Control of Major Accident Hazards (COMAH) Consultancy Services
COMAH Support from Hazard Studies to Safety Reports
Independent Review of Process Safety Systems Across the Asset Lifecycle
The Control of Major Accident Hazards (COMAH) Regulations are the UK’s primary framework for managing risks associated with large-scale industrial hazards.
They apply to establishments handling hazardous substances above defined thresholds and require operators to:
- Prevent major accidents
- Limit consequences to people and the environment
- Demonstrate that risks are reduced to ALARP (As Low As Reasonably Practicable)
COMAH is not a one-time exercise. It is a lifecycle obligation, requiring ongoing demonstration of effective risk management, governance and engineering control.
What Is COMAH?
COMAH requires operators of qualifying sites to take all measures necessary to:
- Identify major accident hazards
- Assess potential consequences
- Implement prevention and mitigation measures
- Maintain a robust Process Safety Management system
Upper tier establishments must prepare and submit a COMAH Safety Report, demonstrating that:
- Hazards have been systematically identified
- Risks have been assessed and reduced to ALARP
- Adequate safety management systems are in place
This report is assessed by the Competent Authority against defined technical criteria.
COMAH establishments are regulated by the Competent Authority, comprising the Health and Safety Executive and the relevant environmental regulator, including the Scottish Environment Protection Agency in Scotland.
The Competent Authority:
- Reviews and assesses Safety Reports
- Conducts inspections
- Can prohibit operation where prevention and mitigation measures are deficient
The HSE Safety Report Assessment Manual provides structured criteria for evaluating Safety Reports.
Demonstrating compliance requires robust hazard identification, risk assessment and governance.
COMAH obligations vary depending on the inventory of hazardous substances present on site and their defined threshold quantities:
These substances typically include:
- Flammable liquids and gases (e.g. hydrocarbons, ethanol, solvents)
- Toxic substances (e.g. chlorine, ammonia)
- Explosive materials
- Oxidising agents
- Environmentally hazardous substances
Thresholds are defined in the COMAH regulations and are based on the type, quantity and hazard classification of substances stored, processed or handled on site.
Lower Tier Establishments
Sites exceeding lower-tier thresholds are required to:
- Prepare a Major Accident Prevention Policy (MAPP)
- Implement appropriate safety management systems
The focus at lower tier is on demonstrating that risks are understood and managed through structured systems and governance.
Upper Tier Establishments
Sites exceeding upper-tier thresholds are subject to more extensive regulatory requirements, including:
- Full COMAH Safety Report
- Demonstration of Major Accident Hazard identification
- ALARP justification and risk reduction measures
- Consequence modelling and emergency planning
- Periodic review and update of the Safety Report
The level of scrutiny and documentation increases significantly at upper tier level.
In practice, COMAH requires operators to:
- Identify major accident hazards
- Assess potential consequences
- Implement effective prevention and mitigation measures
- Maintain a robust Process Safety Management system
- Demonstrate compliance through documentation and evidence
- Engage constructively with the Competent Authority
It is a lifecycle obligation, not a one time submission.
COMAH considerations apply at every stage:
Concept and Feasibility
- Hazardous substance inventory assessment
- Early Major Accident Hazard identification
Design and Development
- HAZID, HAZOP and LOPA
- Consequence modelling
- ALARP demonstration
Construction and Commissioning
- Pre operation Safety Report updates
- Verification of safeguards
Operation and Maintenance
- Periodic Safety Report review
- PSM auditing
- Incident learning
Modification and Decommissioning
- Management of change
- Safety Report revision and resubmission where required
Lifecycle alignment reduces regulatory risk and rework.
Support may include:
- Safety Report preparation for upper tier establishments
- Safety Report review and gap analysis
- Consequence modelling
- ALARP demonstration
- Major Accident Hazard identification
- Integration of PSM systems
- Support during Competent Authority interventions
The objective is not only submission, but defensible and proportionate risk management.
COMAH support may include:
- Safety Report development or update
- Major Accident Hazard identification documentation
- Consequence modelling reports
- ALARP demonstration summaries
- Improvement roadmaps
- Support during regulatory inspection
Deliverables are structured, proportionate and regulator ready.
IDEA’s Experience Supporting COMAH Across Sectors
IDEA has extensive experience supporting COMAH related activities across Scotland, the UK and Europe in high hazard industries.
Our sector experience includes:
We support both lower tier and upper tier establishments, integrating:
Our multidisciplinary capability ensures that COMAH support is aligned with engineering reality and operational practice.
Frequently Asked Questions
Quick answers to questions you may have about our services
Yes. COMAH applies where hazardous substances exceed defined threshold quantities set out in the regulations.
An upper tier site must submit a Safety Report demonstrating identification of major accident hazards, implementation of control measures and reduction of risk to ALARP.
A Safety Report must be reviewed periodically and updated where significant changes occur.
The Competent Authority assesses Safety Reports, conducts inspections and can take enforcement action where measures are inadequate.
Useful References
Health and Safety Executive
Control of Major Accident Hazards Regulations
HSE Safety Report Assessment Manual
Scottish Environment Protection Agency
Environment Agency
Energy Institute
Institution of Chemical Engineers
Chemical Industries Association
CONTACT US
Talk to our Process Safety Team
If you are preparing a COMAH Safety Report, reviewing tier status or seeking independent assurance of compliance arrangements, our Process Safety team can provide structured and proportionate support aligned to your sector and lifecycle stage.