Introduction
The Industrial Hygiene Proficiency Analytical Testing Program (IHPAT) for silica has been administered since 1974 and prior proficiency testing data evaluations were conducted in 19991 and 20142. This report seeks to provide an update to this valuable work. Additionally, AIHA PAT Programs has received multiple requests related to the analysis of silica at lower levels (less than 0.05 mg/filter). This report will answer questions posed by those external sources.
Methods
IHPAT silica rounds are administered four times per year, with four silica samples of various concentration levels sent to participating laboratories during each round. The current concentration range in the IHPAT Scheme Plan for silica is 0.025 mg–0.225 mg. Starting January 1, 2021, the lower end of the concentration range was decreased to 0.025 mg, but as of the data evaluation and writing of this report, no samples at this concentration level have been sent to participants.
As with previous reviews, the results reported by each participating laboratory for the samples received in each round were reviewed together with the analytical method—x-ray diffraction (XRD) or infrared (IR)—and the type of background material—coal mine dust (CMD), talc, CMD with talc, or calcite—used by the participating lab for those samples.
The population dataset was treated to remove any sample value where the calculated z-score was higher than 19; no negative z-scores needed to be trimmed. This left 11 (or 0.22%) of results between +7 and +18.9, which may slightly influence the calculations and visualizations using z-score. Additional treatment of the population dataset, with a narrower criterion for acceptability in the review (e.g., z-scores between -3 and +3, as with previous reviews1) would likely tighten and improve the averages and data visualizations. In total, with the removals noted above, 3,203 rows of data were evaluated.