Live Chat

In the early hours of 11 December 2005 at Buncefield Oil Storage Depot, a series of explosions large enough to be detected by BGS seismometers would cause the largest fire in peacetime Europe. The fires burned for several days, destroying most of the site in Hemel Hempstead, injuring at least 40 people1 as well as causing significant environmental contamination. The incident caused catastrophic damage to both commercial and residential properties in the surrounding area and is thought to have cost the local economy over £1bn2.  

Figure 1: Catastrophic fires at Buncefield Oil Storage Depot. (Source: Getty Images)

An investigation into the event, led by the Health and Safety Executive (HSE) and Environment Agency (EA) led to the convictions of five companies, who were ordered to pay almost £10m in combined fines and costs3.

The cause? A faulty fuel gauge on Tank 912 which allowed the overfilling of thousands of gallons of petrol, creating an explosive vapour cloud of evaporated leaked fuel.

Buncefield stands as a stark example of the significance of COMAH sites and why they should command our attention. It is a testament to the potential risks that lurk within these industrial facilities located across the UK, and the critical need for robust safety measures and stringent regulations. 

Understanding COMAH Sites

COMAH stands for Control of Major Accident Hazards4. It is a set of regulations in the United Kingdom that apply to any establishment storing or handling large quantities of industrial chemicals of a hazardous nature. The regulations are designed to prevent major accidents involving dangerous substances such as Buncefield, and to limit the consequences to people and the environment of any accidents that do occur.

COMAH is enforced by the Health and Safety Executive (HSE) and the relevant regional environmental agencies such as the Environment Agency (EA), the Scottish Environment Protection Agency (SEPA), and Natural Resources Wales (NRW) – working together as the COMAH Competent Authority (CCA)5

Figure 2: Map showing the location of both Upper Tier and Lower Tier COMAH sites in the UK. (Source: ENDS Report)

There are approximately 950 sites located all across Great Britain which are monitored under The Control of Major Accident Hazards Regulations 2015 (COMAH)6. The regulations mainly apply to businesses within the chemical industry as well as on land oil/gas refineries.  However, the regulations also apply to many seemingly inconspicuous sites, including those involved in Scotch whisky industry. COMAH sites are split into either the ‘Upper Tier’ or ‘Lower Tier’ COMAH regime, which is dependent on the quantities of material the site processes.

Upper Tier sites are those facilities that store, handle, or process significant quantities of hazardous substances, such as oil refiners including Buncefield.  

Lower Tier COMAH sites cover a diverse range of businesses such as logistic and distribution centres, smaller oil terminals, gasholders and some power stations. Although deemed to be less hazardous, poorly managed Lower Tier COMAH sites have the potential to cause serious harm and damage.  

For example, less than a year after the Buncefield fire, in September 2006 a chemical leak caused a fire at a Cotswold factory. The site was used for mixing and packaging swimming pool chemicals. A fireball over 20m high was reported on the site and the building was completely destroyed. Additionally, the leaking chemicals from the factory and firefighting fluid discharged to the nearby River Coln, causing vast ecosystem damage.  Consequently, the site operators were fined £66,000 for failure to take all measures to prevent the accident and limit the consequences plus pay £80,00 in costs7. The factory is now closed and chemicals are not stored on site.

The affected Industries and Activities 

Figure 3: COMAH Petrochemicals facility at Grangemouth (Source: Getty Images)

COMAH regulations apply to a wide range of industries and activities that involve the handling, storage, and processing of hazardous substances. Dangerous substances covered by the COMAH regulations include named substances such as hydrogen and ammonium nitrate, as well as substances with health hazards (including acute toxics), physical hazards (including explosives and flammable liquids and gases), environmental hazards (acute and chronic hazards to the aquatic environment), and others that react with water (including those that evolve toxic or flammable gases). 

Sectors likely to be designated under COMAH are those which include the following:

The Importance of Safety Measures and Compliance

Stringent requirements are imposed on COMAH facilities to ensure the highest levels of safety for both workers along with the surrounding communities and the environment8. Within COMAH regulations, Dutyholders play a crucial role in ensuring the safety and compliance of such sites. The Dutyholders include both the Operator and the Emergency Planners.

OperatorEmergency Planners
*Responsible for the day-to-day operations of the COMAH site.
*Duty to assess and manage the risks associated with the hazardous substances present on the site.
*Implement appropriate control measures.
*Conduct regular inspections. Maintain safety standards. 

Operators are responsible for ensuring that the site operates safely, adheres to the necessary safety protocols, and complies with all relevant regulations.
*Responsible for developing and implementing effective emergency response plans. 
*They work closely with the Operator and local emergency services to identify potential risks, establish emergency procedures, and train personnel. 
*Ensure that in the event of a major accident, an effective and coordinated response can be initiated promptly.

Emergency Planners play a critical role in safeguarding lives, minimising the impact of incidents, and protecting the environment.

The collaboration between Operators and Emergency Planners is vital to ensure effective risk management and emergency preparedness at COMAH sites. They should closely work together to identify potential hazards, mitigate risks, and establish robust safety protocols.

Figure 4: Hazardous area response team (HART) (Source: Hazardous area response team – London Ambulance Service NHS Trust)  

Regulation 7 of COMAH Regulations 20159 requires that every operator must prepare and retain a major accident prevention policy (MAPP). Operators of sites notifying as upper-tier sites are subject to more requirements than lower-tier sites. Upper-tier operators are required to have a MAPP, which must be included as a separate document in the safety report and also have additional duties. 

The key aspects that contribute to maintaining safety and compliance at COMAH sites include:

  1. Risk assessment and management: The sites must conduct regular and robust risk assessments to identify potential hazards and implement measures to prevent major accidents and limit their consequences. 
  2. Emergency planning: Every COMAH site must have a well-defined emergency response plan in place and must include evacuation procedures, communication protocols, along with coordination with emergency services.
  3. Training and competence: Personnel working at COMAH sites should be properly trained and competent to carry out their duties safely.
  4. Maintenance and inspection: COMAH sites should have regular maintenance and inspection programs in place to ensure that equipment and facilities are in good working order.
  5. Reporting and record keeping: The sites are required to report certain incidents and keep records of their activities to demonstrate compliance with the regulations.
  6. Inspections, Audits, and Regulatory Oversight: Regulators play a critical role in overseeing COMAH sites to ensure compliance with safety regulations.
  7. Share relevant information: Provide information to local authorities for external emergency planning purposes along with providing certain information to the public about the establishment, its activities, and safety measures.

Non-operational buildings which are located either within or next to COMAH sites may fall outside the direct regulatory framework of COMAH if they are not being used for the storage of hazardous materials. However, despite this the activities within such buildings and/or changes to them (development) may still be subject to strict controls and regulations, even though not explicitly governed by the COMAH framework.

Local planning authorities and regulatory bodies may have specific requirements for the use, proposed development, and safety considerations of non-operational buildings within a COMAH site or in close proximity to it. These requirements aim to ensure the overall safety and environmental protection in the area.

Why Should You Care?

Major accidents at COMAH sites can have far-reaching consequences for public safety, health, and the environment. The Buncefield accident is an example of the devastating impact such sites can have. 

It’s not just about preventing accidents, it’s about safeguarding our environment too. Even relatively minor incidents can lead to significant environmental contamination, impacting air, water, and soil quality. The consequences can easily spread and extend beyond the immediate vicinity of the site, affecting ecosystems and potentially putting residential areas at risk. During the Buncefield response, over 250,000 litres of firefighting foam was used to extinguish the flames10, leading to widespread contamination of watercourses and local drinking water with PFAS, the group of ‘forever’ chemicals of growing and concern11.  See our recent blog on this. 

Being a COMAH site or being located near a COMAH can limit the types of development which are permitted. This includes if a COMAH site wants to expand or change its operations.  The legislation requires local planning authorities to conduct numerous consultations and consider the consequences of any potential accident hazards before they can grant planning permission in relation to establishments.  For developments that would result in a large number of people being in close proximity to a COMAH site and thus at risk if an accident was to occur, it is likely to be a deciding influencer. 

Despite such regulations, the proximity of COMAH sites to residential areas can be surprising. Take, for example, the Redcliffe Bay Fuel Depot, which supplies aviation-grade kerosene for civil and military use across the UK and is considered a potential target for terrorist attack12. The site originally built in the 1950s is now partly surrounded by residential properties, some of which are located only metres from the buried tanks. The Site has been the source of multiple planning appeals with local residents and councillors considering the site to pose  “an unacceptable risk to the safety of people and property at Waterside Park”. Despite the majority of the site’s infrastructure being buried underground beneath grassed mounds, the perception of risk can become a perceived blight to the local area. 

Figure 5: Redcliffe Bay Petroleum Storage Depot, which supplies the region with aviation-grade kerosene for civil and military use. (Source: Redcliffe Bay Petroleum Storage Depot | DCIM\104MEDIA\DJI_04… | Flickr)

COMAH sites have been under recent scrutiny as it reported that “A leaked internal report has revealed that the Environment Agency has ‘failed’ to fully regulate some of England’s most hazardous sites…”. In an article published by the ENDS Report, claims have been made of significant risks in the delivery of the current COMAH regulatory regime, potentially due to a recruitment crisis within the EA. Meaning it is more important than ever to understand what COMAH sites are located in your neighbourhood. 

You can search online for public information about establishments in your area that are covered by the Control of Major Accident Hazards (COMAH) Regulations 2015. The system provides public information about COMAH establishments to enable people to find out about COMAH establishments in their local area. 

Alternatively, the location of COMAH sites are shown in our commercial environmental reports and for environmental consultants in our Groundsure Insight report.   

Our data covers the location, extent and nature of COMAH sites including the type of installation, upper or lower Tier. We provide the complete view on Contaminated Land Information for your client’s property transaction or Project, including information on permits essential to understanding operational environmental risk. 

For more information on our commercial reports or Groundsure Insight contact us at 01273 257755 or email 


  1. Buncefield response (
  2. – Your authority on UK local government – Buncefield’s explosive £1bn cost to residents
  3. Firms ordered to pay almost £10m over Buncefield blast – BBC News
  4. HSE: Control of Major Accident Hazards (COMAH)
  5. The Control of Major Accident Hazard Regulations (COMAH) – FHM | NFCC CPO
  6. Review of COMAH regulatory enforcement in the chemicals industry
  7. Chemical explosion company Biolab UK fined £66,000 – BBC News
  8. HSE: Control of Major Accident Hazards (COMAH)
  9. Control Of Major Accident Hazards Regulations 2015 (COMAH)
  11. Revealed: scale of ‘forever chemical’ pollution across UK and Europe | PFAS | The Guardian