Improving the Repeatability and Reproducibility of the Helmke Drum Test Method

Abstract

The Helmke Drum test method, described in IEST-RP-CC003.2, Garment Systems Considerations for Cleanrooms and Other Controlled Environments, is used to measure particle release greater than 0.5 micrometers (μm) from cleanroom garments. During the current effort to revise IEST-RP-CC003.2, it became clear that the method as currently written required revision. Under "Description of Test Limitations," the current method mentions a 1991 interlaboratory comparison (ILC). However, results from that ILC were too variable to allow meaningful interpretation. A cursory look at the results from this 1991 ILC suggested that a re-evaluation of the data using the statistical analysis outlined in ASTM E691 might yield new insights. The Helmke Drum subcommittee of IEST Working Group 003 proposed several changes to the method and a second ILC was conducted in 2001, in which six participating laboratories tested garments per the revised method. A comparison of the statistical analysis of the 2001 results with the statistical analysis of the 1991 ILC shows the revised method yields more repeatable and more reproducible results. The proposed revisions to the method are expected to be adopted by the IEST Working Group and incorporated into the rewrite of the Recommended Practice.