Manufacturing & Engineering UK-wide

COMAH Compliance for Chemical Sites

Meet COMAH requirements for sites holding dangerous substances.

Updated 16 Feb 2026

Guide summary

You must calculate the total dangerous substances on your site and compare to COMAH thresholds. If you exceed lower or upper tier limits, notify the authorities, create a major accident prevention policy, and set up a safety management system. Upper tier sites must also prepare a safety report and coordinate emergency plans. You face annual charges of £2,000 to over £20,000 and possible fines or imprisonment.

Calculate total inventory of dangerous substances on site
Compare against COMAH qualifying thresholds (e.g. chlorine 10t lower, 25t upper)
Notify HSE and environment agency if you exceed thresholds
Create a Major Accident Prevention Policy (MAPP)
Set up a safety management system (SMS)
Inform local emergency services about hazards
Upper tier: prepare a full safety report (update every 5 years)
Upper tier: work with local authority on off-site emergency plans
Pay annual charge: £2,000-£5,000 (lower tier) or £10,000-£20,000+ (upper tier)
Expect inspections: lower tier every 3 years, upper tier every 12 months

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If your site holds dangerous substances above certain thresholds, you may be subject to the Control of Major Accident Hazards (COMAH) Regulations 2015. COMAH aims to prevent major accidents and limit their consequences.

Determining COMAH status

Calculate total inventory of dangerous substances on site
Compare against qualifying thresholds in COMAH schedule
Use 'aggregation rule' for multiple substances
Lower tier or upper tier status triggers different requirements

COMAH (Control of Major Accident Hazards)

Requirements for establishments holding dangerous substances above COMAH thresholds

Competent authority: HSE + Environment Agency (England) / HSE + SEPA (Scotland) / HSE + NRW (Wales)
Legal basis: COMAH Regulations 2015 (as amended)
Lower tier status: Triggered by exceeding substance-specific tonnage thresholds
Upper tier status: Triggered by exceeding higher tonnage thresholds
Example: Chlorine lower tier: 10 tonnes
Example: Chlorine upper tier: 25 tonnes
Example: LPG lower tier: 50 tonnes
Example: LPG upper tier: 200 tonnes
Safety report (upper tier): Required before operation - full hazard assessment and mitigation measures
Safety report update frequency: Every 5 years or after significant modifications
Inspection frequency (lower tier): At least once every 3 years
Inspection frequency (upper tier): At least once every 12 months
Annual charge (lower tier): Approximately £2,000-£5,000
Annual charge (upper tier): Approximately £10,000-£20,000+
Penalty: Unlimited fine and/or up to 2 years imprisonment

Comply with COMAH Regulations

Step-by-step process for COMAH notification and compliance

Step 1: Calculate dangerous substances inventory: Total all dangerous substances on site and compare against COMAH qualifying thresholds.
Step 2: Determine tier status: Check if you exceed lower tier or upper tier thresholds (varies by substance).
Step 3: Submit COMAH notification: Notify HSE and EA/SEPA/NRW with site details, substances present, quantities, and environmental description.
Step 4: Prepare MAPP: Create Major Accident Prevention Policy outlining commitment to preventing major accidents.
Step 5: Implement safety management system: Establish SMS covering organisation, hazard identification, controls, emergency planning, and monitoring.
Step 6: Notify emergency services: Inform local fire, police and ambulance of major accident hazards at your site.
Step 7: Prepare safety report (upper tier): Full safety report demonstrating hazard identification, risk assessment, safety measures, emergency arrangements.
Step 8: Coordinate emergency planning (upper tier): Work with local authority on off-site emergency plans and public information.
Step 9: Pay annual COMAH charge: Pay cost recovery charge invoiced by HSE/EA (£2,000-£20,000+ depending on tier).