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Immingham East Terminal – Gasoline Overfill Protection
Safety Instrument System
P & I Design Ltd
DOCUMENT NO: SI277001_RPT
2 Reed Street, Thornaby, UK, TS17 7AF
ISSUE:
F
DATE: 31.10.14
Tel: + 44 (0)1642 617444
PAGE 6 OF 29
Fax: + 44 (0)1642 616447
www.pidesign.co.uk5
RISK ANALYSIS AND ALLOCATION OF SAFETY FUNCTIONS
A LOPA Risk Assessment was conducted on a possible, future Gasoline Import and storage
facility on 31
st
January 2007, it was revisited in February, August 2007 and July 2010. The
outcome of the assessment showed a shortfall in protection of SIL1. It was decided however,
due to commonality throughout the ISCo sites, to incorporate a mid-range SIL 2 Safety
Instrumented System.
Document SI057001_RPT details this assessment.
Following the issue of the PSLG guidelines on LOPA, it was decided that there was no point
in revisiting the LOPA and revising it in accordance with PSLG, as it would not be possible
to provide the data in sufficient detail as the facility currently does not store gasoline.
However, as part of a terminal upgrade in overfill protection, it was decided to design,
procure and install all instrument equipment/items on their ability to demonstrate suitability
for a SIL2 system design.
5.1
Interpretation of SIL Levels
The following figure provides an interpretation of SIL levels with reference to Probability of
Failing on Demand, availability and risk reduction factors.
Safety
Integrity
Level
Probability of
failure on
demand
Availability
%
Non
Availability
Continuous
Demand
Risk Reduction
Factor
SIL 1
0.1 to 0.01
90 to 99%
876 to 87.6
hours/year
10 – 100
SIL 2
0.01 to 0.001
99 to 99.9%
87.6 to 8.76
hours/year
100 - 1000
SIL 3
0.001 to 0.0001 99.9 to 99.99%
8.76 to 0.876
hours/year
1000 - 10000
SIL 4
0.0001 to 0.00001
99.99 to
99.999%
52 to 5.2
minutes/year
>10000