AQF Quality Control Blog

Inspection Process

AQL Special Inspection Levels

Already, we have introduced AQL in general and discussed the standard inspection levels. But how do inspection companies do other testing outside of the normal AQL (cosmetics) and how do they select the number of samples needed?

For example, these tests could include:

  1. Seam testing
  2. Special wear testing
  3. Electrical Hi-Pot testing


In these cases, “special testing” may be done at the factory during the inspection. To find how many samples must be picked for these tests, we can use the right side of the same AQL chart used for standard inspections! Using the “special inspection levels” we can find the sampling code corresponding to the special sampling levels (S1-S4), and then at the left in the 2nd chart, we can determine the sampling numbers of these tests.

Generally, these tests alter the appearance, functionality or durability of the products, so relatively few compared to regular AQL inspection levels are checked. For example, when looking at the chart above, if you had a lot size of 1500 pieces, you may only check 5-32 pieces.

If a test is destructive, the sample will be destroyed and cannot be reused. In this case, we will almost always choose an S1 level (like seam testing shown here). If the test consumes too much time, it will also likely be at an S1 sampling level.

For some critical tests involving safety issues, 100% of the AQL sampling may be checked (like in Hi-Pot testing), but at least an s3 or s4 level would be recommended.

Any questions? Leave them in the comments section below!


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8 responses to “AQL Special Inspection Levels”

  1. John Nowell says:

    Hi Claire, Are the Special Inspection levels applicable for garment measurement checks, where the general inspection levels are used for workmanship or material defect issues? Thanks

    • mm Claire Piccinno says:

      @John Nowell: yes that’s right however keep in mind that material non-conformities can also be found during the material check based on the Special Inspection level.

  2. arvin says:

    Hi! does it means that if I’m going to use special levels like S2 and S3 it directly affects the confidence level of inspection? lets say for example i will be using inspection level S3 considering 1%AQL.. Is it correct? or i should assess my inspection by conformed or not? thanks

    • mm Claire Piccinno says:

      @arvin: thank you for your question. During an inspection you have different types of results: AQL, tests, Data measurement checks… S2 and S3 are mainly related to conformity and functionnality checks. If it fails, it affects the quality of the goods purchased however this result is independent from the AQL inspection result.

  3. franco leung says:

    Claire: thanks for your input. I just want to clarify when I use the “special inspection level” S3, do I need to specify the “acceptance quality limits”?

    • mm Claire Piccinno says:

      @franco leung: usually for Special Inspection levels, the answers provided by the QC are conformed or not. Grey areas are more related to the AQL general inspection levels. However the more precise you are the best it is. You will help the QC to understand better your quality requirements.

  4. franco leung says:

    After I take the S3 or S4, what is the acceptance and reject number I should follow?

    • mm Claire Piccinno says:

      @Franco Leung: Special levels are mainly used to test a product. The acceptable quality limits are usually applied to the general AQL level (I, II or III). The limits are defined depending on the quality requirements you have agreed with the supplier.

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