External Explosion Protection; Pre-Purging Phase; Operating Phase; Internal Explosion Protection - Siemens 7MB2531 Operating Instructions Manual

Safety instructions
2.2 Analyzers in hazardous areas
2.2.2

External explosion protection

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.
2.2.2.1

Pre-purging phase

The pre-purging phase serves to displace any combustible gases present prior to switching on
the analyzer. During this time (5 min), the enclosure is purged with 5 times its own volume.
2.2.2.2

Operating phase

The pre-purging phase is followed by the operating phase:
• Ex px with leakage compensation; only the volume of protective gas required to hold an
overpressure of at least 50 Pa (recommended 5 hPa) compared to the atmosphere and the
sample gas is added.
• In Ex px or Ex pz mode with continuous purging, the protective gas flows through the
enclosure at ≥ 1 l/min. An overpressure of at least 50 Pa (recommended 5 hPa) compared
to the atmosphere 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.
2.2.3

Internal explosion protection

Internal explosion protection refers to the sample gas path (containment system CS) in the
analyzer and to the ignition protection of the process gas. A differentiation must be made
between the following cases:
• Non-combustible sample gases and gas mixtures below the LEL:
Flame arrestors can be omitted. However, it must be guaranteed that the sample gas in the
CS always remains below the lower explosive limit!
• Occasionally explosive sample gases:
These may only be introduced into the CALOMAT 6F/CALOMAT 62F and OXYMAT 6F gas
analyzers if the inlets and outlets for sample gas and reference gas have each been provided
with a flame arrestor. The flame arrestors must meet the safety requirements for the
combustible medium.
The following applies to the reference gas path of the OXYMAT 6F:
A flame arrestor can be omitted at the reference gas inlet if it is guaranteed that the
reference gas is introduced before the analyzer is switched on and that the reference gas
pressure is monitored continuously.
The ULTRAMAT 6F analyzer may also be operated without flame arrestors.
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Compact Operating Instructions in accordance with EN 61010-1 and EN 60079-0
Compact Operating Instructions, 09/2018, A5E45779389002-01