Holidays

How do fireworks get their spark?

Fireworks may seem like pandemonium when lit, but they are actually a by-product of careful planning. Chemists precisely measure out ingredients to craft the elegant color scheme and desired explosive volume that will delight their audiences.

Inside their packaging, fireworks have a general anatomy similar to a fruitcake. They consist of an outer shell, composed of cardboard or heavy paper, stuffed throughout with stars, or small pellets that produce bright colors or sparks when ignited. The size of a star can be anywhere from as small as a pea to as large as a tennis ball.

Stars represent the heart of fireworks. Each colorful streak within a firework explosion can be matched to a star, and the number and placement of stars within a shell determines the explosion shape. Stars are packed with three main ingredients: sulfur or carbon-based fuel, oxygen-rich chemicals, such as nitrates, chlorates, or perchlorates, and metal-containing compounds.

The combustion of the fuel and oxygen-rich chemicals inside a star provides heat energy which the metal compounds convert into light. Different metals have their own color fingerprints based on their intrinsic ability to convert heat to light. To summon red, white, and blue, the recipe calls for mixing strontium or lithium for red, aluminum or magnesium for white, and copper for blue.

While the stars provide the eye candy, the explosive pop comes from the outer shell exploding. Increasing the shell thickness allows more pressure to build up before explosion, providing a louder blast. Additional smaller shells can be tucked inside a shell for multiple explosions.

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The toxicity of chemicals used in fireworks have raised concerns about air and water pollution. In response, manufacturers offer some fireworks with more eco-friendly ingredients, such as nitrocellulose, which burn cleaner and produce less smoke. However, the higher cost of using those ingredients rather than nitrates or perchlorates has limited their widespread use. So consider moderation when setting off fireworks, as with everything else this Fourth of July.

Robert Kuo: 916-321-1161; @therobertkuo

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