European Safety Systems Ltd.
Impress House, Mansell Road, Acton, London W3 7QH
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Document D150-00-051-IS Issue 7 26-08-20
Sheet 3 of 3
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10) SIL 2 Reliability Data
Reliability and Functional safety IEC/EN61508
which has been assessed and is considered
suitable for use in low demand safety function:
• Random Hardware Failures and Systematic
Failures (route 2H)
• As an unvoted item (i.e. hardware fault tolerance
of 0) at SIL 2
The product was assessed against failure modes:
• Failure to close a contact when the call point is
struck with specified force
• Failure to open a contact when the call point is
struck with specified force
• Spurious output despite no input
Integrity in respect of failure to close
SIL 2
Total Failure rate
0.133 pmh
“hazardous” failur
e rate (revealed)
0 pmh
“hazardous”
failure rate (unrevealed)
0.1 pmh
“safe” failure rate (re
vealed)
0.033 pmh
“safe” failure rate (unreve
aled)
0
Diagnostic Coverage
99%
System type
A
Hardware Fault Tolerance
0
Safe Failure Fraction
>99%
PFD (hazardous failure)
1.25 x 10
-3
Proof Test Interval
Up to 1 year
