Carbon Monoxide
Carbon Monoxide is a toxic gas produced by fires and
isresponsible for a high proportion of fire fatalities.
Carbon Monoxide is odourless, colourless and
tasteless making it almost impossible for people to be aware of its
presence.
Exposure to relatively low levels of Carbon
Monoxide for just one or two minutes can lead to permanent brain
damage or death. Lower levels of Carbon Monoxide can cause
disorientation and collapse during physical exertion thus hampering
the ability of victims to escape.
For many years it has been known that Carbon
Monoxide can be used as a means of providing early warning of
fire, especially in slow developing and smouldering fires where
Carbon Monoxide is produced significantly before before
traditional detectable smoke (aerosols and particulates).
In these situations, using Carbon Monoxide
fire detectors, detection occurs significantly earlier than
ion-chamber or photo-electric smoke detectors operate.
Because Carbon Monoxide is a gas and more
mobile than smoke, detector positioning relative to the seat of
a fire is less critical, giving a higher likelihood of early
detection.
Slow Smouldering Fires
A disproportionate number of fatalities are caused by fires that
start slowly.
Fires, typically the result of discarded
cigarettes account for only around 18% of all fires, but more than
42% of all deaths, mainly due to inhalation of poisonous gas.
By detecting these fires early the
Carbon Monoxide fire detector ensures evacuation takes place before
the effect of the poisonous gases take their toll and before the
means of escape is blocked.
Typical applications include:
-
Hotels and apartment blocks
-
Hospitals and Rest Homes
-
Cruise liners
-
Schools, colleges and Universities
-
Office blocks and Shopping precincts
Flexible Detector Positioning
Smoke movement is constrained by convection currents created by the
fire, whereas Carbon Monoxide being a gas is much more mobile
than smoke and also moves by diffusion.
The advantage of the Carbon Monoxide fire
detector is that it allows a high tolerance on where the
detectors can be located.
Typical applications:
-
CO detectors will detect fire from
outside the closed door of a cupboard, bedroom or cabin before
spreading outside the room.
This helps to detect fires whilst the means of escape is still
clear.
-
CO detectors will continue to detect
even if incorrectly mounted on a wall or under floor.
-
CO detectors will operate where
thermal barriers inhibit smokemovement such as hot roof spaces
in atria and metal roofed buildings. CO detectors will operate
on beamed ceilings which present obstructions to possible smoke
flow.
Flexible Detector Coverage:
Carbon Monoxide fills a space evenly and the CO fire detector is far
less sensitive to the point where the fire started.
Thus, CO Detectors spaced in the same way as
conventional detectors would provide far better protection and early
warning in large areas where the potential seat of any fire is
difficult to predict.
Applications include:
-
Warehouses and large covered areas
-
Large foyers, halls and reception
areas
-
Cinemas, theatres, concert halls
-
Sports halls and large waiting areas
False Alarm Immunity
A key advantage of the CO fire detector is its resistance to the
false alarms that affect smoke detectors because smoke detector
false alarm sources do not generate CO.
Careful design of the detector thresholds
means that false alarm sources which do contain CO are below the
predefined threshold levels. If the CO levels from false alarm
sources rise above this threshold it should be a cause for concern.
Typical applications include:
-
Hotel rooms and changing rooms where
steam and water mistcan cause problems
-
Manufacturing facilities where large
quantities of dust areproduced
-
Production facilities where chemical
vapours cause traditional detectors to false alarm
-
Kitchens and restaurants where burnt
toast and similar causes of false alarm are prevalent. In these
circumstances the alarm threshold will only be reached once the
toast is actually burning.
-
Farm buildings with high levels of
dust and other airborne materials
Resistance to Dust and Dirt
The Carbon Monoxide fire detector FCO is less prone to reduced
performance due to becoming dirty by the ingress of dust and dirt.
Even if the detection element becomes very
dirty, the fact that CO is a gas means that it can penetrate dirt,
provided that dirt has not produced an impervious coating.
Unsuitable Applications
Some fires generate little or no Carbon Monoxide and as such are not
suitable for protection using the Carbon Monoxide fire detector.
Such fires include the early stages of
electrical fires and burning cable where aspirating systems are more
suitable.
Other non-carbon fires such as pure metal
fires would not be detected by CO fire detectors.
CO fire detectors are also unsuitable for
protection of areas where fast burning chemical fires represent the
main hazard.
In this case ion-chamber or flame detectors
are more suitable.
CO fire detectors will only operate in
situations where combustion takes place, it will not detect
smoke and fumes alone.
Designing Systems
Most detector fire tests which currently exist, such as those
defined in EN54:Pt9 are intended for ionisation and optical
detectors.
Thus, it is not possible to test CO fire
detectors against existing standards around the world.
Nevertheless extensive tests with real fires
show that the CO detector can detect most types of fires.
The nature of CO means that in principle less
CO detectors may be needed to cover an area than traditional
ionisation and optical detectors, however, fire detection systems
using only CO detectors should be designed with the same coverage as
traditional detectors.
When a certified fire alarm system is needed
CO detectors should be regarded as additional detectors and be
placed in high risk spaces according to above.
