The concentration of airborne particles is a critical parameter for cleanrooms, clean zones, and controlled areas. Particle concentration must be measured at representative locations for classification and monitored routinely or continuously at critical locations during operation. Both ISO 14644-1:19991 and the new Draft International Standard (DIS) edition provide nine classes of cleanliness and specify both the number of sample locations for classification and the acceptance criterion for the data.

In the 1999 version of the Standard, the minimal number of sample locations is not based on statistical principles. The acceptance criterion is based on a statistical test, but only if the number of sample locations is less than 10. Thus, classification is based on statistical methods only for a small number of locations.

The revised ISO/DIS 14644-12 replaces this method with a statistical principle for selection of the sample locations. The acceptance criterion in the revised version eliminates the need for applying a statistical test to the data, and thereby simplifies the classification process.

The purpose of this paper is to present and discuss the new sampling plan for cleanroom classification and compare it with the previous approach in ISO 14644-1:1999. Section 2 of this paper presents and discusses the previous method, section 3 describes the new method in the ISO/DIS 14644-1 revision, and section 4 provides a discussion and conclusion. All of the authors are members of ISO Technical Committee (TC) 209, Working Group 1, the group of experts who developed the new ISO/DIS 14644-1. This paper was written on behalf of the entire Working Group.

International Organization for Standardization (ISO). 1999. ISO 14644-1:1999, Cleanrooms and associated controlled environments — Part 1: Classification of air cleanliness. Geneva, Switzerland: ISO.
International Organization for Standardization (ISO). 2010. ISO/DIS 14644-1, Cleanrooms and associated controlled environments — Part 1: Classification of air cleanliness by particle concentration. Geneva, Switzerland: ISO.
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