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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 13 OF 34
Fax: + 44 (0)1642 616447
www.pidesign.co.ukSocietal Risk
In this case, societal risk is not considered an issue as there are no population areas within
400m of the terminal. However, the Societal Risk plot is shown for information (Ref. PSLG
Guidelines, Appendix 2, Clauses 44-50). A detailed plan showing the surrounding area is
shown in Appendix 5. It can be seen that, within the anticipated extent of the gas cloud,
there are no population areas and the number of people in the adjacent industrial buildings
overnight is considered as low < 10.
The criteria adopted by HSE [R2P2] for addressing societal concerns arising when there is a
risk of multiple fatalities occurring in one single event is given below. These were
developed through the use of so-called FN-curves (obtained by plotting the frequency at
which such events might kill N or more people, against N). HSE proposes that the risk of an
accident causing the deaths of 50 people or more in a single event should be regarded as
intolerable if the frequency is more the 1 in 5000 years (i.e. more than 2 x 10
-4
per year).
Historical analysis of accidents has shown that on logarithmic plots (F-N) curves have a
slope close to minus 1. Hence an F-N curve that passes through the intolerable criteria point
with a slope of minus 1 is considered the upper criterion line above which the risk is
intolerable. The ‘Broadly acceptable’ region is a region below a criterion line parallel to the
upper line, but two orders of magnitude lower. The region between the two lines is the
‘Tolerable if ALARP’ region.
In this case the anticipated number of fatalities is considered to be in the order of 10. Thus
the broadly acceptable risk would be in the order of 1 x 10
-5
per year and the intolerable
risk would be in the order of 1 x 10
-3
per year. For the scenario discussed in this LOPA of
an open flammable cloud explosion causing up to 10 fatalities, the calculated frequency is
7.58 x 10
-7
per year, thus this is below the ‘Tolerable if ALARP’ region.
Number of Fatalities