A COMAH Environmental Risk Assessment (ERA) is required for both Upper Tier and Lower Tier sites.

Upper Tier sites are required to submit their ERA for formal inspection and review to the Competent Authority (HSE and relevant Environment Agency), either as part of the Safety Report, or as a stand-alone document.

Lower Tier sites are required to carry out an ERA, and to have it available for inspection when the Competent Authority visit site.

Both types of COMAH site are expected to treat the ERA like any other risk assessment, and make improvements where recommended in the risk assessment. For environmental protection, there can be several methods of achieving the same outcome, and it is important to consider all your options before committing to capital expenditure.

It is important to review environmental protection alongside human safety and health requirements to avoid making an improvement which, although beneficial to the environment, could increase risks to safety or health.

A COMAH Environmental Risk Assessment (COMAH ERA) used to form part of the Safety Report for Upper Tier sites, and was generally descriptive or semi-quantitative in nature.

In 2013, a new methodology was published by the Chemical and Downstream Oil Industries Forum (CDOIF), which has brought a new method of environmental risk assessment into use for COMAH site.

The new method, known as CDOIF ERA, combines the annual probability of a likelihood of a Major Accident To The Environment (MATTE) with the severity of consequences of that MATTE, and sets tolerability boundaries, so that sites can see where improvements are required for environmental protection. This is in addition to the “source-pathway-receptor” model traditionally used for environmental risk assessments, which is still required.

The CDOIF ERA method makes the COMAH ERA process analogous to the human health and safety assessment already within COMAH, and in theory should make it easier for everybody to understand where the “weak points” are within an environmental protection scheme. However, it is not without its own problems, and we have a presentation on this topic available for download (link below).

As environmental consultants to heavy industry, we are experienced in this new COMAH ERA methodology, including its strengths and weaknesses, and can complete this type of assessment successfully.

For more information, call Janet on 01422 24 22 22 or email Janet.

You can view our presentation on CDOIF ERA method below or view it on slideshare.

The slide content in an accessible format (word); COMAH ERA Guidance Presentation Text

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SevaluateTM is an Excel based program which runs your COMAH (Seveso III) calculations for you, provides printable reports showing the main contributors to your COMAH liability, and allows you to predict the impact of changing your COMAH inventory on your COMAH liability.
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External Links


ERA guidance

There are several documents on this page on environmental risk tolerability.