Product description
4.5.1
Zone division
Inside the measuring gas pipes and inside the gas analysis system there are only very small amounts of
gas, whose volume is far below hazardous amounts. Therefore no Ex-zone obtains in this case. Whether
there is an Ex-zone around the gas analysis system or its pipes or not depends on the probability of
the occurrence of an explosive gas mixture. The following describes the actions to be taken to avoid an
explosive atmosphere, which could arise due to the gas analysis system. If the following instructions are
taken into account, there will be no Ex-zone inside the gas analysis system or the feed pipes either.
4.5.2
Flame or explosion propagation over gas bearing lines
With gases belonging to explosion group IIA (methane, biogas), tube and pipe connections with an internal
diameter of 4mm have the same effect as a deflagration arrester (tested length of 11cm). As the distance
from the hose to the relevant ignition sources (sensors) is always less than 50 times the hose diameter,
there is no need for separate deflagration arresters between the analysis device and gas-bearing lines with
larger cross-section and hazardous atmosphere with the explosion group IIA and up to zone 1. There is an
inspection report of an approved ATEX test centre verifying this.
When measuring hydrogen at higher concentrations
1
(special device); or with zone 0, a detonation arrester
must be installed as needed.
4.5.3
Leakage in the Measuring Gas Supply Line
A technically permanently leak-tight pipe is used. This is achieved by using a durable plastic tube or
stainless-steel pipe and corrosion resistant screw connections with resistant sealing. Components like
condensate traps that might be included in the measuring gas pipe also have screw connections. The
pipes are technically permanently leak tight up to the first valve, which can be used to shut off the pipe.
4.5.4
Gas volume
The pipes (< 5m) and sensors inside the gas analysis system contain less than 0.05 l of gas. No risk of
explosion results from this.
4.5.5
Leaks in the Gas Analysis System
Despite the slow reaction of methane with oxygen compared to other gases(55 bar*m/s compared to 550
or 1.415 bar*m/s with hydrogen and acetylene) at a similar maximum pressure (7.1 bar under normal
conditions), the danger for persons at a control box volume of 60 l cannot be completely eliminated if only
due to a deflagration, in the event that an explosive mixture would form inside due to a potentially occurring
tightness error and a subsequent ignition due to unfavourable conditions or an escape of the gas from the
gas analysis system.
1
Biogas with up to 10% hydrogen in the flammable gas portion remains in explosion group IIA (source: BG ETEM/
BAM research project Hydrogen Mixtures).
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