What is Fire?
Fire is rapid, self-sustaining oxidation accompanied by the evolution of varying intensities of heat and light. This definition indicates that fire is a chemical process of decomposition in which the rapid oxidation of a fuel produces heat and light.
Three basic elements must be present for a fire to occur: fuel, heat, and oxygen. These three components make up the fire triangle , and proper combination of these three items invariably results in a fire. There must be oxygen to sustain the combustion, heat to raise the material to its ignition temperature, Fuel to support the combustion and a Chemical reaction between the three elements. The chemical chain reaction between the fuel, heat, and oxygen represents the fourth component of the fire equation. We will refer to this as the fire tetrahedron. Anytime something burns, these four components are present. Preventing the combination of these elements will prevent a fire. If one of the four elements is removed from the fire situation, the fire will be extinguished.
In a fire, it is the vapors that are actually burning, so the closer the fuel is to the vapor state, the easier it is to ignite. Liquids ignite more readily than solids, gases more easily than liquids.
The physical state of the fuel is also important. A solid wooden board is more difficult to ignite than wood shavings due to the mass to surface area ratio. If the mass is large and the surface area small, as with the solid board, the heat of an ignition source is more easily dissipated through the material and hence there is less chance for ignition and fire. If the mass is small and the surface area large, as with wood shavings, the heat cannot be dissipated as quickly, and ignition occurs more easily.
Dust is an example of reducing mass relative to the surface area. Given the proper conditions, many dusts may explode. Grain and coal dust are two common varieties of dust that can explode.