The Science Behind Fireworks

The Science Behind Fireworks

Why you should care

Because it all comes down to chemistry, baby.

Nearly half a million people had gathered along the shores of San Diego, staking out a slice of beach to watch the night sky light up. It was the 2012 Fourth of July Big Bay Boom fireworks show, with fireworks set to launch from five docks. But spectators quickly realized something was going spectacularly wrong:

Eighteen minutes’ worth of fireworks exploded in 25 seconds.

The barge workers fled to disaster shelters. But for our inner child, it was a dream come true. Haven’t we all wondered what such a scenario would be like? In this case, it was five fiery golden balls shaped like hot air-balloons and made up of 7,000 fireworks. The explosion lit up the sky and clouds in oranges and reds. It was as if multiple shimmering bombs had been dropped across the otherwise tranquil bay. Pretty. And loud.

The error wasn’t human, though. This massive blunder was blamed on a glitch in the computer program used to set off the show — the same sort of specially designed pyrotechnic program that allows Disney to sync fireworks to movie soundtracks. But as with any software, lines of code can get crossed. In the Big Bay Bust, as the fateful night has come to be known, the exact nature of the flaw remains a mystery.

By now, “we’ve pretty much done everything we can with gunpowder,” says Ron Hipschman, a physicist with San Francisco’s Exploratorium. Originally invented by the Chinese around 200 B.C, fireworks consisted of gunpowder packed into bamboo shoots and then thrown into fire to ward off evil spirits. Around the 12th century, people began shooting those packed tubes into the air: the first sky rockets. Over time, fireworks became part of celebrations and made their way to Europe. By the Renaissance, pyrotechnic schools, where students could learn the craft of creating fireworks, were all the rage. It’s the Italians, though, who get the real credit for modernizing fireworks. In fact, Garden State Fireworks, the family-owned business behind the botched San Diego show, was founded in 1890 by the protégé of the king of Italy’s master of fireworks. (Garden State Fireworks did not comment for this story, but it did address the 2012 incident here.)

All fireworks have one thing in common: chemistry. A big bang requires a couple of critical elements: an oxidizer (e.g., potassium nitrate) and fuel, like sulfur or charcoal, depending on your desired burn rate and heat output, says Hipschman. To make airborne fireworks, pack those ingredients into an ice-cream-cone-shaped cardboard casing with a fuse, and tuck that into a tube. Voilà! In the early days, colorful explosions were limited to white and gold, but scientists have since discovered how to create new colors by heating certain elements to very high temperatures, which causes the elements to get rid of the heat by emitting wavelengths of light. For example, strontium chloride produces red, barium acetate creates green and copper oxide produces a blue flame — the most difficult color to create, pyrotechnically speaking, says Tom Smith, a chemist and fireworks expert based in London.

There’s one more tricky thing about the chemistry of fireworks, says Smith: “They’re so powerful, they could even burn underwater.” In other words, once you light a 40-second firework, it’ll burn for the entire 40 seconds. From a creative standpoint that’s a boon. From a safety perspective? Not so much. The U.S. Consumer Product Safety Commission estimates that 230 people a day, on average, visit the emergency room with fireworks-related injuries in the month around July Fourth — out of around 10,500 injuries in 2014, down slightly from the previous year. And people have been freaking out about the danger factor since 1731, when colonial officials banned the “mischievous use of pyrotechnics” in Rhode Island after some pyromaniacs committed a series of pranks. The nature of their tomfoolery is unknown, but one thing hasn’t changed since 1731: Fireworks are the foe of fingers and flesh.

This Fourth of July leave the fireworks to the pros and let someone else win the Darwin Award.

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