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Supplement to Guideline – ‘Environmental Risk Tolerability for COMAH Establishments’
Complex Site Example v0.0
Page 7 of 35
generation of individual risk levels for each piece of plant. These compartments could be further split to differentiate, for
example, those tanks which share a common form of secondary containment or where a particular process plant is formed of
a number of interconnecting sub-units. Compartments would then also be split based on the environmental setting of the site
– particularly where releases via the subsurface pathway or overland could impact upon different environmental receptors as
a result of differences in flow direction.
In order to help group risks for different receptors together a series of hydraulic catchments have been defined for the site.
These catchments group compartments together based on the specific surface water receptor which is most likely to receive
direct run-off or baseflow following a release. The main site catchments are A-E while the jetty itself is catchment F.
Catchment definitions are important for a large site since there may be properties associated with the specific which may
contribute to development of specific mitigation factors or which may require specific response approaches to deal with a
release. In addition the specific distances to receptors within a defined catchment are important when considering mitigation
based on in-ground attenuation and when considering the influence of secondary and tertiary containment provisions. For
note in the case study catchment B only comprises office buildings and presents no significant MATTE potential.
Figure 2
provides an overview of the process used to split this site into compartments and the type of information which has
been be collected on each of the assets to enable commencement of assessing relevant accident scenarios. This figure also
illustrates the location of each of the catchments across the main site.