Abstract
The volcanic ash from Mt. St. Helens has, so far, reached Portland, Oregon in three eruptions: May 24–25, 1980; June 12–13, 1980; and October 16–17, 1980. Integrated ash fall samples were collected in a downtown Portland location. The particle-size distribution was determined by dry-sieving. The analysis for crystalline free silica on the respirable and near-respirable fractions of the ash was performed. All ash samples had been pretreated with phosphoric acid to remove silicate interferences and were then analyzed by x-ray diffraction for crystalline silicas. The residue after acid treatment was also examined using optical methods to increase certainty of the free silica identification. The total crystalline free silica content was determined by the Talvitie (colorimetric) method. The colorimetric method was then applied to occupational exposure samples of Portland-area maintenance personnel.