Pipelines

The Health and Safety Executive is responsible for ensuring that those involved with the transmission, distribution and storage of natural gas comply with the relevant legislation.

A Major Accident Hazard Pipeline is a pipeline that transports a flammable liquid, chemical substance or gas. The Pipelines Safety Regulations 1996 ensure that the design, construction, installation, operation, maintenance, and decommissioning of pipelines is to a very high safety standard.

What should I do if I smell gas?

If you smell gas or suspect a gas leak you should phone National Grid 24-hour emergency number immediately: 

• Call: 0800 111 999

What is the risk of pipelines?

Pipelines are considered one of the safest modes of transport for conveying hazardous substances; the likelihood of an explosion in a natural gas pipeline in the UK is low. However, the loss of containment following a pipeline fracture or accidental release could have disastrous consequences, measures are therefore taken to reduce the risks they pose. The following gives an overview of the emergency response to a pipeline incident, showing how the existing procedures of various organisations would be applied and co-ordinated. It follows the recommended national format for Pipeline Safety Plans.

Pipeline System

The operator for the notified Major Accident Hazard Pipelines in this area is National Grid. The product carried is natural gas. For security reasons the location of these pipelines are not made available to the public.

Hazard and Effect

An incident involving a high pressure gas pipeline will be identified by the following features:

Release of gas 

Significant damage to a Major Accident Hazard Pipeline that results in a pipeline puncture or rupture will lead to a pressurised release of natural gas. All pipelines operating under 75 bar (which is used for the National Transmission System) contain odorised gas. If ignited this may give rise to a thermal radiation hazard to individuals in the vicinity. Ignition can be immediate, delayed local ignition, delayed remote ignition, or no ignition at all. Each may have different consequences, hazard ranges and duration and for this reason time scale and sequence of any incident will vary.

Duration of pipeline leaks 

 When a high-pressure pipeline fails, immediate and rapid de-pressurisation occurs over a matter of seconds, and is followed by relatively stable flow as the pipeline unpacks due to the leak and continued pumping of gas into the pipeline. Flow may last for several hours dependant on the location and topography of the pipeline and the time for National Grid personnel to arrive on site to shut down valves not shut remotely from the National Grid Control Centre.

Blast Effects and Projectiles

The pressure blast at the time of failure can be significant in close proximity to the pipeline, cover material over the pipeline may be thrown into the air at high velocity, but the serious effects will diminish with distance. Delayed ignition in the vicinity of buildings may result in loss of window glass as a result of blast over pressure.

Fire and Explosion

The ignition of any release of gas will cause a flare, which may have serious effects due to thermal radiation. People can be shielded indoors but radiation levels may be sufficient for the buildings to catch fire. Techniques are available for estimating the thermal radiation from an estimated quantity of gas released over time. Any failure of pipelines carries the risk of ignition, but experience has shown that in the majority of cases ignition does not occur.

If a release of gas does not ignite immediately, it will form a cloud, which will disperse over large distances. If a cloud of gas ignites it may burn back as a flash fire to the point of origin. As it disperses it will be diluted with air, the concentration falling below the lower explosive level (LEL) when it will no longer present a fire hazard. The distance over which such a release may disperse depends on the type of release and the prevailing weather conditions. Concentrations and duration may be estimated using plume modelling. It is important that ignited gas is not extinguished unless specifically requested by the TNational Grid on site controller.

Noise

The release of high-pressure gas creates a great deal of noise, which can be very intense leading to temporary hearing damage. High noise levels can also be disorientating and may cause unexpected behaviour in people affected.

What should I do if there is a pipeline accident?

More Information

In an emergency the authorities will broadcast safety information on local radio. Local stations covering Berkshire include: 

• Heart - 102.9 FM and 97.0 FM

• BBC Radio Berkshire - 94.6 FM & 95.4 FM
• Kestrel FM - 107.6 FM
• Kick FM – 105.4 FM & 107.4 FM
• Reading 107 FM
• Time - 106.6 FM