Control of major accident hazards (COMAH)

Does COMAH apply to my business?


If your business manufactures, stores or uses any dangerous substances over a certain amount, the Control of Major Accident Hazards (COMAH) Regulations apply to you.

Identify the category of your site

There are two thresholds for dangerous substances under COMAH. These thresholds vary for different substances.

If you store or use an amount meeting the lower threshold for a dangerous substance your site is classed as a lower tier site provided it does not exceed the upper tier threshold. If you store or use more than the upper threshold your site is an upper tier site.

Check rules for classifying dangerous substances

Dangerous substances covered by the COMAH Regulations include:

  • ammonium nitrate
  • oxygen
  • hydrogen
  • formaldehyde
  • halogens
  • petroleum products

Dangerous substances also include those that fall into classifications defined by the European Community Regulation on Classification, Labelling and Packaging of Substances and Mixtures (CLP Regulation). 

You must check your responsibility if you store more than one type of dangerous substance. Even if you don't exceed the threshold amount for some dangerous substances under COMAH, when all the substances you store or use are added together you may need to comply.

Comply with Planning Regulations for dangerous substances

If the COMAH Regulations apply to you, you may also be regulated under planning legislation and need a hazardous substances consent from the Northern Ireland Planning Service. For further information, you should contact the Northern Ireland Planning Service.

COMAH regulator

COMAH is regulated by the HSENI and the Northern Ireland Environment Agency (NIEA). These organisations are jointly referred to as the Competent Authority (CA).

You will have to pay for most of the work the CA does in connection with your site, for example:

  • assessment of safety reports
  • on site inspection of how major hazard risks are managed
  • investigation of major accidents

If you are unsure whether COMAH applies to you, contact the HSENI or the NIEA.