Asbestos - Benchmarks, Standards and Guidelines Established to Protect Public Health

The following is a description of some the benchmarks, standards and guidelines EPA used to evaluate environmental conditions in the aftermath of the World Trade Center disaster.

In evaluating data from the World Trade Center and the surrounding areas, EPA used a protective standard under AHERA, the Asbestos Hazard Emergency Response Act, to evaluate the risk from asbestos in the outdoor and indoor air. This is a very stringent standard that is used to determine whether children may re-enter a school building after asbestos has been removed or abated. It is based on assumptions of long-term exposure. EPA chose to use this standard because it is the most stringent and protective, even though it is unlikely that the public will be exposed to asbestos from the World Trade Center site for extended periods of time.

To determine asbestos levels, air filters were collected from monitoring equipment through which air in the school building has passed and viewed through a microscope. The number of structures – material that has asbestos fibers on or in it – is then counted. The measurements must be 70 or fewer structures per square millimeter before children are allowed inside.

There is also a federal standard for asbestos exposure under OSHA, the Occupational Safety and Health Act, which is used to protect workers on-the-job. The standard is .1 fiber per cubic centimeter averaged over an eight-hour day. To be as protective as possible, EPA is using the school re-entry standard in tests around the World Trade Center.

Levels above 70 structures per square millimeter do NOT imply an immediate health threat. Asbestos exposure becomes a health concern when high concentrations of asbestos fibers are inhaled over a long period. Illness is very unlikely to result from a single, high-level exposure, or from a short period of exposure to lower levels.

In examining the data provided by EPA, the public should be careful to distinguish between data that measures asbestos concentrations in the air and from dust samples taken from the ground or other surfaces. Ambient air samples are more accurate indicators of the potential exposure of the public to contaminants. Also, levels of asbestos in the dust and debris vary from location to location. EPA and other agencies found some dust with levels above 1%, but ambient air sampling has not generally revealed concentrations of asbestos at levels that pose significant threats to public health.