5 dazzling facts about fireworks

Fireworks explode over Hong Kong's Victoria Harbor. (Reuters)

Fireworks have a history going back to ancient China, long before the Founding Fathers led the United States to independence. But patriotic pyrotechnics have become deeply ingrained in the American tradition, with huge annual shows planned from New York Harbor to San Francisco Bay.

As Fourth of July celebrations get underway, the sound and sparkle of fireworks will be inescapable across much of the country. Here are five facts you might not know about those brilliant blasts:

1. The pyrotechnics depend on science
There's a bit of chemistry behind the vibrant colors that burst in fireworks displays. Each firework contains pellets, called "stars," which have hue-altering elements. Barium glows green; copper burns blue; calcium makes orange; and sodium, yellow. As for those weeping willow-like displays? Longer-burning gold or silver can make a nice trailing effect. And the ones that seem to crack and sizzle often contain some sort of flash powder, like magnesium perchlorate.

The different shapes fireworks take from smiley faces to flags to planets depend on the pattern of the pellets inside the shell. Pattern shells were first used in the early 1990s in Washington, D.C., to greet returning Desert Storm troops, creating fireworks that burst in purple hearts and yellow bows. One of the latest innovations in fireworks patterns is the ability to light up the sky with cube-shaped explosions, though designers continue to roll out new, amazing shapes.

2. The biggest ever displays haven't been in America
Despite America's penchant for pyrotechnics around this time of year, the Guinness World Record for the largest fireworks display goes to Kuwait. On Nov. 10, 2012, 77,282 individual fireworks were launched over a 3-mile-long (5 kilometers) stretch of coastline in Kuwait City over the course of 64 minutes. The intense show was part of the celebrations for the 50th anniversary of the nation's constitution. The elaborate spectacle broke a previous record set in Portugal in December 2006, when pyrotechnics experts set off some 66,326 fireworks across 37 launch sites on the island of Madeira. [4th of July Facts: History of Independence]

3. Lights before the booms
Light travels roughly a million times quicker than sound. For that reason, you often see lightning before you hear thunder, and fireworks, too, appear in the sky before you hear their explosions. With a little math, you can estimate how far you are from the action. Here's how: After you see a firework burst, count the seconds until the boom. Divide that number by three to get the distance, in kilometers, between you and the blast. So if the gap between seeing the firework burst and hearing it is 3 seconds, you are standing an estimated 1 kilometer (0.62 miles) away from the brilliant blast.

4. Big bucks for the bang
According to the American Pyrotechnics Association, the country bought 207.5 million lbs (93 million kg) of fireworks last year, spending $645 million. And a large chunk of the fireworks you'll see this week are foreign. The United States imported $227.3 million worth of fireworks in 2012, the vast majority ($218.2 million) from China, according to the U.S. Census Bureau. That's a fraction of the value of fireworks the United States exports: just $11.7 million in 2012. [10 Fiery Facts About Fireworks]

5. Waving a flag is a safer way to celebrate
Without fail, fireworks-related injuries spike around the Fourth of July in the United States. Between June 22 and July 22, 2012, more than 5,000 people ended up in the emergency room after being hurt by fireworks, most with burns to the hands, head or face, according to the U.S. Consumer Product Safety Commission (CPSC). Bottle rockets and sparklers, the favorites of children, were linked to at least one-fifth of those injuries. Besides harming people, fireworks can unsurprisingly cause fires and extensive property damage. In 2011, fireworks were behind an estimated17,800 blazes resulting in about $32 million in damage, according to the National Fire Protection Association.