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Sunday, January 14, 2001

More Info About Carbon Monoxide Detection!


How the First Carbon Monoxide Detectors Worked
Originally, carbon monoxide detectors were simple opto-chemical detectors that indicated the presence of carbon monoxide by exhibiting a color change when carbon monoxide reacted with a chemical on a white pad, producing a brownish or black color. These detectors do not require an external power source to function, but modern designs use audible alarms to confer a higher level of protection:

Biomimetic Carbon Monoxide Sensors
An opto-chemical or gel sensor interacts with synthetic hemoglobin, darkening in color when carbon monoxide is present and lightening in color when carbon monoxide concentrations are low. A light sensor may be used to detect the change in light levels to sound an alarm.

Semiconductor Carbon Monoxide Detectors
An integrated circuit monitors a sensor, tripping the alarm when concentrations of carbon monoxide are high. The sensor is made from thin wires of semiconducting tin dioxide that rest on an insulating ceramic base. Increasing carbon monoxide concentration reduces the electrical resistance of the sensor, causing the alarm to sound.

Electrochemical Carbon Monoxide Detectors
This is 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 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 sulfuric acid. Carbon monoxide is oxidized at one electrode to carbon dioxide while oxygen is consumed at the other electrode. For carbon monoxide detection, the electrochemical cell has advantages over 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 their long-term reliability had limited uptake of this technology in the marketplace, although these concerns are now largely overcome. This technology is now the dominant technology in USA.

Combo detectors can sense both smoke and CO
Combination smoke/CO detectors are appealing for a couple of reasons; first, you only need to worry about changing batteries in a single unit, and second, combining units makes for less clutter. However, there are some drawbacks. There are two types of smoke detectors -- photoelectric, which are better at detecting smoldering fires, and ionization sensors, which are better at sensing high-flaming fires. We cover both types in our report on smoke detectors; in that report, the very best models are those that contain both types of sensors. The problem with combo CO/smoke detectors is that you only get one of the two types of smoke sensors, not both. So, if you want the best protection, you'd still need to install an additional smoke detector.

An example of this type is the battery-powered Kidde KN-COSM-B, which combines a CO detector with an ionization smoke sensor. Consumers applaud its voice warning system that announces a fire, carbon monoxide or a low battery -- a nice feature when the alarm wakes you during the night so you know exactly what the alarm is for. Visual cues include a green LED for normal operation and a flashing red LED when the alarm goes off. The lack of a digital display showing carbon monoxide levels is the main drawback. The warranty period is five years and the CO sensor lasts for about seven years.

Most carbon monoxide detectors only have an effective lifespan of about 2-5 years, so even those that indicate that the battery is good and the alarm works may be ineffective at detecting carbon monoxide. If no one remembers how long the carbon monoxide detector has been installed, or if it came with the coach, it's a good idea to check it for an expiration date or ask the previous owner how old it is. When in doubt, replace it!

Best Features to Look For in Carbon Monoxide Detectors

There are many kinds of carbon monoxide detectors to choose from, and the options can seem a little daunting. However, it is best to choose a carbon monoxide detector that:

  • Is UL-listed (check for the familiar Underwriters Laboratory seal - and read more carbon monoxide safety tips at the UL website).
  • Has a long-term warranty.
  • Is easily installed and tested.
  • Has a display screen showing the PPM (parts per million) of carbon monoxide. Cheaper carbon monoxide detectors don't have a display and may not keep a record of carbon monoxide buildup, but knowing when carbon monoxide buildup occurs can be useful for figuring out why it occurs.
  • Has an "end-of-life" alarm that chirps when the detector needs replacing.

There are many different manufacturers who produce carbon monoxide detectors, but Kidde and First Alert make the some of the best-known and best-reviewed models. Atwood, a familiar name among RVers everywhere, makes a combination CO and smoke detector. 

The Atwood Combination CO/Smoke Detector

Fuel Cell Technology
The new electrochemical sensor contains a proton conducting membrane that generates a current in the presence of Carbon Monoxide (CO). This current is measured; information is processed and then displayed on the Alarm. The sensor is more accurate, uses less current and is less sensitive to humidity and other gases than competitive models. This technology was developed and patented by Atwood Mobile Products.

Battery Operated
The Atwood CO Gas Alarm uses three AA batteries. The easy opening cover gives fast access to the batteries.

Safety Feature
The Atwood CO Gas Alarm cover is designed with a safety feature that makes it difficult to close the cover without batteries in the unit. This helps to prevent the alarm from being mounted without power.

Multiple Location
A picture frame leg allows you to use the CO Gas Alarm at multiple locations. Ideal for locating the CO source or for additional security when sleeping in another room. 



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