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CDOIF
Chemical and Downstream Oil
Industries Forum
CDOIF is a collaborative venture formed to agree strategic areas for
joint industry / trade union / regulator action aimed at delivering
health, safety and environmental improvements with cross-sector
benefits.
It can be seen that in this example that the warehouse fire is by far the biggest
contributor to the risk frequency, and hence this indicates where best to look at additional
control measures.
6.2.1.4 Comparison with tolerability criteria
For the single tank and warehouse example above it was determined
Category B incident frequency = 1.001x10
-3
Category A incident frequency = 1.111x10
-3
These can then be compared to the tolerability criteria as follows:
Frequency per establishment per
receptor per year
(
unmitigated
)
Frequency at which
CDOIF Consequence
Level
is equalled or
exceeded
10
Ͳ8
–10
Ͳ7
10
Ͳ7
–10
Ͳ6
10
Ͳ6
–10
Ͳ5
10
Ͳ5
–10
Ͳ4
10
Ͳ4
–10
Ͳ3
10
Ͳ3
–10
Ͳ2
>10
Ͳ2
D Ͳ MATTE
Intolerable
C Ͳ MATTE
TifALARP
B Ͳ MATTE
Broadly Acceptable
X
A Ͳ MATTE
X
Sub MATTE
Tolerability not
considered by CDOIF
The unmitigated
risk
is depicted above by
X
.
Up to this point in the assessment, no mitigation has been considered. It is now
necessary to consider what forms of mitigation are in place to further reduce risk. The
calculations above need to be repeated to include the Probability of Failure on Demand
(PFD) of any protection layers present (e.g. safety instrumented systems, secondary or
tertiary containment, emergency arrangements) to estimate the mitigated risk to each
receptor, for each consequence category and thus whether mitigated risk is tolerable.
So, for example, if the tank is bunded (PFD = 0.1) and the bunded tank and warehouse
surrounded by site-wide tertiary containment designed to contain fire runoff (PFD = 0.1)
then the mitigated risk to each receptor would be calculated by multiplying the event
frequency with the relevant mitigation layer PFD(s) as follows:
Guideline – Environmental Risk Tolerability for COMAH Establishments v1.0
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