271
Appendix 9: FMEA Severity, 
Occurrence, Detection Tables
The team defines the rating scale (1–10) for the Severity, Occurrence, and
Detection ratings. You and your team choose the levels and numbers (as
long as they are on a scale of 1 to 10).
How severe is it?
Not severe = 1
Somewhat = 3
Moderately = 5
Very severe = 10 (VERY BAD)
How often does it occur?
Never/Rarely = 1
Sometimes = 3
Half the time = 5
Always = 10 (VERY BAD)
How well can you detect it?
Always = 1
Sometimes = 3
Half the time = 5
Never = 10 (VERY BAD)
272 ◾  Appendix 9: FMEA Severity, Occurrence, Detection Tables
Rating Severity of Effect
Likelihood of
Occurrence Ability to Detect
10 Hazardous without warning Very high: Failure is
almost inevitable
Cannot detect
9 Hazardous with warning Very remote
chance of detection
8 Loss of primary function High: Repeated
failures
Remote chance of
detection
7 Reduced primary function
performance
Very low chance of
detection
6 Loss of secondary function Moderate: Occasional
failures
Low chance of
detection
5 Reduced secondary
function performance
Moderate chance
of detection
4 Minor defect noticed by
most customers
Moderately high
chance of detection
3 Minor defect noticed by
some customers
Low: Relatively few
failure
High chance of
detection
2 Minor defect noticed by
discriminating customers
Very high chance of
detection
1 No effect Remote: Failure is
unlikely
Almost certain
detection
Figure A9.1

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