This video shows the raw chemistry (air, fuel and heat) of fire. The carbon in the fuel at room temperature is evaporating, mixing with oxygen allowing the simple application of heat to ignite the fire (it is not the flame of the ignition source but the heat produced from it).
The fire continues to burn due to a continuing cycle of heat, fuel and oxygen.
At the end of the film, you see the air taken away by using an apparently flammable piece of cardboard.
Because the removal of oxygen from the fire is so quick, the flammable cardboard does not have time to heat up and become a fuel source.
This is chemistry at its most basic level.
Note: This was done under controlled conditions. Firefighting equipment was present just outside of frame. Use this video for demonstration and do not attempt at home. Combustible fuels as seen here are highly flammable.