Have a formal process for tracking, recording, and classifying field shipments and failure returns.

If your product was designed well in the first place, even if strict adherence to IEC 61508 was not followed, your field failure rate should be pretty low.

Using Proven-In-Use (PIU) methodology will allow an assessor to waive some requirements regarding systematic capability.  These are process related issues.  The theory goes that if the actual failure rate is below the predicted failure rate (determined with a detailed FMEDA), then sufficient measures were probably in place to meet the intention of IEC 61508 requirements.  But in order to use PIU, a good field return tracking system is needed.  It starts with a good production system where all products have a serial number and shipping history (where and when it left the factory).  Then you need to classify returns as safe or dangerous failures.  You need to evaluate the return “AS FOUND” without doing any cleanup or maintenance updates.  You should be able to trace back any return to a shipping record and determine how long it was in the field.  And if return has a failure that was already fixed, you should record that as well.  So you’ll need a good change management system to keep track of those changes.

There are a few things to consider when putting your field return process in place:

• Realize that all field failures do not get reported.  Your customers may not tell you every time they have a problem, or they may just buy another replacement (either from you or your competitor)
• Realize that all field returns are not failures.  Sometimes the wrong item is ordered, or the wrong item is shipped
• Realize that all reported failures are not real failures.  Fire or flood could have caused the problem, or someone connected a 2-wire transmitter to the 240 vac line.  Even though some failures may look like obvious customer abuse, it’s good to look into these if many returns are due to the same reason: it may be a preventable occurrence
• Keep track of product modifications

If you have a good product with lots of proven field experience, you should be able to claim that good work and let your customers know about it.