Asbestos dust (tiny asbestos fibers) release in the air, and asbestos material residual in the rubble following the collapse of the World Trade Center has remained a concern since the collapse of WTC structures.

Until approximately 33 years ago, asbestos was commonly added to the flame-retardant sprays used for insulating steel building materials -particularly the floor support structures.

In the case of the World Trade Center, emergency evacuation plans called for a four-hour window during which the entire the building was to be evacuated. The asbestos based insulation was intended to delay by at least four (4) hours melting of the steel structures in the case of fire. The emergency plan called for use of helicopters to put out the fire and evacuate occupants from the roof.

In 1971, however, the City of New York had banned the use of asbestos in spray fireproofing. At that time, asbestos insulating material had only been sprayed up to the 64th floor of the World Trade Center towers. The floors above 64th floor were not sprayed with asbestos based fire retardant.

When the two hijacked airliners crashed into floors 96 to 103 of One World Trade Center and floors 87 to 93 of Two World Trade Center, the steel frames of both the towers lasted only under two hours, and asbestos dust was indeed released in air when the WTC towers had collapsed, and remained in the rubble thereafter.

A press release by Occupational Safety and Health Administration (OSHA) on this issue of Asbestos exposure at WTC suggested the following:

Asbestos Exposure in WTC Financial District

OSHA had taken approximately 40 air and bulk samples in the Financial District (the location east of Broadway and south of John Street). Results ranged from "non-detected" to 0.041 fibers per cubic centimeter (f/cc). Further analysis showed all fibers to be non-asbestos. Results showed levels consistent with safe and acceptable standards. OSHA ceased sampling in the Financial District on Sept. 21, 2001.

Asbestos Exposure in WTC Warm Zone:

A 90-square block surrounding the World Trade Center complex and plaza had been designated a secure area with controlled access. It extended south of Chambers Street, west to Broadway, south to Rector Street and east to near the Hudson River. OSHA had taken more than 150 bulk and air samples in the "Warm Zone" through Sept. 24, 2001. OSHA reposted that the Asbestos levels remained safe and consistent, ranging from non-detected to 0.086 f/cc.

Asbestos Exposure in WTC Hot Zone/Rubble Pile:

What had come to be known as "ground zero", the hot zone is the World Trade Center complex area itself. It includeed the remains of both WTC towers, 7 WTC, and other partially collapsed buildings.

During this time period, OSHA took 65 air samples and seven bulk samples in the hot zone. Results showed levels ranging from 0.004 to 0.140 f/cc. The level of 0.140 revealed 90 -95% mineral wool fibers and is below safe levels.

OSHA had indicated that even tough all sampling has resulted in what OSHA considers safe levels of asbestos exposure; still, the agency was recommending workers in the immediate area of the rubble pile wear respirators. OSHA continued to conduct monitoring for asbestos throughout the warm and hot zones.

US Government / OSHA Safety Guidelines for Asbestos Exposure Levels:

• Permissible Exposure Limit (PEL) for asbestos is 0.1 f/cc as an 8-hour time-weighted average.
• Excursion Limit(or short-term exposure limit) is 1 f/cc over a 30-minute period.

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