Carbon Monoxide – The Silent Killer
In my very first Common Science blog on chapelboro.com I told you that had perhaps the best high school chemistry teacher ever, Mrs. Ciolkosz. In this week’s blog I am going to share with you something she taught me. But, first this quick review.
Last week in “Your Mother the Plant
” I discussed the process of adsorption which involves the formation of a relatively weak and easily reversible bond between atoms or molecules. I showed you the chemical structure of hemoglobin (see top of the page for a reprise) and directed your attention to the iron atom in the middle. I explained that oxygen is transported through your blood stream by having oxygen adsorb to the iron atom in the hemoglobin. End of short review.
One day while we were learning about hemoglobin and adsorption in chemistry class Mrs. Ciolkosz gave us a pop quiz. It read, “You have just found someone lying on the ground unconscious from carbon monoxide poisoning. You have 15 minutes to save him/her. Go.” You can get a flavor for why Mrs. Ciolkosz was fun from the phrasing of the question as well as from the fact that she gave essay questions in chemistry class.
Carbon monoxide (CO) is toxic to humans and all red-blooded animals because it adsorbs more strongly to the iron atom in hemoglobin than does oxygen. Based on relative adsorption strengths you can calculate the percentage of hemoglobin which would be associated with CO instead of oxygen in various scenarios. When you do these calculations you find that even very small concentrations of CO in the air that you breathe can rapidly monopolize your hemoglobin with dramatic results. Below is a table of the effects of CO on the human body as a function of concentration.
Carbon Monoxide Concentration in parts per million
Effects on the Human Body
Headache in 2-3 hours
Headache in 1-2 hours
Unconscious in 2 hours
Death in 2 hours
Death in 30 minutes
Unconscious in 2-3 breaths. Death in 3 minutes
Based on the table above, the unconscious person in the pop quiz has likely been exposed to an atmosphere containing somewhere between 800 and 10,000 ppm of CO. Below this range he/she would still be conscious. Above this range he/she would likely already be dead. To attempt to save the person you need to move him/her to fresh air immediately. Breathing fresh air allows the CO on the hemoglobin to slowly be replaced with oxygen. If too much of the person’s hemoglobin was already associated with CO before you moved them to the fresh air, this approach will be too slow to save their life. In these more severe cases, you would need to give the person pure oxygen as opposed to air, to speed the process of reoxygenating their blood. (I’m sure we all keep at tank of oxygen on hand just for these occasions.) To get an A on the quiz you had to go through the calculations for several scenarios to demonstrate if you could save the person on not.
You might wonder why human beings evolved with this vulnerability to CO. The answer is that CO poisoning is an artifact of civilization rather than a risk from nature. Most materials that we burn either to generate heat or to power our vehicles are hydrocarbons such as wood, gasoline, kerosene, natural gas or charcoal. If you burn a hydrocarbon at sufficiently high temperature and with an adequate supply of oxygen, you produce almost exclusively carbon dioxide and water, with just at teeny, tiny bit of CO. In order to create a dangerous amount of CO, you need inefficient combustion from either low temperature conditions, like a car engine before it gets warm, or insufficient oxygen, like a propane space heater with a partially-blocked air intake. Furhter you need to compound the problem by carrying out your inefficient combustion in an enclosed space like a garage, RV, or a small cabin or hut. Humans have only recently started to create these types of situations, at least on an evolutionary time scale. If the ancient atmosphere contained any appreciable concentration of CO, organisms like us, which use hemoglobin to transport oxygen, would never have come to be.
If you don’t already have at least one CO detector in your house, please stop reading now and go buy one. CO is colorless and odorless, so without a detector you will have no warning that a problem is brewing. Please note that smoke detectors do not sense CO. Carbon monoxide has the same density as air so it does not matter if the detector is near the floor or near the ceiling. Most detectors are set to alarm if the CO concentration is 100 ppm for 10 minutes or 400 ppm for one minute. You really should never have any appreciable concentration of CO in your house. I would recommend purchasing a detector which displays the CO concentration and putting it where you can see it. If you see it readings even as low as 30 ppm I recommend getting the family and pets out of the house immediately. While CO concentrations this low are not yet dangerous, a reading of even 30 ppm of CO does indicate that some device in your home is malfunctioning and poisoning the air, a circumstance to take very seriously.
Even better than having a CO detector is preventing a problem in the first place. So please consider following these precautions.
- Never idle your car in the garage. (I think most people know this one.)
- If you need a space heater buy an electric one, not one which burns fuel.
- If you must use a fuel-burning appliance inside your house, RV, or boat, try to select natural gas instead of propane. (There is a long, complicated thermodynamic explanation for this one. The short version is that natural gas is mostly methane and it is very difficult to make CO from methane compared to propane.)
OK, that’s the end of your safety lesson and the end of this blog. In case you were wondering, I got an A on the quiz but sadly my unconscious person died.
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