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How do fireworks work?

July 3, 2012

Category: A Closer Look

Every Fourth of July, Americans gather to watch our favorite display of patriotism: pyrotechnics.

But have you ever wondered how fireworks work? From the bombs bursting in air, to the rockets’ red glare, it’s a chemical reaction that gives them their signature bang and stunning visual effects. Chico State chemistry grad and pyrotechnic specialist Frank Eberle discusses the science behind fireworks.

Eberle helps create fabulous fireworks displays for Yuba City and other communities throughout Northern California—and says what he’s learned in the chemistry classroom has strengthened his understanding and passion for pyrotechnics.

“To put it simply, fireworks contain gunpowder—charcoal, sulfur, and potassium nitrate—and chemical compounds that create the colors and effects,” Eberle said.

Eberle says an aerial firework shell consists of a fuse and two packs of gunpowder: a lifting charge and a bursting charge. The energy created by the lifting charge, located just below the shell, launches the firework into the sky. Once it’s in the air, the bursting charge at the center of the shell creates the explosion. There’s a two-inch fuse between the lifting and bursting charges, which provides a time delay so the shell can explode at the right altitude.

The colors and effects come from “pyrotechnic stars,” pellets that produce light when ignited. The stars contain gunpowder along with chemical compounds, which differ depending on the desired color and effect.

“Each chemical and element burns differently when ignited,” Eberle said. “Magnesium and aluminum make sparkles, copper burns a blue color, boron is green, sodium is orange, lithium is red, and so on.”

And pyrotechnic chemists are experts at tweaking these ingredients to create the best visual shows possible. Eberle says a common goal is to slow down the burning time, because the slower the explosion, the longer, brighter, and more colorful its visual effect. Fireworks makers do this by using larger grains of chemicals, which make it more difficult for the fuel and oxidizer to combine and burn.

“It produces those fireworks that have the palm-tree like effect,” Eberle said. “Longer burning time makes the flame trails fall further down from the blast before they extinguish.”

And what about those fireworks that explode into shapes?
“An outline of the shape is embedded into the bursting charge using the desired color-chemicals—kind of like a cookie-cutter,” Eberle said. “You see those star, heart and happy-face shapes… well, that’s how they are made.”

The fireworks composition is a precise science—and setting them off is an even more meticulous practice. In California, large fireworks displays must be run by licensed professionals because the large aerial shells are extremely dangerous. Eberle says the shells are carefully placed into racks of mortar cylinders. Then, using every safety precaution, the fuses are hand-lit.

By entertaining Californians with the biggest and best displays, licensed pyrotechnic professionals are also preventing them from attempting make their own, which with illegal and dangerous fireworks can result in serious injury. In fact, the Center for Disease Control reports that in 2005, an estimated 10,800 people were treated in U.S. emergency rooms due to fireworks-related injuries. So, the explosives are best left up to the experts.

Eberle is now off to pursue a Ph.D. in Chemical Engineering at the University of Washington. But before he leaves, you can bet he’ll be on-site at several of the community fireworks displays this Independence Day.

Science aside, Eberle says nothing can beat the thrill that pyrotechnics provide.

“Of course, we take all of the safety precautions,” Eberle said. “But you’re still a foot away from a stick of dynamite. It’s an adrenaline rush like nothing I’ve ever experienced.”

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