Greg Bible steers his green pickup along the gravel farm road toward powder magazines 5 and 6. The "product" for the Quantico Fourth of July fireworks show is packed in boxes and loaded in the back.

Scores of coconut-shaped crackling crossettes, thousand-flash salutes, silver vultures and the canlike shells called jumping jacks rest in the boxes, which bear orange "explosives" placards and the warning: "use no hooks."

In the humid dusk behind him, the packing barn is stacked with more: Fat, paper-covered balls of black powder, barium nitrate and strontium carbonate, their four-foot fuses capped and folded like sheathed stingers, sit in boxes labeled "Galesville, Md.," "Crozet, Va.," "Fredericktown, Md.," and many more.

Bible is an elf, if you will, a burly 24-year-old in a sweat-stained baseball cap. This farm, amid the rolling corn fields and white barns of southern Pennsylvania, is his North Pole. And there, waiting by the roadside in a purple T-shirt and denim shorts, is the Santa Claus of the Fourth of July: Denny Coster.

This weekend, Coster, 46, of Whitehall, Md., his workers and "shooters" will package, deliver and fire off more than 100 Fourth of July fireworks displays, mainly in small and medium-size towns in Maryland, Virginia, Pennsylvania and Delaware.

Fanning out in dozens of yellow rental trucks to ballfields, golf courses and parks, the benevolent cannoneers will blast Coster's explosives from makeshift rocket tubes of cardboard, plastic and steel and etch the sky with the glorious chemistry that is a Fourth of July fireworks display.

It is a labor of love, mixed with childlike fascination.

And right now it is extremely hectic at 1-800-765-BANG--Coster's Fireworks Productions Inc.--as he and his workers scramble to get all the displays ready to be picked up this weekend. "We call it hell week," he says.

But on a warm evening earlier this week, as the local pastures filled with fireflies and cows mooed in the distance, Coster and his crew paused to explain their passion for the art and science of pyrotechnics.

The youngest of the four children of a Baltimore tugboat engineer, Coster said he was spellbound by fireworks as a child, when he and his family would attend the annual display in Dundalk, Md.

"We'd go watch the fireworks, and we'd all take turns," he said as he sat in an office at his complex, which includes a metal barn, a cinder-block packing house and steel storage magazines.

"My uncle would kind of lead this thing with my father and my brother, and he'd say, 'All right, the next one is Denny's! The next one is so and so's!' Mine would inevitably be a big color burst. . . . We'd all say, 'Here comes mine!'

"It was just something that I liked," he said. "I can't explain."

But he was hooked. He played with fireworks as a teenager, and finally one day, he approached a shooter at a show, announcing, "I'd really like to learn how you guys do that." The answer was, "No problem."

Coster studied at the feet of that mentor, a retired Baltimore County schoolteacher named Jack Leonard, eventually got licensed himself and began shooting on his own for a big fireworks company.

Meanwhile, he attended Johns Hopkins University at night, got an engineering degree and went to work as an industrial engineer for Baltimore Gas and Electric. His father had hoped he might follow him into the tugboat business. But Coster found it was fireworks that he loved.

In 1990, he formed a business partnership and founded his company--the complex is in Pennsylvania because of less restrictive storage laws. Last year, he bought his partner out.

"We started it out as a hobby," Coster said. "The first year, we did two or three [shows]. The next year we did 10. The third year, we did 50. Then it doubled, like 100, 150. Then it just kept moving and moving, and we never really intended it to."

"Bottom line: Fireworks, they make people happy," said Coster, who still works for BGE. "When you're putting on a fireworks display, you're providing entertainment."

There is also the thrill of lighting a fuse, hearing the blast and watching as the shell rockets skyward, arcs and then "breaks" to the oohs and ahs of thousands. "The fire and the color and sounds," he said, "it's just . . . fascinating."

Coster imports much of his product from abroad, especially from China, where the shells are made. The shells vary in shape, but most are rounded and range in size from that of a grapefruit to that of a baseball.

They are all wrapped in paper, most often light brown. At the shell's base is a small charge of black powder, which gives it a bit of a light bulb shape. All have carefully folded "black match" fuses that stretch out to several feet in length.

The shells are lowered into the bottom of the launching tubes--which are held in wooden racks of four or more--with the fuses hanging over the top lips. The fuse then can be lighted manually with a flare held by the shooter.

The fuse ignites the black powder, which fires the shell out of the tube to an altitude of several hundred feet. There, an internal fuse ignites more powder and the shell explodes.

The color of the blast is determined by substances mixed with the explosive powder: charcoal iron for orange, strontium carbonate for red and barium nitrate for green.

Some shells can be configured to create three circles, to look like Mickey Mouse with ears, or the shapes of hearts or smiling faces. And displays can be choreographed to music. Coster said the "1812 Overture" and "Stars and Stripes Forever" are the easiest pieces to choreograph.

Coster's displays come in four parts: opening, main body, intro to finale and finale. "We always want to keep the sky full." He said he helped pioneer the intro to finale idea, in which the audience is led to believe the show is over and then is hit with the thunderous real ending. "It blows them away," he said.

There are more than 200 companies like Coster's across the country, according to the Bethesda-based American Pyrotechnics Association. A display can run anywhere from a few thousand dollars to more than $50,000.

"Twenty-five hundred to $10,000 would get you a nice show," said John Conkling, the former executive director of the Pyrotechnics Association and now its chief technical adviser. "Twenty-five thousand would get you one that they'd talk about for quite a while. Fifty thousand would be a fairly major show."

The shooters--Coster has a stable of 40 he can hire--are paid by the production company and usually make several hundred dollars.

Wednesday night, Coster strode along the aisles of the packing building, ticking off the names of the shells that sat like vegetables in the storage bins: thunder and rainbow, poinsettia multicolor, crossed circle, silver rain.

He picked one out. It was a "double break," he said. "In other words, boom, it goes out of the tube. Then it'll break open, red, white and then a report, boom!"

For a moment, he seemed like a kid, back again at Dundalk, about to yell that the next one was his.

CAPTION: Curt Main carries a set of racks holding fireworks shells in a Fireworks Productions Inc. warehouse in Glen Rock, Pa.

CAPTION: Denny Coster, owner of Fireworks Productions Inc., packs aerial shells into boxes for holiday displays.