Measurement Unit Rounding Nonconformity - Notified Body Audit

The medical device company I work for recently underwent an audit of our CE technical file from our notified body. During the audit, our scheme manager who was one of the auditors questioned the validity of one of the mechanical safety tests because the load specification was in kilograms and the test was performed in pounds and the nationally recognized test laboratory our supplier used to perform the test rounded the conversion factor to 2.2 causing the test load to be less than the 4X factor of safety times the load specification by about 0.2-0.3%. Investigation by our engineers confirmed the discrepancy is within the tolerance of rounding when the generally accepted scientific principal of significant figures are applied to the calculations. Our notified body was disinterested in debating the validity of the NC during the audit (although we did not clearly formulate the significant figure argument until after they left) and issued us a minor nonconformity claiming we failed to fulfill an essential requirement of the Medical Device Directive related to the design of the device conforming to safety principals taking into account the generally acknowledged state of the art.

We are internally debating whether to address this nonconformity through correction, root cause analysis, and corrective action which most of our technical team believes is not appropriate, or push back with our scheme manager who has been very unresponsive since the audit (it took us over 2 months after the audit was over to get a draft report despite multiple promises that we would have it "the next day", and we still haven't received the final report after 3 months). Our quality leadership is pushing hard for us to not push back further due to the risk of the scheme manager holding it against us during next year's audit and "just fix it". As a member of the quality team, I agree with our technical team that there really isn't much of note to "fix". Any recommendations on how we should handle this?


Involved In Discussions
It sounds like you did not meet the 4x safety factor. Auditors are usually not mathematicians, so they would not be interested in the "tolerance of rounding" idea. The rounding and conversion issues should have been worked out prior to performing the test to ensure the test load was equal to or greater than 4x. I would open a CAPA to determine why this happened and revise your test report to describe and justify the deviation. Other people may have a different opinion, however.


Quality Manager
Medical is completely out of my area so don't take this as an answer. But in our world rounding is not allowed, so I'll be curious to see how it is for medical.
I believe the short answer to both questions of knowing about the conversion and knowing about the rounding is no - our company was not aware of either prior to the audit. What I believe to be true based on discussions with our engineers who investigated after the audit is that our company specified the load in kilograms to our supplier and required the supplier to demonstrate conformance to IEC 60601-1 which is where the 4X factor of safety came into play. Our supplier converted from kilograms to pounds believing the values were equivalent and the NRTL they contracted with performed the test (which is one very specific portion of a much larger suite of tests required by the standard) by applying the rounded load in pounds to the unit under test. The unit survived the test load and the NRTL documented the rounded test load in the details of the test report and marked both the factor of safety portion of the test and the overall test as a pass. The NRTL provided the test report to our supplier who in turn provided it to us. We only reviewed the overall passing result and did not review the details of the test conditions.

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