''If you perform a bulk analysis test of the vermiculite, you can end up with a nondetect,'' Mr. Simons said, meaning that such a test -- which usually involves taking a physical sample of the insulation and examining it under a microscope -- can produce a false negative. ''What we've found is that even if the bulk test showed a nondetect, it is possible that if you disturbed the vermiculite and then took an air sample, you might find levels of contamination.''

As a result, Mr. Simons said, consumers should err on the side of caution and if they discover they have vermiculite, assume that it is contaminated.

But what then?

''We're advising people not to disturb it,'' he said, explaining that any disturbance of contaminated vermiculite has the potential to release asbestos fibers into the air. In cases where homeowners do decide to address the issue more aggressively, he said, it is critical to hire a professional asbestos remediation company.

Cathleen Colella, the owner of the Hazardous Elimination Corporation, a hazardous substance remediation company based in Farmingdale, N.Y., agreed.

''You want to hire a company that is licensed, bonded and insured,'' Ms. Colella said. ''And you should get quotes from three to five reputable companies.'' Generally speaking, she said, the quotes should be within about 5 percent of one another. Companies that offer quotes that are considerably lower or considerably higher than the others, she said, should be viewed with caution. And while Ms. Colella agreed that undisturbed asbestos-contaminated vermiculite generally would not be a problem, it may be difficult to leave it undisturbed.

''There are lots of ways you can cause the vermiculite in an attic to become airborne,'' she said, adding that storing and removing objects, performing maintenance work or even running an attic fan can disperse contaminated vermiculite into the air. In addition, she said, any renovation work in spaces insulated with vermiculite -- including exterior wall cavities -- can result in the release of airborne contaminants.

Moreover, she said, as home buyers become more aware of the potential hazards posed by vermiculite insulation, it becomes more likely that those buyers will insist the insulation be removed as a condition of the sale.