Environmental guidance for your business in Northern Ireland & Scotland

Who COMAH applies to

Who COMAH applies to

If your business manufactures, stores or uses any dangerous substances in amounts that exceed certain thresholds, the Control of Major Accident Hazards (COMAH) Regulations apply to you.

What you must do

Identify the category of your site

There are two thresholds for dangerous substances under COMAH.  These threshold quantities vary for different categories of substances.

If you store or use more than the lower threshold for a dangerous substance your site is classed as a lower tier establishment. If you store or use more than the higher threshold your site is an upper tier establishment.

The COMAH Regulations 2015 change the classification of certain substances and change the threshold values for some dangerous substances. This means that some sites may change their classification, or may have become a COMAH regulated establishment for the first time after 1 June 2015.

Check the rules for classifying dangerous substances at your site

Dangerous substances covered by the COMAH Regulations include named substances (eg hydrogen, ammonium nitrate), and those with:

  • health hazards, including acute toxics;
  • physical hazards, including explosives and flammable liquids and gases;
  • environmental hazards, acute and chronic hazards to the aquatic environment; and
  • other that react with water, including those that evolve toxic or flammable gases.

Find a full list of dangerous substances and relevant threshold quantities:

These are separated into Part 1 (generic categories) and Part 2 (named dangerous substances).

Dangerous substances are categorised in accordance with the Classification, Labelling and Packaging (CLP) Regulations.  If a substance, including waste, does not already have a standard CLP classification you must provisionally assign it to the most similar category or named substance until you can make a full assessment.

When classifying a chemical, you must consider:

  • what sort of harm the substance might cause – the hazards;
  • how certain it is that the substance could actually have this effect;
  • how serious the effect might be; and
  • the concentration of the substance.

Classification of a mixture is generally based on what is known of the constituent substances or similar products.

HSE: Classification of chemicals and mixtures


HSENI: CHIP replaced by CLP

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 any of the dangerous substances under COMAH alone, when all the substances you store or use are added together you may need to comply.

Further information

HSE: Guide to New Entrants

HSE: What to expect from the Competent Authority

HSE: Guidance on the assistance available to new entrants to COMAH

Who regulates COMAH establishments?

COMAH is regulated by a joint competent authority (CA), comprising:

  • in Northern Ireland, the Health and Safety Executive for Northern Ireland (HSENI) and the Northern Ireland Environment Agency (NIEA)
  • in Scotland, the Health and Safety Executive (HSE) and the Scottish Environment Protection Agency (SEPA).

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, including preparation and follow up
  • some aspects of investigation of major accidents.

In this Guideline

Who COMAH applies to

COMAH regulated site responsibilities

COMAH environmental legislation

If you are unsure whether COMAH applies to you:

  • in Northern Ireland, contact the HSENI or the NIEA
  • in Scotland, contact the HSE or SEPA.

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 your local council planning office or your local Planning Authority in Scotland.

Scottish Government: Local planning authorities contact details

Planning Northern Ireland: Local planning offices

Further information

Contact your environmental regulator

HSENI: COMAH Guidance for Northern Ireland

HSENI: Planning control for hazardous substances

HSE: COMAH Guidance for Scotland

HSE: Hazardous substances consent

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NIEA - Apply online

SEPA - Application forms