Planning
48
Building Technologies A6V10209291_f_en_--
Fire Safety & Security Products 05.02.2010
4.2.1 Ambient features
In selecting the optimum parameter set for CO, the following factors must be taken
into account:
Positioning the FDOOTC241
CO gas is slightly less dense than air and spreads evenly through the room when
at a constant temperature.
However if CO is produced in a fire, it is warmer than the surrounding air and rises
towards the ceiling with the smoke. If the FDOOTC241 is used as a fire detector for
this scenario, the positioning rules which apply to fire detectors also apply to the
FDOOTC241.
If the FDOOTC241 is used for the 'Technical CO Alarm' and if the CO gas comes
from cold sources, e.g. gas canisters in the lab, then the FDOOTC241 can be
installed on the wall at around head height rather than on the ceiling. The
positioning rules for gas detectors must be consulted for more details.
Influence of the surroundings
At temperatures in excess of +55 °C (outside the device specification!), the CO
sensor ages faster than expected and the guaranteed 5-year service life for the
FDOOTC241 is reduced.
If the rooms requiring protection constantly have concentrations of ethanol of up to
500 ppm (= MAK value for ethanol), e.g. in breweries or whisky distilleries, since
the electro-chemical cells have slight cross-sensitivity to ethanol, the 'Technical CO
Alarm' is more likely to experience false alarms.
In a very dry and very hot climate, the response time of the CO sensor increases to
around 120 s. The response of the FDOOTC241 to relatively slow increases in the
CO concentration, e.g. in the event of fires, is not therefore affected. But very quick
increases in the CO concentration are detected with a slight delay.
The CO sensor responds faster in very humid air than air of normal humidity. There
are no limits here on use as a fire detector or for the 'Technical CO Alarm'.
The electro-chemical CO sensor of the FDOOTC241 has a slight cross-sensitivity
to hydrogen (H
2
), i.e. H
2
also causes CO signals. As H
2
can be produced when
charging lead batteries and in electroplating plants, robust parameter sets which
only cause an alarm when increased CO concentrations are detected should be
used in such environments.
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