One Hundred Years of Federal Mining Safety and Health Research

other applications. The Libby mine accounted for about three-fourths of worldwide vermiculite
production for many decades.
After discovering the source of the asbestos-containing vermiculite and of NIOSH’s case cluster
finding in 1980, the Ohio fertilizer plant stopped using the vermiculite from Libby. NIOSH
focused investigative efforts at the source of the hazard in Libby. To assess the risk for mine
workers exposed to the asbestiform fibers, NIOSH undertook retrospective exposure assessment
and morbidity and cohort mortality epidemiological studies. The main findings were as follows:
fiber exposures for the vermiculite workers in Libby exceeded federal occupational exposure
limits for asbestos; vermiculite workers at the Libby operations experienced substantial excess
lung cancer mortality, which was dose-related to occupational fiber exposures at the vermiculite
mine and associated processing facilities in Libby; pneumoconiosis and mortality from nonmalignant
respiratory diseases among vermiculite workers in Libby were also associated with
occupational exposure to these fibers. When the studies were completed in the mid-1980s,
NIOSH communicated these findings to MSHA, OSHA, and to local company management,
union representatives, workers, and other interested members of the community. A series of
publications followed in 1987 [Amandus et al. 1987a,b,c]. Finally, the mine at Libby was
permanently closed in 1990.
In late 1999, a series of articles in a Seattle newspaper brought renewed national attention to
concerns over community exposures in Libby and elsewhere. EPA and the Agency for Toxic
Substances and Disease Registry (ATSDR) took leading roles at the federal level in assessing,
communicating, and managing potential community health risks from asbestos exposures
associated with the vermiculite, and NIOSH experts provided EPA and ATSDR with both formal
and informal consultation. In addition, NIOSH has recently updated the mortality study of the
Libby mining operations [Sullivan 2007] and provided formal testimony and comments for
several Congressional hearings relating to Libby vermiculite and in support of MSHA’s lowering
of its PEL for asbestos in 2008 [30 CFR Parts 56, 57, and 71].
6.2.7 Reducing Noise on Mining Machines
MSHA data show that the continuous mining machine is first among all equipment in
underground coal mining whose operators exceed 100 percent noise dosage. Continuous miners
are large underground machines that cut coal at the working face of the mine. They gather up
the cut coal and transport it via an onboard conveyor to the back of the machine. Here, it is
loaded onto other mining equipment designed to carry the coal away from the working face.
One of the main noise sources on a continuous mining machine is the onboard conveyor, which
consists of a chain with flight bars that drags the coal along the base of the conveyor system.
The metal chain and flight bars in contact with the metal base and the coal itself contribute
greatly to the noise exposure of workers at the face. Continuous miner operators stand near the
chain conveyor, at the back of the machine, and receive a great part of their noise exposure from
the conveyor.
The urethane-coated flight bar chain was developed by NIOSH to reduce excessive noise
exposure for operators of continuous mining machines. It has demonstrated an 8-hour Time
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