General Directives For Explosion Protection; External Explosion Protection; Overview; Pre-Purging Phase - Siemens SIPROCESS GA700 Compact Operating Instructions

Safety instructions

2.5 General directives for explosion protection

2.5 General directives for explosion protection
2.5.1

External explosion protection

2.5.1.1

Overview

The external explosion protection serves to prevent penetration of explosive gas mixtures (gas
damp) into the enclosure or ignition on the surface. For this reason, the analyzer is purged
with protective gas and - with category 2 devices (Ex zone 1) - the control panel additionally
operated via an intrinsically-safe isolating component.
2.5.1.2

Pre-purging phase

The pre-purging phase serves to displace any combustible gases present prior to switching
on the analyzer. During this time (10 min), the enclosure is purged with 5 times its own volume.
2.5.1.3

Operating phase

The operating phase starts after the pre-purging phase. In Ex px or Ex pz mode with continuous
purging modes, the protective gas flows through the enclosure at ≥ 1 l/min. An overpressure
of ≥ 50 Pa compared to atmospheric is built up at the same time.
Either inert gas (e.g. nitrogen) or air must be used as the protective gas depending on the
sample gas composition. Dissipation of the protective gas into the Ex zone is only permissible
with spark protection and a particle barrier.
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Devices in explosion-proof design
Compact Operating Instructions, 05/2015, A5E35134047-02