Seattle Home Inspector's Blog


The dark side of Carbon Monoxide Detectors

Carbon Monoxide detectors have been in the news a lot lately and with good reason.  Given that the gas is colorless, odorless and can kill you while you sleep are all good enough reasons for me to pay attention. The building codes themselves require them, and in addition, many states have made laws requiring them.

There is a dark side to CO detectors that is not discussed very much however, and I have blogged about this issue with Carbon Monoxide Detectors in the past. 

This missing information can leave the consumer with a false sense of security. 

Most of the CO detectors required by state laws and the building codes are quite good at detecting Carbon Monoxide in relatively acute doses.  Acute doses are large levels of exposure over relatively short time periods.  They are not very good at detecting Carbon Monoxide at chronic levels—low levels of exposure over longer periods of time.

In fact, the CO detectors required in your home are NOT ALLOWED to signal a problem at levels below 30ppm in order for them to obtain the UL listing necessary to meet the codes (UL 2034).  It is interesting to note that most of these alarms are designed to sound at or below 70ppm within 60 to 240 minutes (I do not think that this information should make anyone feel protected). 

There is a stream of emerging data (see HUD: Healthy Homes Issues: Carbon Monoxide) that there are health risks associated with low levels of CO exposure—levels below what is considered safe by the EPA.  According to the EPA levels of CO below 9 ppm over an 8 hour period, or 35ppm for one hour are considered “safe.”  Research is beginning to show that the elderly, the very young, the unborn and some other individuals experience negative physical, cognitive and emotional effects with exposures below these levels.

There is technology available for detecting low levels of  CO.  These devices do not meet UL 2034 and therefore cannot be “substituted” for the poorer performing listed devices but must instead be used as supplements to the required detectors.

One such device is the “Defender” CO detector.  It is capable of detecting levels as low as 5 ppm for less than a minute.  It has a wide range of sensitivities with different alarms and visual read-outs to display different levels of concern.  These seem like a prudent device for any home. These devices also attempt to deal with the issue of when they have reached the end of their expected life.  They come with a sealed in place battery so when the battery is dead you simply replace the whole device.  I wonder how many regular detectors will continue to give their false sense of security long after the batteries are dead or when batteries are replaced when the units are well past their expected life.

Also keep in mind that there is no substitute for regular servicing of all combustion appliances in the home.  Proper servicing is an essential part of any CO mitigation/detection system installed in the home.


Charles Buell, Real Estate Inspections in Seattle

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Comment balloon 54 commentsCharles Buell • October 27 2013 01:50PM
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