BOSTON — Workers have scurried for days anchoring barges, aiming mortars, and laying computer cable. They labor with all the intensity of technicians preparing a shuttle launch.
The payoff comes on the Fourth of July, when Americans everywhere ease onto lawn chairs and stretch out on blankets to watch the skies erupt in riots of Renoir color.
In smaller communities, the ever-popular Independence Day pyrotechnic display over high-school athletic fields has changed little. But in big cities, the sophistication and technology of the ancient Chinese art are reaching new heights.
Once limited to five colors, the sky-blossoms now come in a more nuanced 16-hue palette. To reduce unwelcome noise and smoke, some shells are launched with bursts of air instead of gunpowder and the star bursts are triggered by embedded microchips. In fact, many urban fireworks spectaculars today are computer synchronized with musical scores. At Penns Landing in Philadelphia - one of the city's five fireworks shows held over 12 days - the celestial explosions will be choreographed to epic movie themes.
No annual event draws bigger crowds. Attendance at the Fourth of July fireworks show is expected to top last year's three-quarters of a million visitors, says Caroline Piven, spokeswoman for Philadelphia's Independence Day celebration, "Welcome America."
But drought and increased fire hazards are snuffing fuses in some areas. In Albuquerque, for instance, city officials have curtailed fireworks shows this year out of concern for touching off brush fires.
Elsewhere, however, the demand for pyrotechnics shows no signs of ebbing.
Smaller communities, where the displays are sponsored by local fire departments or service clubs, typically rely on "ship" shows - prepackaged groups of skyrocket "shells" that locals launch from tubes.
These displays can cost as little as $200 or $300 for a dozen shells, says Bob Kellner, president of Kellner Fireworks in Wesley, Pa. The price rises as the number and complexity of the shells grow. Spectators in major cities such as Boston or New York watch upwards of $100,000 go up in smoke during July 4 displays that last from 20 to 35 minutes and use more than 5,000 shells.
But it takes more than sheer volume of light and noise to turn out a crowd. "The public is more sophisticated ... they are expecting more than stuff shot into the air," says Bernie Durgan, a fireworks production manager for the Disney theme parks in Lake Buena Vista, Fla. As a result, increasing numbers of shows are using computers to design displays, as well as to launch shells timed to punctuate such annual war horse as Tchaikovsky's "1812 Overture" or to augment laser light shows.
In addition, the shells themselves have grown more complex. Over the past several years, the typical star-burst pattern has been beefed-up by five-pointed stars and geometric shapes, notes John Conkling, executive director of the American Pyrotechnic Association, based in Chestertown, Md. Designers literally lay the chemical pellets in a pattern on a piece of paper, set that into the skyrocket tube, and pack the bursting charge around it. The closely guarded secret, he adds, is "how to distribute the bursting charge" to keep the pattern intact.
For large-scale patterns, such as Mickey Mouse's outline above Sleeping Beauty's castle, a subsidiary of the Walt Disney Company has taken a high-tech approach. Instead of relying on the millennia-old method of using black powder as a propellant, engineers for Buena Vista Pictures Distribution Inc. developed mortars that use air pressure to launch the skyrockets. Mr. Durgan says this gives his crews more precise control over the shells' trajectories. But this left engineers with a problem: They no longer had burning propellant to ignite the chemical fuse that touches off the bursting charge and the pellets making patterns.
They turned to the Sandia National Laboratory in Albuquerque, N.M., where scientists for years have been specializing in high-explosives research for, among other uses, US nuclear weapons. The result of their work for Disney is a tiny semiconductor igniter to replace the old chemical time-delay fuses. The final product, Durgan says, is a shell that generates less smoke and noise on launch - of special interest when display designers want airborne explosions, not the dull thud of launch, to punctuate their programs.
Outside of Disney's innovation, the art of fireworks remains mostly that - an art. The US imports about 75 percent of the display fireworks used here. The few remaining US-based fireworks firms are family owned, and their work is often based on family-kept secrets, says Bonnie Kosanke, publisher of the Journal of Pyrotechnics. "They may not know why" they design shells the way they do, "but they know that grandpa always did it that way and it always worked."
This past year, she and her husband, who have coordinated fireworks shows as well as supplied materials for other fireworks companies, started publishing a journal to spread research results among fireworks aficionados. She hopes to put the roughly $125 million-a-year pyrotechnics-display business on a more scientific footing.