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SFF Anomoly
SFF and HWFT - prescriptive elements of risk based standard
The device is better, yet SIL capability has reduced
0.7
2
2.7
λDD
λDU
λs
2006 Value per million hours
SIL 2
Capable
Total failure rate = 5.4
pmh
SFF =
63%
0.5
2.1
1.3
λDD
λDU
λs
Total failure rate = 3.9
SIL 1 Capable
2010 Value per million
hours
SFF =
46.2%