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Salt cavity natural gas storage - Consent and operational issues


This document describes the legal framework and the role HSE has in ensuring safety at salt cavity natural gas storage sites in the UK. HSE's primary role and regulatory responsibilities for ensuring safety are during the design, construction, operation and decommissioning of these sites; and for ensuring appropriate emergency plans are developed. The legal framework and HSE's advisory role in the land use planning system are also described.

The document deals with the arrangements for England and Wales where all of the currently proposed salt cavity storage sites are situated; arrangements for Scotland are comparable but different organisations are involved.

Similar arrangements to those set out below apply to the transport and storage of other dangerous substances.

Salt cavity natural gas storage sites in Great Britain

The use of underground caverns in salt rock formations to store natural gas or other hazardous gases is long established and common around the world. In the UK the practice was first used in 1959 at the Saltholme brine field on Teesside where products such as ethylene, ethane and naptha continue to be stored. The cavities are usually charged and discharged through a single borehole which is designed and constructed to standards similar to those used for offshore oil or gas extraction wells.

The longest established site used for natural gas storage was commissioned in 1979 at Hornsea in East Yorkshire. At the beginning of 2006 there were four operational salt cavity natural gas storage sites in Great Britain: Hornsea, East Yorkshire; Seal Sands, Teesside; Holford, Cheshire; and Hole House, Cheshire.

Land Use Planning and Hazardous Substances Consent

All establishments wishing to hold stocks of certain hazardous substances above a threshold quantity must apply to the Hazardous Substances Authority (HSA) (usually the local planning authority) for hazardous substances consent under the Planning (Hazardous Substances) Regulations 1992[1]. For natural gas the threshold is 15 tonnes. HSE is one of eleven organisations that the HSA must consult as to the advisability or otherwise of locating a major hazard establishment in the location designated.

HSE assesses the risks based on the consent particulars and, in some cases, other plant features which have the potential to significantly affect the risk to people . If HSE does not advise against the HSA granting the consent, it will also recommend whether the consent should be granted subject to any conditions. HSE limits its advice to health and safety issues within its expertise and to those which are covered by the Health and Safety at Work Act; any issues about the scope of planning legislation are a matter for the HSA. There is a large body of planning law, planning circulars and legal precedents that affects what the HSA takes into account.

Where consent is granted, HSE will set a consultation zone around the major hazard site and notify the HSA (and the planning authority if different.) Whenever a development is proposed within the consultation zone HSE is consulted for its advice as to the advisability or otherwise of locating the particular development there.

In England and Wales[2] the HSA makes the decisions on consents applications and the local planning authority decides planning issues. HSE's role is as a consultee to inform the HSA whether there are safety grounds for refusal of consent, or whether any conditions are necessary.

The advice outlined above relates purely to the land use planning process and is not the principal means to achieve safety when the installation starts to operate. That is primarily achieved through the Control of Major Accident Hazards Regulations 1999 (COMAH).

Control of Major Accident Hazards Regulations 1999

The principal legislation covering natural gas storage establishments is the Control of Major Accident Hazards Regulations 1999 (COMAH). Their aim is to prevent major accidents involving dangerous substances and to limit the consequences of any accident to people and the environment. Salt cavity gas storage sites are also subject to the Borehole Sites and Operations Regulations 1995 (BSOR) - see later.

The COMAH regulations are enforced jointly in England and Wales by a Competent Authority (CA) comprising the Health & Safety Executive (HSE) and the Environment Agency (EA)[3]. In the case of gas storage establishments HSE is the lead authority.

An operator who plans to build a new gas storage establishment has to submit information to the CA in a pre-construction safety report (PCSR) before construction starts. Another, similar, report must be sent to the CA before dangerous substances are introduced into the plant - the pre-operational safety report (POSR). The operator has to ensure that the construction and operation of an establishment does not start until he has received from the CA the conclusions of its examination of the relevant report. This does not prevent early preparatory work such as levelling or extending services to the site. However, any work to do with the drilling of boreholes, positioning of processes, storage, pipelines, control rooms or offices which may have a significant impact on safety and would be costly and time-consuming to reverse, must not be started before the competent authority has communicated the conclusions of its examination of the PCSR. Although construction cannot be prohibited, the CA authority will make it clear to an operator if it has identified a deficiency which is sufficiently serious for it to prohibit operation when construction is complete.

The operator is under a duty to take all measures necessary to prevent major accidents and to limit the consequences to people and the environment of any that do occur. The purpose of the PCSR is to ensure that this duty is considered fully at the design stage, and to provide the CA with a comprehensive description of the proposed establishment, its surroundings and any associated hazards. If things need to be improved or altered then it is easier to make those changes at the design stage rather than later on. When the CA assesses a safety report it is looking for a demonstration that adequate safety and reliability have been incorporated into the design, the application of good practice, and for concepts which reduce the risks to being As Low As is Reasonably Practicable (the ALARP Principle). Assessment will be undertaken by inspectors who are experienced in major hazards work, and in the case of downhole safety, by HSE's offshore well engineers.

HSE expects that the European Standard BS EN 1918:1998, in particular Part 3 (Functional recommendations for storage in solution-mined salt cavities ) and Part 5 (Functional recommendations for surface facilities), will be adopted. Operators must, as a minimum, meet recognised good practice and then look at what more can be done to reduce risks ALARP.

The POSR builds on and updates the PCSR to show how any previously outstanding issues have been resolved. It should include elements relating to safety that it would have been unreasonable to expect to be considered in the PCSR. Once the CA has received the POSR, if it considers that there is evidence of serious deficiency in any of the measures to prevent major accidents and to limit the consequences to people and the environment taken or proposed, it will prohibit the operation of those parts of any establishment which it considers are seriously deficient.

As well as assessing the formal safety reports the CA is required to organise an adequate system of inspections while the establishment is operational - this is developed towards the end of the POSR assessment. The inspections must be sufficient to enable planned and systematic examinations of an establishment's systems to ensure that the operator is continuing to carry out his duty.

Regular inspection visits will be made during the construction phase to ensure that the integrity of the plant and equipment is in accordance with the information provided in the PCSR, including adherence to recognised and accepted standards and good practice. Construction activities will be inspected to check that the operator is doing all that is necessary to ensure the health and safety of those at work. The CA will also investigate incidents and accidents that occur on site.

Under COMAH operators of gas storage establishments are also required to produce an on-site emergency plan before the establishment starts to operate and must provide information to the local authority to assist them in their production of an off-site emergency plan. The plan's objectives should cover the full range of possible major incidents and should be designed to contain and control incidents to minimise the effects and to limit damage to persons, the environment and property.

Borehole Sites and Operations Regulations 1995

A place at which an activity or operation is to be undertaken in connection with the extraction of minerals by a borehole is defined as a borehole site and the above regulations apply. As the borehole is initially intended to extract minerals (salt), the Boreholes Safety and Operations Regulations will apply from the beginning of operations on the site and will continue to apply during the life of the establishment until the borehole is abandoned.

Pipelines Safety Regulations 1996

The Pipelines Safety Regulations 1996 (PSR) classify pipelines carrying natural gas at above 8 bar absolute pressure as major accident hazard pipelines. The pipeline operator must ensure that the construction of such a pipeline is not started unless he has notified HSE of its route and design six months beforehand. A further notification is required 14 days before gas is introduced into the pipeline. HSE's specialist pipeline inspectors will assess the pipeline design, and inspect the construction and operation of the pipeline.

Gas and Pipelines Unit
Hazardous Installations Directorate
February 2006

Consent and operational issues summary


Hazardous Substances Consent & Land Use Planning

Pre-construction, pre-operational and operational phases

Intention to create salt cavity gas storage facility

Apply for hazardous substances consent together with sufficient design information for HSE to carry out its statutory risk assessment to advise the Hazardous Substance Authority (HSA). Await grant of consent from HSA. Consultation distance and land-use planning zones determined by HSE and used by the LPA to plan land uses prior to the cavity coming into use. These are based on failure of the well head and above ground installation. Failure of the cavern is addressed in the COMAH assessments.

This marks the start of the project and the operator should submit a pre-construction safety report prior to the commencement of the work.

Safety reports are required to take account of external events such as earthquakes and seismic movement which could lead to a major incident.

Salt cavities

Land-use planning zones may be revisited if the hazardous substance consent is amended, for example if further cavities are proposed or pressures change. HSE will be consulted on any changes and will advise the HSA accordingly. Land-use planning controls remain in force during the lifetime of the cavities whilst filled with the hazardous substance and until the hazardous substance consent is revoked by the HSA.

The safety report should consider the effect of foreseeable hazards such as earthquakes and seismic movement on the salt cavities and any release that may result. However, the assessment is restricted to foreseeable accidental impact - not to terrorist activity. (see below)

The site survey should investigate the geological characteristics of the region in sufficient detail to provide a clear understanding of the physical processes that formed the area, the relationship with other existing and new cavities, as well as the potential for the future seismic activity.

Import / export pipeline

When HSE is notified under The Pipelines Safety Regulations 1996, it advises the local authorities of appropriate land use planning controls along the route of the pipeline on the basis of the information supplied with the notification.

Land use planning controls may be revised if the operator wishes to alter any of the information in the notification.

Under The Pipelines Safety Regulations 1996, the pipeline operator must notify HSE of any new pipeline which is to be constructed to allow the gas from a new establishment to be connected to the national gas transmission system. HSE will assess the pipeline design, and inspect the construction and operation of the pipeline.

Effect on other sites - "Domino effect"

This is not dealt with as part of the consent process but is covered by provisions of the COMAH regulations.

Regulation 16 of the COMAH Regulations requires the Competent Authority to use information provided in notifications and safety reports to designate groups of establishments where the likelihood or consequences of a major accident may be increased because of the location and proximity of dangerous substances at establishments in the group. These are commonly referred to as "domino sites".

The Competent Authority will notify the operators of establishments in such groups of the names and addresses of the other operators in the group who are then obliged to exchange appropriate information about their establishments. The operators must take account of this information in their major accident prevention policy documents, safety reports and emergency plans.

If this regulation applies to a site the operator will be duly notified and advised of the need to take account of potential incidents in neighbouring establishments in the risk assessment for the establishment.

Terrorist activity

The Hazardous Substances Authority is advised by the security services and Home Office on terrorist issues.

The safety reports should consider the risks arising from trespass of an ordinary member of the public. Terrorist issues are a matter for the security services and the Home Office.

Emergency planning

This is not dealt with as part of the consent process but is covered by provisions of the COMAH regulations.

Operators of gas storage sites are required to produce an on-site emergency plan before the establishment starts to operate and must provide information to the local authority to assist them in their production of an off-site emergency plan. The plan's objectives are to contain and control incidents to minimise their effects, and to limit damage to persons, the environment and property.


[1] In addition to applying for hazardous substances consent a separate planning application must also be made to the local planning authority. HSE has no role in such planning applications (unless they fall in the consultation zone of another site) and this document does not address this.

[2] In Scotland the planning authority has the role of the hazardous substance authority

[3] In Scotland the CA comprises HSE and the Scottish Environmental Protection Agency