LF364001_MNL - Overfill Protection SIS Design Manual

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Local Fuel – The Shoreham Oil Terminal
Gasoline Import - Safety Instrument System
P & I Design Ltd DOCUMENT NO: LF364006_RPT
2 Reed Street, Thornaby, UK, TS17 7AF ISSUE: C DATE: 13.05.16
Tel: + 44 (0)1642 617444 PAGE 9 OF 23
Fax: + 44 (0)1642 616447
The proposed IEC61511 Edition 2 has a new requirement for hardware fault tolerance
Table 6 of the standard is reproduced below:
Minimum hardware fault tolerance
(unless clause 11.4.6 applies)
SIL 0 1 2
1 X
2 (low demand mode) X
2 (high demand mode) X
3 X
4 X
The Safety IntelliPoint RFTM Series Point Level Switch is classified as a Type B device
operating in low demand mode and clause 11.4.6 does not apply. Thus in this instance, a
hardware fault tolerance of 0 allows for this single sensor to be used as a 1oo1 sensor for a
SIL2 application.
6.1.4 Sensor Subsystem Summary
From the enclosed calculations and fault tolerance checks the sub-system meets the
requirements of > SIL 2 with a PFD 8.57 x 10-4
Document LF364013_RPT details Testing Procedures.