Great Lakes Fireworks

How Fireworks Work

Just about everyone in the United States has some personal experience with fireworks, either from Fourth of July or New Year's Eve celebrations. For example, you have probably seen both sparklers and firecrackers. It turns out that if you understand these two pyrotechnic devices, then you are well on your way to understanding aerial fireworks! The sparkler demonstrates how to get bright, sparkling light from a firework, and the firecracker shows how to create an explosion.

Firecrackers have been around for hundreds of years. They consist of either black powder (also known as gunpowder) or flash powder in a tight paper tube with a fuse to light the powder. Black powder, discussed briefly in How Rocket Engines Work, contains charcoal, sulfur and potassium nitrate. A composition used in a firecracker might have aluminum instead of or in addition to charcoal in order to brighten the explosion. To find out more about flash powder, which was originally used in photography,

Aerial Fireworks

An aerial firework is normally formed as a shell that consists of four parts:

Container - Usually pasted paper and string formed into a cylinder
Stars - Spheres, cubes or cylinders of a sparkler-like composition
Bursting charge - Firecracker-like charge at the center of the shell
Fuse - Provides a time delay so the shell explodes at the right altitude

Located just below the shell is a small cylinder that contains the lifting charge.

The shell is launched from a mortar. The mortar might be a short, steel pipe with a lifting charge of black powder that explodes in the pipe to launch the shell. When the lifting charge fires to launch the shell, it lights the shell's fuse. The shell's fuse burns while the shell rises to its correct altitude, and then ignites the bursting charge so it explodes.

Simple shells consist of a paper tube filled with stars and black powder. Stars come in all shapes and sizes, but you can imagine a simple star as something like sparkler compound formed into a ball the size of a pea or a dime. The stars are poured into the tube and then surrounded by black powder. When the fuse burns into the shell, it ignites the bursting charge, causing the shell to explode. The explosion ignites the outside of the stars, which begin to burn with bright showers of sparks. Since the explosion throws the stars in all directions, you get the huge sphere of sparkling light that is so familiar at fireworks displays.

Multibreak Shells

More complicated shells burst in two or three phases. Shells like this are called multibreak shells. They may contain stars of different colors and compositions to create softer or brighter light, more or less sparks, etc. Some shells contain explosives designed to crackle in the sky, or whistles that explode outward with the stars.

Multibreak shells may consist of a shell filled with other shells, or they may have multiple sections without using additional shells. The sections of a multibreak shell are ignited by different fuses. The bursting of one section ignites the next. The shells must be assembled in such a way that each section explodes in sequence to produce a distinct separate effect. The explosives that break the sections apart are called break charges.

The pattern that an aerial shell paints in the sky depends on the arrangement of star pellets inside the shell. For example, if the pellets are equally spaced in a circle, with black powder inside the circle, you will see an aerial display of smaller star explosions equally spaced in a circle. To create a specific figure in the sky, you create an outline of the figure in star pellets, surround them as a group with a layer of break charge to separate them simultaneously from the rest of the contents of the shell, and place explosive charges inside those pellets to blow them outward into a large figure. Each charge has to be ignited at exactly the right time or the whole thing is spoiled.