This guide provides background and support for the use ofsequential-sampling plans for the classification of air cleanlinessin cleanrooms and clean zones. Such plans are generally mostappropriate for environments where air cleanliness is expected toqualify as ISO Class 4 or cleaner.
The sequential-sampling plan described herein has been developedto match the operating characteristic (OC) curve of the traditionalsingle-stagesampling plan. As a result, the probability of passingor failing a given classification is about the same for bothplans.
When compared to sampling times required by traditionalsingle-stage-sampling methods, however, sequential sampling isfound to be capable of saving about 80 percent of the sampling timewhen the air sampled is very clean, 35 percent when the air justmeets the class limit, and more than 80 percent when theconcentration of particles in the air exceeds 2.5 times the classlimit.
Sequential sampling is especially applicable as an alternativeto a single-stage-sampling scheme in cases where the upperconfidence limit (UCL) on the grand mean of the particleconcentration is not required or when, with some furtherdevelopment, it can be used to provide an equivalent estimate ofthe UCL.
Objectives The objectives of this guideare:
a) To establish a sequential-sampling plan that has an OC curvewith the same Î± and ÃŸ as the OC curve of the single-stage-samplingprocedure of ISO 14644-1; and
b) To investigate the savings in both sampling time andassociated costs that might result.