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Hazardous Area Operation
Purge Operation
Operation
Purge Overview
A-8
Prima PRO & Sentinel PRO Mass Spectrometers User Guide
In Europe, the ATEX directive encompasses non-electrical (as well
as electrical) ignition sources and this must be considered when
using pneumatic or other non-electrical apparatus in hazardous areas.
Purge
The general principles of operation of a purge protected system have
been outlined above. This section details how purge protection
relates to the Prima PRO Ex and Sentinel PRO Ex systems.
The enclosure is pressurised / purged with compressed air. For
obvious reasons, the compressed air must be from a non-hazardous
area source and free from contaminants such as oil and water.
Typically, instrument grade air is used.
Danger of Asphyxiation!
The standard instrument consists of a single enclosure, and purge air
flows into the top of this main enclosure. A purge monitor unit
located at the bottom left of the main enclosure allows the air to exit
while also maintaining a back pressure in the enclosure.
A continuous dilution and pressurisation (CDP) purge flow is
required to dilute any internal sample leakage and maintain the
internal enclosure pressure. The required flow has been determined
(see below). As noted previously, an initial enclosure purge is
required to remove any possible residual hazardous gas before power
is switched on.
The features of, and differences among, the three purge controller
types used are outlined in the following table.
An inert gas such as nitrogen should not be used for the purge
system.
There is no facility to duct away vented purge gas so the
asphyxiation hazard is considerable if operated in a confined
or poorly ventilated position.
Thermo Fisher Scientific
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