My wife and I had the privilege of shooting fireworks for Pyrotecnico of New Castle, PA for 11 years. We did 4th of July shows in Pennsylvania and Virginia as well as other types of shows. When a pyrotechnician lights the fuse a lift charge propels the shell into the air. The ignition of the lift charge also lights a timer fuse inside the shell which is perfectly timed so that when the shell reaches it maximum height the shell explodes or "breaks" which causes the crowds to utter their, Oooo's and Ahhh's. This is a small bottle rocket shot off by my son-in-law and my first attempt at shooting fireworks as a photographer.