A Comparison of Air Sampling Methods for Airborne Silica in the Diatomaceous Earth Industry

Abstract

The purpose of this study was to derive empirical quantitative relationships from linear regression equations between standard impinger, total mass, and respirable mass sampling methods for silica dust in the diatomaceous earth industry. Dust from one diatomaceous earth processing plant was sampled simultaneously by all three sampling methods.

Two areas within the plant were sampled: one area included only main flux-calcined product; the other included only bag-house flux-calcined product. The baghouse product contains a much higher percentage of small-sized particles than the main product. Results from 61 clusters of the three sampling devices indicate that the particle size distribution of the dust varies with the particle size distribution of the parent product handled in that area. Since the respirable mass method is dependent on the particle size distribution of the dust, separate relationships were derived for main product and baghouse product dust. For bag-house product dust, the relationship is described by the regression equation, respirable mass (mg/m³) = 0.064 (mppcf) impinger count. For main product dust, the regression was respirable mass (mg/m³) = 0.018 (mppcf) impinger count. The relationships between particle counts and total mass are: total mass (mg/m³) = 0.837 (mppcf) impinger count for baghouse product and total mass (mg/m³) = 1.21 for main product. In all four equations, the intercept did not differ significantly from zero, and the correlation coefficients ranged from 0.90 to 0.95. With proper attention to the particle size distribution of the dust historically sampled in a job area, these relationships may be used in the estimation of historical exposures to diatomaceous earth dust.