that take place during a fire. To understand how fire extinguishers work, you need to know about combustion. Information about the Fire Triangle/Tetrahedron and Combustion
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