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Knowledge Base » Health and Safety » What are the 2015 COMAH Regulation Changes?

What are the 2015 COMAH Regulation Changes?

Last updated on 20th December 2023

Unfortunately, there have been many major industrial accidents around the world over the last few decades. There have also been a few in the UK, e.g. the Flixborough (Nypro UK) Explosion 1974, the Piper Alpha explosion 1988 and the Chevron Pembroke Refinery explosion and fire 2011.

Major accidents tend to involve dangerous substances, which can cause events such as fires, explosions and toxic releases or emissions. When a major accident occurs, it does not just affect those in the vicinity. It can have far and wide effects that can be devastating to people, animals and the environment.

Major accidents have led to multiple fatalities, severe life-changing injuries and ill health, extensive property damage and adverse environmental impacts. Fortunately, these types of events are uncommon. However, when they do happen, it can be catastrophic. Therefore, it is vital to have stringent precautions where there is a risk of a major accident.

The Health and Safety Executive (HSE) has many examples of case studies on their website that highlight the devastating impacts and the importance of preventing, controlling or mitigating major accidents. There are also laws surrounding their control. One of these laws is known as the COMAH Regulations 2015.

This article will look at the COMAH Regulations and what the changes were in 2015. It will also cover any changes that have occurred as a result of the UK leaving the EU.

Following COMAH Regulation

The COMAH Regulations 2015

COMAH stands for the Control of Major Accident Hazards Regulations 2015 (COMAH 2015). These Regulations came into force on 1st June 2015 and revoked and replaced the Control of Major Accident Hazards Regulations 1999. The reason for the updated legislation was to implement a European Union (EU) Directive known as the Seveso III Directive (2012/18/EU). This Directive replaced Seveso II (96/82/EC).

The aim of COMAH, according to the HSE, is to prevent and mitigate the effects of major accidents involving dangerous substances which can cause serious damage/harm to people and/or the environment.

The 2015 Regulations brought about significant changes, which affects new and existing establishments that come under the scope of COMAH.

What is a major accident?

The COMAH 2015 Approved Code of Practice defines a major accident as:

“An occurrence such as a major emission, fire, or explosion resulting from uncontrolled developments in the course of the operation of any establishment to which these Regulations apply, and leading to serious danger to human health or the environment (whether immediate or delayed) inside or outside the establishment, and involving one or more dangerous substances”.

If there is a risk of the above, then COMAH 2015 will likely apply.

Where does COMAH apply?

COMAH 2015 applies to certain establishments in Great Britain (England, Scotland and Wales). Northern Ireland has its own COMAH Regulations – the Control of Major Accident Hazards Regulations (Northern Ireland) 2015.

If an establishment manufactures, uses or stores dangerous substances in certain quantities, COMAH 2015 will apply.

It is most likely to apply to those in the chemical industry but can also include establishments that:

  • Are explosive or nuclear sites.
  • Carry out storage activities.
  • Are in other industries that keep or use quantities of dangerous substances at or above the threshold in Schedule 1 of the Regulations.

Under COMAH 2015, establishments will fall into one of the following thresholds:

  • Upper-tier – High-risk establishments that store or use more than the higher threshold. These used to be known as top tiers in COMAH 1999.
  • Lower-tier – Lower-risk establishments that store or use more than the lower threshold, but still need to comply with COMAH.
  • Non-COMAH sites – Establishments that do not fall within the scope of COMAH.

Appendix 1 in the COMAH Approved Code of Practice can help duty holders determine whether the Regulations apply and, if so, the type of establishment and tier they would come under. This is important, as there are more stringent requirements for upper tiers.

The Seveso III Directive

The Seveso Directives

Seveso is a town in the Lombardy region of Italy. On 10th July 1976, there was an industrial accident in a chemical manufacturing plant. A bursting disc on a chemical reactor ruptured, which resulted in the release of a vapour cloud containing highly toxic dioxin.

The accident had a devastating impact on the nearby town of Seveso. There were no human fatalities as a direct result of the incident, but many people fell ill. Thousands of animals also had to be slaughtered to prevent dioxin from entering the food chain.

As a result of the disaster, a European Economic Community (EEC) Directive was adopted in June 1982. The legislation aimed to prevent and control such accidents and impose stronger regulations on those with responsibilities. The Directive was named after the town and was known as the Seveso Directive (82/501/EEC).

The Seveso Directive was amended in 1996 and 2008 because of further incidents, e.g. Bhopal, Toulouse and Enschede. It became Seveso II (96/82/EC). This Directive was implemented in the UK by the Control of Major Accident Hazards Regulations 1999.

There was a further update of the Seveso Directive in 2012, which became Seveso III.

What is Seveso III?

The main reason the Seveso III Directive (2012/18/EU) was adopted was to introduce the Globally Harmonised System (GHS) for the Classification and Labelling of Chemicals into its framework. Its purpose was to align with EU Regulation (EC) No. 1272/2008 – classification, labelling and packaging of substances and mixtures (CLP Regulation).

As Seveso is a Directive from the EU, the UK (as a previous member state) had to assimilate the legislation into national laws. The Seveso III Directive was implemented on 1st June 2015 in Great Britain by the COMAH Regulations 2015. It revoked and replaced the COMAH Regulations 1999, which previously implemented Seveso II.

What has happened since leaving the EU?

As the Seveso III Directive was implemented in the UK by the COMAH Regulations 2015, there were no significant changes made to this legislation on leaving the EU.

However, there were some amendments to wording and also relating to notifying the European Commission and member states of any major accidents (no longer required). The amendments are detailed in Regulation 11 of the Health and Safety (Amendment) (EU Exit) Regulations 2018. The UK will continue to share information on major accidents with the EU for lessons learnt purposes.

If there are subsequent amendments to the Seveso Directive, the UK will not be legally required to implement it in GB laws. However, this is where it gets slightly confusing. Northern Ireland remains aligned with some EU rules as part of the withdrawal agreement (the Northern Ireland Protocol). Northern Ireland has their own set of COMAH Regulations but must still comply with certain EU laws, such as the EU CLP, in addition to GB laws.

The EU CLP Regulation (as amended) has been retained in GB law (GB CLP), which means that Great Britain continues to adopt GHS, independently of the EU (HSE). Therefore, duty holders that store or use dangerous substances need to be aware of the changes. You can find out more about the changes to CLP in our article.

Ensurng COMAH Regulations Are Being Followed

What were the changes to COMAH?

COMAH 2015 introduced some new duties and changes to existing ones.

According to the HSE, the changes included:

  • The list of substances covered by the Regulations was updated and aligned to the CLP Regulation (which used to be CHIP).
  • Some definitions were changed, e.g. top-tier site became upper-tier establishment.
  • There were transition arrangements for safety reports.
  • For emergency planning, a new requirement was introduced for cooperation by designated authorities in tests of the external emergency plan.
  • Stronger requirements for public information were introduced, which now includes a duty for lower-tier establishments to provide public information.
  • The domino effects duty is now broader, regarding the cooperation and sharing of relevant information with neighbouring establishments and non-COMAH sites.
  • Stronger requirements were introduced for the Competent Authority on inspection.
  • Local authorities must now inform people likely to be affected following a major accident.
  • A revision to the Approved Code of Practice (L111).

Despite the changes, there will be many familiar requirements from COMAH 1999.

If an establishment has been a COMAH site for some time, it should already be compliant with the new duties. From 1st June 2015, existing COMAH establishments still within the scope of the new regulations had to submit a new COMAH notification.

If a site is new and falls within the scope of COMAH, duty holders will need to ensure they follow the requirements outlined in COMAH 2015. Not complying with the law can have severe repercussions for businesses. The HSE has a guide for new entrants on its website.

The main reason for the change

The main reason the Seveso III Directive was introduced and the 2015 COMAH Regulations were implemented was to take into account the change in the classification system of dangerous substances, i.e. the Globally Harmonised System (GHS) for the Classification and Labelling of Chemicals and the EU CLP Regulation.

The Seveso III Directive also reinforced many areas, e.g. public access to information and inspection standards.


The EU Dangerous Substances Directive and Dangerous Preparations Directive were implemented in Great Britain as the Chemicals (Hazard Information and Packaging for Supply) (CHIP) Regulations.

The CHIP Regulations were replaced by the EU CLP Regulation on 1st June 2015. You may have noticed the square orange and black (CHIP) symbols on chemical packaging in the past. These have now changed to hazard pictograms (diamonds) which are symbols that are used internationally.

CLP covers the classification, labelling and packaging of substances and mixtures. As a previous member state, the UK had to comply directly with the EU CLP Regulation. On 1st January 2021, the EU CLP Regulation was replaced by the GB CLP Regulation in Great Britain.

This means that businesses based in Great Britain must comply with the GB CLP Regulation. The EU harmonised classification and labelling system was also replaced by Great Britain mandatory classification and labelling (GB MCL). Northern Ireland remained under the EU system as part of the withdrawal agreement.

The CLP Regulation aligns with the Globally Harmonised System (GHS). The GHS is an international voluntary agreement made at the United Nations (UN) on the classification and labelling of chemicals. The GHS aims to protect human health and the environment whilst allowing the free movement of substances. It also provides a global consensus with regards to the classification and labelling of substances.

The GB CLP Regulation has continued to adopt the GHS similar to the EU CLP Regulation. The COMAH Regulations 2015 classify dangerous substances in accordance with the CLP Regulation, which will now be in line with GB CLP.

Showing Someone Working With Dangerous Substances

Providing information to the public

One of the most significant changes in the Seveso III Directive and the COMAH Regulations 2015 was further requirements for public information, which means:

  • All establishments (upper and lower tiers) must provide basic public information electronically by completing a specific information form. The form can be accessed from the HSE’s website and completed online.
  • There are additional requirements for upper-tier establishments, including information relevant to the Public Information Zone (PIZ). The PIZ is an area that is likely to be affected in the event of a major accident.
  • All establishments must provide information on request under the Environmental Information Regulations 2004 or the Environmental Information (Scotland) Regulations 2004.
  • The information must be available permanently in an electronic format and updated if there are any changes.

The information that every establishment needs to provide is detailed in Regulation 17 of COMAH 2015. Upper-tier establishments are required to provide additional information, which is also detailed in Regulation 17.

The HSE and environmental authorities check the information provided for accuracy and content. Therefore, COMAH operators need to ensure the information submitted is correct.

COMAH 2015 requires information to be provided ‘within a reasonable period of time’ after an establishment becomes subject to the Regulations. The HSE state that this should be no longer than three to four months. Existing sites should have already provided the information around the time when COMAH 2015 was introduced.

Members of the public can search for public information on establishments subject to COMAH 2015 from the HSE’s website.


Changes in regulations can be somewhat burdensome for businesses, particularly in the short term. However, the changes in the COMAH Regulations 2015 were about ensuring a global approach when it comes to the classification and labelling of dangerous substances, which can potentially cause major accidents. Even with the UK leaving the EU, this remains unchanged, and COMAH 2015 will apply to those falling within its scope.

Operators of COMAH establishments have a responsibility to prevent, control and mitigate major accidents. They must understand what their legal obligations are. They also need to know what to do to keep employees and their neighbours safe from harm. If they do not, the consequences of a major accident can be devastating and far-reaching.

The HSE have a dedicated section on COMAH on their website. As the COMAH 2015 Approved Code of Practice (ACOP) is a legal series document, operators of COMAH establishments should follow the ACOP to ensure compliance with the law. The penalties for non-compliance can be severe, and if an accident happens, even more so.

COMAH is a large and complex area of health and safety. Therefore, duty holders should obtain professional advice if there are any doubts regarding their compliance with COMAH 2015 and associated laws.

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About the author

Michelle Putter

Michelle Putter

Michelle graduated with an MSc in wildlife biology and conservation in 2012, but her career has taken quite a different turn to the one expected. She started in health and safety in 2009 and has worked in several industries such as electrical engineering, aviation and manufacturing. She has been working with CPD Online College since 2018 and became NEBOSH Diploma qualified in 2020. In her spare time, Michelle's passions are wildlife and her garden. She has volunteered for many conservation organisations and particularly enjoys biological recording. Michelle also likes hiking, jogging and cycling.

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