Fast combustion requires four different things. The first thing that is needed is a combustible substance, such as the wax of a candle. The second thing that is needed is oxygen, which is found in the air around us. The third thing that is needed is a sufficently high temperature, which is usually achieved with a lighter of some sort. The fourth thing that is needed is a chemical reaction that feeds itself. Such a reaction is known as a chain reaction. When a fire is extinguished, it is usually done by limiting one or several of these four requirements. 

Combustion requires oxygen, which is found in the air around us. When a burning candle is covered tightly with a glass jar, its flame will gradually die out. This happens because it has no access to oxygen. The oxygen in the jar has already been transformed into water and carbon dioxide, and more oxygen cannot be found inside the walls of the jar. 

The function of a candlesnuffer is based on the same phenomenon as the glass jar experiment. The flame is covered completely by the bell of the candlesnuffer, until it has no more oxygen to use. 

Carbon dioxide can also be used to extinguish a flame. Carbon dioxide gas is heavier than normal air, which is why it fill cover up the flame. When this happens, the flame cannot find oxygen and will die out. 


Image on the left: The candlesnuffer removes the flame's access to oxygen. Image on the right: Carbon dioxide can also be used to extinguish a flame.