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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 8 OF 34
Fax: + 44 (0)1642 616447
www.pidesign.co.uk3
LAYER OF PROTECTION ANALYSIS (LOPA)
The technique analyses risks which have been identified associated with the defined
operations. The event likelihood for the identified scenarios are assessed as well as the
consequences both in safety and environmental terms. The consequence of the failure
determines the risk reduction required.
The term LOPA (Layer of Protection Analysis) is applied to a family of techniques used for
carrying out a simplified quantified risk assessment of a defined hazardous scenario. LOPA
is often used to identify the shortfall in meeting a predetermined dangerous failure target
frequency. This shortfall, if it exists, is associated with the average probability of failure on
demand of a safety function required to meet the target dangerous failure frequency. The
identified shortfall (if it exists) is equated to the required SIL of a safety instrumented
function (SIF), as defined in BS EN 61511. This potential shortfall is referred to as the Risk
Reduction Factor (RRF) or the failure rate that should be achieved by the SIS. The link
between the RRF factor and the required SIL is shown in Table 1.
Safety Integrity Level Range of Average PFD
Range of RRF
1
10
-2
≤ PFD < 10
-1
100 ≥ RRF > 10
2
10
-3
≤ PFD < 10
-2
1000 ≥ RRF > 100
3
10
-4
≤ PFD < 10
-3
10000 ≥ RRF > 1000
4
10
-5
≤ PFD < 10
-4
100000 ≥ RRF > 10000
Table 1 - Definitions of SILs for Demand Mode of Operation from IEC 61511-1
3.1
Independent Protection Layers