A month after fiery suicide plane attacks pulverized the concrete, steel and glass 110-story twin towers, fires were still burning and gray dust billowed into the acrid-smelling air, creating concern about air quality despite frequent government tests concluding it was safe.

"There absolutely is an asbestos hazard for the workers and I think everyone who's involved agrees," said asbestos expert Dr. Philip Landrigan, chairman of the department of community and preventive medicine at the Mount Sinai School of Medicine in Manhattan.

When the center was built in the early 1970s, asbestos was applied as insulation to steel beams up to the 39th floor of Tower One before a ban on the use of the mineral took effect in 1971.

"It's quite different for the people who are in offices or in the community. There is no question those folks are being exposed to dust but so far as I can tell, the asbestos exposures are very low. I won't say zero, but very low," Landrigan said.

Since the Sept. 11 attack, consistent testing by the U.S. Environmental Protection Agency has shown asbestos levels in such low concentrations it was not deemed dangerous. Tests for other metals were also found to be within safety levels.

Examination of the dust by a private company found ultra-thin fibers, 10,000 times thinner than a human hair, inside buildings up to three blocks away from the site where the towers crumbled and more than 5,000 people killed in the attack by hijacked civilian aircraft.

A report by toxicologists at the company, HP Environmental Inc. of Herndon, Virginia, said laboratory tests from samples collected Sept. 21-28 showed the destruction of the buildings "created an asbestos fiber size distribution not previously encountered."

LUNG CANCER

Experts say asbestosis, scarring of the lungs and lung cancer can occur after long-term exposure to asbestos, usually in a confined space.

Landrigan said "small fibers are more dangerous for the simple reason that they go deeper down into the lungs."

U.S. Health and Human Services Secretary Tommy Thompson this week pledged $5 million to examine homes and schools near the disaster site. The money will also be used to assess the health of recovery workers as asthma and other respiratory ailments were also a concern.

HP Environmental principal Piotr Chmielinski said the methods of cleaning up dust residue in apartments, offices and schools in the area were especially important.

"You do that by moist or lightly wet wiping of the surface and vacuuming areas only with High Efficiency Particle Air filters which can capture 0.3 micron particles and this way you can be sure the dust is not recirculated," Chmielinski said.

The particles found measured as little as 0.25 microns in width, said Chmielinski, whose company oversaw toxicology after the 1993 bombing of the World Trade Center. Last month's study was conducted for a contractor with employees working in the rubble in lower Manhattan.

Construction and engineering companies and government agencies with recovery workers at the disaster site known as "ground zero" have emphasized safety for the crews. Workers digging and sifting through the debris wear respiratory masks and protective clothing.

"This is a very unusual circumstance, this is a site that requires very serious safety procedures. It's a very nontraditional environment," said Lee Benish, vice president and corporate spokesman for AMEC, an engineering and services company among those handling the debris and its removal.

At a meeting for residents this week of the nearby high-rise Battery Park City apartments, Dr. Marc Wilckenfeld of Columbia University Hospital warned people "not to succumb to panic or hysteria" about the dust and air quality.