Fireworks are divided into two parts, aerial or ground. Usually there is a tube that houses the explosives packed in the black powder and a treating fuse on the top of it. Basically it is oxygen that causes fireworks to explode. The black powder which is either carbon or coal causes the firework to explode when it comes in contact with oxygen. When the fuse is lit, the particles become unstable and release oxygen and a reaction is caused with other particles which in turn causes an explosion.