Fire is the sharpest two-edged sword in man’s bag of tools. When under control it was a formidable tool that warmed, comforted, cooked food and kept wild beasts at bay for prehistoric man. Today, it fulfills those and many other needs, yet out of control it is man’s worst nightmare. What greater fear can a pilot have than being at altitude with a fire in the cabin?
Fire is defined as a rapid, persistent chemical reaction that releases heat and light. It is the exothermic combination of a combustible substance with oxygen. The key issue relating to fire is its persistence. Once a fire starts it takes on a life of its own and aggressively searches for nourishment to maintain itself and grow.
Every fire has three fundamentals: oxygen, heat and fuel. Remove any one of them and the fire goes out. The chemical process is oxidation–oxygen atoms combine with hydrogen and carbon to form water and carbon dioxide–the same process that causes rust. With iron the chemical reaction is very slow and the heat energy released is low. With some things, such as wood or paper, the oxidation rate is so fast that the heat cannot be released fast enough and combustion occurs. To earn the name “fire” there must be flames or smoldering present.