What Are The Special Inspection Levels in the AQL Table?

Special Inspection Levels in the AQL Table

Special Inspection Levels_Reliability Tests from Pre-shipment Inspection
Sample size example of reliability tests from a Pre-shipment Inspection

AQL has always been an important standard for the inspection of consumer products in the quality control industry. Please refer to the article “How to Use the AQL“. We explained some keywords about AQL, how to use it, and how you should choose AQL standards and other issues;

Generally, the AQL standard (Acceptance Quality Limit, ISO2859-1:1999) will help you confirm the number of units to be inspected in the shipment and the number of defects required to Fail the inspection.

You can find an example of using “General Inspection Level II” in the article linked above.

According to years of inspection experience, most importers will choose General Level II. However, many customers will notice the Special Inspection Levels when they look at the first table of the AQL chart and often ask about the difference between this special inspection level and the General Inspection level. and what conditions will this special inspection level be used?

What is the difference between the General Inspection Level with the Special Inspection Level?

The first difference is the general level for inspection will provide you with larger sample size, and the special inspection levels will provide you with a smaller sample size.

For example, suppose you have ordered 2,000 hairdryers and you plan to schedule a quality inspection. At this time, you will need to confirm the number of samples to take for inspection.Special Inspection Levels_Hair Dryer voltage test and power

At this time, according to the AQL table query, if you are going to check based on General Inspection Level II, the code letter on the table (based on the batch size from 1,201 to 3,200) will be the letter K, and the corresponding sample number is 125pcs. In the special level S-1, The code letter will be C, and the corresponding sample number will be 5pcs.

Is the sample size that you are satisfied to check during an inspection? and matches with your quality control requirement?

In the specific pre-shipment inspection, how to choose G-II, G-III, and S-1? Under what circumstances is it reasonable to use S-1 or one of the other special inspection levels?

How to use Special inspection levels during the inspection?

When it is determined that an inspection uses AQL standards, the inspector will proceed according to the inspection checklist, which will have many different inspection items.

First, set the general level for the overall inspection, the most common level is General II, and then some tests on the checklist may need to use special inspection levels. In this case, you need to make some settings for the sampling plan, generally, the tests based on Special inspection level usually include:

  1. Destructive testing of the inspected items
  2. Expensive or time-consuming testing
  3. Tend to produce similar results in all items in the batch

Special Inspection Level_ISTA Carton drop testLet’s back to the hairdryer example above, the samples will be:

  • Destructive test

Such as a drop test, in which a carton or a single unit is dropped multiple times from a certain height.

  • Expensive/time-consuming test –

For example, turn on the key switch and let the hairdryer work for 2 hours.

  • Testing of similar results

Such as carton size inspection, internal structure inspection of the hairdryer, etc.

So some tests may use from S-1 to S-4, and for some other tests, you may use General Level II, and you could check these with inspection companies.

Please note that whether (and how) you use a special inspection level, depends on the specific circumstances of your product and your quality control requirements.


Complete quality control requires you to select both general and special inspection levels to jointly control the quality of products. Once you have decided on the test items on the inspection list, you will need to determine the number of samples to be inspected, and a third-party inspector will inspect the goods according to the requirements of the inspection list;

According to the ANSI table and your quality requirements, the sampling quantity will be different for different products and different order quantities;

In most cases, inspection companies use the general inspection level to determine the number of units to be inspected as a whole, while the special level is used for certain specific inspections.

We suggest you work with a quality inspection company to determine the items to be inspected with a special inspection level before the inspector goes to the factory site.


Author: AQI Service as a professional quality control service company in China specialized in providing a complete range of quality inspection and testing certification services in China & Asia for global importers, buyers, retailers, and sellers.

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