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Evaluation of the National Institute for Occupational Safety and Health X-ray diffraction method for the determination of free silica in respirable dust.

Cincinnati, OH: U.S. Department of Health, Education, and Welfare, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Contract 099-74-0051, 1976 May; :1-136
A complete laboratory evaluation of NIOSH Analytical Method PCAM 109, free silica (7631869), quartz (14808607), cristobalite (14464461), and tridymite (15468323) in airborne dust was conducted. This method is applicable to the determination of respirable free silica in airborne dust by X-ray diffraction analysis. Initial studies compared the internal standard and direct measurement (external standard) methods of phase analysis for samples prepared by filtering suspensions of known phase content. Direct measurement consistently gave better results, considering several internal standard phases, a range of free silica levels and measurement reproducibility. Ruggedness testing of the procedure for preparing standards by filtering powder dispersions in a liquid indicated that the method for taking the sample (graduate vs. pipette) could introduce significant error. Further studies of the sampling method are warrented. A dust chamber was constructed permitting simultaneous collection of twelve respirable dust samples on silver membrane filters. Personal samplers were modified to use a 25 mm diameter filter cassette attached to a 10 mm cyclone by a short length of flexible tubing. Sample sets of granite dust and foundry dust supplied by NIOSH were prepared to cover the range 10 to 300 microg free silica. Based upon the analysis of 160 samples, the overall sampling and analysis precision for PCAM 109 was 13 percent for 14 - 38 microg free silica and 4 percent for 49 to 303 microg free silica. As regards accuracy, the method understated the free silica content of foundry dust by 16 percent and overstated the free silica content of granite dust by 4 percent.
NIOSH-Contract; Contract-099-74-0051; Analytical-methods; Sampling; X-ray-diffraction; Dusts
7631-86-9; 14808-60-7; 14464-46-1; 15468-32-3
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Final Contract Report
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National Institute for Occupational Safety and Health