Gas supply emergencies

The Health & Safety Executive’s (HSE) role in gas supply emergencies

Introduction

• If the forthcoming winter is severe there is a risk that gas demand will exceed the gas supply available from Britain’s offshore fields, the interconnector pipeline with Belgium and the Isle of Grain LNG import terminal.   Ofgem has made clear its concerns and monitors the market closely to ensure that anti-competitive behavior is not restricting gas supplies.  A shortage of gas, if not managed properly, could give rise to a risk of a gas supply emergency and this document summarises HSE’s role in this regard.

What is a gas supply emergency?

• A gas supply emergency arises when the pressure of the gas in the pipeline network is reduced, thus causing a danger to the public.^[1]
• Gas has to be transported at an adequate pressure to ensure that gas appliances work safely. If the pressure in the network is too low then appliances may not burn the gas properly resulting in incomplete combustion and noxious fumes.  Alternatively, if the appliance does not have an effective protective device, flames may go out only for the gas to be re-ignited when pressure is restored resulting in a fire or explosion.
• HSE does not have responsibility for the security of gas supplies or the wider social and economic consequences of a shortage of gas. Ofgem’s web-site contains more information on security of supply issues and the winter outlook.

How can shortages of gas result in a gas supply emergency?

• For the pressure in the network to be maintained there has to be a balance between gas supply and demand. Simply, gas taken from the network by consumers has to be replaced by gas flowing into the network from producers, gas processing facilities, storage facilities, interconnector pipelines and LNG import facilities.
• In a severe winter gas demand goes up as households use more gas for heating and other consumers (such as power stations) increase their demand on the network. This demand has to be met but is reliant on gas being available at the right place and time. If there is not enough gas available, demand has to be cut to maintain the safe pressure in the network.

Who is responsible for managing the safety of the gas networks?

• There are several participants in the gas industry. Gas conveyors (also known as transporters) operate the gas network and transport gas through pipes to consumers. The network in the UK consists of over 280,000 km of transmission and distribution pipes transporting gas to some 20 million consumers. Currently there are five major gas conveyors: National Grid who operate the high pressure transmission system and four distribution networks, and four other companies each operating a distribution network. There are a number of smaller gas conveyors who operate networks downstream of these major distribution networks. Each network operator is responsible for ensuring safe pressure in their network and for co-operating where necessary to ensure the safety of other networks.
• The Network Emergency Co-ordinator [NEC] is responsible for coordinating the actions of all gas conveyors to minimise the risk of a gas supply emergency. Currently National Grid is the NEC. The gas networks have to co-operate with the NEC as necessary.
• Gas shippers buy gas from producers to sell to suppliers. They also employ gas transporters to transport gas to supplier’s consumers.
• Suppliers buy gas from shippers to sell to consumers.
• Consumers purchase gas from gas suppliers. Consumers include large industrial sites, gas fired power stations, smaller industrial and commercial sites, hospitals and domestic premises.
• Gas conveyors and the NEC have the prime responsibility for ensuring safe pressure in the networks. They describe their arrangements for doing this through their GSMR safety cases.

Gas Safety (Management) Regulations 1996 [GSMR]

• Under GSMR, each gas conveyor and the NEC has to have a safety case which describes how they manage the safety of the gas networks. How they minimise the risk of a gas supply emergency is a key part of the safety case. The safety cases have to be accepted by HSE before gas can be conveyed in the network. Gas conveyors and the NEC have a legal duty to comply with their safety cases and HSE inspects the conveyors to verify that the arrangements in the safety case are in place and working correctly.  HSE also oversees industry emergency exercises aimed at testing arrangements for dealing with a potential or actual supply emergency.
• Gas conveyors and the NEC rely on other industry participants to enable them to run the networks safely. Therefore GSMR requires gas producers, processing facilities, storage site operators, shippers, suppliers and others, including consumers, to co-operate with them as is necessary, to minimise the risk of a supply emergency. For example, if demand has to be cut to maintain the pressure in the network because there is a shortage of gas, the gas conveyors may instruct gas consumers to stop using gas. There is a hierarchy in which this is carried out so that sites like hospitals and domestic consumers have gas as long as possible.
• Safely isolating certain consumers whilst maintaining safe pressure in the rest of the network is not a supply emergency and forms a key part of the safety case.

Gas in storage

• There are a number of gas storage sites in the UK used by gas shippers and others to store gas. Gas in storage plays an important role in minimising the risk of a gas supply emergency throughout the winter period. Under arrangements in the gas conveyors’ and NEC’ safety cases, a minimum quantity of gas is retained in storage to meet domestic demand, demand from priority consumers and demand from other consumers who are difficult to isolate safely from the network, such as ‘embedded’ industrial and commercial sites. Where necessary, gas is taken from storage to minimise the risk of a supply emergency to these consumers.
• However, there is not enough storage capacity to meet all demand and some consumers, such as large industrial sites, may need to be isolated in a safe and timely manner. Therefore it may be necessary for gas conveyors to direct large industrial sites to stop using gas both to protect them and ensure the safety of the rest of the network.

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[1] The Gas Safety (Management) Regulations 1996 [GSMR] define a gas supply emergency being an ‘emergency endangering persons and arising from the loss of pressure in a network…..’ . The definition of danger is limited to risks from the gas itself.