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Simon Storage Ltd – Immingham East Terminal
Gasoline Import – Layers of Protection Analysis
P & I Design Ltd
DOCUMENT NO: SI057001_RPT
2 Reed Street, Thornaby, UK, TS17 7AF
ISSUE: G DATE: 29.06.12
Tel: + 44 (0)1642 617444
PAGE 26 OF 34
Fax: + 44 (0)1642 616447
www.pidesign.co.ukInitiating Event 3
Cause
Description
Notes
No of
events/year
3
ATG Failure
(Sticks or reads
low). This can
happen during
import.
The most conservative allowable failure
data for an ATG (Not SIL rated) is a
frequency of not better than 1e
-5
/hr. Site
reliability data suggests a figure much
lower than this however this is not readily
verifiable. Manufacturer gives a MTBF (all
modes) of 53 years for ENRAF Gauges.
0.1
AND Enabling Event 1 The Tank has to be on fill and the total
proportion of the year when import to the
tank is ongoing. Probability = 2.11 x 10
-2
(see 5.3.1) This explicitly assumes that the
ATG has not failed at the start of import.
The ATG is monitored at the start of
import, thus the ATG not failed is
confirmed.
2.11 x 10
-2
Overall Frequency of Initiating Event :
(1 x 10
-1
) x (2.1 x 10
-2
)
= 2.1 x 10
-3
per year
Note 1:Reliability Data for ATG/BPCS
The LOPA uses an order of magnitude 0.1 PFD for the level and control system. This is the
maximum that can be taken for a non SIS system not designed to BS EN 61511. However,
there is a modern control system which has been designed with a significant amount of
diagnostics utilising modern process control instrumentation.