For a long time, it has been well known to all
fire technicians that smoke and the spreading of smoke at a fire can
cause major damage.
Smoke content from corrosive gases can cause damage to both the
technical equipment in the building and the building site itself.
For detection of smoke in the ducts, the technique used so far has been that of mounting conventional room smoke detectors in a special
enclosure outside the duct and with probe
into the duct lead a certain part of the air and smoke through the
detector and back into the duct.
The environment in a duct, however, is very
difficult for ordinary room detectors and air pollution and high speed
often give false alarms.
Nowadays, there are smoke detectors that are specially designed for
detecting smoke in the ducts.
The detection part of the detector is placed
inside the duct and can thus detect over the entire surface of the duct.
The detection is made along a line in the duct, an infrared light beam
is emitted from a transmitter to a receiver, and if smoke enters the
duct, the beam is obscured and the alarm is activated.
Today, therefore, unlike previously, there are good opportunities of
detecting smoke in the ventilation ducts with a minimum of false alarms.