Page 33 - igem-g-4 edition 2

IGEM/G/4 Edition 2
non-hazardous area
Area in which an explosive gas/air mixtures is not expected to be present in quantities such as
to require precautions for the construction, installation and use of apparatus.

non-return valve (NRV)
Valve which prevents the reversal of gas or air flow, constructed to meet agreed performance
standards.

non-routine operation procedure
Formal written document used to control complex operations.

normal (operating) conditions
Conditions when no fault exists on any device or stream.

normal operation
Situation when equipment is operating within its design parameters.

normal start-up rate
Gas flow rate at which the main burner is normally ignited.

Ofgem approved meter installer (OAMI)
Ofgem registered gas meter fitters with a specific meter installation qualification.

oil filming, relating to watersealed gas holders
Oil pumped inside in an attempt to prevent gas contents from becoming wet because of
evaporation of the tank water.

one call system
One telephone number for all Utilities.

open at rest regulator
Design of regulator in which the internal flow control element(s) is designed to be in the open
position when all control and sensing connections are removed.

open cut
Method by which access is gained by excavation from ground level to the required level
underground for the installation, maintenance or inspection of a pipe, conduit or cable.

open flue appliance
Appliance designed to be connected to an open flue system.

open flue system
System that evacuates the products of combustion to the outside air and where combustion
air is drawn directly from the room or space containing the appliance, without the use of
mechanical fans or ejectors.

operating levels
Set points of all control devices under operating conditions.

operating margins, relating to transmission system design
Volume of gas required to meet unforeseen circumstances such as:
 the demand forecast, prior to any day, is correct and the supplies set too low, for some
time before the error is discovered. Subsequent within-day forecasts may also be incorrect
 failure of plant to operate
 supply failure.

operating pressure (OP)
Pressure at which a gas system operates under normal operating conditions.

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