International experts have made significant changes to ISO’s airborne cleanliness classification standard—and now is the time for industry to comment.

Since 2000, industries that manufacture products in cleanrooms and other controlled environments have used ISO Standards 14644-1—Part 1: Classification of air cleanliness, and 14644-2—Part 2: Specifications for testing and monitoring to prove continued compliance with ISO 14644-1, as the global standards by which they validate the cleanliness of their cleanrooms. Last December, the ISO Working Group (WG) that developed those two landmark documents issued revised versions as Draft International Standards (DIS). Although the review and approval process for these documents to reach International Standard status will take more than a year, the DIS versions may be used now as trade references per agreement between customers and suppliers. Thus, it is imperative for those involved in cleanroom operations to understand the procedural changes contained in the Draft International Standards, as well as the reasons for those changes.

In the new ISO/DIS 14644-1—Part 1: Classification of air cleanliness by particle concentration, ISO Technical Committee (ISO/TC) 209 WG 1—the global experts who drafted the revisions—have introduced a simplified classification process that utilizes a more accurate, statistically based sampling plan. The new plan calls for a greater number of sample locations and randomized selection of those locations, allowing for different concentration levels in different parts of the cleanroom. This approach is designed to ensure with 95% confidence that at least 90% of the cleanroom area complies with the particle concentration limit.

As in the 1999 Standard, the new DIS edition of ISO 14644-1 provides nine classes of cleanliness, which specify the maximum allowed particle concentration as a function of the particle size for each class (see Table 1). Gordon Farquharson, Convenor of ISO/TC 209 WG 1, points out that WG 1 intentionally avoided making any radical changes to the principles behind the cleanliness classes. Also, as in ISO 14644- 1:1999, the new ISO/DIS 14644-1 specifies the number of sample locations for classification and the acceptance criterion for the data (see Table 2). Users will note critical differences in the content of the latter table versus the guidance for sample locations in the 1999 Standard.