The fire tetrahedron represents all four elements required for a fire to start:
a- Heat
b- Fuel
c- Oxygen
d- The chain reaction among the above elements

Oxygen and fuel feed the combustion; heat takes the fuel to the ignition point, and the chemical reaction among the elements allows the fire to start. As soon as one of the four elements of the tetrahedron is removed, combustion stops. This is the underlying principle for fire prevention