Carbon monoxide detector

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Carbon Monoxide detector connected to a North American power outlet.

A carbon monoxide detector is a device that detects the presence of the toxic gas carbon monoxide, a colorless and odorless compound produced by incomplete combustion and lethal at high levels. Early designs were basically a white or beige element which would fade to a brownish or blackish color if carbon monoxide were present. As carbon monoxide (CO) related deaths rose during the 1990s, audible alarms became the norm.

Carbon monoxide alarms are sold for home use. If a high level of CO is detected, the device sounds an alarm, giving people in the area a chance to ventilate the area or safely leave the building. CO detectors can be placed near the ceiling or near the floor as CO is very close to the same density as air[1]. It is important to install the detector in accordance with the included instructions.

The alarm points on carbon monoxide detectors are not a simple alarm level as in smoke detectors but are a concentration-time function. At lower concentrations (eg 100 parts per million) the detector will not sound an alarm for many tens of minutes. At 400 parts per million, the alarm will sound within a few minutes. This concentration-time function is intended to mimic the uptake of carbon monoxide in the body while also preventing false alarms due to relatively common sources of carbon monoxide such as cigarettes.

The devices, which retail for $20-$60USD and are widely available, can either be battery-operated or AC powered (with or without a battery backup). Since CO is colorless and odorless (unlike smoke from a fire), detection in a home environment is impossible without such a warning device. Some state and municipal governments, including Ontario, Canada and New York City require installation of CO detectors in new units.

It is important to know that CO detectors do not serve as smoke detectors and vice versa. (However, dual smoke/CO detectors are also sold.) When an alarm sounds, action must be taken immediately. This may include evacuating the premise if experiencing CO poisoning symptoms (confusion, headaches, nausea, dizziness, vomiting, etc), ventilation of the premises, and contacting professionals to inspect CO emitting sources. If you suspect you have suffered CO poisoning, go outside immediately and call the emergency number. At high levels, breathing CO gas is fatal within minutes.

All CO detectors have "test" buttons and, like smoke detectors, should be tested regularly.

1 Biomimetic
2 Electrochemical
3 Semiconductor
4 External links

[edit] Biomimetic

A biomimetic (chem-optical or gel cell) sensor works with a form of synthetic hemoglobin which darkens in the presence of CO, and lightens without it. This can either be seen directly or connected to a light sensor and alarm.

[edit] Electrochemical

A type of fuel cell that instead of being designed to produce power, is designed to produce a current that is precisely related to the amount of the target gas (in this case carbon monoxide) in the atmosphere. Measurement of the current therefore gives a measure of the concentration of carbon monoxide in the atmosphere. Essentially the electrochemical cell consists of a container, 2 electrodes, connection wires and an electrolyte - typically sulphuric acid. Carbon monoxide is oxidised at one electrode to carbon dioxide whilst oxygen is consumed at the other electrode. For carbon monoxide detection, the electrochemical cell has advantages over the other technologies in that it has a highly accurate and linear output to carbon monoxide concentration, requires minimal power as it is operated at room temperature, and has a long lifetime (typically commercial available cells now have lifetimes of 5 years or greater). Until recently, the cost of these cells and concerns about thier long term reliability had limited uptake of this technology in the marketplace although these concerns are now largely overcome.

[edit] Semiconductor

Thin wires of the semiconductor tin dioxide on an insulating ceramic base provide a sensor monitored by an integrated circuit. CO reduces resistance and so allows a greater current which if high enough will lead to the monitor triggering an alarm.