The customer to determine the air filter (early, middle and high efficiency filter) is qualified the principles and basis?

For the extraction of a sample, the inspection items in the main item has one or other items are two failed, then the sample is unqualified;
In the sampling of a test failed, then double extraction, such as there is still a failure, the batch of filters for the non-conforming products;
If more than 3 (including 3) filters have the same defect, the entire batch of products for non-conforming products.