Friday, July 6, 2012

How Do Fireworks Work?

I started thinking yesterday about the wonderful fireworks we saw on July 4th and realized that I really don't know how they work. so I decided to research the topic and pass on the information in today's posting.

There's no tradition quite like a Fourth of July fireworks display. In Grand Marais we always celebrate the holiday on the actual calendar day, unlike many communities that select the nearest weekend. This year people started to park their vehicles on July 3rd to save their preferred spot. Several thousand people line the entire perimeter of the bay as well as the beach along the bay. Some brave souls also watch from boats in the bay. Spectators wait for spellbinding colors, thrilling explosions and intriguing shapes to paint the sky. Little kids and big kids watch these beautiful wonders, all the product of meticulous chemistry and clever ballistics.

Inside each handmade firework are small packets filled with special chemicals, mainly metal salts and metal oxides, which react to produce an array of colors. When heated, the atoms of each element in the mix absorb energy, causing its electrons to rearrange from their lowest energy state to a higher "excited" state. As the electrons plummet back down to their lower energy state, the excess energy gets emitted as light. Each element releases a different amount of energy, and this energy is what determines the color or wavelength of the light that is emitted in the firework.

In many large cities the fireworks are set off by an engineer who pushes a button that sends an electrical impulse through wiring. In Grand Marais, our trained volunteers use flares to set off each firework. On the beach at the center of the bay below town they assemble a series of mortar tubes of different sizes. Each firework is packaged in a spherical canister with a fuse. Once placed in the mortar tube, a flare is used to light the fuse. The fuse burns through to a black powder that catapults the shell into the sky. At the same moment, a time-delay fuse is triggered, giving the shell time to soar before bursting. After about 5 seconds the shell peaks, the fuse kindles a bursting charge, and poof!—the casing ruptures, and magnificent tendrils of red, white and blue stream into the sky.

Fireworks start off as handcrafted shells that are fairly unassuming, encased in treated cardboard and heavy paper. But inside these shells are the blueprints that control how a firework will take off, detonate and appear across the canvas of the night sky. The shell innards include fuel, an oxygen producer, a binding resin and color-producing agents all carefully mixed into a recipe that are well protected by the company that produces these colorful wonders. The most familiar characteristics of a firework are its radiant tendrils and plumes that stream out as the shell breaks open.

The particular arrangement of the components within the shell determines how the firework will unfold in space. A smiley face or a star-shaped arrangement, for instance, will burst into fireworks with exactly those shapes. The components that contain the chemicals are packaged into shapes that resemble everyday batteries, stars, or round balls. Special effects including secondary explosions take place when smaller tubes of chemicals are packaged in larger tubes. The individual components packaged into the larger firework tube can be as small as a pea or as large as a clementine. Larger pellets have more material to burn, causing the plume that spews from it to spread farther into space and to last longer.

When the firework shell has soared to its selected height (based upon the amount of powder ignited by the fuse), the bursting charge ignites and burns the chemical components around it, eventually causing the entire shell to explode. The power of the burst charge, the strength of the shell walls and the size and shape of the individual components packed into the larger firework tube all determine the shape and width of the display.  In some cases, there are individual components packaged within others that produce a series of effects rather than just one explosion.

Pyrotechnic displays demonstrate the bright colors produced by both incandescence and gas excitations. While the brilliant whites rely on the incandescence of metals such as magnesium, fireworks manufacturers use elements that react during the pyrotechnic explosion to emit colors by luminescence, through excitation of gas molecules.

Some of the chemical compounds packed into the firework components include:

Calcium - Calcium is used to deepen firework colors. Calcium salts produce orange fireworks.

Carbon - Carbon is one of the main components of black powder, which is used as a propellant in fireworks. Carbon provides the fuel for a firework to launch it out of the mortar tube.

Chlorine - Chlorine is an important component of many oxidizers in fireworks. Several of the metal salts that produce colors contain chlorine.

Copper - Copper compounds produce blue colors in fireworks.

Iron - Iron is used to produce sparks. The heat of the metal determines the color of the sparks.

Lithium - Lithium is a metal that is used to impart a red color to fireworks. Lithium carbonate, in particular, is a common colorant.

Magnesium - Magnesium burns a very bright white, so it is used to add white sparks or improve the overall brilliance of a firework.

Oxygen - Fireworks include oxidizers, which are substances that produce oxygen in order for burning to occur. The oxidizers are usually nitrates, chlorates, or perchlorates.

Phosphorus - Phosphorus burns spontaneously in air and is also responsible for some glow-in-the-dark effects. It may be a component of a firework's fuel.

Potassium - Potassium helps to oxidize firework mixtures. Potassium nitrate, potassium chlorate, and potassium perchlorate are all important oxidizers.

Sodium - Sodium imparts a gold or yellow color to fireworks, however, the color may be so bright that it masks less intense colors.

Sulfur - Sulphur is a component of black powder. It is found in a firework's propellant/fuel.

Strontium - Strontium salts impart a red color to fireworks. Strontium compounds are also important for stabilizing fireworks mixtures.

Titanium - Titanium metal can be burned as powder or flakes to produce silver sparks.

Zinc - Zinc is used to create smoke effects for fireworks and other pyrotechnic devices.

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