Major accidents in industrial facilities can lead to devastating consequences—explosions, toxic releases, and fires that endanger lives, damage the environment, and destroy property. These aren’t just theoretical risks; they’ve happened before in real-world disasters like Seveso (Italy), Buncefield (UK), and Bhopal (India). The Control of Major Accident Hazards (COMAH) Regulations were created to prevent these catastrophes and mitigate the impact when they do occur.
But what exactly is COMAH, and how does it work in practice?
If you’re responsible for safety at a facility that handles hazardous substances, or you’re simply looking to understand how the UK controls risks at high-hazard sites, this article gives you a practical and in-depth look at what COMAH is, why it exists, and how to comply with it.
Let’s break it down.
What is COMAH and Why Does It Exist?
COMAH stands for the Control of Major Accident Hazards Regulations. It’s a UK legal framework aimed at preventing and limiting the consequences of major accidents involving dangerous substances. COMAH applies to facilities that hold specific quantities of hazardous materials, such as flammable gases, toxic chemicals, or explosive substances.
The regulations came into force originally in 1999 and were revised in 2015 to align with the European Union’s Seveso III Directive (2012/18/EU), named after the 1976 Seveso disaster in Italy.
At its core, COMAH is about protecting people and the environment from the worst-case scenarios in industrial operations. It applies to a range of industries including:
-
Oil refineries
-
Chemical manufacturers
-
Storage facilities for fuels and chemicals
-
Food and beverage processors using ammonia or refrigerants
-
Power plants and pharmaceutical companies
The Health and Safety Executive (HSE), in partnership with the Environment Agency (EA) or the Scottish Environment Protection Agency (SEPA), acts as the COMAH Competent Authority (CA). Their role is to enforce the regulations through inspections, reviews, and guidance.
COMAH isn’t just about ticking boxes. It requires a deep and proactive commitment to safety, engineering integrity, emergency planning, and continuous improvement. That’s why it’s considered one of the most robust regulatory frameworks for managing industrial risks in the world.
How COMAH Works: Upper vs Lower Tier Sites
Not all COMAH sites are treated the same way. Based on the quantities of hazardous substances stored or used on-site, COMAH divides sites into two categories:
1. Lower-Tier Sites
Lower-tier COMAH sites hold hazardous substances above threshold levels but not enough to be classified as upper-tier. While these sites still have significant responsibilities, the regulatory requirements are somewhat less demanding compared to upper-tier sites.
Key duties for lower-tier sites include:
-
Notifying the Competent Authority of their status
-
Preparing and reviewing a Major Accident Prevention Policy (MAPP)
-
Demonstrating that they have taken all measures necessary to prevent major accidents
2. Upper-Tier Sites
Upper-tier COMAH sites store or use hazardous substances at much higher quantities, and therefore face stricter requirements. These sites are subject to more intensive inspection and must develop detailed safety reports, on-site emergency plans, and communicate with local authorities for off-site emergency arrangements.
Key obligations include:
-
Submission of a full Safety Report to the HSE
-
Implementation of safety management systems (SMS)
-
Development of internal and external emergency plans
-
Regular review and testing of safety systems
-
Coordination with local emergency services and public communication
The tier classification ensures that regulatory oversight is proportionate to the risks posed by a site.
What Substances Are Covered Under COMAH?
The COMAH regulations are triggered by the presence of “dangerous substances”, a category defined by both the quantity and type of material. The substances include:
-
Explosives
-
Flammable gases and liquids (e.g., LPG, petrol)
-
Toxic chemicals (e.g., chlorine, ammonia)
-
Oxidizing substances
-
Environmentally hazardous chemicals
Schedule 1 of the COMAH 2015 Regulations provides a comprehensive list of substances and their threshold quantities. If your site handles any of these substances above the listed threshold, it may be subject to COMAH regulations.
This list is not just a formality. Misclassification or failure to report the right substances can lead to severe penalties, including prosecution by the HSE. That’s why regular chemical inventory assessments and risk reviews are essential.
Many companies also use tools like Safety Data Sheets (SDS) and chemical hazard databases to ensure compliance with classification criteria under CLP (Classification, Labelling and Packaging) Regulation, which ties into COMAH responsibilities.
What Is a COMAH Safety Report and How Is It Used?
A COMAH Safety Report is a detailed document required from upper-tier sites. It demonstrates how a business identifies, assesses, and controls the risk of major accidents. Think of it as the blueprint for managing catastrophic risk.
The Safety Report must include:
-
A comprehensive description of the site and processes
-
An inventory of hazardous substances
-
Risk assessments of potential major accidents
-
Control measures are in place to prevent escalation
-
Information on technical and organizational safety measures
-
Emergency response planning details
-
An overview of the Safety Management System (SMS)
Once submitted, the COMAH Competent Authority evaluates the report for completeness and credibility. They assess whether the safety measures are “adequate” and “proportionate” to the risks involved.
If approved, it doesn’t mean the site is “safe forever.” The safety report must be reviewed and updated regularly—typically every 5 years or following any significant change in processes, storage, or substances.
Having a strong Safety Report isn’t just about compliance. It also builds trust with regulators, stakeholders, and the public. Poor-quality reports can delay operations, lead to improvement notices, or, in worst cases, force temporary shutdowns.
What is a Major Accident Prevention Policy (MAPP)?
The MAPP is a key requirement under COMAH for both upper- and lower-tier sites. It’s a written policy that outlines how the company aims to prevent major accidents through good management and sound technical practices.
The MAPP must:
-
Clearly define the site’s health, safety, and environmental objectives
-
Describe the leadership’s commitment to preventing accidents
-
Detail the responsibilities of key personnel
-
Outline processes for risk identification and control
-
Demonstrate continual improvement and auditing processes
It’s not enough to just write a MAPP and file it away. It should be an active part of the business’s safety culture, visible across departments, and regularly updated to reflect operational changes or incident learnings.
The HSE recommends that your MAPP aligns with established standards such as ISO 45001 or HSG65 (Managing for Health and Safety). Integration with existing Health and Safety Management Systems can also streamline efforts.
Emergency Planning: On-Site and Off-Site Preparedness
Even with the best preventive measures, accidents can still happen. That’s why COMAH requires robust emergency planning to minimize harm when things go wrong.
On-Site Emergency Plan
Upper-tier sites must develop an on-site emergency plan in consultation with workers and emergency responders. This plan should:
-
Define actions for different emergency scenarios
-
Assign roles and responsibilities
-
Include escape routes, fire-fighting systems, and first aid arrangements
-
Be tested through simulations or drills
Off-Site Emergency Plan
The local authority is responsible for preparing an off-site emergency plan, but the COMAH operator must supply necessary information, including:
-
Nature of hazardous substances
-
Worst-case scenarios
-
Likely consequences and response measures
-
Evacuation strategies for the local population
Both plans must be tested at regular intervals and updated to reflect operational changes or feedback from real-life incidents and drills.
Effective emergency planning isn’t just a regulatory requirement—it’s a moral and practical obligation to protect workers, neighbors, and the environment.
How the COMAH Competent Authority Enforces Compliance
The HSE and Environment Agency (or SEPA in Scotland) are the primary enforcement bodies for COMAH. Their role is not only to check compliance but also to advise, educate, and penalize when necessary.
Their duties include:
-
Reviewing notifications and safety reports
-
Inspecting sites (planned and unannounced)
-
Investigating incidents or near-misses
-
Issuing improvement and prohibition notices
-
Prosecuting serious breaches under the Health and Safety at Work etc. Act 1974
Inspections are often risk-based and focus on:
-
Leadership and safety culture
-
Process safety controls and maintenance
-
Emergency response capabilities
-
Learning from incidents and audits
Companies that fail to comply may face legal action, financial penalties, or even shutdown orders. In 2005, the Buncefield oil storage terminal explosion led to multi-million-pound fines and massive reforms in COMAH enforcement.
Transparency is critical. The HSE publishes COMAH site inspection scores and enforcement actions on its website, allowing the public and stakeholders to see how facilities are performing.
Challenges and Best Practices for COMAH Compliance
Many organizations struggle with COMAH compliance—not because they don’t care, but because it’s complex, technical, and resource-intensive. Here are a few practical challenges and proven best practices:
Common Challenges
-
Incomplete hazard identification or substance classification
-
Poor documentation or outdated safety reports
-
Weak leadership commitment or low safety culture maturity
-
Emergency plans that are theoretical, not practical
-
Lack of training and engagement with frontline staff
Best Practices
-
Conduct regular HAZOPs (Hazard and Operability Studies)
-
Invest in automated safety systems with real-time monitoring
-
Build a cross-functional COMAH team including operations, safety, engineering, and legal
-
Run live drills involving the local fire service and ambulance teams
-
Leverage guidance from the HSE’s COMAH Strategic Forum and CIRIA C736 best practices
By treating COMAH as a continuous improvement process rather than a one-off compliance task, you position your business for long-term resilience and operational excellence.
Final Thoughts: Why COMAH Matters More Than Ever
The risks that COMAH seeks to control are not hypothetical—they are very real. Industrial accidents can devastate communities, destroy ecosystems, and shatter public trust in a company.
In a world facing climate volatility, aging infrastructure, and increasing industrial demand, the importance of robust COMAH compliance has never been more urgent.
Whether you’re a safety manager, business owner, or consultant, understanding how COMAH works is critical to keeping people safe, staying legally compliant, and maintaining a social license to operate.
It’s more than just a regulation—it’s a system built on prevention, preparedness, and accountability.
Related Posts
What is COSHH? What is the full meaning of COSHH
RIDDOR (Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 1995)