scope:

This part of ISO 2859 specifies an acceptance sampling system for inspection by attributes indexed by limiting quality (LQ). This sampling system is used for lots in isolation (isolated sequences of lots, an isolated lot, a unique lot or a short series of lots), where switching rules, such as those of ISO 2859-1, are not applicable. The purpose of this part of ISO 2859 is to supplement ISO 2859-1:1999 by providing sampling plans that are compatible with ISO 2859-1:1999. There is little doubt that in many industrial situations, in which switching rules might be used, they are not applied for a number of reasons or excuses, not all of which may be valid: a) individual ISO 2859-1 plans are used alone but "AQL" protection is still claimed or AQL re-defined to suit so-called unique products; b) "our industry ... product is special so ISO 2859-1 schemes need not apply to us"; c) production is intermittent (not continuous); d) production is from several different sources in varying quantities, i.e. "job lots"; e) lots are small (use of the hypergeometric distribution required); f) lots are isolated; g) lots are re-submitted after inspection. The sampling plans in this part of ISO 2859 are indexed by a series of preferred values of limiting quality (LQ), where a consumer's risk is usually below 10% and is, except for two instances, below 13%. This method of indexing provides a standard procedure, which is more convenient than the special procedure for limiting quality protection of ISO 2859-1:1999 (see 5.4). NOTE The sampling plans in ISO 2859-1 are indexed by inspection levels and by the preferred series of AQLs. During the inspection of a continuing series of lots, the application of switching rules helps to ensure that the process average in that series of lots is kept below the specified AQL. Limiting quality does not have the similar direct relationship with the process average (see 5.4). This part of ISO 2859 is intended for inspection for nonconforming items. In addition it is also applicable for inspection for nonconformities per 100 items except where the LQ is too large. If this part of ISO 2859 is not applicable, users should refer to the special procedure for limiting quality protection given in 12.6.2 of ISO 2859-1:1999 (see 5.4). This part of ISO 2859 is to be used when the supplier and the consumer both regard the lot to be in isolation. That is, the lot is unique in that it is the only one of its type produced. It may also be used when there is a series of lots too short for switching rules to be applied.