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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.
4.
Risk criteria and Evaluating Risks
4.1
Assessing the risk of potential harm
Following the identification of possible environmental receptors around a site, it is
necessary to evaluate whether the substance stored on site (or other substance which
could be present, such as firewater or reaction by-products) has the potential to cause a
MATTE to those receptors. Where this potential could be realised, a risk assessment is
necessary to determine if any further prevention or mitigation (or both) techniques are
required to reduce the risk to Broadly Acceptable or As Low as Reasonably Practicable
(ALARP). The depth of assessment required is discussed in section 2.2.
To complete this assessment, it is necessary to understand the following:
x
For each receptor
o
Is there a potential for a MATTE based on the quantities and types of
substance stored on site? (Note: include substances that might credibly be
produced/introduced in an emergency, such as firewater). This screening step
can also be used to rule out from further assessment areas of larger sites
where there is no MATTE potential if they will have no involvement in other
areas that do have MATTE potential. A site plan may be a useful tool to
highlight those areas which have or do not have MATTE potential.
x
If there is potential
o
Determine unmitigated consequences from credible accident scenarios and
use this to establish the tolerability thresholds per receptor per establishment
per year (this is from the Appendix 4 risk matrix)
o
Determine the unmitigated aggregated risk to the receptor from all credible
scenarios (i.e. risk with no mitigation measures in place)
o
Determine the mitigated risk (with existing measures in place) from all
credible scenarios
o
Determine if further measures are required to reduce the risk to Broadly
Acceptable or TifALARP (If mitigated risk remains in TifALARP then the CA
will require an ALARP justification to demonstrate why further risk reduction is
not reasonably practicable).
The methodology for assessing risk within this guidance begins with determining the
unmitigated
consequence (see definitions below figure 4). The unmitigated consequence
could be sub-MATTE (enabling screening out from further assessment) or MATTE level
A-D. Each MATTE level A-D has associated tolerability thresholds - the greater the
consequence the lower the tolerable frequencies for a MATTE (Appendix 4).
The tolerability thresholds are then compared to the unmitigated risk to the receptor from
the establishment. This approach may well indicate an intolerable risk from the outset.
However once the total unmitigated risk has been calculated, the process then requires
the analysis of mitigated risk by inclusion of all existing mitigation layers – this includes
such elements as good design practices, inspection and maintenance, secondary and
tertiary containment and emergency response procedures. It is important to recognise
Guideline – Environmental Risk Tolerability for COMAH Establishments v1.0
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