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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.
6.2.1.2 Tank farm or group of tanks containing similar substances
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
Tanks 1-4)
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
* 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
On the basis that there are now 4 tanks, the aggregated risk to the receptor for all
credible scenarios (i.e. the frequency of any one of the scenarios at or above the
relevant consequence level occurring from any one of the tanks) can be calculated as
follows:
Category B incident frequency = 4 * (F1) = 4x10
-6
Category A incident frequency = 4 * (F1 + F2 + F3) = 4 * (1x10
-6
+ 1x10
-5
+ 1x10
-4
) =
4.44x10
-4
Guideline – Environmental Risk Tolerability for COMAH Establishments v1.0
Page 37 of 88