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Control of Major Accident Hazards Regulations 1999 (as amended)

Their main aim of COMAH is to prevent and mitigate the effects of those major accidents involving dangerous substances, such as chlorine, liquefied petroleum gas, explosives and arsenic pentoxide which can cause serious damage/harm to people and/or the environment. The COMAH Regulations treat risks to the environment as seriously as those to people.


Major hazard sites are industrial sites that manufacture, process or store dangerous chemicals and substances in quantities that could pose a risk to workers, people in the vicinity of the site, and the environment in the event of a major accident. These ‘major accidents’ include fires, explosions or incidents in which dangerous substances are released. Major accidents are rare, but can occur at sites ranging from large petrochemical plants to chemical storage warehouses.

Under the Control of Major Accident Hazards Regulations 1999, as amended (COMAH), operators of sites with dangerous substances above specified quantities have to take all necessary measures to:

  • Prevent major accidents
  • In the event of such accidents, limit the effects on people and the environment.
  • For certain sites, with particularly high quantities of dangerous substances, operators must also describe their control measures to prevent major accidents in a ‘safety report’.

The COMAH Regulations are enforced by a Competent Authority (CA). In England and Wales the CA comprises the Health and Safety Executive (HSE) and the Environment Agency, and in Scotland, the HSE and the Scottish Environment Protection Agency (SEPA). The CA is responsible for checking that site operators take steps to prevent and limit the effects of major accidents.

What is a safety report?

A safety report is a document written by the site operator and sent to the CA to demonstrate that all the necessary measures have been taken to prevent major accidents and to limit their consequences to people and the environment.

To write a safety report, operators have to look systematically and carefully at how they manufacture, store and use dangerous substances. This helps them to identify any necessary improvements to their management systems, plant, equipment or safety procedures and so reduce the risk of a major accident occurring.

Operators of existing sites have already submitted their safety reports. Operators of new sites need to prepare a report before they build and operate the plant.

Operators must also review the safety report at least every five years, and also when any changes occur that could have a significant effect on the safety of the site. The operator must tell the CA of any changes made to the safety report from these reviews.

What does a safety report contain?>

The legal duty for operating the site safely rests with the site operator. They have to control the risks that site operations could cause to people who live and work nearby, as well as to site workers and to the environment.

The CA will assess whether the safety report has provided sufficient evidence that the site operator is doing this. The safety report must include:

  • A policy on how to prevent major accidents.
  • A management system for implementing that policy.
  • A description of possible major accidents, how likely these are and their potential consequences.
  • Measures (such as safe plant and safe operating procedures) to properly prevent major accidents.
  • Information on the safety precautions built into plant and equipment when it was designed and constructed.
  • Details of measures (such as fire-fighting, relief systems and filters) to limit the consequences of any major accident that may occur.
  • Information about the emergency plan for the site, which is also used by the local authority in drawing up an off-site emergency plan.

Want to know more?

More information about COMAH and how safety reports are assessed can be found on the HSE’s web site at www.hse.gov.uk/comah/

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