Introduction
Here we describe the legal framework and HSE's role in ensuring safety at Great Britain's salt cavity natural gas storage sites. Depleted hydrocarbon extraction reservoirs are also used for natural gas storage and are treated similarly. HSE's regulatory responsibilities primarily concern the design, construction, operation and decommissioning of these sites as well as the development of appropriate emergency plans.
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. They are usually charged and discharged through a single borehole designed and constructed to standards similar to those used for offshore oil or gas extraction wells.
In Great Britain natural gas is injected into storage in salt cavities from a high pressure pipeline connected to the national transmission system (NTS) and returned to the NTS at a later date, typically at times of high demand. The longest established site used for natural gas storage was commissioned in 1979 at Hornsea in East Yorkshire. Further gas storage sites in East Yorkshire, Teesside and Cheshire have since been brought into operation, and more are planned.
Regulatory framework
HSE regulates safety at salt cavity natural gas storage sites using legislation covering four separate areas:
- land use planning
- control of risks at major hazard establishments
- control of risks from pipelines
- boreholes
Land Use Planning (LUP) and Hazardous Substances Consent
Establishments wishing to hold stocks of certain hazardous substances above a threshold quantity must apply to the Hazardous Substances Authority (usually the local planning authority) for hazardous substances consent. The threshold quantity for natural gas is 15 tonnes.
Further information on Land Use Planning (LUP) – public advice is available.
Control of Major Accident Hazards
The principal health and safety legislation covering natural gas storage establishments is Control of Major Accident Hazards Regulations 2015 (as amended) (COMAH). COMAH creates a framework for the regulation of establishments where there is potential for a major accident to people or to the environment to occur. Operators of COMAH establishments are required to demonstrate that they:
- take all necessary measures to prevent major accidents involving dangerous substances
- limit the consequences to people and the environment of any major accidents which do occur
Where salt cavity gas storage is concerned, 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.
Safety reports are required to take account of external events, which could lead to a major incident. Safety reports should include consideration of the following:
- effects of foreseeable hazards such as earthquakes and seismic movement on the salt cavities and any release that may result
- geological characteristics of the region should be considered in sufficient detail to provide a clear understanding of the physical processes that formed the area, the relationship with other existing and new cavities and the potential for the future seismic activity
- risks arising from trespass by an ordinary member of the public (terrorist issues are a matter for the security services and the Home Office)
Information regarding 'down hole' safety included in COMAH safety reports will be assessed by HSE's Wells Inspectors.
The application of COMAH to the storage of natural gas at depleted reservoir and salt cavity sites.
Further information on the control of major accident hazards is available.
Pipelines safety
The Pipelines Safety Regulations 1996 (PSR) classify pipelines carrying natural gas at above 8 bar absolute pressure (ie high pressure gas pipelines) as major accident hazard pipelines. The pipeline operator must ensure that construction is not started unless he has notified HSE of the pipeline route and design six months beforehand. A further notification is required 14 days before gas is introduced into the pipeline. HSE's Pipeline Inspectors will review the design, and inspect the construction and operation of the pipeline.
Further information on Pipelines health and safety is available.
Borehole safety
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. Since the borehole is initially intended to extract minerals (salt), the Boreholes Safety and Operations Regulations 1995 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.
Further information is available in A guide to the Borehole Sites and Operations Regulations 1995. Guidance on Regulations - L72