There are fire detectors
that detect in commercial areas, industrial plants and warehouses, mass
residential areas and home areas. These fire detection systems are connected to
alarms which go off when the smoke content gets too high and in certain
circumstances, some are connected to the local fire department so that the fire
department is dispatched whenever the alarm goes off. Unfortunately there are
some fire detectors systems that go off unintentionally due to high humidity.
Most residential fire alarm systems are disk-shaped plastic objects that are
about 15 centimeters across. They can be photoelectric (optical systems), or
ionization systems. (Some use both of these methods to detect a fire, especially
in commercial areas.)
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The optical sensor fire alarm senses light. It has a light source, which is an
LED or incandescent bulb. There is a space and a photodiode that measures the
amount of light reached to the photodiode. Smoke present during a fire scatters
the light and directs it to the sensor which sends out the signal or alarm. In
very big areas such as auditoriums or gymnasiums, the beam is sent out from one
wall and is picked up by a receiver or is reflected from a mirror on the
opposite wall so that it goes back to a sensor. If the beam cannot be picked up
clearly by the sensor, it sends off an alarm that indicates smoke is in the
auditorium or gymnasium. There is usually a ground floor control panel that
controls the alarm and shuts it off if there is a false alarm
Optical smoke detectors are not as fast as ionization smoke detectors. They have
been found by research to pick up a fire up to thirty seconds after an
ionization smoke detector does. The fire has to be relatively smoky to be picked
up by an optical smoke detector. False alarms are less likely to happen with
optical alarms systems because they can’t easily pick up fumes from someone
cooking or steam from the shower or bath.
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Ionization detectors tend to be cheaper than other detectors. They are more
prone to false alarms because they pick up particles of smoke much easier than
optical alarms. They contain a small amount of a radioactive substance called
Americium 241. The radiation from the Americium 241 passes inside a chamber that
exists between couple of electrodes forming a constant current. If smoke enters
the chamber, it interrupts the current and the alarm is set off.
There is also such a thing as an air sampling fire alarm. This system picks up
small amounts of smoke by drawing air into a pipe or a chamber. Air samples are
taken and if smoke is detected, the alarm goes off. An optical device is a part
of this system and the air sampling technique is highly sensitive to smoke. Such
systems are expensive and are used in high-value areas or in mission-critical
areas, such as computer server rooms or in industry.
DISCLAIMER: The information contained in this article is the opinion of the Author and should not be taken as advice.