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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.
6.2.1.3 Groups (e.g. tank farms) with dissimilar substances/incident consequences
It is likely, particularly on chemical sites, that substances/scenarios will not be sufficiently
similar to group together. However, the Category A, B, C or D incidents can be
aggregated in the same way as indicated in the earlier examples.
Tank 1
Receptor
Warehouse
If we assume that credible scenarios, consequence levels of those scenarios and event
frequencies for each of the tanks are the same (because of substance
grouping/compartmentalisation), and can be defined as follows:
Scenario (Tank Farm Tank
1)
Consequence Level*
Event frequency*
Catastrophic tank failure
B
F1, 1x10
-6
Large hole
A
F2, 1x10
-5
Small leak from tank base
A
F3, 1x10
-4
Scenario (Warehouse)
Consequence Level*
Event frequency*
Warehouse fire
B
F4, 1x10
-3
* Provided for illustrative purposes only, and at this stage does not include mitigation.
For event frequencies refer to section ‘Determining unmitigated risk frequencies’ which is
a sub-section of 6.2. For consequence level, refer to ‘MATTE thresholds’, section 3.2
The aggregated risk to the receptor for all credible scenarios can be calculated as
follows:
Category B incident frequency = F1 + F4 = 1x10
-6
+ 1x10
-3
= 1.001x10
-3
Category A incident frequency = F1 + F2 + F3 + F4 = 1x10
-6
+ 1x10
-5
+ 1x10
-4
+ 1x10
-3
=
1.111x10
-3
Guideline – Environmental Risk Tolerability for COMAH Establishments v1.0
Page 38 of 88