Severity
Does Severity include the likelihood of failure?
No. Severity measures impact/consequence only; likelihood is measured by Occurrence. Combining them prematurely invalidates the RPN calculation.
Can Severity be reduced by better maintenance?
Generally No. Severity is tied to the design of the system (e.g., a pump failure causing a toxic spill). Better maintenance reduces Occurrence (likelihood), not the Severity of the spill itself, unless the design is physically altered.
What is the standard scale for Severity in FMEA/RCM?
The industry standard is a 1–10 scale (where 10 is catastrophic/safety loss), though simplified 1–5 or 1–3 matrices are used for specific CMMS implementations.
In reliability engineering and CMMS, Severity is the categorical measure of the magnitude of consequence if a specific failure mode occurs, assessing how bad the outcome is (e.g., safety injury, equipment damage, production loss) without evaluating likelihood. It is often fixed by system design and rated on a 1–10 scale (1 = least severe, 10 = catastrophic) or a 1–5 matrix.
In shop floor maintenance, Severity is used in criticality scoring within CMMS to assign a Severity score to assets, calculating a Criticality Rating (e.g., Safety × Production × Cost) that dictates preventive maintenance frequency and resource allocation. It is multiplied by Occurrence and Detection to generate a Risk Priority Number (RPN = S × O × D), prioritizing failure modes. In work order triage, Severity tags work orders (e.g., SEV 1 = Critical/Stop Production, SEV 5 = Low Impact), triggering automated escalation rules and response time SLAs.
Confusing Severity with Priority: Teams treat high-severity events as low priority because they haven't occurred, ignoring consequence magnitude.
Subjective/Inconsistent Scoring: Without a standardized matrix, different engineers rate the same failure mode differently, corrupting RPN calculations and asset criticality lists.
Design Ignorance: Treating Severity as mutable based on maintenance quality, when it reflects worst-case consequence of design and should not change unless the physical asset design is modified.