ANSI/AAMI PB70 Sample Size Requirements: Understanding Sampling Plans

ANSI/AAMI PB70 is a classification standard based on the liquid barrier performance of protective apparel and drapes used in healthcare facilities.  The standard helps clinical users in determining the type of protective product most appropriate to a particular situation.  Recently, FDA has been placing a greater focus on a manufacturer’s sampling plan to determine the amounts of specimens to test when performing this barrier testing.  A sampling plan uses lot size, among other factors, to determine the appropriate amount of specimens to test per area.  The previously suggested quantity of 32 may no longer be the correct number to test, unless determined by the sampling plan.  If you do not test the right quantity of specimens per area, this could lead to a denial of your 510k submission.  It is important to understand what a sampling plan entails to ensure the proper numbers of specimens are tested.  Read on to understand the other factors needed to determine the correct sampling plan.

What is needed for a sampling plan?

You need to know the percent of the AQL/RQL needed.  AQL means Acceptable Quality Level; it represents the maximum number of defects allowed that is acceptable.  RQL means Rejectable Quality Level; it represents the minimum number of defects that would lead to rejecting the lot.  When complying with ANSI/AAMI PB70 to determine a barrier performance classification, the AQL requirement is 4% and the RQL requirement is 20%.

Using ISO 2859-1 and ANSI/ASQ Z1.4 as examples, you will need the following information to determine your sampling plan:

• Lot Size: Critical in determining your sampling plan and the amounts to test.
• Inspection Type (normal, reduced, tightened): The normal inspection is usually performed at the beginning.
• General Inspection Level (I, II, or III): Unless otherwise specified, level II is used.

Once determined, use the lot size and general inspection level to determine the sample-size code letter.

The following is an example of a sample-size code letters table from ANSI/ASQ Z1.4, if your lot size is between 501 and 1200 and using general inspection level II:

Shortened Example of Table 1 – ANSI/ASQ Z1.4 sample size code letters

Once the letter code is found, it can then be used in the sampling plans table. The sampling plan table you select depends on your inspection type and the type of sampling plan (single, double, or multiple) and are titled as such. For this example, the table II-A (Single sampling plans for normal inspection) is used.

In the following table, the letter code is on the left-hand side.  The number next to the letter code will determine your sample size.  Continue following the row across with your determined letter code until you reach the AQL level you need (remember, ANSI/AAMI PB70 requires a 4 % AQL).  Once you reach that, the numbers listed determine how many samples can fail but your lot still passes (acceptance number, Ac) and how many failed samples would cause your lot to fail (rejection number, Re).   In the below example, 80 would be your sample size and 7 samples is the acceptable level while 8 samples is the rejection level.

Shortened Example of Table II-A – ANSI/ASQ Z1.4 single sampling plans for normal inspection (Master table)

To comply with ANSI/AAMI PB70 original barrier classification of a product, the sample size determined above should be applied to each area independently (i.e. chest, sleeve seam, front tie attachment) and to a minimum of three different lots.

• Example: Code J, normal inspection, AQL 4% single plan—gives 80 as the sample size. Below is how many samples you would test per area:
  • 80 chest, 80 sleeve seam, 80 front tie attachment (240 total) Lot 1
  • 80 chest, 80 sleeve seam, 80 front tie attachment (240 total) Lot 2
  • 80 chest, 80 sleeve seam, 80 front tie attachment (240 total) Lot 3

A minimum of three lots is required for an original classification.

An example of a sampling plan using code G and 32-sample size is found in ANSI/AAMI PB70 Annex C. This is an example only and new information discussed within standard committee meetings suggest the manufacturers need to establish their own sampling plans based on the lot size, inspection type and level.

Commonly used sampling plans that focus on AQL protection are: ANSI/ASQC Z1.4 (2008), or ISO 2859-1 (1999) and ANSI/ASQC Z1.9, or ISO3951-1 (2005).

Commonly used sampling plans that focus on RQL protection are: Military Standard 1916 (U.S. Department of Defense, 1996) and ANSI/ASQC Standard Q3 (1988).

For help determining ANSI/AAMI PB70 testing requirements and if you need a quote please contact your Nelson Labs sales representative or you can contact our consulting team at (801) 290-7500 or [email protected].