Burning, or combustion, is the chemical reaction between a fuel and oxygen. Burning may be separated into two
classes:

• Burning that is controlled and used for the benefit of mankind (cooking, light, heat, industry, motor vehicle
  and aircraft engines) and
  
• Burning that is uncontrolled, most often unintentionally started and growing into raging infernos if the
  conditions are suitable (wildfires, bush-fires, house fires, conflagrations, explosions ). The basic tools for
  understanding fire are the principles of physics, chemistry and fluid flow.
  

When the burning is slow, without any flames, it is often called smouldering. When it is extremely fast as when a
gas leak mixes with air we sometimes get an explosion. In between we get flaming fires. The burning process is a
continuous chemical reaction between fuel particles and oxygen. It spreads in a fire because of transfer of heat.

For fire to continue the following four things are needed:

1. Fuel
   
2. Oxygen
   
3. Heat
   
4. Chemical reactions
   

These are often represented by the fire tetrahedron. Take away one and the fire goes out.

What is a fire?

In the U.S., fires are generally classified into five groups: A, B, C, D, and K

• Class A: Fires that involve wood, cloth, rubber, paper, and some types of plastics.
  
• Class B: Fires that involve gasoline, oil, paint, natural and propane gases, and flammable liquids, gases,
  and greases.
  
• Class C: Fires that involve any of the materials found in Class A and B fires, but with the introduction of
  electrical appliances, wiring, or other electrically energized objects in the vicinity of the fire.
  
• Class D: Fires that involve combustible metals, such as sodium, magnesium, and potassium.
  
• Class K: Fires that involve cooking oils. Although, by definition, Class K is a subclass of Class B, the special
  characteristics of these types of fires are considered important enough to recognize