For decades, asbestos was the perfect building material -- strong, durable, flexible, soundproof, fireproof and cheap. "It was the miracle product," says W. David Kimbrell, president of Hall-Kimbrell Environmental Services, a Kansas-based engineering firm specializing in asbestos testing and control.

It was also potentially deadly. A generation after asbestos was required as a fire retardant in every new school in the country, a growing body of research implicated it in the 1960s and 1970s as a cause of severe lung disease, including lung cancer, and several other cancers.

Asbestos is ubiquitous. Because of its strength and resistance, it was well-suited to about 3,000 industrial and commercial uses ranging from ceiling tiles to textiles, from brake linings to reinforced concrete. It was first used as an insulator in construction and shipbuilding in the 1930s, and was sprayed into schools, hospitals and offices during the postwar building boom.

"If you've got a commercial building built before the early 1970s, it's 99.9 percent certain you've got asbestos in it," Kimbrell says. "It may be a little or it may be a lot, but you've got it."

The deadly side of asbestos came to light largely as a result of extensive studies of asbestos workers by Dr. Irving Selikoff and his team at the Environmental Sciences Laboratory at the Mount Sinai School of Medicine in New York.

Asbestos is a fibrous mineral that occurs naturally in small amounts in the soil and in concentrated deposits in Quebec, the Soviet Union, South Africa and the United States.

"This is bad news for people who think anything natural is good for you," says Dr. Edwin Holstein, who worked with Selikoff at Mount Sinai and is now president of Environmental Health Associates, an occupational health clinic and consulting firm in Edison, N.J.

Unfortunately, what makes asbestos so commercially valuable -- its durability -- also makes it potentially lethal if its tiny fibers escape into the air, get inhaled and lodge in the lungs. Tens of thousands of asbestos fibers can be inhaled with a single breath.

"It's practically indestructible," Holstein says. "Whatever you breathe in tends to stay there."

The microscopic fibers can cause severe disease, including asbestosis, a debilitating scarring of the lungs, and a rare but almost always fatal form of cancer called mesothelioma.

Between 5,000 and 10,000 Americans a year die of an asbestos-related cancer -- about one an hour, says Holstein. Most of the deaths are in shipyard and construction workers who were exposed to heavy concentrations of asbestos on the job -- particularly smokers. The death toll is expected to peak during the next decade and then decline because of the ban on many industrial uses of asbestos since the early 1970s, when its dangers became known.

One of the most insidious aspects of asbestos is the long latency period -- up to 40 years -- before its health effects show up. One of the cases discovered by Selikoff's Mount Sinai team was a man who died of mesothelioma in 1977 at age 60. His disease was traced to exposure 40 years earlier, when as a student he worked for six weeks one summer in an asbestos factory.

As long as the asbestos insulation in a building remains intact, it appears to pose little or no health hazard. The danger arises when it becomes friable, or crumbly, because of wear and tear, water damage or demolition. Then the fibers are released into the air, where they can be inhaled.

Because it is a proven carcinogen and has been used so widely, asbestos has aroused growing public concern and repeated controversy. The latest example locally is at Tysons Corner Center in Virginia, where workers began removing asbestos from an underground service tunnel two weeks ago.

The removal operation at Tysons was unannounced and was shielded from public view by security guards until a complaint by a worried deliveryman was disclosed last week. Fairfax County health inspectors say the asbestos removal is being done properly and poses no hazard to shoppers or employes. Removal of asbestos from other parts of the shopping mall, including storage areas, is scheduled following the holiday shopping season.

Asbestos experts like Kimbrell try to walk a fine line between indifference and hysteria -- warning people about the serious risk from friable asbestos but emphasizing that most buildings containing asbestos are safe.

"By walking into a shopping center or a bank, you're not going to be exposed to a dangerous level," he says. "It's probably less than you're going to get standing on a street corner in Washington, D.C."

"You can't generalize about buildings and the asbestos problem," Holstein says. "Every building has its own life cycle, just as people do. You have to think about risk from asbestos at every phase of that cycle -- including demolition."

There are some buildings in which the asbestos is perfectly safe, he says. But in others the asbestos "has the consistency of cotton candy and kids can reach out for handfuls and make snowballs out of it, and every time it rains the stuff falls in visible dust on the desks to the point where students can write 'John loves Susan' in the dust."

In 1973, the Environmental Protection Agency banned spraying of insulation containing asbestos in buildings.

In 1982, EPA required that school districts inspect their buildings and notify employes and parents if friable asbestos is found. EPA surveys have estimated that about one third of the nation's schools contain loose, crumbling asbestos that may be a health hazard to students and employes.

In June, EPA announced $45 million in grants and loans to 341 schools around the country -- fewer than 10 percent of the applicants -- to help pay for sealing or removing dangerous asbestos.

Asbestos removal has become a huge industry. A few years ago, says Kimbrell, there were only a handful of asbestos removal contractors in the country. Now there are "probably 5,000."

Some of these are attracted only "by a big dollar sign," says Kimbrell, who advocates regulation of asbestos removal contractors to weed out what he calls "rip-and-run" operators. Only a few states, including Maryland and Virginia, require training and certification of asbestos removal contractors, he says.

"You could have just heard the word 'asbestos' yesterday, bought yourself some equipment, hired a few inexperienced people, and in many states you could hold yourself out as John DoeAsbestos Magic Service," Kimbrell says. "That's spooky, but let me tell you, it happens all the time. I've seen some nightmares that would make your hair curl."

During one asbestos removal operation his company discovered earlier this year, a contractor removed wet asbestos from a school building and proceeded to "squeegee the gook right onto the school playground."

Sloppy removal of asbestos can increase the hazard by releasing fibers into the air. The most important step a building owner or school district can take to ensure safe handling of asbestos is to choose a reputable contractor, Kimbrell advises.

"It has to be removed very carefully, very surgically," he says.

Properly removed asbestos is dampened (to minimize its escape into the air), stuffed in double-lined plastic bags and buried in specially approved landfills.

"The theory is, ashes to ashes," says Kimbrell. "It came from the ground, so put it in the ground."

The asbestos issue is a classic example of the difference between personal risk and public health risk, Holstein says. The risk to the average individual is relatively small, but because millions of people exposed and the latency period is long, the risk to society as a whole becomes large.

"You and I, in our individual private lives, make decisions all the time that involve some element of risk," says Holstein. "But if you're a public health authority, you may not be able to accept a one-in-a-million risk, because you're making decisions that affect thousands or millions of people.

"Take a one-in-a-million risk and apply it to 10 million people, and you've got 10 dead people. You can't take that risk."