FMEA Tool

The main thing you want to get out of an FMEA is to identify those items which are high in severity, high in occurrences, on low in detection. Rath and Strong has an excellent guide of an FMEA rating scale.

For Severity:
10 – Injure a customer of employee
6 – Result in partial malfunction
1 – Be unnoticed and not affect the performance

For Occurrence:
10 – More than once per day (probability > 30%)
6 – Once every 3 months (probability <= .03%)
1 – Once every 6 – 100 years (probability <= 2 per billion)

For detection:
10 – Defect caused by failure is not detectable
6 – Manual inspection with mistake-proofing modifications
1 – Defect is obvious and can be kept from affecting customer

Hope this helps.

I have read an excellent paper to this subject. I suggest that you go over it, it is a little bit involved but it might be useful. Burton H.Lee “Using Bayes Belief Networks In Industial FMEA Modeling And Analysis” Proceedings Annual Relaibility and Maintainability Symposium, PP 7-15, 2001.
The author is a candidate in Mecahincal Engineering at Stanford University. He can help with some of the questions that you might have.