Current Intelligence Bulletin 36: Silica Flour: Silicosis (Crystalline Silica)

This alert recommends control of silica flour exposure and the labelling of products that contain silica flour. NIOSH warns producers and users of silica flour that the risk of developing silicosis may be very high for workers exposed to silica flour. NIOSH determined the status of worker health and surveyed airborne silica dust concentrations at two silica flour mills at the request of the Mine Safety and Health Administration (MSHA). Of 61 current and former workers with 1-14 years of exposure to silica dust, 23 (37%) had chest radiographic evidence of silicosi. Of particular concern are the medical evaluations of four of these affected workers who had relatively short-term silica dust exposures (2.5-6 years), indicating rapidly developing silicosis. Usually, about 20 years of exposure to dust containing silica precedes development of silicosis, NIOSH’s sampling results agreed with the results from past MSHA inspection samples that showed a large percentage of high silica dust concentrations. On the days of sampling, 61 of 91 samples were above MSHA’s exposure limit for silica, and 77 were above NIOSH’s recommended exposure limit. In view of the high prevalence of silicosis after relatively short exposures to silica flour in these two mills, and a history of high silica dust exposures in these and 25 other mills, NIOSH believes workers exposed to silica flour are at serious risk of developing silicosis. This concern extends to workers in industries that use silica flour who may also be at increased risk.

Current Intelligence Bulletin 36: Silica Flour: Silicosis (Crystalline Silica)