Nitrile gloves tested for AQL 1.5 using watertight test method

Quality control is a significant part of any manufacturing process. It’s what ensures that each product meets the highest standards, and it’s also something that is taken very seriously. Without proper quality control measures, companies can end up shipping defective products or even products that are not up to par with customer expectations. When dealing with nitrile gloves, you need to know about AQL. It is a standard that will ensure that the product is ready for the market and that you, as a user, are not buying anything subpar. But what exactly is AQL in Nitrile Gloves?

What Does AQL Mean?

AQL stands for Acceptance Quality Limit. A certain level of AQL means that the gloves meet a certain standard of quality for different defects. However, AQL does not refer to the quality of the gloves that you might expect. Instead, it’s a way to verify that a batch of gloves conforms to the criteria set by the manufacturer. AQL is a crucial way to ensure consistency and give confidence in the product you buy. Every good factory tests each batch of gloves for AQL, but to double-check the factory’s internal tests, the distributors or importers commonly contract third-party companies like SGS and TüV to do a final random inspection (FRI) on the batch.

What is AQL 1.5?

AQL 1.5 is the de-facto standard for medical gloves but is not necessarily a sign of quality. The medical standard in Europe (EN455) and USA (ASTM6319) requires that a batch of gloves has passed a watertight test for pinholes. The AQL indicates that only a specific amount of gloves in a batch is allowed to have pinholes before the entire batch is rejected. The amount of gloves that can have defects is determined by ISO 2859-1 Sampling procedures for inspection by attributes — Part 1: Sampling schemes indexed by acceptance quality limit (AQL) for lot-by-lot inspection

It is, however, essential to note that AQL and ISO 2859-1 does not refer to the medical standards, but only the medical standards refer to AQL 1.5 determined by the ISO 2859-1. Specifically, the medical standards refer to the test for pinholes using “The watertight test method” that should be passed with an AQL of 1.5. 

But, it is easy to find boxes of gloves stating AQL 1.5 that do not conform to the medical standards and have not been tested for pinholes using the watertight test method. Writing AQL 1.5 on a box of non-medical gloves is a common way of misleading consumers into thinking they are buying a quality box of gloves when they are not. Hence, always look for the words EN455, ASTM6319, “Exam” or “Examination” when buying a box of gloves with AQL 1.5.

How Is AQL Determined?

As mentioned above, AQL is determined by ISO 2859-1. A good example is if the AQL is 1.5 and the batch consists of 600.000 gloves, ISO2859-1 tells the inspector that they should take a random sample of 800 gloves, of which 14 can have defects. If the inspector finds 15 gloves with defects, they reject the batch. There are many free AQL calculators on the internet, and we commonly use this one from Tetra Inspection, but any calculator that uses ISO 2859-1 will do the job.

But defects can be many things. When talking about defects, we have to know the difference between physical defects (major defects) and visible defects (minor defects). And within these “defect categories” there can be different testing methods. A major defect can be anything from a glove missing a finger to a small invisible pinhole. These defects are both major because they either make the glove impossible to use or expose a risk to the user. A minor defect would be a defect that is simply visible, like a white or a black spot and does not impose any risk to the user.

Above, we saw that some manufacturers are stating AQL 1.5 even though their gloves are non-medical. This is because they decide to use another method of testing, not the watertight test that is mandatory for medical gloves. Manufacturers may instead use the airtight test method for gloves unable to pass AQL 1.5 for the watertight test. The airtight test method will not expose the smallest pinholes but only slightly larger pinholes. 

What Are the Different Levels of AQL?

It is important to note that not all gloves have to conform to AQL 1.5. Some industries might prefer cheaper gloves and can use gloves with a higher AQL as they are not exposing the gloves to high-risk subjects or chemicals. The most common higher AQL levels are AQL 2.5 and AQL 4.0. In the example of 600.000 gloves, AQL 2.5 allows for 21 defects with the same sample size of 500 gloves, and AQL 4.0 allows 21 defects at a sample size of only 315 gloves. 

The most common uses for AQL 2.5 and AQL 4.0 is food preparation and mechanics work, but in general, we recommend all industries to use AQL 1.5.

On the other hand, we also have surgical gloves conforming to strict AQL parameters; some even have an AQL of 0.10. To put that into perspective, ISO 2859-1 tells us that at LOT size of 600.000 surgical gloves, only 1 glove out of a sample of 500 gloves is allowed to have any major defects.

Final Words

As you can see, the test for AQL is an essential part of the quality control of nitrile gloves. However, it is important to note that because two boxes of nitrile gloves show the same AQL, it does not mean that they are tested in the same way or are the same quality. AQL does not measure the quality of the gloves but confirms that the gloves do not have a lot of major defects. When talking about quality, many other parameters like stickyness, smell, thickness, modulus, chemicals and accelerators used in production, and elasticity come into the equation. We address these quality parameters in other articles, and we recommend that you read this about accelerator-free nitrile gloves.