Summary
In July 1991, the National Institute for Occupational Safety and Health (NIOSH)
received a request for technical assistance from the Mine Safety and Health
Administration (MSHA) to estimate the prevalence of silicosis at specific ground silica
operations by conducting a medical evaluation of active and retired miners.
On August 4-7, 1993, NIOSH conducted a medical survey at Malvern Minerals
Company in Hot Springs, Arkansas. The survey included a questionnaire, spirometry,
and a single view (posterior-anterior) chest x-ray.
The criterion for inclusion in the study population was one year or greater cumulative
tenure since 1970 in the grinding area of the mill or in areas downstream of the grinding
process. Twelve of 15 (80 percent) eligible current workers and eleven of 30 (37
percent) eligible former workers participated in the medical survey.
A chest radiograph was defined as consistent with silicosis if the median, or middle,
classification of small opacity profusion was 1/0 or greater. Overall, 39 percent (9/23) of
the participants had a chest radiograph considered consistent with silicosis; the
prevalence among current workers was 50 percent (6/12). The highest International
Labour Office (ILO) small opacity profusion category among the group was 3/2. Two of
these individuals had radiographs consistent with progressive massive fibrosis (PMF),
both with "B" size large opacities. Four of the nine participants with x-ray evidence of
silicosis were less than 40 years old at the time of the medical survey. Five of the nine
had been employed less than 20 years.
Pulmonary function testing revealed that 26 percent of participants had abnormal
patterns, including five participants who exhibited an obstructive lung pattern and one
participant who exhibited a restrictive lung pattern. Three out of the nine participants
with a positive chest radiograph had abnormal pulmonary test results.
There was a substantial prevalence of silicosis among current and former ground
silica workers at Malvern Minerals Company. Nine of the 23 (39 percent) survey
participants were found to have radiographic changes consistent with silicosis; this
includes 6 of the 12 (50 percent) current workers.
Even if all non-participants are assumed to have negative chest x-rays, and even if
3 participants with exposure to fibrogenic dusts at other jobs are excluded, the study
population prevalence of radiographically-defined silicosis would be 13 percent (6/45).
Recommendations are provided in the complete report (see below for ordering
information.)
KEYWORDS: SIC 1446 (Industrial Sand), Silica, Silicosis, Mineral processing, Ground
silica, Silica flour
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