Health hazard evaluation report: HETA-91-0375-2779, U.S. Silica Company, Berkeley Springs, Berkeley Springs, West Virgina.
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 among active and retired miners at US. Silica Company''s Berkeley Springs plant, in Berkeley Springs, West Virginia Current and former workers with one year or greater cumulative tenure since 1970 in the grinding area or the mill or in areas downstream (by material processing) of the grinding process represented the population of primary interest. On June 14-17,1993, a medical evaluation of current workers was conducted. Former workers were tested on June 18,1993. The medical evaluation included a questionnaire, spirometry and a single view posterioranterior (PA) chest x-ray. Chest x-rays were independently classified according to the 1980 International Labour Office (ILO) system by three NIOSH-certified B readers who were unaware ofthe participant''s age, occupation, occupational exposure, smoking history, or any indentifying information. For the purposes of this evaluation, silicosis was defined on the basis of a chest x-ray with median small opacity profusionn classification of category 1/0 or greater . Fifty-four (89%) of 61current workers and 13 (41%) of 32 former workers who met the study criterion participated in the NIOSH medical evaluation. Of these 67, seven (10%)) had a crest x-ray consistent with silicosis. The highest median ILO profusion category was 2/2. Two of the seven had a crest x-ray consistent with progressive massive fibrosis (PMF), with "B" size large opacities (based on the median of the three readings). Nineteen (28'%) of the 67 participants who performed spirometry had abnormal paterns; 13 (68'%) of the 19 exhibited an obstructive pattern, four (21%) exhibited a restrictive pattern, and two exhibited a combined restrictive and obstructive pattern. An abnormal spirometry pattern was present in four of the seven participants with a positive chest x-ray. . US. Silica''s medical monitoring includes all of the screening tests recommended by the National Industrial Sand Association (NISA) as well as those recommended by NIOSH for workers exposed to ground silica. NISA''s current guidelines also recommend multiple readings of all crest x-rays with a small opacity profusion classification of 1/0 or greater and 5-10% of those crest x-rays classified as 0/1 based on a single reading. Since 1990, due company reportedly seat chest x-rays initially classified 110 or greater by a single reader for additional classifications Of the company records we reviewed, company chest x-rays initially classified as negative (0/0 and 0/1) were not routinely sent for additional readings. Seven (10'%) of the 67 survey participants who met the study criterion were found to have chest x-ray findings consistent with silicosis. These results are consistent with patterns of crystalline silica dust exposure at this facility. There were no cases of silicosis among current or former workers with 15 or less years of tenure; however, becuase of the long latency usually associated with chronic silicosis, this finding is not sufficient to conclude that current crystalline silica dust exposure levels are without adverse effect. The company medical monitoring practice of obtaining additional B reader classifications of those chest x-rays initally classified 1/0 or greater may produce an estimated prevalence no higher than and possibly lower than that obtained with a single reading, and those workers with a positive chest x-ray whose chest x-rays are initially read as 0/0 or 0/1 will not be identified. Recommendations are presented in this report and inclube obtaining at least two readings of all chest x-rays regardless of the initial small opacity profusion classification, increasing the frequency of medical monotoring examinations, and modification if the baseline and routine examinations to include skin testing for tuberculosis (TB).