Definition:
FMEDA is an extension of FMEA that quantifies the failure rates into safe, dangerous detected, and dangerous undetected categories.
FMEDA is done during the design, qualification, or certification phase for devices/equipment intended to be part of a Safety Instrumented System (SIS). It is a quantitative approach.
Purpose of an FMEDA: to generate the failure-rate terms, which then lead into diagnostic coverage (DC), SFF, and PFD/PFH calculations — primarily in support of Route 1H, where SFF drives the architectural constraint tables.
FMEDA studies are typically performed by device manufacturers (e.g., sensor, transmitter, logic solver, valve manufacturers), often with the support of functional safety consultants or certification bodies. It is not done by the facility designing a SIS, it is done by the manufacturers of the SIL rated components in the SIS. It is a type of quantitative risk analysis (although some practitioners catalog it as semi-quantitative).
Key Points:
- Provides failure rate data. This then feeds DC, SFF, and PFDavg calculations for route 1H.
- Basis for SIL device certification.
- FMEDA data is published in manufacturer safety manuals or SIL certificates
Example:
A smart transmitter manufacturer uses an FMEDA to support SIL 2 certification under route 1H. They do it in conjunction with the certification body. This outputs the failure rate, SFFs and diagnostic coverage.
See Also: FMEA, certification body, safety manual, QRA, SFF, DC
Cited Source:
- IEC 61508-2:2010, Clause 7.4
- ENCO comparison between FMEA and FMEDA