How Do They Put 'Fire' in Fireworks?

The show begins with a whoosh! and a bang! as the first of the fireworks shoots into the air and explodes in a shower of sparkling streamers. People for miles around watch as the night sky fills with gold, red, blue, silver, and green displays.

Few watchers are near enough to see the people on the ground who make the show happen. That's how it must be. Those beautiful explosions are just that: chemicals burning in the air. The people who make and set off fireworks train for years to know how to do so safely while making the shows as exciting as possible.

If you look at the fireworks before the show begins, you will see lots of short tubes or balls wrapped in paper and string and set with long fuses. The heart of each "shell" is a bursting charge and "stars." The stars are pellets of chemicals that burn with different colors. When the bursting charge explodes, the stars ignite and are shot outward to make the brilliant displays in the air. Each shell also has a lifting charge that shoots it into the sky.

Long before the show begins, pyrotechnicians prepare the fireworks. "Pyro" comes from the Greek word for "fire," but these professionals work very carefully to make sure no fires happen at the wrong time. Just before the show, each shell is placed in a long, hollow tube called a mortar. In many shows, fuses are not lit by a match or other flame, but by an electrical spark. The mortars are connected to wires, and the pyrotechnicians can stand a long distance away.

Two fuses per shell

When it's time to launch a shell, the pyrotechnician flips a switch. A spark lights the fuse, the lifting charge explodes, and the shell shoots into the air with a loud whoosh! A second, slower fuse keeps burning as the shell rises. As the shell reaches its highest point, the second fuse sets off the bursting charge. This ignites the stars and shoots them outward. The crowd oohs and aahs as the display fills the air.

Different chemicals make different colors when they burn. Some shells are packed with red stars, some with gold, and so on. Each explosion is a "break." A "multibreak" shell may have several explosions and colors.

Some shells carry more than just glowing stars. A "sound charge" makes a loud boom, a lot of smaller pops, or a whistling noise. The boom is a chemical explosion. A lot of smaller explosions create a crackle or popping sounds, and gases escaping from burning chemicals make whistling noises.

Special fireworks can be set off in indoor stadiums. You may have seen them at a sports event or concert. They are not shot into the air, but are set off from a framework high above the crowd. The chemicals burn quickly and completely before they can come close to the people below.

Other displays, called "set pieces," are connected to a large framework on the ground and can be shaped like a flag, a person, or anything else you might want to display. These don't have a lifting charge, because they stay on the framework and their stars are shot outward from the frame.

All these flammable chemicals mean that fireworks have to be made very carefully. Fireworks are made almost entirely by hand. This is the safest way. Machines might make sparks that could set off an explosion. Lubricating oil from a machine might drip onto certain chemicals and cause an explosion.

Why workers wear cotton

Another type of spark is also very dangerous. If you've ever scuffed across a carpet and touched something metal to make a spark, you know what static electricity is. This kind of spark has to be avoided in fireworks factories. Workers wear cotton clothes, never nylon or silk or other materials that create static electricity. Before entering a building that contains chemicals, workers touch their hands to a copper plate. This conducts away any electricity. Sawdust covers the floor. Nothing is ever pushed across a table, which might create a spark. Everything is picked up and carried to its next place.

Many chemicals are stored away from each other in separate buildings, called bunkers. Some of these chemicals ignite just by being mixed together - without a spark! These chemicals are brought together only as needed.

Once the chemicals have been mixed, formed into stars, and packed into shells, the chemicals are far less likely to ignite accidentally. The fireworks can be safely shipped to show locations.

At the show, the shells are carefully loaded in mortars. Everyone not involved in putting on the show is kept a safe distance away.

By the time the show starts, a lot of highly trained people have worked very carefully to make sure the sight is not only spectacular, but also safe. So find a seat, lean back, and enjoy the show!

What's Inside an Aerial Shell

The Chinese invented fireworks more than 1,000 years ago. Here's how those colorful explosions are created today. A typical aerial shell has six parts: a casing, fuses, a propelling charge, and a canister containing a bursting charge and 'stars' (the chemicals that burn to produce the colors).

FIRING: The long leader fuse ignites the lift or propelling charge. The lift charge does not work like a rocket engine. It simply explodes, and the expanding gases of the explosion push the shell out a long tube (called a mortar) at 200 to 400 feet per second. The bigger the shell, the higher it goes - about 100 feet for every inch in diameter.

The leader fuse also ignites a slow-burning time fuse. The time fuse ignites the bursting charge, which breaks open the cardboard canister, ignites the stars, and scatters them in a pattern.

STARS: Stars are made by mixing chemicals to form a dough that is rolled and cut into small pieces. Stars can also be pressed into molds. Stars that change color are made by rolling them in a tumbler. The pellets that form may be rolled in two or three chemical mixes to create layers that will burn different colors. Stars range in size from oat flakes to golf balls.

COLORS: Orange is the easiest color star to make. Blue is the most difficult, especially deep blues and purples. Reds and greens are easier, but good yellows are hard to master. Golds and silvers are popular and not hard to make.

Pyrotechnical Glossary

Black shell: A malfunctioning shell that falls back to earth without exploding.

Break: When the shell explodes in the air. A "multibreak" shell has more than one explosion.

Chrysanthemum: A shell that bursts into a dense spherical pattern of stars.

Crackle: A charge that explodes with lots of small, popping noises.

Flowerpot: A malfunctioning shell that doesn't shoot into the air but bursts in the mortar.

Peony: A loose pattern of stars that breaks up and droops downward when ignited.

Potato: A simple shell that breaks into a single spray of color.

Salute: A shell that makes a flash and a loud boom.

Shell: What we call a "firework." Shells are fired from long tubes called mortars.

Strobe: A shell whose stars flash as they slowly float down.

Weeping willow: A shell whose stars float down in long-lasting streams, like a weeping willow's branches.

Whistle: A shell that makes a whistling noise. (The Japanese call these "mad lions.")