appropriately considered in developing the exposure standard; and to examine the uncertainty, variability, and quality of data and the appropriateness of assumptions used in the derivation of the exposure standard. The subcommittee was also asked to identify deficiencies in the MVF database and, where appropriate, to make recommendations for future research and data development.

THE SUBCOMMITTEE'S APPROACH

The Navy provided the subcommittee with its document Man-Made Vitreous Fibers, which is part of NEHC's Technical Manual (NEHC-TM6290.91-1 Rev. A) (NEHC 1997b), and its associated Health Hazard Information Summary: Man-Made Vitreous Fibers (NEHC 1997a). A background document, Navy Exposure Limit for Man-Made Vitreous Fibers: A Retrospective Look at the Decision History (Krevonick 1998), was also submitted to the subcommittee. During a public meeting, the subcommittee heard presentations on those documents from the Navy and a presentation on the toxicology of MVF from a manufacturer.

The subcommittee reviewed the Navy's documentation supporting the 2-f/cm3 standard. The documentation addressed an array of topics related to MVF, including production and use, chemical and physical properties, sampling and analysis, standards and recommendations, exposure, and toxicological and epidemiological data. The subcommittee began its review with an overview of the manufacturing processes, chemical composition, and classification of MVF, including newly developed fibers. Changes in fiber chemistry resulting from use and thermal stress were also discussed. The subcommittee reviewed the Navy's supporting documentation regarding sampling techniques, analytical methods, and toxicological and epidemiological studies. In the case of several of those topics, the subcommittee identified data gaps or issues that needed to be more thoroughly addressed by the Navy, including dosimetry and fiber biopersistence. The process used by the Navy to derive its occupational exposure standard was also discussed.

In January 1999, the Navy revised its Occupational Safety and Health Program Manual (CNO 1999), changing the occupational exposure limit for MVF to the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) of 1 f/cm3. The subcommittee subsequently expanded its review of the Navy's occupational exposure



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