COMAH Major Accident Hazard Statistics UK: Sites, Inspections & Enforcement

The key UK statistics on COMAH major accident hazard sites — how many establishments there are, how they split into tiers, how often they are inspected and what the Competent Authority charges — drawn from HSE’s annual accounts, its Business Plan and the live public registers, and fully sourced.

At the very top of the chemical-safety pyramid sit Britain’s major accident hazard sites: the oil-storage depots, chemical works, gas terminals and warehouses holding dangerous substances in bulk quantities that trigger the Control of Major Accident Hazards (COMAH) Regulations 2015. This page pulls together the key COMAH statistics — establishment counts, tier splits, inspection volumes, cost-recovery fees and enforcement performance — from the Health and Safety Executive’s (HSE) Annual Report and Accounts, its Business Plan, the official fees-and-charges rates and the live GB and Northern Ireland public registers. Every figure carries its data period, and every source is linked at the end.

One thing to be honest about up front: HSE publishes no annual COMAH incident-count dataset. The numeric spine of major accident hazard regulation is instead the count of sites, the volume of inspections and safety-report assessments, the hourly cost-recovery rates and the regulator’s performance against its own targets — so that is what this page is built on, with the landmark disasters that created the rules covered as case studies rather than a running tally. This is the major-hazard end of the scale that the everyday duties in the COSHH Regulations 2002 connect up to; for the whole-economy picture of hazardous-substance harm, see our COSHH statistics page.

Key facts and figures

• ~950 COMAH establishments operate across Great Britain, upper and lower tier combined — an approximate, periodically updated count rather than a fixed number (HSE/Competent Authority figure).
• 1,600+ major hazard installations in total are regulated by HSE — broader than COMAH alone, taking in offshore, pipelines and explosives (HSE, 2024/25).
• 26 COMAH establishments run under Northern Ireland’s parallel regime — 10 upper tier and 16 lower tier (DAERA NI, live list, re-verified 8 July 2026).
• £218/hr is the Competent Authority’s COMAH cost-recovery rate from 1 April 2026, up from £212/hr (HSE fees and charges).
• 500 onshore major-hazard planned inspections and 67 COMAH safety report assessments are planned for 2025/26 (HSE Business Plan 2025/26).
• £8.93m in COMAH fees was recovered against £10.13m of costs in 2024/25 — a £1.2m deficit (HSE Annual Report and Accounts 2024/25, audited).
• 81% of major hazard safety cases were assessed within their due date in 2024/25 (HSE ARA 2024/25).
• 28 workers were killed at Flixborough in 1974 — the disaster that built the UK’s major-hazard regime (HSE case study).

These are the latest figures available as of July 2026. HSE refreshes the picture in two beats each year — around April, when the cost-recovery rates and the new Business Plan intervention volumes appear, and in November or December, when the Annual Report and Accounts confirm the fee and KPI outturns. The GB and NI public registers are live and can be re-checked at any time; this page is updated when each release lands.

How many COMAH sites are there in the UK?

Around 950 COMAH establishments operate across Great Britain, counting upper-tier and lower-tier sites together. That number is deliberately approximate: sites move in and out of scope as inventories change and businesses open and close, so the Competent Authority treats it as a periodically updated figure rather than a fixed headline. The live count can always be checked against the official establishment register.

COMAH is only one part of a wider major-hazard estate. HSE reports that it regulates more than 1,600 major hazard installations in total (2024/25) — a group with the potential to cause significant harm to workers, communities and the environment. That broader total also takes in offshore installations, high-pressure pipelines and explosives sites, which sit under their own regimes; the ~950 figure is the onshore COMAH slice specifically. Offshore has its own, higher cost-recovery rate, covered here only as a one-line comparison below — the detail lives on the Online CPD Academy offshore oil and gas page.

The regime dates from 1 June 2015, when the COMAH 2015 Regulations came into force, implementing the EU Seveso III Directive and replacing the earlier COMAH 1999 rules. A defining feature is transparency: the public register lets anyone search for establishments within three miles of a postcode, so residents, emergency planners and land-referencing firms can see the major-hazard sites near them.

What is the difference between upper and lower tier COMAH sites?

Two tiers divide the COMAH population, set by the quantity of dangerous substances a site holds against the thresholds in the regulations. Upper-tier sites hold the larger inventories and carry the heaviest duties; lower-tier sites are above the entry threshold but below the upper-tier one, and carry a lighter — though still substantial — set of obligations. The headline difference is the safety report. Upper-tier operators must produce and submit a written safety report demonstrating that all necessary measures have been taken to prevent major accidents and limit their consequences, and that report is formally assessed by the Competent Authority. Lower-tier operators do not submit a full safety report but must still prepare a major accident prevention policy (MAPP) and show it is being implemented. Both tiers must notify their establishment, take all measures necessary to prevent major accidents, and co-operate with emergency planning.

Upper-tier sites also carry the emergency-planning burden in full: the operator prepares an internal plan, the local authority an external plan for the surrounding area, and the public must be given information on how to respond. The tier split is why a single “COMAH site” label can mean very different things — from a modest lower-tier warehouse to a major upper-tier refinery.

How often are COMAH sites inspected?

500 onshore major-hazard planned inspections and 67 COMAH safety report assessments are set out in HSE’s Business Plan for 2025/26, alongside a target to close 1,100 follow-up intervention issues (75% by their due date). COMAH is enforced jointly by a Competent Authority — HSE with the Environment Agency in England, and the equivalent environmental regulators in Scotland and Wales — so an inspection weighs both the safety and the environmental consequences of a potential major accident.

The regulator’s reach goes beyond site visits. For 2025/26 HSE also expects to process around 8,500 land-use planning applications and 80 hazardous substance consent consultations connected to major hazard sites — the machinery that stops incompatible development, such as housing, being built too close to a bulk-chemical installation.

Underneath the annual inspection volumes sit fixed statutory review cycles. Under HSE’s guidance to the regulations (L111), an upper-tier safety report must be reviewed at least every five years, and the internal and external emergency plans reviewed and tested at intervals not exceeding three years. Those cycles set a floor: a site can be visited far more often where its risk profile, incident history or the outcome of an assessment demands it.

What does COMAH regulation cost? Fees and cost recovery

£218 an hour is what the Competent Authority charges for regulatory activity at COMAH sites from 1 April 2026, up from £212/hr in 2025/26. COMAH runs on full cost recovery: operators pay for the regulator’s time on assessments, inspections and follow-up, rather than the taxpayer footing the bill. For comparison, the equivalent rate for offshore installations is higher still at £332/hr — quoted here only as a rate comparison, since offshore is outside COMAH’s onshore scope.

Cost recovery does not always balance. In 2024/25 the regime recovered £8.93m in fees against £10.13m of costs — a deficit of about £1.2m, which HSE attributes largely to turnover among the specialist inspectors it depends on. The prior year was much closer to break-even, at £9.24m against £9.46m, as the table below shows.

How well does the regulator meet its targets?

81% of major hazard safety cases were assessed within their due date in 2024/25, and HSE met its key performance indicator to deliver 90% of major hazard interventions within agreed timescales in the same year. These KPIs are the closest thing the regime has to an annual scorecard: rather than counting incidents, HSE measures whether the preventive machinery — assessments, inspections, follow-up — is being delivered on time.

That distinction matters. A major accident hazard regime is judged less on how many accidents happened last year — catastrophic events are rare — and more on whether the controls that keep them rare are being maintained. An overdue safety report or untested emergency plan is exactly the kind of gap the KPIs surface, much as an overdue examination surfaces failing controls under everyday COSHH — the principle set out in our guide to the COSHH hierarchy of control. The Business Plan numbers are the planned inputs; the Annual Report and Accounts figures above are the delivered outputs, read together across April and November.

How is Northern Ireland’s COMAH regime different?

26 COMAH establishments operate in Northern Ireland under a parallel regime, split into 10 upper-tier and 16 lower-tier sites (DAERA NI live list, re-verified 8 July 2026). NI is outside the Great Britain figures throughout this page because it has its own Competent Authority — the Health and Safety Executive for Northern Ireland (HSENI) with the Northern Ireland Environment Agency (NIEA), part of DAERA — enforcing its own COMAH 2015 Regulations.

The framework is materially the same as Great Britain’s — the tier thresholds, the safety-report duty, the emergency-planning obligations and the public-information requirement all mirror the GB rules, both deriving from the Seveso III Directive. The NI count, like the GB one, drifts as establishments enter and leave scope, so re-check it against the DAERA public list on each refresh.

What was the UK’s biggest major accident hazard incident?

Flixborough, on 1 June 1974, killed 28 workers and injured 36 on site and 53 off site when a cyclohexane vapour cloud ignited at a chemical plant — the disaster that, more than any other, drove the creation of the UK’s major-hazard regulatory regime. It is covered here as a landmark case study, not as part of any annual count; the point of the modern rules is to make events on this scale as close to impossible as regulation can.

The other defining British case is Buncefield. On 11 December 2005 a series of explosions and a fire tore through the Hertfordshire oil-storage depot after a tank overfilled and released a vapour cloud. The blasts injured more than 40 people, with no deaths; five companies were later convicted, with almost £10m in combined fines and costs. The wider bill was far larger — an estimated £1bn cost to the local economy, with more than 250,000 litres of firefighting foam used in the response — and Buncefield reshaped the rules on tank overfill protection, bunding and emergency response for fuel-storage sites nationwide. Neither case argues that major accidents are common; they are the reason the establishment counts, safety reports and inspection cycles in the rest of this page exist at all.

The key numbers at a glance

Eight measures capture the scale and regulation of Britain’s major accident hazard estate, with the latest figure and data period for each below.

Where do these figures come from?

Four official streams supply almost every number on this page: HSE’s Annual Report and Accounts for the audited fee outturns and major-hazard KPIs (each November or December); the HSE Business Plan for the indicative intervention volumes (each spring); the fees-and-charges rates for the hourly cost-recovery figure (each 1 April); and the GB and NI public registers for the live establishment counts and tier splits.

None of these sources provides an annual COMAH incident count — which is exactly why this page is built on establishments, inspections, fees and KPIs. The “around 950” rounding is deliberate, because the register is live and the figure moves, whereas the audited fee and KPI figures are exact for the year stated. Treat the page as a snapshot with a clear refresh cadence: April for the rates and Business Plan, autumn for the account outturns, and the live registers for a current establishment count.

Frequently asked questions

How many COMAH sites are there in the UK?

Around 950 COMAH establishments operate in Great Britain, upper and lower tier combined, with a further 26 in Northern Ireland (10 upper, 16 lower). The GB figure is approximate and periodically updated as sites move in and out of scope; HSE also regulates more than 1,600 major hazard installations in total once offshore, pipelines and explosives are included.

What is the difference between upper tier and lower tier COMAH sites?

The tier is set by the quantity of dangerous substances a site holds. Upper-tier sites hold larger inventories and must submit a written safety report that the Competent Authority assesses, plus full emergency-planning and public-information duties. Lower-tier sites are above the entry threshold but below the upper-tier one; they prepare a major accident prevention policy instead of a full safety report, but still carry substantial duties.

How often are COMAH sites inspected?

HSE’s Business Plan sets out 500 planned onshore major-hazard inspections and 67 COMAH safety report assessments for 2025/26. Statutory review cycles also apply: an upper-tier safety report must be reviewed at least every five years, and internal and external emergency plans reviewed and tested at least every three years. Higher-risk sites are visited more frequently.

What was the UK’s biggest COMAH-type incident?

The Flixborough disaster of 1 June 1974 killed 28 workers and injured dozens more, and is regarded as the event that created the UK’s major-hazard regime. The Buncefield explosions of 11 December 2005 injured more than 40 people with no deaths, led to almost £10m in fines and costs across five companies, and are estimated to have cost the local economy around £1bn. Note that HSE publishes no annual count of COMAH accidents — these are landmark case studies, not entries in a running tally.

Related guides

• COSHH Statistics UK: Hazardous Substances at Work
• Silica Dust Statistics UK: Exposure, Silicosis & Deaths
• Occupational Dermatitis Statistics UK: Work-Related Skin Disease
• COSHH Regulations 2002: A Plain-English Summary
• COSHH Storage Requirements: How to Store Hazardous Substances

Sources & references

• HSE — Annual Report and Accounts 2024/25 (audited fee outturns and major-hazard KPIs)
• HSE — Business Plan 2025 to 2026 (major-hazard intervention volumes annex)
• HSE — Fees and charges: current cost-recovery rates (£218/hr COMAH from 1 April 2026)
• HSE — COMAH 2015 public establishment register and information pages
• DAERA — COMAH public information, Northern Ireland (full NI site list)
• HSE — L111: A guide to the COMAH Regulations 2015 (review and test frequencies, duties)
• HSE — Buncefield incident investigation pages
• HSE — Flixborough (1974) case study
• Groundsure — What are COMAH sites? (secondary corroboration of the ~950 count and Buncefield economics)

Mark McShane

Health & Safety Training Specialist, Online CPD Academy

Mark writes about workplace health & safety, COSHH and accredited online training for COSHH Training, part of Online CPD Academy.