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Local Fuel plc - Shoreham Oil Terminal
Safety Instrument System Functional Safety Assessment Stage 5
P & I Design Ltd
DOCUMENT NO: LF364100_RPT
2 Reed Street, Thornaby, UK, TS17 7AF
ISSUE: A DATE: 15.06.2015
Tel: + 44 (0)1642 617444
PAGE 21 OF 32
Fax: + 44 (0)1642 616447
www.pidesign.co.ukFinal Element:
The PILZ safety relay provides normally open volt free contacts. A 24V dc supply originating
in the Rotork actuator is fed through these contacts and back to the hardwired ESD circuit
contained with the actuator. The actuator is capable of being operated remotely, however,
without the 24V dc input to the ESD circuit the actually will fail closed.
It is certified to BS EN 61508 by SIRA for use in a SIL 2 SIS with HFT = 0. As it has fairly
recently being certified it also has a Systematic Capability assessment with a resulting SC3.
The value used for the actuator in LF364006_RPT utilises the average value from the certified
data. This FSA checked what the overall pfd of the SIS would be if the worst case value was
used, this changed the PFD
SYS
form 3.57x10
-3
to 3.94x10
-3
which is still within the required
5.00x10
-3
required from the LOPA.
The second part of the final element sub-system is a PEKOS ball valve. Exida have certified
this component as SIL 3 capable. In accordance with BS EN 61511 the device can be used in
a SIL 3 with HFT = 1 and SIL 2 with HFT = 0.
Calculation Summary:
From the supplied components and BS EN 61508 certification it confirms that the system does
comply to the requirements of a PFD and HFT for a SIL 2 SIS, with a PFD
SYS
of 3.57x10
-3
.