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A business whose premises were affected by the Buncefield incident.


Acronym for the legal term 'as low as reasonably practicable'. It requires the weighing up of the level of risk against the costs in the widest sense of averting that risk. Only where the dutyholder can show that the costs of averting the risk are grossly disproportionate to the benefits from further reducing the risk can it be said that the risk has been reduced ALARP.


American Petroleum Institution. It is the American national trade association for the petroleum industry, but it has an increasingly collaborative stance with other bodies such as BSI. API produces a number of guides to standards and recommended practices. Of interest in API Recommended Practice 2350 Overfill protection for storage tanks in petroleum facilities which is currently being reviewed.


Automatic tank gauging system.


Formerly British Standards Institution, now the BSI group, it was founded in 1901 as the Engineering Standards Committee, it is now diversified into making standards, certifying management systems, product testing and other engineering services related to quality.

Catherine House

A building affected by the Buncefield incident.

Civil Contingencies Act (CCA)

The Civil Contingencies Act was set up in order to deliver a single framework for civil protection in the United Kingdom. The act is divided into two parts. The first sets out the roles and responsibilities for those involved in emergency preparation and response at a local level, whilst the second updates the 1920 Emergency Powers Act, taking into account the developments over the years, as well as potential risk factors faced in the 21st century.


The Control of Major Accident Hazards Regulations 1999 Regulations (COMAH).

COMAH sites

Sites to which the COMAH Regulations apply.

Competent Authority

The COMAH Regulations are enforced by a joint Competent Authority comprising HSE and EA in England and Wales, and HSE and the Scottish Environment Protection Agency (SEPA) in Scotland. The Competent Authority operates to a Memorandum of Understanding which sets out arrangements for joint working.

Duty holder

In the context of this report, any person or organisation holding a legal duty - in particular those placed by the HSW Act, the MHSWR, and the COMAH Regulations.


The lowest temperature at which a liquid gives off sufficient vapour to form a flammable mixture.


A business whose premises were affected by the Buncefield incident.

Health and Safety Executive

The Health and Safety Executive is a statutory body, established under the Health and Safety at Work etc Act 1974. It is an enforcing authority. Local authorities are also enforcing authorities under the Health and Safety at Work etc Act 1974.

High integrity systems

Systems that are designed and maintained so that they have a high probability of carrying out their intended function. Safety instrumented systems having safety integrity levels in the range SIL1 to SIL4 are regarded as high integrity systems.

Human factors

HSE has defined human factors (also known as Ergonomics) as the environmental, organisational and job factors, and human and individual characteristics which influence behaviour at work.

Improvement Notice

Improvement notices are one of a range of means which enforcing authorities use to achieve the broad aim of dealing with serious risks, securing compliance with health and safety law and preventing harm. An Improvement Notice Improvement Notice allows time for the recipient to comply.


Independent High Level Switch.

Independent overfill protection system

A system that detects when the liquid in a storage tank has reached a level where continued further filling will result in loss of containment and acts to prevent further filling in time to prevent such loss of containment. Where such systems are automatic they do not rely on any human operator action.


See tier.

Manual emergency switches

Simple and robust push switches that will initiate emergency action such as shutting down pumps or interrupting process operations, and which are located at strategic and accessible locations around the site.


A business whose premises were affected by the Buncefield incident.

On- and off-site emergency plans

Operators of top-tier COMAH sites must prepare adequate emergency plans to deal with the on-site consequences of possible major accidents and to assist with off-site mitigation. Local authorities for areas containing top-tier COMAH sites must prepare adequate emergency plans to deal with the off-site consequences of possible major accidents, based on information supplied by site operators.


For a pressure pulse (or blast wave), the pressure developed above atmospheric pressure is called the overpressure.

Primary containment

The tanks, pipes and vessels that normally hold liquids, and the devices fitted to them to allow them to be safely operated.

Prohibition Notice

Issuing improvement or prohibition notices are some of the range of means which enforcing authorities use to achieve the broad aim of dealing with serious risks, securing compliance with health and safety law and preventing harm. A prohibition notice stops work in order to prevent serious personal injury.

Public information zone (PIZ)

An area around a COMAH site, in which site operators are obliged to inform, without request, those who live and/or work within the zone with information on safety measures at the establishment and on the requisite behaviour in the event of a major accident at the establishment. This is in accordance with regulation 14 of COMAH.

Quantified risk analysis/assessment (QRA)

A systematic analytical technique for quantifying the risks associated with hazardous installations, based on assessing a range of foreseeable failure scenarios. The risk to an individual at a specific location is the summation of the risks arising from the different scenarios.

Reasonable practicability

Risks are deemed as low as reasonably practicable (ALARP) where there is gross disproportion between the costs to the dutyholder of doing more, against the benefit gained (in terms of risk reduction) in doing it.


The likelihood that a hazard will cause a specified harm to someone or something.


A business whose premises were affected by the Buncefield incident.

Safety alert

Where the Competent Authority considers that an issue poses significant risk, it can choose to issue a Safety Alert to operators of COMAH sites informing them of the issue and possibly requiring them to undertake certain activity.

Safety integrity level (SIL)

A safety integrity level (SIL) is a measure of safety system performance, in terms of the probability of failure on demand. There are four discreet integrity levels, SIL 1-4. The higher the SIL level, the higher the associated safety level and the lower the probability that a system will fail to perform properly.

Safety reports

The COMAH Regulations require operators of top-tier sites to submit written safety reports to the Competent Authority.

Servo level gauge

Measures the liquid level in tanks

Seveso II

In 1976, a major accident occurred in Seveso, Italy, where the accidental production and release of a dioxin as an unwanted by-product from a runaway chemical reaction led to widespread contamination. A number of such incidents, and the recognition of the differing standards of controls over industrial activities within the European Community, led the European Commission to propose a Directive on the control of major industrial accident hazards. The Directive on the Major Accident Hazards of Certain Industrial Activities (82/501/EEC) was adopted on 24 June 1982, and is generally known as the Seveso Directive. Following a complete review of the Directive by the European Commission a new one, now known as Seveso II, came into force on 3 February 1997 and was implemented in Great Britain on 1 April 1999 by the Control of Major Accident Hazards Regulations 1999, except for land use planning requirements, which were implemented by changes to planning legislation.

Tank farm

A facility where hazardous substance, very often petroleum products, are stored in tanks.


The COMAH Regulations apply where threshold quantities of dangerous substances identified in the Regulations are kept or used. There are two thresholds, known as 'lower-tier' and 'top tier'. Annex 1 gives a brief background to the origins of these Regulations.


See tier.


The volume in the tanks between the normal maximum operating volume and when the tank is completely full of liquid.

Ultimate high-level switch

Part of the system to prevent overfilling of the tank, the ultimate high-level switch is an independent mechanism which should be triggered when the 'ultimate high level' (i.e. the specified maximum capacity) is reached in a tank to which it is fitted, causing an alarm to sound and should shut down the supply of fuel to the tank.

Wind girder

Structural stiffening ring attached to the tank side wall.

Updated 2017-09-06