Regulatory Open Forum

What sample size do you use for incoming inspections for material that is purchased in lengths (e.g. wire, tubing), and are shipped in multiple pieces/units. Our current sample plan is taken from International Organization for Standardization (ISO) "Sampling Procedure for Inspection by Attributes" ISO 2859-1, but this is too simplistic for this specific use case (we think), and we cannot seem to find a resource to address this scenario.  Thank you!

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Sandra Veenstra
Director - Quality Assurance and Regulatory Affairs
Moncton NB
Canada
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Hi Sandra,

I think it depends on what your inspection method is and acceptance criteria.  This may also depend on the product in lengths and if there is some basis of uniformity or if you needed to "cut into" the different lengths.  These components/raw materials also come in different forms which can impact the sample size, e.g. 3 spools of 1000m, sheave of 1000 cut lengths.  In my experience with wires or tubing, often times you can use ISO 2859-1 but needs to be adjusted with some rationale or thought behind the sample size.  As an example, I remember one instance we got a large spool/reel of double-lumen tubing.  The inspection was to take a cross-section of each spool 50m in (yes waste of 50m) but we assumed a uniformity throughout the rest of the spool.  Though we did qualify the supplier, audit the supplier, and they provided their process validation, so this helped with our uniformity assumption.  In another example, we received lengths of tubing in multiple boxes, so the sample size was to ISO 2859-1 and a sample was randomly pulled from each box for dimensional checks.  I can tell you with wire, it was a qualitative inspection looking at the spools for general defects and we relied on the Certificate of Conformance from the supplier.  Again we qualified the supplier, audited them, and confirmed the process validation, so there was an assumption of uniformity throughout each spool of wire.  I should comment that just because there is a standard for sample sizes, it may not fit all circumstances, but within the QMS document decisions made for the inspections and sample sizes based on the materials received.

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Richard Vincins ASQ-CQA, MTOPRA, RAC
Vice President Global Regulatory Affairs
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Original Message:
Sent: 19-May-2022 16:42
From: Sandra Veenstra
Subject: Receiving Inspection Sample Size - Lengths

What sample size do you use for incoming inspections for material that is purchased in lengths (e.g. wire, tubing), and are shipped in multiple pieces/units. Our current sample plan is taken from International Organization for Standardization (ISO) "Sampling Procedure for Inspection by Attributes" ISO 2859-1, but this is too simplistic for this specific use case (we think), and we cannot seem to find a resource to address this scenario.  Thank you!

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Sandra Veenstra
Director - Quality Assurance and Regulatory Affairs
Moncton NB
Canada
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First, it is not too simplistic, but the right approach. There is a sense among some people that compliance requires complexity, but that is the wrong way to think. Simplicity is the best method.

ISO 2859-1 is for lot acceptance sampling by attributes. Consequently, you must define a lot and the attributes to inspect. At incoming inspection, the lot size is the number of items on the pack slip. The attributes are the characteristics to inspect expressed as conforming or non-conforming.

As an example, assume your PO is for 20 spools of red insulated stranded 24 gauge wire with 1,000 meters per spool. The pack slip says the shipment has 20 spools.

To determine the sample size, you need to determine a few parameters for the sampling plan: Level, Sampling method (single, or double), history (normal, reduced, or tightened), and Acceptable Quality Level (AQL). For the example, use Level II, Single sample, Normal, and AQL = 1.0%.

From Table 1 the inspector determines the code letter is C.

From Table 2-A the inspector determines the sampling plan is: sample size 13, accept on 0, reject on 1.

The inspector selects 13 spools at random and checks each one for the length on the sticker on the spool, insulation color, stranding, and gauge. A spool is non-conforming if any one of the attributes is non-conforming. Separate the conforming spools from the non-conforming, count the number of non-conforming spools, and make the lot acceptance decision.

Do not unwind the spool!

Most companies use only a few levels and AQLs, so they usually make a table for inspection instead of having to go through the steps in the standard each time.

To reduce the work load at incoming inspection, use double sampling and implement the switching rules. The standard also allows skip lot sampling, so consider it as well.

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Dan O'Leary CQA, CQE
Swanzey NH
United States
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Original Message:
Sent: 19-May-2022 16:42
From: Sandra Veenstra
Subject: Receiving Inspection Sample Size - Lengths

What sample size do you use for incoming inspections for material that is purchased in lengths (e.g. wire, tubing), and are shipped in multiple pieces/units. Our current sample plan is taken from International Organization for Standardization (ISO) "Sampling Procedure for Inspection by Attributes" ISO 2859-1, but this is too simplistic for this specific use case (we think), and we cannot seem to find a resource to address this scenario.  Thank you!

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Sandra Veenstra
Director - Quality Assurance and Regulatory Affairs
Moncton NB
Canada
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