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LOPA Exercise PSLG WG3
12/02/2009
3
Safety Case LOPA
9
Initiating Events
Overspill
Failure ofATG
whilst filling
Incorrect
Routing
Incorrect
Ullage in
receipt tank
Excess quantity
in ship
Excess quantity
frompipeline
10
Initiating Event 1
Cause
Description
Notes
1
Whilst importing from a
ship oron pipeline
transfer, overfillof
Gasoline Tank due to
incorrect line up.
Operator lines up to an incorrect tank. There are 20 Imports per
year. (Consideration should be givento incorrectproduct
introduced by incorrect lineup)Probability of incorrect line-up:
3.74 x 10
-3
based on HEARTData. (SeeAppendix 2)
Probability based on historicalgroup site date, foroperator
making errorover10 years =1.35 x 10
-4
(Conservative Total
Frequency using HEART:20 x .00374 /yr)
7.48 x 10
-2
AND Enabling Event1
Cross Check:Supervisorchecks routing. Sitedata indicates
that the supervisorpicks up an error50%of the time. (This
indicates a high degree ofdependency between theoperator
and supervisor)
5 x 10
-1
AND Enabling Event2
Cross Check:Operatorattendsselectedtank at startof import
and confirms that, whilst the transfer is at alow flowrate, flow
has started to the correct tank. Oncethe operatorconfirms this
then the flowrate is increased. The start level isrecorded on the
bulk movement sheet. (See Note Below)Probability that
operator fails to acton not seeing a flow commence =0.1
1 x 10
-1
OverallFrequency of Initiating Event :
(7.48 x 10
-2
) x (5 x 10
-1
)x (1 x 10
-1
)
=3.74 x 10
-3
events/year
11
Initiating Event 2
Cause
Description
Notes
2
Whilst importing from a
ship oron pipeline
transfer, overfillof
Gasoline Tank with correct
line up due to the capacity
of the tank being less than
expected.
Operator /Surveyorperformmanualdip and confirm any
discrepancy with book-stock figures are within the accepted
tolerance prior to the startofeach importoperation. 20 Ship
Imports peryear. Probability that the manualdip is incorrect
and under-dipped by a metre ormore. (This is the amount
considered between normal fill alert and overfillwhere thedip
reading could lead to a problem)=2.74 x 10
-3
based on
HEARTData. See Appendix 2) (TotalFrequency:20 x
.002743 /yr). This is conservative as here ithasassumed the
worst case scenario where the quantity being charged is in
excess of the available ullage.
5.49 x 10
-2
AND Enabling Event1
Cross Check:Operator /Surveyorconfirmdip figure with
book-stock figures prior to import. (Using Software)Book-
stock is updated from receipts (from imports)and exports
(Direct from flowmeters). Probability that incorrectullage is
notpicked up by checks and corrected =0.1 (The most
conservative allowable failure data fora system(NotSIL
rated) is a frequency ofnotbetter than 1e
-5
/hr.)
1 x 10
-1
OverallFrequency of Initiating Event :
(5.49 x 10
-2
) x (1 x 10
-1
)
=5.49 x 10
-3
events/year
12