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Immingham Storage Co Ltd - East Terminal
Gasoline Storage Tanks Overfill Safety Instrument System - Functional Safety Assessment Stage 2/3
P & I Design Ltd
DOCUMENT NO: SI277016_RPT
2 Reed Street, Thornaby, UK, TS17 7AF
ISSUE: D DATE: 25.04.13
Tel: + 44 (0)1642 617444
PAGE 8 OF 33
Fax: + 44 (0)1642 616447
www.pidesign.co.uk
The following sequence of events leading to the following hazardous events were
considered from ship imports and tank to tank transfers
o
Overfill of gasoline tank during import from a ship leading to a potential open
vapour cloud explosion
o
Overfill of gasoline tank during import from a ship leading to a potential flash
fire.
o
Overfill of gasoline tank during import from a ship leading to a potential open
vapour cloud explosion, fire with significant smoke; together with a release to
the River Humber corresponding to a potential short-term major environmental
consequence to the River Humber which could constitute a threat to the
environment. This might constitute a short-term MATTE, subject to the
volume, components and duration of the release actually reaching the river.
the following Initiating Events were identified:
Overfill of a gasoline storage tank
o
IE1 Whilst importing from a ship, overfill of Gasoline Tank due to incorrect
line up.
o
IE2 Whilst importing from a ship, overfill of Gasoline Tank with correct line
up due to the capacity of the tank being less than expected.
o
IE3 Failure of Level Instrument on the Gasoline Tank. Radar gauge reads low.
The LOPA considered the requirement for Instrumented Protection and Mitigation
Layers with the following being identified:
Protection Layer 1
BPCS with Level Indication and alarms monitored by Operator
A VTW (Virtual Tank for Windows) system enables the operator to view the tank
levels. The normal fill level and high alarms are software derived from the VTW. The
alarms are audible within the control room and transmitted by radio.
Protection Layer 2
High High Level alarm and automatic closure of import valve Mid-Range SIL 2 SIS
The protection layer will be auditable via the SIS maintenance and testing records.
This consists of an independent high high level switch using a different measurement
technology from the ATG (Automatic Tank Gauging) system
,
operating through a
hard wired and independent electronic protection system to close remotely operated
shut off valves that will shut off a tank side valve. The valve will close quickly, at a
speed commensurate with any surge constraints in the pipelines.