David N. Weissman, M.D.’s Testimony: dimensions of asbestos fibers

Read more from the testimony of Dr. Weissman, who spoke before the Senate’s Committee on the Environment and Public Works about the dangers of asbestos. In this section, he discusses the current dimensions of asbestos fibers.

Currently, a mineral particle is detected by PCM and counted as a fiber if it has a length to width (“aspect”) ratio of 3:1 and length of at least 5 micrometers.

These counting rules include particles with diameters greater than 3 microns, which are unlikely to reach the airways or the gas-exchange regions of the lungs when inhaled.

Also, PCM cannot detect particles with diameters less than about 0.25 micrometers, which, although not visible by PCM, are capable of causing harm.

Finally, although longer fibers have been associated with greater potential for carcinogenicity, studies of fibers deposited in human tissues suggest that fibers less than 5 micrometers in length may also contribute to human disease, including cancer.

The broad goals of the research outlined in the Roadmap are to: 1) provide a scientific framework for evidence-based worker protection recommendations; 2) address the broad range of mineral fibers to which workers are exposed; and 3) refine our understanding of fiber characteristics associated with toxicity.

Strategic goals identified by the Roadmap are to: 1) develop improved sampling and analytical methods for mineral fibers; 2) develop information and knowledge on occupational exposures to the range of mineral fiber types and their health outcomes; and 3) develop a broader understanding of the important determinants of fiber toxicity.

In particular, it would be useful to develop approaches that would make it possible to predict the ability of various mineral fiber types to cause human disease and apply this information for risk management.

NIOSH has solicited public comment on the draft Roadmap document via docket submissions and a public meeting.

The draft document was first made available to the public on February 28, 2007, and public comments were accepted into the docket from the time of posting until May 31, 2007. The public meeting was held on May 4, 2007.

Peer reviewers have been selected and are being provided with a copy of the public comments as well as the draft Roadmap document. Revision of the document will take into account both public and peer review comments. The goals expressed in the Roadmap are ambitious. NIOSH plans to develop a range of partnerships to address these goals, including with other Federal agencies, labor, industry, academia, and other interested parties.

Although NIOSH will focus on occupational safety and health, we will pursue opportunities to ensure that the results of research arising from the Roadmap can be extended outside of the occupational setting.

Courtesy of the U.S. Department of Health and Human Services (HHS): http://www.hhs.gov/asl/testify/2007/06/t20070612c.html

Courtesy of EPA

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