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Flood Preparedness and COMAH

Flood Preparedness and COMAH

Flooding is the most common and widespread natural disaster that not only inflicts financial distress, but also leads to the potential for disastrous environmental consequences. Although we cannot stop nature unleashing extreme rainfall, we can take measures to ensure the risk is fully understood and mitigated wherever possible.

Who is COMAH and what do they do?

The Control of Major Accident Hazards (COMAH) regulations ensure that businesses undertake all necessary measures to prevent major accidents involving dangerous substances. This subsequently limits the potential consequences to people and the environment of any major accidents which may otherwise occur. A COMAH establishment is defined as a business which stores above a certain volume of dangerous substances on site. These are split into Lower Tier and Upper Tier establishments, depending upon the total volume of dangerous substances stored.

COMAH operators in flood risk areas have a legal requirement to comply with the Operational Delivery Guide – Inspection of COMAH Operator Flood Preparedness. COMAH is enforced in the UK by a COMAH Competent Authority (CA) which is formed from five public bodies all working together in partnership.

These bodies are:

  • The Environment Agency
  • The Scottish Environment Protection Agency
  • The Health & Safety Executive
  • The Office for Nuclear Regulation
  • Natural Resources Wales

Do all COMAH sites need a flood risk assessment?

The environmental damage caused by flooding can lead to serious financial consequences and for sites operating under COMAH this can be even more severe. Business owners in known flood-risk

areas must also have a full understanding of potential water pollution sources and pathways. However, this should also be applicable even if you are not in a high risk flood area. Commercial sites are at higher risk from major accident hazards and must avoid complacency by reviewing their protection from flood risk and water pollution.

How can Ashfield Help?

Ashfield has a wealth of expertise in this field and we are familiar with dealing with COMAH Competent Authorities, supporting businesses with flood risk, and ensuring they comply with the Operational Delivery Guide. We use a combination of the most up to date flood modelling information. This is coupled with suitably detailed topographical and critical asset data to verify whether flooding should be deemed an issue on site.

When flooding has been confirmed as a risk that could potentially lead to causing a major accident, we can outline the most suitable preventative measures, as well as develop an action plan that can be implemented should flooding be predicted to occur in future. Many of our clients also rely upon Ashfield’s ongoing knowledge, when ensuring their site is kept up to speed with new flood modelling data which takes the affects of Climate Change into account.


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COMAH regulations play a key role in preventing Major Accidents to the Environment across the UK