92 / 648
Safety and environmental standards for fuel storage sites
Final report
91
reputation risk or business financial risk but much of this report will be of assistance in carrying
out such evaluations.
37 Regulation 4 of the COMAH Regulations requires dutyholders to ‘take all measures necessary
(AMN) to prevent major accidents’. This is equivalent to reducing risks to ALARP. HSE’s semi-
permanent circular
Guidance on ALARP decisions in COMAH
61
states that:
‘The demonstration that AMN have been taken to reduce risks ALARP for top-tier COMAH
sites should form part of the safety report as required by regulations 7 and 8 of the COMAH
Regulations… For high-hazard sites, Societal Risks/Concerns are normally much more relevant
than Individual Risks, but Individual Risk must still be addressed’.
38 See also paragraphs 108 and 109 of
A Guide to the COMAH Regulations
L111.
62
39 For each ‘in scope’ tank with the potential of an explosion following an overflow, the
tolerability of risk of the major accident hazard scenario must be assessed. A risk assessment
should address the categories described in paragraph 25.
Scenario-based safety risk assessment
40 LOPA, like most risk assessment tools, is suitable for this type of risk assessment, using the
following approach:
determine the realistic potential consequence due to the hazardous scenario (in this case the
■
■
number of fatalities due to an explosion following an overflow from a specific tank);
estimate the likelihood of the scenario; and
■
■
locate the consequence and likelihood on the following (or similar) risk matrix (Table 8).
■
■
Table 8
Risk matrix for scenario-based safety assessments
Likelihood of ‘n’ fatalities
from a single scenario
Risk tolerability
10
-4
/yr – 10
-5
/yr
Tolerable if ALARP Tolerable if ALARP Tolerable if ALARP
10
-5
/yr – 10
-6
/yr
Broadly acceptable
Tolerable if ALARP Tolerable if ALARP
10
-6
/yr – 10
-7
/yr
Broadly acceptable
Broadly acceptable
Tolerable if ALARP
10
-7
/yr – 10
-8
/yr
Broadly acceptable
Broadly acceptable
Broadly acceptable
Fatalities (n)
1
2–10
11–50
41 Table 8 is based on HSE’s
Guidance on ALARP decisions in control of major accident
hazards (COMAH)
SPC/Permissioning/12. Note that a scenario-based risk assessment with a
single fatality is not the same as an Individual Risk calculation.
42 This assessment should be repeated for each ‘in-scope’ tank in turn. Where there is a
large number of in-scope tanks (eg ten or more) the aggregate risk from all of the tanks may be
adequately addressed by the individual and societal assessments detailed below, but may require
a separate assessment.
Individual Risk assessment
43 The tank overflow scenario may contribute to the risks to individuals, either on-site or off-
site. Where the total risk of fatality to any individual (the Individual Risk) from the activities at the
hazardous establishment exceeds a frequency of 10
-6
per year (see
Reducing risks, protecting
people
paragraph 130), additional risk reduction measures should be considered, either at the
tank or elsewhere, to reduce the risk so far as is reasonably practicable. This exercise should form
part of the safety report demonstration for an establishment considering the risk from all major
accident hazards.