Natural Gas Pipeline System
The operator for the notified Major Accident Hazard Pipelines in
this area is Northern Gas Networks (NGN). The product carried is
natural gas.
NGN supply maps showing pipeline routes and data to the
Emergency Planning Team. This information is shared with the Fire
Service. The details recorded include data on bore diameter,
operating pressure and above ground equipment such as valves and
pumping stations.
For security reasons this information is not available to the
public. Local Authority Planning and Emergency Planning sections
can request the Pipeline Major Accident Prevention Document
containing the above information from NGN.
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. 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 NGN personnel to arrive on site to
shut down valves not shut remotely.
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 NGN 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 effected.
Emergency Planning
Distances
- NGN have calculated hazard information related to thermal
radiation. This is supplied to the Fire Service and is also
available to planning departments in local authorities.
Plan Activation
- In view of the extreme nature of a
high-pressure pipeline failure it is likely that initial
notification will be by a member of the public either by 999 call
or to the gas emergency number.
The Emergency Services and NGN will follow their standard
procedures to investigate reports. If at any stage they identify a
requirement for additional resources, a mutual decision is taken to
notify other organisations and undertake wider co-ordination. This
process is the same as that employed in response to other major
incidents.
There is a single national gas emergency number for all
notifications: 0800 111 999.
Ethylene Pipeline
System
The operator for the notified Major Accident Hazard Pipelines in
this area is SABIC UK Petrochemicals. The product carried
is ethylene.
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 ethylene.
Blast Effects and
Projectiles
- Release of very high pressure gas from an underground pipeline
would cause soil and stones to be ejected from the formed
crater. There severe chilling will however freeze any
moisture in the ground and may result in it becoming more
stable. Debris thrown is only likely during the first few
minutes of a release and its range would be small.
Noise
- The release of high-pressure gas creates a great deal of
noise, This would have two effects:-
- The hazard would be self advertising.
- Close to the leak with noise levels very
high, people could become disorientated. Permanent hearing
damage would not be likely.
Plan Activation
- The Emergency Services and SABIC UK will follow
their standard procedures to investigate reports. If at any stage
they identify a requirement for additional resources, a mutual
decision is taken to notify other organisations and undertake wider
co-ordination. This process is the same as that employed in
response to other major incidents.
