CDOIF Guidance

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.

6.1.1

Identifying the major accident scenarios

When considering which credible major accident scenarios to consider as part of the risk

assessment, two options are available:

Evaluate all credible scenarios which could have a MATTE potential on the

identified receptor, or

Select a representative set of credible major accident scenarios, in line with the

HSE guidance ‘Risk analysis or ‘predictive’ aspects of COMAH safety reports

guidance for explosive sites’,

Note that when using a representative set of credible major accident scenarios, it is likely

that aggregation of risk will be based on developing scenario based risk criteria as

described in section 4.3.2.

6.1.2

Determining the level of severity

For each credible major accident scenario (or representative set of credible major

accident scenarios) and receptor affected, assign the Level of Severity that would be

associated with the unmitigated consequences (see 4.1):

Table 1 (Severity/Harm criteria for consideration as a major accident) in

Appendix 4 contains consequence descriptions – the “severe” column

represents the lowest level MATTE descriptor (as taken from the DETR 1999

guidance). Consequences lower than this, although pollution incidents are

not regarded as MATTE or covered by COMAH. Consequences greater than

this level may trigger the higher threshold categories in the table.

Each column in the table has a number assigned to it: 1-4. This is the

harm/severity level.

6.1.3

Assigning a duration/recovery category

For each credible major accident scenario (or representative set of credible major

accident scenarios), assign a duration/recovery category that would be associated with

the unmitigated consequences.

It has been recognised that environmental incidents differ in ultimate consequence

depending on the (natural) recovery time of the environment. Longer term harm will

produce a less tolerable consequence than one of only short duration.

For many scenarios there will be opportunities for clean-up and remediation as a post-

incident measure which will reduce environmental harm. However, these should be

disregarded at this stage, but discussed as “mitigation” measures within the ALARP

demonstration.

To assign a duration/recovery category:

Guideline – Environmental Risk Tolerability for COMAH Establishments v1.0

Page 32 of 88