Is Carbon Monoxide Heavier Than Air and Other FAQs

1. Is carbon monoxide heavier than air?
2. What constitutes air?
3. Should I test my carbon monoxide detector with car exhaust?
4. Does a carbon monoxide detector replace a smoke detector?
5. Why doesn’t my carbon monoxide detector sound an alarm immediately when there is a lot of CO present?

 

1. Is carbon monoxide heavier than air?

Carbon monoxide has a density that is about 97% that of air under normal room temperature.  So, to answer the question, no, it is lighter than air. You would think, then, that it would rise.  In real-world conditions, there are a lot of forces that cause the CO to mix rather completely into the air.  Therefore, it will neither rise nor fall.  What might be more important is the temperature of the gases it is part of.  Since it is a combustion product, the hot exhaust gases that contain the CO will rise, but are soon mixed into the air you are breathing. If there is a source of CO present, such as a poorly-maintained stove, the CO level will highest close to the source, and decline with distance.

2. What constitutes air?

Air is a mixture of gases, and the concentration of each gas varies from time to time and place to place. The two biggest gasses making up air are nitrogen (77%) and oxygen (21%), and argon comes in at almost 1% (10,000 ppm). All of the other gases are present in very small quantities. Carbon dioxide, which plants need to survive, is present at about 340 ppm. Carbon monoxide, the silent killer, makes up less than one part per million of all the air on the planet. Obviously, if some of these gases are produced locally (think air pollution sources), the concentrations of some gases can be significantly higher, including CO.

3. Should I test my carbon monoxide detector with car exhaust?

In a word – NO! Exhaust from any internal combustion engine is hot and humid, not to mention that it often contains very high levels of carbon monoxide. It can be very harmful to your health to test a device in this way. Further, it could permanently damage your detector and void your warranty. Don’t do it.

4. Does a carbon monoxide detector replace a smoke detector?

No, it does not. A carbon monoxide detector has been built to be very specific for CO gas. It will not detect smoke, methane, or anything else. That being said, it may alert you to a smoldering object before it breaks out into a fire and produces enough smoke for your smoke detector to go off.

5. Why doesn’t my carbon monoxide detector sound an alarm immediately when there is a lot of CO present?

There are two answers to this question.  The first is explained by the reaction time of the internal sensor to the CO gas.  There are different sensor technologies used in CO detectors, and they all react differently when exposed to CO.  In no case should it take more than 2 minutes for a CO detector to report CO after the device has been exposed to the gas.

The second answer to that question has to do with the standards by which the alarm was built.  Most consumer grade CO detectors in North America are products listed by the Underwriters Laboratories (UL) and the Canadian Standards Association (CSA).  These organizations mandate that CO detectors not sound an alarm immediately when CO is detected, which is why there is a delay.  (See the UL/CSA alarm specifications here.)  So, the next time you watch that YouTube video of someone testing a CO detector, the device may be performing exactly as it was intended to.  The lack of immediate alarming was required by the UL and CSA.