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16. Glossary
Term
Definition
Gas detector
Device used to detect the presence of a target gas and to give its
concentration in the form of an electrical signal.
Flameproof enclosure
(explosion-proof
enclosure)
Enclosure in which the parts which can ignite an explosive
atmosphere are placed. This enclosure can withstand the pressure
created during an internal explosion of an explosive mixture, and
prevent the ignition of an explosive atmosphere outside the
enclosure.
Target gas
Specific gas to be detected, concentration displayed, and used to
trigger alarms.
Alarm set value
A gas concentration value that is set on a gas detector for alarm
activation.
Detection range
A range of target gas concentrations that can be displayed and trigger
alarms.
Maintenance and
inspection
Tasks performed to ensure that equipment operates normally and
correctly.
Alarm delay
The length of time a gas detector takes to activate an alarm after it is
exposed to a target gas concentration higher than the alarm set value
or to some other specified conditions.
Calibration gas
( test gas)
Gas specifically prepared to calibrate/adjust the gas detection and
alarm system.
Hazardous area
An area in which an explosive atmosphere is present, or may be
expected to be present, in quantities such as to require special
precautions for the construction, installation and use of electrical
apparatus.
Non-hazardous area
An area in which an explosive atmosphere is not expected to be
present in quantities such as to require special precautions for the
construction, installation and use of electrical apparatus.
Explosive atmosphere
Mixture of air and flammable substances in the form of dust or vapor
which are within their explosive limits.
LEL
(or LFL)
Lower Explosive Limit (or Lower Flammable Level). Lowest
concentration (percentage) of a gas or vapor in air capable of
producing a flash fire, or explosion in the presence of an ignition
source like arc, flame or heat.
%LEL
Concentrations of combustible gas given in terms of percent of the
lower explosion limit.
vol%
Gas concentrations given in terms of percent of cubic volume.
ppm
Gas concentrations given in terms of millionth part of cubic volume.
