Page 25 - igem-g-4 edition 2

IGEM/G/4 Edition 2
ignition period
Period during which a start-gas flame safety shut-off valve (SSOV) is permitted to be open
before a check is made for the presence of the start-gas flame.

impact moling
Use of a tool which comprises a percussive hammer within a suitable casing, generally torpedo
shaped.

impressed current
System of corrosion protection, using an external electrical source.

indirect purge
Displacement of fuel gas by inert gas/fluid followed by displacement by air, or vice versa.

individual risk
Frequency at which an individual may be expected to sustain a given level of harm from the
realisation of specified hazards, and in the case of pipelines, the frequency at which an
individual at a specified distance from the pipeline is calculated to become a casualty at a
specified level of harm from the realisation of specific hazards

individual risk criteria
Criteria relating to the likelihood with which an individual may be expected to sustain a given
level of harm from the realisation of specified hazards.

individual stresses
Stresses along one axis in pipe/components induced by forces, bending moments and internal
pressure.

induced draught burner
Burner into which the combustion air is introduced by providing a suction in the combustion
chamber by mechanical means, usually an induced draught fan.

inert gas
Any gas or mixture of gases which will neither burn nor support combustion.

initial defect size
Maximum size of defect (or the distribution of actual sizes of defects) which could be left in an
installation following a commissioning hydrostatic test.

initiator
Person who identifies the need for new work, modification or repair.

injector
air blast: Device in which gas is entrained by the action of a jet of air to produce a
gas/air mixture.

atmospheric: Device in which air is entrained by the action of a jet of gas to produce a
gas/air mixture.

inlet isolation valve (IIV)
Valve, normally not being an emergency control valve (ECV) and never installed downstream
of an ECV, to enable isolation of gas to all parts of a building, by an authorised party which
(usually) is not the consumer.

inner lift (first lift or top lift)
Inside lift of a watersealed gasholder, having the smallest diameter, and carrying the crown.

21
©IGEM, IGEM House, High Street, Kegworth, Derbyshire, DE74 2DA. Website: www.igem.org.uk