Boost Quality Inspections with Zero-Acceptance Sample Techniques

Minimize Factory Disruptions through Better Test Practices

Quality Inspections

Quality inspections are a necessary part of the manufacturing process—but they don’t actually add value and can disrupt operations on the factory floor.

Productivity systems professional William A. Levinson argues that those disruptions can be minimized by employing a zero acceptance sampling plan. He outlines the plans in a live webinar for AudioSolutionz, “Minimize Quality Inspections: Implement Zero Acceptance Number Sampling,” and notes that the plan can be implemented using a corresponding ANSI/ASQ Z1.4 plan once you’re confident in the high quality of your process results.

Simplify ANSI/ASQ Z1.4 Protocols

ANSI/ASQ Z1.4 is not only a mouthful of jargon but it’s also a complicated procedure, explains quality systems engineer Mark Durivage in a Quality Magazine article titled “Sample Sizes: How Many Do I Need?” ANSI/ASQ Z1.4 establishes procedures and plans for sampling by inspections and attributes. The Food and Drug Administration (FDA) does not mandate the protocol, only that your sampling plan be statistically valid.

“In medical device manufacturing the key point is to have the plan accept on zero defectives,” notes compliance expert James D. Werner. “This point is not FDA but legalese.”

ANSI/ASQ Z1.4 dates from the mid-1990s but is still current, Werner said. The protocol replaced MIL-STD-1916—which was even more complicated and less practical, Werner added—and allows the American National Standards Institute (ANSI) to continue its maintenance.

The key to simpler procedure, according to Durivage, falls to variable sampling plans, which yield more data and can substantially reduce costs, measurement, and testing thanks to the need to pull fewer specimens.

Process Validation and a Definition of Verification

The FDA has made process validation more important than ever for pharmaceutical companies working to pin down their necessary sample sizes. For the FDA, process validation is a means established by objective evidence that consistently produces a result or product which meets predetermined specs. Verification, meanwhile, is an examination that shows specified requirements have been met.

“Because verification cannot be performed on every critical to quality characteristic (CTQ), validation is essential for cases in which the predetermined requirements of the product can only be assured by destructive testing (sterilized products, tensile strength of a forged part, etc.),” noted Durivage in the Quality Magazine article.

This is where the concept of zero acceptance comes in. Developed by quality management expert Nicholas Squeglia, zero acceptance establishes confidence and reliability levels based on a method using lot sizes to determine the number of items which need to be sampled.

“Using this method, the number of items to sample is dependent upon the size of the lot produced,” the Quality Magazine article explained. “For example, if the lot consists of 5000 pieces, 192 pieces would need to be inspected without a defect for high risk parts, 68 pieces would need to be inspected without a defect for medium risk parts, and 38 pieces would need to be inspected without a defect for low risk parts.”

The method is particularly useful when producing complex products in low numbers or when products that are destroyed during testing. So while ANSI/ASQ Z1.4 is good, says Levinson, zero acceptance sampling is better.

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Jeff Schmerker
About Jeff Schmerker
Jeff has extensive professional experience writing on a variety of topics, from pharmaceutical research to environmental history. He has published more than a half-dozen books, and he has worked as a newspaper reporter, magazine editor and restaurant reviewer. He lives in Missoula, Montana with his wife and son.