Effective April 29, 2008, the Mine Safety and Health Administration (MSHA) will be enforcing a new rule regarding potential asbestos at all metal and nonmetallic mines (and surface areas of coal mines). The new rule is modeled after the Occupational Safety and Health Administration (OSHA) rule in effect since 1994. It lowers MSHA's permissible exposure limit (PEL) substantially.

While most mines do not have excessive airborne asbestos fibers, in an eight-year study of 206 non-asbestos metal and nonmetal mines, MSHA reports it found 29 mines where at least one miner was exposed to what MSHA now considers excessive airborne asbestos fibers.

What is asbestos?

The term "asbestos" refers to certain hydrated silicate minerals that when disturbed, such as during mining or milling, release health threatening fibers that can be trapped in the lungs, chest and abdominal cavity and result in scarring and eventual life-threatening diseases (including asbestosis, mesotheliomas of the chest and abdomen, and other types of cancers).

Asbestiform minerals have been described as "a certain type of mineral fibrosity in which fibers have high tensile strength and flexibility." MSHA explains: "When light pressure is applied to an asbestiform fiber, it bends much like a wire, rather than breaks." It is this characteristic that causes the fibers to be caught in the lungs. (These fibers are to be distinguished from the more usual "cleavage fragments" that break rather than bend and are of a nature that can be cleared during regular breathing.)

Asbestos is designated as a hazardous air pollutant under the Clean Air Act and a hazardous substance under the Comprehensive Environmental Response, Compensation and Liability Act, and in the Environmental Protection Agency's Integrated Risk Information System. MSHA and OSHA have characterized it as a long-term health risk. As MSHA describes this risk: "Most asbestos-related diseases have long latency periods, typically not producing symptoms for 20 to 30 years following initial exposure."

MSHA notes that asbestos exposure of miners can come from either naturally occurring asbestos in the host rock or from asbestos contained in manufactured products. Asbestos is no longer mined as a product in the United States, but it can be found as a pocket, vein or intrusion in other minerals, particularly metamorphic or igneous rock. It can also sometimes be found in sedimentary rock as a result of fragments from eroded asbestos-bearing rock migrating to sedimentary deposits.

Asbestos can be found in limestone, dolomite and talc, as well as in other minerals more commonly associated with asbestos. Mining activities, such as excavating, blasting and grinding can cause asbestos, if present, to become airborne. Milling may turn bulk rock or ore into respirable fibers. MSHA tends to find higher asbestos levels in enclosed mills than in ambient environments, such as pits.

According to MSHA, some mine operators, by examining prospective mining areas and using their knowledge of geology, are trying to avoid encountering deposits that are likely to contain asbestos minerals. In this way, they can avoid having to contend with potential contamination of their process stream and final product.

What is the new PEL?

The previous MSHA permissible exposure limit for asbestos was 2.0 fibers per cubic centimeter of air based on an eight-hour time-weighted average over a full shift. The new PEL is 0.1 fibers per cubic centimeter of air. To be counted, a fiber must be greater than 5 micrometers in length with a length-to-diameter ratio of 3:1.

Michael T. Heenan is an attorney for one of the nation's largest labor and safety law firms. Contact him at Ogletree, Deakins, Nash, Smoak & Stewart, 2400 N. Street, Fifth Floor, Washington, DC 20037. E-mail: michael.heenan@odnss.com