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1. CLASSIFICATION Fire is a chemical reaction involving the rapid oxidation or burning of a fuel. It needs four elements to occur as illustrated below in the tetrahedron. This is described by the following illustration: The first component of the tetrahedron is fuel. Fuel can be any combustible material such as: solid (such as wood, paper, or cloth), liquid (such as gasoline) or gas (such as acetylene or propane). Solids and liquids generally convert to gases or vapors before they will burn. Another component of the tetrahedron is oxygen. Fire only needs an atmosphere with at least 16% oxygen. Heat is also a component of the tetrahedron. Heat is the energy necessary to increase the temperature of the fuel source to a point in which sufficient vapors are emitted for ignition to occur. The final side of the tetrahedron represents a chemical chain. When these components are brought together in the proper conditions and preparations, fire will develop. Take away any one of these elements, and the fire cannot exist or will be extinguished if it was already burning. Fires are classified into four groups according to sources of fuel: Class A, B, C, and D based on the type of fuel source: Class Ordinary combustible materials such as paper, wood, cloth and some rubber and plastic materials. Class 8 Flammable or combustible liquids, flammable gases, greases and similar materials, and some rubber and plastic materials. Class C Energized electrical equipment and power supply circuits and related materials. Class D Combustible metals such as magnesium, titanium, zirconium, sodium, lithium and potassium. II. DETERMINING FIRE HAZARDS Aftchmenl number 2 \n F-5 Page 241