Planning
Technical CO alarm
4
68 | 108
Building Technologies
A6V10305793_m_en_--
Fire Safety
2016-02-15
4.3.2 Ambient features
In selecting the optimum parameter set for CO, the following factors must be taken
into account:
Positioning the point detector
CO is slightly less dense than air and spreads evenly though 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 point detector is used as a fire detector
for this situation, the same positioning rules apply to it as for a fire detector.
If the point detector is used for the 'Technical CO Alarm' and CO is produced from
cold sources, the point detector must be installed in the ceiling too. Cold sources
include e.g. gas cylinders in a laboratory. The positioning rules for gas detectors
must be consulted for more details.
Influence of the surroundings
At temperatures in excess of +50 °C (outside the device specification!), the CO
sensor ages faster than expected and the guaranteed 5-year service life for the
point detector 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 point detector 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 humid air than in dry air. There are no limits here
on use as a fire detector or for the 'Technical CO Alarm'.
The electro-chemical CO sensor of the point detector 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.
