What Causes Fireworks to Explode?

When you stare into the nighttime sky during celebrations like the 4th of July or New Year’s Eve and see the beautiful fireworks and hear the cannon blasts, have you ever wondered what causes fireworks to explode? They are bright and colorful, but they seem to just appear in the night sky, burst open and then disappear. They leave behind the memory of the color and shape but little else. The beautiful display is the result of pyrotechnic talent...but, what causes fireworks to explode?

Since about 1000 AD, the Chinese have been making pyrotechnic projectiles. It was discovered early on that a mixture of saltpeter, sulfur and charcoal could cause an explosion if exposed to an ignition source like a fire.

This discovery of gunpowder prompted the development of rockets and mortars that could be used in celebrations, warfare and spiritual protection. The ancient Chinese believed that evil spirits lived in the sky and would come to cause harm to them. The displays of fire and blasts of loud noise were said to drive them away and to protect the people from them.

Science of Fireworks

Today, there is more of a science associated with the manufacture and preparation of fireworks for public displays. There is much chemistry involved in the selection of materials and chemicals to achieve specific colors and shapes when exploded in the sky.

There are many different colors, shapes and length of display choices that can be made by correct selection of materials. The colors that can be obtained depend on the chemical salts that are combined with the gunpowder of the rocket or payload of the rocket.

Constructing Fireworks

A properly designed aerial firework is constructed by selecting the most visually pleasing and surprising fireworks.

The actual construction of a shell that is used to shoot fireworks into the sky is quite simple. The outer casing of the shell is made of brass, while the inner casing has a double chamber.

The first chamber is centrally located and runs the length of the shell. This chamber is filled with gunpowder to serve as the lift agent. When this layer is ignited, it will lift the payload into the sky allowing the display to be seen. Inside the chamber, containing the lift agent, is the area that will hold the pyrotechnic projectiles.

What Causes Fireworks to Explode?

When the lifting agent is ignited, it begins to burn and expels a large amount of gas out the rear of the projectile. This speeds the payload on its way. At the same time the fuse for the lift agent is lit, the fuse for the inner chamber is also lit. The fuse length of the inner chamber sets the altitude of the display.

The gunpowder contained within the inner chamber ignites and, because there is no place for the developed gas to escape to, it explodes. The pyrotechnic projectiles are released into the sky based on their placement in the inner chamber. Their fuses are also lit as the rocket or shell explodes.

When the fuse lights the projectile, it also explodes and releases its payload of metal salts or shavings into the sky. The metal salts or shavings are ignited by the heat of the explosion and oxidation in the air, resulting in a colored flash or trail of sparks based on the type of metal used.

How Fireworks Create Different Colors

Various metal salts can be used to achieve the desired color of the explosion. Strontium salts will produce red and orange colored displays. Copper salts can be used for blue and purple explosions and magnesium, aluminum or iron can be used for gold to white displays.

With some imagination, virtually every color you could need can be created by mixing the salts in the payload. The arrangement in the payload of the projectiles will determine the shape of the display in the sky, ranging from circular or willow to chrysanthemum or palm. Each has its own beauty and inspiration for ooh’s and aah’s from the viewers. Once the powder is added, the explosion is caused by the generation of gases from the burning of gunpowder into an area of confined space and the beautiful display delights audiences.

This should give you a new appreciation for the next fireworks display you view because now you know what causes fireworks to explode.