Is carbon dioxide harmful in concentrations higher than the 0.033% normally found in the air? That is, what problems, if any, would a human experience in breathing air with a greater percentage of carbon dioxide, assuming the percentage of oxygen remained constant? (Say the CO[sub]2[/sub] is replacing a portion of the air’s argon or nitrogen, not the oxygen.)
Carbon dioxide is not, strictly speaking, poisonous; that is, it is not a toxic substance which is absorbed into the body and interferes with bodily functioning.
It is, however, asphyxiating, for the obvious reason that inhaling it instead of air with about 21% oxygen fails to give you sufficient oxygen to breathe. And since it is the “output” part of the respiratory cycle, more than a certain percentage of CO[sub]2[/sub] in the air interferes with the lungs’ ability to exchange CO[sub]2[/sub] for O[sub]2[/sub] to continue respiration. I don’t have available the ambient-air percentage at which this happens, but I’m sure someone will be by with the information.
That article seems to be conflating decreased oxygen levels with increased carbon dioxide levels:
I’m asking about the specific case where O2 levels are normal but CO2 levels are higher than normal.
Wasn’t this one of the problems faced by the Apollo 13 astronauts? When their air started going bad, they needed not an O[sub]2[/sub] replenisher, but a CO[sub]2[/sub] scrubber.
tries to recall high school chemistry
Carbon dioxide and oxygen exist in equilibrium in the blood. Haemoglobin binds with oxygen where the partial pressure of oxygen is high to form oxyhaemoglobin. This dissolves to form haemoglobin and water again where the partial pressure of oxygen is low. This is how oxygen is distributed throughout the body.
When CO2 levels are high oxyhaemoglobin will dissolve more readily. But this also means that for any given partial pressure of oxygen blood with more CO2 in it will have less oxyhaemoglobin than blood with less CO2. If there is enough carbon dioxide to prevent the haemoglobin from binding with oxygen in the first place then it would probably be a problem. But my recollection is fuzzy so treat this as a WAG if you will.
Our bodies try to maintain a strict limit on the CO2 concentration in our blood. If this is exceeded due to the air being higher in CO2 than normal, our bodies misinterpret this as we aren’t breathing hard enough and we start to hyperventilate. Beyond that, CO2 dissolved in water forms a weak (carbonic) acid, which is why soda water tastes sour. Too much CO2 disrupts the acid/base balance of the body. So while there’s no fundamental biochemical reason for CO2 to be inherently poisonous, our bodies react badly to high levels of it because it throws our biochemical equilibrium off.
I’m with Lumpy. Some people with very low levels of oxygenation (due to severe lung disease) do require the corresponding high level of CO2 to keep breathing. But too much of almost anything can be poisonous and CO2 is no exception.
Are you sure about this? I would have phrased it in the opposite sense, i.e. people with very high levels of carbon dioxide require low levels of oxygen to stimulate them to breath (hence the danger in giving them high flow O2). They are “resistant” to the effect of increased CO2 to stimulate breathing.
Hmmm. But in Bizarro World (where everything is reversed), I’d be right!
The human body was not designed (OOPS that’s a discussion for Great Debates) to operate in abnormally high concentrations of C0[sub]2[/sub] which could impair breathing and other functions or possibly exhibit symptoms of toxicity.
There is a danger in theatrical productions, especially amateur ones, of CO2 overdose.
It’s “common knowledge” around theaters that emptying a CO2 fire extinguisher on the stage will produce a layer of fog. For productions like that of Carousel which have a dream sequence.
But the gas comes out cold and hugs the ground and slides out into the audience, giving the front row coughing fits and headaches.
So, umm… trying to pull together what other people have said in this thread… carbon dioxide isn’t ‘poisonous’ in the traditional sense, but elevated levels are dangerous because they make it harder to breathe the air, even if the oxygen levels in the air are as high as normal?? What about if the oxygen proportion is increased the same time as the carbon dioxide??
It kind of makes sense to me, from what I remember of chemistry and bio, that if the carbon dioxide levels are higher, it would be harder for the lungs to get carbon dioxide out of the red blood cells passing through them about out into the air passages of the lungs. If the carbon dioxide cannot get ‘unloaded’ from the red blood cells, then new oxygen couldn’t get absorbed to them. (And possibly new carbon dioxide might get ‘loaded’ instead of oxygen.)
I’ve heard of carbon dioxide scrubbers in spaceships and such… adding oxygen to the life support compartment to replace what is used by the astronauts is simple enough, just rig up a bottle of oxygen to vent at an appropriate rate. But you also need to eliminate the carbon dioxide from what they’ve breathed out, which is a more complicated task… bubbling the air through a solution of lithium hydroxide (sp?) maybe. CO2 will bond with the OH ions to form a bicarbonate HCO3 ion. Why it has to be lithium I don’t remember. 
And one more question for the chemistry buffy… do I remember correctly that as the carbon dioxide level rises, it will spontaneously give rise to an equilibrium reaction that produces carbon monoxide?? (Carbon dioxide molecules essentially knocking oxygen atoms off of each other, with the freed oxygen atoms pairing up.) How high does the CO2 concentration have to get before the equilibrium concentration of CO would become harmful? (Assuming regular oxygen pressure, if that’s important.)
It’s still bad news.
Carbon dioxide accumulation in the blood is equivalent to accumulation of acid. Too much acid and you die. The coincident amount of oxygen is irrelevant.
In addition to the acidosis due to excess CO2, is the fact that high levels of CO2 will “narcotize” you., i.e. you’ll fall asleep (with a mild headache) and get deeper and deeper, and then you die. (You may have a seizure or two first, I suppose).
Yes, too much carbon dioxide is definitely bad news.
As has been said above, though, it doesn’t fit the term “poisonous.” Neither do other gasses such as nitrogen, which caused some deaths a while back when workers entered a chamber which had too much of it and died of asphixiation.
I’m not sure where carbon monoxide fits here, as it does replace oxygen in the red blood cells and leaves no room for oxygen-carrying for them. And, it binds tighter to the hemoglobin in them than oxygen does, making it extremely nasty…but I don’t think it exactly fits the term poisonous, like cyanide gas would, even though this site says:
Good question, though. Guess it just depends on how strictly you want to define “poisonous.”
As Dr Paprika alluded to, too low levels of CO2 in the blood are not good for you either. It is theorised that some people naturally hyperventilate, and this means less CO2/ These people may suffer from wheezing, breathing problems that look like asthma, or panic attacks. If someone has a panic attack, one effective remedy my wife a GP employs is to tell them to breathe into a paper bag. This restores the CO2 levels in their blood
Mass. You could use sodium or potassium hydroxide, or even caesium hydroxide if you had money to throw away but lithium hydroxide masses less per unit mass of CO[sub]2[/sub] absorbed, and while I forget how many thousand pounds of fuel you have to burn to put a pound of payload in orbit, it’s a fair bet they’d shave every ounce they could.
Btw I think the reaction would go all the way to the carbonate: 2 LiOH + CO[sub]2[/sub] = Li[sub]2[/sub]CO[sub]3[/sub] + H[sub]2[/sub]O.
Or to the bicarbonate (lithium hydrogen carbonate) with an excess of carbon dioxide. :smack:
Warning nt sure of the specifics so I will try to be vague where my knowlege is:
OK, dredging into grey areas of EMT school here. IIRC many asthmatics and or orther forms of COPD (chronic obstrtuctive pulmonary disorders) often have damaged or dysfunctional barrel (sp?) receptors. This is a structure that helps monitor concentrations of certain gases/chemicals in our blood and tell us we need to breathe faster or slower.
If the oxygen detection part is damaged, your body will tend to regulate your respiration by high carbon dioxide level rather than low oxygen levels in the bloodstream.
So if you give one of these people high flow oxygen it tends to supress their drive to breathe because of the low level of carbon dioxide. Of course if they are have trouble drawing breath, as many asthmatics do they are not getting good gas exchange and need higher concentrations of oxygen to stay alive.
All this makes for a delicate balance with alot of judgement calls as to how much oxygen to give someone with this type of problem
Oh, to be totally technical, my initial answer was slightly incorrect: there is a point at which CO[sub]2[/sub] is toxic in the strict sense, when the concentration is high enough to force it across the osmotic barrier in the lungs. But that concentration is well above the point at which it becomes asphyxiating, so for most real-world situations my answer is correct.