Fascinated by fireworks Chemists, amateurs advance explosive entertainment

Retired chemistry professor Bill Bannister, like many chemists, played with explosives as a boy.

In retrospect, he's glad he survived. He knows a guy who blew off the left side of his rear end once in an amateur experiment gone wrong.

"I see him at the bar back home in Terre Haute," Bannister said. The man has a hard time sitting down.

Yet the allure of noisy, colorful, spectacular explosions is undeniable, particularly for the scientifically inclined.

Bannister, who grew up in Indiana, went on to study explosives at the University of Massachusetts Lowell, and still loves a good fireworks show. Many other young experimenters grow up to make fireworks as a hobby. The Pyrotechnics Guild International, an association of amateur and professional fireworks enthusiasts, has about 4,000 members, many of whom invent their own fireworks shapes, colors and sounds.

The crossette, a firework in the shape of a cross, is just one example of an effect developed by hobbyists and adopted by industry, said Camille Coman, president of the guild.

From the beginning, fireworks have been all about science. Explosions, after all, are chemistry. Chemicals are manipulated to release a tremendous amount of energy all at once.

The earliest fireworks in China are thought to have been discovered by serendipity, though other nations also claim to have invented them. Some of the oldest records suggest that Chinese alchemists or herbalists in the 9th century mixed the three basic ingredients of gunpowder - sulfur, charcoal and saltpeter - then lit the mixture and it exploded.

The same basic recipe is still used today to launch aerial fireworks. Charcoal and sulfur, or other forms of fuel, are mixed with saltpeter or similar chemicals, which release a lot of oxygen to make the reaction happen quickly.

A typical aerial firework consists of a round shell wrapped in paste and paper with a cylindrical lift charge stuck on the bottom. The cylinder is full of gunpowder. When somebody lights it, the powder burns in a flash and propels the shell high into the air, creating the bang sound of fireworks.

This first pop also lights a fuse on the shell. The shell is filled with more gunpowder and also pellets or grains of chemicals, called stars, that will create color and sounds when they catch on fire.

The burning fuse reaches the shell just as the shell hits the right height in the sky. The gunpowder within the shell burns so quickly that it blows the shell apart. The stars catch fire and produce their effects as they fall toward the ground.

You may think the goal in fireworks is to make as big an explosion as possible, but actually the trick to fireworks is to keep them slow, Bannister said. Technically, fireworks aren't even explosions.

A true explosion detonates with a shock wave, and that shock wave is what blows the material apart. This is how high-explosive materials such as dynamite work in mining, demolition and bombs.

Gunpowder and other chemical mixtures used in fireworks are called "low explosives." Rather than truly detonating with a shock wave, low explosives just burn up really, really fast.

Christine MacTaylor, an associate professor of chemistry at Salem State College, is proof that you don't have to love explosions as a child to get into the chemistry. The closest she gets to playing with fireworks is an occasional sparkler.

"I like never even lit a match until I was in college," she said. "I was way scared of fire."

But she does find the science of fireworks interesting, particularly the colors.

Some fireworks colors are produced by the glow of burning materials in the stars. A chemist may put flakes of metal, for example, in the shell for the effect they produce when they burn.

"Magnesium and aluminum, they burn bright white," MacTaylor said.

Other colors are produced as a chemical's electrons fall to a lower energy level, a glow known as luminescence. This is how the elements strontium and lithium make reds, calcium makes oranges and copper makes blues.

"Blue is always the toughest," said chemist John Conkling, the retired technical director of the American Pyrotechnics Association.

Copper, the element that emits blue, is finicky about glowing. If it's too hot, the color is washed out, and if it's too cool, it shows no color at all.

Years of experimentation have made a whole rainbow of colors available in fireworks, Conkling said. The Chinese have entire university research programs in pyrotechnics, and amateurs like the Pyrotechnics Guild are continuously working on new fireworks colors.

The trend in the past few years has been to create colors that are brighter, Conkling said.

Fireworks designers are also getting better at creating shapes, such as hearts, stars and Mickey Mouse's face, he said. This is controlled by how the pellets are packed in the shells.

"The more symmetrical the pattern, the easier it is to achieve," Conkling said.

Designers are also getting better at timing fireworks to music, he said. A venue can choose its soundtrack and give the fireworks company a list of songs. The professionals run the songs through a computer and break them down to sound waves and separate out the peaks and valleys. Then they can then match their visuals to the music.

"On a major crescendo, you have all hell breaking loose in the sky," he said.

The phrase "rockets' red glare" in "The Star Spangled Banner" can be matched with red fireworks, followed by noisy salutes for "bombs bursting in air."

The next frontier, Conkling said, is creating the same effects but with even smaller explosions and less noise. This is driven by the demand for fireworks shows in theme parks, stadiums and other tight spaces where there are neighbors who don't want to be disturbed.

For all the advances in science, though, the fascination of fireworks remains the same.

"Almost every country has some holiday or some celebration where fireworks are part of the occasion," Conkling said.

He thinks the appeal is related to our prehistoric dependence on fire for warmth, food and protection, and also the fear and thrill of seeing lightning.

"People love to see the sky explode in color and light and noise," Conkling said. "It's something deep in the psyche."

For Bannister, there's no mystery in his childhood fascination with loud explosions.

"It's daring and doing something that's forbidden," he said. "It's exciting. It's got a little element of danger in it."

The science of explosions

Many things will burn if you get them hot enough. So why do some substances pop when they're heated while others burn out slowly?

It's all about how stable the substance is, said Bill Bannister, a retired chemistry professor at UMass Lowell.

A candy bar has more energy per ounce than dynamite or TNT, he said, but it doesn't explode when you put it in the oven because the energy is in a very stable chemical form (the chemical bonds in sugars, fats and proteins).

Explosive chemicals have bonds that break easily, making their energy unstable.

While most substances need oxygen in order to burn, truly explosive substances pop when they're heated even without oxygen.

Fireworks laws

It is illegal to possess fireworks in Massachusetts, even if you bought them in New Hampshire, where they're legal. The state prohibits all types of consumer fireworks, including sparklers.

In New Hampshire, the state allows cone and cylindrical fountain fireworks, ground spinners, party poppers, snake/glow worm snappers, and wheels. It does not regulate small sparklers, so they, too, are allowed.

Fireworks 101

The Pyrotechnics Guild International is cautious about sharing information on how to make fireworks because of liability, but it encourages people to join a local club or attend a guild convention to learn under the supervision of an expert.

In New England, the New Hampshire Pyrotechnics Association teaches hobbyists how to use fireworks safely and legally. Call Dave Pierson at 978-897-9729 for information.

The guild's annual convention will be held at the Wisconsin International Raceway near Appleton, Wis., this year from Aug. 5 through 11. Visit www.pgi.org for details.

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