The Fairfax County fire marshal's office, responding to complaints from West Springfield and Centreville residents that construction blasts have damaged houses and showered neighborhoods with stones, is strengthening its regulations governing blasting contractors.

"This {existing} code was enacted in June 1976," said Deputy Fire Chief Edward Plaugher. "Needless to say, things are outdated."

A Sept. 29 blast at the Little Rocky Run subdivision near Clifton spewed stones over the area. Stonehunt Way resident Kim Nichols said she was asleep when the crash shook her neighborhood. "I was like, 'Oh my God, what happened . . . . ' I looked out on the street . . . there was this big dust cloud."

The blast hurtled one brick-sized stone an estimated 1,500 feet through Nichols' roof into her family's living room, where it ricocheted off a wall and landed on a coffee table. Other neighbors complained of shattered windows and damaged walls, although no one was hurt.

Battalion Chief Ronald Peck of the Fairfax County Fire Department called it a freak accident. Rock near the blasting site was already naturally fractured before the blast, according to Peck, so it was easily blown apart by the explosion.

"Unless you've got X-ray vision, there's no way you could have told that," he said. The licenses of the blaster, Geodrill of Boyce, Va., and one of its workers were suspended for a week, according to Plaugher, until the company retained an outside consultant to monitor its blasts and agreed to use more dirt and special mats made from tires to cover the blasting sites.

"It was quite alarming, I must say," said Michael Frey, aide to Supervisor Elaine N. McConnell (R-Springfield), who went to the scene of the 5 p.m. blast. He said he was disappointed that the blasting worker's license was so quickly reinstated, saying, "It doesn't send the right message." But he praised Geodrill President David Carter for going quickly to the scene.

Carter said all repairs to damaged houses have been made and homeowners will not have to pay.

Bedrock runs close to the surface in much of the West Springfield area. Until a few years ago, the cost of blasting out cellars and underground utility connections often made construction work prohibitively expensive. But the rising price of houses has spurred development -- and neighbors' complaints about blasting.

"Blasting does not upset me. I'm used to it," said Jim McCarron, vice president of land development for Kettler and Scott, developers of the 1,200-unit Virginia Run development in Centreville, where neighbors also have complained that blast vibrations have cracked walls, chimneys, and china. "{But if} you put your feet up and open a beer and read the newspaper, and all of a sudden the house starts to rumble, you're in panicsville."

McCarron said his company paid about $5,000 to settle neighbors' claims about damage from vibrations after blasting this summer, although he said he could have argued that 99 percent of them were not actually caused by the blasting. McCarron said that frequently after blasting occurs homeowners notice damage that may have existed before the blasting. The claims were for minor problems, such as a crack in a chimney, he said.

To cover liability, blasters in Fairfax must be insured for at least $25,000 for injury to one person in an accident, or $100,000 for injuries to several, not much higher than the amount the state requires a car owner to carry, one industry official noted. Plaugher expected the new regulations would put those figures into the "million-dollar range."

Michael Farah, president of Air Power of Chantilly, one of the region's largest blasting companies, said in a telephone interview that he felt there also should be police background checks for handlers of explosives. "If they're running {driving a vehicle} on an operators' license that has multiple DWIs, you don't want them driving the street with a load of powder," he said.

Plaugher said he expected to require background checks, or to require all blasters in Fair- fax County to receive licenses from state officials, who do perform background checks. He also plans to require blasters to use special mats to cover explosion sites, and require more dirt to cover blast holes.

In Maryland, state fire officials said they require criminal background checks and some insurance, although not any specific minimum amount. Richard LaBrocco, the state's deputy fire marshal for explosives, said he had received few complaints in the last five years in Montgomery and Prince George's counties, except for a blast at a Gaithersburg construction site last summer that shot a stone 100 yards "like a cannon" and did minor damage to an unoccupied parked car.

The blast was conducted properly, he said, but he noted, "With explosives, it's not an exact science."

Construction work is one way cancer-causing fibers of natural asbestos may become airborne. Plaugher said that properly conducted blasting does not release any particles into the air, but said his department would wait for county environmental officials to set standards before making any regulations about this specific issue.

He said he expected to circulate his regulatory proposals to the industry in two to three weeks. "If we were to say all blasting will be greatly restricted . . . that would hurt development. We have to let them explain their side," he said.