The Science Behind Fireworks: what goes into spectacular Canada Day displays

What makes one firework red and another green?

Canada Day is happening this week, and we can expect to see numerous fireworks displays coast to coast. So how do these delightful displays actually happen?

While fireworks come in many shapes, styles, and sizes, each is based on a combination of two basic components — the sparkler and the firecracker.

Remember waiting for the fireworks to begin, filling the time by running around and waving a sparkler through the air? Possibly, while making your parents worried about you potentially hurting yourself or setting something on fire? Well, you may not have realized it, but you were holding in your hand one of the essential components of the colourful displays you were waiting for.

A sparkler. Credit: Getty Images

The characteristic sparks thrown off by a sparkler result from burning a very specific mixture of chemicals and powders. Sometimes combined with charcoal and sulphur, metal powder acts as a fuel source while also providing the colour of the sparks. Chemicals in the mixture such as potassium nitrate, barium nitrate, or strontium nitrate act as oxidizers, supplying oxygen to the flame, and causing the sparks to fly off in random directions. A binder, such as dextrin, keeps the whole mixture together and sticks it to a thin metal handle.

Even though sparklers don't explode, anyone holding one — especially children — should be very careful! They burn at temperatures of at least 1,000°C, which is more than enough to cause severe burns or even ignite clothing. Also, be mindful of where the sparks land, especially if there has been a stretch of dry weather in your area.

A bundle of unlit firecrackers. Credit: Ritesh Man Tamrakar/Flickr (CC BY 2.0)

The firecracker is much a simpler firework. Gunpowder is packed into a paper tube or sphere, and then sealed with a fuse to deliver a flame to the interior. The only purpose of the firecracker is to explode and produce a loud bang when it does. The firecracker's size, and thus the amount of gunpowder contained within it, determines the size of the explosion and the intensity of the noise.

While firecrackers are banned in many places, including Canada, we still see them in one form or another. This is because firecrackers are combined in different ways with sparklers to make firework shells. These shells are the basis for all firework displays, with their big booms and huge, colourful blossoms of light in the sky.

The most basic firework shell is an empty cylinder or sphere made of paper and string. At its core is a firecracker called the burst charge, linked to the outside of the shell by a timing fuse. Into the remaining space in the shell is packed gunpowder, along with a collection of small stars which are made of the same chemicals components as sparklers, but minus the metal handle. These stars can be arranged within the gunpowder in a variety of different configurations, each producing a different type of display.

Some firework shells can be MUCH more complex, like this roughly metre-wide Japanese shell, which features not only sparkler spheres lining the interior but also nested shells that contain even more sparkler spheres, designed to go off well after the initial burst. Credit: Joel(frikitiki)/Flickr (CC BY-ND 2.0)

After the timing fuse is lit, the shell fires into the air from a special launch tube, sometimes using a launch charge incorporated right into the bottom of the shell. The timing fuse is slow-burning compared to the rest of the firework components, and determines the exact time and height above the ground when the firework shell explodes, so that the results are visible for kilometres around. When the burst charge finally detonates, it ignites the gunpowder around it. This simultaneously sets the stars burning and sparking, while causing the shell to blow apart, throwing the burning sparkler stars outwards.

A multi-colour firework burst. Credit: DeltaWorks/Pixabay

Fireworks come in a variety of colours. These are achieved by using specific metals or chemicals in the sparkler stars. Some of the most common are:

White - aluminum or magnesium

Silver - aluminum, magnesium, or titanium powder

Blue - copper chloride or copper compounds

Red - strontium salts or lithium salts

Green - barium chloride

Yellow - sodium nitrate

Orange - calcium chloride

Purple - a mix of strontium and copper compounds

The different metals or chemical compounds that produce the different firework colours. Credit: Base firework image by Artur Strecker/Pixabay, infographic by Scott Sutherland

Multiple stars of different types can also be packed into the same shell, producing a spectacular multi-hued display when it explodes.

When the sparkler stars are packed into a shell randomly, it results in a spherical display known as a peony, named after the flower.

Firework designers can cleverly shape displays to their wishes, though, by combining different coloured stars, different sparkler mixtures, and carefully placing the stars in specific patterns. This is how we get other flower-like displays, such as the dahlia, chrysanthemum, and pistil.

This composite image shows (left to right) peony, chrysanthemum, dahlia, and pistil displays. Credits: Images by Tuan Hung Nguyen/Pixabay, composite by Scott Sutherland

Tree-like palm and willow displays are also popular, and patterns can be arranged to produce rings, stars, spiders, waterfalls, and a host of other shapes as well.

Special effects can be achieved by organizing layers of gunpowder and stars that go off at different times. One way of accomplishing this is by packing a larger shell with several smaller shells. Another way is to change the composition of the stars so that they burn longer, crackle and whistle as they burn, or burn down and then expose a core that explodes.

This New Year's fireworks display shows off the variety of possible patterns and colours. Credit: Nick/Pixabay

And the really great thing is that knowing the science that goes into making these fantastic displays takes absolutely nothing away from the awe they inspire!

In Canada, not all types of fireworks are legal.

According to the Canadian National Fireworks Association, the list of illegal fireworks includes bottle rockets, cherry bombs, M-80 salutes, flash crackers, snaps and throw-down torpedoes, cigarette loads, trick matches, and sprite bombs. Firecrackers are also on the list, although anyone who wishes to use them can apply to Natural Resources Canada for permission.

An M-80 Salute (top left) and Cherry Bomb (bottom left) c/o 'Pyrogrimace/Wikimedia (CC BY 4.0). Flash crackers (top right) c/o Ritesh Man Tamrakar/Flickr (CC BY 2.0). Sprite Bombs and Snaps (bottom right), c/o Natural Resources Canada.

Natural Resources Canada lists several fireworks safety tips, including:

Read all instructions on the fireworks. Plan the order of firing before you begin.

Choose a wide, clear site away from all obstacles. Refer to the safety instructions on the firework for minimum distances from spectators.

Do not fire in windy conditions.

People under 18 years old who use fireworks must be supervised by an adult.

Anchor the fireworks in a good firing base such as a pail filled with earth or sand.

Keep water nearby: Dispose of used fireworks (including debris) in a pail of water.

Light carefully: Always light the fuse at its tip.

Never try to light a firework in your hand, or hold a lit firework, unless the label specifies they are designed to be hand-held.

Wait at least 30 minutes before approaching a firework that did not go off.

Never try to relight a firework that did not go off.

Never try to fix a firework that is defective.

Municipalities also tend to have their own rules and bylaws regarding when and where residents can set off fireworks. If you're planning your own fireworks displays this year, check local bylaws beforehand, just to be sure.